bldc motor is controlled by a variety of different control algorithms. Usually, the voltage of an electric motor is controlled by a power transistor as a linear voltage regulator. This is not realistic when driving high power motors. High power motors must be controlled by PWM, and the microcontroller needs to start and control functions.
Control algorithms must provide three things:
PWM voltage controlled motor speed
Mechanism of commutating motor
Methods using backward EMF or Holzer sensor to estimate rotor position.
Pulse width modulation is used to apply variable voltage to motor windings. The effective voltage is proportional to the duty cycle of PWM. When the commutation is suitable, the torque speed characteristic of bldc motor is the same as that of DC motor. Variable voltage can be used to control motor speed and available torque.
Trapezoidal commutation of bldc motor
One of the simplest control methods of DC brushless motors is the so-called trapezoidal commutation.
In this scheme, the current is controlled one-to-one at a time through the motor terminal, and the third motor terminal is always disconnected from the power supply.
The commutation of the power transistor provides energy for the appropriate windings in the stator to provide the optimal torque generation according to the rotor position. In bldc motor, the single chip microcomputer must know the rotor position and commutate at the appropriate time.