Multi-terminal HVDC grids based on voltage source converters have been considered a good solution to transmit great power bulks coming from different renewable energy sources. Therefore, it is important to generate useful models that contribute to the operational study of such systems. In particular, it is important to make good use of droop schemes, since these are essential for achieving a correct operation. The main contribution of this article is the development of a combined model based on optimal power flow for radial multi-terminal HVDC grids. This model comprises two sub-models. The first sub-model, which considers the droop scheme associated to the active power loop, is established with the objective of minimizing losses over the DC lines. On the other hand, the second sub-model, which considers the droop scheme associated to the reactive power loop, is established with the objective of minimizing the total apparent power in converter stations and, consequently, minimizing their total losses. The combined model allows selecting the parameters and references associated to both droop schemes. The case study presented shows that the use of the combined model results in a correct grid operation, highlighting the contribution to the needs of the AC grid while maintaining the operational restrictions of the entire system. The simulations are obtained using MATLAB/SIMULINK.