Power generation systems employed in small gas engine cogeneration were examined to compare losses in the converter, which converts three-phase alternator power to direct current (DC) voltage, and losses in the inverter, which converts power to high-quality alternating current (AC) voltage that can be connected into electric utility power lines.
It is a characteristic of alternators that their efficiency and output voltage decline in the heavy load range. It was found, therefore, that step-down methods using thyristors operate in a low-efficiency range in order to provide a satisfactory supply of the targeted DC output voltage. Use of switching regulator methods, on the other hand, can generate the target voltage by regulating a switching device after first storing the alternator output in a choke coil. It was found, therefore, that these use the high-efficiency range of the alternator. The converter was found to have a resulting loss decrease of 19.4 W.
For the power switching device in the inverter, the authors turned their attention to metal oxide semiconductor field effect transistors (MOSFETs) with low on-state resistance rather than insulated gate bipolar transistors (IGBTs) with pnp structure. For the LC filter coil, they turned their attention to dust coils of alloy material, which are capable of suppressing the occurrence of eddy current loss in order to reduce iron loss. As a result, a loss decrease of 40W was confirmed when outputs were compared at the same voltage.