【作者】 高志强；

【导师】 纪延超；

【作者基本信息】 哈尔滨工业大学 ， 电力系统及其自动化， 2012， 博士

【摘要】 太阳能以资源丰富、无污染等优点成为解决能源短缺、环境污染和生态破坏问题最重要的新型能源之一。随着人类环保意识不断增强和光伏电池价格逐渐下降，各国都致力于太阳能光伏发电的开发和使用。然而，太阳能光伏发电受外部环境影响比较大，波动的输出功率很难为负载或者电网提供稳定、连续的电能。为了克服这个缺点，具有存储能力的三端口光伏系统广泛应用于独立用户、航天太空站、可调度并网等领域，它不仅增强了太阳能光伏使用的灵活性，而且还提高了系统输出的电能质量。为了进一步提高太阳能光伏模块的利用率和并网的电能质量及延长蓄电池的使用寿命，本文对三端口光伏系统的拓扑结构、能量协调控制、并网控制策略和孤岛检测技术等进行了深入研究。具体内容包括以下几个方面：三端口光伏拓扑结构是光伏发电系统的核心部分，传统拓扑结构因为转换级数和开关器件多及高频变压器的应用不仅增加了系统的体积和重量，而且还增加了系统的损耗。为了克服上述缺点，同时保护蓄电池充放电的安全，本文提出了基于Z源网络的新型三端口光伏拓扑结构，该拓扑结构集升降压、逆变、双向充放电、最大功率点跟踪等功能于一体。其简洁紧凑的结构和高效的工作方式降低了系统体积、重量和成本，提高了太阳能光伏模块的利用率和系统输出的电能质量。基于Z源网络的三端口光伏系统的Z源逆变器部分采用在SPWM零状态处插入直通占空比的单级控制策略，通过调节直通占空比和调制因子分别实现直流母线升压和系统逆变输出的控制，其优点是简单且容易实现。但是在感性负载情况下，逆变输出波形出现畸变现象并且谐波含量大，为此本文提出了一种改进的SPWM控制方法。在不增加外部器件的前提下，换向时开启上桥臂为电流提供续流通道，从而消除输出电流和电压波形的畸变现象，降低了输出电流的谐波含量，提高了系统输出的电能质量。通过建立基于Z源网络的三端口光伏系统的小信号模型分析了Z源网络参数、直通占空比，负载和输入电压等系统参数的变化对其输出特性的影响。太阳能光伏模块输出功率随外界环境变化而变化，具有较大的波动性，将会影响负载的正常运行或注入电网的电能质量。基于Z源网络的三端口光伏系统通过控制蓄电池的充放电，可以消除天气对系统输出的影响。因此三端口的能量管理是保证太阳能光伏模块、蓄电池和负载三者之间高效稳定运行的关键。根据太阳能光伏模块和负载之间的供求关系及蓄电池所处的状态，本文提出了一种适用于基于Z源网络的三端口光伏系统的能量协调控制方法，在保证负载稳定工作的前提下，提高了太阳能光伏模块的利用率和延长了蓄电池的使用寿命。基于Z源网络的三端口光伏系统输出端不仅可连接负载构成独立型光伏系统而且还可连接电网形成可调度型光伏并网系统。其优点是使注入电网的电流值保持恒定，避免了太阳能光伏模块输入功率波动对电网的不利影响，而且还具有调节晚间电网峰值的作用。本文采用准比例谐振并网电流控制方法，提高了系统的动态响应速度，减小了并网电流的波动，并且通过修正调制系数和电网前馈补偿控制消除Z源网络电容电压波动和电网波动对输出电流的影响，进一步提高并网的电能质量。光伏并网系统除了要求具有控制并网电流与电网电压保持同频同相的能力之外，还应具备孤岛检测能力。因为孤岛现象一旦发生，如果光伏并网系统继续工作，可能损坏设备或者威胁到人身安全。由于孤岛危害的严重性，系统的孤岛检测需快速、准确，并且兼顾注入并网的电能质量。为此本文提出一种基于有功功率变化的正反馈主动频移法，将有功功率的变化量引入正反馈偏移量中，增加了频率的偏移量，从而加速公共节点电压频率的偏移，缩短检测孤岛的时间。在上述理论研究和仿真分析的基础上，研制开发了以TMS320F2812为主控制芯片的基于Z源网络的三端口光伏系统实验平台。通过实验平台进行了独立型的三端口能量协调控制实验和并网型的并网电流控制、孤岛检测等实验。实验结果验证了所提出的基于Z源网络的三端口光伏拓扑结构和控制策略的正确性和可行性。更多还原

【Abstract】 Solar energy becomes one of the most important new energy resources that cansolve energy shortages, the problem of environment pollution and ecologicaldamage because of its abundant reserves and no-pollution. With a growingawareness of environmental protection and a gradual decline in photovoltaic price,countries all over the world are devoting to development and utilization of solarphotovoltaic(PV).However, influenced greatly by the external environment, solarPV may result in great fluctuation in the output of the PV module, which makes itdiffficult to provide a stable and continuous energy for the load or grid. Toovercome the problem, three-port PV systems with storage capacity are widely usedin independent users, space station, schedulable grid-connection. It not onlyenhances the flexibility in the use of solar photovoltaic, but also improves theoutput power quality of the inverter. In order to further improve the utilization ofsolar photovoltaic modules and extend the service life of the storage devices, in thispaper, the three-port photovoltaic inverter topology, energy management, grid-connected control strategy and perfect islanding detection was researched in detail.The main contents are as follows:Three-port photovoltaic inverter is the core part of the photovoltaic generationsystem. Because of the application of high frequency transformers, high conversionseries and more switching devices, traditional topology not only increases the sizeand the weight of the system, but also increases losses of the PV system. Toovercome these shortcomings, keep the process of charging and discharging of thebattery safe and to extend the life of battery, this paper proposes a novel three-portphotovoltaic topology based on Z-source network, which has a combined functionof buck and boost, inverter, charge and discharge control, maximum power pointtracking and so on. The simple and compact structure and efficient working modehave not only reduced the cost, volume and weight of the system, but also improvedthe utilization efficiency of PV module.and power quality of system.Simple and easy to implement, Z-source inverter partly of the novel three-portphotovoltaic system using the single-stage control strategy that inserting shoot-through duty in zero state of SPWM, respectively achieve the goal of boosting DClink and controlling the current of the inverter by adjusting the shoot-through dutyand modulation factors. However, the inverter’s output contains lots of distortionand harmonic component in the case of inductive load. This paper presents aimproved SPWM control method, withnot increasing the external device, which opens upper bridge legs to provide freewheeling path on the commutation,eliminates the distortion of inverter output, reduces the harmonic component of theoutput current, improves the power quality of the inverter output. In this paper, wealso establish a small-signal model of three-port PV system based on Z-source, andanalyse the impacts of the various parameters and direct duty cycle of Z-sourcenetwork, load and input voltage on the characteristics of output.Changing with the external environment, the output power of solar PV module,fluctuating greatly, would even affect the normal operation of the load or the powerquality of the injecting grid current. By controlling the charge-discharge of thebattery, three-port PV system based on Z-source can eliminate the effect of theweather. As a result, power management of the three-port system is critical forensuring the efficient and stable running of the PV module, battery and load. In thispaper, based on the supply-demand relationship between load and PV module, anovel power management method suitable for three-port PV system based on Z-source is proposed. On the premise of stable running of load, this powermanagement method improved the utilization efficiency of PV module.andprolonged the life of battery.The inverter’s output of three-port PV system based on Z-source can not onlydirectly provide power to the load of the Stand-alone Photovoltaic System, but alsoconstitute a photovoltaic grid power system which can be dispatched by connectingwith the grid. Its advantage lies in that the current injected into the power grid isconstant, which avoids the fluctuation of the input power and contributes to theregulation of the power grid peak during night. This paper adopts the proportionresonance control method to control the current injected into the grid, whichincreases the dynamic response speed of the system and reduces the fluctuation ofthe grid current. This paper further improves the power quality through correctingthe modulation factor and feed-forward control to eliminate the influence that thefluctuation of the capacitance voltage of Z source network and grid makes on theoutput voltage.Besides the function of keeping the current injected into the grid having thesame frequency and phase with the voltage of grid, photovoltaic grid-connectedsystem must have the ability of perfect islanding detection. Once the islandphenomenon occurs and wasn’t cut off from the photovoltaic grid-connected systemin time, it may result in damage of the equipment and threaten personal safety.Considering the severity of island phenomenon, the islanding detection should berapid and accurate, as well as taking into account of the power quality. This paperproposes a novel feedback active frequency drift method (AFD), which is based onpositive feedback of the change of active power. This method adds the change of active power into the frequency deviation, thus, the frequency deviation of point ofcommon coupling is accelerated, and the time of islanding detection is shortened.On the basis of the work above, a set of experiment device of three-port PVsystem based on Z-source is developed. This device takes TMS320F2812as theprimary control chip and the software and hardware is designed. Results of theexperiment verify the validity and feasibility of the proposed novel three-portphotovoltaic system and control method.更多还原