Influence of DC-DC load converter control bandwidth on small-signal voltage stability in MVDC power systems

Voltage stability is a key problem in Medium Voltage DC (MVDC) power systems. A model of a power system able to give proper stability information as a function of load converters control bandwidth is of fundamental importance, particularly if simple and of simple application. In this paper, a notional system composed by two cascaded DC-DC buck converters is considered. It is modeled at small-signals around its equilibrium point first using a complete model and then it is simplified in order to obtain the well-known Constant Power Load (CPL) model. Furthermore, an intermediate (reduced-order) model between the complete one and the CPL is proposed, which is able to show proper conditions on the load converter bandwidth to assure stability. Small-signals numerical simulations are used to validate the proposed complete and reduced-order models comparing results.