1.2.2 Turbine master load controller with boiler on pressure control
To overcome the previous point about non-linear droop characteristics, a separate load/frequency controller is built having the features shown in Fig 2.5. For any operating frequency, depending on the characteristics, there will be a demanded load determined by this characteristic which is compared with the measured electrical load in the master load controller.
The resulting error signal provides the input to the governor speed setpoint, which changes the load on the turbine to reduce the error. This form of slow-acting integral error correction gives accurate droop characteristics or control to a fixed load (infinite droop), if selected. The master load controller may be included as part of the governing system or may be provided separately in a unit control scheme. Apart from providing accurate linear droop characteristics, the performance of this scheme is very similar to the scheme described in the previous subsection.