A method for carrying out the control of a powertrain unit by an electronic control unit of a pedal assisted electrical bicycle, wherein the powertrain unit includes: - an electrical machine having a stator and a permanent magnet rotor, being rotatable around a driving axis (M-M), the stator including a three-phase stator winding adapted to be supplied in order to cause the rotation of the rotor; - a DC/AC converter controllable in order to supply the stator winding; - a crank spindle, defining a crank axis (X-X) and a pair of pedals mechanically fastened to the crank spindle; - transmission means adapted to transmit the movement from the rotor to the crank spindle; the method including the steps of: a) starting the electrical machine in order to rotate the rotor; b) estimating a back electromotive force produced by the electrical machine; c) estimating the angular position of the rotor with respect to the stator winding starting from the estimation of the back electromotive force; d) controlling the DC/AC converter based on said estimated angular position in order to make it supply the stator winding so that said electrical machine delivers a torque; wherein: - the electronic control unit is adapted and configured to carry out said method; - said transmission means include at least one free wheel (112, 116) in order to be adapted to selectively take an engaged state or a disengaged state; and - said transmission means are adapted to selectively take the engaged state wherein said means allow transmitting the movement from the rotor to the crank spindle or the disengaged state wherein said means prevent transmitting the movement from the rotor to the crank spindle; Characterized in that - said method also includes an initial synchronization step wherein the steps b), c) and d) are carried out sequentially one or more times after starting the electrical machine in the step a), in a condition where said transmission means are in the disengaged state. - an electrical machine having a stator and a permanent magnet rotor, being rotatable around a driving axis (M-M), the stator including a three-phase stator winding adapted to be supplied in order to cause the rotation of the rotor; - a DC/AC converter controllable in order to supply the stator winding; - a crank spindle, defining a crank axis (X-X) and a pair of pedals mechanically fastened to the crank spindle; - transmission means adapted to transmit the movement from the rotor to the crank spindle; the method including the steps of: a) starting the electrical machine in order to rotate the rotor; b) estimating a back electromotive force produced by the electrical machine; c) estimating the angular position of the rotor with respect to the stator winding starting from the estimation of the back electromotive force; d) controlling the DC/AC converter based on said estimated angular position in order to make it supply the stator winding so that said electrical machine delivers a torque; a) starting the electrical machine in order to rotate the rotor; b) estimating a back electromotive force produced by the electrical machine; c) estimating the angular position of the rotor with respect to the stator winding starting from the estimation of the back electromotive force; d) controlling the DC/AC converter based on said estimated angular position in order to make it supply the stator winding so that said electrical machine delivers a torque; - the electronic control unit is adapted and configured to carry out said method; - said transmission means include at least one free wheel (112, 116) in order to be adapted to selectively take an engaged state or a disengaged state; and - said transmission means are adapted to selectively take the engaged state wherein said means allow transmitting the movement from the rotor to the crank spindle or the disengaged state wherein said means prevent transmitting the movement from the rotor to the crank spindle; Characterized in that - said method also includes an initial synchronization step wherein the steps b), c) and d) are carried out sequentially one or more times after starting the electrical machine in the step a), in a condition where said transmission means are in the disengaged state.