Transient Stability Mechanism Analysis of Grid-following MMC-HVDC

doi:10.11985/2023.03.027

Abstract

Abstract:

With the increase of renewable power integration, the modular multilevel converter based high voltage direct current(MMC-HVDC) with grid-following control has gained more importance in the transmission system. The transient stability of MMC-HVDC will affect the secure operation of power system. The transient stability mechanism of grid-following MMC-HVDC is studied. The dynamic model of phase-locked loop(PLL) is developed first. Firstly, the grid-connected dynamic model of MMC with phase-locked loop(PLL) as synchronization unit is established. Then based on the model, the influence of grid strength, fault-ride through control and PLL parameters on the transient stability is studied. The grid-connected transient stability of the MMC enhances when the power grid strength is high and the reactive component of injection current during the fault increases. Reducing the proportion and integral gain of the PLL is beneficial to transient stability. According to the stability mechanism, a control strategy of injection current is proposed for the MMC to improve the transient stability by matching the current angle with the grid impedance angle. The time-domain simulation in PSCAD/EMTDC verified the conclusions and the effectiveness of the proposed enhancement control.

Key words: Modular multilevel converter, transient stability, phase-locked loop, fault ride-through control strategy

CLC Number:

TM712
TM46

XIANG Zhongming, NI Qiulong, LI Zhenhua, XU Jianping, XUE Yicheng, ZHANG Zheren, XU Zheng. Transient Stability Mechanism Analysis of Grid-following MMC-HVDC[J]. Journal of Electrical Engineering, 2023, 18(3): 250-259.

Figures/Tables 16

References 22

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参数	数值
MMC额定容量/(MV·A)	400
MMC直流电压/kV	400
MMC子模块个数	200
MMC阀侧交流电压/kV	210
系统基准容量/(MV·A)	400
电网额定电压/kV	110
系统频率/Hz	60
短路比	1.6
电网等值阻抗角φ_Z/(°)	80
MMC有功、无功指令值/p.u.	0.8/0
PLL参数K_p、K_i	100/220
MMC电流限幅值I_max/p.u.	1.2
交流电压阈值U_thr/p.u.	0.75

参考值I_dref/A	电流角φ_I/(°)	CCT/ms
0.3	-75	595
0.6	-60	150
0.9	-41	75
0.1	-85	137
-0.1	-95	65
-0.3	-104	49

K_i	CCT/ms	K_p	CCT/ms
100	225	60	275
220	203	100	203
400	181	140	156

短路比ρ_SCR	电压u_sq/p.u.	CCT/ms
1.6	0.094	203
2	0.075	262
2.3	0.067	300