Adaptive protection of microgrid through abrupt change analysis and fractional fourier transform

This paper presents adaptive protection of hybrid microgrid to analyse fault characteristics through abrupt change analysis and fractional fourier transform under islanded and grid connected modes of operation. This approach can be extended for fault detection and fault nature classification during different modes of hybrid microgrid operation. Its efficacy in the real time scenario is tested under the series and shunt faults at different locations during different modes of microgrid operation. Different phase faults, earth faults and one or two conductor open faults at different locations are simulated both in islanded and grid connected modes using Matlab/Simulink software. The proposed approach first analysis direct (Id), quadrature (Iq) and zero (I0) components of fault current using fractional fourier transform and abrupt change for the feasibility of adaptive protection scheme. Based on dq0 component analysis different combinations of dq0 components (dq, d0, q0) are tested with adaptive relaying feature for reliable microgrid operation. The waveforms of fault current in Id, Iq and I0 attributes in each mode are detected based on fractional fourier transform. The simulation results show that different modes of microgrid operation contribute to the fault current with different and identifiable abrupt change. Share of Id, Iq and I0 in different modes of microgrid operation help in proper identification and location of fault. The adaptive settings are changed based on abrupt change. Accordingly, a suitable adaptive protection scheme is implemented that is capable of sensing different modes of operation for reliable hybrid microgrid operation. The proposed adaptive protection technique reduces the separate analysis of transients for real time applications and is found out to be more accurate and robust in comparison to other approaches. The simulation results reveal that there are specific distinguishable changes in the fault current contribution for different types of faults in hybrid microgrid operation. Accordingly, intelligent adaptive protection scheme is proposed for fault detection, its location detection and nature of fault to ensure secure and reliable performance of protective relay for hybrid microgrid structures.

As mentioned above hybrid microgrid system is shown in Fig.1. and described as three-phase AC system of 1.5 MVA and 6.6 kV utility side with step-down transformer of 1.5 MVA, 6.6 kV/440 V operating at 50 Hz, connected before point of common coupling (PCC). Low X/R ratio based synchronous generator, PV and wind DGs (1 MVA/440 V each) are connected also connected at PCC in rotation. Two loads of 200 kW each are connected at a distance of 0.8 km from PCC. The proposed microgrid model is simulated to analyse abrupt change and applicability of fractional fourier transform for adaptive relaying. Initially, three phase current components are transformed into dq0 components using park’s transformation as shown in Fig.2. As dq0 components of fault current are independent components so different combinations are tested for effective relaying. After dq0 components are transformed into fractional fourier transform (FFT), abrupt change in final transformed components is used detect the faults and set adaptive settings based on change in microgrid mode of operation.