How to Tune a Digital PID Controller for Buck Converter with STM32F4

Introduction

In this tutorial, we will guide you through the process of implementing and tuning a digital PID controller for a buck converter using the STM32F4 microcontroller. We will leverage the TIM (Timer) and ADC (Analog to Digital Converter) peripherals to achieve optimal transient response. By following these steps, you’ll be able to effectively manage the output voltage of the buck converter in real-time.

Prerequisites

• Basic understanding of PID control theory
• Familiarity with STM32F4 microcontroller programming
• Installed STM32 development environment (e.g., STM32CubeIDE)
• Knowledge of buck converter operation
• Access to an oscilloscope for testing

Parts/Tools

• STM32F4 development board
• Buck converter circuit
• Power supply
• Oscilloscope
• Connecting wires
• Optional: Load resistor for testing

Steps

1. Set Up the Buck Converter
   • Connect the buck converter circuit to the STM32F4 board.
   • Ensure the power supply is connected to the buck converter input.
   • Connect the output of the buck converter to the load resistor (if used).
2. Configure the STM32F4 TIM and ADC
   • Open STM32CubeIDE and create a new project for your STM32F4 device.
   • Enable TIM and ADC in the CubeMX configuration.
   • Set the TIM to generate PWM signals for the buck converter.
   • Configure the ADC to sample the output voltage of the buck converter.
3. Write the PID Control Algorithm

   Implement the PID control algorithm in your main program file.

   
   float Kp = 1.0; // Proportional gain
   float Ki = 0.1; // Integral gain
   float Kd = 0.01; // Derivative gain
   float setpoint = 5.0; // Desired output voltage
   float input, output;
   float integral = 0.0;
   float lastError = 0.0;
   
   void PID_Controller() {
       float error = setpoint - input;
       integral += error;
       float derivative = error - lastError;
       output = Kp * error + Ki * integral + Kd * derivative;
       lastError = error;
   
       // Set PWM duty cycle based on output
       __HAL_TIM_SET_COMPARE(&htim, TIM_CHANNEL_1, output);
   }
           

4. Implement the Main Loop

   In the main loop, call the PID controller and read the ADC values.

   
   while (1) {
       HAL_ADC_Start(&hadc);
       HAL_ADC_PollForConversion(&hadc, HAL_MAX_DELAY);
       input = HAL_ADC_GetValue(&hadc) * (3.3 / 4096); // Assuming 12-bit ADC
       PID_Controller();
   }
           

5. Tune the PID Parameters

   Adjust the PID parameters (Kp, Ki, Kd) for optimal response.

   • Start with Kp and gradually increase until the system responds quickly.
   • Add Ki to eliminate steady-state error, but be cautious of overshoot.
   • Adjust Kd to dampen the response and reduce oscillations.

Troubleshooting

• Output Voltage Not Stable:

  Check the PID tuning parameters. Ensure you have properly set the gains.

• ADC Values Incorrect:

  Verify the ADC configuration and connections. Make sure the ADC is correctly sampling the output voltage.

• PWM Signal Not Generated:

  Check the TIM configuration and ensure the PWM is correctly set up and enabled.

Conclusion

By following this tutorial, you have implemented a digital PID controller for a buck converter using the STM32F4 microcontroller. You have configured the necessary peripherals, written the control algorithm, and tuned the controller for optimal performance. With this knowledge, you can further explore advanced control techniques and improve your power management systems.