Power condition units with MPPT
A power conditioning unit with maximum power point tracking (MPPT) for a dc power source in a photovoltaic panel is provided. The power conditioning unit includes a power injection control block having a sense input coupled to an energy storage capacitor on a dc link for controlling a dc-to-ac converter to control the injected mains power. The power injection control block tracks the maximum power point by measuring a signal on the dc link which depends on the power drawn from the dc power source, and thus there is no need to measure the dc voltage and current from the dc source. The measured signal is a ripple voltage level and the power injection control block controls the amplitude of an ac current output such that the amount of power transferred to the grid mains is dependent on the amplitude of a sinusoidal voltage component on the energy storage capacitor.
1. A power conditioning unit with maximum power point tracking (MPPT), for delivering power from a dc power source to an ac mains power supply output, the power conditioning unit comprising:
an input for receiving power from said dc power source;
an output for delivering ac power to said ac mains power supply;
an energy storage capacitor for storing energy from said dc power source for delivering to said ac mains power supply output;
a dc-to-ac converter coupled to said output for converting energy stored in said energy storage capacitor to ac power for said ac mains power supply output; and
a power injection control block having a sense input coupled to said energy storage capacitor and having an output coupled to said dc-to-ac converter, to control said dc-to-ac converter to control power injected into said ac mains power supply,
wherein, in operation, a voltage on said energy storage capacitor has a sinusoidal voltage component at twice a frequency of said ac mains,
wherein said power injection control block is configured for controlling an amplitude of an ac current provided to said ac mains power supply output such that an amount of power transferred to said ac mains power supply output is dependent on an amplitude of said sinusoidal voltage component on said energy storage capacitor, and
wherein said power injection control block is configured to track a maximum power point of said dc power source by controlling said dc-to-ac converter.
2. The power conditioning unit of claim 1 , wherein said power injection control block is configured to track a maximum power point of said dc power source without measuring a dc voltage or dc current provided from said dc power source.
3. The power conditioning unit of claim 1 , wherein said power injection control block is configured to determine a power transferred from said dc source to said ac mains power supply using a squared value of said sinusoidal voltage component, and to control said dc-to-ac converter responsive to said determined power transferred.
4. The power conditioning unit of claim 1 , wherein said power injection control block is galvanically isolated from said dc power source.
5. The power conditioning unit of claim 1 , wherein said power injection control block is configured to multiply a voltage sensed from said energy storage capacitor by a sinusoidal template to generate a template signal, and to compare said template signal with a signal sensed from said output to control said dc-to-ac converter.
6. The power conditioning unit of claim 1 further comprises a dc voltage amplifier coupled between said input and said energy storage capacitor to increase a voltage from said dc power source by a substantially constant amplification factor.
7. The power conditioning unit as claimed in of claim 6 further comprises a voltage amplifier control block to drive said dc voltage amplifier with a substantially constant duty cycle pulse width modulation control signal, and to provide on-off control of a dc output from said dc voltage amplifier.
8. The power conditioning unit of claim 1 , wherein an energy flow from said dc power source to said energy storage capacitor is substantially proportional to an amount of energy stored in said energy storage capacitor, wherein an amount of energy drawn from said energy storage capacitor and provided to said output is controlled by said power injection control block such that said amount of energy stored in said energy storage capacitor is dependent on said ac power delivered to said ac mains power supply, and wherein said power injection block is able to track said maximum power point by controlling said ac power delivered to said ac mains power supply.
9. The power conditioning unit of claim 1 , wherein said power injection control block is configured to track said maximum power point by controlling said dc-to-ac converter to substantially maximize said amplitude of said sinusoidal voltage component.