VARIABLE SPEED DRIVER FOR INDUCTION MOTOR FOR ROAD TUNNEL JET FAN DRIVEN VIA LONG CABLE

摘要

The purpose of the present invention is to eliminate, when a jet fan is driven via a long cable, possible insulation degradation of an electric motor due to a switching surge of an inverter, an EMI problem with the high frequency band, and an earth leakage circuit breaker malfunction due to a common-mode current that flows between a stray capacitance of the long cable and the ground. Input power is converted from an alternating current to a direct current by an AC/DC converter (131), and the direct current is converted into a variable-frequency variable-voltage three-phase alternating current by an inverter circuit (132). A common-mode reactor (140) and an alternating-current reactor (151) are provided in series with a three-phase output terminal of said inverter circuit, and a star-connected first capacitor circuit (152) is connected in parallel after the alternating-current reactor (151). The terminal voltage of said first capacitor circuit is supplied to a jet fan (400) through a long cable (300). The middle point of the star connection of the first capacitor circuit (152) is connected to the neutral point or the like of the AC/DC converter (131), whereby the in-phase component of the AC/DC converter (131) and the in-phase component of the inverter circuit (132) are caused to circulate in order to reduce a common-mode voltage.