Control-regime Interaction between Power Stations and Supply Grids in a Deregulated Power Supply System - Measures to Reduce Power Station Load

Project Number 306

Research Project Nos. 243 and 285 investigated the control-regime interaction between power stations and supply networks against the background of a deregulated power supply industry. The project findings clearly show that there has been a fundamental change in many of the assumptions and constraints that underlie today’s network codes. As a result, the individual components for the control-regime interaction between power stations and supply grid are no longer fully capable of meeting the current requirements.

The very large trading-induced frequency variations at hour changes, as established in the two forerunner projects, and the potential remedial measures in the form of improved planned-output management, prompted a series of ongoing talks - at a German and European level - between the steering committee and power station operators, dispatch planners and transmission network operators.

There is now broad agreement that because of the increasing frequency of their occurrence and the steady rise in the absolute volume involved these trading-induced frequency variations have to be counteracted, and that a ramped rather than a stepped set-point can make a considerable contribution when it comes to large power switches.

To this effect the first work package of the follow-up project will seek to develop a detailed concept and have this agreed with the various operators involved:

What kind of power station units should be included in such a control regime, how can the implementation be undertaken for the different power station types and where should the ramped implementation be introduced. This point will also involve further talks with operators of hydro power stations and gas turbines.
Proposals for the accounting/billing procedures to be agreed in collaboration with both the network operators and the traders.

The new concept is to be drawn up in the form of a VGB Guideline that will be published in both German and English. Discussions with network operators and power station dispatchers during the preparation phase should produce agreed results whose content may eventually be included in international rules.

Nonlinear tracking filters can be used to prevent continuous actuation of primary-controlled power station units. Research Project No. 285 demonstrated that an uncoordinated, blanket-coverage deployment of nonlinear tracking filters counteracts the actual objective of relieving the actuators from the effects of network frequency noise, as the sought-after equalisation effect is nullified for all power station units. In addition to the filter effect created by the insensitivity of the relevant control circuits of a power station unit the targeted use of nonlinear tracking filters would deprive power station operators of the possibility of employing a low-stress regime, especially in the case of primary-controlled power station units that are subject to high rates of wear.

The second work package of the follow-up project will therefore seek to develop a concept for the coordinated use of nonlinear tracking filters, which will also be set out in a VGB Guideline. A meaningful approach would be based on the equalisation concept presented in the Operation Handbook, to the effect that any deployment of nonlinear tracking filters is to be counterbalanced within the same TSO area. Note here that the relevant frequency components have to be pre-allocated to the power station units. This allocation can for instance be carried out on the basis of various types of nonlinear tracking filters.

The project is to run from July 2007 to Juni 2009 and is being managed by the Department for Power Generation and Automation at the Stuttgart University Institute for Process Technology and Steam Boiler Systems, under the leadership of Tobias Weissbach. The investigations will be supported by the Technical Committee Electrical Engineering, I&C, and IT .