Adaptive current control of grid-connected VSC with LCL-filters using parallel feedforward compensation

This paper deals with the design of a discrete-time adaptive current controller for grid connected voltage source converters with LCL-filter. A mandatory condition to allow the use of discrete-time model reference adaptive control (MRAC) is that the plant must be minimum phase. Even if the system is minimum phase but it has poorly damped zeros, undesired oscillatory modes may appear in some systems variables. This paper proposes the use of parallel feedforward compensation to change the location of the zeros of current controlled grid connected converters with LCL-filter. Then, a discrete-time adaptive state feedback for the augmented system is applied to ensure stability and performance for a wide set of grid conditions. The theoretical background on parallel feedforward compensation as well as on discrete-time adaptive state feedback is briefly presented. Finally, the effectiveness of the proposed controller is confirmed by results that demonstrate the good system performance.