The present invention relates to a method and a
system for controlling a permanent
magnet excited, brushless, electronically commutated, three-phase
electric motor (2) wherein a single-phase main AC
voltage (UN) having a mains frequency (fN) is rectified and supplied to an
inverter (8) via a slender intermediate circuit (6) containing no, or minimum, intermediate circuit
reactance as intermediate circuit
voltage (Uz) pulsating at double the mains frequency (2fN) which is actuated for powering and commutating the
electric motor (2). Control takes place by means of a field-oriented current-
space vector regulator, wherein a q-current (iq) as torque-forming component of the current-
space vector (i) is regulated perpendicularly to the permanent
magnetic field and a d-current (id) can be regulated as a field-influencing component of the current-
space vector (i) in the direction of the permanent
magnet field. In this case,
dynamic field attenuation occurs, wherein the d-current (id) in the negative range is defined with a sinusoidal profile and at double the main frequency (2fN) and wherein the d-current (id) is regulated according to its phase position and its amplitude such that
ripple of the q-current (iq) is minimized. Since the q-current as torque forming component is proportional to the torque, thus the
torque ripple is also minimized, in
spite of the strongly pulsating intermediate circuit
voltage (Uz).