System for producing electric power from renewable sources and a control method thereof

• US 7,952,897 B2
• Filed: 12/22/2005
• Issued: 05/31/2011
• Est. Priority Date: 12/22/2005
• Status: Expired due to Fees

• Current Assignee: Marici Holdings The Netherlands B.V.
• Original Assignee: Power-One Italy S.p.A. (ABB Limited)
• Inventors: Spagnuolo, Giovanni, Femia, Nicola, Macerini, Sauro, De Rosa, Filippo, Nocentini, Danio, Petrone, Giovanni, Vitelli, Massimo, Sirianni, Antonio
• Primary Examiner(s): Riley; Shawn
• Application Number:
  US12/158,723
• Publication Number:
  US 20090091956A1
• Time in Patent Office: 1,986 Days
• Field of Search: 363/41, 323/906
• US Class Current: 363/41
• CPC Class Codes: H02J 2300/24 of photovoltaic origin
• 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: H02M 1/0025 Arrangements for modifying reference values, feedback values or error values in the control loop of a converter
• CPC Class Codes: H02M 3/156 with automatic control of output voltage or current, e.g. switching regulators
• 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

Described herein is a system for generating electric power, comprising: an electric-power source (1) having a preferential point of operation; a double-stage inverter (3A, 3B), which transfers the energy from said source to an external a.c.-voltage electrical network (9); a block (5) for identification of the preferential point of operation, which supplies a reference signal according to the conditions of operation of the electric-power source and to the preferential point of operation of said source; a corrector block (10), provided for setting the parameter for control of the boost converter (3A) of the double-stage inverter (3A, 3B) as a function of the reference signal and of a signal of actual operation of said electric-power source, and for maintaining the source in the proximity of the preferential point of operation.

Claims

1. A system for generating electric power, comprising:

an electric-power source, having a preferential point of operation, correlated to at least one variable parameter that can vary as a function of at least one non-controllable event;

a double-stage inverter having an output coupled to an electrical power network and further comprising as a first stage a DC/DC boost converter, controlled via a control parameter, and as a second stage a DC/AC inverter;

a block for identifying the preferential point of operation, said block supplying a reference signal according to the conditions of operation of said electric-power source and to the preferential point of operation of said electric-power source;

a corrector block comprising a compensator effective to set the control parameter for the boost converter as a function of an error signal generated by a comparison of said reference signal and a signal of actual operation of said electric-power source, wherein said electric-power source is maintained in the proximity of the preferential point of operation; and

the boost converter effective in response to the control parameter to suppress or reduce an effect on said reference signal and said variable parameter of at least one disturbance at a pre-determined frequency coming from the electrical network to which the output of said inverter is connected.

2. The system of claim 1, wherein said signal of actual operation of said electric-power source further comprises said variable parameter.

3. The system of claim 2, wherein said electric-power source comprises at least one field of photovoltaic panels and wherein said preferential point of operation is the point of delivery of the maximum power, the variable parameter being constituted by the voltage across the field of photovoltaic panels, said voltage across the field of photovoltaic panels varying according to the solar power incident on said field of photovoltaic panels.

4. The system of claim 3, wherein said block for identifying the preferential point of operation is a block that executes a maximum power-point tracking (MPPT) algorithm.

5. The system of claim 4, wherein said MPPT algorithm comprises a perturb-and-observe algorithm.

6. The system of claim 5, wherein said reference signal supplied by the block for identifying the preferential point of operation is a reference voltage across the field of photovoltaic panels, and wherein said corrector block determines the value of the parameter for controlling the boost converter as a function of the difference between said reference voltage and of the actual voltage across the field of photovoltaic panels.

7. The system of claim 6, wherein said parameter for controlling the boost converter is the duty cycle of said boost converter.

8. The system of claim 7, wherein said disturbance is constituted by an oscillation of the bulk voltage at output from said boost converter, at the second harmonic of the network voltage.

9. The system of claim 8, wherein said corrector block comprises a regulator with a pass band higher than the second harmonic of the network voltage.

10. A method for controlling the operation of an electric-power source having a preferential point of operation correlated to at least one parameter that can vary as a function of at least one non-controllable event, comprising the steps of:

extracting DC power at an output voltage from said source;

boosting the output voltage from the output value of said source to a higher value DC output voltage by means of a DC/DC boost converter;

converting said DC output voltage into an AC output voltage by means of an inverter;

introducing the AC output voltage from the inverter into an AC-voltage electrical network, to which said inverter is connected;

generating a reference signal, which is a function of the conditions of operation of the electric-power source and of the preferential point of operation of said source;

comparing said reference signal with a signal representative of actual operation of the electric-power source and generating an error signal based on the comparison; and

as a function of said error signal, regulating a parameter for controlling said boost converter via a corrector block sized to suppress or reduce the effect on said signal representative of actual operation and on said reference signal of at least one disturbance at a pre-determined frequency, coming from the electrical network to which said inverter is connected.

11. The method of claim 10, in which said electric-power source comprises at least one field of photovoltaic panels, said method comprising the step of identifying a point of delivery of the maximum power as a function of the conditions of solar irradiation on said field of photovoltaic panels, said signal representative of actual operation being the voltage across the field of photovoltaic panels.

12. The method of claim 11, further comprising the steps of:

determining a reference voltage across the field of photovoltaic panels, corresponding to the preferential point of operation; and

detecting the actual voltage across the field of photovoltaic panels and generating said error signal.

13. The method of claim 12, in which said parameter for controlling the boost converter is the duty cycle.

14. The method of claim 13, in which said point of delivery of the maximum power is identified via a perturb and-observe algorithm.