POWER QUALITY IMPROVEMENT WITH ZIG-ZAG TRANSFORMER AND DSTATCOM

Abstract

This paper proposes a topology consisting of Zig-Zag transformer for neutral current compensation and
DSTATCOM for voltage sag compensation in the presence of unbalanced, non linear loads. The
DSTATCOM is a shunt-connected device which takes care of the power quality problems in the load
currents. There are different topologies for three-phase four-wire DSTATCOM, out of which a DSTATCOM
with SVPWM switched VSC along with a zig-zag transformer is used for compensating power quality
problems in the supply currents. The different voltages induced and currents flowing inside Zig-Zag
transformer shows that Zig-Zag transformer provides low impedance path to zero sequence currents. The
application of a zig-zag transformer for reduction of the neutral current is having an advantage due to
passive compensation, rugged and less complex over the active compensation techniques. The new
application of a zig-zag transformer is to connect in parallel to the load for filtering the zero-sequence
components of the load currents. SVPWM technique offers several advantages like higher output voltage
(15% more than conventional sine-triangle modulation technique and hence, better utilization of DC link),
lower harmonics etc. As the neutral current (total zero sequence current) is being taken care by Zig-Zag
transformer, a SVPWM switched DSTATCOM can be used for voltage sag compensation, load balancing. A
detailed simulation study for the proposed scheme is carried out using MATLAB software.