新型无变压器型并网逆变器拓扑结构、调制原理和优化方法研究

Focused on the requirements of high conversion efficiency and high power quality in distributed generation systems, and based on the overview of the existing studies and technologies in grid-connected inverters, the general laws of the topologies derivation and the modulation principle of transformerless grid-connected inverters are researched and explored in this project. And the novel circuit topology and modulation strategy are proposed by the general law. Furthermore, the common-mode leakage current is eliminated through controlling the additional switches and decoupling the DC and AC sides of the circuit. The double-frequency SPWM strategy is achieved, and the harmonic contents of output currents are reduced and the power quality is improved accordingly. The four-quadrant operation with bidirectional power flow is proposed in order to implement the regulations of active and reactive power. Moreover, the influences of nonideal factors on the operation modes of transformerless grid-connected inverters, such as the switches' parasitical junction capacitance, the grid-connected filter structure, etc., are discussed detailedly. Accordingly, the effective optimization design methods are presented to accord with the grid-connected standards and security specifications of the grid-connected power system. As a result, the project will provide referable theory base and technological solution for the emerging industries including solar energy, electric vehicle, etc.. Furthermore, its implementation will greatly motivate the research and development in grid-connected inverters, strengthen the nation's rhetorical power in the protection of the intellectual property and also its international competitiveness in this field, and accelerate the application and popularization of renewable energies and distributed generation systems.

针对可再生能源分布式并网发电系统高变换效率和高电能质量的要求，本项目在总结无变压器型并网逆变器技术特点的基础上，研究其拓扑结构和调制原理的形成规律和演绎方法，进而提出新型的电路拓扑和调制策略。通过附加开关管的控制解耦，实现共模对地漏电流的消除；通过倍频调制方式，满足并网电能高质量的要求；通过功率双向四象限调制方法，实现并网发电有功和无功的调节。项目还研究非理想条件下开关器件寄生结电容、并网滤波器结构等实际问题对无变压器型并网逆变器工作状态的影响，针对国际标准中严格的并网规范和安规要求，提出相应的优化设计方法，实现理论分析和设计实践的统一。本项目的开展，为太阳能光伏、电动汽车等新兴产业中相关问题的解决提供可参考的理论和技术基础；积极促进国家在并网逆变技术领域的研究和发展，增强国家在该领域知识产权保护的话语权和国际竞争力，加速可再生能源及分布式并网发电技术在我国的应用和推广。

研究围绕无变压器型并网逆变器展开，包括新形电路拓扑、调制方法及性能优化等方面：. 首先分析了无变压器型电路的共模漏电流抑制条件，得到了两类具有共模漏电流抑制能力的单相拓扑结构：基于对称电感配置的电路结构和基于非对称电感配置的电路结构。继而从这两种电路结构分别出发，探索具有共模漏电流抑制能力的单相逆变电路的形成方法以及共模漏电流的优化方案。.其次，从高性能的HERIC电路推导得到了基于对称电感配置结构的混合全桥电路。通过对混合全桥电路的基本工作模态的分析，证明了该电路具有共模漏电流抑制能力的结论。在此基础上，给出了混合全桥电路的PWM控制方法，并且分析了该PWM控制策略下的混合全桥电路的工作特性。并搭建了3kW的实验测试平台，验证了混合全桥结构的正确性。. 再次，提出了一种基于非对称电感配置结构的带有飞跨电容结构的多电平电路。该电路由飞跨电容三电平Buck结构与工频换相结构组合而成，不仅继承了多电平电路转换效率高、滤波电感小的优点，而且保留了工频换相结构对电路中的高频共模漏电流的抑制能力，降低了电路直流输入电压。通过对该电路的工作模态的分析，提出了相对应的PWM控制方法。. 最后，分析了电路中的寄生参数以及参数差异性对基于对称电感结构的无变压器型逆变电路中的共模漏电流的影响，并且以HERIC电路为例，给出了系统寄生参数相关的共模谐振电路模型，得到高频共模电压扰动与电路寄生参数之间的关系。基于上述分析，提出了进一步消除系统高频共模漏电流的共模电压箝位结构，并且将该结构运用于已有的全桥型对称电感配置电路进行优化，有效降低了已有拓扑方案中的共模电压的高频扰动，减小了电路寄生参数对系统共模漏电流的影响。