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Abstract
This article presents a scheme for improving the power output of grid-connected induction generator commonly used in wind energy conversion systems. Generally, the stator of the induction generator is connected in a star with a line voltage of √3 times the rated winding voltage to reduce the line current and, hence, conductor size. To extend the generating operation over a wider speed range, delta-star switchable stator windings are also in vogue. In such cases, the stator is star connected in the lower speed range and switched to a delta connection above a threshold speed. In this study, a new switching scheme is proposed wherein the stator coils are always connected in a star, while the stator is connected to different voltages in low- and high-speed conditions. At low wind speeds, nominal winding voltage is applied to the stator, whereas at higher speeds, the stator applied voltage is √3 times higher than the rated winding voltage. The efficacy of the scheme is demonstrated experimentally with a suitable microcontroller-based switching arrangement. Typical results indicate an increase in output with reduced switching transients. A case study on a 3-Φ, 50-kW induction generator is presented to emphasize the performance improvement with the proposed scheme.
NOMENCLATURE
| i | = | instantaneous current (A) |
| I | = | per-phase steady-state current (A, RMS) |
| L | = | inductance (H) |
| P | = | real power (W) |
| Q | = | reactive power (VAR) |
| R | = | resistance (Ω) |
| s | = | slip |
| v | = | instantaneous voltage (V) |
| V | = | per-phase steady-state voltage (V, RMS) |
| X | = | reactance (Ω) |
| Z | = | impedance (Ω) |
| η | = | efficiency |
| ωms | = | angular frequency of stator flux rad/s (electrical) |
| ωe | = | angular speed of rotor rad/s (electrical) |
First Subscripts
| fe | = | iron loss |
| loss | = | total loss |
| m | = | mutual |
| M | = | mechanical |
| p | = | poles |
| r | = | rotor |
| s | = | stator |
Second Subscripts
| cu | = | copper loss |
| d | = | direct axis |
| q | = | quadrature axis |
Additional information
Notes on contributors
Chellachi Kathiresan Aravind
Chellachi Kathiresan Aravind received his diploma in electrical and electronics engineering from Noorul Islam Polytechnic College, Nagercoil, India; his B.E. from K.S.R. Group of Institution, Namakkal, India; and his M.Tech from VIT University, Vellore, India. From 2009 to 2011, he was with the Department of Electrical and Electronics Engineering, SASTRA University, Tanjore, India. He is currently a full-time research scholar with the National Institute of Technology, Tiruchirappalli, India. His areas of interest include power electronics, renewable energy systems, and flexible AC transmission system controllers.
Ganesan Saravana Ilango
Ganesan Saravana Ilango received his B.E. from University of Madras, Chennai, India, in 2000; his M.E. from Bharathidasan University, Tiruchirappalli, India, in 2001; and his Ph.D. from National Institute of Technology, Tiruchirappalli, India. From 2001 to 2004, he was a lecturer with Noorul Islam College of Engineering, Kumaracoil, India. Since 2006, he has been an assistant professor with the National Institute of Technology. His areas of interest include power electronics, flexible AC transmission systems, and renewable energy systems.
Chilakapati Nagamani
Chilakapati Nagamani received her B.Tech. from Sri Venkateswara University College of Engineering, Tiruapati, India; her M.Tech. from Indian Institute of Technology, Kanpur, India; and her Ph.D. from University of Technology, Sydney, Australia. From 1985 to 1991, she was with the Central Power Research Institute, Bangalore, India. She subsequently joined the Department of Electrical and Electronics Engineering, National Institute of Technology (then known as Regional Engineering College), Tiruchirappalli, India as a lecturer, where she is currently a professor. Her areas of interest include power electronics and drives, renewable energy systems, and flexible AC transmission system controllers.