lgorithm for the Parameters of Double Tuned Filter Xiao Yao Hubei Electric Power Test & Research Institute Wuhan, P. R . China Abstract: On the basis of analyzing the characteristics of the simplest and the basic type of double tuned filter, an algorithm for precisely determining its parameters is presented here. Using this method, the inductances and the capacitances of the filter can be c alc ul at ed h m he known data such as the reactive compensation capacit y, the tuned freque ncies and the parall el resonant frequency, etc. There are various damped types of double tuned filters, they have three pain of tuned frequencies under the conditions of i) the equivalent impedance being minimum; ii) the total reactance being zero; iii) when the dam ping resistors are out of service. Usually the tuned frequencies of condition i) or ii) are selected to determine the parameters of the filter in designing process. The diagram for determining the parameters of damped-types s also developed. Keywords: power system harmonics, power filter, filter I. INTRODUCTION There are m any types of double tuned filters. The simplest and the basic one is shown as Fig. 1, others are damped types illustrated in Fig. 2. They a re widely used in HVDC projects [l] [2]. Besides bypassing the appointed harmonic currents near the tuned frequencies, the filter also provide the fundamental reactive power needed by the converter. Compared to the single tuned filters with same performance, they enjoy a lot of advantages such as only one reactor is subjected to full line voltage, occupies less site, and only one switchgear is needed, etc. The parameters of the doub le tuned filter estimated from two banks of single tuned filters has been introduced in [3], which is subject to that their equivalent impedance near the resonant frequencies are approximately equal, but this is not a pragmatical method. How to calculate the parameters of double tuned filters accurately and directly from the known data such as the tuned frequencies, the reactive capacity of the filter, and the rated voltage of the system has not been introduced in detail so far. The relationships among the parameters of basic type double tuned filter (Fig. 1 are analyzed, so an algori thm for precise calculating the parameters of it according to the known data is conducted in this paper. Based on he analyzing of relationships among the Paper accepted for presentation a t the 8u International Conference on Harmonics and Qualio of Power ICHQP 98, ointly organized by IEEEPES and NTUA, Athens Greece October 1416,1998 0-7803-5105-3/98/ 10.00 1 998 EEE parameters of the simplest filter, the characteristics of the damped-type filters are discussed. There are three pairs of tuned frequencies on the damped-type filters under the conditions of (i) the total impedance being minimum; (ii) the total reactance being (iii) the damping resistors being out of service. Usually tuned frequencies of condition i) or (ii) are selected to determine the parameters of the filters in designing process. The diagram for determining the parameters of them is also developed accordingly. 11. THE RELATIONSHIPS AMONG THE PARAMETERS OF THE BASIC DOUBLE TUNED FILTER The configuration of the basic double tuned filter is shown as Fig. 1, which is the combination of a series resonant circuit L,, ,) nd a parallel resonant circuit L, z). Under the conditions of ignoring the resistance in reactors and dielectric losses in capacitors, t he impedance of the series circuit i s 1) 1 where w is t he angu lar frequency in radians, therefore the ZJW = A d - 1, cut, Fig. 1 The configuration of the basic double tuned filter -. (4 ( 4 Fig. 2 Various damped types of doubl e tune d filters 154
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