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

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.

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.

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

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 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.

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%.

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.

In the burgeoning field of new energy vehicles, silicon carbide representing a new generation of semi-conductor power devices is progressively replacing silicon-based IGBTs, which also sets higher standards for the motor control performance within the corresponding innovative technological ecosystem. The precision of motor parameters is becoming increasingly critical for enhancing the performance of electric control systems as they evolve from the tradi-tional PI control and direct torque control to advanced algorithms such as model predictive control and neural network control. Aimed at the problem that the classic linear model for permanent magnet synchronous motors cannot adapt to complex and variable conditions due to nonlinear factors such as cross-saturation, a nonlinear magnetic flux identifica-tion method based on Gaussian process regression is proposed. By employing a second-order generalized integrator to acquire the magnetic flux data under dynamic conditions, the system identification is completed. Finally, the effective-ness of the proposed approach and the accuracy of parameter identification were verified through simulation and experi-mental results.