Electromagnetic Compatibility (EMC) debugging of power electronics systems depends heavily on the experience of specialists due to the complex mechanisms of electromagnetic noise. In this paper, the time domain approach is used instead of the conventional frequency domain method to identify noise propagation path. The proposed test mode switches the upper or lower transistors of the converter legs simultaneously on and off at a 50% fixed duty ratio. It is called common mode test mode. Because there is no significant functional current flowing, the differential mode noise is minimized and the remaining common mode noise and mixed mode noise are maximized. Therefore, the common mode noise in this test method gives its upper boundary of Electromagnetic Interference (EMI) level when the system is normal operated. A motor drive system is measured to show how this test mode works.@en

Filters used in electromagnetic interference suppression are often described in literature on drive systems and have become a standard solution in industry. The effect of the commercial off-the-shelf filter depends significantly on how it is installed. A model that includes the installation parameters is made first and then the parameters of the model are extracted by transfer ratio measurements. One possibility is to include the filter on the dc-bus inside the converter. The differential mode DC-bus filter is well known, but the common-mode DC-bus filter has received little attention. Our model is used to show that the common-mode DC-bus filter can achieve the same or even better suppression of common-mode noise by careful design. The transfer ratio is used to evaluate the performance of filter design.@en

Filters used in EMI suppression are often described in literature on drive system and have become a standard solution in industry. The effect of the commercial off-the-shelf filter depends significantly on how it is installed. A model that includes the installation parameters is made first and then the parameters of the model are extracted by transfer ratio measurements. One possibility is to include the filter on the DC-Bus inside the converter. The differential mode DC-Bus filter is well known, but the common mode DC-Bus filter has received little attention. Our model is used to show that the common mode DC-Bus filter can achieve the same or even better suppression of common mode noise by careful design. The transfer ratio is used to evaluate the performance of filter design.@en

A new approach to measure the grid and load impedance of converters in-situ at frequency range 2k-150 kHz has been developed. It is called three-probe approach. This approach allows impedance measurements of power supplies and electric appliances without interrupting their normal operations. The measurement accuracy is improved by proper Fast Fourier Transform (FFT) process to obtain both amplitude and phase information in the measurement. With the proposed setup, the equivalent model consisting of both resistive and reactive components can be derived to represent the grid and load in this frequency range. Grid impedance at different locations and load impedance of various solid state lamps and a SMPS are measured and the results are shown in the paper.@en

In this paper, a novel method for EMI (electromagnetic interference) level prediction is proposed. The method is based on the hierarchical structure of the generation of EMI. That is, the determination of EMI level can be divided into three levels, namely the functional level, the transient level and propagation level. The lower level provides parameter values for the higher level. That makes the analysis to be a single direction chain. In functional level, the working points are obtained. Through transient level analysis, the exact noise sources are determined. In propagation level, the high frequency characteristics in the propagation path are expressed including the variation of parasitic parameters. Frequency analysis can be used to get the EMI level measured in the receiver side rapidly. Because this approach is a straight forward method, the impact of any components can be evaluated immediately instead of doing the simulation from begin to end.@en

Optimization aspects of common mode chokes are presented. These are based on a behavioural model for common mode chokes and its sensitivity study. Results are used to show the influence of the designable parameters on the final performance of the choke placed in a circuit.@en

Abstract¿A galvanically isolated three-phase AC/AC converter with a high-frequency AC-link has been analyzed from an EMC point of view. This is a special configuration because of a large number of switches, a high frequency transformer, and a fourwire output. The essential coupling paths are identified. Corresponding suppression remedies are given. The results, before and after measures, have been presented to demonstrate the improvement in EMC. Keywords: AC/AC converter; electromagnetic interference; galvanically isolated@en

Power electronics applications are usually accompanied by high voltage and current amplitudes, and steep voltage and current transients. The EMI (Electromagnetic Interference) issue is regarded as the main side effect of power electronics applications. Noise level prediction is a vital task for filter design, but many difficulties are encountered. For instance, a large amount of experience is needed to build equivalent circuits, the use of simplified models often requires sacrificing details in the high frequency range, individual approaches must be developed for various topologies, etc.. A new method for EMI prediction of power electronics applications is thus desirable. The universal method should overcome the following common characteristics of power electronics circuits: (a) the large difference between the time constants, and (b) the long time required to reach steady state. The time domain approach is very time-consuming. The assumptions used in the frequency domain approach, namely, periodic noise sources and a fixed propagation path, are also not valid. For example, the slopes of voltage and current transients depend on the operating points, and the assumption of periodic noise sources does not apply. Because the junction capacitors of power rectifiers and switches change with the reverse voltage, the values of the components in the noise propagation path also change. In this thesis, a hierarchical approach is proposed for the EMC design of inverters in motor drive systems. It combines the advantage of the time domain and frequency domain approach to achieve a fast, universal and accurate result. The approach is validated by observations in the time domain and the frequency domain. The proposed approach has three steps. In the first step (functional level), a simple model of switches in the system is developed. The operating points of each switching transient and all time intervals are derived and the narrowband signals of the EMI noise can be derived. The second step (transient level) results in detailed transient waveforms which take the variation of the nonlinear switching transient into account. In the third step (propagation level), the noise propagation through the system is described by the transfer ratio, and the EMC performance is evaluated. The approach is described in detail, and then a PWM voltage source inverter feeding an induction motor is analyzed using this approach. This approach is also applied to a resonant inverter that operates under ZVS conditions. The experimental results are compared to calculated results. Two approaches are proposed for EMI suppression in this thesis. The first approach is by adding a passive filter on the dc-bus. It can be concluded that the same noise suppression performance can be achieved using a dc-bus filter as the conventional ac side filter. The advantage of this approach is that the connections can be made very short which can significantly improve the suppression. A new active filter called the "fourth leg compensator" is proposed in this thesis. The fourth leg inverter generates a signal to compensate the transients of other three legs. It can suppress the fast transients of common mode voltages while reducing the amplitude of the common mode voltage by 50%. A method to determine the values of the additional components is described. It is shown that the CM voltage can be compensated, even with nonideal coupling in the CM transformer and when leakage inductance is present.@en