Analysis, design, and implementation of multifunction interfaced inverters for distributed generation

This paper presents generalized models and design procedure for multi-function power electronics interfaced distributed generator (DG). To meet the mandatory requirements of distributed grid, the operational modes of DG consists of normal power delivery mode and multi-function mode, which aim to provide very sinusoidal active power current and compensating current simultaneously. A LCL based filter is placed between interfaced inverter outputs and the distributed network to smooth the output current of DG. The key of the multi-function concept for DG are the filter resonance alleviation, optimal control design, and flexible implementation. In this paper, the equivalent model of multifunction DG is developed first. Then, the proposed control strategy integrating odd-harmonic repetitive control (OHRC) and PR controller is determined to offer zero steady-state tracking error and good dynamic performance according to the equivalent model. A design procedure of LCL filter is also presented, while a cascade closed-loop control structure is employed to reduce the resonance effect. Furthermore, a multiple resonant control (MRC) scheme is discussed and compared with the proposed OHRC scheme based on their internal relationship. Experimental results are provided to validate the effectiveness and advantages of the proposed control strategy.