Influence of high-frequency near-field coupling between magnetic components on EMI filter design

Abstract

This work presents a detailed analysis of magnetic component coupling and its influence on EMI filter design. In contrast with other literature, the novelty of this paper reveals that magnetic coupling should be divided into two categories: low-frequency coupling and high-frequency coupling. It is proven that coupling is frequency related and high-frequency near-field stray flux distribution can be differ dramatically from low frequency condition. The change of the near-field stray flux distribution is caused by displacement current from stray capacitors. By using the Biot-Savart equation, highfrequency near-field distribution can be well predicted and matched with experimental results. In addition, single stage DM LC filters are utilized to demonstrate the influence of high-frequency coupling.

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“…With this, the impacts of the components' self-parasitics are identified [40], which already have an effect at frequencies as low as 500 kHz. Finally, the solid red curve denotes the transfer function of the assembled EMI filter, measured with the Bode100 network analyzer (Omicron Lab [41]), which reveals a decreased attenuation due to the close placement of the different components (leading to couplings [42]) and additional parasitics introduced by the PCB. The 4-phase CM choke would saturate during the measurement of the filter's DM transfer function, as the measurement is only conducted for a single phase, e.g., phase a in Figure 8a.…”

A Modified LLCL Filter With the Reduced Conducted EMI Noise

“…where α is the modulation index, U dc is the dc-link voltage, J n are Bessel functions [17], and ω 0 and ω s are the fundamental and the switching frequencies in radians per second, respectively. During the EMI noise analysis, note that the total EMI noise should not only be related to the background EMI noise caused by the auxiliary power supply of the controller, but also depend much on the parasitic parameters, which are closely related to the circuit layout and the character of the switches [18]- [20]. However, according to [21] and [22], within the frequency range of 150 kHz∼1 MHz, the EMI effect caused by parasitic parameters of the output filter is not so serious.…”

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“…In addition to self-parasitics, mutual parasitics have been known to show an influence on filter performance. In [5], [6] it is shown that a mutual coupling between components have been analyzed in numerous works. For instance in [7]- [10] where coupling between different combinations of passive components were studied.…”