High-Pass Harmonic Filters: General Properties and Design Procedure

Passive harmonic filters are a preferable solution to mitigate higher harmonics, generated by powerful non-linear loads. Generally, such filters contain narrow-band branches tuned to the frequencies of the characteristic harmonics in the spectrum of the load current. Separate branches create high-quality parallel resonant circuits with the supply system inductance. This may cause an amplification of non-characteristic harmonics generated by multiphase non-linear loads. High-pass filters, providing a simultaneous attenuation of several harmonics, are used for damping resonant modes. However, in most cases, traditional methods can be applied to design the second- and the third- order filters. Such filters have insufficient selectivity and characterized by a significant power loss in the damping resistor at the fundamental frequency. Increasing the order of the high-pass filter one can reduce losses in the damping resistor and get the required frequency response. The article describes a general design method for high-pass filters with the specified frequency characteristics of the input impedance. A high-pass filter design is considered as the problem of building a passive LC two-port realizing a specified frequency response. The proposed method is based on minimizing the objective function in space of the filter reactive elements values. Using the proposed method, the values of the different order high-pass filter elements are determined. The performance of the designed filters has been demonstrated. It is shown that the proposed high-pass filters offer significant technical and economic advantages over known solutions.