Supply Voltage and Grid Current Harmonics Compensation Using Multi-Port Interfacing Converter Integrated Into Two-AC-Bus Grid

Abstract

A modified multi-port converter topology is proposed for active power quality control of two-ac-bus grid while maintaining a flexible integration of distributed dc energy sources. In this system, the lower converter cells work in voltage controlled mode to supply power to autonomous local critical loads with reduced harmonic distortions. At the same time, the upper converter cells working in current controlled mode are placed in between the main grid and the lower cells, to block the harmonic current from the local nonlinear loads to pollute the higher voltage grid current. In this proposed system, the upper and lower power cells harmonic control are well decoupled with minimal interferences. This features reduced computational load as there is no need to use any harmonic components extractions in the whole compensation process. In addition, the proposed harmonic compensation method has no interference with the interphase power flow control through zero sequence voltage injection. It has been examined that the proposed power quality control method works well in various conditions including that with large grid impedance and dc rail voltage variations.