Patent ID: 6242895
Filing Date: 2001-06-05
Classification: G05F,H02J,Y02E

Abstract:
A controller (FIG. 18b, SS) for controlling a reactive series compensator (3) serially inserted at compensator terminals (3a, 3b) into a power transmission line (2a, 2b), comprising:a) a line current detection means (24) for detecting the line current (i) flowing in the power transmission line (2a, 2b);b) a DC voltage detection means (26) for detecting a DC voltage (u.sub.DC) of a capacitor (C.sub.DC) connected to a modulator (10, C) of the inverter (7) of the reactive series compensator (3), said modulator (10, C) controlling the application of the capacitor DC voltage (u.sub.DC) of the capacitor (C.sub.DC) via said inverter (7) dependent on a modulation signal;c) a modulation signal generation means (11, 13, 14) for generating a signal m in the form of m=m.sub.d cos (.omega.t)-m.sub.q sin (.omega.t), where .omega. is the line frequency, to be supplied as said modulation signal to the modulator (10, C, 7);d) a current control loop (18, 21, 22, 20) for controlling the line current (i) to a reference value (i.sub.d.sup.ref), a current controller (20) of said current control loop outputting a control signal (cc.sub.out) corresponding to the desired compensator terminal output voltage (u.sub.c) of the compensator (3);e) a voltage control loop (15, 19, 16) for controlling the DC voltage (u.sub.DC) of the DC capacitor (C.sub.DC) to a predetermined reference voltage (u.sub.DC.sup.ref), a DC voltage controller (16) of said voltage control loop outputting the modulation index m.sub.d for said modulation signal m;f1) a control method selection means (SS) receiving as input said control signal (cc.sub.out) outputted by the current controller (15, 19, 16) and having a first output for outputting said modulation index m.sub.q of said modulation signal m and having a second output outputting said predetermined reference voltage (u.sub.DC.sup.ref) of said voltage control loop (15, 19, 16);f21) said control method selection means (SS) outputting a constant modulation index m.sub.q and a reference voltage (u.sub.DC.sup.ref) increasing and decreasing dependent on an increase or decrease of the compensator terminal output voltage (u.sub.c) as indicated by said current controller output (cc.sub.out) when the compensator terminal output voltage (u.sub.c) is larger than a predetermined compensator terminal output voltage threshold (u.sub.cth); andf22) said control method selection means (SS) outputting a substantially constant reference voltage (u.sub.DC.sup.ref) and a modulation index m.sub.q increasing and decreasing dependent on an increase or decrease of the compensator terminal output voltage (u.sub.c) as indicated by said current controller output (cc.sub.out) when the compensator terminal output voltage (u.sub.c) is smaller than said predetermined compensator terminal output voltage threshold (u.sub.cth).