The Impact of Negative-Sequence Control on the Stability of Grid-Connected Converter in Weak Grids

doi:10.12204/j.issn.1000-7229.2021.03.008

Abstract

Abstract:

When converters are connected to grids, the negative-sequence control (NSC) may deteriorate the system’s stability since it changes the typical PLL-based vector control, especially in weak grids. This paper analyzes this issue. Firstly, the proportional-integrational quasi-resonant (PIR) control, as one of the widely-used NSC methods, is introduced. Then, we derive the amplitude-phase impedance model and primal-dual complex circuit of the converter-connected grid for the case that the grid voltage is balanced, in which the converter applies the PIR control. Then, we analyze the impacts of the change caused by the PIR control on the admittance elements of the converter’s amplitude-phase impedance. Besides, the generalized impedance criterion is applied to analyze the impact of NSC on the system’s stability. The analysis results show that the NSC may cause the sub-synchronous oscillation issue and nearly 100 Hz oscillation issue. The simulation results verify the analysis results.

Key words: converter, weak grids, proportional-integrational quasi-resonant (PIR) control, primal-dual complex circuit, generalized impedance criterion

CLC Number:

TM715

LI Dandan, ZHANG Aijun, YUAN Hui, XING Huadong, GAN Qingshan, XIN Huanhai. The Impact of Negative-Sequence Control on the Stability of Grid-Connected Converter in Weak Grids[J]. ELECTRIC POWER CONSTRUCTION, 2021, 42(3): 61-71.

Figures/Tables 13

Fig.1 The one-line diagram of grid-connected inverter with PIR controller

Fig.2 Diagram of PLL based on decoupled double synchronous reference frame

Fig.3 Primal-dual complex circuit of the system

Fig.4 Bode plot of Yg11 and Yg22 when considering PIR control or not

Table 1 Parameters of the grid-connected converter

Table 2 Weakest eigenvalue for different cases

Fig.5 Nyquist plot of the system’s open-loop transfer function for case 1 when considering PIR control or not

Fig.6 Nyquist plot of the system’s open-loop transfer function for case 2 when considering PIR control or not

Fig.7 Primal-dual complex circuit for system resonance in special frequency band

Fig.8 The comparison of active power under unbalanced grid voltage

Fig.9 Current output of the converter in case 1

Fig.10 Current output of the converter in case 2

Fig.A1 Phasor positions during disturbance

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