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The voltage source inverter (VSI) possesses several drawbacks that make it difficult to meet the requirements of automotive applications for inverter volume, lifetime, and cost. The VSI requires a very high performance dc bus capacitor that is costly and bulky. Other characteristics of the VSI not only negatively impact its own reliability but also that of the motor as well as motor efficiency. These problems could be eliminated or significantly mitigated by the use of the current source inverter (CSI). The CSI doesn't require any dc bus capacitors but uses three small ac filter capacitors and an inductor as the energy storage component, thus avoiding many of the drawbacks of the VSI. The CSI offers several inherent advantages that could translate into a substantial reduction in inverter cost and volume, increased reliability, a much higher constant-power speed range, and improved motor efficiency and lifetime.

Fuel cell-powered electric vehicles (FCPEV) require an energy storage device to start up the fuel cells and to store the energy captured during regenerative braking. Low-voltage (12 V) batteries are preferred as the storage device to maintain compatibility with the majority of today's automobile loads. A dc/dc converter is therefore needed to interface the low-voltage batteries with the fuel cell-powered higher-voltage dc bus system (255 V ∼ 425 V), transferring energy in either direction as required. This paper presents a soft-switched, isolated bi-directional dc/dc converter developed at Oak Ridge National Laboratory for FCPEV applications. The converter employs dual half-bridges interconnected with an isolation transformer to minimize the number of switching devices and their associated gate drive requirements. Snubber capacitors including the parasitic capacitance of the switching devices and the transformer leakage inductance are utilized to achieve zero-voltage switching (ZVS).

Visual Computing Systems (VCS) and Oak Ridge National Laboratory (ORNL) are partnered in a research effort to design and build a power inverter for use with an automotive accessory permanent magnet (PM) motor provided by VCS. The inverter is designed so it can fit within the volume of the housing, which is integrated with the motor. Moreover, a modular design for both the inverter and motor is employed for easily expanding the power capability to other applications. A simple back electromotive force (EMF) based position detection scheme is implemented with a digital signal processor (DSP) to eliminate the need for position sensors. Issues related to position detection errors are addressed and correction methods are suggested and implemented in DSP software. Finally, since the motor has very low inductance because of its core-less stator structure, the influences of the low inductance on the motor current ripple are analyzed.