A fuzzy based method for leveling output power fluctuations of photovoltaic-diesel hybrid power system

A Photovoltaic system’s output power fluctuates as insolation varies with weather condition. Fluctuating PV power causes frequency deviations when large PV power is penetrated in the isolated utility. In this paper, a fuzzy based method for leveling the fluctuations of PV power in a PV-diesel hybrid power system is proposed. By means of the proposed method, output power control of PV system becomes possible considering power utility conditions and the conflicting objective of output power leveling and maximizing energy capture is achieved. Here, fuzzy control is used to generate the output leveling power command. The fuzzy control has three inputs of average insolation, variance of insolation, and absolute average of frequency deviation. First, the proposed method is compared with the method where captured maximum power is given to the utility without leveling. Second, the proposed method is compared with a conventional method where captured maximum power is leveled by using an energy storage system and is given to the isolated utility. Simulation results show that the proposed method is effective in leveling PV power fluctuations and is feasible to reduce the frequency deviations of the isolated power utility.     

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.     

基于KF-MPC的光储系统双调节反馈优化控制方法

利用储能技术能够有效平抑光伏功率波动,提高光伏输出功率的稳定性。该文提出一种基于卡尔曼滤波-模型预测控制(KF-MPC)的光储系统双调节反馈优化控制方法,即将卡尔曼滤波和模型预测控制相结合,采用双调节反馈控制实现光储系统的优化控制。在卡尔曼滤波器中引入滤波调节因子,通过自适应调节卡尔曼滤波增益使储能系统在不同工况下有效平抑光伏功率波动。在模型预测控制器中以储能出力最小、荷电状态最优以及光伏波动率最低为目标,通过模型预测控制滚动优化得到储能系统最优出力和最佳荷电状态。通过对某光储电站实际运行数据分析可知,该文所提出的控制策略在平抑光伏功率波动的同时还可有效延长储能系统使用寿命,具有工程应用前景。     

A Coordinated Control Method for Leveling PV Output Power Fluctuations of PV–Diesel Hybrid Systems Connected to Isolated Power Utility

A Photovoltaic (PV) system's power output is not constant and fluctuates depending on weather conditions. Fluctuating power causes frequency deviations and reduction in reliability of the isolated power utility or microgrid when large output power from several PV systems is penetrated in the utility. In this paper, to overcome these problems, a simple coordinated control method for leveling the fluctuations of combined power output from multiple PV systems is proposed. The conflicting objective of output power leveling and acquisition power increase is achieved by means of the proposed method. Here, output power command is generated in two steps: central and local. Fuzzy reasoning is used to generate the central leveling output power command considering insolation, variance of insolation, and absolute average of frequency deviation. In local step, a simple coordination is maintained between central power command and local power commands by producing a common tuning factor. Power converters are used to achieve the same output power as local command power employing PI control law for each of the PV generation systems. The proposed method is compared with the method where a modified maximum power point tracking control is used for smoothing the short-term change in each of the PV system's output. Simulation results show that the proposed method is effective for leveling output power fluctuations and feasible to reduce the frequency deviations of the isolated power utility to maintain reliability.      

考虑风电接入的电压控制区域修正方法研究

传统的电压控制区域（VCA）划分会随风电出力的波动而发生变化,为了获得能够适应各种风电出力的稳定分区,提出一种考虑风电接入下电压控制区域的修正方法。首先,为了研究风电出力的波动性对分区的影响,将风电出力概率分布离散化为多个场景,研究每个出力场景下的潮流、分区。其次,利用雅可比子矩阵建立含有功因素的灵敏度矩阵与电气距离矩阵,采用凝聚的层次聚类法对风电出力不同断面条件下的PQ节点分区。通过Q-V曲线的极小值将与PQ节点无功限值一致的发电机组也归为一组,再利用灵敏度法将剩余的PV节点逐次划分获得全网分区。最后,通过识别VCA边界,利用断线分析法将电压波动不一致的边界节点重新划分,从而提升区域之间的电压解耦程度,实现区域的拓扑优化。将IEEE39节点系统处理为多个风电出力场景,并对每个场景的出力断面进行仿真分析。结果表明,所提方法能合理体现由于风电出力波动导致的分区变化,并可修正不同出力场景下的分区变化,可为系统各区域的电压稳定控制提供条件。     

Advanced grid connected PV system with functions to suppress disturbance by PV output variation and customer load change

The PV array has unstable output patterns dependent on weather conditions. Therefore, assuming high-density grid connection in the future, these unstable output patterns can be one of the main reasons to cause power disturbances such as the voltage variation, the frequency variation and the harmonic voltage generation into utility. And also it should be considered that a sudden customer load change is one of those reasons. Therefore, this study suggested a PV system with suppression functions against such disturbances in the side of amicable relationship with utility and verified the validity of the proposed system by EMTP and ACSL-based analysis.     

Intelligent hybrid power generation system using new hybrid fuzzy-neural for photovoltaic system and RBFNSM for wind turbine in the grid connected mode

Photovoltaic (PV) generation is growing increasingly fast as a renewable energy source. Nevertheless, the drawback of the PV system is intermittent because of depending on weather conditions. Therefore, the wind power can be considered to assist for a stable and reliable output from the PV generation system for loads and improve the dynamic performance of the whole generation system in the grid connected mode. In this paper, a novel topology of an intelligent hybrid generation system with PV and wind turbine is presented. In order to capture the maximum power, a hybrid fuzzy-neural maximum power point tracking (MPPT) method is applied in the PV system. The average tracking efficiency of the hybrid fuzzy-neural is incremented by approximately two percentage points in comparison with the conventional methods. The pitch angle of the wind turbine is controlled by radial basis function network-sliding mode (RBFNSM). Different conditions are represented in simulation results that compare the real power values with those of the presented methods. The obtained results verify the effectiveness and superiority of the proposed method which has the advantages of robustness, fast response and good performance. Detailed mathematical model and a control approach of a three-phase grid-connected intelligent hybrid system have been proposed using Matlab/Simulink.     

Polar coordinated fuzzy controller based real-time maximum-power point control of photovoltaic system

It is crucial to improve the photovoltaic (PV) system efficiency and to develop the reliability of PV generation control systems. There are two ways to increase the efficiency of PV power generation system. The first is to develop materials offering high conversion efficiency at low cost. The second is to operate PV systems optimally. However, the PV system can be optimally operated only at a specific output voltage and its output power fluctuates under intermittent weather conditions. Moreover, it is very difficult to test the performance of a maximum-power point tracking (MPPT) controller under the same weather condition during the development process and also the field testing is costly and time consuming. This paper presents a novel real-time simulation technique of PV generation system by using dSPACE real-time interface system. The proposed system includes Artificial Neural Network (ANN) and fuzzy logic controller scheme using polar information. This type of fuzzy logic rules is implemented for the first time to operate the PV module at optimum operating point. ANN is utilized to determine the optimum operating voltage for monocrystalline silicon, thin-film cadmium telluride and triple junction amorphous silicon solar cells. The verification of availability and stability of the proposed system through the real-time simulator shows that the proposed system can respond accurately for different scenarios and different solar cell technologies.     

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.     

Assessment of massive integration of photovoltaic system considering rechargeable battery in Japan with high time-resolution optimal power generation mix model

Maximizing renewables in the country's power system has been a key political agenda in Japan after the Fukushima nuclear disaster. This paper investigates the potential of PV resource, which could be systematically integrated into the Japanese power system, using a high time-resolution optimal power generation mix model. The model allows us to explicitly consider actual PV and wind output variability in 10-min time resolution for 365 days. Simulation results show that, as PV expands, the growth of PV integration into the grid slows down when the installed PV capacity is more than the scale of the peak demand, although Japan has immense potential of installable PV capacity – equivalent to 40 times of the peak. Secondly, the results imply that a large-scale PV integration potentially decreases the usage ratio of LNG combined cycle (LNGCC) in specific seasons, which is a challenge for utility companies to ensure that LNGCC is used as a profitable compensating generator for PV variability. Finally, a sensitivity analysis on rechargeable battery cost suggests that the reason for suppressing the PV output instead of storing its surplus output by the battery can be attributed to the high battery cost; hence, the improvement of its economic performance is significant to integrate the massive PV energy.     

光伏空气源热泵的研究与开发

基于中国北方地区冬季采暖"煤改电"工程中使用的空气源热泵机组,提出与光伏发电相结合的系统方案.在不改变原有系统结构和控制方式的前提下,白天采用光伏优先、市电保障的双电源供电模式,研究将光伏电能高效注入系统的控制策略,优化光伏阵列容量配置,开发控制器样机.实验结果表明,系统运行稳定,在华北地区光伏阵列的最优容量配置约为系...     

基于BPA软件的地区电网静态电压稳定性分析

电力系统静态电压稳定分析对电力部门的电压稳定控制、调度规划等工作十分重要。基于静态模型提出了求取实际运行电网的功率-电压(P-V)曲线的方法,该方法采用电力系统潮流软件(BPA)作为计算核心,通过设计外部接口实现连续潮流仿真,进行电力系统静态电压稳定裕度分析及绘制P-V曲线。利用该方法对上海电网黄渡分区进行静态电压稳定分析,计算系统的相对电压稳定裕度,找出其存在的电压薄弱点,并提出了进一步提高静态电压稳定水平的若干措施。     

Adaptive sun tracking algorithm for incident energy maximization and efficiency improvement of PV panels

In recent times, sun tracking systems are being increasingly employed to enhance the efficiency of photovoltaic panels by constantly tracking the elevation and azimuth angles of the sun. In this paper, a novel adaptive digital signal processing and control algorithm is presented that optimizes the overall PV system output power by adjusting the position angles of the solar panel on both the elevation and azimuth axes. Since the proposed approach is adaptive in nature, the optimal position angles for the solar panel are iteratively computed using the adaptive gradient ascent method, until the incident solar radiation, and hence the output power is maximized. Furthermore, a Taylor’s series approximation is employed for generating a unique optimal position angle increment/decrement at each iteration. Simulation results show that the proposed technique demonstrates fast convergence and excellent tracking accuracy at all times of the day.     

分布式光伏发电系统改进虚拟同步发电机控制

提出一种计及分布式光伏发电系统源端输出功率波动特征的改进虚拟同步发电机(IVSG)控制策略。对单台虚拟同步发电机功率平衡方程特征值进行分析,明确了光伏电源的基本运行特性,确定了光伏电源稳定运行区域。在传统虚拟同步发电机(VSG)的基础之上进一步采用了直流电压稳定控制技术,提出改进的虚拟同步发电机控制策略。当光伏电源输出功率低于负载需求时起到抑制直流母线电压跌落、维持直流电压稳定的作用,实现按照负荷或并网功率需求进行功率匹配的目的。仿真与实验结果验证了所提控制策略的可行性与有效性。     

Grid-connected photovoltaic power systems: Technical and potential problems—A review

Traditional electric power systems are designed in large part to utilize large baseload power plants, with limited ability to rapidly ramp output or reduce output below a certain level. The increase in demand variability created by intermittent sources such as photovoltaic (PV) presents new challenges to increase system flexibility. This paper aims to investigate and emphasize the importance of the grid-connected PV system regarding the intermittent nature of renewable generation, and the characterization of PV generation with regard to grid code compliance. The investigation was conducted to critically review the literature on expected potential problems associated with high penetration levels and islanding prevention methods of grid tied PV. According to the survey, PV grid connection inverters have fairly good performance. They have high conversion efficiency and power factor exceeding 90% for wide operating range, while maintaining current harmonics THD less than 5%. Numerous large-scale projects are currently being commissioned, with more planned for the near future. Prices of both PV and balance of system components (BOS) are decreasing which will lead to further increase in use. The technical requirements from the utility power system side need to be satisfied to ensure the safety of the PV installer and the reliability of the utility grid. Identifying the technical requirements for grid interconnection and solving the interconnect problems such as islanding detection, harmonic distortion requirements and electromagnetic interference are therefore very important issues for widespread application of PV systems. The control circuit also provides sufficient control and protection functions like maximum power tracking, inverter current control and power factor control. Reliability, life span and maintenance needs should be certified through the long-term operation of PV system. Further reduction of cost, size and weight is required for more utilization of PV systems. Using PV inverters with a variable power factor at high penetration levels may increase the number of balanced conditions and subsequently increase the probability of islanding. It is strongly recommended that PV inverters should be operated at unity power factor.     

High-accuracy maximum power point estimation for photovoltaic arrays

Quantitative information regarding the maximum power point (MPP) of photovoltaic (PV) arrays is crucial for determining and controlling their operation, yet it is difficult to obtain such information through direct measurements. PV arrays exhibit an extremely nonlinear current-voltage (I-V) characteristic that varies with many complex factors related to the individual cells, which makes it difficult to ensure an optimal use of the available solar energy and to achieve maximum power output in real time. Finding ways to obtain the maximum power output in real time under all possible system conditions are indispensable to the development of feasible PV generation systems. The conventional methods for tracking the MPP of PV arrays suffer from a serious problem that the MPP cannot be quickly acquired. Based on the p-n junction semiconductor theory, we develop a prediction method for directly estimating the MPP for power tracking in PV arrays. The proposed method is a new and simple approach with a low calculation burden that takes the resistance effect of the solar cells into consideration. The MPP of PV arrays can be directly determined from an irradiated I-V characteristic curve. The performance of the proposed method is evaluated by examining the characteristics of the MPP of PV arrays depending on both the temperature and irradiation intensity, and the results are discussed in detail. Such performance is also tested using the field data. The experimental results demonstrate that the proposed method helps in the optimization of the MPP control model in PV arrays.     

基于电压预估法的光伏发电系统MPPT算法

光伏发电系统处于复杂光照条件下时,光伏电池阵列的输出特性呈多峰现象,致使传统的MPPT算法追踪结果可能停留在次优点。针对此问题,提出一种基于电压预估法的光伏发电系统MPPT算法,采用DMPPT电路结构的光伏阵列,通过研究其输出特性,得到复杂光照条件下光伏阵列最大功率点对应的工作电压最佳区域,并以该预估到的电压值为基础,设计了一种新型的MPPT控制算法。仿真结果表明,所提算法能有效避免光伏系统工作在次优点,提高了光伏发电的出力。     

一种基于超级电容器的光伏系统电压控制方法研究

根据超级电容器储能特点,建立了用于独立光伏发电的超级电容器储能系统模型,设计了超级电容器电压控制环节,提出了一种带有超级电容器电压模糊反馈的双环控制策略,通过对开环系统bode图的分析,论证了控制系统的稳定性和动态性能。仿真结果表明,在光伏发电系统受到光照及负载扰动的情况下,超级电容器储能系统可以有效地稳定光伏系统的输出电压,提高系统供电的可靠性和电能质量,并且抑制了超级电容器端电压大范围波动对该系统的影响,提高了超级电容器的利用率。     

局部阴影条件下基于改进电导增量法的光伏系统最大功率跟踪方法

在局部阴影的情况下,由于串联式光伏组件的输出特性不同而产生多个极值点,使得传统的最大功率追踪（maximum power point tracking, MPPT）方法陷入局部极值点而失效。文中提出一种针对两级并网光伏系统的改进电导增量法以适应光伏阵列在局部阴影下的多峰值最大功率跟踪,通过分析最大功率点电压的变化范围,设定最大功率电压搜索范围以提高搜索效率,并通过DC/DC Boost变换器占空比实现输入电压控制,保证算法不陷入局部极值点。最后利用仿真实验验证了该算法在有、无阴影情况下均能准确地跟踪光伏方阵最大功率,有效提高了光伏阵列输出效率。