A voltage regulation method for dispersed grid-connected PV systems under high-density connection

This paper describes a voltage regulation method for dispersed grid-connected PV systems under high-density connection. In the near future, many PV systems will be connected to distribution systems. The reverse power flow of the grid-connected PV systems will raise line voltage to the upper limit of the legal voltage range. In the first part of this paper we examine the voltage characteristics of a distribution system under high-density connection, while the second part of the paper describes a voltage regulation method for high-density PV connections, using reactive power proportional to global irradiance. The results of tests clearly demonstrate a restraining effect on voltage during the daytime and a smoothing effect on voltage fluctuation.     

A multi-function grid-connected PV system with reactive power compensation for the grid

According to the theory of instantaneous reactive power, the active and reactive currents of inverter can be regulated by changing the amplitude and the phase of the output voltage of the inverter. Based on this theory, the active power output and the reactive power compensation (RPC) of the system are realized simultaneously at daylight. When the insolation is weak or the PV modules are inoperative at night, the RPC feature of PV system can still be used to improve the utilization factor of the system. The MATLAB simulation results validate the feasibility of the method.     

Solar photovoltaic (PV) energy; latest developments in the building integrated and hybrid PV systems

Environmental concerns are growing and interest in environmental issues is increasing and the idea of generating electricity with less pollution is becoming more and more attractive. Unlike conventional generation systems, fuel of the solar photovoltaic energy is available at no cost. And solar photovoltaic energy systems generate electricity pollution-free and can easily be installed on the roof of residential as well as on the wall of commercial buildings as grid-connected PV application. In addition to grid-connected rooftop PV systems, solar photovoltaic energy offers a solution for supplying electricity to remote located communities and facilities, those not accessible by electricity companies.The interest in solar photovoltaic energy is growing worldwide. Today, more than 3500 MW of photovoltaic systems have been installed all over the world. Since 1970, the PV price has continuously dropped [8]. This price drop has encouraged worldwide application of small-scale residential PV systems. These recent developments have led researchers concerned with the environment to undertake extensive research projects for harnessing renewable energy sources including solar energy. The usage of solar photovoltaic as a source of energy is considered more seriously making future of this technology looks promising.The objective of this contribution is to present the latest developments in the area of solar photovoltaic energy systems. A further objective of this contribution is to discuss the long-term prospect of the solar photovoltaic energy as a sustainable energy supply.     

Development and performance test of smart power conditioner for value-added PV application

It is a disadvantage that PV power generation is only useful for clear daytime. However, a new 24 hours of application in an extended area can be added by active utilization of potential ability of PV power conditioner. For this purpose, a new multi-functional power conditioner was developed, which has a smoothing function to reduce PV output variation and load fluctuation, and also has additional function to compensate harmonics current and reactive power caused by customer's load.As a result of indoor testing, a reduction rate of around for harmonics current and reactive power were achieved. In addition, the reduction rate around for smoothing of PV output variation and load fluctuation were verified.The work was promoted by NEDO as part of the New Sunshine Project in Japan.     

Modeling and simulation of a grid-connected PV generation system for electromagnetic transient analysis

This paper addresses modeling and simulation of a grid-connected photovoltaic system (GCPS) to analyze its grid interface behavior and control performance in the system design. A simple circuit model of the solar array is used to easily simulate its inherent characteristics with the basic specification data. Detailed power and protection control of the GCPS as well as its electrical circuits have been represented by user-defined and built-in components to take into account transients in normal and fault conditions, which are dominated by its power electronic controller. The model has been described with the reference to and implemented in PSCAD/EMTDC, a power system transient software package. Extensive simulation results are presented and analyzed to validate that the proposed simulation model is effective for control and protection performance evaluation of the GCPS in terms of electromagnetic transient analysis.     

Optimal sizing of a grid-connected PV system for various PV module technologies and inclinations, inverter efficiency characteristics and locations

An optimal sizing methodology based on an energy approach is described and applied to grid-connected photovoltaic systems taking into account the photovoltaic module technology and inclination, the inverter type and the location. A model describing the efficiency for m-Si, p-Si, a-Si and CIS is used. The method has been applied on various meteorological stations in Bulgaria and Corsica (France). The main parameter affecting the sizing is the inverter efficiency curve. The influence of the PV module technology seems less important except for amorphous photovoltaic modules for which special remarks have been made. The inclination on the PV system influences the performances particularly when the inverter is undersized compared to the PV peak power.     

Inverter sizing of grid-connected photovoltaic systems in the light of local solar resource distribution characteristics and temperature

Inverter sizing strategies for grid-connected photovoltaic (PV) systems often do not take into account site-dependent peculiarities of ambient temperature, inverter operating temperature and solar irradiation distribution characteristics. The operating temperature affects PV modules and inverters in different ways and PV systems will hardly ever have a DC output equal to or above their STC-rated nominal power. Inverters are usually sized with a nominal AC output power some 30% (sometimes even more) below the PV array nominal power. In this paper, we show that this practice might lead to considerable energy losses, especially in the case of PV technologies with high temperature coefficients of power operating at sites with cold climates and of PV technologies with low temperature coefficients of power operating at sites with warm climates and an energy distribution of sunlight shifted to higher irradiation levels. In energy markets where PV kW h’s are paid premium tariffs, like in Germany, energy yield optimization might result in a favorable payback of the extra capital invested in a larger inverter.This paper discusses how the time resolution of solar radiation data influences the correct sizing of PV plants.We demonstrate that using instant (10 s) irradiation values instead of average hourly irradiation values leads to considerable differences in optimum inverter sizing. When calculating inverter yearly efficiency values using both, hourly averages and 1-min averages, we can show that with increased time resolution of solar irradiation data there are higher calculated losses due to inverter undersizing. This reveals that hourly averages hide important irradiation peaks that need to be considered.We performed these calculations for data sets from pyranometer readings from Freiburg (48°N, Germany) and Florianopolis (27°S, Brazil) to further show the peculiarities of the site-dependent distribution of irradiation levels and its effects on inverter sizing.     

光伏发电系统的并网模糊PID控制

在三相两级式并网逆变器数学模型的基础上,将模糊PID控制策略引入光伏发电系统的并网控制中。通过数字仿真和物理仿真表明模糊控制与PID控制相结合的模糊PID控制,改善了光伏系统并网控制的动态过程,能够实现光伏系统的平滑并网。     

The largest PV installation in Europe: Perspectives of multimegawatt PV

In the frame of the research, development and trial activity for power generation plants from renewable sources, ENEL erected the Serre photovoltaic plant, which ranks first worldwide due to its 3 MWp capacity. This paper contains the output data from the very beginning of the plant operation and particularly focuses on the system's yield. Moreover, to make an assessment of all the components forming part of the power generation process, a highly demanding measurement survey was carried out and plant losses were analysed, also to validate the theoretical design values.     

Multi-objective coordinated droop-based voltage regulation in distribution grids with PV systems

High penetrations of photovoltaic (PV) systems in distribution grids have caused new challenges such as reverse power flow and voltage rise. Reactive power contribution by PV systems has been proposed by grid codes and literature as one of the remedies for voltage profile violation. Recent German Grid Codes (GGC), for instance, introduce a standard active power dependent reactive power characteristic, Q(P), for inverter-coupled distributed generators. Nevertheless, the GGC recommends a voltage dependent reactive power characteristic Q(V) for the near future, recognizing that the Q(P) characteristic cannot explicitly address voltage limits. This study utilizes the voltage sensitivity matrix and quasi-static analysis in order to develop a coordinated Q(V) characteristic for each PV system along a radial feeder using only the local measurement and drooping technique concepts. The aim of this paper is using a multi-objective design to adjust the parameters of the Q(V) characteristic in the proposed droop-based voltage regulation in order to minimize the reactive power consumption and line losses. On the other hand, it is also possible to adjust the parameters in order to reach equal reactive power sharing among all PV systems. A radial test distribution grid, which consist of five PV systems, is used to calculate power flow and, in turn, the voltage sensitivity matrix. The comparison of results demonstrates that both approaches in the proposed droop-based voltage regulation can successfully regulate the voltage to the steady-state limit. Moreover, it is shown that the profile of reactive power consumption and line losses are considerably reduced by the multi-objective design.     

A new estimation method of irradiance on a partially shaded PV generator in grid-connected photovoltaic systems

A new method for estimating the irradiance on a partially shaded photovoltaic generator system is proposed. The basic principle of this method consists of two parts: firstly, an approximation of the obstacles’ outline or the local horizon by a set of linear functions. Here, a survey of the surroundings is based on the reading of the topographic coordinates of the only significant points of all the objects surrounding the photovoltaic generator. Secondly, the irradiance on the photovoltaic plane is estimated using an accurate model such as the Perez et al. model and assuming that the shading affects both the direct radiation and a part of the diffuse component (circumsolar component).The aim of this paper is to present the principles of the proposed method and the algorithm used for calculating the irradiance on shaded planes. In addition, the results of the comparison between the simulated and measured values of this method are presented.     

A decentralized voltage controller involving PV generators based on Lyapunov theory

This paper proposes a decentralized controller to coordinate the reactive power injections of PV generators in order to contribute to the voltage regulation in distribution networks. The control actions are evaluated in the real time by adopting an optimization methodology involving the sensitivity applied to the Lyapunov function. By this approach it is possible to derive an auto-adaptive algorithm that can be implemented on actual distribution network without implying additional costs for infrastructures. Computer simulations have been performed on a MV distribution system to demonstrate the effectiveness of the proposed control scheme at different operating conditions and to confirm its ability to work in the real time.     

光伏发电系统的超导储能设计

超导储能(SMES)具有非常快速的功率调节能力和灵活的四象限运行能力,可完成调节电力系统功率因数、补偿电压跌落等功能。文章针对光伏发电系统的特殊运行方式,提出了利用光伏出力与本地负荷需求的差值作为SMES控制器的功率控制信号策略。在PSCAD/EMTDC仿真平台建立了超导储能系统模型,并对其在光伏发电系统的中的运行控制方式进行研究。研究结果表明,超导储能与光伏系统配合可以很好地解决光伏发电功率易受环境影响、不可调节、难于满足负荷需求的问题,对由负荷变化引起的母线电压波动和故障引起的母线电压跌落具有良好的补偿作用。     

Areal evolution of PV systems

If a large amount of the future penetration of PV systems is imaged, it is likely that they densely concentrate in a certain area. It may not be a simple aggregation of individually optimized system, but a different system image may result by the total optimization of an area. The author frames this new question as the problem of “Areal Evolution” or “PV-AREA”. The following two cases are dealt with and their concrete concepts are given: (1) PV systems for community, (2) global-scale utilization of PV systems.     

Performance results and analysis of 3 kW grid-connected PV systems

Four 3 kW grid-connected photovoltaic (PV) generation systems have been installed and monitored at the Field Demonstration Test Center in Korea since October 2002. To observe the overall effect of meteorological conditions on their operation characteristics by field test, the monitoring system has been constructed for measuring and analyzing the performance of PV systems and components in November 2002. In this paper, the performance of PV systems is evaluated and analyzed not only for component perspective but also for global perspective by reviewing one year of monitoring results and loss factors of PV systems. On the basis of these monitoring results, the performance of PV systems is compared to the measured performance of PV systems with the estimated performance by simulation. These results will indicate that it is highly imperative to develop evaluation, analysis and application technology for PV systems.     

Techno-economical assessment of grid connected PV/T using nanoparticles and water as base-fluid systems in Malaysia

In this study, the techno-economic assessment of GCPVT with nanofluid has been investigated based on theoretical and experimental work in Malaysia. The productivity and utilisation of the PV have been investigated using yield and capacity factors (CFs), respectively. Also, the cost of energy and payback period has been calculated. The system installed, tested, and data have been collected. Evaluation of the system in terms of current, voltage, power and efficiency are presented. The average daily ambient temperature and total global solar energy in Kuala Lumpur are 38.89°C and 4062?Wh/m², respectively. MATLAB software is used to analyse the measured data. The assessment results show that the GCPVT system has annual yield factor, CF, the cost of energy; payback period, and efficiency are (128.34–183.75)?kWh/kWp, (17.82–25.52)%, 0.196?USD/kWh, 7–8 years and 9.1%, respectively. This study indicates that the GCPVT system with nanofluid improved the PV technical and economic performance.     

Modeling and design of phase shift anti-islanding method using non-detection zone

Islanding phenomenon of a grid-connected independent generator like a photovoltaic (PV) system occurs when a section of a utility system is disconnected from the main utility voltage source, but the independent generator continues to energize the utility lines in the isolated section. Since islanding causes a safety hazard to utility service personnel and damage to power supply facilities as a result of unsynchronized reclosure, PV inverter is required to have anti-islanding function. In order to prevent this phenomenon, various anti-islanding methods have been studied. Even though phase shift anti-islanding method including slip mode frequency shift (SMS) method and reactive power variation (RPV) method has been regarded as a highly effective anti-islanding method, the analytical design method of that has not been cleared. This paper proposes a design guideline of the phase shift anti-islanding method based on non-detection zone (NDZ). As leading phase shift anti-islanding methods, both SMS and RPV methods are discussed to verify the validity of the proposed method. Both methods are derived analytically through the modeling and verified visually by simulation and experiment under IEEE Std. 929-2000 test condition. It is shown that both methods designed by the proposed method have effectiveness to detect islanding within 2 s and good power quality above 0.99 power factor. The presented methodology in this paper can be extended to design other active anti-islanding methods.     

Evaluation of performance of MPPT devices in PV systems with storage batteries

In the PV system with storage batteries, as a maximum power point tracking (MPPT) device is used to enhance battery charging, the enhancement must be greater than the internal loss of the device itself, or there will be no net gain at all. To evaluate the MPPT device benefits under different climate, the theoretical calculation models have been constructed. By simulation, a comparative study between two types of PV charge controllers with and without a MPPT device under different atmospheric conditions was presented. The comparison was made by means of the energy production obtained from the PV generator of each system. The climatic conditons of Beijing and Guangzhou in China have been regarded. From the results obtained it can be concluded that the effectiveness of the MPPT device in Guangzhou is not very obvious, however the MPPT device did greatly enhance the output in Beijing in the winter.     

光伏并网逆变器的设计与控制

光伏并网发电具有广泛的应用前景,叙述了并网逆变器在光伏并网发电中所起的作用以及不同逆变器的特点,指出,光伏并网逆变器的技术关键在于对电流和功率的控制。     

基于单相dq变换控制的光伏系统仿真

提出一种基于单相幽变换的光伏系统控制策略,通过将输出电压信号的dq变换值与参考信号的幽变换值进行比较来控制逆变器的输出,实现光伏系统的稳定输出;该策略在选取不同的参考值时能实现光伏系统在并网和独立两种模式下的良好运行。通过Matlab／Simulink建立完整的光伏系统模型,以Meteonorm软件提供的上海地区的气象数据为参考进行一天的仿真,实验结果证明了该控制策略的有效性。