Pumped-storage power plants typically feature very long hydraulic pipelines, which can be modeled by a set of partial differential equations. The estimation of the pressure and volumetric flow along the pipes is an important task for the operation of such a plant. Therefore, this work compares different earlyand late-lumping-based observer designs for this system. Two late-lumping observers, ie, a Lyapunov-based design and an observer using the backstepping design method, are examined. The Lyapunov-based approach uses a simple boundary correction to stabilize the estimation error dynamics. In contrast, the backstepping-based approach allows utilizing additional in-domain correction to obtain a faster rate of convergence. For the implementation of these distributed-parameter observers, the spectral element method as a flexible and computationally efficient discretization method is introduced. It is shown that, compared with that of the Lyapunov-based design, the discretization of the backstepping-based design requires additional spatial grid points for the accurate approximation of its feedback gains. For the early-lumping approach, the spectral element method is used to approximate the model equations by a system of differential equations. Based on this approximation, an extended Kalman filter is designed. All observer designs are validated and compared for a representative test case. KEYWORDS distributed-parameter system, hydraulic pipeline, late lumping, spectral element method, state estimation
INTRODUCTIONNowadays, the amount of electrical energy produced by renewable sources like wind turbines or solar panels is steadily increasing. Despite all their positive properties, most of these energy sources have the major drawback of being highly volatile in comparison to conventional sources like coal or gas. In order to compensate for the differences between generation and load and, thus, to ensure grid stability, large-scale energy storage capabilities like pumped-storage power plants are necessary. 1,2 A typical pumped-storage power plant comprises several turbines (Francis or Pelton type), which are connected to an upper and a lower reservoir by long hydraulic pipelines. The control of pumped-storage power plants, with the aim to react as fast as possible to load fluctuations in the electric grid while respecting the physical limits of the system at Int J Robust Nonlinear Control. 2018;28:2759-2779.wileyonlinelibrary.com/journal/rnc