Complex Current Regulator Design at Low Switching Frequency for Railway Traction Applications

This paper presents a design procedure for a complex type PI current controller with active damping resistor using field-oriented control method for induction machine traction drives, intended for railway applications. In this type of applications, switching frequency must be low to keep losses at a tolerable level which introduces considerable signal delay in control system. This delay consequently has an adverse effect on the dynamics of the current control system. It produces undesired cross-coupling between the current components of d-q. When the ratio of switching frequency to stator frequency is decreased, the adverse influence become evident. The current controller design procedure compensates for the considerable signal delay and proposes analytical approach for the determination of active damping resistor by using inverter and motor characteristic parameters. Theoretical conclusions and experimental results of proposed methods are given, and the controller's reference tracking performance, insensitivity to change of system parameters and elimination of disturbances are verified by experiments performed on both laboratory and the reference vehicle.