Development of a long-life three-phase flywheel UPS using an electrolytic capacitorless converter/inverter

A long-life three-phase flywheel (FW) uninterruptible power supply (UPS) using an electrolytic capacitorless converter/inverter and a transformerless isolating system rating of 200 V and 5 kW-1 min is described. The UPS has the following characteristics: (1) electrolytic capacitorless converter/inverter configuration for long life and smaller size; (2) transformerless isolating system to realize small size and correct weight; (3) batteryless system for maintenance-free long life of about 20 years. The electrolytic capacitorless converter/inverter has a small-film capacitor value of 1/50 times of a conventional one. 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 obtained excellence test results, such as an input power factor of 99.8%, a small output voltage distortion of 1.03%, and 93.8% efficiency at full load.