Development of a Sensor-Less Speed Control Inverter for an Automotive Accessory Permanent Magnet Motor

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. This analysis is used to design a fast current control loop for the inverter to cope with the low inductance. Analytical and experimental results are included to verify the proposed schemes.