Analysis and control of wind-driven self-excited induction generators connected to the grid through power converters

Abstract

The analysis of the wind-driven self-excited induction generators (SEIGs) connected to the grid through power converters has been developed in this paper. For this analysis, a method of representing the grid power as equivalent load resistance in the steady-state equivalent circuit of SEIG has been formulated. The technique of genetic algorithm (GA) has been adopted for making the analysis of the proposed system simple and straightforward. The control of SEIG is attempted by connecting an uncontrolled diode bridge rectifier (DBR) and a line commutated inverter (LCI) between the generator terminals and three-phase utility grid. A simple control technique for maximum power point tracking (MPPT) in wind energy conversion systems (WECS), in which the firing angle of the LCI alone needs to be controlled by sensing the rotor speed of the generator has been proposed. The effectiveness of the proposed method of MPPT and method of analysis of this wind-driven SEIG-converter system connected to the grid through power converters has been demonstrated by experiments and simulation. These experimental and simulated results confirm the usefulness and successful working of the proposed system and its analysis.

Key words： self-excited induction generator (SEIG); renewable power generation; power converters; maximum power point tracking (MPPT); steady state analysis; power generation systems

Acknowledgements

The National Institute of Technology, Tiruchirappalli, India are appreciated for providing all the facilities for carrying out the experiments and simulations for the preparation of this paper. Thanks also goes to NaMPET, an initiative of DIT, Govt. of India for providing fund for infrastructure development of Power Converters Research Laboratory, in which the experiments have been conducted.

Appendix A

Expressions for the performance quantities of SEIGs are

(A1)V_{\mathrm{P}}={\left\{{\displaystyle \frac{R_L^{\mathrm{2}}+X_L^{\mathrm{2}}}{{[(R_{\mathrm{1}}/a)+R_L]}^{\mathrm{2}}+{(X_{\mathrm{1}}-X_L)}^{\mathrm{2}}}}\right\}}^{\mathrm{1}/\mathrm{2}}E,

(A2)\begin{array}{lll}{I}_{\mathrm{P}}=V_{\mathrm{P}}/Z_{\mathrm{L}}& \mathrm{a}\mathrm{n}\mathrm{d}& P_{\mathrm{e}}=\mathrm{3}{V}_{\mathrm{P}}{I}_{\mathrm{P}}(R/Z_{\mathrm{L}})\end{array}

where

(A3)\begin{array}{llll}{R}_{\mathrm{L}}={\displaystyle \frac{R{X}_{\mathrm{C}}^{\mathrm{2}}}{a[a^{\mathrm{2}}{R}^{\mathrm{2}}+{(a^{\mathrm{2}}X-X_{\mathrm{C}})}^{\mathrm{2}}]}},& X_{\mathrm{L}}={\displaystyle \frac{[-X{X}_{\mathrm{C}}+R^{\mathrm{2}}+a^{\mathrm{2}}{X}^{\mathrm{2}}]X_{\mathrm{C}}}{[a^{\mathrm{2}}{R}^{\mathrm{2}}+{(a^{\mathrm{2}}X-X_{\mathrm{C}})}^{\mathrm{2}}]}}& \mathrm{a}\mathrm{n}\mathrm{d}& Z_{\mathrm{L}}={[R^{\mathrm{2}}+a^{\mathrm{2}}{X}^{\mathrm{2}}]}^{\mathrm{1}/\mathrm{2}}\end{array}.

Notations

a	Per unit (p.u.) frequency= fg/fr
b	p.u. speed= N/Ns
C	Excitation capacitance per phase/μF
E	Air-gap voltage per phase/V
fg	Generated frequency/Hz
fr	Rated frequency/Hz.
Idc	DC link current/A
Ig	RMS value of grid current/A
IR1	Fundamental value of diode bridge rectifier input current/A
Is	Stator line current/A
Ldc	DC link inductance/mH
N	Actual rotor speed/(r·min-1)
Ns	Synchronous speed corresponding to the rated frequency/(r·min-1)
Pg	Grid power/W
Pe	Power output of the generator/W
R,X	Per phase load resistance and reactance at the generator terminals/Ω
Re	Equivalent resistance at the generator terminals corresponding to the value of grid power/Ω
R1, X1	Per phase stator resistance and leakage reactance respectively/Ω
R2, X2	Per phase rotor resistance and leakage reactance respectively/Ω
Vdr	Average dc output voltage of the diode bridge rectifier/V
Vdi	Average dc input voltage of LCI terminals/V
Vp	Phase voltage at the generator terminals/V
Xm	Per phase magnetizing reactance/Ω
α	Firing angle/(°)
ω	Angular frequency/(rad·s-1)

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