A comparative study of control techniques for PWM rectifiers in AC adjustable speed drives

Four control techniques for pulse-width modulation (PWM) rectifiers in AC adjustable speed drives are presented. In particular, the so-called virtual-flux oriented control (VFOC) and virtual-flux based direct power control (VF-DPC) schemes are described and compared with their voltage based counterparts. These are the voltage oriented control (VOC) and voltage-based direct power control (V-DPC) techniques. Theoretical background is provided, and results of computer simulations and laboratory experiments are given, documenting advantages and disadvantages of the individual control strategies.

I. Introduction

The rapid growth of ac adjustable speed drives (ASDs) in industry exacerbates the problem of harmonic pollution of the power system caused by the commonly used line-side diode rectifiers. Apart from application of active and passive filters, use of PWM rectifiers constitutes the best solution. The rectifiers have an additional advantage of the bi-directional power flow. Therefore, issues of control of PWM rectifiers have recently been receiving significant attention of researchers. As illustrated in Fig. 1, control techniques for PWM rectifiers can generally be classified as voltage based and virtual-flux based. Overall, four types of these techniques can be distinguished: 1)

voltage oriented control (VOC);

2)

voltage-based direct power control (V-DPC);

3)

virtual-flux oriented control (VFOC);

4)

virtual-flux-based direct power control (VF-DPC).

Fig. 1. Four control techniques for PWM rectifiers discussed in the paper.