QSPICE Schematic Capture “Discrete-Time PI Controller Written in C++"

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Today’s featured design comes from Sandaru Imesh, an electrical engineering undergraduate at the University of Moratuwa in Sri Lanka.

This project demonstrates a digitally controlled buck converter where the traditional analog feedback loop has been replaced with a discrete-time PI controller written in C++. Along the way, Sandaru tackled real-world simulation challenges including variable time-step behavior, integral windup, startup transients, and maintaining continuous conduction mode (CCM).

The result is a controller that automatically adjusts duty cycle to maintain a regulated 12 V output even as the input voltage changes—a great example of using QSPICE to develop and validate digital control algorithms alongside power electronics.

Please send any submissions to me at tim.mccune@qorvo.com (Schematic Capture Post #090)

Screenshot (104)
Screenshot (104)1920×1129 249 KB

buck_conv_pwm.cpp (1.3 KB)
Closed loop control with the gate driver.qsch (31.8 KB)

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Well… I am not entirely sure it is a discrete-time controller, as the math samples at every simulation step.
Here is a discrete-time PID controller project for reference:
https://forum.qorvo.com/t/c-pid-controller-for-qspice-community-project/15690

Regardless of what it is, here are two modifications to the code for a more standard approach when working with Qspice C++:

  1. Change the static variables to member variables (to handle things better if, in the future, you need to include Trunc() for timestep modification).
  2. Make Kp and Ki input attributes instead of hardcoding them into the code.

Closed loop control with the gate driver.qsch (31.9 KB)
buck_conv_pwm.cpp (4.3 KB)

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