Revision 2016/03, 6ELE, V1.14 C-1
Appendix C
How to Select the Right AC Motor Drive
The choice of the right AC motor drive for the application is very important and has great influence on its lifetime. If
the capacity of AC motor drive is too large, it cannot offer complete protection to the motor and motor maybe
damaged. If the capacity of AC motor drive is too small, it cannot offer the required performance and the AC motor
drive maybe damaged due to overloading.
But by simply selecting the AC motor drive of the same capacity as the motor, user application requirements
cannot be met completely. Therefore, a designer should consider all the conditions, including load type, load
speed, load characteristic, operation method, rated output, rated speed, power and the change of load capacity.
The following table lists the factors you need to consider, depending on your requirements.
Item
Speed and
torque
characteristics
Time
ratings
capacity
torque
Load type
Friction load and
weight load
Liquid (viscous)
load
Inertia load
Load with power
transmission
● ●
Load speed
and torque
characteristics
Constant torque
Constant output
Decreasing
torque
Decreasing
output
● ●
Load
characteristics
Constant load
Shock load
Repetitive load
High starting
torque
Low starting
torque
● ● ● ●
Continuous operation, Short-time
operation
Long-time operation at
medium/low speeds
● ●
Maximum output current
(instantaneous)
Constant output current
(continuous)
● ●
Maximum frequency, Base
frequency
●
Power supply transformer
capacity or percentage
impedance
Voltage fluctuations and
unbalance
Number of phases, single phase
protection
Frequency
● ●
Mechanical friction, losses in
wiring
● ●
Duty cycle modification ●
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