Replacing conventional synchronous generator-based power plants with inverter-based renewable energy resources results in a reduction of the inertia in power systems. To sustain the security and reliability of these low-inertia power systems, frequency support is increasingly required in new standards for grid-connected renewable energy resources, especially distributed photovoltaic (DPV) systems. This article proposes a frequency droop-based control in DPV inverters to improve frequency response in power grids with high penetration of renewable energy resources. A predefined power reserve is kept in the DPV inverter, using flexible power point tracking. The proposed algorithm uses this available power reserve to support the grid frequency. Furthermore, a recovery process is proposed to continue injecting the maximum power after the disturbance, until frequency steady-state conditions are met. The positive inertia using the proposed recovery mode, leads to recovery of the frequency in a shorter period. A composite load model of a distribution feeder, including DPV, is developed to assess the effectiveness of the proposed frequency support algorithm in power systems with high penetration of DPV inverters. The dynamic performance of the proposed frequency support algorithm with over frequency and under frequency events is also evaluated experimentally.