Low Voltage Ride-through in DFIG Wind Generators by Controlling the Rotor Current without Crowbars

Jaime Arribas,Adrián Rodríguez,Ángel Muñoz,Carlos Nicolás

doi:10.3390/en7020498

Jaime Arribas, Adrián Rodríguez + Show 2 more

Open Access

https://doi.org/10.3390/en7020498

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Abstract

Among all the different types of electric wind generators, those that are based on doubly fed induction generators, or DFIG technology, are the most vulnerable to grid faults such as voltage sags. This paper proposes a new control strategy for this type of wind generator, that allows these devices to withstand the effects of a voltage sag while following the new requirements imposed by grid operators. This new control strategy makes the use of complementary devices such as crowbars unnecessary, as it greatly reduces the value of currents originated by the fault. This ensures less costly designs for the rotor systems as well as a more economic sizing of the necessary power electronics. The strategy described here uses an electric generator model based on space-phasor theory that provides a direct control over the position of the rotor magnetic flux. Controlling the rotor magnetic flux has a direct influence on the rest of the electrical variables enabling the machine to evolve to a desired work point during the transient imposed by the grid disturbance. Simulation studies have been carried out, as well as test bench trials, in order to prove the viability and functionality of the proposed control strategy.

Highlights

As wind power increases its share of total energy production, more and more responsibility must be assumed by wind turbine generating systems, or WTGSs
In keeping with the referenced works, this paper proposes a new control strategy based on a simpler solution that controls rotor current and provides
This figure illustrates the effect of the transient state introduced by the voltage dip, the effect of the proposed control strategy and the evolution of the relevant electric variables attained during the voltage sag through the correction of the rotor currents as suggested in Expressions (8) and (9)

Summary

Introduction

As wind power increases its share of total energy production, more and more responsibility must be assumed by wind turbine generating systems, or WTGSs. There are other approaches that study machine behavior in detail during a voltage dip in order to propose an adequate modification of the machine’s control during the mentioned fault These last solutions have the great advantage of not requiring additional devices that increase maintenance and installation costs. Solutions should be considered that calculate the current that must be injected into the rotor in order to achieve a perfect compensation of the current that is present at the stator [14] This is a similar idea to the first control method proposed in this paper, with the difference that in [14] the authors only try to mitigate the over-currents caused by the fault without taking into consideration the active and reactive power references imposed by Grid Codes during a fault.

Description of the Proposed Control Strategy

Improvement of the Control Strategy

Computer-Based Simulation

Experimental Results on Laboratory Test-Bench

Conclusions