This block adds an offset to the input u, or to zero if use_u is false.
If fixedOffset = false, then the offset is a free parameter, that needs to be determined by an additional initial equation on the system, otherwise the offset is fixed to zero. This block can be used to adjust the set point of controllers that have additional initial equations to fix their controlled outputs to the start values given by the load flow. The value of the fixedOffset parameter is set by default by the system object, depending on the value of systemPowerGrids.initOpt.
For example, if systemPowerGrids.initOpt = InitializationOption.localSteadyStateFixedPowerFlow is set, the AVR model adds one extra initial equation to the overall system to prescribe the machine voltage. As a consequence, the initial value of the AVR setpoint signal must be free, so that the Modelica tool can compute it backwards to match the required voltage, if possible, or to set it in order to get a specified oversaturation of the actuator otherwise. This extra degree of freedom is provided by this component.