Electric power converter for railway traction vehicle

The converter (10) has a closed cooling loop (14) comprising a heat exchanger applied against an electric power component i.e. semiconductor switching unit (22). The heat exchanger comprises capillary evaporators (30A-30D), where each evaporator has a capillary wick to assure complete vaporization of coolant i.e. methanol, received at liquid state, at the level of meniscus in the wick. The coolant circulates in the cooling loop under the effect of pressure generated at the level of a liquid/vapor interface in the evaporator, for forming a capillary pumping loop.