A method to start a voltage source converter used to convert direct voltage into alternating voltage and by that to control electric power supply from a direct voltage link to a sensorless permanent magnet motor in a vehicle in a state when a rotor of said motor provided with permanent magnets is rotating, said converter having three phase legs each comprising a series connection of at least two current valves, each comprising a rectifying member with the characater of a rectifying diode, a mid point between said current valves of each phase leg being connected either to a winding each or to the connection point between two windings of a stator of said motor through a motor disconnecting member, a separation contactor connecting the direct voltage link to an electric power supply being kept open when carrying out the method and the method comprising the following steps: a) closing said motor disconnecting members, b) measuring currents on the alternating voltage side of said converter, induced in said stator windings through rotation of the permanent magnet rotor in relation to said stator windings and flowing through the rectifying members of said current valves, c) when no current may be measured in step b) lowering the voltage of said direct voltage link by partly discharging at least one capacitor constituting said direct voltage link until currents from said stator windings may be measured, d) measuring the voltage of the direct voltage link simultaneously as the measuring of currents induced in the stator windings by rotation of the permanent magnet rotor, e) estimating the stator frequency, and by that the speed of said rotor, and the stator current angle by using the values of the currents in the stator windings measured, in which the stator current angle is estimated by using a phase locked loop with an input of on one hand said values of the currents in the stator windings and on the other hand of a value of the speed of the vehicle measured, f) calculating the position of the permanent magnets in said rotor with respect to the windings of the stator by using known parameters in the form of inductance (L d, L q) and magnetic flux (Ψ M) of the motor, the stator current and the voltage of the direct voltage link, and g) starting the converter by starting to control the current valves thereof based on information about the position and speed of the rotor calculated. a) closing said motor disconnecting members, b) measuring currents on the alternating voltage side of said converter, induced in said stator windings through rotation of the permanent magnet rotor in relation to said stator windings and flowing through the rectifying members of said current valves, c) when no current may be measured in step b) lowering the voltage of said direct voltage link by partly discharging at least one capacitor constituting said direct voltage link until currents from said stator windings may be measured, d) measuring the voltage of the direct voltage link simultaneously as the measuring of currents induced in the stator windings by rotation of the permanent magnet rotor, e) estimating the stator frequency, and by that the speed of said rotor, and the stator current angle by using the values of the currents in the stator windings measured, in which the stator current angle is estimated by using a phase locked loop with an input of on one hand said values of the currents in the stator windings and on the other hand of a value of the speed of the vehicle measured, f) calculating the position of the permanent magnets in said rotor with respect to the windings of the stator by using known parameters in the form of inductance (L d, L q) and magnetic flux (Ψ M) of the motor, the stator current and the voltage of the direct voltage link, and g) starting the converter by starting to control the current valves thereof based on information about the position and speed of the rotor calculated.