Offshore wind generation currently provides 7% of the total installed capacity in the UK. This is set to increase significantly in the coming decade as the Crown Estate releases larger swathes of coast and seabed for development. The increasing penetration of offshore wind and other renewable sources is changing the traditional energy mix and adding very fast, low inertia power electronic systems to a traditionally slower, high inertia network. Given the large number of planned voltage-source converter based high voltage direct current (VSC-HVDC) links, and the rapid scheduled rollout of the technology, utilities and government have an urgent need for improved information in this area. A key weakness is that presently most public domain research and development on VSC-HVDC is based on simplified simulation models which may not always capture key hardware complexities and realistic converter operation. The research presented in this thesis includes the development of a low-power modular multilevel converter (MMC) with an industrially representative control architecture which has been designed to investigate these complexities, and provide a platform for future research. In this thesis, the design, construction, programming and testing of a MMC hardware prototype (CHP) is discussed in detail, providing a contribution to public-domain knowledge on the technology and enabling other institutions to bridge the gap into hardware research. Hardware outputs from the CHP have been compared against simulation results from a matching detailed equivalent model (DEM) to study the impact of real internal converter control on power system simulation fidelity. A time delay associated with the internal control systems has been identified and quantified as a useful additional element to achieve more accurate models, and this has been analysed in detail. The time delay indicates a requirement for limits on the bandwidth of outer controllers and impacts the converter response rate to network transients. A simple method to incorporate this delay into a PSCAD/EMTDC simulation is then discussed, assisting in the improvement of power system simulation models.