| 摘要 |
PCT No. PCT/GB83/00323 Sec. 371 Date Jul. 17, 1984 Sec. 102(e) Date Jul. 17, 1984 PCT Filed Dec. 7, 1983 PCT Pub. No. WO84/02404 PCT Pub. Date Jun. 21, 1984.Motor power-factor controllers (12) act, in the presence of varying motor loads, to maintain the phase lag angle ( phi M) between motor voltage and current at a preset demand or reference phase-lag value ( phi R) by regulating the firing angle of gate-controlled switching devices (11) connected in series with the motor supply (A, B, C). The optimum reference phase-lag value ( phi R) depends on the motor characteristics and will be as small as possible while providing for a stable, unambiguous control characteristic. A reference-setting unit (14) is provided for automatically setting an appropriate reference phase lag ( phi R). This unit (14) monitors the motor phase lag ( phi M) during start up and sets the reference phase lag ( phi R) to a value corresponding to the minimum monitored phase lag plus a predetermined amount (for example 8 DEG ). The unit (14) can be arranged to seek to improve on the set reference ( phi R) during motor running by repeatedly comparing the actual phase lag ( phi M) plus said predetermined amount, with the set reference ( phi R) and resetting the latter to the former if this has a lesser value. |
