Diesel generator based auxiliary power units (DG-APU) are commonly used in military and civil applications as energy sources. In typical 28V systems, DG-APU is combined with Lead-Acid batteries (LAB) to maintain supply stability and allow engine starting. Synchronous generator-based DG-APUs employ automatic voltage regulators in order to regulate its output voltage. Consequently, such a unit may be controlled by varying the throttle position only, which is a difficult procedure that demands high precision actuators in addition to fast and robust control. According to the manufacturer provided specific fuel consumption (SFC) curve, high load operation results in much higher SFC than low-load operation. Nevertheless, most of the battery charging process in typical systems is conducted under low load. Consequently, instead of controlling the throttle, simple on/off method is proposed in the paper in order to utilize the DG-APU under high loads only. The main goal of this method is to keep the engine operating under heavy load for a short period of time thus achieving high efficiency of fuel consumption. Such an operation allows to minimize fuel consumption as well as to reduce operation time. The latter would obviously improve the machine wear and increase maintenance period time. Experimantal results are given to verify the proposed method.
