Advanced Process Controller (APC) for Power Plant
The APC-based unit control concept for main steam pressure control Figure 5 can be differentiated from the conventional unit control approach in several important ways:
The APC is able to fully stabilize the non-self-stable loop. Therefore, it is not necessary to use the steam turbine to help stabilize steam pressure. The stabilization structure, which modifies the turbine load set point as a function of the pressure control deviation, can be omitted. As a result, the electrical load will follow its set point with a very high accuracy.
The APC can be used as a full-pressure controller without encountering any stability issues. Dynamic tracking of the pressure set point in case of load changes or frequency disturbances is not necessary. For this reason, determination of the corresponding model parameters is no longer required. In comparison to the conventional control concept, the commissioning time for an APC-based controller is reduced drastically.
There is no need to perform a dynamic feed-forward calculation for the required overtiring. Only a static feed-forward calculation of the boiler load set point as a function of the steady-state unit load is performed. The required overtiring is determined automatically by the APC, which uses the pressure control deviation as an input value. Eliminating the testing required to determine these model parameters results in much lower commissioning and testing costs.
Only a boiler time constant and steam storage time constant are required by the APC. The APC is very robust in terms of these parameters so that a highly accurate measurement is less important.