SERIES SYSTEM COMPENSATOR EMPLOYING 24 ARM AC/AC DIRECT CONVERTER CIRCUIT

PROBLEM TO BE SOLVED: To reduce the size and cost by converting an AC three-phase voltage, individually for each phase, into an AC three-phase voltage having arbitrary amplitude, phase and frequency and inserting the converted three-phase voltage into a system line through a series transformer thereby eliminating a DC intermediate circuit. SOLUTION: Switching operation of switching circuits 5-1,..., 5-3 is controlled, for every semiconductor switching element connected with same AC terminal, in combination with semiconductor switching elements connected with AC three- phase input terminals R, S and T and the ratio thereof to be connected with AC three-phase output terminals U, V and W is controlled for each of them. Consequently, an AC three-phase voltage can be converted individually for each phase, into an AC three-phase voltage having arbitrary amplitude, phase and frequency. The converted voltage excites the secondary of a series converter 2 connected in series with a system and a voltage having arbitrary amplitude, phase and frequency is inserted, in series, into each of three phase of a system line. Since a Dc intermediate circuit is not required, the size can be reduced correspondingly.