Optimal dynamic operation of pumped storage power plants with variable and fixed speed generators

Abstract

This paper studies the optimal dynamic operation of pumped storage power plants with variable and fixed speed generators. A control strategy for the dynamic operation is proposed based on a detailed physics-based plant model. It combines a stationary optimizer with a nonlinear model predictive control strategy and a nonlinear state observer for non-measurable system quantities. Contrary to earlier works on this topic, all system constraints are systematically taken into account, e.g., the pressure limits over the whole hydraulic system. The physics-based model allows for an easy model and controller parametrization and application to different plant topologies. This work studies the optimal combined operation of multiple (different) generators in the turbine and pump mode. The results show that a synchronous generator with a full-rated converter is the optimal choice for single-unit operation and that a synchronous generator with a converter-fed synchronous generator is the optimal combination of two units. A clear advantage of variable speed units is identified in the dynamic operation. The performance of the combined operation of variable and fixed speed generators is only slightly lower than for two variable speed units since the proposed control strategy allows to partially mitigate the shortcomings of the fixed speed unit by the variable speed unit.