Stability and transient-behavioural assessment of power-electronics based dc-distribution systems. Part 2: The frequency response approach

Abstract

Ideas and developments in electrical systems are being stimulated by progress in power electronics; nowhere is this more apparent than in the marine industry. Indeed, it may be that such advances may lead to dc-distribution systems appearing once again in vessels. Concomitant with these developments is the need for new methods, or adaptation of known methods, to be found to deal with design and analysis problems that will invariably arise.The problem considered in this paper is identical to that considered in Part 1, ie that of a dc-supply feeding a constant-power load. This arrangement is one that is susceptible to stability problems. Work on this problem, using the Nyquist criterion-based method has been reported1 and, more recently, using the root-locus technique.2 This paper is concerned with tackling this same problem using frequency-response methods, specifically Bode diagrams. A stability assessment of the system can be made and some notion of the robustness of this stability ascertained.Further, it is shown that if gain and phase margins can be determined and if the characteristic response of the system is dominated by the existence of a pair of complex-conjugate roots, means of extracting the damping-factor and natural-frequency of an approximating second-order system can be easily established. Once this is achieved, transient behaviour of the system to disturbances can be estimated.