Control strategy of a standalone variable speed wind energy conversion system based on direct drive permanent magnet synchronous generator

Abstract

In this paper, we propose a control strategy for a stand-alone wind energy conversion system (WECS) based on a direct drive permanent magnet synchronous generator (PMSG), loaded on a DC-type charge. In the considered wind-power generating system, the generator provides a DC voltage to the load through a three-phase rectifier, controlled by the Pulse Width Modulation (PWM) technique. The main control strategy target is to maintain the DC voltage insensitive to fast changes in wind speed and load, by offsetting the generator output current with the charge current. The approach adopted in this paper is based on the estimate of the PMSG electromagnetic torque assuming that wind velocity remains quasi-stationary in a steady state. The instant power reference is assessed by the charge controller according to the rated DC bus voltage, using actual electrical measurements as the voltage and current. To achieve adequately the power decoupling, the field-oriented control is used with conventional PI-type regulators to provide direct and quadrature control reference voltages and ensure DC bus voltage regulation. To assess the proposed control strategy efficiency, the simulation model was subjected to different load and wind speed variations. Simulation results performed using the MATLAB Simulink model show high accuracy and strength during steady-state and transient operations.