Single-phase transformerless inverters are widely installed in grid connected photovoltaic systems due to their outstanding advantages, namely, high efficiency, low cost and high power density. The lack of galvanic isolation leads to common-mode voltage (or current) issues, which are solved by means of modifications to topologies, control schemes and modulation strategies. This study proposes a novel multilevel inverter for single-phase transformerless photovoltaic systems. The topology is based on the neutral-point-clamped inverter, and is aimed to attenuate the leakage ground current. The latter is caused by the common-mode voltage fluctuations affecting the stray capacitances formed between the photovoltaic cells and the grounded frame. On the one hand, the proposed multilevel inverter can synthesise a seven levels output voltage, which reduces the total harmonic distortion. On the other hand, the magnitude of the output voltage can reach up to 1.5 times the DC input voltage, which eliminates the need of a voltage-boosting stage for grid interconnection. This study also presents three dedicated pulse-width modulation strategies, all of them based on the level-shifted multicarrier sinusoidal pulse-width modulation scheme. Numerical simulations and experimental tests in a 1 kW setup have been performed to evaluate the performance of the proposed topology

中文翻译：

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基于升压七电平中性点钳位逆变器的TL-PVS拓扑

单相无变压器逆变器由于其突出的优点，即高效率，低成本和高功率密度而被广泛安装在并网光伏系统中。缺乏电流隔离会导致共模电压（或电流）问题，可通过修改拓扑，控制方案和调制策略来解决。本研究提出了一种用于单相无变压器光伏系统的新型多电平逆变器。该拓扑基于中性点钳位的逆变器，旨在衰减漏地电流。后者是由共模电压波动引起的，该波动影响光伏电池与接地框架之间形成的杂散电容。一方面，建议的多电平逆变器可以合成七个电平的输出电压，这样可以减少总谐波失真。另一方面，输出电压的幅度可以达到DC输入电压的1.5倍，这消除了用于电网互连的升压级的需要。这项研究还提出了三种专用的脉冲宽度调制策略，它们均基于电平移位多载波正弦脉冲宽度调制方案。在1 kW的设置中进行了数值模拟和实验测试，以评估建议拓扑的性能 它们都基于电平移位多载波正弦脉冲宽度调制方案。在1 kW的设置中进行了数值模拟和实验测试，以评估建议拓扑的性能 它们都基于电平移位多载波正弦脉冲宽度调制方案。在1 kW的设置中进行了数值模拟和实验测试，以评估建议拓扑的性能