This paper presents flexible control strategy of a squirrel cage induction generator (SCIG) featuring transition between stand-alone and grid-connected systems. The consistent load voltage supply in both the modes is ensured with smooth transition of the controls of stand-alone and grid connected modes. In the proposed technique, dc bus voltage controller of the stand-alone system is maintaining the input power same as the demand by controlling the speed. On the other hand, the same dc bus voltage controller of the grid-connected system maintains the output power at same level as input power. The transient performances of different variables of the system, during this flexible control are found to be satisfactory and THD remains within 3% throughout the study. The flexible control for both the modes is presented for the first time in available literature. The model is helpful for interfacing into wind-energy system.
Induction generator, current control, voltage control, Pulse Width Modulation (PWM), Squirrel cage induction generator (SCIG), Total Harmonics Distortion (THD)
 Chen Z, Guerrero JM, Blaabjerg F. ( 2009). A review of the state of the art of power electronics for wind turbines. IEEE Trans. Power Electron 24(8): 1859–1875.
 Tapia G, SantamarÍa G, Telleria M, Susperregui A. (2009). Methodology for smooth connection of doubly fed induction generators to the grid. IEEE Transactions Energy Conversion 24(4): 959-971.
 Blaabjerg F, Chen Z, Kjaer SB. (2004). Power electronics as efficient interface in dispersed power generation systems. IEEE Transactions on Power Electronics 19(5): 1184-1194.
 Pena R, Cardenas R, Blasco R, Asher G, Clare J. (2001). A cage inductiongenerator using back-to-back PWM converters for variable speed grid connected wind energy system. Proc. IECON Conf. (2): 1376–1381.
 Hazra S, Sensarma P. (2011). Vector approach for self-excitation and control of induction machine in stand-alone wind power generation. IET Renewable Power Generation 5(5): 397-405.
 Yang L, Xu Z, Ostergaard J, Dong ZY, Wong KP. (2012). Advanced control strategy of DFIG wind turbines for power system fault ride through. IEEE Transactions on Power Systems 27(2): 713-722.
 Zandzadeh MJ, Vahedi A, Zohoori A. (2012). A novel direct power control strategy for integrated DFIG active filter system. 20th Iranian Conference on Electrical Engineering (ICEE2012), Tehran, pp. 564-568.
 Ghosh S, Kamalasadan S. (2016). An energy function-based optimal control strategy for output stabilization of integrated DFIG-flywheel energy storage system. IEEE Transactions on Smart Grid (99): 1-10.
 Pattnaik M, Kastha D. (2010). Control of double output induction machine based stand alone variable speed constant frequency generator with nonlinear and unbalanced loads. IEEE PES General Meeting, Minneapolis, pp. 1-8.
 Combes P, Jebai AK. (2018). Modeling and analyzing the stability of an induction motor drive system using an output LC filter. PCIM Europe 2018; International Exhibition and Conference for Power Electronics, Intelligent Motion, Renewable Energy and Energy Management, Nuremberg, Germany, pp. 1-8.
 Balaguer IJ, Lei Q, Yang S, Supatti U, Peng FZ. (2011). Control for grid-connected and intentional islanding operations of distributed power generation. IEEE Trans. Ind. Electron. 58(1): 147–157.
 Bose R, James J. (2014). Control schemes for intentional islanding operation of distributed generation. 2014 International Conference on Power Signals Control and Computations (EPSCICON), Thrissur, pp. 1-6.
 Teodorescu R, Blaabjerg F. (2004). Flexible control of small wind turbines with grid failure detection operating in stand-alone and grid-connected mode. IEEE Trans. Power Electron 19(5): 1323–1332.
 Kulkarni OV, Doolla S, Fernandes BG. (2017). Mode transition control strategy for multiple inverter-based distributed generators operating in grid-connected and standalone mode. IEEE Transactions on Industry Applications 53(6): 5927-5939.
 Mahmood H, Jiang J. (2014). A control strategy of a distributed generation unit for seamless transfer between grid connected and islanded modes. 2014 IEEE 23rd International Symposium on Industrial Electronics (ISIE), Istanbul, pp. 2518-2523.
 Arafat MN, Palle S, Sozer Y, Husain I. (2012). Transition control strategy between standalone and grid-connected operations voltage-source inverters. IEEE Transactions on Industry Applications 48(5): 1516-1525.
 Mishra R, Saha TK. (2016). Development of a standalone VSCF generation scheme through three stage control of SCIG. 2016 IEEE Region 10 Conference (TENCON), Singapore, 2016, pp. 3538-3541.