Modeling and Validation of Rolling Rotor Switched Reluctance Motors for Automotive Applications

Electric machines are widely used in modern automotive technologies. Generally, automotive applications require robust and low cost electric motors for the reason of their mass production and operation in different environments. Permanent magnet motors have been used in automotive applications for their high power density when compared to other existing types of motors. Recent years, the price of permanent magnets is sharply increasing and this trend is expected to continue in future. Moreover, brittle nature of permanent magnets make this type of motor less reliable in high vibration applications. Therefore, interest in switched reluctance motors (SRM) for automotive applications are increasing. These machines have number of advantages like: windings are placed only in stator and hence brushes can be excluded, permanent magnets are replaced with electromagnets. All these leads to lower cost in production and higher robustness of the motor. For high torque, low speed applications SRM must be used together with speed reduction mechanisms, resulting in larger dimensions. Even though high efficiency of the speed reduction system is a main design goal in many application, for some applications irreversibility of the speed reducer might be necessary. Rolling rotor switched reluctance motors (RRSRM) comprise all advantages of switched reluctance motors and due to rolling motion of the motor covers also the function of speed reduction mechanism. Wide range of analyzed literature on RRSRM studies, showed that there is no generalized method which allows dimensioning of this type of motor to achieve required specifications. To fill this gap the analytical model based on magnetic circuit analysis and numerical model based on finite element nonlinear analysis to study the performance of motor have been developed. The validation of the developed models was performed on a prototype of rolling rotor motor that was designed and built within the scope of the present study. Furthermore, main parameters to achieve the system irreversibility are defined by considering toothed wheels of RRSRM as an one stage cycloidal speed reducer.