Harmonic Control Approach 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 convertersare able to improve the distribution system efficiency and power quality. This paperfocuses on the distribution system harmonic control through the DG–grid interfacingconverters.This paper focuses on the technology of SOGI-PLL.Then the paper makes acomparative analysis on the control mechanism of a VSI: current control method (CCM)and voltage control method (VCM).Conventionally, CCM is widely adopted in active power filters (APFs) to mitigatesystem harmonics.However, for microgrid applications, particularly considering thepossible autonomous islanding operation, the DG units are desired to operate with VCMas it can provide direct voltage and frequency support for the loads. In this case, thecurrent-controlled harmonic compensation schemes which are traditionally used for APFapplications cannot be implemented directly. In order to overcome this limitation, a novelVCM-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 proposedvoltage-based method can be seamlessly incorporated into a voltage-controlled DG unit,which is important to 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 detail comparison of these twomethods is carried out. The voltage-controlled harmonic compensation method can beeasily incorporated into the V–f droop control scheme of DG systems in a microgrid.Simulation results reveal that the novel scheme has better compensation performance. Experimental results from a three-phase DG prototype based on TMS320F2812areprovided to validate the discussion.