A shaft generator system is widely used to provide sufficient power for the electric apparatus in large ships because this system can reduce fuel and operation costs. In Fig. 1 a configuration of shaft generator system is shown. This system consists of a shaft generator driven by the main engine to provide ac power needed in the ship, a thyristor rectifier, an externally commutated thyristor inverter, an AC reactor, and a synchronous compensator to feed reactive power into loads and inverter thyristors for commutation. We have already analyzed the steady-state characteristics and open-loop transient performances of this type of generating system in some detail. The output voltage and frequency of this system should be kept constant for any system conditions. However, the transient performances of the shaft generator system for the case with closed-loop control system have been investigated little.In this paper, the closed-loop control systems for constant output voltage and constant frequency of the shaft generator system are developed, and the transient performances of the systems are investigated. A basic control system for constant output voltage and constant frequency of the system is composed first. The effects of the duplex reactor, with which output voltage harmonics can be eliminated, and the controller constants on the transient performances of the system for the case of increase in the load are clarified. And experimental transient responses when the load was changed are compared with simulated results. Fig. 2 shows an example of the transient responses of the output frequency f , output line-to-line voltage V l−l when the load was increased. The steady-state operating values and other conditions for the responses are given in the figure, and the parameters for closed-loop control system are selected to keep the output voltage and frequency almost constant. From this figure, when load is increased, V l−l is decreased, and f is increased for the case of open-loop control. On the other hand, in the case of closedloop control it can be seen that f and V l−l are kept almost constant.In order to give generality to the results, average constants of the shaft generator system are chosen and the transient performances of the system having the average constants are also analyzed. It is shown that the transient responses become oscillatory for case of the system with the average constants. This oscillation can be substantially diminished by introducing current minor-loops to the control system.Main conclusions drawn from this study are as follows:(1) A basic control system for shaft generator system having two feedback loops which control the output frequency and output voltage with leading angle and field voltage, respectively, is proposed, and it is clarified that output frequency and voltage can be kept almost constant for the case with closed-loop control system.(2) The effects of duplex reactor on the closed-loop responses when the system load is increased have been investigated. It has been clarified that ...
