In this article, a common-mode voltage reduction pulsewidth modulation (CMV-R PWM) for three-level neutral point clamped inverter based on the simplification of the three-level space-vector diagram into that of a two-level inverter is studied. By replacing the switching sequence of two-level space-vector PWM with that of CMV-R PWM, the common-mode voltage of the proposed method can be restricted to one-sixth of the dc-link voltage. With the new switching sequences, the neutral-point voltage control by calculating an optimized injected zero-sequence voltage is introduced. Simulation and comparative analysis is given to illustrate the features of the proposed method. The effectiveness and correctness of the proposed method is verified by experiment.

Detecting and locating the fault of IGBT rapidly and accurately are the keys to ensuring the security and reliability of the active power filters (APF) system. A fault diagnosis algorithm based on the mathematical model of ac side output voltages for three-phase four-wire three-leg two-level shunt APF is proposed in this paper. According to the different relationships between the APF's ac side output voltages and turn-on duty cycle of the corresponding IGBT under normal condition and fault condition, the fault diagnosis algorithm can detect and locate the open-circuit (OC) faults with no additional hardware or sensors required. All the signals used in this algorithm have already been employed in the APF stem controller. All possible OC fault conditions can be detected and located quickly and reliably by the algorithm. In addition, the algorithm is highly free from the load changes and can be used during the dynamic process of load changes. The efficiency of the proposed algorithm, under single and multiple faults conditions, is verified by the simulation and experimental results.

On control of the grid‐connected inverter (GCI) with LCL filter, the inverter‐side current model predictive control is adopted conventionally. The ultimate grid‐side current is controlled indirectly by control of inverter‐side current. The ideal scenario is that grid‐side current is directly controlled. However, the conventional control model is complicated and the calculation is heavy. This study proposed a novel direct grid‐side current model predictive control (GSC‐MPC) for GCI with LCL filter. Based on timing coordination of both forward and backward difference methods, a direct connection is established between the grid‐side output current and the inverter‐side output voltage. Meanwhile, a proper mathematical model is built for an improved model predictive control. The exact required voltage vector in the next sampling interval is predicted and calculated by this model. The output optimal voltage vector is modulated by space vector pulse width modulation technique to control the inverter. Furthermore, the proposed GSC‐MPC is rather robust to parameter variation. Simulation and experimental results present that the proposed GSC‐MPC can improve the current control performance effectively for GCI with LCL filter.

Compared with traditional single L-type filters, LCL filters for three-phase grid-connected inverters can suppress the switching voltage and current ripple better, thus reducing harmonic pollution to the power grid. However, the increase in system order also makes it difficult to control the system. To solve the problems of complex model and severe coupling of LCL filter in the d-q coordinate system, the decoupling control of current inner loop by the linear extended state observer (LESO) was proposed based on the analysis of mathematical model of grid-connected inverter with an LCL filter. Moreover, given the relatively low speed of system response in traditional active disturbance rejection control (ADRC), the tracking differentiator (TD) was removed, and the nonlinear control law was replaced with the PI controller. Compared with the conventional feedforward decoupling method, the reasonably designed LESO used in this work can not only realize decoupling control of the original system to improve its performance, but also save the cost of sensor and achieve a better decoupling effect. The effectiveness of the proposed current control strategy was verified by experimental results.

At present, virtual flux voltage oriented control strategy is one of the widely used control strategies without grid voltage sensor. To solve the dc bias resulting from voltage vector integration in vector calculation of virtual flux and further to avoid the steady state error, a virtual flux observer with negative feedback resonant filter is presented in this paper based on virtual flux principle. A delay compensation algorithm is also proposed to solve the virtual flux delay. In addition, the control system diagram of PWM rectifier without grid voltage sensor is proposed. Then, simulation algorithm and experimental platform are established to simulate and test the rectifier respectively to verify the correctness and feasibility of the proposed algorithm.

In the traditional model predictive control(T-MPC), only inverter side current of LCL inverter is treated as a control target. Grid side current is controlled indirectly by controlling the inverter side current directly. The control performance of the algorithm can be further improved. In this paper, a complete model predictive control algorithm(C-MPC) which take the grid side current as control target directly is proposed. The equivalent mathematical model and the equivalent circuit model are established based on active damping of capacitive current proportional feedback, then system predictive control model is established by the equivalent mathematical model and the circuit model. In order to make the output current track the directive current accurately at the next moment, the output voltage vector needed at this moment is calculated by the predictive control model. Finally, the required voltage vector is reproduced through space vector modulation(SVM). The simulation results and experimental measurements verify the developed control schemes and show high quality of grid side current (low THDi value).