The output voltage of UPS is distorted by abrupt load current. Conventional control methods to adjust output voltage, PI controller, states feedback control, dead beat control method, so on, are proposed as the control method which controls the inverter switches to generate the required pulse width modulated (PWM) pattern to produce low total harmonic distortion (THD) sinusoidal output voltage. The control methods, however, must regard robustness of the controller associated with LC filter. Because of the system parameter deviation, undesirable voltage fluctuation arises.This paper adopts sliding mode control to control the output voltage of UPS. This method is robust with respect to parameter deviation and nonlinearity of the system. As the most valuable feature of author's proposed method is that the feedback gain is changed with state variable by adaptation process, hence the system has good voltage control quality even if the system is subjected to unexpected load disturbance. This useful features and validity are shown in simulations.
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