Analytical Model of Small Hydropower Plant Working at Variable Speed

In this paper, a small hydropower plant working at variable speeds is analyzed. The energy conversion system contains a propeller turbine, which is coupled directly with a permanent magnet synchronous generator that is connected with a power system through a power electronic converter (PEC). The PEC that consists of a diode bridge rectifier and a DPC-SVM controlled inverter is described using the average value modeling method. The presented analysis considers only the fundamental harmonic component of ac currents and voltages. The system components are structured in the form of equivalent circuits that also include the power losses. The turbine model consists of the discharge and torque characteristics, which are approximated by analytical formulas based on the turbine hill diagram. The dynamic features represent the speed limiter of the guide vane governor and the mass of water, which fills the turbine chamber and the inlet and outlet pipes. The model is verified on a prototype hydropower plant with nominal power of 150 kW by the steady-state characteristic and a transient performance comparison. Such approach is found to minimize the necessary measurement, simplify the description, and provide satisfactory accuracy of the hydroset model.