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“ Minimization and Enhancement of BLDC actuators for applications on Mechanical Systems by implementing Mechanical Field Weakening method ”
Magnetic Field Guidance
Halbach Array
Halbach array is to be applied to the rotor (magnet) design. Using this array, we can confine the magnetic flux to the center of the motor, which will increase the efficiency of the motor and smaller magnets can be used to achieve the same performance compared to the normal array rotor design.
Rotor Types
For about BLDC motor, there are two different construction types.
1) Inrunner type : rotor[magnets] – inside / stator[coils] – outside
2) Outrunner type : rotor[magnets] – outside / stator[coils] – inside
Because inrunner type rotor has small radius than outrunner type, inrunner makes faster RPM, out runner makes more torque. For BLDC motor, heat must be dissipated through the center of the motor. Inrunner type has outside stator which is waste heat generator, so it is more efficient. And about the velocity constant Kv, inrunner has higher Kv than outrunner. Lastly, to make same specification, inrunner has small diameter and long length, outrunner has long diameter and small length.
We chose outrunner type because by applying field weakening, we can increase RPM but torque decreases (trade-off relation). To make enough torque after field weakening effect is applied, we need enough torque. Torque decrease can be compensated by two characteristic of outrunner type.
1) Electrical gearing effect of outrunner type ( No transmission needed )
2) Max torque trait
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