DE102013213096A1 - Method and device for operating an electric or hybrid vehicle - Google Patents

Abstract

An electric or hybrid vehicle includes a high voltage electrical system (HV_Sys). The high-voltage system (HV_Sys) comprises a high-voltage energy store (Batt), at least one high-voltage consumer (Load), at least one electric machine (EM) and power electronics (LE). The power electronics (LE) is energetically coupled with the at least one electric machine (EM), with the high-voltage energy storage (Batt) and with the at least one high-voltage consumer (Load). The high-voltage energy storage (Batt) is energetically coupled with the at least one high-voltage consumer (load). A rotational speed (n_EM) of the at least one electric machine (EM) is determined, and an energy storage-related extreme traction torque is determined as a function of the determined rotational speed (n_EM) and dependent on a predetermined calculation rule based on a predetermined second-order approximation function. In this case, the approximation function approximates a profile of a predetermined characteristic curve, which represents a power loss of the electric machine (EM) as a function of a torque (M_EM) of the electrical machine.

Description

The invention relates to a method and a corresponding device for operating an electric or hybrid vehicle and a computer program product.

Hybrid vehicles comprise at least one electric motor or one electric machine in addition to the internal combustion engine. In hybrid serial vehicles, a generator is driven by the internal combustion engine, with the generator supplying electric power to the electric motor driving the wheels. Furthermore, parallel hybrid vehicles are known in which an addition of the torques of the internal combustion engine and at least one connectable to the internal combustion engine electric machine. The task of a torque distribution or a hybrid operating strategy in hybrid vehicles is the distribution of the driver's desired torque or the driver's desired power to the internal combustion engine and the at least one electric machine. For this purpose, a torque structure is used, which includes a modular description of the torques present in the drive train of the vehicle.

The object underlying the invention is to provide a method and an apparatus for operating an electric or hybrid vehicle and a computer program product, which enable a reliable operation of the electric or hybrid vehicle.

The object is solved by the features of the independent claims. Advantageous developments of the invention are characterized in the subclaims.

The invention is characterized according to a first and second aspect by a method and a corresponding device for operating an electric or hybrid vehicle comprising a high-voltage electrical system. The high-voltage system comprises a high-voltage energy storage device, at least one high-voltage consumer, at least one electric machine and power electronics. The power electronics is energetically coupled with the at least one electric machine, with the high-voltage energy storage and with the at least one high-voltage consumer. The high-voltage energy storage is energetically coupled with the at least one high-voltage consumer. A rotational speed of the at least one electric machine and an energy storage-related extreme traction torque are determined as a function of the determined rotational speed and dependent on a predetermined computing rule based on a predetermined second-order approximation function. In this case, the approximation function approximates a profile of a predetermined characteristic curve, which represents a power loss of the electrical machine as a function of a torque of the electrical machine.

Advantageously, such an energy storage-related maximum and / or minimum traction torque can be determined analytically. The used prefix "extreme" denotes an extremum, ie a maximum or a minimum. An energy storage-related maximum traction torque takes into account a maximum energy storage capacity. An energy storage-related minimum traction torque takes into account a minimum energy storage capacity.

For calculating the energy storage-related extreme traction torque little computing power and little memory space is required because only coefficients of the approximation function must be provided. The second-degree approximation function is preferably a second-order approximation polynomial. It is not necessary to provide a multiplicity of sample points of the characteristic curve representing the power loss of the electrical machine as a function of the torque. The power loss information of the electric machine can thus be characterized with only very few data - mainly by means of the coefficients of the approximation function. The power loss information of the electrical machine can thus be transmitted sufficiently quickly in the form of the coefficients of the approximation function also over a relatively slow and bandwidth-limited vehicle bus, for example a CAN bus (Controller Area Network). This makes it possible that the power loss information of the electric machine need not be stored centrally, but a partitioning of a control system of the electric or hybrid vehicle can be flexible.

The high-voltage energy storage is preferably designed as a battery. Instead of energy storage-related extreme traction torque also the term energy-related extreme traction torque can be used.

In an advantageous embodiment according to the first and second aspects, coefficients of the approximation function are determined as a function of the rotational speed of the at least one electrical machine. Advantageously, this makes it possible to take into account an efficiency of the electric machine. In a further advantageous embodiment of the first and second aspects, a temperature of the electrical machine is determined and at least one of the coefficients is determined depending on the temperature of the electrical machine. Preferably, the coefficient of the approximation function representing an absolute term is determined depending on the temperature. Determining the energy storage-related extreme traction torque depending on the temperature makes it possible to consider an efficiency of the electric machine. On the other hand, a calculation of the energy storage-related extreme traction torque as a function of the temperature by means of characteristic curve curves with a large number of interpolation points of the characteristic curve requires the provision and processing of an enormous amount of data, since in this case three-dimensional characteristic diagrams have to be evaluated.

In a further advantageous embodiment of the first and second aspects, an electrical extreme system traction torque for the electrical high-voltage system is determined depending on the energy storage-related extreme traction torque and a predetermined extreme traction torque of the electric machine and / or a predetermined power electronics related extreme traction torque. Advantageously, this enables an available extreme electrical system traction torque to be determined for limiting a torque structure of the engine control. The torque structure is dependent on the respective torque limits. For calculating the available extreme electrical system traction torque, power losses or efficiency information of the electric machine are preferably taken into account. This allows a conversion between mechanical and electrical domain. For a consideration of the power loss of the electric machine and the power electronics, therefore, a power loss approximation in the form of a polynomial of the second degree, in particular the predetermined approximation function, is used for a current operating point of the electrical machine. This makes it possible to analytically calculate the energy storage related extreme traction torque. The coefficients of the approximation function for power loss approximation are provided to the calculation rule for determining the energy storage-related extreme traction torque.

The extreme electrical system torque is a key element for monitoring compliance with component limits of the high-voltage system. Preferably, the electrical extreme system traction torque is determined as a function of a maximum or minimum energy storage capacity. As energy storage capacity, short-term energy storage performance values are used here. The extreme electrical system drag torque preferably does not consider foresight, strategic degradation, torque reserves, and / or performance constraints.

An analytical calculation of the energy storage-related extreme traction torque enables efficient calculation of extreme electrical system torque and a modular structure of a control system of the electric and hybrid vehicle in which interfaces can be precisely defined, thus minimizing coordination effort and development effort.

In a further advantageous embodiment of the first and second aspects, the high-voltage electrical system comprises at least a first and a second electric machine and the extreme electrical system traction torque with respect to the first electric machine is determined depending on a predetermined extreme correlation traction torque having a torque distribution between the characterized first and second electric machine. Advantageously, this allows a torque distribution between the first and second machines to be taken into account in determining the extreme electrical system traction torque and thereby more accurately determine the extreme system traction torque.

In a further advantageous embodiment of the first and second aspects, the respective extreme traction torques, energy storage related extreme traction torque, extreme traction torque of the electric machine, power electronics related extreme traction torque and extreme correlation traction torque respectively represent maximum torques and the one extreme traction torque is expressed as extreme torque. Determines system traction torque having the smallest value. In the case that the high-voltage system has only one electric machine, no extreme correlation torque is to be considered.

In a further advantageous embodiment of the first and second aspects, the respective extreme traction torques, energy storage-related extreme traction torque, extreme traction torque of the electric machine, power electronics related extreme traction torque and extreme correlation traction torque respectively represent minimum torques, and that extreme traction torque is expressed as extreme torque. Determines system traction torque that has the largest value. In the case that the high-voltage system has only one electric machine, no extreme correlation torque is to be considered.

In a further advantageous embodiment of the first and second aspects, an extreme traction energy storage capacity is determined as a function of the determined extreme system traction torque. Furthermore, a rotational speed of the second electric machine is determined and a second energy storage-related extreme traction torque with respect to the second electrical machine determined depending on the determined speed of the second machine, depending on the extreme traction energy storage capacity and depending on the predetermined calculation rule, the second on the predetermined approximation function Grades based. In this case, the approximation function approximates a course of a predetermined characteristic curve which represents a power loss of the second electric machine as a function of a torque of the second electric machine. Advantageously, this allows an energy storage power distribution between the first and second machines to be taken into account in determining the extreme electrical system traction torque and thereby more accurately determine the extreme system traction torque with respect to the second machine.

The invention is characterized according to a third aspect by a computer program for operating an electric or hybrid vehicle, wherein the computer program is designed to carry out a method according to the first aspect when executed on a data processing device.

The invention is characterized according to a fourth aspect by a computer program product. The computer program product comprises executable program code, wherein the program code, when executed by a data processing device, performs the steps of the method according to the first aspect. In particular, the computer program product comprises a medium which can be read by the data processing device and on which the program code is stored.

Advantageous embodiments of the first aspect also apply to the third and fourth aspects.

Embodiments of the invention are explained below with reference to the schematic drawings.

Show it:

1 an equivalent circuit diagram of a high-voltage electrical system of an electric or hybrid vehicle,

2 a diagram with a first and second curve, each representing power losses of the electric machine in dependence on a torque of the electric machine,

3 a signal flow diagram of a first program for operating the electric or hybrid vehicle,

4 a signal flow diagram of a second program for operating the electric or hybrid vehicle,

5 a second diagram with a torque characteristic of a high-voltage system and

6 an exemplary block diagram for a control device for operating the electric or hybrid vehicle.

Elements of the same construction or function are provided across the figures with the same reference numerals.

1 shows an equivalent circuit diagram of a high-voltage electrical system HV_Sys an electric or hybrid vehicle and an associated control system Crtl_Sys. The high-voltage system HV_Sys comprises drive electronics with at least one electric machine EM and power electronics LE, one High-voltage energy storage Batt and at least one high-voltage load load. The high-voltage energy storage Batt is preferably designed as a battery. In 1 For example, two high-voltage loads are shown. Furthermore, in 1 respectively associated control devices BCU, EKVM, SME, AE, DME shown in dashed lines. The control system Crtl_Sys comprises, for example, a motor control DME, a drive electronics control device AE, a control device SME of the high-voltage energy store Batt, a body control device BCU and a control device EKMV for an electric refrigerant compressor. The engine control DME can also be called digital engine electronics. The engine controller DME includes, for example, a torque structure of the electric or hybrid vehicle. The torque structure includes a modular description of torques present in the powertrain of the electric or hybrid vehicle.

For the current account of the high-voltage system HV_Sys: P_AE + P_BAT + P_DC - Load = 0, Eq. 1 where P_AE represents the power of the drive electronics, P_BAT represents the power of the high-voltage energy store Batt, and P_DC-Load represents the power of the high-voltage load load.

The power P_AE of the drive electronics is in accordance with Eq. 2 together from a mechanical power P_mech_EM of the electric machine EM, which emits the machine EM, and the power loss P_Verlust_EM of the electric machine EM or the power loss P_Verlust_LE of the power electronics LE: P_AE = P_mech_EM + P_Verlust_EM; EE Gl. 2

The power loss P_Verlust_EM the electric machine EM can be determined depending on a torque M_EM the electric machine EM. The power loss P_Verlust_LE the power electronics can be determined depending on a current I_EM, which is delivered to the electric machine EM. Here, the power loss P loss EM of the electric machine EM and the power loss P_Verlust_LE the power electronics LE can be converted into each other and as a term P_Verlust_EM; LE be taken into account.

For calculating an available extreme electrical system traction torque, power losses or efficiency information of the electric machine EM are preferably taken into account. For a consideration of the power loss P_Verlust_EM the electric machine EM or the power electronics P_Verlust_LE a loss power approximation in the form of a polynomial is used for a current operating point of the electric machine EM. This makes it possible to analytically calculate an energy storage-related extreme traction torque.

2 shows the course of the power loss P_Verlust_EM the electric machine EM as a function of the torque M_EM the electric machine EM. A first curve KE shows a characteristic curve and thus measured values for the power loss P_Verlust_EM the electric machine depending on a respective current torque. A second curve AP shows an approximate profile of the power loss P loss EM of the electric machine EM.

The first curve KE and the second curve AP each represent the power loss for a specific speed and for a specific temperature of the electric machine EM.

In an analogous manner, the power loss P_Verlust_LE the power electronics in dependence on the current I_EM, which flows through the electric machine can be used.

The power loss P_Verlust_EM of the electric machine EM can be approximated by a second-order approximation function. P_Verlust_EM; LE = a (n _EM ) M 2 / EM + b (n _EM ) M _EM + c (n _EM , T _EM ), Eq. 3 where n _{EM is} the rotational speed n_EM of the electric machine EM, M _{EM is} the torque M_EM of the electric machine EM and T _{EM is} a temperature of the electric machine EM and a, b, c are coefficients of the approximation function. The power loss P_Verlust_EM; LE depends on the speed n_EM and the temperature of the electric machine EM. Preferably, the absolute member c of the approximation function is dependent on the temperature of the electric machine EM.

The coefficients can be determined and stored for the respective rotational speeds and the respective temperatures of the electric machine EM in advance.

Below is an exclusive calculation of maximum values. A calculation of minimum values takes place analogously.

wobei P_Bat eine aktuelle Leistung des Hochvolt-Energiespeichers Batt repräsentiert.Using Eq. 1 results:

where P _{Bat represents} a current power of the high-voltage energy storage Batt.

The current performance of the high-voltage energy storage insert will be the maximum power of the high-voltage energy storage P max / Bat associated P _Bat = P max / Bat.

An energy storage-related maximum traction torque M_EM_max, Bat is determined as a function of a determined current rotational speed n_EM of the electric machine EM and dependent on a predetermined calculation rule which is based on the specified second-order approximation function according to Eq. 2 based. The calculation rule is in Eq. 4 indicated.

The coefficients are determined depending on the current speed from the set of previously stored coefficients. In particular, the absolute member c is in this case additionally determined depending on the current temperature of the electric machine EM from the amount of the previously stored absolute members c.

3 shows an exemplary signal flow diagram for a first program for operating an electric or hybrid vehicle. The electric or hybrid vehicle has in this case a first and a second electric machine EM1, EM2.

In a step S12, the energy storage-related maximum traction torque M_EM1_max, Batt with respect to the first electric machine EM1 according to Eq. 4 determined.

In this case, the maximum energy storage power P_Batt, max, the power P_DC-load of the high-voltage consumers, the determined rotational speed n_EM1 of the first electric machine EM1 and the coefficients a1, b1, c1 determined for the determined rotational speed n_EM1 are used as input variables.

In a step S14, a maximum system traction torque M_EM1_max, Sys with respect to the first electric machine EM1 is determined. In step S14, a comparison of the energy storage-related maximum traction torque M_EM1_max, Batt with a predetermined maximum traction torque M_EM1_max, EM of the first electric machine EM1, a predetermined power electronics-related maximum traction torque M_EM1_max, LE and a predetermined maximum correlation traction torque M_max, KorEM1, the a torque distribution between the first and second electric machine EM1, EM2 characterized. In step S14, the maximum traction torque is determined to be the maximum system traction torque M_EM1_max, Sys having the smallest value.

In a step S16, a maximum traction energy storage capacity P_BattTr, max is determined as a function of the determined maximum system traction torque M_EM1_max, Sys, which was determined with reference to the first electric machine EM1.

In a step S18, a second energy storage-related maximum traction torque M_EM2_max, Batt with respect to the second electric machine EM2 is determined as a function of a determined rotational speed n_EM2 of the second engine and dependent on the maximum traction energy storage power P_BattTr, max and depending on the predetermined calculation rule according to Eq. 4, which is based on the predetermined second-order approximation function, the approximation function in this case approximating a course of a predetermined characteristic curve, which represents a power loss of the second electric machine EM2 in dependence on a torque of the second electric machine EM2.

A maximum system traction torque M_EM2_max, Sys with respect to the second machine EM2 can be determined as a function of the second energy storage-related maximum traction torque M_EM2_max, Batt analogous to the maximum system traction torque M_EM1_max, Sys of the first machine. The torque limits of the electric and hybrid vehicle can thus be calculated as a function of the rotational speeds n_EM1, n_EM2, temperature, a power electronics state LE, and a state of the high-voltage energy store Batt. The maximum system traction torques M_EM1_max, Sys, M_EM2_max, Sys are preferably determined at predetermined time intervals, for example every 10 ms, and supplied to the torque structure.

4 shows an exemplary signal flow diagram for a second program for operating an electric or hybrid vehicle. The electric or hybrid vehicle also has a first and a second electric machine EM1, EM2 in this case. The second program has further optional steps. These additional program steps make it possible to take into account special characteristics of the Batt high-voltage energy storage and / or an intermediate circuit.

The second program also has the steps S12 to S18. The second routine continues if the energy storage-related maximum traction torque M_EM1_max, Batt with respect to the first machine is greater than the maximum system traction torque M_EM1_max, Sys with respect to the first machine, and thus the first electric machine EM1 and / or the power electronics LE responsible for torque limitation is. In this case, the maximum system traction torque M_EM1_max, Sys is preferably not determined with a current battery voltage.

In this case, a maximum battery voltage is determined in a step S20 as a function of the maximum traction energy storage power P_BattTr, max determined in step S16. In a step S22, a further maximum traction torque M_EM1_max, EM_ii of the first electric machine EM1 and / or a further power electronics-related maximum traction torque M_EM1_max, EM_ii is determined as a function of the determined maximum battery voltage.

In a step S24, a comparison is made of the energy storage-related maximum traction torque M_EM1_max, Batt and the determined further maximum traction torque M_EM1_max, EM_ii of the first electric machine EM1 and the determined further power electronics-related maximum traction torque M_EM1_max, LE_ii.

In step S24, the maximum traction torque is determined to be the maximum system traction torque M_EM1_max, Sys_ii to be used with respect to the first electric machine EM1 having the smallest value.

5 shows a second diagram representing a torque characteristic of the high-voltage electrical system HV_Sys. The dashed curve in 5 For example, represents the energy storage related maximum traction torque M_EM_max, Batt. The continuous curves represent the maximum traction torque M_EM_max, EM of the electric machine EM for a particular intermediate circuit voltage Uz.

It can be seen that at lower speeds, the energy storage-related maximum traction torque M_EM_max, Batt is smaller than the maximum traction torque M_EM_max, EM of the electric machine EM and thus a current performance of the high-voltage energy storage Batt system-limiting for the torque distribution in the electric or Hybrid vehicle is.

Depending on a dimensioning of the power electronics LE, a performance and a power electronics-related maximum traction torque M_EM_max, LE derived therefrom may be less than the energy storage-related maximum torque M_EM_max, Batt and the maximum traction torque M_EM_max, EM of the electric machine EM and thus a current performance of the power electronics LE system limiting for the torque distribution in the electric or hybrid vehicle. The power electronics LE can for example comprise a pulse inverter and / or a DC / DC converter.

6 shows a block diagram of a control system Ctrl_Sys an electric or hybrid vehicle. The control system Ctrl_Sys comprises, for example, the engine control DME which has a torque structure and / or is designed to determine a torque distribution for the electric or hybrid vehicle. The engine control DME determines, for example, a respective traction torque M_EM1_ctrl, M_EM2_ctrl to be set for the first electric machine EM1 and the second electric machine EM2.

The engine controller DME provides, for example, a maximum correlation traction torque M_max, KorEM1 for the first electric machine EM 1 and forwards it to the drive electronics control device AE. The respectively to be set traction torque M_EM1_ctrl, M_EM2_ctrl is forwarded to a control device SG_EM1 the first electric machine EM1 or to a control device SG_EM2 the second electric machine EM2. The respective control device SG_EM1, SG_EM2 respectively sets the maximum traction torque M_EM1_max, EM, M_EM2_max, EM, the power electronics-related maximum traction torque M_EM1_max, LE, M_EM2_max, LE, the current rotational speed n_EM1, n_EM2 and the coefficients a1 determined as a function of the rotational speed. a2, b1, b2, c1, c2 and forwards them to the drive electronics control device AE.

Furthermore, the control system Ctrl_Sys comprises the control device SME of the high-voltage energy store Batt. For example, the control device SME of the high-voltage energy store Batt forwards the maximum power P_Batt, max of the high-voltage energy store Batt to the drive electronics control device AE. Optionally, the drive electronics control device AE has a current-voltage monitor which optionally adapts the maximum power P_Batt, max of the high-voltage energy store Batt and forwards the adapted maximum power of the high-voltage energy store Batt to the drive electronics control device AE.

The drive electronics control device AE comprises, for example, a calculation module TQP which is designed to determine the energy storage-related maximum traction torque M_EM1_max, Batt, M_EM2_max, Batt and the maximum system traction torque M_EM1_max, Sys, M_EM2_max, Sys for the respective machines EM1, EM2.

Furthermore, the drive electronics control device AE comprises a degradation module DEGR, to which the maximum electrical system torque M_EM1_max, Sys, M_EM2_max, Sys of the first and second electric machines EM1, EM2 is forwarded. The respective maximum electrical system torque M_EM1_max, Sys, M_EM2_max, Sys is forwarded, for example, to the torque structure of the engine control DME.

LIST OF REFERENCE NUMBERS

• a1, b1, c1; a2, b2, c2

  Coefficients of an approximation function

  AE

  Drive Electronics controller

  Batt

  High-voltage energy storage

  ECU

  Body Control Module

  c

  absolute term

  Crtl_Sys

  control system

  DEGR

  Degradationsmodul

  DME

  motor control

  ECMT

  Control device for an electric refrigerant compressor

  EM

  electric machine

  EM1

  first electric machine

  EM2

  second electric machine

  HV_Sys

  High-voltage system

  I_EM

  Electricity of the electric machine

  LE

  power electronics

  Load

  High-voltage consumers

  M_EM

  Torque of the electric machine

  M_EM1_max, EM

  Maximum traction torque of the first electric machine

  M_EM1_max, Batt, M_EM2_max, Batt

  energy storage related maximum traction torque

  M_EM1_max, LE

  power-electronics-related maximum traction torque

  M_EM1_max, Sys

  electrical maximum system torque

  M_EM1_max, Sys_ii

  further maximum electrical system torque

  M_max, KorEM1

  Maximum correlation traction torque

  n_EM1,

  n_EM2 speed

  P_BatTr, max

  Maximum traction battery power

  P_Verlust_EM

  Power loss of the electric machine

  P_Verlust_LE

  Power loss of the power electronics

  SG_EM1

  Control device of the first electric machine

  SG_EM2

  Control device of the second electric machine

  SME

  Control device of the high-voltage energy storage

  TQP

  calculation module

  Uz

  Intermediate circuit voltage

Claims (11)

Method for operating an electric or hybrid vehicle comprising a high-voltage electrical system (HV_Sys) with a high-voltage energy storage (Batt), at least one high-voltage load (Load), at least one electric machine (EM) and power electronics (LE), wherein the power electronics (LE) is energetically coupled with the at least one electric machine (EM), with the high-voltage energy storage (Batt) and with the at least one high-voltage load (Load) and the high-voltage energy storage (Batt) is energetically coupled to the at least one high-voltage consumer (Load), in which - A speed of the at least one electric machine is determined and - An energy storage-related extreme traction torque is determined depending on the determined speed and dependent on a predetermined calculation rule based on a given second-order approximation function, wherein the approximation function approximates a course of a predetermined characteristic curve, the power loss of the electric machine (EM) in dependence of a torque (M_EM) of the electric machine (EM). Method according to Claim 1, in which coefficients of the approximation function are determined as a function of the rotational speed of the at least one electrical machine. The method of claim 1 or 2, wherein a temperature of the electric machine (EM) is determined and at least one of the coefficients is determined depending on the temperature of the electric machine (EM). Method according to one of the preceding claims, wherein an electrical extreme system traction torque for the electrical high-voltage system (HV_Sys) is determined depending on the energy storage-related extreme traction torque and a predetermined extreme traction torque of the electric machine (EM) and / or a predetermined Leistungselektronikbezogene extremely traction torque. The method of claim 4, wherein the high voltage electrical system (HV_Sys) comprises at least first and second electric machines (EM1, EM2) and extreme electric system traction torque with respect to the first electric machine (EM1) in response to a predetermined extreme correlation torque that characterizes a torque distribution between the first and second electric machines (EM1, EM2). The method of claim 4 or 5, wherein the respective extreme traction torques, energy storage related extreme traction torque, extreme traction torque of the electric machine (EM), power electronics related extreme traction torque and extreme correlation traction torque respectively represent maximum torques and that extreme traction torque is extreme -Systemtraktionsdrehmoment is determined, which has the smallest value. The method of claim 4 or 5, wherein the respective extreme traction torques, energy storage related extreme traction torque, extreme traction torque of the electric machine (EM), power electronics related extreme traction torque and extreme correlation traction torque respectively represent minimum torques and the extreme traction torque as extreme -Systemtraktionsdrehmoment is determined which has the largest value. Method according to one of the preceding claims 4 to 7, in which An extreme traction energy storage capacity is determined as a function of the determined extreme system traction torque, - A speed (n_EM2) of the second electric machine (EM2) is determined and A second energy storage-related extreme traction torque with respect to the second electrical machine is determined as a function of the determined rotational speed of the second machine, depending on the extreme traction energy storage capacity and dependent on the predetermined calculation rule, which is based on the predetermined second-order approximation function, wherein the approximation function is a course a predetermined characteristic curve is approximated representing a power loss of the second electric machine (EM2) in response to a torque (M_EM2) of the second electric machine (EM2). Device for operating an electric or hybrid vehicle, comprising a high-voltage electrical system with a high-voltage energy storage (Batt), at least one high-voltage load (Load), at least one electric machine (EM) and power electronics (LE), wherein the Power electronics (LE) is energetically coupled with the at least one electric machine (EM), with the high-voltage energy storage (Batt) and with the at least one high-voltage load (Load) and the high-voltage energy storage (Batt) is energetically coupled with the at least a high-voltage load and the device is designed to carry out a method according to one of claims 1 to 8. Computer program for operating an electric or hybrid vehicle, wherein the computer program is designed to carry out a method according to one of claims 1 to 8 when executed on a data processing device. Computer program product comprising executable program code, wherein the program code executes the method according to one of claims 1 to 8 when executed by a data processing device.

Images