Study On VSCF Control Of Doubly-Fed Induction Generator

Wind Power is becoming more and more popular nowadays. For wind energy conversion, the most widely used technology in the world is Doubly-Fed Induction Generator (DFIG) working in the mode of Variable Speed Constant Frequency (VSCF). In this paper, basic principles of Doubly-Fed Induction Generator are given, along with their equivalent circuits and the mathematic model of them. Several control strategies of DFIG such as Flux Orientation Control (FOC), Direct Torque Control (DTC) and Direct Power Control are discussed with the comparison of the theories, the complexities of hardware and software and the performances. As in Direct Power Control of DFIG with constant switching frequency proposed by the School of Electronics, Electrical Engineering of Queen's University, a simulation to a 3kW wound rotor induction generator is conducted by using Matlab Simulink environment. The possibility and effectiveness of the DPC control strategy on the specific 3kW grid-connected induction generator is verified by the results of the simulation. Its active power and reactive power could be separately adjusted, with good system stability and transient performance. A power converter for excitation of the 3kW induction generator is designed and manufactured. It is designed with intelligent power module (IPM) as the core device, together with the DSP controller, drives of the IPM, signal sampling and the protection circuit. Space vector PWM technology and serial communication are implemented. LabVIEW on PC is used to control the converter where variable frequency and variable AC voltage are experimentally realized, which gives a nice platform based on LabVIEW for further experimental study on VSCF.