Patent ID: 7554279

Claim:
A method of operating an electronically commutated motor ( 20 ) on a DC power network, which motor includes a permanent-magnet rotor ( 22 ); a first series circuit ( 40 ) in which a first stator winding strand ( 30 ) is connected in series with a first controllable semiconductor switch ( 34 ); a second series circuit ( 50 ) in which a second stator winding strand ( 32 ) is connected in series with a second controllable semiconductor switch ( 44 ); which two series circuits ( 40 , 50 ) are connected in parallel to form a parallel circuit ( 52 ); a third controllable semiconductor switch ( 60 ), arranged in a supply lead to said parallel circuit ( 52 ), for controlling energy supply to the motor ( 20 ) from the DC power network; comprising the steps of: alternately, influenced by a rotational position of the rotor, activating the possibility of energy supply from the DC power network to one winding strand during a potential current-flow phase, and deactivating the possibility of energy supply from the DC power network to the other winding strand during said potential current-flow phase, the potential current-flow phase of the one winding strand being separated in time, by a respective commutation procedure, from the potential current-flow phase of the other winding strand; during a potential current-flow phase, at a switchover instant (t 64 ) switching over the third controllable semiconductor switch ( 60 ), for the purpose of initiating a commutation procedure, from a conductive into a non-conductive state, in order to interrupt energy supply to said winding strands from the DC power network; maintaining in a conductive state whichever semiconductor switch ( 34 , 44 ) was conductive at the switchover instant (t 64 ), so that, after blockage of the third controllable semiconductor switch ( 60 ), a circulating current (i 31 ) flows in the parallel circuit ( 50 ) and thereby generates a driving torque in the motor; monitoring amplitude of said circulating current; when said circulating current reaches a predetermined low absolute value (|i 31 |), blocking that one of said first and second semiconductor switches which was hitherto conductive; depending on the rotational position of the rotor ( 22 ), as part of a commutation procedure, deactivating the potential current-flow phase of the one strand, and activating the potential current-flow phase of the other strand; and again switching on the third semiconductor switch ( 60 ), in order to reactivate the possibility of energy supply to the motor ( 20 ) from the DC power network.