Electricity + Control March 2019

DRIVES, MOTORS + SWITCHGEAR

Advancing motor drive solutions

This article looks at the challenges companies face in the implementation, operation, maintenance and upgrade of drive control systems for a variety of market applica- tions with different selection criteria. The upheaval in factory automation with the Industrial Internet of Things (IIoT) or Industry 4.0 is considered, as is its impact on the selection of drives.

Take Note!

1. Different motor types suit different applications. 2. Eachmotor type needs spe- cific drive characteristics and feedback processing for optimal performance. 1 2

D rives for ac motors have become an indus- try in themselves with various types offer- ing control of speed, torque and positional accuracy from sub-kilowatt power levels to mega- watts.The ac power sources might be from 200Vac to industrial 690 Vac, three-phase. While motors controlled can be induction, permanent magnet or servo-controlled types in common applications, ad- ditional applications emerge because of the value the drive gives. For example, entertainment theatre equipment is increasingly automated with preci- sion control of curtains, floors, scenery and light- ing. Full-featured drives enable remote controlled and programmable positioning and movement for smooth transitions. Communications back to the controller report on loading and performance. Motors are chosen for intended application. Induction types might be used when wide speed range is not a factor, cost is important and efficien- cy is not critical although this does lead to higher operating costs. Permanent magnet motors are more efficient and more expensive than induction motors but give lower operating costs and can give quicker payback. They are smaller than induc- tion motors for the same rating and can approach the positional accuracy of servomotors if feedback is applied. Closed-loop servomotors are relatively expensive but can provide optimum accuracy to +/-0.001% of base speed at rated torque, current and voltage. With their smaller rotors giving low inertia and fast dynamic response, they can reach high speeds with high peak torque and accelera- tion. They can be 25% to 50% smaller than other

motor types while typically achieving over 85% efficiency.

Induction, permanent magnet and servo motors from the Control Techniques range.

The motor type chosen for an application depends on the motor load. For example, an induction mo- tor might be used in constant torque/speed appli- cations such as conveyors and a permanent mag- net type for liquid pumping with wide and variable speeds. A servomotor would find its niche in ro- botics where fast acceleration to a precise position is necessary. Each motor type needs specific drive characteris- tics and feedback processing, if used. This, if the drive programming is optimal, results in optimal functional performance. Modern drives can form part of Industry 4.0, which combines automation with communication in real time to optimise pro- duction processes and save energy, improve prod- uct quality and provide operational flexibility. In the extreme instance, the system becomes self-learn- ing and removes the variabilities of human inter- vention. Using motor drives – opportunities and challenges

4 Electricity + Control

MARCH 2019