Hysteresis Current Controllers with Limited Switching Frequency for Electric Traction Systems with Asynchronous Motor and Rotor Field Orientation Control

The aim of this paper is the substantiation, implementation and validation of a principle to limit the switching frequency for the closed loop current control systems based on hysteresis controllers. The proposed system was designed for a traction system for electric locomotives based on voltage inverter and induction motor with rotor field orientation control. As the switching frequency depends on the system parameters and the chosen hysteresis band, the frequency limitation is obtained by adapting the hysteresis band on the measured mean switching frequency. This system is capable to reduce the mean switching frequency to the imposed value as the frequency controller is able to increase the hysteresis band from a minimum value to a maximum value. The switching frequency remains variable, but it is sufficiently lowered to reduce the switching losses and to avoid the power IGBTs to exceed the maximum switching frequency.