All modern era lifts are equipped with VSD/VFD, Variable Speed Drive (VSD) controls to control Motor speed, Acceleration / deceleration, Smooth start & stop of the elevator for Ride comfort, Energy efficiency and Precise floor leveling.
Basic system of VSD are in three stage, AC to DC by using diode or Thyristor, DC BUS controls stable DC voltage by using capacitor, and DC to AC inverter by using IGBT to generate accurate frequency to control motor speed based on feedback.
Harmonic are generated due to load drawing current in pulses, only conduct at voltage peaks creates non sinusoidal current harmonics.
VSD harmonics, 3rd harmonic from LED lamp & regeneration breaking create elevator problem, Automatic rescue device (ARD), and Emergency rescue device (ERD) malfunction, stuck elevator door & landing mal-operation. The triplen, also called third or zero sequence harmonics current, from the building’s LED lamps and other electronic gadgets don’t get cancelled but add up at the neutral wire. It creeps into building’s electronic equipment and causes elevator malfunction and VSD card failures, ARD failure. VFD drives are the primary source of harmonic distortion in a building’s power system. It generates a significant percentage of 5th and 7th order current harmonics which in interaction with the building’s electrical system impedance creates voltage harmonic. Depending upon harmonics distortion these industrial type 5th and 7th harmonics primarily affect the elevator’s position control mechanism and cause uneven floor landing. The elevator floor level does not align with its landing floor level. If harmonic distortions are high, it causes failure in the VFD drive and electronic cards. VFD drive during regenerative breaking cycle creates significant percentage of 3rd harmonic current that in addition to 5th and 7th harmonic currents. Today’s buildings are filled with loads those predominantly generate third harmonic current like LED lights, myriads of SMPS based electronic gadgets and computerized equipment. Unlike phase currents 3rd harmonic current also called zero sequence current or triplen harmonic current, does not get cancelled but trebled at neutral. It’s all pervasive and with any infirmness in the building’s neutral/ ground system; it’s a serious electrical fire risk that could strike as like a bolt from the blue. Triplen harmonic currents easily penetrate into the elevator’s control system and confuse its functioning. Elevator doors randomly get stuck and does not open until power reset. Its operation becomes erratic, and with a confused control system it lands at a wrong floor.

Harmonic mitigation solutions improve power quality by reconstructing harmonically distorted waveform back into sine wave, balance 3phase voltage and currents and is an effective surge suppressor. It effects energy conservation, extends motor life and elevator performance, and protects sensitive equipment in elevator and escalator applications. JIJI Innovation Solution does the complete in depth study for the Lift Issue and suggesting customized Filter sizing and providing comprehensive solution to above problems.