Cascaded switching power converter for coupling a photovoltaic energy source to power mains

A method of providing an AC power output from a photovoltaic power source, the method comprising:

• generating an AC power output at a line frequency from a capacitive storage element using an inverter, wherein the inverter draws charge from the capacitive storage element cyclically at half-periods of the line frequency and thereby causes a ripple variation in a voltage across the capacitive storage element;
• charging the capacitive storage element with an output of a DC-DC converter that draws power from the photovoltaic power source;
• and
• varying a conversion ratio of the DC-DC converter by controlling a switching circuit of the DC-DC converter such that the output of the photovoltaic power source is maintained at a substantially constant voltage, and wherein the conversion ratio of the DC-DC converter varies at the half-periods of the line frequency as the output of the DC-DC converter follows the ripple variation in the voltage across the capacitive storage element.

A method of providing an AC power output from a photovoltaic power source, the method comprising:

• generating an AC power output at a line frequency from a capacitive storage element using an inverter;
• charging the capacitive storage element with an output of a DC-DC converter that draws power from the photovoltaic power source;
• measuring a voltage across the capacitive storage element;
• and
• controlling an output current of the inverter in conformity with a result of the measuring.

A power converter for providing an AC power output from a photovoltaic power source, the power converter comprising:

• a capacitive storage element;
• an inverter circuit having an input coupled to the capacitive storage element and an output providing the AC power output at a line frequency;
• and
• a DC-DC converter having an input coupled to an output of the photovoltaic power source, and an output coupled across the capacitive storage element, wherein a conversion ratio of the DC-DC converter is varied by controlling a switching circuit of the DC-DC converter such that the output of the DC-DC converter has a high impedance permitting voltage variation due to an input current of the inverter, and such that the input of the DC-DC converter has a low impedance so that the output of the photovoltaic power source is maintained at a substantially constant DC voltage.

A method of providing an AC power output from a photovoltaic power source, the method comprising:

• generating an AC power output at a line frequency from a capacitive storage element using an inverter, wherein the inverter draws charge from the capacitive storage element cyclically at half-periods of the line frequency and thereby causes a ripple variation in a voltage across the capacitive storage element;
• charging the capacitive storage element with an output of a DC-DC converter that draws power from the photovoltaic power source;
• and
• varying a conversion ratio of the DC-DC converter by controlling a switching circuit of the DC-DC converter such that the output of the DC-DC converter has a high impedance permitting voltage variation due to an input current of the inverter, and such that the input of the DC-DC converter has a low impedance so that the output of the photovoltaic power source is maintained at a substantially constant DC voltage.