A THD-Based Fault Protection Method Using MSOGI-FLL Grid Voltage Estimator

Abstract

The rapid growth of the distributed generators (DGs) integration into the distribution systems (DSs) creates new technical issues; conventional relay settings need to be updated depending on the network topology and operational mode as fault protection a major challenge. This emphasizes the need for new fault protection methods to ensure secure protection and prevent undesirable tripping. Total harmonic distortion (THD) is an important indicator for assessing the quality of the grid. Here, a new protection system based on the THD of the grid voltages is proposed to address fault events in the electrical distribution network. The proposed protection system combines the THD with the estimates of the amplitude voltages and the zero-sequence component for defining an algorithm based on a finite state machine (FSM) for the detection, identification, and isolation of faults in the grid. The algorithm employs communication lines between all the protective devices (PDs) of the system to transmit tripping signals, allowing PDs to be coordinated. A second order generalized integrator (SOGI) and multiple SOGI (MSOGI) are used to obtain the THDs, estimated amplitude voltages, and zero-sequence component, which allows for fast detection with a low computational burden. The protection algorithm performance is evaluated through simulations in MATLAB/Simulink and a comparative study is developed between the proposed protection method and a differential relay (DR) protection system. The proposed method shows its capability to detect and isolate faults during different fault types with different fault resistances in different locations in the proposed network. In all the tested scenarios, the detection time of the faults has been between 7–10 ms. Moreover, this method gave the best solution as it has a higher accuracy and faster response than the conventional DR protection system.

A Comparative Study of Smart THD-Based Fault Protection Techniques for Distribution Networks

“…According to [ 36 , 43 ], the SOGI-FLL and FFT methods were implemented into a DSP, and the computational burden was computed in the number of processor cycles (c) used to compute the SOGI, the FLL, and the FFT blocks. In [ 43 ], it was reported that the SOGI needs 149c, the FLL 49c, and the FFT 7019c per phase.…”

“…The method described in [ 36 ] is used to obtain the harmonic components of the grid in order to calculate the THD. In [ 36 ], an MSOGI is employed together with a Frequency Locked-Loop (MSOGI-FLL) to obtain the fundamental and the 3rd, 6th, and 9th harmonics of the grid voltages.…”

“…The method described in [ 36 ] is used to obtain the harmonic components of the grid in order to calculate the THD. In [ 36 ], an MSOGI is employed together with a Frequency Locked-Loop (MSOGI-FLL) to obtain the fundamental and the 3rd, 6th, and 9th harmonics of the grid voltages. The MSOGI uses multiple SOGIs operating in parallel and a cross-feedback cancellation network to remove the unnecessary components from the input signal, ensuring that each SOGI receives only the necessary component.…”

“…The method for measuring THD outlined in [ 37 ] is employed in this paper, in which the SOGI approach is used to obtain the harmonic components required for calculating THD [ 42 , 43 ]. The technique described in [ 37 ] uses the definition of THD outlined in [ 38 , 39 ], which is calculated using Equation (1). A SOGI-FLL is employed for 1 of the 3 phases of the grid voltage, while only a SOGI is utilized for the remaining two phases, as is provided to them by the FLL stage of the 1st SOGI.…”

“…To overcome the previous issues, two THD-based protection techniques for detecting and isolating different types of faults (symmetrical and unsymmetrical) in MV DSs were presented in [ 36 , 37 ]. The methods are based on the measurement of the THD levels of the grid voltages, defined as , the estimated amplitude voltages , and the zero-sequence components .…”