| 摘要 |
The load currents, supplied by a three-phase AC power source to a three-phase load, are established and maintained at a preset desired level by sensing those currents and producing a feedback voltage which is compared with a reference potential. Anytime the load currents differ from the desired level the comparison produces a difference or error signal which causes an adjustment of the amplitudes of the three load currents such that they automatically return to the desired level, thereby regulating the current flow to the load. At start-up, the feedback arrangement is also effective in preventing instant current build-up to avoid sudden power surges. When the load is a three-phase motor, limiting the current flow facilitates a soft start with the motor gradually accelerating to full operating speed. Two overload protection circuits shut the system down in response to different overload or overcurrent conditions. One operates when the peak-to-average ratio of the load currents is higher than normal, and the other protection circuit actuates when the peak current is higher than desired.
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