Fixed switching frequency sliding mode control for single phase unipolar inverters

ABSTRACT: For the application of UPS inverters. The aim of the UPS is to provide the necessary loads with a sinusoidal output voltage at low harmonic distortion. The controller has to be able to handle any external disturbances may occur, and should have a fast response at low steady state error. For that purpose; the sliding mode controller is applied to the UPS system here. Sliding mode controller has the advantage of robustness to parameter variations and disturbances, but still suffers from chattering problem when the state of the error approaches the equilibrium point. In this thesis, the control input has been saturated in narrow boundary, aiming to reduce the chattering problem. Pulse width modulation is used to compare the smoothed control function with a reference carrier resulting a fixed switching frequency for the unipolar UPS inverter. The output voltage of the inverter has low total harmonic distortion according to IEC62040-3 standard. The proposed controller is fast and robust as the simulations show. Keywords: Pulse width modulation, voltage source inverter, sliding mode control. …………………………………………………………………………………………………………………………