Dependable Open-Phase Detection For Inverter-Based Distributed Energy Resources (ders)

Integrating inverter-based distributed energy resources (DERs) into distribution systems has yielded operational concerns and challenges. One of these challenges is to reliably detect an open phase at the interconnection point. Conventional methods of open-phase detection are optimized for power systems with rotating machine sources and hence struggle to maintain reliability when applied at inverter-based DER interconnection points. Additionally, the presence of some types of interconnection transformers can impose additional challenges to open-phase detection.

In this paper, we introduce a current-based open-phase detection method designed to maintain reliability when the DER is an inverter-based source. This method detects open phase when there is sufficient current flowing between the inverter-based DER and the area electric power system (EPS). The absence of current on the disconnected phase while current continues to flow on the connected phases combined with supervisory conditions is used to detect the open phase. Voltage-based open-phase detection methods were established in the technical paper, “Field Experience With Open-Phase Testing at Sites With Inverter-Based Resources.” These voltage-based open-phase detection methods are employed to maintain reliability when there is insufficient current flowing between the inverter-based DER and the area EPS.

We use field events to demonstrate the overall reliability of combining the previously employed voltage-based open-phase detection scheme and the proposed current-based open-phase detection scheme at the interconnection point for inverter-based DER applications. Furthermore, we use a real-time digital simulator to demonstrate the reliability of the proposed current-based open-phase detection scheme.