Research On AC Power Dynamometer Based On Improved Vector Control Of Induction Motor

Power Dynamometer is a new type dynamometer, which is able to transfer the power back to the grid or other electric devices to form energy cycle. On one hand, it can achieve energy, on the other hand, the dynamic performance and stability of the dynamometer system has improved significantly. Based on analyzing of the basic principles and characteristics of the different type of power dynamometers, this thesis proposed two AC power dynamometer program based on vector control technology, which were stand-alone energy feedback power dynamometer system and closed power dynamometer system. Both programs use squirrel-cage three-phase induction motor as dynamometer motor because of the advantages of simple structure, reliable operation. The two programs can achieve efficient, energy-saving purposes, which have a large engineering practical value.The main circuit of the two dynamometer programs is AC-DC-AC configuration. In stand-alone energy feedback power dynamometer system, in order to realize bi-directional power flow and better dynamic and static performance, it adopts three-phase PWM technology for AC-DC conversion control and vector control technology of induction motor for DC-AC conversion control. In closed power dynamometer system, the double machine side model is used to achieve energy cyclesutilization. The simulation and experimental results verify the feasibility of the two programs.Through the analysis and research of the traditional vector control method used in induction motor, in order to decrease the influence of the cross-coupling voltages after coordinate transformation which could decrease the dynamic response capability of system, a new feedforward decoupling compensation method is introduced to the inner cuurent loop. At the same time, when calculating coupling items, the given values such as power or torque of the outer loop are directly introduced in to improve the currents dynamic response better. Also the fuzzy adaptive PI regulator is used to instead of the traditional PI regulator in outer loop of the system to improve the dynamic response of power and torque which influence the dynamometer performance directly. In order to obtain the fastest speed of torque and power response, this thesis simplified the fuzzy rules to make it easier to digital implementation and fixed the fuzzy rules and membership functiuns by finding the optimal semantics trajectory. This method effectively improve the dynamic performance of the system.In closed power dynamometer system, sudden applied or reduction load will cause a large DC-bus voltage fluctuations making the DC bus voltage less stable becacuse of the common-DC bus structure. This paper studies the impact of the inverter output and motor performance caused by the DC-bus voltage fluctuations, and proposed an improved VVVF control method to improve anti-disturbance ability of the system and ensure the stable operation of the power dynamometer system.Through the research and experimental results, it can be verified that the key technologies for stand-alone energy feedback power dynamometer system and closed power dynamometer system have good steady-state performance, dynamic performance, excellent energy saving effect, and have a good application value.