A Distribution Static Synchronous Compensator Application to Mitigate Voltage Variation for Distribution Feeders

Round 1

Reviewer 1 Report

The paper addresses an important topic related to the challenges faced by utilities in managing the increasing penetration of distributed energy resources. The use of DSTATCOM and DERMS to improve voltage control and hosting capacity is an interesting approach. However, there are some areas where the paper can be improved to enhance its clarity and scientific rigor. The following suggestions are provided to guide the authors in revising and improving the paper.

The description of the feeder network topology is somewhat unclear. More details are needed to understand how the AM/FM database and the Oracle database within Taipower's AM/FM system are utilized to create distribution network models and perform the customer-to-transformer mapping process.

Provide a clearer explanation of how the RETU functions and its role in data processing and communication. 

Expand on the benefits and significance of using LoRa RF communication for transmitting voltage data from RETUs to the data concentration unit (DCU).

Explain in more detail how the hosting capacity analysis is performed using the collected data, including the feeder topology, loadings of service zones, and field solar equipment. 

Clarify the relationship and interaction between the DERMS and the distribution automation system (DAS). How does the DAS transmit the status of line switches to the DERMS? How is the input data file updated based on this information?

It will be helpful to include a brief explanation of why the test feeder XD45 was chosen for the simulation. What characteristics or criteria make it suitable for evaluating the effectiveness of the DSTATCOM? 

Describe the specific criteria used to evaluate the hosting capacity of the test feeder with and without the DSTATCOM. What are the voltage variation or reliability limitations mentioned?

Discuss the limitations and potential drawbacks of the proposed DSTATCOM and DERMS solution.

The English usage in the paper is generally understandable, but there are areas where improvement is needed. Some sentences and phrases are unclear or lack precision, leading to difficulties in fully grasping the intended meaning. Additionally, there are instances where sentence structures could be enhanced for clarity and flow.

I would recommend that the authors revise the English usage in the paper. This could involve clarifying ambiguous statements, refining sentence structures for better readability, and ensuring consistent terminology and grammar throughout the text. A thorough proofreading by a native English speaker or professional editor would be beneficial to polish the language and improve the overall quality of the paper.

Author Response

Responses to the reviewer1’s comments

Manuscript ID: sustainability-2499768

Title: DSTATCOM Application to Mitigate Voltage Variation for Distribution Feeders

Dear Sir:

We would like to thank the reviewer’s valuable comments. The paper has been revised according to the comments. The followings address the response to the comments.

For reviewer 1:

1. The attributes of distribution components, such as line segments, distribution transformers, renewable energy, etc., have been retrieved from the automated mapping/facilities management/geographic information system (AM/FM/GIS) in the Oracle database to analyze the impact analysis of renewable energy sources. The network configuration of a distribution feeder is then identified by performing the topology process according to the connectivity attributes of distribution components. The daily load patterns of customer classes, derived by load survey study, and the customers' monthly energy consumption in the customer information system (CIS) database are used to solve each customer's hourly power demand. With the customer-to-transformer mapping, the hourly loading of each distribution transformer is solved by integrating the power profiles of all customers served. The distribution feeder model can be created automatically for the three-phase load flow input data. The voltages of all buses with and without PV in Eq. (1) can be calculated by executing the three-phase load flow analysis. The text has been modified in Section 2.
2. For power generation from a solar plant, the voltages at PCC are subsequently recorded in the connected storage medium. They are then transmitted by the RETU to the data concentration unit (DCU) using LoRa RF communication on a minute-by-minute basis. The DCU gathers all the collected voltages and sends them to the DERMS through public 4G communication for the impact analysis and the voltage regulation of the DSTATCOM.
3. LoRa is a modulation that provides a significantly greater communication range with low bandwidths than other competing wireless data transmission technologies like cellular, WiFi, Bluetooth, or ZigBee for transmitting voltage data from RETUs to the data concentration unit (DCU).
4. The hosting capacity is analyzed by performing the three-phase load flow program. The input data of the three-phase load flow is created by collecting the feeder topology, loadings of service zones, and the power generation of PV systems.
5. The network configuration of a distribution feeder often varies with the operations of line switches when executing the load transfer between two neighboring feeders to achieve service restoration after a fault contingency and to support the non-interruptible load transfer during scheduled maintenance. With the high penetration of PV integration in distribution feeders, system overvoltage may be expected due to the excessive PV power generation and the increase in the feeder length after load transfer. Therefore, the information about which line switches will be operated for load transfer is transmitted from the DAS to the DERMS to perform feeder network reconfiguration and update the input data file for the impact analysis of the PV system integration. The new bus voltages are solved by executing a three-phase load flow analysis. After solving the decision-making for the voltage control of the DSTATCOM, the control command is transmitted by the DERMS master station to the DSTATCOM using the public 4G communication network.
6. The test feeder XD45, with a total length of 7.3 km, is to supply power to residential and agricultural customers. The total capacity of the existing PV systems is 1.2 MWp. The new PV capacity of 4 MWp will be installed in 2024. It is expected that excessive voltage rise, or overvoltage, can occur during maximum solar production; large voltage deviations can occur during partly cloudy days when the solar output becomes intermittent. The utility considers the effectiveness of DSTATCOM in mitigating the overvoltage problem of the test feeder XD45.
7. In Taipower’s grid codes for PV integration, the new PV systems should be followed the voltage variation criteria in Eq. (1). To demonstrate the effectiveness of the DSTATCOM, the criteria are considered in the hosting capacity analysis.
8. Although the proposed integration of DSTATCOM and DERMS provides a high-performance distribution-class voltage regulation solution for the high solar PV penetration of the distribution feeder. The main drawback when comparing a STATCOM against an SVC is the cost, with the STATCOM typically costing about 15% to 20% more for similar ratings. Of course, the cost will also depend on factors outside the main components; civil, available footprint, losses, noise, etc.
9. Grammatical and writing style errors in the original version have been corrected by our colleague, who is a native English speaker.

 

 

Your assistance in reviewing the paper is highly appreciated.

 

Best Regards,

Professor Chia-Hung Lin  e-mail: [email protected]

Author Response File: Author Response.pdf

Reviewer 2 Report

1.     Authors have not mentioned the power injection capacity of the distributed solar plants. The geographical distribution is another important factor while controlling the voltage profile and reactive power flows. The authors are suggested to incorporate the effect of these parameters in the decision of DERMS. 

 

2.     Based upon the information of the distances of the renewable plants from the load centers, the location of DSTATCOM may be optimized for voltage and reactive power profile. The simulation studies must be updated to optimize the location of DSTATCOM.

 

3.     Figure 1 shows that one inverter is integrated via transformer while other inverter is directly interfaced with the feeder, how the reactive power compensation is controlled in this configuration, that has not been explained.

 

4.     There is confusion about the positioning of the DSTATCOM, either there is a single unit or multiple units? The authors are suggested to provide the algorithm used for rerouting of the network to optimize the system profile.

 

5.     Figure 7 shows three devices but does not present the configurations which can be achieved by decision making.

 

6.     The renewable inverters have the capacity of operation near the unit power factor and grid injection can be controlled with inverter control, there does nor not appear any coordination with inverters to control the voltage and reactive power flow control. 

7.     The decision strategy is missing in the manuscript, only three locations have been tested randomly. The authors are suggested to provide detail and clear picture of decision making for the positioning, configuration and coordination of the grid equipment.

Minor updates are required.

Author Response

Responses to the reviewer2’s comments

Manuscript ID: sustainability-2499768

Title: DSTATCOM Application to Mitigate Voltage Variation for Distribution Feeders

Dear Sir:

We would like to thank the reviewer’s valuable comments. The paper has been revised according to the comments. The followings address the response to the comments.

For reviewer 2:

1. The attributes of distribution components, such as line segments, distribution transformers, renewable energy, etc., have been retrieved from the automated mapping/facilities management/geographic information system (AM/FM/GIS) to analyze the impact analysis of renewable energy sources. The network configuration of a distribution feeder is then identified by performing the topology process according to the connectivity attributes of distribution components. For power generation from a solar plant, the voltages at PCC are subsequently recorded in the connected storage medium. They are then transmitted by the RETU to the data concentration unit (DCU) using LoRa RF communication on a minute-by-minute basis. The DCU gathers all the collected voltages and sends them to the DERMS through public 4G communication for the impact analysis and the voltage regulation of the DSTATCOM. The distribution feeder model, including PV power generation, can be created automatically for the input data of the three-phase load flow. The voltages of all buses with and without PV in Eq. (1) can be calculated by executing the three-phase load flow analysis. The text has been modified in Section 2.
2. The location of DSTATCOM will affect the effectiveness of voltage regulation on the high penetration of PV integration feeders. This project chooses three candidate locations to perform the hosting capacity analysis. The hosting capacity in scenario 3 (5.4 km from the substation) is achieved than those of scenario 1 (without DSTATCOM), scenario 2 (2.5 km from the substation), and scenario 4 (7.2 km from the substation) because the DSTATCOM is located near the large-scale solar facility point (Bus 15) of interconnection. Some optimal algorithms, such as genetic algorithm, ant colony optimization, particle swarm optimization, etc., for DSTATCOM placement will be considered in future studies.
3. Most solar inverters in Taiwan are not utility-grade, utility-owned voltage regulation equipment. The power factor of these solar inverters is fixed at 1.0 so that only the real power is generated. The distribution system control center of Taipower could not communicate with or be coordinated with the customer-owned inverters to perform the reactive power compensation. Therefore, Taipower considers the DSTATCOM to operate autonomously in the Volt/Var mode for correcting voltage problems by injecting or absorbing reactive power.
4. Three candidate locations (2.5 km, 5.4 km, and 7.2 km from the substation) are chosen to install a three-phase DSTATCOM bank to perform the hosting capacity analysis. The text has been modified in Section 4.1.
5. Figure 7 shows that a three-phase DSTATCOM of ±1 MVAR is directly connected on the upstream (Bus 6, 5 km from substation, Scenario 2), middle (Bus 15, 5.4 km from substation, Scenario 3) or downstream (Bus 31, 7.2 km from substation, Scenario 4) of test feeder to evaluate the hosting capacity. The hosting capacities are compared with that of the Baseline (without DSTATCOM, Scenario 1) when a DSTATCOM is installed at the three candidate locations of the test feeder. The text has been modified in Section 4.1.
6. Although real power curtailment can effectively mitigate the overvoltage problem, it will extend the payback period and affect the benefit of the PV owners. Renewable inverters have the capacity of operation at PF=-0.9~0.9, and grid injection can be controlled. Most solar inverters in Taiwan are not utility-grade, utility-owned voltage regulation equipment. The power factor of these solar inverters is fixed at 1.0 so that only the real power is generated. Therefore, Taipower considers the DSTATCOM to operate autonomously in the Volt/Var mode for correcting voltage problems by injecting or absorbing reactive power.
7. The location of DSTATCOM will affect the effectiveness of voltage regulation on the high penetration of PV integration feeders. The three candidate locations for installing DSTATCOM are decided by collecting bus voltages from the RETUs in the field and executing the three-phase load flow. The hosting capacity analysis is then performed to decide the near-optimal location (Bus 15). The text has been modified in Section 4.1. Some optimal algorithms, such as genetic algorithm, ant colony optimization, particle swarm optimization, etc., for DSTATCOM placement will be considered in future works added in the conclusion and future work section.

We would greatly appreciate your help in reviewing the paper.

Best Regards,

Professor Chia-Hung Lin  e-mail: [email protected]

Reviewer 3 Report

This paper develops a distributed energy resources management system (DERMS) to provide more effective control of a DSTATCOM that can help achieve a substantial increase of hosting capacity and mitigate overvoltage problem with the existing feeder. The topic is timely and interesting. However, there are several problems in the current text:

1. The language in this paper should be improved. There are many grammar and spelling mistakes in this paper.

2. Please avoid continuous citations in the introduction section. The authors are recommended to explain each reference clearly to make the paper more readable.

3. The texts in Fig. 1, 7 and 10 are too small. The authors should carefully display their texts inside figures to make readers easier to understand the article.

4. The authors are recommended to list their findings in the conclusion section one by one for readers to understand.

 

5. The future research directions are missing in the conclusion section. The authors should add the future research directions for further development of DSTATCOM.

English can be improved.

Author Response

Responses to the reviewer3’s comments

Manuscript ID: sustainability-2499768

Title: DSTATCOM Application to Mitigate Voltage Variation for Distribution Feeders

Dear Sir:

We would like to thank the reviewer’s valuable comments. The paper has been revised according to the comments. The followings address the response to the comments.

For reviewer 3:

1. Grammatical and writing style errors in the original version have been corrected by our colleague, who is a native English speaker.
2. The continuous citations have been modified in the introduction section.
3. The texts in Fig. 1, 7, and 10 have been modified.
4. The findings have been listed in the conclusion section.
5. Future works are added in the conclusion section.

We would greatly appreciate your help in reviewing the paper.

Best Regards,

Professor Chia-Hung Lin  e-mail: [email protected]

Round 2

Reviewer 2 Report

I would like to thank the authors for addressing all the queries and updating the manuscript. 

Reviewer 3 Report

The authors have fully addressed my concerns. The reviewer does not have more questions.

English in the current version is acceptable.