Evaluation of EMI Filter Performance for Uninterruptible Power Supply

• Main Authors: LIAO KANG-YU, 廖康佑
• Other Authors: LIN KEN-HUANG
• Format: Others
• Language: zh-TW
• Published: 1999
• Online Access: http://ndltd.ncl.edu.tw/handle/12199476437336245843

碩士 === 國立中山大學 === 電機工程學系 === 87 === The performance of an EMI filter usually is difficult to predict precisely when uninterruptible power supply (UPS) manufacturers try to fix conducted electromagnetic interference problems. They normally involve a cut-and-trial process that wastes a lot of time and increases the production cost. This paper tries to alleviate this annoyance by taking the impedance of noise source into account. Based on the insertion loss, three methods are proposed for comparison. The first method considers neither the noise source impedance nor the parasitic elements, the second method only considers parasitic elements, and the third method considers both. Two different filter topologies are used to evaluate the performance of the three methods. Because EMI filter performance depends not only on the filter itself but also on the noise source impedance, we find the third method is closest to the measurement data, the second method is next, yet the first method has the maximum difference. In the first filter topology, the third method gives an accurate estimate of filter performance with a mean error of 3.14 dB. For the same topology, the second method is worse than the third method by 20 dB, and the first method is worse than the second method by another 30 dB. In the second filter topology, the third method also provides an accurate estimate of filter performance with a mean error of 2.66 dB. Similarly, the second method is worse than the third method by 20 dB, and the first method is worse than the second method by another 40 dB. Two power combiners and an HP 4194A impedance/gain-phase analyzer are used in our measurement. The former includes a power combiner for measuring CM noise and a power combiner for measuring DM noise. The latter is used to measure the frequency responses of filter elements and the parameters of matrix. Using the methods proposed in this paper, EMI engineers can solve the problems quickly, and manufacturers can shorten development time of new products and reduce the production cost.