A hydrogen generation system for fuel cell hybrid electric vehicles (FCHEVs) which generates large amount of hydrogen rapidly by hydrolysis of powdery sodium tetrahydrob-orate (NaBH ₄ ) has been proposed and developed. The system has some problems; one of the problems is difficulty of controlling the supply amount of the hydrogen which is generated by the system to a fuel cell (FC) stack. This problem may cause the degradation of the FC or the imbalance of generated electrical power between each cell because of the continuous fluctuation of the hydrogen pressure at the stack under the rapid load variation. As a solution of the degradation of FC caused by specific frequency components in the output power of the FC stack, a control method of a multiple power converter to suppress the rapid variation of the stack output power and to absorb surplus or supply shortage of the power required by inverter was proposed. In this paper, it is verified in simulations and test runs using a prototype vehicle that the proposed control can suppress the specific components in the FC stack output power and improve the performance of the hydrogen pressure control.