Implementation of FPGA Based MPPT Techniques for Grid-Connected PV System

Global energy demand is growing rapidly owing to industrial growth and urbanization.Alternative energy sources are driven by limited reserves and rapid depletion of conventional energy sources(e.g.,fossil fuels).Solar photovol-taic(PV),as a source of electricity,has grown in popularity over the last few dec-ades because of their clean,noise-free,low-maintenance,and abundant availability of solar energy.There are two types of maximum power point track-ing(MPPT)techniques:classical and evolutionary algorithm-based techniques.Precise and less complex perturb and observe(P&O)and incremental conduc-tance(INC)approaches are extensively employed among classical techniques.This study used afield-programmable gate array(FPGA)-based hardware arrange-ment for a grid-connected photovoltaic(PV)system.The PV panels,MPPT con-trollers,and battery management systems are all components of the proposed system.In the developed hardware prototype,various modes of operation of the grid-connected PV system were examined using P&O and incremental con-ductance MPPT approaches.

Soft-switching Grid-connected PV Inverter With Interleaved Flyback Topology

提出一种应用于单个光伏组件的软开关交错反激并网逆变器拓扑及其软开关控制策略。针对反激变压器漏感问题，提出漏感能量吸收回馈电路，实现了漏感能量吸收再利用，并实现了开关管漏源电压的钳位，提高了变换效率同时降低了开关管关断电压尖峰；提出基于数字处理器的反激变换器变开关频率谐振软开关控制策略，实现了开关管的零电压开通，同时改善了逆变器的电磁兼容特性；提出的交错并联反激逆变器有助于减小变压器和滤波器的体积，提高功率密度。详细分析变换器的工作原理，分析变开关频率谐振软开关控制方式的原理和实现条件，最后进行实验验证。

Long Term Assessment of a Grid Connected Solar PV System in Sydney

This paper assesses 4 years of operation of a 1.75 kW roof top solar PV system installed in a Sydney suburban house. The system consists of 10 PV panels, a DC/AC inverter, and a grid connected gross meter. Solar electricity delivered to grid is verified with the results from a computer simulation package （PVSYST） by adopting the installed component specifications, operation conditions, and weather data of the site. The results show high consistency between the values of energy delivered to the grid measured by the energy company and the energy estimated by system simulation. New system performance indicator is developed and called the optimum performance compliance ratio （PCR）. It is a measure of the compliance of the output of the designed PV system with the output which would be produced by the same system with a solar tracker. This indicator provides system designers, contractors and energy providers with the actual capacity of the system that they can offer the end-users.

Low Voltage Ride through Control Capability of a Large Grid Connected PV System Combining DC Chopper and Current Limiting Techniques

This paper presents the development and performance capability of a comprehensive Low voltage ride through (LVRT) control scheme that makes use of both the DC chopper and the current limiting based on the required reactive power during fault time. The study is conducted on an 8.5 MW single stage PV power plant (PVPP) connected to the Rwandan grid. In the event of fault disturbance, this control scheme helps to overcome the problems of excessive DC-link voltage by fast activation of the DC chopper operation. At the same instance, AC current is limited to the maximum rating of the inverter as a function of the injected reactive current. This helps overcome AC-over- current that may possibly lead to damage or disconnection of the inverter. The control scheme also ensures voltage support and power balance through the injection of reactive current as per grid code requirements. Selected simulations using MATLAB are carried out in the events of different kinds of fault caused voltage dips. Results demonstrate the effectiveness of the proposed LVRT control scheme.

H6 Non-isolated Full Bridge Grid-connected PV Inverters With Low Leakage Currents

为满足非隔离光伏并网发电系统对共模漏电流的限制，提出一种六开关逆变器拓朴（H6拓扑）。所提出的H6拓扑在功率传输模态时，进网电流半个工频周期流过3支开关管，而另半个工频周期流过2支开关管，故相对于H5拓扑，降低了通态损耗，有利于热应力均衡，且仍满足续流阶段光伏电池输出端与电网脱离的要求。详细分析拓扑的工作原理，并推论给出H6非隔离光伏并网逆变器的其它3种拓扑结构；比较分析了H5拓扑、Heric拓扑和H6拓扑的损耗和成本。通过1kW通用样机平台对比验证了上述3种拓扑的效率和共模特性。实验结果表明，H6拓扑的变换效率高于H5拓扑、但略低于Heric拓扑，共模特性优于Heric拓扑、但略劣于H5拓扑。

Analyzing the Impact of Bapco 5 MW Solar PV Grid-Connected Project on Bahrain’s Outlook for Energy-Mix Production

The impact of Bapco 5 MW solar PV grid-connected project on Bahrain’s outlook for clean energy and energy-mix production was analyzed since solar electricity obtained from PV installation is considered as a non-linear system. Several positive impacts were counted. These impacts were on business, economy, environment, research, green jobs creation and rooftop installation and other large-scale installation. This project had attracted public, investors, developers to invest in similar projects in the Kingdom of Bahrain;especially it is an environmentally friendly and smart technology. This innovative smart grid-connected 5 MW solar PV power plant is enough to electrify 500 houses @ 10 kW and had answered lots of frustrating questions such as the effect of dust on PV performance, need of man-made cleaning compared to naturally cleaned PV panels, reliability of the system, greenhouse gases reduction and pay-back period.

基于PVsyst的光伏系统研究

基于PVsyst软件,以吐鲁番地区某民居为模拟对象,对当地的气象数据进行分析,并构建了一套安装在屋顶的光伏并网发电系统。对光伏并网系统的安装倾角进行优化,并对光伏组件进行选型,对系统损失进行分析。最后根据模拟结果,对影响系统发电效率的因素进行分析并提出了一些优化方案,以及得出吐鲁番地区19.1 kW的光伏并网系统全年发电量为27.9 MW·h,系统效率为80.9%,能量回收期为2.98年,每年可减少32790 kg的CO_(2)排放量,具有一定的环境效益;若按新疆光伏上网电价0.262元(/kW·h)进行计算,每年还可带来7309.8元的收入。该研究对实际光伏并网系统的设计施工具有一定的参考意义。

Comparison of Experimental and Theoretical Output Power of Grid Connected Photovoltaic System in Super Mega Factory

In this paper, the performance of grid connected PV system that is installed in Super Mega Factory is presented. The output parameters of 4 kW PV is collected and analyzed. Then, according to the results the weak points of the system were found and the theoretical output power was compared. After that we try to get the maximum output power making the correction of collector angle and place suitable panel position.

Evaluation of the Performances of the First Grid-Connected Photovoltaic System in Sénégal

This document presents the evaluation and the monitoring of the performances of the first grid-connected photovoltaic system installed in the Center of Studies and Researches on the Renewable Energies (CERER) inaugurated on December 4th, 2012 by the governmental authorities of Senegal and Tenerife. This mini power plant of 3.15 kWc is a perfect example of the political will of the government which is to reduce the production cost of the electricity, with the diversification of the sources of production, and the greater use of the other sources such as the natural gas, the coal, the renewable energies. The evaluation of the performances of the installation is realized by using the indicators of efficiency and performance as the photovoltaic surface yield, the ratio of photovoltaic performance, the photovoltaic specific yield, and the losses of captures. The obtained results show that a big part of the energy shone during the period of observation was not able to be used further to circumstances such as the losses of conductivity, the heat losses or for example the defects on components. The analysis also shows that a large part of the produced energy is not injected because of the dilapidation of the network, the defects of landing but especially one disjunction sees frequently at the level of the point of injection.

Influence of Control Modes of Grid-Connected Solar Photovoltaic Generation on Grid Power Flow

Integration of Solar Photovoltaic (PV) generation into an existing distribution system has many impacts on the system, with the power flow being one of the major issues. This impact is not generic for any network, but it may manifest itself either positively or negatively, depending on the grid configuration, interface control modes, operation mode, and load profile. Grid-connected PV systems have three control options of the local voltage controller of the interface DC-AC converter. These control modes are Power Factor control, voltage control, and Droop Voltage control. This paper aims at evaluating and comparing the impacts of those control modes on the grid power flow. A set of evaluation criteria and indices is defined and mathematically formulated. Based on the requirements of the used program (Power Factory Dig Silent V14.1.3), a computation plan (algorithm) has been proposed. The algorithm has been applied to a typical weak network and a wide range of simulations has been carried out. Simulation results have been thoroughly discussed and important findings have been concluded.

太阳光照环境对于光伏并网逆变器温升影响的研究

光伏并网逆变器需长期工作在太阳光照暴露环境中,目前关于太阳光照对于光伏并网逆变器运行稳定性的影响的相关研究却几乎没有,光伏并网逆变器的相关检测、认证也无光照条件方面的要求。但部分光伏电站的运维人员却发现光伏并网逆变器在较强光照条件下会出现降载、停机等故障,其引发的弃光限电问题愈发受到重视。本文通过研究在不同辐照度的太阳光照环境下光伏并网逆变器各部件温升的数据分析发现,在温升试验时,额外施加的太阳光照对光伏并网逆变器的温升有着额外的提升,且越高辐照度的太阳光照对光伏并网逆变器的温升影响越大。本文可为光伏并网逆变器的设计安装及电站运维提供参考。

新型电力系统下分布式光伏规模化并网运行关键技术探讨

推进分布式光伏规模化并网是实现“碳达峰·碳中和”目标和构建新型电力系统的重要举措。基于此背景探讨面向新型电力系统的分布式光伏规模化并网运行关键技术。首先,归纳并阐述分布式光伏发展现状、并网方式及运行模式,分析大规模分布式光伏接入给电网调度运行带来的挑战。其次,面对上述挑战,从信息集成、监测预测、平衡调度、聚合控制等视角提出系统调度运行关键技术,助力电网调控模式转型升级。然后,考虑实际工程需求,构思满足电网安全稳定运行的分布式光伏技术标准体系,以期促使分布式光伏“可观可测、可调可控、友好互动”。最后,调研并梳理国外分布式光伏规模化并网运行先进经验,并对我国分布式光伏并网协同探索、运行服务支持及市场交易参与等课题提出建议。

弱电网下光伏并网逆变器谐振抑制方法综述

“双碳”目标背景下电力系统形成“高比例可再生能源”和“高比例电力电子设备”的“双高”趋势,以致电网呈现弱电网特性。弱电网下电网阻抗实时变化,导致光伏并网逆变器谐振频率偏移、逆变器集群多谐振峰等稳定性问题。针对光伏并网逆变器在弱电网下最新的谐振抑制方法尚未得到系统地归纳总结,从弱电网下逆变器单元谐振抑制方法和逆变器集群谐振抑制方法两方面综述“双高”电力系统下光伏并网逆变器谐振抑制热点控制方法,为光伏并网逆变器的稳定性提升指明发展方向。

基于光伏动态电流参考值的两级式光伏并网系统低电压穿越控制策略

随着光伏接入容量的不断提升,电网电压跌落时光伏脱网会影响系统稳定运行,因此光伏系统应具备低电压穿越(LVRT)能力。然而,目前常用的两级式光伏并网系统LVRT控制策略存在光伏动态响应慢及控制效果受限于光伏P–U特性曲线的数学模型精度等问题,且未考虑局部阴影条件下的适用性。基于此,提出一种基于光伏动态电流参考值的LVRT控制策略。首先,在建立两级式光伏并网系统及光伏电池P–U特性数学模型的基础上,分别对目前常用的基于定直流母线电压和基于光伏P–U特性曲线的LVRT控制的原理及不足进行了分析。其次,针对前级boost电路的控制构造了具有自适应收敛特性的光伏输出电流动态参考值以对光伏工作点进行直接调整。该策略无需对光伏P–U特性曲线数学模型进行求解,避免求解误差的同时加快了光伏动态响应速度。此外,在最大功率跟踪(MPPT)算法中引入故障解耦模块,在电网低电压故障期间对MPPT输出电压参考值进行锁定,避免MPPT无效运算带来的电压参考值偏移,使系统在故障结束时能以最快速度恢复至最大功率点。最后,通过仿真将所提策略与目前常用的基于定直流母线电压和基于光伏P–U特性曲线的LVRT控制策略在多种环境条件下进行对比。仿真结果表明:与定直流母线电压控制策略相比,所提策略下光伏动态响应快;与现有基于光伏P–U特性曲线的控制策略相比,所提策略不受P–U特性误差的影响,在辐照度变化尤其局部阴影条件下均能很好地实现低电压穿越。

基于交流储能的光伏柔直系统多时间尺度调压控制

由于光伏发电受光照强度等因素影响明显,导致其与模块化多电平换流器(modular multilevel converter,MMC)并网运行时功率不均衡,影响系统直流电压稳定性。该文针对光伏接入柔直系统的多时间尺度功率不平衡问题进行研究,提出光伏送电端交流侧储能方案及附加功率反馈环控制策略,协调消纳多时间尺度及交流故障场景下系统产生的不平衡功率。所搭建21电平35 k V光伏并网柔直模型的仿真结果表明,在光照强度突变至600 W/m2的情况下,采用附加功率反馈环控制策略时储能系统对直流电压波动的抑制水平可达11.9%,交流故障时其对直流电压波动的抑制水平可达23.7%,验证了该方案及控制策略的可行性。

光伏发电-超级电容储能并网系统的直流母线电压稳定控制

光伏发电并网系统因太阳能的周期性和间歇性会对电网造成扰动,影响电网的安全稳定运行。针对双级式光伏并网发电系统,在直流母线侧增加超级电容储能可以平抑光伏发电功率的波动。从控制功能的角度,将光伏发电-超级电容储能并网系统分为光伏发电、逆变器和超级电容储能3个功能独立的子系统;建立了各子系统的数学模型,并在此基础上分析确定各子系统分别实现最大功率跟踪控制、恒功率控制和直流母线电压稳定控制的具体方案;针对直流母线电压的稳定控制,提出一种基于鲁棒渐近跟踪控制的方法。通过模拟不同辐照强度,不同电网有功-无功功率需求等多种工况进行仿真验证。结果表明,所提控制功能划分合理,控制方法有效且兼有较好性能。

电动汽车与电网互联技术在新能源并网中的应用

V2G (Vehicle-to-Grid,电动汽车与电网互联)技术的应用可以实现电网与车主的双赢。从电网角度,可以发挥削峰填谷、平抑新能源功率波动、延缓电网升级改造等作用;从用户角度,在满足用车的要求下可获取附加效益。随着电动汽车的推广和新能源并网规模的发展,V2G技术得到更多的关注。然而,V2G技术的发展仍然面临规模化互动、运营、调度等技术及经济性问题。因此,从V2G技术发展的现状出发,重点阐述V2G技术在新能源并网中的作用和应用模式;并对V2G技术在新能源并网中的充放电策略、电池寿命预测以及综合价值进行了探讨。V2G技术在新能源并网中的推广应用不仅可以提升新能源并网利用率,还可进一步提升电动汽车的减排效果。

计及辐照波动的光伏自同步电压源直流电容选型方法

光伏自同步电压源型并网逆变器因其模拟同步发电机的频率及电压控制特性,可显著改善新能源发电系统的并网稳定性;而其直流电容可支撑辐照波动下逆变器交直流侧的有功功率差额,从而平抑直流电压波动,对逆变器的直流电压稳定性尤为重要。为此,提出了一种计及辐照波动的光伏自同步电压源直流电容选型方法。通过对光伏自同步电压源系统进行暂态建模,构建了辐照度与直流电压的关系模型,并在此基础上提出直流电容选型方法。所提方法可准确预测和评估辐照波动下的直流电压变化,有效避免直流欠压,实现光伏自同步电压源在辐照波动下的直流电压稳定。算例及仿真验证了所提方法的有效性。

基于LIBSVM识别并网PV系统阻抗的输电线电流保护自适应策略研究

为解决并入配电网的光伏系统功率波动性导致输电线电流保护拒/误动问题,提出一种基于LIBSVM的PV并网系统输电线电流保护自适应策略。基于Matlab/Simulink仿真平台搭建了结合低电压穿越控制策略模型的并网光伏系统动态仿真模型。在不同故障位置与故障类型情况下,针对正常运行时光伏功率的波动输出,仿真分析了光伏系统与低电压穿越控制策略协调下的故障特性及对配电网输电线电流保护产生的影响。在此基础上提出了一种基于支持向量机(SVM)识别PV并网系统不同输出功率时等效阻抗的方法,制定了输电线电流自适应保护判据,依据光伏系统输出功率和运行方式变化动态调整整定值。仿真验证表明:所提出的自适应保护策略避免了保护拒/误动,提高了保护装置性能。