Abstract: An uninterruptible power system has a transformer with a primary connected to input terminals, a secondary connected to output terminals, a static switch connected between the input terminals and the primary, and an auxiliary primary connected to an inverter which is supplied by a battery to provide output voltage to the output terminals when a main AC power system connected to the input terminals has failed. The primary has multiple taps at different voltage levels and a buck-boost winding. The taps of the transformer are switched and the buck-boost winding is controlled to provide either buck, boost, or pass-by to allow control of the output voltage from the transformer to within a few percent of a desired voltage level despite large changes in the input voltage.

Abstract: A backup power system has power supply lines extending from input terminals, connectable to a main AC power system, and output terminals, connectable to a load, with a relay connected in a power supply line. The AC input power is monitored and when a fault in the power is detected, the relay is opened and an inverter is simultaneously turned on to provide backup power from a battery to the output terminals at a phase and frequency synchronized with the AC input voltage before the fault occurs. When the AC power system power is restored, the inverter power is again synchronized with the AC input power at the input terminals, the relay switch is closed and the inverter is turned off to allow the main power system to provide power to the load. The inverter may be providing power to the power lines before the relay contacts are opened to minimize the disruption of power supplied to the load during transfers.

Abstract: Phase and frequency locking of a controlled signal to a reference signal is obtained in a digital phase locked loop using efficient computational procedures which are carried out rapidly with minimal computational burden on a digital processor. During each cycle of the controlled signal, the time difference between the periods and the phases of the reference signal and the controlled signal are measured. These measured variables determine the predicted changes of the period of the controlled signal to bring the controlled signal into phase and frequency lock with the reference. The change allowed in the period between each discrete cycle is constrained to be less than or equal to a selected maximum amount of time.

Abstract: Instabilities in the output voltage provided from an AC power supply system connected to a power factor correcting load are suppressed by a stabilizer which is connected across the output lines from the power supply system to the load. The stabilizing apparatus includes a rectifier having AC input nodes connected to the power supply system output lines, and DC output nodes at which DC voltage appears. A capacitor and resistor are connected in parallel across the output nodes of the rectifier. During normal operation, where the peak AC voltage from the power supply system is substantially constant, the capacitor charges up to a voltage level near the zero to peak value of the AC voltage waveform, with the charge on the capacitor slowly dissipated through the parallel resistor at a rate that does not substantially dissipate the charge between peaks of the AC voltage waveform.

Abstract: A battery in a back-up power system is charged during the time that power is available from the main AC power system by utilizing the main power transformer and the main inverter. When power is available from the main AC power source, an AC voltage appears across the primary of the transformer, which is connected to the inverter. Switches in the bridge inverter are turned on for a relatively brief period of time to short the primary of the transformer causing current through the leakage inductances of the transformer to rapidly build up. When the switching devices are turned off, the inductances induce a current to continue to flow from the primary into the inverter through anti-parallel diodes, normally back biased by the voltage from the battery, into the battery thereby charging the battery with the energy stored in the transformer inductances. The inverter current reaches zero when the energy stored in the inductance is fully discharged.