As an important parameter in power electronic converters, the leakage inductance of high-frequency transformers is of great significance in improving the operating mode and power transmission characteristics of isolated DC-DC converters. Compared with the solid round wire, the Litz wire can reduce eddy current losses in high-frequency magnetic components. However, the complicated structure of the Litz-wire windings poses a serious challenge to predicting leakage inductance in high-frequency transformers. On the one hand, it is difficult to precisely extract the magnetic field energy in various regions of the core window. On the other hand, it is hard to accurately characterize the multi-stranded and twisting structures of the Litz wires. Therefore, this paper presents a fast calculation method of leakage inductance in the high-frequency transformer with Litz-wire winding.

Firstly, a homogenized equivalent process for Litz wire is proposed to enhance the flexibility of modeling and the efficiency of computation. The magnetic field energy variation with frequency inside the Litz-wire conductors are analyzed. Then, the 2-D magnetic field energy inside the core window is extracted based on the method of images to eliminate the impact of the edge effect. The internal and external magnetic fields at different locations in the winding are accurately characterized by introducing the meshing into the method of images, and a coordinate transformation method is proposed to consider the twisting structure of the Litz wires. Finally, two high-frequency transformer prototypes with different structures are designed and fabricated. Compared with the measurement results and two existing methods, the accuracy and efficiency of the proposed approach are verified.

The following conclusions can be drawn. (1) A homogenized equivalent model of the Litz-wire twisting structure is developed by introducing the relative complex permeability, which simplifies the model building and reduces the computational cost. The variation of the magnetic field energy in the Litz wires with frequency is analyzed, and the magnetic field energy stored in the Litz wires gradually decreases with the frequency increase. (2) The meshing process is introduced into the method of images, and the coordinate transformation method is proposed to characterize the twisting structure of the Litz wire. It can counteract a part of the external magnetic field and reduce the magnetic field energy in the conductors. (3) Considering the twisting characteristics of the Litz wire and the high-frequency effect, a leakage inductance prediction model is developed based on the magnetic field energy variation with frequency. (4) The accuracy and efficiency of the proposed method are verified compared with the measurement and the current two analytical methods. The maximum error does not exceed 4% throughout the measurement frequency range, and the calculation time is about 20 seconds. Moreover, the proposed method can be effectively applied to fast iterative calculations in the optimal design of high-frequency transformers.

Fractional-order elements (FOEs) serve as fundamental components in fractional-order circuits, forming the cornerstone of research into fractional-order circuit systems. Unlike single-component counterparts, the multi-component method offers greater flexibility in selecting constituent elements, enabling the adjustment of order and impedance coefficients for enhanced practicality. This paper provides a comprehensive overview of prevailing construction methods to facilitate the selection of appropriate multi-component FOEs for specific application needs. These methods are classified into three categories based on the type of constituent devices: passive devices, operational amplifiers, and power electronic converters.

In the construction method based on passive devices, two approaches involving Foster RLC ladder circuits are discussed. Passive RLC networks are used to create circuits that match the impedance characteristics of the transfer function. Reducing phase error requires increasing the order and using numerous components, leading to complex structures and cumbersome calculations. When standard off-the-shelf components cannot be used, replacing analytical parameters with standard ones increases the phase angle deviation. Adjusting the FOE order or impedance coefficients requires replacing all circuit components. This method is most suitable for fixed FOE order and impedance coefficients, which are effective in medium to low-frequency scenarios.

Next, the paper introduces the construction method based on operational amplifiers. The method of constructing FOEs based on generalized impedance converter (GIC) circuits can realize FOEs with orders varying from -2 to 2. However, the limited open-loop gain and gain instability of operational amplifiers often result in significant deviations of the obtained FOE performance from its ideal characteristics. Therefore, exploring how to use other active devices, such as operational transconductance amplifiers (OTA) and current feedback operational amplifiers (CFOA), to construct FOEs is an exploration direction. GIC circuits offer great integration and functionality, making them suitable for applications where precise impedance and phase characteristics are crucial.

The construction method based on power electronic converters is also discussed in detail. Multi-component FOEs based on power electronic converters have wide applications because their power level depends on the inverter, and their order and impedance can be adjusted by changing the control parameters. However, different structures of filters affect the operating performance of fractional-order elements. Therefore, exploring the application of different filter structures on multi-component FOEs and optimizing the parameters of the filters become the direction of development for power electronic converter-based FOEs. Power electronic converters provide the advantage of handling higher power levels and dynamic adaptability. The ability to digitally control the fractional order and impedance in real-time makes these elements highly versatile.

Lastly, this paper proposes a three-phase fractional-order electrical spring (TPFES). TPFES controls the order of the equivalent fractional-order capacitance of each phase and the pseudo-capacitance. The effect of stabilizing the load voltage is realized, the power factor is improved, and the power is balanced. The application in grid power compensation demonstrates that multi-component FOEs can effectively enhance the performance of practical circuit systems. This work provides a reference for future applications of fractional order components in electrical engineering.

In wireless power transfer (WPT) systems, achieving accurate voltage regulation and efficient operation are critical. Current research achieves constant voltage output and zero voltage switch (ZVS) with additional DC-DC converters and variable resonant networks. However, these approaches increase system losses and costs. Therefore, this paper proposes a two-sided LCL phase-shifting control strategy. The internal phase shift angle of the inverter and active rectifier (AR) is used to achieve constant voltage output and maximum efficiency tracking, and the external phase shift angle between the two converters achieves ZVS of all switching tubes. By analyzing the power loss, the constraint condition between the internal phase shift angle is obtained. The minimum external phase shift angle δ_opt of ZVS is further determined, and the system’s high efficiency is realized. In addition, the power angle θ_power is introduced as the intermediate variable, and the frequency synchronization of the primary and secondary sides is realized using the voltage-controlled oscillator (VCO).

Firstly, utilizing the fundamental wave equivalent model, the constant voltage characteristics of the system and the constraint conditions of the inverter output voltage and AR input voltage pulse-width ratio D₁ and D₂ are analyzed. The results show that transmission efficiency peaks when the AC voltage ratio α =1. With load variations, achieving constant voltage output and maximum efficiency tracking is feasible by adjusting D₁ and D₂. Secondly, based on the time-domain harmonics model, the derivation and simplification of the time-domain expression of inductance current are conducted. The simplified model is then analyzed to determine the external phase shift angle δ. By comparing δ of the inverter and AR, the δ_opt is obtained. Thirdly, the overall control strategy is introduced. The constant voltage output is achieved by adjusting D₁ and D₂. The introduction of θ_power as an intermediate variable establishes the relationship between δ and θ_power, enabling indirect control of δ through the regulation of θ_power. Subsequently, the frequency synchronization of the primary and secondary sides is realized using a VCO, effectively solving the synchronization challenge associated with an active rectifier.

Finally, system simulations and experiments were conducted. The experimental results show that the system can achieve ZVS for all MOSFETs and maintain a constant voltage output regardless of load variations. Moreover, the proposed synchronous control strategy can effectively track the switching frequency of the inverter and precisely adjust the required δ_opt. As D₁ and D₂ consistently adhere to the maximum efficiency constraints during system adjustments, the system also achieves maximum efficiency tracking. When the coupling coefficient k is 0.31, the transmission efficiency of the system is the highest, and the maximum efficiency is 93.8%.

In order to realize the freedom of placing pots, the free zone induction cooker with multiple induction heating coils is gradually developing. It can perform user-customized heating of different pots, greatly improving the flexibility of using the induction cooker. In actual work, the induction heating coil in the corresponding area needs to be triggered based on the real-time position. Therefore, the correct identification of the pot position affects the working status and heating performance of the free zone induction cooker system. As a result, pot position identification has become a key factor that needs to be solved urgently. Traditional pot position identification methods are easily affected by fluctuations in external factors, require a large amount of sample data, and need to improve the accuracy and speed of pot position identification. This paper indicates that the misalignment of the pot affects the mutual inductance M between the pot and the induction heating coil, thereby affecting the impedance and current phase of the system. An identification method is proposed using the current phase to control the switch array, which achieves positioning and heating of the pot. The proposed pot position identification strategy requires a small amount of sample data, and the branch current phase is only related to the position of the pot. It is not easily affected by system voltage and current fluctuations, so the position of the pot can be judged in real-time.

Secondly, regarding the impact of pot misalignment on current and power, this paper introduces a power regulation strategy based on an adjustable capacitor circuit. Under the misaligned working condition of the pot, the disturbance observation method of maximum current search is used to adaptively adjust the adjustable capacitor. The maximum power output of the induction cooker is obtained, and the heating speed of the pot is improved. The pot position identification strategy and the power regulation strategy coordinate to ensure accurate identification of the pot position and rapid heating, which only needs to collect the current information of the system branch. Thus, the sampling circuit is simplified.

Finally, an experimental prototype of a free zone induction cooker based on three coils was built. Experimental results show that in the pot position identification strategy, the accuracy of the theoretical and experimental phases is over 96%, and the identification speed is 0.8 ms. The maximum temperature rise within three minutes is 17.3℃ using the power regulation strategy, higher than without the power regulation strategy. The proposed pot position identification strategy can correctly identify the exact position of the pot and achieve the maximum power output of the induction cooker after the power regulation strategy. The correctness of the pot position identification strategy and the power regulation strategy are verified.

The equivalent circuit is valuable for designing an induction machine and its driving system, and its parameters are essential for analyzing the electromagnetic performance and establishing the driving model, especially the magnetizing inductance that characterizes the main flux distribution in the machine. The finite element analysis can precisely determine the magnetizing inductance. However, it is unsuitable for the initial design stage when the design parameters need frequent adjustment. Traditional analytical calculations like the flux linkage method neglect the influence factors, such as core saturation, tooth-slot effect, and rotor movement in the actual operation, causing accuracy issues. The improved analytical calculation method can significantly enhance the accuracy. However, the magnetic circuit in each core segment still needs to be more accurate, and the local saturation points are easily ignored. Besides, the solving process contains nonlinear iterations of multi-segment of the magnetic circuit, which has repeating calculations under different slips.

This paper proposes an elementary layer method based on the main and leakage magnetic circuits to calculate the magnetizing inductance. Firstly, the magnetic voltage drop of each pole of the main magnetic circuit under different air-gap flux densities is calculated, and the magnetic voltage drop and the air-gap flux density are converted into the electromotive force and the magnetizing current to obtain the objective function. Secondly, the distribution of the leakage flux in the stator slot and the current induced in the rotor bar is analyzed to calculate the slot leakage inductance of the stator and rotor, together with the rotor AC resistance. The stator terminal voltage expression is constructed as the constraint condition. Finally, each set of the electromotive force and the magnetizing current on the objective function are substituted into the constraint condition to make the results equal to the rated phase voltage of the stator. The ratio of the set is the value of the magnetizing reactance, and therefore, the magnetizing inductance is obtained. In the main and leakage flux circuits, the irregular and nonlinear magnetic and electric circuits are regularized and linearized using the thin layer elements to substitute theoretical integral. Hence, the tooth-slot structure and the nonlinear material properties can be considered more accurately when calculating the magnetic voltage drop and leakage inductance.

A wet submersible induction machine is an example of the analytical calculation of the magnetizing inductance using the proposed elementary layer method and the traditional flux leakage method. Besides, the steady-state outputs of the equivalent circuit are obtained. The prototype test and the finite element simulation under the magnetic saturation of the stator teeth are conducted. The results show that the elementary layer method considers the distribution of the magnetic voltage drop in the core segment, which is more effective than the flux linkage method when the tooth magnetic circuit is saturated. Therefore, the calculation of the magnetizing inductance is more accurate, and in the steady-state outputs of the equivalent circuit, the stator current, input power, and power factor curves are consistent with the finite element analysis. The error is less than 0.5% when the finite element results are used as the reference. The proposed method links the design parameters and the magnetizing inductance, providing convenience for the initial design and optimization of the submersible induction machine and other types of machines.

The doubly salient electric-excited motor has many advantages such as a simple structure, low manufacturing cost and high reliability, making it a good candidate for applications in electric vehicles, aerospace, and other fields. However, its large torque ripple and low torque density limit its development and applications. This paper proposes a new topology structure for the doubly salient electromagnetic machine (DSEM).

The topology structure and working mechanism of the proposed DSEM are analyzed in detail. The combination of stator poles and rotor poles is elaborated, and the winding method of armature windings is described with the influence on the harmonics of EMF. The relationship between the pole-combination and harmonics of the magnetic field, together with the output torque, is investigated according to the magnetic field modulation mechanism, and the air-gap flux density harmonics of 18/10 and 18/11 DSEMs are obtained by finite element analysis. The influence of pole combination on motor characteristics is analyzed by finite element analysis, including the no-load electromagnetic performance, the torque features, and the loss characters, which shows the superiority of the DSEM with odd-number rotor poles. Finally, a prototype of the new 18/11 DSEM is manufactured and tested.

The results show that due to the new winding method, the flux in armature windings changes bipolar, resulting in high sinusoidal flux linkages and, thus, a high sinusoidal EMF. The DSEM with odd-number rotor poles has more effective space magnetic harmonics than that with even-number rotor poles, almost with odd orders, resulting in higher output torque. Besides, due to the offset of even-order time-harmonics, the DSEM with odd-number rotor poles has higher sinusoidal EMFs and lower torque ripples. In addition, different rotor poles show different characteristics, as seen from the simulation results.

The following conclusions can be drawn. (1) By adjusting the winding method of the field winding and the armature winding, the new type of DSEM realizes the bipolar change of the armature flux, and the back EMF has a high sinusoidal degree. (2) As can be seen from equations (21) and (26), the effective harmonics’ frequency of air-gap flux density in the odd-rotor pole motor is different from that in the even-rotor pole motor, resulting in different torque harmonics. (3) If the number of rotor poles is even, there are more even order harmonics in the motor back EMF, and the cogging torque and torque ripple are also large; if odd, the armature coils with opposite polarity are connected in series, and the even harmonics in the motor back EMF cancel each other, resulting in smaller harmonic content, cogging torque, and torque ripples. (4) The motor performance is optimal for the proposed DSEM with 18 stator poles when the rotor pole number is 11 or 13.

The demagnetization fault of permanent magnet synchronous motors (PMSM) reduces output performance and load capacity, seriously affecting the motor’s service life. Establishing an accurate fault motor analytical model, conducting rapid electromagnetic performance analysis, and obtaining operational data such as current and torque under fault conditions are beneficial for early prediction and diagnosis of demagnetization faults.

A parameter D is introduced for the partial demagnetization fault of the surface-mounted PMSM prototype, representing the spatial angle of the demagnetized region, defined as the ratio of the spatial angle occupied by the demagnetized region to that of one pole arc. The radial and tangential component equations of the residual magnetization Fourier coefficients as a function of parameter D are derived, which reflect the influence of the spatial angle of the demagnetized region on the magnitude and the waveform of the residual magnetization. An analytical model of PMSM under partial demagnetization is established.

In addition, regarding the control system’s circuit interface in practical applications, an analytical model of demagnetization faults in a PMSM driven by a voltage source inverter with magnetic flux linkage as the intermediate variable is established. This model is applied to the vector control circuit. Thus, a co-simulation model combining the analytical model and the control circuit is created.

The load performance of the prototype is calculated under normal conditions and partial demagnetization using the co-simulation model. Compared with the simulation results from the Ansys/Simplorer time-stepping finite element method and the measured results from the prototype on the experimental platform, the conclusions are as follows. (1) The proposed partial demagnetization analytical model reflects the influence of the demagnetized region on the magnitude and the waveform of the residual magnetization. This model is more consistent with actual conditions than the method of equating partial demagnetization to an overall reduction in magnetic flux linkage. (2) The calculation results of the co-simulation model are in good agreement with the time-stepping finite element simulation results, with the relative errors for the stator flux linkage, stator current, and electromagnetic torque less than 1.5% under normal and partial demagnetization conditions. Furthermore, the computation time of the co-simulation model is only 1/20 that of the finite element model, which greatly improves the operation efficiency. (3) The current waveforms of the prototype under the same control strategy are measured on the experimental platform and subjected to spectral analysis. The results are consistent with the co-simulation results, which validate the accuracy of the co-simulation model, combining the analytical model and the control circuit.

A Bi-stable permanent magnet actuator (BPMA) shares the same magnetic circuit as the breaking and closing coils, and the magnetic flux generated by any coil passes through the breaking and closing air gaps. The permanent magnet automatically distributes the permanent magnetic flux according to the dynamic reluctance of the air gaps. The electromagnetic flux and permanent magnetic flux in the upper and lower air gaps always cause the moving iron core to be coupled by two opposite magnetic forces. As the motion of the moving iron core and the change of coil current, the magnetic circuit quickly saturates, and the electromagnetic flux and permanent magnetic flux interact, exacerbating the complexity of nonlinear coupling in the breaking and closing air gaps. To flexibly control the action characteristics of permanent magnet switches, it is necessary to simultaneously control the air gap flux and the magnetic force pointing to the breaking and closing positions. Therefore, this paper proposes an air gap flux decoupling control method based on finite control set-model predictive control (FCS-MPC). Decoupling control can be achieved by rapidly weakening the magnetic force pointing to the non-excited coil and rapidly increasing the magnetic force pointing to the excited coil.

Firstly, according to the operating principle of BPMA, the vector magnetic force acting on the moving iron core depends on the “magnetic flux squared difference” of the breaking and closing air gaps. Therefore, only controlling this vector magnetic flux square difference in real-time can dynamically control BPMA. Secondly, a predictive model of the breaking and closing air gap magnetic flux is designed through discretization of the voltage balance equation, which can predict the magnetic flux at the next moment based on the voltage and current values collected at the current moment. Thirdly, the breaking and closing air gap magnetic flux and the mechanism drive circuit are regarded as a whole. A set of switching states is constructed through the excitation intensity analysis under different switching states. Predictive magnetic flux is obtained by traversing all switching state combinations. Finally, a decoupling control cost function is designed, the predictive magnetic flux under different switching combinations is input into the cost function, and the optimal control is selected for the next control period. In rolling optimization over multiple control periods, the breaking and closing air gap magnetic flux quickly approaches their respective reference values, achieving decoupling control.

A co-simulation platform for intelligent control is designed based on LabVIEW and Multisim, and hardware testing circuits are constructed. The simulation and experimental waveforms show that this proposed scheme can effectively control the breaking and closing air gap flux. As a result, the non-excited air gap flux to zero is quickly reduced, approaching the set reference value of the excited air gap flux and effectively weakening the coupling between the air gaps. Compared with the traditional current closed-loop control scheme, the proposed control scheme reduces the energy loss during the entire action process and improves the response and action time of the core action.

Permanent magnet synchronous motors are widely used in industrial production and other fields due to their advantages of high power density, high reliability, and high efficiency. Real-time and accurate three-phase current feedback is the key to AC drive system control. Compared with the traditional multi-current sensor drive control, using a single current sensor to achieve three-phase current reconstruction can reduce costs and improve the reliability of the motor system under complex working conditions. Combined with the improved IRTPWM algorithm and the BSPWM algorithm, this paper forms a hybrid pulse width modulation algorithm to solve the low-key brake dead zone and the reconstructed dead zone at the sector boundary. Then, an improved two-point sampling strategy is adopted to eliminate the second type of time-sharing sampling error and simplify the current compensation step, which fixes the sampling time of the two samples and the sampling spacing as the minimum sampling time.

Based on the traditional RTPWM algorithm, the improved IRTPWM algorithm calculates the action time of the other two effective voltage vectors. The action time of the vector is fixed with the least influence on the synthetic reference voltage vector among the three vectors, and the three effective voltage vectors and zero vectors are recorded. It collects the phase current at the beginning and end of the optimal measurement vector.

The traditional RTPWM algorithm cannot achieve medium and high-speed operation alone. The measurement phase backward shift modulation method (BSPWM) is proposed to eliminate the dead zone of current reconstruction by combining the measurement phase backward shift modulation method and the IRTPWM algorithm outside the working area of the IRTPWM algorithm. The mixed pulse width modulation algorithm can complete the current acquisition twice at two fixed particular sampling points, and the first type of time-sharing sampling error only needs to be compensated. Therefore, the current compensation steps of the traditional mixed pulse width modulation algorithm are reduced from four steps to two steps, and the computing burden of the processing unit is reduced.

The simulation and experimental results show that the error between the reconstruction and the actual current is tiny, which proves that the proposed current reconstruction has high accuracy in both steady-state and transient states. Under the dynamic working conditions of fixed load torque of 2 N·m with the rotation speed of 300 r/min and 600 r/min back and forth and fixed speed of 400 r/min with load torque switching back and forth between 1 N·m and 3 N·m, the motor speed, q-axis current, and three-phase current do not cause great disturbance due to the switching of the algorithm.

The following conclusions can be drawn. (1) The combination of the IRTPWM algorithm and BSPWM algorithm effectively eliminates the influence of the dead zone of current reconstruction. (2) The IRTPWM algorithm has higher current reconstruction accuracy and lower current harmonic value than the traditional RTPWM, and the BSPWM algorithm has higher current reconstruction accuracy than the traditional phase-shifting method. (3) The improved two-point sampling strategy can reduce the number of current compensations and current reconstruction errors, simplifying the experimental algorithm and improving the control performance of PMSM.

Permanent magnet linear synchronous motors with section power supply are affected by disturbances like load force, detent force, and friction force. In the field of electromagnetic drive, the stator track is long. Linear motors usually adopt a segmented structure to save inverter capacity. However, it is difficult to ensure that the air gap of each segmented stator is equal during installation. Therefore, the mover is affected by the normal force. In addition, the load is usually accelerated to the target speed in a short time, so electromagnetic drive devices are usually operated under high current and high acceleration conditions, where the motor parameters are prone to change. Due to the lack of intermediate transmission devices in PMLSMs, these disturbances will directly affect the motor drive system and are included in the output of the controller. An SMSC with a novel convergence law is designed to ensure the fast convergence of speed and suppress the chattering. The designed TSMDO observes the disturbance output to ensure the disturbance suppression performance. Then, the acceleration fluctuations are reduced, and the thrust fluctuations are suppressed in the motor output.

Firstly, a mechanical motion model of PMLSM is established based on Newton's second law. It takes the disturbances as the lumped disturbance d(t) caused by load force, detent force, friction force, normal force, and parameter variation. Secondly, the shortcomings of conventional sliding mode control are analyzed, and a new adaptive sliding mode approaching law is proposed. The designed sliding mode approaching law ensures that variables can approach the sliding mode surface at a fast speed. As the state variables of the system gradually approach the sliding mode surface, the designed sliding mode approaching law can reduce the speed to weaken chattering. Then, due to the presence of d(t) in the output of the sliding mode speed controller, the TSMDO is designed to compensate for it. This observer is equivalent to a first-order low-pass filter. Finally, the proposed SMSC strategy is compared with PI control and conventional SMSC.

The experiments show that the PI controller can improve the dynamic tracking performance of speed by increasing h. However, this increases the acceleration fluctuation. At the same time, there is a noticeable overshoot when the rotor enters the constant speed range. The conventional SMSC has better dynamic tracking performance than PI control, resulting in small acceleration fluctuations. However, due to the fixed sliding mode gain, the increasing sliding mode gain increases the overshoot. The proposed SMSC has a faster tracking speed and better dynamic response than the conventional approaching law because of the new sliding mode approaching law. The proposed SMSC can adaptively change its gain when the speed state changes, ensuring good speed-tracking performance and reducing overshoot. The designed TSMDO effectively reduces the impact of thrust disturbances, acceleration fluctuations, and thrust fluctuations.

The main conclusions are as follows. (1) The proposed new sliding mode approaching law has a fast convergence speed due to the adaptive gain function f(x₁, s) for adaptively adjusting the sliding mode gain. It can weaken chattering, ensuring speed dynamic tracking performance and convergence speed. (2) The designed TSMDO has a small chattering phenomenon. The introduction of TSMDO effectively suppresses the total disturbance d(t) in the SMSC output, reduces acceleration fluctuations, and ensures stable thrust output of the motor.

Implementing sensorless control is necessary to reduce the system volume of linear oscillatory machines (LOM) used in linear compressors and achieve efficient and reliable operation. The existing piston stroke observers have low observation accuracy and are susceptible to DC components, resulting in a decrease in system compression performance or cylinder collision risk. Therefore, this paper designs an improved high-precision piston stroke observer for linear oscillation machines based on a high-order generalized integrator (HOGI).

Firstly, a theoretical analysis is conducted on traditional back electromotive force integration, low-pass filter (LPF), and second-order generalized integrator (SOGI), elucidating the existence of integral saturation problems in back electromotive force integration, amplitude attenuation, and phase shift problems in LPF. SOGI performs slightly better than the previous two but still cannot eliminate the DC component. When operating at low resonant frequencies or in systems with large DC components, SOGI is no longer applicable. Secondly, in response to the shortcomings of traditional integrators, this paper adopts HOGI as a piston stroke observer. This method can eliminate the DC component, and no DC bias exists in the observed stroke signal. The paper also uses the forward Euler method to derive the digital implementation method of HOGI. Finally, experiments are conducted to compare SOGI and HOGI. The experimental results show that the piston stroke observed by HOGI is more accurate than SOGI without additional DC bias. Furthermore, when an additional 0.2 A DC bias is added, the piston stroke average offset observed by SOGI at the given value of 5 mm, 6 mm, and 8 mm is 1.367 5 mm, 1.365 mm, and 1.351 5 mm, respectively. The piston stroke observed by HOGI is unaffected by DC bias. Therefore, the piston stroke observer with HOGI is suitable for occasions with serious DC disturbance.

The contributions of this paper are as follows. (1) Based on traditional SOGI, an improved HOGI piston stroke observation structure is designed. Multiple filtering feedback characteristics are used to eliminate the influence of DC components on stroke observation results, improving the accuracy of the piston stroke observation. (2) The complex frequency domain method is used to analyze the pure integrator, LPF, SOGI, and HOGI. The superiority of HOGI is theoretically proven. (3) Based on the forward Euler method for discretization and digital implementation of HOGI, this method has the advantages of simple calculation and easy implementation.

Regarding the sensorless control system of permanent magnet synchronous motors (PMSM), this paper combines extended Kalman filtering (EKF) and improved inertial active disturbance rejection control (IADRC). By establishing a mathematical model under the new coordinate system and applying the EKF algorithm, the state of the motor is accurately estimated, thus ensuring the accuracy and stability of the control system. Aiming at the current harmonic disturbance caused by the sudden load change, this paper introduces the second-order oscillation function to optimize the traditional linear active disturbance rejection control and proposes an improved IADRC strategy, which significantly attenuates the harmonic disturbances and strengthens the system's immunity to disturbances.

According to the traditional mathematical model of the PMSM motor under the $\gamma \delta $-axis, the mathematical model of the PMSM motor under the estimated rotational coordinate system $\gamma \delta $ is constructed, and the angle ${{e}_{\theta \gamma }}$ between the dq-axis and the $\gamma \delta $-axis is directly estimated, eliminating the influence of the other observers. After that, through the mutual validation of simulation and the mathematical model, the second-order oscillating function is connected in parallel to suppress current harmonics. The 3rd, 5th, and 7th periodic harmonics with high harmonic contents are suppressed. Its effectiveness and stability are proved by Bode's plot and the Nyquist curve plot, respectively.

The EKF's direct estimation method of error angle ${{e}_{\theta \gamma }}$ in $\gamma \delta $ coordinate system is verified Through simulation and experiment, speed step, sudden load addition, and starting with rated load. Meanwhile, compared with the traditional PI control and LADRC control, IADRC plays a role in suppressing the low harmonics when the motor is running stably at 1 000 r/min with rated load. The 5th and 7th harmonic contents are reduced by 50.5% and 77.4% compared to PI. The IADRC algorithm based on the LADRC algorithm can suppress specific harmonics, with a 41.3% reduction in 5th harmonic content compared to the LADRC and a 49.4% reduction in 7th harmonic content compared to the PI. Comparative analysis of the three-phase currents after a sudden change in the rated load shows that compared to PI, the 5th harmonic content of the LADRC is reduced by 70.5%, the 7th harmonic content is reduced by 79.1%, and the 3rd harmonic content is reduced by 54.8%. Meanwhile, compared to LADRC, the 5th harmonic decreases by 44%, the 7th harmonic decreases by 13%, and the 3rd harmonic decreases by 88%.

In the inverter-driven permanent magnet synchronous machine (PMSM) control system, high-frequency current harmonics near the switching frequency and its multiples are generated using space vector pulse width modulation (SVPWM), which brings high-frequency electromagnetic vibration. Therefore, a double random SVPWM control method combining random switching frequency and random zero vector is applied to the high-frequency current harmonic spectrum expansion. Meanwhile, the random number is generated by the improved Mersenne twister (MT) algorithm, which enhances the random performance of the random sequences and ensures the spreading effect of the double random SVPWM control method.

Firstly, random zero vector control can be achieved by changing the action time of the zero vector and reassigning the randomized zero vectors into the space vectors. Secondly, the switching frequency of the traditional SVPWM control method is fixed, and the random switching frequency control can be achieved by changing the fixed switching frequency of the inverter and dispersing the harmonics at the switching frequency and its multiples into the specified frequency domain. Thirdly, the random number is generated by the improved MT algorithm, which is applied to the double random SVPWM control of the permanent magnet synchronous machine to enhance the degree of freedom and spatial traversal of the random sequence. The new control method proposed is named LKMT-DRC.

Experimental verifications are conducted on a 4.4 kW fractional-slot permanent magnet synchronous machine. The PMSM phase current harmonics and vibration acceleration under the conventional SVPWM control and LKMT-DRC control are compared, and the vibration suppression effect of the LKMT-DRC control is analyzed using different spreading ranges. Under the inverter power supply mode, the harmonic frequencies introduced by the SVPWM control mode are mainly f_k±2f₀ and f_k±4f₀, and the frequency of the introduced high-frequency radial electromagnetic force wave is mainly f_k±f₀. Compared with the traditional SVPWM control mode, the high-frequency harmonics concentrated on the switching frequency. Its integer multiples can be effectively dispersed using LKMT-DRC control mode, and the vibration suppression effect caused by the high-frequency electromagnetic force wave can be significantly reduced. Meanwhile, the random numbers generated by the proposed LKMT algorithm can improve the randomness and spatial traversability of the random sequences, which ensures the effectiveness of the double-random SVPWM control method.

The contributions of the proposed double random SVPWM control method based on the improved MT algorithm are as follows. (1) A mathematical model of the high-frequency radial electromagnetic force introduced by PMSM under inverter power supply conditions is derived, and the effect of the high-frequency electromagnetic force under inverter power supply mode on motor vibration is analyzed. (2) The LKMT-DRC control method is proposed, which effectively reduces high-frequency harmonic content and suppresses high-frequency electromagnetic vibration. (3) The effects of different spreading ranges on the final damping under the LKMT-DRC control mode are analyzed, and the appropriate ranges are indicated.

The coupling between spatial-harmonic and time-harmonic currents in asymmetric multiphase motors (AMM) increases torque ripple and decreases efficiency, limiting their widespread application. Currently, active harmonic suppression strategies rely on complex filters or observers to extract harmonics and require the construction of numerous proportional resonance (PR) controllers at different frequencies, making the complexity and impracticality of harmonic suppression. Therefore, this paper proposes a single-frequency PR harmonic suppression strategy without filters based on the harmonic mapping law.

Firstly, based on the magnetic electromotive force equivalence principle, the universal space vector decoupling matrixes for AMM are established. Then, a mapping formula for harmonics of different frequency components on the subspaces is established. The general formula is decomposed into two independent components: amplitude and phase. The amplitude and phase mapping law of harmonics on the subspaces is derived according to the characteristics of the two components. Secondly, three criteria are proposed to search for the AMM with the minimum number of phases to ensure the unique mapping of harmonics. Based on the graphical representation of the mapping laws, the mapping trajectories of all harmonics are obtained to optimize the AMM topology and establish the subspaces for harmonic mapping. Then, based on the current phase-shifting method, a virtual AMM is constructed, and harmonics are extracted through the vector decoupling transformation subspaces. Finally, after unifying the frequency through linear space rotation transformation, PR controllers with the same resonant frequency are used to regulate harmonics.

Harmonic extraction and suppression experiments under steady-state and transient conditions are conducted using a dual three-phase motor. The extracted harmonic amplitudes can reach over 92% of the actual harmonics, demonstrating that the proposed algorithm can effectively separate harmonics. In the harmonic suppression experiment, the strategies of no harmonic suppression, current harmonic suppression under multiple synchronous rotating frames, and the proposed harmonic suppression strategy are compared. The proposed strategy decreases the proportions of the 5th, 7th, 11th, and 13th harmonic currents from 13.92%, 5.31%, 4.05%, and 2.96% before suppression to 3.02%, 0.43%, 0.39%, and 1.19%, respectively. The total harmonic distortion (THD) is decreased from 15.36% to 2.86%. Moreover, the harmonic suppression exhibited robustness under various operating conditions across the entire speed range.

The following conclusions can be drawn. (1) There are two harmonic mapping methods: full mapping with equal amplitudes and partial mapping with reduced amplitudes. The phase of mapping components can be divided into the α component leads or lags the β component by π/2. (2) Based on the harmonic mapping law, an optimal AMM topology selection criterion is established, and a virtual AMM is constructed, effectively avoiding the complex and inaccurate problem of harmonic extraction caused by constructing filters or harmonic observers. (3) The features of harmonic pair mapping on the selected subspace are that the difference in frequency order is equal, and the phase sequence is opposite. Thus, linear spatial rotation coordinate transformations are applied to unify frequencies, which enables single-frequency PR controllers with half the number of harmonics to regulate all harmonics.

Due to the existence of important loads, the new distribution network needs to be supplied with power when the equipment of the original distribution network is overhauled. Two closing types exist when accessing the new distribution network: loop and ring-closing. The distribution network is cut off for loop closing, leading to power supply interruption, or the ring of the distribution network is directly closed, producing a large impulse current due to the large voltage difference between the two distribution networks. As a result, the relay protection malfunction occurs, which affects the reliability and stability of the power grid. Two ways are adopted to avoid the above issues. One is to provide the loop closing condition through theoretical calculation, and the voltage of the loop closing point is similar by controlling the whole distribution network. The loop is directly closed after meeting the ring closing conditions. However, the control process is more complex, and the loop closing current is still large. The second is to use the voltage regulating device to change the voltage of one side of the ring closing point and carry out the ring-closing. Although the control effect of the ring-closing device is better, the price and maintenance costs are high.

This paper proposes an improved phase shifter (IPST) with an amplitude modulation winding (ETm) based on the amplitude modulation winding (ETp) of the traditional phase shifter. It can flexibly change the voltage amplitude and phase by adjusting the gears of ETp and ETm, thereby changing the voltage at the closing point. The voltage between the two distribution networks is similar, and the loop closure is realized. In addition, the voltage quality on the load side is degraded because of the internal impedance of the IPST after the load transfer. An IPST equivalence model is established based on the multi-port network theory. The impedance characteristics of the IPST port are converted into the equivalent analytical formula. The functional expressions of the regulation voltage on the amplitude modulation gear T_m and phase modulation gear T_p are derived. Thus, the target gear of the IPST is predicted, and the voltage quality is improved. Thirdly, to address the problem of the inrush current generated when the IPST exits bypass closing, the functional relationship of the inrush current on the IPST gear is derived. The IPST target gear is predicted by combining the current regulation target and the voltage quality constraint. The voltage quality can be ensured, and the impulse current can drop and safely exit the IPST. Finally, the impedance expression’s correctness and the control strategy’s effectiveness are verified through PSCAD/ EMTDC.

Electrical isolation in advanced power supply systems typically relies on power frequency transformers or high-frequency isolation DC-DC converters. However, the transformers result in multiple converter stages and increase the system’s complexity and cost. To reduce the cost of advanced traction power supply system, this paper proposes a two-phase to single-phase non-isolated power electronic transformer (NI-PET) topology based on the existing traction transformer and has the advantages of fewer transformation stages and higher system efficiency.

Some switch states can result in short-circuit paths of the DC-link capacitance in NI-PET topology. The traditional modulation strategy fails to avoid the short-circuit paths. A three-dimensional space-vector pulse width modulation (3D-SVPWM) strategy is proposed based on the 3D space vector distribution diagram, taking the vectors of three ports as the coordinate axis. According to the number of available vectors, the 3D space is divided into different ranges. In addition, the proposed strategy determines the range of reference voltage vectors and selects available space vectors to complex the demanded reference vector. Finally, based on the V-v traction transformer, the simulation model and experimental platform are built.

Simulation and experimental results show that compared to the traditional space pulse width modulation (SPWM) strategy, the proposed modulation strategy can realize the stable operation of the system. When the load and grid-side voltage fluctuate repeatedly in a short period, the two-phase to single-phase NI-PET system restores a steady state within 0.2 s, the grid-side power factor remains above 0.99, and the THD of input and output current is less than 3%. With the same load, the three-phase current unbalance degree of the proposed topology is about 45% less than the traditional power supply system. It is verified that the proposed topology and modulation can adapt to harsh conditions such as continuous load and grid-side voltage fluctuations. Compared to PET, NI-PET avoids the loss caused by the isolation stage, thus significantly improving the efficiency. In the low-power experimental platform, the efficiency of NI-PET is about 10% higher than PET.

The following conclusions can be drawn. (1) The proposed two-phase to single-phase NI-PET topology can adapt to the harsh conditions of advanced traction power supply systems. It has the advantages of low cost and good power quality. (2) Compared to the traditional modulation strategy, the proposed one can avoid the short-circuit paths of DC-link capacitance. There is no short-circuit current that is much larger than the load current on the cascade line. (3) The proposed topology can achieve about 10% efficiency improvement in a low-power experimental platform and is expected to increase the efficiency by about 2% in industrial PET.

The single-stage Totem pole dual active bridge (DAB) AC-DC converter has the advantages of low component count, high power density, and low cost, which has a broad application prospect in the field of on-board chargers (OBC). However, in the available research, the traditional single phase shift (SPS) and extended phase shift (EPS) modulation strategies are unable to optimize the quality of grid-connected current and efficiency of the Totem pole DAB AC-DC converter at the same time due to the problem of insufficient modulation degrees of freedom, limiting the further application in on-board chargers.

This paper introduces the asymmetric modulation based on the extended phase shift modulation strategy when the duty cycle of the secondary side switching tubes is no longer 50%. An asymmetric extended phase shift (AEPS) modulation strategy with three degrees of freedom is proposed. Accordingly, a multi-objective optimal modulation strategy is solved by considering the simultaneous optimization of the grid-connected current quality and efficiency of the Totem pole DAB AC-DC converter.

Firstly, the steady-state analytical model of AEPS modulation is established by using the time domain analysis method. The initial value decoupling constraint of the inductor current is considered to optimize the quality of grid-connected current, and the peak-to-peak inductor current is taken as the optimization objective. According to the Lagrange algorithm and Karush Kuhn Tucker conditions, the above multi-objective optimization problem is transformed into mathematical equations to solve the optimization solution of modulation variables. Matlab simulations show that the inductor current’s initial value decoupling and peak-to-peak value optimization are realized under the AEPS optimization modulation strategy. Compared with the SPS and EPS modulation, the proposed AEPS optimization modulation strategy reduces the peak-to-peak and RMS levels of the inductor current in the full power band, which reduces the conduction loss of the converter. Moreover, the optimized solutions in different operating modes under APES modulation are continuous, making seamless switching between different operating modes available.

An experimental prototype of a totem pole DAB AC-DC converter with a rated power of 800 W is constructed. Experimental results show that the converter achieves a peak efficiency of 93.5% under the proposed AEPS optimized modulation strategy, 5% and 14.7% higher than the SPS strategy at full load and light load, respectively; 1.5% and 14.7% higher than the EPS modulation strategy at full load and light load, respectively. The converter's grid-connected current THD is significantly reduced in the full power range, improving its grid-connected current quality. Simulation and experimental results verify the effectiveness of the proposed AEPS-optimized modulation strategy.

As a typical multilevel inverter, a neutral point clamped (NPC) three-level inverter is suitable for large-capacity and high-voltage converters, which can effectively reduce current harmonic content. However, the NPC three-level inverter has the problem of neutral point voltage imbalance due to the structural characteristics of capacitive voltage division. The traditional virtual space-vector pulse width modulation (VSVPWM) has limited ability to suppress neutral point voltage fluctuation. Correcting its offset is challenging, especially in the medium and high modulation depths. Therefore, this paper proposes a sector reconfiguration VSVPWM. By introducing equivalent medium vectors and reconstructing sectors in medium and high modulation depths, small and medium vectors can fully participate in neutral point balance adjustment while retaining fixed sector division. This method can effectively suppress the neutral point voltage fluctuation and accelerate the recovery of the neutral point offset. There is only one balance coefficient for each fixed sector, which is easy to implement.

Firstly, the equivalent relationship between a large vector and a medium vector is analyzed. An equivalent medium vector with constant amplitude is then constructed. The equivalent medium vector can participate in the neutral point balance by adjusting the proportion of medium and large vectors. After that, a virtual vector group, including equivalent medium vectors, is constructed. Furthermore, an equivalent medium vector VSVPWM (EMV-VSVPWM) is proposed, which improves the neutral point adjustment ability in the sector with a medium vector. Secondly, the level of modulation depth is divided based on the operational sector position, and the neutral point margin of the EMV-VSVPWM strategy depths is analyzed in one modulation period. It is found that the regions with weaker capacity of neutral point balance exist in high modulation depth. Therefore, a sector reconstruction VSVPWM (SR-VSVPWM) is then designed. The sector boundary and vector selection boundary in the medium and high modulation depths are separated to increase the proportion of small and medium vectors in such regions, which can enhance the neutral point adjustment margin. Furthermore, the neutral point balance coefficient of small and medium vectors is unified to reduce the computational complexity. Meanwhile, the vector sequence is optimized according to the principle of constant switching state, and the switching loss is reduced.

The initial neutral point voltage offset and modulation depth experiments are carried out on a hardware experimental platform in the loop. The results indicate that the SR-VSVPWM strategy can achieve the fast balance of the middle point in pure resistor load and resistor-inductance load conditions. Compared with the traditional VSVPWM single small vector adjustment, the neutral point voltage offset is eliminated, and the balance time in the high modulation depth is reduced by about 46%. In addition, the current harmonics are also reduced. When the experiment on variable modulation depth is considered, SR-VSVPWM still exhibits strong suppression of neutral point fluctuations and good current quality in high modulation depth. After the switching frequency is reduced to 5 kHz, the neutral point fluctuation level of SR-VSVPWM is 79.1% of the traditional VSVPWM.

During the charging process of flywheel driving by permanent magnet synchronous motor, the three-level converter operates in a low modulation index for a long time, and the traditional virtual space vector pulse width modulation (VSVPWM) strategy frequently generates narrow pulses. Due to the discrete nature of digital control, the sector boundaries in the traditional VSVPWM strategy can shift, exacerbating the narrow pulse issue. These narrow pulses lead to significant distortion in the voltage and current waveforms of the converter and even damage the power devices.

This paper proposed an analysis method considering the discreteness of motor digital control and a hybrid VSVPWM strategy based on vector sequence optimization. Firstly, the variation characteristics of the voltage reference vector and its influence on sector boundary under digital control were studied based on the steady-state mathematical model of the motor. Then, the minimum pulse width function was established to quantitatively analyze the distribution of narrow pulses in the traditional VSVPWM within the low modulation index region. Consequently, according to the narrow pulse distribution law, a hybrid VSVPWM strategy based on vector sequence optimization was proposed.

The traditional VSVPWM (Seg9_VSVPWM), the thirteen-segment VSVPWM (Seg13_VSVPWM), and the proposed hybrid VSVPWM (LH_VSVPWM) were compared. The simulation results show that when the modulation index is 0.1 and 0.3, Seg9_VSVPWM continuously presents narrow pulses less than 2 μs at the boundary between sectors F and A with 672 and 219 times within 1 s. When the modulation index is 0.5, Seg13_VSVPWM would produce the narrowest pulses and accumulate 1 102 times within 1s. However, when the modulation index is 0.1, the proposed LH_VSVPWM eliminates the narrow pulse by optimizing the vector sequence. In addition, LH_VSVPWM has the fewest switching action times in the modulation index of 0.3 and 0.5, which is 5 836 and 5 875 times in 1s, respectively. Meanwhile, the proposed strategy performs well in limiting narrow pulses, occurring only 11 and 32 times within 1 s. The experimental results further demonstrate that LH_VSVPWM can effectively suppress the narrow pulse and keep the minimum pulse width above 6 μs in low modulation index region. Moreover, LH_VSVPWM improves the three-level converter’s output current waveform quality, with THD values of 22.24%, 13.78%, and 17.47% in the modulation index of 0.1, 0.3, and 0.5, respectively. It is the lowest among the three modulation strategies. Compared with Seg9_VSVPWM, the proposed LH_VSVPWM keeps the neutral-point potential balanced during motor start.

The following conclusions can be drawn. (1) The discreteness of motor digital control affects the variation characteristics of the voltage reference voltage and sector boundary of VSVPWM, which aggravates the narrow pulse problem. (2) In the low modulation index region of three-level converters, the effective vector durations are short, and the first vector of switching sequence changes between sectors F and A, B and C, and D and E. Therefore, the traditional VSVPWM maximum coding vectors are prone to narrow pulses at the boundary of these sectors. (3) The proposed method effectively suppresses the narrow pulse and reduces the switching times of power devices. Besides, LH_VSVPWM improves output waveform quality and solves the problem of neutral-point potential imbalance during motor startup.

Boost PFC converter is commonly utilized in rectifier circuits due to its ability to achieve a high power factor and low input current distortion. For the single-phase boost PFC converter, large-capacity and low-priced aluminum electrolytic capacitors (AECs) are typically employed to balance the instantaneous power deviation between the input and the output. However, the failure-prone nature of electrolytic capacitors may result in system instability or even collapse. Therefore, the real-time detection of electrolytic capacitor status information, assessment of its service life, and timely replacement of the soon-to-be-failed electrolytic capacitor can provide an important technical guarantee for the reliability of PFC power supply operation. This paper proposes an improved "zero-crossing removal interval" harmonic injection method for online detection of capacitance parameters to solve current zero-crossing distortion caused by harmonic injection. Additionally, based on the harmonic response of the bus voltage, the harmonic capacitor current reconstruction is achieved, and a model for calculating the C_R and R_E parameters without capacitor current sampling is constructed.

Firstly, the AC and DC input-output power action characteristics of the Boost PFC converter are fully utilized, i.e., the high harmonic current injection of the current control loop produces a high harmonic voltage splitting phenomenon on the output voltage. The two split harmonic voltage signals are employed to reconstruct the capacitor current; the capacitor's low-frequency impedance model is used to estimate C_R; a mid-frequency domain harmonic capacitor parameter computation model is established to estimate the R_E. In addition, the high harmonic current injection in the current loop inevitably results in an asymmetric zero-crossing distortion of the input current, directly affecting the accuracy of the capacitance parameter computation model. Consequently, the zero-crossing removal interval harmonic current injection method is employed to solve zero-crossing distortion caused by inter-area injection. The improved “zero-crossing removal interval” method avoids the reconstructed high-order capacitor current calculation error, enhancing C_R and R_E accuracy.

Eighteen types of capacitor conditions are selected for simulation calculation, and 48 W/72 W/144 W Boost PFC experimental prototypes are established. The proposed detection method is verified under an input voltage of 60 V, a switching frequency of 100 kHz, and an output voltage of 120 V. The results demonstrated that the method exhibits high detection accuracy under symmetrical injection conditions with a 10% zero-crossing removal interval, a 10 V injection amplitude, and a 650 Hz frequency. Furthermore, the improved “zero-crossing removal interval” method can achieve parameter detection error within 5% under different loads (100 Ω, 200 Ω, and 300 Ω) and capacitor conditions (196 mΩ/412 μF and 216 mΩ/617 μF), regardless of light or heavy loads.

This paper presents the following conclusions. (1) The proposed method considers the impact of current on distortion caused by harmonic injection. A “zero-crossing removal interval” harmonic injection method improves the accuracy of capacitance parameter detection. (2) In the “zero-crossing removal interval” method, the capacitor current is obtained through algorithmic reconstruction, which avoids high-precision capacitor current sampling. The harmonic injection is achieved by the control algorithm without additional hardware equipment. (3) The proposed capacitance parameter calculation model is derived based on the AC-DC power balance, making it straightforward to extend to similar AC-DC converters.

The LLC converter plays a pivotal role in the infrastructure supporting electric vehicles, where efficiency and reliability are paramount. Its ability to efficiently transfer energy between different voltage levels makes it particularly suitable for EV charging stations, where power conversion efficiency directly impacts operational costs and environmental sustainability.

Synchronous rectification has emerged as a promising strategy for optimizing LLC converter performance. By replacing traditional diode rectifiers with active switches that operate synchronously with the converter's switching frequency, synchronous rectification minimizes energy losses and improves overall efficiency. However, existing synchronous rectification methods have faced challenges, such as complex control algorithms, sensitivity to load variations, and the need for high-frequency sampling.

Unlike conventional approaches that rely on high-frequency sampling for precise timing control, the novel synchronous rectification scheme utilizes a streamlined time-domain analysis. This approach dynamically adjusts the timing of the synchronous rectifier based on real-time feedback from the LLC converter's operating modes, ensuring optimal efficiency across a wide range of operating conditions with high-frequency sampling and alleviating the computational burden.

By reducing the complexity of control algorithms and eliminating the need for high-frequency sampling circuits, the scheme not only lowers manufacturing costs but also enhances reliability by reducing potential points of failure. This simplification is particularly advantageous in high-power applications like EV charging stations, where robustness and operational uptime are essential.

Simulation studies have validated the effectiveness of the proposed scheme under different load conditions and frequencies. Simulations have shown significant efficiency improvements compared to traditional methods, highlighting the scheme's potential to reduce energy losses and improve overall system performance.

Furthermore, experimental validation using a 6.6 kW prototype shows that the proposed scheme delivers consistent and efficient operation under steady-state and dynamic conditions, further supporting its potential for commercial EV charging infrastructure integration.

The adoption of the proposed synchronous rectification scheme promises to enhance the efficiency and reliability of LLC converters and accelerate the transition to electric mobility. As governments and industries worldwide prioritize sustainability goals and seek to reduce carbon footprints, improvements in energy conversion technologies play a crucial role in supporting the widespread adoption of electric vehicles.

In conclusion, the synchronous rectification scheme represents a significant step in evolving LLC converters for electric vehicle charging infrastructure. By overcoming traditional limitations and leveraging streamlined control strategies, the scheme enhances performance and contributes to the sustainability of transportation systems. As research continues to refine and optimize power conversion technologies, the ongoing advancements in LLC converter designs underscore their pivotal role in shaping a cleaner, greener future for global transportation.

In servo systems, the bandwidth of the current loop is increased by raising the switching frequency. However, the dead-time nonlinearity of the voltage source inverter (VSI) intensifies with the increase of switching frequency, causing the deviation between the actual and the theoretical output voltage, resulting in serious distortion of the inverter output current waveform.

The requirement of computational power constrains the implementation of high switching frequency control. Consequently, the dead-time nonlinearity compensation strategy should be more straightforward to decrease computational time, especially for high switching frequency applications. The amplitude increase is relatively modest at a low switching frequency but significantly surges at a high one, bringing on a severe degradation of the linear modulation region. It is an imperfect solution to compensate after the occurrence of dead-time, which unavoidably introduces compensation errors. Furthermore, the accurate solution of inverter nonlinear voltage error (INVE) under different currents represents a crucial aspect of achieving exact INVE compensation. Nevertheless, the existing methods are complex.

This paper proposes a novel strategy that combines no-dead-time double modulation wave pulse-width modulation (PWM) and inverter nonlinearity compensation for analyzing the dead-time nonlinearity and the nonideal characteristics of the inverter on the output voltage error. Firstly, according to the continuous current characteristics of the anti-parallel diode, the drive vacancy area is added between the complementary drive pulses to avoid the introduction of dead time. Compared with the ideal space vector pulse width modulation (SVPWM), an auxiliary modulating wave is added. Depending on the current polarity, its amplitude is adjusted up or down from the original modulating waveform. The underlap periods are generated between the complementary drive pulse by contrasting the double-modulating and the triangular carrier waves. It is practical to avoid both the bridge arm shoot-through and the introduction of dead time. Most importantly, the actual output voltage of this method is identical to the optimal voltage, which directly eliminates the dead-time nonlinearity and removes the limitation of dead time on the output duty cycle at a high switching frequency. Moreover, the control signals of each switching device are obtained based on the comparison between the double-modulating and the carrier wave. No additional control loop calculations are required, while the generated PWM signals are symmetric about the carrier midpoint.

Secondly, the inverter nonlinearity is equated to the INVE, which varies with the current. When the motor is at a standstill of ${{\theta }_{\text{e}}}={{0}^{\circ }}$, by injecting the ramp current signal into the direct axis and applying Kirchhoff's voltage law, the sum of INVE containing the nonlinear factor of the two-phase VSI is obtained. Finally, the relationship between the INVE and the current amplitude is calculated using the linear iterative interpolation approach, and the online compensation of the INVE is achieved.

The results show that the proposed strategy can increase the linear modulation region of the output voltage, eliminate the output duty cycle limitation derived from the dead-time, and effectively suppress the current harmonic distortion phenomenon caused by the dead-time nonlinearity of high switching frequency inverters. In addition, the strategy is easy to implement without additional control loop calculations, which can be applied to servo drive control systems requiring high switching frequencies.

The rotating rectifier is the key part of multiphase annular brushless excitation systems. Nevertheless, the rectifiers often experience faults caused by diode failures, which brings security risks in practice. Accurately diagnosing faults in the rotating rectifier is pivotal for ensuring the safe operation of multiphase annular brushless excitation systems. However, the types of rotating rectifier faults are diverse, and the characteristics of different faults are inherently weak. Traditional mechanism-driven diagnostic schemes offer interpretability but often struggle with precise fault diagnosis. New data-driven diagnostic schemes exhibit speed and accuracy but encounter challenges in training and debugging in practical applications. This paper proposes a hybrid mechanism-data-driven diagnostic scheme for rotating rectifier faults.

Based on the fault mechanism, the frequency domain characteristics of the excitation current after the fault are derived, and the fault characteristic patterns are summarized. Then, thresholds of the mechanism diagnosis model are calculated using finite element simulation data. Extracting the frequency domain characteristics of the excitation current allows the fault mechanism to be clearly described, thus providing a solid foundation for subsequent fault diagnosis. The current waveform under normal operation and different fault conditions can be simulated by adjusting the models, which allows for determining thresholds for various operating conditions.

Then, the fast dynamic time warping (Fast-DTW) algorithm is introduced to calculate the similarity of excitation current time-domain waveforms, subsequently forming a data-driven model combined with the k-nearest neighbors (kNN) classifier. The fast-DTW algorithm can align waveforms of different time lengths and start points to capture subtle differences between waveforms. By combining the fast-DTW algorithm with the kNN classifier, the data-driven model can realize the diagnosis of rotating rectifier faults.

Mechanism-driven and data-driven diagnostic schemes are integrated based on ensemble learning principles. Ensemble learning significantly enhances the overall performance of the model by combining the results of multiple learners. Five mechanism-driven and five data-driven models are established to obtain a final diagnostic result based on the absolute majority voting method. The hybrid diagnostic scheme exhibits the advantages of mechanism-driven and data-driven models, effectively overcoming the limitations of a single-driven model.

Finally, the verification of prototype experiments indicates that the hybrid scheme’s diagnostic accuracy reaches 100%, significantly surpassing single-driven models. Establishing diagnostic models requires offline simulation data, reducing training difficulty and improving practicality on-site. The hybrid scheme maintains a reasonable diagnostic speed while ensuring high accuracy.

In conclusion, the proposed hybrid mechanism-data-driven fault diagnosis scheme combines mechanism analysis and data-driven methods to enhance the accuracy and robustness of fault diagnosis, demonstrating excellent test performance in prototype experiments. The diagnostic approach based on the time-frequency characteristics of the excitation current demonstrates excellent interpretability, achieving accurate fault diagnosis solely through training with simulation data.

The bipolar DC distribution network offers high power supply reliability, extensive transmission capacity, and adaptable voltage levels. Developing a bipolar DC distribution network represents an effective strategy for constructing a new type of distribution network. Voltage unbalance constitutes a distinctive power quality issue within bipolar DC distribution networks. Power flow calculation serves as the fundamental tool for analyzing voltage imbalance. Nevertheless, conventional power flow calculation methods merely illustrate the transfer outcomes of voltage unbalance, failing to depict its transfer process within the network. Furthermore, in practical engineering, power is often the measured electrical quantity rather than current, making the existing power flow model based on injected current unsuitable for meeting the application requirements. Hence, this paper proposes a power-injection equation to analyze and quantify the transfer characteristics associated with voltage unbalance.

Initially, the generation and transfer mechanism of voltage unbalance within the bipolar DC distribution network is studied. The voltage unbalance transfer matrix grounded on sensitivity is established to depict the transfer characteristics of voltage unbalance factors at individual nodes. Furthermore, the analytical formulations for each component of the voltage unbalance transfer matrix are derived, and a power flow calculation technique based on the Newton-Raphson method is proposed for determining the matrix. The suggested method employs a power-injection equation for power flow modeling and integrates droop control and comprehensive load models of distributed generation. Finally, the effectiveness of the proposed approach is validated via the modified IEEE 33-node test system. Three case studies are conducted.

Numerical results reveal the following findings. (1) The proposed power flow calculation method exhibits a negligible sacrifice in accuracy, with no more than a 0.83% deviation and a calculation efficiency enhancement of 44%. Additionally, it offers the advantage of accommodating constant power loads, which is suitable for high prevalence power load or load data readily available scenarios. (2) The voltage unbalance transfer matrix effectively illustrates voltage unbalance factors’ alterations and transfer conditions at each node under disturbance conditions. Disturbances induce voltage unbalances that propagate throughout the network following the direction of power flow. Measures must be implemented to block or suppress it at critical network nodes. For instance, strategies such as load switching and energy storage scheduling encourage multi-point loads to adjust in a more balanced manner simultaneously, curtailing unbalanced transfer. Moreover, incorporating a power spring in series with a constant resistance load near the line's terminus can introduce intelligent load management, affording greater flexibility in system voltage unbalance adjustment. The deployment of voltage-regulating equipment, such as DC transformers and voltage balancers, is instrumental in obstructing unbalanced voltage transfer.

Power electronic transformer with cascaded H-bridge (CHB-PET) can realize the flexible interconnection of AC/DC microgrid and renewable energy sources such as energy storage devices and DC loads. In a practical project, CHB-PET is connected to different bus segments through two short leads that are standby for each other. Considering the fault occurring AC side of CHB-PET, the spare short lead needs to be put into operation quickly to realize the rapid recovery of power supply. However, the conventional scheme cannot distinguish whether there is a fault before the spare short lead is put into operation, and there is a risk of connecting the faulty short lead. To solve this problem, this paper proposes a scheme based on the cooperative control of CHB-PET and DC microgrid, which achieves safe input of short leads by actively injecting characteristic voltage.

Firstly, CHB is blocked to achieve fault isolation after fault occurring. The energy storage device is switched to DC voltage control mode, maintaining the DC bus voltage and ensuring the normal operation of DC microgrid load and other equipment. Secondly, CHB is unlocked and switched to the U/f control. CHB-PET can inject characteristic voltage into the spare line to detect whether there is a fault point in the line. Furthermore, a fault detection method considering the current imbalance factor is proposed to reduce the time required for fault detection, so as to realize the rapid and safe investment of spare short lead.

The verification results on PSCAD/EMTDC simulation platform show that the scheme based on characteristic voltage injection can give accurate detection results when the spare line is fault-free. When three-phase fault, phase-phase fault, double-phase to ground fault and single-phase to ground fault occur in the spare line, the transition resistance of the phase-to-phase fault is 200 Ω, and the transition resistance of the ground fault is 300 Ω. The proposed scheme can also give accurate detection results. Through the simulation verification and experimental verification of the proposed scheme in different scenarios, the consistent results are obtained, which confirms the accuracy of the simulation model and the feasibility of the proposed scheme.

Through the simulation analysis, the following conclusions can be drawn: (1) The scheme uses the CHB-PET ontology to inject characteristic voltage with controlled amplitude and frequency into the standby line. According to the difference of electrical characteristics of the standby line in different scenarios, proposed scheme can accurately detect whether there is a fault in the standby line. (2) In three stages of the proposed scheme, the collaborative control of CHB-PET and DC microgrid energy storage device is used to ensure the normal operation of each equipment in the DC microgrid after the AC short lead fault, which is conducive to the rapid recovery after the fault. (3) In the fault detection stage of spare short lead, the fault detection criterion is constructed by using the product of the characteristic current imbalance factor and the current integral value. Compared with the direct use of the current integral value, the fault detection time under high resistance fault is reduced and the protection action speed is improved.