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.

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.

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%.

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.

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.

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.

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.

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.