Modeling and stability analysis of energy storage dq impedance of VSG-type configuration network considering the influence of multiple control loops

doi:10.19799/j.cnki.2095-4239.2024.0629

Abstract

Abstract:

The reduction in the proportion of synchronous machines in the new power system brings challenges to maintaining the stable operation of the system. Consequently, the constructed-grid energy storage system has received immense attention due to its voltage source external characteristics and good weak-grid stability. Nevertheless, the nature of grid-constructed energy storage is still a power electronic device with multiple control loops and control parameters; thus, the stability of grid-constructed energy storage needs to be considered. Numerous studies have focused on the stability of multi-loop controlled energy storage, while there are fewer studies on the stability of structural network type. This paper examines the main circuit and power ring of grid-constructed energy storage using a virtual synchronous generator (VSG). We analyzed the voltage, current, and virtual impedance loops from the perspective of actual control demand, selected the dq coordinate system, and established the multi-loop small-signal and the equivalent output impedance models. Subsequently, the influence of the control loop parameters on the impedance characteristics of different frequency bands is analyzed, followed by a grid-connected small-signal stability analysis using the impedance method. Finally, these results were confirmed by simulation. The findings indicated that the VSG-type grid-connected energy storage exhibits negative damping characteristics in the low-frequency band (1—10 Hz), with the power loop inducing an elevation in the low-frequency negatively damped resonance frequency. Furthermore, the voltage loop induces negative damping characteristics in the middle-frequency band of the system (10—100 Hz), whereas the current loop induces negative damping characteristics in the high-frequency band of the system (100—10000 Hz). Under a weak grid condition, the reduction in power ring damping and the increase of virtual inertia, along with a decrease in voltage ring proportionality coefficient and an increase in integral coefficient, can induce low-frequency oscillations that may lead to destabilizing the system, while the current ring has a small effect on system stability. With a short circuit ratio (SCR) of 2, introducing the virtual impedance loop enlarges the area of the stabilization region of the power loop control parameter by about 1.67 times and the area of the stabilization region of the voltage loop control parameter by about 4.5 times.

Key words: grid-forming energy storage, multiple control loops, dq-frame impedance modeling, small-signal stability

CLC Number:

TM 74

Jianrong CHEN, Bo ZHAO, Bingyang ZHAO. Modeling and stability analysis of energy storage dq impedance of VSG-type configuration network considering the influence of multiple control loops[J]. Energy Storage Science and Technology, 2025, 14(1): 222-239.

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参数	数值
有功指令值P_ref/kW	500
滤波电感L_f/mH	3
无功指令值Q_ref/kvar	0
滤波电感寄生内阻R_f/Ω	0.01
直流母线电压U_dc/V	700
滤波电容C_f/μF	20
电网相电压有效值U_g/V	220
虚拟阻尼系数D_p/(W·s/rad)	200
额定角频率ω_n/(rad/s)	100π
转动惯量J/(kg·m²)	0.5
电压环比例系数K_p_u	9
电压环积分系数K_i_u	300
电流环比例系数K_p_i	5
电流环积分系数K_i_i	50

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