An Analysis of the Small-Signal Voltage Stability in MVDC Power Systems with Two Cascade Controlled DC-DC Converters

Voltage stability is an important problem in Medium Voltage DC (MVDC) power systems. A previous paper analyzed a model of a power system with one controlled load converter, achieving useful stability conditions on the controller bandwidth connected to system parameters. In this paper, a further study has been carried on, concerning the stability analysis of the two converters (the feeder buck and the load buck) with simple integral controls. The above-mentioned power system, composed by two cascaded DC-DC converters, is modelled using a fourthorder nonlinear system of differential equations. Then, the system is linearized around its equilibrium point and the input admittance is found. The Routh-Hurwitz criterion is applied to find the conditions on both controllers bandwidths that assure stability. The results are simple and of simple application. They may be very useful for what concerns the system stability analysis because the influence of the feeder controller on the load controller is made clear. Small-signals numerical simulations are used to validate the proposed model.