Load-controller design for a regulating coal-fired unit

The design of a load controller suitable for loading a regulating coal-fired unit is described. The target power and loading rate to reach the target are set by the unit operator. Such loading is achieved by setting the fuel demand and controlling the governor valves to maintain the final steam pressure to a set point value. Frequency regulation is facilitated both by modifying the fuel input and manipulating the pressure set point to release boiler stored energy. This ensures that the stored energy is preserved for short-term regulation and is not used for less urgent requirements. A generated power-trim loop is included to compensate for plant variations and nonlinearities and, additionally, the fuel input to the boiler is reduced if the steam pressure continues to rise once the governor valves are fully open. An analysis of the stability of the plant when coupled to the grid system shows an improvement relative to the stability when employing conventional master pressure control of steam pressure.