Why power factor improving capacitors need not be insisted for the V3f driven Lift Motors?
V3f (Variable Voltage Variable Frequency) drive consists of 3 blocks. A diode bridge rectifier gives DC supply to a Dynamic Braking Unit. Now this DC supply is inverted to AC and fed to the Lift Motor. The power factor to the AC line at the input side of the bridge rectifier is near to unity. The output may have an inductive, or lagging, PF due to the motor’s inductive reactance. However, the motor’s reactive current is circulated between the motor and the inverter but not to the input line. Hence, capacitor is not necessary for such variable speed drives for power factor improvement. More over, the power factor improving capacitors connected to the motor terminals may become overheated due to the potential high frequency noise transmitted from inverter. The V3F drive results in good ride comfort with 50% energy savings compared to single-speed elevators. The V3F drive will adjust and maintain the rotational speed of the motor in accordance with the load and position of the car relativ
