Harmonic Controlapproach Through Voltage-controlled DG-grid Interfacing Converters

The increased penetration of nonlinear loads and power-electronics-based distributedgeneration (DG) systems may introduce power quality issues to the distribution powersystem.However, if controlled and regulated properly, the DG–grid interfacing converters areable to improve the distribution system efficiency and power quality. This paper focuses on thedistribution system harmonic control through the DG–grid interfacing converters.The control mechanism of a VSI mainly consists of two types: current control method(CCM) and voltage control method (VCM).Conventionally, CCM is widely adopted in activepower filters (APFs) to mitigate system harmonics.However, for microgrid applications,particularly considering the possible autonomous islanding operation, the DG units are desiredto operate with VCM as it can provide direct voltage and frequency support for the loads. Inthis case, the current-controlled harmonic compensation schemes which are traditionally usedfor APF applications cannot be implemented directly. In order to overcome this limitation, anovel VCM-based harmonic control method,which does not require a harmonic currentreference and a current tracking control loop, is developed in this paper. In addition, byavoiding the implementation of a harmonic current tracking loop, the proposed voltage-basedmethod can be seamlessly incorporated into a voltage-controlled DG unit, which is importantto provide direct voltage and frequency support in a microgrid.This paper starts with a brief review of the harmonic compensation based on CCMfirstly.Then the VCM-based harmonic control scheme is developed and presented. Theproposed VCM-based scheme is more flexible and can achieve similar compensationperformance compared to CCM-based compensation. A detailed comparison of these twomethods is carried out. The voltage-controlled harmonic compensation method can be easilyincorporated into the V–f droop control scheme of DG systems in a microgrid. Simulationresults reveal that the novel scheme has better compensation performance. Experimentalresults from a three-phase DG prototype based on TMS320F2812are provided to validate thediscussion..