Sensorless Control of Brushless Doubly Fed Induction Generator with Nonlinear Loads for Stand-Alone Power Generation Systems

Wantai Liu,Weicai Xie,Yunong Lv,Zhan Zhou

doi:10.1155/2020/6507593

Abstract

This paper presents a sensorless control scheme for the stand-alone brushless doubly fed induction generator (BDFIG) feeding nonlinear loads. The fundamental and harmonic components of the distorted power winding (PW) voltage caused by the nonlinear loads are extracted and controlled separately. A rotor speed observer is employed to estimate the speed based on the PW voltage and control winding (CW) current without the need of any other machine parameters except for the number of pole pairs. Since the d- and q-axis references of the CW current from the PW voltage control loop contain both dc and ac components, which cannot be tracked easily by conventional PI controllers, a CW predictive current controller is designed to regulate the CW current. Finally, the performance of the proposed control scheme is verified by comprehensive experiments on a 35-kVA prototype BDFIG.

Highlights

A nonlinear load would result in a distorted power winding (PW) three-phase current, which could produce harmonic voltage drops across the three-phase impedances of the PW, resulting in a distorted PW voltage
A direct voltage control scheme has been developed under linear load conditions [11]. e transient control of reactive current for the load side converter (LSC) in the stand-alone brushless doubly fed induction generator (BDFIG) power generation system has been proposed in [12] to improve the quality of the output voltage
Design of Control Scheme e overall control scheme for the enhanced sensorless control of the stand-alone BDFIG with nonlinear loads is shown in Figure 4. e PW fundamental-voltage controller, based on the PW fundamental-voltage vector orientation, is employed to regulate the amplitude and frequency of the PW fundamental voltage. e PW harmonic-voltage controller can eliminate the fifth and seventh harmonic components of the PW voltage. en, it summarizes the outputs of both PW fundamental- and harmonic-voltage controllers in order to get the references of the control winding (CW) d- and q-component currents

Summary

Operational Principle and Dynamic Model of BDFIG

In order to keep ωp constant, ωc should be changed with the variation of the rotor speed according to the following expression derived from (1): ωc ωr􏼐pp + pc􏼑 − ωp. E unified reference frame vector model proposed in [17] is employed in this paper. In the fundamental reference frame (dq+1) rotating at the speed of ωp, this model can be expressed as. Where udq, idq, and ψdq represent the voltage, current, and flux vectors, Rp, Rc, and Rr the resistances of PW, CW, and rotor, Lp, Lc, and Lr the self-inductances of PW, CW, and rotor, Lcr and Lcr the coupling inductances between the stator and rotor windings, respectively, s the differential operator d/dt, and superscripts +1 the fundamental reference frame

System Analysis and Modelling

Experimental Results

Without activation of PW