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The Basic working:
Thus the brushed D.C motor should never be used for operations that demand long life and reliability. Fort this reason and the other reasons listed in the introduction, BLDC motors are used in most of the modern devices. Efficiency of a BLDC motor is typically around 85-90%, whereas the conventional brushed motors are only 75-80% efficient. BLDC motors are also suitable for high speed applications ( 10000 rpm or above). The BLDC motors are also well known for their better speed control.
Three phasis BLDC motor working principle is quite simple:
BLDC motor consists of two most important parts - stator and rotor.
Rotor – is moving engine part which has permanent magnets.
Stator – more complex engine part which has few electromagnets groups.
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The stator has a coil arrangement, as illustrated; The internal winding of the rotor is illustrated in the picture below (core of the rotor is hidden here). The rotor has 3 coils, named A, B and C.
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Out of these 3 coils, only one coil is illustrated for simplicity. By applying DC power to the coil, the coil will energize and become an electromagnet.
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The operation of a BLDC is based on the simple force interaction between the permanent magnet and the electromagnet. In this condition, when the coil A is energized, the opposite poles of the rotor and stator are attracted to each other (The attractive force is shown in green arrow). As a result the rotor poles move near to the energized stator.
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This process is repeated, and the rotor continues to rotate. The DC current required in the each coil is shown in the following graph.
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As the rotor nears coil A, coil B is energized. As the rotor nears coil B, coil C is energized. After that, coil A is energized with the opposite polarity.
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A humorous analogy help to remember it is to think of BLDC operation like the story of the donkey and the carrot, where the rabbit tries hard to reach the carrot, but the carrot keeps moving out of reach.
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Further improving the BLDC Performance
| Even though this motor works, it has one drawback. You can notice that, at any instant only one coil is energized. The 2 dead coils greatly reduce the power output of the motor. Here is the trick to overcome this problem. When the rotor is in this position, along with the first coil, which pulls the rotor, you can energize the coil behind it such a way that, it will push the rotor. |
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For this instant, a same polarity current is through the second coil. The combined effect produces more torque and power output from the motor. The combined force also makes sure that a BLDC has a beautiful, constant torque nature. Such torque nature is difficult to achieve in any other type of motors.
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The current form required for the complete 360 degree rotation is shown in the graph below.
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| With this configuration 2 coils need to be energized separately, but by making a small modification to the stator coil, we can simplify this process. Just connect one free end of the coils together. |
When the power is applied between coils A and B, let’s note the current flow through the coils. It is clear that, the current flow is just like the separately energized state.
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Use of an ECU (Electronic controller unit)
That’s how a BLDC works. But, you might have some intriguing doubts in your mind. How do I know which stator coils to energize? How do I know when to energize it, so that I will get a continuous rotation from the rotor? In a BLDC we use an electronic controller unit (ECU) for this purpose. A sensor determines the position of the rotor, and based on this information the controller decides, which coils to energize.
The schematic figure above shows, how the ECU controls task of energizing the coil. This task is known as commutation. Most often, a Hall-effect sensor is used for this purpose. The Hall-effect sensor is fitted on the back of the motor as shown in the picture below.
This is base information to show how BLDC motor works. This type of engine is tool and in order to have advantage from this tool you have to know basics how it works. All this information is only tip of the iceberg, however you can work with Miromax and we help you to achieve success in your project.
Information used from – www.learnengineering.org
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