Comparative analysis of closed-loop current control of grid connected converter with LCL filter

Voltage source inverters (VSIs) with output LCL filters are the key interfaces for today´s distributed energy resource. There are mainly two groups of current control methods of a VSI: direct error tracking control with PWM, and closed-loop feedback control. Direct current error control, such as predictive control and hysteresis control, has some drawbacks like system parameter sensitivity, variable switching frequency, etc. On the other hand, the closed-loop feedback control could eliminate many drawbacks of direct error tracking PWM method while with the limited of control bandwidth. Closed-loop current control of a VSI can be of two types namely single-loop and multiple-loop VSI control. According to the feedback currents or number of current sensors used, the closed-loop current control can also be classified into single current sensor and two current sensors feedback system. The stability and dynamic performance of these control schemes differs from each other. However, a thorough understanding of the differences and the reasons behind is not available. This paper presents a comparative analysis of different closed-loop current control method for a VSI with output LCL filters. Effect of LCL filter parameter variation on their stability is investigated. Recently proposed generalized closed-loop control (GCC) platform is used to explain the comparison results. Simulation and experimental results of different VSI control systems are presented.