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This presents a system that provides improved position feedback, but now requires the motor manufacturer to add both Hall sensors in the motor, along with an incremental encoder after assembly. To accomplish this, incremental encoders can be paired to the BLDC motor in addition to Hall effect sensors. In today's world, systems that require BLDC motors need far more precision in position measurement than ever before. Additionally, the controller only gets a partial picture of the motor's position from the Hall effect sensors, which can cause problems in systems where precise position feedback is required to operate properly. While the BOM cost of the Hall effect sensors is low, the cost of integrating these sensors into the BLDC can double the total cost of the motor. Unfortunately, there are some drawbacks to this method of position feedback. The three sensor outputs are commonly noted as U, V, and W channels. The Hall effect sensors are embedded into the stator of the motor to detect rotor position, which is used to switch the transistors in the 3-phase bridge to drive the motor. In a typical scenario, 3 sensors are required for 3-phase control. Hall effect sensors have been the popular choice for commutation feedback since the inception of the brushless motor. 6-step pattern for BLDC motor commutationįor the controller to commutate the motor effectively, it must always have accurate information on the position of the rotor. These 6 steps, or commutation phases, move an electromagnetic field which causes the permanent magnets of the rotor to move the motor shaft. Therefore, a motor controller is used to generate a 6-step commutation pattern on the 3 motor phases. Because the rotor of a BLDC motor is influenced by the revolving stator poles, the stator pole position must be tracked to effectively drive the 3 motor phases.
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The number of phases match the number of windings on the stator, while the rotor poles can be any number of pairs depending on the application. The most common configuration of BLDC motors is 3-phase. In this blog post we will review BLDC motor basics, look at common methods of commutating BLDC motors, and introduce a new solution for gathering position feedback.
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Brushed motors have physical brushes to achieve this process twice per rotation, while BLDC motors do not, and due to the nature of their design, they can have any number of pole pairs for commutation. Unlike their brushed relatives, BLDC motors rely on an external controller to achieve commutation, which is the process of switching current in the motor phases to generate motion. Brushless direct current electric motors, or BLDC motors, are electronically commutated motors powered by a dc electric source via an external motor controller.