Comparison of Three leg and Four Leg VSC DSTATCOM for Power Quality Assessment

Abstract

A new three-phase four-wire DSTATCOM (distribution static compensator) based on three-leg VSC (voltage source converter) and a star/delta transformer is proposed for power quality improvement. The star/delta transformer connection mitigates the neutral current and the 3-leg VSC compensates harmonic current, reactive power and balances the load. Three single phase transformers are connected as star/delta transformer for interfacing to a three phase four-wire power distribution system and the required rating of the VSC is reduced. However, a 4-leg VSC (voltage source converter) based DSTATCOM (Distribution Static Compensator) is used for the load compensation and neutral current compensation in 3-phase 4-wire distribution system. For extracting the reference source currents, Instantaneous Symmetrical Component Theory (ISCT) based control algorithm is modified for voltage regulation and used with indirect current control technique for controlling the DSTATCOM currents. The DSTATCOM is controlled for power factor correction and voltage regulation at PCC (point of common coupling). Simulations are performed for various load conditions such as a reactive linear load, an unbalanced load and a non-linear load in Power Factor Correction (PFC) mode and in Zero Voltage Regulation (ZVR) mode in MATLAB environment using SIMULINK and Sim Power System (SPS) toolbox.