System and method for power conversion for renewable energy sources
View Patent ↗A power converter is configured to transfer energy from a photovoltaic (PV) array to a DC bus internal to the power converter. The power converter executes a modulation module to selectively connect one or more switching devices between the output of the PV array and the DC bus. The power converter is configured to operate in multiple operating modes. In one operating mode, the converter operates with a fixed modulation period and a variable on time, and in another operating mode, the converter operates with a variable modulation period and a fixed on time. The improved power converter provides highly efficient low power energy capture, improving power efficiency and enabling energy capture in low light conditions with reduced converter losses.
1. A power converter comprising:
an input configured to receive power from a DC source;
a DC bus having a positive and a negative rail;
at least one switching device selectively connecting the input to the DC bus as a function of a corresponding control signal;
a memory device storing a series of instructions; and
a controller configured to execute the series of instructions to:
determine a magnitude of power generated by the DC source,
generate the control signal for each of the at least one switching devices in a first operating mode when the magnitude of power generated by the DC source exceeds a predefined threshold, and
generate the control signal for each of the at least one switching devices in a second operating mode when the magnitude of power generated by the DC source is less than the predefined threshold, wherein:
the series of instructions includes a modulation module having a modulation frequency and an on time,
during the first operating mode, the controller executes the modulation module to generate control signals at a fixed modulation frequency with a varying on time, and
during the second operating mode, the controller executes the modulation module to generate control signals at a varying modulation frequency with a fixed on time.
2. The power converter of claim 1 wherein the memory device stores a lookup table defining a rate of change of the modulation frequency during the second operating mode as a function of the modulation frequency at which the controller is presently executing the modulation module.
3. The power converter of claim 1 wherein the modulation frequency varies from about 10 kHz to about 50 Hz.
4. A method of converting power from a renewable energy source having a variable power generation capability to a voltage potential present on a DC bus via a power converter, the method comprising the steps of:
monitoring a magnitude of power generated by the renewable energy source;
controlling at least one switching device in the power converter via a corresponding control signal to selectively connect the renewable energy source to the DC bus;
executing a modulation module in the power converter to generate the control signals in a first operating mode when the magnitude of power generated by the renewable energy source exceeds a predefined threshold; and
executing the modulation module in the power converter to generate the control signals in a second operating mode when the magnitude of power generated by the renewable energy source is less than the predefined threshold, wherein:
the modulation module determines an on time for each of the control signals within a switching period, the switching period defined as the inverse of a modulation frequency,
during the first operating mode, the modulation module generates control signals at a fixed modulation frequency with a varying time, and
during the second operating mode, the modulation module generates control signals at a varying modulation frequency with a fixed on time.
5. The method of claim 4 wherein executing the modulation module in the power converter to generate the control signals in the second operating mode further comprises the steps of:
reading a desired change in the modulation frequency from a look up table stored in a memory device of the power converter, and
varying the modulation frequency includes adding or subtracting the desired change as a function of the magnitude of power generated by the renewable energy source.
6. The method of claim 4 wherein the modulation frequency varies from about 10 kHz to about 50 Hz.