Impedance-Based Stability Criterion for Grid-Connected Inverters

Grid-connected inverters are known to become unstable when the grid impedance is high. Existing approaches to analyzing such instability are based on inverter control models that account for the grid impedance and the coupling with other grid-connected inverters. A new method to determine inverter-grid system stability using only the inverter output impedance and the grid impedance is developed in this paper. It will be shown that a grid-connected inverter will remain stable if the ratio between the grid impedance and the inverter output impedance satisfies the Nyquist stability criterion. This new impedance-based stability criterion is a generalization to the existing stability criterion for voltage-source systems, and can be applied to all current-source systems. A single-phase solar inverter is studied to demonstrate the application of the proposed method.

[1]  P.J.M. Heskes,et al.  Harmonic interaction between a large number of distributed power inverters and the distribution network , 2004, IEEE Transactions on Power Electronics.

[2]  S. Cobreces,et al.  Influence analysis of the effects of an inductive-resistive weak grid over L and LCL filter current hysteresis controllers , 2007, 2007 European Conference on Power Electronics and Applications.

[3]  R. D. Middlebrook,et al.  Input filter considerations in design and application of switching regulators. , 1976 .

[4]  I.A. Hiskens,et al.  Control of inverter-connected sources in autonomous microgrids , 2008, 2008 American Control Conference.

[5]  Gerard Ledwich,et al.  Connection of inverters to a weak grid , 2000, 2000 IEEE 31st Annual Power Electronics Specialists Conference. Conference Proceedings (Cat. No.00CH37018).

[6]  Jian Sun,et al.  Small-Signal Methods for AC Distributed Power Systems–A Review , 2009, IEEE Transactions on Power Electronics.

[7]  S. M. Halpin,et al.  Determination of Allowable Penetration Levels of Distributed Generation Resources Based on Harmonic Limit Consideration , 2002, IEEE Power Engineering Review.

[8]  Massimo Bongiorno,et al.  Input-Admittance Calculation and Shaping for Controlled Voltage-Source Converters , 2007, IEEE Transactions on Industrial Electronics.

[9]  Fred C. Lee,et al.  Impedance specifications for stable DC distributed power systems , 2002 .

[10]  M. Liserre,et al.  Stability of photovoltaic and wind turbine grid-connected inverters for a large set of grid impedance values , 2006, IEEE Transactions on Power Electronics.

[11]  Jian Sun,et al.  Optimal damping of EMI filter input impedance , 2009, 2009 IEEE Energy Conversion Congress and Exposition.

[12]  Frede Blaabjerg,et al.  Overview of Control and Grid Synchronization for Distributed Power Generation Systems , 2006, IEEE Transactions on Industrial Electronics.