Harmonic Oscillation Source Identification and Stability Improvement Method for Multi-Infeed System of Grid-Connected Inverter
Gao Jiayuan1, Huang Shuai1, Zhan Runkun1, Jiang Fei1, Tu Chunming2
1. School of Electrical and Information Engineering Changsha University of Science and Technology Changsha 410004 China; 2. National Electric Power Conversion and Control Engineering Technology Research Center Hunan University Changsha 410082 China
Abstract：The large-scale integration of grid-connected inverters (GCI) into the power grid has formed a multi-infeed system, where GCI interactions are highly likely to induce harmonic oscillations, posing a threat to the stable operation of the entire system. Research on suppressing the system harmonic oscillation by adjusting the control loops of the multi-infeed GCI system has been widely conducted due to its reliable theoretical analysis and significant harmonic-oscillation-suppression effects. However, these methods often require adjustments to the control loops of each GCI, which is not practical for engineering implementation. Moreover, because the control structures and parameters of each GCI differ, it is challenging to determine which GCI should execute the control strategy or parameter adjustments. Therefore, this paper presents a novel method for identifying the source of harmonic oscillation in GCI. By considering key factors, such as the network structure of the multi-infeed system, line impedance, and grid impedance, a current-oscillation mode gain model is developed for the multi-infeed GCI system across a range of control parameter settings. The harmonic-oscillation characteristics are systematically analyzed, and the dominant harmonic-oscillation source is identified via participation factor calculations. Notably, the proposed modeling method addresses the challenge of identifying and locating harmonic oscillation sources. Subsequently, a stability-improving method for asymmetric impedance remodeling that combines suppression of the PLL positive feedback loop and q-axis phase compensation is proposed. It can adjust the control loop of the harmonic oscillation source to ensure that the harmonic source GCI maintains sufficient stability margin in the multi-feed system. In the case of grid impedance variation, theoretical analysis and RT-Lab experimental verification are conducted. The results show that when harmonic oscillation occurs in the system, the time-domain current waveform of the harmonic-oscillation source GCI, identified through theoretical analysis, exhibits higher harmonic distortion than that of other GCI. Meanwhile, the proposed asymmetric impedance remodeling method can effectively improve the adaptability range of the multi-feed system to grid impedance variations. Therefore, the stability of the multi-feed system has been significantly enhanced. The following conclusions are drawn. (1) The constructed current oscillation mode gain model incorporates the coupling characteristics of the grid structure and the control characteristics of the GCI, laying a model foundation for the reliable identification of harmonic oscillation sources. (2) When the harmonic oscillation occurs in the multi-feed GCI system, the identification of the harmonic oscillation source provides a selected GCI for the design of harmonic oscillation suppression strategies in the multi-feed system. (3) For the identified harmonic oscillation source, an asymmetric impedance reshaping stability improvement method is proposed via the PLL positive feedback loop suppression and q-axis phase compensation, effectively suppressing the harmonic oscillations and enhancing the stability of the multi-feed GCI system.
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2026, Vol. 41 
