Enhanced torque control in a DFIG connected to a DC grid by a diode rectifier

Abstract

This paper considers the control of a doubly fed induction machine (DFIG) connected to a dc-bus or dc-grid by using a diode rectifier placed on the stator-side and a single PWM converter on the rotor. In this system, the torque and the frequency have to be regulated simultaneously, in order to make the prime mover operating at the maximum power point and to guarantee at the same time a flux level near the rated value. Since this system is based on a unique reduced-power controlled converter and a diode rectifier, a noticeable reduction of the costs of the power electronics can be achieved. However, the diode bridge causes stator current and voltage harmonics which produce a noticeable torque ripple. A regulation scheme able to reduce the torque ripple is proposed in this paper: resonant current controllers are implemented to track the sixth harmonic components in the reference rotor current commands, in such a way to kill the corresponding harmonic in the electromagnetic torque

Voltage control in a DFIG-DC system connected to a stand-alone dc load

“…The frequency controller PI ωs is designed according to the small signal model of the current controlled DFIG-DC system deduced in [8]. The frequency estimation is obtained by the following relation [15] (…”

“…Such a problem in the DFIG-DC system has been tackled in [15]- [16], where an improved rotor current tracking has been implemented using resonant controllers in such a way to eliminate the main component of the torque ripple.…”

Torque Ripple Reduction in a DFIG-DC System by Resonant Current Controllers

“…In [28], a refinement of the FOC scheme in [9] has been proposed: resonant controllers are used with the aim to improve the rotor current tracking, in such a way to kill the main component of the torque ripple. However, [28] reports only preliminary simulation results and does not include any discussion about the tuning of the current controllers.…”

“…However, [28] reports only preliminary simulation results and does not include any discussion about the tuning of the current controllers.…”

“…This paper provides the theoretical framework for the scheme proposed in [28] and includes a systematic experimental validation. Other recent works dealing with the DFIG control enhancement by RCs [25]- [26] are based on the classical FOC, namely: the d-axis rotor current is used either for the reactive power regulation or for the voltage regulation in stand-alone systems.…”