风力发电的MPPT快速响应控制方法

为了提高风力发电的能量转换效率，根据风车的空气动力特性，要用到最大功率点追踪(Maximum Power Point Tracking,MPPT)控制方法。作者开发了一种新的MPPT控制方法，和以往的MPPT控制方法相比，主要不同之处是：(1)追踪步长根据风速的变化而变化，即变扰动MPPT控制方式；(2)为了消除逆变器死区所造成的风车功率波动影响，MPPT控制周期和发电机的转速是同步的；(3)电磁转矩对风车转速实行完全控制，即在适当的时候，给风车提供能量使其加速，使风车转速能跟踪快速变化的风速；(4)在MPPT的输出端使用低通滤波器来平滑风车转速控制的指令值。实验结果表明，本方法可以跟踪0．2Hz快速变化的风速，和传统的MPPT控制方法相比，当风速快速变动时，可以显著增加发电量，从而提高了风力发电的效率。     

Comprehensive review and performance evaluation of maximum power point tracking algorithms for photovoltaic system

A photovoltaic array is environmentally friendly and a source of unlimited energy generation. However, it is presently a costlier energy generation system than other non-renewable energy sources. The main reasons are seasonal variations and continuously changing weather conditions, which affect the amount of solar energy received by the solar panels. In addition, the non-linear characteristics of the voltage and current outputs along with the operating environment temperature and variation in the solar radiation decrease the energy conversion capability of the photovoltaic arrays. To address this problem, the global maxima of the PV arrays can be tracked using a maximum power point tracking algorithm (MPPT) and the operating point of the photovoltaic system can be forced to its optimum value. This technique increases the efficiency of the photovoltaic array and minimizes the cost of the system by reducing the number of solar modules required to obtain the desired power. However, the tracking algorithms are not equally effective in all areas of application. Therefore, selecting the correct MPPT is very critical. This paper presents a detailed review and comparison of the MPPT techniques for photovoltaic systems, with consideration of the following key parameters: photovoltaic array dependence, type of system (analog or digital), need for periodic tuning, convergence speed, complexity of the system, global maxima, implemented capacity, and sensed parameter(s). In addition, based on real meteorological data (irradiance and temperature at a site located in Addis Ababa, Ethiopia), a simulation is performed to evaluate the performance of tracking algorithms suitable for the application being studied. Finally, the study clearly validates the considerable energy saving achieved by using these algorithms.     

Bidirectional energy storage photovoltaic grid-connected inverter application system

A novel topology of the bidirectional energy storage photovoltaic grid-connected inverter was proposed to reduce the negative impact of the photovoltaic grid-connected system on the grid caused by environmental instability. Using the proposed Inverter as a UPS power supply in case of a grid failure, storage electrical energy and regulating the energy delivered to the grid for reducing the pressure on the grid. A new artificial fish-swarm algorithm and variable step voltage perturbation method were presented to track the maximum power point of the solar panels. Analysis was done to reduce the output ripple of the inverter and sinusoidal pulse width modulation (SPWM) was selected to control the inverter. Model simulation was performed using PSpice software to obtain the volt-ampere characteristic curve of the solar panel output. The solar array simulator was used to verify the effect of maximum power point tracking at different light intensities. The study concludes that the maximum power point tracking (MPPT) efficiency of the bidirectional energy storage photovoltaic grid-connected inverter designed was as high as 99.9%. The distortion rate of the grid-connected current waveform was within 2% and the DC current component was less than 0.5%. The output voltage and power were in full compliance with the grid connection standard.     

Solar photovoltaic charging of lithium-ion batteries

Solar photovoltaic (PV) charging of batteries was tested by using high efficiency crystalline and amorphous silicon PV modules to recharge lithium-ion battery modules. This testing was performed as a proof of concept for solar PV charging of batteries for electrically powered vehicles. The iron phosphate type lithium-ion batteries were safely charged to their maximum capacity and the thermal hazards associated with overcharging were avoided by the self-regulating design of the solar charging system. The solar energy to battery charge conversion efficiency reached 14.5%, including a PV system efficiency of nearly 15%, and a battery charging efficiency of approximately 100%. This high system efficiency was achieved by directly charging the battery from the PV system with no intervening electronics, and matching the PV maximum power point voltage to the battery charging voltage at the desired maximum state of charge for the battery. It is envisioned that individual homeowners could charge electric and extended-range electric vehicles from residential, roof-mounted solar arrays, and thus power their daily commuting with clean, renewable solar energy.     

Improvement of proton exchange membrane fuel cell overall efficiency by integrating heat-to-electricity conversion

Proton exchange membrane fuel cells (PEMFCs) have shown to be well suited for distributed power generation due to their excellent performance. However, a PEMFC produces a considerable amount of heat in the process of electrochemical reaction. It is desirable to use thermal energy for electricity generation in addition to heating applications. Based on the operating characteristics of a PEMFC, an advanced thermal energy conversion system using “ocean thermal energy conversion” (OTEC) technology is applied to exploit the thermal energy of the PEMFC for electricity generation. Through this combination of technology, this unique PEMFC power plant not only achieves the combined heat and power efficiency, but also adequately utilizes heat to generate more valuable electricity. Exergy analysis illustrates the improvement of overall efficiency and energy flow distribution in the power plant. Analytical results show that the overall efficiency of the PEMFC is increased by 0.4-2.3% due to the thermal energy conversion (TEC) system. It is also evident that the PEMFC should operate within the optimal load range by balancing the design parameters of the PEMFC and of the TEC system.     

Design and testing of a separate-type lighting system using solar energy and cold-cathode fluorescent lamps

This paper presents a solar-powered lighting system, using cold-cathode fluorescent-lamps (CCFLs), with its battery-charging circuit and lamp-ignition circuit being separated so that its solar panels can be installed at any distance deemed necessary away from the lighting site in order to receive the maximum solar energy available. This system adopts the maximum-power point tracking (MPPT) method to control the power output of the solar panels and uses the zero-voltage switching (ZVS) DC–DC converter, as the charging circuit, to increase the panels’ power generation efficiency and the charging circuit’s conversion efficiency. The electronic ballast circuit for the CCFL is constructed with a half-bridge inverter, a resonant inductor, and a Rosen-type piezoelectric transformer, which forms a piezoelectric resonant-type inverter: to simplify the circuitry and to improve the power conversion efficiency, the ballast circuit is designed to directly step up the battery voltage in igniting the lamp. We also establish the transmission-parameter model for the piezoelectric resonant-type inverter to provide the base for the electric-power circuit design. Our experimental results indicate that the proposed system possesses some advantages, such as greater energy efficiency, circuitry simplicity, and so on, and is suitable for night lighting in house yards, parks and advertising panels.     

Maximum photovoltaic power tracking for the PV array using the fractional-order incremental conductance method

This paper proposes maximum photovoltaic power tracking (MPPT) for the photovoltaic (PV) array using the fractional-order incremental conductance method (FOICM). Since the PV array has low conversion efficiency, and the output power of PV array depends on the operation environments, such as various solar radiation, environment temperature, and weather conditions. Maximum charging power can be increased to a battery using a MPPT algorithm. The energy conversion of the absorbed solar light and cell temperature is directly transferred to the semiconductor, but electricity conduction has anomalous diffusion phenomena in inhomogeneous material. FOICM can provide a dynamic mathematical model to describe non-linear characteristics. The fractional-order incremental change as dynamic variable is used to adjust the PV array voltage toward the maximum power point. For a small-scale PV conversion system, the proposed method is validated by simulation with different operation environments. Compared with traditional methods, experimental results demonstrate the short tracking time and the practicality in MPPT of PV array.     

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.     

A novel flame energy grading conversion system: Preliminary experiment and thermodynamic parametric analysis

The focus of this study is to improve the efficiency of the thermal power cycle from the perspective of photo energy and thermal energy grading conversion. A new concept of combined radiation and heat engine model was proposed to establish a novel flame energy grading conversion system based on photovoltaic conversion and the Rankine cycle. From the perspective of energy utilization, the spectral radiative energy characteristics in oxy-coal combustion were experimentally investigated, and a preliminary thermodynamic model of the new system was established based on the experimental results. Finally, energy and exergy analyses were conducted to determine the general characteristics of the proposed system and assess the improvements to the Rankine cycle. The results indicated that temperature was the main factor affecting the short-waveband energy ratio. Compared with the Rankine cycle, the new flame energy grading conversion system improved the system efficiency by about 3.5%. The exergy analysis indicated that the proposed system reduced the exergy loss factor in the heat transfer of the boiler by about 3% to 6%. This study provides references for improving the thermal power cycle efficiency.     

基于改进扰动观察法的光伏电池最大功率跟踪

有效地提高光伏电池的利用率对光伏系统至关重要,为此建立了具有通用性的光伏电池工程实用模型及相应的Boost转换电路,采用改进的扰动观察法控制Boost电路占空比实现光伏电池最大功率跟踪(MPPT),阐述了其实现策略并进行仿真验证。结果表明,外界温度、光照变化条件下该方法可精确跟踪光伏电池的最大功率点,实现光伏电池的高效转换。     

风力机模拟平台的MPPT快速响应控制方法

作者开发了一种新的MPPT(Maximtm Power Point Tracking，MPPT)控制方法，和以往的MPPT、控制方法相比，主要不同之处是：(1)追踪步长根据风速的变化而变化，即变扰动MPPT控制方式；(2)为了消除逆变器死区所造成的风力机功率波动影响，MPPT控制周期和发电机的转速是同步的；(3)利用电磁转矩对风力机转速实行完全控制，即在适当的时候，给风力机提供能量使其加速，使风力机转速能跟踪快速变化的风速；(4)在MPPT的输出端使用低通滤波器来平滑风力机转速控制的指令值。采用风力机模拟平台的实验结果表明，该方法可以跟踪0．2Hz快速变化的风速，和传统的MPVT控制方法相比，当风速快速变动时，可以显著增加发电量，从而提高了风力发电的效率。     

海洋热能利用进展

海洋热能储量巨大,随时间变化相对稳定,具有广阔的开发利用前景。当前,海洋热能利用技术主要包括海洋温差能发电技术、海洋温差能制淡技术以及海水源热泵技术。发电技术要求海水温差不小于20℃,制淡技术要求海水温差不小于10℃,海水源热泵技术则在不同纬度地区、不同季节均能应用。本文重点分析了海洋温差能发电技术的3种循环方式,针对低温差导致低发电效率的问题,提出了利用太阳辐射加热温海水以提高温差和利用波浪能驱动泵以降低系统能耗两种提高发电效率的方法。     

New maximum power point tracker for PV arrays using fuzzy controller in close cooperation with fuzzy cognitive networks

The studies on the photovoltaic (PV) generation are extensively increasing, since it is considered as an essentially inexhaustible and broadly available energy resource. However, the output power induced in the photovoltaic modules depends on solar radiation and temperature of the solar cells. Therefore, to maximize the efficiency of the renewable energy system, it is necessary to track the maximum power point of the PV array. In this paper, a maximum power point tracker using fuzzy set theory is presented to improve energy conversion efficiency. A new method is proposed, by using a fuzzy cognitive network, which is in close cooperation with the presented fuzzy controller. The new method gives a very good maximum power operation of any PV array under different conditions such as changing insolation and temperature. The simulation studies show the effectiveness of the proposed algorithm.     

A novel two-mode MPPT control algorithm based on comparative study of existing algorithms

In this paper, the effectiveness of these three different control algorithms is thoroughly investigated via simulation and a proposed efficiency evaluation method of experimentation. Both the steady-state and transient characteristics of each control algorithms along with its measured efficiency are analyzed. Finally, a novel two-mode maximum power point tracking (MPPT) control algorithm combining the modified constant voltage control and IncCond method is proposed to improve the efficiency of the 3 kW PV power generation system at different insolation conditions. Finally, a novel two-mode MPPT control algorithm combining the modified constant voltage control and IncCond method is proposed to improve the efficiency of the 3 kW PV power generation system at different insolation conditions. Experimental results show that the proposed two-mode MPPT control provides excellent performance at less than 30% insolation intensity, covering the whole insolation area without additional hardware circuitry.     

A novel adaptative maximum power point tracking algorithm for small wind turbines

A novel maximum power point tracking algorithm for small wind turbines is proposed. The solution presented here is an adaptive intelligent algorithm that uses a new advanced perturb and observe method to search for the optimum relationship of the system for tracking the maximum power point even under variable wind conditions. The validity of the proposed algorithm is analysed and the design procedure is presented. Its main virtue resides in its capability to adapt to changes in the turbine and in the surrounding environment, even under variable wind conditions, improving the efficiency of the system. The experimental results confirm the validity of the proposed algorithm.     

基于遗传算法的直驱式海浪发电系统最大功率跟踪控制

针对直驱式海浪发电系统在非规则海浪中能量捕获效率较低问题,提出遗传算法控制方案。以规则海浪下发电系统模型为基础,推导出非规则海浪下发电系统输出功率模型。采用遗传算法对参数种群进行选择、交叉、变异、迭代,辨识出符合当前海况的最优发电系统参数,结合空间矢量控制算法实现发电系统最大功率跟踪控制。仿真对比结果表明,该算法能有效提高海浪发电系统能量捕获效率。     

A high efficiency photovoltaic module integrated converter with the asymmetrical half-bridge flyback converter

A module integrated converter (MIC) for a photovoltaic (PV) cell is important part of power conditioning system (PCS). It performs maximum power point tracking of a PV cell to generate the power as much as possible from solar energy. There are several methods for connection between the PV modules and the MICs. In order to avoid partial shading effects, converter-per-module approach was proposed. The MIC that performs maximum power point tracking (MPPT), if it is low efficiency, is no use. The MIC whose output is connected to the output of PV module was proposed for high efficiency. However, there are some problems. In this study, an asymmetrical half-bridge flyback converter is proposed instead of the original flyback converter with same method to solve the problems. The proposed MIC was built to verify the performance. The new topology using soft switching technique showed good performance for the efficiency. At the higher power, the efficiency of the proposed converter is higher than existing converter.     

Performance assessment of a solar hydrogen and electricity production plant using high temperature PEM electrolyzer and energy storage

This paper investigates the performance of a high temperature Polymer Electrolyte Membrane (PEM) electrolyzer integrated with concentrating solar power (CSP) plant and thermal energy storage (TES) to produce hydrogen and electricity, concurrently. A finite-time-thermodynamic analysis is conducted to evaluate the performance of a PEM system integrated with a Rankine cycle based on the concept of exergy. The effects of solar intensity, electrolyzer current density and working temperature on the performance of the overall system are identified. A TES subsystem is utilized to facilitate continuous generation of hydrogen and electricity. The hydrogen and electricity generation efficiency and the exergy efficiency of the integrated system are 20.1% and 41.25%, respectively. When TES system supplies the required energy, the overall energy and exergy efficiencies decrease to 23.1% and 45%, respectively. The integration of PEM electrolyzer enhances the exergy efficiency of the Rankine cycle, considerably. However, it causes almost 5% exergy destruction in the integrated system due to conversion of electrical energy to hydrogen energy. Also, it is concluded that increase of working pressure and membrane thickness leads to higher cell voltage and lower electrolyzer efficiency. The results indicate that the integrated system is a promising technology to enhance the performance of concentrating solar power plants.     

不同容量和地区下光煤混合发电变工况性能研究

在构建系统集成模型的基础上,阐述光煤混合发电系统变工况性能计算方法。以3个地区和4种容量燃煤机组为例,研究集成模型、取代份额、辐射强度、地区和容量对光煤混合发电系统性能的影响规律。结果表明:机组容量和地区一定的情况下,全部取代1级抽汽且辐射强度最大时的系统节能效果最优;同机组不同地区开展混合发电时,太阳能资源丰富地的集热场面积最小,集热场换热效率和太阳能热电转换效率最大,年累计节能减排量大,静态投资回收期最短;同地区不同容量机组开展混合发电时,大容量机组年平均太阳能热电转换效率和年累计节能减排量最大,静态投资回收期最短。     

双轴跟踪和单轴南北向跟踪CPV/T系统的热电性能研究

分别搭建了采用双轴跟踪和单轴南北向跟踪这2种跟踪方式的聚光光伏光热(CPV/T)系统实验平台,并对不同跟踪方式下的系统的热、电性能进行了测试.在实验条件基本相同的情况下进行了多次测试,结果表明,双轴跟踪C P V/T系统的平均光电转换效率和平均光热转换效率分别为13.0％和52.6％,均高于单轴南北向跟踪C P V/T...