Converter-based Microgrid Testing Platform Development and Fault Detection Method for Inverter-based Resources by Utilizing Instantaneous Power Theory

Renewable energy sources (RESs) are rapidly being installed into electric systems. Most RESs are inverter-based distributed generations (IDGs). To better manage energy from IDGs, microgrids will play a crucial role. However, microgrids that have high penetration of IDG will have modification in fault current levels and bidirectional power flow causing protective devices to misoperate, so the traditional protection system does not correctly function in the microgrids. Therefore, the integration of IDGs into the microgrids establishes some significant consequences on protection systems.

Overcurrent protection is widely utilized in the electric distribution systems today; however, it is sometimes difficult to distinguish between transient conditions and faults in microgrids due to low fault current contribution of IDGs. So, transient conditions behaviors, including motor start and transformer energization, and fault behaviors have been studied and compared before a new protection scheme development to distinguish between faults and normal inrush currents in these systems.

To deal with the varieties of IDGs, a new fault detection method by utilizing instantaneous power calculation is proposed to improve protection systems accuracy and reliability. Both active and non-active power will be calculated in real-time while monitoring voltage and current levels. The proposed fault detection method is a combination of active power, non-active power, voltage and current.

To verify the proposed fault detection method, the Banshee microgrid has been chosen to demonstrate the performance of the proposed fault detection method. At the Center for Ultra-Wide-Area Resilient Electric Energy Transmission Networks (CURENT), a converter-based hardware testbed (HTB) was developed to emulate power systems in real-time. However, the microgrid cannot be tested in the existing platform since the microgrid has different topology and line impedance. Therefore, a converter-based microgrid platform has been developed on the existing HTB to implement and test the proposed fault detection method.

Additionally, the HTB has been modified to support inverter control parameters testing including proportional (P) and integral (I) values. The inverter control parameters can be adjusted in real-time, so inverter dynamic response during transient conditions can be studied in the HTB. Finally, as the future power system would become 100% renewable, all generation in HTB has been modified to IDGs. Thus, the effects of a droop control of IDGs to the system can be also studied.