A Brushless Direct Current (BLDC) motor comprises three essential elements: a wound stator, a permanent magnet rotor assembly, and rotor position sensing devices that can be integrated internally or mounted externally. These position sensors deliver real-time feedback that allows for precise adjustment of both the frequency and amplitude of the stator voltage reference, providing smooth torque generation and continuous rotor rotation.
The motor's architecture, featuring a permanent magnet rotor core surrounded by external stator windings, provides multiple performance advantages:
Low rotor inertia for improved dynamic response
Great heat dissipation through efficient thermal pathways
Compact design enabling reduced overall motor dimensions
BLDC motors can exhibit either trapezoidal or sinusoidal Back Electromotive Force (BEMF) characteristics. This document specifically addresses motor control implementation for BLDC motors with sinusoidal BEMF waveforms (1). Follow the motor control principles below:
- Synchronous motor construction: Permanent magnets are rigidly fixed to the rotating axis to create a constant rotor flux. This rotor flux usually has a constant magnitude. The stator windings when energized create a rotating electromagnetic field. To control the rotating magnetic field, it is necessary to control the stator currents.
- The actual structure of the rotor varies depending on the power range and rated speed of the machine. Permanent magnets are suitable for synchronous machines ranging up-to a few Kilowatts. For higher power ratings the rotor usually consists of windings in which a DC current circulates. The mechanical structure of the rotor is designed for number of poles desired, and the desired flux gradients desired.
- The interaction between the stator and rotor fluxes produces a torque. Since the stator is firmly mounted to the frame, and the rotor is free to rotate, the rotor will rotate, producing a useful mechanical output as shown in Figure 2-1.
- The angle between the rotor magnetic field and stator field must be carefully controlled to produce maximum torque and achieve high electromechanical conversion efficiency. For this purpose a fine tuning is needed after closing the speed loop using sensorless algorithm to draw minimum amount of current under the same speed and torque conditions.
- The rotating stator field must rotate at the same frequency as the rotor permanent magnetic field; otherwise the rotor will experience rapidly alternating positive and negative torque. This will result in less than optimal torque production, and excessive mechanical vibration, noise, and mechanical stresses on the machine parts. In addition, if the rotor inertia prevents the rotor from being able to respond to these oscillations, the rotor will stop rotating at the synchronous frequency, and respond to the average torque as seen by the stationary rotor: Zero. This means that the machine experiences a phenomenon known as pull-out. This is also the reason why the synchronous machine is not self starting.
- The angle between the rotor field and the stator field must be equal to 90ÂșC to obtain the highest mutual torque production. This synchronization requires knowing the rotor position to generate the right stator field.
- The stator magnetic field can be made to have any direction and magnitude by combining the contribution of different stator phases to produce the resulting stator flux.
- Includes library overview, software setup, hardware setup, and more. BLDC motors with a sinusoidal BEMF waveform are also commonly referred to as Permanent Magnet Synchronous (PMSM) motors.