| 摘要 |
<p>Induction motors run at much reduced efficiency below rated load and a microprocessor based system for overcoming this problem is described. A microprocessor 14 keeps a count which varies from a preset number to zero in 60 DEG of the supply voltage waveform and each time zero is reached a selected thyristor, such as 10 or 11, is fired to supply a motor. Phase lag of current behind voltage is determined for each phase using the values of the said count when current and voltage sensors 12 and 21 sense cessation of phase current and phase voltage zero, respectively. The phase lag is compared with a desired reference value, the resultant error signal is filtered and the count adjusted in the microprocessor so that the firing time of the thyristors is varied to correct the phase lag. <IMAGE></p> |
