**An Improved Inverse-Time Over-Current Protection Method for a Microgrid with Optimized Acceleration and Coordination**

#### **Liang Ji 1, Zhe Cao 2, Qiteng Hong 3, Xiao Chang 4, Yang Fu 1,\*, Jiabing Shi 5, Yang Mi 1 and Zhenkun Li 1**


Received: 30 August 2020; Accepted: 24 October 2020; Published: 2 November 2020

**Abstract:** This paper presents an improved inverse-time over-current protection method based on the compound fault acceleration factor and the beetle antennae search (BAS) optimization method for a microgrid. The proposed method can not only significantly increase the operation speed of the inverse-time over-current protection but also improve the protection coordination by considering the possible influential factors in terms of microgrid operation modes, distributed generation (DG) integration status, fault types, and positions, which are marked as the most challenging problems for over-current protection of a microgrid. In this paper, a new Time Dial Setting (TDS) of inverse-time protection is developed by applying a compound fault acceleration factor, which can notably accelerate the speed of protection by using low-voltage and short-circuit impedance during the fault. In order to improve the protection coordination, the BAS algorithm is then used to optimize the protection parameters of the pick-up current, TDS, and the inverse time curve shape coe fficient. Finally, case studies and various evaluations based on DIgSILENT/Power Factory are carried out to illustrate the effectiveness of the proposed method.

**Keywords:** microgrid; distributed generation; inverse-time over-current protection; coordination optimization
