Since lithium-ion batteries have been widely applied in energy storage systems and electric vehicles, the accurate estimation of their state-of-health(SOH) is a necessary condition for ensuring the reliable and safe operation of the system. SOH is analyzed from the perspective of capacity, with seven health indicators which are extracted from the constant current-constant voltage charging voltage and temperature curves as input. Based on the data-driven method, a sparrow search algorithm-back propagation neural network(SSA-BPNN) SOH estimation method for lithium-ion batteries is proposed, and data enhancement is applied to further improve the model's robustness. Finally, this method is verified on the NASA Randomized Battery Usage Dataset. Compared with the traditional BP neural network without data enhancement, the SOH estimation accuracy of the proposed method is significantly improved. The maximum absolute error and root mean square error of SOH estimation on the test set are less than 3% and 1.32%, respectively. Experimental results show that this method has advantages of small error, fast convergence, global search capability and adaptation to different characteristics of battery aging.

To improve the reliability and efficiency of a T-type three-level inverter, a discontinuous pulse width modulation (DPWM) strategy is proposed to reduce the common-mode voltage while reducing the switching loss, which is also named as the RCVDPWM strategy. According to the mechanism of switching sequence in the T-type three-level topology which acts on the common-mode voltage, five DPWM clamping methods for common-mode voltage reduction are summarized. It can be found that there is at least one clamping method for common-mode voltage reduction at any modulation ratio or phase angle. For those phase angle regions where multiple clamping methods exist, the switch tube of the phase with the largest absolute value of current is preferentially selected for clamping to reduce the switching loss. Meanwhile, the proposed strategy can ensure that the DC component of neutral-point voltage is zero, and thus the neutral point shows a self-balancing capability. Experimental results verify the feasibility and effectiveness of the proposed RCVDPWM strategy.

To improve the dynamic response performance of a dual active bridge (DAB) converter with dual phase shift(DPS) control during load switching and reduce the current stress, a novel dual phase shift (NDPS) control method is studied. By changing the shifting direction of the internal phase shift angle in traditional dual phase shift (TDPS), the relationship between the transmission power and phase shift ratio is reconstructed, and the adjusting range of phase shift ratio is extended. The solving method for the optimal phase shift ratio of DPS control under the condition of current stress minimization is studied, and the dynamic response characteristics of NDPS and TDPS control under load switching conditions are compared and analyzed. Finally, an experimental platform of DAB converter was built to verify the theoretical analysis, and experimental results show that the optimal phase shift ratio combination based on current stress minimization can effectively reduce the current stress under light load conditions. At the same time, NDPS control has better dynamic response characteristics than TDPS control.

Along with the widespread applications of lithium batteries in industry and daily life, the efficiency and speed under balanced charging strategies for lithium battery packs have become increasingly important. A modular cell-to-pack-to-cell(CPC) balanced charging system is constructed to solve the problem of fast equalization charging for lithium battery packs. First, the equalization system is modularized, and the equalization circuits within and between modules are established. Then, an optimization strategy for balanced charging is proposed, under which the proposed model is solved hierarchically, i.e., the charging time is calculated using the binary method in the top layer, and the charging current is optimized using the gradient descent method in the bottom layer. Finally, through a comparison with the charging time, equalization time, cell terminal voltage and equalizer voltage under the non-modular balanced charging strategy, the feasibility and effectiveness of the proposed strategy are verified.

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.

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.

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.

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.

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 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.