Investigation and evaluation of active frequency drifting methods in multiple grid-connected inverters

As the development of distributed generation goes on, more grid-connected inverters are being inevitably connected to the same local electrical power system and the perturbations exerted by each inverter for islanding detection might interfere with each other. The islanding detection principle of commonly used active frequency drift (AFD), sandia frequency drift and slip-mode frequency shift are comprehensively investigated and improved algorithms are proposed as well for better detection performance. Moreover, the interaction of these strategies applied in multiple-inverter systems especially with frequency measurement errors is systematically analysed. The corresponding detection performance is summarised, which can also serve as an effective guideline for designing AFD methods in multi-inverter systems. Finally, simulation and experimental results are provided to verify the islanding detection performance of these methods under multiple-inverter operation.