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.

 

 

 

 

Related Specification

 

 

 

 

Item

Speed and

 

Time

Overload

Starting

 

 

 

torque

 

 

 

 

 

 

ratings

capacity

torque

 

 

 

 

characteristics

 

 

 

 

 

 

 

 

 

 

Friction load and weight

 

 

 

 

 

 

 

 

load

 

 

 

 

 

 

 

Load type

Liquid (viscous) load

 

 

 

 

 

Inertia load

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Load with power

 

 

 

 

 

 

 

 

transmission

 

 

 

 

 

 

 

Load speed and

Constant torque

 

 

 

 

 

 

 

Constant output

 

 

 

 

 

 

 

torque

 

 

 

 

 

Decreasing torque

 

 

 

 

 

characteristics

 

 

 

 

 

 

 

Decreasing output

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Constant load

 

 

 

 

 

 

 

Load

Shock load

 

 

 

 

 

 

 

Repetitive load

 

 

 

characteristics

 

 

 

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

 

 

 

 

 

 

 

 

 

 

 

 

 

Revision June 2008, 04EE, SW--PW V1.11/CTL V2.11

 

 

 

 

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Delta Electronics VFD-E manual Appendix C How to Select the Right AC Motor Drive, Related Specification