Stochastic harmonic analysis of mass rapid transit power systems with uncontrolled rectifiers

The stochastic harmonic distortion of a mass rapid transit (MRT) system is investigated by considering the dynamic load behaviour of train sets. A mathematical model of 12-pulse uncontrolled rectifiers without interphase transformers is derived and applied to the harmonic load flow analysis to workout the power demand and the harmonic injection currents at traction substations for each time snapshot. According to the mean values and standard deviation of harmonic currents, the stochastic harmonic load flow analysis is performed to find the average and the confidence interval of harmonic voltage distortion for all system buses. A comparison with the conventional harmonic load flow analysis, which considers only the average load demand and the mean harmonic injection current, reveals that the method proposed can evaluate the voltage harmonic distortion of the system more accurately to provide better guidance for the strategy of harmonic mitigation.