PWM Sine-Wave Filter LCF

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  • Passive Harmonic Filter (PHF)
  • PWM Sine-Wave Filter LCF


The PWM voltage waves generated in the output side of inverter based motor speed controller are transient, causing a variety of problems, such as dielectric breakdown of cable, transformer, or motor. The LC sine-wave filter (LCF) is excellent at converting PWM waves to sine waves and securing stability of device.
Problems of harmonic
    • High ripple voltage
    • Motor operation and lifespan shortening
    • Cable damage
    • Transformer damage if step-up transformer is installed
    • Productivity reduction
    • Voltage induced inverter lifespan reduction and internal failure
    • Malfunction of precision control device
    • Instantaneous overvoltage caused by voltage wave distortion
    • Distribution line overheating
  • ① Application loads: motor and device using inverter (inverter output side and inter-load)
  • ② Application systems : 220V, 380V, 440V, 3~1000HP
  • ③ Application places: factory, ironworks, power plant, sewage treatment plant, dam, incineration plant, intake facility

Product Features

  • Improvement in voltage and current waveform

    LCF converts the distorted PWM waveform to sine waves so as to prevent overvoltage of motor terminal and dv/dt. Usually, a motor increases its capability in the condition of sine wave use. It is designed to prevent dielectric breakdown of motor and expand lifespan of motor.

    Reduction in motor peak voltage

    A motor running with PWM inverter can increase its terminal peak voltage to the value almost two times higher than DC bus voltage.
    It means that the terminal peak voltage of motor increases up to 1700V.
    LCF prevents an insulator from being broken down by voltage transient so as to protect a motor and a cable.

    Reduction in ripple and surge of the inverter output side

    A long-distance cable based motor running with PWM inverter can face its enhanced voltage amplification. In the case, a relevant factor is determined by motor surge impedance, cable surge impedance, and cable length. The voltage reflection coefficient R is referred to as the value calculated in the way of converting the reflection value generated by an impedance difference in a connection terminal to the ratio of input voltage to reflection voltage. In short, it is a figure representing a reflection value for input.

    HP R Zm Zc
    25HP 0.9 1500 ohms 80 ohms
    50HP 0.83 750 ohms 70 ohms
    100HP 0.76 375 ohms 50 ohms
    200HP 0.65 188 ohms 40 ohms
    400HP 0.52 94 ohms 30 ohms

    [Table 1. Typical reflection coefficient and surge impedance]

    Zm: motor surge impedance, Zc: cable surge impedance
    Motor terminal peak voltage = (1 + R) × DC bus voltage

    LCF reduces a reflection coefficient with the total surge impedance and the reactor surge impedance of LCF.


    The available distance of voltage amplification is called critical cable length which is determined with a voltage rise time and an electromagnetic pulse move speed .

    Voltage Rise Time R
    6 μsec 300 meters
    1 μsec 50 meters
    0.5 μsec 25 meters
    0.1 μsec 5 meters

    A general speed is 100m/us. A voltage rise time means the time of DC bus voltage rising from 10% to 90%.
    LCF delays the voltage rise time of motor, and therefore reduces dv/dt and expands a critical cable length.

Product Principles

Installation effects

    • Absorption of over-ripple voltage for the prevention of dielectric breakdown
    • Product defect reduction and productivity improvement through the secured performance of precision device
    • Prevention of inductive communication disturbance and expansion of the lifespan of electric device
    • Capacity overcurrent control and power factor improvement

PWM waveform including Transient

  • Before LCF installation

  • After LCF installation

Product Specification

게시판 리스트
Type name Load capacity Enclosure dimension [mm]
LCF38001 1 0.75 350 500 500
LCF38005 5 3.7 350 500 500
LCF38008 7.5 5.6 350 500 500
LCF38010 10 7.5 420 730 1000
LCF38015 15 11 420 730 1000
LCF38020 20 15 420 730 1000
LCF38025 25 19 600 900 1200
LCF38030 30 22 600 900 1200
LCF38040 40 30 600 900 1200
LCF38050 50 37 600 900 1200
LCF38060 60 45 600 900 1200
LCF38100 100 75 600 900 1200
LCF38150 150 112 900 900 2150
LCF38200 200 149 900 900 2150
LCF38400 400 198 900 900 2150

※ A type name is based on voltage and HP (e.g., 440V, 1HP = LCF44001).
※ Parts can also be supplied. Therefore, it is possible to install them in existing or new panel.
※ Rated voltage 220V and 440V products are provided. A product size can be different depending on an installation location or condition. Therefore, please make sure to check it before placing an order.