Patent ID: 8067855

Claim:
A photovoltaic power conditioning circuit for providing power from a photovoltaic device to an alternating current mains power supply line, the circuit comprising: a DC input to receive DC power from said photovoltaic device; an AC output configured for direct connection to said AC mains power supply line; a DC-to-AC converter coupled to said DC input and to said AC output to convert DC power from said photovoltaic device to AC power for output onto said power supply line; an electronic controller directly coupled to said power supply line to measure a voltage of said power supply line and a current in said power supply line and to control said DC-to-AC converter responsive to said measuring, and wherein said controller is configured to determine first and second frequencies of said voltage in said power supply line and of said current in said power supply line respectively, and to control said DC-to-AC converter responsive to a difference between said first and second frequencies, and wherein said controller is further configured to control said DC-to-AC converter to change an operating frequency of said converter, to monitor said first and second frequencies of said voltage in said power supply line and of said current in said power supply line, respectively, to determine whether said first frequency substantially follows said second frequency during said change, and upon determining that said first frequency substantially follows said second frequency during said change, inhibiting power output from said photovoltaic device to said mains power supply line.