Transient Modeling and Characteristic Comparative Analysis of Grid-Forming VSC with and Without Current Control

doi:10.16183/j.cnki.jsjtu.2023.416

Abstract

Abstract:

As the support capacity of renewable energy generation equipment for the power grid needs enhancement, grid-forming control has attracted extensive attention, among which the virtual synchronous generator (VSG) has emerged as a key research frontier and is already being applied in engineering demonstration. Voltage source converter (VSC) with VSG as the synchronization link can be classified into voltage and current dual loop control and direct voltage control according to whether there is a current control loop in the structure. The difference in the two control structures has a significant impact on the transient characteristics of VSC. To study the difference between transient characteristics of two kinds of VSCs, the transient models are developed based on the “power excitation-internal voltage response” model, and the formation mechanism of internal voltage and transient characteristics are comparatively analyzed. Since the VSG simulates the operation characteristics of the synchronous machine, the equivalent inertia and equivalent damping of the VSC are analytically obtained at the electromechanical scale, and their transient behaviors are compared. It is found that the equivalent inertia and damping of a VSC with direct voltage control remain constant, while those of a VSC with voltage and current dual loop control exhibit time-varying characteristics and are numerically smaller than of the direct voltage control system. Finally, the validity of the theoretical analysis is confirmed by electromagnetic transient simulation.

Key words: grid-forming voltage source converter (VSC), voltage and current dual loop control, direct voltage control, “power excitation-internal voltage response” model, comparison of transient characteristics

CLC Number:

TM712

REN Xiancheng, LI Shangzhi, LI Yingbiao, HU Jiabing, XU Taishan, BAO Yanhong, WU Feng. Transient Modeling and Characteristic Comparative Analysis of Grid-Forming VSC with and Without Current Control[J]. Journal of Shanghai Jiao Tong University, 2025, 59(7): 971-982.

Figures/Tables 19

Fig.1

Fig.2

Fig.3

Fig.4

Tab.1

Fig.5

Tab.2

Parameters of system

参数	取值	参数	取值
VSC1滤波电感, $L f 1 p . u .$	0.006	VSC2滤波电感, $L f 2 p . u .$	0.008
变压器1电感, $L T 1 p . u .$	0.009	变压器2电感, $L T 2 p . u .$	0.01
线路单位长度电阻, $r 1 p . u .$ /km^-1	0.0001	线路单位长度电感, $l 1 p . u .$ /km^-1	0.001
线路单位长度电容, $c 1 p . u .$ /km^-1	0.00175	线路长度/km	110
有功负荷1,P_Load1/MW	967	无功负荷1,Q_Load1/Mvar	100
有功负荷2,P_Load2/MW	1467	无功负荷2,Q_Load2/Mvar	100
无功补偿1,Q_C1/Mvar	200	无功补偿2,Q_C2/Mvar	200
接地电阻, $R k p . u .$	0.01	接地电感, $L k p . u .$	0.1

Tab.2

Tab.3

Control parameters of VSC with voltage and current dual loop control

控制参数	数值
惯量系数, $T j p . u .$	5
阻尼系数,D_p.u.	25
端电压控制比例系数, $k p_v p . u .$ ;积分系数, $k i_v p . u .$	2,50
电流控制比例系数, $k p_i p . u .$ ;积分系数, $k i_i p . u .$	1,100

Tab.3

Fig.6

Tab.4

Control parameters of VSC with direct voltage control

控制参数	数值
惯量系数, $T j p . u .$	5
阻尼系数,D_p.u.	15
端电压控制比例系数, $k p_v p . u .$ ;积分系数, $k i_v p . u .$	0.5,10

Tab.4

Fig.7

Fig.8

Fig.9

Fig.10

Fig.11

Fig.12

Fig.13

Fig.14

Fig.15

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	电压电流双环控制VSC	直接电压控制VSC
时间尺度特征	有功和无功输入经由电压环、电流环、交叉解耦项ωL_fi_g_d和ωL_fi_g_q等环节生成θ^V和内电势幅值E,内电势幅值和相位均呈现交流电流、直流电压、机电3个时间尺度特征	内电势幅值直接由端电压控制生成,仅呈现直流电压尺度特征;内电势相位等于VSG输出相角θ_VSG,仅呈现机电尺度特征
非线性特征	由于电压电流等效替代和直角坐标-极坐标变换环节的存在,所以内电势幅值、相位与有功、无功功率输入呈现非线性关系	端电压幅值等效替代使得内电势幅值与有功、无功功率输入呈现非线性关系,而内电势相位由有功功率线性驱动
耦合特征	极坐标变换环节使得内电势幅值和相位形成耦合关系,内电势幅值和相位动态相互影响	内电势幅值直接由端电压控制生成,内电势相位受有功功率驱动,幅值和相位解耦