A day-ahead EMS for transformer aging mitigation in distribution systems via coordinated PV-BESS inverter control under dynamic thermal constraint

Abstract

This paper proposes a novel day-ahead energy management system (EMS) that integrates dynamic thermal rating (DTR) of distribution transformers into the co-optimization of active and reactive power flows from photovoltaic (PV) and battery energy storage systems (BESS). The model comprehensively incorporates inverter and battery degradation costs transformer insulation aging and inverter losses while respecting operational and thermal constraints through both soft and hard constraint formulations. Simulations are performed on a modified IEEE 33-bus distribution system under three operational scenarios. Results demonstrate that aging-related costs can be reduced by up to 78 % through the inclusion of aging cost as a soft constraint and up to 85 % via the enforcement of hard hot-spot temperature (HST) constraints-without the need for transformer or BESS capacity increases. In comparison increasing the BESS capacity from 750 kWh to 1250 kWh yields a 2.4 % decrease in operational cost and 21 % reduction in aging cost. Increasing the transformer capacity from 3000 kVA to 4000 kVA further reduces aging cost by 96 % and operational cost by 5.8 % albeit at significant capital expenditure. The proposed DTR-aware EMS allows for safe transformer operation beyond nominal ratings enabling deferred infrastructure upgrades while maintaining system reliability and economic efficiency.