Patent Publication Number: US-2023155535-A1

Title: Method for controlling a drivetrain of an electric vehicle, data processing device, drivetrain and electric vehicle

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present disclosure claims the benefit of priority of co-pending European Patent Application No. 21 208 303.4, filed on Nov. 15, 2021, and entitled “METHOD FOR CONTROLLING A DRIVETRAIN OF AN ELECTRIC VEHICLE, DATA PROCESSING DEVICE, DRIVETRAIN AND ELECTRIC VEHICLE,” the contents of which are incorporated in full by reference herein. 
     TECHNICAL FIELD 
     The present disclosure relates to a method for controlling a drivetrain of an electric vehicle during direct current (DC)-charging of a traction battery of the drivetrain. The drivetrain includes the traction battery, a N-phase traction inverter unit and a N-phase electric machine. The electric machine is electrically coupled to the traction battery via the inverter unit. 
     Moreover, the present disclosure is directed to a data processing device having means for carrying out the steps of the above method. 
     Additionally, the present disclosure concerns a drivetrain for an electric vehicle, the drivetrain including such a data processing device, and an electric vehicle having such drivetrain. 
     BACKGROUND 
     When charging the traction battery of a drivetrain, the N-phase traction inverter together with the N-phase electric machine may be used as a DC-DC converter. Essentially, the power switches of the N-phase traction inverter are used together with the magnetic coils of the N-phase electric machine to perform the DC-DC conversion. If the DC-voltage of the traction battery is higher than the DC voltage of a corresponding charging station, the traction inverter and the electric machine connected thereto may operate as a so-called DC-DC-boost converter. 
     In such a drive train a supplementary, so-called on-board charger may be omitted which leads to reduced weight and costs of the drivetrain. 
     It is known in this context that the DC-DC conversion produces a so-called current ripple, i.e. a generally undesired alternating current (AC) component having high frequency and high amplitude which is superimposed over the output DC current. The amplitude of the current ripple generally depends on the phase inductances of the electric machine, the switching frequency and the voltage difference between the charging station and the battery voltage. Current ripple produces losses in the electric machine which leads to the generation of heat. 
     In order to mitigate the problems resulting from the current ripple, usually capacitors are used as filter elements. 
     The problem to be solved by the present disclosure consists in further reducing the problems and negative effects being caused by the current ripple. 
     SUMMARY 
     The problem is at least partially solved or alleviated by the subject matter of the present disclosure. 
     According to a first aspect, there is provided a method for controlling a drivetrain of an electric vehicle during DC-charging of a traction battery of the drivetrain, the drivetrain including the traction battery, a N-phase traction inverter unit, a N-phase electric machine and a charging circuit, the electric machine being electrically coupled to the traction battery via the inverter unit, the charging circuit including at least partially the traction inverter unit and at least partially the electric machine, the method including: controlling the traction inverter unit such that the traction inverter unit operates as a DC-DC converter, receiving a position of a rotor of the electric machine, selecting a number out of the N phases of the electric machine as components of the charging circuit, the selection being dependent on the position of the rotor of the electric machine, and controlling the traction inverter unit such that the selected number out of the N phases of the electric machine forms part of the charging circuit. 
     The general idea underlying the present disclosure is to make use of an anisotropy of the electric machine with respect to the inductances being provided when seen from the traction inverter unit&#39;s perspective. The higher the inductances are, the better current ripple may be suppressed and the lower are the high frequency losses in the electric machine. These inductances are known if the position of the rotor of the electric machine is known. Based thereon, a number out of the N phases of the electric machine may be selected as components of the charging circuit. This number is chosen such that the best available suppression of current ripple is achieved. The number of the N phases being selected as components of the charging circuit is thus a particular number. 
     The fact that the charging circuit includes at least partially the traction inverter unit and at least partially the electric machine means that the traction battery is charged via the traction inverter unit and the electric machine. Thus, the traction inverter unit and the electric machine are used both for charging and for providing traction power. This dual use has the effect that the corresponding drive train is compact. Furthermore, the costs for the drivetrain are reduced. 
     For the present disclosure, receiving a position of a rotor of the electric machine means receiving an information, a parameter or a value characterizing the mechanical position of the rotor of the electric machine, e.g. a value referring to a number of degrees designating a rotational position. Thus, the position of the rotor of the electric machine can be designated a mechanical position. 
     In the present context a number of the N phases of the electric machine may includes any subset of the N phases and all N phases. 
     It is noted that the electric legs of the traction inverter being connected to non-selected phases of the electric machine are not used for charging. Consequently, the charging is performed by the number of the N phases only. It is thus possible to use a number of the N phases that is less than the total number of phases for charging. The non-selected phases of the electric machine and the corresponding electric legs of the inverter unit are electrically disconnected by opening the corresponding power switches of the inverter unit. The selection of the phases, thus, is performed by sending a switching signal to the relevant power switches which may be formed as transistors. 
     Generally speaking, the traction inverter unit may use semiconductor parts and therefore may be designated a semiconductor traction inverter. 
     Using the method according to the present disclosure leads to reduced current ripple which results in reduced high frequency losses. In other words, the efficiency of DC-DC charging is enhanced. This also results in an extended lifetime of the components of the drivetrain. Moreover, a size of a filter capacitor can be reduced since usually the lowest possible inductance value is considered for dimensioning the filter capacitor. As a consequence thereof, size and cost of the drivetrain may be reduced. 
     The traction inverter unit may be controlled to operate as an interleaved DC-DC converter, interleaving the selected ones of the N phases. As has been described before, the selected ones of the N phases may be all of the N phases or a subset of the N phases. Interleaving means that the selected ones of the N phases are used according to a predefined timing schedule. This reduces the output current ripple. 
     According to an example, out of the available combinations of numbers of the N phases, the alternative offering the highest equivalent inductance is selected. It has already been mentioned that a high inductance leads to an efficient and effective suppression of current ripple. Thus, the equivalent inductance is a well-suitable parameter for deciding on the best choice of the number of the N phases. The equivalent inductance is always assessed from the perspective of the traction inverter unit. The equivalent inductance includes both self inductance and mutual inductance. Consequently, the present example offers a simple and reliable way of reducing current ripple. 
     It is possible that the equivalent inductance of all available combinations of numbers of the N phases in function of the position of the rotor of the electric machine is received from a look-up table. Such a look-up table may also be designated a map of inductances. The look-up table may for example be generated during a test of the electric machine at the end of its production. Alternatively, the look-up table can be generated using a computer simulation. The look-up table is a simple and reliable manner of providing the relevant information about the equivalent inductances. Furthermore, the use of a look-up table is computationally efficient. 
     In the look-up table, the equivalent inductances may be represented in function of at least one of a current and a duty cycle. The duty cycle depends from the difference between the voltage offered by the charging station and the operational voltage of the traction battery. From the duty cycle, a current for charging can be derived. The look-up table can, thus, for example be entered with a motor position and a current. Consequently, the equivalent inductances are available for at least a great variety of operational conditions, if not for all operational conditions. 
     In an example, out of the available combinations of numbers of the N phases, the alternative offering the lowest electromagnetic losses may be selected. In this context, the electromagnetic losses include iron losses, copper losses, and permanent magnet losses. As explained before, the higher the ripple amplitude is, the higher are the losses. The losses may lead to undesired heat production and low efficiency of charging. Thus, the losses are also a well-suitable parameter for deciding on the number of the N phases to be selected. Thus, the present example offers a simple and reliable way of reducing current ripple. 
     To this end, the electromagnetic losses of all available combinations of numbers of the N phases may be received from a look-up table in function of the position of the rotor of the electric machine. Such a look-up table may also be designated a map of losses. The look-up table may for example be generated during a test of the electric machine at the end of its production. Alternatively, the look-up table can be generated using a computer simulation. The look-up table is a simple and reliable manner of providing the relevant information about the losses. Furthermore, the use of a look-up table is computationally efficient. 
     It is understood that the above-mentioned equivalent inductances and the electromagnetic losses may be provided by a common or combined look-up table. 
     In the look-up table, the magnetic losses may be represented in function of at least one of a current and a duty cycle. As before, the duty cycle depends from the difference between the voltage provided by the charging station and the operational voltage of the traction battery. From the duty cycle, a current for charging can be derived. The look-up table can for example be entered with a motor position and a current. Consequently, the relevant losses are available for at least a great variety of operational conditions, if not for all operational conditions. 
     In a further example, the selection of all N phases as components of the charging circuit may be excluded if a duty cycle to be performed falls within a predefined duty cycle range, and all N phases may be pre-selected as components of the charging circuit if the duty cycle to be performed falls outside the predefined duty cycle range. This example is based on the finding that within a predefined duty cycle selecting all N phases seldom or never leads to the best available suppression of current ripple. Consequently, this alternative is excluded. This enhances the efficiency when performing the method according to the present disclosure. The predefined duty cycle range may be 40% to 60%. It is also possible that the predefined duty cycle range is 45% to 55% or 48% to 50%. Thus, using all the N phases as components of the charging circuit may be excluded if the duty cycle is roughly 50%. 
     Alternatively or additionally, the electromagnetic losses of all N phases may be compared to the electromagnetic losses being produced by the subset of the N phases having the highest electromagnetic losses and by selecting all N phases as components of the charging circuit only if the electromagnetic losses produced by all N phases are lower than the electromagnetic losses produced by the subset of the N phases having the highest electromagnetic losses. In doing so, it is guaranteed to select the number of the N phases leading to the most effective suppression of current ripple. 
     According to a second aspect, there is provided a data processing device having means for carrying out the steps of the method according to the present disclosure. The data processing device is for example a control unit or a controller for at least one of the drivetrain and the traction inverter. Such a data processing device leads to reduced current ripple which results in reduced high frequency losses. In other words, the efficiency of DC-DC charging is enhanced. This also results in an extended lifetime of the components of the drivetrain. Moreover, a size of a filter capacitor can be reduced since usually the lowest possible inductance value is considered for dimensioning the filter capacitor. As a consequence thereof, size and cost of the drivetrain may be reduced. 
     If look-up tables, e.g. as described above, are used, they can be stored in a memory of the data processing device. Alternatively, the look-up table may be provided externally to the data processing device. In the latter case, the data processing device includes an interface for receiving the relevant data from the look-up table. 
     In an example, the data processing device includes a first control interface being connectable to the traction inverter unit such that the traction inverter unit is controllable by the data processing device and a second control interface being connectable to a controller of the electric machine, the second control interface being configured for receiving a position of the rotor of the electric machine. Consequently, the data processing device may be easily integrated into a drivetrain. 
     According to a third aspect, there is provided a drivetrain for an electric vehicle, the drivetrain including a data processing device according to the present disclosure, a traction battery, a N-phase traction inverter unit and a N-phase electric machine, the electric machine being electrically coupled to the traction battery via the inverter unit and the data processing device being communicatively connected to at least the traction inverter unit such that the traction inverter unit is controllable by the data processing device. In such a drivetrain current ripple occurring during DC-DC charging is reduced and as a consequence thereof, high frequency losses are minimized. In other words, the efficiency of DC-DC charging is enhanced. This also results in an extended lifetime of the components of the drivetrain. Moreover, a size of a filter capacitor can be reduced since usually the lowest possible inductance value is considered for dimensioning the filter capacitor. As a consequence thereof, size and cost of the drivetrain may be reduced. 
     According to a fourth aspect, there is provided an electric vehicle having a drivetrain according to the present disclosure. The electric vehicle includes at least one wheel being coupled to the drivetrain. The traction battery of such a vehicle may be efficiently charged in a DC-DC charging scenario. 
     The above-described method may be at least partly computer-implemented, and may be implemented in software or in hardware, or in software and hardware. Further, the method may be carried out by computer program instructions running on means that provide data processing functions. The data processing means may be a suitable computing means, such as an electronic control module etc., which may also be a distributed computer system. The data processing means or the computer, respectively, may include one or more of a processor, a memory, a data interface, or the like. 
     It should be noted that the above examples may be combined with each other irrespective of the aspect involved. Accordingly, the method may be combined with structural features of the data processing device, the drivetrain or the vehicle and, likewise, the data processing device, the drivetrain or the vehicle may be combined with features described above with regard to the method. 
     These and other aspects of the present disclosure will become apparent from and elucidated with reference to the examples described hereinafter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Examples of the disclosure will be described in the following with reference to the following drawings. 
         FIG.  1    shows a vehicle according to the present disclosure having a drivetrain according to the present disclosure, wherein the drivetrain includes a data processing device according to the present disclosure including means for carrying out the steps of the method according to the present disclosure, 
         FIG.  2    shows details of selected components of the drivetrain of  FIG.  1   , 
         FIG.  3    shows exemplary self inductances and exemplary mutual inductances in function of a rotor position of the electric machine of  FIG.  2   , 
         FIG.  4    shows exemplary equivalent inductances in function of the rotor position for each phase of the electric machine of  FIG.  2    being derived from the exemplary self inductances and exemplary mutual inductances of  FIG.  3   , 
         FIG.  5    shows exemplary inductances of a first subset of two phases of the electric machine in function of a rotor position, 
         FIG.  6    shows exemplary inductances of a second subset of two phases of the electric machine in function of a rotor position, 
         FIG.  7    shows exemplary inductances of a third subset of two phases of the electric machine in function of a rotor position, 
         FIG.  8    shows steps of an example of a method according to the present disclosure, and 
         FIG.  9    shows steps of a further example of a method according to the present disclosure. 
     
    
    
     The figures are merely schematic representations and serve only to illustrate examples of the disclosure. Identical or equivalent elements are in principle provided with the same reference signs. 
     DETAILED DESCRIPTION 
       FIG.  1    shows an electric vehicle  10  having a total of four wheels  12  and a drivetrain  14 . 
     Two out of the four wheels  12  are driven wheels, i.e. these two wheels  12  are drivingly coupled to the drivetrain  14 . 
     The drivetrain  14  includes a traction battery  16 , a N-phase traction inverter unit  18  and a N-phase electric machine  20 . 
     The electric machine  20  is electrically coupled to the traction battery  16  via the inverter unit  18 . This means that the electric machine  20  is electrically coupled to the traction inverter unit  18  and the traction inverter unit  18  is electrically coupled to the traction battery  16 . 
     The electric machine  20  is further coupled to the two driven wheels  12  via an axle gearing  22 . 
     In the present example, the traction inverter unit  18  and the electric machine  20  have three phases respectively, i.e. N is three. 
     Moreover, the electric vehicle  10  includes a DC charging interface  24 . 
     The charging interface  24  is electrically connected to the inverter unit  18  and the electric machine  20  such that the inverter unit  18  and the electric machine  20  may form part of a charging circuit  26 . 
     In the example shown in  FIG.  1   , the vehicle  10  is electrically coupled with a DC charging station  28 . Since the charging station  28  does not form part of the vehicle  10  it is represented in dashed lines. An alternative name for the charging station  28  is electric vehicle supply equipment (EVSE). 
     As an input filter for the current being provided by the charging station  28 , the charging circuit  26  includes a capacitor C x  which is arranged electrically parallel to the charging station  28 . 
     The drive train  14  also includes a data processing device  30  being communicatively connected to the traction inverter unit  18  such that the traction inverter unit  18  is controllable by the data processing device  30 . 
     In other words, the data processing device  30  is a control unit of the traction inverter unit  18 . 
     In more detail, the data processing device  30  includes a first control interface  32  being connectable to the traction inverter unit  18  such that the traction inverter unit  18  is controllable by the data processing device  30 . 
     Moreover, in the present example, the data processing device  30  includes a second control interface  34  being connectable to the electric machine  20 , more specifically to a controller of the electric machine  20 . 
     As will be explained in detail later, the second control interface  34  is configured for receiving a position of a rotor of the electric machine  20 . 
     In the present example, the position of the rotor of the electric machine  20  is a mechanical position. 
     The data processing device  30  has also means  36  for carrying out the steps of a method for controlling the drivetrain  14  of the electric vehicle  10  during DC-charging of the traction battery  16  of the drivetrain  14 . 
     The means include for example a processor  38  and a memory  40 . 
     The method is represented in  FIG.  8    and in a first step ST 1 , the method controls the traction inverter unit  18  such that the traction inverter unit  18  operates as a DC-DC converter and such that the charging circuit  26  includes at least partially the traction inverter unit  18  and at least partially the electric machine  20 . 
     This means that a current originating from the DC charging station  28  is led through the resistances R A , R B , R C  and the inductances L A , L B , L C  of the three phases A, B, C of the electric machine  20  (cf.  FIG.  2   ). 
     As can best be seen from  FIG.  2   , each of these phases A, B, c is connected to a corresponding leg of the inverter unit  18  at a respective connection point. Each of the legs includes two of the power switches S 1 , S 2 , S 3 , S 4 , S 5 , S 6  and two corresponding diodes D 1 , D 2 , D 3 , D 4 , D 5 , D 6 . 
     In the present example, the voltage being provided by the charging station  28  is lower than the operational voltage of the traction battery  16 . Consequently, the power switches S 1 , S 2 , S 3 , S 4 , S 5 , S 6  of the inverter unit  18  are operated such that, in combination with the inductances L A , L B , L C  of the electric machine  20  the DC voltage of the charging station  28  is boosted to the voltage of the traction battery  16 . 
     It is noted that in the example of  FIG.  2   , the plus pole of the charging station  28  is connected to the neutral point of the electric machine  20  and the minus pole of the charging station is connected to the minus pole of the traction battery  16 . 
     In a second step ST 2 , the method receives a position of a rotor of the electric machine  20 . This is done via the second interface  34 . 
     In a third step ST 3  a number out of the three phases A, B, C of the electric machine  20  is selected as components of the charging circuit  26 . This selection is dependent on the position of the rotor of the electric machine  20 . 
     This means that not necessarily all three phases A, b, C of the electric machine  20  form part of the charging circuit  26 . 
     In a first example, the numbers out of the three phases A, B, C is selected such that the alternative offering the highest equivalent inductance is chosen. 
     This will be explained in detail with additional reference to  FIGS.  3  to  7   . 
       FIG.  3    shows the self inductances Laa, Lbb and Lcc of the inductances of the respective phase A, B, C of the electric machine  20  in function of a rotor position of the electric machine  20 . Moreover, all mutual inductances Lab, Lba, Lac, Lca, Lbc, Lcb are shown. 
     The rotor position is represented in electrical degrees. 
     Based thereon, equivalent inductances can be calculated for each phase A, B, C of the electric machine  20 . 
     These equivalent inductances are denote LequA, LequB, LequC and are represented in  FIG.  4   . 
     However, as has been mentioned before, not necessarily all phases A, B, C are used. 
       FIG.  5   , for example shows a case where phase B is not used. The resulting mutual inductances Lac and Lca resulting from the use of phases A and C are represented in function of a rotor position (electric degrees). 
       FIG.  6    shows an example, where phase C is not used. The resulting mutual inductances Lab and Lba resulting from the use of phases A and B are represented in the figure in function of a rotor position (electric degrees). 
       FIG.  7    shows a further example, where phase A is not used. The resulting mutual inductances Lbc and Lcb resulting from the use of phases B and C are represented in function of a rotor position (electric degrees). 
     It can thus be seen from  FIGS.  4  to  7    that the inductances vary in function of the rotor position. 
     Consequently, for performing the method, a look-up table is provided in the memory  40  of the data processing device  30 , wherein the equivalent inductances of all available combinations of numbers of the three phases A, B, C are represented in function of the position of the rotor of the electric machine  20 . Moreover, the equivalent inductances are represented in function of at least one of a current and a duty cycle. Obviously, the look-up table includes the values being represented in  FIGS.  4  to  7   . 
     It is thus easy, based on a given rotor position, to select the number of phases A, B, C such that the highest equivalent inductance is provided. 
     Subsequently, in a fourth step ST 4 , the traction inverter unit  18  is controlled such that the selected number out of the three phases of the electric machine  20  forms part of the charging circuit  26 . For example, the power switches S 2  and S 5  may be opened such that phase B of the electric machine  20  does not form part of the charging circuit (cf.  FIG.  2   ). 
     In this context, the traction inverter unit  18  is operated as an interleaved DC-DC converter, interleaving the selected ones of the three phases. In the above example, the phases A and C are interleaved. 
     It is noted that the same applies if instead of phase B phase A or phase C are not selected. 
     According to an alternative of step ST 3 , the number of the three phases is selected such that the lowest electromagnetic losses are produced. This means that out of the available combinations of numbers of the three phases the alternative offering the lowest electromagnetic losses is chosen. 
     This is also done using a look-up table being provided in the memory  40  of the data processing device  30  which in this example contains the electromagnetic losses of all available combinations of numbers of the three phases in function of the position of the rotor of the electric machine  20 . Moreover, the electromagnetic losses can be represented in the look-up table in function of at least one of a current and a duty cycle. 
     Again, in a fourth step ST 4 , the traction inverter unit  18  is controlled such that the selected number out of the three phases of the electric machine  20  forms part of the charging circuit  26 . 
     A further example of the method for controlling the drivetrain  14  of the electric vehicle  10  during DC-charging of the traction battery  16  will be explained in conjunction with  FIG.  9   . 
     In this example, a duty cycle is evaluated (cf. step ST 5 ) and if the duty cycle falls within a predefined duty cycle range, it is determined that only two phases of the electric machine  20  and the corresponding portions of the inverter unit  18  will be used (step ST 6 ). This means that if the duty cycle falls within the predefined duty cycle range, the selection of all three phases A, B, C as components of the charging circuit is excluded. 
     The predefined duty cycle range is for example 49% to 51%. 
     In this case, using at least one of the above-mentioned look-up tables the subset of two phases is selected which offers the minimum electromagnetic losses or the maximum inductance (step ST 7 ). Then the inverter unit  18  is controlled such that the selected phases are used as part of the charging circuit (ST 8 ). 
     If the duty cycle to be performed falls outside the predefined duty cycle range, all three phases A, B, C are pre-selecting (ST 9 ) as components of the charging circuit. 
     Subsequently, the maximum inductance or the minimum losses of this solution is determined using the above-mentioned look-up tables (ST 10 ). 
     Thereafter, the losses or the inductance of the pre-selected three phases is compared to a worst case, i.e. a case of maximum losses or minimum inductance being achievable with two phases only (ST 11 ). 
     If the losses are bigger or the inductance is smaller than in the two-phase alternative, then the method is continued at step ST 6 , i.e. only two phases are used. Otherwise, all three phases are used (ST 12 ). 
     It is noted that the numbering of the steps has been performed for the ease of explanation only and does not imply any number of steps or an order according to which the steps are performed. 
     Other variations to the disclosed examples can be understood and effected by those skilled in the art in practicing the claimed invention, from the study of the drawings, the disclosure, and the appended claims. In the claims the word “comprising” does not exclude other elements or steps and the indefinite article “a” or “an” does not exclude a plurality. A single processor or other unit may fulfill the functions of several items or steps recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. A computer program may be stored/distributed on a suitable medium such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems. Any reference signs in the claims should not be construed as limiting the scope of the claims.