Improved Coordinated Control Strategy of Multi-terminal DC Grids Considering Frequency Adaptation and Fast Stabilization Characteristics

doi:10.11930/j.issn.1004-9649.202406059

Abstract

Abstract:

Multi-terminal flexible DC transmission (VSC-MTDC) technology has a wide range of application prospects in large-scale and wide-range multiple types of renewable energy grid-connection and outward transmission. To address the influence of AC-DC coupling on DC voltage and AC system frequency under large unbalanced power disturbances of flexible DC network, an improved coordinated control strategy based on DC voltage sag control is firstly proposed to eliminate the DC network voltage deviation from the rated operation point before and after the disturbances. And then the adaptive sag coefficients are introduced to improve the DC network voltage steady state recovery rate and certain control reliability. Thirdly, the adaptive capacity enhancement of the improved coordination control frequency is analyzed in order to realize the participation of converter station in AC system frequency regulation and control, and to make up for the lack of AC-side FM capacity. Finally, a simulation model of new energy transmission via four-terminal DC grid is constructed based on the PSCAD/EMTDC, which verifies the feasibility and effectiveness of the proposed improved coordinated control strategy and its AC grid frequency regulation.

Key words: voltage source converter multi-terminal DC, sag control, coordinated control, acceleration strategy, frequency control

Yunrui WU, Jianpo ZHANG, Xincheng TIAN, Kaifeng YING, Zhong CHEN. Improved Coordinated Control Strategy of Multi-terminal DC Grids Considering Frequency Adaptation and Fast Stabilization Characteristics[J]. Electric Power, 2025, 58(3): 31-42.

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URL: https://www.electricpower.com.cn/EN/10.11930/j.issn.1004-9649.202406059

https://www.electricpower.com.cn/EN/Y2025/V58/I3/31

Figures/Tables 15

Fig.1 Four-port VSC-MTDC model

Fig.2 New energy station pole U/f control model

Table 1 Comparison of coordinated control modes

控制策略	模式切换	站间通信	不平衡功率	稳态电压偏差	主要缺陷
主从控制	需要	需要	主站承担	无差	动态特性差，稳定速度慢
电压裕度控制	需要	不需要	主站承担	无差	电压裕度整定复杂
直流电压下垂控制	不需要	不需要	共同承担	有差	功率分配精度低

Fig.3 Frequency regulation sag control block diagram

Fig.4 Frequency regulation sag control voltage-frequency-output characteristic analysis

Fig.5 Acceleration strategy principle

Fig.6 ICC control block diagram

Fig.7 Frequency adaptive ICC control principle

Table 2 Basic parameters of the simulation model

参数名称		数值
额定直流电压/kV		500
VSC1侧额定交流电压/kV		500
VSC1额定输送容量/MW		800
VSC2侧额定交流电压/kV		500
VSC2额定输送容量/MW		800
VSC3侧额定交流电压/kV		500
VSC3额定输送容量/MW		1200
VSC4侧额定交流电压/kV		500
VSC4额定输送容量/MW		1200

Table 3 Main parameters of each control mode

参数	VSC2	VSC4
主从控制 P_refj/MW		–750
下垂控制 P_refj/MW	–500	–750
下垂系数 k_j/(kV·MW^–1)	0.2	0.1
改进协调控制 P_refj/MW	–500	–750
单位下垂功率 ∆P_refj/MW	50	50
功率分配系数 K_j	0.1	0.2
频率下垂系数 k_fj	200	200
频率调节效应系数 K_sj/(MW∙Hz^–1)	1000	1000

Fig.8 VSC1 decommissioning simulation analysis

Fig.9 Simulation analysis of accelerated resilience

Fig.10 Frequency modulation simulation comparison of frequency adaptative ICC participating in scenario 1

Fig.11 Verification of frequency modulation capability for load increasing and generator triping

Fig.12 Verification of frequency modulation capability for load reduction and generator triping

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