Digital Representations of Analog Systems for Control System Applications

Digital controllers can be created from an analog (or continuous) model. This is especially useful when a processor is used to control an analog system or to implement a filter. Peter Way, the author of a new whitepaper tried several approaches and two were selected for excellent results: Tustin's Method and Hold Equivalence. In the paper, these are evaluated to show how they compare with an analog system.

10/29/2009


The full article is available as a downloadable PDF.

Digital Representations of Analog Systems for Control System Applications by Peter Way

 

Digital controllers can be created from an analog (or continuous) model. This is especially useful when a processor is used to control an analog system or to implement a filter. Peter Way, the author of a new whitepaper tried several approaches and two were selected for excellent results: Tustin's Method and Hold Equivalence. In the paper, these are evaluated to show how they compare with an analog system. Some methods are algebra-intensive and now much easier to implement with symbolic math tools.

Way says there are two main options for designing a digital controller:
Method 1: Design an analog controller. Then convert it to digital form including the effects of sampling the analog plant and holding the output at the DAC. This approach is most intuitive for the designer since you are working in the familiar s-domain (Laplace domain).

Method 2: Convert the Plant, DAC/ZOH and ADC to digital form. Then design a digital controller to meet performance requirements. This model is not as intuitive, since the dynamic specifications for the system need to be defined in the discrete domain (z-domain). It does have the advantage of handling plants with delays easily.

Way assumes Method 1 for his paper and says, "You may have done a compensator design, either as a PID or a more sophisticated one. Since compensators are essentially filters, the discussion will show how to convert an example analog filter to a digital one. Then the whole system can be simulated to show differences between the digital and continuous systems."

- Edited by Renee Robbins, senior editor
Control Engineering News Desk





No comments
The Engineers' Choice Awards highlight some of the best new control, instrumentation and automation products as chosen by...
The System Integrator Giants program lists the top 100 system integrators among companies listed in CFE Media's Global System Integrator Database.
The Engineering Leaders Under 40 program identifies and gives recognition to young engineers who...
This eGuide illustrates solutions, applications and benefits of machine vision systems.
Learn how to increase device reliability in harsh environments and decrease unplanned system downtime.
This eGuide contains a series of articles and videos that considers theoretical and practical; immediate needs and a look into the future.
Big Data and IIoT value; Monitoring Big Data; Robotics safety standards and programming; Learning about PID
Motor specification guidelines; Understanding multivariable control; Improving a safety instrumented system; 2017 Engineers' Choice Award Winners
Selecting the best controller from several viewpoints; System integrator advice for the IIoT; TSN and real-time Ethernet; Questions to ask when selecting a VFD; Action items for an aging PLC/DCS
This digital report will explore several aspects of how IIoT will transform manufacturing in the coming years.
Motion control advances and solutions can help with machine control, automated control on assembly lines, integration of robotics and automation, and machine safety.
This article collection contains several articles on the Industrial Internet of Things (IIoT) and how it is transforming manufacturing.

Find and connect with the most suitable service provider for your unique application. Start searching the Global System Integrator Database Now!

Future of oil and gas projects; Reservoir models; The importance of SCADA to oil and gas
Big Data and bigger solutions; Tablet technologies; SCADA developments
SCADA at the junction, Managing risk through maintenance, Moving at the speed of data
Automation Engineer; Wood Group
System Integrator; Cross Integrated Systems Group
Jose S. Vasquez, Jr.
Fire & Life Safety Engineer; Technip USA Inc.
click me