| 摘要 |
<p>A frequency changer circuit 10 for supplying one or more synchronous electrical machines, as shown groups 1 to 4 of hysteresis motors driving high speed centrifuges, is provided with power storage members 14, 15, 16 and a frequency control element 17 for controlling the frequency of the inverter 12. The motors are connected to the inverter via switches 5-8. It is necessary to protect the motors from overloading, when one or more of the groups is switched on or off. To this end means 21, 22 are provided for sensing when the inverter voltage rises above a predetermined response level and a member 23 supplies a transient signal Figure 3 (not shown) to the frequency control element 17 when this level is exceeded to cause the motors to be briefly changed over from synchronous to asynchronous operation, thus increasing the power requirement of the motors. The member 23 causes the inverter frequency to increase suddenly by a preset amount, so that the power surplus in members 14, 15, 16 is absorbed by the motors to reduce the transient overvoltage produced by switching the motor group(s). Further reduction is possible by decreasing the voltage of rectifier 13 through members 19, 28 also controlled by member 22. <IMAGE></p> |
