A Three Phase UPS Systems Operating Under Nonlinear Loads with Modified SPWM Controller

Abstract

This paper presents the design of a high-performance sinusoidal pulse width modulation (SPWM) controller
for three phase uninterruptible power supply (UPS) systems that are operating under highly nonlinear loads. The
classical SPWM method is quite effective in controlling the RMS magnitude of the UPS output voltages. However, it is
not good enough in compensating the harmonics and the distortion caused specifically by the nonlinear currents drawn
by the rectifier loads. The distortion becomes more severe at high power where the switching frequency has to be
reduced due to the efficiency concerns. This study proposes a new design strategy that overcomes the limitations of the
classical RMS control. It adds inner loops to the closed-loop control system effectively that enables successful reduction
of harmonics and compensation of distortion at the outputs. Simulink is used to analyze, develop, and design the
controller using the state-space model of the inverter. By using SPWM Controller THD of the system can be reduced
along with Magnitude of RMS voltage.