Battery regulated bus spacecraft power control system

• US 5,530,335 A
• Filed: 05/11/1993
• Issued: 06/25/1996
• 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 K., Loftis, Charles B. Jr.
• Primary Examiner(s): Wong, Peter S.
• Assistant Examiner(s): TSO, EDWARD H
• Application Number:
  US08/060,103
• Time in Patent Office: 1,141 Days
• Field of Search: 320/5, 320/12, 320/22, 320/32, 320/39, 320/40, 320/48, 323/222, 323/906, 323/225, 324/207.15, 324/207.16, 324/239, 244/173, 307/66
• US Class Current: 320/102
• 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

A system for supplying d.c. power to an electrical load, in which such load includes a rechargeable battery, is characterized by a plurality of power sources connected in common to the electrical load, wherein the current generated by the multiple power sources is combined to supply such electrical load. Each of the power sources includes a solar panel and a controlled variable transconductance device, such as a Buck converter, connected in electrical series circuit. A digital processor, including a stored program, coupled to the control inputs of the variable transconductance devices, selectively individually sets the duty cycle of each transconductance device under control of a stored program, whereby the electrical power supplied by said power sources to said electrical load is individually controlled by the digital processor.

Claims

1. A power system for supplying electrical power over a power bus to at least one power consuming electrical device, comprising:

a plurality of uni-directional current conducting power sources, said power sources being connected to said power bus for supplying DC current thereto;

each of said power sources, comprising;

a solar panel for converting solar energy to a dc voltage and a variable transconductance means connected in electrical series circuit, said variable transconductance means having a controllable duty cycle, whereby the quantity of current that passes therethrough is a dependent function of the value of said duty cycle thereof, and control input means for setting said value of said duty cycle responsive to a control input voltage;

rechargeable battery means connected to said power bus for normally receiving current from said power bus and, responsive to interruption of said power sources, for supplying current to said bus to power said at least one electronic device; and

digital processor means, including stored program means, coupled to said control input means of said variable transconductance means in each of said plurality of power sources for selectively individually setting the duty cycle of each of said variable transconductance means under control of said stored program means, whereby electrical power supplied by said power sources to said power bus is individually controlled by said digital processor means.

2. The invention as defined in claim 1, wherein each said variable transconductance means comprises a Buck converter.

3. The invention as defined in claim 1, further comprising:

battery current sensor means for determining depletion of current from and replenishment of current to said rechargeable battery means; and

wherein said digital processor means further includes;

battery state of charge status detecting means for periodically sampling said battery current sensor means for determining a state of charge of said rechargeable battery.

4. The invention as defined in claim 3, wherein said digital processor means includes:

means for determining when said battery state of charge status detecting means represents said rechargeable battery as being in a fully charged state and, in response thereto, for selectively setting said control inputs of each of said variable transconductance means to values sufficient to permit supply of electrical current from said power sources to provide (a) the current required by any electronic devices connected to said power bus and (b) a trickle charge current required by said battery means.

5. The invention as defined in claim 3 wherein each of said variable transconductance means comprises a Buck converter.

6. The invention as defined in claim 5, wherein said digital processor means further includes:

detect and set means for determining when said battery state of charge status detecting means represents said rechargeable battery as being in a fully charged state and, in response to said battery being in a fully charged state, for selectively setting control inputs of each of said buck converters to values sufficient to permit said power sources to supply electrical current to said power bus in such amount as provides only a trickle charge current to flow to said battery in addition to any current required by said electronic devices and, responsive to said battery being in less than 0.90 of a fully charged state, for selectively setting control inputs of each of said buck converters to values sufficient to permit said power sources to supply electrical current to said bus in such amount as provides a full charge current to flow to said battery in addition to any current required by said electronic devices.

7. The invention as defined in claim 6 wherein said detect and set means sets a first one of said Buck converters to a first duty cycle, wherein less than a high output current is supplied therethrough, and sets a plurality of the remaining Buck converters to a second duty cycle, wherein high output current is supplied therethrough.

8. The invention as defined in claim 7 wherein said detect and set means varies said first duty cycle in incremental steps, while retaining said second duty cycle at a fixed value, to finely adjust the total current generated by said power sources.

9. The invention as defined in claim 1 wherein said digital processor means includes timing means for establishing periodic cycles and wherein said digital processor means sets said duty cycle of each of said variable transconductance means in said plurality of power sources in serial order during different ones of said periodic cycles.

10. A solar power supply system of the type containing a rechargeable battery clamping a power bus, comprising:

a plurality of DC power sources, each of said DC power sources comprising a solar panel and a computer controlled variable transconductance means connected in electrical series circuit to said power bus and to said rechargeable battery;

said solar panel producing DC voltage responsive to sunlight and said variable transconductance means, associated with said solar panel, passing DC current produced by said solar panel in dependence upon the transconductance value to which said variable transconductance means is set; and

digital computer means for individually controlling said transconductance value of each said variable transconductance means of said plurality of DC power sources, whereby said digital computer means controls DC electrical power flowing into said power bus, and DC current from said power bus flows into said rechargeable battery.

11. The power supply system as defined in claim 10, further comprising:

computer readable battery current sensor means for monitoring current into and from said battery, said battery current sensor means being periodically read by said digital computer means for permitting said digital computer means to compute the state of charge of said rechargeable battery;

said digital computer means containing program means for prescribing transconductance levels for each of said variable transconductance means responsive to said state of charge of said rechargeable battery.

12. The power supply system as defined in claim 11, further comprising:

means for periodically adjusting said transconductance level of at least one of said variable transconductance means that is supplying current to said power bus to a transconductance level falling between low transconductance and high transconductance so long as said battery current sensor means does not detect a prescribed value of battery current, while maintaining the remainder of said variable transconductance means that are also supplying current to said power bus at high transconductance.

13. The invention as defined in claim 12 wherein said prescribed value of battery current is a trickle charge current prescribed for said rechargeable battery.

15. The power supply system as defined in claim 10, wherein said digital computer means includes timing means for establishing a predetermined program cycle;

and further comprising;

computer readable battery current sensor means for monitoring current into and from said battery, said battery current sensor means being periodically read by said digital computer means at least once during each said program cycle for permitting said digital computer means to compute the state of charge of said rechargeable battery;

said digital computer means including program means for prescribing transconductance levels for each of said variable transconductance means of said DC power sources responsive to said state of charge of said rechargeable battery; and

, further including, amp-second integration means for integrating said periodic readings from said battery current sensor means to define said state of charge of said rechargeable battery.

16. The invention as defined in claim 10 wherein said digital computer means further includes:

memory means for storing information, said memory means storing a first prescribed value representing a maximum allowable recharge rate of current for said battery, a second prescribed value representing a trickle charge rate of current for said battery, and a third value representing the state of charge of said battery;

timing means for establishing predetermined program cycles; and

further comprising;

computer readable battery current sensor means for monitoring current into and from said battery, said battery current sensor means being periodically read by said digital computer means at least once during each said program cycle for permitting said digital computer means to compute the state of charge of said rechargeable battery and update said state of charge information stored in said memory;

said digital computer means further containing selection means for selecting during each program cycle said first prescribed value from memory responsive to said battery state of charge information representing less than full charge or, alternatively, said second prescribed value from memory responsive to said battery state of charge information representing full charge;

said digital computer means containing setting program means for prescribing transconductance levels for each of said variable transconductance means in dependence upon said value selected by said selection means.

14. A solar power supply system of the type containing a rechargeable battery clamping a power bus, comprising:

a plurality of DC power sources, each of said DC power sources comprising a solar panel and a computer controlled variable transconductance means connected in electrical series circuit to said power bus and to said rechargeable battery;

said solar panel producing DC voltage responsive to sunlight and said variable transconductance means, associated with said solar panel, passing DC current produced by said solar panel in dependence upon the transconductance value to which said variable transconductance means is set; and

digital computer means for individually controlling said transconductance value of each said variable transconductance means of said plurality of DC power sources, whereby said digital computer means controls DC electrical power flowing into said power bus, and DC current from said power bus flows into said rechargeable battery;

computer readable battery current sensor means for monitoring current into and from said battery, said battery current sensor means being periodically read by said digital computer means for permitting said digital computer means to compute the state of charge of said rechargeable battery;

said digital computer means including program means for prescribing transconductance levels for each of said variable transconductance means responsive to said state of charge of said rechargeable battery; and

means for periodically adjusting said transconductance level of at least one of said variable transconductance means that is supplying current to said power bus to a transconductance level falling between low transconductance and high transconductance so long as said battery current sensor means does not detect a prescribed value of battery current, while maintaining the remainder of said variable transconductance means that are also supplying current to said power bus at high transconductance, and wherein said prescribed value of battery current is a full charge current prescribed for said rechargeable battery and wherein said computer readable battery current sensor means comprises;

a first magnetic amplifier type current sensor, said first magnetic amplifier type current sensor containing a magnetic core, a first winding for receiving current to be measured, and an output winding for producing an output voltage, Vrdg1, in dependence upon current through said first winding and a predetermined sensor gain slope of G₁ ;

a second magnetic amplifier type current sensor, said second magnetic amplifier type current sensor containing a magnetic core, a first winding for receiving current to be measured, a bias winding and an output winding for producing an output voltage, Vrdg₂, in dependence upon current through said first winding and said bias winding and a predetermined sensor gain slope of G₂ ;

means coupling said first winding of each of said first and second magnetic amplifier type current sensors in electrical series circuit to an electrical load, whereby current to said electrical load passes through both said first windings;

means providing a dc bias current in said bias winding of said second current sensor only to produce an offset current X for said second magnetic amplifier type current sensor;

means for reading the output voltage of each of said first and second magnetic amplifier type current sensors in quick succession to provide two voltage readings, Vrdg₁ and Vrdg₂, said respective voltage readings being representative of the respective load current through said first winding of each said first and second magnetic amplifier type current sensors, respectively;

correlation means for correlating said two voltage readings, said correlation means comprising;

first means for computing first and second potential load current values from said two voltage readings, Vrdg₁ and Vrdg₂ according to the following equation 1-1;

space="preserve" listing-type="equation">Current (+)=(Vrdg-Voff)×

G, 1-1

where

Vrdg is said voltage reading at said respective sensor output,

Voff is the offset voltage, where

Voff=X/G, and

X is said respective sensor offset current,

G is said sensor gain slope;

second means for computing third and fourth potential load current values from said two voltage readings, Vrdg₁ and Vrdg₂ according to the following equation 1-2;

space="preserve" listing-type="equation">Current(-)=-(Vrdg+Voff)×

G, 1-2

where Vrdg is a positive number; and

means for defining a predefined error band of differences in current values;

means for determining the difference between said first and second computed current values;

means for determinging the difference between said third and fourth computed current values;

means for determining the absolute value of said first and second differences and comparing said absolute vaules to determine which of said absolute values yields the smallest difference;

means for selecting said smallest difference in absolute values and determining whether such difference falls within said error band and, if not falling within said error band, then selecting the next difference computation and determining whether said next difference computation falls within said error band;

means responsive to selection of said difference computation that falls within said error band for providing an output signal representative of one of said two current values used to determine said difference computation that falls within said error band, whereby said output signal comprises an indication of load current magnitude.

17. In a power supply system for supplying dc power over a power bus to an electrical load, said system including adc current generating means coupled to said power bus for supplying current to said electrical load with said generating means being interruptable, a rechargeable battery coupled to said power bus for supplying dc current to said bus in the absence of current from said dc current generating means, whereby electrical charge stored in said battery is depleted and receiving charging current from said dc current generating means over said power bus, whereby electrical charge in said battery is replenished, the improvement comprising:

stored program computer means, including a program, for regulating the rate of charge of said battery from between a maximum allowable charge rate and a trickle charge rate in dependence upon the amount of electrical charge depleted from said battery during any prior period of time during which said battery was supplying current to said power bus;

current monitoring means for monitoring electrical current exiting said battery and supplying information thereon to said computer;

said computer integrating said information in accordance with said stored program to determine the electrical charge depleted by said battery and the amount of electrical charge required thereby to replenish said charge in said battery; and

computer controlled regulator means coupled between said power bus and said dc current generating means for regulating the level of current applied from said dc current generating means to said bus, said computer controlled regulator means being controlled by said stored program computer means to cause said generating means to provide current levels prescribed by said program over time intervals prescribed by said program to supply electrical current required by said electrical load and specified levels of charging current to recharge said battery.

18. The invention as defined in claim 17 wherein said dc current generating means comprises:

a plurality of solar panels, each of said solar panels for converting solar energy to dc current; and

wherein said regulator means, comprises;

a plurality of variable transconductance means, with each of said plurality of variable transconductance means being associated in electrical series circuit with a corresponding one of said plurality of solar panels and with the output of each such variable transconductance means being coupled to said power bus.

19. The invention as defined in claim 18 wherein each of said variable transconductance means further comprises a Buck converter, said Buck converter having an adjustable duty cycle and a transconductance, said transconductance being functionally dependent upon said duty cycle, whereby the level of DC current passing through said Buck converter is dependent upon the duty cycle.

20. In a power supply system for supplying dc power to an electrical load over a power bus, said power supply system including generating means coupled to said power bus for supplying current to said electrical load with said generating means being of an interruptable characteristic;

a rechargeable battery coupled to said power bus for supplying dc current to said power bus during interruption of said generating means, whereby charge stored in said rechargeable battery is depleting, and alternately for receiving dc charging current from said generating means over said bus, whereby charge depleted from said rechargeable battery is replenished;

the improvement comprising;

stored program computer means, including a program, for regulating the rate of charge of said rechargeable battery from between a maximum rate and a trickle charge in dependence upon the amount of charge depleted from said battery during any interval in which said battery supplied dc current to said power bus;

current monitoring means for monitoring the current discharged from said battery and supplying information thereon to said stored program computer means, said stored program computer means checking said current monitoring means in accordance with said stored program and integrating such information in accordance with said stored program to determine the amount of charge depleted from said battery; and

computer controlled regulator means coupled between said power bus and said generating means for regulating the instantaneous level of dc current applied from said generating means to said bus, said computer controlled regulator means being controlled by said computer to cause said generating means to provide prescribed current levels for prescribed increments of time prescribed by said stored program, responsive to less than full charge in said rechargeable battery, to provide current to said load and full charge current to said rechargeable battery and, responsive to said battery attaining a full state of charge, to supply current required by said load and a trickle current required by said rechargeable battery.

21. A computer controlled solar array type electrical supply system for converting solar energy to electricity and supplying such electricity to an electrical load requiring a predetermined load current, comprising:

a plurality of M solar panels, M being a number greater than two;

a plurality of M buck converters, each of said buck converters being associated with a corresponding one of said solar panels to form a plurality of solar panel and buck converter combinations, with each of said solar panel and buck converter combinations being adapted to be selectively connected in common to an electrical load to supply current thereto;

means for selecting K panels from amongst said M solar panels, where K is a number equal to or less than the quantity M, and applying an output of each said selected solar panel and buck converter combinations to said electrical load for supplying current to said electrical load and leaving any remainder of said solar panel and buck converter combinations in reserve, effectively disconnected from said electrical load;

means for programming a plurality of N of said buck converters from within said group of K solar panel and buck converter combinations to each produce a high current output, said plurality N being no greater than the number (K-1);

means for programming one of said buck converters from within the remaining K-N solar panel and buck converter combinations to produce a low current output; and

wherein the sum of said high current outputs from said N Buck converters and said low currrent output of said one Buck converter equals said predetermined load current.

22. The invention as defined in claim 21, further comprising:

wherein said electrical load includes;

rechargeable battery means for normally receiving current from said solar panel and buck converter combinations and, responsive to interruption of said solar panel and buck converter combinations, for supplying current to the remainder of said electrical load.

23. A computerized solar array electrical supply system, comprising:

A plurality of M solar panels;

a plurality of M programmable Buck converters, each of said buck conveters being associated with a corresponding one of said solar panels to form a plurality of solar panel and buck converter combinations, with each of said solar panel and buck converter combinations being adapted to be selectively connected in common to an electrical load;

said Buck converters having a programmable duty cycle and in which the transconductance thereof is variable as a dependent function of the duty cycle;

means for periodically determining the load demand current of said electrical load;

means for periodically calculating the number of solar panel and buck converter combinations, K, where K is equal to or less than the quantity M, required to produce said load demand current;

means for periodically selecting said K panels from amongst said M solar panels and applying an output of each said selected solar panel and buck converter combinations in common to said electrical load for supplying current thereto and leaving any remainder, M-K, of said solar panel and buck converter combinations in reserve inhibited from supplying current to said electrical load;

means for programming a plurality of N of said buck converters from within said selected K solar panel and buck converter combinations to each produce a high current output, said plurality N being no greater than the number (K-1); and

means for programming one of said buck converters from within the remaining ones of said selected K solar panel and buck converter combinations to produce a low current output.

24. The combination as defined in claim 23, wherein said electrical load includes electronic apparatus and a rechargeable battery to produce a load demand current, said load demand current being dependent at least in part on the state of charge of said rechargeable battery;

said battery and said electronic apparatus being connected in common to an electrical bus.

25. The combination as defined in claim 24, wherein said means for periodically determining said load demand current, further comprises:

amp-second integration means for determining the state of charge of said rechargeable battery;

means for specifying a level of charging current for said battery in dependence upon said state of charge, wherein a first level of charging current is specified if said state is below a predetermined amount and a second trickle charge current level, less than said first level, is specified should said state of charge be at or above said predetermined amount.

26. The invention as defined in claim 25, further comprising:

inhibiting means responsive to said rechargeable battery attaining a full level of charge for inhibiting said amp-second integration means while said battery remains in a full charge state to inhibit amp-second integration of trickle charge current applied to said battery;

said inhibiting means being disabled responsive to subsequent detection of a discharge current from said rechargeable battery.

27. An electrical current sensor for providing an indication of load current magnitude and direction, said current sensor having wide dynamic range comprising:

a first magnetic amplifier type current sensor, said first magnetic amplifier type current sensor containing a magnetic core, a first winding for receiving current to be measured, and an output winding for producing an output voltage, Vrdg1, in dependence upon current through said first winding and a predetermined sensor gain slope of G;

a second magnetic amplifier type current sensor, said second magnetic amplifier type current sensor containing a magnetic core, a first winding for receiving current to be measured, a bias winding and an output winding for producing an output voltage, Vrdg2, in dependence upon current through said first winding and said bias winding and a predetermined sensor gain slope of G;

means coupling said first winding of each of said first and second magnetic amplifier type current sensors in electrical series circuit to an electrical load, whereby current to said electrical load passes through both said first windings;

means providing a dc bias current in said bias winding of said second magnetic amplifier type current sensor only to produce an offset current X for said second magnetic amplifier type current sensor;

means for contemporaneously reading the output voltage of each of said first and second magnetic amplifier type current sensor to provide two voltage readings, Vrdg₁ and Vrdg₂, said respective voltage readings being representative of the respective load current through said first winding of each said first and second magnetic amplifier type current sensors, respectively;

means for computing first and second potential load current values from said two voltage readings, Vrdg₁ and Vrdg₂ according to the following equation 1--1;

space="preserve" listing-type="equation">Current (+)=(Vrdg-Voff)×

G, 1--1

where

Vrdg is said respective DC voltage read at the sensor output from said respective output winding,

Voff is an offset voltage, where

Voff=X/G, and

X is said magnetic amplifier type current sensor offset current,

G is said magnetic amplifier type sensor gain slope in amps per volt;

means for computing third and fourth potential load current values from said two voltage readings, Vrdg1 and Vrdg2, according to the following equation 1-2;

space="preserve" listing-type="equation">Current(-)=-(Vrdg+Voff)×

G, 1-2

where Vrdg is a positive number; and

means for selecting the two respective computations of said load current from amongst said four computed values that are essentially equal in value as the indication of load current magnitude.

28. A computer assisted electrical current sensor for providing an indication of load current magnitude and direction, said current sensor having a wide dynamic range, comprising:

a first magnetic amplifier type current sensor, said first magnetic amplifier type current sensor containing a magnetic core, a first winding for receiving current to be measured, and an output winding for producing an output voltage, Vrdg1, in dependence upon current through said first winding and a predetermined sensor gain slope of G₁ ;

a second magnetic amplifier type current sensor, said second magnetic amplifier type current sensor containing a magnetic core, a first winding for receiving current to be measured, a bias winding and an output winding for producing an output voltage, Vrdg₂, in dependence upon current through said first winding and said bias winding and a predetermined sensor gain slope of G₂ ;

means coupling said first winding of each of said first and second magnetic amplifier type current sensors in electrical series circuit to an electrical load, whereby current to said electrical load passes through both said first windings;

means providing a dc bias current in said bias winding of said second current sensor only to produce an offset current X for said second magnetic amplifier type current sensor;

means for contemporaneously reading the output voltage of each of said first and second magnetic amplifier type current sensor to provide two voltage readings, Vrdg₁ and Vrdg₂, said respective voltage readings being representative of the respective load current through said first winding of each said first and second magnetic amplifier type current sensors, respectively;

correlation means for correlating said two voltage readings, said correlation means comprising;

first means for computing first and second potential load current values from said two voltage readings, Vrdg₁ and Vrdg₂ according to the following equation 1-1;

space="preserve" listing-type="equation">Current (+)=(Vrdg-Voff)×

G, 1--1

where

Vrdg is said voltage reading at said respective sensor output,

Voff is the offset voltage, where

Voff=X/G, and

X is said respective sensor offset current,

G is said sensor gain slope;

second means for computing third and fourth potential load current values from said two voltage readings., Vrdg₁ and Vrdg₂ according to the following equation 1-2;

Current(-)=-(Vrdg+Voff)×

G, 1-2

where Vrdg is a positive number; and

;

third means for defining a predefined error band of differences in current values;

fourth means for determining the difference between said first and second computed current values;

fifth means for determinging the difference between said third and fourth computed current values;

sixth means for determining the absolute value of said first and second differences and comparing said absolute vaules to determine which of said absolute values yields the smallest difference;

seventh means for selecting said smallest difference in absolute values and determining whether such difference falls within said error band and, if not falling within said error band, then selecting the next difference computation and determining whether said next difference computation falls within said error band;

eighth means responsive to selection of said difference computation that falls within said error band for providing an output signal representative of one of said two current values used to determine said difference computation that falls within said error band, whereby said output signal comprises an indication of load current magnitude.