A calculation method for torque limit of new energy vehicle motor

Abstract

The present invention provides a method for calculating the torque limit of a motor of a new energy vehicle, which can fully exert the battery charging and discharging capacity while avoiding the battery power from exceeding the allowable range by controlling the motor torque within the limit. The method comprises the following steps: a. obtaining the conversion efficiency through bench test, and processing the test results to obtain the efficiency table map_test(N, Pbat) about the rotation speed and the battery power; b. defining an actual efficiency table map in the vehicle controller, whose initial value is equal to the efficiency table map_test obtained by the bench test; when the controller is running, the efficiency table value of the corresponding working point is iteratively updated according to the actual efficiency of the motor at each moment; c. using the updated efficiency table map(t) to calculate the driving torque Tmax_tra(t); or calculating the braking torque limit Tmax_bra(t); wherein when driving, the electromechanical conversion efficiency of the motor system is eff_tra, and the current motor driving torque limit Tmax_tra=Pmax_dis*eff_tra / N is obtained by inference; when braking and charging, the motor braking torque limit Tmax_bra=Pmax_cha / eff_bra / N.

Description

Technical Field

[0001] The present invention relates to the technical field of drive axle structures, and in particular to a method for calculating a torque limit value of a motor of a new energy vehicle. Background Art

[0002] Compared with traditional vehicles, new energy vehicles have an additional motor drive system, which is usually powered by a high-voltage power battery. The system converts electrical energy into mechanical energy through an inverter and a motor to drive the vehicle forward. In actual control, the vehicle controller or motor controller calculates the torque that the motor needs to output based on the driver's needs. At the same time, in order to avoid damaging the battery or affecting the battery life, the battery charging and discharging power needs to be controlled within the allowable range, so the motor torque calculated above needs to be limited.

[0003] The existing calculation method regards efficiency as a fixed value, and the deviation generated during the initial calibration cannot be corrected. For example, during bench testing, if the measurement results are biased due to some reason, then this deviation will continue to lead to inaccurate calculation of the motor torque limit. In order to avoid setting deviations that cause the battery charging and discharging to exceed the allowable range, the existing method usually reserves a certain margin when calculating. This reservation in turn causes the battery's charging and discharging capabilities to not be effectively utilized. Summary of the invention

[0004] In view of the above problems, the present invention provides a method for calculating the torque limit of a new energy vehicle motor, which can control the motor torque within the limit, thereby fully utilizing the battery charging and discharging capacity while avoiding the battery power exceeding the allowable range.

[0005] A method for calculating the torque limit of a new energy vehicle motor, characterized in that it comprises the following steps:

[0006] a. Obtain the conversion efficiency through bench test, and process the test results to obtain the efficiency table map_test(N,Pbat) about the speed and battery power, so as to obtain the corresponding eff_tra and eff_bra;

[0007] b. Define an actual efficiency table map in the vehicle controller, whose initial value is equal to the efficiency table map_test obtained by the bench test mentioned above; when the controller is running, the efficiency table value of the corresponding working point is iteratively updated according to the actual efficiency of the motor at each moment;

[0008] c Using the updated efficiency table map(t), according to the current motor speed N(t) and the battery discharge power limit Pmax_dis, look up the table to obtain eff_tra(t), and then calculate the driving torque Tmax_tra(t); or according to the updated efficiency table map(t), according to the current motor speed N(t) and the battery charging power limit Pmax_cha, look up the table to obtain eff_bra(t), and then calculate the braking torque limit Tmax_bra(t);

[0009] When driving, the electromechanical conversion efficiency of the motor system is eff_tra, and the relationship between the maximum drive power Pmax_mot allowed to be output by the motor and the maximum allowable discharge power Pmax_dis of the battery is: Pmax_mot = Pmax_dis*eff_tra. Further, according to the current motor speed N, the current motor drive torque limit Tmax_tra = Pmax_dis*eff_tra / N can be obtained;

[0010] During braking and charging, the motor braking torque limit Tmax_bra=Pmax_cha / eff_bra / N, where Pmax_cha is the maximum allowable charging power of the battery and eff_bra is the braking conversion efficiency of the motor system.

[0011] It is further characterized by:

[0012] In step a, the working area of ​​the motor, i.e., the speed and torque range, is divided into several grids, Narray[k] = {N1, N2, ... Nk-1, Nk},

[0013] Tarray[m] = {T1, T2, ... Tm-1, Tm}, through bench test, test the conversion efficiency of each grid, process the test results, and obtain an efficiency table map_test (N, Pbat) about the speed and battery power;

[0014] In step b, firstly, the actual conversion efficiency eff(t) at the current working point is calculated according to the torque T(t), motor speed N(t) and battery power Pbat(t) fed back by the motor; then, the efficiency value map(t-1) corresponding to the working point (N(t), Pbat(t)) in the efficiency table before update is calculated; finally, eff(t) and map(t-1) are fused to update the value of the working point in the efficiency table: map(t) = f(map(t-1), eff(t)), where f is the fusion algorithm.

[0015] After adopting the present invention, it can continuously correct and obtain accurate efficiency values, so there is no need to reserve margin, and the battery capacity can be fully utilized. As the motor is used for a longer time, demagnetization will inevitably occur, which will cause efficiency changes; on the other hand, the equivalent DC resistance of the motor controller and the high-voltage wiring harness itself will also slowly increase, both of which will cause changes in the conversion efficiency of the system. The method proposed by the invention can automatically identify efficiency changes, so that the torque limit value always matches the system state. The overall method is simple and reliable, with less calculation and low occupation of the controller's calculation resources, which is very suitable for practical engineering applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 MAP (N, T) and efficiency table corresponding to the specific embodiment of the present invention;

[0017] Figure 2 A three-dimensional coordinate diagram of torque, speed and efficiency corresponding to a specific embodiment of the present invention;

[0018] Figure 3 MAP(N,P) corresponding to the specific embodiment of the present invention bat ) and efficiency tables;

[0019] Figure 4 It is a coordinate diagram of electric power, rotation speed and efficiency corresponding to a specific embodiment of the present invention. DETAILED DESCRIPTION

[0020] A method for calculating the torque limit of a new energy vehicle motor comprises the following steps:

[0021] a. Divide the working area of ​​the motor, i.e., the speed and torque range, into several grids, Narray[k] = {N1, N2, ... Nk-1, Nk}, Tarray[m] = {T1, T2, ... Tm-1, Tm}. Through bench tests, the conversion efficiency of each grid is tested and the test results are processed to obtain an efficiency table map_test(N, Pbat) about the speed and battery power.

[0022] b. Define an actual efficiency table map in the vehicle controller, whose initial value is equal to the efficiency table map_test obtained by the bench test mentioned above; when the controller is running, the efficiency table value of the corresponding working point is iteratively updated according to the actual efficiency of the motor at each moment; in specific implementation, first calculate the actual conversion efficiency eff(t) at the current working point according to the torque T(t), motor speed N(t) and battery power Pbat(t) fed back by the motor; then calculate the efficiency value map(t-1) corresponding to the working point (N(t), Pbat(t)) in the efficiency table before update; finally, fuse eff(t) and map(t-1) to update the value of the working point in the efficiency table: map(t) = f(map(t-1), eff(t)), where f is the fusion algorithm;

[0023] c Using the updated efficiency table map(t), according to the current motor speed N(t), the battery discharge power limit Pmax_dis, look up the table to obtain eff_tra(t), and then calculate the driving torque Tmax_tra(t), Tmax_tra=Pmax_dis*eff_tra / N; or according to the updated efficiency table map(t), according to the current motor speed N(t), the battery charging power limit Pmax_cha, look up the table to obtain eff_bra(t), and then Tmax_tra=Pmax_dis*eff_tra / N; calculate the braking torque limit Tmax_bra(t), Tmax_bra=Pmax_cha / eff_bra / N;

[0024] When driving, the electromechanical conversion efficiency of the motor system is eff_tra, and the relationship between the maximum drive power Pmax_mot allowed to be output by the motor and the maximum allowable discharge power Pmax_dis of the battery is: Pmax_mot = Pmax_dis*eff_tra. Further, according to the current motor speed N, the current motor drive torque limit Tmax_tra = Pmax_dis*eff_tra / N can be obtained;

[0025] During braking and charging, the motor braking torque limit Tmax_bra=Pmax_cha / eff_bra / N, where Pmax_cha is the maximum allowable charging power of the battery and eff_bra is the braking conversion efficiency of the motor system.

[0026] For specific embodiments, see Figure 1-Figure 4 :According to the bench test, the motor torque, speed and efficiency to be tested were obtained, and the Figure 1 Table and Figure 2 The three-coordinate diagram of the motor to be tested was obtained according to the bench test, and the torque, speed and efficiency of the motor to be tested were made. Figure 3 Table and Figure 4 Three-coordinate diagram of .

[0027] In specific implementation, according to the above-mentioned updated efficiency table or efficiency diagram, according to the current motor speed N(t), the battery discharge power limit Pmax_dis, the table is looked up to obtain eff_tra(t), and then the driving torque Tmax_tra(t) is calculated, Tmax_tra=Pmax_dis*eff_tra / N; or in the braking charging state, according to the current motor speed N(t), the battery charging power limit Pmax_cha, the table is looked up to obtain eff_bra(t), and then the braking torque limit Tmax_bra(t) is calculated, Tmax_bra=Pmax_cha / eff_bra / N.

[0028] The existing calculation method regards efficiency as a fixed value. The method proposed in the invention considers that efficiency will change; the existing calculation method cannot correct the deviation generated during the initial calibration. For example, during the bench test, if the measurement result is biased due to some reason, then this deviation will continue to cause inaccurate calculation of the motor torque limit; the method proposed in the invention does not rely entirely on the initial calibration, and even if the deviation is large, it can be corrected during the subsequent operation; it proposes a simple and effective automatic iteration method, and the controller can simply use the actual feedback results to update its own control parameters (efficiency table) in each operation cycle.

[0029] Its beneficial effects are as follows:

[0030] 1 In order to avoid setting deviations and causing the battery to charge and discharge beyond the allowable range, existing calculation methods usually reserve a certain margin, which in turn will cause the battery's charging and discharging capacity to be unable to be effectively utilized. The method proposed in the invention can continuously correct and obtain accurate efficiency values, so there is no need to reserve a margin, and the battery capacity can be fully utilized;

[0031] 2. As the motor is used for a longer time, it will inevitably demagnetize, which will cause efficiency changes. On the other hand, the equivalent DC resistance of the motor controller and the high-voltage wiring harness itself will also slowly increase, both of which will cause the conversion efficiency of the system to change. The method proposed in the invention can automatically identify the efficiency change, so that the torque limit value always matches the system state.

[0032] 3 The method proposed in the invention is simple and reliable, has a small amount of calculation, occupies low computing resources of the controller, and is suitable for practical engineering applications.

[0033] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

[0034] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A method for calculating the torque limit of a new energy vehicle motor, characterized in that: It includes the following steps: a. Obtain the conversion efficiency through bench testing, and process the test results to obtain the efficiency table map_test(N,Pbat) about the rotation speed and battery power, so as to obtain the corresponding eff_tra and eff_bra; b. Define an actual efficiency table map in the vehicle controller, whose initial value is equal to the efficiency table map_test(N,Pbat) obtained by bench test; when the controller is running, the efficiency table value of the corresponding working point is iteratively updated according to the actual efficiency of the motor at each moment; c Using the updated efficiency table map(t), according to the current motor speed N(t) and the battery discharge power limit Pmax_dis, look up the table to obtain eff_tra(t), and then calculate the driving torque Tmax_tra(t); or according to the updated efficiency table map(t), according to the current motor speed N(t) and the battery charging power limit Pmax_cha, look up the table to obtain eff_bra(t), and then calculate the braking torque limit Tmax_bra(t); When driving, the electromechanical conversion efficiency of the motor system is eff_tra, and the relationship between the maximum drive power Pmax_mot allowed to be output by the motor and the maximum allowable discharge power Pmax_dis of the battery is: Pmax_mot = Pmax_dis*eff_tra. Further, according to the current motor speed N, the current motor drive torque limit Tmax_tra = Pmax_dis*eff_tra / N can be obtained; During braking and charging, the motor braking torque limit Tmax_bra=Pmax_cha / eff_bra / N, where Pmax_cha is the maximum allowable charging power of the battery and eff_bra is the braking conversion efficiency of the motor system; In step a, the working area of ​​the motor, i.e., the speed and torque range, is divided into several grids, Narray[k] = {N1, N2, ... Nk-1, Nk}, Tarray[m] = {T1, T2, ... Tm-1, Tm}, and the conversion efficiency of each grid is tested through bench tests. The test results are processed to obtain an efficiency table map_test(N, Pbat) about the speed and battery power; In step b, firstly, the actual conversion efficiency eff(t) at the current working point is calculated according to the torque T(t), motor speed N(t) and battery power Pbat(t) fed back by the motor; then, the efficiency value map(t-1) corresponding to the working point (N(t), Pbat(t)) in the efficiency table before update is calculated; finally, eff(t) and map(t-1) are fused to update the value of the working point in the efficiency table: map(t) = f(map(t-1), eff(t)), where f is the fusion algorithm.

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