How to Implement and Tune a PID Controller for Buck Converter with STM32

Implementing and Tuning a PID Controller for a Buck Converter using STM32

In this tutorial, we will walk through the process of implementing and tuning a PID (Proportional, Integral, Derivative) controller for a buck converter with a 100kHz switching frequency using STM32’s TIM peripherals. This guide covers the necessary prerequisites, required components, and step-by-step instructions to successfully implement the PID controller.

Prerequisites

• Basic understanding of control theory and PID controllers
• Familiarity with STM32 microcontrollers and their programming
• Knowledge of buck converter operation
• STM32 development environment set up (e.g., STM32CubeIDE)

Parts/Tools

• STM32 microcontroller (e.g., STM32F4 series)
• Buck converter circuit
• Oscilloscope for monitoring output voltage
• Multimeter for measuring current and voltage
• Power supply

Steps

1. Set Up Your Development Environment
   1. Install STM32CubeIDE from the STMicroelectronics website.
   2. Create a new project for your specific STM32 microcontroller.
2. Configure TIM Peripheral
   1. Open STM32CubeMX and select the TIM peripheral.
   2. Set the timer frequency to 100kHz.
   3. Configure the PWM output for the buck converter.
   4. Generate the code and open it in STM32CubeIDE.
3. Implement PID Controller
   1. Define the PID parameters in your project:

   
   #define KP 1.0  // Proportional gain
   #define KI 0.5  // Integral gain
   #define KD 0.1  // Derivative gain
               

   2. Create a PID control function:

   
   float PID_Controller(float setpoint, float measured_value) {
       static float integral = 0;
       static float previous_error = 0;
       
       float error = setpoint - measured_value;
       integral += error;
       float derivative = error - previous_error;
       previous_error = error;
   
       return (KP * error) + (KI * integral) + (KD * derivative);
   }
               

4. Read Feedback from the Buck Converter
   1. Use ADC to read the output voltage of the buck converter:

   
   float Read_Voltage() {
       // Code to read voltage via ADC
       return measured_voltage;
   }
               

5. Control the PWM Output
   1. In your main loop, implement the PID controller:

   
   void loop() {
       float setpoint = 5.0; // Desired output voltage
       float measured_value = Read_Voltage();
       float control_value = PID_Controller(setpoint, measured_value);
       
       // Update PWM duty cycle based on control_value
       __HAL_TIM_SET_COMPARE(&htim2, TIM_CHANNEL_1, control_value);
   }
               

6. Tuning the PID Controller
   1. Start with KP and set KI and KD to zero.
   2. Gradually increase KP until the system oscillates.
   3. Increase KI to eliminate steady-state error.
   4. Adjust KD to reduce overshoot and improve stability.

Troubleshooting

• Output Voltage is Too High/Low:
  • Check the feedback voltage reading from the ADC.
  • Verify that the PID parameters are set correctly.
• System is Oscillating:
  • Reduce the KP value if oscillations are present.
  • Increase the KD value to dampen oscillations.
• PID Controller is Unresponsive:
  • Ensure that the control loop is executing at the correct frequency.
  • Check the connections in the buck converter circuit.

Conclusion

Implementing and tuning a PID controller for a buck converter using STM32 can greatly enhance the performance and stability of your power supply design. By following the steps outlined in this tutorial, you should be able to effectively manage the output voltage of your buck converter. Remember to carefully tune your PID parameters for optimal results, and always validate your setup with proper testing equipment.