Steady-state And Stability Analysis Of A Doubly-fed Machine And Its Simulation

Doubly fed machines are another alternative for variable speed drive systems. The doubly fed machines have several attractive advantages for variable speed drive applications, the most important one being the significant cost reduction with a reduced power converter rating. Furthermore, it can improve the power factor through the power converter which is supplying the machine rotors with three-phase power of variable magnitude and frequency. Benefited from the flexible and multiplex control methods, doubly fed machines have greater potential for applications in variable speed drive system, wind power generators and pumped hydroelectric storage.This paper processes some research on the variable speed drive systems for the doubly fed machine. Firstly, the characteristics of doubly fed machine are obtained through comparing with asynchronous motor. Operational principle, different field orientation control strategy and the steady-state investigation of a doubly fed machine are analyzed. Then, a rotor flux two-axis dynamic model is established, based on which a flexible active and reactive power control strategy can be developed. Super-synchronous and sub- synchronous operation of the drive system are obtained through advanced control methods. Their feasibility is proved through computer simulation. Following, the models under open loop voltage, open loop current and field orientation control are established. Stability analysis, computer simulation analysis of the drive system with the machine are also presented. In the end, the whole hardware configuration and partial software flow on the doubly-fed machine vector control variable speed system is set forth.