DE102011078958A1 - Method for operating an electric machine coupled to an internal combustion engine in a motor vehicle - Google Patents

Abstract

The present invention relates to a method for operating an engine coupled to an internal combustion engine in a motor vehicle, wherein the electric machine comprises a stator winding, a rotor winding, a rotor winding associated field controller and a stator winding downstream power converter with controllable switching elements, wherein an excitation current through the Rotor winding is given in response to an operating mode of the electric machine, wherein the electric machine is operated in a first generator operating mode as a generator to decelerate the motor vehicle, wherein the thereby recovered braking energy is stored.

Description

The present invention relates to a method for operating an engine coupled to an internal combustion engine in a motor vehicle.

State of the art

As electric machines Klauenpolgeneratoren are often used in electric vehicles with electrical excitement. 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. The regulation prevents, for example, that due to the very different engine speeds the generator would deliver strongly fluctuating voltage values which could possibly damage the downstream electrical system.

It is also known to use electrical machines as starter generators, on the one hand to start ("start up") the internal combustion engine during engine operation of the electric machine and, on the other hand, to generate electricity for the vehicle electrical system and for charging the motor vehicle battery during generator operation of the electric machine.

Electric machines, which are also used for vehicle propulsion, are known from the field of hybrid vehicles. A goal here is to support the engine at low speeds at which it does not yet deliver its full torque, so-called. Boost operation, turbo lag compensation). The term "recuperation system" refers to systems in which an electric machine is operated as a generator with the greatest possible torque in order to decelerate the vehicle and to buffer the braking energy recovered in the process. Usually permanent magnet synchronous machines are used for this purpose, which are operated at higher voltages (usually> 100 V). This leads to a complex system structure associated 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 make hybrid and / or recuperation operation economically possible even with conventional electric machines.

Disclosure of the invention

According to the invention, a method for operating an electric machine coupled to an internal combustion engine in a motor vehicle having the features of patent claim 1 is proposed. Advantageous embodiments are the subject of the dependent claims and the following description.

Advantages invention

The invention makes it possible to make a conventional electric machine (for example a claw-pole generator or belt-driven starter generator, etc.) also suitable for hybrid and / or recuperation purposes by providing a special type of exciting current specification. In particular, the exciting current is provided differently depending on the operating mode of the electric machine, wherein in particular a plurality of generator operating modes and / or a plurality of engine operating modes are distinguished. The excitation current is adjusted so that it is as optimal as possible for the respective operating mode. In particular, the exciter current bias is not the same for all modes of operation. The exciting current is thus provided in at least two operating modes according to a different regulation, for example in the first generator operating mode as a function of a desired braking torque and in another operating mode as a function of the desired generator voltage.

By using conventional electrical machines, almost no modifications to the powertrain are necessary. The efficiency of the electric machine can be increased. If the default is set as a control, the desired excitation current ("IErr") can be maintained particularly accurately.

As an operating mode can first be roughly distinguished between a motor operation and a generator operation of the electric machine. In addition, the off-mode, in which the excitation current is switched off, can be taken into account.

A motor operation expediently comprises a starting process ("starting"), a start / stop operation and / or an electrically assisted driving operation (so-called boost mode).

The type of generator operation is controlled substantially by appropriate control of the switching elements of the power converter. The generator operation expediently includes operation as a boost converter (HSS) with charging of the battery, as an active rectifier (AGLR, in which the switching elements are switched in the natural commutation time, resulting in a similar behavior as in the conventional diode rectifier) with charging the battery, AGLR with electric Zero moment and / or AGLR with electric braking.

The specification of the excitation current is carried out in one embodiment preferably as a function of the I-U characteristic of the motor vehicle battery. In this case, the battery is first charged with a defined nominal current and then with a defined nominal voltage. The specification of the excitation current (IErr) is also preferably carried out as a function of speed (nG) and required torque (MWunsch). It may depend on other sizes, such. As temperature (T), stator voltage (UG) and / or stator current (IG). The specification of the excitation current is also preferably carried out as a function of consumer voltages and currents that are delivered to the electrical system.

Preferably, the specification of the excitation current in dependence on one or more of the operating modes explained below. The speed threshold of 3,000 rpm (= rpm) selected here is purely exemplary and dependent on the so-called starting speed of the electric machine.

0. Mode (1st engine operating mode): Start combustion engine

The excitation current is expediently set to its maximum permissible value (IErr_Grenz) in order to obtain the largest possible magnetic flux, so that the electric machine provides the internal combustion engine with a maximum starting torque with minimum phase current. The maximum phase current (IPhase_Max) is regulated.

1st mode (1st engine operating mode): Start combustion engine (start / stop)

The excitation current is expediently set to its maximum permissible value (IErr_Grenz) in order to obtain the largest possible magnetic flux, so that the electric machine provides the internal combustion engine with a maximum starting torque with minimum phase current. The maximum phase current (IPhase_Max) is regulated. During start / stop operation, a small excitation current can be kept during the stop phase. This has the advantage that the subsequent engine start can take place without delay.

2nd mode (2nd engine operating mode): torque support of the internal combustion engine (hybrid operation, boost operation)

In this operating mode, the control takes place via the stator as well as the exciting current as control variables in order to set a desired setpoint torque. As is known in the literature, the stator current is described in the rotor-fixed dq coordinate system, so that the three control variables Id, Iq and IErr result. The maximum stator current (IG_Max) is regulated. At higher speeds, the electric machine reaches its voltage limit and is operated in the field weakening. This field weakening can be adjusted in the present independent machine both via the stator current component Id (pre-commutation angle alpha = displacement angle between rotor and stator field) and via the exciter current in the rotor. The field weakening is selected depending on the operating point so that the desired desired torque can be set with the optimum efficiency. The relationship between the control variables and the desired desired torque (MWunsch) is preferably stored in the form of a characteristic map: (Id, Iq, IErr) = f (MWunsch, speed).

A dependence on the temperature (T) and / or the generator speed (nG) and / or the stator voltage (UG) can be provided.

In order not to exceed a maximum allowable battery current, the control variables may additionally be dependent on the battery current.

3rd mode (2nd generator operating mode): generator operation below a speed threshold of, for example, 3000 rpm (rpm)

Since the generator can not deliver power in this speed range with conventional rectification, the power converter is operated in this operating mode as a boost converter. As control variables serve as in the mode 2, the sizes Id, Iq and IErr. The exciter current (IErr) is preferably set to its maximum permissible value, as in mode 1, and the regulation takes place via Id and Iq. The maximum phase current (IPhase_Max), the stator current (IG) and the stator voltage (UG) are controlled.

In a further embodiment, low part loads can also be controlled with a lower exciter current. The control variables are in turn suitably stored in the form of a characteristic diagram: (Id, Iq, IErr) = f (refset, rotational speed)

Again, a maximum charging voltage or a maximum charging current of the battery should not be exceeded, so that the control variables can also depend on these battery parameters. Preferably, the charging of the battery takes place only up to a first charging threshold (state of charge - SOC).

4th mode (3rd generator operating mode): Regenerative operation above the speed threshold of, for example, 3000 rpm

In this speed range, the machine is operated with active rectification (AGLR). The control variable here is exclusively the excitation current, since the control of the stator is predetermined by the natural commutation. A dependency on the temperature (T) and / or the generator speed (nG) and / or the stator current (IG) and / or the stator voltage (UG) can be provided. The stator current (IG) and stator voltage (UG) are regulated.

In order to charge the battery according to a specific characteristic curve, it is possible to specify battery current and / or battery voltage as nominal values:
IErr = f (USoll, speed) or IErr = f (ISoll, speed)

Preferably, the charging of the battery takes place only up to a second charging threshold value. Further preferably, the second charging threshold is higher than the first charging threshold.

5th mode (4th generator operating mode): idling

In this state, no generator current is requested and the excitation current is set so that the stator current is zero. This is the case in particular with IErr = 0. This mode is used, for example, to relieve the internal combustion engine when starting or accelerating from the generator torque or to deliver the recovered energy to the electrical system after a recuperation phase. This state is expediently maintained until a third charging threshold is reached or undershot.

6. Mode (1st generator operating mode): Electric braking

In this case, depending on the desired braking torque of the engine management, the excitation current is predetermined so that the maximum braking energy is collected. This is stored, used in particular for charging the battery. The battery is charged up to an upper charging threshold. The excitation current to be set then results from a characteristic diagram of the form: IErr = f (refset, rotational speed). A dependency on the temperature (T) and / or the generator speed (nG) and / or the stator current (IG) and / or the stator voltage (UG) can be provided.

The stator current (IG) and stator voltage (UG) are regulated.

7. Mode: "Engine Off"

Optionally, the excitation current can be switched off in this operating mode. Also, this state is expediently maintained only as long as the third or a fourth charging threshold is exceeded.

A preferred selection of parameters relevant in a respective operating mode is shown in the following table in FIG 4 summarized. This lists the eight operating modes described above ("Mode" line).

The line "Request" lists which system requests the mode and which conditions must prevail. If different modes are requested, the lowest numeric mode is selected in the Priority field.

The engine management (system) performs the control or regulation of the driver's desired torque with regard to drive and braking torque and the coordination of engine standstill requirements.

The charge management (system) ensures that the battery is charged via a UI characteristic (I characteristic: constant braking torque, constant charging current U characteristic: constant voltage). In addition, the goal is to collect as much braking energy and to allow the start / stop and sailing requirements with sufficient residual energy. For this purpose, the request is controlled according to the priority and state of charge of the battery via the individual operating modes.

If the electric machine is operated in motor operation with a voltage which is above the usual vehicle electrical system voltage of 12 V, but below a permissible contact voltage of 60 V, the torque output by the machine is increased, without particularly costly additional safety measures would be necessary. Due to the fact that the voltage is clearly higher than 12 V, the additional mode 3 (boost converter), which is not intended for conventional generators, is used. Due to the fact that the voltage is significantly lower than in known hybrid systems, the machine reaches its voltage limit even at significantly lower speeds and is operated in field weakening (mode 2).

An arithmetic unit according to the invention, for. As a control device of a motor vehicle is, in particular programmatically, adapted to perform a method according to the invention.

Also, the implementation of the method in the form of software is advantageous because this is special Low costs caused, especially if an executive controller is still used for other tasks and therefore already exists. Suitable data carriers In particular, floppy disks, hard disks, flash memories, EEPROMs, CD-ROMs, DVDs etc. are available to provide the computer program. 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

1 shows an embodiment of an electric machine with power converter with controllable switching elements, as it can be based on the invention.

2 shows an embodiment of a recuperation system of a motor vehicle with an electric machine, in particular according to 1 ,

3 shows a relationship between operating mode and battery state of charge according to a preferred embodiment of the invention.

4 FIG. 12 shows a preferred selection of the relevant parameters in a respective operating mode for the eight operating modes described above.

Embodiment (s) of the invention

In 1 is an electrical machine, as can be based on the present invention, shown in a circuit diagram and a total of 100 designated. 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 only schematically in the form of star-shaped interconnected stator windings 11 and a field connected to a diode exciter or rotor winding 12 shown. The rotor winding is powered by a circuit breaker 13 that with a connection 24 the power converter component 20 connected, switched clocked. The activation of the circuit breaker 13 takes place in accordance with a field controller 15 , where the circuit breaker 13 as well as the rotor winding 12 parallel-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 here designed as a B6 circuit and has switching elements 21 on, for example, as a MOSFET 21 can be executed. The MOSFET 21 are, for example via busbars, with the respective stator windings 11 connected to the generator. Furthermore, the MOSFETs are with connections 24 . 24 ' connected and provide with appropriate control in generator operation of the electric machine, a DC power for a vehicle electrical system including battery 30 a motor vehicle available. The control of the switching elements 21 takes place by a drive device 25 via control channels 26 of which for reasons of clarity not all are provided with reference numerals. The drive device 25 receives over one or more phase channels 27 in each case the phase voltage of the individual stator windings. To provide these phase voltages, further devices can be provided, which however are not shown for the sake of clarity.

The drive device 25 takes in the (synchronous) rectifier operation an evaluation of the over the phase channels 27 provided phase voltages and determines therefrom a respective on and off timing of a single MOSFET 21 , The control via control channels 26 affects the gate terminals of the mosfet 21 out.

Known field controllers, such as the field controller provided in the context of this embodiment 15 , have a so-called terminal V connection 19 on, 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 in the controller 15 evaluated and used depending on the characteristics of this signal to enable or disable the controller operation and ultimately to control the circuit breaker 13 via a control line 14 , The phase signal for the phase signal input 19 can, as shown, by the drive device 25 be guided.

In engine operation, the electric machine 100 used to drive the vehicle alone or in combination with an internal combustion engine. Preferably, a battery is used as the power supply, which has a higher voltage (eg 40 V) than the usual vehicle electrical system voltage of 12 V. In generator operation, the electric machine 100 used to generate energy and possibly decelerate the vehicle.

In 2 is a recuperation system of a motor vehicle, as can be based on the present invention, shown in a circuit diagram and a total of 200 designated. The recuperation system 200 has an electric machine 201 , in particular the electric machine 100 according to 1 on.

The recuperation system 200 has a region A with a higher voltage (eg 40 V) than the usual vehicle electrical system voltage and a region B with the usual vehicle electrical system voltage (eg 12 V). The higher voltage is in any case below a permissible contact voltage (about 60 V), so that no costly protective measures are necessary, the electric machine 201 however, can deliver an increased torque. Areas A and B are via a DC / DC converter 204 coupled.

In area A is a first as a "high voltage" battery 202 trained battery arranged, the example. The machine 201 powered during engine operation. Possible high voltage consumers 203 are also arranged in area A.

In area B is a second as "normal voltage" battery 205 formed battery, which serves to supply the area B in phases, in which the machine 201 not operated as a generator. Possible consumers 206 . 207 are also located in area B.

In generator mode, the machine powers 201 the areas A and B and charges the batteries 202 and 205 ,

Depending on the operating mode of the electric machine, the specification of the exciter current takes place within the scope of the invention.

In 3 FIG. 3 shows a relationship between the operating modes Mod 1 to Mod 7 and the battery state of charge SOC in% according to a preferred embodiment of the invention for the operating modes listed at the front in the table. Are several batteries available, such as in 2 As shown, the battery state of charge conveniently refers to the particular battery of interest, that is, the one being charged or the one driving the electric machine.

The selection of the operating mode to be used is expediently such that the maximum braking energy can be collected. The selection of the operating mode to be used is carried out in particular according to priority and defined thresholds of engine speed, desired torque, temperature and SOC. The excitation current is then set according to the selected operating mode.

Out 3 also go the charging thresholds described. For example, the first charging threshold is 40% (see lower limit Mod 3), the second 50% (see lower limit Mod 4) and the third approx. 37% (see lower limit Mod 5).

Claims (16)

Method for operating an electric machine coupled to an internal combustion engine ( 100 ; 201 ) in a motor vehicle, wherein the electric machine has a stator winding ( 11 ), a rotor winding ( 12 ), one of the rotor winding ( 12 ) assigned field controller ( 15 ) and one of the stator winding ( 11 ) downstream converters ( 20 ) with controllable switching elements ( 21 ), wherein an excitation current through the rotor winding ( 12 ) is given depending on the current operating mode of the electric machine, wherein the electric machine ( 100 ; 201 ) is operated in a first generator operating mode (Mod 6) as a generator to decelerate the motor vehicle, wherein the thereby recovered braking energy is stored. The method of claim 1, wherein the excitation current in the first generator operating mode (Mod 6) in dependence on a requested braking torque and / or the rotational speed of the electric machine is predetermined. Method according to one of the preceding claims, wherein the operating mode of the electric machine ( 100 ; 201 ) depending on the state of charge of a battery to be charged ( 202 . 205 ) is given. Method according to one of the preceding claims, wherein the electric machine ( 100 ; 201 ) is operated as a motor to deliver a torque to the internal combustion engine. The method of claim 4, wherein the excitation current is maximized in a first engine operating mode (Mod 1). A method according to claim 4 or 5, wherein the exciting current is given in a second motor operating mode (Mod 2) in dependence on at least one of the following variables: rotational speed of electric machine, target torque specification, stator voltage, stator current, temperature in the electric machine. Method according to one of the preceding claims, wherein in a second generator operating mode (Mod 3) at a rotational speed of the electric machine ( 100 ; 201 ) below a speed threshold value of the exciter current as a function of the state of charge of a battery to be charged ( 202 . 205 ) is set so that the battery is not charged beyond a first charging threshold. Method according to one of the preceding claims, wherein in a third generator operating mode (Mod 4) at a rotational speed of the electric machine ( 100 ; 201 ) above a speed threshold value of the exciter current as a function of the state of charge of a battery to be charged ( 202 . 205 ) so that the battery is not charged beyond a second charging threshold. The method of claim 7 and 8, wherein the second charging threshold is higher than the first charging threshold. Method according to one of the preceding claims, wherein the excitation current in a generator operating mode according to a predetermined IU characteristic of a battery to be charged ( 202 . 205 ) is given. The method of claim 10, wherein the excitation current is set so that an upper temperature threshold of the battery to be charged ( 202 . 205 ) is not exceeded. Method according to one of the preceding claims, wherein the excitation current in a fourth generator operating mode (Mod 5) is set such that upon rotation of the rotor winding ( 12 ) no current in the stator winding ( 11 ) is induced. The method of claim 12, wherein the electric machine is operated only in the fourth generator operating mode (Mod 5) when a state of charge of a battery ( 202 ) for supplying the electric machine ( 100 ; 201 ) exceeds a third lower charging threshold. Method according to one of the preceding claims, wherein the excitation current is switched off in a shutdown operating mode (Mod 7). Method according to one of the preceding claims, wherein the electric machine ( 10 ) is operated in a motor operating mode (Mod 1, Mod 2) with a voltage above the usual vehicle electrical system voltage, preferably between 12 V and 60 V, preferably more than 30 V. Arithmetic unit which is adapted to carry out a method according to one of the preceding claims.

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