ABSTRACT: The advancement of automobile technology has taken great strides in recent years with the popularity of pure-electric vehicles and hybrid-electric vehicles. These vehicles are in demand because of consumer and government requirements for a cleaner more fuel efficient vehicle. These advancements toward an electric and hybrid vehicle marketplace affect many areas of the automobile. One area that is affected is the automobile. s power steering system. Conventional power steering systems provide assist to the driver of the automobile by using hydraulic pressure that is created by a pump that is directly connected to the engine. This hydraulic pump is continuously putting a load on the engine even when zero steering assist is required. This type of power steering system includes parasitic losses that decrease the fuel efficiency of the car. Also, in some cases, particularly with a pure electric vehicle there is no engine to drive a hydraulic pump. Hence, there is a need for an engine independent power steering system. One solution that fits this need is the Electric Power Steering (EPS) system.
An EPS systems consists of a assist motor, an electronic controller, and a mechanism to interface with the manual steering system. Considering that the EPS system must be compact, safe, reliable, and efficient, design consideration centers upon the motor used to create the power steering assist. This study centers on the design, Finite Element Analysis (FEA), and Parameter Estimation of Brushless Permanent-
Magnet Motors (BPMM). BPMM' s are considered an ideal choice to be used in EPS systems because they are efficient, reliable, small and powerful.
This study first considers the design requirements for a BPMM to be used in an EPS system. Next, based upon these requirements a motor is designed using a set of empirical relations. Once the motor is designed, which includes material type and motor geometry, the BPMM is analyzed using FEA. FEA is used to verify that the motor meets the design requirements specified by the customer. Finally, after the motor has been designed and analyzed using FEA, the motor is built and a dynamic circuit model is established. The dynamic model is based upon a dq-axis circuit with a generic structure and unknown parameters. The model structure is identified and its parameters are estimated using stand-still input-output test data. This study was performed using a variable speed, 12 Volts (18V max), 0.4 Horsepower (300W), 3 phase Y-connected, four pole, 24 slot brushless permanent-magnet motor.
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