高频非隔离光伏并网逆变器零开关损耗运行理论及规模化应用中的阻抗匹配方法

At present, the transformerless photovoltaic grid-connected inverters (TLI) are still on hard switching state, their switching frequency has been selected in low level for achieving higher conversion efficiency. As a result, the volume and cost are difficult to reduce; on the other hand, the lower switching frequency limits the control bandwidth of the TLI, is not convenient to match the output impedance of the TLI with the grid impedance, the resonance likely occurs. In this proposal, the switching frequency has been gained by combining the soft switching technology and the TLI, and the idea that directly introducing the high performance soft switching resonant tank in the DC-DC converters into the TLI is proposed. The resonant tank generation rules based on the resonant state plane trajectory optimizing, and simplification method by using the resonant components share and time division multiplex access are developed. And then the zero switching loss (ZSL) concept for the TLI is proposed. In the process of transforming from mass grid-connected system stability to individual TLI stability, the forbidden region optimization method with low conservative will be explored, and the individual TLI impedance specification will be obtained. According to the individual impedance specification obtained, the impedance shaping methodology of the high frequency TLI for achieving mass grid-connected system stability is developed. Finally, the project will push the development of the TLI to higher power density, lower cost, and more mass application.

当前非隔离光伏并网逆变器为硬开关方式，为达到较高的运行效率其开关频率一般较低。如此，一方面使得并网逆变器的体积成本很难降低；另一方面，较低的运行频率限制了逆变器的控制带宽，不利于并网逆变器输出阻抗与电网阻抗的匹配设计，容易发生谐振。本项目将软开关与非隔离并网逆变器结合以提高开关频率，提出直接引进直流变换器中高性能软开关网络到非隔离光伏并网逆变器中的软开关实现思路。研究基于谐振状态平面轨迹优化的软开关拓扑生成规律和基于分时复用的谐振网络简化方法，提出零开关损耗型非隔离光伏并网逆变器概念；研究规模化并网系统稳定到单机分散稳定的低保守性禁区优化方法，推导出满足规模化并网稳定的单机逆变器输出阻抗限值，研究基于高频软开关并网逆变器的输出阻抗修整方法，从而实现高频并网逆变器在设计阶段就可满足规模化应用的安全稳定要求。本项目的实施将推动非隔离光伏并网逆变器向高功率密度、低成本方向发展和促进规模化应用。

当前非隔离光伏并网逆变器为硬开关方式，为达到较高的运行效率其开关频率一般较低。如此，一方面使得并网逆变器的体积成本很难降低；另一方面，较低的运行频率限制了逆变器的控制带宽，不利于并网逆变器输出阻抗与电网阻抗的匹配设计，容易发生谐振。本项目将软开关与非隔离并网逆变器结合以提高开关频率，实现直接将直流变换器中高性能软开关网络（ZVT、ZCT等）引入到非隔离光伏并网逆变器中，发明“续流谐振腔逆变器”架构，并实现零开关损耗运行目标。建立并网逆变器简化阻抗模型，提出规模化并网系统稳定到单机分散稳定的低保守性禁区优化方法，推导出满足规模化并网稳定的单机逆变器输出阻抗限值。本项目的实施推动了非隔离光伏并网逆变器向高功率密度、低成本方向发展和促进规模化应用。

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