Tor Inge Reigstad and Kjetil Uhlen
Virtual inertia, synthetic inertia, virtual synchronous generator,virtual synchronous machine, variable speed hydropower
Variable speed hydropower (VSHP) is well suited for virtual inertia (VI) control as it can utilize the kinetic energy of the turbine and generator to provide a fast power response to a frequency deviation. Moreover, governor control of the turbine can effectively regain the optimal turbine rotational speed. Despite this advantage, no investigation into different VI control structures for VSHP has been performed previously. In this paper, the results of dynamic simulations and eigenvalue analysis show that all five tested control structures deliver fast power reserves to maintain grid stability. The VI controllers based on the virtual synchronous machine (VSM) algorithm provide the best response in terms of inertia; however, a proportional controller must also be added to provide frequency containment reserves (FCRs). The virtual synchronous generator (VSG) is concluded to be the overall best alternative. It is better at reducing frequency deviations, provides fast frequency reserves (FFRs), and contributes more effectively to power oscillation damping in the two-area power system. The behaviour of the hydraulic system is similar for all VI control structures. However, a more advanced control system is needed to optimize the internal control of the VSHP plant while considering the constraints of the hydraulic system.
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