[The 13th Electronic Design Competition of Wuhan University of Technology] DC Motor Control System

First Prize of the 13th Electronic Design Competition of Wuhan University of Technology

Team: Tossing Team

Members: Xu Shikang, Zhang Yuzhen, Li Bingyin

Instructor: Zhang Jialiang

Competition topic: DC motor control system

1. Overall system plan

The main system is a motor control system, which consists of six parts: STM32F407 microcontroller, boost module, auxiliary power module, motor drive module, current detection module, and encoder. The motor's rotational angular displacement and armature current are sent to the microcontroller through the encoder and current detection module. Then the microcontroller performs PID control operations and outputs PWM signals to the motor drive module. The motor drive module controls the motor input voltage and then controls the motor rotation.

The auxiliary measurement system is mainly composed of STM32F407 microcontroller, OLED module, HC-05 Bluetooth module, encoder, etc. It mainly completes the measurement and display functions of speed and distance.

The structural block diagram of the system is shown in Figure 1:

Figure 1 Overall framework diagram of the system

2. Hardware circuit

1. Motor drive design

The rated input voltage of the motor drive circuit is 6-28V, and there is a total of 660uF power filter electrolytic capacitor on the board. The BTN7971B driver chip used at the same time has a peak current of 90A below 85 degrees Celsius and a pulse width of 10ms, which can meet the requirements of the 775 motor used in the experiment. Large starting current requirements.

2. Auxiliary power supply design

The auxiliary power supply uses the LM317 chip, which has the advantages of wide voltage regulation range, good voltage stabilization performance, low noise, and high ripple suppression ratio. Since it mainly supplies power to the microcontroller, the output voltage is set to 5V. Taking into account the current of some circuits such as encoders, If the detection module has a non-5V power supply, adjust it with an adjustable resistor. It can output a relatively stable voltage of 5V, and after debugging and testing, it can stably change between 1.5-5.5V to meet the power supply needs of various sensors in the system.

3.DC-DC boost circuit design

Connect a stable DC voltage of 12V to the boost chopper circuit. When the control signal is high level, the switch Q1 is turned on, the DC power supply provides current to the inductor, and the energy is stored in the inductor L. When the control signal is low level, the switch Q1 is turned off and Q2 is turned on. At this time, the energy stored in the inductor charges the capacitor C through Q2 and is provided to the load at the same time. Therefore, by adjusting the PWM duty cycle to change the switching tube opening and closing time, the output voltage is adjusted to 15V.

3. Software program design

The motor control system uses STM32F407 as the main control chip of this system, which mainly completes mode selection, current signal and speed signal processing, and PID control. The auxiliary measurement system uses STM32F407 as the main control chip, which mainly completes the measurement and display of speed and distance, and will instantaneously The measurement results are transmitted to the PC through the HC-05 Bluetooth module for verification. When actually monitoring the motor current, the current sampling value is often mixed with interference noise. For example, the current mutation during the turn-on and cut-off process of the power tube will produce harmonic interference and spike interference. In order to accurately measure the current value, filtering must be performed to weaken or eliminate interference. Periodic power frequency or high-frequency interference can be suppressed by adding RC low-pass filter hardware to the circuit. For low-frequency periodic interference and random interference, digital filtering must be used to solve it. It is planned to use the sliding average filtering method to filter the A/D sampling values, which can effectively suppress periodic interference and improve the smoothness of the current sampling values.