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Application for Power Generation
Power management and stabilization of the grid are of growing importance, in particular with the increase of wind or solar farms. Pump-storage stations are the most efficient technology to store large amounts of electrical energy. With the development of new power electronics components, high-power converters can be designed to build variable speed pump-storage stations with higher flexibility and efficiency. The typical solution is the doublyfed induction machine with a converter feeding the rotor. In high power applications, cyclo-converters with large thyristors were used so far. Converteam proposes to apply Voltage Source Inverters (VSI) in this power range using MV7000 Drives.
A variable speed PSPP therefore consists of Doubly Fed Induction Generator Motor (DFIGM) with a VSI Drive connected to the rotor.
The VSI carries out 4 main functions:
- AC Excitation: the VSI controls the DFIGM stator voltage, output power as well as power factor like an excitation system does
- Speed variation, i.e. adjust the frequency of the current injected to the rotor; the VSI adjusts the shaft line speed in whatever operating modes (Pump and Turbine) in order to cope with the water head variation between upper and lower reservoir, keeping the Pump/Turbine operating at its highest efficiency
- Soft starter in pump mode: to start-up the unit while the Pump/Turbine wheel is dewatered, the DFIGM stator is short-circuited: the VSI feeds the rotor with variable voltage and frequency and the machine behaves like a squirrel cage machine until it is coupled to the grid
- The VSI control system contributes to the unit "Fault Ride Through" operation. It keeps on running during voltage disturbances, restores power generation as soon as the grid recovers, compensates voltage drop by providing reactive power, thus improving grid stability.