Design of Three Phase UPS system using Multi-Loop Fuzzy Logic Controller for Linear and Non-Linear Loads”

Abstract

This Paper proposes 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. In a UPS system, the inverter is responsible for synthesizing sinusoidal voltages from a dc source through the pulse width modulation (PWM) of the dc voltage. The classical SPWM method and space vector modulation are quite effective in controlling the RMS magnitude of the UPS output voltages but couldn't effectively compensate the harmonics and distortions caused specifically by the nonlinear loads. The distortion becomes more severe at high power where the switching frequency has to be reduced due to the efficiency concerns. It adds inner loops to the closed loop feedback control system effectively that enables successful reduction of harmonics and compensation of distortion at the outputs. The fuzzy based multi-loop controller eliminates the periodic errors on the output voltages due to inverter voltage nonlinearity and load disturbances.The steady-state RMS voltage regulation, total harmonic distortion and dynamic performance of the three-phase UPS is investigated in detail. The theory of the control strategy is analyzed by means of simulink using the state-space model of inverter.