Inductance and Motor Control

Understanding motor inductance is a key part of successful motor control as it can have a major bearing on the potential performance of a motor. Equally, it can render certain types of controller unable to work.

The 3 types of inductance

At Zikodrive, we have divided motors into 3 different brackets of inductance;

  • Normal inductance
  • Low inductance
  • Super low inductance

It’s important to emphasise that these are not industry recognised brackets. This is a system that we’ve developed in order to help us when making the right controller choice.

1. Normal inductance – 15mH +

We count normal inductance motors as any motor with an inductance of 15mH or more. These motors will respond well to a wide range of drive methods and back-EMF and related measurements are easy for controllers to pickup.

These motors tend to be very easy to operate and are the most common in use today. The downside of such motors is that they are not quite as efficient as lower inductance options but they are still significantly more efficient than alternative motors such as brushed DC.

2. Low inductance – 5-15mH

Low inductance motors are classed as anything between 5 and 15mH. These motors can be driven easily using standard controllers but will typically be operable at much higher speeds than a normal one as the current can flow through the coils much faster.

Increasing numbers of motor manufacturers are developing motors in this range, especially where higher speeds are required or improved power density.

3. Super – low inductance – <5mH

Super low inductance motors are increasingly being developed by a number of motor manufacturers for applications such as drones or high speed tooling. These motors offer dramatically increased power density over normal inductance motors and are typically very expensive.

That said, as new technologies are developed and the use of such motors are rolled out, it is widely anticipated that the cost of such technology will come down.

This inductance bracket is where the vast majority of innovation in motor design is currently taking place and the challenges for motor control specialists such as ourselves is designing controllers that can get the best out of such motors without adding excess weight.

Typical control options in the past have used inductors on the controller itself to get around some of the issues caused by low inductance, but where power density is a key factor in the design of the motor this is simply not acceptable.

Understanding inductance

Understanding the importance of inductance and how it can impact on motor performance is hugely important in finding the right option for your project. As with all engineering, there are trade-offs between different options which can directly affect the overall performance of the final product you build.

Lower inductance can deliver more efficiency if done right but it may make certain performance aspects, for example lower speed operation, quite difficult to achieve.

If you’re working on a project and would like to talk to one of our team about finding the right option then please contact us directly and we’ll be happy to help.