dc motor controller will produce a constant torque under rated load performance, due to the armature magnetic field between the rotor magnetic field and constant maintain 90 degrees, so it must be through the carbon brush and commutator, in the process of the functioning of the motor controller is likely to cause a spark damage to components. Ac motor controller without carbon brush and commutator, so don't need the corresponding maintenance, but the performance is better than the performance of dc motor controller control effect is much more complicated. Semiconductor switching frequency is more rapid, so can have obvious ascending to the performance of the drive motor controller, microprocessor is becoming more and more fast, ensure the ac motor controller to control, to achieve a proper control in the two weeks, right Angle coordinate system, due to many other microprocessor to control the motor controller has the necessary function, so the volume is more and more small. Position sensor in brushless dc motor plays a role that can locate the position of the rotor magnetic pole, to provide the correct logical switch circuit in the phase information, the rotor magnetic pole position signal into electrical signal, and then to control the phase of the stator winding. Position sensor sort is more, and each has its characteristics. Common in brushless dc motor position sensor has the following kinds: electromagnetic position sensors, photoelectric sensors, magnetic susceptibility type location close to the sensor. Electromagnetic position sensor in brushless dc motor, use morer is open the transformer. Used for three-phase brushless dc motor tracking open transformer by the stator and rotor of two parts. Stator generally there are six pole, the interval between them is 60 degrees respectively, three of them in a winding around, and in series with high frequency power supply, after another three pole respectively on secondary winding around the WA, WB, WC. Among them are 120 degrees apart, respectively. Tracking the rotor is a cylinder made of non magnetic materials, and with a 120 - degree on it sector magnetic materials. It is combined with motor shaft when installation, the position corresponding to a pole. High frequency produced by a winding on the rotor flux by tracking to this material coupling to the secondary winding, therefore, the induced voltage in the secondary winding, the secondary winding and the other two phase because of no coupling loop winding is connected the same time, the induced voltage to near zero. With the rotation of the motor rotor, the segment also spins, from the current coupling and a winding down a winding near at a time. In this way, as the motor rotor movement, in the opening on the transformer secondary winding induction voltage respectively. The fan of permeability generally slightly larger than 120 KWH, often USES about 130 KWH Angle. In a three-phase control circuit, in order to meet the demands of commutation decoder, fan permeability Angle of the Angle of 180 degrees of electricity. At the same time, the number of fan permeability piece should be very equal logarithm with brushless dc motor.
