单相逆变器共模EMI分析及有源抑制技术研究

AbstractWith the development of power electronics,PWM inverters are getting more widelyused,such as PWM drives,UPS etc.However,high frequency switching of powersemiconductor devices like IGBTs and MOSFETs bring high dv/dt and di/dt,whichproduce large electromagnetic interference (EMI)from several kilo hertz to tens of millionhertz and the electromagnetic compatibility (EMC)standard is not met.The research workof this paper includes three aspects:1)analysis of typical characteristics of common mode(CM)EMI and prediction of CM EMI spectrum of single-phase full-bridge inverter;2)reduction of CM EMI through automatic tuning of gating signals;and 3)evaluation of CMnoise level based on the energy of CM current.The source and propagation path of CM EMI in single-phase inverters areinvestigated.The conclusion is that CM EMI is due to the dv/dt charging anddischarging the parasitic capacitors of the power devices.After examining the existingcircuit model of CM current,some shortage of the model has been found.A new parallelcircuit model is proposed.Time-and frequency-domain analysis are conducted to obtainCM current waveforms under trapezoidal excitement and CM noise spectra in150kHz-30MHz frequency range.The CM current is of decaying oscillatory waveform.The simulated CM EMI waveforms and spectra are compared with the experimental resultsto verify the validity of the proposed model.The impacts of modulation strategy on CM emissions are discussed.Theoretically,forsingle-phase full-bridge inverters,if bipolar SPWM is used,the two phase-legs provideperfect CM compensation for each other and the CM current can be cancelled outautomatically.Due to inevitable deviation in signal transmission characteristics of devices,transmission delay of each gating signal can be different,so the CM current cannot becancelled out perfectly.To address this,a simple solution is to fine-tune the gating signalsⅡ