Design procedure of firing angles for harmonic reduction in a thyristor-controlled reactor by asymmetrical firing control

Abstract

A thyristor-controlled reactor (TCR) has been investigated and developed for a VAR compensator. Its application to industry is put into practice. This system has, however, inherently a disadvantage of generating many lower-order harmonic currents. Some countermeasures to reduce harmonics have been proposed up to the present day. The TCR based on an asymmetrical firing control (AFC-type TCR) has been already proposed for one of the positive countermeasures by the authors. The paper presents the systematic design procedure of the setting of firing angles which satisfy the design specifications of the TCR; that is, each harmonic, the total content of the harmonics and the capacitances of the thyristor and reactor. The use of computer-aided design (CAD) for the choice of firing angles is developed in accordance with the above procedure. Furthermore, the limit of harmonic reduction of the TCR based on an asymmetrical firing control and the effect of multiplexing units on the harmonic reduction are also discussed for the use of CAD.List of principal symbols e = instantaneous value of AC source voltage i 5 i l5 i 2 = instantaneous values of line current, and currents of two branches in AFC-type TCR, respectively = inductance of reactor = reactance of reactor 5 P Q,Qu •" n ' * un L X Thl, Th2, Th\ ThA = thyristors of AFC-type TCR a = firing angle of thyristor a A , a B = firing angles of thyristor in AFC-type TCR 0 ^ <x A ^ a B ^ n = extinction angle of thyristor = reactive powers in AFC-type and UMconcept-type TCRs, respectively = maximum reactive power controlled in TCRs = harmonic currents in AFC-type and UMconcept-type TCRs, respectively = maximum value of fundamental component of line current P nk = peak points in each harmonic distribution (n = the order of harmonics and k = the sequence of peak points) r/i3> ^Th*-t n e current carrying capacities of the thyristors I Thn = current carrying capacity of a thyristor in a conventional TCR = reactive-power capability of the reactor = reactive-power capability of a reactor in a conventional TCR = the number of multiplexing units

Design of an Almost Harmonic-free TCR

“…In addition, these filters are vulnerable to the effects of other sources of harmonics in the AC network, thus they may become less efficient. Many techniques were presented to treat TCR harmonics without using harmonic filters such as using sequential control of transformer taps and asymmetrical firing to a TCR to minimize certain harmonics, but both techniques have limited outcomes (Patel and Dubey, 1983;Funabiki and Himei, 1985).…”