柔性光伏微逆变器的功率解耦及高频交流升降压控制研究

The micro-inverter can solve the maximum power point tracking (MPPT) problem which exists in series and parallel photovoltaic cells generation system. This project aims at the following performances of the photovoltaic micro-inverter: The power loss mathematical models for the existing topologies are established to discriminate and evaluate their advantage and disadvantage, which can be the basis for exploring novel topology. According to the adaptive power range of the each topology and the output power of the photovoltaic cell, the flexible topologies for the micro-inverter will be built, which can greatly improve the weighted efficiency for the single photovoltaic cell generation system. The mathematical model for parameter-controlled magnetic element will be constructed by analyzing the function of the magnetic element in the inverter. The project also analyzes mechanism of how the parameter-controlled magnetic element influences the efficiency of the micro-inverter and proposes the method to realizing the inductor current boundary conduction mode (BCM) and fixed-frequency control, which can effectively reduce the device current stress and guarantee the soft-switching. The mechanism of how the variable input and output voltage influence the system efficiency will be analyzed. The operation principle and the design rules of high-frequency AC buck-boost strategy are studied, which are the basis for the relevant control strategy construction. The potential function of the switching devices in the flexible topology will be explored and these switching devices will be developed to share with the power decoupling function module, which can greatly improve the life the micro-inverter and guarantee the high efficiency. The breakthroughs in the above technologies can build a stable foundation for the high-performance and high-efficiency micro- inverter in photovoltaic generation systems.

微逆变器可以解决集中式并网难以实现所有光伏电池的最大功率输出问题。本课题旨在提高光伏微逆变器的以下性能：建立现有光伏微逆变器电路各项损耗的数学模型，以甄别、评价各自电路的优缺点并发掘新型的电路拓扑，根据拓扑的功率适应范围和光伏模块的输出功率，构建光伏微逆变器的柔性可变拓扑，保证宽输入功率范围内高效变换；分析并建立参数外部可控磁性元件的数学模型，研究可变磁性元件对柔性拓扑微逆变器效率的影响机制，保证微逆变器中器件的软开关并进一步降低器件电流应力；分析微逆变器输入、输出电压波动对系统效率的影响机制，研究移相控制高频交流升降压变流的工作机理，归纳高频交流升降压拓扑的设计规律，建立与主电路相应的控制策略，指导微逆变器的效率优化；发掘柔性拓扑中已有的可以发挥潜在效能的开关器件并加以复用，实现输入、输出功率解耦，消除影响模块寿命的电解电容；上述技术的突破可为光伏分布式发电的高效、高性能并网运行提供坚实的理论基础。

光伏微逆变器中，输入电压波动范围大、运行环境恶劣、单体功率小造成的相对成本高、效率低制约了其在市场上的竞争力。本课题旨在解决光伏微逆变器在实际应用中光伏电池输出电压受天气影响变化范围宽造成的性能降低、运行环境恶劣造成的寿命受制于某一元件的问题，实现光伏微逆变器高加权效率、长寿命、高性能可靠的运行。主要研究内容包括：高频交流升降压控制策略、柔性拓扑光伏微逆变器控制策略、柔性元件光伏微逆变器控制策略、低频电流纹波抑制策略等关键技术研究。.针对光伏电池输出电压受环境影响大的特征，项目提出了基于高频交流升降压理论，极大地降低了输入电压波动对变换器的影响，保证了光伏微逆变器前级变换中电流应力最优化；为进一步简化微逆变器的拓扑，在高频交流升降压理论的基础上又提出了高频交流降压理论，所依托的拓扑和控制复杂性得到了大大简化，且保留了高频交流升降压理论的优点。.针对市场上对光伏微逆变器的加权效率要求高，常用变换器不能在宽功率范围都实现较高效率的情况，项目提出了柔性拓扑的控制策略，将改进双管正激拓扑与桥式拓扑通过合理的方式集成为一个电路，在低功率范围运行改进双管正激拓扑，在高功率范围运行桥式拓扑，保证宽功率范围内，微逆变器均能取得高效运行，从而实现高加权效率。此外，提出了柔性自适应电感的光伏微逆变器，根据光伏电池输出功率合理确定柔性电感值，保证光伏微逆变器运行在电流BCM状态，既保证软开关运行，又实现了低电流应力。.针对光伏微逆变器长寿命的要求，研究了低频电流纹波抑制策略。提出基于功率预测的低频纹波抑制策略，一方面避免了采用复杂的谐振控制器设计，另一方面可有效抑制光伏侧输出电流中低频纹波含量，保证了变换器的性能；提出基于双占空比电流型桥式变换器，采用两个互相解耦的占空比控制变换器中两个功率流向，实现输入输出电压匹配，同时保证器件优化的电流应力与优良的低频纹波抑制效果。.上述技术的改进，可以保证光伏微逆变器取得高效率、高性能、长寿命的运行，增强了其在市场上的竞争力。