Regulation of inverter DC input voltage in photovoltaic arrays

• US 9,106,105 B2
• Filed: 01/31/2012
• Issued: 08/11/2015
• Est. Priority Date: 02/10/2011
• Status: Active Grant

• Current Assignee: Also Energy Incorporated
• Original Assignee: Draker Laboratories Incorporated (Also Energy Incorporated)
• Inventors: McCaslin, Shawn R., Sandbote, Sam B., Williams, Bertrand J.
• Primary Examiner(s): Barnie, Rexford
• Assistant Examiner(s): SHIAO, DAVID A
• Application Number:
  US13/362,214
• Publication Number:
  US 20120205974A1
• Time in Patent Office: 1,288 Days
• Field of Search: None
• US Class Current: 1/1
• CPC Class Codes: H02J 2300/26 involving maximum power point tracking control for photovoltaic sources
• CPC Class Codes: H02J 3/381 Dispersed generators
• CPC Class Codes: H02J 3/46 Controlling of the sharing of output between the generators, converters, or transformers
• CPC Class Codes: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers
• CPC Class Codes: Y10S 323/906 Solar cell systems

Abstract

A converter unit configured to couple to a photovoltaic panel (PV) may include a controller to sense an output voltage and output current produced by the photovoltaic panel, and manage the output voltage of a corresponding power converter coupled to a DC bus to regulate the resultant bus voltage to a point that reduces overall system losses, and removes non-idealities when the panels are series connected. The controller may also adapt to output condition constraints, and perform a combination of input voltage and output voltage management and regulation, including maximum power point tracking (MPPT) for the PV. The output voltage and output current characteristic of the power converter may be shaped to present a power gradient—which may be hysteretically controlled—to the DC bus to compel an inverter coupled to the DC bus to perform its own MPPT to hold the DC-bus voltage within a determinate desired operating range.

Claims

1. A control module for controlling a power converter configured to couple to a solar panel to provide an output voltage and an output current to a bus, the control module comprising:

a plurality of input ports, each given input port of the plurality of input ports configured to receive a different one of a plurality of parameters comprising;

a first parameter indicative of an input current of the power converter provided by the solar panel;

a second parameter indicative of an input voltage of the power converter provided by the solar panel;

a third parameter indicative of an output voltage of the power converter; and

a fourth parameter indicative of an output current of the power converter; and

a controller configured to regulate the input voltage, input current, output voltage, and output current of the power converter according to a maximum power point tracking (MPPT) algorithm and an output power control algorithm, using the first, second, third, and fourth parameters as input values;

wherein according to the output power control algorithm, the controller is configured to;

allow changes in the output voltage of the power converter to move the input voltage of the power converter away from a maximum power point (MPP) voltage value corresponding to an MPP of the solar panel, and create localized power gradients of a characteristic of output power of the power converter versus an overall voltage on the bus;

track, over a time period of specific duration, minimum voltage output values and maximum voltage output values for the output voltage of the power converter; and

upon expiration of the time period;

identify a peak minimum voltage output value of the tracked minimum voltage output values and a peak maximum voltage output value of the tracked maximum voltage output values; and

control a timing and slope of the localized power gradients according to the peak minimum voltage output value and the peak maximum voltage output value.

2. The control module of claim 1, wherein to regulate the input voltage, input current, output voltage, and output current of the power converter, the controller is configured to provide one or more control signals to the power converter, wherein the controller is configured to determine respective values of the one or more control signals according to the MPPT algorithm, the output power control algorithm and the input values used by the MPPT algorithm and the output power control algorithm.

3. The control module of claim 1, wherein each of the localized power gradients compels an inverter coupled to the bus and performing MPPT to hold the overall voltage of the bus within a target operating range defined at least by the localized power gradient, while minimizing a corresponding system efficiency loss.

4. The control module of claim 3, wherein the controller is configured to center each of the local power gradients on a present value of the overall voltage of the bus, wherein a sign of a slope of the localized power gradient determines a desired direction of a movement of the overall voltage of the bus.

5. The control module of claim 3, wherein the controller is configured to choose a slope of the localized power gradient that results in the overall voltage of the bus moving towards a specified target voltage.

6. The control module of claim 3, wherein the controller is configured to no longer create the localized power gradient once the overall voltage of the bus is within the target operating range.

7. The control module of claim 3, wherein the control module is configured to receive external control directives comprising values for the target operating range for the overall voltage of the bus.

8. A control system for controlling a power converter configured to couple to a solar panel to provide an output voltage and output current to a voltage bus residing at an overall bus voltage, the control system comprising:

a sensing circuit configured to sense input current and input voltage of the power converter derived from the solar panel, and further configured to sense the output voltage and the output current of the power converter;

a controller configured to;

regulate the input voltage of the power converter according to the sensed input current and sensed input voltage of the power converter and according to the sensed output voltage and sensed output current of the power converter, to optimize power derived from the solar panel according to a maximum power point (MPP) of the solar panel;

allow changes in the output voltage of the power converter to move the input voltage of the power converter away from an MPP voltage value corresponding to the MPP of the solar panel, and create localized power gradients of a characteristic of output power of the power converter versus the overall bus voltage, wherein each of the localized power gradients compels an inverter coupled to the voltage bus and performing maximum power point tracking (MPPT) to track the overall bus voltage and maintain the overall bus voltage within an overall bus voltage range that ensures that the overall bus voltage is at a specified preferred value; and

track, over a time period of specific duration, minimum voltage output values and maximum voltage output values for the output voltage of the power converter; and

upon expiration of the time period;

identify a peak minimum voltage output value of the tracked minimum voltage output values and a peak maximum voltage output value of the tracked maximum voltage output values; and

control a timing and slope of the localized power gradients according to the peak minimum voltage output value and the peak maximum voltage output value.

9. The control system of claim 8, wherein the controller is further configured to apply the localized power gradients transiently, and synchronize the localized power gradients to an MPPT probe signal applied to the voltage bus by the inverter.

10. The control system of claim 8, wherein the controller is further configured to compute output voltage threshold values based on the peak minimum voltage output value and the peak maximum voltage output value, and control the timing and the slope of the localized power gradients according to the computed output voltage threshold values.

11. The control system of claim 10, wherein the controller is further configured to determine an average value of the output voltage of the power converter, and compare the average value of the output voltage against the computed output voltage threshold values in controlling the timing and the slope of the localized power gradients, to provide hysteretic control of the localized power gradients.

12. The control system of claim 11, wherein the controller is further configured to:

activate a first state upon the average value of the output voltage rising above a highest threshold of the computed output voltage threshold values, and maintain the first state until the first state is released;

release the first state upon the average value of the output voltage falling below a middle lower threshold of the computed output voltage threshold values;

activate a second state upon the average value of the output voltage falling below a lowest threshold of the computed output voltage threshold values, and maintain the second state until the second state is released; and

release the second state upon the average value of the output voltage rising above a middle upper threshold of the computed output voltage threshold values.

13. The control system of claim 12, wherein the controller is further configured to:

present a negative power versus output voltage gradient to the voltage bus when the first state is active and the output voltage becomes greater than the average value of the output voltage; and

present a positive power versus output voltage gradient to the voltage bus when the second state is active and the output voltage becomes lower than the average value of the output voltage.

14. The control system of claim 8, wherein to regulate the input voltage of the power converter, the controller is configured to execute a Maximum Power Point Tracking (MPPT) algorithm to:

measure first output power of the power converter at a first value of the input voltage representative of a target input voltage value;

measure second output power of the power converter at a second value of the input voltage representative of a present input voltage value;

if the measured second output power is greater than the measured first output power;

increase the target input voltage value by a first amount if the second value is greater than the first value; and

decrease the target input voltage value by a second amount if the second value is less than the first value;

if the measured second output power is less than the measured first output power;

decrease the target input voltage value by a third amount if the second value is greater than the first value; and

increase the target input voltage value by a fourth amount if the second value is less than the first value.

15. The control system of claim 14, wherein the controller is further configured to execute the MPPT algorithm to:

generate a new first value of the input voltage and a new second value of the input voltage.

16. The control system of claim 14, wherein the controller is further configured to algorithmically determine the first amount, second amount, third amount, and fourth amount.

17. A method for controlling a power converter coupled to a solar panel to provide an output voltage and an output current to a voltage bus, the method comprising:

monitoring input voltage and input current of the power converter;

monitoring the output voltage and the output current of the power converter;

regulating the input voltage of the power converter according to a Maximum Power Point Tracking (MPPT) algorithm using parameters corresponding to;

the monitored input voltage and monitored input current of the power converter; and

the monitored output voltage and output current of the power converter; and

regulating output power of the power converter, comprising;

deliberately allowing changes in the output voltage of the power converter to move the input voltage of the power converter away from a maximum power point (MPP) voltage value corresponding to an MPP of the solar panel, and creating localized power gradients of a characteristic of output power of the power converter versus an overall bus voltage, wherein the power gradient compels an inverter coupled to the voltage bus and performing MPPT to track an overall bus voltage of the voltage bus and maintain the overall bus voltage within a specified preferred range;

tracking, over a time period of specific duration, minimum voltage output values and maximum voltage output values for the output voltage of the power converter; and

upon expiration of the time period;

identifying a peak minimum voltage output value of the tracked minimum voltage output values and a peak maximum voltage output value of the tracked maximum voltage output values; and

controlling a timing and slope of the localized power gradients according to the peak minimum voltage output value and the peak maximum voltage output value.

18. The method of claim 17, wherein said monitoring comprises obtaining digitized values corresponding to the input voltage and input current of the power converter and the output voltage and output current of the power converter, and using the digitized values as the parameters.

19. The method of claim 17, further comprising specifying a point in time at which to enable a corresponding power gradient of the localized power gradients, to regulate the output voltage of the power converter to a particular voltage range.

20. The method of claim 17, wherein said allowing changes in the output voltage comprises moving the input voltage of the power converter in a specific direction independent of a direction of movement of the output voltage of the power converter.

21. The method of claim 17, further comprising:

when the output voltage of the power converter is below a specified first value, creating a power gradient of the localized power gradients that results in an increase in the overall bus voltage;

when the output voltage of the power converter is between the specified first value and a specified second value, maintaining a present output voltage of the power converter; and

when the output voltage of the power converter is above the specified second value, creating a power gradient of the localized power gradients that results in a decrease in the overall bus voltage.

22. The method of claim 17, further comprising:

algorithmically determining output threshold values for the output voltage of the power converter;

determining an average value of the output voltage of the power converter over a time period of specific duration;

comparing the average value of the output voltage against the output threshold values; and

controlling a timing and a slope of a corresponding power gradient of the localized power gradients according to results of said comparing to provide hysteretic control of the power gradient.

23. The method of claim 22, further comprising:

activating a first state upon the average value of the output voltage rising above a highest threshold of the output threshold values, and maintaining the first state until the first state is released;

releasing the first state upon the average value of the output voltage falling below a middle lower threshold of the output threshold values;

activating a second state upon the average value of the output voltage falling below a lowest threshold of the output threshold values, and maintaining the second state until the second state is released; and

releasing the second state upon the average value of the output voltage rising above a middle upper threshold of the output threshold values.

24. The method of claim 23, further comprising:

presenting a negative power versus output voltage gradient to the voltage bus when the first state is active and the output voltage becomes greater than the average value of the output voltage; and

presenting a positive power versus output voltage gradient to the voltage bus when the second state is active and the output voltage becomes lower than the average value of the output voltage.

25. The method of claim 17, wherein said regulating the output power of the power converter comprises regulating the output power of the power converter according to a specified function that provides a mapping between the output voltage of the power converter and the input voltage of the power converter.

26. The method of claim 25, wherein the specified function is nonlinear, wherein said regulating the power converter according to the specified function comprises:

initiating a negative power gradient to be presented to the voltage bus for a period of time when the output voltage is above a specified first threshold;

releasing the negative power gradient when the output voltage falls below a specified second threshold;

initiating a positive power gradient to be presented to the voltage bus for a period of time when the output voltage is below a specified third threshold; and

releasing the positive power gradient when the output voltage rises above a specified fourth threshold.

27. The method of claim 26, wherein the first, second, third, and fourth thresholds are specified to have values that provide hysteresis for said initiating the positive power gradient and negative power gradient, and said releasing the positive power gradient and negative power gradient.

28. A converter unit comprising:

a power converter having an input configured to couple to a solar panel to obtain an input voltage and input current from the solar panel, and an output configured to couple to a voltage bus to provide a converter output voltage and a converter output current to the voltage bus; and

a control unit comprising;

one or more input ports configured to receive a plurality of parameters comprising;

a first parameter indicative of an input current of the power converter;

a second parameter indicative of an input voltage of the power converter;

a third parameter indicative of the converter output voltage; and

a fourth parameter indicative of the converter output current; and

a controller configured to;

implement a Maximum Power Point Tracking (MPPT) algorithm using the first, second, third, and fourth parameters as input values, to regulate the input voltage, input current, output voltage, and output current of the power converter;

deliberately allow changes in the output voltage of the power converter to move the input voltage of the power converter away from a maximum power point (MPP) voltage value corresponding to an MPP of the solar panel, and create localized power gradients of a characteristic of output power of the power converter versus an overall voltage on the voltage bus, wherein the localized power gradients allow tracking to a specified value of the overall voltage on the voltage bus, for maximum power transfer over the voltage bus;

track, over a time period of specific duration, minimum voltage output values and maximum voltage output values for the output voltage of the power converter; and

upon expiration of the time period;

identify a peak minimum voltage output value of the tracked minimum voltage output values and a peak maximum voltage output value of the tracked maximum voltage output values; and

control a timing and slope of the localized power gradients according to the peak minimum voltage output value and the peak maximum voltage output value.

29. The converter unit of claim 28, wherein the controller is configured to implement a mapping of the converter output voltage to the input voltage by mapping a triangular probe waveform seen at the output of the converter unit onto a square wave seen at the input of the converter unit.

30. The converter unit of claim 29, wherein the mapping is nonlinear and is discontinuous, wherein in implementing the power curve shaping algorithm, the controller is configured to:

initiate a negative power gradient to be presented to the voltage bus for a period of time when the output voltage is above a specified first threshold;

release the negative power gradient when the output voltage falls below a specified second threshold;

initiate a positive power gradient to be presented to the voltage bus for a period of time when the output voltage is below a specified third threshold; and

release the positive power gradient when the output voltage rises above a specified fourth threshold.

31. The converter unit of claim 30, wherein the first, second, third, and fourth thresholds are specified to have values that provide hysteresis for initiating the positive power gradient and negative power gradient, and for releasing the positive power gradient and negative power gradient.

32. The converter unit of claim 28, wherein the power converter is a switching DC/DC converter.

33. A system for harnessing photonic energy to provide power to one or more loads, the system comprising:

a plurality of solar power panels, wherein each given solar panel of the plurality of solar panels provides a respective output current and a respective output voltage;

a DC voltage bus providing a DC bus voltage;

a plurality of converter units coupled to the DC voltage bus, each converter unit of the plurality of converter units configured to provide a respective converter output voltage to the DC voltage bus, wherein each given solar panel is coupled to a corresponding converter unit of the plurality of converter units to provide its respective output current and its respective output voltage as inputs to its corresponding converter unit, wherein each corresponding converter unit comprises a switching power module that produces a respective converter output voltage and respective converter output current, and wherein each corresponding converter unit is configured to;

regulate an input voltage of its switching power module according to an MPPT (maximum power point tracking) algorithm receiving parameters as inputs, wherein the parameters correspond to one or more of;

the input voltage and input current of the switching power module; and

the respective converter output voltage, and the respective converter output current; and

regulate the respective converter output voltage according to a function of output power provided by the switching power module with respect to the converter output voltage, wherein according to the function, the corresponding converter unit is configured to deliberately allow changes in the respective converter output voltage to move the input voltage of its switching power module away from a maximum power point (MPP) voltage value corresponding to an MPP of the given solar panel, and create localized power gradients of a characteristic of output power of the respective switching power module versus the DC bus voltage;

track, over a time period of specific duration, minimum voltage output values and maximum voltage output values for the output voltage of the power converter; and

upon expiration of the time period;

identify a peak minimum voltage output value of the tracked minimum voltage output values and a peak maximum voltage output value of the tracked maximum voltage output values; and

control a timing and slope of the localized power gradients according to the peak minimum voltage output value and the peak maximum voltage output value; and

a DC/AC inverter that performs MPPT and inverts the DC bus voltage to an AC power signal for distribution to one or more AC loads.

34. The system of claim 33, wherein the plurality of converter units are series connected to the DC voltage bus via their respective outputs.

35. The system of claim 33, wherein the plurality of converter units are configured to receive external control signals to set target values for the respective converter output voltages.