Regulating control circuit for photovoltaic source employing switches, energy storage, and pulse width modulation controller

• US 5,270,636 A
• Filed: 02/18/1992
• Issued: 12/14/1993
• Est. Priority Date: 02/18/1992
• Status: Expired due to Fees

• Current Assignee: Donald L. Lafferty
• Original Assignee: Donald L. Lafferty
• Inventors: Lafferty, Donald L.
• Primary Examiner(s): Stephan, Steven L.
• Assistant Examiner(s): Dougherty, Thomas M.
• Application Number:
  US07/837,328
• Time in Patent Office: 665 Days
• Field of Search: 323/222, 323/223, 323/299, 323/351, 323/906, 320/62, 136/292, 136/293
• US Class Current: 320/101
• CPC Class Codes: G05F 1/67 to the maximum power available from a generator, e.g. from solar cell
• CPC Class Codes: H02J 7/35 with light sensitive cells
• CPC Class Codes: H02M 3/158 including plural semiconductor devices as final control devices for a single load
• CPC Class Codes: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers
• CPC Class Codes: Y10S 136/293 Circuits
• CPC Class Codes: Y10S 323/906 Solar cell systems

Abstract

A regulating circuit controls current flow from a photovoltaic power source (20) to a storage battery (38) to improve the conversion of solar energy to electric energy. Two transistors (22, 30) are switched on and off at high frequency to regulate the average current flow to the battery. A pulse-width-modulator control chip (42) varies the on-time of each transistor independently to provide separate control of source voltage and circuit output voltage. The source is regulated to produce maximum power and the output voltage is regulated to provide an optimum battery charging voltage. The maximum available energy is transferred from the source to the battery, thereby improving the conversion efficiency of the system.

Claims

1. A regulating circuit for transferring maximum energy at a selected voltage from a photovoltaic source to a battery, comprising:

a main first energy flow path for connecting said source to said battery

first switch means for opening and closing said main first energy flow path to provide a first energy pulse,

first storage means for receiving and storing said first energy pulse,

an auxiliary first energy flow path for connecting said source to said battery,

second switch means for opening and closing said auxiliary first energy flow path for transfer of said first energy pulse from said first storage means,

second storage means for receiving and storing said first energy pulse,

a main second energy flow path for connecting said source to said battery

third switch means for opening and closing said main second energy flow path to provide a second energy pulse,

third storage means for receiving and storing said second energy pulse,

an auxiliary second energy flow path for connecting said source to said battery,

fourth switch means for opening and closing said auxiliary second energy flow path for transfer of said second energy pulse,

fourth storage means for receiving and storing said second energy pulse for subsequent transfer of the energy of said second energy pulse to said battery,

control means for controlling said switches in response to a plurality of error signals,

a source feedback loop for supplying a first error signal to said control means,

a battery feedback loop for supplying a second error signal to said control means,

said control means being arranged to open and close said first switch means and simultaneously close and open said second switch means with a first duty cycle determined by said first error signal, and

said control means also being arranged to open and close said third switch means and simultaneously close and open said fourth switch means with a second duty cycle determined by said second error signal.

2. A regulating circuit for transferring maximum energy at a selected voltage from a photovoltaic source to a battery, comprising:

a photovoltaic power source having first and second output terminals, said second output terminal being opposite in polarity to the voltage at said first terminal,

first switching means having an input for connection to said first output terminal of said photovoltaic power source, said first switching means having an output,

first magnetic energy storage means having an input connected to said output of said first switching means and an output for connection to said second output terminal of said photovoltaic power source,

second switching means having an output also connected to said output of said first switching means and to said input of said first magnetic energy storage means, said second switching means having an input,

first electric energy storage means having an output connected to said input of said second switching means and an input connected to said second terminal of said photovoltaic source,

third switching means having an output connected to said output of said first electric energy storage means, said third switching means having an input,

second magnetic energy storage means having an output connected to said input of said third switching means and an input connected to said second terminal of said photovoltaic source,

fourth switching means having an input connected to said output of said second magnetic energy storage means, said fourth switching means having an output,

second electric energy storage means having an output connected to said second terminal of said photovoltaic source and an input connected to said output of said fourth switching means and to a first terminal of a battery, said battery having a second terminal opposite in polarity to said first terminal connected to said second terminal of said photovoltaic source,

a source feedback loop for supplying a first error signal representative of the potential of said source,

control means, responsive to said first error signal, for causing a first control signal to have a first duty cycle with relative on and off times determined by said first error signal,

a battery feedback loop for supplying a second error signal representative of the state of charge of said battery, said control means also being responsive to said second error signal for causing a second control signal to have a second duty cycle with relative on and off times determined by said second error signal,

drive means for supplying said first control signal for opening and closing said first switch means, and simultaneously closing and opening said second switch means so as to control the power flow to said first magnetic storage means and thence to said first electric storage means,

said drive means also being responsive to said second control signal for causing third switch means to open and close, and simultaneously, thereby causing said fourth switch means to close and open, so as to effect said power flow from said first electric storage means to said second magnetic storage means and from there to said second electric storage means for transfer to said battery.

3. The switching circuit of claim 2 wherein said first switching means is a first transistor.

4. The switching circuit of claim 2 wherein said first magnetic energy storage means is a first inductor.

5. The switching circuit of claim 2 wherein said second switching means is a first diode.

6. The switching circuit of claim 2 wherein said first electric energy storage means is a first capacitor.

7. The switching circuit of claim 2 wherein said third switching means is a second transistor.

8. The switching circuit of claim 2 wherein said second magnetic energy storage means is a second inductor.

9. The switching circuit of claim 2 wherein said fourth switching means is a second diode.

10. The switching circuit of claim 2 wherein said second electric energy storage means is a second capacitor.

11. The switching circuit of claim 2 wherein said control means is a pulse-width modulator.

12. The switching circuit of claim 2 wherein said second switching means is a third transistor.

13. The switching circuit of claim 2 wherein said fourth switching means is a fourth transistor.

14. A circuit for transferring maximum available energy at selected voltage from a photovoltaic source to a battery to be charged, comprising:

a switching network for coupling said photovoltaic source to said battery, said switching network including a plurality of switches, each of said switches having a current-transmission on state and a current-blocking off state, so that said network can regulate energy flow from said source to said battery in accordance with the relative on and off times of said plurality of switches,

source reference voltage means for deriving a source reference voltage from an unloaded photovoltaic cell,

source error signal means for comparing the voltage of said photovoltaic source to said source reference voltage to provide a source error signal,

battery error signal means for deriving a battery error signal from a comparison of a battery voltage signal, indicative of the state of charge of said battery, to a standard reference voltage, and

coupling means for coupling said source error signal and said battery error signal to said switching network so that the relative on and off times of said plurality of switches, and hence the energy transferred from said source to said load, will be controlled by said source error signal and said battery error signal.

15. A circuit for transferring maximum energy at a selected voltage from a photovoltaic source to a battery, comprising:

first regulator means, comprising a first plurality of switches and energy storage elements, for regulating current flow from said source,

source error signal means for deriving a source error signal from a comparison of the voltage of said source to the open circuit voltage of an unloaded photodiode,

a source feedback system for providing a first control signal to said first regulator means for opening and closing said first plurality of switches in response to said source error signal,

second regulator means, comprising a second plurality of switches and energy storage elements, for regulating current flow to said battery,

battery error signal means for deriving a battery error signal from a comparison of a battery voltage signal, indicative of the state of charge of said battery, to a standard reference voltage, and

a battery feedback system for providing a second control signal to said second regulator means for opening and closing said second plurality of switches in response to said battery error signal.

16. The circuit of claim 15 wherein the first regulator means is a first inverting regulator.

17. The circuit of claim 15 wherein the second regulator means is a second inverting regulator.