DE102015214555A1 - Vehicle, device and method for determining a current setpoint vector for a synchronous motor of an electromechanical steering - Google Patents

Abstract

A means of locomotion, a device and a method for determining a current desired vector (Id_soll, Iq_soll) for a synchronous motor of an electromechanical steering are proposed. The method comprises the steps:
- reading out a first characteristic field (4) from a memory which has a dependence of a d-current (Id)
- Of a nominal torque (Msoll) of the synchronous motor and
Of a temperature (θmot) of the synchronous motor describes
- Reading a second map (5) from a memory, which has a dependence of the d-current (Id)
- Of a speed (φ ') of the synchronous motor and
- describes an intermediate circuit voltage (Uz) for the operation of the synchronous motor, and
- Determining a first d-current target vector (Id_soll) by means of the first map (4) and the second map (5).

Description

State of the art

The present invention relates to a means of locomotion, a device and a method for determining a current setpoint vector for a synchronous motor. In particular, the present invention relates to a simplified determination of a current target vector for a synchronous motor of an electromechanical steering for a means of transportation.

In the prior art increasingly electromechanically assisted steering systems are proposed. In the electromechanical steering, a permanent magnet synchronous machine with a large reluctance torque is sometimes used. This means that the motor current must also have a d-component in the armature adjustment range so that a desired torque can be achieved with the minimum current. The optimum distribution of the motor current to the d-component and the q-component is a function of the setpoint torque, the speed, the temperature of the motor and the DC link voltage (in most cases the voltage across the DC link capacitor). A direct representation of the d-current and the q-current in the control program can thus take place in the form of a four-dimensional characteristic diagram. This relationship is very complex, computationally expensive, and in practice can only be calculated offline (i.e., not by the steering program of a steering system). The space required for this and the computational effort for the interpolation in a 4D map are therefore unacceptably large for automotive applications. It is therefore an object of the present invention to determine the determination of a current setpoint vector on the one hand as accurately as possible, on the other hand by means of the least possible computational effort.

Disclosure of the invention

The object identified above is achieved by a method for determining a current setpoint vector for a synchronous motor of an electromechanical steering system. The current setpoint vector may have a d-set component and a q-set component. The current setpoint vector can be described, for example, as an orthogonal superimposition of a d-set current and a q-setpoint current in the rotor-fixed coordinate system of a synchronous machine. For background information describing electrical operations and magnitudes in a synchronous motor, reference is made to the pertinent literature.

In a first step, a first map is read from a memory, wherein the first map describes a dependence of the d-current of the current setpoint vector of a desired torque of the synchronous motor and a temperature of the synchronous motor. The temperature can be measured, for example, by means of a corresponding temperature sensor and / or determined on the basis of further metrologically available parameters, in particular on the basis of a thermal model of the synchronous motor. In a corresponding manner, a second map is read from the memory, which describes a dependence of the d-current of a rotational speed of the synchronous motor and of an intermediate circuit voltage for the operation of the synchronous motor. The speed may be a current actual speed of the synchronous motor. The DC link voltage can be present in a DC link, which converts a DC power supply into an AC variable for the operation of the synchronous motor. In particular, the synchronous motor can be designed in three phases. Based on the two maps, a first d-current target vector is then determined by the target torque, the temperature, the speed and the DC link voltage determined and used in conjunction with the maps to read out a value for the first d-current setpoint vector. As a result, the known in the prior art high computational effort for the transmission of the electrical quantities current and voltage in the rotor fixed coordinate system or from the rotor fixed coordinate system is avoided. Powerful processors are eliminated by using the two maps. In this way, the determination of the current desired vector can be carried out according to the invention exactly and yet with a low computational outlay.

The dependent claims show preferred developments of the invention.

The first d-current target vector can be determined, for example, as the minimum of a second d-current target vector, which is determined from the first map, and a third d-current target vector, which is determined from the second map. On the basis of a given operating state, respective output variables of the first characteristic diagram and of the second characteristic field are determined, and the smaller output variable is used as the new d-current desired vector.

For example, the first map may be optimized for an engine speed of 0 revolutions per minute and an intermediate circuit voltage corresponding to its rated value (eg, 12.8 volts). In other words, the variables contained in the second map are assumed to be constant in a predefined manner when the first map is created.

The second map can be created for a constant temperature of the synchronous motor or be optimized. For example, the temperature may be in the range of -20 ° C because the magnetic strength and the induced electromotive force are higher at low temperatures.

M

das Sollmoment des Synchronmotors,

ZP

die Polpaarzahl eines Rotors des Synchronmotors,

F(T)

ein temperaturabhängiger Permanentmagnetschluss, welcher über ein Kennfeld oder über eine Berechnung ermittelt wird,

Ld

die Induktivität eines Stators des Synchronmotors in d-Richtung,

Lq

die Induktivität eines Stators des Synchronmotors in q-Richtung und

Id

der ermittelte erste d-Stromsollvektor ist.

Preferably, a q-current desired vector can be determined on the basis of the following motor equation: Iq = 2/3 * M / Zp / (F (T) + (Ld-Lq) * Id), in which

M

the nominal torque of the synchronous motor,

ZP

the pole pair number of a rotor of the synchronous motor,

F (T)

a temperature-dependent permanent magnet closure, which is determined via a characteristic field or via a calculation,

Ld

the inductance of a stator of the synchronous motor in the d-direction,

Lq

the inductance of a stator of the synchronous motor in q-direction and

id

the determined first d-current target vector is.

Here, the temperature-dependent permanent magnet F (T) can be specified as a characteristic or as a calculation formula, since the dependence of the magnetic strength of the temperature is almost linear.

Preferably, a third characteristic map can be read from a memory, which describes a dependency of a maximum operating-point-dependent engine torque on a rotational speed of the synchronous motor and on an intermediate circuit voltage for operation of the synchronous motor. The maximum torque of the synchronous motor is thus implemented as a pre-calculated 2D map. The third characteristic map can be created, for example, for a maximum temperature of the synchronous motor, in particular between 90 ° C and 110 ° C.

Favor so the setpoint of the d-current is set via two 2D maps. The first 2D map represents a dependency of the d-current on the nominal torque and the motor temperature. This map is pre-calculated offline for the so-called "anchorage range" and takes into account the temperature influence on the magnetic strength. The optimization of the characteristic map is carried out for the operating points with two constant operating parameters. The engine speed is assumed to be 0 and the intermediate circuit voltage equal to a nominal value of 12.8 volts. In the context of the present invention, an "offline" pre-calculation is understood to mean that the characteristic field itself is already in data form when the method according to the invention is carried out. This means that, in particular during a starting process of a means of transport configured according to the invention, the first characteristic map and the second characteristic field, in particular also the third characteristic field, are stored in a memory. In particular, a conditioner may be in a delivery state and / or in a workshop visit. Therefore, the relationships that can be determined from the first, second and third maps need not be calculated in real time, for which a considerable computational effort would have to be operated, but rather tables whose information can be read out on the basis of the input variables can be used to represent this information, in particular in a discrete form be kept ready. From the two d current values calculated by the first and second maps (e.g., both 2D maps), the minimum value (both values are negative) and the value having the largest magnitude, respectively, are used as the set value for the d current of the synchronous motor.

According to a second aspect of the present invention, there is provided an apparatus for detecting a current command vector for a synchronous motor (eg, an electromechanical steering). The device comprises a data memory and an evaluation unit, which can be used, for example, as a microcontroller, programmable processor, nanocontroller or the like. can be designed. The evaluation unit is set up to read out a first characteristic map from the memory which describes a dependence of a d-current on a nominal torque of the synchronous motor and on a temperature of the synchronous motor. Accordingly, the evaluation unit is set up to read out a second characteristic map from the memory which describes a dependence of the d-current on a rotational speed of the synchronous motor and on an intermediate-circuit voltage for operation of the synchronous motor. Finally, the evaluation unit is set up to determine a first d-current setpoint vector by means of the first characteristic diagram and the second characteristic diagram. In this way, the device according to the invention is set up to carry out a method as has been described above in detail in connection with the first-mentioned aspect of the invention. The features, feature combinations and the advantages resulting from these correspond to those of the method according to the invention in such a way that reference is made to avoid repetition of the above statements.

According to a third aspect of the present invention, there is proposed a means of locomotion (eg, a car, a van, a truck, a motorbike) having an electromechanical steering provided by a synchronous machine (eg, permanent magnet excited) for generating a steering assist torque is driven. In addition, the means of transportation includes a device according to the second-mentioned aspect of the invention, so that the features, feature combinations and resulting from these advantages result in a corresponding manner.

The present invention enables a particularly high energy efficiency in an electric synchronous drive.

Brief description of the figures

Hereinafter, embodiments of the invention will be described in detail with reference to the accompanying drawings. In the drawings:

1 a schematic view of components of an embodiment of a means of transport according to the invention with an embodiment of an inventive device for determining a full current vector for a synchronous motor electromechanical steering of the means of locomotion;

2 a flowchart illustrating the signal flows and their processing in an embodiment of a device according to the invention; and

3 a flowchart illustrating steps of an embodiment of a method according to the invention for determining a current target vector for a synchronous motor of an electromechanical steering.

Embodiments of the invention

1 shows a car 10 as a means of locomotion in which an inventive electromechanical steering system 1 is arranged. Via a steering wheel (steering wheel) 6 and a steering column 7 the driver can use a steering gear 8th a force on a rack 9 exercise, passing through a synchronous motor 13 The steering assist is assisted to the wheels 11 to steer the front axle. A resolver 2 is mechanical and information technology with the steering column 7 coupled, so that an evaluation unit 14 an amplifier 12 can control with a current setpoint vector determined according to the invention. A data line 15 connects the resolver 2 and the evaluation unit 14 , A data store 23 is information technology to the evaluation unit 14 connected so that instructions representing the method steps of the method according to the invention and in particular data sets representing the maps used in the invention are available for use.

2 shows a signal flow diagram of an embodiment of a steering system according to the invention or a device according to the invention. A 2D map 3 as claim according third characteristic map describes a dependence of an engine torque M of an engine speed φ ' _MOT and a DC link voltage U _z . From the 2D map 3 a maximum torque M _{max is} determined by which a desired torque M _SOLL in a limiter 15 is converted into a limited setpoint torque M _{SOLL_LIM} . The limiter 15 The value of the setpoint torque M _SOLL continues to be unchanged if the magnitude of the setpoint torque M _{SOLL is} less than the maximum torque M _max . If the maximum torque is exceeded, the value of the maximum torque M _{max is} forwarded with the corresponding sign. The limitation of the setpoint torque M _Soll reduces the resultant deviation of the calculated target currents of optimal values. This limited setpoint torque M _{SOLL_LIM} becomes a multiplier 16 in which it is multiplied by 2/3 · Zp and a divider 17 is supplied. In addition, the limited setpoint torque M _{SOLL_LIM becomes} a 2D characteristic map 4 fed as demanding first characteristic map, which additionally receives a current engine temperature θ _{MOT of} the synchronous motor as input. The output of the 2D map 4 represents a first possible d-current setpoint vector Id_teil1, which is a minimum value determiner 20 is supplied. Another 2D map 5 as a second demanding map receives a current engine speed φ ' _{MOT of} the synchronous motor and an intermediate circuit voltage U _Z , from which a second possible d-current setpoint Id_teil2 emerges and the minimum value determinator 20 is supplied. The output signal of the minimum value detector 20 is output as the first d-current target vector Id_setpoint and in addition to a multiplier 19 which multiplies the first d-current target vector Id_soll by the difference between the inductances (Ld-Lq) and the result to an adder 21 supplies. A 1D characteristic 22 receives as input the motor temperature θ _MOT , from which a current magnetic flux is determined and the summer 21 is supplied. The output signal of the summer 21 becomes the divider 17 supplied, which outputs a q-current target vector Iq_soll.

3 shows steps of an embodiment of a method according to the invention for determining a current setpoint vector for a synchronous motor of an electromechanical steering. This will be done in step 100 a map read from a memory, which describes a dependence of a maximum operating point-dependent engine torque of a rotational speed of the synchronous motor used to generate a steering assist torque and a DC link voltage for operation of the synchronous motor. In step 200 a first map is read from a memory, which describes a dependence of a d-current of a nominal torque of the synchronous motor and a temperature of the synchronous motor. In step 300 a second map is read from a memory, which describes a dependence of the d-current of a speed of the synchronous motor and a DC link voltage to the operation of the synchronous motor. It should be noted that the aforementioned maps have not been created in particular during the operation of the means of transport, but have already been stored at an earlier date in a data memory of the means of transport. In step 400 is determined from the maps a first d-current target vector. This can be done for example by a minimum value consideration of the output variables of the two maps. In step 500 a q-current setpoint vector is determined on the basis of a motor equation of the synchronous motor. This is: Iq = 2/3 * M / ZP / (F (T) + (Ld-Lq) * Id)

As a result, a very accurate result is determined with the least possible computational effort, based on which a current setpoint vector for the operation of a synchronous motor of an electromechanical steering system is available. The current setpoint vector unambiguously predetermines the currents required in each phase of the stator winding for generating the setpoint torque.

Although the aspects and advantageous embodiments of the invention have been described in detail with reference to the embodiments explained in connection with the accompanying drawings, modifications and combinations of features of the illustrated embodiments are possible for the skilled person, without departing from the scope of the present invention, the scope of protection the appended claims are defined.

LIST OF REFERENCE NUMBERS

1

contraption

2

resolver

3

third 2D map

4

first 2D map

5

second 2D map

6

Steering wheel (steering wheel)

7

steering column

8th

steering gear

9

rack

10

car

11

steerable front wheel

12

final stage

13

synchronous motor

14

evaluation

15

signal line

16

multipliers

17

divider

18

inductance difference

19

multipliers

20

Minimum value calculator

21

adder

22

1D characteristic

23

data storage

100 to 500

 steps

M

engine torque

I

electricity

Θ

temperature

U

tension

φ

rotation speed

L

inductance

Z

number of pole pairs

Claims (10)

Method for determining a current setpoint vector (Id_setpoint, Iq_setpoint) for a synchronous motor ( 13 ) comprising the steps of: - reading ( 200 ) of a first characteristic map ( 4 ) from a memory ( 23 ), which determines a dependence of a d-current (Id) on a setpoint torque (Msetpoint) of the synchronous motor ( 13 ) and - of a temperature (θmot) of the synchronous motor ( 13 ), - readout ( 300 ) of a second characteristic map ( 5 ) from a memory ( 23 ), which has a dependence of the d-current (Id) - of a rotational speed (φ ') of the synchronous motor ( 13 ) and - from a DC link voltage (Uz) to the operation of the synchronous motor ( 13 ), and - determining ( 400 ) of a first d-current setpoint vector (Id_soll) by means of the first characteristic diagram ( 4 ) and the second characteristic map ( 5 ). Method according to claim 1, wherein the determination of the first d-current desired vector (Id_soll) - a determination of a second d-current desired vector (Id_teil1) from the first characteristic field ( 4 ), - determining a third d-current desired vector (Id_teil2) from the second characteristic diagram ( 5 ) and - determining the first d-current target vector (Id_soll) as a minimum of the second d-current target vector (Id_teil1) and the third d-current target vector (Id_teil2). Method according to claim 1 or 2, wherein the first characteristic map ( 4 ) for an engine speed of 0 rpm and an intermediate circuit voltage (Uz) is optimized according to its nominal value. Method according to one of the preceding claims, wherein the second characteristic map ( 5 ) for a constant temperature (θmot) of the synchronous motor ( 13 ) is determined. Method according to one of the preceding claims further comprising - Determine ( 500 ) of a q-current target vector based on the following relationship: Iq = 2/3 * M / Zp / (FT) + (Ld - Lq) * Id, where - M is the nominal torque (Msoll) of the synchronous motor ( 13 ), Zp is the pole pair number of a rotor of the synchronous motor ( 13 ), - F (T) is a temperature-dependent permanent magnet flux, - Ld is the inductance of a stator of the synchronous motor ( 13 ) in d-direction - Lq the inductance of a stator of the synchronous motor ( 13 ) in q-direction and - Id is the determined first d-current target vector (Id_soll). Method according to one of the preceding claims further comprising - readout ( 100 ) of a third characteristic map ( 3 ) from a memory ( 23 ), which has a dependence of a maximum, operating-point-dependent engine torque (Mmax) - of a rotational speed (φ ') of the synchronous motor ( 13 ) and - from a DC link voltage (Uz) to the operation of the synchronous motor ( 13 ) describes. Method according to claim 6, wherein the third characteristic field ( 3 ) for a maximum temperature of the synchronous motor ( 13 ), in particular between 90 ° C and 110 ° C, created. Device for determining a current setpoint vector (Id_soll, Iq_soll) for a synchronous motor ( 13 ) comprising - a memory ( 23 ) and - an evaluation unit ( 14 ), whereby the evaluation unit ( 14 ), - a first map ( 4 ) from the memory ( 23 ) which reads out a dependence of a d-current (Id) on a setpoint torque (Msetpoint) of the synchronous motor ( 13 ) and - of a temperature (θmot) of the synchronous motor ( 13 ), - a second map ( 5 ) from the memory ( 23 ), which has a dependence of the d-current (Id) - of a rotational speed (φ ') of the synchronous motor ( 13 ) and - from a DC link voltage (Uz) to the operation of the synchronous motor ( 13 ), and - a first d-current setpoint vector (Id_soll) by means of the first characteristic diagram ( 4 ) and the second characteristic map ( 5 ) to investigate.  Apparatus according to claim 8, further arranged to carry out a method according to any of the preceding claims 1 to 7. Means of transportation ( 10 ) comprising - an electromechanical steering ( 1 ), - a, in particular permanent magnet excited, synchronous machine ( 13 ) for generating a steering assist torque and - a device according to any one of the preceding claims.

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