What's the important factors you will consider when selecting a variable frequency drive?

We know variable frequency drive is used for motor speed control. It's also for energy saving and motion control.

So when you select the variable frequency drive, which are the important factors that will affect your decision?

The brand? The reliability? The performance? The service? and other things?

First i would consider the power/current/voltage ratings of the variable frequency drive. but that's an obvious.

The second thing i would look at is the switching frequency of the SCRs or IGBTs. Overall switching and conduction losses are also of main importance.

The overload rating (and the time it can withstand overload) is another factor i would look at. Now personally, for me it is also important the method of control; for instance Delta-Hysteresis, PWM, Sine-triangle, or Third harmonic injection.

Obviously there are more factors to consider of the VFD, but these are few of many.

you need to evaluate the average switching + conduction losses of the semiconductor devices under maximum torque and speed conditions (worst case) to determine the size of heat sink and thus keep the device junction temperature at acceptable level. Remember the switching loss depends mainly on frequency whilst conduction loss depends chiefly on the current through the device. You can optimize the VFD efficiency and lifetime this way, i.e. through proper thermal modeling.

For your application, consider if you will have enough DC voltage headroom at maximum speed (peak back EMF) in order to push sufficient current necessary to sustain the machine torque. If not, please apply phase advance especially for BLDC machines.

Lastly, take protection design into account if you must operate the variable frequency drive safely and reliably.

I would say that all these technical & financial matters are all important ones, but the most important is before all to clearly understand what will be the application and process where will be the VFD, note that you can have high quality drive if you use it for fan you'll lose money, efficiency, time to commission...at the opposite if you take a fan drive for roller mill application it will not work....

so 1st thing is to define clearly application and process because it will tell you what you need to control as much as possible and will give you some ideas where to go..... important values to control, torque, speed, efficiency & power on network, several single drive, one converter and several inverter, brake, regenerative, cos phi, motion application, open loop, close loop, direct torque control, V/F control, current control....to define the best drive, before define at best your need and regulation type, the ROI is only important in HVAC system, for big application like tunnel boring machine is efficiency and torque regulation, for Pipelay system is efficiency, harmonic (not acceptable on a boat) torque and speed regulation with master and several slave controls....

so clearly 1st application and regulation, then you'll find easily the dive type....to finish, I would say that going with the fact that more than 75-80% of world application are pump and fan, all drive manufacturers can manage this, so just need to check harmonic, efficiency and reliability.

The Application should be considered first, as this tells the majority of the story which should include what the application, drives and motor placement environment will be, the driven motor should also have been properly selected for the application and environment and utilized for Drive Sizing allowing adequate headroom for current and bus voltage levels to include motor lead length and input supply and output waveform filtering requirements, proper carrier frequency selection again for the application, proper cooling for both Drive and Motor, adequate and proper Voltage and Current Power Supply and conductors, proper grounding and grounding conductors, properly selected Output conductors considering length to motor, proper wiring layout, both control and power and correct sheilding/separation of types and voltage levels, correct control system architecture to support the application, stable and fast communications capability and selection which is necessary in the majority of systems today, also select the drive that can be supported and serviced in whatever part or parts of the globe the drive will be in when the unexpected occurs, with applications engineering support as well as technical and sales support. After you look at all of this, call ABB, they'll be happy to assist and supply your every need.