Inverter Based Islanded Microgrid Protection Using Discrete Wavelet Transform

One of the main drawbacks of the Inverter Interfaced Distributed Generator (IIDG) is that the protection of the inverter switch limits the fault current through the inverter control system to be almost equal to the rated current. As a result, traditional overcurrent relays cannot operate to protect the distribution lines in islanded microgrid connected with IIDG during different types of short circuits. In this paper, a new protection scheme is proposed by utilizing the Discrete Wavelet Transform (DWT) to detect faults by extracting high-frequency current oscillations associated with short-circuit currents. The discrete wavelet energy is calculated from the DWT output, accumulated, and compared to the threshold value. The main advantages of this protection algorithm are that it does not need to depend on the short-circuit current increased values to detect the fault and communication is not required between relays. The proposed protection scheme is verified by using PSCAD / EMTDC simulation program. The results validate the proposed IIDG protection strategy by considering different fault types and locations.