To reduce the cost and the number of components while ensuring the safe operation of the circuit, a single-phase isolated Δ-source AC-AC converter is proposed. This novel converter can provide a wider range of Buck-Boost output voltage, and the input voltage and output voltage can be in-phase or out-phase. Meanwhile, the surge and harmonic currents are suppressed, and the circuit reliability is improved. The working principle for the proposed circuit is analyzed, the voltage values of main components in each working process are deduced, and the relationship between input voltage and output voltage is formulated, which is further compared with those of other improved AC-AC converters. The theoretical analysis proves the performance of the novel AC-AC converter. A simulation model and an experimental model were built according to the designed parameters for verification, and simulation and experimental results verified the correctness and feasibility of the theoretical analysis.

A novel two-channel light emitting diode (LED) driver is proposed, and its operating principle and characteristics are analyzed in detail. This driver uses a novel Z-source resonant network and an active switch which has the same ground properties as the power supply, and the current balance is automatically realized by balancing capacitors, so its current control is simple. At the same time, owing to the use of Z-source resonant network to transfer energy, the proposed driver has advantages such as soft switching, high efficiency, small volume and low voltage stress. To verify the effectiveness of this driver, a 80 W prototype was built and tested.

When a modular multilevel converter (MMC) adopts the traditional carrier phase-shifted pulse width modulation strategy, the additional capacitor voltage balance strategy for submodules will cause the number of submodules in each phase circuit of the MMC to jump at a high frequency. Therefore, a large induced pulse voltage will appear on the inductance of the bridge arm, which will generate a high-frequency harmonic circulating current, thereby increasing the voltage and current stress of components. Based on the study of the traditional carrier phase-shifted modulation strategy and its application to the MMC, the implementation process is improved to ensure that the number of submodules in each phase circuit of the MMC is constant at any time, so as to avoid the above problems. The improved carrier phase-shifted modulation strategy is analyzed in detail, and the corresponding capacitor voltage balance control strategy is given. Simulation and experimental results show that the circulating current amplitude of the bridge arm is reduced after adopting the improved carrier phase-shifted modulation strategy.

To achieve the target of carbon neutrality, renewable energy power generation represented by photovoltaic (PV) power generation has become an important means. PV power generation systems usually require multiple PV modules to be connected in series to obtain a high output voltage. However, in series-connected PV modules, the mismatch of component characteristics due to partial shading or different degrees of aging of components will cause a serious loss of power generation. Therefore, many technical schemes have been proposed to solve this problem. The PV equalizer has become a promising solution, and it uses a power electronic converter to transfer the mismatched power and change the operating point of the component to obtain the maximum output power. First, the basic concepts and principles of PV equalizers are elaborated, then, the PV-bus, PV-PV and other special types of PV equalizers topologies are introduces in detail. In addition, a comparison and analysis of the paremeters and performance of the existing PV equalizer topologies is performed. Finally, the topological structures of PV equalizers are summarized and evaluated, providing a reference for engineers and practitioners in this field.

To address the issue that a dual-active-bridge DC-DC converter will produce large current stress when voltages mismatch and result in a large reduction of its efficiency, a combined dual-phase-shifting (CDPS) control strategy is proposed, which combines dual-internal-phase-shifting (DIPS) and interlaced-dual-phase-shifting (IDPS). First, the working principles of the two control strategies are analyzed, and the mathematical models of transmission power and current stress are established. Second, with the minimum current stress as the objective, the optimal phase-shifting ratios are solved by using the Lagrange multiplied method under the Karush-Kuhn-Tucker condition. Third, the optimization methods under the two control strategies are combined according to different voltage ratios and transmission power. The CDPS control is used to obtain the optimal solution of current stress, which is compared with those obtained under the existing single-phase-shifting and dual- phase-shifting control strategies. Results show that the proposed control strategy can further reduce the current stress and reactive power under the condition of high voltage ratios and improve the efficiency. Finally, an experimental prototype was built to verify the feasibility of the proposed control strategy.

Aimed at the time-delay oscillation of a bidirectional H4 bridge converter in a single-phase energy storage inverter, a unified control method for the bidirectional H4 bridge converter is proposed. In this method, a voltage regulator is used to control the power flow of the converter, and a set of bidirectional feasible control parameters are derived based on the power balance theory. At the same time, in order to realize AC current tracking input voltage without static error and increase the stability, the current inner-loop adopts a quasi proportional resonance controller, and a second-order generalized integrator is used to design a phase-locked loop. PSIM simulation and experimental results show that the proposed method can realize seamless switching between the rectification and active inverter modes, and it also has a good effect in the startup and switching between different modes. Therefore, it can realize stable control of the bidirectional AC-DC bridge converter in a single-phase photovoltaic energy storage system and obtain a good dynamic performance.

The application of multi-phase interleaved parallel coupled inductors technology can effectively reduce the phase current ripple and improve the dynamic response speed. Aimed at different design objectives, the influencing factors for the steady-state and dynamic performances of direct- and indirect-coupled inductors are analyzed. Subsequently, based on the invariant equivalent dynamic inductance before and after coupling, the direct- and indirect-coupled inductors are designed to enhance the steady-state performance. Similarly, based on the invariant equivalent steady-state inductance before and after coupling, direct- and indirect-coupled inductors are designed to improve the dynamic performance. Finally, the cor-rectness and effectiveness of the theoretical analysis were verified by experimental results, demonstrating that the two different coupling methods can significantly enhance the steady-state and dynamic performances of the converter, respectively.

An anti-offset method for a wireless power transmission (WPT) system based on constant-voltage output interval tracking is proposed to deal with the problem of output voltage fluctuation when the coupling mechanism in the WPT system is shifted. First, a model of a CLC-S WPT system is established, and the relationship between the mutual inductance and output voltage gain in resonant and non-resonant states of the system is analyzed. Based on the analysis, it is found that the system has a stronger anti-offset capability in the constant-voltage output interval when it works in the non-resonant state. Second, an inductance compensation sequence is designed, and a constant-voltage output interval tracking control strategy is proposed to realize the constant output voltage control of the WPT system and improve its anti-offset capability. Finally, a simulation model and a test platform were built, and simulation and experimental results show that the constant-voltage output interval tracking control strategy can effectively reduce the output voltage fluctuation, thus verifying the robustness of the system under strong mutual inductance interference. Compared with the WPT system without constant-voltage output interval tracking, the CLC-S WPT system has a better dynamic regulation capability of output voltage.

Limited by the switching frequency, the frequency-controlled LLC resonant converter is difficult to achieve a wide output voltage range. To solve this problem, an expandable variable-mode interleaved parallel LLC resonant converter is studied. The secondary-side of this converter adopts a voltage doubling rectifier circuit, which can work in a parallel or series mode according to different switch combinations of two half-bridges on the primary-side, and it can adapt to the wide output voltage range of 1-3N times. A fixed-frequency PWM control method is proposed. In the middle region between the parallel and series modes, the fixed switching frequency is taken as the resonant frequency, and the duty cycle of one bridge arm is changed to realize voltage control. PSIM simulation results show that the wide output voltage range of 1-3N times can be realized by expanding 2N resonator cavities. The experimental results of a 100 W prototype demonstrate that the wide output voltage range of 1-3 times can be achieved with two half-bridges and two resonant cavities, and the effectiveness of the proposed converter and its control strategy was verified.

The development of industry and economy has caused a huge consumption of energy, which brings serious energy crisis and environmental pollution. Therefore, building a safe and clean energy interconnection network is a way to solve the relationship among social development, environment and energy at present. Nowadays, different countries have proposed their policies for the development of new energy electric vehicles (EVs). As the core component of EVs, lithium-ion batteries are directly related to the driving performance and safety of EVs. The state-of-charge (SOC) estimation is a core parameter of lithium-ion batteries used in various industries, and the estimation accuracy is directly related to the service life and efficiency of batteries. In this paper, the problem of battery SOC estimation accuracy in EV applications is studied, and an SOC estimation method based on the extended Kalman filter (EKF) optimized by the whale optimization algorithm (WOA) is proposed. On the basis of constructing the covariance matrix of system noise and observation noise, the improved and optimized WOA-EKF algorithm is used to optimize the noise covariance matrix under dynamic conditions, thus improving the SOC estimation accuracy. The model parameter identification and comparative simulation verification are carried out in MATLAB/ Simulink. Results show that the SOC estimation of lithium-ion batteries based on the WOA optimized EKF algorithm can control the SOC estimation error to be within 2% under different working conditions, which is of significance to the promotion of develop- ment of batteries in the new energy field.