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Revision August 2006, SE08, SW V2.61
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 and the performance. If the capacity of AC motor drive is too large, it cannot offer
complete protection to the motor and it may be damaged. If the capacity of AC motor drive is too
small, it cannot offer the required performance and the AC motor drive may be damaged due to
overloading.
But by simply selecting the AC motor drive of the same capacity as the motor, user application
requirements cannot always be fully met. 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.
Related Specification
Item
Speed and
torque
characteristics
Time
ratings
Overload
capacity
Starting
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
●