ENERGY STORAGE SYSTEM FOR PHOTOVOLTAIC ENERGY AND METHOD OF STORING PHOTOVOLTAIC ENERGY
An energy system for renewable energy applications includes a renewable energy source, a bidirectional inverter connected an AC bus and a DC bus, an energy storage unit connected to the bidirectional DC/DC converter, and a control system comprising one or more controllers coupled to the bidirectional inverter and the bidirectional DC/DC converter. The bidirectional inverter is connected to the renewable energy source and a bidirectional DC/DC converter through the DC bus. The system is configured to capture low power of a photovoltaic (PV) array, energy typically lost to inverter clipping, and through the utilization of ramp rate control.
1 . A power system for capturing clipped energy from a power source, the power system comprising:
the power source coupled to a DC bus;
a DC/DC power converter coupled to the DC bus and an energy storage device;
a power inverter coupled to the DC bus and an AC bus; and
a control system, the control system comprising one or more controllers configured to:
monitor an output power of the power inverter;
compare the output power of the power inverter to a predetermined threshold;
when the output power of the power inverter is greater than the predetermined threshold, control the DC/DC power converter to store output power of the power source that exceeds the predetermined threshold in the energy storage.
2 . The power system of claim 1 , wherein the predetermined threshold is a maximum power rating of the power inverter.
3 . The power system of claim 1 , wherein the output power of the power inverter is monitored continuously, and the control system continuously controls the DC/DC power converter and the power inverter to transition between storing and not storing output power of the power source in the energy storage.
4 . A power system for controlling a ramp rate, the power system comprising:
a power source coupled to a DC bus;
a DC/DC power converter coupled to the DC bus and an energy storage device;
a power inverter coupled to the DC bus and an AC bus; and
a control system, the control system comprising one or more controllers configured to:
monitor an output power of the power inverter and a rate of change of the output power of the power inverter;
compare the rate of change of the output power of the power inverter with a pre-defined ramp rate; and
control the DC/DC converter to charge or discharge the energy storage when the rate of change of the output power of the power inverter differs from the pre-defined ramp rate by more than a predetermined amount.
5 . The power system of claim 4 , wherein the output power of the power inverter and a rate of change of the output power of the power inverter is monitored continuously, and the control system continuously controls the DC/DC power converter to charge or discharge the energy storage until the rate of change of the output power of the power inverter no longer differs from the pre-defined ramp rate by more than the predetermined amount.
6 . The power system of claim 4 , wherein the DC/DC power converter supplies power to the energy storage when the rate of change of the output power of the power inverter is greater than the pre-defined ramp rate by more than the predetermined amount.
7 . The power system of claim 4 , wherein the DC/DC power converter discharges power from the energy storage to a power grid through the power inverter when the rate of change of the output power of the power inverter is less than the pre-defined ramp rate by more than the predetermined amount.