Increasing amounts of distributed generation (DG) connected to distribution networks may lead to the violation of voltage and thermal limits. This paper proposes a virtual energy storage system (VESS) to provide voltage control in distribution networks in order to accommodate more DG. A VESS control scheme coordinating the demand response and the energy storage system was developed. The demand response control measures the voltage of the connected bus and changes the power consumption of the demand to eliminate voltage violations. The response of energy storage systems was used to compensate for the uncertainty of demand response. The voltage control of the energy storage system is a droop control with droop gain values determined by applying voltage sensitivity factors. The control strategy of the VESS was applied to a medium-voltage network and the results show that the control of the VESS not only facilitates the accommodation of higher DG capacity in the distribution network without voltage violations or network reinforcements but also prolongs the lifetime of the transformer's on-load tap changer.