An active power filter (APF) plays an important role in compensating the harmonic component of a nonlinear load current. In this paper, deadbeat control (DBC), which has high control performance and fast dynamic response, is used as a current controller for an APF. An improved DBC (Imp_DBC) is introduced to suppress the adverse effect of the current sampling error and to enhance the interference rejection capability of the control system. The characteristics of the conventional DBC and Imp_DBC are analyzed using transfer functions in the discrete-time domain. The robustness of the system is improved with the inductance variation. Specifically, aiming at the dramatic change of the harmonic component of the nonlinear load current, a current-tracking error compensation method is proposed. The phenomena of the upper co-nvex and lower concave in grid current are eliminated. Finally, the experimental setup of three-phase three-line APF is built, and the effectiveness of this method is verified by experiments.

Virtual space vector pulsewidth modulation (VSVPWM) for the neutral-point (NP)-clamped three-level inverter is briefly reviewed in this paper, as well as its carrier-based realization. The carrier-based VSVPWM (CB_VSVPWM) is featured with dual modulation waves and a single carrier. Although CB_VSVPWM can make NP voltage unfluctuating in theory, it does not have the NP voltage recovery ability. In practice, due to the effect of nonidea factor effects, NP voltage may shift. Thus, active NP voltage control (ANPVC) is necessary. To achieve that, three ANPVC approaches are proposed based on CB_VSVPWM in this paper. The NP voltage control ability of CB_VSVPWM with ANPVC is analyzed. Finally, comprehensive experiments are carried out to verify the feasibility of the proposed method.

In this letter, space vector pulse width modulation (SVPWM) and virtual SVPWM (VSVPWM) for the neutral-point-clamped (NPC) three-level inverter (TLI) are reviewed briefly. The relationship between VSVPWM and carrier-based PWM is revealed based on the PWM model of TLI with NP current equation. Then, carrier-based VSVPWM (CB_VSVPWM) is proposed. The CB_VSVPWM is implemented by comparing double modulation waves with a single carrier, and the two modulation waves for each phase are deduced. The CB_VSVPWM can simplify the implementation of VSVPWM to a great extent. Moreover, comparisons between SVPWM and CB_VSVPWM are provided in detail. At last, the simple method proposed in this letter is verified by experiments.

The parallel three-phase grid-connected converters sharing dc and ac bus can increase the system power level effectively. However, the zero sequence circulating current (ZSCC) will occur inevitably under space vector pulse width modulation or discontinuous pulse width modulation (DPWM). In this paper, the mechanism and the mathematical model of ZSCC are studied. Then, a hybrid PWM (HPWM) strategy is proposed to suppress the ZSCC based on the same zero sequence voltage injected, which is dependent on the common grid information. The dc voltage utilization of HPWM can be extended compared with sinusoidal PWM (SPWM). The number of parallel modules can be infinity theoretically by using HPWM. It is noted that there is no internal commutation among modules (expect the dq current reference). Finally, the feasibility and the effectiveness of the proposed method are verified by experiments.

Deadbeat control (DBC) is developed based on the system model, which is commonly used to achieve good control performance for a three-phase grid connected converter (GCC). Unbalanced grid voltage is a common phenomenon in power systems. In this study, an improved DBC based on current predictive correction (CPC_DBC) is used to control GCC under an unbalanced grid voltage. The main purposes of CPC_DBC are to reduce the adverse effects due to random sampling error to improve current control performance, and to enhance the interference rejection capability of the control system. Then, the characteristics of CPC_DBC and the conventional DBC (Con_DBC) are analyzed by transfer functions in the discrete time domain. Several common control objectives under an unbalanced grid voltage are used to demonstrate the superiority of CPC_DBC. Finally, the experimental results indicate that CPC_DBC can effectively reduce the adverse effects of random sampling error; the robustness of system due to the uncertain value of the filter inductance is improved as well.

A novel carrier-based discontinuous pulsewidth modulation (CB_DPWM) strategy for T-type three-level converter is proposed in this article. Because one significant advantage of the proposed CB_DPWM is the reduction of common mode voltage (CMV), it is named as RCMV_CB_DPWM hereafter. It also can reduce switching loss and remove dc offset from the neutral point voltage (NPV) simultaneously. RCMV_CB_DPWM has two design freedoms, one is modulation wave and the other is carrier wave. By injecting zero sequence voltage properly, the corresponding clamping mode can be acquired. Moreover, reduced CMV can be achieved by arranging carrier wave flexibly. The integrity of RCMV_CB_DPWM is analyzed as well as its NPV self-equilibrium ability, and an active NPV control method is then introduced. Moreover, its realization is discussed briefly. Finally, the experiments are carried out to verify the effectiveness of the proposed method.