ANALYSIS OF MONITORING DATA ON THE OPERATION OF PV-INVERTERS CONNECTED TO DISTRIBUTION NETWORK

The article deals with the problems of the PV plants operation in the low voltage network (LVN), namely the influence of PV generation on bus voltages and stability of network, as well as disconnecting the inverters from network in order to avoid overvoltages. The operating of PV inverter tied to LVN is considered on the framework of the reduced two-bus equivalent circuit. One bus of this circuit describes the inverter which is connected to the step-up transformer via short line and second one is the equivalent representation of LVN. The reduced two-bus circuit in contrast to the multi-bus schemes has exact solutions for power flows between PV plant and network. The analytical solutions obtained for this model allows us to determine the voltage stability region, the disconnecting conditions from the network (islanding), the dependence of the bus voltages on the levels of generation and load. On the base of this model, the monitoring data for power and output voltages of three-phase Growatt 30 kW inverter were analyzed. The inverter is tied to LVN by a relatively short line segment with known parameters which is typical for private and small industrial photovoltaic systems. The stable operation of PV plant in the network depends on the ratio of generation and consumption levels at the bus on the plant side, as well as on the capacity of the connecting line. Under analyzing of an overvoltage in the inverter bus appearing due to large solar radiation, one should take into account the limited inverter’s possibility to reduce the output power by changing the operating point on the curve “voltagepower”. The article performs the optimization calculations which determine the parameters characterizing the inverter and line capacity. The developed method for analyzing monitoring data of modern inverters can be a useful tool in solving problems of PV plant equipment diagnostics, as well as of predicting the electricity amount supplied to the network.

1. Eltawil M.A., Zhao Z. Grid-connected photovoltaic powers systems: Technical and potential problems – A review. Renewable and Sustainable Energy Reviews, 2010;14:112–129.

2. Teoh W.Y., Tan C.W. An Overview of Islanding Detection Methods in Photovoltaic Systems. – International Scholarly and Scientific Research & Innovation, 2011;5:1341–1349.

3. IEC. Photovoltaic (PV) systems - characteristics of the utility interface (second edition). International standard (CEI IEC 61727), 2004: 1–24.

4. VDE, Selbsttatige schaltstelle zwischen einer netzparallelen eigenerzeugungsanlge und den offentlichen niederspannungsnetz. Deutche Kommission Elektrotechnik Elektronic Informationstechnik, 2006; VDE V 0126-1-1: 1–15.

5. Gaevsky A. Yu., Golentus I. E. Voltage stabilization by compensating reactive power by PV inverters (Stabilizatsiya napryazheniya v seti putem kompensatsii reaktivnoy moshchnosti invertorami FES). Materials of the XIV International Conference “Energy Innovation of the 21st Century”, Krim, 2013; pp. 243–245 (in Russ.).

6. Yandulsky O. S., Trunina G.O. Determination of zones of effective regulation of voltage by sources of renewable generation with inverter connected to distribution electrical network (Vyznachennia zon efektyvnoho rehuliuvannia napruhy dzherelamy rozoseredzhenoi heneratsii z invertornym pryiednanniam u rozpodilnii elektrychnii merezhi). Scientific works of VNTU. Power engineering and electrical engineering, 2014;4:62–64 (in Ukrain.).

7. Lezhnyuk P.D., Rubanenko O.Ye., Gunko I.O. Influence of solar power stations on consumer’s voltage 0.4 kV (Vplyv soniachnykh elektrychnykh stantsii na napruhu spozhyvachiv 0,4 kv). Power Engineering: Economics, Technology, Ecology, 2015;3:7–13 (in Ukrain.).

8. Sosnina E., Chivenkov A., Shalukho A. et al. Power flow control in a virtual power plant LV network. International Journal of Renewable Energy Research, 2018;8:328–335.

9. Wang Zh., Xia M., Lemmon M. Voltage stability of weak power distribution networks with inverter connected sources [E-resource]. Available on https://www3.nd.edu/~lemmon/projects/accenture-2012/pubs/2012/acc2012-zwang.pdf. (10.12.2018).

10. Azadani E.N., Canizares C., Bhattacharya K. Modeling and stability analysis of distributed generation [E-resource]. Available on: http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.699.2223&rep=rep1&type=pdf. (12.10.2018).

11. Development and integration of microgrids. Edited by W.P. Cao and J.I. Yang. Publisher: InTech, 2017; 282 p., doi: 10.5772/65582 [E-resource]. Available on: https://www.intechopen.com/books/development-andintegration-of-microgrids (12.10.2018).

12. Lasseter R.H. Microgrids and distributed generation. Journal Intelligent Automation & Soft Computing, 2010;16(2):225–234.

13. Yingyun S.Z., Sun Y., Shen Z.J. Microgrid stability: Classification and a review. Renewable and Sustainable Energy Reviews, 2015;58:167–179.

14. Reno M.J., Broderick R.J., Grijalva S. Formulating a simplified equivalent representation of distribution circuits for PV impact studies. SANDIA Report, SAND2013-2831, Unlimited Release, 2013; 30 p. [Eresource]. Available on: http://prod.sandia.gov/techlib/accesscontrol.cgi/2013/132831.pdf. (12.10.2018).

15. Lammert G., Yamashita K., Ospina L.D. P. et al. Modelling and dynamic performance of inverter based generation in power system studies: An international questionnaire survey. 24 th. International Conference on Electricity Distribution, Glasgow, 2017; pp. 1899–1902.

16. Kothari D.P., Nagrath I.J. Modern Power System Analysis. Third Edition, New Delhi: McGraw Hill, 2009; 694 p.

17. Idelchik V.I. Calculations and optimization of electrical networks and systems (Raschety I optimizatsiya rezhimov elektricheskih setey I sistem). Moscow: Energoatomizdat Publ., 1988; 288 p. (in Russ.).

18. Tabatabaee S., Karshenas H. R., Bakhshai A. et al. Investigation of droop characteristics and X/R ratio on small-signal stability of autonomous microgrid. In Proc. of the 2nd Power Electronics, Drive Systems and Technologies Conference, Tehran,2011; pp. 223–228.

19. Bolognani S., Zampieri S. On the existence and linear approximation of the power flow solution in power distribution networks. IEEE Transactions on Power Systems. 2016; 31:163–172 [E-resource]. Available on: https://arxiv.org/pdf/1403.5031.pdf. (10.12.2018).