Hierarchical control strategy for MVDC distribution network under large disturbance

Abstract

The DC distribution technology brings challenges and opportunities to the penetration of large-scale distributed renewable energy sources. In a medium-voltage DC (MVDC) distribution network, operation mode switch occurs owing to some large disturbances. To manage these disturbances and achieve seamless switch of the operation mode, a hierarchical control strategy with two layers, namely local and global layers, is proposed in this work. The novel local layer controller called P–U–I controller is designed to enhance the voltage stability, improve system controllability and suppress overcurrent under large disturbances. This controller only needs local information and does not rely on fast communication. Furthermore, as the scale of the DC distribution network expands continuously, the number of system operation mode increases in geometric progression. Therefore, a global layer controller based on breadth-first search algorithm is proposed. This controller can automatically identify the system topology and adjust the control mode of converters to optimise the system operating characteristics. Thus, this hierarchical control strategy can accurately control the system power in steady state, suppress overcurrent under large disturbances and suit large-scale DC distribution networks. Finally, a three-terminal MVDC distribution network simulation model established on power systems computer-aided design and RT-LAB validates the proposed strategy.