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 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.

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%.

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.

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.

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.

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.

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.

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.

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.