Mathematical Modelling of Grid Connected Fixed- Pitch Variable-Speed Permanent Magnet Synchronous Generators for Wind Turbines

Abstract

This project develops the mathematical model of a 10kW permanent magnet synchronous generator (PMSG), which is designed for a fixed-pitch variable-speed wind turbine, and its corresponding simulation model for the control of the PMSG for grid connection using MATLAB/Simulink. The model includes sub-modules, such as a model of the wind speed, a model of the PMSG, a model of the rectifier circuit, a model of the boost chopper circuit, a model of the space vector pulse width modulation (SVPWM) inverter, and a model of the power grid voltage sag detection for low voltage ride through (LVRT). The rectifier is a 3-phase uncontrolled diode full-bridge circuit. The boost chopper circuit offers a direct current (DC) power supply with constant voltage for the inverter. Sampled signals of instantaneous 3-phase voltage (from the power grid) to obtain the phase angle, frequency and amplitude, are used to generate SVPWM signals to control the inverter’s output. In the model of the power grid voltage sag detection, a novel direct-quadrature (DQ) transformation is introduced to detect the voltage sag of the power grid.

This thesis systematically analyses the mathematical model along with its sub-modules, and creates simulation models using MATLAB/Simulink. The simulation results demonstrate that both the mathematical model and simulation model are correct, and the parameters of the generator output are synchronised with the main grid.