Harmonics Measurement Analysis for a Stand Alone Photovoltaic System with Linear and Non-Linear Loads

Transcription

1 Journal of Materials Science and Engineering A 4 (5) (2014) D DAVID PUBLISHING Harmonics Measurement Analysis for a Stand Alone Photovoltaic System with Linear and Non-Linear Hamisu Usman, Ramatu Aliyu Abarshi and Sani M. Lawal Electrical/Electronic Engineering Department, College of Engineering, Kaduna Polytechnic, PMB 2021, Kaduna, Nigeria Received: April 09, 2014 / Accepted: April 21, 2014 / Published: May 10, Abstract: Nowadays Photovoltaic systems have become one of the dominant renewable energy sources for generating electricity in the world. The photovoltaic system is a clean, friendly and non-polluting energy source with the reduced carbon dioxide (CO 2 ) emission, when compared with the conventional energy sources, which pollutes the environment and makes it hazardous to human health. However, the output wave forms of Voltage and Current generated by the Photovoltaic systems produce harmonics. This is due to the power electronic converters and the non-linear loads connected to the PV systems. In this paper, we present experimental results and analysis for an interactive standalone Photovoltaic system connected with different linear and non-linear loads. The experiment was performed with HIOKI 3196 power quality analyzer. The percentage of the total harmonics distortion (THD) of the Voltage (THDV) and Current (THD I ) have been studied in this paper. Results of the THD are presented and compared with IEEE standard. Key words: Stand-alone PV, power quality, measurement, THD, waveforms. 1. Introduction Photovoltaic electricity generation is one of the promising and friendly renewable energy that is free from environmental emission. Presently, PV cells are one of the fasted means of electricity generation in at least over 100 countries in the world [1]. Almost about 16,600 MW of PV arrays were installed in the World, with barely half of this capacity installed and utilized in 2010 in Germany alone [2]. Moreover, the deregulation of power system generation in the world, has given an autonomous freedom to generate and sale the produced renewable power to the commercial and individual consumers in the energy market in the world [3]. Some of the major draws back of this Photovoltaic power generation are, disturbances caused by irradiance and temperature variations due to the surrounding weather condition within the installed PVs arrays. Similarly, the harmonics injected by the power electronics devices Conressponding autor: Hamisu Usman, Engr., research fields: power quality, power electronics and power system analysis. hamisuusman94@yahoo.com. like rectifiers, inverters, and mostly the non-linear connected loads associated with the PVs, adversely affect the system generated output Voltage/Current wave forms. Harmonics injected by these devices as a standalone PVs generation results in a serious severe problems which causes over heating in the supply cables, interference in the nearby neighboring communication facilities, equipment failure, loads unbalanced, power loses, and pre matured ageing failure of equipment [4]. The problems of harmonics in power system are the most devastating factors that seriously affect the power system performances which lead to the power quality issues. It has become very imperative to look at these harmonics distortion problems and similar power quality issues that militates the disoperation of equipment to consumers. In order to safe guard the life expectancy of the consumers equipment and to ensure proper operation and reliability of the power system, it is so important to make measurements on the system Voltages/Currents in order to know the harmonics level at which the equipment are operated. The measured harmonic

2 184 Harmonics Measurement Analysis for a Stand Alone Photovoltaic System with Linear and Non-Linear distortions should be analyzed and study it impacts in order to propose a remedial solution to the disturbances [5]. The results of these power quality issues problems leads to a unique solution of the harmonics distortion, with an appropriate device like filters to mitigate the unwanted harmonics within the system to it minimal THD% level, and within the IEEE standard norms. In this paper, we presents an experimental results and analysis for a 2.16 kw stand-alone Photovoltaic generation connected with different linear and non-linear loads in order to study the behavior of the THD% of Voltage (THDv) and Current (THD I ) wave forms. Results presented, show the THD% of the various linear and nonlinear loads, and were compared with the IEEE standard. 2. The Proposed Site under Study A 14.8m 2 cabin was built for the purpose of researchers in PV System, for the graduate students of Electrical and Electronics Engineering Department, University Putra Malaysia. The cabin consists of twelve numbers (12) of PV modules, connected in series and parallel mode. Each module of capacity 180W, with total installed capacity of 2,160 W. The proposed system comprises of the following components, with their respective rating capacity. Twelve number of PV modules rated 2,160 W, Lead-acid battery of capacity 325 Ah at 48 V, Charge controller rated at 48 A, and a sine wave inverter of capacity 3,000 W. The overall system as shown in Fig. 2, various harmonics measurements have been conducted with linear and non-linear loads at the point of common coupling (PCC) i.e., between the inverter and the loads. The harmonics measurement results were observed and monitored via HIOKI 3196 power quality analyzer. The quality meter allows measuring and displaying various Power quality problems such as, Voltage sag, Flicker, Voltage swell, as well as THD% Fig. 1 The site under study, front view and side view. Fig. 2 Complete block diagram of the proposed study.

3 Harmonics Measurement Analysis for a Stand Alone Photovoltaic System with Linear and Non-Linear 185 of the Voltage and Current. 3. Imposed IEEE Standard for Harmonics Voltage Distribution Limit Photovoltaic system inherits serious deterioration of Power quality problems nowadays. Power quality effect caused by the interactive power electronics converters such as rectifiers, inverters, and the non-linear loads connected with the system are the major contributing devices militating power quality problems in Photovoltaic generation. However, the atmospheric weather condition such as irradiance from the sun, ambient temperature of the surrounding air are also affecting the system performance for the PV output Voltage and Current generated by the system. In line with these problems, IEEE standard were first imposed in 1981 and revised in 1992, that aimed at providing a standard limit for the THD% of the system Voltage and Current caused by the modern electronics converters and the non-linear loads in a distribution system [6]. Table 1 depicts the IEEE 519 imposed standard. In another development, IEEE standard recommended practice for utility interface of Photovoltaic system, this standard gives guides for system operation and equipment concerning the validity operation of Photovoltaic distribution and system networks. This standard highlight, some vital information about the limits for personnel (individual) hazards and safety of utility system operation of equipment devices and similar power quality issues regarding the Photovoltaic system [7]. Table 1 Harmonic voltage distribution limits in percent of nominal fundamental frequency voltage. Bus Voltage at PCC, V n (kv) Individual harmonic Voltage distortion (%) V n < V n V n > Source: IEEE Standard , Table Total Voltage distortion, THDV n (%) 4. Definition of Terms 4.1 Power Quality Any deviation manifested in voltage, Current or frequencies that can cause mis operation or failure in consumer s equipment are called power quality. 4.2 Harmonics Any deviation in the main supply fundamental frequency sine wave that can result in non-sinusoidal wave form due to integer multiples of the supply frequency (50HZ or 60HZ) the phenomenon is known as harmonics Linear Are electrical loads in which voltage and current are purely sinusoidal in nature. In linear loads the current is directly proportional to the system voltage. Examples of linear loads are incandescent lamps, capacitors, electric stoves etc. 4.4 Non-Linear Are electrical loads in which voltage and current are non-sinusoidal in nature. In non-linear loads, the current is not directly proportional to the applied voltage. Non-linear loads normally produce distortion in the current wave forms. Examples of non-linear loads are air conditioner, computers, monitors, fluorescent fittings etc. 5. Experimental Results and Discussion The experimental results for various linear and non-linear loads for the measurement of harmonics distortions are presented in this work. The experiment was conducted during the day time, were the inverter is fully utilized and the battery storage device was in standby mode operation due to the sufficient solar irradiance during the day time. Table 2 and 3 shows the type and the ratings of the linear and non-linear loads that are used in this measurement respectively. However, Figs. 2a-2d are the current waveforms for

4 186 Harmonics Measurement Analysis for a Stand Alone Photovoltaic System with Linear and Non-Linear Table 2 Linear. Load Rating (Watts) 3 incandescent lighting bulbs 300 Electric filament stove 1,000 Resistive load 500 Table 3 Non-linear. Load Rating (Watts) Air conditioner 746 PC and Monitor ft fluorescents ballast fitting 80 Lap top 200 air conditioner, personal computer and its monitor, fluorescent lamps and air conditioner with incandescent lighting bulbs all under distorted conditions, respectively. These results of the nonlinear loads are extremely distorted and they need to be mitigated. In Fig. 3a, the voltage and current wave forms are clearly presented for both air conditioner/personel computer with its monitor respectively. In another vein, Fig. 3b depicts the voltage and current wave forms for personel computer, air conditioner and laptop under load conditions. The voltages wave forms for Figs. 3a and 3b are purely sinusoidal in nature, while their corresponding current wave forms are highly distorted due to their non linearity in nature. Basically, with the presence of non-linear loads, THD V are within the stipulated guidelines of the IEEE standard. However, sometimes certain harmonics loads are not within the required IEEE (c) (d) Fig. 2 Current wave form for air conditioner under distortion, PC and it monitor under distortion, (c) 2 number 4 ft fluorescent lamps, (d) air conditioner + incandescent lighting bulb.

5 Harmonics Measurement Analysis for a Stand Alone Photovoltaic System with Linear and Non-Linear 187 Fig. 3 Voltage and Current wave forms for air conditioner + PC and it monitor and PC + air conditioner + laptop. (c) (d) Fig. 4 Harmonic Current values for air conditioner, PC + monitor, (c) 2 flourescent lamps and (d) air conditioner + incandescent lamps.

6 188 Harmonics Measurement Analysis for a Stand Alone Photovoltaic System with Linear and Non-Linear (c) (d) Fig. 5 Harmonic voltage values for air conditioner, PC + monitor, (c) 2 flourescent lamps and (d) air conditioner + incandescent lamps. standard [8]. In the other way, the THD I results for all the Currents distortions measurements are out of range for the imposed IEEE standard. Figs. 4 and 5 show the results of the total harmonic distortions for the currents and Voltages, respectively. 6. Conclusions In this paper, harmonics measurements analysis for a standalone Photovoltaic System with linear and non-linear loads is presented. Harmonics distortions behaviors in both Voltages and Currents for the interactive linear and non-linear loads are studied and presented in this paper. Results of the Voltage measurements indicates that, no distortions were observed in Voltage wave forms, this showed that, the THD V are within the standard and did not exceed the required limits. THD I of Fig. 4b indicates the highest current distortion of the non-linear loads. However, the Current wave forms measurements for the proposed study shows that, the THD I are out of ranges of the IEEE standard limits. We therefore, recommend the use of shunt active Power filter in mitigating the proliferation of harmonics distortions disturbances in the proposed scheme.

7 Harmonics Measurement Analysis for a Stand Alone Photovoltaic System with Linear and Non-Linear 189 Acknowledgments The authors acknowledged University Putra Malaysia for providing this research equipment for the purpose of research students in the Department of Electrical Engineering, faculty of engineering University Putra Malaysia. References [1] R. Rahmani, M. Fard, A.A. Shojaei, M.F. Othman, R. Yusuf, A complete model of stand alone photovoltaic array in MATLAB/SIMULINK Enviroment, IEEE Students conference on research and development, 2002, pp [2] E.P. Institute, Earth policy Institute), 2010, (accessed at: 2010) [3] P.K. Tripathy, D. Manjure, E. B. Makram, Harmonic analsis in a selected distributed generator device, Internet. [4] M. Durgesh, Effect of nonlinear loads on power system harmonics, M.sc. Thesis, Clemson University, 1999, p. 27. [5] A.L. Ahmed, Harmonic impact of photovoltaic inverter systems on low and medium voltage distribution system, M.sc. Thesis, University of wollongong, [6] B. Indranil, D. Yuhang, S.Y. Simon, Active filters for harmonics elimination in solar photovoltaic grid connected and stand alone systems, 2nd Asian symposium on quality electronic design, 2010, pp [7] IEEE Standard Association, , IEEE recommended practice for utility interface of photovoltaic (PV) systems: [8] B. Marco, L. Massimiliano, P. Marcello, P. Gionpaolo, Experimental analysis of power quality issues in a mobile house supplied by renewable energy sources, in: International Conference on Renewable Energy and Power Quality, 2007, pp. 1-8.