In this thesis, several design methodologies are presented to improve the reliability of dual traction inverters in hybrid electric vehicles (HEVs). Several power inverter topologies including the two-level voltage-source inverter, the boost voltage-source inverter, the Z-source inverter, and reduced-parts inverters are compared in terms of power ratings, volume, and efficiency. The comparison results show that the two-level voltage-source inverter presents higher efficiency, higher power density, and lower cost. Therefore, the back-to-back two-level voltage-source inverter is selected. DC-link capacitor and power modules are the most vulnerable components in dual traction inverters. The lifetime of capacitor is mainly determined by the core temperature. In this thesis, an interleaving control scheme is proposed to reduce the capacitor power loss by decreasing the total DC-link current harmonics. With reduced capacitor power loss, the core temperature of capacitor is reduced. Therefore, the lifetime of capacitor is improved. In addition, a fast electro-thermal model of traction inverters is proposed to estimate the junction temperatures of power devices. Practical switching losses are measured and thermal coupling effects between multiple devices are considered. The calculation rate of junction temperature is reduced by considering both power loss profiles and properties of the thermal impedance. With this model, over-temperature protection and lifetime evaluation can be implemented to enhance the reliability of traction inverters. Finally, a current sensor fault-tolerant operation scheme with six-phase current reconstruction technique is proposed to improve the reliability of dual inverters. In order to get the missing phase currents, the PWM signals are phase shifted to create the reconstruction conditions. With measured DC-link current, all phase-currents of dual inverters are obtained at the expense of slight degradation of maximum allowable modulation index. Therefore, when some or all of the phase current sensors are failed, the dual traction inverters can operate normally. / Thesis / Doctor of Philosophy (PhD)