Toyota Motor Corporation has been actively pursuing the development of fuel cell vehicles (FCVs) to respond to global environmental concerns and demands for clean energy. Toyota developed the first fuel cell (FC) bus to receive vehicle type certification in Japan. Subsequently, a new FC bus has been developed, which adopts two FC systems and four high-voltage batteries to achieve the required high power performance and durability. For enhanced durability, the FC system is controlled to maximize usage of the high-voltage batteries and to reduce the number of electric potential changes of the fuel cell. To accomplish this, the voltage of the FC stack must be kept high and FC power must be kept low. The high-voltage batteries were used to actively minimize FC power during acceleration. When the high voltage battery cannot supply power because of a low battery state of charge (SOC), such as during a long hill climb, the lower limit voltage of the FC is temporarily reduced to increase the FC power. A lifetime durability test was carried out, including conditions under which the high-voltage battery cannot supply power, and it was found that the FC power reduction rate was improved.
