Sinusoidal voltage control of a single phase uninterruptible power supply by a high gain PI circuit

This paper presents analysis and design of a new control method of a single-phase voltage-source uninterruptible power supply (UPS) inverter with a high Q L-C low-pass filter. When a PWM inverter is used to feed the load, a L-C low-pass filter must be employed to eliminate the switching frequency component of output voltage harmonics. But, it may be observed that the high Q L-C low-pass filter causes oscillation of the output voltage on light load because the inverter is not able to decide on the one optimum control gain on all regions of the output power. Therefore, it is proposed to develop high-gain control which is accomplished by increasing the controller gain without additional sensors to avoid such problems and achieve a high reliability. The developed high speed high-gain control must be adopted with the following compensators; (a) saturation compensator of the normal controller; and (b) integrator wind-up compensator. In this paper, the developed high-gain control is applied to a UPS having a flywheel energy storage element. As a result, it is confirmed that the developed new high-gain control method reduces the oscillation of the output voltage and the system is stable