Research On Direct Torque Control Of Induction Motor Based On Space Vector Modulation

At present the application of AC motor occupies an irreplaceable position in social life,among the technologies of VVF,Vector Control(or Field Oriented Control,FOC)and Direct Torque Control(DTC)technologies are research hotspots.Compared with FOC,DTC has a simpler system structure,less depend on motor parameters that such as stator or rotor resistance,stator or rotor inductance,and DTC has a faster torque response.But the traditional DTC use two hysteresis comparators to adjust the motor torque and stator flux respectively,and it is due to hysteresis controller that result in inverter switching frequency is changing.In addition,because of using discrete and limited voltage vectors to adjust the flux and torque,will inevitably increase the torque ripple.In order to overcome the obvious shortcomings of traditional DTC,there are several new schemes appear in succession,such as DTC based on twelve-voltage vector,DTC based on torque predictive,DTC based on Space Vector Modulation(SVM-DTC)and so on.Although,the former two have reduced the torque ripple to a certain extent and improved the current and magnetic flux waveform,but the effect is not very significant,and the problem of unfixed switching frequency is still not solved.The latter has solved the defects that carried by limited and fixed voltage vector fundamentally,reduced the torque ripple effectively,fixed the switching frequency to a particular frequency and without losing the robustness to the changing parameters of traditional DTC,at the same time.It is precisely because of these advantages that this paper will focus on the study of SVM-DTC.At present,most of the researchs on SVM-DTC are still in the stage of theory and simulation.In this paper,each module of SVM-DTC system is analyzed in detail,the calculation methods about the magnitude of stator flux vector and the vector angle have been improved,and a new kind of voltage reconstruction technology considering the switch tube dead time is used here,to make the new system easy to be achieved by microprocessor and other hardware resources.Then,use PLECS software to build simulation model,take advantage of three-level NPC inverter experimental equipment,and take the simulation and experimental analysis respectively,the simulation results prove that the new SVM-DTC system has a good performance in either no-load or load,high speed or low speed conditions,and the waveforms of torque,staor flux and staor current are ideal.