This paper presents a complete review of MVDC applications and their required technologies. Four main MVDC applications were investigated: rail, shipboard systems, distribution grids, and offshore collection systems. For each application, the voltage and power levels, grid structures, converter topologies, and protection and control structure were reviewed. Case studies of the varying applications as well as the literature were analyzed to ascertain the common trends and to review suggested future topologies. For rail, ship, and distribution systems, the technology and ability to implement MVDC grids is available, and there are already a number of case studies. Offshore wind collection systems, however, are yet able to be implemented. Across the four applications, the MVDC voltages ranged from 5–50 kV DC and tens of MW, with some papers suggesting an upper limit of 100 kV DC and hundreds of MV for distribution networks and offshore wind farm applications. This enables the use of varying technologies at both the lower and high voltage ranges, giving flexibility in the choice of topology that is required required.

Electricity grids are seeing dramatic changes due to increased power converter penetration, causing variations in grid strength, X/R ratio, and new dynamic bandwidths, which present stability challenges that need to be captured in models. The use of appropriate modelling techniques is critical to achieve an accurate stability assessment; however, it is also important to balance this accuracy with computational burden. This paper compares three key small signal models of a grid following converter; a full detail small signal model, a model order reduction (MOR) method, and a simplified phasor model. They are compared for their ability to represent transient accuracy, eigenvalue stability and identifying the presence of key modes that could cause sub-synchronous oscillations. Previous literature has failed to define the bandwidth and accuracy of the different modelling approaches in specific conditions. This paper addresses the need for parametric sensitivity studies, and presents a methodology of evaluation of lower detail models, for highlighting instability, and the sub-synchronous, oscillatory modes that low detail models fail to capture, even when they are expected to. Results show that the MOR performs slightly better than the simplified phasor model, however, both fail to capture critical stability information regarding oscillatory modes at sub-synchronous frequencies in certain parameter conditions. Additionally, they both have reduced accuracy in representing system instability, especially at low short circuit ratios, when the full detail model should be used.

The global transition to renewable energy is transforming power systems, necessitating advanced transmission solutions to ensure reliability and resilience. High-voltage direct current (HVdc) systems, particularly multiterminal dc (MTdc) networks, are pivotal in integrating diverse renewable energy sources into hybrid ac/dc networks. These systems facilitate efficient power transfer over long distances and enable dynamic energy sharing across regions. However, the increasing penetration of inverter-based resources introduces complex control challenges that must be addressed to maintain grid stability and resilience.