Design of a direct PI controller without the feedforward terms for a VSC-based PMSG wind turbine.

Abstract

Renewable energy (RE) sources – wind and solar, have received attention in South Africa and across the world from investors. The development of the Voltage Source Converter (VSC) has enabled large amount of RE to be integrated to the grid. Direct-drive permanent magnet synchronous generators (PMSGs) are now widely available. A PMSG wind turbine employs a full back-to-back VSC arrangement which is controlled via a pulse width modulated system of insulated gate bipolar transistors (IGBTs). Conventional PI vector controllers have been widely used to control VSC based PMSGs. This thesis proposes a new direct PI controller which excludes the decoupled terms in the configurations. A 690 V, 2 MW direct-drive PMSG wind turbine is modelled in PowerSim (PSIM) to investigate the proposed vector control configuration performance under varying wind speeds. A detailed mathematical model of a wind turbine and a PMSG is developed. Then a VSC-HVDC detailed modelled is presented. The proposed control configuration is introduced. An optimal torque control Maximum Power Point Tracking (MPPT) algorithm and vector control method are applied to implement the system. Finally, simulation studies are carried out to investigate the performance of the proposed controller configuration. A deduction from the results obtained, this thesis successfully implemented the new proposed controller configuration. It can be concluded, therefore, that VSC-based PMSG can be implemented in practice using a direct PI controller to reduce system complexity and improve controller performance.