Method for detecting the rotor position of an electric machine, and device for the same

#The invention generally relates to the detection of the rotor position, particularly for electronically commutating an electric motor with the aid of the detected rotor position.

#The electronic commutation of electric machines requires knowledge of the absolute angular position of the rotor, the rotor position. The rotor position can be detected by means of suitable sensors such as, e.g., incremental-resolution rotary transducers, Hall sensors etc. Alternative position detection arrangements manage without position sensors by evaluating, e.g., the phase current or the phase voltage of a winding phase of the stator winding and calculating the rotor position by suitable methods. For example, the rotor position can be determined in such a method by evaluating the third harmonic of the variation of a phase current or of a phase voltage with the aid of the “Back-EMF method” and the like.

#The methods for detecting the rotor position on the basis of the evaluation of the phase current or of the phase voltage, however, have the disadvantage that they do not, or only with inadequate accuracy, detect the rotor position at low rotational speeds and/or at very high rotational speeds or in the case of a load, so that an electronic commutation based on a rotor position detected in this manner is not reliably possible at low rotational speeds. For example, during the determination of the rotor position by evaluating the third harmonic, the latter is distorted by saturation effects and differences therebetween, as a result of which it becomes unanalyzable. At high rotational speeds, the “Back-EMF method” can no longer be used since there are no longer any currentless time domains in this method.

#In the text which follows, preferred embodiments of the invention will be explained in greater detail with reference to the attached drawings, in which:

#FIG. 1 shows a diagrammatic block representation of a motor system having a device for operating an electric machine; and

#FIG. 2 shows a diagrammatic block representation of the determination of the rotor position in the motor system of FIG. 1.

#FIG. 1 shows a diagrammatic block representation of a motor system 1 having a synchronous motor 2 as electric machine. The synchronous motor 2 has three phase windings (not shown) which are driven by an inverter 4 by corresponding phase lines 3. The inverter 4 receives an actuating variable S externally which is used for specifying the torque of the synchronous motor. Furthermore, the inverter can also receive information about or a nominal rotational speed (set rotational speed). Furthermore, the inverter 4 receives a drive signal via a signal line 5 for operating the synchronous motor 2.

#Furthermore, a control device 6 is provided which outputs the drive signal via the signal line 5 to the inverter 4. The control device 6 comprises a calculating unit 7 for calculating the magnet-wheel flux. For this purpose, the calculating unit 7 receives a phase current from a current detector 8 which has, e.g. a sensing resistor (shunt) and also determines the phase voltage u1 at the same phase at which the phase current is also determined. The phase voltage can be measured directly or derived from the pulse-width-modulated drive signal, e.g. via the corresponding pulse duty ratio. Phase voltage u1 and phase current i1 are provided to the calculating unit 7, which determine the magnet-wheel flux in accordance with the formulae

#U 1  ( t ) = U p  ( t ) + L   i  ( t )  t + R * l  ( t ) ( 1 ) U 1  ( t ) = U p  ( t ) + L   l  ( t )  t   ϕ p  ( t ) = ϕ 1  ( t ) - L * l 1  ( t )   with ( 2 ) ϕ = ∫ u   t ( 3 )