Microgrids are used to incorporate distributed generators (DGs) together so that DGs can be scheduled to satisfy the load demand. Usually droop controllers are adopted so that each DG shares the load equally. To improve the flexibility in system configuration with DGs of different capacities, droop controllers should be updated. In order to share the load among DGs in proportion to each unit’s capacity and improve power supply quality, in this paper an improved droop controller is presented which is based on adaptive virtual impedance. By means of low bandwidth communication, two variables, i.e., the average distribution ratio of active and reactive power, are introduced. And through two integrators, the voltage reference and virtual impedance of every DG are tuned online. For the proposed controller, the system dynamic is discussed. It is shown that active or reactive power sharing convergences can be guaranteed when some inequalities are satisfied. Furthermore, the design of controller coefficients is discussed while considering convergence speed and system stability at the same time. The proposed droop controller reduces the amplitude and frequency shift usually caused by the traditional droop controller. It also improves the output voltage quality of the whole microgrid system. Finally, through simulations and experiments the effectiveness of the proposed droop controller is verified.

中文翻译：

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具有自适应虚拟阻抗的改进下垂控制器的设计与收敛性分析

微电网用于将分布式发电机 (DG) 结合在一起，以便可以对 DG 进行调度以满足负载需求。通常采用下垂控制器，以便每个 DG 均分负载。为了提高具有不同容量 DG 的系统配置的灵活性，应更新下垂控制器。为了按各机组容量按比例分担DGs间的负荷，提高供电质量，本文提出了一种基于自适应虚拟阻抗的改进下垂控制器。通过低带宽通信，引入了两个变量，即有功功率和无功功率的平均分配比。并通过两个积分器在线调整每个DG的电压参考和虚拟阻抗。对于所提出的控制器，系统动态进行了讨论。结果表明，当满足一些不等式时，可以保证有功或无功功率共享收敛。进一步讨论了控制器系数的设计，同时考虑了收敛速度和系统稳定性。所提出的下垂控制器减少了通常由传统下垂控制器引起的幅度和频率偏移。它还提高了整个微电网系统的输出电压质量。最后，通过仿真和实验验证了所提出的下垂控制器的有效性。所提出的下垂控制器减少了通常由传统下垂控制器引起的幅度和频率偏移。它还提高了整个微电网系统的输出电压质量。最后，通过仿真和实验验证了所提出的下垂控制器的有效性。所提出的下垂控制器减少了通常由传统下垂控制器引起的幅度和频率偏移。它还提高了整个微电网系统的输出电压质量。最后，通过仿真和实验验证了所提出的下垂控制器的有效性。