Design and simulation of a unified power quality conditioner fed by solar energy
Introduction
The renewable energy resources are the best solutions for the clean energy requirement of the recent communities. Due to its wide application areas, easy construction and maintenance, the photovoltaic (PV) solar energy is the most promising green energy field [1], [2], [3]. Thus, the numerous examples of successfully deployed PV systems are already available for commercial usages and also technical researches [4], [5], [6]. The PV based solar energy explorations have been improved further by focusing on their grid integration. In fact, the improvements in power electronics technology have accelerated the usage of PV supplied inverter systems as much as grid integration capabilities efficiently [7]. However, the proliferation of nonlinear loads due to their compact size and better controllability such as static power converters has deteriorated power quality by switching actions. Whenever, these systems are connected to the utility, they cause certain harmonics, subharmonics or superharmonics in voltage and current patterns [8], [9]. They also pose themselves as loads having poor displacement, which draw considerable reactive power from the utility [10], thereby these problems can cause a malfunctioning in the electrical equipment. Different types of passive filters have been proposed to filter these harmonics and to compensate reactive power. On the other hand, a numerous drawbacks of the passive filters exist such as causing larger system size and resonant problems, being effective for only specified harmonic ranges such as 5th, 7th, 11th and 13th and for specific loads [10], [11], [12]. Therefore that gives a good motivation to carry out researches in the area of passive filter.
In order to enhance the quality of power by considering voltage and current distortion limits for non-linear loads, many systems have been proposed [8], [9], [10], [11]. In addition to suppress the current/voltage distortion, one may also handle other problems for instance, swells, sags, current/voltage imbalance, flickers, surges, reactive currents, frequency oscillation, interruptions [13]. Mainly the systems are classified into three categories: First is the unified power flow controller (UPFC) which performs power flow control, voltage regulation and reactive power compensation as an equipment for compensation at the system frequency. Second is the unified power quality conditioner (UPQC) which combines a series active filter for harmonics-voltage compensation with a shunt active filter for harmonic-current compensation as a new equipment controlled to perform current and voltage compensation. Third is the universal active power line conditioner (UPLC) which aggregates the functions of the UPFC and the UPQC into a signal power conditioner [9].
To avoid an additional cost and hardware for the UPQC system, some studies discussed these systems with the PV. This latter injects active power to the grid and filters the load current/voltage harmonics. Furthermore, in one of our previous papers [6], a shunt active power filter (APF) fed by a PV system has been confirmed in terms of performance.
In the present study, a UPQC has been adopted and modeled to improve the power quality influenced by a harmonic disturbance and to export active power to the grid. The proposed system is supplied by the PVs containing a combination of two active power filters, in parallel and series shared a common DC voltage generated by the PVs. While the parallel APF has been controlled by the instantaneous reactive power theory in order to compensate the current distortion caused by a non-linear load, it is also export energy generated by PV system to the grid. The series APF has used the unit vector templates generation to filter the load voltage distortion in the power supply. The PVs have also exported a certain amount of active power to the grid through the parallel APF, the boost converter and the maximum power point tracking (MPPT) unit. The latter have defined the current reference signal to control the active power injected to the grid. The paper is organized as follows: The configuration of the UPQC fed by the PV will be presented in Section 2. It also underlines the required units such as power source, nonlinear load, UPQC and the control technique algorithms. Later, the main simulation results, current and voltage waveforms and THD analyses will be discussed in Section 3. Finally, the paper will be completed by the concluding remarks.
Section snippets
Description of PV system
Despite of high specific costs, PV systems present an attractive solution for the electricity supply especially for remote locations because of low maintenance requirement, high reliability, long lifetime and stability with unrotating units [5], [6], [7]. Frequently, the application areas of PVs are dominated by the stand-alone systems such as household electrification and water pumping, however the grid-connected applications of PVs also flourish in cities as well as rural areas. In order to
Results and discussion
To demonstrate the efficiency of the proposed UPQC fed by PV system with a back-to-back combination of the series APF and shunt APF, the power circuit given in Fig. 4 has been established with MATLAB/Simulink software. Table 2 summarizes the optimized parameters of the power circuit.
Before the application of the proposed system, the shape of the load voltage has been totally distorted as shown in Fig. 5. Here the signal includes the 5th and 7th harmonic components. The analysis proves that high
Conclusions
A new unified power quality conditioner (UPQC) supplied by photovoltaic system has been realized at the limits of standards. In the proposed system, the overall PVs with the 64 PV panels, boost converter, PI controllers and MPPT algorithm have been designed to generate the maximum active power, which is exported to the network through the shunt APF function of the UPQC. The UPQC is composed of back-to-back connected series APF and shunt APF, which are share a common DC voltage generated by the
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