Design of nonlinear resistor for filter performance improvement

The use of nonlinear filters realized by adding a nonlinear resistance in parallel to filter inductance in electrical plants or networks supplying distorting loads, such as static power converters, is discussed. The occurrence of filter-line parallel resonances corresponding to noncharacteristic harmonic currents present in the plant can enhance the voltage and current distortion and produce dangerous harmonic overvoltages which are difficult to control even by an appropriately designed linear, selective, or high-pass filter. The use of properly designed nonlinear filters to deal with this problem is proposed. The behavior of the nonlinear filter is shown by means of appropriate examples, and its satisfactory distortion-compensation performance is demonstrated for both transient and steady-state conditions. The study was carried out by computer simulation using the ElectroMagnetic Transient Program.