计及光伏出力随机性的电网运行风险评估

针对光伏发电输出功率具有随机性、可能带来电网运行风险的问题,利用蒙特卡洛模拟法对太阳光辐照度分布区间进行模拟,建立了光伏随机输出模型,对整个系统的设备及光伏电源出力进行随机抽样;结合风险理论,对并网光伏系统随机出力情况下电网的运行风险指标进行了计算。以IEEE-RTS79系统为例,分析了不同光伏并网点和不同并网容量对电网运行风险的影响。结果表明,在负荷较重区域增设光伏并网,可以有效地降低电网运行风险。因此,选择适当的光伏并网点和容量可以降低电网运行风险。     

Probabilistic load flow using Monte Carlo techniques for distribution networks with photovoltaic generators

Connections of distributed generation (DG) systems to distribution networks are increasing in number, though they may often be associated with the need of costly grid reinforcements or new control issues to maintain optimal operation. Appropriate analysis tools are required to check distribution networks operating conditions in the evolving scenario. Load flow (LF) calculations are typically needed to assess the allowed DG penetration level for a given network in order to ensure, for example, that voltage and current limits are not exceeded.

The present paper deals with the solution of the LF problem in distribution networks with photovoltaic (PV) DG. Suitable models for prediction of the active power produced by PV DG units and the power absorbed by the loads are to be used to represent the uncertainty of solar energy availability and loads variation. The proposed models have been incorporated in a radial distribution probabilistic load flow (PLF) program that has been developed by using Monte Carlo techniques. The developed program allows probabilistic predictions of power flows at the various sections of distribution feeders and voltage profiles at all nodes of a network.

After presenting theoretical concepts and software implementation, a practical case is also discussed to show the application of the study in order to assess the maximum PV peak power that can be installed into a distribution network without violating voltage and current constraints. A comparison between Deterministic Load Flow (DLF) and PLF analyses is also performed.     

Grid connected fuel cell and PV hybrid power generating system design with Matlab Simulink

Renewable energy sources have been taken the place of the traditional energy sources and especially rapidly developments of photovoltaic (PV) technology and fuel cell (FC) technology have been put forward these renewable energy sources (RES) in all other RES. PV systems have been started to be used widely in domestic applications connected to electrical grid and grid connected PV power generating systems have become widespread all around the world. On the other hand, fuel cell power generating systems have been used to support the PV generating so hybrid generation systems consist of PV and fuel cell technology are investigated for power generating. In this study, a grid connected fuel cell and PV hybrid power generating system was developed with Matlab Simulink. 160 Wp solar module was developed based on solar module temperature and solar irradiation by using real data sheet of a commercial PV module and then by using these modules 800 Wp PV generator was obtained. Output current and voltage of PV system was used for input of DC/DC boost converter and its output was used for the input of the inverter. PV system was connected to the grid and designed 5 kW solid oxide fuel cell (SOFC) system was used for supporting the DC bus of the hybrid power generating system. All results obtained from the simulated hybrid power system were explained in the paper. Proposed model was designed as modular so designing and simulating grid connected SOFC and PV systems can be developed easily thanks to flexible design.     

Systems-based modeling of generation variability under alternate geographic configurations of photovoltaic (PV) installations in Virginia

With increased focus on renewable energy in our modern era, it is increasingly important to understand the impact of policies on the performance and reliability of regional energy systems. This research develops a model to understand how geographic dispersion of PV installations impacts the reliability of electricity generated from the total PV network, measured by the variance of the distribution of generated electricity. Using NREL data, beta probability distributions of sunlight (kWh/m²/day) in various regions of Virginia are estimated using a fitting method that minimizes the Kolmogorov–Smirnov test statistic. A Monte Carlo simulation model is developed to measure PV electricity generation from multiple centralized and dispersed configurations over 100,000 days of probabilistic sunlight.     

A stochastic method for battery sizing with uninterruptible-power and demand shift capabilities in PV (photovoltaic) systems

This paper presents a stochastic simulation using Monte Carlo technique to size a battery to meet dual objectives of demand shift at peak electricity cost times and outage protection in BIPV (building integrated photovoltaic) systems. Both functions require battery storage and the sizing of battery using numerical optimization is popularly used. However, the weather conditions, outage events and demand peaks are not deterministic in nature. Therefore, the sizing of battery storage capacity should also be based on a probabilistic approach. The Monte Carlo simulation is a rigorous method to sizing BIPV system as it takes into account a real building load profiles, the weather information and the local historical outage distribution. The simulation is split into seasonal basis for the analysis of demand shifting and outage events in order to match the seasonal weather conditions and load profiles. Five configurations of PV (photovoltaic) are assessed that cover different areas and orientations. The simulation output includes the predicted PV energy yield, the amount of energy required for demand management and outage event. Therefore, consumers can base sizing decisions on the historical data and local risk of outage statistics and the success rate of meeting the demand shift required. Finally, the economic evaluations together with the sensitivity analysis and the assessment of customers’ outage cost are discussed.     

Experimental study on flicker emissions by photovoltaic systems on highly cloudy region: A case study in Malaysia

Photovoltaic (PV) systems are the most promising renewable energy sources in Malaysia because of its location being around the equatorial region where sunlight is available throughout the year. However, the country is warm and surrounded by the South China Sea and Malacca Straits. A large amount of clouds is created and passed over the region. The impacts of the passing clouds on the PV power outputs and voltage magnitude have to be studied thoroughly. Therefore, an experimental low-voltage network integrated with a PV system is set up. The experimental results show that the passing clouds result in the frequent and rapid fluctuations of PV power outputs, hence producing a large amount of flickers to the distribution networks. Some of the flickers are actually greater than the statutory limits. To mitigate this power quality issue, a dynamic load controller is proposed to be the solution because its components are cheap. The load controller is made of a number of 200 W power resistors and solid-state relays. A central controller switches the resistors on and off very rapidly based on the fluctuations of the network voltage. The experimental results show that the dynamic load controller is able to reduce the flickers effectively on the distribution networks. The studies and solution presented in this paper are very valuable to different parties, such as the government, policy makers, utility companies and owners of the PV systems, in order to ensure an effective growth of the PV systems without compromising the quality of electricity supply to the customers.     

Enhancement of grid-connected photovoltaic system using ANFIS-GA under different circumstances

In recent years, many different techniques are applied in order to draw maximum power from photovoltaic (PV) modules for changing solar irradiance and temperature conditions. Generally, the output power generation of the PV system depends on the intermittent solar insolation, cell temperature, efficiency of the PV panel and its output voltage level. Consequently, it is essential to track the generated power of the PV system and utilize the collected solar energy optimally. The aim of this paper is to simulate and control a grid-connected PV source by using an adaptive neuro-fuzzy inference system (ANFIS) and genetic algorithm (GA) controller. The data are optimized by GA and then, these optimum values are used in network training. The simulation results indicate that the ANFIS-GA controller can meet the need of load easily with less fluctuation around the maximum power point (MPP) and can increase the convergence speed to achieve the MPP rather than the conventional method. Moreover, to control both line voltage and current, a grid side P/Q controller has been applied. A dynamic modeling, control and simulation study of the PV system is performed with the Matlab/Simulink program.     

Performance evaluation of a 10 kWp PV power system prototype for isolated building in Thailand

This paper describes the design and testing of a 10 kW_p photovoltaic (PV) system and summarizes its performance results after the first 6 months of operation. This system functions as a stand-alone power system that is used to supply electricity for isolated buildings and is designed for integration with a micro-grid system (MGS), which is the future concept for a renewable energy-based power network system for Thailand. The system is comprised of the following components. An array with three different types of PV modules consisting amorphous thin film of 3672 W, polycrystalline solar cell of 3600 W and hybrid solar cell of 2880 W, making up a total peak power of 10.152 kW. In addition, there are three grid-connected inverters of 3.5 kW each, three bi-directional inverters of 3.5 kW each and an energy storage system of 100 kWh. After the first 6 months of system operation, it was found that all the components and the overall system had worked effectively. In total, the system had generated about 7852 kWh and the average electricity production per day was 43.6 kWh. The average efficiency of amorphous thin film panel, polycrystalline panel, hybrid solar cell panel and entire PV panel system was 6.26%, 10.48%, 13.78% and 8.82%, respectively. From the analysis of the daily energy production, daily energy consumption and energy storage, the results seem to indicate that there was some mismatching between energy supply and demand in the system. However, this can be overcome by integrating the system to a micro-grid network whereby the energy from the system can be diverted to other loads when there is a surplus and additional energy can be drawn from external sources and fed to the system when the internal supply is insufficient.     

A critical review of electric vehicle charging using solar photovoltaic

The application of renewable sources such as solar photovoltaic (PV) to charge electric vehicle (EV) is an interesting option that offers numerous technical and economic opportunities. By combining the emission‐free EV with the low carbon PV power generation, the problems related to the greenhouse gases due to the internal combustion engines can be reduced. Over the years, numerous papers, including several review work, have been published on EV charging using the grid electricity. However, there seems to be an absence of a review paper on EV charging using the PV as one of the energy sources. With growing interest in this topic, this review summarizes and updates some of the important aspects of the PV‐EV charging. For the benefit of a wider audience, it provides the background on the EV fundamentals, batteries and a brief overview on the PV systems. Two types of PV‐EV charging, namely the PV‐grid and the PV‐standalone, are comprehensively covered. Moreover, a case study is carried out in comparison to the grid‐only charging to critically analyse the technical and the economical feasibilities of both types using Matlab simulation. At the end, recommendations and future directions are presented. It is envisaged that the material gathered in this paper will be a valuable source of information for the researchers working on this topic. Copyright © 2015 John Wiley & Sons, Ltd.     

State coordinated voltage control in an active distribution network with on-load tap changers and photovoltaic systems

Decreasing costs and favorable policies have resulted in increased penetration of solar photovoltaic (PV) power generation in distribution networks. As the PV systems penetration is likely to increase in the future, utilizing the reactive power capability of PV inverters to mitigate voltage deviations is being promoted. In recent years, droop control of inverter- based distributed energy resources has emerged as an essential tool for use in this study. The participation of PV systems in voltage regulation and its coordination with existing controllers, such as on-load tap changers, is paramount for controlling the voltage within specified limits. In this work, control strategies are presented that can be coordinated with the existing controls in a distributed manner. The effectiveness of the proposed method was demonstrated through simulation results on a distribution system.     

Real-time simulation platform for photovoltaic system with a boost converter using MPPT algorithm in a DSP controller

Recently, real-time simulation of renewable energy sources are indispensible for evaluating the performance of the maximum power point tracking (MPPT) controller, especially in the photovoltaic (PV) system in order to reduce cost in the testing phase. Nowadays, real time PV simulators are obtained by using analog and/or digital components. In this paper, a real-time simulation of a PV system with a boost converter was proposed using only the digital signal processor (DSP) processor with two DC voltage sources to emulate the temperature and irradiation in the PV system. A MATLAB/Simulink environment was used to develop the real-time PV system with a boost converter into a C-program and build it into a DSP controller TMS320F28335. Besides, the performance of the real-time DSP-based PV was tested in different temperature and irradiation conditions to observe the P-V and V-I characteristics. Further, the performance of the PV with a boost converter was tested at different temperatures and irradiations using MPPT algorithms. This scheme was tested through simulation and the results were validated with that of standard conditions given in the PV data sheets. Implementation of this project helped to attract more researchers to study renewable energy applications without real sources. This might facilitate the study of PV systems in a real-time scenario and the evaluation of what should be expected for PV modules available in the market.     

Impact of residential photovoltaic power systems on the electric utility in Cairo, Egypt

The impact of utility-interactive residential photovoltaic (PV) power systems on the electric utility was studied. Power flow analyses were performed before and after the introduction of PV, on a subtransmission and distribution network model of an actual residential utility feeder serving a suburban area of Helwan in Cairo, Egypt. The changes in bus voltages and utility power factor were used to assess the impacts caused by the PV introduction. PV systems were examined at different penetration levels and were introduced in the low- and high-voltage buses of the distribution circuit. PV power factors as low as 0·7 were used to account for various power conditioner designs. PV-utility interconnection at the high-voltage distribution level is recommended since it results in acceptable voltage regulation throughout the network as well as a good utility power factor.     

Impact of active power curtailment on overvoltage prevention and energy production of PV inverters connected to low voltage residential feeders

As non-controllable power sources, photovoltaics (PV) can create overvoltage in low voltage (LV) distribution feeders during periods of high generation and low load. This is usually prevented passively by limiting the penetration level of PV to very conservative values, even if the critical periods rarely occur. Alternatively, one can use active power curtailment (APC) techniques, reducing the amount of active power injected by the PV inverters, as the voltage at their buses increase above a certain value. In this way, it is possible to increase the installed PV capacity and energy yield while preventing overvoltage. This paper investigates a number of approaches for sizing and controlling the PV power generated by 12 net-zero energy houses equipped with large rooftop PV systems in a typical 240 V/75 kVA Canadian suburban radial distribution feeder. Simulations of a one year period with typical solar irradiance and load profiles are conducted with PSCAD to assess the performance of the different approaches in terms of overvoltage occurrence, sharing of the burden for overvoltage prevention per house and total energy yield of the residential PV feeder.     

Combined operation of DC isolated distribution and PV systems for supplying unbalanced AC loads

This paper describes a DC isolated network which is fed by distributed generation (DG) from photovoltaic (PV) renewable sources to supply unbalanced AC loads. The battery energy storage bank has been connected to the DC network via DC/DC converter called storage converter to control the network voltage and optimize the operation of the PV generation units. The PV units are connected to the DC network via its own DC/DC converter called PV converter to ensure the required power flow. The unbalanced AC loads are connected to the DC network via its own DC/AC converter called load converter without transformer. This paper proposes a novel control strategy for storage converter which has a DC voltage droop regulator. Also a novel control system based on Clarke and Park rotating frame has been proposed for load converters. In this paper, the proposed operation method is demonstrated by simulation of power transfer between PV units, unbalanced AC loads and battery units. The simulation results based on PSCAD/EMTDC software show that DC isolated distribution system including PV units can provide the balanced voltages to supply unbalanced AC loads.     

基于混沌自适应人工鱼群算法的含家庭储能配电网快速重构方法

针对分布式电源接入配电网具有波动性和随机性的特点,提出一种基于混沌自适应人工鱼群算法的含分布式电源配电网快速化重构方法。在风电、光伏和家用储能的数学模型和节点划分基础上,以电网网损、开关次数以及失电负荷成本最小为目标函数,建立基于多目标优化的含分布式电源配电网的优化重构模型。利用混沌自适应人工鱼群算法对模型进行求解,通过对鱼群的混沌初始化和自适应动态调整步长参数,提高了算法的全局搜索能力和收敛速度。根据电化学储能系统出力特性划分配电网网架重构的典型工作场景,通过含分布式电源的IEEE 33节点测试系统仿真实例验证了该文方法的有效性。仿真结果表明,与单独考虑电网网损成本相比,由该文方法得到的配电网优化重构成本降低了50%以上,优化重构时间均小于0.9 s,实现了含分布式电源配电网的快速自愈。     

考虑需求响应与光伏不确定性的电力系统经济调度

针对光伏不确定性对电网的影响日益增加,该文提出一种考虑需求响应的源网荷经济调度方法。首先以光伏历史数据,利用非参数估计来拟合光伏出力,同时利用蒙特卡洛进行场景表征,并利用基于马氏距离场景缩减技术进行场景缩减;其次,结合随机规划方法,建立考虑需求响应下系统运行成本最小的电力系统源网荷经济调度模型;最后以IEEE39节点模型进行分析,结果表明采用所提出的优化模型可实现对光伏的不确定性调度,并能降低用户用电成本,对未来电力系统需求响应下的多能互补提供理论支撑。     

Impact of widespread photovoltaics generation on distribution systems

Prompted by the need for clean energy sources, increasing numbers of photovoltaic (PV) generators are being connected to electricity distribution systems around the world. There is thus a growing imperative to understand and quantify the technical impact that high penetrations of such generators may have on the operation and performance of electricity distribution systems. Detailed simulations of a very high penetration of PV within a typical UK urban distribution network (11 kV, 400 V and 230 V) are reported. The study performed unbalanced three-phase load-flow analysis on an entire feeder within a time-domain simulation framework using load and generation data at 1 minute intervals. The results indicate that even at very high penetrations of PV, network voltage rises are small and unlikely to cause problems. Effects on network power flows and losses are also quantified and discussed     

基于最大投资回报率的风光联合并网情况下输电网规划

江苏省电力设计院, 江苏 南京 211102     

Model of a synthetic wind speed time series generator

Wind energy has assumed a great relevance in the operation and planning of today's power systems due to the exponential increase of installations in the last 10 years. For this reason, many performed studies have looked at suitable representations of wind generation for power system analysis. One of the main elements to consider for this purpose is the model of the wind speed that is usually required as input. Wind speed measurements may represent a solution for this problem, but, for techniques such as sequential Monte Carlo simulation, they have to be long enough in order to describe a wide range of possible wind conditions. If these information are not available, synthetic wind speed time series may be a useful tool as well, but their generator must preserve statistical and stochastic features of the phenomenon. This paper deals with this issue: a generator for synthetic wind speed time series is described and some statistical issues (seasonal characteristics, autocorrelation functions, average values and distribution functions) are used for verification. The output of the model has been designed as input for sequential Monte Carlo simulation; however, it is expected that it can be used for other similar studies on wind generation. Copyright © 2007 John Wiley & Sons, Ltd.     

基于平抑风光出力波动的主动配电网优化调度

因风电、光伏光出力波动特性,并网运行将对主动配电网运行的稳定性造成影响。结合储能系统,将主动配电网中功率波动幅度大的风电、功率具有间歇特性的光伏搭建为风光储联合发电系统。通过改变柔性负荷边际效益增强其参与调度意愿,提高主动配电网消纳分布式可再生能源的能力及运行的稳定性。为提高粒子群算法的收敛性,利用模糊推理规则对学习因子动态调整。基于IEEE 30节点仿真算例,以系统日运行综合经济性为目标,使用模糊自适应粒子群算法寻优。算例仿真与分析验证了该文模型有效性。