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BASICS OF AC DRIVE BASICS OF AC DRIVE

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  • BASICS OF AC DRIVEBASICS OF AC DRIVE

  • Why Use Adjustable Speed?Why Use Adjustable Speed?

    Machine or Process Requirements

    Energy Savings

    Automated Factory Concept

    Productivity Increases

  • EfficiencyEfficiency

    Power In - Power Out = Power Lost

    The less power lost,the higher the efficiency

    Power Out

    Power In= % Efficiency

  • TorqueTorque

    The turning force

    applied to a shaft

    tending to cause

    rotation.

  • TorqueTorque

    Torque is the product ofForce x Lever Arm Length (Radius)

    Clockwise and Counter-Clockwiseefforts are distinguished by

    differences in sign, + or -

  • Why Does

    A Motor

    Stop?

  • Stopping Time

  • STOPPING CHOICES

  • RegenerationRegeneration

    The Motor begins to act like a Generator when:

    The CEMF is greater thanthe Applied Voltage (DC)

    or

    The Rotor is rotating faster thanthe Stator Field (AC)

  • Power Factor

    For Simple Applications:Cosine of the Displacement Angle Between Voltage and Current

    However: When one of the waveforms is non-sinusoidal(such as PWM Current)

    True Power Factor = Real Power

    Apparent Power

    Which includes both the Fundamental and Harmonic Waveforms

  • Synchronous Speed

    RPM = 120 x Applied Frequency

    Number of Poles per Phase

  • Base Speed

    The Speed Produced by Applying

    Motor Nameplate Rated Voltage

    at

    Rated Frequency

  • Motor Slip

    O rpm 750 rpm 1460BaseSpeed

    1500SyncSpeed

    40 rpmSlip

  • Motor Slip

    N

    Slip Speed = Synchronous Speed Rotor Speed

  • AC Motor Review

    In an AC motor, speed varies by:

    RPM = 120FP

    Where:F is frequency in hertzP is the # of motor polesSlip is in RPM

    - Slip

  • AC Motor Review

    In an AC motor, Torque Varies by:

    T = K x ( )2 x I LineEF

    Where:K is a constantE is applied voltageF is input frequencyI Line is motor current

  • AC Motor Review

    Horsepower of an AC motor can be determined by:

    HP = Torque x Speed

    5252Where:

    Torque is in lb-ftSpeed is in RPM5252 is a constant

  • Typical Current & Torque Relationship

    for Squirrel Cage Induction Motor

    0

    % Currentand

    % Torque

    % Speed

    Current

    200

    400

    600

    25 50 75 100

    Torque

  • Speed / Torque Curve

    0

    % Torque

    % Speed

    Maximum orBreak-Down Torque

    100

    200

    25 50 75 100Synchronous

    Torque

    150

    225Pull-Up Torque

    Breakaway orStarting Torque

    150% Torque

    Rated Torque

  • PWM Inverter

    Constant Input Power Factor Wide Speed Range High Efficiency Ride Through Open Circuit Protection Common Bus Regeneration

    Requires Extra Hardware for Regeneration to Line

    Complexity Audible Motor Noise

    Benefits Limitations

    AC InputFixedFrequency

    AC Motor

    Fixed DC BusInverterDiode AC

    OutputVariableFrequencyRectifier

    LC

  • CUSTOM BUILT V/F RATIOS