METHOD FOR OPERATING AN ELECTRIC MACHINE, CONTROL DEVICE AND ELECTRIC MACHINE - Patent application

Abstract

The invention relates in particular to a method for operating an electric machine (5) of a turbocharger (1), the electric machine (5) having multiphase drive windings, the drive windings being energized by sinusoidal commutation in at least a first rotational speed range as a function of the angular position of a rotor (7) of the electric machine (5), the angular position of the rotor (7) being determined as a function of the phase currents induced in the drive windings by the rotor, in order to generate torque, the drive windings being energized by square wave commutation in a second rotational speed range below the first rotational speed range.

Description

[Technical field]

[0001] The invention relates in particular to a method for operating an electric machine of a turbocharger, the electric machine having a stator with multi-phase drive windings and a rotatably supported rotor, in which the drive windings are energized by sinusoidal commutation at least within a first rotational speed range as a function of the angular position of the rotor in order to generate torque, the angular position of the rotor being determined as a function of the phase currents induced in the drive windings by the rotor.

[0002] Furthermore, the invention relates to a control device for operating an electric machine as previously described, the control device being adapted to implement the previously described method.

[0003] Furthermore, the invention relates to an electric machine equipped with a control device of the above mentioned type.

[0004] Furthermore, the invention relates to a turbocharger comprising at least one compressor wheel mounted non-rotatably on a shaft and an electric machine as described above for driving the shaft. [Background technology]

[0005] Background technology The method, the electric machine and the turbocharger with an electric machine in the above-mentioned form are already known from the prior art. In order to ensure a high drive torque even at low engine speeds, it is known to precede the engine with a turbocharger having a compressor that can be driven by an electric motor. The drive by the electric motor makes it possible to adjust the air supply into the cylinders of the engine independently of the exhaust gas flow rate of the engine. This distinguishes the turbocharger driven by the electric motor in terms of its dynamic behavior from a simple exhaust gas turbocharger driven by the exhaust gas flow of the engine. It is also known to combine the exhaust gas turbocharger with an electric auxiliary drive and to integrate an electric machine in the exhaust gas turbocharger in order to decouple the compression characteristic of the exhaust gas turbocharger from the corresponding exhaust gas flow of the engine. Ideally, this electric machine is already able to provide the maximum torque at low engine speeds of the turbocharger, in particular from standstill to maximum engine speed. In order to electronically commutate the electric machine, it is therefore essential to know the instantaneous angular position of the rotor (rotor position). It is known to determine this angular position as a function of the voltage induced in the drive windings in the reverse direction by the rotational movement of the rotor, the so-called "back emf". For this purpose, the induced phase currents of the drive windings are evaluated. In order to achieve high power outputs of the electric machine, it is further known to drive the electric machine by sinusoidal commutation, at least within a certain speed range. Summary of the Invention [Means for solving the problem]

[0006] Disclosure of the Invention The method according to the invention having the features of claim 1 has the advantage that an accurate rotor position determination is easily ensured even at low rotational speeds. Furthermore, the overall power of the electric machine is increased. For this purpose, it is specified according to the invention that the drive windings are energized with square-wave commutation in a second rotational speed range below the first rotational speed range. At higher rotational speeds, i.e. in the first rotational speed range, the already used sinusoidal commutation is maintained, whereas at lower rotational speeds, i.e. in the second rotational speed range, a switchover to square-wave commutation is made. This achieves the avoidance of fault signals due to branch interruption times which prevail at low rotational speeds with high phase currents due to sinusoidal commutation at low rotational speeds. The resulting current plateaus at the zero crossings of the phase currents due to this fault signal are shortened or completely avoided. As a result, fault voltages induced in the drive windings and which lead to errors in the back emf are reduced in the stator circuit.

[0007] According to a preferred embodiment of the invention, the second speed range starts at zero speed, i.e. at standstill, whereby the lowest speed range of the electric machine is square-wave commutated and thus advantageously achieved.

[0008] Furthermore, the second speed range is preferably specified up to the lowest speed of sinusoidal commutation at which the angular position of the rotor can be reliably or sufficiently accurately determined (in terms of the accuracy of the angular position) by the back EMF. That is to say, the upper limit of the second speed range is selected at which it is possible to reliably use the conventional method of sinusoidal commutation based on determining the angular position of the rotor by the back EMF. This speed can be determined for all types of electric machines, for example by tests or calculations. This is achieved by using reliable square wave commutation in the speed range where it is not possible to reliably perform sinusoidal commutation, and by performing sinusoidal commutation in the speed range where it is possible to reliably perform sinusoidal commutation, ensuring the maximum power of the electric machine.

[0009] Preferably, a square wave commutation of 120° is used in the second speed range, as this allows an advantageous estimation of the back EMF.

[0010] In particular, this form of square wave commutation is used in three-phase drive windings, where one of the phase drive windings is always de-energized and it is therefore clear that the back EMF induced in this phase is well suited to detecting rotor position.

[0011] Preferably, the rotor position is determined according to the progression of the induced voltage in the de-energized phase.

[0012] Alternatively, it is preferred that the course of the induced voltage is determined by an additional sensor winding on the stator side, which has the advantage that the coil ends of each additional sensor winding are available to the downstream electronic device without potential restrictions.Several sensor windings are connected, for example, at a neutral point.

[0013] Preferably, a voltage divider and a filter or a Zener diode are used to determine the angular position. After suitable voltage division and filtering, in particular the zero crossings of the induced voltage are detected. Alternatively, in the case of clocked square wave commutation, the detection of the zero crossings can be performed during the pulse pauses, preferably at the end of each pulse. This simplifies the dissipation of wiring. That is, instead of the voltage divider and the filter, the aforementioned Zener diode is used, preferably with a suitable electrical resistance. To evaluate the zero crossings, the voltage drop through the Zener diode is taken into account.

[0014] The control device according to the invention having the features of claim 10 is distinguished in that it is specially adapted to carry out the method according to the invention as described above, thereby obtaining the advantages already mentioned.

[0015] An electric machine having the features of claim 11 is distinguished by a control device according to the invention, which provides the advantages already mentioned.

[0016] A turbocharger according to the invention having the features of claim 12 is superior to an electric machine according to the invention for driving a shaft, which gives rise to the advantages already mentioned.

[0017] Further advantages and preferred features and feature combinations emerge from the foregoing and from the claims.The invention will now be described in greater detail with reference to the drawings, in which:FIG. [Brief description of the drawings]

[0018] [Figure 1] 1 is a simplified diagram of a turbocharger. [Diagram 2] FIG. 2 shows the output electronics of a control device for operating a turbocharger. [Diagram 3] FIG. 1 illustrates advantageous square wave commutation. [Figure 4] FIG. 1 shows an advantageous configuration of a control device. [Diagram 5] FIG. 4 shows another advantageous configuration of the control device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] In Figure 1 a turbocharger 1 for an internal combustion engine of a motor vehicle (not shown) is shown in a simplified diagram. The turbocharger 1 has a housing 2. In the housing 2 a shaft 3 is rotatably mounted. The shaft 3 carries at one end a compressor wheel 4. The compressor wheel 4 can be supplied with a gas flow in the axial direction, which gas flow is compressed and forced out of the housing 2 in the radial direction, as indicated by the arrows.

[0020] Furthermore, the turbocharger 1 comprises an electric machine 5. This electric machine 5 comprises a stator 6 which is stationary with respect to the housing and a rotor 7 which is arranged on the shaft 3 so as not to rotate relative to it. The stator 6 comprises a multiphase drive winding, in the illustrated embodiment a three-phase drive winding with the phases U, V and W. By energizing the phases U, V and W, a stator magnetic field is generated. This drives the rotor 7 and thus the shaft 3 and the compressor wheel 4. For this purpose, a control device 8 is provided which controls the phases U, V and W.

[0021] 2 additionally shows in a simplified diagram the power electronics 9 of the control device 8. The power electronics 9 comprises a B6 bridge circuit with three half-bridges 10, 11, 12 each with two semiconductor switches TH10, TL10, TH11, TL11, TH12, TL12 that can be controlled by the control device 8. The half-bridges 10, 11, 12 are each connected to one of the phases U, V, W.

[0022] Maximum RPM n max Up to, n x From max In a first speed range up to 1000 rpm, the phases U, V, W are controlled by sinusoidal commutation. However, at low speeds, the sinusoidal commutation results in fault signals due to branch interruption times that predominate at lower speeds under high phase currents. Undesirable current plateaus then occur at the zero crossings of the phase currents. These current plateaus cause additional voltage ripples in the stator or stator circuit, which in turn cause errors in the back EMF and thus in the rotor angle detection. Thus, in the illustrated embodiment, the phases U, V, W are controlled by sinusoidal commutation from n0 (where n0=0) to n x In a second, lower speed range up to 100 rpm, the phases U, V, W are controlled by square wave commutation.

[0023] In addition, in Fig. 3, a 120° square wave commutation is shown in a simplified diagram for the phases U, V, W in the second speed range. With three phases and a 120° square wave commutation, it is achieved that one of these phases is de-energized. This phase is then used during the rotational operation and the (rotational) angular position of the rotor 7 is determined as a function of the back EMF induced in this phase by the rotor magnetic field. This angular position is determined via the course of the induced voltage in the de-energized phase.

[0024] Alternatively, the course of the induced voltage is detected via a sensor coil additionally arranged on the stator 6. This has the advantage that both coil ends of each sensor coil are available potential-free to downstream evaluation electronics.

[0025] In addition, the sensor coil system is shown in a simplified diagram in FIG. 5. Each phase U, V, and W has one sensor air-core coil H U ,H V ,H W are assigned to the sensor coils, and these sensor coils are connected in a star shape by one point S.

[0026] The subsequent evaluation is carried out in a particularly typical manner. After suitable voltage division and filtering, the zero crossings of the induced voltage in the de-energized phases are detected. Alternatively, in the case of clocked square wave commutation, the detection of the zero crossings can be carried out during the pulse pauses, preferably at the end of each pulse pause. This simplifies the waste of connections, since the voltage divider and the filter are replaced by a Zener diode that is pre-wired to a suitable resistor. To evaluate the zero crossings, the voltage drop across the Zener diode is used, for example, as illustrated in FIG. 4 with phase U, neutral S, Zener diode 13 and resistor R.

[0027] The required pulse pause is provided by a current limiting means, preferably without torque loss. Furthermore, a simplified connection can be used directly at the phase terminals of the electric machine 5, i.e. without sensor windings. In addition to detection of crossings for sensorless speed regulation by square-wave commutation in the lower speed range, inductance or observer or model-based methods can likewise be used. The latter methods in particular have the advantage of avoiding the voltage ripples mentioned at the beginning, which occur with sinusoidal commutation in the lower speed range.

Claims

1. A method for operating an electric machine (5), the electric machine (5) having multi-phase drive windings, the drive windings being energized by sinusoidal commutation at least within a first speed range as a function of an angular position of a rotor (7) of the electric machine (5) to generate torque, the angular position of the rotor (7) being determined as a function of phase currents induced in the drive windings by the rotor, the method comprising: energizing the drive winding by square wave commutation within a second rotational speed range below the first rotational speed range; A Zener diode (13) is used to determine the angular position; an upper limit of the second rotation speed range reaches a minimum rotation speed of the sinusoidal commutation at which the angular position of the rotor (7) can be determined by a back electromotive force; A method comprising:

2. The second rotation speed range starts from a rotation speed of 0. The method of claim 1.

3. characterised in that 120° square wave commutation is used within the second speed range. The method according to claim 1 or 2.

4. The 120° square wave commutation is used in a three-phase drive winding. The method according to claim 3.

5. The angular position is determined according to a transition of an induced voltage in a non-energized phase.

5. The method according to any one of claims 1 to 4.

6. The course of the induced voltage is determined by an additional sensor winding on the stator side. The method according to claim 5.

7. - examining zero crossings of the detected voltage transitions to determine the angular position.

7. The method according to any one of claims 1 to 6.

8. characterised in that the electric machine (5) is an electric machine (5) of a turbocharger (1), 8. The method according to any one of claims 1 to 7.

9. A control device (8) for operating an electric machine (5) having a stator (6) with multi-phase drive windings and a rotatably supported rotor (7), the control device (8) being configured to energize phases of the drive windings as a function of the angular position of the rotor (7) to generate torque, A control device (8), characterized in that it is arranged to carry out the method according to any one of the claims 1 to 8.

10. An electric machine (5) comprising a stator (6) with a multiphase drive winding, a rotatably supported rotor (7) and a control device (8) according to claim 9.

11. characterised in that the electric machine (5) is an electric machine (5) for a turbocharger (1) of an internal combustion engine, An electric machine (5) according to claim 10.

12. A turbocharger (1) for an internal combustion engine of a motor vehicle, comprising a compressor wheel (4) mounted non-rotatably on a shaft and an electric machine (5) for driving said shaft (3), A turbocharger (1), characterized in that it comprises a configuration of an electric machine (5) according to claim 10 or 11.

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