Real-Time Models of Electromechanical Power Systems, Based on the Method of Average Voltages in Integration Step and Their Computer Application
Round 1
Reviewer 1 Report
When talking about electrotechnical systems what domain are you referring to? Are we talking about just the power electronics domain? Are we considering the power grid itself? If so, where are the power delivery elements? It is not clear what you mean by electrotechnical systems, please, I consider it will be easier to address the paper by directing the reader to the specific domain, including the papers title.
In literature, power electronics model is a more conventional expression to cover the author’s work instead of electrotechnical system.
The models and the simulation are developed in time domain; however, it feels like if the author goes around trying to explain it. Please, I strongly suggest that by setting a discussion about how time domain models represent an important computational burden is enough to address the introduction. This topic has been covered by several authors for years and I think that presenting this as a literature review is enough to present the problem. Then, the author can go after the contributions in this work.
I wonder why all the equations in these types of papers are always presented as differential equations, why not to present them in the discrete time domain (Z) to link them to their implementation within a computer. Has it been done before, if not, why?
The conclusions are not linked to the abstract and the introduction. Abstract and introduction talk about electrical systems in general, then the conclusions go specifically for generator blocks of Nuclear and Thermal Power Plants. Please be consistent, if generator blocks of Nuclear and Thermal Power Plants are the target of this paper, these should be mentioned from the beginning so the reader will know what to expect and gain interest.
Author Response
Comment 1. When talking about electrotechnical systems what domain are you referring to? Are we talking about just the power electronics domain? Are we considering the power grid itself? If so, where are the power delivery elements? It is not clear what you mean by electrotechnical systems, please, I consider it will be easier to address the paper by directing the reader to the specific domain, including the papers title. In literature, power electronics model is a more conventional expression to cover the author’s work instead of electrotechnical system.
Response 1. We consider electromechanical systems that contain electrical machines and semiconductor converters connected to a power grid. We agree with your comment about the need to specify the object of study, including the paper title. As a result, we have revised the paper title to "Real-time models of electromechanical power systems, based on the method of average voltages on integration step and their computer application". Also, the article abstract was modified (lines 11 - 24). Appropriate changes were also made to the text. Thank you for this right remark.
Comment 2. The models and the simulation are developed in time domain; however, it feels like if the author goes around trying to explain it. Please, I strongly suggest that by setting a discussion about how time domain models represent an important computational burden is enough to address the introduction. This topic has been covered by several authors for years and I think that presenting this as a literature review is enough to present the problem. Then, the author can go after the contributions in this work.
Response 2. Proposed method algebraizes differential equations of electromechanical systems power circuits within numerical quanta of time, which are synchronized in the hybrid models with signal quanta of time from a physical object. Other method of algebraization are possible, for example, in the frequency domain. However, in our opinion, using time domain with one-step algebraization method is optimal for real-time models of electromechanical systems with electric machines nonlinearities and semiconductor converters. Our opinion is the same as the opinion of the authors:
- Naredo JL, Mahseredjian J, Kocar I, Gutierrez-Robles JA, Martinez-Velasco JA. Chapter 3: frequency domain aspects of electromagnetic transient analysis. In: Martinez-Velasco JA, editor. Transient analysis of power systems: solution techniques, tools and applications. 1st ed.Wiley-IEEE Press; 2015. p. 33–71.
- Dufour C, Belanger J. Chapter 4: real-time simulation technologies in engineering.In: Martinez-Velasco JA, editor. Transient analysis of power systems: solutiontechniques, tools and applications. 1st ed.Wiley-IEEE Press; 2015. p. 72–99.
In order to take into account your comment we have made a corresponding supplement with the above references in the introduction (lines 47 - 58).
It should be noted that the purpose of the article is to develop models using the author's method defined in the paper title, and the purpose of a thorough comparison of this method with other known methods was not raise in the paper.
Comment 3. I wonder why all the equations in these types of papers are always presented as differential equations, why not to present them in the discrete time domain (Z) to link them to their implementation within a computer. Has it been done before, if not, why?
Response 3. The method provides analytical-digital algebraization of differential equations of power circuits of electromechanical systems. The equations (11) - (13) obtained for the electrical circuits and (22) - (24) obtained for the synchronous machine are not differential but algebraized within numerical quanta of time. In these equations the values of currents, voltages on capacitors and their derivatives at the beginning of the time quantum corresponding to the integration step are used as initial conditions.
Comment 4. The conclusions are not linked to the abstract and the introduction. Abstract and introduction talk about electrical systems in general, then the conclusions go specifically for generator blocks of Nuclear and Thermal Power Plants. Please be consistent, if generator blocks of Nuclear and Thermal Power Plants are the target of this paper, these should be mentioned from the beginning so the reader will know what to expect and gain interest.
Response 4. We are grateful to you for this comment and we agree with it. The conclusions were adjusted as follows (lines 332 - 355)
"The method of average voltages on an integration step provides numerical stability for hybrid real-time models and ensures the analytical-numerical algebraization of differential equations of electromechanical power circuits on time quanta, which are synchronized with time quanta of control systems signal. This is important for the operation of hybrid models for an unlimited range of time.
The method is correct for systems, which variables are described on the integration step by polynomials of different order, for example: voltage on the capacitance and current in the branch with series-connected inductance and capacitance, as well as the rotor speed and angle in the electric machines.
Mathematical models of elements are represented as multipole that provide the generality of electromechanical systems models. The use of models-multipolar makes it possible to parallelize the calculation and increase the speed of performance.
The developed real-time models of power schemes of Nuclear and Thermal Power Plants generator blocks work both in conjunction with the real excitation control system of generator during diagnosing and testing of ones. In particular, the use of real-time model of the generator blocks allows to test and tune-up the real automatic excitation controllers of generators at power plants, as well as to train of service staff.
The use of the author's method of average voltage on the integration step enables to increase the numerical stability and performance of models and ensures their continuous operation in a real time mode in combination with physical objects.
The models provide high precision instantaneous modeling with an error of less than 10% and which is determined by precision of identification of power scheme parameters. That is ensured by the high completeness of the description of electric machines and converters, taking into account their nonlinearity."
Reviewer 2 Report
the paper present an interesting method, I have two major concerns/questions.
the paper is very hard to read due to significant problems with the English language.
what are the modeling limitations ? the integration idea is very interesting but is it applicable to any generic circuit ? is it mandatory to have a capacitor in every node and an inductor in every branch (or to transform the system to such topology when possible) ?
Author Response
Comment 1. The paper is very hard to read due to significant problems with the English language.
Response 1. Your comment has been taken into account. The paper was substantially corrected.
Comment 2. What are the modeling limitations ? the integration idea is very interesting but is it applicable to any generic circuit ? is it mandatory to have a capacitor in every node and an inductor in every branch (or to transform the system to such topology when possible) ?
Response 2. Proposed method is applicable to any circuit, which includes any combination of R, L, C elements. The components of equations (11), (12), (13), which include capacitance, are zero in case of capacitance absence in the circuit branch. In other words, it must substitute voltage Uc0 for zero and capacitance for infinity in these equations for exclusion of capacitance. Inductances L1, L0 are zero in case of absence of inductance.
The paper is supplemented with an appropriate explanation (lines 134 - 138). An example of the application of the method for non-capacitive circuits is the model of a synchronous machine described in the paper. Thank you for your comments.
Round 2
Reviewer 1 Report
Good changes, now the paper makes more sense, good job.
Author Response
Thank you for your comments that helped us to improve our paper.
To improve English language we used editing service provided by MDPI (certificate added).
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The language is in my opinion still inadequate for an international journal and require some work.
Author Response
To improve English language we additionally used editing service provided by MDPI (certificate added).
Thank you for your comments that help us to improve our paper.
Author Response File: Author Response.pdf
Round 3
Reviewer 2 Report
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