Investigation of undesired ripple voltage across power source side and solutions in military low-frequency immunity tests

The MIL-STD-461 CS101 test is one of the essential low-frequency conducted immunity tests for military and aerospace equipment, however it includes some challenges in application. The major challenge is the necessity for the measurement of injected CS101 ripples under the power frequency of the EUT. The measurement of CS101 ripples on the power frequency is almost impossible without taking some extra precautions. In addition to the hard necessity of measuring the CS101 ripple voltage induced across the EUT power input, the other challenge of measuring the ripple voltage that drops across the power source side under the AC power frequency of the EUT is now required by MIL-STD-461G, which aggravates the severe CS101 test conditions of AC devices. In this paper, we propose a FFT-based time domain solution and a method to instantly check the ripple voltage that drops across the power source side, in other words across the 10 μF test capacitor, during the test under the AC EUT power frequency and to verify that it is low enough and not affecting the reliability of the test. The method proposed in this paper significantly overcomes the CS101 test challenges and makes CS101 test results more accurate. In this paper, we also extensively focused on effective solutions to reduce the ripple voltage induced across the power source side along with measurement uncertainty analysis.