Tobias Weissbach

Improvement of the Performance of Scheduled Stepwise Power Programme Changes within the European Power System

Abstract Since the deregulation of the electrical energy market, the technical realisation of power transactions based on energy market contracts often effects large stepwise power programme changes – especially at the change of the hour. Originating from mainly economic reasons, these stepwise power programme changes lead to remarkable power imbalances within the European Power System causing large unintended frequency deviations with a negative impact on the control performance of power plants and power system. Within the framework of this paper, possible causes for the resulting poor control performance are analysed. Subsequently, measures for an improvement of the performance of scheduled stepwise power programme changes are proposed.

Monitoring of inter-area oscillations within the european interconnected network based on a wide area measuring system

To monitor the dynamic behavior of large power systems, like inter-area oscillations, measurements at different points of the power system are required. For this purpose, a wide area measuring system is currently built up within the European Power System. The obtained measurements are used to analyze the different power system oscillation modes and to validate respective simulation models. The main objective is the observance of trends regarding inter-area oscillations against the background of a changing power system, which is influenced by an increasing penetration of decentralized generation and wind power feed-in as well as deregulated energy market conditions. First measurements and simulations are shown in the paper and prove the functioning of the wide-area measuring system as well as the importance of the availability of measurement data for wide area power system analyses. The measuring system is intended solely for research purposes and follows no operational or commercial aspects.

Flatness-Based Feedforward in a Two-Degree-of-Freedom Control of a Pumped Storage Power Plant

Pumped storage power plants are typically controlled using a two-degree-of-freedom control structure in which the feedforward part is static. For set point changes of the generator output, this control structure leads to pressure oscillations due to the non-minimum phase nature of pumped storage power plants. In order to improve the control performance, a flatness-based feedforward is developed as an add-on for the already existing two-degree-of-freedom control. Thereby a differentially flat dynamic model of a real power plant, derived on first principles, is used for both the design of a dynamic feedforward part and the design of consistent smooth trajectories for set point changes of the generator output. In view of trajectory planning, the effect of using different trajectory function types is addressed in detail. The improved control performance using the new control concept is shown in simulations, also in comparison with the widespread conventional two-degree-of-freedom control with static feedforward part.

Oscillation Behaviour of the Enlarged UCTE Power System Including the Turkish Power System

Abstract Due to deregulated energy market conditions and the planned extension of the UCTE power system towards Eastern Europe, as well as towards the Middle East and North Africa to close the so called “Mediterranean Ring”, the oscillation damping behaviour of the UCTE power system is gaining more and more in importance. Within the present paper, the oscillation damping behaviour of the enlarged UCTE power system after the synchronous connection with the Turkish power system is analysed, using time and frequency domain methods. Firstly the Turkish power system is analysed as a separate network in isolated operation as the case still is today. Subsequently the enlarged UCTE-system, including the Turkish power system is analysed. Differences in the oscillation behaviours are shown, precarious system constellations are identified and measures to solve occurring problems are given and discussed.

Trajectory Planning for Flatness-based two-degree-of-freedom control of a pumped storage power station

Abstract A pumped storage plant is one of the fastest reacting types of power generating units within power systems. Typically, the desired value curves for the power output during set point changes are provided in form of non-smooth ramp shaped curves. These cannot be followed exactly by the plant process due to its physical limitations. Resulting oscillations of the water pressure with potentially high pressure peaks can cause severe damage to the plant. Therefore, the gradients of set point changes of the power output have to be carefully limited. In order to improve the control performance, a flatness-based two-degree-of-freedom control concept is applied: smooth trajectories for set point changes of the generator output are provided, which take the plant dynamics into account. The matter of trajectory planning is thereby addressed in detail. The improved control performance is shown by simulations, also in comparison with the widespread conventional PID control concept.

CONTROL PERFORMANCE OF LARGE SCALE STEAM POWER PLANTS AND IMPROVEMENTS

Abstract Current energy market developments stimulate a dual electric power supply, which correspondingly increases the demands concerning flexibility and manoeuvrability of large-scale steam power plants. For these purposes, a joint research project between the University of Stuttgart and Vattenfall Europe Generation 1 has been initiated with the objective of creating an improved unit control concept, using advanced control techniques like nonlinear model-based and flatness-based feed-forward control. In a first step, however, the dynamic behaviour of existing large-scale generating units had to be analysed, which not only included an isolated analysis of each considered unit, but also the novel approach of a comparing analysis. Discrepancies in the control behaviour even between structurally identical units were detected. Considering the mentioned background, the overall results show that the currently dominating linear unit control concepts have several dynamic and static restrictions, especially when a unit is participating in the network frequency control.