Parallel string voltage support
This disclosure provides systems, methods and apparatus for an energy storage system. In one aspect, the energy storage system includes a controller configured to connect a first capacitor system and a second capacitor system in series with an output of a battery system during a high current demand event such that the voltage of the output of the battery system is supported within the voltage constraints of the output of that battery system.
1. An apparatus for providing voltage support for an output of a battery system, comprising:
a first branch comprising a first capacitor and a first charging circuit, the first charging circuit coupling a positive terminal of the first capacitor to a positive terminal of a battery;
a second branch comprising a second capacitor and a second charging circuit, the second charging circuit coupling a negative terminal of the second capacitor to ground;
a third branch comprising the battery, the positive terminal of the battery further coupled to the positive terminal of the second capacitor and an output node, wherein the first and second branches are connected in parallel with one another and the third branch and wherein outputs from the first branch, the second branch, and the third branch are connected to a load through the output node; and
a controller configured to:
connect the first capacitor to the first charging circuit via a first switch and connect the second capacitor to the second charging circuit via a second switch;
disconnect the first capacitor from the first charging circuit via the first switch when a voltage of the first capacitor reaches a first fixed target voltage;
disconnect the second capacitor from the second charging circuit via the second switch when a voltage of the second capacitor reaches a second fixed target voltage;
compare a detected voltage of the output of the battery to a first voltage threshold,
detect a current demand event at the load, and
connect the positive terminal of the first capacitor to the negative terminal of the second capacitor through the connecting switch in response to (1) a determination that the voltage of the output of the battery is at or below the first voltage threshold and (2) detecting the current demand event at the load such that:
the first capacitor and the second capacitor are connected in series to the load,
a sum of the outputs from the series connected first and second capacitors is in parallel with the output from the battery, and
the series connected first and second capacitors provide voltage support to the battery connected to the load at voltages greater than the voltage of the output of the battery.
2. The apparatus of claim 1 wherein the controller is further configured to disconnect the battery from the load when the first and second capacitors are connected to the load in series via the connecting switch.
3. The apparatus of claim 1 wherein the first fixed target voltage, the second fixed target voltage and a maximum voltage of the output of the battery are approximately equal.
4. The apparatus of claim 1 wherein the controller is further configured to open a blocking circuit switch to block a reverse current from the second capacitor to the battery when the controller connects the first and second capacitors and to close the blocking circuit switch when the controller disconnects the first and second capacitors.
5. The apparatus of claim 1 wherein the first voltage threshold is approximately a maximum discharge voltage threshold of the battery.
6. The apparatus of claim 1 wherein the first and second fixed target voltages are each approximately half of a maximum voltage desired at the output.
7. The apparatus of claim 1 wherein the first charging circuit comprises a first resistor and the second charging circuit comprises a second resistor.
8. A method of providing voltage support from a first capacitor and a second capacitor for an output of a battery, comprising:
connecting the first capacitor to a first charging circuit via a first switch and connecting the second capacitor to a second charging circuit via a second switch;
disconnecting the first capacitor from the first charging circuit via the first switch when a voltage of the first capacitor reaches a first fixed target voltage; and
disconnecting the second capacitor from the second charging circuit via the second switch when a voltage of the second capacitor reaches a second fixed target voltage;
comparing a detected voltage of the output of the battery to a first voltage threshold, the battery being part of a battery branch and a positive terminal of the battery coupled to a positive terminal of the second capacitor and an output node;
detecting a current demand event at a load coupled to the output node; and
connecting a positive terminal of the first capacitor to a negative terminal of the second capacitor in response to (1) a determination that the voltage of the output of the battery is at or below the first voltage threshold and (2) the detecting the current demand event at the load, such that:
the first capacitor and the second capacitor are connected in series to the load via the output node,
a sum of outputs from the series connected first and second capacitors is in parallel with the output from the battery, and
the series connected first and second capacitors provide voltage support to the battery system connected to the load at voltages greater than the voltage of the output of the battery;
wherein the first capacitor is disposed in a first branch in parallel with a second branch in which the second capacitor is disposed, wherein the first branch comprises the first capacitor and the first charging circuit, the first charging circuit coupling the positive terminal of the first capacitor to the positive terminal of the battery, and wherein the second branch comprises the second capacitor and the second charging circuit, the second charging circuit coupling the negative terminal of the second capacitor to ground.
9. The method of claim 8 wherein the first fixed target voltage, the second fixed target voltage, and a maximum voltage of the output of the battery are approximately equal.
10. The method of claim 8 further comprising disconnecting the battery from the output via a third switch when the controller connects the first and second capacitors.
11. The method of claim 8 wherein the first voltage threshold is approximately a maximum discharge voltage threshold of the battery.
12. The method of claim 11 wherein the first and second fixed target voltages are each approximately half of a maximum voltage desired at the output.
13. The method of claim 8 further comprising opening a blocking circuit switch to cause a diode to block a reverse current from the second capacitor to the battery.
14. An apparatus for providing voltage support for an output of a battery, comprising:
a first capacitor having a positive terminal;
a second capacitor having a positive terminal at a same voltage potential as a positive terminal of a battery and a negative terminal;
a first charging circuit connected between the output of the battery and the positive terminal of the first capacitor, the first capacitor and the first charging circuit forming a first branch;
a second charging circuit connected between the negative terminal of the second capacitor and ground, the second capacitor and the second charging circuit forming a second branch; and
a controller configured to:
connect the first capacitor to the first charging circuit via a first switch and connect the second capacitor to the second charging circuit via a second switch;
disconnect the first capacitor from the first charging circuit via the first switch when a voltage of the first capacitor reaches a first fixed target voltage;
disconnect the second capacitor from the second charging circuit via the second switch when a voltage of the second capacitor reaches a second fixed target voltage;
compare a detected voltage of the output of the battery to a first voltage threshold,
detect a current demand event at a load, and
connect the positive terminal of the first capacitor to the negative terminal of the second capacitor in response to (1) a determination that the voltage of the output of the battery is at or below the first voltage threshold and (2) detecting the current demand event at the load, such that:
the first capacitor and the second capacitor are connected in series to the load,
a sum of the outputs from the series connected first and second capacitors is in parallel with the output from the battery, and
the series connected first and second capacitors provide voltage support to the battery connected to the load at voltages greater than the voltage of the output of the battery.
15. The apparatus of claim 14 , wherein the controller is further configured to connect the positive terminal of the first capacitor to the negative terminal of the second capacitor and open the first and second switches when the voltage of the output of the battery is at or below a first voltage threshold.
16. The apparatus of claim 14 , wherein the controller is further configured to open a blocking circuit switch to block a reverse current from the second capacitor to the battery when the controller connects the positive terminal of the first capacitor to the negative terminal of the second capacitor.
17. The apparatus of claim 14 wherein the first and second charging circuits comprise resistors.