inverters under net metering are highly promoted. According to the utility regulatory requirements, solar PV grid tie inverters that are used, should comply with ...
Annual Sessions of IESL, pp. [1 - 10], 2015 Annual Sessions of IESL, pp. [513 - 520] 2015 © The Institution of Engineers, Sri Lanka © The Institution of Engineers, Sri Lanka
Developing a Test Bench to Test Grid Tie Inverters P.Y.T.D. Gunarathna, Asanka S. Rodrigo, T.M.L. Arachchi, H.D. Weerarathna and C.K. Wickramanayake Abstract: The need of electricity through-out the world is growing day by day at a considerable rate. The electricity demand of its consumers has already exceeded the supply. Hence, switching towards green energy is a must to remove this imbalance conditions between the electricity supply and demand. At this particular point, there is a higher tendency of the electricity consumers for moving towards domestic solar power. The grid tie inverters are the main building. So, the proper operation of an inverter is highly important. Although there exists an already provided data sheet by the manufactures along with the inverters, sometimes we can identify mal-operation conditions of these inverters irrespective of the data sheet provided and therefore, many complaints are aroused by the solar consumers. The issue is that there does not exist proper equipment to engage with all types of inverter testing schemes that had been listed in the IEEE 1547 standard; which is the relevant safety standard for interconnecting distributed resources with electric power systems. So, a test bench to test the grid tie inverters was developed according to IEEE 1547 standard. Tests that are stated in the standard were conducted with a higher accuracy data acquisition system and the relevant results were analyzed to determine whether a particular inverter operates within the limits at abnormal situations as described in the standard. Finally, a test report was generated to provide the solar power consumer informing the operation status of the inverter. This paper elucidates relevant inverter tests, the proposed methodologies to conduct the tests, the logic behind those tests for analysing purposes and the test results obtained for the calculations of the necessary test parameters, thus, the entire outcome will be highly important for the industry. Keywords: Grid Tie Inverter, Abnormal Voltage, Total Harmonic Distortion, Data acquisition, Graphical User Interface, Automatic Test Report Generation
1.
Introduction
1.2 Reference standard The following table shows the tests that have to be performed to verify the performance of grid tie inverters [3]. The tests that were implemented were given under the status.
1.1 Need of an Inverter Test Bench The concept of green energy is very much popular among many people all around the world, mainly as a solution for the energy crisis. At this particular instant, both the residential and the commercial solar energy systems are rapidly emerging. Distributed solar PV arrays connected to grid via grid tie inverters under net metering are highly promoted. According to the utility regulatory requirements, solar PV grid tie inverters that are used, should comply with the requirements of the IEEE 1547 which is the safety standard for interconnection of the distributed resources with the power systems. In Sri Lanka‟s point of view, only a few institutes have been nominated as havingthe testing facilities, but there is no proper equipment to engage with all the tests specified for the inverters as in the standard. Therefore, the ultimate objective of the project is to develop a test bench to test grid tie inverters and also a graphical user interface is going to be introduced with an automatically generated inverter test report.
Miss. P.Y.T.D. Gunarathna, SMIE(Sri Lanka), Final year undergraduate student of the Department of Electrical Engineering, University of Moratuwa-Sri Lanka. Eng. (Dr.) Asanka S. Rodrigo, PhD(HKUST), MSc(Moratuwa), BScEng(Moratuwa), AMIE(Sri Lanka),Senior Lecturer, Department of Electrical Engineering, University of Moratuwa-Sri Lanka. T.M.L. Arachchi, SMIE(Sri Lanka), Final year undergraduate student of the Department of Electrical Engineering, University of Moratuwa-Sri Lanka. H.D. Weerarathna, SMIE(Sri Lanka), Final year undergraduate student of the Department of Electrical Engineering, University of Moratuwa-Sri Lanka. C.K. Wickramanayake, SMIE(SL), Final year undergraduate student of the Department of Electrical Engineering, University of Moratuwa-Sri Lanka.
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Table 1 – Standard Clauses for Relevant Tests Relevant Our Status Test Details Clause to IEEE 1547 Response to Yes 4.2.3 Abnormal Voltage Yes Harmonics 4.3.3 Limitation of DC Yes 4.3.1 injection Reconnection to Area Yes 4.2.6 EPS Unintentional Yes 4.4.1 islanding No Synchronization 4.1.3 Response to Future 4.2.4 abnormal frequency Extension
Table 3 - Maximum Harmonic Current Distortion in Percent of Fundamental Current Harmonic Distortion (HD) h < 11 11 ≤ h < 17 17 ≤ h < 23 23 ≤ h < 35 35 ≤ h THD
1.2.3 Limitation of DC Injection DC injection from the power electronic Inverters to the AC system is a threat. This is due to badly designed and structured PE devices. Small DC components in a AC current is much difficult to detect and measure as stated in the IEEE 1547. Transformers and PE devices can be designed to eliminate DC injection. DC injection from these PEs embedded in solar power, wind power, energy storage etc. cause rise to AC components to give frequencies around the fundamental one.[4] We have to consider the amount of injected DC current by the inverter (or the distributed resource) along with its interconnection system. In the IEEE 1547 standard, it has been stated that the injected DC current should not be greater than 0.5 % with respect to the full rated output current at the PCC [3],[5].
Table 2 – Interconnection System Response to Abnormal Voltages
i. ii. iii. iv.
V < 50 50
