Abstract: An apparatus for measuring the direction of power flow through conductors connecting a load to a source of alternating electric current, the load being capable of generating electric current, and the source of alternating electric current being capable of accepting power flow from the load. The invention comprises at least one wattmeter connected so that the sum of their outputs is proportional to the power flow through the conductors and the sign of the sum of their outputs is indicative of the direction of the power flow. A detector is provided for detecting the sign of the output of the at least one wattmeter. The detector is capable of generating an indicator signal. The indicator signal has a first value when the power flows from the source of alternating electric current into the load and the indicator signal has a second value when power flows from the load into the source of alternating electric current.

Abstract: An inverter for supplying electric alternating current (AC) to a load from a DC source of electric current has a DC bus. The DC bus has a positive conductor and a negative conductor. A plurality of switches are connected to the DC bus, and each of the switches has a conducting state and a nonconducting state. The switches are connected so that electric current may flow from the DC bus through at least one of the switches into the load. Means are provided for switching each of the switches from the nonconducting state into the conducting state at a predetermined time for each of the switches. Means are provided for switchably connecting the DC bus to the DC source of electric current. Means are provided for switchably shorting the positive conductor of the DC bus to the negative conductor of the DC bus in order to interrupt the current flow through the switches and thereby drive the switches into the nonconducting state.