Method of checking solar panel characteristics in an operating solar electrical system

• US 5,648,731 A
• Filed: 02/05/1996
• Issued: 07/15/1997
• Est. Priority Date: 05/11/1993
• Status: Expired due to Term

• Current Assignee: Northrop Grumman Systems Corporation (Northrop Grumman Corporation)
• Original Assignee: TRW Limited (Zeppelin - Stiftung der Stadt Friedrichshafen)
• Inventors: Decker, Darwin Kent, Loftis, Charles B. Jr.
• Primary Examiner(s): Nguyen, Vinh P.
• Application Number:
  US08/596,842
• Time in Patent Office: 526 Days
• Field of Search: 324/158.1, 324/767, 324/73.1, 320/5, 320/39, 320/20, 320/23, 320/32, 363/95, 136/290
• US Class Current: 324/761.01
• CPC Class Codes: G05F 1/67 to the maximum power available from a generator, e.g. from solar cell
• CPC Class Codes: H01M 10/465 with solar battery as charging system
• CPC Class Codes: H02J 4/00 Circuit arrangements for mains or distribution networks not specified as ac or dc
• 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: Y02E 60/10 Energy storage using batteries
• CPC Class Codes: Y10S 136/293 Circuits

Abstract

In a solar electric supply system in which an electrical load is supplied with current produced by a solar array formed of multiple solar panels, each solar panel is individually selected and tested to ensure proper performance by varying the duty cycle of an associated variable transconductance device connected between such solar panel and the electrical load. The method determines the respective solar panel'"'"'s open circuit voltage, its full-load current and obtains various output voltage and current values responsive to different duty cycles, whereby the maximum power point for the solar panel may be determined.

Claims

1. The method of determining the voltage and current characteristics of a solar panel and variable transconductance device combinations from amongst a plurality of such combinations in and during operation of a solar powered power supply system that produces and supplies electrical power to a load via a bus, said load including a rechargable battery and said bus being clamped to a bus voltage, Vbus, each of such solar panel and variable transconductance device combinations being connected to deliver electrical power to said load, comprising the steps of:

selecting one solar panel and variable transconductance device combination for test from amongst said plurality of such solar panel and variable transconductance device combinations;

prescribing in sequence each of a plurality of duty cycles from a plurality of test duty cycle values and adjusting said variable transconductance device to each selected duty cycle in said sequence, and at least one of said plurality of duty cycles being equal to zero per cent and at least one other of said plurality of duty cycles being equal to one-hundred per cent;

measuring electrical current generated by and the electrical voltage at the output of said solar panel in said solar panel and variable transconductance device under test at each said plurality of duty cycles to produce a series of values of voltage and current in respect of each respective duty cycle; and

determining from said series of values each of the solar panel'"'"'s open circuit voltage, Voc;

the solar panels short circuit current, Isc, when clamped to a bus voltage, Vbus;

the maximum power point voltage, Vmp;

the maximum power point current, Imp; and

the ratio of Vmp to Voc, Ratio.

2. The method as defined in claim 1 further comprising the additional step of storing said determined values.

3. The method as defined in claim 1 further comprising the additional steps of defining a curve which fits essentially to the values of voltage produced as plotted against current produced.