Abstract
This paper analyses different control strategies for the speed control loop of a variable-speed pump-turbine unit equipped with a doubly fed induction generator, operating in generating mode in an isolated power system with high penetration of intermittent renewable energy. The control strategies are evaluated and compared to each other in terms of the amount of water discharged through the pump-turbine and of the wicket gates fatigue while providing primary and secondary load-frequency control. The influence of the penstock length and the initial operating point on the performance of each control strategy is studied in detail. For these purposes, several simulations have been performed with a suitable dynamic model of the pumped-storage hydropower plant and the power system. The results of the paper indicate that a proper control strategy would consist in updating the reference speed according to the power generation schedule and keeping it constant within each scheduling period (typically 1 h).
Highlights
The integration of intermittent energy sources in the grid is one of the most important challenges for hydropower plants nowadays [1]
This paper studies and compares to each other different control strategies for the speed control loop of a Pumped storage hydropower plants (PSHPs) equipped with a pump-turbine and a Doubly fed induction generators (DFIG) when it operates in generating mode
In expressions of Equations (12) and (13), ∆pd (p.u.) is the variation in the load demand at rated frequency, ∆pg (p.u.) is the variation in the electric power delivered to grid by the PSHP, M (s) is the equivalent mechanical inertia of the power system, R (p.u.) is the equivalent permanent droop of the synchronized thermal units, Dnet (p.u./p.u.) the power system damping constant and Tnet (s) is the time constant of the primary load-frequency control provided by the synchronized thermal unit
Summary
The integration of intermittent energy sources in the grid is one of the most important challenges for hydropower plants nowadays [1]. In [10] two control schemes are proposed for variable speed pumped-storage units operating in generating mode. In the load control scheme, the power injected into the grid is regulated by the rotor-side converter and the turbine governor is in charge of restoring the unit running speed to the reference value. Variable speed pumped-storage units are expected to provide primary and secondary load-frequency control both in generating and pumping mode. As it is well known, variable speed allows increasing the efficiency in turbine mode. This paper studies and compares to each other different control strategies for the speed control loop of a PSHP equipped with a pump-turbine and a DFIG when it operates in generating mode.
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