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Nowadays, the three-level T-type inverters (3LT2Is) are widely employed in applications with high-performance requirements. The 3LT2Is commonly suffer from neutral point voltage (NPV) unbalance and common-mode voltage (CMV) variation. The medium vector pulse width modulation (MVPWM), which generates the reference voltage using medium and V0[OOO] zero voltage vectors, eliminates the CMV variation in 3LT2Is. However, it cannot keep the NPV balance, negatively affecting power quality. This article proposes a hybrid method to simultaneously eliminate CMV variation and guarantee the NPV balance without topological change or extra hardware. The proposed method uses MVPWM when NPV is balanced, eliminating CMV variation. If NPV goes unbalanced, it utilizes novel high/low triangle PWM (H/LPWM) and MVPWM in a hybrid manner to balance the NPV. The H/LPWM, similar to MVPWM, synthesizes voltage using medium and V0[OOO] voltage vectors to maintain the CMV elimination advantage during the NPV balancing process. However, the difference between H/LPWMs and MVPWM switching patterns adjusts the average neutral point current to balance the NPV. Noteworthy that the proposed method provides NPV balancing ability for the entire power factor range. As a result, it is usable for various applications of 3LT2I, such as photovoltaic inverters and motor drives. The proposed method is carrier-based, which reduces the execution time and simplifies the practical implementation. The simulation study and experimental evaluation have been accomplished, and their results demonstrate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Distributed generation has attracted great attention in recent years, thanks to the progress in new-generation technologies and advanced power electronics. The Microgrid has been a successful example by integrating various generation sources with the existing power distribution network through power electronic converters. Microgrid converters are required to operate in a decentralized fashion, and power-frequency and reactive-power-voltage droop controls have been adopted for this purpose. In this paper, a droop control technique for imbalance compensation within the three-phase ac distributed generation system is proposed for Microgrid converters. The proposed technique allows even sharing of imbalance current among various converters and can thus be seamlessly integrated with the existing active-power-frequency and reactive-power-voltage droop controls to improve the power quality within the distributed power system. Its control functionalities are discussed, and simulation and laboratory test results are also presented to validate the proposed method. Index Terms--Distributed power system, droop control, voltage imbalance.

The dramatic growth of power electronics applications has led to serious harmonic pollutions in the power system. The phenomenon of harmonic resonance resulting in severe voltage distortion has been reported. Various suppression techniques have been proposed to resolve this problem. The distributed active-filter system (DAFS) is a more effective solution by deploying multiple shunt active filter units (AFUs) in the system to cooperatively damp the harmonic resonance. This paper proposes a dynamic tuning scheme for the DAFS to enhance its filtering performance. Based on the measured voltage harmonic distortion at the installation point, each AFU can dynamically adjust its own filtering volt-ampere (VA) capacity to maintain the total harmonic distortion of the line voltage at an allowable level. The proposed strategy can be integrated with the droop control between the conductance command and VA consumption so that the harmonic-filtering workload is evenly shared among various AFUs. The operation principles and dynamic analyses are presented in this paper, and test results based on simulations and experiments validate the proposed approach. Index Terms--Active filters, distributed active-filter systems (DAFSs), harmonic damping, harmonic resonance.

An adaptive control of DPWM implementable in clamped-three-level inverters with two strings of photovoltaic (PV) panels in cascaded connection is proposed in this paper. The proposed modulation is developed based on the so-called circuit-level decoupling concept. It is able to provide balance line voltage even under unbalanced dc links. The unequal dc voltages appeared due to asymmetric maximum point of power trackings (MPPTs) are controlled by proper injection of zero-sequence voltage to the common mode voltage, while the total dc voltage is regulated based on the voltage commands generated by the MPPT of each string. Thus, both PV strings are able to be operated based on their MPPTs while there is almost no low-order harmonic distortion at the inverter output current. Compared with the previous methods, the high capability of the proposed method is evaluated by simulation study and experimental tests. [ABSTRACT FROM AUTHOR]