Research on Direct Torque Control of Brushless Doubly-fed Machines
Brushless Doubly-Fed Machines(BDFM) has the remarkable superiority in the adjustable-speed drive. The power through its control winding\\\’s power inverter only accounts for a small part of motor total power, the capacity of the inverter is greatly reduced, and the cost of the adjustable-speed system is significantly reduced, therefore it is especially suitable for the AC drive system and generating system of wind power and water power.Firstly, the operation principle, various operating mode, power flows and d-q mathematical model are analyzed. Then the simulation model of BDFM is build with the Matlab/Simulink, and the open-loop characteristics simulation of various operating mode is carried out, simulation results show the relation of theoretical analysis and simulation is basically coincided, this provides a basis for closed-loop control of BDFM adjustable-speed drive system.Secondly, DTC principle of BDFM is elaborated, the simulation model of BDFM DTC system based on u-i flux model is build, in different occasions better performance of BDFM DTC system is verified by observing waveform. And the defects of u-i flux model is discovered, at low speed, the flux is affected by stator resistance through voltage space vector, causes the system shake. In order to solve this problem, a flux observing method of model reference adaptive is proposed, and simulation model of BDFM DTC based on it is build, by simulation the results show the method not only resolves the problem, but also get better performance at the whole range of speed.Finally, torque ripple of BDFM DTC system is researched, through mathematic analysis, it is know that torque hysteresis width and sampling period are the causes to produce torque ripple. According to the reasons, three methods to decrease torque ripple are proposed, for improving the performance of BDFM DTC system provide reference programs.
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