| 摘要 |
PROBLEM TO BE SOLVED: To improve the accuracy by sampling each phase current which is fed to an induction motor each time, when the voltage across a bus decreases toward zero immediately before the zero voltage is reached. SOLUTION: When a DC bus reaches a zero voltage, it is detected by a regulator 22 responsive to the voltage on a line 43 and then switches 155-160 are turned on to short-circuit the bus, which is thereby reset to zero always during each resonance cycle. Signals on the lines 27, 32, 33 are used for detecting the moment of time immediately preceding the turn off of a clamp 170 for resetting the bus voltage to zero. Scaling amplifiers 45, 46 reduce the voltage level of lines 32, 33 and apply the reduced voltage to comparator circuits 49, 50 through lines 47, 48. An output is delivered, when the indication of clamp current on the line 27 is lower than that when the clamp transistor 170 is turned off. When outputs are fed from the comparator circuits 49, 50 onto the lines 51, 52, an AND circuit 55 delivers a sampling signal on a line 56 to current sensor gates 19-21. |
