Investigate dynamic and transient characteristics of microgrid operation and develop a fast-scalable-adaptable algorithm for fault protection system

A microgrid (MG) system mainly consists of renewable energy sources, distributed generators, loads and energy storage devices. Development of the microgrid brings some emerging challenges. One of them is a microgrid fault protection system. In order to develop an optimal fault protection algorithm, this paper surveys dynamic and transient behaviours with respect to two operation modes of a microgrid, namely, islanded and grid-connected modes. Modelling and simulation of the MG's operation are performed by PSCAD/EMTDC software. A surveyed typical MG structure includes one dispatchable power source of microturbine (μT) system, another non-dispatchable power source of photovoltaic (PV) generation system and one battery power conditioning system (PCS). Whereas dynamic characteristics of the MG are investigated in cases of power change of loads or sources and motor starting, transient properties are surveyed through staged fault tests (e.g. single-phase and three-phase to ground faults) and the MG's operation transition between grid-connected and islanded modes. Simulation results are compared to actual experiment results performed at a 380 V microgrid at Institute of Nuclear Energy Research (INER), Taiwan. From achieved dynamic and transient properties, this paper proposes a fast-scalable-adaptable (FSA) computing algorithm for a fault protection system to improve MG's reliability and adaptability operation. This new algorithm uses parameters of current, voltage and angle phase along with a communication network to protect online the microgrid. The proposed algorithm can solve challenging problems of high penetration of inverter-based distributed generators, reduced fault current values and non-directional power flow. Moreover, the algorithm can get a critical fault clearing time within one fault cycle, high accuracy and reliability for fault detection, identification of different types of faults and optimal isolation of faulted zones. Simulation and experiment results validate the proposed fast-scalable-adaptable fault protection algorithm.