DE102021005149A1 - Method of operating an electric vehicle - Google Patents

Abstract

The invention relates to a method for operating an electric vehicle with at least two electric drive units (1.1, 1.2) and a respective inverter (2.1, 2.2), wherein
- A total target torque is determined from a driver request (FW),
- Based on the total target torque and available torques (Mv) of the electric drive units (1.1, 1.2), a minimum and maximum possible all-wheel drive torque distribution is determined from a driving dynamics point of view,
- A total power loss of the two electric drive machines (1.1, 1.2) based on power loss characteristics (VLKF) is determined, when all-wheel drive torque distributions of 0 and/or 100% are permissible and an operating mode of open terminals for the respective electric drive machine ( 1.1, 1.2) is possible, the power loss for the all-wheel drive torque distributions of 0 or 100% is determined on the basis of power loss characteristics (VLKL _OK ) with open terminals for the respective other electric drive machine (1.1, 1.2),
- the all-wheel torque distribution with the lowest total power loss is determined,
- When a power loss advantage is greater than a threshold value, the four-wheel drive torque distribution with the lowest total power loss is set, the open terminals operating mode being set for one or none of the electric drive machines (1.1, 1.2).

Description

The invention relates to a method for operating an electric vehicle according to the preamble of claim 1.

In vehicles with an electric drive, in particular by means of permanent magnet synchronous machines (PMSM), energy can be saved if the PMSM is switched to an open clamp state (six switch open) under certain conditions. The otherwise carried out operation of the electrical machine with 0Nm causes more losses with pulse width modulation than switching the open terminals state.

DE 10 2017 202 393 A1 describes a switching control unit which ON/OFF controls switching elements of a power conversion circuit, comprising a power-supply-side abnormality determining unit, and a regeneration abnormality response processing selection unit which performs either three-phase short-circuit processing in which all switching elements of an upper stage side or all switching elements of a lower stage side are turned on, or six-switch opening processing which all switching elements of the power conversion circuit are turned off, as processing to be executed when the power-supply-side abnormality determining unit determines that a power-supply-side abnormality has occurred, selecting the three-phase short-circuit processing and the six-switch opening processing according to a motor operating state of the AC motor at the time of the determination.

The object of the invention is to reduce the losses during the operation of an electrically driven vehicle.

The object is achieved according to the invention by a method for operating an electric vehicle according to claim 1.

Advantageous configurations of the invention are the subject matter of the dependent claims.

• - eine Antriebssteuereinheit aus einem Fahrerwunsch, umfassend eine Stellung eines Gaspedals und/oder eines Bremspedals, ein Summen-Soll-Drehmoment ermittelt, und
• - basierend auf dem Summen-Soll-Drehmoment und verfügbaren Drehmomenten der elektrischen Antriebsmaschinen eine minimal und maximal mögliche Allrad-Momentenverteilung aus fahrdynamischer Sicht ermittelt wird.

In a method according to the invention for operating an electric vehicle with at least two electric drive machines, each electric drive machine is controlled with a respective inverter, where

• - A drive control unit from a driver's request, comprising a position of an accelerator pedal and / or a brake pedal, a total target torque determined, and
• - Based on the total target torque and available torque of the electric drive units, a minimum and maximum possible all-wheel drive torque distribution is determined from a driving dynamics point of view.

• - eine Summen-Verlustleistung der beiden elektrischen Antriebsmaschinen bei den minimal und maximal möglichen Allrad-Momentenverteilungen, basierend auf Verlustleistungskennfeldern ermittelt wird, wobei dann, wenn Allrad-Momentenverteilungen von 0 und/oder 100% zulässig sind und zusätzlich auch eine Betriebsart Offene Klemmen bei der jeweiligen elektrischen Antriebsmaschine möglich ist, die Verlustleistung für die Allrad-Momentenverteilungen von 0 bzw. 100% auf Basis von Verlustleistungskennlinien VLKL_OK bei offenen Klemmen für die jeweils andere elektrische Antriebsmaschine ermittelt wird,
• - die Allrad-Momentenverteilung mit der geringsten Summen-Verlustleistung ermittelt wird,
• - ein Verlustleistungsvorteil als Differenz aus der Allrad-Momentenverteilung mit der geringsten Summen-Verlustleistung und einer Verlustleistung für die bislang eingestellte Allrad-Verteilung gebildet wird,

wobei dann, wenn der Verlustleistungsvorteil größer als ein Schwellwert ist oder wenn ein aufintegrierter Verlustleistungsvorteil größer als der Schwellwert ist, die Allrad-Momentenverteilung mit der geringsten Summen-Verlustleistung eingestellt wird, wobei betriebspunktabhängig aus den folgenden Varianten der Energie-effizienteste Betrieb gewählt wird:

• - Nutzen der Betriebsart Offene Klemmen für eine der elektrischen Antriebsmaschinen und Stellen des Drehmoments gemäß Fahrerwunsch auf einer anderen der elektrischen Antriebsmaschinen,
• - Betreiben von beiden Invertern mit Pulsweitenmodulation und Aufteilen des Drehmoments gemäß Fahrerwunsch auf beide elektrischen Antriebsmaschinen mit wirkungsgrad-optimierter Verteilung.

According to the invention it is provided that

• - A total power loss of the two electric drive machines at the minimum and maximum possible all-wheel drive torque distributions, based on power loss maps, is determined, in which case, if all-wheel drive torque distributions of 0 and / or 100% are permissible and also an operating mode open terminals at the respective electric drive machine is possible, the power loss for the all-wheel drive torque distributions of 0 or 100% is determined on the basis of power loss characteristics VLKL _OK with open terminals for the other electric drive machine in each case,
• - the all-wheel torque distribution with the lowest total power loss is determined,
• - a power loss advantage is formed as the difference between the all-wheel drive torque distribution with the lowest total power loss and a power loss for the previously set all-wheel drive distribution,

where, if the power loss advantage is greater than a threshold value or if an integrated power loss advantage is greater than the threshold value, the four-wheel drive torque distribution with the lowest total power loss is set, with the most energy-efficient operation being selected from the following variants depending on the operating point:

• - Use of the open terminals operating mode for one of the electric drive machines and setting the torque according to the driver's request on another of the electric drive machines,
• - Operation of both inverters with pulse width modulation and distribution of the torque according to the driver's request to both electric drive units with efficiency-optimized distribution.

Depending on the driving style or cycle, the solution according to the invention achieves a significant consumption and range advantage in a vehicle with two electric drives.

Exemplary embodiments of the invention are explained in more detail below with reference to drawings.

• 1 eine schematische Ansicht eines Verfahrens zum Betrieb eines Elektrofahrzeugs mit mindestens einer elektrischen Antriebsmaschine und mindestens einem Inverter,
• 2 eine schematische Ansicht eines Flussdiagramms zur Optimierung einer Drehmomentverteilung über die elektrischen Antriebe,
• 3 ein schematisches Diagramm von Drehmomenten der Inverter über einer Drehzahl ohne Nutzung einer Betriebsart Offene Klemmen, und
• 4 ein schematisches Diagramm der Drehmomente der Inverter über der Drehzahl mit Nutzung der Betriebsart Offene Klemmen.

show:

• 1 a schematic view of a method for operating an electric vehicle with at least one electric drive machine and at least one inverter,
• 2 a schematic view of a flowchart for optimizing a torque distribution over the electric drives,
• 3 a schematic diagram of torques of the inverters versus a speed without using an open terminal mode, and
• 4 a schematic diagram of the torques of the inverters versus the speed using the operating mode open terminals.

Corresponding parts are provided with the same reference symbols in all figures.

1 is a schematic view of a method for operating an electric vehicle with at least one electric drive machine 1.1, 1.2, each electric drive machine 1.1, 1.2 being controlled with a respective inverter 2.1, 2.2.

According to the present invention, at least one of the electric drive machines 1.1, 1.2, in particular a permanent magnet synchronous machine (PMSM), in an electric vehicle, in particular an exclusively electrically driven vehicle, uses the operating state open terminals during torque-free operation. The electric drive machine 1.1, 1.2 is operated by means of an inverter 2.1, 2.2 and pulse width modulation (PWM).

For this purpose, a drive control unit 3 based on a driver request FW, for example based on the position of an accelerator pedal and/or a brake pedal, sends a request for a torque M1, M2 to the inverters 2.1, 2.2 and receives feedback R1, R2 from them as to whether the current operating conditions and when a torque M1, M2 of 0 Nm is requested (regardless of the currently requested torque M1, M2), the open terminals operating mode would be possible. According to the invention, it is provided that this decision is made as a function of a battery voltage and the current speed n _a , namely in such a way that the feedback R1, R2 that the open terminals operating mode is possible is transmitted when, as a result of the retroactive electromotive force of the electric drive machine 1.1, 1.2 induced voltage is less than the battery voltage and / or when the current speed _na is less than a predetermined threshold. The availability of the open terminals operating mode is determined in software for the electric drive, ie the respective inverter 2.1, 2.2, under the stated conditions and communicated to the drive control unit 3.

The drive control unit 3 now decides in a step S2 whether the at least one inverter 2.1, 2.2 or at least one of the two or more inverters 2.1, 2.2 or both or all inverters 2.1, 2.2 is/are switched to the open terminals operating mode or whether both inverters 2.1, 2.2 are operated in order to apply the requested torque M1, M2 distributed in an energy-efficient manner by both or all drive machines 1.1, 1.2.

If only one electric drive machine 1.1 or 1.2 is provided in the vehicle, the open terminals operating mode can only be switched when the driver requests torque-free operation (e.g. coasting) and the above criteria for the open terminals operating mode are met.

If several electric drive machines 1.1, 1.2 are provided in the vehicle, then the drive control unit 3 decides based on the driver's request FW, the availability of the open terminals operating mode and an intelligent strategy based on the power losses of the electric drives with pulse width modulation (entire operating range) and in the operating mode Open terminals, whether open terminals should be switched.

2 is a schematic view of a flow chart for optimizing a torque distribution over the electric drives, each comprising an electric drive machine 1.1, 1.2 and an inverter 2.1, 2.2.

In a step S1, drive control unit 3 determines a total target torque from driver request FW, for example based on the position of an accelerator pedal and/or a brake pedal, a recuperation stage, a brake recuperation request, external requirements such as a cruise control system, speed limiter, etc.

In a step S2, based on the total target torque and the available torques Mv of the electric drives, the minimum and maximum possible all-wheel drive torque distribution is determined from a driving dynamics point of view and optionally from a comfort point of view. The all-wheel drive torque distribution is defined as the quotient of the rear axle torque and the sum of the rear and front axle torques in percent. The minimum and maximum available torques Mv of the electric drives are provided by the electric drives, for example on a CAN bus.

In a step S3, a total power loss of the two electric drives is determined at the above-mentioned minimum and maximum all-wheel drive distribution limits, based on power loss characteristic diagrams VLKF. If distributions of 0 and/or 100% are permissible, i.e. lie within the above distribution limits, and the open terminals operating mode is also possible for the respective electric drive, then the power loss for the distributions is 0 or 100% on basis determined from power loss characteristics VLKL _OK with open terminals for the respective other electric drive. For this purpose, the electric drives transmit a current speed _na and information as to whether the open terminals operating mode would be possible when a torque M1, M2 of 0 Nm is requested. The power loss characteristic diagrams VLKF, in which a power loss is shown as a function of an intermediate circuit voltage, the speed n and the torque M1, M2, are stored in the drive control unit 3. Also stored in the drive control unit 3 are power loss characteristics VLKL _OK of both electric drives, in which the power loss when the terminals are open is shown as a function of the speed n.

In a step S4, the four-wheel drive torque distribution with the lowest total power loss (golden section) is determined. Step S4 can be repeated several times with a number N of iterations, for example 10.

In a step S5, the all-wheel drive torque distribution with the lowest total power loss is available from the previously performed optimization. In addition, the power loss for the previously set all-wheel drive distribution is determined. The difference gives the power dissipation benefit. As long as no other all-wheel drive distribution is set, this power loss advantage is integrated.

In a step S6, it is checked whether the power loss advantage is greater than a threshold value or whether the integrated power loss advantage is greater than the threshold value.

If this is the case, the all-wheel drive torque distribution with the lowest total power loss is set in a step S7. The new target distribution is set correspondingly gradient-limited. Otherwise, in a step S8, the four-wheel drive distribution set up to now is retained.

In a step S9, if the vehicle is equipped with a mechanical disconnect clutch (disconnect unit) on the front electric drive, the power loss when the disconnect clutch is open is determined based on the power loss characteristic map VLKF of the rear electric drive and a drag loss characteristic curve SVLKL of the front electric Drive with open separating clutch. For this purpose, the current speed _na is transmitted by the electric drives. The power loss characteristic diagrams VLKF, in which a power loss is shown as a function of an intermediate circuit voltage, the speed n and the torque M1, M2, are stored in the drive control unit 3. Furthermore, drag power loss characteristic curves SVLKL of both electric drives, in which the power loss when the separating clutch is open as a function of the speed n, can be stored in the drive control unit 3 .

In a step S10 it is checked whether the separating clutch is currently engaged.

If this is the case, it is checked in a step S11 whether the difference between the power loss when the separating clutch is open and the power loss with all-wheel drive torque distribution with the lowest total power loss is greater than a certain power (for example: 50 W) and in this case (continued) closing of the disconnect clutch requested.

Otherwise, in a step S12 it is checked whether the difference between the power loss when the separating clutch is open and the power loss with all-wheel drive torque distribution with the lowest total power loss is greater than a certain power (e.g. 500 W) and in this case the separating clutch is closed requested.

3 12 is a schematic diagram of the torques M1, M2 of the inverters 2.1, 2.2 over the speed n without using the open terminals operating mode.

The power loss characteristic diagrams VLKF of the electric drives are stored in the drive control unit 3 via speed n, torque M1, M2 and DC voltage. At a current vehicle speed (current speed n _a ), the driver's request FW can be implemented as desired within the maximum limits of the two drives according to curves K1, K2, K3, K4. For example, given a driver's request FW for a torque M1, M2 of 100 Nm, a uniform distribution of 50 Nm is possible for each of the electric drives. In order to make this more efficient, the loss maps are searched for the most energy-efficient combination and this is adjusted. For example, with a driver request FW for a torque M1, M2 of 100 Nm, 30 Nm are then possible for the inverter 2.1 and 70 Nm for the inverter 2.2.

4 12 is a schematic diagram of the torques M1, M2 of the inverters 2.1, 2.2 versus the speed n using the open-clamp operating mode.

The power loss maps VLKF of the electric drives are stored in the drive control unit 3 via speed n, torque M1, M2 and DC voltage. In addition, power loss characteristics VLKL _OK are stored for the open terminals operating mode. In order to drive the electric drives even more efficiently, when searching through the power loss characteristics VLKL _OK , a check is made as to whether or not the open terminals operating mode is available for the inverters 2.1, 2.2, for example from a CAN signal CS provided by the electric drives. For example, if the driver requests FW for a torque M1, M2 of 100 Nm, then 100 Nm is possible for inverter 2.1 and the open terminals operating mode is possible for inverter 2.2.

• Im Ergebnis können folgende Zustände angesteuert werden:
  • - Nutzen der Betriebsart Offene Klemmen auf einer Vorderachse und Stellen des Drehmoments M1, M2 gemäß Fahrerwunsch FW auf einer Hinterachse,
  • - Nutzen der Betriebsart Offene Klemmen auf der Hinterachse und Stellen des Drehmoments M1, M2 gemäß Fahrerwunsch FW auf der Vorderachse, oder
  • - Betreiben von beiden Invertern 2.1, 2.2 mit PWM-Taktung und Aufteilen des Drehmoments M1, M2 gemäß Fahrerwunsch FW auf beide elektrischen Antriebe mit wirkungsgrad-optimierter Verteilung.

Using an online optimization process, the most energy-efficient operation is selected from the following variants depending on the operating point:

• As a result, the following states can be controlled:
  • - Using the open clamps operating mode on a front axle and setting the torque M1, M2 according to the driver's request FW on a rear axle,
  • - Using the open clamps operating mode on the rear axle and setting the torque M1, M2 according to the driver's request FW on the front axle, or
  • - Operation of both inverters 2.1, 2.2 with PWM clocking and splitting the torque M1, M2 according to the driver's request FW on both electric drives with efficiency-optimized distribution.

If the drive control unit 3 commands the open terminals operating mode, software in the electric drive then checks whether the comfort function is still preventing this. If this is not the case, the open terminals operating mode is set. In addition, a comfortable transition to the open terminals operating mode is ensured in the software.

Depending on the driving style or cycle, the solution according to the invention achieves a significant consumption and range advantage in a vehicle with two electric drives.

Reference List

1.1, 1.2

electric drive machine

2.1,2.2

inverters

3

drive control unit

fw

driver request

K1, K2, K3, K4

Curve

M1, M2

torque

MV

available torque

n

number of revolutions

N

Number

n / A

current speed

R1, R2

Return message

S1 to S12

Step

SVLKL

drag power loss characteristic

VLKF

power dissipation map

VLKLOK

Power loss characteristic with an open terminal

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was 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.

Patent Literature Cited

• DE 102017202393 A1 [0003]

Claims (7)

Method for operating an electric vehicle with at least two electric drive units (1.1, 1.2), each electric drive unit (1.1, 1.2) being controlled with a respective inverter (2.1, 2.2), wherein - a drive control unit (3) from a driver request (FW) , comprising a position of an accelerator pedal and/or a brake pedal, determining a total target torque, - based on the total target torque and available torques (Mv) of the electric drive machines (1.1, 1.2), a minimum and maximum possible four-wheel drive Torque distribution is determined from a driving dynamics point of view, characterized in that - a total power loss of the two electric drive units (1.1, 1.2) at the minimum and maximum possible all-wheel drive torque distributions, based on power loss characteristic maps (VLKF), is determined, and then when all-wheel -Torque distributions of 0 and/or 100% are permissible and an operating mode with open terminals is also possible for the respective electric drive machine (1.1, 1.2), the power loss for the four-wheel drive torque distributions of 0 or 100% based on power loss characteristics (VLKL _OK ) is determined with open terminals for the respective other electric drive machine (1.1, 1.2), - the four-wheel drive torque distribution with the lowest total power loss is determined, - with a power loss advantage as the difference from the four-wheel drive torque distribution with the lowest total power loss and a power loss for the all-wheel drive distribution set up to now is formed, - in which case, if the power loss benefit is greater than a threshold value or if an integrated power loss benefit is greater than the threshold value, the all-wheel drive torque distribution with the lowest total power loss is set, depending on the operating point, the most energy-efficient operation is selected from the following variants: - Use of the open terminals operating mode for one of the electric drive machines (1.1, 1.2) and setting the torque (M1, M2) according to the driver's request (FW) on another of the electric drive machines (1.1, 1.2), - Operation of both inverters (2.1, 2.2) with pulse width modulation and splitting the torque (M1, M2) according to the driver's request (FW) to both electric drive machines (1.1, 1.2) with efficiency-optimized distribution. procedure after claim 1 , characterized in that the driver request (FW) also includes a recuperation level and / or a brake recuperation request and / or data of a cruise control system and / or a speed limiter. procedure after claim 1 or 2 , characterized in that at least one of the electric drive machines (1.1, 1.2) is used to drive a front axle and at least one other of the electric drive machines (1.1, 1.2) is used to drive a rear axle. Method according to one of the preceding claims, characterized in that when the open terminals operating mode is requested, it is checked whether a comfort function is preventing this operating mode and that otherwise the open terminals operating mode is set. Method according to one of the preceding claims, characterized in that the drive control unit (3) on the basis of the driver's request (FW) gives a request for a torque (M1, M2) to the inverters (2.1, 2.2) and from them feedback (R1, R2) receives whether the open terminals operating mode would be possible under the current operating conditions and when a torque (M1, M2) of 0 Nm is requested, whereby the feedback (R1, R2) that the open terminals operating mode is possible is then transmitted , if a voltage induced as a result of the retroactive electromotive force of the respective electric drive machine (1.1, 1.2) is lower than the battery voltage and/or if the current speed (n _a ) is lower than a predetermined threshold value. Method according to one of the preceding claims, characterized in that the vehicle is a purely electrically powered vehicle. Method according to one of the preceding claims, characterized in that in the event that the vehicle is equipped with a mechanical separating clutch on the front electric drive, based on the power loss characteristic map (VLKF) of the rear electric drive and a drag loss characteristic curve (SVLKL) of the front electric drive when the separating clutch is open, the power loss is determined when the separating clutch is open, with the electric drives transmitting their current speed (n _a ) for this purpose, with the power loss characteristic diagrams (VLKF), in which a power loss is dependent on an intermediate circuit voltage, the speed (n) and the torque (M1, M2) is shown, as well as drag power loss characteristics (SVLKL) of both electric drives, in which the power loss when the separating clutch is open as a function of the speed (n) is shown in which Drive control unit (3) are stored, with the separating clutch being checked whether the difference between the power loss when the separating clutch is open and the power loss with all-wheel drive torque distribution with the lowest total power loss is greater than a specific first power and in this case a closing or closed Holding the separating clutch is requested, otherwise it is checked whether the difference between the power loss when the separating clutch is open and the power loss at all-wheel drive torque distribution with the lowest total power loss is greater than a specific second power and in this case a closing of the separating clutch is requested.

Images