We develop a numerical modeling framework for planar solid-oxide fuel cell (PSOFC) based vehicular auxiliary power unit (APU). The power-conditioning system (PCS) model comprises the comprehensive transient models of PSOFC, balance-of-plant and power-electronics subsystems (i.e., BOPS and PES, respectively), and application load (AL). It can be used for resolving the interactions among PSOFC, BOPS, PES, and AL, control design and system optimization, and fuel-cell durability studies. The PCS model has several key properties including the following: i) it can predict simultaneously predict spatial as well as temporal dynamics; ii) it has two levels of abstraction: comprehensive (for detailed dynamics) and reduced-order (for fast simulation); and iii) the fastsimulation model can be implemented completely in Simulink/Matlab environment, thereby significantly reducing the cost as well as time and provides the avenue for real-time simulation and integration with vehicular power-train models using the widely used ADVISOR. We compared the computational overhead and accuracy of the fast-simulation and comprehensive models and the show significant savings in time obtained using the former without compromising accuracy.