The stability of DC power systems feeding constant power loads

The advantages of utilising direct current electricity for the transmission of power has many acknowledged advantages and it is now receiving serious consideration for adoption in the marine and naval sectors, and design studies for future naval platforms in many of the world's navies are favouring DC. But in addition to the manifold advantages such as power transmission density, efficiency and flexibility there is one inherent weakness - stability when supplying constant power loads - which whilst not an incurable problem first needs to be understood in order that a robust design can be achieved in all operating conditions. The problem is highly non-linear and has resulted in several papers applying complex and highly arcane methodologies. However in the authors' view the problem is tractable to the ubiquitous control analysis of linearisation about a set point - even though the problem itself being a physical manifestation of hardware characteristics is not strictly within the control engineer's domain. This paper explains the source of the instability illustrates the analysis methodology, assesses a method of compensation and compares the linearised approach to a non-linear approach.