Study on Measurement Method of Electromagnetic Interference from Large Electric Equipment

Abstract

In recent years, measurement methods for large-scale systems composed of multiple devices have been discussed mainly by the CISPR (Comité International Spécial des Perturbations Radioélectriques) subcommittee B. For example, DC/DC converters, which are component of photovoltaic system, are usually composed of a large number of units, and an AC/DC converter is required for connection to AC power grids. The limits and measurement methods for electromagnetic noise of a DC/DC converter and AC/DC converter are specified in the international standard CISPR 11. Since it is difficult to measure the conducted disturbance of an individual devices in a system composed of multiple devices, another method by measuring the radiated magnetic field should be examined. However, radiation measurement using a turntable in a test site is difficult in a case of large-scaled system. In such cases, an alternative method for radiated emission measurements is required. In this paper, the common-mode current, magnetic field, and electric fields radiated from an equipment under test that assumed a large-scale system consisting of many DC/DC converters and an AC/DC converter are measured and the electromagnetic characteristics are analyzed. By comparing the results of the conventional measurement method and of the proposed alternative method, it was confirmed that the peak frequencies of the spectrum coincided with each other, although the level of the electromagnetic noise was different. As a result, if the relationship between the measurement distance and the emission level was clarified at an appropriate measurement point, it was found that the proposed method was applicable for an alternative measurement method.