Research And Simulation For The Over-voltage On Motor Terminal Of Variable-frequency Drive Caused By Long Cable Application And Design For Dv/dt Filter

The power devices are developing to high frequency working mode with the progress of modern power electronic technology. As the key component of variable-frequency drive, IGBT usually have the high switching frequency from 2 to 20 k Hz. With the significant improvement of the induction motor’s performance through high speed switching and advanced PWM technology solution, high dv/dt will impact on the insulation of the motor simultaneously. In the field of practical industrial application, drive and motor may be in a different position and need a long cable to connect. The transmission will generate high frequency damping oscillation and reflected voltage which amplitude is almost same as the forward-traveling wave. These damping oscillation and reflected voltage will lead to over voltage on motor terminal through PWM pulse and also make the insulation and lifetime of motor worse.This article will make analysis and calculation about the over voltage and reflected voltage according to the above issues. A solution that adds a dv/dt filter between the output of drive and motor is proposed. In order to optimize the cost and improve the accuracy of design, a method using MATLAB simulation software to build and verify some mathematical model including the high frequency model of long cable, PWM pulse model, high frequency model of motor, and the dv/dt filter model is also described in the paper.It is necessary to establish the precise model since the entire models above have parasitic parameters under high frequency which will affect the final results of simulation. Design Steps:(1) Put forward the initial model based on the theoretical basis.(2) Calculate the model parameters through the impedance measurement method.(3) Verify the accuracy of model by using simulation software.(4) System simulation. Set up the test platform in lab: Drive + long cable + dv/dt filter + ac induction motor. Compare the rise time and the over voltage level under one same pulse to validate the model, the filter parameters can be optimized through the comparison results as well.In the end, the experimental results indicate that dv/dt decreased from 3 k V/ ?s to 500 V/ ?s after adding the filter. The over voltage level conform to the criteria and meet the marketing requirement of the drive product that achieve satisfactory consequence.