Beyond Traditional Induction & Servo

Super Power of BLDC motor unparalled to any other

For a lot of application today speed control has become a norm, for this most engineers use Induction motor with inverter and for application that demands better performance we need to switch to Servo motors, this increases applications cost and complexity significantly.

But do you know that Brushless DC motor offer advantages at a cost that is unparalleled to any motor in today's.

These motors offers much better performance at a lower cost than servo motors and also offers much more features compared to AC induction motor for a small price increase ( in lot of application it even reduces the overall cost of the entire application).

Today we will look into these Pro's and Con's and look into how you can use BLDC motor to get the best out of it.

Why should you avoid AC Induction motor

AC induction motor is a very old technology, it is bulky, inefficient, has a lower power density, it is asynchronous, generate slip ( it does not run at a fixed speed, keeps changing with change in load) and was designed to be operated at a fixed rated speed, to mitigate the challenge of speed control a VFD drive is used to to help these motor perform at variable speed.

But it can only operate across wide speed without creating additional limitation, such as reducing the speed of motor will also reduce it fan speed and eventually heat up the motor and degrade its performance there are many such limitation faced, Another issue is that this system is an Open-Loop System ( there is no feedback of actual speed of motor to VFD ), this will create deviation of speed from our desired speed. One more important limitation we need to look at is its impossible synchronise multiple motor without upgrading to additional and costly hardware.

How Servo motor becomes default choice and when you should avoid them

Due to the above limitation when an application demands one the above stated feature a natural inclination towards servo motor are seen.

But now you ask what is the problem with Servo and why should one bother to use BLDC or another motor instead of servo? Let me answer you. Although Servo motor are highly feature packed but they are very costly and complex to setup and use, the maintenance cost is very high as well. In most cases customer ends up spending 5x-15x more cost than AC induction motor. this is where BLDC becomes the holy grail and gives best of both worlds, let us dive more into it.

Why BLDC?

BLDC is relatively new technology, you can read more about it here. BLDC motor are compact, highly efficient, high power density, flat torque speed curve, it is synchronous ( it can operate at fixed speed), does not generate slip, can be operated at wide speed ranges and there is much more to it. And it cost much lower than servo motor.

One thing we need to make note is like servo motor BLDC motor need a BLDC motor controller to operate, this controllers not only drives the motor but also provide additional features such as motor lock detect, Over Current protection, Over and under voltage protection and many more.

When should you upgrade to BLDC from AC induction motor.

If you are using an AC induction motor with a VFD, we straight up recommend you to upgrade to BLDC motor because the Benefits outweighs the cost, even though we do not factor in any other benefits and we only consider the increased efficiency of motor provided by BLDC just the payback of period can be as low as one year, also for certain application if the selection is done rightly the BLDC motor can become cheaper that combination of induction motor and VFD.

In case you are using AC induction motor as standalone, there are many benefits that you can harvest from BLDC motor which can help you with better feature and overall cost saving of your application. You can use take benefit of its compact size and reduce the overall size of your application, better efficiency can help save operating cost of motor in the long run also for battery operated application it can give a longer battery life, by using safety features of BLDC controllers, you can remove additional safety equipment used with induction motor such as overload protection or thermal overload circuits.

Working

We will try and understand working of sensored type BLDC motor. These motors are connected to a driver and the driver is supplied a DC voltage as per rated on motor, the driver will sense the position of the magnet in the motor using hall sensor, and it will look up the commutation table, the commutation table which is inbuilt in the driver provides the information on which coils of the motor to excite depending on the rotor position, the driver then excited a particular set of coil which will turn to rotor to the next slot position where this cycle repeats and the motor will start rotating.

Why Should you use BLDC motor?

If you are developing a new application or are currently using Induction motor or Brushed DC motor for your application below table will help you compare all the motors and state the advantage of BLDC motor.

From the above table it is evident that BLDC motors are much better suited than Induction motor or Brushed DC motor in wide number of features, due to this it can perform better than both motors in almost all application and help your application, and if taken advantage rightly it can help your application modernise completely, it can help add more features, reduce size and save overall cost.