Topology comparative assessment for hybrid medium-voltage AC/DC networks

Recently, there has been significant growth in integrating renewable energy generation and electric vehicles and deploying new technologies into the electrical networks, leading to new challenges for planning, design, operation, control and protection of the distribution grid. In particular, an increasing amount of large-scale DC load and generation is expected to be connected to the distribution system, especially at the MV level. Thus, adoption of new grid topologies is required and among others, hybrid AC/DC networks have emerged as an attractive pathway to meet new grid operational requirements. This paper evaluates future hybrid AC/DC distribution systems at the MV level, considering potential network topologies and new technologies. Steady-state analysis is performed to compare five topologies of hybrid MV AC/DC networks. Key technologies for such hybrid grids such as voltage source converters and fast charging stations are considered. The results provide quantitative comparisons between topologies regarding large-scale DC load and generation integration capability, contingency operation, sensitivity analysis. Several challenges presented to the protection and fault location that are caused by the adoption of new topologies are also identified. The topologies are compared by network losses, voltage and power factor constraints, analysing the different benefits and drawbacks of the hybrid AC/DC topologies.