To provide a controlling method directed to magnetic fields for an electric driving apparatus having a plurality of electric motors which achieves a tensioning mechanism, particularly, the tensioning mechanism for a strand means and/or a toothed-wheel-mechanism means, and to provide an electric-motor apparatus suitable for performing the controlling method, and further, to provide a driving method of the electric-motor apparatus.

In the controlling method, two synchronous motors are connected in series with each other via their phase windings, and therein, the magnetic-pole wheels and the rotor magnetic fluxes of the two motors are rotated so as to have phase or angle differences each other. A common controlling device including a positional controller and/or a velocity controller is allocated to the two synchronous motors so as to couple it to a current converter for the starting controls thereof. Thus, the same phase currents are fed from the common current converter to the two synchronous motors, respectively.