Bi-directional optimizers for battery storage systems with galvanic isolation
Equalization of the state of health of multiple serial strings of battery cells connected in parallel to a common direct current bus in an energy storage system utilized with a utility-sized renewable energy system or other system where optimum operational battery health is a requirement, and in particular is provided by a separate bi-directional DC-to-DC converter in each serial string that controls the charge and discharge of the multiple serial strings of battery cells to maximize efficiency of the stored energy and also provides galvanic isolation between the direct current bus and the multiple serial strings of battery cells.
1. An optimized battery state of health sustaining system for an electrical energy storage intermittently receiving a DC power from an alternative DC energy source having a rated output of at least 100 kilowatts and supplying a controlled DC power to an alternating current output of a DC-to-AC inverter and a transformation network via a common DC bus to an electrical grid, the optimized battery state of health sustaining system comprising:
a plurality of bi-directional galvanically isolated current optimizers, each one of the plurality of bi-directional galvanically isolated current optimizers having a pair of bus terminals connected to the common DC bus and a pair of battery terminals connected to one of a plurality of series connected strings of battery cells, each one of the plurality of series connected strings of battery cells contained in a separate battery rack whereby each one of the plurality of series connected strings of battery cells is galvanically isolated from the common DC bus; and
an energy storage system controller further comprising an optimizer controller, in communication with each one of the plurality of bi-directional galvanically isolated current optimizers for an independent charging control or an independent discharging control of a battery current in each one of the plurality of series connected strings of battery cells.
2. An optimized battery state of health sustaining system of claim 1 wherein the separate battery rack comprises a plurality of battery modules for a distributed containment of each one of the plurality of series connected strings of battery cells.
3. An optimized battery state of health sustaining system of claim 1 further comprising an insulation resistance monitor circuit for monitoring an insulation resistance from a battery rack positive terminal and a battery rack negative terminal to an earth ground of the separate battery rack.
4. An optimized battery state of health sustaining system of claim 1 further comprising a separate charge optimizer processor integrated in each one of the plurality of bi-directional galvanically isolated current optimizers, the separate charge optimizer processor in communication with the energy storage system controller and a battery management system.
5. An optimized battery state of health sustaining system of claim 4 wherein each of the plurality of bi-directional galvanically isolated current optimizers comprises at least one galvanically isolated DC-to-DC converter.
6. An optimized battery state of health sustaining system of claim 5 wherein the at least one galvanically isolated DC-to-DC converter comprises at least one combination full H bridge inverter and active rectifier full H bridge, the at least one combination full H bridge inverter and active rectifier full H bridge comprising a plurality of silicon carbide MOSFET power transistors and silicon carbide diodes.
7. An optimized battery state of health sustaining system of claim 6 further comprising the energy storage system controller and the battery management system in communication with the optimizer controller, the optimizer controller in communication with the at least one combination full H bridge inverter and active rectifier full H bridge for a selective operational control of the at least one combination full H bridge inverter and active rectifier full H bridge between a full H bridge inverter mode and a full H bridge active rectifier mode.
8. An optimized battery state of health sustaining system of claim 7 further comprising a gate pulse generator circuit in the optimizer controller for generating a plurality of gate pulses to the at least one combination full H bridge inverter and active rectifier full H bridge for the selective operational control of the at least one combination full H bridge inverter and active rectifier full H bridge between the full H bridge inverter mode and the full H bridge active rectifier mode.
9. An optimized battery state of health sustaining system of claim 8 wherein a frequency and a pulse width of the plurality of gate pulses are responsive to a battery charge current mode and a current charging magnitude command or a battery discharge current mode and a current discharging magnitude command from the energy system storage system controller.
10. An optimized battery state of health sustaining system of claim 5 wherein the at least one galvanically isolated DC-to-DC converter comprises at least two combination half-H bridge inverter and active rectifier half-H bridge, the at least two combination half-H bridge inverter and active rectifier half-H bridge comprising a plurality of silicon carbide MOSFET power transistors and silicon carbide diodes.
11. An optimized battery state of health sustaining system of claim 10 further comprising the energy storage system controller and the battery management system in communication with the optimizer controller, the optimizer controller in communication with the at least two combination half-H bridge inverter and active rectifier half-H bridge for a selective operational control of the at least two combination half-H bridge inverter and active rectifier half-H bridge between a half-H bridge inverter mode and half-H bridge active rectifier mode.
12. An optimized battery state of health sustaining system of claim 11 further comprising a gate pulse generator circuit in the optimizer controller for generating a plurality of gate pulses to the at least two combination half-H bridge inverter and active rectifier half-H bridge for the selective operational control of the at least two combination half-H bridge inverter and active rectifier half-H bridge between the half-H bridge inverter mode and the half-H bridge active rectifier mode.
13. An optimized battery state of health sustaining system of claim 12 wherein a frequency and a pulse width of the plurality of gate pulses are responsive to a battery charge current mode and a current charging magnitude command or a battery discharge current mode and a current discharging magnitude command form the energy system storage system controller.
14. A method of sustaining the optimized battery state of health for an electrical energy storage intermittently receiving a DC power from an alternative DC energy source having a rated output of at least 100 kilowatts and supplying a controlled DC power to an alternating current output of a DC-to-AC inverter and a transformation network via a common DC bus to an electrical grid, the method comprising:
providing a dedicated one of a plurality of bi-directionally galvanically isolated current optimizers between the common DC bus and each one of a plurality of series connected strings of battery cells, each one of the plurality of series connected strings of battery cells contained in a separate battery rack to galvanically isolate each one of the plurality of series connected strings of the battery cells from the common DC bus; and
independently controlling a battery charge current or a battery discharging current for each one of the plurality of series connected strings of battery cells.
15. The method of claim 14 further comprising monitoring a positive battery rack terminal resistance from earth ground and a negative battery rack terminal resistance from earth ground for each one of a plurality of battery racks and disconnecting one or more of the plurality of battery racks if the positive or negative battery rack terminal resistance from earth ground if a leakage current exceeds a preset leakage current value.
16. The method of claim 14 wherein each one of the plurality of bi-directionally galvanically isolated current optimizers comprises a pair of full H bridges electrically isolated by a transformer with the pair of full H bridges comprising a DC bus connected full H bridge and a dedicated series string of battery cells connected full H bridge, the method further comprising either operating each one of the plurality of bi-directionally galvanically isolated current optimizers in a battery charging mode or a battery discharging mode;
the battery charging mode comprising operating the DC bus connected full H bridge in a DC bus connected inverter mode and operating the dedicated series string of battery cells connected full H bridge in a battery cells connected active rectifier mode; and
the battery discharging mode comprising operating the DC bus connected full H bridge in a DC bus connected active rectifier mode and operating the dedicated series string of battery cells connected full H bridge in a battery cells connected inverter mode.
17. The method of claim 16 further comprising generating a plurality of gate pulses to the pair of full H bridges for a selective operational control in the battery charging mode or the battery discharging mode.
18. The method of claim 14 wherein each one of the plurality of bi-directionally galvanically isolated current optimizers comprises a double half bridges electrically isolated by a transformer with the double half bridges comprising a DC bus connected half bridges and a dedicated series string of battery cells connected half bridges, the method further comprising either operating each one of the bi-directionally galvanically isolated current optimizers in a battery charging mode or a battery discharging mode;
the battery charging mode comprising operating the DC bus connected half bridges in a DC bus connected inverter mode and operating the dedicated series of battery cells connected half bridges in a battery cells connected active rectifier mode; and
the battery discharging mode comprising operating the DC bus connected half bridges in a DC bus connected active rectifier mode and operating the dedicated series of battery cells connected half bridges operating in a battery cells connected inverter mode.
19. The method of claim 18 further comprising generating a plurality of gate pulses to the double half bridges for a selective operational control in the battery charging mode or the battery discharging mode.
20. An optimized battery state of health sustaining system for an electrical energy storage intermittently receiving a DC power from an alternative DC energy source having a rated output of at least 100 kilowatts and supplying a controlled DC power to an alternating current output of a DC-to-AC inverter and a transformation network via a common DC bus to an electrical grid, the optimized battery state of health sustaining system comprising:
a plurality of bi-directional galvanically isolated current optimizers, each one of the plurality of bi-directional galvanically isolated current optimizers comprising at least one galvanically isolated DC-to-DC converter and having a pair of bus terminals connected to the common DC bus and a pair of battery terminals connected to one of a plurality of series connected strings of battery cells, each one of the plurality of series connected strings of battery cells contained in a separate battery rack comprising a plurality of battery modules for a distributed containment of each one of the plurality of series connected strings of battery cells whereby each one of the plurality of series connected strings of battery cells is galvanically isolated from the common DC bus;
a separate charge optimizer processor integrated in each one of the plurality of bi-directional galvanically isolated current optimizers, the separate charge optimizer processor in communication with an energy storage system controller and a battery management system; and
the energy storage system controller further comprising an optimizer controller, the optimizer controller in communication with each one of the plurality of bi-directional galvanically isolated current optimizers for an independent charging control or an independent discharging control of a battery current in each one of the plurality of series connected strings of battery cells.