Method and apparatus for controlling a hybrid energy storage system

A method of controlling two or more energy storage units in a hybrid energy storage system associated with an electrical grid comprising one or more electrical buses, wherein at least two of the energy storage units have different energy storage characteristics and the method comprises:

• generating a power-sharing command signal individually for each energy storage unit with a respective one of at least two power-sharing controllers that correspond to respective ones of the energy storage units, the power-sharing command signal based on:
• obtaining an input signal for each energy storage unit that reflects load variations on the electrical grid;
• filtering the input signal for each corresponding energy storage unit via a filter circuit having a filter response that is tailored to the energy storage characteristics of the energy storage unit, to obtain a filtered input signal;
• combining the filtered input signal for each corresponding energy storage unit with a steady-state command signal for the corresponding energy storage unit, said steady-state command signal representing a targeted steady-state condition of the corresponding energy storage unit, to thereby obtain the power-sharing command signal for the corresponding energy storage unit;
• and
• controlling the discharging and charging of each energy storage unit via one of at least two charging-state controllers that correspond to respective ones of the energy storage units, the charge-state controllers each being configured to control a local converter unit associated with the respective energy storage unit in response to the power-sharing command signal individually generated for the energy storage unit;
• wherein the at least two energy storage units comprise first and second energy storage units and wherein a first power-sharing controller and a first charging-state controller correspond to the first energy storage unit, and a second power-sharing controller and a second charging-state controller correspond to the second energy storage unit, and wherein the first and second power-sharing controllers are coupled in a series arrangement, such that the input signal to the second power-sharing controller is provided as an output signal from the first power-sharing controller, wherein the input signal to the second power-sharing controller has a communication latency due to the input signal being fed from the first power-sharing controller such that local grid measurements indicated by the input signal are delayed with respect to instantaneous local grid conditions, and wherein the second power-sharing controller further includes a latency-compensation circuit that is configured to compensate for the communication latency based on predicting values of the input signal as a function of the local grid measurements indicated by the input signal and actual values of the local grid measurements obtained for the second energy storage unit.