Energy storage system and method of control
DC power is converted to AC power and provided to AC loads and/or AC electrical utility grids. The amount of current and/or voltage provided by DC-DC converters to a DC bus is controlled to maintain a desired power level at an output of an AC-DC inverter that is coupled to the DC bus. These operations are automatically performed during system operation and automatically react or adapt to the addition or removal of AC loads and/or connection to the AC utility grid.
1. A system for powering an alternating current (AC) load from direct current (DC) power, the power converter comprising:
one or more DC-DC power converters each having a first port connected to a battery or energy source, each of the converters also having a second port;
a DC-AC power inverter having a DC port electrically connected to the second port of each of the DC-DC power converters and an AC port configured to provide AC power to one or more of an AC load or AC utility grid;
a sensor configured to detect a power flow variable at the AC port of the DC-AC power inverter; and
a controller in communication with the sensor and each of the DC-DC power converters, the controller configured to:
determine a current output for each of the DC-DC power converters based at least in part on the power flow variable of the sensor; and
send a command to the one or more of the DC-DC power converters causing the one or more DC-DC converters to output a DC current conforming to the determined current output, the DC current being sent from the second port to the DC port of the DC-AC power inverter.
2. The system of claim 1 wherein the controller is configured to determine the current output of each of the DC-DC power converters based further on one or more of a power available from a DC power source, a state-of-charge of the battery, a storage capacity of the battery, state of health of the battery, and a temperature of the battery.
3. The system of claim 1 , wherein the current output is determined dynamically.
4. The system of claim 1 , wherein the energy source comprises a solar power source.
5. The system of claim 1 , wherein the controller communicates a control command to each of the DC-DC power converters to output the current output.
6. The system of claim 1 , wherein at least some of the DC-DC converters have a single phase non-isolated configuration.
7. The system of claim 1 , wherein the DC-AC inverter has a neutral point clamp configuration.
8. The system of claim 1 , wherein the controller communicates with each of the DC-DC power converters via a separate serial link.
9. The system of claim 8 , wherein the serial link protocol includes one or more of CAN, RS485, and Ethernet.
10. A method of controlling an energy storage system, the system including a DC-AC power inverter and at least one DC-DC power converter, the at least one DC-DC power converter configured to provide power to the DC-AC power converter and the DC-AC power converter having an AC port to provide power to an AC load, the method comprising:
detecting power flow from the AC port of the DC-AC power inverter;
determining a current output for the at least one DC-DC power converter based at least in part on the power flow from the AC port; and
causing the at least one DC-DC power converter to output the determined current output.
11. The method of claim 10 wherein the at least one DC-DC power converter includes a plurality of DC-DC power converters, and
wherein causing the at least one DC-DC power converter to output the determined current output includes causing each one of the plurality of DC-DC power converters to output current to collectively achieve the determined current output.
12. The method of claim 11 , wherein determining the current output comprises apportioning the determined current output to each of the DC-DC power converters based at least in part on one or more of a state-of-charge, a storage capacity, a state of health, and a temperature of the battery associated with each DC-DC power converter.
13. The method of claim 12 , wherein the apportioning is performed dynamically.
14. The method of claim 10 , wherein a controller performs the steps and communicates with each of the DC-DC power converters via a separate serial link.