DE102011078958B4 - Method for operating an electric machine coupled to an internal combustion engine in a motor vehicle - Google Patents

Abstract

Method for operating an electrical machine (100; 201) coupled to an internal combustion engine in a motor vehicle, wherein the electrical machine has a stator winding (11), a rotor winding (12), a field controller (15) associated with the rotor winding (12) and a converter component (20) connected downstream of the stator winding (11) with controllable switching elements (21), wherein an excitation current through the rotor winding (12) is predetermined depending on the current operating mode of the electrical machine, wherein the electrical machine (100; 201) is operated as a generator in a first generator operating mode (Mod 6) in order to brake the motor vehicle, wherein a braking energy recovered in the process is stored, wherein in a second generator operating mode (Mod 3) at a speed of the electrical machine (100; 201) below a speed threshold value, the excitation current is predetermined depending on the state of charge of a battery (202, 205) to be charged such that the battery does not exceed a first charging threshold value, wherein in a third generator operating mode (Mod 4) at the speed of the electric machine (100; 201) above the speed threshold value, the excitation current is predetermined depending on the state of charge of the battery to be charged (202, 205) such that the battery is not charged beyond a second charging threshold value.

Description

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

State of the art

Claw pole generators with electrical excitation are often used as electrical machines in motor vehicles. The current through the rotor winding serves as a control variable for regulating the desired output voltage and is specified by an associated field controller. The control prevents, for example, the very different engine speeds from causing the generator to deliver strongly fluctuating voltage values, which could potentially damage the downstream electrical system.

It is also known to use electric machines as starter generators, on the one hand to start (“crank”) the internal combustion engine in the motor mode of the electric machine and on the other hand to generate power for the on-board electrical system and to charge the vehicle battery in the generator mode of the electric machine.

Electric machines that are also used to drive vehicles are known from the field of hybrid vehicles. One aim here is to support the combustion engine at low speeds, at which it does not yet deliver its full torque (so-called boost mode, turbo lag compensation). The term "recuperation system" refers to systems in which an electric machine is operated as a generator with the highest possible torque in order to brake the vehicle and temporarily store the recovered braking energy. Permanently excited synchronous machines are usually used for this purpose, which are operated at higher voltages (usually >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 level of integration effort, such a system leads to high additional costs.

The DE 44 30 670 A1 shows a control device for an electric generator/motor that can prevent overcharging and insufficient charge state of an electric power storage device. A control device controls the electric generator/motor in the electric generator mode when a total value of the reclaimable electric energy calculated on the basis of the vehicle state and a current charge state of the electric storage device is less than a certain reference charge state. The control device carries out the motor mode of the generator/motor, ie the application of torque, within a range in which the charge state of the electric storage device does not fall below a certain minimum charge state required to control the vehicle auxiliary devices. The control device effects a motor mode of the electric generator/motor with continuously changing reclaimable electric energy that is in a positive correlation with an effective amount of operation of a brake pedal. The control device carries out the application of torque when a total value of the reclaimable electric energy is greater than a certain minimum charge state value.

The EN 60 2004 012 838 T2 shows a control device for an internal combustion engine with a combustion control unit that controls the combustion process in the internal combustion engine when the internal combustion engine is stopped, an inertia energy control unit that controls a predetermined state of the mass inertia energy of the internal combustion engine at a predetermined time, and a stop control unit that stops the internal combustion engine using the mass inertia energy in a predetermined crank angle position, wherein the inertia energy control unit controls the speed of the internal combustion engine such that it lies in a range of a predetermined engine speed, and controls the mass inertia energy by a motor provided for driving the internal combustion engine.

The AT 009 756 U1 relates to a method and a device for controlling the hybrid drive of a motor vehicle with the components: internal combustion engine, manual transmission, at least one electric machine, at least one clutch and an energy storage device, and at least one driven axle, whereby maximum efficiency and service life of the components are to be achieved. To this end, based on the driver's wishes and operating state, a decision is made as to which operating modes are possible, and for the possible operating modes, a decision is made as to which transmission gears are possible, so that a larger number of modes are available to choose from. For all of these modes, operating points corresponding to the driver's wishes are determined taking into account the operating state and system state, the modes are evaluated, and the most favorable mode is selected.

The EN 699 22 221 T2 shows a method for controlling the operation of a hybrid vehicle which is in a more number of different modes, the vehicle having an internal combustion engine for providing torque up to a maximum torque output, a clutch device for selectively coupling or decoupling the internal combustion engine to or from the wheels of the vehicle, a first electric motor operable as a generator and coupled to the internal combustion engine, a second electric motor coupled to wheels of the vehicle, a battery bank for accepting electrical energy from the first electric motor and providing electrical energy to the second electric motor, and a control unit for controlling the operation of the internal combustion engine, the first and second electric motors, the clutch device and the flow of electrical energy between the electric motors and the battery bank, the method comprising at least the following modes for operating the hybrid vehicle, the modes depending on operating parameters of the vehicle and the actuation status of at least one actuator to control the speed of the vehicle: a highway cruising mode which is entered when the torque required by the vehicle is below the maximum torque output of the internal combustion engine and wherein the internal combustion engine is coupled to the wheels and the vehicle is propelled by the torque provided by that engine; and an acceleration mode which is entered at least when the torque required by the vehicle is above the maximum torque output of the internal combustion engine and wherein the second electric motor provides torque to propel the vehicle. A low speed mode is entered when the torque required by the vehicle is below a set point predetermined as a predetermined percentage of the maximum torque output wherein the internal combustion engine is decoupled from the wheels and the engine is turned off and the vehicle is propelled only by the second electric motor; entering a low speed battery charging mode while the hybrid vehicle is operating in the low load mode and the condition of the battery bank is below a predetermined level, the internal combustion engine driving the first electric motor which supplies electrical energy to the battery bank; entering the highway driving mode when the torque required by the vehicle is above the predetermined point; and coupling the internal combustion engine to the wheels in the acceleration mode so that its maximum torque output drives the vehicle together with the torque provided by the second electric motor.

The EN 10 2010 029 299 A1 shows a method for operating a system for a motor vehicle, the system comprising a controller, a high-voltage on-board network, a low-voltage on-board network, a DC/DC converter that connects the high-voltage on-board network and the low-voltage on-board network, and an electrical machine, in particular a starter or motor generator. In order to make the system more efficient and usable with greater functionality, an operating mode of the system is varied depending on operating requirements, in particular an operating state of the motor vehicle.

Based on this, the task is to make hybrid and/or recuperation operation economically possible even with conventional electric machines.

Disclosure of the invention

This object is achieved by a method for operating an electrical machine coupled to an internal combustion engine in a motor vehicle with the features of patent claim 1. Advantageous embodiments are the subject of the subclaims and the following description.

Advantages Invention

The invention makes it possible to make a conventional electrical machine (e.g. a claw pole generator or belt-driven starter generator, etc.) usable for hybrid and/or recuperation purposes by providing a special type of excitation current specification. In particular, the excitation current is provided differently depending on the operating mode of the electrical machine, with a distinction being made in particular between several generator operating modes and/or several motor operating modes. The excitation current is set so that it is as optimal as possible for the respective operating mode. In particular, the excitation current specification is not the same for all operating modes. The excitation current is thus provided in at least two operating modes in accordance with a different rule, for example in the first generator operating mode depending on a desired braking torque and in another operating mode depending on the desired generator voltage.

By using conventional electrical machines, almost no modifications to the drive train are necessary. The efficiency of the electrical machine can be increased. If the specification is made as a control, the desired excitation current ("lErr") can be maintained particularly precisely.

As an operating mode, a rough distinction can be made between motor operation and generator operation of the electrical machine. In addition, the off mode, in which the excitation current is switched off, can also be taken into account.

Engine operation conveniently includes a starting process (“cranking”), a start/stop operation and/or an electrically assisted driving operation (so-called boost mode).

The type of generator operation is essentially controlled by appropriate control of the switching elements of the power converter component. Generator operation conveniently includes operation as a boost converter (HSS) with charging of the battery, as an active rectifier (AGLR; here the switching elements are switched at the natural commutation time, resulting in a similar behavior to that of a conventional diode rectifier) with charging of the battery, AGLR with electrical zero torque and/or AGLR with electrical braking.

In one embodiment, the excitation current is preferably specified as a function of the I-U characteristics of the motor vehicle battery. The battery is first charged with a defined target current and then with a defined target voltage. The excitation current (IErr) is also preferably specified as a function of the speed (nG) and the required torque (MWunsch). It can depend on other variables, such as temperature (T), stator voltage (UG) and/or stator current (IG). The excitation current is also preferably specified as a function of consumer voltages and currents that are fed into the vehicle electrical system.

Preferably, the excitation current is specified depending on one or more of the operating modes explained below. The speed threshold of 3,000 rpm (=rpm) selected here is purely exemplary and depends on the so-called starting speed of the electrical machine.

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

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

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

The excitation current is set to its maximum permissible value (IErr_Grenz) in order to obtain the greatest possible magnetic flux, so that the electric machine provides the combustion engine with maximum starting torque at minimum phase current. The maximum phase current (IPhase_Max) is regulated. In start/stop operation, a small excitation current can be maintained 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 combustion engine (hybrid operation, boost operation)

In this operating mode, control is carried out using both the stator and excitation current as control variables in order to set a desired target torque. As is known from the literature, the stator current is described in the rotor-fixed dq coordinate system, resulting in the three control variables Id, Iq and IErr. The maximum stator current (IG_Max) is controlled. At higher speeds, the electrical machine reaches its voltage limit and is operated in field weakening. In the case of the separately excited machine in question, this field weakening can be set both via the stator current component Id (pre-commutation angle alpha = displacement angle between rotor and stator field) and via the excitation current in the rotor. The field weakening is selected depending on the operating point so that the desired target torque can be set with the optimum efficiency. The relationship between the control variables and the desired target torque (Mdesired) is preferably stored in the form of a characteristic map: $$\left(\text{ID},\text{Iq},\text{IErr}\right)=\text{e}\left(\text{MWish},\text{number of revolutions}\right).$$

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

In order not to exceed the maximum permissible battery current, the control variables can also depend on the battery current.

3. Mode (2nd generator operating mode): Generator operation below a speed threshold of e.g. 3000 rpm

Since the generator cannot deliver any power in this speed range with conventional rectification, the converter component is operated as a boost converter in this operating mode. As in mode 2, the control variables are Id, Iq and IErr. As in mode 1, the excitation current (IErr) is preferably set to its maximum permissible value; control is carried out via Id and Iq. The maximum phase current (IPhase_Max), the stator current (IG) and the stator voltage (UG) are controlled.

In another embodiment, small partial loads can also be controlled with a lower excitation current. The control variables are again conveniently stored in the form of a characteristic map: $$\left(\text{ID},\text{Iq},\text{IErr}\right)=\text{e}\left(\text{MSoll},\text{number of revolutions}\right)$$

Here, too, 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 battery is only charged up to a first charging threshold value (state of charge - SOC).

4th mode (3rd generator operating mode): Generator operation above the speed threshold of e.g. 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 via 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 target values: $$\text{IErr}=\text{e}\left(\text{USoll},\text{number of revolutions}\right)\text{or}.\text{IErr}=\text{e}\left(\text{ISoll},\text{number of revolutions}\right)$$

Preferably, the battery is only charged up to a second charging threshold. Further preferably, the second charging threshold is higher than the first charging threshold.

5. Mode (4th generator operating mode): Idle

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

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

Depending on the desired braking torque of the engine management, the excitation current is set so that the maximum braking energy is collected. This is stored and used in particular to charge the battery. The battery is charged up to an upper charging threshold. The excitation current to be set is then determined using a characteristic map of the form: IErr = f (MSoll, 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.

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. This state is also only maintained as long as the third or fourth charging threshold is exceeded.

A preferred selection of the parameters relevant in a particular operating mode is shown in the table in 4 This lists the eight operating modes described above (row “Mode”).

The "Requirement" line lists which system is requesting the mode and which conditions must prevail. If different modes are requested, the mode with the lowest numerical value in the "Priority" field is selected.

The engine management system regulates or controls the driver's desired torque with regard to drive and braking torque and coordinates engine standstill requests.

The charging management system ensures that the battery is charged using a Ul characteristic (I characteristic: constant braking torque, constant charging current U characteristic: constant voltage). In addition, the aim is to collect as much braking energy as possible and to enable the start/stop and sailing requests when there is enough remaining energy. To do this, the request is controlled according to the priority and charge level of the battery via the individual operating modes.

If the electric machine is operated in motor mode with a voltage that is above the usual on-board voltage of 12 V, but below a permissible contact voltage of 60 V, the torque delivered by the machine is increased without particularly complex additional safety measures being necessary. Because the voltage is significantly higher than 12 V, the additional mode 3 (boost converter) (not provided for in conventional generators) is used. Because the voltage is significantly lower than in known hybrid systems, the machine reaches its voltage limit at significantly lower speeds and is operated in field weakening (mode 2).

A computing unit according to the invention, e.g. a control unit of a motor vehicle, is set up, in particular in terms of programming, to carry out a method according to the invention.

Implementing the process in the form of software is also advantageous, as this is particularly cost-effective, particularly if an executing control unit is used for other tasks and is therefore already available. Suitable data storage devices for providing the computer program are in particular floppy disks, hard disks, flash memories, EEPROMs, CD-ROMs, DVDs, etc. It is also possible to download a program via computer networks (Internet, intranet, etc.).

Further advantages and embodiments of the invention emerge from the description and the accompanying drawings.

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

Short description of the drawings

• 1 shows an embodiment of an electrical machine with a generator component and a power converter component with controllable switching elements, as can form the basis of 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 charge state according to a preferred embodiment of the invention.
• 4 shows a preferred selection of the parameters relevant in a particular operating mode for the eight operating modes described above.

Embodiment(s) of the invention

In 1 is an electrical machine, such as the one on which the present invention is based, shown in circuit diagram form and designated overall by 100. The electrical machine has a generator component 10 and a converter component 20. The converter component is usually operated as a rectifier in generator operation of the machine, and as an inverter in motor operation.

The generator component 10 is only shown schematically in the form of star-connected stator windings 11 and an excitation or rotor winding 12 connected in parallel to a diode. The rotor winding is switched in a clocked manner by a power switch 13, which is connected to a connection 24 of the converter component 20. The power switch 13 is controlled in accordance with a field controller 15, whereby the power switch 13 as well as the diode connected in parallel to the rotor winding 12 are generally 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 fewer or more phase generators, for example five-phase generators.

The converter component 20 is designed here as a B6 circuit and has switching elements 21, which can be designed as MOSFETs 21, for example. The MOSFETs 21 are connected to the respective stator windings 11 of the generator, for example via busbars. The MOSFETs are also connected to connections 24, 24' and, when appropriately controlled, provide a direct current for an on-board network including battery 30 of a motor vehicle when the electric machine is in generator operation. The The switching elements 21 are controlled by a control device 25 via control channels 26, of which not all are provided with reference symbols for reasons of clarity. The control device 25 receives the phase voltage of the individual stator windings via one or more phase channels 27. Additional devices can be provided to provide these phase voltages, but these are not shown for the sake of clarity.

In (synchronous) rectifier operation, the control device 25 evaluates the phase voltages provided via the phase channels 27 and uses this to determine the respective switch-on and switch-off times of an individual MOSFET 21. The control via control channels 26 affects the gate connections of the MOSFET 21.

Known field controllers, such as the field controller 15 provided in this embodiment, have a so-called terminal V connection 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, depending on the characteristics of this signal, is used to activate or deactivate 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, also be passed through the control device 25.

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

In 2 a recuperation system of a motor vehicle, as may be the basis of the present invention, is shown in circuit diagram form and designated overall by 200. 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 (e.g. 40 V) than the usual vehicle electrical system voltage and a region B with the usual vehicle electrical system voltage (e.g. 12 V). The higher voltage is in any case below a permissible contact voltage (approx. 60 V), so that no complex protective measures are necessary, but the electric machine 201 can deliver an increased torque. The regions A and B are coupled via a DC/DC converter 204.

In area A, a first battery designed as a “high-voltage” battery 202 is arranged, which supplies the machine 201 during engine operation, for example. Possible high-voltage consumers 203 are also arranged in area A.

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

In generator mode, machine 201 supplies areas A and B and charges batteries 202 and 205.

Depending on the operating mode of the electrical machine, the excitation current is specified within the scope of the invention.

In 3 a relationship between the operating modes Mod 1 to Mod 7 and the battery charge level SOC in % is shown according to a preferred embodiment of the invention for the operating modes listed in the table at the front. If several batteries are present, as for example in 2 As shown, the battery charge state conveniently refers to the relevant battery, ie the one being charged or the one driving the electric machine.

The operating mode to be used is selected in such a way that the maximum braking energy can be collected. The operating mode to be used is selected in particular according to priority and defined threshold values of machine speed, desired torque, temperature and SOC. The excitation current is then specified according to the selected operating mode.

Out of 3 The charging threshold values described are also shown. 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 (14)

Method for operating an electrical machine (100; 201) coupled to an internal combustion engine in a motor vehicle, wherein the electrical machine has a stator winding (11), a rotor winding (12), a rotor winding (12) associated field regulator (15) and a converter component (20) connected downstream of the stator winding (11) with controllable switching elements (21), wherein an excitation current through the rotor winding (12) is predetermined depending on the current operating mode of the electrical machine, wherein the electrical machine (100; 201) is operated as a generator in a first generator operating mode (Mod 6) in order to brake the motor vehicle, wherein a braking energy recovered in the process is stored, wherein in a second generator operating mode (Mod 3) at a speed of the electrical machine (100; 201) below a speed threshold value, the excitation current is predetermined depending on the state of charge of a battery (202, 205) to be charged such that the battery is not charged beyond a first charging threshold value, wherein in a third generator operating mode (Mod 4) at the speed of the electrical machine (100; 201) above the speed threshold value, the excitation current is predetermined depending on the The state of charge of the battery to be charged (202, 205) is specified such that the battery is not charged beyond a second charging threshold value. Procedure according to Claim 1 , wherein the excitation current in the first generator operating mode (Mod 6) is predetermined as a function of a requested braking torque and/or the speed of the electric machine (100; 201). Method according to one of the preceding claims, wherein the operating mode of the electric machine (100; 201) is predetermined depending on the state of charge of a battery (202, 205) to be charged. Method according to one of the preceding claims, wherein the electric machine (100; 201) is operated as a motor in order to deliver a torque to the internal combustion engine. Procedure according to Claim 4 , whereby the excitation current is maximized in a first motor operating mode (Mod 1). Procedure according to Claim 4 or 5 , wherein the excitation current in a second motor operating mode (Mod 2) is specified as a function of at least one of the following variables: speed of the electrical machine, target torque specification, stator voltage, stator current, temperature in the electrical machine. A method according to any preceding claim, 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 is predetermined according to a predetermined I-U characteristic curve of a battery (202, 205) to be charged. Procedure according to Claim 8 , wherein the excitation current is specified such that an upper temperature threshold value 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 predetermined such that no current is induced in the stator winding (11) when the rotor winding (12) rotates. Procedure according to Claim 10 , wherein the electric machine (100; 201) is only operated 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 value. 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 (100; 201) is operated in an engine operating mode (Mod 1, Mod 2) with a voltage above the usual vehicle electrical system voltage. Computing unit configured to carry out a method according to one of the preceding claims.

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