A dual loop current control structure with improved disturbance rejection for grid connected converters in the synchronous rotating reference frame

Abstract

The increase in renewable energy penetration in the past few years has led to grave power quality issues in the utility grid. This has ushered in the need for a robust and stable control system for reference tracking and disturbance rejection with respect to grid connected converters. Typically, a simple proportional integrator (PI) controller is used in the synchronous reference frame (dq) for current control of grid connected systems. However, the PI controller in itself may be insufficient for disturbance rejection, when the utility grid voltages contain other harmonics in addition to the fundamental component. This paper introduces and analyzes a dual loop current control structure which utilizes two independent controllers, one for reference tracking and the other for disturbance rejection in the dq frame. A small signal model of the dual loop current control has been presented and its robustness under grid inductance variation, examined. Simulation and experimental results are presented to validate the dual loop strategy for improved disturbance rejection capability and filtering action during the presence of grid voltage harmonics and unbalances, without compromising on the reference tracking performance.