Energy storage systems can be coupled to an electrical grid for one or more of various purposes. For example, an energy storage system can be used in conjunction with an intermittent power source (e.g., wind farm) to absorb excess power during a ramp up and/or to supplement power output during a ramp down.
Generally, energy storage systems are implemented using one or more energy storage devices that have a fixed storage capacity. Having a fixed storage capacity typically limits a device's ability to mitigate the risk of exceeding a ramp rate limit (i.e., a ramp rate violation). For example, a system having a 50% state of charge may be able to avoid a ramp rate violation in either direction for finite, and approximately equal, periods of time, assuming equal, worst-case-rates of change and equal ramp rate limits.
In operation, such systems may implement a target state of charge (SOC) around which the storage device is managed. When the SOC of the device drops below this target or moves beyond this target, the energy storage device is controlled such that the SOC returns to the target SOC in preparation for the next event.