Improved Control of DFIG Systems During Network Unbalance Using PI–R Current Regulators

Abstract

This paper presents a new control strategy for a doubly fed induction generator (DFIG) under unbalanced network voltage conditions. Coordinated control of the grid-and rotorside converters (GSC and RSC, respectively) during voltage unbalance is proposed. Under an unbalanced supply voltage, the RSC is controlled to eliminate the torque pulsation at double supply frequency. The oscillation of the stator output active power is then compensated by the active power output from the GSC, to ensure constant active power output from the overall DFIG generation system. In order to provide precise control of the positive-and negative-sequence currents of the GSC and RSC, a current control scheme consisting of a proportional integral (PI) controller and a resonant (R) compensator is presented. The PI plus R current regulator is implemented in the positive synchronous reference frame without the need to decompose the positiveand negative-sequence components. Simulations on a 1. 5-MW DFIG system and experimental tests on a 1.5-kW prototype validate the proposed strategy. Precise control of both positive-and negative-sequence currents and simultaneous elimination of torque and total active power oscillations have been achieved. Index Terms-Converter, doubly fed induction generators (DFIGs), proportional integral (PI) plus resonant (R; PI-R), voltage unbalance, wind energy. NOMENCLATURE V g and I gGrid-side converter (GSC) output voltage and current vectors. V s and V r Stator and rotor voltage vectors. I s and I r Stator and rotor current vectors. ψ s and ψ r Stator and rotor flux linkage vectors. ω s , ω r , and ω slip Stator, rotor, and slip angular frequencies. P s and Q s Stator output active and reactive powers. P g and Q g GSC output active and reactive powers. P total Total output active from the doubly fed induction generator (DFIG) system.

Reactive Current Assignment and Control for DFIG Based Wind Turbines during Grid Voltage Sag and Swell Conditions

“…where K p , K i and K r are the proportional, integral and resonant parameters, respectively, and with ω c being the cutoff frequency, introduced into the resonant part of the controller to reduce its sensitivity to slight frequency variations at the resonant pole [26]. It is worth noting that the proposed PI-R controller is insensitive to parameter variations, which has been demonstrated in [27], [28].…”

Passivity-Based Control of a Doubly Fed Induction Generator System under Unbalanced Grid Voltage Conditions

“…Unbalanced current leads to unbalanced power. The power relationship of a DIFG system under unbalanced grid voltage conditions can be expressed as [27]: …”

Sliding-Mode Control for a DFIG-Based Wind-Power Generation System with Series Grid-Side Converter under Unbalanced Grid Voltage Conditions

“…In [10], an auxiliary PI controller has been added to the dual PI one to adjust rotor compensator current. A proportional-integral-resonance controller is used in order to prevent positive and negative sequences extractions of rotor current [11][12]. Direct torque control (DTC) technique which is robust against changes in machine parameters has been used for induction machine [13][14].…”