The Liebert EXL S1 with Dynamic Grid Support provides static and dynamic frequency regulation by controlling the input power and the batteries charge/discharge based on frequency activation thresholds. It also supports demand management services when the commands to modulate the UPS response are related to demand control flexibility. By enabling UPS grid services with elevated speed of response to frequency variations, data center owners can participate in specific demand/response programs, such as peak shaving. The UPS must be capable of adjusting its power demand on the utility to participate in ancillary services while keeping the critical load backed up with sufficient remaining battery runtime to allow for normal transfer to generators in the event of utility failure. When a grid frequency variation is detected by the external controller, the UPS is commanded to follow this request for both positive and negative regulation by charging or discharging the batteries within their operational limits.
The UPS controls the input power to achieve certain targets or services by working in the following operating modes.
- Standard UPS operation (normal operation): With 100% input power from main utility grid through the rectifier, the UPS behaves as a standard double- conversion UPS.
- Discharge mode (Full Disconnection): Full disconnection from the grid, 100% of the power to the load is coming from the battery after the command has been received from the external controller.
- Discharge mode (Partial disconnection): The input power from the grid is adjusted and reduced following the external controller command. The remaining power for the load is coming from the batteries.
- Recharge mode: When battery State of Charge (SOC) is below 100% (e.g. 80%), the utility starts to charge the batteries following an over frequency detection. Available maximum recharge power is typically 20- 25% of maximum UPS capacity (current limit). Recharging power is also limited by the battery recharge capacity and maximum input current.