How are BLAC motors wound and what makes them different from BLDC motors?

In summary: A home-built brushless AC motor is a BLAC motor that is built from CD-ROM motors or parts you can buy. -BLAC motors use three hall effect sensors to time the commutation.
  • #1
KLoux
176
1
Hello,

I've recently read a couple of things about brushless motors that have spurred quite a few questions. Googling has solved some of them, but I'm hoping that you can help with the rest :smile:

Apparently there are two types of permanent magnet brushless motors - DC and AC. This is what I've gathered so far:

- BLDC motors have a trapzoidal back-EMF waveform (phase-to-phase), whereas BLAC motors have a sinusoidal back-EMF waveform
- Either type can be driven with a trapezoidal-type or sinusoid-type commutation scheme, although using the correct scheme for the motor increases efficiency
- BLDC motors can use three hall-effect sensors to time the commutation, but for a sinusoidal commutation scheme, much better rotor position resolution is needed

My question is how do you wind a BLAC motor? I've been reading about home-built BLDC motors made from CD-ROM motors or from parts you can buy (www.gobrushless.com) - seems to be popular with the RC airplane crowd - but no one uses BLAC motors, probably because you need better feedback and more complicated controls to use them. The (short) Wikipedia entry for BLAC motors says "the stator windings of a brushless AC motor are sinusoidally distributed windings, while those of a brushless DC motor are salient field coils."

In my head "sinusoidally distributed windings" looks something like each phase getting wound around almost every tooth, but maybe the number of winds around each tooth changes? And each phase has maximum wind counts occurring 120 electrical degrees from the previous phase, with the number of electrical degrees being determined by the magnets?

I would appreciate any references you can recommend, online or in print.

Thanks for your help!

-Kerry
 
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  • #2
BLAC is a seldom used term. It means an AC synchronous motor with permanent magnet field. It can have salient poles like BLDC or it can be a round rotor with sinusoidaly distributed windings.
 

1. What is a brushless AC motor?

A brushless AC motor is a type of electric motor that operates using alternating current (AC) power. Unlike traditional AC motors, brushless AC motors do not use brushes and commutators to transfer electrical energy to the rotor. Instead, they use electronic commutation, which involves switching the direction of current flow in the stator windings to create rotation.

2. How do brushless AC motor windings work?

The windings in a brushless AC motor are responsible for creating the magnetic fields that interact with the permanent magnets on the rotor to produce rotation. These windings are typically made of copper wire and are arranged in specific patterns, such as a three-phase configuration. The windings are energized by the electronic commutation, causing the stator and rotor to interact and produce motion.

3. What are the advantages of brushless AC motor windings?

Brushless AC motor windings offer several advantages over traditional AC motors with brushes. They are more efficient, have a longer lifespan, and require less maintenance due to the absence of brushes. They also offer smoother and more precise control over motor speed and torque, making them ideal for use in applications that require high precision.

4. What are the common types of brushless AC motor windings?

The most common types of brushless AC motor windings include single-phase, two-phase, and three-phase configurations. Single-phase windings are used in simple applications, while two-phase and three-phase windings are used in more complex applications that require higher performance. Other types of windings include fractional-slot, concentrated, and distributed windings, which vary in their design and performance characteristics.

5. What are some applications of brushless AC motor windings?

Brushless AC motor windings are used in a wide range of applications, including electric vehicles, industrial machinery, robotics, and HVAC systems. They are also commonly used in household appliances, such as washing machines, refrigerators, and air conditioners. Additionally, brushless AC motor windings are used in renewable energy systems, such as wind turbines and solar panels, to convert mechanical energy into electrical energy.

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