Abstract: An uninterruptible power supply (UPS) includes a plurality of UPS modules. Each of the UPS modules has a battery that provides power to a protected load in the event of a utility power failure. A plurality of controllers control how much power each of the batteries deliver to the protected load, and a communication bus allows the controllers to exchange information about the battery voltages. One of the controllers calculates the average battery voltage of the plurality of batteries and adjusts the amount of energy provided by an individual battery such that the battery voltage is about equal to the average battery voltage.

Abstract: An uninterruptible power supply (UPS) system includes a first UPS module that has a first power source, a second power source and a controller operable to selectively connect the first or second power source to a load. A second UPS module is connected in parallel with the first UPS module. The second UPS module also includes a first power source, a second power source and a controller operable to selectively connect the first or second power source to a load. The controller of the first UPS module gradually transfers power from the first power source of the first UPS module to the first power source of the second UPS module to detect the presence of the first power source of the second UPS module.

Abstract: Devices and methods for improved voltage source transfer switching. First and second voltage sources (primary and alternate) are connectable to a load via corresponding first and second switches, which may comprise SCRs. A controller operates the switches according to various transfer methods. In some transfer methods, the timing of the switching operation is critical. For example, switching times may be optimized to reduce or prevent transformer saturation due to the dc flux built up during the transfer event. The controller force commutates off the primary source switch by turning on the appropriate alternate source switch for a brief period of time. In this case, the alternate source switches are “pulsed” (rather than being turned on continuously), so that the switches will naturally commutate off at the next current zero cross. Subsequently, the volt-second balancing control logic will permanently turn on these switches at the appropriate time.

Abstract: This disclosure is concerned with devices and methods for voltage source transfer switching that reduces or eliminates transformer saturation due to DC flux built up during a transfer event. First and second voltage sources (primary and alternate) are connectable to a load via corresponding switches. A transformer is connected downstream of the switches. A controller operates the switches according to various transfer methods wherein a switching time is determined to minimize downstream saturation current.