Power factor control in a wind energy conversion system via synchronous generator excitation

Abstract

For high power wind turbines current sources converter (CSC) topologies offer favourable features such as a simple structure, grid friendly waveforms, and reliable grid short circuit protection. Several topologies have been proposed to achieve maximum power point tracking (MPPT) in a wind energy conversion system (WECS) and control the output power factor within a wide range of wind speeds. Some of these topologies are reviewed and a novel approach and control strategy is proposed. The proposed system consists of an electrically excited synchronous generator (EESG), a diode rectifier on the generator-side, and a pulse wave modulated (PWM) current source inverter (CSI) on the grid-side. In the proposed control scheme, the diode rectifier does not offer any control freedoms, therefore controlling the output power and the power factor falls on the EESG and the PWM CSI. The generator excitation is controlled according to the wind speed value to improve operation range whereby the desired grid side power factor can be maintained, while the control freedoms of the CSI are used to regulate the power output of the WECS and to perform maximum power point tracking (MPPT). Theoretical analysis was conducted to investigate the feasibility and limits of this approach and the factors affecting it, and computer simulations confirmed the validity of this approach, showing an improved wind speed range where the desired power factor was maintained.