Modeling and twin nonlinear controller design for ac/dc voltage source converters driven dc series motors

Modeling, control design and stability of series-connected dc motors fed by three-phase ac/dc voltage source converters are investigated. The design developed in this paper results in a twin nonlinear controller structure each acting as an oscillator with damped frequency and complementary tasks, i.e. to achieve precise motor speed regulation and operation with unity power factor. An extended passivity-based analysis shows that the proposed approach guarantees the system damping which is essential for stability analysis. To this end, by using the sequence of linear time-varying approximations method, it is proven that the system with the external unknown input is attracted to the desired equilibrium. Furthermore, it becomes clear that the proposed controller does not need any measurement or knowledge of the system conditions and parameters. Stability analysis and these properties constitute the main advantages of this control design approach with respect to other existing schemes. Simulation results verify the controller performance under speed reference and load torque changes.