Product Manual

combined with feedback devices such as tachometers, encoders and
resolvers in a closed-loop system, are continuing to replace DC drives in
demanding applications.
By far the most popular AC drive today is the pulse width modulated
type. Though originally developed for smaller-horsepower applications,
PWM is now used in drives of hundreds or even thousands of horsepower
– as well as remaining the staple technology in the vast majority of small
integral and fractional horsepower “micro” and “sub-micro” AC drives.
Pulse width modulated refers to the inverter’s ability to vary the output
voltage to the motor by altering the width and polarity of voltage pulses.
The voltage and frequency are sythesized using this stream of voltage
pulses. This is accomplished through microprocessor commands to a
series of power semiconductors that serve as on-off switches. Today,
these switches are usually IGBTs, or isolated gate bipolar transistors. A
big advantage to these devices is their fast switching speed resulting in
higher pulse or carrier frequency, which minimizes motor noise.
“One Piece” Motor/Drive Combinations
Variously called intelligent motors, smart motors or integrated motors
and drives, these units combine a three-phase electric motor and a
pulse width modulated inverter drive in a single package. Some designs
mount the drive components in what looks like an oversize conduit box.
Other designs integrate the drive into a special housing made to blend
with the motor. A supplementary cooling fan is also frequently used
for the drive electronics to counteract the rise in ambient temperature
caused by being in close proximity to an operating motor. Some designs
also encapsulate the inverter boards to guard against damage from
vibration.
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“Sub-micro” drives provide a
wide array of features in a very
small package.