A New Approach to Mitigate CM and DM Voltage dv/dt Value in PWM Inverter Drive Motor Systems
Department of Electrical Engineering, Harbin Institute of Technology, 92 West Da-zhi Street, Harbin, 150001 China
DOI: 10.1109/APEX.2007.357669 Conference: Applied Power Electronics Conference, APEC 2007 - Twenty Second Annual IEEE
In this paper, a novel passive filter installed at PWM inverter output terminals was proposed with an objective of reducing the high common-mode(CM) and differential-mode (DM) voltage dv/dt value generated by PWM inverter simultaneously. For determining the parameters of the passive filter, the filter transfer function was utilized to achieve a desirable filtering performance. The detailed design procedure of the filter parameters was given. The validity and effectiveness of the proposed filter were supported by the simulation and experimental results carried out on 380V/3kW induction motor system. Further investigations also demonstrate that by making the line-to-line output voltage of inverter sinusoidal, the proposed filter permits motor to be connected with inverter through a long cable. By lowing the dv/dt value of CM and DM voltage, the side-effects induced by them such as shaft voltage, bearing current CM leakage current and over-voltage at motor terminals could be mitigated effectively.
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ABSTRACT: Due to rapid developments of IGBT technology, switching time and frequency are dramatically increased. At higher carrier frequencies, IGBTs induce more capacitive coupled current into a rotor and a stator frame and lead to faster bearing damage. Common mode voltage enables motor to create shaft voltage through electrostatic couplings between the rotor and the stator windings and between the rotor and the frame, and it can caused bearing currents when the shaft voltage exceeds a breakdown voltage level of the bearing grease. Also, high frequency leakage current occurs through stray capacitors between stator winding and the motor frame due to a high rate of the common mode dv/dt at motor terminals which can produce induced shaft voltage. Conducted and radiated Electromagnetic Interference (EMI) emissions are major problems in recent motor drives that produce undesirable effects on electronic devices. In modern power electronic systems, increasing power density and decreasing cost and size of system are market requirements. Switching losses, Harmonics and EMI are the key factors which should be considered at the beginning stage of a design to optimise a drive system. In most of power electronic designs, EMI issues have not been taken into account as one of the main factors; and mitigation techniques for EMI are considered at the last stage of design. This paper presents main EMI issues in a modern AC drive system.
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