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

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 for the plant is thereby addressed in detail. The improved control performance using the new control concept is shown by simulations, also in comparison with the widespread conventional PID-control concept.