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PMBLDC motors

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Citharthan Durairaj

1) The document discusses permanent magnet brushless DC (PMBLDC) motors and their control. It explains that the desired current waveform for each phase must be estimated based on the instantaneous rotor position to satisfy the maximum torque at minimum current principle. 2) The desired current is provided to the phases through driver circuits containing six transistors, which are switched on based on whether the desired current is positive or negative. 3) Rotor position is typically sensed using three Hall sensors spaced 120 degrees apart, though sensorless control is also possible using back EMF measurements. Control circuit design and operation are also briefly outlined.

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PMBLDC MOTORS D.Citharthan Assistant Professor EEE Department, CKEC Coimbatore
1) We need to estimate the desired current waveform on each phase for the instantaneous rotor position (we need to find!!!) of the PMBLDC motor such that the desired current should satisfy Maximum torque at minimum current (MTMC) principle. 2) The desired current waveform should be given to the phases through the drivers. Drivers are usually build up of six transistors(T1 to T6). Based on the desired current (Positive / Negative) on the phases we will switch on the transistors T1 to T6. 3) Usually the rotor position will be sensed by 3 HALL sensors displaced by 120 degree. This type of control is called sensor control . If we measure the rotor position by the measuring the Back EMF induced in the stator winding we don’t need any Hall sensors . This type of control is called sensorless control. Steps to be followed to control the PMBLDC motor
Control circuit of PMBLDC motors
The circuit was designed by PSIM software. Position feedback takes care of Field Oriented Control (FOC) (i.e, maintaining 90 degree angle between rotor magnetic field and stator magnetic field) by switching appropriate transistors. Speed feedback is used to maintain the speed of the motor as per the reference speed given.
PMBLDC motors
PRINCIPLE OF OPERATION Driver Circuit Hall sensor signals(based on rotor position)
PMBLDC motors
PMBLDC motors

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PMBLDC motors

  • 2. 1) We need to estimate the desired current waveform on each phase for the instantaneous rotor position (we need to find!!!) of the PMBLDC motor such that the desired current should satisfy Maximum torque at minimum current (MTMC) principle. 2) The desired current waveform should be given to the phases through the drivers. Drivers are usually build up of six transistors(T1 to T6). Based on the desired current (Positive / Negative) on the phases we will switch on the transistors T1 to T6. 3) Usually the rotor position will be sensed by 3 HALL sensors displaced by 120 degree. This type of control is called sensor control . If we measure the rotor position by the measuring the Back EMF induced in the stator winding we don’t need any Hall sensors . This type of control is called sensorless control. Steps to be followed to control the PMBLDC motor
  • 3. Control circuit of PMBLDC motors
  • 4. The circuit was designed by PSIM software. Position feedback takes care of Field Oriented Control (FOC) (i.e, maintaining 90 degree angle between rotor magnetic field and stator magnetic field) by switching appropriate transistors. Speed feedback is used to maintain the speed of the motor as per the reference speed given.
  • 6. PRINCIPLE OF OPERATION Driver Circuit Hall sensor signals(based on rotor position)