Commissioning PI Control – Integrating Process

When the control objective is to maintain the controlled parameter of an integrating process at setpoint under all operating conditions, then using PI (proportional-integral or proportional plus reset) controller, it is possible to automatically compensate for changes in disturbance inputs and maintain the controlled parameter at setpoint. However, the application of PI control to an integrating process can be quite challenging. Boiler drum level control, illustrated below, is an example of an integrating processes where the control objective is to maintain the level at setpoint.

At key factor in commissioning PI control of an integrating process is to correctly determine the reset that is applied. Once the reset is established then the proportional gain can be adjusted to achieve the desired response.

When working with an integrating process, IMC and Lambda tuning rules agree on the setting of the reset:

As discussed in Chapter 4 of Advanced Control Foundation – Tools, Techniques, and Applications, Model based tuning using the IMC or Lambda rules has some advantages over other tuning rules such as the SIMC method for the tuning of an integrating process.

If you would like to gain experience tuning PI control of an integrating process, then I would encourage you to explore the three element drum level control workshop that is contain on the web site for Control Loop Foundation – Batch and Continuous process. A YouTube video showing the workshop solution can be accessed by selection the Solution tab.