A Model of Output Power Control Method for Fault Ride-Through in a Single-Phase NPC Inverter-Based Power Conditioning System with IPOS DAB Converter and Battery

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

My comments.

1. The existing problems in FRT for PCS should be clarify in the abstract, and the proposed solutions should also be included.
2. NPC TL is a common circuit for PCS. Thus, this cannot be a contribution of this paper.
3. For a single-phase system, the discussed circuit is too complex.
4. Part 2 can be removed from the paper.
5. Part 3 is too simple, and more detailed theoretical analysis should be added. Besides, the contribution is minor.
6. The comparisons with other solutions should be added.
7. No experimental results, the conclusions are not sounded.
8. In Table I, the switching frequency is too low for this application. Besides, why not 20kHz?
9. In Fig.9, is contains low frequency harmonic, why?
10. The discussion about efficiency in the Part 4 is meaningless because simulation results in PSIM are not convinced.
11. In the line 334, the system miniaturization and cost reduction are not proven.

Comments on the Quality of English Language

Proof reading is required.

Author Response

Comments 1: The existing problems in FRT for PCS should be clarify in the abstract, and the proposed solutions should also be included.
Response 1: Thank you for your suggestion. The authors completely agree with your comment. The abstract has been revised to clearly describe the existing problems in FRT for PCS and to include the proposed solutions.

Comments 2: NPC TL is a common circuit for PCS. Thus, this cannot be a contribution of this paper.
Response 2: The authors fully agree that the three-level NPC inverter topology is a well-established and widely used configuration in PCS applications. However, the novelty of this study does not lie in the use of the NPC topology itself, but rather in its integration with an input-parallel output-series (IPOS) dual-active-bridge (DAB) converter to form a single-phase bidirectional PCS. This configuration enables both charging and discharging power flow between the grid and the battery. Moreover, in conjunction with the proposed output power control strategy, the system can dynamically balance the grid power and satisfy the FRT requirements under voltage dip conditions. Therefore, the main contribution of this paper lies not in the use of the NPC circuit itself, but in the integration of a bidirectional NPC–DAB architecture and the development of a simple yet effective FRT-compliant power control method.
To clarify this point in the manuscript, explanatory sentences have been added to Section 1 (Introduction, lines 87–91) to explicitly state that the proposed system integrates the NPC inverter and IPOS-DAB converter to realize bidirectional power flow and FRT-compliant control.

Comments 3: For a single-phase system, the discussed circuit is too complex.
Response 3: The authors understand your concern that the proposed configuration may appear complex for a single-phase system. However, each component in the proposed PCS has been purposefully selected to achieve the key design goals of miniaturization and high efficiency. The three-level NPC inverter allows for a reduction in the size of the output filter (a filterless configuration is adopted in this study), while the input-parallel output-series (IPOS) DAB converter improves overall power transfer efficiency. In addition, the interleaved operation of the dual DABs effectively reduces the current ripple, enabling further downsizing of the LC filter. Thus, although the structure may seem intricate, the overall design is well-balanced to meet the compactness and efficiency requirements of single-phase PCS applications.

Comments 4: Part 2 can be removed from the paper.
Response 4: The authors understand that Part 2 may appear redundant at first glance. However, this section defines the overall system configuration, circuit parameters, and the interleaving control method of the IPOS-DAB converter, which are fundamental for understanding the subsequent discussion of the proposed FRT control strategy. Removing this section would make it difficult for readers to clearly follow the design rationale and control principles presented in the later parts of the paper. Therefore, Part 2 has been retained to ensure the technical completeness and readability of the manuscript.

Comments 5: Part 3 is too simple, and more detailed theoretical analysis should be added. Besides, the contribution is minor.
Response 5: The authors fully agree that the previous version of Section 3 lacked sufficient theoretical discussion and did not clearly emphasize its contribution. In the revised manuscript, Section 3 has been substantially rewritten to include a more detailed theoretical analysis of the proposed output power control method during voltage dips.
Specifically, detailed explanations and supporting equations have been newly added throughout Section 3 to clarify the design rationale and theoretical foundation of the proposed control method, including the inverter current–power relationship, current limitation, and adaptive power reference adjustment based on the retained voltage level.

Comments 6: The comparisons with other solutions should be added.
Response 6: The authors agree that comparisons with previous studies are essential to clarify the advantages of the proposed method. Therefore, Table 1 has been newly added in Section 1 to provide a comprehensive comparison with representative FRT-related studies. The table highlights that most previous works primarily focused on reactive current injection or voltage support functions, while few have addressed dynamic active power control or bidirectional power flow capabilities. In contrast, the proposed NPC–IPOS-DAB system achieves both FRT compliance and grid power balancing through a simple, power-based control structure.

Comments 7: No experimental results, the conclusions are not sounded.
Response 7: The authors acknowledge that the present paper includes only simulation results and that experimental validation has not yet been conducted. To address this point, the conclusion section has been revised to clarify the practical relevance of the simulation. Specifically, it now states that the simulation model was developed using the same configuration and control parameters as those intended for the experimental setup, and that the control algorithm was integrated into PSIM via a DLL to operate synchronously with the switching carrier, as in the actual hardware. These detailed simulations, which incorporate the electrical characteristics of the Si-MOSFET devices, reproduce realistic switching and conduction behaviors and support the feasibility of the proposed approach. A prototype of the proposed PCS is currently under development, and future work will focus on experimental verification under real operating conditions.

Comments 8: In Table I, the switching frequency is too low for this application. Besides, why not 20kHz?
Response 8: Thank you for your deeply review. The authors acknowledge that the reason for selecting the switching frequency was not explicitly explained in the original manuscript. Therefore, an additional explanation has been included in Section 4 (lines 276–281) to clarify the rationale for choosing a switching frequency of 20.4 kHz. Since the proposed system is intended for residential PCS applications, the switching frequency was set to 20.4 kHz, which is the minimum feasible value that satisfies the integer condition required for the t/4-delay block while remaining above the audible range to ensure silent operation. At present, the frequency is determined primarily based on the audible range consideration; however, in future experimental studies, we plan to further optimize the switching frequency by considering computational capability, switching losses, and system miniaturization in a comprehensive manner.

Comments 9: In Fig.9, is contains low frequency harmonic, why?
Response 9: Thank you for your valuable comment. The authors acknowledge that the reason for the low-frequency harmonic observed in Fig. 9 was not clearly described in the original manuscript. This component originates from the second-order ripple of the DAB converter’s secondary-side voltage, which fluctuates at twice the grid frequency due to the power pulsation transferred through the high-frequency transformer. However, its average value over one grid period accurately follows the power reference, indicating that the proposed control method properly regulates the output power under these conditions. This explanation has been added to Section 4 (lines 349–352) of the revised manuscript.

Comments 10: The discussion about efficiency in the Part 4 is meaningless because simulation results in PSIM are not convinced.
Response 10: The authors acknowledge that the efficiency discussion in the original manuscript may have seemed insufficiently supported. In the revised version, the explanation in Section 4 (Lines 323–332) has been revised to more clearly describe the modeling assumptions, evaluation scope, and the loss-reduction mechanism of the proposed system. The PSIM model already included detailed device parameters, such as the on-state resistance and body-diode forward voltage drop of the Si-MOSFETs (IXYS, IXFK150N30P3 and IXFR180N15P) used in the NPC inverter and DAB converter. These parameters allow the simulation to realistically represent the steady-state conduction losses. Although transient switching losses can be modeled in PSIM, they were not included in this system. Therefore, the efficiency analysis focuses on steady-state conduction losses, which can be accurately evaluated using the actual device parameters. In addition, Section 4 now explains that the proposed configuration reduces the secondary-side voltage and conduction current of the DAB converter, thereby lowering conduction losses. This effect is expected to become even more pronounced in an actual transformer owing to the reduction of copper and core losses. Despite these simplifications, the obtained results still provide a reliable estimation of the steady-state efficiency and sufficiently demonstrate the practical effectiveness of the proposed control method.

Comments 11: In the line 334, the system miniaturization and cost reduction are not proven.
Response 11: The authors acknowledge that the explanation regarding system miniaturization and cost reduction was insufficient in the original manuscript. Therefore, Section 4 has been substantially revised. In the revised version, a quantitative discussion of miniaturization and cost reduction has been added, together with a practical magnetic design example based on the area-product method [27]. Specifically, the relationship between inductance and core volume, as well as an example design using amorphous cores, is presented to demonstrate the effect. These explanations and the citation have been incorporated into Section 4 (lines 380–406).

Reviewer 2 Report

Comments and Suggestions for Authors

 

Dear authors, I have the following suggestions for improving the paper:

1. Please clarify the aim and the novel contribution of the paper. You might want to refine the final paragraph of part one.
2. Please clarify the component values in Table 1. The converter design could be presented as a case study.
3. The study relies solely on a model and simulation. This is understandable, but you might consider using “A model of ...’ in the title.
4. The simulation results could be clarified with better explanations.

Thank you for the interesting paper.

 

 

 

 

 

Author Response

Comments 1: Please clarify the aim and the novel contribution of the paper. You might want to refine the final paragraph of part one.
Response 1: Thank you for your valuable comment. The authors have revised the final paragraph of the Introduction to clearly state the aim and the novel contributions of this study. To better highlight the differences from previous works, a comparison table has been added, along with explanatory comments, to make the objectives and contributions more explicit and easier to understand.

Comments 2: Please clarify the component values in Table 1. The converter design could be presented as a case study.
Response 2: Thank you for your valuable comment. As noted, the component values in Table 1 are explained in detail in the subsequent sections (lines 173–176). To improve readability, we have also added a brief clarification immediately after the existing statement, indicating that the parameters correspond to a 6 kW residential PCS designed for a 20.4 kHz switching frequency and a 360 V DC-link.

Comments 3: The study relies solely on a model and simulation. This is understandable, but you might consider using “A model of ...’in the title.
Response 3: As suggested, the title has been revised to include “A model of …” to clearly indicate that the study is based on a model and simulation.

Comments 4: The simulation results could be clarified with better explanations.
Response 4: Thank you for your valuable comment. The authors have revised Section 4 to include additional explanations of the simulation results. Specifically, we clarified the origin of the low-frequency components, the conditions used for efficiency evaluation, and the quantitative discussion on system miniaturization.

Reviewer 3 Report

Comments and Suggestions for Authors

Paper review

Output Power Control Method for Fault Ride-Through in a Single-Phase NPC-Inverter-Based Power Conditioning System with IPOS DAB Converter and Battery

Authors: Reo Emoto, Hiroaki Yamada and Tomokazu Mishima

The subject of the paper is of interest in the context of non-conventional energy systems that are tied in the public grid. In this context, solutions for maintaining the stability of the energetic system in case of disturbances are studied. The authors propose a solution for the case of single-phase systems, using a system inverter converter.

Both the description of the system and the simulation results are well and clear presented. The experimental results are conducted for the cases of normal working conditions and different voltage dip conditions, showing power recovery in very short time. It would be recommended the method to be also studied using a real experimental installation for a better estimation of the real performances of the method.

 

Based on these remarks the paper presents a valuable contribution that would be of interest for the readers and consequently I recommend the paper to be accepted in the present form.

Author Response

Comments 1: Both the description of the system and the simulation results are well and clear presented. The experimental results are conducted for the cases of normal working conditions and different voltage dip conditions, showing power recovery in very short time. It would be recommended the method to be also studied using a real experimental installation for a better estimation of the real performances of the method.

Response 1: Thank you for your kind review. We deeply agree with your comments. We are now starting to construct the experimental setup for confirming the validity of proposed method. 

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

No other questions.

Comments on the Quality of English Language

Proof reading is required.