The Research On Direct Torque Control Of Asynchronous Motor Based On DSP

As a novel promising speed regulation scheme, Direct Torque Control (DTC) shows simple structure, perfect dynamic and static performance. The performance of inverter that uses DTC is great improved, there is demand for this kind of inverter on the market. Implementing the speed regulation of inverter by using DTC technology is the research goal of this paper.Firstly, this paper introduces the basic concept of space voltage vector. The derivative formulas establish the relationship among torque, stator flux, space voltage vector. Each block forming the conventional DTC system is described in detail. Secondly, in order to reduce torque ripple as much as possible, a DTC scheme applying space vector modulation technology is investigated, which is also called SVM-DTC. Based on the error of torque, this scheme can synthesize proper reference voltage vector. The way to obtain reference voltage vector and procedure for modulating space voltage vector are fully discussed. Thirdly, better performance depends on accurate observation of stator flux. The precision of stator flux estimated by pure integrator is affected by initial integral value and direct current drift. To compensate for drawback of pure integrator, this paper introduces a modified stator flux observer, which is based on first order low pass filter and contains the amplitude and phase compensation of stator flux. Basically, the phenomenon of flux saturation and drift is avoided. Fourthly, a method used for compensation for dead zone effect is discussed briefly, this method requires the polarity of current. Simulation result verifies that this theory is right. Fifthly, the hardware circuit is designed, including signal conditioning circuit, inverter circuit, rectifier circuit and so on.TMS320F28335 is the core unit of entire hardware system. Finally, the control algorithm program is written by using C language under the software development environment called CCS. The motor overcurrent protection program is embedded in the control algorithm program. The flow diagram of program describes the execution step of whole programs. The experiment compares torque, stator flux and speed between two DTC schemes, the experimental results prove that SVM-DTC exhibits the better performance.