In this paper, a nearly decentralized voltage regulation algorithm is proposed that effectively coordinates the operation of distributed generation (DG) units in order to minimize the active power losses and the total reactive power consumption in medium-voltage (MV) networks with radial topology. This control requires minimum communication infrastructure, whereas decisions are individually taken by each DG unit based on local and remote measurements. Furthermore, a new cooperative on-load tap changer control is employed to further reduce the network losses. The proposed controls are validated by time-domain and time-series quasi-static simulations in a radial MV network. The former highlights the fast response and the robustness of the proposed voltage regulation algorithm, while comparisons with well-known decentralized control schemes and an optimal power flow method show the improved performance of the proposed controls.