A power converter apparatus for an electric train, including at least a first modular power converter unit having a main circuit formed of switch for interrupting power from a D.C. power source, a first D.C.-A.C. power converter connected to the switch, an isolation transformer connected between the D.C.-A.C. power converter and a rectifier and a second D.C.-A.C. power converter connected to the rectifier. The switch and the first D.C.-A.C. power converter are controlled by a control signal derived from the difference between the output voltage of the first D.C.-A.C. power converter and the sum of a delayed soft starting control signal and a settable reference signal. The second D.C.-A.C. power converter is pulse width modulated. Preferably a second modular power converter unit having the same construction as the first unit is provided and has inputs connected in series or in parallel with inputs of the first unit. Load balance between the power converter units is maintained by detecting the output current of each unit and utilizing the detected output currents in conjunction with the control signal used to control switching of the switch and the first D.C.-A.C. power converter.
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