Method for Determining a Rotor Position of an Electric Rotating Machine, and an Electric Rotating Machine for Carrying out a Method of this kind

Abstract

A method determines a rotor position of an electric rotating machine which is fed by a PWM-controlled inverter. Specific injection voltages, which are composed of predefined voltages and high-frequency voltages, are converted into corresponding PWM duty factors by a controller and the inverter is correspondingly actuated with these PWM duty factors. Current profiles of phase currents are then determined by measuring at least one first phase current and at least one second phase current. The measurement is carried out within a PWM period, in each case in the chronologically last third of a passive switched state. The rotor position is then determined in accordance with the ascertained current profiles and the fed-in high-frequency voltages.

Claims

1. A method for determining a rotor position of a rotating, at least three-phase, electric machine operably connected to a pulse width modulated (PWM)-controlled inverter, the method comprising: determining injection voltages during a controller sampling period, the injection voltages composed of (i) voltages predetermined by a controller for actuating the electric machine, and (ii) additional high-frequency voltages; determining PWM duty factors as a function of the determined injection voltages, such that a passive switching state ends in a middle of a PWM period and/or at an end of the PWM period; actuating the inverter with the determined PWM duty factors in at least one PWM period after the controller sampling period in order to actuate the electric machine accordingly; conducting PWM-synchronous measuring of at least one first phase current and simultaneously a second phase current in order to obtain a current profile of all phase currents of the electric machine, the measuring taking place within the at least one PWM period in a last third of the passive switching state; and determining the rotor position as a function of the obtained current profiles and the additional fed in high-frequency voltages.

2. The method according to claim 1, the conducting the PWM-synchronous measuring comprising: measuring at least the at least one first phase current and the second phase current at the end of the passive switching state.

3. The method according to claim 1, the determining PWM duty factors comprising: determining the PWM duty factors such that a time duration of the passive switching state during which the measurements are to be made during the conducting the PWM-synchronous measuring is maximally long.

4. The method according to claim 1, wherein: the determining the PWM duty factors comprises determining the PWM duty factors such that a first passive switching state ends in the middle of the PWM period and a second passive switching state end at the end of the PWM period, and the conducting PWM-synchronous measuring comprises measuring at least the first phase current and the second phase current once per passive switching state within the PWM period.

5. The method according to claim 4, the determining PWM duty factors comprising: determining the PWM duty factors such that time durations of the two passive switching states during which measurements are to be made during the conducting the PWM-synchronous measuring are essentially the same size.

6. The method according to claim 1, the determining PWM duty factors comprising: determining the PWM duty factors such that positive PWM pulses of the PWM duty factors for all phases within the at least one PWM period have a common vertical axis symmetry.

7. The method according to claim 1, the determining PWM duty factors comprising: determining the PWM duty factors such that a time duration between the ends of two successive passive switching states, during which at least the first phase current and the second phase current are to be measured, is constant.

8. The method according to claim 1, the conducting the PWM-synchronous measuring comprising: measuring at least the first phase current and the second phase current using (i) at least one current sensor for each phase to be measured, and (ii) at least one analog to digital converter, wherein the analog to digital converter is configured to measure the phase currents in each case at a predetermined point in time, and wherein the analog to digital converter includes a successive approximation register (SAR) analogue-digital converter.

9. The method according to claim 1, wherein the electric machine is configured.

Description

DRAWINGS

[0038] FIG. 1 shows an exemplary embodiment of a method according to the invention for determining a rotor position of an electric rotating machine.

[0039] FIG. 2 shows an exemplary embodiment of an electric rotating machine according to the invention, which is designed to carry out a method according to the invention.

[0040] FIGS. 3a to 3d show different possibilities of certain PWM duty factors. A centered PWM from the prior art is shown in FIG. 3a. In contrast, PWM duty factors according to the invention are shown in FIGS. 3b to 3d.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0041] FIG. 1 shows an exemplary embodiment of a method according to the invention for determining a rotor position of an electric rotating machine. The electric machine 10, for example, according to FIG. 2, has a winding group 30 and a PWM-controlled inverter 40 for feeding the winding group 30.

[0042] In the method shown in the exemplary embodiment according to FIG. 1, after the start S, injection voltages u.sub.inj are determined in a method step a during a controller sampling period, wherein the injection voltages u.sub.inj are composed of voltages u.sub.control and additional high-frequency voltages u.sub.hf predetermined by a controller 50 for actuating the electric machine 10. The duration of the controller sampling period and thus the duration between the first controller sampling step and the second controller sampling step can particularly be selected such that it is many times greater than a PWM period duration T.sub.PWM.

[0043] Subsequent to method step a, in a method step b, PWM duty factors are determined as a function of the injection voltages u.sub.inj determined in method step a such that a passive switching state ends in the middle of the PWM period t.sub.PWM,M and/or at the end of the PWM period t.sub.PWM,E. For this purpose, a PWM unit 70 converts the determined injection voltages u.sub.inj into PWM duty factors.

[0044] Subsequently, in a method step c, the inverter 40 is actuated with the PWM duty factors determined in method step b in at least one PWM period after the controller sampling period in order to actuate the electric machine 10 accordingly.

[0045] Then, in a method step d, at least one first phase current i.sub.a and one second phase current i.sub.b are each PWM-synchronously measured simultaneously in order to obtain a current profile of all phase currents i.sub.a, i.sub.b, i.sub.c, wherein the measurement within the at least one PWM period takes place in the last third of a passive switching state. In particular, the phase currents i.sub.a, i.sub.b are measured at the end of the respective passive switching state. The measurement also takes place between two controller sampling steps, that is, during a controller sampling period which follows the controller sampling period of method step a.

[0046] If, for example, only the first phase current i.sub.a and the second phase current i.sub.b are measured in a three-phase electric machine 10, a third phase current i.sub.c can thus be determined from the first phase current i.sub.a and the second phase current i.sub.b using Kirchhoff's first law:

i.sub.c=−i.sub.a−i.sub.b

[0047] Alternatively, the third phase current i.sub.c can also be measured.

[0048] Finally, in a method step e, the rotor position of the electric machine 10 is determined as a function of the current profiles obtained in method step d and the fed-in high-frequency voltages u.sub.hf, and the method is then ended. The rotor position can particularly be determined by determining the change in current which is produced by changing the predetermined voltage u.sub.control in method step a. The change in current is determined as a function of the current profiles of the phase currents i.sub.a, i.sub.b, i.sub.c obtained in method step d and the fed-in high-frequency voltages u.sub.hf. For this purpose, the current profiles obtained in method step d are divided into a first current, which would flow without changing the predetermined voltages u.sub.control, and a second current, which is generated by changing the predetermined voltages u.sub.control The second current can be determined, for example, by forming a difference between the phase currents i.sub.a, i.sub.b, i.sub.c obtained in method step d. Furthermore, the first current can be determined, for example, by forming an average value of the phase currents i.sub.a, i.sub.b, i.sub.c obtained in method step d.

[0049] In an alternative exemplary embodiment, not shown, the method can be restarted regularly in order to continuously determine the rotor position of the electric machine.

[0050] FIG. 2 shows an exemplary embodiment of an electric rotating machine according to the invention, which is designed to carry out a method according to the invention.

[0051] An electric machine 10 is shown. The electric machine 10 has a permanent magnetic rotor 15 which is surrounded by a winding group 30. The electric machine 10 is designed particularly to be three-phase, but this is not shown in the figure. The winding group 30 is arranged on a stator (not shown).

[0052] Furthermore, the winding group 30 is connected to an inverter 40, which energizes the winding group 30 and which can be designed, for example, as a B6 bridge. The inverter 40 is in turn connected to a PWM unit 70 which actuates the inverter 40. Here, the PWM unit 70 receives predetermined voltages u.sub.control from a controller 50 and high-frequency voltages u.sub.hf from a high-frequency excitation unit 80, which are added to the predetermined voltages u.sub.control and then converted as injection voltages u.sub.inj by the PWM unit 70 into corresponding PWM duty factors.

[0053] The electric machine 10 has a current sensor 55 each for at least a first phase and a second phase, wherein only one current sensor 55 is shown as an example. A corresponding phase current i.sub.a, i.sub.b, i.sub.c can in each case be sampled by means of this current sensor 55. In addition, the electric machine 10 also has an analogue-digital converter, which is not shown here, but is integrated into the current sensor 55. The analogue-digital converter is designed particularly such that the phase currents i.sub.a, i.sub.b can be measured at a predetermined point in time, wherein the analogue-digital converter is particularly an SAR analogue-digital converter. The current sensor 55 can be designed, for example, as a measuring resistor or as a Hall sensor.

[0054] The values of the detected phase currents i.sub.a, i.sub.b, i.sub.c are made available both to the controller 50 and to a rotor position unit 90. The rotor position unit 90 is designed to determine a rotor position of the rotor 15 as a function of the corresponding current profiles of the phase currents i.sub.a, i.sub.b, i.sub.c and the high-frequency voltages u.sub.hf and to transmit this rotor position to the controller 50, among other things. The controller 50 is designed to determine the predetermined voltages u.sub.control as a function of the current profiles of the phase currents i.sub.a, i.sub.b, i.sub.c and the obtained rotor position. These predetermined voltages u.sub.control are then added to the high-frequency voltages u.sub.hf and the sum is transmitted to the PWM unit 70 as certain injection voltages u.sub.inj, as already described above.

[0055] FIGS. 3a to 3d show different possibilities of certain PWM duty factors. A centered PWM from the prior art is shown in FIG. 3a. In contrast, PWM duty factors according to the invention are shown in FIGS. 3b to 3d.

[0056] A centered PWM from the prior art is shown in FIG. 3a. An entire PWM period having a PWM period duration T.sub.PWM and the end of the previous and the beginning of the following PWM period are shown. The PWM duty factors of the individual phase voltages u.sub.a, u.sub.b and u.sub.c are shown here over time t and selected centered on the middle of the PWM period t.sub.PWM,M. The phase currents i.sub.a, i.sub.b, i.sub.c are typically measured in the middle of the PWM period t.sub.PWM,M and/or at the end of the PWM period t.sub.PWM,E.

[0057] In FIG. 3b, PWM duty factors are shown by way of example which have only one passive switching state per PWM period duration T.sub.PWM, wherein this passive switching state ends at the end of the PWM period t.sub.PWM,E. Appropriately determining the PWM duty factors selects a maximum time duration of the passive switching state, particularly, wherein the injection voltages u.sub.inj determined by the controller 50 are achieved.

[0058] The first and second phase currents i.sub.a, i.sub.b can then be detected within the last third of the passive switching state in which eddy currents that have occurred due to the injection voltages u.sub.inj being fed in according to the PWM duty factors have already decayed. Particularly, a phase current measurement takes place at the end of the PWM period t.sub.PWM,E so that the eddy currents have decayed as much as possible. Furthermore, it can be seen that the positive PWM pulses of the PWM duty factors for all phases within the at least one PWM period have a common, vertical axis symmetry.

[0059] On the other hand, FIGS. 3c and 3d show PWM duty factors which have two passive switching states per PWM period duration T.sub.PWM. A first passive switching state here ends in the middle of the PWM period t.sub.PWM,M and a second passive switching state ends at the end of the PWM period t.sub.PWM,E. The phase currents i.sub.a, i.sub.b here can then be measured twice per PWM period within the last third of the respective passive switching state, but particularly once in the middle of the PWM period t.sub.PWM,M and once at the end of the period t.sub.PWM,E and thus at the respective end of the passive switching state. Due to the corresponding determination of the PWM duty factors, the time durations of the two passive switching states are, particularly, essentially the same size.

[0060] Furthermore, it can also be seen here that the positive PWM pulses of the PWM duty factors for all phases within the at least one PWM period have a common, vertical axis symmetry.

[0061] Particularly, the PWM duty factors are also chosen such that a time duration between the ends of two successive passive switching states, during which at least the first phase current i.sub.a and the second phase current i.sub.b are to be measured, is constant and a constant sampling frequency for the phase current measurement can thus be achieved. For this purpose, the points in time of the successive phase current measurements must of course also be selected accordingly.