The invention provides a power grid frequency modulation device applied to a photovoltaic direct current side. The device comprises an energy storage connecting terminal, a low-voltage direct-currentbus, a charging circuit, a discharging circuit, a high-voltage direct-current bus, a charging and discharging connecting terminal and a controller, wherein the energy storage connecting terminal is used for connecting an energy storage battery, a charging and discharging control unit is used for connecting a photovoltaic module and a photovoltaic inverter in parallel, the charging circuit and thedischarging circuit are connected in parallel between the low-voltage direct-current bus and the high-voltage direct-current bus, the energy storage connecting terminal is conductively connected withthe low-voltage direct-current bus, and the charging and discharging control unit is connected with the high-voltage direct-current bus, and the controller is connected with the charging circuit and the discharging circuit and used for controlling the charging circuit and the discharging circuit to work. When the device is applied to a photovoltaic power grid, the upper limit and the lower limit of adjustment of the photovoltaic inverter can be improved, moreover, the power grid frequency modulation device applied to the photovoltaic direct-current side is applied to the photovoltaic direct-current side, and the device is simple to install and low in cost, and facilitates transformation of a photovoltaic power grid in the prior art.