control optimization - flownex simulation … · control optimization flownex-labview integration...

CONTROL OPTIMIZATION

FLOWNEX-LABVIEW INTEGRATION

This case study shows how integration of LabVIEW & Flownex was used to design controllers on a “soft” plant and eliminate the need for costly live plant start-ups and shut downs generally used to obtain the control parameters for LabVIEW.

CONTROL DESIGN/SIMULATION

www.flownex.com [email protected]

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PRODUCTS USED:

LabVIEW 8.2, PID Toolkit, LabVIEW real time module and DSC module Flownex version 7.009

THE CHALLENGE

Designing a control system for a First Of A Kind (FOAK) pebble bed experimental facility (Heat Transfer Test Facility (HTTF)) and testing the controllers before the plant is complete. This project and its timeous results contribute to the development of the Pebble Bed Modular Reactor.

In order to design controllers without an actual plant requires a “soft” plant where controllers are applied on a simulation of the actual plant. Ideally this simulation must be able to predict the exact plant behaviour especially during the transient events where the thermal inertia of the plant should be taken into account. This simulation must also be easy to use and manipulate. The designing and implementation of this simulator must contribute to the timeous completion of the project, thus it should not add any unnecessary time requirements.

THE SOLUTION

The solution was the development of a LabVIEW-Flownex engineering simulator. An engineering simulator can be defined as follows:

Engineering is the design, analysis, and/or construction of works for practical purposes.

A Simulator is used to simulate an imitation of some real thing, state of affairs, or process. The act of simulating something generally entails representing certain key characteristics or behaviours of a selected physical or abstract system.

An Engineering Simulator is used to design, implement and test or analyze certain key characteristics and/or requirements of an actual plant/works before or during the actual construction and commissioning thereof. It can also be used to assist and train technical personnel.

CONTROL DESIGN/SIMULATION

Designing a control system for a First Of A Kind (FOAK) pebble bed experimental facility (Heat Transfer Test Facility (HTTF)) and testing the controllers before the plant is complete.


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The requirements for the engineering simulator are defined as follows:

• Design and test controllers for a First Of A Kind (FOAK) plant before the actual plant is commissioned.

• Actual plant Supervisory Control And Data Acquisition (SCADA) and controllers should be used.

• The exact dynamic plant behaviour should be predicted by taking the thermal inertia of the plant into account.

• Simulation should be easy to use and manipulate. • Actual plant look and feel should be replicated in the

simulator to enable training of operators. • Should assist in fault detection during commissioning. • Fast and user friendly implementation of simulator to

contribute to timeous completion of project. • Real time simulations.

INTRODUCTION

Flownex is an advanced component scale systems level thermal-fluid simulation software that can deal with both steady-state and dynamic problems. ‘Component scale’ refers to 2D or even 3D fine porous component models in addition to 0D or 1D models in most pipe network codes. 2D or 3D fine porous component models are used to model complex heat exchangers, nuclear reactors, solid structures or flow through porous media. ‘Systems level’ refers to the modelling of complete thermal-fluid systems such as steam, gas turbine, combined cycle or nuclear power plants; refrigeration systems, ventilation networks or water distribution networks. 1

HPTU PLANT BACKGROUND

The Heat Transfer Test Facility (HTTF) consists of two clearly distinguishable test units namely the High Temperature Test Unit (HTTU) and the High Pressure Test Unit (HPTU). The purpose of the facility is twofold namely:

1 www.flownex.com

Flownex is an advanced component scale systems level thermal-fluid simulation software that can deal with both steady-state and dynamic problems.

LABVIEW - FLOWNEX ENGINEERING SIMULATOR


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• To validate the correlations that are currently used to model the relevant heat transfer and fluid flow phenomena required for the integrated simulation of a pebble bed core, via a comprehensive set of separate effects tests.

• To generate results that may be used to validate the different simulation methodologies applied in the integrated models that represent the entire pebble bed core, via a comprehensive set of integrated effects tests.

The HPTU plant operating conditions vary such that the coolant density for two tests can differ with a factor of 50 and the mass flows with a factor of 1000 in a Nitrogen environment. One of the control challenges involved the control of a heated sphere power input at a constant offset surface temperature of 50°C above the cold nitrogen gas stream for various mass flow rates at different densities.

The HPTU is already in the operational phase but the LabVIEW – Flownex engineering simulator was not used for the design of the controllers on this project. The controllers were designed and implemented during the commissioning phase of the project. It was planned to design the controller inputs by linking another SCADA and controller to a Flownex model of the HPTU. The PID controller inputs obtained by this simulator were then added to the LabVIEW 7 controllers used to control the HPTU plant. The idea was to eliminate the need for costly actual plant start-ups and shut downs to obtain the control parameters for LabVIEW. The difference in control algorithms used in the simulator compared to the LabVIEW controllers caused the LabVIEW controllers to behave different to the anticipated behaviour obtained from the other control software package. As a result the programming of the controllers caused a lot of precious down time during the commissioning of the plant. Most of the controller inputs had to be obtained by testing on the actual plant. This implied that each commissioning modification to the plant caused the design of the controller to halt, since the plant could not be started. The opposite was also true: the commissioning tests was greatly dependent and delayed due to controller testing and programming. Although the plant was delivered on time for the start of the operational phase, great amounts of overtime and expensive “rush job” costs could have been avoided.

The idea was to eliminate the need for costly actual plant start-ups and shut downs to obtain the control parameters for LabVIEW.


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Figure 1: The High Pressure Test Unit that is already in operation.

HPTU SIMULATOR LESSONS LEARNT

The following Simulator challenges were encountered on the HPTU:

• The difference in control algorithms between the other simulator and LabVIEW caused the LabVIEW controllers to behave different to the anticipated simulator behaviour.

• Inputs to the programmed user parameters can’t be dynamically changed during simulation and the simulation had to stop after each user adjustment.

• Adjustment of the time step during simulation to get the optimum performance and accuracy was not possible.

• Most of the controller inputs had to be obtained by testing on the actual plant.

• Every transient simulation needed to be pre-programmed.

HTTU PLANT BACKGROUND

The HTTU plant differed from the HPTU in the sense that very high temperatures are used during the testing and the physical plant is almost four times as large as the HPTU. The thermal inertia associated with the large quantities of graphite used in the tests planned for the HTTU introduced another requirement that was not that critical in the HPTU plant. With these requirements in mind and the valuable lessons learnt on the HPTU, a serious rethink of the simulator to be used to design the controllers was required.

The difference in control algorithms between the other simulator and LabVIEW caused the LabVIEW controllers to behave different to the anticipated simulator behaviour.


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Figure 2: HTTU in the design phase.

Figure 3: HTTU basic plant layout.

Test section

Blower

Main Heat exchanger

Low flow Heat

exchanger

Flow meters

4 x gas cycles

Gas supply bank

Cooling tower Water tank

Pump Pump

Pump

Pump

Pump

Stem cooler supply pumps

Test section

Blower

Main Heat exchanger

Low flow Heat

exchanger

Flow meters

4 x gas cycles

Gas supply bank

Cooling tower Water tank

Pump Pump

Pump

Pump

Pump

Stem cooler supply pumps


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The HTTU project thus required a real time simulator that can be used to design and test the controllers and control algorithms before the construction of the plant is complete.

LabVIEW is used to develop the SCADA system for the HPTU and the HTTU and in order to simulate any control scenario correctly the simulator need to use LabVIEW for its control applications.

THE LABVIEW-FLOWNEX SIMULATOR

The motivation to use LabVIEW and Flownex for the simulator involved the following:

• Flownex is a very accurate systems CFD thermal fluid code. • Flownex is an easy to use systems CFD code and has

much faster simulation times compared to its contenders. This makes for an ideal simulator engine: Quick and Accurate.

• Flownex and LabVIEW use the same type of graphical programming elements, functions and wires.

• Data logging is handled by LabVIEW through shared variables logging functions, thus no extra data logging programming is required that simplifies the setup of the simulator.

• By using the same language for the simulator and the control system the developed controllers or PID control algorithms can only be downloaded directly to the compactFieldPoint controller.

• This simulator setup does not require any pre-determined simulation sets. This implies that the user can adjust any variable at any time.

• The user can investigate any plant behaviour without putting the plant at risk.

• The user can also increase or decrease the speed of the simulator to get the optimum performance and accuracy.

For very large or complex simulation models the simulation times can become slower than real time, for example the model of the High Temperature Test Unit. The Flownex network shown in Figure 4 is a simplified network of the complete HTTU plant. This model consists of very accurate and detailed models for each system in the plant as the data acquired will be used for controller design. This involved models for the pebble bed, the heat exchangers, the water jacket model, auxiliary systems, etc.

Flownex is an easy to use systems CFD code and has much faster simulation times compared to its contenders. This makes for an ideal simulator engine: Quick and Accurate.


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Figure 4: LabVIEW – Flownex engineering simulator provides the integration between the soft plant and the actual LabVIEW user interface.

The only method of increasing the speed of any simulation is either increasing the computer performance or decreasing the simulation accuracy. The LabVIEW-Flownex simulator has the solution for this all known computer performance problem. By subdividing the models of the plant into separate Flownex models, the plant can be simulated separately and if the user wants to investigate the effect of the plant as a complete model the subdivided models can be linked together. If the user requires to increase the performance of the simulator even further as a result of a much larger and more detailed plant, the models can be divided between more than one computer.

Figure 5 illustrates the expandability of the LabVIEW-Flownex engineering simulator. The user executes the divided Flownex models on any number of workstations. The LabVIEW-Flownex interface VI collects all the input and output data and connect them to Shared variables. The user interface can run on any of the model workstations or a separate workstation (depends on the free resources of a workstation). The user interface uses the binding ability of shared variables to connect to all the model’s shared variables.

LabVIEWLabVIEW SCADA and SCADA and controlcontrol

Flownex real time Flownex real time plant simulationplant simulation

LabVIEWLabVIEW SCADA and SCADA and controlcontrol

Flownex real time Flownex real time plant simulationplant simulation

The LabVIEW-Flownex simulator has the solution for this all known computer performance problem.


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Figure 5: Expandability of LabVIEW-Flownex simulator.

The heater element for example is positioned in the centre of the annular graphite pebble bed as shown in Figure 6. The heater element, pebble bed and water jacket, which forms only a part of the main thermal fluid Flownex network shown in Figure 4, can thus be modelled as a separate Flownex model as shown in Figure 7. This separate model can with the help of the shared variables in LabVIEW be linked to the other separate detailed models on the same or different computers or processors. A typical section of the LabVIEW programming to enable the communication between LabVIEW and Flownex inputs and outputs are shown in Figure 8. The combined simulation power, speed and accuracy are then integrated and displayed on the LabVIEW SCADA and control interface as shown in Figure 9. The figure illustrates the behavior of the test section model of the heater, pebble bed and waterjacket during transient events specified by the user on the LabVIEW interface. The display for the different interlocks and the fault or bridge indications are also shown in Figure 9.

External Control set External Control set External Control set

Flownex Interface VI and Shared Variables

Shared Variables using Bindings

User Interface

WORKSTATION 1 WORKSTATION 2 WORKSTATION N

WORKSTATION 1,2 or N



POWERFULL LABVIEW FLOWNEX SIMULATOR

Heat exchanger model Heater model Water jacket modelExternal Control set External Control set External Control set


Shared Variables using Bindings

User Interface

WORKSTATION 1 WORKSTATION 2 WORKSTATION N

WORKSTATION 1,2 or N



POWERFULL LABVIEW FLOWNEX SIMULATOR

Heat exchanger model Heater model Water jacket model

The LabVIEW-Flownex interface VI collects all the input and output data and connect them to Shared variables. The user interface can run on any of the model workstations or a separate workstation (depends on the free resources of a workstation).


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Figure 6: Heater element position relative to the test section and waterjacket.

Figure 7: Heater element, pebble bed and water jacket Flownex model in the test section.

1200

mm

Graphite

Graphite spheres in Pebble bed

Heater Elements

Water Jacket

Graphite central reflector

1200

mm

Graphite

Graphite spheres in Pebble bed

Heater Elements

Water Jacket

Graphite central reflector

Heater Element

Water jacket

Graphite

reflectors

Heater Element

Water jacket

Graphite

reflectors


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Figure 8: Typical LabVIEW programming to link inputs and outputs to and from LabVIEW and Flownex.

Figure 9: LabVIEW - Flownex engineering simulator interface for the heater, pebble bed and water jacket in the test section during simulation.


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CONCLUSIONS

Using the LabVIEW-Flownex engineering simulator the controllers have already been designed by the time the plant commissioning starts. There are also sufficient operators trained before the commissioning even commence.

Thus, to summarize the advantages and capabilities of the LabVIEW-Flownex simulator:

• No predetermined simulation setups are required, the user can simulate without stopping the simulator.

• The simulation speed can be adjusted by increasing the computer load or by adjusting the accuracy during simulation.

• Simulation speed can be increased by either using a faster computer or by splitting up the models on different computers.

• The simulator setup/connection to Flownex is very easy to use. • The simulator setup file is small - approximately 36 Kbytes. • The Flownex models can provide accurate results at faster than

real time speed.

The Flownex models can provide accurate results at faster than real time speed.

control optimization - flownex simulation … · control optimization flownex-labview integration...

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