Electric power converter arrangement and electric rolling stock control

Abstract

An electrical power converter having a phase converter constituted by positive side semiconductor switching elements connected in series and negative side semiconductor switching elements connected in series which converts a DC voltage to an AC output phase voltage having at least three potential levels, resulting in three possible modulation modes: dipolar, partial dipolar and unipolar. Dipolar modulation is realized by alternating positive and negative output pulses. Unipolar modulation is realized by output pulses having only the same polarity as the corresponding fundamental modulation wave. Transition is accomplished via partial dipolar modulation which is realized by alternating positive and negative output pulses in a first period of a half cycle by outputting alternating positive and negative pulses and in a second period by outputting pulses having only the same polarity as the corresponding fundamental modulation wave. A control unit for the converter turns the semiconductor switching elements on and off depending on an input voltage amplitude command for a fundamental modulation wave. The intervals of the first and second periods in the half cycle of the AC output phase voltage varies dependent upon the voltage amplitude command.