Transient characteristics for load changes of a doubly-fed induction generator applied to gas engine cogeneration system in stand-alone operation

Application of a doubly-fed induction generator (DFIG), which is one of variable speed generators, to a gas engine cogeneration system has been investigated. To operate during a blackout as an emergency power supply is one of important roles for the gas engine cogeneration system. However, recent lean-burn and miller-cycle gas engine, which realizes high electrical efficiency, has relatively slow response performance to load changes compared with a diesel engine. Therefore in the case of conventional constant speed synchronous generator, the amount of load input at a time is limited to 30% of the rated power. On the other hand, DFIG is expected to increase the amount of load input at a time during the stand-alone operation because DFIG generates power at constant frequency irrespective of its rotational speed. In this paper, it is demonstrated experimentally that an increase in the gas engine speed resulted in an increase in the maximum amout of load input at a time using a real gas engine. In addition, experimental results also show that disconnection of load was successfully done. These results suggest that this system will improve the performance of emergency power supply.