Nonlinear Modeling and Identification of a DC-Motor with Friction and Cogging

In the presented work a nonlinear, analytic model of a permanent magnet direct current motors with brushes is proposed. Besides the theoretical modeling an automated identification algorithm for this detailed model is deduced. The resulting model includes the electromechanic and electromagnetic effects of the direct current machine, like voltage induction or motor torque, and additional nonlinear phenomena. These nonlinearities include cogging torque, eddy current, hysteresis losses and tribological aspects. The cogging torque is caused by a variation of the magnetic flux density, which manifests itself as a periodic oscillation in the torque curve. In addition, eddy current and hysteresis losses arise by the commutation of the magnetic field in the armature, are also captured by the motor model. The tribological aspects of all friction regimes are modeled utilizing the elasto-plastic friction model. This model can reflect the linear spring damper behavior of the elastic friction domain as well as velocity depending friction behavior of the plastic friction domain. The parameters are separately identified through specific experiments referring to their physical equivalents. Therefore, two testing benches are developed in order to capture the different effects in the direct current motor.