Phase-locked loop control circuit based on second-order oscillation link under high permeability

Abstract

The invention relates to a phase-locked loop control circuit based on a second-order oscillation link under high permeability, and belongs to the field of electronic circuits. A function relationship between an output phase angle of the phase-locked loop and a disturbance quantity is utilized to reveal a main reason for system robustness reduction, and main defects of a traditional pre-filter phase-locked loop are analyzed. Therefore, a novel phase-locked loop design scheme based on a second-order oscillation link is provided, an equivalent transfer function of the novel phase-locked loop is deduced, and meanwhile a specific parameter design method is provided. Theoretical analysis shows that the novel phase-locked loop has the same harmonic attenuation characteristic as that of a traditional preposed second-order low-pass filter phase-locked loop, the system robustness is guaranteed, and grid-connected common point unity power factor network access can be achieved without an additional phase compensation link. And finally, verifying the effectiveness of the novel phase-locked loop design scheme through a simulation result.

Description

technical field [0001] The invention belongs to the field of electronic circuits, and relates to a phase-locked loop control circuit based on a second-order oscillation link under high permeability. Background technique [0002] With the rapid growth of installed capacity of new energy sources such as photovoltaics and wind power, the penetration rate of new energy power generation has increased year by year. Since new energy power stations are usually distributed in remote areas, when the transmission and distribution lines of the system are long and there are many isolation transformers in the regional power grid, the power grid is prone to present a weak power grid characterized by "high grid impedance". ratio, SCR) to distinguish the strength of the grid. [0003] In recent years, the research on the stability of LCL filter grid-connected inverters at high penetration rates can be roughly divided into two aspects. First, in the mid-to-high frequency range of several hu...

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Problems solved by technology

The second is that the inverter system is in the frequency band of the phase-locked loop PLL bandwidth of several hundred Hz, and the coupling effect between the PLL link and the grid impedance will also seriously threaten the stability of the system.

Literature (Xu Jinming, Bian Shen Yiyang, Qian Qiang, et al. Single-phase inverter phase-locked loop based on grid current feedforward under weak grid [J]. Chinese Journal of Electrical Engineering, 2020, 40(8): 2647-2656 .) Using the grid-connected current to introduce negative coefficient feedforward at the input end of the PLL, the effect of this scheme is obvious, but the differential link is difficult to realize, and an additional phase correction link is required

[0007] 3) Phase angle compensation is performed on the equivalent output impedance of the system, but this scheme requires a clear compensation frequency range and may cause fundamental frequency phase deviation

[0008] 4) The robustness of the inverter system can be improved by increasing the damping ratio of the phase-locked loop system, but this scheme cannot adapt to wide-ranging changes in grid impedance

[0009] To sum up, the problem of system instability caused by phase-locked loops under high permeability has not been fully studied, and there are few solutions for the improved design of phase-locked loop structures

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