微网孤岛运行时基于逆变器的新型功率控制

提出了一种在微网孤岛运行下逆变器无信号线功率分配的新型控制策略——动态功率平衡。当微网被动或主动地与上级电网断开时，微网会处于孤岛工作模式。在这种情况下，通过逆变器连接的电源则表现为电压源，其幅度和频率则通过下垂特性得到控制。然而，当负载重载或轻载时，这种下垂特性会产生大的频率偏移；平缓的下垂特性可以避免频率的过大偏差，但却使得逆变器之间难以功率分配。与传统的下垂控制相比，通过动态地改变大容量逆变器中下垂曲线的位置，动态下垂曲线控制则可将系统频率控制在一个设定的范围内，这样不但使得微网中大部分电源工作在额定功率下，在负载降低时也能充分利用新能源发电，同时这些逆变器仍可以保持原有的功率分配特性。还给出了控制方法的分析与设计，通过应用PSCAD/EMTDC仿真，验证了此种控制方法。

A Novel Power Distribution Strategy for Parallel Inverters in Islanded Mode Microgrid

A novel wireless load-sharing control strategy, active droop positioning, for islanding parallel inverters in an ac-distributed system is presented. Normally, the microgrid is intended to operate in islanded mode when the disconnection from the upstream MV network occurs. Thus, the inverter-interfaced microsources acts as a voltage source, with the magnitude and frequency of the output voltage controlled through droops. However, under overload or underload circumstances, this droop characteristic may lead to large frequency deviation. The mild droop characteristic can avoid large deviation, but it is hard to realize a good power sharing among inverters. Compared to conventional droop control method, by automatically changing the droop position of some large capacity microsources, the proposed strategy can bind the system frequency deviations in an endurable range. Under this control strategy, almost all the micro sources in the microgrid can work around rated power, when the load reduces dramatically, the distributed energy resources (like wind power and solar power) can also be taken full advantage. The analysis of the proposed method and design procedure are provided. Simulation and experimental results validate the strategy.