| Mathematics of Electronic Motor Control |
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Multi-phase motor basics Brushless DC motors are generally, although not always, three phase devices. They are wired in either a Wye or Delta configuration, but in either case there are three connecting wires, and the current input to any two coils must be output through the third. That is, C = –(A + B) where A, B, and C are the current flowing through each leg of the 3-phase brushless motor. The three coils generate the magnetic field of the stator (the non-rotating outer portion of the motor), while the rotor magnetic field is created by permanent magnets. This is why this motor is also frequently referred to as a brushless PM motor.  Three-phase brushless DC motor Figure 1 shows two kinds of force that are generated by the magnetic field interactions. They are known as the Q (quadrature) force and the D (direct) force. An ideal controller for a brushless DC motor will maximize Q force generation, which is oriented exactly 90 degrees from the N-S axis of the rotor, and minimize the D force, which is aligned with the rotor’s NS axis, and therefore creates no useful torque. |
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