UNDERSTANDING UPS OPERATIONEATON Powerware® 9390 UPS (20–80 kVA) Installation and Operation Manual 164201603 Rev 2 www.powerware.com 7-13If at any time during the battery discharge the input power becomes available again,the rectifier begins to supply DC current to the inverter. At this point, the unit returnsto Normal mode. If at any time during the battery discharge the AC input powerbecomes available again, each rectifier turns on, assumes the inverter load from thebatteries, and begins recharging the batteries. Depending on the total load and theduration of the battery discharge, battery and rectifier input current limit alarms maybe seen for a short time due to the current required to recharge the batteries.7.3 Functional DescriptionThe UPS is a true online double-conversion unit with a transformerless power train.A high-frequency active rectifier powers a high-frequency three-phase inverter. Thebypass circuit uses a solid-state continuous-duty static switch. The UPS operatesfrom battery strings from 192 cells (384V) to 240 cells (380V/400V/415V/480V).7.3.1 Input RectifierThe rectifier is a three-phase, high-frequency PWM, IGBT-based power conversionstage that provides input power factor correction and low input current harmonicdistortion. The rectifier maintains a DC level that is optimized for maximum inverterefficiency. A precharge system charges the energy storage elements in the powertrain prior to energizing the rectifier.7.3.2 InverterThe inverter is a three-phase, high-frequency PWM, IGBT-based power conversionstage that continuously supplies the critical load with high-quality AC power. TheIGBTs are modulated to maintain the highest efficiency.7.3.3 Battery Charger and ABMThe charger is a high-frequency, IGBT-based power conversion stage. The UPS usesABM technology, which isolates the battery from the electrical environment, exceptfor periodic charging or reserve mode operation, extending its life.ABM extends battery life by keeping the batteries charged and performing periodicbattery testing.An ABM charging cycle starts with the charger driving the battery voltage, atmaximum current limit, to a battery charge level of 2.34 volts/cell. The time it takesfor the voltage to reach to the battery charge level is saved as the battery chargetime. If the battery charge time exceeds 100 hours, an alarm sounds.As soon as a battery charge level of 2.34 volts/cell is reached, the battery is chargedat a float level of 2.31 volts/cell for 48 hours (battery float time) plus 150% of batterycharge time. Twenty-four hours into the float period, a series of battery tests areperformed to check the battery health. The float level charge continues after asuccessful test.At initial startup, the battery run time on the front panel display indicates two minutes.After the 24-hour float charging period and battery testing, the actual battery run timeis determined and the actual battery run time is displayed.After the float period is completed, the charger is disconnected and the batteries areallowed to rest for 672 hours (28 days) maximum rest time. If the battery voltage fallsbelow the opportunity charge level of 2.1 volts/cell during the first 240 hours of therest period, an alarm sounds.
