PWM-Based Optimal Model Predictive Control for Variable Speed Generating Units

This article investigates the dc-link voltage control of an active rectifier that is supplied by a variable speed permanent magnet synchronous generator. This configuration is commonly encountered in gearless wind energy conversion systems as well as in variable speed generating units. The proposed control strategy uses an optimal voltage vector based modulated model predictive control (MPC) to achieve direct power control. The studied scheme combines the advantages of finite control set MPC and control techniques that use pulsewidth modulator. The fast dynamics of the former are obtained during large transients, and the constant switching frequency operation, of the latter, is ensured in steady state. At each sampling instant, all the switching states are evaluated and the two adjacent states that give minimum error in the controlled variables are selected. The duty cycle of each of these vectors is computed through linear combination and appropriately limited for overmodulation. Simulations and cosimulation results presented in this article show interesting results. The control strategy has been developed on a field-programmable gate array control platform and experimental results at steady state are shown, with the aim to demonstrate the computational feasibility of the control strategy.