Modelling and control of direct drive variable speed wind turbine with Interior Permanent Magnet Synchronous Generator

The interest in wind energy system is growing worldwide to reduce dependency on fossil fuel and to minimize the adverse impact of climate change. Currently, doubly fed induction generator (DFIG) based variable speed wind turbine technology with gearbox is dominating the world market share. However, the problems associated with induction generator based wind turbines are reactive power consumption, mechanical stress and poor power quality. Moreover, the gearbox requires regular maintenance as it suffers from faults and malfunctions. Therefore, it is important to adopt technologies that can enhance efficiency, reliability and reduce system cost of wind based power generation system. The performance of a variable speed wind turbine can be enhanced significantly by using a low speed permanent magnet synchronous generator (PMSG) without a gearbox. The main features of PMSG based wind turbines are; gearless operation, higher efficiency, enhanced reliability, smaller size, reduced cost and low losses. The main aim of this thesis is to develop improved control strategies for an efficient and reliable grid interface system for a gearless, direct drive variable speed wind turbine. This thesis focuses on several aspects of modelling and control of interior permanent magnet (IPM) synchronous generator based grid connected variable speed wind turbine with maximum power extraction (MPE). Both the indirect and direct control strategies are addressed for IPM synchronous generator based variable speed wind turbines. The main contributions of this thesis are; (i) development of parameter measurement methods to determine the parameter of an IPM synchronous generator, (ii) development of an improved indirect vector control scheme for the IPM synchronous generator based direct drive variable speed wind turbine, incorporating maximum torque per ampere trajectory (MTPA) and maximum power extraction (MPE) algorithm (iii) development of direct torque and flux (DTFC) control scheme for the IPM synchronous generator based direct drive variable speed wind turbine, and (iv) development of control and power management strategy for a three level converter based STATCOM with Supercapacitor energy storage to enhance the performance of the proposed wind energy conversion system under various disturbances.