Event-Based Control in a Wireless World

The First International Conference on Event-Based Control, Communication, and Signal Processing was held June 17-19, 2015 in Krakow, Poland and took place on the campus of AGH University of Science and Technology. Some of the world leaders in Event-Based Control attended and talked in the conference. From the US, Professor Cassandras, Boston University, Professor Tsividis, University of Minnesota, Professor Antsaklis, University of Notre Dame, and Professor Baras, University of Maryland, were keynote and plenary speakers.

Emerson’s Terry Blevins presented two industry talks. He presented the first, Industrial Advances in Wireless and Event Driven Control, to the entire conference. His presentation addressed:

Emerson's Terry Blevins


Click to enlarge

Click to enlarge

…how the traditional PID positional and velocity algorithms may be restructured as PIDPlus to use the slow, non-periodic measurement updates of a wireless transmitter. A combination of event triggered and periodic execution is used to address control of faster processes such as liquid and gas flow using wireless transmitters and wireless valves. Examples are used to demonstrate how this capability has been incorporated into commercial control systems.

Terry shared how control performance was achieved in field applications using wireless transmitters and/or wireless throttling valves. He also provided future areas of event driven control in the process industry, in particular model predictive control (MPC) using wireless measurements.

Terry teamed with Emerson’s Willy Wojsznis on two papers that they along with Emerson’s Mark Nixon coauthored. Terry presented, Event Based Control Applied to Wireless Throttling Valves. Here’s the abstract from this presentation:

Emerson's Willy Wojsznis


Emerson's Mark Nixon


This paper addresses the PID modifications and communication support that enable effective control using wireless throttling valves. To conserve the battery power used by a wireless positioner, the PID in a control system can be modified to minimize changes to the actuator position. Effectively, a controller’s output to an actuator is event-driven. It is not based on regular scan periods. A new WirelessHART command is proposed that allows the PID to compensate for communications delays from the control system to wireless throttling valve. This paper presents the performance achieved in a flow lab using an industrial size prototype wireless throttling valve in closed loop control of a liquid flow process. In this wireless control field trial, control performance using a wireless valve was evaluated using both a wired and wireless transmitter for the flow measurement.

Willy presented the second paper, Model Predictive Control With Event Driven Operations. Here is this presentation’s abstract:

MPC operation is based on the process model, which can be conveniently used in the event based MPC operation. The process model can estimate control parameters when a measurement fails or when lab sampling is used as a control parameter. Lab sampling is available in general in irregular and significantly larger than MPC operation scan intervals. Another case when event based MPC operation is required is wireless control, which includes both slow sampling and randomness. The event based MPC operation is based on a principle: MPC uses a measurement flag which directs MPC to use the simulated process model measurement when a wireless measurement reading is not available or update the model and use a new measurement reading when the wireless reading becomes available.

Model Predictive Control with wireless measurements

Model Predictive Control with wireless measurements

MPC wireless operation has been validated on a divided wall column (DWC) process which can provide potentially huge savings in energy and capital cost compared to a conventional column design. In the installation at the University of Texas, WirelessHART transmitters are applied for many of the process measurements used in control. MPC application is crucial for achieving operational stability and effective operation of the DWC process.

The paper details event driven wireless MPC operation concept and design and discusses the application challenges illustrated by test results.

I hear that the presentations were recorded and will follow up in another post with the presentation recordings. In the interim, you can connect and interact with other wireless and advanced control experts in the Wireless and DeltaV groups in the Emerson Exchange 365 community.

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