Mid- and High-Frequency Oscillation Suppression Strategy for MMC-HVDC System Based on DC Current Feedback

doi:10.11930/j.issn.1004-9649.202309116

Abstract

Abstract:

The serious mid-and high- frequency oscillation issue in modular multilevel convertor based high voltage direct current (MMC-HVDC) systems poses a significant threat to the normal operation of power systems. In this paper, we firstly established an AC-side impedance model of the MMC based on its dynamic phase vector model. Secondly, we analyzed the impact of control loops and control parameters on MMC impedance characteristics using the impedance method, and identified the power outer loop, current inner loop and control loop delay as the main factors causing MMC to present negative damping characteristics. And then, based on an analysis of the limitations of existing oscillation suppression strategies that are based on voltage feedforward loops and current inner loops, we proposed an oscillation suppression strategy that adds DC current feedback to the power outer loop, which can greatly eliminate harmonic components in the system and improve MMC impedance characteristics. Finally, the correctness and effectiveness of the theoretical analysis and proposed suppression measures were verified through electromagnetic simulation software.

Key words: modular multilevel convertor (MMC), stability analysis, mid- and high-frequency oscillation, oscillation suppression

Yechun XIN, Shangxuan LI, Yanxu WANG, Yihua ZHU, Jiawei YU, Dongxu CHANG. Mid- and High-Frequency Oscillation Suppression Strategy for MMC-HVDC System Based on DC Current Feedback[J]. Electric Power, 2025, 58(1): 39-49.

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URL: https://www.electricpower.com.cn/EN/10.11930/j.issn.1004-9649.202309116

https://www.electricpower.com.cn/EN/Y2025/V58/I1/39

Figures/Tables 20

Fig.1 Single phase circuit topology of MMC

Fig.2 The relationship between electrical coordinate system and control coordinate system

Table 1 Main parameters

参数		数值
系统	网侧交流电压/kV	525
	额定直流电压/kV	840
	额定功率/(MV·A)	1250
变压器	变压器变比/kV	525/437
变压器	变压器短路比/%	14
MMC	桥臂子模块数/个	500
	桥臂等效电阻/Ω	0.5
	桥臂等效电感/mH	140
	桥臂子模块电容/μF	11000
控制器	锁相环PI参数(k_pPLL、k_iPLL)	2000、3000
	功率外环PI参数(k_ppq、k_ipq)	0.3、10
	电流内环PI参数(k_pi、k_ii)	0.4、16.7
	环流抑制PI参数(k_pi2、k_ii2)	0.4、40
	Pade近似延时时间/μs	300

Fig.3 Impedance of MMC under different PLL control parameters

Fig.4 Impedance of MMC under different outer loop control parameters

Fig.5 Impedance of MMC under different inner loop control parameters

Fig.6 Impedance of MMC under different CCSC parameters

Fig.7 Impedance of MMC under different control link delays

Fig.8 Impedance of MMC after adding a filter to the voltage feedforward link

Fig.9 Additional damping link in the current inner loop

Fig.10 Impedance of MMC after adding a filter to the current inner loop

Fig.11 Adding DC current feedback link to the power outer loop

Fig.12 Adding DC current feedback to the power outer loop

Fig.13 Impedance model of MMC

Fig.14 Impedance of MMC and AC system of Condition 1

Fig.15 FFT analysis of valve side AC voltage of Condition 1

Fig.16 Valve side AC voltage of Condition 1

Fig.17 Impedance of MMC and AC system of Condition 2

Fig.18 FFT analysis of valve side AC voltage of Condition 2

Fig.19 Valve side AC voltage of Condition 2

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