# Experimental Study of Radiated Emission Due to Secondary Common-Mode Current in Buck Converters
###### Abstract  
High switching frequency and fast switching speed of wide bandgap power semiconductor device-based power converters may increase radiated emissions more than conventional silicon-power device-based power converters. Based on the background, this article experimentally investigates radiated emission sources in buck converters. The experimental system constructed in this article has two common-mode noise paths, the primary common-mode and the secondary common-mode. First, this article outlines that a secondary common-mode voltage source is caused by a primary common-mode current and an imbalance of power supply side impedances, and the secondary common-mode current path acts as a monopole antenna. The common-mode currents and the radiated emissions are measured in an anechoic chamber when the common-mode inductor for each mode is connected. The measurement results show that the primary common-mode current generates the secondary common-mode noise, and the secondary common-mode noise is the dominant source of radiated emission in the experimental system.  
EMI; primary common-mode; radiated emission; secondary common-mode +
Footnote †: journal: _Sci._  
0000-0002-313-0000-0000-0000-0000-0000-0000-00  
Research has also addressed the use of the loss resistance of magnetic cores to suppress radiated emission from cables [20]. Moreover, an active-filtering technique for reducing radiated emission from power cables has been investigated [22]. On the other hand, power converters with ground wires and shielded cables form the secondary common-mode (SCM), in addition to the conventionally defined primary common-mode (PCM). Electromagnetic noise propagating through the SCM has been investigated for shielded cables of signal transmission systems [27; 28; 29]. However, the relationship between the SCM noise and radiated emission in power converters has yet to be investigated.  
This article investigates the generation mechanism of radiated emission in power converters with ground wires, experimentally. The contribution of this article is to clarify that the SCM noise is a radiated emission source in power converters with ground wires and that the PCM current and an unbalance of the power supply side impedances cause the SCM noise. The rest of this article is composed as follows. First, Section 2 shows that an experimental system has two major noise propagation paths, PCM and SCM. Section 3 describes the generation mechanism of the SCM noise in the experimental system. Section 4 clarifies that the PCM current and unbalance of impedances of the power supply side causes the SCM voltage source, based on the measurement results of CM and SCM currents. Moreover, measurements of radiated emission from the experimental system are performed in a semi-anechoic chamber. The measurement results verify that the SCM noise is the source of radiated emissions in the experimental system. Note that this article is not intended to meet radiated-EMI standards in any particular power conversion system. This article aims to experimentally clarify the generation mechanism of radiated emission in power converters with the ground wire. The radiated emission generation mechanism demonstrated in this article widely applies to power converters using ground wires or shielded cables. By applying effective radiated emission suppression techniques based on this article's result, the time and cost spent for suppressing radiated emissions are expected to be reduced.