Model Validation of Full-power Converter Variable Speed Hydro Generators

Speed control of hydro generators can be implemented by controlling either a doubly fed induction machine or a synchronous machine connected to the grid through a full-power converter.

In the case of a synchronous machine connected to the grid via a full-power converter, the converter comprises two voltage-source converters (the machine-side converter and the gridside converter) operating in pulse-width modulation, coupled via a DC link capacitor. The hydro turbine is equipped with a speed governor. A unit controller coordinates the control of the synchronous machine and the hydro turbine.

A large Spanish generating company is converting two of the four units at the Torrejón pumpedstorage hydro station (4x32 MW) to variable-speed operation. The Torrejón pumped storage hydro station belongs to the Tagus river system. The conversion aims to extend the Torrejón head's operating range in pumped mode, enabling the storage of up to 210 GWh by connecting the upstream and downstream reservoirs of Torrejón (Valdecañas and Alcántara). The rapid expansion of renewable energy sources in Spain is making energy storage facilities highly attractive. By the end of 2025, the installed capacity of wind and solar photovoltaic (PV) generation was 33 GW and 40 GW, respectively, accounting for 22% and 19% of total generation. The grid connection of the new units requires compliance with the European Network Code on

Requirements for Grid Connection of Generators and its Spanish implementation. The network code includes compliance monitoring by system operators. Among other requirements, steadystate and dynamic models should be provided and validated.

The authors have developed and reported a very detailed fundamental model of a full-power converter variable-speed hydro generator. Such a model was intended to investigate interactions between synchronous machine and turbine controls. This model is an alternative to the encrypted manufacturer models.

Reduced-order models have also been proposed in the literature. Reduced-order models offer greater computational robustness when incorporated into large power system dynamic simulation models.

This paper reports the successful validation of the author's fundamental model against the manufacturer's model and a reduced-order model against measurements from the commissioning test of Torrejón generating unit number 3. Small-disturbance tests have been carried out. Steps at the setpoints of active and reactive powers have been applied. Active and reactive powers supplied by the synchronous machine, together with the gate, have been recorded and compared.