Performance Boundaries of Hybrid Photovoltaic–Battery Inverters Under Dynamic, Unbalanced, and Grid Disturbance Conditions

Abstract

Hybrid photovoltaic (PV)–battery inverters are increasingly required to provide functions extending beyond conventional energy conversion, including zero-export operation, battery coordination, grid support, and backup supply. However, rated power and peak efficiency alone do not adequately describe their practical operating limits. This study proposes a multi-scenario dynamic assessment framework for a 10 kW hybrid PV–battery inverter under twelve normal and stressed operating conditions. The model includes PV curtailment dynamics, a first-order Thevenin battery representation with State of Charge (SOC)-, current-, voltage-, and power-dependent constraints, DC-link energy balance, dq-frame current control, current circle limitation, low-voltage ride-through (LVRT)-oriented reactive-current support, and grid-connected/islanded operation. The simulations reveal distinct limitation mechanisms that remain hidden under nominal conditions. Peak unintended export reaches approximately 3.50 kW following sudden load rejection and 3.94 kW at high battery SOC. Nonlinear loading increases the current-related comparative harmonic stress indicator to HI= 10.73, while a severe grid voltage sag increases it to HI = 14.30, produces a maximum DC-link deviation of approximately 4.66%, and activates current saturation during 10.83% of the simulation interval. Under islanded overload, peak unserved power reaches approximately 1.45 kW, corresponding to 0.278 Wh of unserved energy. A Hybrid Inverter Stress Index (HISI) is introduced as a secondary normalized measure for cross-scenario comparison, with the highest value of approximately 0.530 obtained during the voltage-sag case. The results demonstrate that hybrid inverter capability should be assessed using dynamic power balance, battery headroom, DC-link, current limitation, comparative harmonic stress, and supply capability indicators in addition to conventional rated specifications.