Photo: Courtesy of State Grid Qingdao Power Supply Company

On October 8, Zhou Maoxin, zone manager of the SCO Demonstration Area power supply office under the State Grid Qingdao Power Supply Company, inspected the pilot-built SCO “Autonomous Microgrid” to ensure its stable operation. This digital and intelligent “Autonomous Microgrid” has created a replicable and scalable model for building a secure, controllable, smart and user-friendly new power system, Zhou said.

Using AC/DC flexible interconnection technology, the SCO “Autonomous Microgrid” connects a 200 kVA power supply office zone and a 630 kVA public charging station zone within the SCO Demonstration Area. Given the differences in load characteristics between these zones, which include distributed photovoltaic (PV) systems, charging piles, and energy storage devices, a three-tier management structure has been established. This structure includes strategy customization, coordinated control, and local execution, enabling three key functions: mutual power supply between zones, collaborative operation of “main, distribution, and micro” grids, and sub-second power restoration.

When an overload occurs in the interconnected zones of the SCO “Autonomous Microgrid,” an alarm threshold is triggered, switching to the AC/DC hybrid interconnection mode. Surplus capacity from adjacent zones is smoothly transferred, achieving dynamic load balancing and avoiding peak overloads. If load balancing on the AC side is insufficient, the system initiates DC mutual assistance, transferring capacity through parallel inverters to support the high-load zone on the AC side.

Leveraging advanced digital simulation and flow prediction technologies, the SCO “Autonomous Microgrid” can accurately predict load curves and regulate energy storage charge/discharge states and PV output in real time, effectively mitigating large fluctuations in load rates. This innovation helps address the challenges of implementing distributed PV prediction and balancing grid regulation with user benefits, supporting the broader adoption of distributed energy.

In emergencies, the “sub-second power restoration” capability of the SCO “Autonomous Microgrid” is notable. Under varying load conditions, the average power restoration time within the zone has been reduced from three hours to less than two minutes. For dual-zone outages, the system prioritizes important loads, reducing the average restoration time to five minutes.

Since its commissioning on July 15, the daily peak load rate of the SCO “Autonomous Microgrid” has dropped from an average of 78.5 percent to 53.2 percent, with no incidents of peak overload. All distributed photovoltaic power has been utilized locally, with no reverse current issues. The interconnected zones now feature intelligent perception, autonomous analysis, and stable control, with dynamic load balancing and enhanced power supply quality through complementary grid resources. The establishment of the SCO “Autonomous Microgrid” marks a significant step forward for State Grid Qingdao Power Supply Company in speeding up the digital transformation of its distribution network.