A track-bound vehicle converter for conversion between DC and AC, comprising: • a block wave generator configured to be connected to a direct voltage source and having current valves, • first control unit configured to control said current valves to generate block voltage pulses being alternatively positive and negative on an output of said block wave generator, • a series resonance link with at least one first capacitor and at least one inductance connected by a first end thereof to the output of the generator and designed to make said block voltage pulses to generate semi sinusoidal current pulses (A, B) on a second end of said link, • a direct converter comprising at least one phase leg (42-44, 70, 71) having on one hand one switch connected to said second link end and able to block voltages in both directions there-across and conduct current in both directions therethrough and on the other a second capacitor connected in series with said one switch, said direct converter having a converter output (51-53, 60, 61) between said one switch and said second capacitor for the voltage across this capacitor, • second control unit configured to control said one switch to alternatively block or let through said current pulses from said series resonance link to said second capacitor for controlling the voltage on said converter output by charging or discharging said second capacitor, said track-bound vehicle converter being further defined in that said block wave generator has two branches (24, 25) configured to be connected in parallel to a direct voltage source and each having two current valves connected in series, that each current valve has at least one semiconductor device of turn-off type and a rectifying member, such as a diode, connected in anti-parallel therewith, and that the two mid points (32, 33) between the current valves of each branch form the output of the generator, characterized in that said track-bound vehicle converter comprises a further switch able to block voltages in both directions thereacross and conduct current in both directions therethrough in a current path in parallel with said at least one phase leg, and that said track-bound vehicle converter comprises means configured to check the synchronization of the voltage of said first capacitor with the polarity of the direct voltage from the direct voltage source and a third control unit configured to control said further switch to discharge the first capacitor through said current path if said synchronization is lost and then charge the first capacitor to a voltage with the opposite polarity to obtain said synchronization again. • a block wave generator configured to be connected to a direct voltage source and having current valves, • first control unit configured to control said current valves to generate block voltage pulses being alternatively positive and negative on an output of said block wave generator, • a series resonance link with at least one first capacitor and at least one inductance connected by a first end thereof to the output of the generator and designed to make said block voltage pulses to generate semi sinusoidal current pulses (A, B) on a second end of said link, • a direct converter comprising at least one phase leg (42-44, 70, 71) having on one hand one switch connected to said second link end and able to block voltages in both directions there-across and conduct current in both directions therethrough and on the other a second capacitor connected in series with said one switch, said direct converter having a converter output (51-53, 60, 61) between said one switch and said second capacitor for the voltage across this capacitor, • second control unit configured to control said one switch to alternatively block or let through said current pulses from said series resonance link to said second capacitor for controlling the voltage on said converter output by charging or discharging said second capacitor, said track-bound vehicle converter being further defined in that said block wave generator has two branches (24, 25) configured to be connected in parallel to a direct voltage source and each having two current valves connected in series, that each current valve has at least one semiconductor device of turn-off type and a rectifying member, such as a diode, connected in anti-parallel therewith, and that the two mid points (32, 33) between the current valves of each branch form the output of the generator, characterized in that said track-bound vehicle converter comprises a further switch able to block voltages in both directions thereacross and conduct current in both directions therethrough in a current path in parallel with said at least one phase leg, and that said track-bound vehicle converter comprises means configured to check the synchronization of the voltage of said first capacitor with the polarity of the direct voltage from the direct voltage source and a third control unit configured to control said further switch to discharge the first capacitor through said current path if said synchronization is lost and then charge the first capacitor to a voltage with the opposite polarity to obtain said synchronization again.