DS-Based 2-DOF PID Controller of a Regasification System for LNG-Fueled Marine Engine
Round 1
Reviewer 1 Report
Comments for author File: 
Comments.pdf
Author Response
Subject: DS Based 2-DOF PID Controller of a Regasification System for LNG-Fueled Marine Engine
We would like to thank you for your detailed observations and advice in the examination of papers, and we will answer your points as faithfully as possible.
- What are basic heat exchange parameters, which type, is it counter flow, one pass or several passes? Please give more data on that?
- There is no data, what temperature is in questions and what range is controlled there? What are steam parameters.
Response 1, 2:
- To reflect what you pointed out, in Section 2 (2. Structure of Regasification System and Modelling), the following contents were added and modified. : The cryogenic LNG in the primary loop is boosted by the HP pump to approximately 250 to 300 [bar], converted into a gaseous state of about 35 to 45[° C] while passing through HP vaporizer, and fed into the marine engine cylinder via an injector. At this time, heat is supplied to the LNG from the glycol. On the other hand, the glycol cooled in HP vaporizer in the secondary loop needs to be reheated by the hot steam supplied to the heat exchanger. The heat exchanger used in the regasification system is shell and tube type, and the flow type is counter flow with several passes. In summary, heat exchange occurs between LNG and glycol in the primary loop, and between glycol and steam in the secondary loop [33,34]. The core equipment of the regasification system is a shell and tube type heat exchanger. To maintain the outlet temperature of the glycol at the desired value (for example, about 50[° C]), it is necessary to properly control the steam flow rate supplied to the heat exchanger in the secondary loop. The parameters of the heat exchanger, actuator, and control valve included in the regasification system are detailed in Table 1 in the ‘parameter tuning’ of Section 4.
- Conclusion is generally written without exact results.
Response 3: Based on the main contribution and numerical data, the conclusion section was revised as follows.
- In this paper, a DS based 2-DOF PID controller was suggested to simultaneously improve the set-point tracking and input disturbance rejection performance for glycol temperature control of LNG-fueled marine engine, and how to tune the parameters of the PID controller was The 2-DOF PID controller comprises of a PID controller for rejecting an input disturbance in the regulatory response and a set-point filter for reducing the overshoot in the servo response. The core contribution of this paper is that it is very easy to tune because there is only one adjustment variable for tuning the PID parameters, and the overshoot can be reduced by using a set-point filter. To show the effectiveness of the proposed method, a simulation of the glycol temperature control of the regasification system for LNG-fueled marine engines was performed and compared with the results of the two existing methods. In the case of nominal process, the proposed method reduced IAE by about 61~71% compared to the other methods, especially in the disturbance rejection response. In the case of parameter uncertainty, the proposed method decreased IAE by about 42~57% reduction in the disturbance rejection response. Using set-point filters reduces the IAE value from about 53 to 46, OS [%] from about 2.9 to 0.6, and settling time from about 35 to 30. Proposed controller was robust against uncertainty in heat exchanger parameters and was effective in both set-point tracking performance and disturbance rejection performance.
- In addition to what you pointed out, sentences and phrases in the paper have been revised and supplemented to reduce the redundancy of those expressed in other papers in the literature.
We are grateful once again for the detailed opinions and advice, and write and send our own response to the review comments.
Your comments are marked in red. And Other reviewer's comments are marked in yellow. The common points are marked in green.
Author Response File: Author Response.pdf
Reviewer 2 Report
(1) Direct synthesis approarch seems to be simple and can not describe the system procinples. Since recently the modelling methods are improved too much, why the direct synthesis is still used in the simulations in the paper.
(2) Is it possible to verify with the approarch describe in the paper with experimants?
(3) The results part is seems simple as well, probably caused by the direct synthesis approarch.
Author Response
Author's Reply to the Review Report (Reviewer 2)
Subject: DS Based 2-DOF PID Controller of a Regasification System for LNG-Fueled Marine Engine
We would like to thank you for your detailed observations and advice in the examination of papers, and we will answer your points as faithfully as possible.
1, 2: Direct synthesis approach seems to be simple and can not describe the system principles. Since recently the modelling methods are improved too much, why the direct synthesis is still used in the simulations in the paper. Is it possible to verify with the approach describe in the paper with experiments?
Response 1, 2:
- In the literature, IMC and DS methods are often used in model-based controller design. The principles of the direct synthesis method and the IMC method are similar, but each has its own advantages and disadvantages.
- Although the IMC method is somewhat superior in set-point tracking performance, it has a long settling time in disturbance suppression performance. However, although the direct synthesis method has good disturbance rejection performance, there are some overshoots in the set-point tracking response.
- The reasons for using the direct synthesis method are as follows:
- The DS method is excellent in disturbance rejection performance. However, a set-point filter was used to reduce overshoot, which is a disadvantage.
- There are three parameters that need to be tuned in the PID controller, but using the DS method, it is possible to tune the 3 parameters of the PID controller with only one desired constant time.
- Therefore, tuning the controller is easy and simple.
3: The results part is seems simple as well, probably caused by the direct synthesis approarch.
Response 3: Based on the main contribution and numerical data, the conclusion section was revised as follows:
- In this paper, a DS based 2-DOF PID controller was suggested to simultaneously improve the set-point tracking and input disturbance rejection performance for glycol temperature control of LNG-fueled marine engine, and how to tune the parameters of the PID controller was The 2-DOF PID controller comprises of a PID controller for rejecting an input disturbance in the regulatory response and a set-point filter for reducing the overshoot in the servo response. The core contribution of this paper is that it is very easy to tune because there is only one adjustment variable for tuning the PID parameters, and the overshoot can be reduced by using a set-point filter. To show the effectiveness of the proposed method, a simulation of the glycol temperature control of the regasification system for LNG-fueled marine engines was performed and compared with the results of the two existing methods. In the case of nominal process, the proposed method reduced IAE by about 61~71% compared to the other methods, especially in the disturbance rejection response. In the case of parameter uncertainty, the proposed method decreased IAE by about 42~57% reduction in the disturbance rejection response. Using set-point filters reduces the IAE value from about 53 to 46, OS [%] from about 2.9 to 0.6, and settling time from about 35 to 30. Proposed controller was robust against uncertainty in heat exchanger parameters and was effective in both set-point tracking performance and disturbance rejection performance.
- In addition to what you pointed out, sentences and phrases in the paper have been revised and supplemented to reduce the redundancy of those expressed in other papers in the literature.
We are grateful once again for the detailed opinions and advice, and write and send our own response to the review comments.
Your comments are marked in green. And Other reviewer's comments are marked in red and yellow.
Author Response File: Author Response.pdf
Reviewer 3 Report
The author presented a model of the regasification system of a LNG fueled ship engine. The main task was to tune the controller of the valve for the steam passing through the heat exchanger.
The topic is important since LNG fueled shipping is one of the solutions for ship emisions reductions.
The papaer has an adequate introduction, modelling description, results presentation and conclusion.
The paper is suported by extensive list of references.
The thing that should be improved is the addition of the description of the many used acronimes (DS, DOF, PID, SIMC, RCGA...).It might be that automation is not my main subject and these are well known in the field, but it would enlarge the understanding to a vider range of readers.
"Cell tube" type of heat exchanger, did You mean Shell and tube?
Author Response
Author's Reply to the Review Report (Reviewer 3)
Subject: DS Based 2-DOF PID Controller of a Regasification System for LNG-Fueled Marine Engine
We would like to thank you for your detailed observations and advice in the examination of papers, and we will answer your points as faithfully as possible.
- The author presented a model of the regasification system of a LNG fueled ship engine. The main task was to tune the controller of the valve for the steam passing through the heat exchanger. The topic is important since LNG fueled shipping is one of the solutions for ship emissions reductions. The paper has an adequate introduction, modelling description, results presentation and conclusion. The paper is supported by extensive list of references. The thing that should be improved is the addition of the description of the many used acronimes (DS, DOF, PID, SIMC, RCGA...). It might be that automation is not my main subject and these are well known in the field, but it would enlarge the understanding to a wider range of readers. "Cell tube" type of heat exchanger, did you mean Shell and tube?
Response 1:
- As you pointed out, we made a huge mistake while typing. we corrected it with shell and tube.
- The description of GA is well explained on line 76
- The description of DS is well explained in line 196.
- 2-DOF is described in the first part of the paper where 2-DOF is mentioned.
- PID is described in the first part of the paper where PID is mentioned.
- In addition to what you pointed out, sentences and phrases in the paper have been revised and supplemented to reduce the redundancy of those expressed in other papers in the literature.
We are grateful once again for the detailed opinions and advice, and write and send our own response to the review comments.
Your comments are marked in yellow. And Other reviewer's comments are marked in red. The common points are marked in green.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Thank you for taking into account my suggestions for your article, which was interesting to read for me.
Reviewer 2 Report
I am satisfied with the resopond and revison
