This paper deals with a parallel processing uninterruptible power supply (UPS) for sudden voltage fluctuation in power management to integrate power quality improvement, load voltage stabilization and UPS. To reduce the complexity, cost and number of power conversions, which results in higher efficiency, only one voltage-controlled voltage source inverter (VCVSI) is used. The VCVSI is connected in series on the DC battery side and in parallel on the AC grid side with a decoupling inductor. The system provides sinusoidal voltage at the fundamental value of 220V/60Hz for the load during abnormal utility power conditions or grid failure. Also, the system can be operated to mitigate the harmonic current and voltage demand from nonlinear loads and provide voltage stabilization for loads when sudden voltage fluctuation occur, such as sag and swell. The experimental results confirm the system protects against outages caused by abnormal utility power conditions and sudden voltage fluctuations and change.
 W. J. Ho, J.B. Lio and W.S. Feng, “Economic UPS structure with phase-controlled battery charger and input-power-factor improvement,” IEE Proc. Eletr. Power Appl., vol. 144, no. 4, pp. 221-226, July 1997.
 M. Ashari, W.W.L. Keerthipala, and C.V. Nayar, “ A single phase parallel connected uninterruptible power supply/demand side management system”, IEEE Trans. Energy Convers., vol. 15, no. 1, pp. 97-102, Mar. 2000.
 S.H. Ko, S.R. Lee, H. Dehbonei, and C.V. Nayar, “Application of Voltage and Current Controlled Voltage Source Inverters for Distributed Generation Systems,” IEEE. Trans. Energy Conver., vol. 21, no. 3, pp. 782-792, Sept. 2006
 S.H. Ko, , S.R. Lee, C.V.Nayar and C.Y Won, ”Design Considerations for a Distributed Generation System Using a Voltage-Controlled Voltage Source Inverter,” Journal of Power Electronics, vol. 9, no.4, pp. 643-653, July 2009