Study On Self-Excited Oscillation For Induction Motor System Fed By A Voltage Source Inverter

A self-excited oscillation phenomenon maybe happens for AC drives composed by the voltage source inverter and an induction motor under the conditions of some frequencies (for example in the range of 20Hz to 30Hz) under no load or light load. It not only causes harmful mechanical vibration, but also the sharp motor current oscillates and rotating speed fluctuates seriously, so that service lifetimes of the motor and other electric equipment become shorter and accuracy and reliability of the systems are also affected greatly. With the develop of AC drive technology, in order to improve system performances further, how to analyze the oscillation phenomenon and to resolve this problem become one of research objectives.Firstly, the mathematical model for a three-phase asynchronous motor is introduced in this paper, and a motor model with flux saturation is also established. Secondly, the impact of parameter variations of the induction motor and the inverter on the oscillation and the influence of the dead-time effect on output voltage and output current of the inverter are analyzed in detail. In the meanwhile, the impact of dead-time effect on the reactive power feedback under two-phase modulation mode is analyzed. The oscillation mechanism is analyzed based on the inherent mechanical properties of the asynchronous motor and power transmission balance, respectively. Some conclusions are drawn: the inherent factor of an induction motor is the root of oscillation, and the dead-time effect is the most important stimulation source, and the flux saturation degree has an important impact on the oscillation. Finally, in order to suppress the oscillation, three schemes based on phase current detection to adjust output frequency or voltage reference value are analyzed in detail.Simulations and experiments are carried out based on three schemes in this paper, the results shows that three schemes are effective for suppressing the oscillation and not affected by the motor or inverter parameters, therefore they can be easily applied to the existing AC drive system.