EP2319169A1

EP2319169A1 - Method for detecting the rotor position of an electric machine, and device for the same

Info

Publication number: EP2319169A1
Application number: EP09781268A
Authority: EP
Inventors: Daniel Kocher; Rolf Jaros; Kurt Reutlinger
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2008-08-26
Filing date: 2009-07-30
Publication date: 2011-05-11
Also published as: WO2010023057A1; DE102008041549A1; US20110215744A1; JP2012501157A

Abstract

The invention relates to a method for providing information on a rotor position of a rotor of an electric machine (2) for utilization in a function connected downstream, comprising the following steps: - determining at least one electric operating variable of a stator winding of the electric machine, particularly a phase current and/or a phase voltage; - determining a rotor position as a function of the electric operating variable – providing information on the rotor position determined as a function of the electric operating variable for the function connected downstream if the rotational speed of the electric machine (2) exceeds a threshold rotational speed (SW).

Description

- -

ROBERT BOSCH GMBH, 70442 Stuttgart

description

title

Method for detecting the rotor position of an electrical machine and device for this purpose

Technical area

The invention generally relates to the detection of the rotor position, in particular for the electronic commutation of an electric motor by means of the detected rotor position.

State of the art

For electronic commutation of electrical machines, the knowledge of the absolute angular position of the rotor, the rotor position, is required. The rotor position may be determined by means of suitable sensors, e.g. incremental resolution encoders, Hall sensors, etc. are detected. Alternative position detections can be done without position sensors, e.g. Evaluate the phase current or the phase voltage of a winding strand of the stator winding and calculate the rotor position using suitable methods. For example, the rotor position in such a method by evaluating the third harmonic of the course of a

Strand current or a strand voltage, using the "back-EMF method" and the like. Be determined.

However, the methods for detecting the rotor position based on the evaluation of the strand current or the strand voltage have the disadvantage that this at - -

low rotational speeds and / or at very high speeds or in the load case, the rotor position or detect only with insufficient accuracy, so that an electronic commutation based on such a detected rotor position at low speeds is not reliable possible. For example, In the determination of the rotor position by evaluation of the third harmonic, these are distorted by saturation effects and differences between them, which makes them un-evaluable. At high speeds, the back-EMF process can no longer be used because there are no longer current-free time ranges.

It is an object of the present invention to provide a method and a device for the sensorless determination of the rotor position, in which malfunctions of a downstream function, such as e.g. electronic commutation can be avoided due to unreliable information about the rotor position.

Disclosure of the invention

This object is achieved by the method according to claim 1 and by the device and the motor system according to the independent claims.

Further advantageous embodiments of the invention are specified in the dependent claims.

According to a first aspect, a method is provided for providing information about a rotor position of a rotor of an electrical machine, in particular a synchronous machine, for use in a downstream function. The method comprises the following steps: determining at least one electrical operating variable of a stator winding of the electric motor Machine, in particular a strand current and / or a - -

Phase voltage;

- Determining a rotor position depending on the electrical operating variable;

- Providing the information about the determined depending on the electrical operating variable rotor position for the downstream function, when the rotational speed of the electric machine exceeds a threshold speed.

One idea of the invention is to provide the rotor position determined by an evaluation of the phase current and / or the phase voltage only at speeds above a speed threshold value. In this way, either a rotor position is provided only if it is sufficiently accurate or sufficiently reliable, so that an electronic commutation of the electric machine is possible.

As the downstream function, an electronic commutation of the synchronous machine can be carried out depending on the determined by means of the electrical operating variable rotor position.

Furthermore, if the rotational speed of the electric machine does not exceed the threshold speed, no rotor position can be determined. In particular, information can be provided which indicates that no information about a rotor position can be provided.

Thus, it is envisaged to provide no rotor position information below the speed threshold value, and in particular to communicate in a suitable manner information indicating that no indication of a rotor position is available, whereby e.g. the subordinate function is able to perform a function which does not require any information about the rotor position, such as e.g. the realization of a stepping operation of the electric motor.

In particular, as the downstream function, an electronic commutation of the electric machine depending on with the help of - -

rotor position of the electrical machine determined by the electrical operating variable, wherein the rotor of the electric machine is controlled by ramping up, in particular by a drive signal of increasing frequency, e.g. is operated for a stepping operation, independently of the provision of information about the rotor position, when the rotational speed of the electric machine does not exceed the threshold speed or information is provided indicating that no indication of a rotor position is available.

Furthermore, the method can have the further steps:

Determining an inductance of one of the stator windings; - Determining a rotor position depending on the specific inductance;

- Providing the determined using the specific inductance rotor position for the downstream function when the speed of the electric machine does not exceed the threshold speed.

This provides rotor position information, as determined by a rotor position sensing technique used to detect rotor position at lower speeds or at standstill, i. are suitable for speeds below the speed threshold.

According to one embodiment, as the subordinate function, an electronic commutation of the electric machine can be carried out depending on the rotor position determined with the aid of the electrical operating variable, if the rotational speed of the electric machine exceeds the threshold speed, wherein as the downstream function an electronic commutation of the electric machine depends on the determined by means of the specific inductance rotor position is performed when the speed of the electric machine does not exceed the threshold speed.

According to a further aspect, an apparatus for providing information about a rotor position of a rotor of an electric machine for - -

Use provided in a downstream function. The device comprises:

- A calculation unit for determining at least one electrical operating variable of a stator winding of the synchronous machine, in particular a strand current and / or a strand voltage; a conversion unit for determining a rotor position as a function of the electrical operating variable;

- A control unit for driving a selection unit to provide the information about the determined depending on the electrical operating variable rotor position for the downstream function, when the rotational speed of the electric machine exceeds a threshold speed.

The apparatus may further comprise an alternative operation unit configured to provide information indicating that no indication of rotor position is available, the control unit being configured to drive the selection unit to provide the information indicating that No information about the rotor position can be provided if the speed of the electric machine exceeds a threshold speed.

According to a further aspect, a motor system is provided with the above device and an inverter for driving the synchronous motor, wherein the inverter is designed,

- To carry out the electronic commutation of the synchronous machine depending on the determined by means of the electrical operating variable rotor position when the inverter receives the determined using the electrical operating variable rotor position, and

- To drive the rotor of the electric machine by controlled start-up, in particular by a drive signal increasing frequency, regardless of providing information about the rotor position when the inverter receives the information indicating that no information about a rotor position can be provided. - -

Alternatively, the device can be provided with an alternative operating unit which is designed to determine an inductance of one of the stator windings, to determine a rotor position as a function of the specific inductance and to provide information about the rotor position determined with the aid of the determined inductance, the control unit provided with the aid of the determined inductance rotor position via the selection unit to the inverter when the speed of the electric machine does not exceed the threshold speed.

Alternatively, the engine system with the above device and a

Inverter be provided for driving the electric machine, wherein the inverter is designed to perform as a subordinate function of the electronic commutation of the electric machine depending on the information provided about the rotor position.

Brief description of the drawings

Preferred embodiments of the invention are explained below with reference to the accompanying drawings. Show it:

Fig. 1 is a schematic block diagram of an engine system with a

Apparatus for operating an electrical machine; and

Fig. 2 is a schematic block diagram of the rotor position determination in the

Motor system of FIG. 1.

Description of embodiments

Fig. 1 shows a schematic block diagram of an engine system 1 with a synchronous motor 2 as an electric machine. The synchronous motor 2 has three phase windings (not shown) via corresponding phase lines. 3 - -

be controlled by an inverter 4. The inverter 4 receives a manipulated variable S from externally, which serves to specify the torque of the synchronous motor. Furthermore, the inverter can also get an indication of or a control speed (target speed). Furthermore, the inverter 4 receives a drive signal for operating the synchronous motor 2 via a signal line 5.

Furthermore, a control device 6 is provided, which outputs the control signal via the signal line 5 to the inverter 4. The control device 6 comprises a calculation unit 7 for calculating the pole wheel flow. For this purpose, the calculation unit 7 receives a phase current from a current detector 8, e.g. has a measuring resistor (shunt), and further determines the

Phase voltage ui on the same phase at which the phase current is determined. The phase voltage may be measured directly or taken from the pulse width modulated drive signal, e.g. be derived via the corresponding duty cycle. Phase voltage ui and phase current h are provided to the calculation unit 7, which corresponds to the formulas

(1 )

U ₁ (I) = U ^ z) ^ L ^ (2)

, (t) = φ ₁ (τ) - L * i ₁ (t) with φ = i uάt

(3)

determine the pole wheel flow. The formula (2) corresponds to a voltage equation of a strand of a permanent magnet excited machine (according to formula (1)) - -

neglecting the ohmic voltage drop with respect to the other voltage components. By integrating the formula (1), one obtains the flux linkages in the machine (formula (3)), which is a reduced formula of the mathematical machine model. The main flux φi (t) represents the integral over the strand voltage ui (t). High frequency components in the terminal voltage, e.g. caused by the PWM clock of the inverter, have a much lower share after integration. The high-frequency voltage components have a lower proportion of the total flux linkage φi (t) corresponding to the frequency. Accordingly, the pole wheel flux φp (t) is calculated from the integrated line voltage ui (t) in the line current ii (t), which is multiplied by the factor of the winding inductance L.

The rotor flux position φp (t) thus determined can be assigned to the rotor flux. The conversion of the Polradflusses in the rotor position is performed in the conversion unit 9. The determination of the rotor position via the Polradfluss is especially suitable if the phase currents do not go missing, i. when the phase windings of the synchronous motor are permanently energized (for example, sinusoidal current).

FIG. 2 shows a schematic block diagram of the calculation unit 7 and of the conversion unit 9. The calculation unit 7 adapts the received voltage signal and the received current signal respectively in signal adaptation units 21 and integrates the adapted voltage signal Ui 'in an integration block 22 and amplifies the adapted current signal h' in FIG a gain block 23. The outputs of the integration block 22 and the gain block 23 are added in a summation block 24. In the

Conversion unit 9 is assigned to the value at the output of the summation 24 a rotor position.

Furthermore, a switch 11 (selection unit) controlled by a control unit 10 is provided, which is switched so that at a speed of the - -

Synchronous motor 2, which is above a predetermined speed threshold SW, which is determined by the conversion unit 9 rotor position via the signal line 5 to the inverter 4 is transmitted. In this case, the inverter 4 carries out an electronic commutation of the synchronous motor 2 based on the transmitted rotor position.

The speed is determined from the detected phase current, which is sinusoidal. The period is proportional to the speed of the synchronous motor 2.

The speed threshold SW is preferably selected to indicate the lowest possible speed at which the determination of the rotor position based on the phase current and / or the phase voltage still provides a sufficiently reliable value that allows electronic commutation.

If the control unit 10 determines that the rotational speed of the synchronous motor 2 does not exceed the rotational speed threshold SW, then the changeover switch 11 is switched so that the signal line 5 is connected to an output of an alternative operating unit 12. The alternative operating unit 12 may provide that at speeds of the synchronous motor 2 below the speed threshold SW, as is the case for example in a start phase of the synchronous motor 2, first a controlled start-up of the synchronous motor 2 is effected. For this purpose, in the alternative operating unit 12, a control circuit for the operation of the synchronous motor 2 at low speeds, such as a ramp circuit may be provided which outputs via the signal line 5 to the inverter 4 a frequency drive signal constant or increasing frequency. The frequency control signal is suitable to start the synchronous motor 2 with increasing frequency until a certain speed, which is indicated by the frequency of the signal transmitted via the signal line 5 frequency drive signal is exceeded. The frequency drive signal with a constant frequency is suitable for operating the synchronous motor 2 at a speed corresponding to the frequency, for example in step mode. - -

If the ramp circuit of the alternative operating unit 12 has reached a frequency which represents a rotational speed of the synchronous motor 2 which corresponds to or exceeds the rotational speed threshold SW, the control unit 10 switches the changeover switch 11 so that the rotor position determined and output by the conversion unit 9 is transmitted via the Signal line 5 is transmitted to the inverter 4 instead of the frequency drive signal. The inverter 4 recognizes, based on the type of the signal transmitted via the signal line 5, whether it is a frequency drive signal of the alternative mode unit 12 or rotor position information from the conversion unit 9. This may be achieved, for example, in the inverter by e.g. in a corresponding discrimination unit (not shown), it is detected that the received signal is an analog frequency drive signal or digital rotor position information when the rotor position information is provided in digital form.

If the inverter 4 receives the frequency drive signal, the inverter generates phase-shifted frequency signals for driving the synchronous motor 2 for the three phase lines. If the inverter 4 instead receives the rotor position information, then the inverter 4 will have an electronic commutation based on the rotor position information and dependent on the rotor position information

Perform manipulated variable S. Alternatively, information about the switching position of the changeover switch 11 or any other signal may be used to indicate the type of information transmitted via the signal line to the inverter 4. According to a further alternative, the inverter can also be operated in a clocked manner in accordance with a specification via the signal line 5, wherein the timing of the conversion unit 9 or the alternative operating unit 12 can be specified.

In an alternative embodiment, it can be provided that the alternative operating unit 12 likewise provides rotor position information - -

wherein the rotor position is determined by another sensorless method. For example, For example, the alternate operation unit 12 may determine a rotor position using the test pulse method, which detects and uses asymmetries of the rotor to determine the rotor position by association. In the test pulse method, the inductance of a stator coil (stator winding) changes depending on the position of the rotor. Since the rotor has different inductances in the longitudinal and transverse direction due to its structure, the course of the inductance of a stator coil via a rotation of the rotor is characteristic, so that thus the rotor position can be detected by comparing with previously learned or provided inductance profiles. However, the test pulse method is suitable for rotor position determination with a stationary rotor or at low rotational speeds of the rotor. Thus, the test pulse method is a good complement to those methods for determining the rotor position, which are based on the course of the measurement of a phase current and / or a phase voltage and therefore can only be used at higher speeds.

Alternatively, the controlled start-up function of the synchronous motor 2 may also be fully implemented in the inverter 4, the alternative operating unit 12 outputting only a specific signal received from the inverter 4 via the signal line 5. By the specific signal, the inverter 4 can be signaled that the controlled

Startup should now be activated. The control unit 10 may then timed the switching of the changeover switch 11, wherein the time period during which the alternate operation unit 12 applied the determined signal to the inverter 4 is selected depending on the time in which the synchronous motor has probably reached the necessary rotation speed which is necessary to perform an electronic commutation based on the determined by the calculation unit 7 and the converter unit 9 rotor position.

Claims

- -Claims:

1. A method for providing information about a rotor position of a rotor of an electric machine (2), in particular a synchronous machine, for use in a downstream function, comprising the following steps: - determining at least one electrical operating variable of a stator winding of the synchronous machine, in particular a string current (h ) and / or a strand voltage (U2);

- Determining a rotor position depending on the electrical operating variable;

- Providing the information about the determined depending on the electrical operating variable rotor position for the downstream function when the speed of the electric machine (2) exceeds a threshold speed (SW).

2. The method of claim 1, wherein as the downstream function, an electronic commutation of the electric machine (2) is performed depending on the determined using the electrical operating variable rotor position.

3. The method of claim 1, wherein, when the rotational speed of the electric machine does not exceed the threshold speed (SW), no rotor position is determined.

4. The method of claim 3, wherein information is provided indicating that no indication of rotor position is available.

5. The method of claim 3 or 4, wherein as the downstream function of an electronic commutation of the electric machine (2) is performed depending on the determined using the electrical operating variable rotor position, wherein the rotor of the electric machine (2) by controlled startup , in particular by a drive signal increasing frequency, is operated independently of the provision of information about the rotor position when the - -

Speed of the electric machine (2) does not exceed the threshold speed (SW) or information is provided indicating that no information about a rotor position is available.

6. The method of claim 1, further comprising the steps of: - determining an inductance of one of the stator windings;

- Determining a rotor position depending on the specific inductance;

- Providing the determined using the specific inductance rotor position for the downstream function when the speed of the electric machine (2) does not exceed the threshold speed (SW).

7. The method of claim 6, wherein as the subordinate function of an electronic commutation of the electric machine (2) is performed depending on the determined using the electrical operating variable rotor position when the speed of the electric machine (2) exceeds the threshold speed (SW) , wherein as the downstream function an electronic commutation of the electric machine (2) is performed depending on the determined by means of the determined inductance rotor position when the rotational speed of the electric machine (2) does not exceed the threshold speed (SW).

8. A device (6) for providing information about a rotor position of a rotor of a synchronous machine for use in a downstream function, comprising:

- A calculation unit (7) for determining at least one electrical operating variable of a stator winding of the electric machine (2), in particular a strand current and / or a strand voltage;

- A conversion unit (9) for determining a rotor position depending on the electrical operating variable;

- A control unit (10) for driving a selection unit (11) to the information about the determined depending on the electrical operating variable - -

Provide rotor position for the downstream function when the speed of the electric machine (2) exceeds a threshold speed (SW).

9. Device (6) according to claim 8, having an alternative operating unit (12), which is designed to provide information indicating that no information about a rotor position can be provided, wherein the control unit (10) is designed to operate the selection unit (10). 11), so that the information is provided which indicates that no information about the rotor position can be provided if the rotational speed of the electric machine (2) exceeds a threshold speed (SW).

10. Motor system (1) with a device (6) according to claim 9 and an inverter (4) for driving the electric machine (2), wherein the inverter (4) is formed,

to carry out the electronic commutation of the electric machine (2) as a function of the rotor position determined with the aid of the electrical operating variable when the inverter (4) receives the rotor position determined with the aid of the electrical operating variable, and

- To drive the rotor of the electric machine (2) by controlled start-up, in particular by a drive signal increasing frequency, regardless of providing information about the rotor position when the inverter (4) receives the information indicating that no indication of a rotor position is available.

11.Vorrichtung (6) according to claim 8 with an alternative operating unit (12) which is adapted to determine an inductance of one of the stator windings, to determine a rotor position depending on the determined inductance and a

To provide information about the rotor position determined with the aid of the determined inductance, wherein the control unit (10) provides the rotor position determined with the aid of the determined inductance via the selection unit (11) to the inverter (4) when the rotational speed of the electric machine (2) Threshold speed (SW) does not exceed. - -

12. Motor system with a device (6) according to claim 11 and an inverter (4) for driving the electric machine (2), wherein the inverter (4) is formed as a downstream function, the electronic commutation of the electric machine (2) depending on perform the information provided about the rotor position.