Aimed at the problems of a large number of switching devices and complex control strategy for an inverter in the multi-motor drive system of a 800 V high-voltage platform for electric vehicles, a fifteen-switch three-level dual-output inverter is proposed, which simplifies the inverter topology and reduces its cost by device multiplexing. First, a detailed analysis of the proposed inverter topology and working principle is performed, its structural characteristics are summarized, and the effective switching state and maximum voltage stress analysis are given, providing a theoretical basis for the selection of switching devices and system design. Then, a single-leg independent model prediction current control strategy is put forward, and a prediction model of single-leg dual-output port current is established, which effectively reduces the prediction operation under the premise of realizing three-leg independent prediction control and single-leg dual-output current integrated optimal control. Finally, the correctness and effectiveness of the proposed inverter and its control strategy were experimentally verified based on a Typhoon HIL 402 platform.

A novel active-neutral-point-clamped (ANPC) seven-level inverter based on the principle of switched-capacitor is proposed in this paper, which employs ten switches, two diodes and one switched-capacitor. With an input amplitude of V'_DC the peak output from this topology can reach 1.5V_DC through the switched-capacitor. Compared with other APNC inverters, the novel topology has lower switch stress and a higher Boost capability. Without the auxiliary control methods, the voltage-sharing capacitors in the DC link can be self-balanced at 0.5V'_DC and the switched-capacitor can be self-balanced at V_DC. The operation principle for the proposed topology and the self-balancing mechanism for capacitors are described in detail. Through a comparison with the latest topologies, the advantages of the proposed topology such as fewer components, a higher Boost capability, lower overall voltage stress and a self-balancing capability of capacitors are also demonstrated, showing that it is suitable for distributed generation, electric vehicles and other applications. Finally, the Boost capability of this topology and the self-balancing capability of capacitors were verified by simulation and experimental results.

To solve the problem of uncontrollable area of bus neutral-point potential under high modulation depth of conventional virtual space vector pulse-width modulation (VSVPWM), an optimized VSVPWM algorithm was proposed to realize the rapid balance of neutral-point potential in the whole linear modulation area. A virtual medium vector was reconstructed based on the principle of VSVPWM bus neutral-point potential balancing. To ensure the voltage equalization performance of the reconstructed virtual medium vector while improving the adaptability of the algorithm with respect to the perturbation of system parameters, the fuzzy reasoning for the closed-loop control of neutral-point potential was designed to determine the reconstruction factor for optimizing the VSVPWM. Even in the case of asymmetric DC bus capacitance, the optimized VSVPWM can realize rapid voltage equalization control in the full range of the linear modulation region. The algorithm was further simplified in a 60° coordinate system, so that the number of subsector judgment conditions of reference voltage vector and volt-second equilibrium equations can be reduced from 30 to 5. Experimental results show that the proposed control strategy has good performance, the voltage equalization regulation time is significantly reduced, and the steady-state deviation of DC bus neutral-point potential can be controlled within 1.14%. In addition, the total harmonic distortion of grid-connected current is lower compared with that under the conventional VSVPWM.

A current source pulse width modulation (PWM) rectifier has advantages of continuously adjustable current and strong capability to limit the short-circuit current, which is suitable for DC ice-melting application. However, it still has problems of a low switching frequency and a low filter cut-off frequency, possibly causing the problem of harmonic amplification. The active and reactive characteristics of the current source PWM converter are studied under constant-current load and constant-resistance load conditions, which is helpful in designing an LC filter to realize the high power factor of the rectifier. On the basis of stability analysis, a controller based on active damping and decoupling control is designed. Simulation results show that compared with the traditional non-decoupling control, the proposed method has better DC transient characteristics, so that it can effectively suppress lower-order harmonic current to eliminate the possible problem of harmonic amplification.

The rapid and accurate acquisition of harmonic components in the output waveforms from power grid or inverters is of significance for inverter control and harmonic compensation. However, the commonly used method of second-order generalized integrator (SOGI) suffers from the problem of resonance point offset during the discretization process, which affects the separation and extraction accuracy. To solve this question, a technique of non-static error harmonic extraction observer (HEO) which can rapidly and accurately separate and extract harmonics is proposed, whose implementation process can be directly equated to a set of second-order difference equations with a simple structure and easy digital implementation. The principle and performance of the proposed HEO are analyzed in detail, and its performance is compared with that of the conventional SOGI method. Meanwhile, in order to avoid the phenomenon of mutual interference during the observation of multiple harmonics, a cross-suppressed modified HEO method is further put forward, and the corresponding implementation principle and structure are discussed in depth. Finally, the simulation and experimental results of a singlephase system show that the proposed HEO can quickly and accurately separate and extract the fundamental wave and each harmonic component in the single-phase system, with advantages of fast response and small observation deviation.

To meet the requirements of new welding process, it is necessary to design a single-power source multi-output constant-current welding power supply. Under this background, a novel converter with constant-current output was designed, which can output dual DC current or single AC current according to the requirements of different welding processes. The working principle for this converter was analyzed in detail, the small-signal models in DC and AC working modes were established respectively on the basis of considering the effect of load current changes on the circuit performance, and the output impedance from the two kinds of output was derived. In addition, the frequency-domain simulations verified the small-signal models, and the load transient response speed of the converter was analyzed. Finally, an experimental prototype was built, and the theoretical analysis was validated by experimental results.

To reduce the input current harmonic content of a single-phase PWM rectifier and improve the suppression effect on specific low-frequency harmonics in grid-side current, fuzzy multi-PR control based on PR control is studied, so as to solve the problem of influences due to uncertain factors such as constant parameters under multi-PR control, inability to adapt to variations in parameters in the process of control and system disturbance. Finally, the effectiveness of this method was verified by simulations on MATLAB/Simulink and experiments on an experimental platform. Results show that the proposed control strategy can effectively reduce the total distortion rate of grid-side current, and it can also improve the dynamic and anti-interference performance of the system to a certain extent.

The traditional power factor correction (PFC) converter can only control itself to avoid causing harmonic interference to the power grid, but it cannot improve the total harmonic distortion of current flowing into the power grid at the point of common coupling of local distribution network. To solve this problem, an adaptive harmonic compensation method based on a Boost PFC converter is proposed. By detecting the input voltage and further adding harmonic compensation components to the input current, the harmonic current flowing into the power grid at the point of common coupling can be offset while ensuring the PFC function of the converter. The current controller is designed as a combination of an embedded repetitive control link and single-zero single-pole compensation to achieve small steady-state errors. At the same time, by adding a repetitive controller and a band-pass filter to the reference current signal generation link, a harmonic compensation reference current signal can be generated adaptively under different grid impedance conditions. The small signal modeling method is also used to prove that the input impedance of the PFC converter under the proposed control method is effectively reduced at each harmonic frequency. Finally, a 500 W experimental prototype was built to verify the correctness and feasibility of the theoretical analysis.

The access of high-penetration distributed generations (DGs) poses significant challenges to the operation of active distribution network (ADN). With the consideration of the flexible and efficient regulation capability of soft open point (SOP) in ADN, a three-layer coordinated planning model of DG and SOP was proposed, which was combined with system planning and operation optimization. The planning of DG was determined by maximizing the annual revenue of a DG operator in the upper layer, the planning of SOP was determined by minimizing the annual comprehensive cost of distribution companies in the middle layer, and the system operation condition was optimized by minimizing the loss of distribution network in the lower layer. The scenario analysis technology was utilized to deal with the randomness of DG output, and a hybrid algorithm based on improved grey wolf optimization algorithm and second-order cone programming was put forward to solve the model. Finally, an IEEE 33-node system was taken as an example to verify the feasibility of the planning model and the corresponding solving algorithm.

At present, there are numerous modulation schemes for eliminating the common-mode voltage. Although the existing zero common-mode voltage modulation scheme does not change the target voltage vector output, it will increase the harmonic content of three-phase current on the motor side and grid side, resulting in total harmonic distortion. To ensure the zero common-mode voltage modulation while reducing the harmonic content of a dual pulse width modulation (PWM) converter system, a model predictive control algorithm based on the dual PWM converter system is proposed. Based on the symmetry of the dual PWM converter system, the PWM strategy has more degrees of freedom, and the zero common-mode voltage modulation can be realized within the range of degrees of freedom. On this basis, an energy model of current harmonics is designed and established, and the modulation strategy with the minimum harmonic content in each control cycle is obtained by model predictive control. Finally, the optimization effect of the proposed algorithm was verified by simulation and experimental results.