تاثیر سیستم فتوولتائیک بر کیفیت نیرو در شبکه های توزیع برق Effect of Photovoltaic System on Power Quality in Electrical Distribution Networks

Reduction of fossil fuel sources increases governments’ interest to the importance of penetration of renewable energy sources such as wind energy and solar energy to assess power system performance [1]. One of most interested recent technologies is the solar energy which has become the most popular renewable energy source in recent years. The solar energy is extracted directly from sun by integrating photovoltaic (PV) modules to the distribution systems [2]. The rapid increase in the penetration levels of PV systems has been noticed. Solar PV power systems are being considered as a practical unconventional energy resource for many world countries as well as in Egypt [3]. Therefore, future electricity generation plans countries around the world expect more contribution of renewable energies in the electric power systems especially for PV systems. PV systems have the potential of general applications as an alternative safe and clean energy source in the nearest future [4]. The target of some utilities is to penetrate around of 20% renewable energy of total required energy by 2020 while other utilities expect 50% by the year 2050 [5]. The integration of PV system to electrical distribution networks can be divided into two main categories off-grid (standalone applications) and on-grid (grid-connected applications) [6]. The stand-alone PV systems provide the needed power demand for remote loads only while grid-connected applications are implemented to provide required energy for local loads and able to exchange power with utility grids. The salient features of PV systems are their ability to enhance the operation of power systems by improving the voltage profile and by reducing the energy losses of distribution feeders at lowest maintenance costs. Compared to other renewable technologies, PV systems still face major problems and may lead to undesirable effects to the system, such as overloading of the feeders, harmonic pollution, high investment cost, low efficiency, and low reliability [7]. Moreover, variations in solar radiation may cause power deviation and voltage flicker, resulting undesirable effects on high penetrated PV systems in the distribution network. Several control procedures, that controlled the produced voltage and the current of the PV array, are developed to improve the efficiency of PV systems [8]. The accurate detection of undesired disturbances is necessary for electrical utilities [9]. Urgent disturbances are that related to the quality of utilized generated power. Two view point about power quality definitions. In the view point of utility, the power quality is defined as the reliability and characteristic of the power supply that enable the equipment to work correctly. On the other side, consumers define the power quality as any problem in voltage, current frequency deviations that lead to failure or operation loss of customer equipment. Examples of the power quality disturbances are voltage sag, swell, surge, flickers, interruption and harmonics [10]-[12]. Electric power pollution has increased due to the power converter, distribution and transmission networks with the growth of non-linear loads like switch-mode-power-supplier and phase control rectifiers. The poor power quality occurs mainly due to the influence of harmonics and reactive power [11]. The power quality problems areised in power system and the ways to solve these problems were presented in [12]. The existence of non-linear loads and distributed generation technologies change the voltage and current waveforms their characteristics [13]. Harmonics are presented in the output PV current because of the use of power converters and variable power flow of the PV system. These currents, flowing through the impedances of the distribution system result in distortion of system voltage [14]. Harmonic reduce the power systems equipment’s life. The filter design has become essential for industrial distribution systems [15]. The harmonic effects on the system are defined by the following issues [16] and [17]: • Equipment overheating that leads to equipment failure or damage • System malfunction or operation failure of equipment • Protection equipment mal and fail operation • Process disturbance The penetration of PV systems in distribution network is one of the main sources of harmonic distortion of current and voltage waveforms. Therefore, that is becoming a huge problem [18] especially for distribution systems. This paper is concerned on studying the power quality problem that associated with the PV penetration into distribution systems and provide a detailed comparative between the system performance. Also, this paper proposes an ETAP procedure for choice the optimal design of single tuned filters that able to reduce the effects of voltage and current harmonic contents to be within the accepted limits of the Egyptian code.