Table of contents
5. Square wave control and vector control
6. Closed-loop control (position loop, speed loop, current loop)
7. Two types of motors commonly used in brushless motors
8. SPWM and SVPWM modulation methods
10. The general process and functions of FOC (vector control method)
1. Basic structure of motor
External structure diagram:
Internal structure map:
Stator : The fixed part of the motor (casing), composed of coils or magnets.
Rotor : The part of the motor that rotates.
Torque : When the stator is energized, the magnetic field generated interacts with the magnetic field of the rotor to generate torque, causing the rotor to rotate.
2. Brush and brushless
Brush : A brushed motor uses a mechanical structure of carbon brushes and collector rings . These carbon brushes are in contact with the brushes of the motor rotor, and the rotor rotates by continuously changing the polarity of the brushes.
Brushless : A brushless motor does not have carbon brushes and collector rings. It uses an electronic controller to control the permanent magnets on the rotor to realize the rotation of the rotor.
Summary : Brushed motor brushes are easily damaged and require maintenance. Therefore, brushless motors have a longer life and better performance than brushes, so the price of brushless motors is relatively more expensive .
3. DC and AC
| DC | comminicate | |
| direction | constant in direction | cyclical changes |
| production methods | Mostly battery (power supply) | Engine (with plug plugged into power supply) |
| distance | Suitable for long distance transmission | Suitable for short distance and distributed power transmission |
4. Feeling and non-feeling
Sensory: Generally there are sensors that measure the position of the motor (Hall and encoder, note: generally those with Hall are called non-inductive, and those with encoders are called servo)
Non-sensory: No sensor, relying on current to determine the motor position.
5. Square wave control and vector control
Disadvantages of square wave control:
(1): When the square wave is driven, the phase current of the motor has only two states of on and off. Even if the duty cycle is small and the average current is small, the pulsating peak current of the coil current will be very large. The square of the current is proportional, so when driven by a square wave, the system generates more heat and loses more.
(2): During square wave control, the magnetic field is not continuous but jumps, so it will cause torque pulsation. In situations where torque requirements are high, square wave drive is not suitable because it will cause the system to malfunction. stability, the control accuracy will be reduced accordingly.
(3): Since the pulsation of torque will cause vibration and noise in the system, the vibration will interfere with the stability of the system itself and degrade the performance of the onboard chip or sensor.
Advantages of square wave control:
The control algorithm is simple and the hardware cost is low. Currently, many products on the market still use square wave drive technology.
6. Closed-loop control (position loop, speed loop, current loop)
Mainly the PI control within the PID control.
In the non-inductive motor, the observer calculates the rotor position and the feedback speed; the feedback speed and the command speed are controlled by PI to calculate the command current; the command current and the phase current read by the ADC undergo a series of transformations to obtain the feedback current. Perform PI control and finally input three-phase voltage control PWM.
7. Two types of motors commonly used in brushless motors
BLDC (Brushless DC Motor) Square Wave Control
PMSM (permanent magnet synchronous motor) sine wave control
They are all DC motors.
8. SPWM and SVPWM modulation methods
What to prepare? Modulates the PWM input.
SPWM: sine wave modulation technology
SVPWM: space vector modulation technology
SPWM and SVPWM are both modulation techniques used to control AC motors, which can achieve precise control of the motor output voltage and frequency. Both can achieve frequency conversion speed regulation of the motor and improve the efficiency and control accuracy of the motor. Different control effects can be achieved by adjusting modulation parameters, such as adjusting output voltage, frequency and torque.
九、DI、DO、AI、AO
Dl: DigitalInput digital input
DO: DigitalOutput digital output
AI: AnalogInput analog input
AO:AnalogOutput analog output
10. The general process and functions of FOC (vector control method)
references:
[1] Zhiyuan/Zhang Jian. "In-depth understanding of brushless DC motor vector control technology". Science Press, 2020-8.