Implementatie van een controlesysteem op een experimentele ORC testbank
By | Marcio Verhulst | Master of Science in de industriële wetenschappen: elektromechanica | Universiteit Gent, Ingenieurswetenschappen en Architectuur, Industrieel Systeem- en Productontwerp
Promotor(s) | prof. Martijn van den Broek, Sergei Gusev
Year | 2013-2014
As Organic Rankine Cycle (ORC) systems are designed by means of parametric calculations and simulations, tests should be performed to check if the real setup can deliver the promised specifications. Therefore the research group ORCNext has built a test bench for ORC systems which is capable of delivering thermal oil, Therminol 66, at a maximum temperature of 350°C and with heat exchange capacity of 250kW. For the cold side a cooling loop was built with a cooling capacity of 480kW at an average coolant exchange temperature of 80°C and outside air temperature of 20°C. As this system did not meet the performance level, required for the next phase of the ORCNext project, it has been modified and rebuilt to meet the requirements once again and this has been done in such a way the system can be adapted for future needs in an easy way.
Because almost every ORC setup is customer-specific, the heat source simulator is capable of simulating a wide variety of standard load patterns such as steady state with added distortion signals, block wave functions, etc. If required, custom load patterns can easily be uploaded and simulated through the LabVIEW control application which was designed in-house. As the simulator is built to simulate even very dynamic heat sources, it is capable of making large heat supply jumps within seconds (positive and negative).
This way ORCs can be tested in both steady state and dynamic behaviour and control strategies can be designed and tested in a fast, easy manner. Considering the large amount of energy for a laboratory environment, and to ensure a stable and safe operation, a Programmable Logical Controller (PLC, in this setup a Siemens S7 1200 series) takes care of the execution of the IO from the LabVIEW control application and has built-in safety procedures.
When designing new control strategies for an ORC application, not only the heat and cold source are controlled by this LabVIEW and PLC configuration, also the ORC system is controlled by the latter, offering direct control over the various ORC components and ensuring optimal measurement data.
Another benefit of this system is the continuous safety monitoring of the components and complete system. Whilst designing a controller / control strategy, a variety of errors can occur during tests, not always keeping the ORC within its design limits. Therefore it is possible to implement an algorithm in the PLC which automatically switches to a standard controller, bringing back the ORC to a steady and safe state if the application is going out of design limits.