Using LabVIEW and the Authors' Models Created in The MathWorks, Inc. MATLAB® Software in the HIL of the Hydropower Unit Speed Control

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"A critical problem in the design of high head hydropower units is the proper sizing of bypass valves that are supposed to reduce the impact of waterhammer. The authors’ research work in this field highlighted the need for accurate waterhammer models in modern simulation software."

- Nicolae Vasiliu, Universitatea POLITEHNICA Bucuresti, FLUID POWER SYSTEMS

The Challenge:
Incorporating an accurate model of the waterhammer phenomenon that occurs in the pipelines of high head hydraulic turbines in a modular hardware-in-the-loop(HIL) test stand for hydropower unit governors.

The Solution:
Creating a test stand that used software modules called from LabVIEW, with each module containing the mathematical model of an element of the hydropower unit (turbine, generator, governor, and waterhammer) to interface with the hardware composed of two servomechanisms. The waterhammer model was implemented using the LabVIEW MathScript RT Module, which allowed improvements to the authors' previous modeling and simulation work in the field.

Author(s):
Nicolae Vasiliu - Universitatea POLITEHNICA Bucuresti, FLUID POWER SYSTEMS
Radu Puhalschi - Honeywell Building Solutions

The phenomenon known as waterhammer appears as a pressure wave occurring in a pipeline as a result of changes in flow conditions. Waterhammer is an important phenomenon in the design of high head hydropower units, whose operation includes frequent changes in the flow conditions because of either normal operation (changes in power demand), faults (unload and so on), or external factors. A critical problem in the design of such units is the proper sizing of bypass valves that are supposed to reduce the impact of waterhammer. The authors’ research work in this field highlighted the need for accurate waterhammer models in modern simulation software.

The initial work led to the implementation of well-known waterhammer numerical analysis methods in The MathWorks, Inc. MATLAB® software, which the authors chose because of its robustness in handling the numerical integration of complex differential equations. Though the MATLAB implementation produced the expected performance and accuracy results, further research directions highlighted several shortcomings that needed to be addressed.

The program was intended to be offered as a tool for waterhammer study to researchers and students, but the program lacked a graphical interface that allowed users to control the model. The authors estimated that the effort and knowledge needed to develop this interface were significantly larger than that needed for the program itself. The modifications were therefore limited to users with good programming knowledge because any modification to the model's parameters needed to be implemented directly in the code.

Also, to conduct proper research in the field of sizing bypass valves, the authors needed to integrate the waterhammer model in a larger mathematical model of an entire hydropower unit that was part of an HIL laboratory test stand. This proved to be quite difficult in the MATLAB implementation.

The solution involved the use of LabVIEW MathScript RT. By allowing user-created MATLAB code to interoperate with LabVIEW, MathScript gave the authors access to LabVIEW’s built-in graphical interface, which is one of the key features of LabVIEW, as well as an extremely easy-to-use environment for real-time simulation and DAQ around which the authors could build the HIL test stand.

The hardware component of the test stand consisted of a pair of electrohydraulic servomechanisms with functional characteristics similar to those used for actuating the wicket gates and bypass valves of hydropower units.

The software consisted of two LabVIEW applications. The first one ran on an embedded Windows computer that allowed an operator to easily access the test stand’s configuration parameters, conduct start and stop simulations, view the collected data during the simulation, and save the data to a file for further analysis. The second application ran in real time on an NI PXI industrial PC and included the software component of the HIL test stand, the mathematical models of the turbine, the generator, the governor, and the pipeline with waterhammer. It was designed as a modular application. Each mathematical model was implemented in its own subVI (LabVIEW subprogram) so it could be removed, changed, or added as needed to allow for the simulation of any hydropower unit architecture and operating conditions.

The authors have used the test stand to perform unload simulations to evaluate the efficiency of a new architecture of the numerical speed and power governor for the Raul Mare-Retezat hydropower plant. It also has been used to simulate the sizing of the corresponding bypass valve, and the results have been very good.

Results

By using LabVIEW with LabVIEW MathScript RT, the authors could make better use of their previous work with MATLAB by quickly building a robust and modular real-time application, which allowed more time to focus on the research activity.

Author Information:
Nicolae Vasiliu
Universitatea POLITEHNICA Bucuresti, FLUID POWER SYSTEMS
313 Splaiul Independentei
Bucharest 060042
Romania
Tel: +4021 3169643
Fax: +4021 3169645
vasiliu@fluid-power.pub.ro

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