A single-phase grid-connected inverter with an unfolding circuit consists of a first-stage dc/dc converter, which generates fully rectified sinusoidal waveforms, and a second-stage unfolding inverter, which switches every 180° of line frequency waveform. This converter exhibits low switching loss and high efficiency. Digitally controlled unfolding inverters can be used in numerous applications, such as power supplies to resistive loads and single-phase grid-connected inverters. The operating principle of an unfolding inverter is typically synchronous voltage and current. However, a reactive power supply function with a leading power factor (pf) (lagging pf from the grid perspective) is typically required for grid-connected inverters to suppress the terminal overvoltage. Limited studies have been focused on the operation of inverters with pf less than unity. Such an operation results in large overshoot and oscillation in the output voltage because of the difficulty in coping with large current fluctuations after voltage zero crossing. To this end, we propose a novel control scheme that enables leading pf operation without additional circuitry and overcomes the aforementioned limitations. When the unfolding inverter is operated with leading pf, a special mode called “all-conduction mode” occurs after voltage zero crossing. The proposed scheme implements appropriate dc current control to terminate this mode, resulting in a smooth transition to the normal mode steady state with pf less than unity. The scheme verifiably showcases exceptional efficiency in the conducted simulations and experiments.

中文翻译：

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采用展开电路的单相并网逆变器超前功率因数运行控制方案

具有展开电路的单相并网逆变器由产生完全整流正弦波形的第一级 DC/DC 转换器和每 180° 线路频率波形切换的第二级展开逆变器组成。该转换器具有低开关损耗和高效率。数控展开逆变器可用于多种应用，例如电阻负载的电源和单相并网逆变器。展开逆变器的工作原理通常是同步电压和电流。然而，并网逆变器通常需要具有超前功率因数 (pf)（从电网角度来看滞后 pf）的无功电源功能来抑制终端过电压。有限的研究集中在 pf 小于 1 的逆变器的操作上。由于难以应对电压过零后的大电流波动，这样的操作会导致输出电压出现较大的过冲和振荡。为此，我们提出了一种新颖的控制方案，无需额外电路即可实现领先的 pf 操作，并克服了上述限制。当展开逆变器以超前 pf 运行时，电压过零后会出现一种称为“全导通模式”的特殊模式。建议的方案实施适当的直流电流控制来终止此模式，从而平滑过渡到 pf 小于 1 的正常模式稳态。该方案在进行的模拟和实验中可验证地展示了卓越的效率。由于难以应对电压过零后的大电流波动，这样的操作会导致输出电压出现较大的过冲和振荡。为此，我们提出了一种新颖的控制方案，无需额外电路即可实现领先的 pf 操作，并克服了上述限制。当展开逆变器以超前 pf 运行时，电压过零后会出现一种称为“全导通模式”的特殊模式。建议的方案实施适当的直流电流控制来终止此模式，从而平滑过渡到 pf 小于 1 的正常模式稳态。该方案在进行的模拟和实验中可验证地展示了卓越的效率。由于难以应对电压过零后的大电流波动，这样的操作会导致输出电压出现较大的过冲和振荡。为此，我们提出了一种新颖的控制方案，无需额外电路即可实现领先的 pf 操作，并克服了上述限制。当展开逆变器以超前 pf 运行时，电压过零后会出现一种称为“全导通模式”的特殊模式。建议的方案实施适当的直流电流控制来终止此模式，从而平滑过渡到 pf 小于 1 的正常模式稳态。该方案在进行的模拟和实验中可验证地展示了卓越的效率。