Solar power conditioning unit
The present invention relates to a power conditioning unit for delivering power from a dc power source to an ac output, particularly ac voltages greater than 50 volts, either for connecting directly to a grid utility supply, or for powering mains devices independent from the mains utility supply. We describe a power conditioning unit for delivering power from a dc power source to an ac mains output, the power conditioning unit comprising an input for receiving power from said dc power source, an output for delivering ac power, an energy storage capacitor, a dc-to-dc converter having an input connection coupled to said input and an output connection coupled to the energy storage capacitor, and a dc-to-ac converter having an input connection coupled to said energy storage capacitor and an output connection coupled to said output, wherein said energy storage capacitor has a capacitance of less than twenty microfarads.
1. A solar power conditioning unit for delivering power from a solar or photovoltaic panel dc power source to an ac mains power supply, the power conditioning unit comprising:
a power conditioning unit input for receiving power from said dc power source;
a power conditioning unit output for delivering ac power;
a non-electrolytic energy storage capacitor;
a dc-to-dc converter having an input connection coupled to said power conditioning unit input and an output connection coupled to the non-electrolytic energy storage capacitor; and
a dc-to-ac converter having an input connection coupled to said non-electrolytic energy storage capacitor and an output connection coupled to said power conditioning unit output;
a power extraction control block to control said dc-to-dc converter to control power extracted from said dc power source and provided to said non-electrolytic energy storage capacitor; and
a power injection control block to control said dc-to-ac converter to control power injected into said ac mains power supply from said non-electrolytic energy storage capacitor,
wherein said power extraction control block has an input coupled to said power conditioning unit input for receiving power from said dc power source and has an output to control said dc-to-dc converter and is configured to regulate a voltage of said dc power source to control power extracted from said dc power source to said non-electrolytic energy storage capacitor, and
wherein a fluctuating sinusoidal component of a dc voltage on the non-electrolytic energy storage capacitor has a frequency that is determined by an energy mismatch between the dc power source and the ac power output.
2. The power conditioning unit of claim 1 , wherein said power injection control block and said power extraction control block operate independently.
3. The power conditioning unit of claim 1 , wherein said power injection control block and said power extraction control block share a common microcontroller.
4. The power conditioning unit of claim 1 , wherein said power injection control block has an input coupled to said non-electrolytic energy storage capacitor and an output to control said dc-to-ac converter and is configured to control an amplitude of an ac current provided to said ac mains power supply.
5. The power conditioning unit of claim 1 , wherein said power injected into said ac mains power supply has a sinusoidal shape, and wherein said power extraction control block is configured to extract a substantially constant power from said dc power source over a period of said sinusoidal shape.
6. The power conditioning unit of claim 1 , wherein an instantaneous ac power output of said power conditioning unit has a sinusoidal shape, wherein said power extracted from said dc power source is substantially constant over a cycle of said instantaneous ac power output, and wherein a difference between said power extracted from said dc power source and said instantaneous ac power output defines the energy mismatch which appears as said fluctuating sinusoidal component of said dc voltage on said non-electrolytic energy storage capacitor.
7. The power conditioning unit of claim 1 , wherein said dc-to-dc converter comprises at least one power transistor for transferring power from the input connection of the dc-to-dc converter to the output connection of the dc-to-dc converter, wherein said power extraction control block comprises:
a sensing circuit for sensing a voltage on said input connection; and
a driver circuit for driving said power transistor responsive to the sensed voltage to control said power transfer.
8. The power conditioning unit of claim 7 , wherein the power extraction control block further comprises a reference voltage generator, wherein the driver circuit is configured to substantially minimize a difference between a reference voltage from said reference voltage generator and the sensed voltage.
9. The power conditioning unit of claim 7 further comprising a system for performing maximum power point tracking of said dc power source by maintaining a voltage or current from the dc power source substantially at a reference voltage or current, wherein said system for performing maximum power point tracking is configured to control said power transistor responsive both to a voltage or current of said dc power source and to a voltage or current of said non-electrolytic energy storage capacitor.
10. The power conditioning unit of claim 1 , wherein said frequency is twice that of said ac power.
11. The power conditioning unit of claim 1 , wherein said non-electrolytic energy storage capacitor has a capacitance of less than twenty microfarads.
12. The power conditioning unit of claim 1 , wherein said non-electrolytic energy storage capacitor comprises a film-type capacitor.
13. The power conditioning unit of claim 1 , wherein said dc-to-dc converter includes a transformer coupled between said input connection and said output connection.
14. A solar power conditioning unit for delivering power from a solar or photovoltaic panel dc power source to an ac mains power supply, the power conditioning unit comprising:
a power conditioning unit input for receiving power from said dc power source;
a power conditioning unit output for delivering ac power;
a non-electrolytic energy storage capacitor;
a dc-to-dc converter having an input connection coupled to said power conditioning unit input and an output connection coupled to the energy storage capacitor; and
a dc-to-ac converter having an input connection coupled to said energy storage capacitor and an output connection coupled to said power conditioning unit output;
a power extraction control block to control said dc-to-dc converter to control power extracted from said dc power source and provided to said energy storage capacitor; and
a power injection control block to control said dc-to-ac converter to control power injected into said ac mains power supply from said energy storage capacitor,
wherein said power extraction control block has an input coupled to said power conditioning unit input for receiving power from said dc power source and has an output to control said dc-to-dc converter and is configured to regulate a voltage of said dc power source to control power extracted from said dc power source to said energy storage capacitor,
wherein said power injected into said ac mains power supply has a sinusoidal shape, and wherein said power extraction control block is configured to extract a substantially constant power from said dc power source over a period of said sinusoidal shape, wherein an instantaneous ac power output of said power conditioning unit has a sinusoidal shape, wherein said power extracted from said dc power source is substantially constant over a cycle of said instantaneous ac power output, and wherein a difference between said power extracted from said dc power source and said instantaneous ac power output defines an energy mismatch which appears as a fluctuating sinusoidal component of a dc voltage on said energy storage capacitor.
15. The power conditioning unit of claim 14 , wherein said power injection control block and said power extraction control block operate independently.
16. The power conditioning unit of claim 14 , wherein said power injection control block and said power extraction control block share a common microcontroller.
17. The power conditioning unit of claim 14 , wherein said power injection control block has an input coupled to said energy storage capacitor and an output to control said dc-to-ac converter and is configured to control an amplitude of an ac current provided to said ac mains power supply.
18. A solar power conditioning unit for delivering power from a solar or photovoltaic panel dc power source to an ac mains power supply, the power conditioning unit comprising:
a power conditioning unit input for receiving power from said dc power source;
a power conditioning unit output for delivering ac power;
a non-electrolytic energy storage capacitor;
a dc-to-dc converter having an input connection coupled to said power conditioning unit input and an output connection coupled to the energy storage capacitor; and
a dc-to-ac converter having an input connection coupled to said energy storage capacitor and an output connection coupled to said power conditioning unit output;
a maximum power point tracking (MPPT) system to perform maximum power point tracking of said dc power source by maintaining a voltage or current from the dc power source substantially at a reference voltage or current;
a power extraction control block to control said dc-to-dc converter to control power extracted from said dc power source and provided to said energy storage capacitor; and
a power injection control block to control said dc-to-ac converter to control power injected into said ac mains power supply from said energy storage capacitor,
wherein said power extraction control block has an input coupled to said power conditioning unit input for receiving power from said dc power source and has an output to control said dc-to-dc converter and is configured to regulate a voltage of said dc power source to control power extracted from said dc power source to said energy storage capacitor,
wherein said dc-to-dc converter comprises at least one power transistor for transferring power from the input connection of the dc-to-dc converter to the output connection of the dc-to-dc converter,
wherein said power extraction control block comprises a sensing circuit for sensing a voltage on said input connection and a driver circuit for driving said power transistor responsive to the sensed voltage to control said power transfer,
wherein said MPPT system is configured to control said power transistor responsive both to a voltage or current of said dc power source and to a voltage or current of said energy storage capacitor.
19. The power conditioning unit of claim 18 , wherein said power injected into said ac mains power supply has a sinusoidal shape, and wherein said power extraction control block is configured to extract a substantially constant power from said dc power source over a period of said sinusoidal shape.
20. The power conditioning unit of claim 18 , wherein the power extraction control block further comprises a reference voltage generator, and wherein the driver circuit is configured to substantially minimize a difference between a reference voltage from said reference voltage generator and the sensed voltage.