Inertia Enhancement Control Strategy of Grid Connected Converter Based on Frequency Lock Loop

LI Xing; ZHAI Baoyu; LIANG Shuchao; TANG Weihan; CHEN Zhangyong; CHEN Yong

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Inertia Enhancement Control Strategy of Grid Connected Converter Based on Frequency Lock Loop

LI Xing^1,2, ZHAI Baoyu², LIANG Shuchao², TANG Weihan¹, CHEN Zhangyong¹, CHEN Yong¹

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Abstract

[Objective] With the increasing penetration of renewable energy sources, the overall inertia of power systems has significantly declined due to the gradual replacement of traditional rotating machines by power electronic converters. This reduction in inertia poses serious challenges to frequency stability and system disturbance rejection. To address this issue, grid-connected converters are required to actively provide synthetic inertia support. [Methods] Based on a power-sharing control strategy, this paper analyzes the pole-zero distribution characteristics of conventional Phase-Locked Loop (PLL)-based control structures and highlights the associated stability degradation under weak grid conditions. To overcome these limitations, an inertia enhancement control scheme based on an improved Frequency-Locked Loop (FLL) structure is proposed. By proportionally integrating the frequency derivative signal with the reference active power, the proposed method effectively mitigates power oscillations and enhances the inertial response of the converter. Furthermore, a modified Model Predictive Control (MPC) strategy is employed to replace the conventional inner current loop, significantly improving the system's transient performance. [Results] Comparative studies of frequency step responses demonstrate the superiority of the proposed FLL-based structure in maintaining frequency stability under weak grid conditions. The active power control strategy under the improved FLL framework is detailed, along with the principle of inertia emulation and the tuning of associated parameters. [Conclusions] The proposed method avoids high-frequency noise issues caused by direct differentiation of frequency signals and eliminates the stability problems typically introduced by PLL. As a result, the frequency response of the system is substantially improved, and the goal of synthetic inertia enhancement is achieved. The effectiveness of the proposed control strategy is further validated through Hardware-in-the-Loop (HIL) simulation experiments.

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grid connected inverters / power oscillation / frequency locked loop (FLL) / inertial enhancement technology

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LI Xing, ZHAI Baoyu, LIANG Shuchao, TANG Weihan, CHEN Zhangyong, CHEN Yong. Inertia Enhancement Control Strategy of Grid Connected Converter Based on Frequency Lock Loop[J]. Electric Power Construction. 0

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