Definition and Verification of the Control Loop Performance for Different Power Plant Types

Project Number 331

Final technical approvals for measurings, controls, instrumentations and automation systems are generally stipulated by contract for new power plant units under construction as well as for retrofits. However, requirements regarding the control loop performance in conventional thermal power plants are not defined systematically. In practice, they are inconsistent and mostly based on one single indicator, for example the maximum value deviation. The customer's requirements, corresponding supplier's acceptances or declarations and the practically observed values often differ widely from each other. Furthermore, the specification of the control loop performance occurs as a rule without consideration of different operating conditions (steady-state operation, load ramp, frequency control).

The control loop performances for thermal power plants are rudimentarily included in the series of German guidelines VDI/VDE 35xx (VDI 3500, 1996 - VDI 3508, 2003). However, these are considered as insufficient, because a high control loop performance today is not only a guarantee of secure system operation and the fulfilment of system rules given by the transmission system operator (TSO). A high control loop performance is moreover the necessary basis for an economical and flexible power plant operation. This is reflected by the fact, that many operators improve the digital control system of their power plant units and invest in an even "higher" control performance. In particular, there are no investigations of the correlation between a high control loop performance and its economical impact on power plant operation, e.g. by increasing unit flexibility and efficiency or reducing the wear of actuators (e.g. reduction of durability consumption of the thick-walled components).

Therefore, the overall view of the control loop performance of conventional steam power plants is no longer considered to be state of the art. This should be seen in the light of the fact that today's higher unit control behaviour requirements concerning flexibility and efficiency require some other control loop performance definitions, besides the requirements, which are purely geared to operational safety.

The research project pursues the following aims:

  • Definition of the meaningful control loop performance indicators for conventional thermal power plants in modern grid operation.
  • Evaluation of the control loop performance influence on the economical efficiency of the power plant operation.
  • Formulation of guidelines for contractual agreements or consideration in directives and standards.

Headed by Dr. Tobias Weißbach, the project is carried out from September 2009 to August 2011 by the Department of Power Generation and Automatic Control at the Institute of Combustion and Power Plant Technology, Stuttgart University. The Working Panel Control and Instrumentation and IT is accompanying the investigations.