Conditioning circuit for a power supply at the maximum power point, a solar generator, and a conditioning method

• US 6,984,970 B2
• Filed: 09/22/2003
• Issued: 01/10/2006
• Est. Priority Date: 09/19/2002
• Status: Expired due to Fees

• Current Assignee: Alcatel SA (Nokia Corporation)
• Original Assignee: Alcatel SA (Nokia Corporation)
• Inventors: Capel, Antoine
• Primary Examiner(s): Patel, Rajnikant B.
• Application Number:
  US10/665,017
• Publication Number:
  US 20050017697A1
• Time in Patent Office: 841 Days
• Field of Search: 323/906, 323/299, 323/303, 323/222, 363/95, 363/98, 363/97, 363/55, 363/56, 363/80
• US Class Current: 323/299
• CPC Class Codes: G05F 1/67 to the maximum power available from a generator, e.g. from solar cell
• CPC Class Codes: H02J 2300/26 involving maximum power point tracking control for photovoltaic sources maximum power point systems in particular G05F1/67
• CPC Class Codes: H02J 7/35 with light sensitive cells
• 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

The invention relates to a conditioning circuit that measures operating points of a power supply to deduce therefrom the current-voltage characteristic thereof and to determine directly the voltage corresponding to its maximum power point, without using any kind of tracking algorithm that causes the operating point of the power unit to oscillate about the maximum power point. The maximum power point voltage VMPP is supplied to a controller which regulates a power cell by slaving it to the input voltage until the output voltage of the supply is equal to the maximum power point voltage V_MPP. The invention also relates to a solar generator and an associated conditioning method. One particular application is to high-power satellites.

Claims

1. A circuit for conditioning a power supply having a current-voltage characteristic that is an exponential function for which a graph of the power supplied as a function of the voltage at the terminals of said power supply features a maximum power point, said conditioning circuit comprising:

a power cell with one input that is supplied with power by said power supply and one output that supplies power to a load, and

a control circuit for controlling said power cell via a control signal applied to said power cell to slave the input voltage of said power cell, wherein

said control circuit comprises;

calculation means comprising means for receiving instantaneous measurements of points on said current-voltage characteristic and a program that determines said exponential function of said current-voltage characteristic on the basis of four points on said current-voltage characteristic and determines a reference voltage, and

control means for supplying said control signal representative of the difference between the reference voltage calculated by said calculation means and an instantaneous voltage at the output of the power supply so as to cancel out said control signal.

2. The circuit claimed in claim 1 wherein, said current-voltage characteristic of said power supply being of the form:

i=i_SC−

i_R(exp(av)−

1),

said calculation means determines the parameters of the above equation from the following equations;

$\begin{array}{c}a=<br><br>\frac{1}{v_1-v_2}<br><br>\mathrm{Log}<br><br>\left(\frac{d<br><br>i_1}{d<br><br>i_2}<br><br>\frac{d<br><br>v_2}{d<br><br>v_1}\right)\\ i_R=<br><br>-\frac{d<br><br>i}{d<br><br>v}<br><br>\frac{1}{a<br><br><br><br>\exp <br><br>\left(\mathrm{av}\right)}\\ i_{\mathrm{SC}}=<br><br>i-i_R<br><br>\left(\exp <br><br>\left(\mathrm{av}\right)-1\right).\end{array}$

3. The circuit claimed in claim 1 wherein said calculation means determines said reference voltage using the Newton-Raphson method applied to said exponential function of siad current-voltage characteristic.

4. The circuit claimed in claim 1, further comprising a current sensor that measures an instantaneous current in a regular manner and wherein said calculation means launches said program when a current variation between the instantaneous current and a maximum power point current exceeds a predetermined threshold.

5. The circuit claimed in claim 1, wherein said control circuit comprises an adder for comparing the instantaneous voltage at the output of said power supply and the reference voltage generated by said calculation means, said adder delivering at its output a signal representative of the difference between the latter magnitudes at the input of said control means.

6. A solar generator comprising a power supply for which a graph of the power supplied as a function of the voltage at the terminals of said power supply features a maximum power point, wherein said solar generator is adapted to be conditioned by the circuit claimed in claim 1.

7. A method of using a conditioning circuit to condition a power supply having a current-voltage characteristic that is an exponential function for which a graph of the power supplied as a function of the voltage at the terminals of said power supply features a maximum power point, said conditioning circuit comprising:

a power cell with one input that is supplied with power by said power supply and one output that supplies power to a load, and

a control circuit for controlling said power cell via a control signal applied to said power cell to slave the input voltage of said power cell, wherein said conditioning method comprises;

a step of determining said exponential function of said current-voltage characteristic using four points on said current-voltage characteristic,

a step of determining a reference voltage, and

a step of transmitting said control signal representative of the difference between the calculated reference voltage and an instantaneous voltage at the output of said power supply so as to cancel out said control signal.

8. The method claimed in claim 7 wherein, said current-voltage characteristic of said power supply being of the form:

i=i_SC−

i_R(exp(av)−

1),

wherein the parameters of the above equation are determined from the following equations;

$\begin{array}{c}a=<br><br>\frac{1}{v_1-v_2}<br><br>\mathrm{Log}<br><br>\left(\frac{d<br><br>i_1}{d<br><br>i_2}<br><br>\frac{d<br><br>v_2}{d<br><br>v_1}\right)\\ i_R=<br><br>-\frac{d<br><br>i}{d<br><br>v}<br><br>\frac{1}{a<br><br><br><br>\exp <br><br>\left(\mathrm{av}\right)}\\ i_{\mathrm{SC}}=<br><br>i-i_R<br><br>\left(\exp <br><br>\left(\mathrm{av}\right)-1\right).\end{array}$

9. The method claimed in claim 7 wherein said determination of said reference voltage uses the Newton-Raphson method applied to said exponential function of said current-voltage characteristic.

10. The method claimed in claim 7 wherein said conditioning circuit further comprises a current sensor that measures an instantaneous current in a regular manner, wherein said method determines said exponential function and said reference voltage as soon as a current variation between said instantaneous current and said current corresponding to said maximum power point exceeds a predetermined threshold.

11. The method claimed in claim 7, wherein said method uses four points on said current-voltage characteristic, one of which is said maximum power point, and the other three points being obtained by application of successive voltage levels at the output of said power cell and by sensing corresponding currents.