Development of economical UPS system having active filter across DC-bus

This paper proposes an economical single-phase flywheel uninterruptible power supply (UPS) having active filter across the dc-bus. The proposed UPS consists of diode rectifier, inverters, LC filter and flywheel energy storage unit, and it has many features such as low production cost, long life of the system. The proposed UPS has the active filter ability across the dc-bus, which realizes unity power factor operation without both PWM rectifier and bulky electrolytic capacitor. A three-phase inverter regulates PM motor/generator speed with flywheel and compensates the harmonic input current to the sinusoidal input current. The dc-bus line has the absolute waveform of input voltage. The output voltage obtains the sinusoidal waveform by using synchronous switched single-phase inverter. The simulation results point out that the proposed economical flywheel UPS system has the desired sinusoidal input current and output voltage. Moreover, the proposed system realizes maintenance free system, small size, long life and very low production cost