Electrical load control of a wind turbine generator

Abstract

The thesis describes a method for control of wind turbine generator power coefficient by variation of load with wind speed changes. Steady state characteristics of horizontal axis propeller type wind turbines are shown and development of the tip speed ratio power coefficient curve is given. Taking account of the theory of the horizontal axis propeller turbine, a three bladed windmill of six metres diameter with fixed pitch was designed and constructed. Self excited induction generators are described in detail in terms of the steady state characteristics. It is shown that the currently used induction machine equivalent circuit model, employed for determination of the steady state characteristics) inadequately describes the observed operation of the machine. This is shown using phasor diagrams. An alternative equivalent circuit model is suggested. A controllable rectifier was designed and used in conjunction with the self excited induction generator. The rectifier is capable of operating over a wide frequency range with large amounts of harmonic present at the input. Use of the self excited induction generator in conjunction with the controllable rectifier in the wind turbine generator is described and shown to provide a practical form of turbine load control. Control of the turbine power coefficient is obtained by controlled variation of rectifier delay angle. A microprocessor is used to determine power available in the wind and subsequently estimates the required load power to obtain the desired power coefficient. Results of the turbine operating in windy conditions show that such a system can operate satisfactorily. Suggestions are also made for further research to be carried out on the wind turbine generator.