Robust Control of an Uninterruptible Power System (UPS) Using a Discrete Fuzzy Logic Sliding Mode Controller Approach

Abstract

A Discrete Fuzzy Logic Sliding Mode Control or DFLSMC for the uninterruptible power system (UPS) is presented, which is tracking a sinusoidal ac voltage with specified frequency and amplitude. The control function is derived to guarantee the existence of a sliding mode. The rules of the proposed DFLSMC are independent of the number of system state variables because the input of the suggested controller is fuzzy quantity sliding surface value. Hence the rules of the proposed DFLSMC can be reduced. The application of DFLSMC to the UPS at sinusoidal frequency has show that the proposed approach can improved the tracking performance and the output waveform of the controlled PWM inverter is much more smooth that that of the previous study methods, like the VSC and PI strategies. Furthermore, its can achieve the requirements of robustness and can supply a high-quality voltage power source in the presence of plant parameter variations, external load disturbances and nonlinear dynamic interactions.