Prediction And Analysis Of Conduction Electromagnetic Interference In PWM Inverter

Conducted electromagnetic interference (EMI) in power electronic equipment is animportant factor restricting the development of power electronics technology. And theresearch is of great hot and difficulty. Aiming at PWM inverter system, the frequencycharacteristics of interference source and propagation path are analyzed; modeling predictionand the impact of passive devices on conducted EMI are studied too.First, the frequency models of the passive devices are built by measurements. The papermeasures the external characteristic of the device by impedance analyzer and obtains themodel parameters to build the frequency models of the capacitor and inductor. The cablemodel is built by using N Ladder RLC unit and the transformer model is built by the methodof resonance frequency. The differences between the different types of capacitors orinductors are compared by simulation and experimental results. The effect of the strayparameters in conducted EMI is analyzed.Second, a simulation study is made for the PWM inverter by using time domain modeland frequency domain model. The software Saber is used to build the time domain modeland the model of the switching devices are built by using curve fitting. For interferencesource in frequency domain model, double Fourier integral transform is applied. Combinedwith the impedance of propagation path, the common-mode interference can be predictedrapidly. The methods are verified accurate by the experiment.Third, the impact of passive devices for conducted EMI is analyzed. The unbalancedexcitation current of the three-phase core-type transformer is calculated and the influence ofthe unbalanced excitation current in the DC-link is analyzed. Then, the impedance ofcommon-mode noise propagation path is analyzed and the relationship between pathimpedance and noise is studied through a three-phase non-shielded cable. The theoreticalanalyses are verified by the experiment.