Most grid-connected inverters can operate in both grid-connected and islanded modes with usually different control schemes adopted in each mode. The control schemes, if noticeably complex and different, can result in inrush currents and voltage distortions at instants of mode transfer. An existing grid-connected form of droop control has hence been developed from the usual islanded droop control to better streamline the transfer. However, the grid-connected droop control does not regulate the grid current directly, causing it to distort by grid voltage harmonics and respond slower during a transient. The motivation here is thus to propose another highly unified droop control scheme that can regulate the grid current directly with a transfer dynamic lasting only two fundamental cycles. This is in addition to the usual targets of seamless transfer and proper power sharing among the islanded inverters. The hypothetical approach followed is to reformulate the grid-connected and islanded control schemes, so that mode transfer can simply be treated as a normal change of voltage reference, rather than an inner change of control structure. The final unified scheme has been tested in simulation and experiments with results apparently confirming its precise grid-current regulation, islanded voltage regulation and seamless mode transfer within two fundamental cycles.

中文翻译：

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并联光伏逆变器系统的无缝传输方案

大多数并网逆变器可以在并网和孤岛模式下运行，每种模式通常采用不同的控制方案。如果控制方案明显复杂和不同，则可能会在模式转换的瞬间导致浪涌电流和电压失真。因此，已经从通常的孤岛式下垂控制中开发了一种现有的并网形式的下垂控制，以更好地简化传输。但是，并网的下垂控制不能直接调节电网电流，从而导致电网电压谐波使它失真，并且在瞬变期间响应速度较慢。因此，这里的动机是提出另一种高度统一的下垂控制方案，该方案可以通过仅持续两个基本周期的传输动态直接调节电网电流。这是通常的目标，即在孤岛式逆变器之间实现无缝传输和适当的功率共享。遵循的假设方法是重新设计并网和孤岛控制方案，以便将模式转换简单地视为参考电压的正常变化，而不是控制结构的内部变化。最终的统一方案已经在仿真和实验中进行了测试，结果显然证实了其在两个基本周期内的精确电网电流调节，孤岛电压调节和无缝模式转换。而不是控制结构的内在变化。最终的统一方案已经在仿真和实验中进行了测试，结果显然证实了其在两个基本周期内的精确电网电流调节，孤岛电压调节和无缝模式转换。而不是控制结构的内在变化。最终的统一方案已经在仿真和实验中进行了测试，结果显然证实了其在两个基本周期内的精确电网电流调节，孤岛电压调节和无缝模式转换。