Multi-cellular photovoltaic panel system with DC-DC conversion replicated for groups of cells in series of each panel and photovoltaic panel structure

• US 8,044,538 B2
• Filed: 01/09/2009
• Issued: 10/25/2011
• Est. Priority Date: 01/10/2008
• Status: Active Grant

• Current Assignee: STMicroelectronics SRL (STMicroelectronics NV)
• Original Assignee: STMicroelectronics SRL (STMicroelectronics NV)
• Inventors: Di Fazio, Salvatore, Ragonese, Domenico, Nigido, Nicola, Ilardo, Santo, Pulvirenti, Francesco, Aiello, Natale
• Primary Examiner(s): Fureman; Jared
• Assistant Examiner(s): AMAYA, CARLOS DAVID
• Application Number:
  US12/351,360
• Publication Number:
  US 20090179500A1
• Time in Patent Office: 1,019 Days
• Field of Search: 307/43, 307/71, 307/72, 307/82
• US Class Current: 307/82
• CPC Class Codes: H02J 1/10 Parallel operation of dc sources
• CPC Class Codes: H02J 2300/24 of photovoltaic origin
• CPC Class Codes: H02J 3/381 Dispersed generators
• CPC Class Codes: H02J 3/388 Islanding, i.e. disconnection of local power supply from the network
• CPC Class Codes: H02M 1/007 Plural converter units in cascade push-pull DC/DC converters with pre-regulator H02M3/3374; DC-AC converters following a DC-DC stage including a high frequency transformer H02M7/4807; DC-AC converters following a DC-DC conversion stage generating periodically varying voltages H02M7/4826
• CPC Class Codes: Y02A 30/60 Planning or developing urban green infrastructure
• CPC Class Codes: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers

Abstract

A photovoltaic energy conversion system includes a distributed control structure for groups of cells of each multi-cellular panel, the components of which are entirely physically integrated in the photovoltaic panel. Each multi-cellular photovoltaic panel has a DC bus, supplied in parallel by a plurality of DC-DC converters, each provided with a controller that controls the working point of the photovoltaic cells coupled to the input of the DC-DC converter for a maximum yield of electric power by implementing a relatively simple MPPT algorithm. The controller includes a logic circuit and A/D converters of analog signals representing the input voltage and the input current generated by the group of cells that is coupled to the input of the DC-DC converter and optionally also of the output voltage of the converter, and a relatively simple D/A converter of the drive control signal of the power switch of the DC-DC converter.

Claims

1. A photovoltaic energy conversion system, comprising:

a plurality of multi-cellular photovoltaic panels, each panel including;

a plurality of groups of photovoltaic cells structured to generate voltages, respectively;

a DC bus coupled to the plurality of multi-cellular photovoltaic panels; and

a plurality of DC-DC converters formed on each photovoltaic panel, each converter having inputs coupled to a respective group of photovoltaic cells on the photovoltaic panel and outputs coupled to the DC bus, each converter structured to individually regulate the voltage generated by the respective group of photovoltaic cells;

each converter including a power switch and a control logic circuit structured to process monitored values of at least one of electrical input and output parameters and execute an algorithm of maximum power point tracking of the corresponding group of photovoltaic cells of the photovoltaic panel to produce a drive control signal to control the power switch of the DC-DC converter, each converter structured to perform individual regulation that includes;

comparing an output power of the corresponding group of photovoltaic cells at a current sampling instant with an output power of the corresponding group of photovoltaic cells at a preceding sampling instant; and

updating, based on the comparing, a tracked reference value of a working point of maximum electrical power yield of the corresponding group of photovoltaic cells, by incrementing or decrementing by a fixed quantity a reference signal that is applied to a input of a drive comparator of the corresponding DC-DC converter.

2. The conversion system of claim 1, further comprising a DC-AC converter having an input connected to said DC buses of the multi-cellular photovoltaic panels.

3. The conversion system of claim 2, further comprising an anti-islanding control system coupled to the DC-AC converter and structured to analyze a public grid voltage for recognizing any programmed or accidental grounding or interruption on a public distribution grid and of electrically isolating the conversion system from the public grid.

4. The conversion system of claim 1, wherein said DC-DC converters of each multi-cellular panel are step-up or boost converters and are each structured to increase an output voltage in respect to the voltage generated by the corresponding group, which voltage corresponds to the sum of voltages individually generated by the photovoltaic cells of the corresponding group.

5. The conversion system of claim 1, wherein said DC-DC converters are boost, buck or buck-boost converters and are structured to stabilize an output voltage at a smaller or larger value than the voltage generated by the corresponding group, which voltage corresponds to the sum of individual voltages generated by the photovoltaic cells of said group.

6. The conversion system of claim 1, wherein the control logic circuit of each DC-DC converter is realized via hardware and includes:

logic circuitry structured to generate a digital control value;

a digital-to-analog converter structured to convert the digital control value into an analog reference signal; and

a PWM drive comparator having an input coupled to receive the analog reference signal and an output coupled to the power switch of the DC-DC converter.

7. The conversion system of claim 6, wherein each DC-DC converter includes a multiplier having an output coupled to said logic circuitry and structured to produce a digital value of power yielded from the group of cells at a sampling instant, the multiplier being structured to produce the digital value by multiplying instantaneous values of current delivered by the corresponding group of photovoltaic cells by the voltage produced by the corresponding group of photovoltaic cells.

8. The conversion system of claim 7, wherein, for each DC-DC converter, the drive comparator of the DC-DC converter is structured to control the power switch of the DC-DC converter in voltage mode by comparing the analog reference signal with a ramp signal of a frequency, implementing a constant frequency PWM control.

9. The conversion system of claim 7, wherein the logic circuitry of each DC-DC converter is structured to continuously update a tracked reference value of a working point of maximum electrical power yield of the corresponding group of photovoltaic cells, by incrementing or decrementing by a fixed quantity said reference signal that is applied to the input of said drive comparator of the DC-DC converter, in function of a comparison of an output power of the corresponding group of photovoltaic cells at a current sampling instant with an output power of the corresponding group of photovoltaic cells at a preceding sampling instant.

10. The conversion system of claim 9, wherein, for each DC-DC converter, the output of the DC-DC converter is coupled to an input of the logic circuitry of the DC-DC converter, which logic circuitry is structured to use a current digital value of the output voltage of the DC-DC converter to limit to a pre-established threshold the output voltage by conditioning an execution or a non-execution of said incrementing or decrementing operation.

11. The conversion system of claim 9, wherein, for each DC-DC converter, the output of the DC-DC converter is coupled to an input of the logic circuitry of the DC-DC converter, which logic circuitry is structured to use a current digital value of the output voltage of the DC-DC converter to establish a maximum safety threshold of the output voltage, upon attainment of which said reference value is reduced to a pre-established value.

12. The conversion system of claim 1, wherein the control logic circuit of each DC-DC converter includes a variable frequency PWM control circuit structured to control the power switch of the DC-DC converter in current mode.

13. The conversion system of claim 1, wherein the control logic circuit of each DC-DC converter includes a variable frequency PWM control circuit structured to control the power switch of the DC-DC converter in voltage mode.

14. A multi-cellular photovoltaic panel, comprising:

connection terminals structured to connect the panel to an external circuit;

an inner DC bus coupled to the connection terminals;

a plurality of groups of photovoltaic cells structured to generate voltages, respectively;

a plurality of DC-DC converters formed on the panel, each converter having inputs coupled to a respective group of photovoltaic cells and outputs coupled to the DC bus, each converter structured to regulate voltage generated by the respective group of photovoltaic cells to which it is coupled, each DC-DC converter including;

a power switch; and

a control logic circuit structured to process monitored values of electrical input or output parameters and execute an algorithm of maximum power point tracking of the corresponding group of photovoltaic cells of the panel to produce a drive control signal to control the power switch of the DC-DC converter, wherein the control logic circuit of each DC-DC converter is realized via hardware and includes;

logic circuitry structured to generate a digital control value;

a digital-to-analog converter structured to convert the digital control value into an analog reference signal; and

a PWM drive comparator having an input coupled to receive the analog reference signal and an output coupled to the power switch of the DC-DC converter,

wherein each DC-DC converter includes a multiplier having an output coupled to said logic circuitry and structured to produce a digital value of power yielded from the group of cells at a sampling instant, the multiplier being structured to produce the digital value by multiplying instantaneous values of current delivered by the corresponding group of photovoltaic cells by the voltage produced by the corresponding group of photovoltaic cells.

15. The multi-cellular photovoltaic panel of claim 14, wherein each DC-DC converter includes an output diode and the power switch of each DC-DC converter is a MOS switch having an integrated structure that defines an intrinsic diode structured to provide, together with the output diode of the DC-DC converter, a by-pass path for current in case of underexposure or electrical interruption of one or of all the photovoltaic cells of the corresponding group.

16. The multi-cellular photovoltaic panel of claim 14, wherein said plurality of DC-DC converters are physically realized on a printed circuit board accommodated in a connection terminals box present on a backside of the photovoltaic panel.

17. A photovoltaic energy conversion method, comprising:

producing photovoltaic energy using a plurality of multi-cellular photovoltaic panels, each panel having at least two groups of photovoltaic cells, each group of photovoltaic cells having a DC-DC converted coupled thereto, the producing including;

generating respective voltages from respective groups of photovoltaic cells on each photovoltaic panel; and

individually regulating the respective voltages, the regulating including;

DC-DC converting the voltages using the DC-DC converters respectively coupled to the groups of photovoltaic cells; and

processing monitored values of at least one of electrical input and output parameters and executing an algorithm of maximum power point tracking of said respective group of photovoltaic cells of the panel to produce a drive control signal that controls a power switch of a corresponding one of the DC-DC converters, wherein the individually regulating includes;

comparing an output power of the corresponding group of photovoltaic cells at a current sampling instant with an output power of the corresponding group of photovoltaic cells at a preceding sampling instant; and

updating, based on the comparing, a tracked reference value of a working point of maximum electrical power yield of the corresponding group of photovoltaic cells, by incrementing or decrementing by a fixed quantity a reference signal that is applied to a input of a drive comparator of the corresponding DC-DC converter.

18. The method of claim 17, wherein, for each DC-DC converter, the output of the DC-DC converter is coupled to an input of the logic circuitry of the DC-DC converter, which logic circuitry is structured to use a current digital value of the output voltage of the DC-DC converter to establish a maximum safety threshold of the output voltage, upon attainment of which said reference value is reduced to a pre-established value.

19. The method of claim 17, including controlling the power switch of each DC-DC converter in current mode using a variable frequency PWM control circuit.

20. A photovoltaic energy conversion system, comprising:

a plurality of multi-cellular photovoltaic panels each including;

a plurality of groups of photovoltaic cells structured to generate voltages, respectively;

a DC bus; and

a plurality of DC-DC converters having respective inputs coupled respectively to the groups of photovoltaic cells and respective outputs connected to said DC bus, each converter being structured to regulate the voltage generated by a corresponding group of the groups of photovoltaic cells;

each converter including a power switch and a control logic circuit structured to process monitored values of at least one of electrical input and output parameters and execute an algorithm of maximum power point tracking of said corresponding group of photovoltaic cells of the panel for producing a drive control signal for controlling the power switch of the DC-DC converter;

wherein the control logic circuit of each DC-DC converter is realized via hardware and includes;

logic circuitry structured to generate a digital control value;

a digital-to-analog converter structured to convert the digital control value into an analog reference signal; and

a PWM drive comparator having an input coupled to receive the analog reference signal and an output coupled to the power switch of the DC-DC converter; and

wherein each DC-DC converter includes a multiplier having an output coupled to said logic circuitry and structured to produce a digital value of power yielded from the group of cells at a sampling instant, the multiplier being structured to produce the digital value by multiplying instantaneous values of current delivered by the corresponding group of photovoltaic cells by the voltage produced by the corresponding group of photovoltaic cells.

21. The conversion system of claim 20, wherein said DC-DC converters of each multi-cellular panel are step-up or boost converters and are each structured to increase an output voltage in respect to the voltage generated by the corresponding group, which voltage corresponds to the sum of voltages individually generated by the photovoltaic cells of the corresponding group.

22. The conversion system of claim 20, wherein said DC-DC converters are boost, buck or buck-boost converters and are structured to stabilize an output voltage at a smaller or larger value than the voltage generated by the corresponding group, which voltage corresponds to the sum of individual voltages generated by the photovoltaic cells of said group.

23. The conversion system of claim 20, wherein, for each DC-DC converter, the drive comparator of the DC-DC converter is structured to control the power switch of the DC-DC converter in voltage mode by comparing the analog reference signal with a ramp signal of a frequency, implementing a constant frequency PWM control.

24. The conversion system of claim 20, wherein the logic circuitry of each DC-DC converter is structured to continuously update a tracked reference value of a working point of maximum electrical power yield of the corresponding group of photovoltaic cells, by incrementing or decrementing by a fixed quantity said reference signal that is applied to the input of said drive comparator of the DC-DC converter, in function of a comparison of an output power of the corresponding group of photovoltaic cells at a current sampling instant with an output power of the corresponding group of photovoltaic cells at a preceding sampling instant.

25. The conversion system of claim 24, wherein, for each DC-DC converter, the output of the DC-DC converter is coupled to an input of the logic circuitry of the DC-DC converter, which logic circuitry is structured to use a current digital value of the output voltage of the DC-DC converter to limit to a pre-established threshold the output voltage by conditioning an execution or a non-execution of said incrementing or decrementing operation.

26. The conversion system of claim 24, wherein, for each DC-DC converter, the output of the DC-DC converter is coupled to an input of the logic circuitry of the DC-DC converter, which logic circuitry is structured to use a current digital value of the output voltage of the DC-DC converter to establish a maximum safety threshold of the output voltage, upon attainment of which said reference value is reduced to a pre-established value.

27. The conversion system of claim 20, wherein the control logic circuit of each DC-DC converter includes a variable frequency PWM control circuit structured to control the power switch of the DC-DC converter in current mode.

28. The conversion system of claim 20, wherein the control logic circuit of each DC-DC converter includes a variable frequency PWM control circuit structured to control the power switch of the DC-DC converter in voltage mode.