Research On Asynchronous Dynamometer Direct Torque Controlled With Space Vector Pulse Width Modulation

Dynamometers are used in these fields such as electrical motor testing, enginetesting, car bench testing, transmission testing, rotating machinery testing andautomobile&motorcycle parts testing and so on. By means of mimic or regulate theload characteristics of motor under testing through the electromagnetic torque ofdynamometer being controlled to test the performance of motor under testing withoutreal load. Simultaneously, the energy from motor under testing is absorbed by thedynamometer.AC dynamometer with excellent control characteristics, fast dynamic responsebecome a research hotspot. AC dynamometer can realize energy-efficient testing suchas energy feedback, electrical isolation, and multi-machine parallel, which mechanicaldynamometers can not be realized. In combination with computer technology andvirtual instrument technology enables intelligent motor test system.In the process of test, energy flows between motor under test and dynamometerin Asynchronous dynamometer systems based on common DC bus, and the powerinto line just need to meet the energy loss in the power converters and power lines,thus significantly reducing power consumption during measuring.Direct torque controlled dynamometer has many merits, such as simple structure,fast dynamic response, strong robustness, and it can accurately and directly calculatethe value of electromagnetic torque in the stator coordinate system without torqueinstrument. However, the inherent defects existing in direct torque control, such astorque ripple, inconstant inverter switching frequency, is bound to affect theperformance and accuracy of electromagnetic torque of dynamometer under control. In addition, it is difficult to maintain the voltage of the common DC bus constant, as aresult of the fluctuations of the power grid voltage and the effects of variations of theload, which directly affect the accuracy of test power and electromagnetic torque ofdynamometer.In this thesis, a new method of direct torque control was proposed withintegration of the advantages of improved methods of direct torque control. Theproposed method is used two PI regulators and based on space vector pulse widthmodulation (SVPWM). The proposed method can be easily realized and significantlyreduce the torque ripple, thus can increase the accuracy of electromagnetic torque ofthe dynamometer. In order to meet the demands of the electrical power supply inmotor testing, this thesis proposed test power voltage SVPWM method and thismethod was applied to being electrical power supply for motor under testing. TheSVPWM technology was applied both to the method of testing power and the controlscheme of dynamometer, in order to keep the switching frequency of invertersconstant, and eliminate the impact on dynamometer system caused by the fluctuationsof DC bus voltage thus ensuring the test power supply and electromagnetic torque ofdynamometer being controlled accurate and reliable. In this thesis, the application ofSVPWM to eliminate the effect by the variation of the voltage of common DC bus ismore concise, compared to the method to keep the voltage of common DC busconstant before.Moreover, this thesis proposed the method of SVPWM direct torque controlledbased on PI regulation for asynchronous dynamometer system, and completed the T-ncurve of i asynchronous motor in all speed range. The proposal can enableasynchronous motor run bi-directionally, that is both in electric and power generationstate, high-performance of four-quadrant torque control and improve the performanceof electrical motor testing system.