Distributed electric drive vehicle crawling control system and method

Abstract

The invention provides a crawling control system and method for a distributed electrically-driven vehicle, which comprehensively considers a driving scene that the vehicle is switched into a crawling state from a high speed or a low speed, and sets a lookup interval range of a proportional regulation factor and an integral regulation factor. Smooth transition of the vehicle from different driving states can be achieved, and the vehicle is stabilized at the creeping target vehicle speed. According to the method, the running state and the fault state of each motor are considered in torque distribution, the motors can respond to the creeping target torque as much as possible through fault-tolerant distribution control, even if the motors break down, the sufficient response speed of the vehicle can still be guaranteed, the problems of unexpected speed reduction and the like are avoided, and the service life of the vehicle is prolonged. Therefore, the method and the device can achieve a plurality of beneficial effects which are not achieved in the prior art.

Description

Technical Field

[0001] The present invention belongs to the technical field of electric vehicle control, and in particular relates to a creep control system and method for a distributed electric drive vehicle. Background Art

[0002] At present, some fuel or new energy vehicles with strong off-road capabilities on the market are often equipped with creeping functions to ensure the vehicle's passability when facing special road conditions such as steep slopes, rainy and snowy roads, rocky roads, and sandy land. For pure electric drive new energy vehicles, since their motors often do not have a minimum stable speed, the creeping function needs to be implemented with the help of torque control at the software level. However, the existing creeping control usually only considers the working conditions of the vehicle entering the creeping state from a standstill or low-speed start, and there are few control methods suitable for the working conditions of the vehicle switching from high speed to the creeping state. In addition, the current more mature creeping control methods are mainly designed for fuel engine torque control, and creeping control methods and systems suitable for distributed electric drive configuration vehicles with more than two axes are extremely rare, especially for the creeping torque distribution problem of such vehicles when the drive motor fails. The field obviously lacks sufficient understanding and corresponding solutions. Summary of the invention

[0003] In view of this, in view of the technical problems existing in the art, the present invention provides a creep control system of a distributed electric drive vehicle, which is composed of an upper creep torque calculation module and a lower creep torque distribution module;

[0004] Among them, the creep torque calculation module is used to obtain the creep energy signal, the current vehicle speed v, the creep target vehicle speed v target As well as the road slope information, the creep demand torque T is obtained by performing the following calculation req Output to the lower layer of the control system:

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

[0006] In the formula, v error is the creep target speed v target The speed difference during creeping between the vehicle speed v and the current vehicle speed v. When the vehicle enters creeping state from high speed, v error <0, when the vehicle enters creeping state from low speed, v error >0;k p and k I are respectively the proportional adjustment coefficient and the integral adjustment coefficient for PI control; U is the feedforward of PI control; the proportional adjustment coefficient k p , integral adjustment coefficient kI The feedforward amount U is specifically calculated by the creep torque calculation module according to the vehicle speed difference v during the creep process. error , vehicle speed during creeping power and creeping target speed v target The enabling speed difference v′ between the two and the slope information are used to determine the current working condition of the vehicle, and a table lookup is performed to determine the corresponding parameter values ​​respectively;

[0007] The creep torque distribution module calculates the creep torque based on the creep torque requirement 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, 1 represents the left motor, 2 represents the right motor; at the same time, according to the motor operation fault level information fed back by each drive motor, the current allowable torque value of each motor is determined Comprehensively consider the pre-output torque value T Mot,ij and allowable torque value Distribute the actual output torque to each motor

[0008] Furthermore, the creep torque calculation module obtains the creep enable signal only if the following conditions are met: the gear is forward gear or reverse gear; the driving pedal and brake pedal openings are both 0; the parking brake is not activated; the current vehicle speed v is less than the creep enable vehicle speed v Enable , the creeping energy vehicle speed v Enable Greater than the set creep target speed v target .

[0009] Furthermore, the creep torque calculation module obtains the value k of the proportional adjustment coefficient and the integral adjustment coefficient from the corresponding table MAP1 according to the enabling vehicle speed difference v′>0, that is, when the vehicle enters the creep state from a low speed p =k p1 and k I =k I1 ; When the enabling speed difference v′<0, that is, the vehicle enters the creeping state from the high speed, k is obtained from the corresponding table MAP2 p =k p2 and k I =k I2 For the feedforward amount U, the creep torque calculation module specifically calculates the current slope i and the set slope threshold i * Compare, when the slope i is greater than the slope threshold i * , that is, when the vehicle is in an uphill state, the feedforward amount U is taken as a positive value, and U>U′, U′>0 is a basic feedforward amount; when the slope i is less than -i * , that is, when the vehicle is in a downhill state, the feedforward amount U is 0; when the slope is -i * <i<i *, that is, 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's creep start on a horizontal road.

[0010] Furthermore, the creep torque distribution module specifically calculates the pre-output torque value T by the following formula: Mot,ij :

[0011]

[0012] Furthermore, the creep torque distribution module specifically calculates the speed n of each motor fed back by the motor controller. ij , Current motor torque capacity value T MotLimit,ij And the motor fault level is calculated to obtain the current allowable torque value of each motor

[0013]

[0014] Among them, T MotN,ij The motor external characteristic torque limit is obtained based on the motor external characteristics and motor torque and is calculated using the following formula:

[0015]

[0016] Among them, T max is the peak torque of the motor, P max is the peak power of the motor, n p is the motor base speed T FalutLevel,ij The motor fault level is determined in the following way based on the feedback from the motor controller:

[0017]

[0018] Among them, T MotLimit,ij is the current motor torque capacity value, which can be directly obtained from the information fed back by the motor controller.

[0019] Furthermore, the creep torque distribution module distributes the actual output torque to each motor The specific steps include:

[0020] 1) Calculate the allowable torque value T of each axis 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 axis as the allowable torque value of the axis. The specific calculation method is:

[0021]

[0022] 2) Determine the allowable torque T of each axis Axle,i The sum of the creep torque T req size; if This indicates that through fault-tolerant control, the sum of the torques allocated to each motor can meet the creep torque requirement, and the allocation in step 3) is performed; if This indicates that the current operating status of each motor cannot meet the creep torque requirement. The motors on the left and right sides of each axis use half of the allowable torque value of each axis as the actual output torque of the motors on the left and right sides of the axis, that is,

[0023] 3) Targeting In the case of the above, the actual output torque of the left and right motors of each axis is allocated using the following formula

[0024]

[0025] Furthermore, the creep torque calculation module specifically includes two submodules, namely, a PI parameter optimization submodule and a feedforward quantity optimization submodule, which are used to respectively look up a table to determine the proportional adjustment factor k p , integral adjustment factor k I And the value of the feedforward quantity U.

[0026] Furthermore, the creep torque distribution module is specifically composed of a torque pre-distribution calculation submodule, a motor torque capacity limit calculation submodule and a torque fault tolerance control submodule, which are used to calculate the pre-output torque value T Mot,ij , Allowable torque value And the actual output torque

[0027] Accordingly, the present invention also provides a creep control method for a distributed electric drive vehicle implemented by the above system, which comprises the following steps in sequence:

[0028] Get creeping energy signal, current vehicle speed v, creeping target vehicle speed v target And the road slope information, and calculate the creep demand torque T req Output to the lower layer of the control system;

[0029] To calculate the creep torque T req The proportional adjustment coefficient k required for PI control p , integral adjustment coefficient k I And the feedforward amount U, specifically according to the vehicle speed difference v during the creeping process error , vehicle speed during creeping power and creeping target speed v target The enabling speed difference v′ between the two and the slope information are used to determine the current working condition of the vehicle, and a table lookup is performed to determine the corresponding parameter values ​​respectively;

[0030] Based on the calculated creep 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 current allowable torque value of each motor Comprehensively consider the pre-output torque value T Mot,ij and allowable torque value Distribute the actual output torque to each motor

[0031] The creep control system and method of the distributed electric drive vehicle provided by the present invention take into full account the driving scenarios of the vehicle switching from high speed or low speed to creep state, and by setting the range of the lookup table of the proportional adjustment factor and the integral adjustment factor, the vehicle can smoothly transition from different driving states and stabilize at the creep target speed; the operating state and fault state of each motor are taken into account in the torque distribution, and through fault-tolerant distribution control, the motor can respond to the creep target torque as much as possible, and even in the event of a motor failure, the vehicle can still ensure sufficient response speed and avoid problems such as unexpected deceleration, so that the present invention can achieve many beneficial effects that the prior art does not have. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a functional framework schematic diagram of the creep control system of the distributed electric drive vehicle of the present invention;

[0033] Figure 2 This is a schematic diagram of the torque distribution algorithm provided by the present invention. DETAILED DESCRIPTION

[0034] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] The present invention provides a distributed electric drive vehicle creep control system, such as Figure 1 As shown, it is composed of an upper creep torque calculation module and a lower creep torque distribution module;

[0036] Among them, the creep torque calculation module is used to obtain the creep energy signal, the current vehicle speed v, the creep target vehicle speed v target As well as the road slope information, the creep demand torque T is obtained by performing the following calculation req Output to the lower layer of the control system:

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

[0038] In the formula, v error is the creep target speed v target The speed difference during creeping between the vehicle speed v and the current vehicle speed v. When the vehicle enters creeping state from high speed, v error <0, when the vehicle enters creeping state from low speed, v error >0;k p and k I are respectively the proportional adjustment coefficient and the integral adjustment coefficient for PI control; U is the feedforward of PI control; the proportional adjustment coefficient k p , integral adjustment coefficient k I The feedforward amount U is specifically calculated by the creep torque calculation module according to the vehicle speed difference v during the creep process. error , vehicle speed during creeping power and creeping target speed v target The enabling speed difference v′ between the two and the slope information are used to determine the current working condition of the vehicle, and a table lookup is performed to determine the corresponding parameter values ​​respectively;

[0039] The creep torque distribution module calculates the creep torque based on the creep torque requirement 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, 1 represents the left motor, 2 represents the right motor; at the same time, according to the motor operation fault level information fed back by each drive motor, the current allowable torque value of each motor is determined Comprehensively consider the pre-output torque value T Mot,ij and 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 obtains the creep enable signal only if the following conditions are met: the gear is forward gear or reverse gear; the drive pedal and brake pedal openings are both 0; the parking brake is not activated; the current vehicle speed v is less than the creep enable vehicle speed v Enable , the creeping energy vehicle speed v Enable Greater than the set creep target speed v target For example, you can set v target =3km / h, creeping energy speed v Enable =5km / h. The value is greater than the creep target speed in order to achieve that when the vehicle enters the creep state from high-speed gliding, when the speed drops to 5km / h, the vehicle starts to generate driving force to overcome the driving resistance, and the vehicle deceleration gradually decreases to zero, ensuring that the vehicle can enter the creep state from high-speed gliding, and the speed is stable at around 3km / h. Enable=3km / h, then the vehicle will only generate driving force when the speed drops to 3km / h, and due to the hysteresis of the PI algorithm, the initial creep torque requirement is small and it is difficult to overcome the driving resistance. Although the vehicle deceleration will decrease, it will not decrease to zero, so the vehicle speed will continue to decrease, and may even drop to nearly 0km / h. This will cause the vehicle to glide from high speed to nearly stationary, and then start from nearly stationary, and the speed will rise back to 3km / h, resulting in poor drivability of the vehicle. If v Enable The selection is greater than v target , the above problems can be avoided and the vehicle speed can be stabilized from high speed to v target .

[0041] In a preferred embodiment of the present invention, the creep torque calculation module specifically obtains the value k of the proportional adjustment coefficient and the integral adjustment coefficient from the corresponding table MAP1 according to the enabling vehicle speed difference v′>0, that is, when the vehicle enters the creep state from a low speed. p =k p1 and k I =k I1 ; When the enabling speed difference v′<0, that is, the vehicle enters the creeping state from the high speed, k is obtained from the corresponding table MAP2 p =k p2 and k I =k I2 ; Vehicle speed difference v error The interval range is: [-v error_limit ,v error_limit ]. p1 Lookup table Map1, k I1 The lookup table Map1, in [-v error_limit ,v error_limit ] interval, the corresponding k p , k I are all positive values; the k p2 Lookup table Map2, k I2 The lookup table Map2, in [-v error_limit ,0], the corresponding k p , k I is a negative value, in [0, v error_limit ], the corresponding k p , k I The following Tables 1-5 show the condition coefficient and feedforward MAP table obtained by the actual vehicle test calibration based on the present invention:

[0042] Table 1 k p1 Map1

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

[0044] Table 2 k I1 Map1

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

[0046] Table 3 k p2 Map2

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

[0048] Table 4 k I2 Map2

[0049] <![CDATA[v error (km / h)]]> -4 -3 -1 -0.5 0 1 2 3 4 <![CDATA[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 value U, the creep torque calculation module specifically calculates the current slope i and the set slope threshold i * For comparison, the threshold is set considering that in real driving scenarios, there is no completely horizontal road and the slope sensor has noise. * , that is, when the vehicle is in an uphill state, the feedforward amount U is taken as a positive value, and U>U′, U′>0 is a basic feedforward amount; when the slope i is less than -i * , that is, when the vehicle is in a downhill state, the feedforward amount U is 0; when the slope is -i * <i<i * , that is, 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 creep start on the horizontal road; in this embodiment, the basic feedforward amount U′ can be taken as 350, and the slope threshold value is 1°.

[0053] It should be noted that k p1 , k I1 Look up table Map1 and k p2 , k I2 The difference between the lookup table Map2 is that v error <0. For k p1 With k p2 , when the speed difference is negative, k p1 The value is positive, and k p2 The value is negative, for k I1 With k I2 The reason for this difference is that the two are used in different scenarios.

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

[0055] For the condition of high-speed coasting entering creep state, when the vehicle speed drops from high-speed coasting to 5km / h, the creep state enable signal is activated, and the creep control system begins to intervene and calculate the creep demand torque. At this time, since the current vehicle speed is greater than the creep target speed, v error <0, look up the table to get k p and k I All are negative values, and the feedforward amount U>0. According to the calculation method of the feedforward PI controller, the calculated creep demand torque is a positive value, and the vehicle generates a driving force to overcome the current driving resistance of the vehicle, so that when the vehicle speed drops from 5km / h to about 3km / h, the deceleration of the whole vehicle gradually decreases and generates acceleration, achieving the effect that when the vehicle glides into the creeping condition, the vehicle is stable at the creeping target speed, avoiding the phenomenon that when the vehicle glides at high speed into the creeping state, the vehicle is reduced to an extremely low speed and then creeps and starts to stabilize to the creeping target speed, thereby greatly improving the vehicle's driving performance.

[0056] like Figure 2 As shown, in a preferred embodiment of the present invention, the creep torque distribution module specifically calculates the pre-output torque value T by the following formula: Mot,ij :

[0057]

[0058] In a preferred embodiment of the present invention, the creep torque distribution module specifically determines the speed n of each motor fed back by the motor controller. ij, Current motor torque capacity value T MotLimit,ij And the motor fault level is calculated to obtain the current allowable torque value of each motor

[0059]

[0060] Among them, T MotN,ij The motor external characteristic torque limit is obtained based on the motor external characteristics and motor torque and is calculated using the following formula:

[0061]

[0062] Among them, T max is the peak torque of the motor, P max is the peak power of the motor, n p is the motor base speed T FalutLevel,ij The motor fault level is determined in the following way based on the feedback from the motor controller:

[0063]

[0064] Among them, T MotLimit,ij is the current motor torque capacity value, which can be directly obtained from the information fed back by the motor controller.

[0065] In a preferred embodiment of the present invention, the creep torque distribution module distributes the actual output torque to each motor. The specific steps include:

[0066] 1) Calculate the allowable torque value T of each axis 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 axis as the allowable torque value of the axis. The specific calculation method is:

[0067]

[0068] 2) Determine the allowable torque T of each axis Axle,i The sum of the creep torque T req size; if This indicates that through fault-tolerant control, the sum of the torques allocated to each motor can meet the creep torque requirement, and the allocation in step 3) is performed; if This indicates that the current operating status of each motor cannot meet the creep torque requirement. The motors on the left and right sides of each axis use half of the allowable torque value of each axis as the actual output torque of the motors on the left and right sides of the axis, that is,

[0069] 3) Targeting In the case of the above, the actual output torque of the left and right motors of each axis is allocated using the following formula

[0070]

[0071] In a preferred embodiment of the present invention, the creep torque calculation module specifically includes two submodules: a PI parameter optimization submodule and a feedforward quantity optimization submodule, which are used to respectively look up a table to determine the proportional adjustment factor k p , integral adjustment factor k I And the value of the feedforward quantity U.

[0072] In a preferred embodiment of the present invention, the creep torque distribution module is specifically composed of a torque pre-distribution calculation submodule, a motor torque capacity limit calculation submodule and a torque fault tolerance control submodule, which are used to calculate the pre-output torque value T Mot,ij , Allowable torque value And the actual output torque

[0073] Accordingly, the present invention also provides a creep control method for a distributed electric drive vehicle implemented by the above system, which comprises the following steps in sequence:

[0074] Get creeping energy signal, current vehicle speed v, creeping target vehicle speed v target And the road slope information, and calculate the creep demand torque T req Output to the lower layer of the control system;

[0075] To calculate the creep torque T req The proportional adjustment coefficient k required for PI control p , integral adjustment coefficient k I And the feedforward amount U, specifically according to the vehicle speed difference v during the creeping process error , vehicle speed during creeping power and creeping target speed v target The enabling speed difference v′ between the two and the slope information are used to determine the current working condition of the vehicle, and a table lookup is performed to determine the corresponding parameter values ​​respectively;

[0076] Based on the calculated creep 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 current allowable torque value of each motor Comprehensively consider the pre-output torque value T Mot,ij and allowable torque value Distribute the actual output torque to each motor

[0077] It should be understood that the size of the serial numbers of the steps in the embodiment of the present invention does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiment of the present invention.

[0078] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A creep control system for a distributed electric drive vehicle, Features: It consists of an upper creep torque calculation module and a lower creep torque distribution module; Among them, the creep torque calculation module is used to obtain the creep energy signal, the current vehicle speed v, the creep target vehicle speed v target As well as the road slope information, the creep demand torque T is obtained by performing 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 creep target speed v target The speed difference during creeping between the vehicle speed v and the current speed v. When the vehicle enters creeping state from high speed, v error <0, when the vehicle enters creeping state from low speed, v error >0;k p and k I are the proportional adjustment coefficient and integral adjustment coefficient for PI control respectively; U is the feedforward of PI control; the proportional adjustment coefficient k p , integral adjustment coefficient k I The feedforward amount U is specifically calculated by the creep torque calculation module according to the vehicle speed difference v during the creep process. error , vehicle speed during creeping power and creeping target speed v target The enabling speed difference v′ between the two and the slope information are used to determine the current working condition of the vehicle, and a table lookup is performed to determine the corresponding parameter values ​​respectively; The creep torque distribution module is based on the creep torque demand torque T provided by the creep torque calculation module. reg 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, 1 represents the left motor, 2 represents the right motor; at the same time, according to the motor operation fault level information fed back by each drive motor, the current allowable torque value of each motor is determined Comprehensive consideration of the pre-output torque value T Mot，ij Permissible torque value Distribute the actual output torque to each motor 2. The creep control system of a distributed electric drive vehicle as claimed in claim 1, Features: The creep torque calculation module obtains the creeping enable signal only when the following conditions are met: the gear is forward or reverse; the drive pedal and brake pedal openings are both 0; the parking brake is not activated; the current vehicle speed v is less than the creeping enable speed v Enable , the creeping energy vehicle speed v Enable Greater than the set creep target speed v target .

3. The creep control system of a distributed electric drive vehicle as claimed in claim 1, Features: The creep torque calculation module specifically obtains the value k of the proportional adjustment coefficient and the integral adjustment coefficient from the corresponding table MAP1 according to the enabling vehicle speed difference v′>0, that is, when the vehicle enters the creep state from a low speed p =k p1 and k I =k I1 ; When the enabling speed difference v′<0, that is, the vehicle enters the creeping state from the high speed, k is obtained from the corresponding table MAP2 p =k p2 and k I =k I2 ; Vehicle speed difference v error The interval range is: [-v error_limit , v error_limit ], the k p1 Lookup table Map1, k I1 The lookup table Map1, in [-v error_limit , v error_limit ] interval, the corresponding k p , k I are all positive values; the k p2 Lookup table Map2, k I2 The lookup table Map2, in [-v error_limit , 0], the corresponding k p , k I is a negative value, in [0, v error_limit ], the corresponding k p , k I is a positive value; for the feedforward amount U, the creep torque calculation module specifically calculates the current slope i and the set slope threshold i * Compare, when the slope i is greater than the slope threshold i * , that is, when the vehicle is in an uphill state, the feedforward amount U is taken as a positive value, and U>U′, U′>0 is a basic feedforward amount; when the slope i is less than -i*, that is, the vehicle is in a downhill state, the feedforward amount U is 0; when the slope -i * <i<i * , that is, 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's creep start on a horizontal road.

4. The creep control system of a distributed electric drive vehicle as claimed in claim 1, Features: The creep torque distribution module specifically calculates the pre-output torque value T through the following formula: Mot，ij :

5. The creep control system of a distributed electric drive vehicle as claimed in claim 1, Features: The creep torque distribution module is based on the speed n of each motor fed back by the motor controller. ij , Current motor torque capacity value T MotLimit，ij And the motor fault level is calculated to obtain the current allowable torque value of each motor Among them, T MotN,ij The motor external characteristic torque limit is obtained based on the motor external characteristics and motor torque and is calculated using the following formula: Among them, T max is the peak torque of the motor, P max is the peak power of the motor, n p Base speed of the motor T FalutLevel，ij The motor fault level is determined in the following way based on the feedback from the motor controller: Among them, T MotLimit，ij is the current motor torque capacity value, which can be directly obtained from the information fed back by the motor controller.

6. The creep control system of a distributed electric drive vehicle as claimed in claim 1, Features: The creep torque distribution module distributes the actual output torque to each motor The specific steps include: 1) Calculate the allowable torque value T of each axis 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 axis as the allowable torque value of the axis. The specific calculation method is: 2) Determine the allowable torque T of each axis Axle，i The sum of the creep torque T req size; if This indicates that through fault-tolerant control, the sum of the torques allocated to each motor can meet the creep torque requirement, and the allocation in step 3) is performed; if This indicates that the current operating status of each motor cannot meet the creep torque requirement. The motors on the left and right sides of each axis use half of the allowable torque value of each axis as the actual output torque of the motors on the left and right sides of the axis, that is, 3) Targeting In the case of the above, the actual output torque of the left and right motors of each axis is allocated using the following formula 7. The creep control system of a distributed electric drive vehicle as claimed in claim 1, Features: The creep torque calculation module specifically includes two submodules: a PI parameter optimization submodule and a feedforward quantity optimization submodule, which are used to look up the table to determine the proportional adjustment factor k p , integral adjustment factor k I And the value of the feedforward quantity U.

8. The creep control system of a distributed electric drive vehicle as claimed in claim 1, Features: The creep torque distribution module is specifically composed of a torque pre-distribution calculation submodule, a motor torque capacity limit calculation submodule, and a torque fault tolerance control submodule, which are used to calculate the pre-output torque value T Mot，ij , Allowable torque value And the actual output torque 9. A method for controlling a creeping motion of a distributed electric drive vehicle implemented by using the creeping motion control system of a distributed electric drive vehicle as claimed in any one of claims 1 to 8, Features: The following steps are included in sequence: Get creeping energy signal, current vehicle speed v, creeping target vehicle speed v target And the road slope information, and calculate the creep demand torque T req Output to the lower layer of the control system; To calculate the creep torque T req The proportional adjustment coefficient k required for PI control p , integral adjustment coefficient k i And the feedforward amount U, specifically according to the vehicle speed difference v during the creeping process error , vehicle speed during creeping power and creeping target speed v target The enabling speed difference v′ between the two and the slope information are used to determine the current working condition of the vehicle, and a table lookup is performed to determine the corresponding parameter values ​​respectively; Based on the calculated creep 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 current allowable torque value of each motor Comprehensive consideration of the pre-output torque value T Mot，ij Permissible torque value Distribute the actual output torque to each motor

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