Minimization and identification of conducted emission bearing current in variable speed induction motor drives using PWM inverter |
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Authors: | A Ramachandran M Channa Reddy Ranjan Moodithaya |
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Affiliation: | (1) Vemana Institute of Technology, Bangalore, 560 034, India;(2) National Aerospace Laboratories, Bangalore, 560 017, India |
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Abstract: | 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 dBμ V, common mode voltage
in dBμ V and the bearing current in dBμ A with out and with minimizing circuits. |
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Keywords: | EMI a c drives bearing current |
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