A mathematical model of a ship's electrical power system

The work described in this thesis concerns the time-domain simulation of various items of plant for a limited-size electrical power system. Initially an isolated 3-phase synchronous generator is considered, with the electrical equations being expressed in the phase reference frame, since this copes easily with both unbalanced fault and load switching conditions. The study looks at theoretical results for a 3-phase short circuit test on a generator as provided by the computer model and by a conventional dqo approach. In addition, the generator model is used in investigations of various unbalanced load conditions. The single generator study is then extended to a multi-generator power system, and models for the following items of plant are developed: a) A 3-phase synchronous generator driven by a diesel engine. The engine is governor speed controlled, and the generator has an automatic voltage regulator CA VR) to maintain a constant generator output voltage. b) A motor/generator set, comprising a 3-phase synchronous machine, mechanically coupled to a separately-excited dc machine. c) Section switches and a bus-coupler, which may be switched both in or out during the simulation. d) A fully controlled 3-phase bridge converter with back-to-back thyristors, which is capable of both rectification and pulse-width-modulated (PWM) inversion. A method of numerical analysis based on Kron's diakoptic approach is used to investigate the behaviour of the complete system. For the purpose of calculation the system is torn into 5 sub-networks and for each separate sub-network a set of differential equations is solved. Using numerical data derived from each sub-network, the currents and voltages of the complete system are then obtained using inverse transformations. Finally, the performance of the system is illustrated by considerations for a variety of balanced and unbalanced switching conditions.