Control of a commercial scale MHD/ steam power plant

A model for a commercial scale l000 MW MHD/Steam power plant was developed and used to study control problems.

To determine the behavior of the system state variables in the presence of load demand perturbations, a linear incremental model was constructed for the plant. The model made use of a fuel dependent MHD channel and the known characteristics of the downstream steam plant.

Using the Megawatt-Frequency concept, various control techniques for dealing with a step change in electric load demand were studied. Both continuous and digital control functions were applied to limit the frequency deviation on the utility grid.

It was found that the fuel and air inputs to the combustor are sufficient to control the plant. The large lags in the steam section are overcome by the relatively fast response of the MHD section and result in a satisfactory transient response with no auxiliary boiler present.

By using only proportional-integral-derivative (PID) control, the simulated plant settled to a new steady state point within 35-50 seconds. Optimal state variable feedback gave a low settling time (40-60 seconds) with a reduced control effort. A peak control criteria was used to select an acceptable continuous control technique.

For digital control, a finite-time settling time control algorithm was applied to the discrete plant model. For sampling periods of one to five seconds, the plant settles to a new steady state in 10-50 seconds with acceptable level of control effort. This technique is recommended for real time process control of the combined MHD/Steam power plant.