Method for operating a brushless and sensorless multi-phase electric motor, and drive device with an electric motor

Abstract

A method for operating a brushless and sensorless multi-phase electric motor. At least two phase voltages and at least two phase currents of the electric motor are determined. A voltage vector is determined from the phase voltages and/or a current vector is determined from the phase currents. A position substitute signal is determined as a measure of a rotor position on the basis of an angle of the current vector and/or of the voltage vector. A rotation value is calculated on the basis of the position substitute signals, and the electric motor is controlled by open-loop and/or closed-loop technology on a basis of the rotation value.

Claims

1. A method of operating a brushless and sensorless multiphase electric motor, the method comprising: determining at least two phase voltages and at least two phase currents of the electric motor; ascertaining a voltage vector from the phase voltages and a current vector from the phase currents, determining a position substitute signal as a measure for a rotor position on a basis of an angle formed by a difference between the angle of the current vector and the voltage vector; calculating a rotation variable on a basis of the position substitute signal; and controlling the electric motor on a basis of the rotation variable.

2. The method according to claim 1, wherein the controlling step comprises controlling with an open-loop control or a closed-loop control.

3. The method according to claim 1, which comprises taking into account an additional phase angle in determining the angle of the current vector.

4. The method according to claim 1, which comprises controlling the electric motor to thereby minimize the angle of the current vector.

5. The method according to claim 1, which comprises controlling the phase voltage of the electric motor on a basis of the rotation variable.

6. The method according to claim 1, which comprises limiting the rotation variable on a basis of a stored minimum speed.

7. The method according to claim 6, which comprises adjusting a value of the minimum speed in dependence of a temperature.

8. The method according to claim 1, which comprises increasing the angle for determining the position substitute signal depending on an operating situation.

9. The method according to claim 1, which comprises carrying out a Clarke transformation of the phase voltages and/or phase currents in order to ascertain the voltage vector and/or the current vector.

10. The method according to claim 1, which comprises carrying out a Clarke transformation of the phase voltages in order to ascertain the voltage vector.

11. The method according to claim 1, which comprises carrying out a Clarke transformation of the phase currents in order to ascertain the current vector.

12. An electric drive, comprising: a brushless and sensorless multiphase electric motor; a vector device for ascertaining a voltage vector and/or a current vector; a controller connected to said electric motor for determining a position substitute signal; an observer connected to said controller for determining a rotation variable without a sensor; and a current regulator for controlling said electric motor; and wherein said electric motor, said vector device, said controller, and said observer are commonly configured for carrying out the method according to claim 1.

13. The electric drive according to claim 12, wherein said current regulator is configured to control said electric motor by open-loop control or by closed-loop control.

14. A method of operating a brushless and sensorless multiphase electric motor, the method comprising: determining at least two phase voltages and at least two phase currents of the electric motor; ascertaining at least one of a voltage vector from the phase voltages or a current vector from the phase currents, determining a position substitute signal as a measure for a rotor position on a basis of an angle of at least one of the current vector or the voltage vector; calculating a rotation variable on a basis of the position substitute signal; and controlling the electric motor on a basis of the rotation variable and to thereby minimize the angle of the current vector.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 shows an electric (electromotive) drive having a current source and having an electric motor as well as having a power converter interconnected in between;

(2) FIG. 2 shows a phase-voltage-regulated drive;

(3) FIG. 3 shows three phase windings of a three-phase electric motor connected in a star circuit;

(4) FIG. 4 shows a bridge module of a bridge circuit of the power converter for actuating a phase winding of the electric motor;

(5) FIG. 5 shows an equivalent circuit diagram of the current source;

(6) FIG. 6 shows a controller and an observer of the drive in a first embodiment;

(7) FIG. 7 shows the controller and the observer in a second embodiment; and

(8) FIGS. 8 to 10 show the controller in various embodiments.

DETAILED DESCRIPTION OF THE INVENTION

(9) Mutually corresponding parts and variables are provided with the same reference signs throughout the figures.

(10) FIG. 1 shows an electric or electromotive drive 2 for an adjustment system of a motor vehicle, for example a window lifter or a seat adjustment system. The drive 2 comprises a brushless and sensorless three-phase electric motor 4, which is connected to a current source (voltage supply) 8 by way of a power converter 6. In this exemplary embodiment, the current source 8 comprises a vehicle-internal energy storage device 10, for example in the form of a (motor vehicle) battery, and a (DC) intermediate circuit 12, which is connected to said energy storage device and which extends at least partly into the power converter 6.

(11) The intermediate circuit 12 is essentially formed by an outgoing line 12a and a return line 12b, by means of which the power converter 6 is connected to the energy storage device 10. The lines 12a and 12b are fed at least partly into the power converter 6, in which an intermediate circuit capacitor 14 and a bridge circuit 16 are interconnected between said lines.

(12) During the operation of the drive 2, an input current IE which is fed to the bridge circuit 16 is converted to a three-phase output current (motor current, three-phase current) IU, IV, IW for the three phases U, V, W of the electric motor 4. The output currents IU, IV, IW, which are subsequently also referred to as phase currents, are fed to the corresponding motor phases or phases (phase windings) U, V, W (FIG. 3) of a stator, which is not illustrated in any more detail.

(13) FIG. 3 illustrates a star circuit 18 of the three phase windings U, V, W. The phase windings U, V, W are fed to a respective bridge module 26 (FIG. 3) of the bridge circuit 16 by way of a respective (phase) end 20, 22, 24, and are interconnected by way of the respective opposite end with one another in a star point 28 as common connecting terminal.

(14) In the illustration of FIG. 3, the phase windings U, V and W are each shown by means of an equivalent circuit diagram in the form of an inductance 30 and an ohmic resistor 32 and a respective voltage drop 34, 36, 38. The voltage 34, 36, 38 dropped in each case across the phase winding U, V, W is schematically represented by arrows and results from the sum of the voltage drops across the inductance 30 and the ohmic resistor 32 and the induced voltage or the induced phase current 40. The phase current 40 (back EMF) induced by way of a movement of a rotor of the electric motor 4 is schematically illustrated in FIG. 3 using a circle.

(15) The star circuit 18 is actuated by means of the bridge circuit 16. The bridge circuit 16 is embodied together with the bridge modules 26 in particular as a B6 circuit. In this embodiment, during operation, at each of the phase windings U, V, W there is a switchover, clocked at a high switching frequency, between a high (DC) voltage level of the outgoing line 12a and a low voltage level of the return line 12b. The high-voltage level is in this case in particular an intermediate circuit voltage UZK of the intermediate circuit 12, wherein the low voltage level is preferably a ground potential UG. This clocked actuation is embodied as a PWM actuation—illustrated in FIG. 1 by means of arrows—by way of a device 42 as regulator, by way of which control and/or regulation of the rotational speed, the power and the direction of rotation of the electric motor 4 is possible.

(16) The bridge modules 20 each comprise two semiconductor switches 44 and 46, which are illustrated in FIG. 3 purely schematically and by way of example for the phase W. The bridge module 26 is connected on one side to the outgoing line 12a and thus to the intermediate circuit voltage UZK by way of a potential connection 48. On the other side, the bridge module 26 is contact-connected to the return line 12b and thus to the ground potential UG by way of a second potential connection 50. The respective phase end 20, 22, 24 of the phase U, V, W is able to be connected either to the intermediate circuit voltage UZK or to the ground potential UG by means of the semiconductor switches 44, 46. If the semiconductor switch 44 is closed (on) and the semiconductor switch 46 is opened (off), the phase end 20, 22, 24 is connected to the potential of the intermediate circuit voltage UZK. Accordingly, when the semiconductor switch 44 is opened and the semiconductor switch 46 is closed, the phase U, V, W is contact-connected to the ground potential UG. As a result, by means of the PWM actuation of the device 42, it is possible to supply two different voltage levels to each phase winding U, V, W.

(17) FIG. 4 illustrates an individual bridge module 26 in a simplified manner. In this exemplary embodiment, the semiconductor switches 44 and 46 are realized as MOSFETs (metal-oxide semiconductor field-effect transistor), which switch over between an on state and an off state in a clocked manner by means of the PWM actuation. To this end, the respective gate connections are fed to corresponding control voltage inputs 52, 54, by means of which the signals of the actuation 42 are transmitted.

(18) FIG. 5 shows an equivalent circuit diagram for the current source 8. During operation, the energy storage device 10 generates a battery voltage UBat and a corresponding battery current IBat to operate the power converter 6. In FIG. 5, the internal resistance of the energy storage device 10 is illustrated as an ohmic resistor 56 and an inherent inductance of the energy storage device 10 is illustrated as an inductance 58. A shunt resistor 60, at which the intermediate circuit voltage UZK drops, is connected in the return line 12b.

(19) In the exemplary embodiment of FIG. 1, the phase currents IU, IV, IW are detected by means of an ammeter 62 and fed to the device 42. A vector device 64 determines from the detected phase currents IU, IV, IW and calculated phase voltages UU, UV, UW a current vector and a voltage vector in a coordinate system. The coordinate system may be an ab system fixed with respect to the stator or a dq system fixed with respect to the rotor, with the result that the corresponding current vectors are denoted as Iab and Idq and the voltage vectors are denoted as Uab and Udq in the following text. Components of the current or voltage vectors along a coordinate axis a, b, d, q are accordingly denoted as Ia, Ib, Id, Iq and Ua, Ub, Ud, Uq.

(20) The current vector Iab, Idq and the voltage vector Uab, Udq are transmitted to a controller 66, which determines a position substitute signal PES on the basis of an angle α of the voltage and/or current vectors Iab, Idq, Uab, Udq.

(21) The angle α is determined for example by forming the difference between the phase angles of the current vector Iab, Idq and of the voltage vector Uab, Udq, that is to say as a relative phase position. To this end, for example, the phase angles αU and αI of the voltage vector Uab, Udq and the current vector Iab, Idq are determined by means of an expanded arctangent function, what is known as the arctan 2 function (atan 2), and the difference is subsequently formed. Therefore, the result in the ab system is for example:
α=atan 2(Ua,Ub)−atan 2(Ia,Ib).

(22) The angle α is multiplied, for example, by an amplification factor, an algebraic sign, or a scaling factor k1.

(23) The position substitute signal PES is fed to an observer 68, which, for example, filters the position substitute signal PES and calculates or estimates a rotation variable θ, ω, that is to say the rotor position θ and/or the (rotor) rotational speed ω. This calculated or estimated rotation variable θ, ω is fed as a manipulated variable to a current regulator 70, which generates the PWM actuation signals. In this case, it is possible, for example, that the position substitute signal PES is used as manipulated variable instead of the rotation variable θ.

(24) When the rotation variables θ, ω are calculated, the difference between the expected value θ, ω and the position substitute signal PES is preferably formed. This “error” is used as a control deviation for correcting the expected values θ, ω. As an alternative thereto, the angle α can also be used as input variable and be interpreted as “error” or “error signal.” As a result, the required computational load is reduced.

(25) The current regulator 70, or current controller 70, controls (open loop) and/or regulates (closed-loop) the operation of the electric motor 4 in particular to the extent that the angle α is minimized, preferably regulated to zero.

(26) FIG. 2 shows a relatively simple illustration of an embodiment of the drive 2, in which phase-voltage-regulated operation of the electric motor 4 is made possible. In this embodiment, the vector device 64 or the functionality thereof is integrated into the controller 66. In this embodiment, the phase currents IU, IV, IW and the phase voltages UU, UV, UW are measured or detected directly and fed to the controller 66.

(27) The function of the controller 66 and that of the observer 68 is explained in more detail below based on FIGS. 6 to 10 and based on a plurality of exemplary embodiments.

(28) In the exemplary embodiment according to FIG. 6, the rotor position θ determined by the observer 68 is fed back to the controller 66 and added to the angle α in order to generate the position substitute signal PES. In the observer 68, the rotor position θ is subtracted again and the rotation variables θ, ω are determined based on the angle α. Typical methods—such as incremental sensors, for example—ascertain a position, which is subsequently processed in the observer. This conventional structure is reproduced by the addition and subtraction, such that simple implementation of the method in existing systems is made possible.

(29) In order to determine the rotational speed or speed ω, the angle α is multiplied by a factor kw. The rotational speed ω is subsequently calculated by means of integration 72 over time. In order to determine the rotor position θ, the angle α is multiplied by a factor kt, and the speed ω or the change in rotor position is subsequently added. The new rotor position θ is then calculated by way of a division 74 of the elapsed period.

(30) In the exemplary embodiment according to FIG. 7, the angle α is sent directly to the observer 68 as position substitute signal PES. The controller 66 thus generates the angle α as an error signal or control deviation for the observer 68.

(31) FIG. 8 shows an exemplary embodiment of the controller 66, which is suitable and set up in particular for the drive 2 illustrated in FIG. 2. In this exemplary embodiment, the current regulator 70 regulates the current in the q direction of the position estimation. This means that the current component Id is equal to zero (Id=0). As a result, the position direction and the current vector lab correspond to an offset or phase angle P of 90° or Π/2. As a result, a simplified configuration of the controller 66 is possible.

(32) In the exemplary embodiment according to FIG. 9, the current is regulated by the current regulator 70 in the q direction of the position estimation (Id=0). Therefore, it is sufficient to consider only the voltage component Ud in order to identify whether the phase voltage leads or lags the phase current. In an embodiment without feedback of the rotor position θ, the voltage component Ud or the corresponding angle α is multiplied by a factor k1 equal to negative 1 (k1=−1) and is sent as position substitute signal PES.

(33) The exemplary embodiment of FIG. 10 shows an embodiment of the controller 66 in a steady state of the electric motor 4. If the electric motor 4 is in the steady state, the position direction and the voltage vector Uab, Udq correspond to an offset or phase angle P of 90° or Π/2. In this embodiment, the voltage angle αU is multiplied by a factor k1=2. In other words, regulation is carried out with respect to the square of the phase voltage. The phase angle P is subsequently subtracted therefrom and the difference with respect to the current angle αI is formed in order to generate the angle α or the position substitute signal PES.

(34) It will be understood that the invention is not restricted to the exemplary embodiments described above. Rather, other variants of the invention can also be derived therefrom by the person skilled in the art without departing from the subject matter of the invention. In particular, furthermore, all individual features described in association with the exemplary embodiments are also able to be combined with one another in a different way, without departing from the subject matter of the invention.

(35) The control and/or regulation method and the device 42 can be combined with an initial position or position identification method.

(36) Furthermore, it is conceivable, for example, that the speed of the observer 68 is limited to a minimum speed for calculating the rotation variable θ, ω. As a result, the calculated rotation variable θ, ω increases with a minimum gradient, even if the values at the input of the observer 68 remain constant.

(37) For example, it is possible that the angle α for determining the position substitute signal PES is increased by means of the factor k1 depending on an operating situation or an operating point of the electric motor 4. In this case, the minimum speed is also preferably adjusted or varied depending on the operating point or an operating situation of the electric motor 4. The value of the minimum speed in this case is preferably adjusted in particular in dependence on a temperature.

(38) The following is a summary list of reference numerals and the corresponding structure used in the above description of the invention: 2 Drive 4 Electric motor 6 Power converter 8 Current source 10 Energy storage device 12 Intermediate circuit 12a Outgoing line 12b Return line 14 Intermediate circuit capacitor 16 Bridge circuit 18 Star circuit 20, 22, 24 Phase end 26 Bridge module 28 Star point 30 Inductance 32 Resistance 34, 36, 38 Voltage drop 40 Phase current 42 Apparatus/regulator 44, 46 Semiconductor switch 48, 50 Potential connection 52, 54 Control voltage input 56 Resistance 58 Inductance 60 Shunt resistor 62 Ammeter 64 Vector device 66 Controller 68 Observer 70 Current regulator 72 Integration 74 Division IE Input current IU, IV, IW Phase current U, V, W Phase UZK Intermediate circuit voltage UG Ground potential IBat Battery current UBat Battery voltage UU, UV, U Phase voltage Iab, Idq Current vector Uab, Udq Voltage vector Ia, Ib, Id, Iq Current vector component Ua, Ub, Ud, Uq Voltage vector component αI Current angle/phase position αU Voltage angle/phase position α Angle PES Position substitute signal k1, kw, kt Factor θ Rotation variable/rotor position ω Rotation variable/rotational speed P Phase angle/offset