Control mode of 120 DC brushless motor and stepping motor
China's motor control application is maturing day by day, and MCU products specially oriented to the Chinese market are needed to cope with it, which can realize high processing performance through the lowest power consumption, enhanced computing power and peripheral equipment functions. . . . . .
Under the dual pressure of energy shortage and strict environmental protection requirements, higher energy efficiency, better dynamic performance and lower operating noise have become the inevitable trend of motor drive design.
Therefore, from the traditional AC motor design to the brushless DC motor (BLDC)/Stepping motor (SM)
, Is also becoming a hot spot for motor control application designers. 120 °
As we all know, the control mode of DC brushless motor and stepping motor is 120 degrees between the three hall sensors.
Each hall signal is switched according to the direction of the rotating magnetic pole.
According to the state of the three hall signals, it can be at every 60(There are 6 modes per cycle)Get the location information once.
If the conduction mode of each phase changes and switches according to this timing, the rotating magnetic flux will be generated as shown in the following figure, thus the rotor will obtain torque and rotate.
Fig. 1 six conduction modes and rotor position range, calculation of motor rotation speed, are calculated from the current timer count value and 2 & pi; [rad]The difference between the previous timer count values is obtained.
The timer count value is obtained through an external interrupt triggered by a hall signal, during which the timer TAU is always counting freely.
This speed measurement method is also applicable even if there are position deviations in the three hall sensors.
In order to start the motor and obtain the position information of the rotor, it is necessary to provide a 60The startup sequence.
This triggers the external interruption corresponding to the Hall signal and continuously performs commutation control, thus allowing the motor to rotate. And at any time (n)
The adjustment value of duty cycle is calculated by the following formula, thus realizing the adjustment of motor rotation speed.
Stepping motor is an open-loop control motor that converts electrical pulse signals into angular displacement or linear displacement.
Under the condition of non-overload, the rotation speed and stop position of the motor only depend on the frequency and number of pulses of the pulse signal and are not affected by load changes.
When the stepping driver receives a pulse signal, it drives the stepping motor to rotate at a fixed angle in the set direction, which is called'Step angle'
Its rotation runs step by step at a fixed angle.
The angular displacement can be controlled by controlling the number of pulses, so as to achieve the purpose of accurate positioning, and the speed and acceleration of motor rotation can also be controlled by controlling the pulse frequency, thus achieving the purpose of speed regulation.
Fig. 2 stepping motor principle tag dc brushless motor