A generator set controller includes a dead bus sensor producing a dead bus signal indicative of a power failure on a power bus that is an input to the controller on a digital input channel. The controller also receives a voltage signal from a phase of a power bus.

The resolution of two asynchronous three-phase power sources such that an optimal phase to phase matchup may be made between them. This is achieved with a logic system that receives a data point at the zero-voltage crossings of the three waveforms from each source. The data points create distinct "states" of the three-phase waveform for each power source. There are six data points for each power source per cycle. The states of the load and source, along with information pertaining to the connection configuration of the present source of power to the load, are used to determine the optimum configuration for connecting an alternate or new source to the load based on information obtained from a lookup table.

A power converter system includes: a circuit breaker having one terminal connected to a power system and another terminal connected to a load; a transformer for interconnection; a power converter; and a controller for controlling the power converter, wherein, during a return to grid connected operation, the power converter is controlled such that the phase of an output voltage of the power converter matches the phase of the system voltage, and the circuit breaker is closed, so as to prevent an overcurrent during a changeover from the self commutated operation to the grid connected operation of the power converter.

An automatic transfer switch (ATS) system and method of operating an ATS system are disclosed. The ATS system includes at least one input port capable of being coupled to at least one power source to receive an input power, a first internal component that requires internal power satisfying a first criterion in order to properly operate, and a power converter such as a switch mode power supply that is coupled to the first internal component and to the at least one input port. The power converter is capable of receiving the input power by way of the at least one input port and converting the input power into the internal power to be provided to the first internal component. The internal power provided by the power converter satisfies the first criterion, even though at least one characteristic of the input power varies within a range.

Methods and apparatus for switching a load between first and second sources is shown to include first and second solid state switches connected to the load. First and second mechanical breakers are connected between the switches and the sources so that each source is connected to the load through a circuit breaker and solid state switch. A controller is connected to sense the voltage from the first and second sources. The controller is connected to the first and second switches and the first and second mechanical breakers. The controller senses the phase difference between the voltages from the first and second sources. The controller causes the first and second mechanical breakers to open and close in response to sensing the phase difference between the sources. The first and second mechanical breakers can include medium voltage vacuum breakers. In a preferred embodiment, when the controller senses that the phase difference between sources is more than 30 degrees out of phase, the controller will open the circuit breaker connected to the alternate source. In this manner voltage stress on the solid state switching devices is minimized.