LCL 필터를 사용하는 계통 연계형 인버터의 새로운 전류 제어 기법

Abstract

The LCL filter for grid connected inverter system has good features of excellent harmonic reduction capability and smaller filter size and weight compared with the conventional L filter. Therefore, the LCL filter has been widely used to meet the harmonic components requirement of IEEE-519. However, current resonance phenomenon must be considered when designing the grid connected inverter system with the LCL filter. In order to reduce the resonant current, passive damping or active damping are used at the inverter system. Passive damping reduces the efficiency of the system, and active damping methods are quite complex. If the current controller is designed considering the inverter delay and ZOH, there is an area where the system can be stabilized without any damping method according to the ratio of the resonant frequency of the LCL filter to the sampling frequency of the digital system. If the sampling frequency to the resonant frequency is larger than 1/6, the system is in the stable region in case of the grid side current is controlled. On the other hand, the system is in the stable region in case of the inverter side current is controlled if the sampling frequency to the resonant frequency is smaller than 1/6. However, if the variation of the grid impedance is high in case of the grid side current control, although the system is designed to exist in the stable region, it can be moved to the unstable region. Moreover, since the LCL filter has to have a large resonant frequency in order to design the system without any damping method in the case of controlling the inverter side current, there is a disadvantage that the volume of the system becomes large. This Paper proposes a novel current control method for a grid connected inverter to provide a large stable region in case of the grid side current is controlled, and to reduce the LCL filter size and weight in case of the inverter side current is controlled without any damping method. 3[kW] grid connected inverter system with the LCL filter is designed, analyzed, simulated and experimented with experimental set up. The validity of the proposed method is verified through simulation and experimental results.