Method and apparatus for controlling an inverter using pulse mode control

1. A method for controlling a photovoltaic module inverter, the method comprising:

determining an output frequency of the inverter;

determining a pulse width value for an output waveform of the inverter, the pulse width value being less than a half-wave period of a full-cycle sinusoidal waveform at the output frequency; and

generating a sinusoidal output pulse waveform comprising a plurality of pulses having a pulse width equal to the pulse width value.

2. The method of claim 1 , wherein determining an output frequency of the inverter comprises:

sensing a grid frequency of a power grid to which the inverter is connected, and

setting the output frequency substantially equal to the grid frequency.

3. The method of claim 1 , wherein determining the pulse width value comprises:

determining an output power of the inverter; and

determining a pulse width value for the output waveform as a function of the output power.

4. The method of claim 3 , wherein determining the pulse width value for the output waveform comprises determining a pulse width value of the output waveform that is directly proportional to the output power.

5. The method of claim 3 , further comprising adjusting the pulse width value in response to a change in the output power of the inverter.

6. The method of claim 5 , wherein adjusting the pulse width value comprises decreasing the pulse width value in response to a decrease in the output power of the inverter.

7. The method of claim 1 , wherein determining the pulse width value comprises determining the pulse width value as a function of a grid voltage of a power grid.

8. The method of claim 1 , wherein determining the pulse width value comprises determining the pulse width value according to a predetermined equation.

9. The method of claim 1 , wherein generating the sinusoidal output pulse comprises generating switching signals to the output converter only for a duration equal to the pulse width value.

10. The method of claim 1 , wherein generating the sinusoidal output pulse comprises generating a sinusoidal output current pulse waveform.

11. The method of 1 , further comprising:

determining a voltage of a direct current (DC) bus of the inverter; and

determining an amplitude of the sinusoidal output pulse as a function of the voltage of the DC bus to maintain the DC bus at a reference voltage level.

12. The method of claim 1 , further comprising:

determining a phase of a grid waveform of a power grid, and

wherein generating the sinusoidal output pulse comprises generating a sinusoidal output pulse that is in phase with the grid waveform.

13. The method of claim 12 , wherein generating the sinusoidal output pulse comprises:

generating a positive sinusoidal output pulse in phase with a positive half-cycle of the grid waveform, and

generating a negative sinusoidal output pulse in phase with a negative half-cycle of the grid waveform.

14. The method of claim 1 , further comprising:

comparing an output power of the inverter to a reference output power level; and

operating the inverter in a normal run mode to generate a full-cycle sinusoidal output waveform in response to the power output of the inverter exceeding the reference output power level.

15. An inverter for converting direct current (DC) power received from a renewable energy source to an alternating current (AC) power, the inverter comprising:

an output converter to generate an output waveform at an output frequency in response to a plurality of switching signals; and

an output converter controller coupled to the output converter and configured to:

(i) determine a pulse width value for the output waveform of the inverter, the pulse width value being less than a half-wave period of the output frequency, and

(ii) generate the plurality of switching signals to cause the output converter to generate a sinusoidal output pulse having a pulse width equal to the pulse width value.

16. The inverter of claim 15 , wherein to determine the pulse width value comprises to:

determine an output power of the inverter; and

determine the pulse width value for the output waveform as a function of the output power.

17. The inverter of claim 16 , further comprises a memory device having stored therein a data table that correlates output power to pulse width values, and

wherein to determine the pulse width value comprises to access the data table to retrieve the pulse width value from the data table as a function of the output power.

18. The inverter of claim 16 , wherein the output converter controller is further configured to adjust the pulse width value in response to a change in the output power of the inverter.

19. The inverter of claim 15 , further comprising a DC bus electrically connected to the output converter, wherein the output converter controller is further configured to determine an amplitude of the sinusoidal output pulse as a function of a voltage of the DC bus to maintain the DC bus at a reference voltage level.

20. An apparatus comprising:

a solar panel comprising a plurality of solar cells configured to generate a direct current (DC) power output in response to receiving an amount of sunlight; and

an inverter coupled to the solar cell panel and configured to convert the DC power output to an AC power output, the inverter comprising:

a converter circuit to generate an output waveform at an output frequency; and

a converter control circuit to control the operation of the converter circuit, the converter control circuit configured to:

(i) determine an output power of the inverter;

(ii) operate the inverter in a normal run mode to cause the converter circuit to generate a full-cycle sinusoidal output waveform at the output frequency in response to the output power being equal to or greater than a reference output power threshold; and

(iii) operate the converter circuit in a pulse mode to cause the converter circuit to generate a sinusoidal pulse output waveform having a pulse width less than a half-wave period of the full-cycle sinusoidal output waveform in response to the output power being less than the reference threshold.