基于无功电流注入的光伏逆变器低电压穿越策略

大量的光伏电站接入电网,为了提高电力系统的稳定性,需考虑光伏发电的低电压穿越能力。文章基于无功电流电压支撑方案,提出使用电流单环控制的低电压穿越策略,当电网电压因故障而降低时,逆变器由电压电流双环控制切换到电流单环控制,升压电路由最大功率控制(MPPT)切换到稳压控制。经仿真表明,所提出的电流单环控制策略能在电网发生故障时,有效的完成电压的稳定过渡,实现低电压穿越,具有实用价值。     

集散式光伏逆变系统低电压穿越控制策略

针对集散式光伏逆变系统低电压穿越时稳定性差的问题,提出了一种低电压穿越控制策略。该策略以智能控制器和逆变器相互耦合的直流母线电压为参考量,对智能控制器和逆变器进行协调控制,实现低电压穿越时的功率平衡。并通过负序电流指令补偿,抑制电网电压不平衡时直流母线电压2次纹波。1 MW集散式光伏逆变系统LVRT试验结果表明,该方法具有良好的动态响应和稳态性能,低电压穿越时,直流母线电压控制稳定;低电压穿越恢复时,有功功率恢复平稳快速。研究成果有重要的工程应用价值。     

一种快速跟踪功率参考值的光伏并网低电压穿越控制策略

为了解决传统光伏并网低电压穿越控制策略动态响应慢导致直流母线电压失稳的问题,提出了一种基于图形法和模型预测控制的快速跟踪功率参考值的低电压穿越策略。该策略首先根据网侧电压跌落程度,算出交直流侧的参考功率,然后直接控制光伏阵列和逆变器输出相应参考功率,达到交直流侧的快速平衡。仿真结果表明,当功率参考值发生改变时,传统控制策略直流侧响应时间为200 ms,交流侧有功响应时间为16.5 ms,无功响应时间为17 ms,而本文所提策略响应时间为5.000、0.140、0.135 ms,验证了所提控制策略的快速性。     

光伏并网逆变器无差拍控制系统的研究

在分析无差拍电流控制方法工作原理的基础上,给出了基于无差拍控制的并网逆变器的脉宽调制(PwM)算法和占空比的推导过程,将该控制策略应用于两级式单相光伏并网发电系统逆变器的控制中,使光伏并网系统具有快速利用太阳能电池组件的能源、改善电能质量的功能,增强了先伏并网系统的实用性.在此基础上研制出一台实验样机.实验结果表明,采用该控制方案的逆变器具有良好稳态特性和动态性能,计算简单,易于实现.     

漂浮式光伏发电系统的发电性能研究

漂浮式光伏发电技术是未来光伏发电的应用方向之一。在同一地点建立了1座6.3 kW漂浮式光伏发电系统及1座6.3 kW陆上光伏发电系统,分别对其发电性能进行数据采集与分析。试验表明,漂浮式光伏发电系统的总发电量比陆上光伏发电系统高2%,总体发电效率更高,漂浮式光伏发电系统降低温度损耗对系统发电功率的影响较明显。     

低压配网中光伏发电系统调压策略

分布式光伏发电系统接入配电网后引起的电压越限,一方面会影响配电网的安全和可靠运行,另一方面会限制其并网能力。文章从电压降落角度研究了光伏发电系统输出有功功率、无功功率与光伏并网点电压的关系,提出了一种光伏发电系统电压调整策略。正常情况下,该策略根据本地电压信息调节并网点电压;在紧急情况下,通过简单通信使同一馈线上的光伏发电系统共同进行电压调节。仿真结果表明,文章所提电压调整策略可以有效减小并网点电压偏差,提高并网点电压合格率。     

光伏发电系统的并网模糊PID控制

在三相两级式并网逆变器数学模型的基础上,将模糊PID控制策略引入光伏发电系统的并网控制中。通过数字仿真和物理仿真表明模糊控制与PID控制相结合的模糊PID控制,改善了光伏系统并网控制的动态过程,能够实现光伏系统的平滑并网。     

基于FMPC的储能系统跟踪光伏发电计划控制策略

为了最大限度地提高跟踪光伏发电计划的能力,文章提出一种适用于储能系统的模糊模型预测控制(FMPC)充放电控制策略。基于模型预测控制(MPC)方法,建立了以储能系统剩余容量偏离理想值、并网功率与发电计划偏差最小为目标的控制模型,通过引入模糊控制(Fuzzy Control),即时调节目标函数中的权重系数以获得最佳跟踪效果。以光伏电站实际运行数据进行仿真分析,结果表明,与传统MPC和普通控制策略相比,所提出的基于FMPC的储能系统控制方法具有独特的灵活性和适应性。     

余热发电两级能量转换系统的研究

为提高余热发电的经济性,提出余热热水发电的两级能量转换系统,并建立了该系统的两级闪蒸和两级双工质循环的热力计算的数学模型;对电站的功率和效率进行了计算,以此对单级及两级能量转换系统进行了比较。结果表明:在计算所给的热水温度(100～200℃)和冷凝温度下,两级闪蒸比单级闪蒸的发电量多24.8%～31.2%;两级双工质循环比单级双工质循环的发电量多14.5%～24.0%;两级闪蒸比两级双工质循环的发电量多7.2%～67.5%。     

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.     

基于物联网的光伏电站SCADA系统

在光伏电站中,应用监控系统来保障其安全、稳定运行是必须的手段。文章针对大型光伏电站监控系统中存在的诸多问题提出了一种解决方案——开发基于物联网的光伏电站数据采集与监视控制(SCADA)系统。该系统可实现光伏电站的无人值守,并结合物联网先进技术实现数据的无线传输、网络接入等功能,为光伏电站运营商提供了一个集中监控多个跨地域光伏电站群的良好平台。     

Long-term field test of solar PV power generation using one-axis 3-position sun tracker

The 1 axis-3 position (1A-3P) sun tracking PV was built and tested to measure the daily and long-term power generation of the solar PV system. A comparative test using a fixed PV and a 1A-3P tracking PV was carried out with two identical stand-alone solar-powered LED lighting systems. The field test in the particular days shows that the 1A-3P tracking PV can generate 35.8% more electricity than the fixed PV in a partly-cloudy weather with daily-total solar irradiation H_T = 11.7 MJ/m² day, or 35.6% in clear weather with H_T = 18.5 MJ/m² day. This indicates that the present 1A-3P tracking PV can perform very close to a dual-axis continuous tracking PV (Kacira et al., 2004). The long-term outdoor test results have shown that the increase of daily power generation of 1A-3P tracking PV increases with increasing daily-total solar irradiation. The increase of monthly-total power generation for 1A-3P sun tracking PV is between 18.5-28.0%. The total power generation increase in the test period from March 1, 2010 to March 31, 2011, is 23.6% in Taipei (an area of low solar energy resource). The long-term performance of the present 1X-3P tracking PV is shown very close to the 1-axis continuous tracking PV in Taiwan (Chang, 2009). If the 1A-3P tracking PV is used in the area of high solar energy resource with yearly-average H_T > 17 MJ/m² day, the increase of total long-term power generation with respect to fixed PV will be higher than 37.5%. This is very close to that of dual-axis continuous tracking PV.The 1A-3P tracker can be easily mounted on the wall of a building. The cost of the whole tracker is about the same as the regular mounting cost of a conventional rooftop PV system. This means that there is no extra cost for 1A-3P PV mounted on buildings. The 1A-3P PV is quite suitable for building-integrated applications.     

A maximum power point tracking control strategy with variable weather parameters for photovoltaic systems with DC bus

In photovoltaic (PV) system, the most commonly used DC/DC converter is the basic buck or boost circuit to implement the maximum point power tracking (MPPT) due to their simple structure and low cost while there are some MPPT constraint conditions. By contrast, the conventional buck/boost DC/DC converter without MPPT constraint condition is seldom used because of its high cost or poor performance. To keep the advantages of these three DC/DC converters while overcoming their shortcomings, in this paper, the constraint conditions of capturing the maximum power point (MPP) of PV systems with direct-current (DC) bus are found out. Then, on the basis of this work, a MPPT control strategy with variable weather parameters is proposed. In this strategy, a new buck/boost DC/DC converter is proposed, which not only avoids the MPPT constraint conditions of basic buck or boost DC/DC converter but also overcomes the shortcomings of conventional buck/boost DC/DC converter. Finally, lots of simulated experiments verify the accuracy of MPPT constraint conditions, test the feasibility and availability of proposed MPPT control strategy, analyze the MPPT performance of proposed PV system and compare the output transient-state performance with conventional perturb and observe (P&O) method.     

光伏发电系统的超导储能设计

超导储能(SMES)具有非常快速的功率调节能力和灵活的四象限运行能力,可完成调节电力系统功率因数、补偿电压跌落等功能。文章针对光伏发电系统的特殊运行方式,提出了利用光伏出力与本地负荷需求的差值作为SMES控制器的功率控制信号策略。在PSCAD/EMTDC仿真平台建立了超导储能系统模型,并对其在光伏发电系统的中的运行控制方式进行研究。研究结果表明,超导储能与光伏系统配合可以很好地解决光伏发电功率易受环境影响、不可调节、难于满足负荷需求的问题,对由负荷变化引起的母线电压波动和故障引起的母线电压跌落具有良好的补偿作用。     

A multi-function grid connected PV system with three level NPC inverter and voltage oriented control

In this paper a grid connected photovoltaic (PV) system is presented. The grid integration of the PV system is carried out via a three phase three level neutral point clamped (NPC) inverter. To control the inverter a modified version of voltage oriented control (VOC) method and the space vector pulse width modulation (SVPWM) technique have been applied. With the proposed modification the PV system operates as a shunt active power filter (SAPF), a reactive power compensator, and a load’s current balancer simultaneously. In this way the PV system operates more efficiently compared to the conventional PV systems and offers ancillary services to electric power system. The effectiveness of the proposed control scheme is established through simulation results with Matlab/Simulink in steady state and transient response of the electric power distribution system.     

A power allocation strategy of a hybrid energy storage system for a PV grid-connected system

针对光伏并网系统中光伏微电源出力的波动性和间歇性,将蓄电池和超级电容器构成的混合储能系统HESS（hybrid energy storage system）应用到光伏并网系统中可以实现光伏功率平滑、能量平衡以及提高并网电能质量。在同时考虑蓄电池的功率上限和超级电容的荷电状态（SOC）的情况下,对混合储能系统提出了基于超级电容SOC的功率分配策略;该策略以超级电容的SOC和功率分配单元的输出功率作为参考值,对混合储能系统充放电过程进行设计。超级电容和蓄电池以Bi-direction DC/DC变换器与500 V直流母线连接,其中超级电容通过双闭环控制策略对直流母线电压进行控制。仿真结果表明,所提功率分配策略能对混合储能系统功率合理分配,而且实现了单位功率因数并网,稳定了直流母线电压。     

Development and performance test of smart power conditioner for value-added PV application

It is a disadvantage that PV power generation is only useful for clear daytime. However, a new 24 hours of application in an extended area can be added by active utilization of potential ability of PV power conditioner. For this purpose, a new multi-functional power conditioner was developed, which has a smoothing function to reduce PV output variation and load fluctuation, and also has additional function to compensate harmonics current and reactive power caused by customer's load.As a result of indoor testing, a reduction rate of around for harmonics current and reactive power were achieved. In addition, the reduction rate around for smoothing of PV output variation and load fluctuation were verified.The work was promoted by NEDO as part of the New Sunshine Project in Japan.     

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.