An intelligent power flow controller for autonomous operation of islanded micro-grids

This paper presents a novel power flow control method for autonomous operation of micro-grids in islanded mode. The proposed power flow controller makes use of a new adaptive estimation unit (AEU), which can estimate the amplitude, phase, and frequency of the fundamental component of the potentially non-stationary power signal, as well as the associated active and reactive power. The AEU is based on a sinusoid-tracking algorithm (STA), which is recently proposed as an improved phase-locked loop (PLL). The proposed method is stable for any grid perturbation. The performance of the proposed method is illustrated on a micro-grid that includes an inverter and a synchronous generator. Low pass and washout filters are used in the proposed power flow control method to adjust the amount of power flow through the inverter and synchronous generator to the load after islanding. The estimated frequency and the amplitude by the AEU are used to adjust the governor and the field controller of the synchronous generator, respectively. Since the AEU estimates the power signal properties of each phase independently, the proposed method can be applied to single-phase and unbalanced micro-grids as well. The results show that without the controller, the inverter will not share the power with the synchronous generator after islanding. By using the controller, the power flow from inverter and synchronous generator to the load is under control. The application of the proposed method offers significant advantages, especially in multi-machine based micro-grids.