A converter based adjustable speed drive for doubly fed induction machine with centrifugal loads

Adjustable speed drive is quite attractive for pump, compressor and other centrifugal load applications in sense of its flexibility and high operating efficiency, compared with the conventional constant speed drive system. In this paper, a slip power recovery scheme combined with the constant volts/hertz control for doubly fed induction machine (DFIM) is proposed and investigated. The machine is started and accelerated to the setting speed region by constant volts/hertz control without the help of starting resistors or auto-transformer. Two starting alternatives can be used according to different turns ratios between the stator and rotor windings. After grid synchronization, the vector control scheme takes over and regulates the machine speed in the setting speed region based on the machine mathematical model. Some important application issues such as ldquosoft grid connectionrdquo and rotor position estimation are also discussed. The proposed control scheme has been experimentally verified through the DSP-controlled 30 kW system by starting from the rotor side. The drive system can successfully run in the full speed range with the proposed control method and control sequences.