DE102015117614A1 - Method for operating a permanent-magnet synchronous machine, in particular a servomotor in a steering system - Google Patents

Abstract

In a method for operating a permanent-magnet synchronous machine, which is operated redundantly with at least two sub-machines, in a case of a loss of function of a sub-machine, the maximum torque provided by the further sub-machine is successively reduced in a transition phase to a limit torque which is smaller than the maximum of the remaining part of machine producible torque maximum.

Description

The invention relates to a method for operating a permanent-magnet synchronous machine, in particular a servomotor in a steering system.

Are known methods for controlling a permanent-magnet synchronous machine via a field-oriented control, in which the difference of actual and target currents as input receives in a control unit and a pulse width modulation and a power output stage from a battery voltage an alternating voltage with three different phases is generated, each phase a strand winding of the synchronous motor is assigned. The field-oriented regulation is, for example, in the DE 10 2013 222 075 A1 described.

When using a permanent magnet synchronous machine as a servomotor in a steering system, a redundant design with a subdivision of the various phases of the engine in sub-machines, which are controlled independently of each other for safety reasons. In the event of a failure of a dividing machine, the assist torque provided by the servomotor abruptly reduces, which can lead to an unpleasant haptic effect in the steering system for the driver.

The invention has for its object to control a permanent-magnet, divided into sub-machines synchronous machine in such a way that in case of failure of a sub-machine operation with increased security is guaranteed.

This object is achieved with the features of claim 1. The dependent claims indicate expedient developments.

The inventive method is used to operate a permanent-magnet synchronous machine, which is used for example as a servomotor in a steering system. The synchronous machine advantageously has permanent magnets on the rotor side and coils or windings on the stator side, which are subjected to phase currents. The control is preferably carried out via a field-oriented control or via a field-oriented control.

The synchronous machine can be operated in the form of at least two sub-machines, which are independently controllable via a respective power output stage. Each power output stage is operated via a field-oriented control. The division into two, optionally more than two sub-machines has the advantage that in this way a redundant design of the synchronous machine is achieved, so that even if one sub-machine fails, a torque can be generated via the remaining sub-machine. The division into several sub-machines is preferably carried out by forming subsets of the phase currents, so that, for example, in the case of two sub-machines, a first subset of the phase streams of the first sub-machine and a second subset of the phase streams of the second sub-machine is assigned. Each subset preferably contains the same number of phases. Additionally or alternatively, it is also possible to achieve the division into sub-machines by assigning windings or coils to a respective sub-machine. There are also versions with a power amplifier per phase possible.

The method is based on an operation of the permanent-magnet synchronous machine with at least two sub-machines, which can be controlled independently of each other. The torque generated by the synchronous machine is composed by summing the individual moments of each sub-machine, each sub-machine provides the same maximum single torque. In the event of a loss of function in a sub-machine or a unit associated with this sub-machine, for example a logic unit or a power output stage, this sub-machine can no longer contribute torque to the total torque of the synchronous machine. Accordingly, the torque maximum, which can be delivered by the synchronous machine, reduced to the sum of the individual moments of the remaining sub-machines.

In order to ensure operation of the synchronous machine with the remaining sub-machines over a long period of operation, it is expedient to operate the remaining sub-machines not with maximum power, but at a level below the maximum power. In the event of a failure of a sub-machine, therefore, the torque provided by the further sub-machines is reduced to a limit torque which is below the maximum torque maximum that can be generated by the remaining sub-machines. The limit torque ensures compliance with minimum safety requirements. In case of failure of another sub-machine torque loss is limited accordingly.

So that in particular the subjective sensation during the fall of the torque from the initial level to the limit torque is not perceived as significant and disturbing, the reduction of the maximum torque that can be generated by the remaining submachines to the limit torque does not occur abruptly after the failure of a submachine, but successively. The successive transition from that of the remaining part machines generated maximum possible torque on the limit torque prevents uncomfortable state change of the synchronous machine and thereby prevents, for example, startle reactions, for example, in the case of use of the synchronous machine as a servomotor in a steering system of a vehicle. The reduction of the torque maximum of the remaining sub-machines to the limit torque is usually lower than the reduction of the torque maximum of all sub-machines at maximum demand on the maximum torque of the remaining sub-machines, the successive transition, for example, not noticed by a driver of a vehicle or only as an insignificant reduction becomes.

With the method according to the invention a maximum comfort is ensured even in the event of failure of a part machine.

The limit torque can be set to a defined, defined level, which is, for example, 60% or 70% of the torque maximum that can be generated by the remaining sub-machines. In the case of two sub-machines, in which the synchronous machine is divided, therefore, after the failure of a sub-machine, the maximum torque of the remaining sub-machine is 30% or 35% of the maximum torque of both sub-machines.

The reduction of the torque from the torque maximum of the remaining part machines to the limit torque is preferably linear. However, non-linear reduction functions are also possible.

The reduction in torque during the transition phase can be set to a defined period of time, for example 1 s. It may be expedient to define a minimum period of time in order, for example, in the case of an electric servomotor in a steering system, to carry out a transition which is not noticeable to the driver or hardly noticeable, up to the limit torque.

The reduction to the limit torque occurs for those cases where the demand torque is greater than the limit torque. Thus, a capping of the requested torque is performed on the limit torque.

In contrast, advantageously, the torque provided by the at least one functional sub-machine is optionally set to a level below the limit torque, if the request torque is less than the limit torque. In these cases, a cap is not required.

If an error occurs in the case of a requirement torque below the limit torque, the distribution of the torque between the sub-machines is expediently designed such that in total there is no change in the output torque. In this case, if appropriate, the torque of a submachine can be increased.

Conveniently, the synchronous machine is divided into two sub-machines. However, it may also be advantageous to provide more than two sub-machines, for example, four sub-machines with, for example, two logic units and 12 power amplifiers, each logic unit controls two sub-machines, each with three power output stages.

According to yet another expedient embodiment, the torque is divided equally between the various part machines of the synchronous machine. This is true in normal operation, so that, for example, in two properly functioning sub-machines, a split of 50% of the torque takes place on the sub-machines. But even in case of failure, with a loss of function of a sub-machine, the torque can be divided equally among the remaining working lathes.

According to a further advantageous embodiment, the permanent-magnet synchronous machine has one logic unit per submachine and advantageously one or more final output stages. If necessary, a logic unit can control several submachines. The error or loss of function can occur, for example, in a logic unit or a power output stage.

Further advantages and expedient embodiments can be taken from the further claims, the description of the figures and the drawings. Show it:

1 a schematic representation of a steering system in a vehicle, with an electric servomotor, which is designed as a permanent-magnet synchronous machine,

2 a block diagram with a permanent-magnet synchronous machine, which is operated in the form of two sub-machines, each sub-machine is assigned a logic unit and a power output stage,

3 a graph with the torque curve with fully functional synchronous machine and in case of failure of a sub-machine,

4 one 3 corresponding graph, but in addition with registered limit torque.

This in 1 illustrated steering system 1 for a vehicle includes a steering wheel 2 , a steering shaft or spindle 3 , a steering or transmission housing 4 and a steering linkage with a steering rack 5 , about which a steering movement on the steerable wheels 6 of the vehicle is transmitted. The gearbox 4 takes a steering gear 8th with a steering pinion and the steering rack 5 on, wherein the steering pinion rotatably with the steering shaft 3 is connected and with the steering rack 5 combs.

The driver gives over the steering wheel 2 with which the steering shaft 3 is firmly connected, a steering angle δ _L before that in the steering gear 8th in the gearbox 4 on the steering rack 5 of the steering linkage is transmitted, whereupon the steerable wheels 6 sets a wheel steering angle δ _V.

To support the applied by the driver hand torque is an electric servomotor 7 provided via the a servo torque in the steering gear 8th can be fed. The electric servomotor 7 is designed as a permanent-magnet synchronous machine having rotor-side permanent magnets and stator-energizable coils, which are controlled via a field-oriented control (FOR). The servomotor 7 may optionally also sit on the steering shaft.

It may be appropriate in the steering system 1 To arrange a torque sensor for determining the generated by the driver hand torque. The torque sensor for determining the manual torque sits, for example, on the steering shaft above the steering gear.

In 2 is the permanent magnet synchronous machine 7 schematically shown in a block diagram including the driving units. The synchronous machine 7 is operated in the form of two sub-machines, each sub-machine is driven in each case with a subset of the phases of the synchronous machine. For example, a total of six phases can be provided, of which each of the two sub-machines of the synchronous machine 7 operated with three phases.

Each submachine of the synchronous machine 7 is a sensor 9a , b, a logic unit 10a , b with a field-oriented control 11a , b and a power amplifier 12a , b assigned. Every sensor 9a , B comprises a rotor position sensor for determining the current rotor position of the synchronous machine 7 , a target torque sensor for determining, for example, the current manual torque in the steering system and sensors for voltage and current measurement. The logic unit 10a , b comprises with the field-oriented control 11a , b the control logic for each submachine. In the power output stage 12a , b the required phase currents are provided.

In a target torque specification 13 in the logic unit 10a the setpoint torque is specified by the synchronous machine 7 Total to be generated. The setpoint torque specification can also be used in the other logic unit for redundancy reasons 10b to be available. The distribution of the target torque on both sub-machines of the synchronous machine 7 takes place within a logic unit in the nominal torque specification. The transmission of the setpoints to the respective other logic unit via a distribution unit 14 between the logic units 10a and 10b is arranged. In the normal case advantageously takes place a uniform distribution of the target torque input to the two sub-machines.

The target torque specification 13 receives information from a moment sensor 15a , if necessary, in the sensor system 9a can be integrated.

For redundancy reasons, an additional torque sensor can also be used on the part of the second submachine 15b be arranged.

The jagged cloud in the power output stage 12b , which is assigned to the second sub-machine, symbolizes a failure of this power output stage 12b which leads to a loss of function of the second sub-machine. In this case, only the first part machine of the synchronous machine 7 Release torque.

3 shows the course of the torque T as a function of time t. The torque curve is divided into three sections T ₁ between the time 0 and the time t ₁ , T ₂ between the times t ₁ and t ₂ and T ₃ between the times t ₂ and t ₃ . The torque curve shown with the subsections T ₁ , T ₂ and T ₃ represents the maximum, currently deliverable torque of the synchronous machine. The first torque section T ₁ is 100% and is divided into each 50% maximum power or torque output of each submachine , At time t ₁ , the second power output stage drops 12b ( 2 ), accordingly, the maximum deliverable torque decreases to 50%, which can be provided by the maximum functioning of the first part of the machine. For safety reasons, however, the maximum torque to be delivered is reduced to 30%, which corresponds to that of the remaining first part of the machine can be generated maximum torque.

The transition T ₂ in the torque curve from 50% of the maximum torque of the first part machine to 30% of the first part machine is linear. The time span during which the transition T _{2 is carried out} between the times t ₁ and t ₂ is, for example, 1 s. This successive transition from 50% torque maximum of the remaining first part machine to 30%, which represent a limit torque, prevents an uncomfortable state change and irritation of the driver.

At time t _3, the limit torque T ₃ falls to 0. The jagged cloud at time t ₃ symbolizes a further loss, which relates to the first remaining portion machine.

In the diagram according to 4 In addition to the course of the torque with the sections T ₁ , T ₂ and T ₃ , a request torque T _{A is also} entered, which represents the actually required, requested torque. In the embodiment according to 4 T _{A is} at a level below the limit torque T ₃ and thus can be completely provided by the remaining, intact first part machine. A limitation of the requested torque only takes place if the requested torque would exceed the limit torque T ₃ .

LIST OF REFERENCE NUMBERS

1

steering system

2

steering wheel

3

steering shaft

4

gearbox

5

Steering rack

6

front

7

electric servomotor / synchronous machine

8th

steering gear

9a

sensors

9b

sensors

10a

logic unit

10b

logic unit

11a

field-oriented regulation

11b

field-oriented regulation

12a

power output stage

12b

power output stage

13

Target torque setting

14

distribution unit

15a

torque sensor

15b

torque sensor

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102013222075 A1 [0002]

Claims (11)

Method for operating a permanent-magnet synchronous machine ( 7 ), in particular a servomotor in a steering system ( 1 ), which has permanent magnets and energizable coils, the synchronous machine being operated redundantly with at least two dividing machines and the dividing machine being controlled independently of one another, wherein in the case of a loss of function in a part machine or a unit associated with this part unit the maximum torque to be provided by the further dividing machines a transition phase is successively reduced to a limit torque which is smaller than the maximum torque of the remaining sub-machines can be generated. A method according to claim 1, characterized in that the reduction of the torque provided by the at least one further sub-machine to the limit torque in the transition phase is linear. A method according to claim 1 or 2, characterized in that the reduction of the torque provided by the at least one further sub-machine is carried out on the limit torque in the transition phase over a defined minimum period of time, for example, 1 s. Method according to one of claims 1 to 3, characterized in that the provided by the at least one further sub-machine torque is adjusted to the level of a request torque, if this is below the limit torque. Method according to one of claims 1 to 4, characterized in that the synchronous machine is divided into two or four sub-machines. Method according to one of claims 1 to 5, characterized in that the torque is divided equally between the sub-machines of the synchronous machine. Method according to one of claims 1 to 6, characterized in that the limit torque is 30% or 35% of the maximum torque of all sub-machines. Permanent magnet synchronous machine, in particular servomotor ( 7 ) in a steering system ( 1 ) for carrying out the method according to one of claims 1 to 7, with one or more logic units for one or more submachines. Synchronous machine according to claim 8, characterized in that the target torque between the sub-machine is distributed via a distribution unit. Synchronous machine according to claim 8 or 9, characterized in that each sub-machine is controlled by one or more power amplifiers. Steering system with a permanent-magnet synchronous machine ( 7 ) as a servo motor according to one of claims 8 to 10.

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