Studies On Direrct Torque Control (DTC) Of Induction Motor And Brushless Double-Fed Machine (BDFM)

The Direct Torque control (DTC) technology has been paid high attention for its excellent performance in the AC adjust Speed field. Brushless doubly-fed machine (BDFM), as a new type of AC machine,is simple and stable, can run at the state of Asynchronism or synchronization .Compared induction motor, the BDFM need the less capacity for transducer than gernaral AC Motor, therefore, there is extensive applied foreground in the great capacity AC adjust speed systerm and in variable speed,constant frequecy and voltage systerm from wind and water force.It is important for AC timing field to combine the direct torque control and bushless double-fed motor.The large torque ripple at low speed is the main problem for conventional direct torque control.So the scholar in our country and abroad has put forward many strategies to reduce the torque ripple, for example , DTC based on torque prediction, DTC based discrete space vector control and so on.In order to decrease torque and flux ripple, a new method is proposed on the basis of torque and flux characteristic for direct torque contol, to calculate hysteresis value oftorque and flux.To improve the performance of conventional DTC at low speed, The paper pay attention to a strategy that DTC based on torque prediction .Simulate and experimental result show that it can reduce the torque ripple and improve the waveform of stator flux and current at low speed.In order to make the structure simple and be easy to programme, a strategy that improved DTC based on torque predict is proposed. Simulate and experimental result show that it not only maintain the advantage of DTC based on torque prediction also enhance the speediness quality when start.With the idea of discret space vector modulate(DSVM), a strategy that improved DTC based on DSVM is studied in this paper. Simulate and experimental result show that it also reduce the torque ripple and improve the waveform of stator flux and current at low speed, and make the start as fast as the DTC based on improved torque predict.The experiment is achieved on the 2.2kW platform with DSP chip TMS320LF2407A as control core for conventional DTC, DTC based on torque prediction, DTC based improved torque prediction, DTC based improved DSVM.The experimentation is mainly on load, unload, start at low and medium speed. The experiment result show that the DTC based on improved DSVM has acquire better effect than other three methods on reducing torque ripple , improving stator flux and current waves , starting nature.Besides, it depend parameter of motor less than DTC based on torque prediction. On the side, ex perimental result show that the systerm can run with rated load at very low speed.The paper have a research on BDFM and BDFM systerm based on DTG, a flux observe model that is fit for full speed range is proposed.The paper introduce DSVM technology into BDFM based on DTC, simulate results show that it can reduce the torque ripple and improve the waveform of the two stator winding flux and current in BDFM systerm based on DTC.