Parallel redundant and load sharing regulated AC system

An electrical power system is provided having two power sources, one being a commercial power source and the other being an inverter. Both power sources are connected to the load so as to share the load, approximately equally. A voltage regulator is in series with the commercial power source, and the inverter is synchronized to the commercial power source. Means are provided for failure sensing and isolation of the inverter; and means are associated with the voltage regulator which is connected in series with the commercial power source to block and sense reverse power flow in a direction from the load towards the first power source and to initiate isolation of the first power source from the load when reverse power flow is sensed. Means may also be provided for sensing line quality parameters, particularly voltage, current and frequency of the commercial power source and for isolating it if any such sensed quality is outside of predetermined limits, so that the regulated inverter would be required to assume the load. On the other hand, if the inverter fails the commercial power line assumes the whole load, of which it already has approximately half, so that the system becomes line redundant. The invention may also be applicable to parallel operated line-regulated AC lines each deriving power from independent commercial AC sources.