What are the methods of starting a brushless DC motor without Hall?

There are various ways to start a brushless DC motor without Hall, the following four are common, today we will introduce them to you
1. Externally synchronous three-stage open-loop starting method
The three-stage starting method consists of a rotor preposition, an external synchronous acceleration and a self-synchronous phase. First, two phases of the stator are conducted arbitrarily with the other phase disconnected, followed by two pre-positioned motors to reach the desired position. The next step is the external synchronization of the rotor; after that, the motor speed switches to self-synchronization, which allows to determine the position of the motor rotor.

2. Pre-positioned starting method
When the motor is first started, the stator is given a specific energized state, causing the rotor to rotate to a specific initial position. The energized state of the motor is then changed, causing the rotor to rotate to a different specific position due to the electromagnetic torque. The motor is then switched to brushless motor operation while the rotor is rotating and the rotor position is detected using the counter-electromotive force method.
3. Upsampled frequency and voltage synchronous starting method
This technique relies on inverter starting of synchronous motors, with the DSP's own event manager generating PWM waveforms to control the inverter as the motor begins to synchronize while the commutation frequency of the inverter slowly increases and causes the stator voltage of the DC brushless motor to start small and gradually increase, allowing the motor rotor speed to gradually increase so that the DC brushless motor can achieve permanent magnet-like performance.

4. Short-time detection pulse rotor positioning starting method
The short-time detection pulse rotor positioning start method is based on the effect of the permanent magnet rotor on the stator winding with the iron core, magnetizing and demagnetizing it and increasing or decreasing the inductance of the stator winding. The implementation of this method can be broken down into three processes: pre-positioning, acceleration and switching, but it differs from the pre-positioning and acceleration methods described above.
These are the four starting methods of Hall-less DC brushless motor, more related information welcome to consult us at any time