Logarithmic Absolute Square Error Based Differential Protection Scheme for AC Microgrid

Differential protection offers better selectivity and performance for distribution networks integrated with microgrid. However, its effectiveness can be impacted by the high impedance fault, noise, measurement error and effect of time synchronization error. Therefore, this paper proposes a Logarithmic Absolute Square Error (LASE) based differential protection scheme for AC microgrid, utilizing the phase current magnitude as fault detection parameter. The proposed differential scheme calculates the Superimposed Phase Current Magnitude (SPCM) at local ends of the line, triggering the protection scheme when the SPCM exceeds disturbance alarm indicator at both line ends. The LASE based approach computes the log of the square of the absolute difference of SPCM, calculated at both ends of the line. This square approach enhances sensitivity, i.e. enabling fault detection up to 600Ω fault resistance, in both grid and islanding operating modes of AC microgrid, while also facilitating faulty phase identification. To prevent undefined values in logarithmic calculations when the difference is zero, a constant factor (unity value) is incorporated into the LASE scheme. The proposed scheme is applicable to various network configurations, i.e., mesh, ring and radial. It is stable for different system transients, external faults and is insensitive to noise, measurement error and time synchronization error effects. The LASE based scheme has high accuracy and provides fast fault identification <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(\text{1. 5 m s}-\text{1 9. 1 5 m s}$</tex> for 50 Hz). A comparative analysis of the LASE based scheme is also performed with the recent schemes to highlight its superior speed, sensitivity, and selectivity.