光伏并网逆变器入网检测平台实现方案研究

随着光伏发电在传统配电网中的大规模接入,对配电网的电压调节、潮流控制、继电保护和综合自动化等带来新的挑战,同时,光伏发电系统通过并网逆变器连接到电网,由此带来的电能质量问题也会给用户的设备安全带来隐患。文章结合光伏并网逆变器主要检测内容及相关标准,构建了光伏并网逆变器入网检测平台,利用该平台可开展光伏逆变器入网检测,实现包括电能质量、保护功能、逆变效率、低电压穿越和高电压穿越等功能的测试。     

太阳能光伏发电系统的系统分类

正太阳能光伏发电系统分为独立光伏发电系统、并网光伏发电系统及分布式光伏发电系统。a)独立光伏发电系统也叫离网光伏发电系统。主要由太阳能电池组件、控制器、蓄电池组成,若要为交流负载供电,还需要配置交流逆变器;b)并网光伏发电系统就是太阳能组件产生的直流电经过并网逆变器转换成符合市电电网要求的交流电之后直接接入公共电网。并网光伏发电系统有集中式大型并网光伏电站,一般都是国家级电站,主要特点是     

基于无差拍控制的光伏并网逆变器直流分量抑制研究

直流分量抑制是非隔离型光伏并网逆变系统的关键技术之一,国际并网认证标准中普遍要求光伏并网逆变器注入电网的直流分量不可超过额定电流的0.5%。文章在分析无差拍并网控制策略的基础上,通过对电压指令校正及电流指令校正两种控制方法的直流分量抑制效果进行对比,采用一种简单有效的直流分量检测及零点校正方法进行直流分量抑制。对3 kW单相非隔离型光伏并网逆变器进行相关试验,结果证明了控制算法的有效性。     

单级式并网光伏逆变器

按照功能对光伏并网发电系统进行了分类。叙述了单级式并网光伏逆变器的构成和实现;对单级式并网光伏逆变器进行了理论分析。试验表明:单级光伏并网逆变系统结构简单,实现容易,适于大规模推广。     

一种低漏电流五开关非隔离单相光伏并网逆变器

针对非隔离光伏发电系统漏电流问题,提出一种低漏电流五开关非隔离单相光伏并网逆变器。其中1个开关管高频通断得到直流脉冲,其余4个开关管分作两组,它们以电网频率交替导通来改变电流方向,实现逆变并网,该电路拓扑经高性能二极管续流。通过分析漏电流,该光伏逆变器续流阶段电网侧与直流侧隔离,使得寄生电容两端不含高频分量,将漏电流限制到±20 mA以内。仿真和实验结果表明该拓扑能有效抑制单相光伏并网逆变器的漏电流。     

太阳能逆变器

<正>太阳能逆变器是将直流电转换成交流电的设备。逆变器按运行方式可分为独立运行逆变器和并网逆变器。a)独立运行逆变器用于独立运行的太阳能电池发电系统,为独立负载供电;b)并网逆变器用于并网运行的太阳能电池发电系统。逆变器按输出波型可分为方波逆变器和正弦波逆     

多支路型光伏并网逆变器

阐述了多支路型光伏并网逆变器的基本原理和研制的关键技术.通过对光伏并网逆变器最大功率点跟踪、并网控制技术和孤岛效应等问题的分析,提出了相应的解决方案:采取最大功率跟踪方法,系统能在光强变化时,迅速、准确地跟踪太阳能电池阵列的最大功率点;以多输入支路的独立最大功率跟踪策略,解决了由于太阳能电池阵列参数不一致造成的输出功率降低的问题;在并网逆变技术上采用电流超前跟踪,简单实现了输出功率因数为1,有效地提高了输出电能质量.     

逆变器死区建模及其对大型光伏并网系统的影响

光伏并网系统中逆变器的死区及开关延时等非线性环节将会影响并网系统的稳定性及并网电能质量。为分析逆变器死区对并网系统的影响,该文首先根据逆变器的工作机理,建立包含死区效应的逆变系统开关平均模型;然后在大型光伏并网系统多逆变器并联结构的基础上推导出并网系统的等效模型,并据此探讨死区及光伏电站容量变化对并网电能质量和系统稳定性的影响。研究发现,死区效应对光伏系统相位裕度的影响随光伏系统容量的增加而降低,但光伏系统容量变化可能使系统在死区引入的谐波频率处发生不完全谐振,从而降低系统的并网电能质量。最后仿真和实验验证了理论模型的正确性。     

基于阻抗分析的LCL型并网逆变器相角补偿控制

弱电网条件下,电网阻抗的存在会增加并网电流的谐波含量,甚至造成光伏并网逆变器不稳定。该文以三相LCL型逆变器为研究对象,以阻抗模为出发点,使用阻抗稳定判据分析弱电网在常规电流控制方式下的系统稳定性降低机理,提出在电容电流前馈支路上附加超前校正网络的相角补偿控制策略,通过提高系统输出阻抗的相角提高并网逆变器稳定性。仿真结果表明,该方法可有效解决较高电网阻抗带来的失稳现象,并具有良好的稳态性能和动态响应能力。     

宽范围电网下并网逆变器延时小信号建模及不连续稳定区间分析

该文以光伏并网逆变器为例,借助pade近似方法,建立考虑控制延时环节的光伏并网逆变器状态空间小信号模型,利用特征值分析方法研究宽范围电网强度下考虑控制延时的光伏并网逆变器稳定性问题.算例仿真分析结果表明:在考虑控制延时的光伏并网逆变器系统中,当电网强度在较宽范围内变化时,系统存在不连续稳定区间;考虑控制延时的系统小信号...     

光伏发电并网逆变器建模及电能质量评估

鉴于光伏发电并网逆变器的建模对于光伏大规模接入、保障系统稳定运行具有重要意义,提出了系统仿真方案,利用Hammerstein-Wiener(HW)非线性模型对光伏并网逆变器的运行进行仿真。通过试验获得直流逆变器电压电流波形、交流逆变器电压电流波形、电压公共耦合点、电网和负荷电流;利用编程确定各种模拟波形并搜索与实际波形相比最准确的模型,同时将该方法运用到电能质量分析中,进而完成对系统的分析和建模。模拟结果表明,该模型效果较好,可以为系统规划、防止系统故障和改善电能质量等方面提供理论依据。     

Optimal energy control of a PV-fuel cell hybrid system

This paper deals with a real time implementation of a fuzzy logic-based power management of a small scale generation hybrid power system. The system consists of a photovoltaic array and a fuel cell stack, supported by a single-phase grid that supplies a stand-alone AC load. The proposed supervisory algorithm guaranties the system to switch smart between two operation modes, according to the load demand, the gas level and the PV availability. Obviously, the PV side DC–DC converter is controlled to track permanently the maximum power point by using a fuzzy logic MPPT method; whereas, the fuel cell stack and the grid converters are tuned to cover the remaining power, or alternatively, injecting the exceeding power to the utility. Besides, to feed the AC load with a pure sine wave, a Back stepping algorithm is proposed to control the front-end single-phase inverter. To test the effectiveness of the proposed algorithms, experimental results obtained with a given load profile are presented and commented.     

Advanced concept for dispersed power supply system using AC modules

A method of for estimating the reliability of new conceptual stand-alone dispersed power supply systems using AC modules with self-contained logic was proposed and system reliability estimated using a yearly scale simulation. The AC module is able to supply AC power on each module and has the flexibility to enable construction of a grid-connected system. Power storage devices were required when applying AC modules to the stand-alone power supply system. For these power storage devices, we used a battery with a built-in DC/AC micro bi-directional inverter known as AC battery. To maintain the flexibility of the system extension, the AC modules and AC batteries were controlled by self-contained logic. This logic performs parallel operations for the voltage control inverter and keeps supply and demand in balance.     

Constraints on the effective utilization of wind power in China: An illustration from the northeast China grid

Even though China's wind power industry has experienced a rapid growth since the beginning of this century, the utilization of wind power is still worrisome. In 2010, about 30% of China's total installed capacity could not get access to the grid. And about 10% of China's total wind power generation was curtailed. The problem of wind power curtailment is more prominent in Northeast-China region. The main particularity of Northeast China Grid is as follows: during the long heating period in winter, combined heat and power thermal plants need to modify the turbine generator's output to meet the heating demand and thus the thermal power peak regulation capacity is reduced, as a result the barriers of wind power consumption are increased. This paper provides a new perspective of the constraints on the effective utilization of wind power in the Northeast China Grid. We argue that there are two categories of constrained factors: structural factor and operational factor. The former includes grid structure, wind source structure, power source structure, and market structure. The latter includes power price mechanism, dispatch mode arrangement, wind power integration codes, and wind power forecast. At last, we make policy recommendations: promote the coordination between wind farm investment and grid construction, strengthen interprovincial power trade mechanism, implement flexible pricing mechanisms as well as improve current dispatch mode, etc.     

Optimum operation strategy and economic analysis of a photovoltaic-diesel-battery-mains hybrid uninterruptible power supply

This paper presents the optimum operation strategy and economic analysis of a photovoltaic-diesel-battery-mains hybrid uninterruptible power supply (UPS). The system involves a photovoltaic, battery and bi-directional inverter that is connected in parallel to the grid. A diesel generator is required when the grid is not available for a longer time. The optimum operation strategy of the system is proposed for the diesel-connected mode (when the grid fails for several hours), while the economic analysis is evaluated for the grid-connected mode. The optimum strategy determines the ‘set point’ value for starting and stopping the diesel generator, resulting in a lower system operation cost within its lifetime. The optimum value is obtained by comparing the cost of the diesel fuel consumption and the battery wear. The economic analysis includes the system operation as UPS and demand side management. The system will reduce the power flow from the mains by increasing the power from the inverter to the load when the tariff is high. However, when the grid tariff is low, the power from the mains is used to charge the battery and to meet the load simultaneously.     

Energy storage for enhancing transmission capacities and trans-regional reserves of a UHV AC/DC power grid

探索应用储能为弱受端电网提供故障后大功率支撑以提升特高压交直流输电线稳态输送能力,同时兼作送端电网调峰的跨区备用源以增加新能源发电空间,以有效促进新能源跨区外送降低弃风弃光率。基于特高压交直流馈入受端电网的功率缺额与频率变化间的对应关系,提出在电网频率最低点满足要求的前提下,电网受电能力提升程度与储能容量配置间的数学模型;依据送端电网典型日各时段负荷特性建立可释放的新能源发电空间与所需储能备用调峰容量间的数学模型。结合考虑事故功率支撑与跨区调峰备用的容量需求特性及优先级别,探索两种功能联合应用下的容量需求方案和技术经济可行性。以交直流馈入的弱受端河南电网及新能源富集的送端新疆电网为例,验证了该新能源消外送纳能力提升方案的有效性。     

Turbine, generator, system modeling and impact ofvariable-frequency ripple currents on torsional stressing of generatorsin Poland and Sweden: Lithuania/Poland and Sweden/Poland HVDC links

This paper analyzes rectifier ripple current superimposed on the direct current of a 600 MW asynchronous bipolar link between Lithuania and Poland and a 600 MW asynchronous monopolar link between Poland and Sweden in evaluating possible torsional vibrations in steam turbine-generator-exciter shafts. The studies are performed for machines in Northeastern Poland and in Southern Sweden close to the inverter station which are most at risk. Analyses are performed for the generators in Poland for the Lithuania/Poland link and for the generators in Sweden for the Poland/Sweden link. The paper examines system scaling factors for the Lithuania/Poland Link. It then examines AC system scaling factors and generator scaling factors for modulation product harmonic currents impressed on generators connected to the Swedish Grid Network by the inverter. Amplitude of shaft torsional torque due to resonant excitation imposed by the link on the generators in Sweden is evaluated for different scenarios of system and generator load. First, theory which relates magnitude of harmonic AC current injected into the AC system by the inverter is summarized. Dispersion of the injected harmonic AC current to proportion the current to individual generators is then reviewed, considering impedance of the generators, loads, and other system elements. Significance of simple and detailed shaft train models of machine shafts as well as approximate (Id, Iq) and detailed (2d, 3q) generator damper models on resonant torques is reviewed. Then, effects of both power factor and generator load on generator scaling factors is illustrated     

用于海上风电场直流输电的新型变换器

针对永磁直驱风力发电机变流技术的特点,并根据柔性直流输电系统的电压和功率控制要求,提出了一种新型的直流变换器。该变流器采用三电平拓扑结构、内环电流峰值控制,以及适用于三电平Boost变换器电流峰值控制的双梯形波补偿控制方法,经Matlab／Simulink仿真,研究结果证明该变流器具有功率开关电压应力小、电抗器电流脉动小,以及运行可靠、动态响应性能好等优点,适用于海上风电柔性直流输电等大功率、高电压场合。     

Digital power factor control and reactive power regulation for grid-connected photovoltaic inverter

The overall efficiency of photovoltaic (PV) systems connected to the grid depends on the efficiency of direct current (DC) of the solar modules to alternate current (AC) inverter conversion. The requirements for inverter connection include: maximum power point, high efficiency, control power injected into the grid, high power factor and low total harmonic distortion of the currents injected into the grid. An approach to power factor control and reactive power regulation for PV systems connected to the grid using field programmable gate array (FPGA) is proposed. According to the grid demands; both the injected active and reactive powers are controlled.In this paper, a new digital control strategy for a single-phase inverter is carried out. This control strategy is based on the phase shift between the inverter output voltage and the grid voltage, and the digital sinusoidal pulse width modulation (DSPWM) patterns, in order to control the power factor for a wide range of the inverter output current and consequently the control and the regulation of the reactive power will be achieved. The advantage of the proposed control strategy is its implementation around simple digital circuits.In this work, a simulation study of this strategy has been realized using Matlab/Simulink and PSIM. In order to validate its performance, this control has been implemented in a FPGA. Experimental tests have been carried out demonstrating the viability of this control in order to control the power factor and the injected power into the grid.