Research On AC Variable-frequency Dynamic Power Dynamometer Based On PWM Rectifier And DTC Of Induction Machine

The dynamometer is core equipment of motor performance test station, mechanical drive test station and engine performance test station. The typical dynamometers including hysteretic dynamometer, eddy current dynamometer, mechanic dynamometer and waterpower dynamometer transfer generating energy into heat energy, so not only waste energy but also need some equipment to dispel heat energy. A type of novel AC VF dynamic power dynamometer project is presented based on PWM rectifier and direct torque control (DTC) of induction machine in this dissertation, on the basis of systemic expatiation the basic theory and characteristic of all kinds of dynamometers. The dynamometer not only can feed back generating energy to AC mains, but also can run in electro motion state, the others have no this function. A squirrel cage induction machine is used as its dynamo eclectic machine of testing power because of its simple construction and high reliability, which resolves lower reliability and noise of direct current power dynamometer on account of commutator. The variable-frequency main circuit of the dynamometer is AC-DC-AC configuration. In order to realize high power factor, bi-directional power flow and better dynamic and static performance, it adopts three-phase PWM technology for AC-DC conversion control and direct torque control of induction machine for DC-AC conversion control. This dynamometer that uses PWM rectifier and DTC possess biggish practicality value.The dissertation sets up the mathematical model of voltage source three-phase PWM rectifier, adopts direct current control technology, and designs the controller which consists of voltage and current double closed loop control. The controller inducts current state feedback and carries through forward compensation with AC main voltage to dismiss current coupling in dq coordinate. The dismissed-coupling current becomes separate dq current component, it can accurately track the current without static error in steady state, but also has quickly dynamic respond performance.Adopting voltage-oriented control (VOC) PWM commute control strategy, the dissertation puts forward an easy digital arithmetic to realize VOC, so calculation is reduced greatly. The simulated and experimental results show that the voltage and current of the three-phase PWM rectifier have better respond preference, the current aberrance is smaller and the voltage is steady under this control strategy. The PWM rectifier can implement PWM commute with unity power factor, but also feed back the energy to AC mains with unity power factor.Based the mathematics model of induction machine, the dissertation deeply analyzes flux linkage and torque control theory of DTC and presents a reasonable voltage- vector switch table. After studying on all kinds of flux observation model of DTC, the dissertation put forwards a type of full speed range stator flux observation u-i-n digital model, to improve the performance of DTC.The large torque ripple exists in induction machine based on conventional DTC, especially at a low speed. On the basis of traditional DTC, the dissertation presents a torque prediction strategy. Torque of the next control period is predicted by the proposed equation, and operational time of voltage space-vector in the correspondingperiod is determined based on the predicted torque as well. The experimental results show that the proposed strategy can quickly converge on the given torque and decrease the torque ripple effectively, and also keep a better dynamic performance as the conventional DTC.In order to overcome the weakness of Bang-Bang controller in conventional DTC, the fuzzy logic idea is adopted in the dissertation. The dissertation presents a full-speed fuzzy model DTC strategy, adopt fuzzy controller to optimize select of the voltage vector. The experimental results show that the torque response is improved, and torque ripple is effectively decreased in full-speed range, especially at a low speed, The system has a better dynamic and static performance. The dissertation provides a feasible intel...