REAL TIME CONTROL OF DOUBLY FED INDUCTION GENERATOR. Benmeziane Meriem, Zebirate Soraya, Chaker Abelkader Laboratory SCAMRE, ENPO, Oran, Algeria

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1 REAL TIME CONTROL OF DOUBLY FED INDUCTION GENERATOR Benmeziane Meriem, Zebirate Soraya, Chaker Abelkader Laboratory SCAMRE, ENPO, Oran, Algeria

2 This paper presents a real time simulation method of wind power generation system with doubly fed induction generator (DFIG) using our OPAL-RT digital real time simulator which is based on RT-LAB platform with the models build in Simulink. With the ever increasing energy demand and the depleting natural resources of fossil fuels, renewable energy technologies, specifically wind power plants, have become one of the most popular sources of energy over the last decades. Variable speed operation of wind turbine is usually used to provide energy with best efficiency. Those based on doubly fed induction generators are widely used especially in high power fields thanks to different advantages it presents namely: reducing the size of the converter, operating in a large game of speed, and the possibility of controlling independently the generated active and reactive powers

3 A doubly-fed induction generator is a standard wound rotor induction machine. -The stator is directly connected to the grid and the rotor is fed from a back-to-back AC/DC/AC converter set as shows. -The rotor side converter (RSC) controls the wind turbine output power and the voltage measured at the grid side. -The grid side converter (GSC) regulates the DC bus voltage and interchange reactive power with the grid, allowing the production or consumption of reactive power. Block diagram of the simplified model of the GADA

4 The DFIG Modeling The classical electrical equations of the DFIG in the Park frame are written as follows V ds = R s I ds + dφ ds V qs = R s I qs + dφ qs V dr = R r I dr + dφ dr V qr = R r I qr + dφ qr ω s φ qs ω s φ ds ω r φ qr ω r φ qr

5 The stator flux can be expressed as: φ ds = L s I ds + L m I dr φ qs = L s I qs + L m I qr The rotor flux can be expressed as: φ dr = L s I dr + L m I ds φ dr = L s I qr + L m I qr The electromagnetic torque is expressed as: T em = 3 2 p L m L r (φ sd I rq φ sq I rq )

6 Active and reactive power control Direct Control We present the regulation independent of the powers active and reactive by the machine. It was highlighted the link enters, on the one hand the active power and the Vqr on the other hand the reactive power and the Vdr. Vector oriented control stator flux To easily control the production of electricity from wind, we will achieve an independent control of active and reactive power by the stator flux orientation. The idea is to align along the axis of the rotating frame stator flux. We therefore: =0 and consequently φ ds = φ s. φ qs = dφ qs This choice is not random but is justified by the fact that the machine is often coupled with a powerful network voltage and constant frequency, which leads to a finding stator flux of the machine. Neglecting the resistance of the stator windings, often accepted hypothesis for high power machines: The systems of equations can be simplified as follows:

7 V ds = R s I ds + d φ ds 0 V qs = R s I qs + θ s φ ds θ s φ s V dr = R r I dr + σl r d i dr V qr = R r I qr + σl r d i qr e q + e d + e Φ φ s = L s I ds + MI dr 0 = L s I qs + MI qr φ dr = σl r I dr + M L s φ ds φ qr = σl r I qr C em = p φ s M L s i qr

8 The stator active and reactive power in the orthogonal coordinate system can be written: P s = V ds I ds + V qs I qs Q s = V qs I ds V ds I qs Under the assumption of a stator flux oriented, this system of equations can be simplified as: P s = V qs I qs Q s = V qs I ds From the expressions of the stator flux, we can write: i ds = φ s L s M L s i dr i qs = M L s i qr P s = v s M L s i qr

9 Implementation of the regulation If one looks at the relation which binds the rotor currents to the stator powers, one sees appearing the term (MV_s)/L_s. In our study, we considered that the wind-engine was connected to a grid of strong power and stable, therefore this term is constant. We will thus not place of regulator between the rotor currents and the powers. We will neglect the terms of coupling between the two axes of control because of low value of the slip. We then obtain a vectorial control with only one regulator by axis.

10 I r( d / q ) PI-D decoupled controller The controller PI is simple to elaborate. Figure 3 shows the block diagram of the system implemented with this controller. The terms k p and k i represent respectively the proportional and integral gains. I r d / q ref + - K p + K i p L m V s L s R r + pl s (L r L m 2 L s ) V r(d/q) For the synthesis of this PI controller the pole compensation method is used. The time response of the controlled system will be fixed at τ=10ms. This value is sufficient for our application and a lower value might involve transients with important overshoots. The calculated terms are: K P = 1 τ K i = 1 τ L s L r L m 2 L s R r L m V s L m V s Ls

11 Real-Time simulation Details of master and slave block diagrams respectively as implemented in RT-Lab environment.

12 12 x Active Power (w) Ps Pref Time (s) 12 x Qmes Qref Reactive Power (var) Time (s)

13 Conclusion In this work, we have presented a real-time simulation of DFIG using RT- Lab platform and Matlab/Simulink environment for educational purpose. Also this paper is an important contribution to rapid prototyping of high Performance induction machine controllers since real time simulations are required by hardware in the loop applications.

14 THANK YOU