Modeling Of Near Field Coupling For Conducted EMI In Power Converter

Power converter generates serious Electromagnetic Interference (EMI) problem which has attracted interests of researcher in power electronics areas. This dissertation mainly focus on near field modeling of power converter, magnetic coupling cancellation techniques, and conducted common mode EMI suppression techniques.Based on analysis the propagation paths of differential mode and common mode conducted EMI, the effects of near field couplings including both magnetic and electric coupling that exist in power converter are modeled. Based on the modeling of inductor and capacitor, and estimating both inductive and capacitive couplings using Z parameters or Y parameters obtained by Ansoft HFSS software, the model of near field couplings is set up. This model is verified by comparison of simulated and measured voltage gains.This dissertation also investigates the magnetic coupling cancellation techniques. Although the shielding can absorb and reflect the magnetic field, the cost is increased. Another cancellation can be achieved by PCB layout, but it maybe need larger area of PCB. The dissertation proposes two methods to cancellation the magnetic coupling. One of them is called PCB inductor cancellation method, and the other is solid inductor method. The design procedures of these two methods are given, then the experiment is set up to verify these cancellation methods.A novel method named "Construction stable potential common mode EMI suppression technique" is proposed in this dissertation. Taking a boost converter as an example, the method has been explained in detail. The major common-mode conducted EMI generated at the high dv/dt nodes in the converter can be cancelled by changing placement of the boost inductor and using the common-anode diode. Theoretical analysis and experimental results verified this method. This method can be used in other converters such as Buck, Buck-boost, Flyback and PFC circuits etc. A novel common-mode EMI filter is also proposed in this paper. Because no power current passes through the CM choke, the size of this filter is reduced largely comparing with the conventional CM filter. Experimental results verify that this filter can reduce the CM noise effectively.