Electromagnetic Interference Mitigation for Inverter fed AC Drives

Problem statement: In switched mode PWM inverter EMI noise occurs during high (dv/dt) transient period. This EMI noise is mitigated using Active Common mode EMI filter in front of the source. Approach: This study proposes a new active common mode Electromagnetic Interference (EMI) filter for switched mode PWM Inverter applications. The proposed filter is based on current sensing and compensation circuit which utilizes fast transistor amplifier for current compensation. The amplifier is biased with an isolated low voltage DC power supply. Hence it is possible to construct an active filter independent of the source voltage of equipment. Thus this filter can be used in any application regardless of working voltage. The proposed switched mode PWM inverter operated in 180° mode of operation. It’s otherwise called as quasi square wave mode. Results: Simulation of output wave form is verified by using MATLAB Simulink model results and also its effectiveness has been verified hardware output wave forms. The hardware for this project is designed and developed for 50V, 50Hz three phase Fractional Horse Power (FHP) motor. Conclusion: In this Study the concept of the new active common mode EMI filter and quasi square PWM inverter has been proposed. The corresponding simulated output waveforms are verified with the Active Common mode EMI filter; it is possible to use low-voltage transistors for the amplifier by introducing coupling capacitors between the power line and the amplifier circuit. Thus the ACEF can be applied to various power electronic systems regardless of the working voltage. Also it helps in improving the performance of additional filter stages.