Digital protection scheme for microgrids using wavelet transform

The dynamic nature of microgrids compromises the efficiency and accuracy of the conventional power system protection strategies. This paper proposes a novel digital and microprocessor based protection scheme for microgrids using signal processing techniques. Digital relays are employed with fault detection algorithm. Fault detection is done based on a relatively new signal processing technique called Wavelet Transform (WT). The dq0 decomposition technique is used to reduce the computation time of the relay algorithm. The WT is used to decompose dq0 axis components of current and voltage signals to obtain high-frequency details of the same which is used to detect high frequency transient disturbances due to the fault. Fault location and isolation is done using power high-frequency details, which are calculated as the product of the high-frequency details of current and voltage. A threshold is defined for the cumulative sum of the power high-frequency details, deviation from which is observed only on the faulty bus, thus, triggering a tripping action. The system has been tested for various faults within the microgrid for different operating modes. Software simulation and hardware testing results were obtained for the proposed method and it has been inferred that the proposed protection scheme detects and isolates faults in a fast and accurate manner.