A full sequence impedance modelling and stability analysis of the virtual synchronous generator with inner loops

Abstract

Virtual synchronous generator (VSG) has been widely studied owing to its inertia support to the grid. However, the stability of VSG is not analysed accurately for actual applications in previous studies that overlook voltage and current inner loops of VSG. Since inner loops are essential to control output voltage and current accurately in practical engineering, this study focuses on stability analysis of the interconnection system of VSG and the grid by sequence impedance modelling of VSG with inner loops. The complete sequence impedance model for VSG with inner loops is built and compared with that of the VSG‐ignoring inner loops, and then the stability is analysed based on that. It shows that inner loops bring the risk of instability and oscillation for VSG, which was not predicted in previous studies. Then, the influence of each parameter of inner loops on the impedance and oscillation is analysed, showing that the oscillation can hardly be eliminated by tuning the parameters of inner loops. Therefore, corresponding virtual resistor with proper value is studied and adopted in VSG with inner loops to avoid oscillation. Finally, the correctness of theoretical analysis and the effectiveness of the adopted virtual resistance are verified by the hardware‐in‐the‐loop experiments.

Grid Forming Inverter Modeling, Control, and Applications

“…The stability of a GFMI connected to a system can be guaranteed if each inverter has a passive synchronization behavior, which means the frequency-power characteristic of each GFMI impedance has a positive real value for all the frequency ranges. Moreover, the effects of the inner control loops of a VSG on its output impedance are taken into consideration in the stability analysis in [80]. The study in [80] reveals the adverse impacts of the inner loops on the system stability.…”

“…Moreover, the effects of the inner control loops of a VSG on its output impedance are taken into consideration in the stability analysis in [80]. The study in [80] reveals the adverse impacts of the inner loops on the system stability. Furthermore, the relations between the control parameters in the inner loops and the VSG's output impedance are also studied in this work.…”

State of the Art of the Techniques for Grid Forming Inverters to Solve the Challenges of Renewable Rich Power Grids

“…In this method, the desired oscillation frequencies are set using the decoupling network block and then the desired attenuation at these frequencies are performed through the virtual rotors. The study in [70] analyzes the stability of a VSG-based grid connected system by considering the effect of VSG inner control loops. This study shows the significant effect of inner loops on VSG output impedance and its adverse effects on the system stability.…”

Few‐shot learning based multi‐weather‐condition impedance identification for MPPT‐controlled PV converters

“…The few-shot learning opens a new door to identifying the broadband impedance of PV converters with machine learning methods. Among the existing few-shot learning algorithms, the model agnostic meta-learning (MAML) method is one of the most typical algorithms and the one used in this paper [18,22].…”

“…In [17], sequence impedance models for voltage source converters are built, with consideration of DC bus dynamics. Furthermore, [18] builds the complete impedance model for converters with multi control loops, showing that the inner‐loop control can have a negative impact on system stability. For the direct measurement method, since the measurements process of sequence impedance is simpler as well comparing to that of DQ impedance, the analysis for sequence impedance has become a trend in recent years.…”