Research On Common-mode Interference Of The Motor Side And Its Impact On Communication System In ASD System

With the improvement of performance in Adjustable Speed Drives (ASD) system, the inverter-fed ASD becomes widely used in modern industry. However, the inverter also brings non-ignorable electromagnetic interference (EMI) problems. On the motor side of the inverter, High-frequency common-mode (CM) voltage is produced by high speed switching patterns. These CM voltages impact on parasitic capacitances which produce CM currents on the motor side. And then, sensitive equipment of the system is effected by these CM currents through near-field coupling. Therefore, it is of great theoretical and practical significance to study the generation mechanism and modeling method of the CM interference on the motor side of ASD system.Firstly the waveform of CM interference on the motor side of the system was theoretically analyzed, and then the influence of switching frequency, duty cycle and the rise time of ASD system on CM interference was given theoretically in this paper.Secondly the influence of the switching frequency, the output frequency (the speed of the motor), the grounding condition and reference point selection on CM interference was summed up through a large number of experimental analyses. At the same time, the influence of different length and type of motor cable on CM current of the system was revealed by measuring the CM currents at both sides of the motor cable.Thirdly the CM interference model of ASD system was established by using time-domain method and frequency-domain method. The influence degree of different cable length, motor parasitic parameters and the rise time on the common mode interference was confirmed through time-domain simulation. In addition, a novel frequency-domain extraction method for CM impedance of an inverter-fed induction motor was proposed in this paper. The simulation model is verified by comparing with the experimental results.Finally take the communication system for example, the main reason that causes the failure of communication between the inverter and programmable logic controller (PLC) was analyzed. In addition, the error rate was introduced to evaluate the influence of different CM current on communication performance. After measuring the error rate and CM current, the highest strength of CM current on communication lines that cause 0% error rate was revealed in this paper.