A system and method for controlling a distributed electric drive vehicle in a creep mode

Abstract

The application provides a kind of control system and method of distributed electric drive vehicle's inching, comprehensively considers the driving scene of vehicle from high speed or low speed cut into inching state, by setting the interval range of proportion adjustment factor and integral adjustment factor look-up table, vehicle can be smoothly transitioned from different driving states and stabilized at the target speed of inching;In torque distribution, the operating state and fault state of each motor are considered, and through fault-tolerant distribution control, the motor can respond to the target torque of inching as much as possible, even in the case of motor failure, it can still ensure the response speed of vehicle, avoid unexpected deceleration and other problems, so that the application can have many beneficial effects that the prior art does not have.

Description

Technical Field

[0001] This invention belongs to the field of electric vehicle control technology, specifically relating to a creep control system and method for a distributed electric drive vehicle. Background Technology

[0002] Currently, many gasoline or new energy vehicles with strong off-road capabilities are equipped with crawl control to ensure their passability in special road conditions such as steep slopes, rainy or snowy roads, rocky roads, and sandy terrain. For pure electric vehicles, since their motors often lack a minimum stable speed, crawl control requires software-level torque control. However, existing crawl control systems typically only consider the condition of a vehicle entering crawl mode from a standstill or low speed, and rarely offer control methods suitable for transitioning from high speed to crawl mode. Furthermore, current mature crawl control methods are primarily designed for the torque control of gasoline engines; crawl control methods and systems suitable for vehicles with two or more axles and distributed electric drive configurations are extremely rare. In particular, the field clearly lacks sufficient understanding and corresponding solutions regarding the crawl torque distribution problem in such vehicles when the drive motor fails. Summary of the Invention

[0003] In view of this, and in response to the technical problems existing in this field, the present invention provides a creep control system for a distributed electric drive vehicle, which consists of an upper-level creep torque calculation module and a lower-level creep torque distribution module.

[0004] The creep torque calculation module is used to obtain the creep driving energy signal, the current vehicle speed v, and the creep target vehicle speed v. target In addition to road slope information, the creep demand torque T is obtained by performing the following calculations. req Output to the lower level of the control system:

[0005] T req =k p ×v error +k I ×∫v error +U

[0006] In the formula, v error The target speed for creeping vehicle is v target The speed difference between the current speed v and the speed v during the creeping process, when the vehicle enters creeping mode from high speed, v error <0, when the vehicle transitions from low speed to crawling mode, v error >0;k p and k I These are the proportional and integral control coefficients used for PI control, respectively; U is the feedforward quantity for PI control; the proportional control coefficient k... p Integral adjustment coefficient kI The feedforward amount U is specifically calculated by the creep torque calculation module based on the vehicle speed difference v during the creep process. error The speed of the vehicle during creep driving and the target speed of creep driving, v target The enabling speed difference v′ and the gradient information determine the current operating condition of the vehicle, and the corresponding parameter values ​​are determined by looking up the table.

[0007] The creep torque distribution module is based on the creep torque demand T provided by the creep torque calculation module. req Determine the pre-output torque value T allocated to each drive motor Mot,ij Where i = 1, 2, ..., n, n is the number of axles of the vehicle, j = 1, 2, where 1 represents the left motor and 2 represents the right motor; simultaneously, based on the motor operation fault level information fed back by each drive motor, the allowable torque value of each motor is determined. Taking into account the pre-output torque value T Mot,ij With allowable torque value Distribute the actual output torque to each motor

[0008] Furthermore, the creep torque calculation module needs to meet the following conditions to obtain the creep driving power signal: the gear is forward or reverse; the opening of both the drive pedal and brake pedal is 0; the parking brake is not activated; and the current vehicle speed v is less than the creep driving power speed v. Enable The creep-assisted vehicle speed v Enable The creeping target speed v is greater than the set target speed. target .

[0009] Furthermore, the creep torque calculation module specifically obtains the values ​​k of the proportional control coefficient and the integral control coefficient from the corresponding table MAP1 when the vehicle enters the creep state from the enabled speed difference v′>0. p =k p1 and k I =k I1 When the speed difference v′ is enabled (i.e., the vehicle transitions from high speed to crawl mode), k is obtained from the corresponding table MAP2. p =k p2 and k I =k I2 For the feedforward quantity U, the creep torque calculation module specifically compares the current slope i with the set slope threshold i. * When comparing, if the slope i is greater than the slope threshold i * That is, when the vehicle is going uphill, the feedforward quantity U is taken as a positive value, and U>U′,U′>0 is a basic feedforward quantity; when the slope i is less than -i * That is, when the vehicle is going downhill, the feedforward amount U is 0; when the slope is -i * <i<i *When the vehicle is on a horizontal road, the feedforward amount U is taken as the basic feedforward amount U' to improve the response speed of the vehicle when starting to creep on a horizontal road.

[0010] Further, the creep torque distribution module calculates the pre-output torque value T Mot,ij :

[0011]

[0012] Further, the creep torque distribution module calculates the allowable torque value T ij of each motor according to the motor speed n MotLimit,ij , the current motor torque capability value T

[0013]

[0014] where T MotN,ij is the motor external characteristic torque limit value obtained according to the motor external characteristic and the motor torque, which is calculated by the following formula:

[0015]

[0016] where T max is the motor peak torque, P max is the motor peak power, n p is the motor base speed T FalutLevel,ij The motor fault level is fed back by the motor controller, and the following method is used to determine it:

[0017]

[0018] where T MotLimit,ij is the current motor torque capability value, which can be directly obtained from the motor controller feedback information.

[0019] Further, the creep torque distribution module distributes the actual output torque T to each motor in the following specific steps:

[0020] 1) Calculate the axle allowable torque value T Axle,i of each axle (i = 1, 2, … n): take twice the minimum value of the allowable torque values of the left and right motors on the same axle as the axle allowable torque value of the axle, and the specific calculation method is as follows:

[0021]

[0022] 2) Determine the size of the sum of the axle allowable torque T Axle,i of each axle and the creep demand torque T req ; if It is indicated that the sum of the torque allocated to each motor can meet the crawling demand torque through fault-tolerant control, and then the allocation of step 3) is performed; if It is indicated that the current operation state of each motor cannot meet the crawling demand torque, and the motors on the left and right sides of each shaft are allocated with the actual output torque of the motors on the left and right sides of the shaft as half of the shaft allowable torque value of each shaft, that is

[0023] 3) For the case of , the actual output torque of the motors on the left and right sides of each shaft is allocated by using the following formula

[0024]

[0025] Further, the crawling torque calculation module specifically includes a PI parameter optimization submodule and a feedforward quantity optimization submodule, which are used to determine the values of the proportional adjustment factor k p , the integral adjustment factor k I and the feedforward quantity U by table lookup, respectively.

[0026] Further, the crawling torque allocation module specifically consists of a torque pre-allocation calculation submodule, a motor torque capacity limit calculation submodule and a torque fault-tolerant control submodule, which are used to calculate the pre-output torque value T Mot,ij , the allowable torque value and the actual output torque

[0027] Correspondingly, the application also provides a crawling control method for a distributed electric drive vehicle using the foregoing system, which sequentially includes the following steps:

[0028] The crawling enable signal, the current vehicle speed v, the crawling target vehicle speed v target and the road slope information are obtained, and the crawling demand torque T req is calculated and output to the lower layer of the control system.

[0029] For the proportional adjustment factor k p , the integral adjustment factor k I and the feedforward quantity U required for PI control when calculating the crawling demand torque T req , the current working condition of the vehicle is determined according to the speed difference v error during the crawling process, the enable speed difference v' between the vehicle speed and the crawling target vehicle speed v target when the crawling is enabled, and the slope information, and the corresponding parameter values are determined by table lookup.

[0030] Based on the calculated crawling demand torque T req , the pre-output torque value T Mot,ijMeanwhile, the allowable torque value of each motor is determined according to the motor operation fault level information fed back by each motor The pre-output torque value T Mot,ij is comprehensively considered The actual output torque is allocated to each motor

[0031] The crawling control system and method of the distributed electric drive vehicle provided by the application comprehensively consider the driving scene of the vehicle from high speed or low speed to the crawling state, and through setting the interval range of the lookup table of the proportional adjustment factor and the integral adjustment factor, the vehicle can be smoothly transitioned from different driving states and stabilized at the crawling target speed; in the torque allocation, the operation state and fault state of each motor are considered, and through the fault-tolerant allocation control, the motor can respond to the crawling target torque as much as possible, even in the case of motor failure, the vehicle can still ensure sufficient response speed, avoid unexpected deceleration and other problems, so that the application can have many beneficial effects that the prior art does not have. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 The figure is a functional framework schematic diagram of the crawling control system of the distributed electric drive vehicle of the application;

[0033] Figure 2 The figure is a torque allocation algorithm flowchart provided by the application. DETAILED DESCRIPTION

[0034] The technical solutions of the application will be described clearly and completely below with reference to the drawings. Obviously, the described embodiments are part of the embodiments of the application, not all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the application.

[0035] The crawling control system of the distributed electric drive vehicle provided by the application, as shown in the figure, is composed of an upper-layer crawling torque calculation module and a lower-layer crawling torque distribution module; Figure 1

[0036] The crawling torque calculation module is used to obtain the crawling enable signal, the current vehicle speed v, the crawling target vehicle speed v target and the road slope information, and obtain the crawling demand torque T req through the following calculation and output to the control system lower layer:

[0037] T req = k p × v error + k I × ∫v error + U​

[0038] In the formula, v error The target speed for creeping is v target The speed difference between the current speed v and the speed v during the creeping process; when the vehicle enters creeping mode from high speed, v error <0, when the vehicle transitions from low speed to crawling mode, v error >0;k p and k I These are the proportional and integral control coefficients used for PI control, respectively; U is the feedforward quantity for PI control; the proportional control coefficient k... p Integral adjustment coefficient k I The feedforward amount U is specifically calculated by the creep torque calculation module based on the vehicle speed difference v during the creep process. error The speed of the vehicle during creep driving and the target speed of creep driving, v target The enabling speed difference v′ and the gradient information determine the current operating condition of the vehicle, and the corresponding parameter values ​​are determined by looking up the table.

[0039] The creep torque distribution module is based on the creep torque demand T provided by the creep torque calculation module. req Determine the pre-output torque value T allocated to each drive motor Mot,ij Where i = 1, 2, ..., n, n is the number of axles of the vehicle, j = 1, 2, where 1 represents the left motor and 2 represents the right motor; simultaneously, based on the motor operation fault level information fed back by each drive motor, the allowable torque value of each motor is determined. Taking into account the pre-output torque value T Mot,ij With allowable torque value Distribute the actual output torque to each motor

[0040] In a preferred embodiment of the present invention, the creep torque calculation module needs to meet the following conditions to obtain the creep driving power signal: the gear is forward or reverse; the opening of both the drive pedal and the brake pedal is 0; the parking brake is not activated; and the current vehicle speed v is less than the creep driving power speed v. Enable The creep-assisted vehicle speed v Enable The creeping target speed v is greater than the set target speed. target For example, v can be set. target =3km / h, creeping speed v Enable =5km / h, a value greater than the target creep speed, is chosen to ensure that when the vehicle transitions from high-speed coasting to creep, it begins to generate driving force to overcome driving resistance as its speed decreases to 5km / h. The vehicle's deceleration gradually decreases to zero, ensuring that the vehicle speed remains smoothly stable around 3km / h when transitioning from high-speed coasting to creep. If the creep driving speed v Enable= 3km / h, only when the vehicle speed drops to 3km / h, the vehicle will generate driving force, and due to the hysteresis of the PI algorithm, the initial creep demand torque is small, it is difficult to overcome the running resistance, the vehicle deceleration will decrease, but it cannot decrease to zero, so the vehicle speed will continue to decrease, and even it may decrease to nearly 0km / h, which causes the vehicle to slide from high speed to nearly stationary, and then start from nearly stationary, and the vehicle speed rises to 3km / h, which causes the vehicle to have poor drivability. If v Enable is greater than v target , the above problem can be avoided, and the vehicle speed can be smoothly and stably maintained at v target .

[0041] In the preferred embodiment of the present application, the creep torque calculation module specifically obtains the values of the proportional adjustment coefficient and the integral adjustment coefficient k p = k p1 and k I = k I1 from the corresponding table MAP1 when the enabled speed difference v' > 0, i.e. when the vehicle enters the creep state from low speed; when the enabled speed difference v' < 0, i.e. when the vehicle enters the creep state from high speed, k p = k p2 and k I = k I2 are obtained from the corresponding table MAP2; and the speed difference v error ranges from [-v error_limit , v error_limit ]. The look-up table Map1 of k p1 and the look-up table Map1 of k I1 correspond to positive values of k p and k I in the interval [-v error_limit , v error_limit ]; and the look-up table Map2 of k p2 and the look-up table Map2 of k I2 correspond to negative values of k p and k I in the interval [-v error_limit , 0], and correspond to positive values of k p and k I in the interval [0, v error_limit ]. The condition coefficient and feedforward quantity MAP tables obtained based on the present application are shown in Tables 1-5 below:

[0042] Table 1 look-up table Map1 of k p1

[0043] v error (km / h) -4 -3 -2 -1 0 1 2 3 4 k p1 ]]> 200 200 120 100 0 185 210 300 325 ​

[0044] Table 2 k I1 Map1

[0045] v error (km / h) -4 -3 -2 -1 0 1 2 3 4 k I1 ]]> 8 8 7 6 0 12 14 18 20

[0046] Table 3 k p2 Map2

[0047] v error (km / h) -4 -3 -1 -0.5 0 1 2 3 4 k p2 ]]> -100 -100 -100 -50 0 100 150 300 325

[0048] Table 4 k I2 Map2

[0049] v error (km / h) -4 -3 -1 -0.5 0 1 2 3 4 k I2 ]]> -6 -6 -6 -2 0 7 10 18 20

[0050] Table 5 Feedforward Map

[0051] i(°) -8 -6 -4 -1 0 1 4 6 8 U 0 0 0 350 350 350 450 500 600

[0052] For the feedforward U, the creep torque calculation module compares the current slope i with a set slope threshold i * , which is set considering that there is no completely horizontal road in real driving scenarios and the slope sensor has noise. When the slope i is greater than the slope threshold i * , i.e. the vehicle is in an uphill state, the feedforward U takes a positive value, and U>U', U'>0 is a basic feedforward; when the slope i is less than -i * , i.e. the vehicle is in a downhill state, the feedforward U takes 0; when the slope -i * <i<i * , i.e. the vehicle is in a horizontal road, the feedforward U takes the basic feedforward U' to improve the response speed of the vehicle starting on a horizontal road; in this embodiment, the basic feedforward U' can take a value of 350, and the slope threshold takes a value of 1°.

[0053] It should be noted that k p1 , k I1 Map1 is different from k p2 , k I2 Map2 in the value of v error <0. For k p1 and k p2 , when the speed difference is negative, k p1 takes a positive value, while k p2 takes a negative value, and the same is true for k I1 and k I2 . The reason for this difference is that they are applied in different scenarios.

[0054] For the working condition of starting at low speed and entering the creep state, when the vehicle speed has not reached the creep target speed, v error> 0, look up table to obtain k p and k I are positive values, the feedforward amount U > 0, according to the calculation method of the feedforward PI controller, the calculated crawling demand torque is positive at this time, the vehicle obtains driving force, the vehicle accelerates, and as the vehicle speed gradually approaches the crawling target speed, k p and k I are continuously reduced, the vehicle speed difference v error is also continuously reduced, and the vehicle driving force is continuously reduced, but due to the overshoot of the PI control method and the hysteresis caused by the integral element, when the vehicle speed is equal to the crawling target speed, the vehicle driving force is still greater than zero, the vehicle continues to accelerate, resulting in a vehicle speed higher than the crawling target speed, at this time v error < 0, look up table to obtain k p and k I are positive values, at this time the calculated value of the proportional adjustment element of the PI controller is negative, and v error < 0, at this time the increment value of the integral adjustment element is also negative, which can quickly attenuate the crawling demand torque to reduce the overshoot of the vehicle speed and quickly and smoothly maintain the current vehicle speed at the crawling target speed of 3 km / h.

[0055] For the working condition of entering the crawling state from high-speed sliding, when the vehicle speed is reduced from high-speed sliding to 5 km / h, the crawling state enabling signal is activated, and the crawling control system starts to intervene and calculate the crawling demand torque. At this time, since the current vehicle speed is greater than the crawling target speed, v error < 0, look up table to obtain k p and k I are negative values, the feedforward amount U > 0, according to the calculation method of the feedforward PI controller, the calculated crawling demand torque is positive, the vehicle generates driving force to overcome the current vehicle running resistance, so that when the vehicle speed is reduced from 5 km / h to about 3 km / h, the deceleration of the vehicle is gradually reduced and an acceleration is generated, realizing the effect of stably maintaining the vehicle at the crawling target speed when the vehicle enters the crawling working condition from high-speed sliding, avoiding the phenomenon that the vehicle is reduced to a very low speed and then stably starts to crawl to the crawling target speed when the vehicle enters the crawling working condition from high-speed sliding, greatly improving the driving performance of the vehicle.

[0056] As Figure 2 shown, in the preferred embodiment of the present application, the crawling torque distribution module specifically calculates the pre-output torque value T Mot,ij according to the following formula:

[0057]

[0058] In the preferred embodiment of the present application, the crawling torque distribution module specifically calculates the pre-output torque value T ij, the current motor torque capability value T MotLimit,ij and the motor fault level to obtain the allowable torque value of each motor

[0059]

[0060] wherein T MotN,ij is the motor external characteristic torque limit value obtained according to the motor external characteristic and the motor torque, and is calculated by the following formula:

[0061]

[0062] wherein T max is the motor peak torque, P max is the motor peak power, n p is the motor base speed T FalutLevel,ij According to the motor fault level feedback by the motor controller, the following method is used to determine the motor fault level:

[0063]

[0064] wherein T MotLimit,ij is the current motor torque capability value, which can be directly obtained from the motor controller feedback information.

[0065] In the preferred embodiment of the present application, the crawling torque distribution module distributes the actual output torque T to each motor, and the specific steps include:

[0066] 1) Calculate the shaft allowable torque value T Axle,i of each shaft (i = 1, 2, … n): take twice the minimum value of the allowable torque values of the left and right motors on the same shaft as the shaft allowable torque value of the shaft, and the specific calculation method is as follows:

[0067]

[0068] 2) Determine the size of the sum of the shaft allowable torque T Axle,i of each shaft and the crawling demand torque T req ; if , it means that through fault-tolerant control, the sum of the torques distributed to each motor can meet the crawling demand torque, and then proceed to step 3) of distribution; if , it means that the current operating state of each motor cannot meet the crawling demand torque, and then the left and right motors on each shaft are distributed according to half of the shaft allowable torque value of each shaft as the actual output torque of the left and right motors on the shaft, i.e.

[0069] 3) For the case of , the actual output torque of the left and right motors of each shaft is distributed by the following formula:

[0070]

[0071] In the preferred embodiment of the present application, the crawling torque calculation module specifically comprises two sub-modules, i.e., a PI parameter optimization sub-module and a feedforward amount optimization sub-module, for respectively determining the values of the proportional adjustment factor k p , the integral adjustment factor k I and the feedforward amount U through table lookup.

[0072] In the preferred embodiment of the present application, the crawling torque distribution module specifically comprises a torque pre-distribution calculation sub-module, a motor torque capability limit calculation sub-module and a torque fault-tolerant control sub-module, for respectively calculating the pre-output torque value T Mot,ij , the allowable torque value and the actual output torque

[0073] Correspondingly, the present application also provides a crawling control method for a distributed electric drive vehicle, which is implemented by using the aforementioned system and comprises the following steps in sequence:

[0074] The crawling enable signal, the current vehicle speed v, the crawling target vehicle speed v target and the road slope information are acquired, and the crawling demand torque T req is calculated and output to the lower layer of the control system.

[0075] For the proportional adjustment factor k req , the integral adjustment factor k p and the feedforward amount U required for calculating the crawling demand torque T I , the current working condition of the vehicle is determined according to the vehicle speed difference v error , the enable vehicle speed difference v′ between the vehicle speed when the crawling is enabled and the crawling target vehicle speed v target and the slope information during the crawling process, and the corresponding parameter values are determined through table lookup.

[0076] The pre-output torque value T Mot,ij to be distributed to each drive motor is determined based on the calculated crawling demand torque T req ; meanwhile, the allowable torque value of each motor is determined according to the motor operation fault level information fed back by each drive motor. The actual output torque is distributed to each motor by comprehensively considering the pre-output torque value T Mot,ij and the allowable torque value

[0077] It should be understood that the size of the serial number of each step in the embodiments of the present application does not mean the order of execution, and the execution order of each process should be determined according to its function and inherent logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0078] Although embodiments of the present application have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and alterations can be made thereto without departing from the principles and spirit of the present application, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A creep control system for a distributed electric drive vehicle, characterized in that: The upper layer creep torque calculation module and the lower layer creep torque distribution module are composed. Wherein, the crawling torque calculation module is used for obtaining the crawling enable signal, the current vehicle speed v, the crawling target vehicle speed v target And the road slope information, and the crawling demand torque T is obtained by executing the following calculation req Output to the lower layer of the control system: T req = k p × v error + k I × ∫v error + U In the formula, v error is the target vehicle speed v target during the crawling process, when the vehicle enters the crawling state from high speed, v error < 0, when the vehicle enters the crawling state from low speed, v error > 0; k p and k I are the proportional and integral adjustment coefficients for PI control respectively; U is the feedforward quantity of PI control; the proportional adjustment coefficient k p , the integral adjustment coefficient k I and the feedforward quantity U are determined by the crawling torque calculation module according to the vehicle speed difference v error during the crawling process, the enabling speed difference v' between the vehicle speed when the crawling is enabled and the target vehicle speed v target during the crawling, and the slope information to determine the current working condition of the vehicle, and are determined by table lookup respectively; The crawling torque distribution module distributes the crawling torque T reg The pre-output torque value T allocated to each drive motor is determined Mot，ij where i = 1, 2,... n, n is the number of axes of the vehicle, j = 1, 2, 1 represents the left motor, and 2 represents the right motor; and the allowable torque value of each motor is determined according to the motor operation fault level information fed back by each drive motor The pre-output torque value T is comprehensively considered Mot，ij The allowable torque value The actual output torque is allocated to each motor 2. The system for creep control of a distributed electric drive vehicle of claim 1, wherein: The following conditions need to be met for the crawling torque calculation module to obtain the crawling enable signal: the gear is in forward gear or reverse gear; the drive pedal and brake pedal opening are both 0; the parking brake is not activated; the current vehicle speed v is less than the crawling enable vehicle speed v Enable , and the crawling enable vehicle speed v Enable is greater than the set crawling target vehicle speed v target .

3. The system for creep control of a distributed electric drive vehicle of claim 1, wherein: The creep torque calculation module specifically calculates the values ​​of the proportional and integral control coefficients k from the corresponding table MAP1 when the vehicle enters creep mode from a low speed, based on the enabled speed difference v′>0. p =k p1 and k I =k I1 When the speed difference v′ is enabled to be less than 0, i.e., the vehicle enters a creeping state from high speed, k is obtained from the corresponding table MAP2. p =k p2 and k I =k I2 Speed ​​difference v error The interval range is: [-v error_limit v error_limit The k mentioned p1 Lookup table Map1, k I1 The lookup table Map1, in [-v error_limit v error_limit Within the interval, the corresponding k p k I All are positive values; the aforementioned k p2 Lookup table Map2, k I2 The lookup table Map2, in [-v error_limit Within the interval [0, 0], the corresponding k p k I For negative values, in [0, v error_limit Within the interval [], the corresponding k p k I It is a positive value; for the feedforward quantity U, the creep torque calculation module specifically compares the current slope i with the set slope threshold i. * When comparing, when the slope i is greater than the slope threshold i * When the vehicle is going uphill, the feedforward quantity U is positive, and U > U′, U′ > 0 is a basic feedforward quantity; when the slope i is less than -i*, i.e., when the vehicle is going downhill, the feedforward quantity U is 0; when the slope i is less than -i*, i.e., when the vehicle is going downhill, the feedforward quantity U is 0; when the slope i is less than -i*, the feedforward quantity U is 0. * <i<i * That is, when the vehicle is on a level road, the feedforward amount U is taken as the basic feedforward amount U′, so as to improve the response speed of the vehicle's creep start on a level road.

4. The system for creep control of a distributed electric drive vehicle of claim 1, wherein: The crawling torque distribution module calculates the pre-output torque value T by the following formula Mot，ij :

5. The system for creep control of a distributed electric drive vehicle of claim 1, wherein: The crawling torque distribution module specifically calculates the allowable torque value of each motor according to the motor speed n ij , the current motor torque capacity value T MotLimit，ij and the motor fault level where T MotN,ij is the motor external characteristic torque limit value obtained from the motor external characteristic and the motor torque, calculated by the following equation: where T max is the peak torque of the electric machine, P max is the peak power of the electric machine, n p is the base speed of the electric machine T FalutLevel，ij The motor fault level is determined in particular in accordance with the motor controller feedback by means of: where T MotLimit，ij is the current motor torque capability value, which can be obtained directly from the information fed back from the motor controller.

6. The system for creep control of a distributed electric drive vehicle of claim 1, wherein: A crawling torque distribution module distributes actual output torque to each motor The specific steps include: 1) Calculate the shaft allowable torque value T of each shaft Axle，i (i = 1, 2,... n): Take twice the minimum value of the allowable torque values of the motors on the left and right sides of the same shaft as the shaft allowable torque value of the shaft, and the specific calculation method is: 2) judging the sum of the shaft allowable torques T of the axes Axle，i and the size of the creep demand torque T req ; if it is indicated that the sum of the torques allocated to the individual motors can satisfy the creep demand torque through fault-tolerant control, the allocation of step 3) is performed; if it is indicated that the current operating state of the individual motors cannot satisfy the creep demand torque, the motors on the left and right sides of each axis are allocated the actual output torque of the left and right motors of the axis as half of the shaft allowable torque value of the axis, i.e. 3) for In the case of the above, the actual output torque of each axis left and right motor is allocated using the following equation 7. The system for creep control of a distributed electric drive vehicle of claim 1, wherein: The crawling torque calculation module specifically comprises a PI parameter optimization submodule and a feedforward quantity optimization submodule, which are used to respectively determine the values of the proportional adjustment factor k p , the integral adjustment factor k I , and the feedforward quantity U by table lookup.

8. The system for creep control of a distributed electric drive vehicle of claim 1, wherein: The crawling torque distribution module is specifically composed of a torque pre-distribution calculation submodule, a motor torque capacity limit calculation submodule, and a torque fault-tolerant control submodule, and is used for respectively calculating a pre-output torque value T Mot，ij , a permissible torque value , and an actual output torque 9. A method for controlling a distributed electric drive vehicle to creep, implemented by using the system for controlling a distributed electric drive vehicle to creep according to any one of claims 1-8, characterized in that: The steps are sequentially comprised of: The crawling enabling signal, the current vehicle speed v, the crawling target vehicle speed v target and the road slope information are acquired, and the crawling demand torque T req is calculated and output to the lower layer of the control system. For calculating the crawling demand torque T req the proportional adjustment coefficient k p , the integral adjustment coefficient k i and the feedforward amount U for PI control, according to the vehicle speed difference v error , the enabling vehicle speed difference v′ between the vehicle speed during the crawling process and the crawling target vehicle speed v target and the slope information, the corresponding parameter values are determined by table lookup respectively. Based on the calculated crawling demand torque T req Determine the pre-output torque value T allocated to each drive motor Mot，ij ; At the same time, according to the motor operation fault level information fed back by each drive motor, determine the allowable torque value of each motor at present Comprehensively consider the pre-output torque value T Mot，ij And the allowable torque value Allocate actual output torque to each motor

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