EP2673159A2

EP2673159A2 - Method for adjusting an actual torque delivered by an electric motor in a motor vehicle to a target torque

Info

Publication number: EP2673159A2
Application number: EP12703049.2A
Authority: EP
Inventors: Rolf Jaros; Julian Roesner
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2011-02-10
Filing date: 2012-02-01
Publication date: 2013-12-18
Also published as: DE102011003946A1; WO2012107330A3; CN103347728B; CN103347728A; WO2012107330A2

Abstract

The invention relates to a method for adjusting an actual torque delivered by an electric motor in a motor vehicle to a target torque, wherein the electric motor comprises a stator winding (11), a rotor winding (12), a field rheostat (15) associated with the rotor winding (12), and a power converter (20) which is connected downstream of the stator winding (11) and has actuatable switch elements (21), wherein the actual torque is adjusted to the target torque in that a commutation angle is set by deliberately actuating the switch elements (21) and/or in that a current is deliberately set by the stator winding (12).

Description

Description title

A method for controlling an output from an electric machine in a motor vehicle actual torque to a desired torque

The present invention relates to a method for regulating an output from an electric machine in a motor vehicle actual torque to a desired torque.

State of the art

Claw pole generators with electrical excitation are usually used as electric machines in motor vehicles. The current through the rotor winding serves as a manipulated variable for controlling the desired output voltage and is specified by an assigned field controller. It is also known to use electrical machines as starter generators, on the one hand to start the engine during engine operation of the electric machine and on the other hand to generate power for the electrical system and for charging the motor vehicle battery in the generator mode of the electric machine.

DE 103 17 207 A1 describes a method for delivering the largest possible torque in a belt-driven starter generator when starting the engine. For this purpose, the commutation angle and exciting current are set as a function of the rotational speed in such a way that the maximum possible starting torque results.

Generators, which are also used for vehicle propulsion, are known in the field of hybrid vehicles. The aim here is the engine at low speeds, where this is not yet its full torque provides support (so-called boost mode, turbo lag compensation). Usually, permanent magnet synchronous machines are used, which are operated at higher voltages> 100V. This leads to a complex system structure, combined with major changes in the drive train and complex protective measures due to the high voltage. In addition to a high integration cost, such a system leads to high additional costs.

It is desirable to provide an easy way to operate an electrical machine in a motor vehicle so that it can be used to drive it and deliver a desired setpoint torque.

Disclosure of the invention

According to the invention, a method is proposed for regulating an actual torque output by an electric machine in a motor vehicle to a setpoint torque with the features of patent claim 1. Advantageous embodiments are the subject of the dependent claims and the following description.

The invention provides a simple way to use an electrical machine in a motor vehicle for driving the same. In particular, a boost function can be realized which requires only comparatively minor modifications to the vehicle and nevertheless enables optimum torque support of the internal combustion engine. A preferred use for a boost mode implements a control such that the summation torque of the engine and electric machine corresponds to the driver's desired torque.

The invention leads to a significant improvement of the starting behavior by torque support in the lower speed range. Pure electric driving at low speeds (so-called creep operation) becomes possible. An inserted internal combustion engine can be performed less efficient ("downsizing") and thus more environmentally friendly, cost-effective and low-consumption, since the associated with the downsizing deterioration of the starting behavior by the electrical torque assistance is compensated. The solution remains overall cost-effective, since only small changes in the drive train must be made. According to the invention, an electric machine in a motor vehicle is controlled by selective adjustment of the commutation angle and / or the rotor current (also referred to below as the exciter current) for delivering a desired torque. The possibility of influencing the torque via an adjustment of the commutation angle and the rotor current, although described in principle in the aforementioned DE 103 17 207 A1. However, it has now been recognized in the context of the invention that this can also be used for the simple regulation of the torque in an engine operation of the electric machine for driving the vehicle. One or both parameters can serve as manipulated variable in the control.

The control is preferably block commutated, so that only a small DC link capacity is required. In a block commutation, for example, always exactly two out of three three-phase windings are energized. Although a disadvantage of the block-commutated control is that, in contrast to sinusoidal control, the current can not be limited. This results in particular in operation at low speeds to the fact that the power electronics must be dimensioned to a very high rated current. As the speed increases, but the current decreases rapidly due to the higher inductive resistance of the stator winding, so that no current limit is necessary here.

The invention is preferably carried out only above a minimum speed. The minimum speed is chosen so that the current is already below a desired maximum value due to the inductive resistance of the stator winding, so that the power electronics can be dimensioned correspondingly small.

More preferably, the invention is carried out only below a maximum speed. The maximum speed results from the fact that the certifiable moment and thus the economy decreases with increasing speed.

The invention can be used advantageously in generators whose output voltage is rectified by a power converter with controllable switching elements. Such a power converter can be operated as a synchronous rectifier, as a boost converter, as buck converter, as a pulse inverter, etc. By appropriate control of the switching elements, the commutation angle is then influenced.

According to a preferred embodiment, the commutation angle is predetermined speed-dependent and the excitation current is used as a manipulated variable, so that by increasing the excitation current, the actual torque is also increased and by reducing the excitation current, the actual torque is also reduced. The specification of the commutation angle can

Based on a speed-dependent characteristic.

According to another preferred embodiment, the exciting current is specified as a function of the speed and the commutation angle is used as the manipulated variable.

When the electric machine is operated with a voltage above the usual 12 V supply voltage, but below a permissible contact voltage of 60 V, the torque output by the machine is increased without the need for particularly complex additional safety measures.

An arithmetic unit according to the invention, e.g. a control unit of a motor vehicle, is, in particular programmatically, configured to perform a method according to the invention.

The implementation of the method in the form of software is also advantageous, since this causes particularly low costs, in particular if an executing control device is still used for further tasks and therefore exists anyway. that is. Suitable data carriers for the provision of the computer program are, in particular, floppy disks, hard disks, flash memories, EEPROMs, CD-ROMs, DVDs and the like. It is also possible to download a program via computer networks (Internet, intranet, etc.).

Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination indicated, but also in other combinations or in isolation, without departing from the scope of the present invention.

The invention is illustrated schematically with reference to an embodiment in the drawing and will be described in detail below with reference to the drawing.

Brief description of the drawings

Figure 1 shows an embodiment of a starter generator with power converter with controllable switching elements, as he may underlie the invention.

FIG. 2 shows the relationship between the torque output by an electrical machine and the speed for different operating voltages.

FIG. 3 shows the relationship between the torque output by an electrical machine and the commutation angle for different exciter currents.

FIG. 4 shows a flowchart of an embodiment of a method according to the invention. Embodiment (s) of the invention

In FIG. 1, an electric machine, on which the present invention is based, is shown in the form of a circuit diagram and designated by 100 as a whole. The electric machine has a generator component 10 and a

Power converter component 20 on. The power converter component is usually operated as a rectifier in regenerative operation of the machine, and as an inverter in motor operation. The generator component 10 is shown only schematically in the form of star-connected stator windings 1 1 and an exciter or rotor winding 12 connected in parallel with a diode. The rotor winding is switched by a power switch 13 which is connected to a terminal 24 of the power converter component 20, clocked. The control of the power switch 13 takes place in accordance with a field controller 15, wherein the power switch 13 as well as the parallel to the rotor winding 12 connected diode are usually integrated in an application-specific integrated circuit (ASIC) of the field controller. In the context of the present application, a three-phase generator is shown. In principle, however, the present invention can also be used with less-or multi-phase generators, for example five-phase generators. The power converter component 20 is designed here as a B6 circuit and has

Switching elements 21, which may be embodied for example as a MOSFET 21. The MOSFETs 21 are, for example via busbars, connected to the respective stator windings 1 1 of the generator. Furthermore, the MOSFETs are connected to terminals 24, 24 'and provide, with appropriate control, a direct current for a vehicle electrical system including battery 30 of a motor vehicle. The actuation of the switching elements 21 takes place by a control device 25 via control channels 26, of which not all are provided with reference numerals for reasons of clarity. The control device 25 receives the phase voltage of the individual stator windings via phase channels 27. To provide these phase voltages, further devices can be provided, which however are not shown for the sake of clarity.

In the (synchronous) rectifier operation, the control device 25 evaluates the phase voltages provided via the phase channels 27 and determines therefrom a respective ON and OFF time of a single MOSFET 21. The control via control channels 26 affects the gate terminals of the MOSFET 21 off. Known field controller, as provided in the context of this embodiment

Field controller 15, have a so-called terminal V-terminal 19 which is connected to a phase of the stator winding of the generator. The frequency of the terminal V signal or the phase input signal is evaluated in the controller 15 and serves depending on the characteristics of this signal for activating or deactivating the controller operation and ultimately for controlling the

Circuit breaker 13 via a drive line 14. The phase signal for the phase signal input 19, as shown, are also performed by the drive means 25. In engine operation, the electric machine 100 is used to operate alone or in

Combined with an internal combustion engine to drive the motor vehicle. Here, the power converter component 20 is operated according to an embodiment of the invention as described with reference to FIG. Preferably, a battery is used as the voltage supply, which has a higher voltage (for example 40 V) than the usual vehicle electrical system voltage of 12 V.

To explain the relationships according to the invention, reference is now made to FIGS. 2 and 3. In FIG. 2, in a diagram 200 on the ordinate the dependence of the emitted actual torque M _RS G of an electric machine on the rotational speed n is plotted on the abscissa for different battery voltages. A graph 201 corresponds to a battery voltage of 12.5 V, a graph 202 corresponds to one Battery voltage of 28 V and a graph 203 corresponds to a battery voltage of 42 V.

In Figure 2 it is first clear that by operating the electric machine at higher voltages and a higher torque can be generated. Furthermore, it is clear that the output torque drops at higher speeds. In order to generate a maximum motor torque even at high speeds, the electric machine is preferably operated in the field weakening mode. In the case of a separately excited synchronous machine, this can be done by rotor-side field weakening by reducing the exciter current and / or by stator-side field weakening by changing the commutation angle.

FIG. 3 plots the dependence of the given actual torque M _RS G of an electrical machine on the ordinate on the ordinate on the abscissa for different exciter currents in a diagram 300 on the ordinate. A graph 301 corresponds to an excitation current of 3.3 A, a graph 302 corresponds to an excitation current of 4.5 A, a graph 303 corresponds to a excitation current of 5.5 A and a graph 304 corresponds to a excitation current of 6.5 A. The Messun - gen were recorded at a speed of n = 3000 min ^"1 .

In FIG. 2 it is first clear that a higher torque can also be generated by higher exciter currents. Further, that the output torque is dependent on the commutation and for the here vorlie- constricting speed of n = 3000 min ^"1, a commutation angle α of about 50 ° is clearly provides the highest torque. This angle depends on the speed and decreases with increasing speed It is therefore advantageous to deposit the commutation angle to be set, for example as a speed-dependent characteristic curve

Moments of the excitation current, so in a first approximation, a proportional relationship. The excitation current is therefore preferably used as a manipulated variable for implementing the torque request. A particularly preferred embodiment of the invention will now be described with reference to Figure 4 with reference to a flow chart, wherein in the present case a support of the internal combustion engine by the electric machine ("Boostbetrieb") is described.

The method for regulating the actual torque to a desired torque begins in a step 400, wherein a driver's desired torque - usually based on an accelerator pedal position - is determined.

In a step 401, the torque currently generated by the internal combustion engine is determined, for example, map-based from the quantities injection quantity and speed.

In a step 402, the difference between the driver's desired torque and the torque currently generated by the internal combustion engine is determined as the desired torque for the electric machine.

In a step 403, the actual torque of the electric machine is determined, for example, map-based from the variables excitation current, commutation angle and speed.

In a step 404, a suitable commutation angle is specified as a function of the rotational speed, preferably characteristic-based.

Finally, in a step 405, the excitation current is predetermined as a function of the setpoint torque or of the control deviation between the setpoint torque and the actual torque, in particular by clocking between 0 and 100%.

The steps 401 to 405 take place within the scope of a regulation. A certain time sequence is only conditionally necessary. In essence, the steps take place simultaneously.

Motor operation is terminated as soon as a suitable speed range is left or the driver's desired torque is withdrawn. When stopping the engine operation, first the excitation current is withdrawn. The control of the inverter is maintained until the excitation current has decayed to zero (typically about 100ms). A shutdown in a different order could cause the electric machine to switch immediately from motor to generator mode, resulting in clearly noticeable and thus undesirable torque jumps.

Claims

claims

A method for controlling a given by an electric machine in a motor vehicle actual torque to a desired torque, wherein the electric machine, a stator winding (1 1), a rotor winding (12), one of the rotor winding (12) associated field controller (15) and one of the stator winding (1 1) downstream power converter (20) with controllable switching elements (21), wherein the actual torque is controlled to the target torque by a commutation angle is adjusted by targeted control of the switching elements (21) and / or by an excitation current through the rotor winding (12) is set specifically.

The method of claim 1, wherein the control of the switching elements (21) for setting the commutation angle is block by block.

The method of claim 1 or 2, which is performed above a predetermined minimum speed of the electric machine (10).

Method according to one of the preceding claims, which is performed below a predefinable maximum speed of the electric machine (10). 5. The method according to any one of the preceding claims, wherein the electrical

Machine (10) is operated with a voltage above the usual vehicle electrical system voltage, preferably between 12 V and 60 V.

6. The method according to any one of the preceding claims, wherein the commutation angle is set speed-dependent and the excitation current as

Control value for the control is used.

7. The method according to any one of the preceding claims, wherein the target torque is set so that the sum of one of a Ver engine output torque and the target torque corresponds to a driver's desired torque.

8. The method according to any one of the preceding claims, wherein upon termination of the scheme, first the excitation current is turned off and the targeted

Control of the switching elements (21) is terminated only when the excitation current has subsided.

9. drive unit (100), in particular for a motor vehicle, comprising an electric machine (10) with a stator winding (11), a rotor winding (12), a rotor winding (12) associated field controller (15) and one of the stator winding (1 ) downstream power converter (20) with controllable switching elements (21), characterized by means (25) for regulating an output from an electric machine in a motor vehicle actual torque to a desired torque, which are adapted to the actual torque to regulate the desired torque by adjusting a commutation angle by selective control of the switching elements (21) and / or an excitation current through the rotor winding (12). 10. Drive unit (100) according to claim 9, wherein the means (25) for regulating an output from an electric machine (10) in a motor vehicle actual torque are formed on a target torque as a computing unit, which is adapted to a method to carry out according to one of claims 1 to 7.