毕业设计——英文文献及翻译——电气电子信息类专业.docx

毕业设计（外文翻译材料）学 院：专 业：学生姓名：指导教师：电气与电子工程学院电子信息工程谭博学2020年 4 月 Minimization and identification of conducted emission bearing current in variable speed induction motor drives using PWM inverterAbstract. The recent increase in the use of speed control of ac induction motor for variable speed drive using pulse width modulation (PWM) inverter is due to the advent of modern power electronic devices and introduction of microprocessors. There are many advantages of using ac induction motor for speed control applications in process and aerospace industries, but due to fast switching of the modern power electronic devices, the parasitic coupling produces undesirable effects. The undesirable effects include radiated and conducted electromagnetic interference (EMI) which adversely affect nearby computers, electronic/electrical instruments and give rise to the flow of bearing current in the induction motor. Due to the flow of bearing current in the induction motor, electrical discharge machining takes place in the inner race of the bearing which reduces the life of the bearing. In high power converters and inverters, the conducted and radiated emissions become a major concern. In this paper, identification of bearing current due to conducted emission, the measurement of bearing current in a modified induction motor and to minimize the bearing current are discussed. The standard current probe, the standard line impedance stabilization network (LISN)), the electronics interface circuits are used to measure high frequency common mode current, bearing current and to minimize the conducted noise from the system. The LISN will prevent the EMI noise entering the system from the supply source by conductive methods, at the same time prevents the EMI generated if any due to PWM, fast switching in the system, will not be allowed to enter the supply line. For comparing the results with Federal Communications Commission (FCC) and Special Committee on Radio Interference (CISPR) standards, the graphs are plotted with frequency Vs, line voltage in dB μ V, common mode voltage in dB μ V and the bearing current in dB μ A without and with minimizing circuits.Keywords. EMI; bearing current.1. IntroductionWith the development of power electronic devices like the insulated gate bi-polar transistor (IGBT), the power MOSFET and the advances in microprocessors, the ac induction motor is becoming popular in variable speed drives with PWM inverter circuits. Since the rise time and fall time of the IGBT are less than 200 nanoseconds, the dissipation loss across the device becomes very less and there by increases the performance of the circuit. However, due to the fast switching action of the device the dv/dt of the inverter output becomes large. This high dv/dt voltage transition coupled with parasitic stray capacitance in the system causes high frequency line to ground current or common mode current and hence bearing current; introducing large EMI in the system.In figure 1, Ilg (the magnitude of ground current) depends on the cable capacitance, machine capacitance, parasitic capacitance of the devices, the output voltage rise time (tr ise ) and the system voltage. Voltage gets induced in the rotor shaft of the induction motor due to fast switching. This induced voltage generates circulating current and flows to the ground through the bearing resulting in an electrical discharge machining (EDM) action at the inner race of the bearing.Due to the EDM, the life of the bearing reduces. The common mode voltage Vng (figure 1) can be measured from the star point of the stator winding of the induction motor (IM) or connected node of three 1MΩ resistors to the ground in case of the IM connected in delta. The reasons for common mode voltage generation are already discussed.It is noted that the sum of sinusoidal balanced phase voltages in a 3-phase IM at the star point is equal to zero. Therefore,Vng=(Van+Vbn+Vcn)/3 (1) Common mode current=Cdv/d t (2)Where ‘C’ is the total capacitance of the system and Van,Vbn and Vcn are the voltages between the respective phases and the star point in the stator winding.Figure 1 Schematic diagram of the drive system. conducted emission, bearing current identification and measurement methodsVarious methods have been proposed to reduce the conducted emission common mode voltage and the measurement of bearing current. An output reactor connected to the inverter out put reduces the dv/dt of the inverter output voltage, which in turn reduces the common mode voltage at the star point of the IM and the flow of bearing current. Various configurations of L-C filter have been reported. The inductance ‘L’ and capacitance ‘C’ are designed according to the permitted insertion loss for the given power rating of the inverter. The draw back of the filter method is the voltage drop across the filter.In the passive filter method, the。