具有无功功率补偿和谐波抑制的光伏并网功率调节器控制研究

提出一种将有源滤波和无功功率补偿与光伏并网发电相结合的新型光伏并网功率调节系统。利用瞬态无功功率理论中的瞬时无功和谐波电流检测原理,采用电流矢量控制技术,以DSP数字信号处理器为基础,在30KVA光伏并网功率调节器样机中成功地实现了有源滤波、无功功率补偿和光伏并网发电三者的统一控制,使光伏并网功率调节器在向电网提供有功能量的同时也提供无功负载所需的无功能量,从而节省了设备投资,同时也改善了电网的供电质量。     

基于DSPIC30F6010A双闭环控制的并网逆变器的研究与实践

光伏并网发电是光伏发电应用发展的趋势.并网逆变器是光伏并网发电系统核心部件之一,基于DSPIC30F6010A芯片控制的并网系统,利用DSP丰富的外围电路和强大的功能实现并网系统的所有工作、控制和相应的保护功能等.针对输出电流谐波含量大的特点,提出了基于同步PI内环控制和直流电压前馈外环控制的双闭环电流控制思路,并网逆变器采用前级DC/DC的boost升压结构电路,减少系统体积和重量;后级DC/AC逆变器采用全桥逆变电路;且具有最大功率跟踪和反孤岛效应等功能.仿真和实验证明:利用提出的算法,可有效减少并网电流的谐波,光伏并网系统具有可靠性强,工作效率高,稳定性好等优点.     

大规模光伏并网电站接入系统若干问题的探讨

结合光伏并网发电的发展趋势,分析了大规模光伏并网电站的特点．对其接入电力系统时的防孤岛效应、谐波控制、无功功率调节能力、光伏电站接入点的短路电流、并网电压及升压变压器的选择等方面做了研究和探讨。     

光伏并网与电能质量治理统一控制

为提高光伏并网系统利用率,并使其具备主动参与电网电能质量治理的能力,提出一种协调并网发电与网侧电能质量治理的统一控制策略。研究基于光伏组件出力的运行模式切换与直流侧电压控制方法,提出基于无功/谐波优先级的逆变器容量分配和指令电流合成策略。设计并研制基于FPGA+RT架构的并网控制器,构建DC/AC单级结构的光伏并网实验系统。实验验证统一控制策略的可行性和有效性,为分布式光伏电源可定制电能并网发电提供基础。     

光伏发电系统低功率运行并网电流谐波抑制研究

以低功率运行的光伏发电系统为研究对象,通过理论分析和实验研究的方法,对光伏发电系统低功率运行时并网逆变器输出电流畸变恶化的问题进行探讨,并设计一种减小并网电流谐波的解决方案,最后进行实验验证。结果表明:提出的解决方案可有效减小并网逆变器低功率运行时输出的低次电流谐波,实现光伏发电系统低功率运行时并网电流总谐波畸变率满足IEEE Std.1547-2003标准。     

基于户用型太阳能光伏发电并网设备的研究

针对开发住宅光伏并网发电技术,阐述了并网设备的系统组成、研究内容,对并网控制的关键技术进行了分析和研究,并展望了光伏并网发电技术的应用前景。     

光伏并网系统隔离变压器联接方式的应用研究

对光伏并网系统隔离变压器进行了仿真与实验,探讨适于光伏并网系统的变压器连接方式.对隔离变压器及其作用进行了简要论述,对谐振过电压、系统故障检测及系统谐波等问题进行了理论分析,确定了光伏并网系统隔离变压器连接方式选择的基本准则.研究结果表明,在单级式光伏并网发电系统中,隔离变压器的连接选择△/Yn方式较合适,为今后大容量光伏并网电站的发展提供了基础和依据.     

光伏并网系统的谐波检测与分析

光伏系统并网运行会对电网带来一系列问题,其中谐波污染就是问题之一,这也是光伏系统实现真正并网运行必须解决的一个难题,而进行谐波检测则是解决该问题的先决条件。通过使用适当的加窗插值算法,验证了加窗插值FFT算法检测谐波各项参数的有效性,并应用此算法对光伏并网模型的谐波电流进行了检测与分析。     

光伏发电系统输出功率特性分析及其平滑控制研究

为解决光伏发电系统受光照、温度等外部环境因素影响大、输出功率波动频繁以及并网电流谐波含量大等问题,在分析光伏并网发电系统输出功率特性的基础上,提出一种基于蓄电池和超级电容复合储能的并网功率平滑控制策略。详细分析不同光照、温度环境下系统输出功率的特性及其对电网的影响,给出复合储能型光伏并网发电系统的实现方案,并提出改进的系统并网控制方法,实现系统并网功率高、低频波动分量的平滑控制。仿真结果表明:该控制策略能有效平抑系统输出功率波动,同时降低并网电流的谐波含量。     

基于分区控制的光伏并网发电运行研究

具有无功补偿功能的光伏并网发电对改善电网电压分布、降低网损及提高电网末端地区的供电质量、节省无功补偿设备投资具有重要作用。提出分区控制的思想用于光伏并网功率调节控制,给出了区域划分的基本原则,详细分析了光伏并网发电系统的运行区域及耦合电感的选择等问题,讨论了当光照条件不变时并网点电压变化对分区运行点的影响,并提出基于全微分思想的修正方法。通过算例模拟了分区控制的过程,结果表明,所提光伏发电系统并网后对配电网电压水平具有显著的改善作用,验证了分区控制方法的有效性。     

Power quality improvement of solar photovoltaic transformer-less grid-connected system with maximum power point tracking control

This paper presents a transformer-less single-stage grid-connected solar photovoltaic (PV) system with active reactive power control. In the absence of active input power, grid-tied voltage source converter (VSC) is operated in the reactive power generation mode, which powers control circuitry and maintains regulated DC voltage. Control scheme has been implemented so that the grid-connected converter continuously serves local load. A data-based maximum power point tracking (MPPT) has been implemented at maximum power which performs power quality control by reducing total harmonic distortion (THD) in grid-injected current under varying environmental conditions. Standards (IEEE-519/1547) stipulates that current with THD greater than 5% cannot be injected into the grid by any distributed generation (DG) source. MPPT tracks actual variable DC link voltage while deriving maximum power from PV array and maintains DC link voltage constant by changing the converter modulation index. Simulation results with the PV model and MPPT technique validations demonstrate effectiveness of the proposed system.     

Two-loop controller for maximizing performance of a grid-connectedphotovoltaic-fuel cell hybrid power plant

Maximizing performance of a grid-connected photovoltaic (PV)-fuel cell hybrid system by use of a two-loop controller is discussed. One loop is a neural network controller for maximum power point tracking, which extracts maximum available solar power from PV arrays under varying conditions of insolation, temperature, and system load. A real/reactive power controller (RRPC) is the other loop. The RRPC achieves the system's requirements for real and reactive powers by controlling incoming fuel to fuel cell stacks as well as switching control signals to a power conditioning subsystem. Results of time-domain simulations prove not only the effectiveness of the proposed computer models of the two-loop controller but also its applicability for use in stability analysis of the hybrid power plant     

Harmonic distortion assessment for a single-phase grid-connected photovoltaic system

Nowadays, grid-connected photovoltaic (PV) systems constitute an emerging technology. This has given rise to concerns about their contribution to harmonic distortion levels in utility grids. Valuable insight into the electrical behavior of such a system, including its impact on power quality, can be obtained through extensive simulation studies. In this paper, models are developed with a focus on not only accurate but also fast simulation of grid-connected PV systems. First, time-consuming processes are identified and discussed. These are mainly associated with the semiconductor power switching devices and the non-linear characteristics of the system components (isolation transformer, PV generator). Next, models are developed in order to increase simulation speed by avoiding time-consuming procedures. The validity of the approach is ascertained by comparing simulation results with published measurements. A case study is then performed in order to obtain current and voltage waveforms and, subsequently, harmonic distortion levels. Further simulations are carried out using different values for various system parameters in order to make an assessment of their impact in terms of waveform distortion.     

A Single-Stage Three-Phase Grid-Connected Photovoltaic System With Modified MPPT Method and Reactive Power Compensation

Single-stage grid-connected photovoltaic (PV) systems have advantages such as simple topology, high efficiency, etc. However, since all the control objectives such as the maximum power point tracking (MPPT), synchronization with the utility voltage, and harmonics reduction for output current need to be considered simultaneously, the complexity of the control scheme is much increased. This paper presents the implementation of a single-stage three-phase grid-connected PV system. In addition to realize the aforementioned control objectives, the proposed control can also remarkably improve the stability of the MPPT method with a modified incremental conductance MPPT method. The reactive power compensation for local load is also realized, so as to alleviate grid burden. A DSP is employed to implement the proposed MPPT controller and reactive power compensation unit. Simulation and experimental results show the high stability and high efficiency of this single-stage three-phase grid-connected PV system.     

New control strategy for 2-stage grid-connected photovoltaic power system

This work deals with the performances and responses of a grid-connected photovoltaic (PV) plant in normal and disturbed modes. The system is composed of a solar array, a dc–dc converter and a three-phase inverter connected to the utility grid. On the one hand a suitable control of the dc–dc converter is developed in order to extract the maximum amount of power from the PV generator. On the other hand an active and reactive power control approach (PQ) has been presented for the inverter. This method can provide a current with sinusoidal waveform and ensure a high power factor. Therefore, the grid interface inverter transfers the energy drawn from the PV into the grid by ensuring constant dc link voltage. Modeling and controlling were carried out using the informational graph of causality and the macroscopic energy representation methods. The simulation under MATLAB/SIMULINK and the experimental results show the control performance and dynamic behavior of grid-connected PV system in normal and disturbances modes.     

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.     

运用虚拟同步机技术的新型兆瓦级光-储并网结构

提出一种新型的VSG光-储分布式发电系统结构,该方案在传统光-储并网发电系统的逆变器后端另外添置了一套储能电池。这样不但可提高光伏组件的工作效率,避免光伏出力变化对系统频率造成影响,而且还可根据电网负荷的异常波动情况及时有效地输出有功及无功功率,达到稳定电网频率、电压的作用。系统的动态分析及仿真结果证明了该新型光-储并网发电系统结构能够实现新能源并网的目标与要求。     

Power quality investigation of a solar PV transformer-less grid-connected system fed DVR

This paper presents a single stage transformer-less grid-connected solar photovoltaic (PV) system with an active and reactive power control. In the absence of active input power, the grid-tied voltage source converter (VSC) is operated in a reactive power generation mode, which powers the control circuitry, and maintains a regulated DC voltage to the VSC. A data-based maximum power point tracking (MPPT) control scheme which performs power quality control at a maximum power by reducing the total harmonic distortion (THD) in grid injected current as per IEEE-519/1547 standards is implemented. A proportional-integral (PI) controller based dynamic voltage restorer (DVR) control scheme is implemented which controls the grid side converter during single-phase to ground fault. The analysis includes the grid current THD along with the corresponding variation of the active and reactive power during the fault condition. The MPPT tracks the actual variable DC link voltage while deriving the maximum power from the solar PV array, and maintains the DC link voltage constant by changing the modulation index of the VSC. Simulation results using Matlab/Simulink are presented to demonstrate the feasibility and validations of the proposed novel MPPT and DVR control systems under different environmental conditions.     

A review of current anti-islanding methods for photovoltaic power system

Islanding phenomenon is undesirable because it leads to a safety hazard to utility service personnel and may cause damage to power generation and power supply facilities as a result of unsynchronized re-closure. Until now, various anti-islanding methods (AIMs) for detecting and preventing islanding of photovoltaic and other distributed generations (DGs) have been proposed. This paper presents an overview of recent anti-islanding method developments for grid-connected photovoltaic (PV) power generation, focusing on the concept and operating principle, mainly based on single phase system. For the performance comparison, the experimental results of the various AIMs with 3 kW PV inverter are provided based on the islanding detection capability and power quality. As a result, the active AIMs have better islanding detection capability rather than the passive one. However, the active AIMs have power quality degradation on harmonic distortion or displacement power factor based on the injected active signal type. In addition to the evaluation and comparison of the main anti-islanding methods, this paper also summarizes the related anti-islanding standards to evaluate anti-islanding capability for PV system. This paper can be used as a useful anti-islanding reference for future work in DG like PV, and wind turbine.