跟网型逆变器同步稳定性分析及增强控制方法

doi:10.19595/j.cnki.1000-6753.tces.250588

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Abstract

Renewable energy resources (RESs) such as wind power and photovoltaic power have been developed rapidly and applicated in large scale in recent years. The phase-locked loop (PLL) based grid-following inverters (GFLIs) are widely used to connect RESs to the power system due to their advantages of high efficiency, flexibility and controllability. However, with the continuous increase in penetration of power electronic devices and RESs within the power system, GFLIs are prone to loss synchronous stability under transient events like grid voltage sage, grid short circuit and so on, resulting in disconnection of RESs and threatening the safe and stable operation of the power system. Therefore, it is crucial to study the stability issues of GFLIs under transient events. The analysis results reveal that the PLL poses a negative damping effect, which will decrease GFLI’s synchronous stability during transient events, especially under weak grid condition. To address this issue, a stability control method is proposed in this work to enhance GFLI’s synchronous stability during transient events in weak grid condition.
The basic idea of the proposed stability control method is to reduce the negative damping effect introduced by the PLL. Base on this, a feedback loop that uses the deviation of the angular speed between the PLL and the grid as feedback signal is added to the conventional PLL, thereby reducing the negative damping effect of the PLL. Theoretical analysis shows that the stability control method improves the small-signal stability margin of GFLI, increases the equivalent inertia and damping coefficient of GFLI, and thus enhances system’s synchronous stability. The parameter design principle of the stability control method is given with consideration of different grid conditions.
Simulation and hardware-in-the-loop (HIL) experiment results validate that the proposed stability control method can enhance the stability of GFLI under the conditions of grid voltage sag, sudden changes in grid impedance and grid phase. With the traditional PLL that doesn’t adopt the stability control method, the system losses synchronous stability when grid voltage drops from 1pu to 0.63pu, grid impedance steps from 1p.u. to 1.58p.u. and grid phase steps 190°. On the contrary, with the stability control method, the GFLI grid-connected system can maintain stability when grid voltage drops to 0.58pu, grid impedance steps to 1.68p.u. and grid phase steps 200°.
The following conclusions can be drawn through the research presented in this paper: (1) The necessary condition for GFLI grid-connected system to maintain stability during transient events lies in the existence of a post-fault steady-state equilibrium point (SEP), which must satisfy the small-signal stability criterion. (2) The smaller the voltage sage, grid inductance, PLL’s integral coefficient, and the system active current, the greater the system stability. PLL’s proportional coefficient poses dual effects on GFLI’s stability. Within a certain range, increased proportional coefficient can enhance system’s synchronous stability. However, excessive proportional coefficient will induce overspeed angular velocity in the GFLI, even make the system fail to meet the small-signal stability condition, thereby deteriorating system’s stability. (3) The proposed stability control method can not only enhance the small-signal stability margin of GFLI, but also strengthen synchronous stability.

Key words： Renewable energy power generation grid-following inverter phase-locked loop synchronous stability stability control

Received: 11 April 2025

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TM464

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	Wang Pengfei
	Chen Jiawei
	Luo Chao
	Gu Haohan
	Cai Haiqin

Cite this article:

Wang Pengfei,Chen Jiawei,Luo Chao等. Synchronous Stability Analysis and Enhancement Control Method for Grid-following Inverters[J]. Transactions of China Electrotechnical Society, 0, (): 20250588-20250588.

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https://dgjsxb.ces-transaction.com/EN/10.19595/j.cnki.1000-6753.tces.250588 OR https://dgjsxb.ces-transaction.com/EN/Y0/V/I/20250588

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