Energy transfer circuit and method

1. A method for transferring energy to and from a load using an energy transfer circuit comprising a first capacitor, a second capacitor, an inductor, a first switch between the inductor and the first capacitor, a second switch between the inductor and the second capacitor, and a control unit, the method comprising:

connecting the load in parallel with the first capacitor of the energy transfer circuit;

connecting a primary energy source having a first voltage in parallel with the first capacitor of the energy transfer circuit;

connecting a secondary energy source having a second voltage in parallel with the second capacitor of the energy transfer circuit;

communicating status information from the primary energy source to the control unit;

communicating status information from the secondary energy source to the control unit;

communicating energy requests from the load to the control unit;

controlling the opening and closing of the first switch and the second switch using the control unit;

responding to charging currents from the load;

responding to power demands from the load;

responding to energy requests for the primary energy source and the secondary energy source; and

keeping the first switch and the second switch open unless responding to the charging currents, power demands or energy requests from the load, the primary energy source or the secondary energy source;

wherein responding to charging currents from the load comprises:

determining whether either of the primary energy source or the secondary energy source has a charge priority;

charging the primary energy source when the primary energy source has the highest charge priority;

charging the secondary energy source when the secondary energy source has the highest charge priority;

running a trickle charge routine when neither of the primary energy source or the secondary energy source has the charge priority;

discontinuing the response to the charging current from the load when the charging current ceases; and

discontinuing the response to the charging current from the load after a limited time.

2. The method of claim 1 , wherein charging the primary energy source comprises:

keeping the first and second switches open to charge the primary energy source with power from the load.

3. The method of claim 1 , wherein the energy transfer circuit further comprises a second diode in parallel with the second switch, the second diode biased to conduct current from the inductor towards the second capacitor, and charging the secondary energy source comprises:

closing the first switch and keeping the second switch open to charge the inductor with power from the load;

then opening the first switch and discharging the inductor through the second diode to charge the secondary energy source;

then repeating these steps at a desired frequency to charge the secondary energy source.

4. The method of claim 3 , wherein charging the secondary energy source further comprises the following steps to be repeated as part of the repeating step:

closing the second switch after opening the first switch and discharging the inductor through the second switch to charge the secondary energy source;

then opening the second switch and continuing to discharge the inductor through the second diode to charge the secondary energy source.

5. A method for transferring energy to and from a load using an energy transfer circuit comprising a first capacitor, a second capacitor, an inductor, a first switch between the inductor and the first capacitor, a second switch between the inductor and the second capacitor, and a control unit, the method comprising:

connecting the load in parallel with the first capacitor of the energy transfer circuit;

connecting a primary energy source having a first voltage in parallel with the first capacitor of the energy transfer circuit;

connecting a secondary energy source having a second voltage in parallel with the second capacitor of the energy transfer circuit;

closing the first switch to put the primary energy source in parallel with the inductor and to transfer energy between the primary energy source and the inductor;

closing the second switch to put the secondary energy source in parallel with the inductor and to transfer energy between the secondary energy source and the inductor;

communicating status information from the primary energy source to the control unit;

communicating status information from the secondary energy source to the control unit;

communicating energy requests from the load to the control unit;

controlling the opening and closing of the first switch and the second switch using the control unit;

responding to charging currents from the load;

responding to power demands from the load;

responding to energy requests for the primary energy source and the secondary energy source; and

keeping the first switch and the second switch open unless responding to the charging currents, power demands or energy requests from the load, the primary energy source or the secondary energy source;

wherein responding to power demands from the load comprises:

determining whether the power demand is a multiple source power demand or a single source power demand;

executing a highpower routine when the power demand is the multiple source power demand; and

executing a single unit power routine when the power demand is the single source power demand; and

wherein executing a highpower routine comprises:

determining whether the primary energy source is in a primary highload operating range;

determining whether the secondary energy source is in a secondary highload operating range;

transferring power from both the primary and secondary energy sources to the load when the primary energy source is in the primary highload operating range and the secondary energy source is in the secondary highload operating range;

monitoring the state of charge of the primary and secondary energy sources;

discontinuing the highpower routine when the primary energy source goes outside the primary highload operating range;

discontinuing the highpower routine when the secondary energy source goes outside the secondary highload operating range;

discontinuing the highpower routine when the power demand ceases; and

discontinuing the highpower routine after a limited time.

6. The method of claim 5 , wherein the energy transfer circuit further comprises a first diode in parallel with the first switch, the first diode biased to conduct current from the inductor towards the first capacitor, a second diode in parallel with the second switch, the second diode biased to conduct current from the inductor towards the second capacitor; and transferring power from both the primary and secondary energy sources to the load comprises:

providing power to the load from the primary energy source regardless of the positions of the first and second switches;

closing the second switch and keeping the first switch open to charge the inductor with power from the secondary energy source;

opening the second switch and discharging the inductor through the first diode to charge the load;

closing the first switch after opening the second switch and discharging the inductor through the first switch to charge the load;

opening the first switch and continuing to discharge the inductor through the first diode to charge the load; and

repeating these four steps at a desired frequency to charge the load.

7. A method for transferring energy to and from a load using an energy transfer circuit comprising a first capacitor, a second capacitor, an inductor, a first switch between the inductor and the first capacitor, a second switch between the inductor and the second capacitor, and a control unit, the method comprising:

connecting the load in parallel with the first capacitor of the energy transfer circuit;

connecting a primary energy source having a first voltage in parallel with the first capacitor of the energy transfer circuit;

connecting a secondary energy source having a second voltage in parallel with the second capacitor of the energy transfer circuit;

closing the first switch to put the primary energy source in parallel with the inductor and to transfer energy between the primary energy source and the inductor;

closing the second switch to put the secondary energy source in parallel with the inductor and to transfer energy between the secondary energy source and the inductor;

communicating status information from the primary energy source to the control unit;

communicating status information from the secondary energy source to the control unit;

communicating energy requests from the load to the control unit;

controlling the opening and closing of the first switch and the second switch using the control unit;

responding to charging currents from the load;

responding to power demands from the load;

responding to energy requests for the primary energy source and the secondary energy source; and

keeping the first switch and the second switch open unless responding to the charging currents, power demands or energy requests from the load, the primary energy source or the secondary energy source;

wherein responding to power demands from the load comprises:

determining whether the power demand is a multiple source power demand or a single source power demand;

executing a highpower routine when the power demand is the multiple source power demand; and

executing a single unit power routine when the power demand is the single source power demand; and

wherein executing a single unit power routine comprises:

determining an operating condition of the primary energy source;

determining an operating condition of the secondary energy source;

transferring power from the primary energy source to the load when the primary energy source is in as good or better operating condition than the secondary energy source;

transferring power from the secondary energy source to the load when the secondary energy source is in better operating condition than the primary energy source;

discontinuing the single unit power routine when the power demand ceases; and

discontinuing the single unit power routine after a limited time.

8. The method of claim 7 , wherein the energy transfer circuit further comprises a first diode in parallel with the first switch, the first diode biased to conduct current from the inductor towards the first capacitor, a second diode in parallel with the second switch, the second diode biased to conduct current from the inductor towards the second capacitor; and transferring power from the secondary energy source to the load comprises:

closing the second switch and keeping the first switch open to charge the inductor with power from the secondary energy source;

opening the second switch and discharging the inductor through the first diode to power the load;

closing the first switch after opening the second switch and discharging the inductor through the first switch to power the load;

opening the first switch and continuing to discharge the inductor through the first diode to power the load; and

repeating these four steps at a desired frequency to charge the load.