Coordinated Control Strategy of Modular Multi-level Converter-Based Multi-terminal Direct Current System for Onshore Wind Power Faults

doi:10.11930/j.issn.1004-9649.202308031

Abstract

Abstract:

This paper proposed a coordinated control strategy of multiple wind farm modular multilevel converters (WFMMCs) and wind turbines using energy control to address the issue of surplus power during faults in the onshore alternating current (AC) power grid of a modular multilevel converter based multi-terminal direct current (MMC-MTDC) system for offshore wind power. During the fault period, some WFMMCs first initiate energy control, raising the energy reference value based on changes in direct current (DC) voltage to absorb surplus power in the DC system. The remaining WFMMCs predict the DC voltage, and when the predicted DC voltage exceeds the limit, the remaining WFMMCs activate energy control to absorb surplus power. The WFMMCs adopt voltage reduction control on the wind turbine while absorbing surplus power and reduce the reference value of the AC voltage on the wind turbine side based on the increase in energy storage at the WFMMC. The grid side converter of the wind turbine adjusts the reference value of the d-axis current based on changes in AC voltage, reducing the active power transmitted to the MMC-MTDC system and avoiding the DC voltage exceeding the limit of the MMC-MTDC system. Finally, different types of faults were simulated in PSCAD/EMTDC to verify the effectiveness of the proposed coordinated control strategy.

Key words: multi-terminal flexible and direct current system, AC fault, surplus power, energy control, voltage reduction control, coordinated control

Ping ZHAO, Haosen JIA, Hengxiao GAO, Zhenxing LI. Coordinated Control Strategy of Modular Multi-level Converter-Based Multi-terminal Direct Current System for Onshore Wind Power Faults[J]. Electric Power, 2024, 57(8): 85-95.

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URL: https://www.electricpower.com.cn/EN/10.11930/j.issn.1004-9649.202308031

https://www.electricpower.com.cn/EN/Y2024/V57/I8/85

Figures/Tables 14

Fig.1 Topology of MMC-MTDC for offshore wind power

Table 1 Parameters of MMC-MTDC system for offshore wind power

参数	数值	参数	数值
WFMMC1额定容量/(MV·A)	400	直流电缆电感/(mH·km^–1)	0.16
WFMMC2额定容量/(MV·A)	300	直流电缆1长度/km	200
GSMMC1额定容量/(MV·A)	400	直流电缆2长度/km	200
GSMMC2额定容量/(MV·A)	300	直流电缆3长度/km	200
额定直流电压/kV	400	直流电缆4长度/km	200
桥臂的子模块个数	200	交流架空线长度/km	50
子模块额定电压/kV	2	交流电网1容量/(MV·A)	4000
子模块电容/μF	4000	交流电网2容量/(MV·A)	3000
桥臂电抗器/mH	133	交流电网1电源装机容量/MW	5000
直流电缆电阻/(Ω·km^–1)	0.01	交流电网2电源装机容量/MW	3750
直流电缆电容/(μF·km^–1)	0.23

Fig.2 Control strategy of wind turbines

Fig.3 Control strategy of GSMMC

Fig.4 Control strategy of WFMMC

Fig.5 Energy control strategy of WFMMC

Fig.6 Coordinated control strategy of MMC-MTDC for offshore wind power

Fig.7 Characteristic curve of energy reference value for WFMMC

Fig.8 Characteristic curve of reference value for AC voltage

Fig.9 Characteristic curve of reference value for d-axis current

Fig.10 Coordinated control flow of MMC-MTDC for offshore wind power

Fig.11 Waveform of single-phase grounding fault

Fig.12 Waveform of two-phase grounding fault

Fig.13 Waveform of three-phase grounding fault

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