Silicon carbide metal-oxide-semiconductor field effect transistor (SiC MOSFET) has attracted attention from the industry owing to its excellent characteristics such as high voltage, high frequency and low conduction loss. However, compared with the silicon-based IGBT, the problem of gate oxide reliability caused by the high defect density at the SiC/SiO2 gate oxide interface has become a key bottleneck restricting the large-scale applications of SiC MOSFET devices. By sorting out and analyzing the research results of the gate oxide reliability of SiC MOSFET at home and abroad in recent years, the causes of the gate oxide reliability problems at present were elaborated upon, and various commonly-used gate oxide reliability evaluation methods were summarized and compared. Finally, the gate oxide reliability of SiC MOSFET under extreme operating conditions and the development status of technologies for improving its performance were discussed.

The traditional linear control method for a Boost converter has a poor dynamic performance and weak robustness to load disturbance. To solve this problem, a fixed-frequency sliding mode current control method based on power balance is proposed. First, the observed value of load current is used to calculate the input power, which is required to maintain the stability of output voltage. Then, the input power of the converter is adjusted by controlling the inductor current, so that the system's state trajectory is restrained on the sliding mode surface that possesses invariance to load disturbance, thus ensuring the system's large signal stability and improving its dynamic performance. Finally, based on the equivalent control principle, the equivalent sliding mode control is achieved through the PWM technique to avoid problems of chattering and unstable switch frequency. Simulations of the Boost converter under the condition of step load change are carried out in Simulink, and the proposed method is compared with the traditional linear control method. Results show that when using the proposed method, the system's dynamic performance is better and its large signal stability under large load disturbances is guaranteed.

The design of DC-DC converters which are applied to vehicle auxiliary power modules (APMs) is taken as a research object, the topology of a two-stage DC-DC converter consisting of a three-level Boost (TL-Boost) topology and a half-bridge LLC resonant topology is proposed, and its working principle is analyzed. The front-stage TL-Boost topology converts a wide range of input voltage into a stable voltage, ensuring the high-efficiency operation of the back-stage half-bridge LLC resonant topology. The feasibility and correctness of the proposed DC-DC converter were verified by establishing an experimental platform and carrying out relevant experiments.

Under the background of energy crisis and environmental issues, the high-gain DC-DC converter is indispensable in renewable energy applications. A dual-switch quadratic structure is proposed to enhance the voltage gain of the traditional quadratic boost converter while reducing the current stress of switches. On this basis, by combining the switched capacitors and a coupled inductor, a dual-switch quadratic high-gain DC-DC converter with a couple inductor is put forward. This converter has advantages such as a very high voltage gain, a pair of switches with the same phase, low voltage stress of switches and output diode, and zero-current switching off in many diodes. The operating principle and steady-state performance of the converter are analyzed in detail, including the voltage gain derivation and the voltage and current stresses of components. Finally, a 120 W prototype was fabricated to verify the theoretical analysis and the feasibility of the converter.

In the application of wide output voltage range, some problems exist in an LLC resonant converter under the traditional frequency control, such as a wide switching frequency regulation range, a large circulation current and difficulty in high-efficiency operation. To solve these problems, a dual-full-bridge LLC resonant converter under a fixed-frequency phase-shift and fixed-frequency PWM hybrid control strategy is proposed, which is suitable for the wide range of output voltage. This converter is composed of two full-bridge LLC resonant converters sharing one bridge arm, and the output voltage is modulated by the hybrid control, so that a quadruple voltage gain and a wider output voltage range of the resonant converter can be realized. Meanwhile, the problems that the large circulation current exists under the traditional frequency control and the soft switching cannot be realized at a small phase shift angle are solved, thus improving the system efficiency. The switching frequency of the converter is always equal to the resonance frequency, and the voltage gain is independent of load, which is helpful for the design of the magnetic element. At the same time, the soft switching can be realized in the full load range. Finally, a detailed analysis of the circuit principle was given, which was further verified by simulations. An experimental platform was also established to validate the feasibility and effectiveness of the proposed converter.

The dual-active-bridge (DAB) converter is a key device in a bidirectional power transmission system. In this paper, its fundamental operation principle and topologies are reviewed at first. Then, four basic modulation strategies for the DAB converter are introduced, including single-phase-shifted, dual-phase-shifted, extended-phase-shifted and triple-phase-shifted strategies. Moreover, the modeling and optimization methods based on these four modulation strategies are compared and analyzed. Finally, some problems faced by practical applications and the corresponding solutions are discussed. Along with the development of DC power distribution, energy storage and distributed energy resources, DAB converters will have broad application prospects.

Aimed at the problems of a traditional dual-active-bridge (DAB) converter such as large switching loss, large circulating current, narrow range of load variation and low operating efficiency, a novel power control method for DAB converter based on variable inductance and phase shift (PS) angle is proposed, in which the variable inductance and PS angle are taken as the main control parameters to improve the operating efficiency of the DAB converter in a wider range of load variations. In addition, the transfer function of the DAB converter is linearized to improve the practicality and convenience of the controller. Because the device saturation is controllable in the proposed method, the core size can be reduced to optimize the converter size. Finally, the effectiveness and superiority of the proposed method were verified by experiments. Results show that under the condition of maximum PS angle, the inductance variation significantly affected the power transmission of the DAB converter, and its overall operating efficiency was about 5% higher than that of the traditional DAB converter under both the light and heavy load conditions.

Based on the two-stage (AC/DC and DC/DC) structure of a DC charging pile for electric vehicles(EVs) and through the analysis of the functional requirements of the two-stage circuit structure, a MATLAB/Simulink simulation model is built with a main circuit which consists of a Vienna circuit as the front-stage AC/DC rectifier and a Buck-Boost circuit as the rear-stage DC/DC voltage conversion circuit. Simulations are performed with load set as a pure resistive load and the PNGV model of a battery, respectively. Simulation results meet the requirement of parameters such as output voltage stability accuracy, output voltage ripple and input current harmonics, which proves that the model can be used to analyze the power grid loaded by EVs and promote the study on the impact of EVs on power grid.

Aimed at the problems in the existing nine-level inverter such as many devices and a complex modulation strategy, a novel switched capacitor nine-level inverter is proposed. The topology of this inverter is composed of only one single DC power supply, nine switches, two capacitors and two diodes, and it can output nine levels and double the boost at the same time. The voltages of capacitors are self-balancing, and the complex control algorithm and external voltage sharing circuit are not required. The phase disposition PWM strategy is adopted to modulate the inverter. The working states of four pairs of switches in the inverter are complementary, and the NOT gate logic circuit can be used to reduce the complexity of the modulation strategy. First, the topology and working principle of the inverter are analysed theoretically. Second, the modulation strategy is introduced in detail, and the advantages of this topology are introduced by comparing it with other nine-level inverters. Finally, the feasibility and effectiveness of the proposed topology and modulation strategy were verified based on the established simulation circuit and experimental platform.

Aimed at the disadvantages of a traditional AC-AC variable frequency converter such as too many power devices, complex control and low power factor, a control method for an AC-AC variable frequency circuit with continuous output frequency based on the plugged pulse AC-AC variable frequency circuit control principle is proposed. The circuit topologies and working principle of a three-phase to three-phase converter and a six-phase to three-phase converter are presented in detail. The simulation models of these two variable frequency speed control systems are established in a MATLAB/Simulink simulation environment, and the simulation results are consistent with the theoretical analysis. Finally, prototypes were fabricated, and the effectiveness and feasibility of the proposed novel control method for variable frequency speed control system were verified by simulation and experimental results.

With a substantial increase in the proportion of power electronic grid-connected devices in a power system, the output characteristics on the power supply side are obviously different from the output characteristics of traditional power supply represented by synchronous generators. The fault analysis of power electronics dominated power systems, especially the network asymmetrical fault analysis, faces new challenges. However, the existing fault analysis methods basically do not realize the time-varying amplitude/frequency characteristics of the devices' internal voltage, and the available time-varying amplitude/frequency symmetrical components method based on time-varying amplitude/frequency signals is just a set of mathematical decomposition formulas without explicit physical connotation as a support. Under this background, the characteristics of the relationship between the three-phase instantaneous values formed by the positive-and negative-sequence time-varying amplitude/frequency rotating vector are analyzed, and the

In the traditional power system, the synchronous generator independently forms the internal voltage amplitude/frequency, which is connected to grid to establish the system voltage. However, the establishment of grid voltage at present is increasingly dependent on renewable energy equipment. Under the phase-locked synchronization, the grid-connected converter needs to detect the grid voltage to form the internal voltage, which seems to be different from the synchronous machine that independently forms the internal voltage and further establishes the system voltage. On this basis, the mechanism of internal voltage amplitude/frequency formed by the current control of the phase-locked synchronous converter is studied, and it is explicitly stated that the internal voltage amplitude/frequency is uniquely determined by current, which is essentially the same as the synchronous generator independently forming the internal voltage to establish the system voltage. In this paper, based on the control structure and the nature of forming the AC instantaneous value, it is explained that the converter output is essentially the internal voltage amplitude/frequency. Then, starting from the closed-loop dynamic process of equipment and network, the redundant relationship between terminal voltage and current is clarified. After the input current is determined, the internal voltage amplitude/frequency can be uniquely determined accordingly. Finally, combined with the simulation analysis, the correctness of uniquely determining the internal voltage amplitude/frequency by input current is demonstrated.

Although the LCL filter has a good performance of suppressing high-frequency harmonics, it may cause problems such as resonance oscillation and instability. For an LCL grid-connected inverter, the conventional capacitor-current-feedback type active damping method can suppress the resonant peak effectively, at the cost of additional current sensors. Under this background, a novel active damping control strategy based on an H∞ filter is proposed. The state space model and process noise model of the LCL filter are derived to solve the H∞ filter. The filter capacitor current can be estimated according to the information about grid current and the voltage at a point of common coupling, and feedback is further completed. The system damping is improved, and the estimation accuracy can be guaranteed even if parameter perturbations exist in the LCL filter. Simulation and experimental results show that the proposed method was insensitive to changes in the parameters of the LCL filter and the grid impedance, thereby verifying its feasibility and superiority.

In a certain environment where regional wind farms distribute irregularly, the traditional convolutional neural network prediction method cannot reflect the distribution states or influence relationship of regional wind farms, and it is difficult to accurately predict the wind speed. First, to solve this problem, the technology of graph convolutional networks is used for feature modeling, and the connected graph and weight matrix are established according to the topology of multiple wind farms and the cross-correlation coefficient of wind speed in each region. Second, depending on the time dynamic characteristics of wind speed at wind farms, an improved parallel convolution structure is used to obtain the correlation between wind speed series in multiple time periods at the same wind farm. Third, based on the spatial correlation and delay effect of wind speed at wind farms, the spatio-temporal characteristics of wind speed in different regions are aggregated by using a second-order aggregation method. Finally, the verification of data from one regional wind farm shows that the proposed method can extract the spatio-temporal characteristics and improve the performance of ultra short-term wind speed prediction for multiple wind farms on 0-4 h prediction scale.

Affected by factors such as wind speed and light intensity, wind power generation has characteristics of randomness, intermittence and large fluctuation, so its direct grid connection will cause damage to power grid. To realize a smooth grid connection of wind power and provide safe and reliable power supply to an urban rail transit system, a hybrid energy storage system composed of super capacitors and lithium batteries is proposed as a stabilizing measure. As the traction load of urban rail transit also fluctuates greatly, the hybrid energy storage system not only stabilizes the output of wind and photovoltaic (PV), but also stabilizes the traction load. The wavelet packet decomposition technology is used to decompose and reconstruct the traction load and wind and PV output power signals on multiple scales, the low-frequency wind and PV grid-connected power and medium-and high-frequency components are obtained, and batteries and super capacitors are used to absorb the medium-and high-frequency components, respectively. Aimed at the minimum comprehensive cost of hybrid energy storage system, the state-of-charge and power limit of the hybrid energy storage system are taken as constraints. The differential evolution particle swarm optimization algorithm with shrinkage factor is used to minimize the annual comprehensive cost of

To solve the instability problem caused by time-varying communication delay and uncertain faults in an isolated island AC microgrid, a novel robust hierarchical control method is proposed, which includes cascade current loop, voltage loop, virtual impedance and droop control loop. First, a robust controller based on adaptive backward integral non-singular fast terminal sliding mode control is designed in the current loop to adjust and track the current reference value under unknown bounded uncertainties and external disturbances. Second, the hybrid H2/H∞ control is used in the voltage loop, and the state feedback control law is used to generate the inner loop reference value to increase the robustness of the controller to disturbances, and sufficient conditions are given based on the linear matrix inequalities. Considering the unstable effects of time-varying delay (TVD), a distributed protocol based on consistency is adopted in the second control layer to improve the robustness of the controller against TVD. Third, droop control and virtual impedance loop are used to improve the system's power distribution accuracy. Finally, the performance of the proposed control method was evaluated by hardware-in-the-loop simulation, and its effectiveness was verified. Simulation results show that compared with the existing methods, the proposedmethod has advantages in transient response, steady-state performance and fault crossing capability under large and small signal disturbances.

The use of virtual synchronous generator (VSG) strategy for a photovoltaic (PV) inverter can achieve inertia and damping support. The traditional VSG cannot provide transient reactive voltage support for the system and cannot meet the demand for voltage regulation during the low-voltage ride-through (LVRT) periods. After the occurrence of a grounding fault, the VSG control of the PV inverter is switched to model predictive control (MPC). After the grounding fault is removed, the MPC is switched back to the VSG control strategy. To improve the target current tracking capability during the LVRT periods, an adaptive objective function is set in the MPC. MATLAB/ Simulink simulation and experimental results show that the PV VSG under the novel MPC has an LVRT capability. During the LVRT periods, the MPC current control is precise, and there is no transient current surge during the switching from the MPC to VSG control.

The grid-forming(GFM) converter is one of the main components of high-permeability power electronic equipment, and its fault ride-through(FRT) capability is an important basis for ensuring the stable operation of a power system with a high degree of power electronics. On this basis, an FRT strategy for GFM converter is proposed, which not only considers the hardware constraints(i.e., current constraints) of the converter, but also can keep it running in protected mode under symmetric and asymmetric faults. First, the FRT-related problem of the GFM converter is analyzed in detail. Then, an appropriate FRT model and the corresponding control method are established. Finally, the effectiveness of the proposed method was verified by power-hardware-in-the-loop simulation and experiment. Results show that compared with a grid-following converter, the proposed control method can guarantee the instantaneous injection of reactive current when the GFM converter fails to prevent the overcurrent problem, and the GFM converter can still operate fault-tolerant under serious fault conditions.

Aimed at the problem that the traditional virtual inertia control method cannot restore the DC bus voltage to its rated value at the frequency recovery stage, a virtual inertia control method using a high-pass filter is proposed. MATLAB/Simulink simulation results show that the changes in DC bus voltage can reflect the microgrid frequency in real-time, and the novel virtual inertia control strategy can ensure the frequency stability in the entire changing process. At the frequency recovery stage, the virtual inertia is reduced to accelerate the frequency recovery, providing sufficient time margin for subsequent frequency adjustment. The high-pass filter virtual inertia control method can restore the DC bus voltage to its initial value and maintain the DC bus voltage stability of the new energy storage microgrid without changing the inertia support of the super capacitor energy storage.

Aimed at uncertainties in the output from grid-connected wind turbine, the scenario analysis method based on probability occurrence is adopted to transform the uncertainty model into a multi-scenario problem with different occurrence probabilities, and a reactive power optimization model with the goal of minimizing the active power loss and voltage deviation is established. In view of the poor diversity of Pareto frontiers obtained using the traditional methods, an adaptive grid multi-objective particle swarm optimization (AG-MOPSO) algorithm is proposed, which uses adaptive grids to obtain the density of particles in external archives, selects the global optimal particles and maintains the scale of the external storage library according to the density information as well as the betting mechanism, thus effectively ensuring the uniformity and diversity of the Pareto frontier distribution. This algorithm is used to perform reactive power optimization calculations on an IEEE 33-bus system with wind power, and it is also compared with the existing NSGA-II algorithm. Results show that the Pareto frontier obtained using this algorithm is better, which verifies the feasibility of the proposed model and algorithm.

The traditional phase-locked loops (PLLs) in a VSC-HVDC system such as a synchronous reference frame PLL (SRF-PLL) and a dual second-order generalized integrator PLL (DSOGI-PLL) cannot accurately track the positive-sequence voltage phase of grid fundamental wave under non-ideal power grid, which will cause different degrees of phase-locked error, affect the control performance of VSC and reduce the system stability. To solve this problem, an improved DSOGI-PLL scheme is proposed. First, the attenuation characteristics of SOGI-QSG at different frequencies are analyzed according to the Bode diagram, and the limitations of DSOGI-PLL applications are obtained. Then, based on the voltage of harmonic grid, the internal model of repetitive control is introduced on the basis of DSOGI to realize the real-time tracking and regulation of harmonic signals, thus suppressing the harmonic voltage interference. At the same time, considering the DC bias and voltage frequency fluctuation of power grid, a method of DC bias elimination and frequency adaptation is proposed to realize the adaptive phase tracking of power grid. Finally, the superiority of the proposed strategy was verified through a comparison between the simulation and experimental results.

To improve the metal object detection performance for an electric vehicle wireless charging system, a sensitivity optimization method for the detection coil was proposed. The equivalent electromagnetic model of a rectangular detection coil with a metal object approaching was established. The changing mechanism of the physical parameters of the coil was studied, and a theoretical formula for changes in the parameters of the detection coil which were caused by metal objects of different sizes was obtained. The influence of several configuration parameters on the sensitivity of the detection coil was analyzed, and the configuration of the detection coil was optimized by combining the actual operating conditions of wireless charging. Through the electromagnetic field simulation and experimental verification, the accuracy of the theoretical model was proved. Finally, a metal object detection experiment was carried out in a 3 kW wireless charging system, which verified that the metal object detection system built on the basis of the optimized detection coil can detect metal objects with a size of 25 mm and above. In addition, it had anti-interference capability.

Compared with the traditional plug-in charging method, it is safer and more convenient to employ an inductive power transfer (IPT) system to charge autonomous underwater vehicles (AUVs). To alleviate the strong magnetic field inside the AUV hull and the dramatic power fluctuation caused by the rotation misalignment of the AUV under the turbulent water, a three-phase IPT system with a novel coupling structure is proposed. The coupler is composed of three transmitting coils and four receiving coils connected in alternating reverse series, which can suppress the central magnetic field and improve the anti-rotation misalignment performance simultaneously. The Maxwell simulation results show that when the AUV hull rotates, the equivalent mutual inductance Meq fluctuation is less than 2%, and the magnetic field of the AUV center always maintains a low level. In addition, to simplify the system analysis, a decoupling method based on a passive component is adopted to decouple the three transmitting coils. A laboratory-scale prototype based on an LCC-S compensation topology was built to verify the feasibility of the system. Experimental results show that when AUV rotated, the output power varied from 536 W to 595 W with a maximum fluctuation of 9.91%. The maximum DC-DC efficiency of the system was 86.28%.

At present, the transmitting coil in a dynamic wireless charging system for electric vehicles usually adopts a segmented guide rail structure to realize the relay dynamic wireless charging. However, the problem of mutual inductance drop will occur at the switching of the guide rail and result in the reduction of the system transmission efficiency, and this is more prominent at the corner. A corner dynamic wireless charging model was established, and the relationship between the mutual inductance of primary and secondary coils and the deflection angle was deduced through theoretical analysis. An improved structure of the guide rail transmitting coil at the corner was proposed and simulated, and a corner dynamic wireless charging platform based on resonance magnetic coupling was built. Simulation and experimental results show that by using the improved guide rail transmitting coil structure, the mutual inductance drop of the wireless charging system was significantly reduced, and the system transmission efficiency was improved by 8.66% at the maximum deflection angle, thereby verifying the effectiveness of the improved coil structure.

The state-of-charge(SOC) of lithium-ion battery is an important parameter for the operation and maintenance of a battery management system(BMS), and its accurate estimation is related to the real-time monitoring and safety control of lithium-ion battery. The traditional unscented Kalman filter(UKF) algorithm has the risk of making the covariance matrix negative when estimating the SOC of lithium battery, and the estimation accuracy is not optimal. To solve the shortcomings of this algorithm, a ternary lithium-ion battery is taken as the research object, and a second-order RC equivalent circuit model is established to describe the working characteristics of the battery. Based on the traditional UKF algorithm, a square-root double unscented Kalman filter(SR-DUKF) algorithm with double unscented transformation is proposed, and it is verified under multiple working conditions. Experimental results show that the improved SR-DUKF algorithm can better estimate the SOC of lithium-ion battery based on the second-order RC equivalent circuit. The average errors under HPPC and BBDST conditions are 0.59% and 0.52%, respectively, and the convergence times are 60 s and 110s, respectively, which verifies that the improved SR-DUKF algorithm has a higher estimation accuracy, better convergence and better robustness.

To obtain the state-of-charge (SOC) estimation value well, a second-order equivalent circuit model is selected as the research object. Aimed at the disadvantage that the recursive least squares method with a forgetting factor is easy to be disturbed by environmental factors such as noises in the parameter identification, a bias compensation recursive least squares method is proposed to realize the accurate identification of model parameters, and the SOC is estimated combined with the unscented Kalman filter algorithm. In view of the disadvantages of the unscented Kalman filter algorithm such as poor stability, the weight vectors are used to update the Kalman filter gain in the filter algorithm. Experimental results show that the total error of the proposed algorithm in estimating SOC was controlled within 2.7%, which verified the robustness and effectiveness of the algorithm.

Simulation substation batteries often work under discontinuous operation conditions, which will result in capacity regeneration of batteries during their performance degradation. The degradation of batteries shows nonstationary and random characteristics, leading to a low prediction accuracy for the remaining useful life(RUL). Aimed at the problem of RUL prediction of batteries with capacity regeneration, a prediction method is proposed based on variational mode decomposition(VMD) and bat optimized kernel extreme learning machine(Bat-KELM). First, VMD is employed to decompose the battery state-of-health(SOH) time series into overall degradation components and capacity regeneration components. Then, Bat-KELM is used to construct prediction models of each component, so that the prediction accuracy of component trend is improved. At last, the prediction results of all components are blended together to yield the accurate battery SOH prediction results as well as the RUL results. The proposed method is applied to the analysis of battery degradation instance data, and results show its superiority in terms of prediction accuracy compared with the KELM and VMD-KELM models.

The light-emitting diode (LED) driver usually needs a large electrolytic capacitor to reduce its low-frequency current ripple. Therefore, the short life of the electrolytic capacitor is an important factor restricting the life of LED driver, and eliminating the electrolytic capacitor is a key to the long-life LED driver. Under this background, a two-switch electrolytic capacitor-less LED drive circuit topology based on flyback converter is proposed. The auxiliary power balance circuit and flyback converter are integrated, and a balance between the instantaneous input power and output power is realized through two switches. The electrolytic capacitor is eliminated, the low-frequency ripple of output current is suppressed, and a high power factor is realized. The working principle of this topology is analyzed in detail, and a control strategy for its circuit topology is put forward. Finally, a 30 W prototype was built, and experimental results verified the feasibility of the proposed topology.

Aimed at the current imbalance problem in parallel connected multiple light-emitting diode (LED) strings, an efficient multi-output LED driver is proposed to achieve current sharing among different LED strings and improve the efficiency of the circuit. A Boost converter and a series-resonant converter are cascaded to achieve current sharing and a high voltage gain. The transformer leakage inductance suppresses the switch's current rising rate in the turn-on period, which provides the zero-current-switch (ZCS) condition. Moreover, a lossless snubber circuit is added to slow down the switch's voltage rising rate in the turn-off period to significantly reduce the switching loss, and a large magnetizing inductance of transformer is selected to reduce the transformer loss. Meanwhile, only one active switch is used, which reduces the circuit cost and simplifies the control. Therefore, current sharing, high efficiency and high voltage gain are obtained, and the cost is low. The circuit operational principle and operating characteristics together with the specific procedure of parameter design are analyzed and presented in detail. Finally, a 7.9 W two-output prototype with 12 V input voltage was built to verify the effectiveness of the proposed LED driver.

The wide applications of insulated gate bipolar transistors (IGBTs) pose high requirements for their switching performance. However, the conventional gate drive(CGD) has limited regulation effect on voltage and current overshoots in the switching process of IGBTs, because it always sacrifices the switching time and switching loss while reducing overshoots. A novel active gate drive(AGD) control method is proposed to suppress the current and voltage overshoots generated in the switching process of IGBTs, i.e., the driving voltage at the high di/dt and dv/dt stages of IGBTs is adjusted to reduce the changing rates of current and voltage, so as to suppress the current and voltage overshoots. Experimental results show that compared with the conventional driving methods, the proposed method can significantly reduce the current and voltage overshoots in the switching processes of IGBTs without reducing the switching speed or increasing the switching loss.

In a closed-loop control system, the aging monitoring method for power devices based on electrical parameters is one of the difficulties in the field of power electronics reliability. The direct torque control (DTC) system of a permanent magnet synchronous motor (PMSM) is taken as an example, and an on-line monitoring method for the aged state of power devices in a power inverter is studied based on the phase diagram of flux linkage and current. First, the aged characteristics of power devices are analyzed, and it is concluded that the on-state resistance will increase due to the aging of bond wires. Second, the relationship between power device bond wires aging and the phase diagram of flux linkage and the relationship between aging and direct axis current and three-phase current peak value are studied, and the aging monitoring methods are proposed accordingly. Finally, through several groups of simulation experiments, it is verified that both the monitoring method based on the phase diagram of flux linkage and the monitoring method based on current can realize on-line monitoring of the aged state of power device bond wires in the power inverter. The monitoring method based on the phase diagram of flux linkage is easy to observe when there are some fluctuations in the system flux, so it is not desirable considering that the power device has already been in a failure state at the same time. In comparison, the monitoring method based on three-phase current can more accurately monitor the aged state of power devices, and its effect is more advantageous.

In the design of switching power supply inductors, the calculation of magnetic circuit parameters is of significance. For inductors with an open air gap in the column of EE-type iron cores, the total magnetic flux is divided into seven equivalent magnetic fluxes by using the method of magnetic field division through finite element simulation and theoretical analysis. The concept of invalid number of turns is proposed, and the analytical expression for equivalent area of air gap permeability is obtained on the basis of fully considering the influences of diffusion magnetic flux, bypass magnetic flux and uneven distribution of magnetic flux in the core. In addition, according to the equivalent magnetic circuit model, the analytical expression for inductance factor A₁ is obtained. The concept of inhomogeneity coefficient of magnetic flux density distribution is also proposed, and based on the maximum magnetic flux density per unit current, the analytic expression for saturation current I₁ is obtained. Afterwards, the magnetic circuit parameters are accurately calculated using Excel. Finally, the accuracy of the proposed formulas was verified by experimental measurements, providing a useful reference for designers.

Under certain parameters, a permanent magnet synchronous motor (PMSM) will exhibit nonlinear chaotic behavior, which is mainly manifested in torque and speed oscillation, resulting in unstable system performance. Under this background, a sliding mode control (SMC) experiment was carried out on an actual motor platform. After a reasonable process of data, the corresponding system phase diagram was drawn, and it was compared with that without SMC, thereby verifying the chaotic phenomenon from another point of view. Based on the analysis model of chaotic motion of PMSM, the chaotic dynamic behavior of PMSM was studied theoretically by using the stability theory and equilibrium point properties. It was found that the experimental results were consistent with the numerical simulation, which verifies the existence of chaos and the correctness of theoretical analysis and shows that SMC has a better inhibitory effect on the chaotic phenomenon.

Aimed at the high harmonic content of a model predictive controller (MPC) without modulation modules, a novel model-based variable sampling period MPC strategy is proposed and applied to a five-phase induction motor drive system. The problem caused by the fixed-discretization of time in the MPC is analyzed, but the introduction of modulation or modulation substitution to solve this problem will increase the complexity of the control system. Therefore, a simpler and more natural idea is adopted. Specifically, the sampling interval is changed based on the pursuit algorithm, and the optimal control action and implementation time are determined by combining with the MPC, thus realizing the variable sampling period MPC strategy. Experiments were carried out using the five-phase induction motor drive system, and experimental results verified the excellent reference tracking and current harmonic performance of the novel variable sampling period MPC.

In view of the problems of dual-stator winding induction machines (DSWIMs) under traditional direct torque and flux control such as large torque, large flux and large current ripple, and considering that it is difficult to control the flux at low speed and the corresponding noise level is high, a novel direct control method for speed and flux based on super twisting sliding mode controller (STSMC) is proposed for DSWIMs. A nonlinear controller with zero convergence error in finite time is designed, which meets the Lyapunov stability condition. On this basis, a novel torque allocation algorithm for DSWIMS is put forward, which can make the DSWIMs run in a wider speed range, including zero speed. The electromagnetic torque is provided by two sets of winding according to its rated power. In addition, a full-order observer based on sliding mode control is designed for DSWIMs, which can accurately estimate the winding flux, flux angle and rotor speed to achieve the optimal flux state. Finally, an experimental test was carried out on a 3.3 kW DSWIM drive system to evaluate the performance of the proposed DSWIM control scheme. Experimental results show that the proposed control method, torque allocation algorithm and full-order observer were effective in different speed regions.