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.

Aimed at the problem that the traditional control methods are difficult to achieve soft-switching in a wide load range due to the limitation of resonant inductor volume and duty cycle loss in phase-shifted full-bridge converters, a hybrid control method based on peak current and Burst mode is proposed. The output voltage is stabilized to a reference value by adjusting the Burst duty cycle, and the phase shift angle is changed to maintain the minimum primary current so as to realize the lagging bridge arm zero voltage switching. A simulation platform was built for the proposed control method, and a 250 W prototype was developed. The hybrid control of a phase-shifted full-bridge converter was realized through a digital signal processor, and the feasibility of the control method was verified by simulation and experimental results.

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 coupling between the boost control and neutral-point voltage balance control of a quasi-Z-source three-level inverter seriously limits its control performance. To solve this problem, a neutral-point voltage balance control strategy based on a virtual space-vector pulse width modulation method is proposed. The neutral-point voltage balance control is realized through a closed-loop control of the DC-bus capacitor voltage, and the low-frequency fluctuations in the neutral-point voltage are eliminated. Meanwhile, a constant shoot-through boost modulation strategy is employed, which avoids the adverse impact on the neutral-point voltage and guarantees an ample boosting capacity of the quasi-Z-source network. Finally, simulation and experimental results verified the validity of the proposed control strategy.

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.

Three-phase chain-link energy storage converters (TPCLESCs) are promising in enhancing the controllability of renewable energy in power grid, such as wind and solar power. Aimed at the problem of state-of-charge (SOC) imbalance of energy storage battery among phases of a TPCLESC, a phase-to-phase SOC balance method based on phase-to-phase circulating current power closed-loop control is proposed. Through the zero-sequence voltage injection into phases a, b and c, the active circulating current among phases is generated to realize the SOC balance in the three-phase energy storage battery groups. A mathematical model of the maximum phase-to-phase circulating current power of the chain-link energy storage converter and SOC deviation is established. On this basis, the phase-to-phase SOC balance in battery groups is realized at the maximum circulating current power through the phase-to-phase circulating current active power closed-loop control. As a result, the phase-to-phase SOC reaches its balance at the maximum speed, and the process of phase-to-phase SOC balance is accelerated. Finally, the correctness and feasibility of the proposed method were verified by a MATLAB simulation model and an experimental platform.

The flying capacitor clamped three-level converter has many advantages, e.g., it can reduce the voltage stress of a switch and the volume of a filter inductor. Under its operation, it is necessary to stabilize the flying capacitor voltage at half of the high-voltage side voltage, so a control strategy of adjusting the duty cycle is often used. However, this method has the problem of coupling control between flying capacitor voltage and output voltage, resulting significant fluctuations of inductance current in the process of flying capacitor voltage regulation. To solve this problem, the advantages of using the phase-shifting control strategy to realize the decoupling control of flying capacitor voltage and output volt-age are analyzed, and the corresponding control characteristics are also studied. Through the establishment of a harmonic model of flying capacitor voltage, the relationship between flying capacitor voltage and phase-shifting angle is given. A low-order harmonic function relationship is constructed, which indicates that the flying capacitor voltage is affected by the switch duty cycle D and phase-shifting angle ∆φ. The effective duty cycle interval of phase-shifting control and the duty cycle that optimizes the performance of phase-shifting control are delimited by combining with a time-domain model. A simulation model was established, and an experimental prototype with 3.6 kW was built. The control strategies of adjusting flying capacitor voltage based on phase-shifting angle and duty cycle are compared to verify the decoupling advantages and control characteristics of phase-shifting control.

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 improve the capability of microgrid in coping with new energy output and load uncertainty, an optimal control strategy for microgrid considering flexible resources is proposed. According to the source-storage-load characteristics of various flexible resources, a two-layer optimal scheduling model for microgrid is established. In the user layer, user-side flexibility resources are introduced, with an optimization goal of minimizing the difference between user costs and net load and decision variables of electric vehicles and output power of translatable loads. In the source-storage layer model, flexible resources are added to the energy storage and power generation sides, with an optimization goal of minimizing the microgrid operators’ cost and load loss rate and decision variables of gas turbines, main network tie-line and output power of energy storage unit. A case study based on scenario-reduced seasonal typical daily data is simulated, and the improved MOEA/D(multi-objective evolutionary algorithm based on decomposition) algorithm is used to solve the two-layer optimal scheduling model. Results show that the average annual user cost is reduced by 6.85%, the average annual total cost of operators is reduced by 14.68%, and the average annual load loss rate is reduced by 6.65%. The results verified the correctness and effectiveness of the proposed method.