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AC Drive, DC Drive, VFD Horsepower
Variable frequency drive, Variable speed drive, VFD input voltage
Variable frequency drive, Variable speed drive, VFD output current
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Manufacturers of Variable frequency drive, Variable speed drive, VFD
 
 
 

Variable Frequency Drives (VFD)

Description / CharacteristicsTypes Description / CharacteristicsTypes
  • Phase Converter VFD More info..
    Input: 230VAC Single Phase. Output: 230VAC Three phase. Horsepower: ¼ to 30 HP Application: Single Phase, 220 ~ 240VAC power source. Constant Torque and 100% duty cycle
    Variable Torque VFD More info..
    Input: 115VAC, 230VAC or 460VAC. Output: 230VAC or 460VAC (Three phase). Horsepower: ¼ to 175 HP Application: Pump, Fan and applications with low starting torque.
    Sensorless Vector VFD More info..
    Input: 115VAC, 230VAC or 460VAC. Output: 230VAC or 460VAC (Three phase). Horsepower: ¼ to 20 HP Application: Constant Torque.
    Flux Vector Drive More info..
    Input: 115VAC, 230VAC or 460VAC. Output: 230VAC or 460VAC (Three phase). Horsepower:1 to 500 HP Application: High starting torque.


    Variable Frequency Drive (VFD) / Inverter Drive Operation


    The converter section rectifies the 3Ø Alternating Current (AC) voltage to Direct Current (DC) voltage via rectifying diodes. Then DC voltage is stored and smoothed in the DC Bus capacitors.


    Variable Frequency Drive (VFD) / Inverter Drive Operation



    The stored DC voltage is then feed to the Inverter section. Which when called for pulses the DC out to the motor windings. Creating a Pulse Width Modulated (PWM) AC wave form as seen below.


    Variable Frequency Drive (VFD) Pulse Width Modulated (PWM) AC wave


    This PWM AC wave can be shaped and changed to any frequency besides the AC line frequency. The output voltage can also vary between 0 ~ AC line Voltage.



    Since the motors revolutions per minute (RPM) are directly related to the frequency they are ran on. Varying the frequency then changes the RPM of the motor.


    Variable Frequency Drive (VFD) motors revolutions per minute (RPM)


    This then allows the driven machines to run at variable rates to improve performance based on manufacturing needs.



    A VFD’s full output voltage is achieved at the Base frequency. It is adjustable in most drives to match the driven motors frequency and voltage. Most motors in the USA have a Base frequency of 60 Hz for their rated RPM and voltage.



    The control algorithm in the drive can adjust for different load types.



    In constant torque mode as seen below. A reduction of half speed or 30 Hz out of the VFD, decreases the output voltage by half. Usually used in machine tools, spindles, conveyors, centrifuges.


    Variable Frequency Drive (VFD) in constant torque mode


    For standard 460 VAC motor the voltage to hertz ratio is 7.67V AC per 1 Hz.



    In reduced torque operation. The output voltage is reduced at lower frequencies below the constant torque curve. This is due to the load requiring less power at lower speeds. This is used in Fan and pump applications to save energy.


    Variable Frequency Drive (VFD) in reduced torque operation

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