As penetration of distributed generation increases, the electrical distribution networks may encounter several challenges mainly related to voltage control. The situation may deteriorate in case of a weak grid connected to an intermittent source such as photovoltaic (PV) generation. Fast varying solar irradiance can cause unacceptable voltage variations that may not be easily compensated by slow-responding utility equipment. The PV inverter can be used to control the grid voltage by injecting/absorbing reactive power. A small-signal model is derived in order to study the stability of a PV inverter exchanging reactive power with the grid. This paper also proposes a method that utilizes the available capacity of the PV inverter to support the grid voltage without violating the rating of the inverter and the maximum voltage that the inverter's switching device can withstand. The method proposed in this paper is validated using PSCAD/EMTDC simulations.