A Study on the Key Technologies for Sub- and Super-Synchronous Operations of Squirrel-Cage Induction Generators

Compared with many kinds of renewable energy systems, wind power system possesses a lot of advantages and has been widely adopted in the Mega Watt level distributed generation system. Double-fed induction generators (DFIG) are known as a variable speed machine since the electromagnetic torque can be conditioned by controlling the rotor current through a power converter. This advantage, in favor of accommodating wind turbine to a widespread operating speed for the purpose of aerodynamic efficiency optimization, leads 70% market shares. However, for the DFIG, bulky structure and the brushes tapped to the rotor circuit increase not only the run-time cost but four times of the initial cost of the squirrel-cage induction generator (SCIG). Although the SCIG has simple and robust construction, the short rotor circuit scheme reduces the controllability in electromagnetic torque. To facilitate the SCIG with controllable electromagnetic torque under sub- and super-synchronous operating conditions and establish the self-contented technologies of industry, this two-year project is devoted to the development of key technologies for the SCIG. The first year project is to develop a torque control solution for the SCIG under super-synchronous operating mode. In this phase, the stator flux control is the main means to alter the electromagnetic torque. The studies arranged in this year are summarized as follows: (1) series inverter modeling; (2) series inverter design; (3) high noise immunity current PLL; (4) robust and self-tuning voltage control; (5) orthogonal stator flux observer; (6) real and reactive power control; (7) grid-tied SCIG torque and speed control; (8) digital filter design; (9) DSP-controlled series inverter. The second year project is to develop a torque control solution for the SCIG under sub-synchronous operating mode. The sub-harmonic voltage injection and active current filtering to the stator circuit are the main means to control the electromagnetic torque. For the studies arranged in this year are summarized as follows: (1) subharmonic SCIG modeling; (2) shunt inverter modeling; (3) shunt inverter design; (4) high noise immunity subharmonic voltage PLL; (5) robust and self-tuning current control; (6) active current filter design; (7) DSP-controlled 表 C011 共2 頁第 2 頁 series and shunt inverters; (8) application of the proposed key technologies in a 3kW SCIG generation system; (9) efficiency and performance evaluation for the proposed key technologies. It is noted that the SCIG stator circuit in the proposed approach is connected to the grid through the coupling transformer, the capacity of the combined series and shunt inverter would not exceed that of the back-to-back inverter employed in the DFIG. The key technologies developed in this project with the superiority of the simple control and circuit construction will be a revolution in the wind power market.

Project ID:PB10408-5695
External Project ID:MOST104-2221-E182-036