# Brushless Motor Model

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#### Vikas Meshram

Hi everybody

I want to model DC brushless motor. As per the construction of the
brushless DC motor it more like syncronous motor. So I am consfused.

Vikas

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Vikas W. Meshram
Scientific Officer,
Laser Instrumentation,
Indore- 452 013, MP,INDIA.
Email:[email protected]

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#### Alex Ruderman

> I want to model DC brushless motor. As per the
> construction of the brushless DC motor it more
> like syncronous motor. So I am consfused.

Vikas,

what do you mean by DC brushless - trapezoidal (6-step) or sinusoidal motor / control?

What is the purpose of your simulation, e.g., torque ripple at low speed, or operation w/o current loop, or Hall position sensorless operation, or phase advance to enlarge torque-speed area at high speed?

I have written "DC Brushless Commutation Theory" report (about 50-60 pages with a lot of drawings). It explains how to simulate trapezoidal (6-step) DC brushless (making difference between commutational interval and interval between commutations) and covers much of the above.

-Alex
[email protected]

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#### Curt Wilson

A "DC brushless" motor is fundamentally the same thing as an "AC synchronous" motor, although they may differ in design optimization details.

The "DC" refers to the supply voltage, not the motor design, and its use stems from historical marketing use, not fundamentals of engineering. Traditionally DC brush motors were used in many types of systems to avoid the complexity and cost of electronic commutation. But their use caused a whole family of problems, and when electronic commutation started to become feasible and cost-effective, marketing people wanted to sell the idea of having a "drop-in" replacement for the DC brush motors, but without the brushes.

The early electronic commutation schemes had simple "six-step" switching logic, so to minimize the torque ripple, the backEMF/torque waveforms are squarer than the sinusoidal waveforms of a classic AC synchronous motor. These motors are often said to be "trapezoidally wound" instead of "sinusoidally wound".

Now that more sophisticated commutation algorithms are available, which produce a good sinusoidal voltage from a DC bus, many brushless motors are sinusoidally wound to match. Unfortunately, there is no agreement on the terminology for this market -- some call them AC brushless, some call them DC brushless, but emphasize the sinusoidal windings.

Curt Wilson
Delta Tau Data Systems

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#### Murty V. Rama

Hi Everybody
We want to design a synchronous brushless permanent magnet DC motor for a proprietory application. The maximum design time allowed for us is 7 months. Please advise

Murty V. Rama