This paper includes the development and validation of a dynamic model suitable for control design and stability analysis of a HVDC diode-based rectifier grid connection for offshore wind power plants. The modular design of the model allows for a relatively easy extension to different grid topologies and control strategies. The developed models include the effects of communication delays and a non-stationary off-shore ac-grid frequency. The developed models have been validated with detailed PSCAD/EMTDC simulations (including distributed cable models). The developed model has been used to carry out a detailed study on the effects of parametric uncertainty on the dynamic stability.