A hybrid static/rotary UPS system

An uninterruptible power supply (UPS) system that employs a rotary converter (motor-generator, or MG, set) as a post conditioner for a simple rugged inverter that can operate either from rectified utility power or batteries to provide regulated sinusoidal power with good transient capacity, low distortion, and complete isolation of the load from the utility is described. A system with total load capacity of 200 kW was constructed using a single inverter to power two induction MG sets: a 125 kVA 60 Hz unit (1800 r/min with flywheel) and a 75 kVA 3600 r/min MG with 400 Hz output. After factory testing, the system was installed at a large computer facility in a location where severe power supply quality problems existed. No instability or other difficulty with multiple MG operation occurred in spite of the size and construction differences between the MG sets