Development of a Long Life Three Phase Flywheel UPS Using an Electrolytic Capacitor-Less Converter/Inverter

A long life three phase flywheel (FW) uninterruptible power supply (UPS) using an electrolytic capacitor-less converter/inverter and a transformer-less isolating system rating of 200V and 5kW-1min is described. The UPS has following characteristics. (1) Electrolytic capacitor-less converter/inverter configuration which makes long life and small size. (2) Transformer-less isolating system to realize small size and right weight. (3) Battery less system for maintenance free and long life about 20 years. The electrolytic capacitor-less converter/inverter has a small film capacitor value of 1/50 times of a conventional ones. The converter/inverter is controlled by a current and voltage follow-up method using PWM control. Charging and discharging abilities of the FW energy is achieved only by controlling the instantaneous slip frequency of the induction machine. The UPS has excellence test results which are obtained such as input power factor of 99.8%, small output voltage distortion of 1.03% and 93.8% efficiency at full load.