SPEED SEARCH METHOD FOR INVERTER SYSTEM, CAPABLE OF SMOOTHLY OPERATING MOTOR WHEN POWER IS RE-SUPPLIED AFTER INSTANTANEOUS POWER INTERRUPTION

摘要

PURPOSE: A speed search method is provided to prevent a motor stall and allow a motor to operate smoothly when an inverter re-starts. CONSTITUTION: A speed search method comprises a first step of adjusting a target frequency in consideration of power factor, power outage time, inertia of motor, and load, performing a voltage/frequency operation, and judging whether the present current value is larger than the current value measured before power outage; a second step of maintaining an operating frequency constant if the present current value is smaller, increasing output voltage to a normal voltage/frequency, and judging whether the output voltage is same as the voltage/frequency; a third step of judging whether the present current value is larger than the current value measured before power outage, in accordance with the result of judgement of the second step; a fourth step of decreasing the operating frequency and output voltage if the present current value is judged as smaller in the third step, and repeating the third step; a fifth step of maintaining the operating frequency constant if the present current value is judged as larger in the third step, increasing output voltage, and judging whether the size of the output voltage is half of the voltage/frequency; and a sixth step of repeating the fifth step until the output voltage becomes half of the voltage/frequency if the output voltage is not half of the voltage/frequency, and performing a normal voltage/frequency operation if the output voltage is half of the voltage/frequency.