PhD defence of Ehsan Dehghanpour – Short Circuit Protection of Microgrids Integrating Inverter-Based Distributed Energy Resources
Abstract
By utilizing distributed renewable energy resources, Microgrid is considered as an alternative to solve the energy crisis and decrease carbon dioxide emissions. Recently, inverters are employed as the interface between the distributed energy resources (DER) and the electric grid. Employing Inverters can improve the controllability of DERs. However, inverter-based resources are different from conventional synchronous generators; inverters adopt different control schemes which make their fault current analysis and estimation more complex; inverters have limited fault current. Moreover, the fault current magnitude varies significantly when a microgrid transfers from the grid-connected mode to the island mode of operation; because of the mentioned features the fault detection and protection of the microgrids that include inverter-based distributed resources is challenging.
This thesis proposes a protection scheme for microgrids integrating inverter-based DERs which detects different types of faults including impedance faults in the microgrid in both operating modes. Firstly, two parameters named voltage phase angle shift and D parameter are introduced for fault detection. Then, by using the proposed parameters, a fault detection element is proposed. In addition to fault detection, determination of the fault current direction is essential to have selective protection. Because of the inverters’ specific fault current characteristics, conventional directional elements may maloperate in the presence of inverter-based DER in a microgrid. Therefore, a directional element is introduced in this thesis to determine the current direction during fault. The proposed directional element determines the fault current direction based on the current phase angle shift.
In addition to fault detection and directional elements, a coordination element and a backup protection element are also proposed in this thesis to have a coordinated protection scheme that can provide backup protection in case of primary relay’s breaker failure or communication loss. Then, it is explained how the proposed elements are working together as a protection relay, and the protection scheme implemented by the proposed relay is introduced.
The performance of the proposed scheme is evaluated by simulating different scenarios in different microgrid configurations. The results are also verified through Controller Hardware In the Loop setup. The obtained results confirm the high performance of the proposed protection scheme in microgrids.