双支路光伏最大功率跟踪的并网逆变器的研制

阐述了具有双支路光伏最大功率跟踪功能的并网型逆变器的基本原理和关键技术。对双支路光伏阵列的最大功率跟踪、并网逆变器的反孤岛效应以及并网控制策略等进行分析,提出解决方案,并研制出3kW的样机,通过实验验证了方案的可行性。     

光伏发电最大功率跟踪技术研究

对太阳能电池的工作原理及工作特性进行介绍,详细分析太阳能电池工作的等效电路和数学模型;介绍了几种最大功率点跟踪的控制方法;分析光伏并网逆变器的控制目标,研究其控制策略,并设计了基于SPWM的电压/电流型并网逆变器控制的控制系统数学模型。     

3 kW光伏并网逆变器

阐述了3kW光伏并网逆变器的关键技术。通过对光伏并网逆变器最大功率点跟踪、孤岛效应和并网控制等问题的分析，提出了具体的解决方案。并且通过对最大功率跟踪算法的改变及变压器切换的控制，使逆变器在轻载的条件下，依然可以获得较好的工作效率。     

光伏发电系统MPPT改进方法研究

研究了适合最大功率跟踪算法的新型变步长和改进型扰动观察法,以及将目标点扩展为一个区域的概念。改进最大功率跟踪方法,可有效应对光伏阵列的非线性和时变性,提高系统的有效产能,针对经典扰动观察法存在的振荡、误判问题,考虑到光伏阵列输出曲线最大功率点两侧斜率变化不一致和P-V曲线在工作区间内单峰性的特点。仿真结果表明,该方法提高了系统的稳定性和跟踪速度,在PSCAD环境下建立的三相并网系统中也得到了良好的仿真曲线,提高了光伏并网系统对光能的利用率,对并网电能质量方面的问题产生了积极作用。     

基于MPPT运行模式的光伏发电系统低电压穿越无功控制策略

针对光伏发电系统通常以单位功率因数运行,造成故障时光伏并网逆变器一定视在功率浪费的现状,提出一种低电压穿越无功控制策略。分析光伏并网逆变器的有功、无功功率解耦控制和其无功功率输出极限,建立光伏逆变器无功功率输出与并网点电压跌落的关系,通过比较故障前光伏阵列发出有功功率与光伏逆变器允许输出最大有功功率,确定光伏发电系统在低电压穿越过程以最大功率模式运行或者以非最大功率模式运行。利用RTDS软件搭建仿真算例,验证该低电压穿越无功控制策略的可行性。     

基于粒子群优化神经网络光伏并网最大功率点跟踪技术研究

针对电导增量法无法搜索全局光伏系统最大功率点的不足,文章将神经网络与电导增量法相结合,提出一种新型光伏并网最大功率点跟踪算法。该算法在不同光照和温度情况下,采集光伏阵列电压值和电流值,建立神经网络模型。通过人工神经网络预测光伏阵列输出电压,并将此电压作为电导增量法参考电压,从而实现局部阴影下最大功率点跟踪。实验结果表明,神经网络与电导增量法相结合可以准确实现局部阴影下光伏阵列最大功率点跟踪,具有较高的跟踪精度。     

新型MPPT算法在两级式光伏并网系统中的应用

以光伏发电系统为研究对象,分别结合相应的控制算法建立了一种带有最大功率点跟踪(MPPT)功能的光伏并网系统,并利用Matlab软件进行了仿真。仿真结果表明,前级Boost电路基于新型算法——变步长扰动观察法实现了最大功率点跟踪的功能;后级逆变电路采用电压外环、电流内环的双闭环控制方式,使逆变器的输出能准确、快速地跟踪电网电压变化,并与电网电压保持同频、同相。该系统的输出为纹波较少的正弦波形,功率因数接近于1,可满足光伏并网对逆变器的要求。     

基于Matlab/Simulink的两级式光伏并网系统仿真分析

研究一种单相光伏并网发电控制仿真系统。利用Matlab2008b/Simulink,采用boost电路和逆变电路两级式结构,其中采用电导增量法的最大功率跟踪功能在boost电路中实现,并网控制通过采集电网电压参数和逆变输出电流电压参数在逆变电路中通过PI调节实现。通过光伏阵列通用模型验证最大功率跟踪模块的正确性,通过并网实验验证并网跟踪性能。基本实现了光伏阵列最大功率点的快速、准确跟踪功能和逆变输出电流电压与电网电压的同频同相,保证了输出电流为正弦波形且纹波较少,能够快速跟踪电网电压的变化。证明此系统在实际中是可行的。     

基于MPPT的两级单相光伏并网发电系统控制策略研究

文章对两级单相光伏并网发电系统进行研究,系统前级使用新型变步长电导增量法,来实现最大功率点跟踪;后级逆变器采用P-Q控制方式,实现快速电网电压跟踪;使用电压外环,电流内环的双环控制,使逆变器输出稳定的无功和有功功率。在Simulink中搭建仿真模型,结果验证系统不仅能够有效提高跟踪速度和精度,而且可以较好的抑制系统在最大功率处的波动,满足光伏发电对并网逆变器的要求。     

采用电流寻优的MPPT光伏阵列并网逆变器的研究

针对光伏阵列模型之特点,提出了一种具有最大功率点跟踪（MPPT）的新型光伏阵列正弦波并网逆变器控制方案,该方案一改并网逆变器常规的双环（电压外环,电流内环）控制模式,而采而由MPPT控制器输出直接进行电流控制的新模式,使控制结构更加简单,动态性能更加优越,基于80C196MC控制的电流预估控制策略,实现了网侧电流正弦化,且为单位为功率因数。     

基于交替单相PWM控制的三相光伏并网系统

提出了可用于多支路型三相光伏并网逆变器的交替单相PWM控制方法。该控制方法在一个工频周期内,逆变器有6种开关模式,每种开关模式中只须对三相中的一相桥臂进行PWM控制,从而有效降低了功率管开关损耗,在多支路光伏并网结构提高能量转换效率的基础上,进一步提高系统效率。采用电流滞环PWM跟踪控制,能够简单实现逆变正弦电流输出,跟踪性能好,并网功率因数为1,系统稳定性好,电流总谐波畸变率(THD)较低,可满足并网要求。通过Matlab仿真验证了该控制方法的正确性和有效性。     

A grid-connected photovoltaic power conversion system with single-phase multilevel inverter

This paper presents a grid-connected photovoltaic (PV) power conversion system based on a single-phase multilevel inverter. The proposed system fundamentally consists of PV arrays and a single-phase multilevel inverter structure. First, configuration and structural parts of the PV assisted inverter system are introduced in detail. To produce reference output voltage waves, a simple switching strategy based on calculating switching angles is improved. By calculated switching angles, the reference signal is produced as a multilevel shaped output voltage wave. The control algorithm and operational principles of the proposed system are explained. Operating PV arrays in the same load condition is a considerable point; therefore a simulation study is performed to arrange the PV arrays. After determining the number and connection types of the PV arrays, the system is configured through the arrangement of the PV arrays. The validity of the proposed system is verified through simulations and experimental study. The results demonstrate that the system can achieve lower total harmonic distortion (THD) on the output voltage and load current, and it is capable of operating synchronous and transferring power values having different characteristic to the grid. Hence, it is suitable to use the proposed configuration as a PV power conversion system in various applications.     

一种多逆变器太阳能光伏并网发电系统的组群控制方法

对光伏发电系统中的光伏阵列一逆变器对进行轮循分组控制,在逆变器输入功率小于设定的下限阈值时,部分光伏阵列并联后连接到一台逆变器输出;在并联开关分合闸过程中,一直保持光伏阵列以最大功率不问断输出;并且该方法对光照突变情况进行自适应判断,作为控制的预启动条件。此方法的优点是：能够同时提高逆变器和光伏阵列的转换效率,改善电能质量,降低并联开关和逆变器的动作次数,延长设备使用寿命,并且控制过程系统输出功率平稳。     

Photovoltaic solar system connected to the electric power grid operating as active power generator and reactive power compensator

In the case of photovoltaic (PV) systems acting as distributed generation (DG) systems, the DC energy that is produced is fed to the grid through the power-conditioning unit (inverter). The majority of contemporary inverters used in DG systems are current source inverters (CSI) operating at unity power factor. If, however, we assume that voltage source inverters (VSI) can replace CSIs, we can generate reactive power proportionally to the remaining unused capacity at any given time. According to the theory of instantaneous power, the inverter reactive power can be regulated by changing the amplitude of its output voltage. In addition, the inverter active power can be adjusted by modifying the phase angle of its output voltage. Based on such theory, both the active power supply and the reactive power compensation (RPC) can be carried out simultaneously. When the insolation is weak or the PV modules are inoperative at night, the RPC feature of a PV system can still be used to improve the inverter utilisation factor. Some MATLAB simulation results are included here to show the feasibility of the method.     

基于LC滤波的光伏逆变器电感电流反馈控制策略研究

针对光伏并网逆变器的特点,基于电感电流反馈控制的光伏并网逆变器,提出了参考电流相位超前的电流内环控制策略。通过分析单相并网逆变器结构,推导了LC滤波器上电压电流矢量关系。加入电网电压瞬时值前馈解耦控制,研究了比例调节和准比例谐振调节两种策略下参考电流与输出电流的关联。基于一台3 kW逆变器为实验平台的理论分析和实验结果表明,采用该策略的逆变器并网电流时刻跟踪电网电压频率和相位,功率因数为1,并网电流谐波失真度低于3%。     

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.     

新型H6拓扑无隔离单相光伏并网逆变器研究

与带隔离变压器相比,无隔离变压器的光伏并网逆变器成本低、体积小、效率高,但无隔离光伏并网系统的漏电流将影响系统的安全运行,必须进行有效抑制,同时逆变器应具有向电网提供无功功率的能力。对此提出了一种新型的H6拓扑单相并网逆变器,该拓扑能有效抑制漏电流,且能向电网输出无功功率,采用单极性调制策略,输出电压具有三电平特性。基于对拓扑结构、工作过程及无功功率控制的详细分析,建立了Matlab/Simulink仿真模型验证理论分析的正确性,并搭建了1kW的实验平台,对理论分析和仿真结果进行了试验验证。     

Intelligent photovoltaic farms for robust frequency stabilization in multi-area interconnected power system based on PSO-based optimal Sugeno fuzzy logic control

Currently, the grid-connected large PV farms are extensively installed in power systems. Nevertheless, in addition to the load change, the intermittent power output of PV farms may lead to the serious problem of the system frequency fluctuation. To handle this problem, this paper proposes a new design of Sugeno fuzzy logic controller based on particle swarm optimization (PSO-SFLC) of intelligent PV farms for the frequency stabilization in a multi-area interconnected power system. To handle various scenarios, the frequency deviations and solar insolations are used as input signals of the PSO-SFLC. The output signal of the PSO-SFLC is a command signal for adjusting PV output power. The output power of PV is controlled by the PSO-SFLC to meet the load demand so that the system frequency fluctuation can be suppressed. Without the difficulty of trial and error, the optimal input and output membership functions, and control rules of PSO-SFLC are automatically achieved by PSO. Simulation study in a three-area loop interconnected power system with large PV farms elucidates that the frequency stabilizing performance and robustness of the PV equipped with the PSO-SFLC is much superior to that of the PV with the SFLC and the PV with the maximum power point tracking control in scenarios with various solar insolations and loading conditions.     

Input output feedback linearization control and variable step size MPPT algorithm of a grid-connected photovoltaic inverter

In this paper, the power factor of a grid-connected photovoltaic inverter is controlled using the input output Feedback Linearization Control (FLC) technique. This technique transforms the nonlinear state model of the inverter in the d–q reference frame into two equivalent linear subsystems, and then applies a pole placement linear control loops on this subsystem in order to separately control the grid power factor and the dc link voltage of the inverter. Maximum Power Point Tracker (MPPT) that allows extraction of maximum available power from the photovoltaic (PV) array has been included. This MPPT is based on variable step size incremental conductance method. Compared with conventional fixed step size method, the variable step MPPT improves the speed and the accuracy of the tracking.     

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.