Impact of PWM switching on modeling of low frequency power oscillation in electrical rail vehicle

For stability investigation of complex power systems, simplified system models are in need in order to reduce the model complexity and the simulation time. In this paper the effect of modelling a voltage source converter (VSC) for traction power system with and without the detailed pulse width modulated (PWM)-switch model is modeled in PSCAD and analyzed. The same disturbance is imposed for the two models and the low frequency oscillation of the DC- link voltage response is compared and analyzed. The effect of semiconductor switching on the stability limit of the system is also investigated. Furthermore, the performance of a PWM time delay compensation technique during transient is analyzed. The result shows that in the model including the switching the DC- link voltage oscillation is damped and has a better stability limit compared to the average model. In the detailed switching model a converter loss is included while in the average model a no loss ideal case scenario is considered. The delay in DC- link voltage control loop caused by the switching dead-time effect was improved by compensation of dead-time in the inverse-park transformation block of the control loop. The comparison of the compensated and non-compensated model proves that the compensated model is better in terms of the overshoot of amplitude of transient.