Control of an uninterruptible power system (UPS) using a feedforward integral variable structure controller

A feedforward integral variable structure control (FIVSC) for the uninterruptible power system (UPS) are presented, which is tracking a sinusoidal AC voltage with specified frequency and amplitude. The FIVSC algorithm combines feedforward strategy with the conventional variable structure control (VSC). The control function is derived to guarantee the existence of a sliding mode. Furthermore, the chattering in the control signal is suppressed by replacing the sign function in the control function with a smoothing function. The simulation results illustrate that the purposed approach gives a significant improvement on the tracking performances when compared with some existing control methods, like the IVSC and modified IVSC strategies. Moreover, 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.