A virtual power plant aggregates electrically separated resources while local transformer limits remain. Jain’s EV study illustrates transformer-specific loading/thermal constraints [1]. A portfolio dispatch must retain that local boundary and current resource mapping.
Make the resource-to-transformer relation explicit
Retain resource identity, connection point, transformer, phase assignment and the effective time of the mapping. Identify the evidence behind the map and any uncertain assignments. A software group created for customer administration may not match an electrical group.
| Mapping field | Why dispatch needs it | Invalidation example |
|---|---|---|
| Transformer identity | Groups resources behind the local capacity limit | Feeder transfer changes the supplying transformer |
| Phase or phase pair | Checks the most-loaded winding | Verified wiring change alters phase allocation |
| Measurement boundary | Interprets household and transformer power consistently | Meter or resource configuration changes |
| Effective time and quality | Distinguishes present topology from an old record | Delayed network update leaves an obsolete assignment |
Disaggregate the request inside the local feasible regions
Start with the aggregate request, then allocate among electrical groups with verified device availability and service/energy reserves for the requested interval. Adding nameplate power does not establish that availability.
For a simplified power balance, aggregate requested response is the sum of the chosen local responses. Each local response still needs its own feasibility check. If one group cannot contribute, redistribute only to groups with verified remaining capability; do not increase their allocation solely to preserve the headline commitment.
A topology change also changes the constraint group
After a transfer, resources may face another transformer’s loading, cooling and thermal state. IEC 60076-7’s public scope concerns mineral-oil transformer loading, temperature and ageing [2]; it provides no resource-map protocol. Coordinate the new topology’s effective time with telemetry and dispatch rather than carrying over the previous group’s allowance.
Define the treatment of uncertain topology. A conservative aggregation or temporary exclusion may be appropriate under the operating arrangement, but the choice should be explicit. The controller should not silently treat an unknown connection as spare capacity.
Verify local response before crediting the portfolio
Compare achieved measurements at each relevant transformer with its allocated response. Keep local infeasibility and device nonresponse visible even if the portfolio total happens to match the request. Compensation from another group can meet the aggregate goal while leaving the first group’s model error unresolved.
Use the resource-map version that applied when the interval allocation was issued. Compare it with local measurements after dispatch. Without that time-specific electrical mapping, a software portfolio can assign flexibility to one transformer while its physical response occurs behind another.
References
- A. Jain and M. Karimi-Ghartemani, Mitigating Adverse Impacts of Increased Electric Vehicle Charging on Distribution Transformers, Energies 15, 9023, 2022. DOI: 10.3390/en15239023.
- IEC, IEC 60076-7:2018, Power transformers – Part 7: Loading guide for mineral-oil-immersed power transformers.