This paper presents a six-pulse low frequency (LF) fluctuating high voltage dc bus based power system architecture for the fuel cell vehicles (FCVs) application. A novel hybrid modulation techniques consisting of six-pulse modulation (SPM) at LF scale and secondary modulation and 33% sine pulse width modulation (33% SPWM) at high frequency (HF) scale. Three-phase ac waveforms are produced for the propulsion system in FCVs. It significant reduces the switching losses of the bidirectional dual-stage inverter: 1) the zero current soft switching (ZCS) of primary side devices and zero voltage soft switching (ZVS) of secondary side devices of front-end current-fed full-bridge converter is realized. 2) at any moment, only one leg of back-end 3-phase inverter is switched at HF while the other two legs are kept in on or off state. This tremendously reduces the bidirectional inverter's switching losses and improves the system efficiency. Besides, switching loss can be further reduced since all the inverter switches are switched at the low current range. The LF fluctuating high voltage dc bus allows the elimination of large electrolytic dc-link capacitor. This paper presents the operation, analysis, and design of a bidirectional inverter implementing the proposed hybrid modulation technique. Simulation results obtained from power electronics simulation software PSIM and experimental results from the lab prototype clearly validate the effectiveness of the proposed modulation technique.