Simulink Control Design™ - MathWorks

Design PID Controller Using Plant Frequency Response

Near Bandwidth

This example shows one of several ways to tune a PID controller for plants that cannot be

linearized. In this example, you use the Frequency Response Based PID Tuner to

automatically characterize the frequency response of a buck converter around the control

bandwidth, and then tune the PID controller.

Buck Converter Model

Buck converters convert DC to DC. The model in this example uses a switching power

supply to convert a 30V DC supply into a regulated DC supply. The converter is modeled

using MOSFETs rather than ideal switches to ensure that device on-resistances are

correctly represented. The converter response from reference voltage to measured

voltage includes the MOSFET switches. Traditional PID design requires a linear model of

the system from "the reference voltage" (controller output) to measured voltage. Here,

however, because of the switches, automated linearization results in a zero system. When

a model linearizes to zero, several alternatives are available:

• Re-linearize the system. Linearize the model at a different operating point or
  simulation snapshot time.


• Identify a new plant. Use measured or simulated data to identify a plant model
  (requires System Identification Toolbox).


• Frequency response based tuning. Use simulated data to obtain the frequency
  response for the plant.

For this example, use the Frequency Response Based PID Tuner to estimate the

frequency responses of the system and tune the PID controller. For an example that uses

system identification to identify a plant model, see “Design PID Controller Using

Simulated I/O Data”.

For more information on creating a buck converter model, see “Buck Converter”

(Simscape Electrical).

open_system('scdbuckconverter')

7 PID Controller Tuning