With the massive growth of the electric vehicle (EV) market, the applications of EV charging equipment have also increased. Aimed at the disadvantages of traditional EV charging converters such as a small voltage-gain range, a low efficiency in low voltage output mode and a high voltage stress in rectifier diodes on the secondary side, the topology of a three-level LLC resonant converter with integrated flying-capacitor cell is improved, and a Burst control strategy with variable pulse width is proposed to enhance the efficiency in low voltage output mode. Through the hybrid control composed of pulse frequency modulation and the proposed Burst control strategy with variable pulse width, a wide output voltage is achieved, and the voltage-gain range under the Burst control strategy with variable pulse width is analyzed using first harmonic approximation. Finally, an experimental prototype with maximum power of 2 000 W was built, and results verified the feasibility of the novel topology of the improved three-level LLC resonant converter with integrated flying-capacitor cell and its Burst control strategy with variable pulse width.

A flexible DC-DC converter with four output connectors is proposed, which can freely switch between a three-level Boost topology and a totem-pole Boost topology according to different connections of output connectors. The operation modes and steady-state performance of these two topologies are analyzed, along with the corresponding application scenarioof each topology. In addition, the topology switching condition and practical implementation are also discussed. It is found and verified that the totem-pole Boost topology features a large step-up ratio. A circuit model is built in the PSIM simulation environment, the component parameters are designed, and the related simulation results are given. A 640 W hardware prototype with a peak efficiency of 98.5% was tested, and part of the key waveforms were plotted. Simulation and experimental results show that this flexible DC-DC converter has characteristics of application flexibility, a simpler circuit structure and a higher efficiency.

The grid-forming photovoltaic systems with traditional three-phase pulse width modulation (PWM) inverters has problems such as large harmonics and low efficiency, and the main modeling research on grid-forming virtual synchronous generator (VSG) control at present does not take into account the influences of inverter topology and multilevel converter on the system stability. Since the T-type three-level has advantages including small harmonics and low switching loss, a universal T-type three-level state space average model applied to grid-forming VSG is proposed. An equivalent controlled source circuit is formed with a substitution of the controlled source by averaging the switching devices in the circuit, and a complete state space equation is established for stability analysis. Finally, simulations and experiments were carried out to verify the adaptability of the established equivalent controlled source model and the actual circuit. Results show that the output characteristics of the VSG mathematical model based on the controlled source are almost consistent with those of the actual model, and it has good stability.

Under over-resonant operating conditions, a CLLLC resonant converter with frequency modulation control will generate excessive current stress. On the basis, a control strategy based on phase-shift frequency modulation is proposed to suppress the current stress. A resonant current model under phase-shift frequency modulation control is established by the first harmonic approximation method. According to the soft switching condition and transmission power characteristics of the converter, the phase-shift values on the primary and secondary sides of the isolation transformer are obtained. Combined with the switching frequency obtained by frequency modulation control, the resonant current stress is reduced. Finally, a circuit simulation model and an experimental system of the CLLLC resonant converter were built to verify the analytical conclusions, and results show that the proposed strategy has a significant inhibitory effect on current stress.

To improve the stability of a vehicle-mounted flywheel energy storage system (FESS) under changes in speed and load, a charge and discharge control strategy for switched-reluctance machine (SRM) driven FESS (SRM-FESS) based on fuzzy proportional integral derivative (PID) was proposed. This strategy is based on the basic structure and principle of the system, and a fuzzy PID controller with adaptive parameters and the control models of charge and discharge were constructed. During the charging process, a dual closed-loop control of speed and current was adopted, where the fuzzy PID control was used for the outer-loop speed control, while the low-speed current chopper and high-speed angle position control were used for the inner-loop current control to achieve the stable operation at variable speeds. During the discharging process, a dual closed-loop control of voltage and current was used to stabilize the output voltage and limit the current. Finally, the simulation results under multi-condition operation prove that the fuzzy PID control can effectively improve the response speed and reduce the overshoot of speed and voltage, indicating that the charge and discharge control strategy realize the stable operation of FESS under sudden changes in speed and load.

The state-of-charge (SOC) estimation of batteries generally uses the principle of ampere-hour integration to construct SOC models, which are further combined with filtering algorithms. To address the problems of a slow convergence speed and complex calculation, a predictive static open circuit voltage (PSOCV) method is proposed based on the open circuit voltage principle and second-order RC circuit models. The feasibility of discrete-time forward and backward difference state-space equations was discussed, and the parameter accuracy was also compared between linear interpolation (LI) fitting and least squares (LS) fitting. Experimental results show that LI fitting is generally better than LS fitting. The average absolute error of SOC estimation obtained using the LI-PSOCV algorithm under HPPC and UDDS operating conditions is below 1%. Compared with the cubature Kalman filter (CKF), the LI-PSOCV algorithm can converge instantly when the initial SOC value deviates and run faster.

The curve of relationship between the state-of-charge (SOC) and open-circuit voltage (OCV) of lithium-ion batteries is the core factor affecting the SOC estimation accuracy. However, the traditional methods obtain the SOC-OCV curve through incremental OCV tests, which require a lot of time. Under this background, a method for reconstructing SOC-OCV curves at different temperatures is proposed in this paper, so as to improve the SOC estimation accuracy while reducing the experimental time. First, a small number of key OCV test points are determined by the SOC-OCV curve obtained from the traditional incremental OCV test at room temperature. At other temperatures, the particle swarm optimization algorithm is used to identify the OCV value in untested areas, with the determined key OCV test points as the boundary and 5% SOC as an interval. Based on the test and identified values of OCV, the SOC-OCV curves at different temperatures are reconstructed. This method improves the accuracy of SOC-OCV curves while reducing the OCV test points. Based on reconstructed SOC-OCV curves, the SOC is estimated by an adaptive extended Kalman filter. Results show that the root mean square error of SOC estimation decreased by at least 40% at different temperatures.

Aimed at the problem that the performance of a proton-exchange membrane fuel cell (PEMFC) is affected by fuel delivery and water management, based on a single-channel PEMFC, a three-dimensional numerical analysis method is used to compare and study the effects of three types of blocking blocks on the performance of PEMFC due to the diversion or suppression effect on the windward and leeward surfaces. Results show that the output performance of the channel with added blocking blocks is improved compared with those of traditional channels, with a fan shaped section block having the best effect. For a flow channel with the fan shaped section block, when the output voltage is 0.5 V, the current density increases by 6.52% compared with the traditional flow channels. Moreover, when the blocking block acts as a guide on the windward side and suppresses the gas flow on the leeward side, it can maximize the output performance of PEMFC. When both the windward and leeward sides of the blocking block serve as a guide, the performance improvement is the least significant. This research provides a novel standard for the selection of blocking blocks and has certain guiding significance for improving the net power density of PEMFC.

To improve the consistency difference in series battery pack, a modular layered active equalization method based on inductive energy storage is proposed. First, by combining the characteristics of high equalization accuracy of inductive energy storage, a novel topology is proposed, and its parameters are designed through a detailed analysis of its working principle. Second, based on the equalization principle, an adaptive equalization control strategy is designed to match the proposed topology. Third, the analysis of its topological cost and equalization performance shows that the novel topology has advantages of a simple structure, a low cost and a fast equalization speed. Finally, a simulation model is built in MATLAB/Simulink, the effectiveness of the novel equalization method under different working conditions is verified, and it is found that this method is superior to similar equalization methods in terms of equalization speed.

The power conversion system (PCS) for energy storage uses a virtual synchronous generator (VSG) control system that simulates the rotation and excitation characteristics of synchronous motors, so as to achieve the applications of energy storage in the field of power system frequency regulation. Under frequency modulation conditions, electrochemical batteries frequently charge and discharge, and they often require the PCS to operate under reduced load. In this case, the power difference can cause changes in the power angle and voltage of the VSG, resulting in circulating current within the equipment. A variable-parameter virtual impedance scheme coupled with the power change rate is proposed to match the equivalent impedance with the variation in PCS power. In response to the problem of poor output voltage anti-interference capability caused by changes in the energy storage power, a second-order linear auto-disturbance rejection control method including an error robust integral tracking module is put forward, so as to achieve the stable output voltage from the energy storage. Simulation results based on PSCAD show that the matching of variable-parameter virtual impedance with the power variation of PCS can effectively suppress circulating current within the equipment, and the second-order linear auto-disturbance rejection control can effectively improve the voltage control link’s capability of suppressing voltage fluctuations, thereby enhancing the robustness of the energy storage VSG control system.