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

Luca Bigarelli,Pericle Zanchetta,Marco Di Benedetto,Luca Solero,Alessandro Lidozzi,Shafiq Ahmed Odhano

doi:10.1109/tia.2019.2955662

Abstract

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.

Highlights

Permanent magnet (PM) machines are generally employed for servo and traction applications [1]
With a direct-drive permanent magnet synchronous generator (PMSG), a varying wind speed means variable frequency ac voltages being induced at the generator terminals
The aim of this paper is to show the effectiveness of the proposed solution for PMSG with phase inductance and fundamental frequency of about thousands μH and Hz respectively, as is the case of the PMSG employed in variable speed generation applications, where the increase in the fundamental frequency value allows to reduce the size and the weight of the electric machine and of the overall system

Summary

Introduction

Permanent magnet (PM) machines are generally employed for servo and traction applications [1]. They are a viable solution in applications that demand high power density, such as integrated starter generators in aerospace sector [2]. These machines are very effective in gearless wind energy conversion systems where bulky mechanical gearboxes are avoided for minimizing load on wind turbine towers [3]–[5]. An active front end (AFE) converter that replaces diodes with bidirectional power electronic switches alleviates this discontinuous conduction problem. The control of this AFE converter has been widely reported in the literature [7]-[11]

Objectives

Results

Conclusion