Adaptive Virtual Inertia Control for Two-Stage Grid-Forming PV Inverter Considering DC-Link Dynamics

Two-stage grid-forming (GFM) photovoltaic inverters leverage the dynamic characteristics of the DC-bus capacitor to emulate the inertia of synchronous generators. However, under conditions of drastic solar irradiance fluctuations or sudden increases in grid load, fixed virtual inertia parameters struggle to simultaneously ensure both effective grid frequency support and stable DC-bus voltage, often leading to DC voltage dips or even system disconnection. To address this issue, this paper proposes an adaptive virtual inertia control strategy that takes into account the dynamic resources on the DC side. First, based on the dynamics of the DC-bus voltage, the synchronous equations for the inverter are derived, and a quantitative mapping relationship between the control parameters and the virtual inertia, as well as the damping coefficient, is established. Second, an inertia control law that adaptively adjusts according to the photovoltaic output power is designed. When solar irradiance is abundant, the virtual inertia is increased to provide sufficient frequency support, and vice versa. At the same time, a damping coordination mechanism with power-difference feedforward is introduced, which enhances the system’s dynamic response under complex operating conditions. Verification using the PLECS RT-Box hardware-in-the-loop (HIL) experimental platform demonstrates that, compared to the conventional fixed-parameter control, the proposed strategy effectively suppresses DC-bus voltage dips during sudden changes in solar irradiance, thereby avoiding undervoltage protection trips. Under load-transient conditions, the strategy dynamically adjusts the inertia response based on the photovoltaic output status, achieving a balance between transient system stability and grid friendliness.