DE10108173A1 - Torque control or regulation for electric motor e.g. for vehicle steer-by-wire system, involves estimating motor magnetic flux using phase currents and voltages, and controlling or regulating torque depending on estimated flux - Google Patents

Abstract

The method involves estimating the magnetic flux of the electric motor (13) using the phase currents (i1-i3)and the phase voltages (u1-u3) applied to the motor and controlling or regulating the torque depending on the estimated magnetic flux (Psis). A control parameter for a torque controller is determined using the estimated magnetic flux. Independent claims are also included for the following: an arrangement for electric motor torque control or regulation, a controller for a steer-by-wire system, a memory element for a controller and a computer program for implementing the method.

Description

The present invention relates to a method or a Device for controlling or regulating one of a Electric motor delivered torque. The torque control or control is subordinated to the current of the electric motor regulated. The electric motor is powered by a converter controlled.

The present invention also relates to a control device for a steer-by-wire steering system of a motor vehicle. That Control device is used, among other things, for control or regulation one of an actuator of the steer-by-wire steering system given moment. The actuator is called an electric motor educated. The torque control or regulation is one Current control to regulate the current of the electric motor subordinate. The electric motor is powered by a converter controlled.

The invention also relates to a storage element for a control unit of a steer-by-wire steering system Motor vehicle. The storage element is, for example, as a read Only memory, as a random access memory, or as a Flash memory formed. There is a Computer program stored on a computing device, in particular can run on a microprocessor.

Finally, the present invention also relates to a Computer program that runs on a computing device, in particular on a microprocessor, is executable.

State of the art

A method and an apparatus of the type mentioned at the beginning Art can be used for torque control or regulation of an in any areas usable electric motor used will. The method and the device are in particular Can be used with electric motors where a torque-forming current component and a flux-forming Current share are coupled to one another, as for example electrically commutated three-phase machines is the case. A preferred area of application in a steer-by-wire steering system of a motor vehicle reference taken. This is exemplified by a as Three-phase machine trained actuator of the steer-by-wire Steering system delivered torque controlled or regulated.

A steer-by-wire steering system is assumed, the an electric steering actuator (valve actuator (VA) motor) has, via a transmission or directly to a Torsion bar of a rack and pinion power steering is attached. A The driver's request is carried out on a steering wheel of the steering system tapped a suitable sensor. The repercussions of the roadway are attached by one to the steering wheel Steering wheel actuator (steering wheel actuator (LRA) motor) to the driver transmitted.

The steering actuator and the steering wheel actuator can in principle as a direct current or as a three-phase machine be trained. DC machines have the advantage that they are easy to regulate because they have anchor and The excitation circuit is the torque generating and the Flow-forming current components regulated separately from each other can be. DC machines have a disadvantageous effect However, the wear and tear on the brushes, which increases the Can significantly increase the probability of failure. the end Reasons of reliability and security are therefore three-phase machines are increasingly used in steer-by-wire steering systems used as actuators.

The current of a three-phase machine can be used as a vector in a stator fixed αβ coordinate system or in a dq coordinate system that is fixed to the rotor flux. In the dq-system the current vector has a moment-generating one Current component and a flow-forming current component. in the In contrast to DC machines, the regulation is for electrically commutated three-phase machines very complex, because here the torque-generating current component and the flux-forming current components are coupled to one another.

According to the prior art, the target steering feel is through the steering wheel actuator either through a fixed connection (Torque control) specified or by a Torque control in a setpoint for a converted torque-generating current of the steering wheel actuator. This current setpoint is then after running through a subordinate current control regulated in such a way that the Steering wheel actuator (LRA motor) the driver the appropriate (artificially generated) counter-torque on the steering wheel delivers. This the driver gets to feel it directly. A problem with the is known from the prior art torque generation both in torque control and in the Magnetic flux of the torque control to be taken into account Electric motor. The magnetic flux can move into Change over time depending on the operating conditions. the end In the prior art it is known for the magnetic Use a fixed value for flow and a setpoint for the torque to be controlled or regulated as a function of of this fixed size. An exact dosage of the moment is therefore not possible. at It is from the state of the art in torque control Also known, an actual torque value based on a To determine torque sensor. In the actual torque value temporal changes of the magnetic flux also flow which are taken into account in the torque control can. However, the use of the torque sensor causes additional costs and requires additional installation space in the steer-by-wire steering system.

The present invention is therefore the object based on a torque control or regulation of a On the one hand, the electric motor is as accurate and reliable as possible and on the other hand as simple and inexpensive as possible realize.

In order to achieve this object, the invention proposes as a starting point of the method for torque control or regulation of the type mentioned above that based on on the Phase currents and phase voltages applied to the electric motor a magnetic flux of the electric motor is estimated and the moment as a function of the estimated magnetic Flow is controlled or regulated.

Advantages of the invention

According to the invention, the use of an observer is proposed which estimates the magnetic flux Ψ _p on the basis of the phase currents and the phase voltages of the electric motor. The estimation of the magnetic flux takes place online, ie during the control or regulation of the motor torque. Since the magnetic flux is continuously estimated, changes in the operating conditions or parameter changes, which are also reflected in the observed measured variables, can also be taken into account in the magnetic flux. This enables particularly precise control or regulation of the torque output by the electric motor.

According to an advantageous development of the present invention, it is proposed that, in the case of a torque control, a reference variable for the current of the current control is determined on the basis of the estimated magnetic flux. The reference variable is advantageously determined using the equations

determined, where M ^{* is} a nominal torque value, Ψ _{s is} an estimated value of the magnetic flux Ψ _p and Z _{p is} a number of pole pairs of the electric motor.

The input variable of a torque control is the setpoint of the torque. The torque setpoint value M ^* can, for example, be formed proportionally to an instantaneous motor current at the electric motor. A reference variable i _s ^* for the stator current of the subordinate current control is formed from the setpoint. In a dq coordinate system that is fixed to the rotor flux, the reference variable i _s ^{* is divided} into a torque- _{generating current component i sq} ^* and a flux-forming current component i _sd ^* . The flux-forming current component i _sd ^* is equal to 0. The torque- _{forming current component i sq} ^* results from the equation:

where z _{p is} a pole wheel number and Ψ _{p is} the magnetic flux of the electric motor. The magnetic flux Ψ _p estimated according to the method according to the invention is used for the magnetic flux Ψ _p .

According to another advantageous development of the present invention, it is proposed that, in the case of a torque control, an estimated actual torque value is determined on the basis of the estimated magnetic flux Ψ _s . The actual torque value is advantageously determined using the equation

determined, where z _{p is} the number of pole pairs and i _{sq is} the torque-generating component of the stator current of the electric motor.

In the case of torque regulation, the actual value M of the torque output by the electric motor is measured either by means of a torque sensor or according to an equation

calculated as a function of the torque-generating current component i _{sq of} the stator current. _{In this equation, too, the magnetic flux Ψ s} estimated according to the method according to the invention is used as the magnetic flux Ψ _{p of} the electric motor.

According to a preferred embodiment of the present Invention is proposed that based on the String voltages an estimated value for the on the electric motor applied current is determined based on the string currents the current applied to the electric motor is determined and the estimated magnetic flux from the difference of the Estimated value and the current is determined. The estimate for the current is advantageously by means of a model of the electric motor is determined based on the phase voltages.

A moment-forming and a flux-forming one To be able to specify current components independently of each other, it is also proposed that the phase currents and the strand tension prior to estimating the magnetic Into a coordinate system that is fixed to the rotor flux be transformed.

As a further solution to the problem of the present Invention is based on the device for Torque control or regulation of the type mentioned at the beginning suggested that the device be an observer Estimating a magnetic flux of the electric motor based on the string currents applied to the electric motor and strand tension, wherein the device has the Moment depending on the estimated magnetic Flow controls or regulates.

According to an advantageous development of the present Invention it is proposed that the device means for carrying out the method according to the invention.

As yet another solution to the problem of the present Invention is based on the control unit for a Steer- by-wire steering system of the type mentioned at the beginning proposed that in the control unit means for Implementation of the method according to the invention realized are.

The realization of the method according to the invention in the form of a Storage element that is used for a control unit of a steer-by Wire steering system of a motor vehicle is provided. Included is a computer program on the memory element stored on a computing device, in particular on a microprocessor, executable and for the execution of the method according to the invention is suitable. In this case So the invention is based on a memory element stored computer program implemented so that this memory element provided with the computer program in represents the invention in the same way as the method, the computer program is suitable for its execution. as The storage element can in particular be an electrical one Storage medium are used, e.g. a read-only Memory, a random access memory or a flash memory.

Finally, the invention also relates to a Computer program that is used to execute the inventive Method is suitable if it is on a computing device, in particular on a microprocessor. Particularly It is preferred if the computer program is on a Storage element, in particular on a flash memory, is saved.

drawings

Further features, possible uses and advantages of the The present invention will emerge from the following Description of embodiments of the invention, the are shown in the drawing. Everyone educates features described or shown on their own or in any combination the subject matter of the invention, regardless of their summary in the Claims or their back-reference as well as independently on their formulation or representation in the description or in the drawing. Show it:

Fig. 1 is a schematic view of a steer-by-wire steering system;

FIG. 2 shows a structure of a torque control of a steering wheel regulator of the steer-by-wire steering system from FIG. 1; FIG.

Fig. 3 shows a loop structure of a torque control of a steering wheel controller of the steer-by-wire steering system of FIG. 1;

Figure 4 is a control loop structure of a torque control according to the invention with an observer for estimating the magnetic flux. and

FIG. 5 shows a schematic representation of the observer of the torque control from FIG. 4.

Description of the exemplary embodiments

In FIG. 1, a schematic representation of a steer-by-wire steering system for a motor vehicle is denoted in its entirety by the reference symbol 1. In the steer-by-wire steering system 1 , a conventional mechanical steering column is dispensed with. The task of the mechanical steering column is implemented electronically with the help of a steering actuator 2 (valve actuator (VA) motor). A hydraulic steering assistance valve is actuated via the steering actuator 2. To implement the hydraulic steering assistance, the steering system 1 has a hydraulic pump 3 which conveys a hydraulic fluid in a hydraulic circuit 4.

A driver of the motor vehicle communicates his steering request to the steering system 1 by means of a steering wheel 5 .

Steering angle sensors 6 , 7 detect the driver's _{steering request δ LR} and pass it on to a block 8 for the purpose of generating setpoints. In block 8 , the driver's steering request δ _{LR is} modified as a function of the vehicle speed v. As a result, a speed-dependent steering assistance can be implemented. The setpoint δ _{LR *} is present at the output of block 8 and is passed on to a steering controller 9 . The steering actuator 2 is attached via a gear or directly to a torsion bar 10 of a rack and pinion steering. The steering actuator 2 is designed as an electrically commutated three-phase machine. It is controlled by the steering controller 9 with the aid of a converter 11 (VA converter).

The lack of road feel due to the omission of the steering column, which is expressed by the restoring torque on the steered wheels 12 or by the manual torque M on the steering wheel 5 and on which the driver's steering request depends heavily, is compensated for with the help of a steering wheel actuator 13 (steering wheel actuator (LRA) - Engine) restored. The steering wheel actuator 13 is designed as an electrically commutated three-phase machine. The steering wheel actuator 13 is coupled to the steering wheel 5 via a transmission or directly. It is controlled by a steering wheel controller 14 by means of a converter 15 (LRA converter).

The target manual torque M ^* is determined with the help of the angle difference δ _VA - δ _pinion . δ _VA is the angle measured with an angle sensor 16 at the steering actuator 2 . δ _pinion is the angle measured on a pinion of the rack and pinion steering. The pinion angle δ _pinion is measured with an angle sensor 17 attached to the pinion and / or with a displacement or angle sensor 18 attached to a rack of the rack and pinion steering. Alternatively, the target manual torque M ^{* is determined} from the current i _{VA of} the steering actuator 2 . The target manual torque M ^* is fed to the steering wheel controller 14 , which controls the steering wheel actuator 13 in such a way that the manual torque M is transmitted to the steering wheel 5. The subject matter of the present invention is a torque control or regulation of a three-phase machine, in particular an actuator for a steer-by-wire steering system, which works particularly precisely and reliably and is nevertheless constructed simply and inexpensively.

To carry out the method according to the invention, the steer-by-wire steering system 1 has a control unit 34 with a microprocessor 35 . A computer program which is suitable for carrying out the method according to the invention can run on the microprocessor 35. The computer program is stored on a memory element 36 of the control device 34 designed as a flash memory and is loaded into the microprocessor 35 via a data line 37 before or during the execution of the method. The control unit 34 receives a large number of state variables 38 both of the steering system 1 and of other components of the motor vehicle, such as the internal combustion engine. On the basis of these state variables 38 , the control unit 34 generates control signals 39 for actuators 2 , 13 of the steering system 1 and possibly for actuators of other vehicle components while the computer program is being processed or while the method according to the invention is being carried out.

The basic structure and the mode of operation of the steering controller 9 and the steering wheel controller 14 are described in detail in another patent application DE 101 05 154 entitled "Method for steering a motor vehicle with steer-by-wire steering" by the same applicant. Reference is expressly made to this application.

The current of a three-phase machine can be described as a vector in a stator-fixed αβ-coordinate system or in a rotor-flux-fixed dq-coordinate system. In the dq system, the current vector i _{s has} a torque- _{forming current component i sq} and a flux-forming current component i _sd . The advantage of considering the current in a rotor flux-proof dq system is that the torque and flux-forming variables can be specified independently of one another.

In Fig. 2, the structure of a torque control 19 of the steering wheel actuator 13 is shown. The torque control 19 is implemented, for example, in the steering wheel controller 14 of the steer-by-wire steering system from FIG. 1. The torque control is designated in its entirety with the reference number 19 . A current control 20 for controlling the stator current i _{s of} the steering wheel actuator 13 is subordinate to the torque control 19 . The current regulator 20 comprises a current regulator 22 and a controlled system 23 . The current regulator 22 used has the structure of a multivariable regulator. In it, a vectorial manipulated variable u _{s is} formed from the vectorial reference variable i _s ^* and the vectorial controlled variable i _s , which acts on the controlled system 23 consisting of the steering wheel actuator 13 and the converter 15. For the torque control, however, only the torque-generating current component i _{sq of} the controlled variable i _{s is} important. The current control 20 produces a torque M on the steering wheel actuator 13 , which the driver feels as a counter-torque in the event of a predetermined change in the steering wheel angle.

The input variable of the torque control 19 is the reference variable (the setpoint) M ^{* of} the torque. The target value M ^* can, for example, be formed proportionally to an instantaneous motor current at the steering actuator 2 of the steering system 1 . For this target value M ^* is a command value i ^* _s made for the stator current of the current control 20 in the rotor flux dq system in a transmission block 21st The reference variable i _sq ^* for the torque-generating current component of the steering wheel actuator 13 results from the equation:
where M ^{* is} a nominal torque value, z _{p is} a number of pole pairs and Ψ _p

is the magnetic flux of the steering wheel actuator 13 . _{According to the invention, a magnetic flux Ψ s} estimated by means of an observer B (cf. FIGS. 4 and 5) is used for the magnetic flux Ψ _p .

The control loop structure of a torque control 24 is shown in FIG. 3. The current control 20 is subordinate to the torque control 24 . The torque control 24 comprises a torque controller 25 which determines the reference variable i _s ^* for the stator current i _{s of} the current control 20 from the difference between the torque setpoint value M ^{* and the actual torque value M.} The actual torque value M can either be measured by means of a torque sensor 26 or calculated from the actual stator current value i _s in a block 27. The calculation of the actual torque value M in the block 27 takes place according to the equation:

depending on the torque-generating current component i _sq . Here too, according to the invention, _{a value Ψ s} for the magnetic flux estimated by means of the observer B (cf. FIGS. 4 and 5) _{is used for the magnetic flux Ψ p.}

According to the invention, an estimated value Ψ _s for the magnetic flux is determined by means of the observer B. A corresponding control loop structure is shown in FIG . The steering wheel actuator 13 , designed as a three-phase machine, is controlled in a manner known per se by a current regulator 22 via the converter 15 . Since the current regulator 22 only supplies the artificial manipulated variables u _sd and u _sq , these variables must be converted back into physical manipulated variables u _w1 , u _w2 and u _w3 via a coordinate transformation in block 28 . From this, pulse-width-modulated signals are formed in a block 29 , which are then fed to the converter 15.

With the help of the phase voltages u ₁ , u ₂ and u ₃ measured at the steering wheel actuator 13 and the applied _{phase currents i 1} , i ₂ , i ₃ , the magnetic flux Ψ _{s can} be estimated by means of the observer B. The measured phase voltages u ₁ , u ₂ , u ₃ are transformed in a block 30 into the quantities u _sq , u _{sd of} the dq system. The measured phase currents i ₁ , i ₂ , i _{3 are also transformed} in a block 31 into the torque- _{forming current component i sq} and the flux-forming current component i _sd in the dq system.

Using the estimated magnetic flux Ψ _s , the equation

an estimated value M _s can be determined for the actual torque value. The estimated torque M _s , together with the torque setpoint M ^{*, is} fed to a torque controller 25 , which either alone _{supplies the current setpoint i s} ^* or, together with a torque control including the transmission block 21, enables particularly sensitive metering of the engine torque M.

The magnetic flux Ψ _s is continuously estimated. As a result, operational parameter changes, which are also reflected in the measured phase voltages u ₁ , u ₂ , u ₃ and the measured phase currents 11 , 12 , 13 , can also be taken into account in the magnetic flux Ψ _s. This allows a particularly precise control or regulation of the torque M of the steering wheel actuator 13 .

Finally, the estimated magnetic flux Ψ _s also enables better current control by replacing the constant magnetic flux Ψ _p required for current control with the continuously estimated magnetic flux value Ψ _s .

In FIG. 5, the observer B of the torque control from FIG. 4 is shown. The observer B is based on a model 32 of the steering wheel actuator 13 which, as a function of the voltages u _sd and u _{sq, supplies} estimated values i sqs, i _sds for the torque-generating and flux-generating current components of the motor current i _s . Then the difference between the measured and subsequently transformed currents i _sq , i _sd and the estimated quantities i _sqs , i _{sds is} formed. This difference is then amplified in a block 33 , and the estimated magnetic flux Ψ _{s is obtained} . In a block 34 , the estimated torque M _{s is} calculated according to equation (3) on the basis of the estimated magnetic flux Ψ _s and the measured and transformed torque-forming current component i _sq.

Claims (14)

1. A method for controlling ( 19 ) or regulating ( 24 ) a torque (M) delivered by an electric motor ( 13 ), the torque control ( 19 ) or torque control ( 24 ) being subordinated to the current (i _sd ; i _sq ) of the electric motor ( 13) is regulated (20) and driven the electric motor (13) from an inverter (15), characterized in that based on to the electric motor (13) adjacent strand currents (i _1, i _2, i ₃₎ and phase voltages (u ₁ , u ₂ , u ₃ ) a magnetic flux (Ψ _s ) of the electric motor ( 13 ) is estimated and the torque (M) is controlled or regulated as a _{function of the estimated magnetic flux (Ψ s).} 2. The method according to claim 1, characterized in that in a torque control ( 19 ) a reference variable (i _s ^* ) for the current (i _s ) of the current control ( 20 ) based on the estimated magnetic flux (Ψ _s ) is determined. 3. The method according to claim 2, characterized in that the _{reference variable (i s} ^* ) using the equations
is determined, where M ^{* is} a desired torque value and z _{p is} a number of pole pairs of the electric motor ( 13 ). 4. The method according to claim 1, characterized in that in a torque control ( 24 ) an estimated actual torque value (M _s ) is determined on the basis of the estimated magnetic flux (Ψ _s ). 5. The method according to claim 4, characterized in that the estimated actual torque value (M _s ) using the equation
is determined, where z _{p is} a number of pole pairs and i _{sq is} a torque-generating component of the current (i _s ) of the electric motor ( 13 ). 6. The method according to any one of claims 1 to 5, characterized in that based on the phase voltages (u ₁ , u ₂ , u ₃ ) an estimated value (i _sds , i _sqs ) for the current applied to the electric motor ( 13 ) is determined, the current (i _sd , i _sq ) applied to the electric motor ( 13 ) is determined based on the phase currents (i ₁ , i ₂ , i ₃ ) and the estimated magnetic flux (Ψ _s ) from the difference in the estimated value (i _sds , i _sqs ) and the current (i _sd , i _sq ) is determined. 7. The method according to claim 6, characterized in that the estimated value (i _sds , i _sqs ) for the current by means of a model ( 32 ) of the electric motor ( 13 ) based on the phase voltages (u ₁ , u ₂ , u ₃ ) is determined. 8. The method according to any one of claims 1 to 7, characterized in that the _{phase currents (i 1} , i ₂ , i ₃ ) and the phase voltages (u ₁ , u ₂ , u ₃ ) before the estimation of the magnetic flux (Ψ _s ) can be transformed into a coordinate system (dq) that is fixed to the rotor flux. 9. Device ( 14 ) for controlling ( 19 ) or regulating ( 24 ) a torque (M) delivered by an electric motor ( 13 ), with a current control ( 20 ) subordinate to the torque control (19 ) or torque control ( 24 ) for regulating the current (i _sd , i _sq ) of the electric motor ( 13 ), the electric motor ( 13 ) being controllable by a converter ( 15 ), characterized in that the device ( 14 ) has an observer (B) for estimating a magnetic flux (Ψ _s ) of the electric motor ( 13 ) on the basis of phase currents (i ₁ , i ₂ , i ₃ ) and phase voltages (u ₁ , u ₂ , u ₃ ) applied to the electric motor (13 ), the device ( 14 ) having the torque (M ) controls or regulates depending on the estimated magnetic flux (Ψ _s). 10. The device ( 14 ) according to claim 9, characterized in that the device ( 14 ) has means for carrying out a method according to one of claims 2 to 8. 11. Control unit ( 34 ) for a steer-by-wire steering system ( 1 ) of a motor vehicle for controlling ( 19 ) or regulating ( 24 ) an actuator ( 13 ) of the steer-by-wire which is designed as an electric motor ( 13) - Steering system ( 1 ) delivered torque (M), the torque control ( 19 ) or torque control ( 24 ) being subordinated to a current control ( 20 ) for controlling the current (i _sd , i _sq ) of the electric motor ( 13 ) and the electric motor ( 13 ) can be controlled by a converter ( 15 ), characterized in that means for executing a method according to one of claims 1 to 8 are implemented in the control unit (34). 12. Memory element ( 36 ), in particular read-only memory, random access memory or flash memory, for a control unit ( 34 ) of a steer-by-wire steering system ( 1 ) of a motor vehicle on which a computer program is stored which is executable on a computing device, in particular on a microprocessor ( 35 ), characterized in that the computer program stored on the memory element (36 ) is suitable for executing a method according to one of claims 1 to 8. 13. Computer program, characterized in that the computer program is suitable for executing a method according to one of claims 1 to 8 when it runs on a computing device, in particular on a microprocessor ( 35 ). 14. Computer program according to claim 13, characterized in that the computer program is stored on a memory element (36 ), in particular on a flash memory.