A digital controlled PV-inverter with grid impedance estimation for ENS detection

The steady increase in photovoltaic (PV) installations calls for new and better control methods in respect to the utility grid connection. Limiting the harmonic distortion is essential to the power quality, but other requirements also contribute to a more safe grid-operation, especially in dispersed power generation networks. For instance, the knowledge of the utility impedance at the fundamental frequency can be used to detect a utility failure. A PV-inverter with this feature can anticipate a possible network problem and decouple it in time. This paper describes the digital implementation of a PV-inverter with different advanced, robust control strategies and an embedded online technique to determine the utility grid impedance. By injecting an interharmonic current and measuring the voltage response it is possible to estimate the grid impedance at the fundamental frequency. The presented technique, which is implemented with the existing sensors and the CPU of the PV-inverter, provides a fast and low cost approach for online impedance measurement, which may be used for detection of islanding operation. Practical tests on an existing PV-inverter validate the control methods, the impedance measurement, and the islanding detection.

[1]  F. Blaabjerg,et al.  Online grid measurement and ENS detection for PV inverter running on highly inductive grid , 2004, IEEE Power Electronics Letters.

[2]  Shoji Nishimura,et al.  Advanced technology to identify harmonics characteristics and results of measuring , 2000, Ninth International Conference on Harmonics and Quality of Power. Proceedings (Cat. No.00EX441).

[3]  Keiju Matsui,et al.  Development of an on-line impedance meter to measure the impedance of a distribution line , 2001, ISIE 2001. 2001 IEEE International Symposium on Industrial Electronics Proceedings (Cat. No.01TH8570).

[4]  M. Sumner,et al.  Estimation of power supply harmonic impedance using a controlled voltage disturbance , 2001, 2001 IEEE 32nd Annual Power Electronics Specialists Conference (IEEE Cat. No.01CH37230).

[5]  Keiju Matsui,et al.  On-line impedance meter to measure the impedance of a distribution line using inverter , 2001, IECON'01. 27th Annual Conference of the IEEE Industrial Electronics Society (Cat. No.37243).

[6]  J. P. Rhode,et al.  Complete characterization of utilization-voltage power system impedance using wideband measurement , 1996, Proceedings of 1996 IAS Industrial and Commercial Power Systems Technical Conference.

[7]  J. W. Resende,et al.  Practical approaches for AC system harmonic impedance measurements , 1991 .

[8]  M. Baran,et al.  Instrumentation for measurement of line impedance , 1994, Proceedings of 1994 IEEE Applied Power Electronics Conference and Exposition - ASPEC'94.

[9]  Steven B. Leeb,et al.  A power quality prediction system , 2000, IEEE Trans. Ind. Electron..

[10]  F. Blaabjerg,et al.  Power electronics as efficient interface in dispersed power generation systems , 2004, IEEE Transactions on Power Electronics.

[11]  Leszek S. Czarnecki,et al.  On-line measurement of equivalent parameters of distribution system and its load for harmonic frequencies , 1995, Proceedings of 1995 IEEE Instrumentation and Measurement Technology Conference - IMTC '95.

[12]  Mark Sumner,et al.  Power system impedance measurement using a power electronic converter , 2000, Ninth International Conference on Harmonics and Quality of Power. Proceedings (Cat. No.00EX441).

[13]  Mark Sumner,et al.  A technique for power supply harmonic impedance estimation using a controlled voltage disturbance , 2002 .

[14]  Mark Sumner,et al.  Experimental evaluation of active filter control incorporating on-line impedance measurement , 2002, 10th International Conference on Harmonics and Quality of Power. Proceedings (Cat. No.02EX630).

[15]  Paulo F. Ribeiro,et al.  Guide for assessing the network harmonic impedance , 1997 .

[16]  M. Liserre,et al.  A new control structure for grid-connected LCL PV inverters with zero steady-state error and selective harmonic compensation , 2004, Nineteenth Annual IEEE Applied Power Electronics Conference and Exposition, 2004. APEC '04..

[17]  Z. Staroszczyk.  Problems in real-time wide band identification of power systems , 1998, IMTC/98 Conference Proceedings. IEEE Instrumentation and Measurement Technology Conference. Where Instrumentation is Going (Cat. No.98CH36222).

[18]  P. Zanchetta,et al.  Estimation of load impedance in a power system , 2000, Ninth International Conference on Harmonics and Quality of Power. Proceedings (Cat. No.00EX441).

[19]  Niels Kjølstad Poulsen,et al.  Short-circuit impedance measurement , 2003 .

[20]  M. Liserre,et al.  Stability of grid-connected PV inverters with large grid impedance variation , 2004, 2004 IEEE 35th Annual Power Electronics Specialists Conference (IEEE Cat. No.04CH37551).

[21]  Z. Staroszczyk,et al.  Real-time power system linear model identification: instrumentation and algorithms , 2000, Proceedings of the 17th IEEE Instrumentation and Measurement Technology Conference [Cat. No. 00CH37066].

[22]  F. Blaabjerg,et al.  Implementation and test of on-line embedded grid impedance estimation for PV-inverters , 2004, 2004 IEEE 35th Annual Power Electronics Specialists Conference (IEEE Cat. No.04CH37551).

[23]  Mark Sumner,et al.  System impedance measurement for use with active filter control , 2000 .

[24]  H. Stemmler,et al.  Stationary frame generalized integrators for current control of active power filters with zero steady state error for current harmonics of concern under unbalanced and distorted operation conditions , 2000, Conference Record of the 2000 IEEE Industry Applications Conference. Thirty-Fifth IAS Annual Meeting and World Conference on Industrial Applications of Electrical Energy (Cat. No.00CH37129).