An improved in-line uninterruptible power supply system

This paper presents an improved in-line uninterruptible power supply system, which has voltage sag compensation and power factor improvement. The system employs a voltage-source voltage-controlled converter with battery storage. The converter voltage is synchronised to the grid voltage and a link inductor is inserted between the converter and the grid. The load is connected directly to the converter output voltage. The magnitude of the converter voltage is maintained constant through the sinusoidal PWM signal that provides stabilisation from any voltage sags and large fluctuation of the mains voltage. The power factor correction is controlled through the power flow of the system. The inverter is maintained to supply the reactive power to the load, therefore, the grid supplies the active power. Results from simulation using PSCAD/EMTDC and laboratory tests are included.