Reference:
Guoguo Junior: Detailed explanation of H-bridge motor drive circuit.
Equipment management and maintenance: Motor classification science worth reading
1. Classification of motors
2. Introduction to some motors
2.1 DC brush motor
Brushed DC (BDC for short), because of its simple structure, convenient operation, low cost, and good bias and speed control performance, it is widely used in various power devices, as small as toys and buttons. Adjustable car seats can be seen in production machinery such as printing machinery.
The electric energy of the DC power supply enters the armature winding through the brush and the commutator to generate armature current. The magnetic field generated by the armature current interacts with the main magnetic field to generate electromagnetic torque, which makes the motor rotate to drive the load.
Advantages: low price and convenient control.
Disadvantages: due to the existence of brushes and commutators, brushed motors have complex structure, poor reliability, many failures, large maintenance workload, short life, and commutation sparks are prone to electromagnetic interference.
2.2 Stepper motor
A stepper motor is an actuator that converts electrical pulses into angular displacement; more generally speaking: when the stepper driver receives a pulse signal, it drives the stepper motor to rotate a fixed angle in a set direction. We can control the angular displacement of the motor by controlling the number of pulses, so as to achieve the purpose of precise positioning; at the same time, we can also control the speed and acceleration of the motor rotation by controlling the pulse frequency to achieve the purpose of speed regulation.
Advantages: simple control, large low-speed torque, low cost;
disadvantages: stepper motors have no-load starting frequency, so stepper motors can run normally at low speeds, but they cannot start when they are higher than a certain speed, accompanied by sharp howling At the same time, the stepping motor is open-loop control, and the control accuracy and speed are not as high as the servo motor.
2.3 Servo motor
Servo motors are widely used in various control systems. They can convert the input voltage signal (or pulse number) into the mechanical output on the motor shaft and drag the controlled component to achieve the control purpose. The servo motor system is shown in the figure below. Generally, the torque is required to be controlled by the current output by the controller; the response of the motor should be fast, the volume should be small, and the control power should be small. Servo motors are mainly used in various motion control systems, especially servo systems.
Servo motors are divided into DC and AC. The earliest servo motors are general DC brushed motors. When the control accuracy is not high, general DC motors are used as servo motors. With the rapid development of permanent magnet synchronous motor technology, most of the servo motors refer to AC permanent magnet synchronous servo motors or DC brushless motors.
Advantages: It can control the speed and position accuracy very accurately, high efficiency and long life.
Disadvantages: The control is complicated and expensive, requiring professionals to control.
2.4 Brushless DC motor
Brushless DC motor [BLDCM] is developed on the basis of brushed DC motor, but its driving current is out-of-the-box AC. Generally, there are two types of brushless motor drive currents, one is trapezoidal wave (square wave), and the other is sine wave. The square wave drive is called brushless DC motor (BLDC); the sine wave drive It is called a permanent magnet synchronous motor (PMSM), which is actually a servo motor.
Brushless DC motors and servo motors have similar advantages and disadvantages. BLDC motors are cheaper than PMSM motors, and their drive control methods are simpler.
3. Introduction of motor drive circuit
3.1 DC motor drive design
DC motor rotation: power on the two wires of the motor, the motor can rotate, apply positive voltage, the motor rotates forward, and the opposite voltage, the motor reverses; the higher the voltage, the faster the motor rotates, the lower the voltage, and the lower the speed .
Generally, we can use STM32 microcontroller to easily adjust the motor speed, but the voltage and current of the IO interface of STM32 are generally very limited. The voltage is 3.3V and the current is 8mA. Therefore, in order to facilitate the control, it is necessary to add between the microcontroller and the motor. Drive circuit board, the motor drive board has two input lines: power input line and control signal input line. The power input line is generally required to provide a large current power supply that can provide the rated power of the motor. Generally speaking, what is the voltage and rated current required by the motor, then how much voltage and current should be provided to the motor drive board, which is to provide power to the motor origin of. The control signal line is connected with the signal line of the microcontroller, which is a method of realizing speed regulation, which is generally an adjustable square wave signal of PWM. The motor drive board also has an output line and two interfaces, which are directly connected to the pins of the DC motor. Note that the output line of the motor drive board here is output after a series of circuits, that is, the output line modulated by the input signal. Motor control must have a driver.
If you don't need forward and reverse rotation control (one-way rotation), you can use the following drive circuit to achieve one-way speed control of the motor.
The motor forward and reverse control circuit is shown in the figure below. Such a simple control switch state can control the direction of selection of the motor. As you can see from the figure below, its shape is similar to the letter "H", and the DC motor as the load is built on it like a "bridge"; so it is called "H-bridge drive". The position of the 4 switches is called the "bridge arm". There are triodes and MOS tubes that can be used as electronic switches in the circuit. These two devices can be used instead of switches to achieve this.
- When switches A and D are closed, and B and C are open, the DC motor rotates normally, and the rotation direction is recorded as the positive direction.
- When switches B and C are closed, and A and D are disconnected, the DC motor rotates normally, and the rotation direction is recorded as the opposite direction.
- The DC motor does not rotate when switches A and C are closed, B and D are opened, or when switches B and D are closed, and A and C are opened. At this time, it can be considered that the motor is in the "brake" state, and the electric potential generated by the motor's inertial rotation will be short-circuited, forming a back EMF that hinders the movement, forming a "brake" effect.
- When switches A and B are closed or when switches C and D are closed, the power supply will be directly short-circuited, which will burn the power supply. This situation is strictly prohibited.
- When the four switches A, B, C, and D are all off, it is considered that the motor is in a "idling" state, and the electric potential generated by the inertia of the motor will not be able to form a circuit, so there will be no back EMF that hinders movement, and the motor will Inertia rotation for a long time.