Study of Understanding Electro-Magnetic Interferences Caused by Power Electronic Equipment and its Mitigation

点击翻译按钮获取中文摘要

Remarkable progress of power semiconductor devices has enabled an increase in the carrier frequency of a voltage-source PWM inverter using IGBTs. This has brought significant improvements in controllability of voltage, current, and torque to adjustable-speed motor drive systems. It also contributes to reducing acoustic noise. However, a step-wise common-mode voltage with a high value of dv/dt may induce not only high-frequency ground leakage current but also motor shaft voltage and the ensuing bearing current leading to bearing failure.Many technical papers concerning passive and active EMI filters have focused on eliminating high-frequency leakage current from an inverter-driven motor. However, no one has proposed practical EMI filter in terms of cost and performance. When a common heat sink for electrically-insulated diode and IGBT modules is grounded, a high-frequency leakage current may flow through the heat sink and parasitic capacitors existing inside the diode and IGBT modules. … More The leakage current flowing through the motor frame is referred to as the motor-frame leakage current, while the leakage current flowing through the heat sink is referred to as the heat-sink leakage current, in order to distinguish the two leakage currents clearly.This research discusses a passive EMI filter far the purpose of eliminating bearing current, heat-sink leakage current, and motor-frame leakage current from an inverter-driven motor. Two sets of experimental systems was designed and constructed : One consists of a two-level voltage-source PWM inverter operated at a carrier frequency of 15 kHz, and an induction motor rated at 200 V and 3.7 kW, and the other consists of a three-level voltage-source PWM inverter operated at a carrier frequency of 8 kHz, and an induction motor rated at 400 V and 15 kW. Experimental waveforms obtained from the 200-V 3.7 kW system equipped with no EMI filter reveal that a non-negligible amount of leakage current with a frequency of about 3 MHz flows through the grounded heat sink, not into the system ground, but into the motor frame. These understandings lead to illustrating an equivalent common-mode circuit taking into account the parasitic capacitors existing inside the diode and IGBT modules. This equivalent circuit suggests that the EMI filter proposed by the authors is effective in attenuating not only the heat-sink leakage current and the ground leakage current but also the bearing current circulating inside the motor. Experimental results verify the effectiveness and viability of the EMI filter. Less