Interconnecting Power Converter Control Role Assignment in Grids With Multiple AC and DC Subgrids

In emerging Multi-Terminal High Voltage Direct Current (MT-HVDC) systems interconnecting different Alternating Current (AC) asynchronous areas by means of Interconnecting Power Converters (IPC) different challenges arise. One of them is the control role assignment of IPCs present in these systems. Broadly speaking, the IPC controls can be classified into grid-forming or grid-following schemes for both AC and DC terminals of IPCs. This paper presents a methodology to optimize the control role assignment of the IPCs considering i) small-signal stability and, ii) control performance for different combinations of IPC roles and network power flows. The method considers multiple power flows, determines the steady-state deviations, and small-signal stability following selected events. While presenting this methodology different results on the small-signal and steady-state analysis of these systems are analyzed. Using high-fidelity linearized dynamical models, an optimization problem is formulated to assign control modes to IPCs to ensure stability and performance of the system for a set of given power flow scenarios.