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Abstract

In response to the inability of the flexible DC transmission system connected to the AC grid under conventional control strategies to provide inertia to the system as well as to participate in frequency regulation, a virtual synchronous generator (VSG) control strategy is proposed for a voltage source converter (VSC)-based multi-terminal high-voltage direct current (VSC-MTDC) interconnection system. First, the virtual controller module is designed by coupling AC frequency and active power through virtual inertia control, so that the VSC-MTDC system can provide inertia response for AC grid frequency. Second, by introducing the power margin of the converter station into the droop coefficient, the unbalanced power on the DC side is reasonably allocated to reduce the overshoot of the DC voltage in the regulation process. Finally, the power regulation capability of the normal AC system is used to provide power support to the fault end system, reducing frequency deviations and enabling inter-regional resource complementation. The simulation model of the three-terminal flexible DC grid is built in PSCAD/EMTDC, and the effectiveness of the proposed control strategy is verified by comparing the conventional control strategy and the additional frequency control strategy.
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Authors and Affiliations

Congshan Li
1
ORCID: ORCID
Xiaowei Zhang
1
Ping He
1
ORCID: ORCID
Zikai Zhen
1
ORCID: ORCID
Kefeng Zhao
1

  1. College of Electrical Information Engineering, Zhengzhou University of Light Industry, China
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Abstract

Aiming at the problem of DC voltage control deviation and instability caused by a large-scale renewable energy access VSC–MTDC system, this paper combines voltage margin control and droop control. A strategy for controlling collaborative optimization in a sparsely distributed communication network has been proposed. Firstly, the distributed modeling of the system is carried out by combining MAS technology with small signal modeling. Then, a distributed model predictive controller is designed for a single droop control converter station. On this basis, a distributed cooperative optimization control strategy is proposed. According to the DC voltage deviation, the system adopts different control methods to control the receiving converter station. Finally, based on PSCAD/EMTDC and MATLAB co-simulation platforms, a six-terminal flexible HVDC system is built to verify the effectiveness of the control strategy under different conditions such as input power fluctuation, any converter station out of operation and system communication failure.
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Authors and Affiliations

Jingye Li
1
Haiying Dong
2

  1. School of Automation and Electrical Engineering, Lanzhou Jiaotong University, China
  2. School of New Energy and Power Engineering, Lanzhou Jiaotong University, China
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Abstract

In the asynchronous interconnected power grid that is composed of the multiterminal voltage-source converter high voltage direct current (VSC-MTDC) system, the control methods of each converter station and the frequency of the connected AC system are not the same. When a fault occurs in any place of the asynchronous interconnected system, it will cause the system to have power shortage or surplus, affecting the safe and stable operation of the interconnected power grid. In order to solve the problem of insufficient regional active power reserve, based on the VSC-MTDC asynchronous regional interconnection system and the principle of regional sharing, the dynamic power controller under disturbance conditions is established, and the controller parameters are set to achieve the accuracy of unbalanced power in the disturbance area measuring. Then, according to the degree of the disturbance power, considering the factors that affect the support effect of the converter station, an emergency DC power support (EDCPS) scheme under different power disturbances is formulated to achieve power compensation for the disturbance area. Based on PSCAD/EMTDC software, the proposed control strategy is simulated. The result shows that the converter station closer to the disturbance area has a better support effect, and the dynamic active power controller can timely and accurately deliver to the disturbance area when the active power reserve is insufficient.
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Bibliography

[1] Li X., Zeng Q.,Wang Y., Zhang Y., Control strategies of voltage source converter based direct current transmission system, Gaodianya Jishu/High Voltage Engineering, vol. 42, no. 10, pp. 3025–3037 (2016).
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[3] Huang R., Zhu Z., Chen J., Chen M., Zou C., Xu S., Research and Experimental Validation of Control and Protection Strategy of HVDC Circuit Breaker in Fault Condition Application in Nan’ao Multi- Terminal VSC-HVDC System, Dianwang Jishu/Power System Technology, vol. 42, no. 7, pp. 2339–2345 (2018).
[4] Guo X., Zhou Y., Mei N., Zhao B., Construction and Characteristic Analysis of Zhangbei Flexible DC Grid, Dianwang Jishu/Power System Technology, vol. 42, no. 11, pp. 3698–3707 (2018).
[5] Xu T. et al., Design and Application of Emergency Coordination Control System for Multi-infeedHVDC Receiving-end System Coping with Frequency Stability Problem, Dianli Xitong Zidonghua/Automation of Electric Power Systems, vol. 41, no. 8, pp. 98–104 (2017).
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[12] Zhu R., Li X., Ying D., A frequency stability control strategy for interconnected VSC-MTDC transmission system, Dianwang Jishu/Power System Technology, vol. 38, no. 10, pp. 2729–2734 (2014).
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[14] XuT. et al., Coordinated Control Strategy of Multi-DC Emergency Power Support to Improve Frequency Stability of Power Systems, Dianli Xitong Zidonghua/Automation of Electric Power Systems, vol. 42, no. 22, pp. 69–77+143 (2018).
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Authors and Affiliations

Congshan Li
1
ORCID: ORCID
Tingyu Sheng
1
ORCID: ORCID
Yan Fang
1
ORCID: ORCID
Yikai Li
1
ORCID: ORCID

  1. School of Electrical and Information Engineering, Zhengzhou University of Light Industry, China
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Abstract

Voltage source converter-based multi-terminal high-voltage direct current (VSCMTDC) transmission system can realize a multi-point power supply, multi-drop power receiving, and mutual coordination between the converter stations to ensure the reliability of the transmission. Based on the PSCAD/EMTDC platform, a five-terminal DC transmission system model is established. According to the fast power regulation capability and overload capacity of theVSC-MTDC power transmission system, an analysis of additional emergency power support for a transmission system under large disturbance conditions was carried out. A new control strategy for emergency power support that introduces its basic principle is proposed in this paper. It uses the short-term overload capability of the DC system. By changing the power reserve of the converter station and the electrical distance between the converter stations, the influence of the power reserve and the electrical distance on the emergency power supply guarantee is analyzed the stability of the system is improved, thereby improving the sudden change of power caused by voltage fluctuations, and the feasibility of the control module is verified by PSCAD simulation. The simulation results show that when the system power supply suddenly changes, the converter stations at a short distance and large power reserve has a better effect on emergency power supply protection. A comparative study of the active power support of a single converter station and multiple converter stations is carried out. The research results show that the use of emergency power support in the DC transmission system has a good effect on maintaining the stability of the inter-connection system and the reliability of the power supply.
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Authors and Affiliations

Congshan Li
1
ORCID: ORCID
Zikai Zhen
1
ORCID: ORCID
Tingyu Sheng
2
ORCID: ORCID
Yan Liu
1
ORCID: ORCID
Pu Zhong
1
Xiaowei Zhang
1

  1. Zhengzhou University of Light Industry, College of Electrical and Information Engineering, China
  2. Maintenance Company of State Grid Henan Electric Power Company, China

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