Control system for alternating current electric motor driving shutter, comprises means for measuring the motor voltage and current and comparing the actual phase difference with a reference value

摘要

A shutter operating alternating current motor has forward and reverse windings (2A,2B), a coupling capacitance (7) and electronic selector switches (8A,8B). The motor voltage and current are detected (9, 10, 13) and their phase difference measured (11). The actual phase difference at any time is compared (12) to a reference value and used to stop the motor at the end of travel