【文章內(nèi)容簡(jiǎn)介】 （ 原文 ） 7 machined and insulated in such way that the main body and the end plates are electrically isolated. Therefore the induced voltage and the capacitive coupling voltage in the shaft do not get grounded through the main body of the induction motor. But it will be grounded from the rotor through the bearing. The current through the bearing from the shaft to the ground is measured using a current probe. A digital storage oscilloscope as shown in figure 4 measures the shaft voltage. The bearing current is measured without minimization circuit for the mon mode voltage and also with minimization circuit. The graphs show the differences. After insulating the end plates from the main body,there may be capacitive coupling from both the ends of the stator winding to both the end plates。 but this coupling will be minimum, since the airgap from the end of the winding of the stator to the end plates are paratively larger. Hence it is assumed that there is no coupling current. Therefore the shaft induced voltage produces rotor current and will flow through the bearing to the ground via the end plate, hence that current is called bearing current. In addition, both sides end plates are isolated hence there is no chance of circulating current between them. Based on the above reasoning there will not be much difference in mon mode voltage by insulating the end plates. The theory of ‘shaft voltage and bearing current’ was discussed in a detailed manner and similarly the papers on ‘bearing current and the relationship to PWM drives’ and ‘A solution to Rotor Shaft Voltage Buildup and Bearing current’ was discussed. 外文翻譯 （ 原文 ） 8 Figure 5a Waveform without minimizing control circuit..(200:1) Star point (cap) and gnd voltage. Ch2(200:1) Line voltage applied to IM. . Vector sum of phase current (current probe output in volts).. Bearing current (current probe output in volts). Figure 5b Waveform with minimizing control : (20:1) Star point and ground voltage. Ch. 2(200:1) line voltage (TM). : Vector sum of phase current 外文翻譯 （ 原文 ） 9 (current probe output in volts) : . Current (current probe output in volts). Figure 6a FFT waveform of star point and ground voltage up to 5000Hz(without minimizing circuit). Figure 6b FFT of star point and ground voltage up to 5000Hz(with minimizing circuit). 4. Experimental results The system shown in figure 3 was implemented on 400 V, 3phase ac induction motor drive system with a PWM of 25 kHz switching carrier frequency. The circuit reduces the mon mode high frequency voltages and the mon mode current to the limit accepted to FCC/CTSPR standards. The IM line voltage, mon mode voltage, vector sum of phase current and bearing current without minimizing circuit are shown in the figure 5a. In figure 5a, the channel2, reads the line voltage. The waveform looks that it is curved and distorted. The reason is that the capacitor at the 外文翻譯 （ 原文 ） 10 output of the converter bridge is not enough to smoothen it. Refer the figure 5b, for the line voltage of the stator winding with mitigation. Figure 7a FFT waveform of star point and ground voltage up to 1MHz (without minimizing circuit). Figure 7b FFT of star point and ground voltage up to 1MHz (with minimizing circuit). Figure 8a FFT waveform line voltage up to 1MHz (without minimizing circuit). 外文翻譯 （ 原文 ） 11 The mon mode current is passed to the ground through standard current probe and the mon mode current is puted using the current probe secondary voltage. Ip = (Es/Zt ). (3) Figure 8b FFT of line voltage applied to IM up to 1MHz (with minimizing circuit). Figure 9a FFT of vector sum of phase current (current probe output in volts) up to 5000Hz (without minimizing circuit). 外文翻譯 （ 原文 ） 12 Figure 9b FFT of vector sum of phase current (current probe output in volts) up to 5000Hz(with minimizing circuit). Where,IP=unknown primary current, ES = measured EMT volts. ZT = transfer impedance(2Ω ) The IM line voltage, mon mode voltage, vector sum of phase current and bearing current without minimizing circuit are shown in figure 5a. The IM line voltage, mon mode voltage, vector sum of phase current and the mon mode current with minimizing circuit are shown in the figure 5b. The graphs of dBμ V/dBμ A against frequency for various parameters are shown in figures 6a–15. Figure 10a FFT of vector sum of phase current (current probe output in volts) up to 1MHz (without minimizing circuit). 外文翻譯 （ 原文 ） 13 Figure 10b FFT of vector sum of phase current (current probe output in volts) up to 1MHz(with minimizing circuit). Figure 11a. FFT of LISN output voltage up to 1MHz (without minimizing circuit). results Figures 6a–7b show the FFT graph of star point to ground voltage in dBμ V against frequency of the inverter without and with minimizing control circuit. Figures 8a and 8b show the FFT graph of line voltage in dBμ V against frequency of the inverter out put voltage applied to the induction motor without and with minimizing c