Optimal active and reactive power scheduling for inverter-integrated PV and BESS under inverter current constraints

Abstract

The intermittent nature of renewable energy complicates grid integration, requiring an efficient Energy Management System (EMS). This study addresses day-ahead EMS in distribution systems (DS) with a focus on active and reactive power scheduling, utilizing the reactive power support of inverters in Photovoltaic (PV) and Battery Energy Storage Systems (BESS). A novel current-based method is proposed, accounting for current limits, bus voltage, inverter lifetime reduction costs, and inverter losses modeled as load. This method impacts load flow, bus voltage, and voltage-dependent loads, enabling optimal decisions for compensating inverter losses via the grid, BESS, or PV. Simulations on the IEEE 33 test system show a 5% reduction in inverter losses with the current-based method and 6% with the traditional power-based method. Inverter lifetime reduction costs were minimized by 42% and 58% with the current- and power-based methods, respectively, under summer conditions. In winter, reductions reached 49% and 14%. Crucially, inverter output depends on bus voltage, challenging the assumption of constant rated power. At voltages below 1.00 p.u., inverters underperform, achieving only 209 kVA of a 215 kVA rating. These findings emphasize the need for accurate modeling to improve EMS performance and reliability in renewable energy systems.