ELECTRONIC RELAY FOR SINGLE PHASE INDUCTION MOTOR

摘要

The present invention relates to an electronic relay for a single-phase induction motor which can integrate and perform a start function and a protection function through program control. The relay according to the present invention includes a triac, a window comparator, and a Central Processing Unit (CPU). The triac is connected between a start winding and start capacitor of the single -phase induction motor, and turns on/off a current flow of the start winding. The window comparator compares a both-end voltage variation of the triac with a first reference voltage to detect a zero-point voltage of a motor voltage before start, and compares the both-end voltage variation of the triac with a second reference voltage to detect a zero-point current of a start winding current under start. The CPU controls a gate of the triac to turn on the triac when the window comparator detects the zero-point voltage after supplying the first reference voltage before start, applying a gate current to the triac to maintain a turn-on state of the triac when the window comparator detects the zero-point current of the start winding current which occurs for each half cycle of an Alternating Current (AC) power source after supplying the second reference voltage under start of the motor, receives an induced voltage of the start winding proportional to an angular velocity of the motor under start, calculates an induced voltage variation rate proportional to a start torque of the motor to check that a start torque of the motor is beyond a maximum value, and performs control for the triac to be turned off when decrease of the induced voltage variation rate is begun.