Mechatronics | PartQuest™ Explore

This example shows a motor speed control loop that uses a PID control strategy (Proportional, Integral and Derivative), with continuous function blocks representing the controller up to the ideal voltage motor drive.

The parameter values of the generic DC motor model were calibrated to represent an FRC - First Robotics Competition CIM Motor, as described in the article “<a href="https://www.systemvision.com/blog/first-robotics-frc-motor-modeling-may-6-2016">First Robotics (FRC) Motor Modeling</a>”. The voltage drive, the motor and the mechanical fan load were “assembled” using a conservation-based modeling approach. This approach to system modeling is much like assembling a hardware prototype, and does not require the user to develop an analytical model of the “plant” being controlled. Both the static and dynamic system characteristics “emerge” naturally from the model, simply because they are connected on the schematic. Additional electrical circuit components, mechanical loads and other “physical” elements can easily be added by simply placing them on the schematic and “wiring” them together. In fact, a more detailed implementation of the motor drive is shown in the companion example, “<a href="https://www.systemvision.com/groups/mikedonnellys-workspace/designs/pid-speed-control-loop-switching">PID Speed Control Loop – Switching</a>”. In that example, a design for the logic and power electronics needed to implement a PWM-based, switched MOSFET H-bridge drive is included.

Because this version simulates very quickly compared to the switching version, it is well suited for early validation of the control strategy and PID tuning, as well as loop stability and frequency response analysis. Note that the P, I and D "gains" for this nominal design were computed using the <a href="https://en.wikipedia.org/wiki/Ziegler%E2%80%93Nichols_method">Ziegler-Nichols</a> classic PID tuning method.

Another version of this design, which simulates quickly but includes the important and practical aspect of a limited drive voltage range, is show in “<a href="https://www.systemvision.com/groups/mikedonnellys-workspace/designs/pid-speed-control-loop-continuous-and-limited">PID Speed Control Loop – Continuous and Limited</a>”. It is instructive to compare the speed step response between that design and this one.

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