WO2022095132A1

WO2022095132A1 - Braking energy recovery method for electric vehicle

Info

Publication number: WO2022095132A1
Application number: PCT/CN2020/130199
Authority: WO
Inventors: 陈清付; 胡维超; 周乐栓; 简瑞谦; 宁德胜
Original assignee: 广东高标电子科技有限公司
Priority date: 2020-11-06
Filing date: 2020-11-19
Publication date: 2022-05-12
Also published as: TW202218908A; TWI756937B; CN112440751A

Abstract

Disclosed is a braking energy recovery method for an electric vehicle. Said method comprises the following steps: S11, acquiring an equipment parameter and a drive parameter for an electric vehicle; S12, calculating a motor braking torque instruction according to a vehicle braking time, causing the motor braking torque instruction T_Eb ^** to increase linearly with a vehicle braking time count value, and to approach a motor rated braking torque T _e; S13, calculating a target braking torque instruction according to the rotational speed of a motor and a maximum charging power of a battery; and S14, calculating a current braking torque instruction according to an SOC value of the battery and the temperature of the battery. Advantages thereof are: improving the driving experience of a driver; improving energy recovery efficiency; and preventing damage to a battery due to long duration high current charging, guaranteeing the service life of the battery.

Description

An electric vehicle braking energy recovery method

technical field

The invention relates to an energy recovery technology in feedback braking of an electric vehicle controller, in particular to a braking energy recovery method of an electric vehicle, which belongs to the technical field of motor vector control.

Background technique

Two-wheeled electric vehicles have quickly become the best choice for people's green travel due to their advantages of zero emission and flexibility, but low battery energy density and low driving range have also become bottlenecks hindering their development. Energy recovery technology enables electric vehicles to store part of the braking energy in the form of electrical energy through a conversion device during the braking process, and reuse it when driving, thereby improving energy utilization and vehicle driving mileage.

At present, the application of energy recovery technology in the field of two-wheeled electric vehicles is seriously insufficient. The existing energy recovery strategies of two-wheeled electric vehicles mainly rely on the driver to operate the brake handle switch or let the motor work in the state of generating electricity when the vehicle is in a free coasting state. Thereby the energy is recovered into the energy storage device. However, after research, it is found that the energy recovery method of this strategy does not consider the characteristics of the motor and the state of the battery, and there are disadvantages such as low energy recovery efficiency and short service life of the power battery.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to provide an electric vehicle braking energy recovery method which can greatly improve the energy recovery efficiency and prolong the service life of the power battery.

In order to solve the above-mentioned technical problems, the electric vehicle braking energy recovery method of the present invention comprises the following steps:

S11, obtaining the driving parameters and equipment parameters of the electric vehicle;

S12. Calculate the motor braking torque command according to the braking time, so that the motor braking torque command T _eb ^** increases linearly with the braking time count value, and approaches the motor rated braking torque T _e ;

S13. Calculate the target braking torque command according to the motor speed and the maximum charging power of the battery;

S14: Calculate the current braking torque command according to the battery SOC value and the battery temperature.

In the step S11, the driving parameters and equipment parameters include the braking signal, the motor speed n, the current battery SOC value, the battery temperature and the battery maximum charging power P _{chg_max} .

The calculation formula of the motor speed n is:

The battery SOC value and battery temperature are determined by sampling by the controller, and reflect the actual remaining power of the battery and the working state of the battery; the maximum battery charging power P _{chg_max} is the battery nominal voltage U _dc × the battery maximum charging current I _dc .

In the step S12, the brake signal is a brake handle signal or a brake button signal.

In the step S12, the motor braking torque command T _eb ^** is linearly increased with the braking time count value, and approaches the rated braking torque T _e of the motor, that is:

The specific flow method of the step S13 is as follows:

S131, preset motor parameters: a first rotational speed threshold n ₁ , a second rotational speed threshold n ₂ and a third rotational speed threshold n ₃ , where n ₁ <n ₂ <n ₃ <n _max , and n _max is the maximum rotational speed value of the motor;

S132, determine whether the motor speed n is less than the first speed threshold n ₁ , if it is not less than the threshold, execute step S133; if it is less than the threshold, the motor does not perform regenerative braking, and the target braking torque command T _eb ^* is 0;

S133, determine whether the motor speed n is less than the second speed threshold n ₂ , if it is not less than the threshold, execute step S134; if it is less than the threshold, start the motor regenerative braking, and the target braking torque command T _eb ^* follows the motor The speed n increases and increases;

S134, determine whether the motor speed n is less than the third speed threshold n ₃ , if it is less than the threshold, the target braking torque command T _eb ^* is the motor braking torque command T _eb ^** , and the motor output torque is constant at this time; Otherwise, the target braking torque command T _eb ^* decreases as the motor speed n increases, and the motor output power is constant at this time;

S135: Calculate the target braking torque command T _eb ^* according to the maximum charging power P _{chg_max} of the battery. During the regenerative braking process, the actual feedback power P _{reg_chg} provided by the motor to the battery is within the maximum charging power P _{chg_max} of the battery, and the actual feedback power of the motor is within the maximum charging power P chg_max of the battery. P _{reg_chg} is:

During the regenerative braking process, the target braking torque command T _eb ^* is limited, and the limited target braking torque command T _eb ^* is:

In the step S133, the target braking torque command T _eb ^*

It is calculated by the following formula:

In the step S134, the target braking torque command T _eb ^* is calculated by the following formula:

The process operation method of step S14 is as follows:

S141, look up a table according to the battery SOC value and the battery temperature T, such as obtaining the battery influence factor k _soc ;

S142, correcting the target braking torque command T _eb ^* according to the obtained battery influence factor k _soc to obtain the current braking torque command T _eb ;

S143 , controlling the motor to transition from the current torque to the target torque according to the current braking torque command.

The advantages of the present invention are:

(1) The change of braking torque is controlled according to the braking time, so that the vehicle will not produce obvious braking shock and frustration during the energy recovery process, and the driving experience of the driver is improved;

(2) By combining the characteristics of the motor and adjusting the braking strength of the motor according to the motor speed, the regenerative braking ability of the motor can be maximized within a reasonable range, and the energy recovery efficiency is improved;

(3) By monitoring the status of the battery equipment in real time, the battery influence factor ksoc is introduced to correct the braking strength of the motor, which prevents the battery from being damaged by long-term high-current charging and ensures the service life of the battery.

(4) Considering the battery factor in the whole recycling system not only ensures the service life of the battery, but also considers the charging and discharging efficiency of the energy storage system at different temperatures and SOCs to maximize the efficiency.

Description of drawings

1 is a flowchart of Embodiment 1 of the present invention;

FIG. 2 is a flowchart of step S13 in Embodiment 1 of the present invention;

3 is a schematic diagram of the relationship between the motor speed and the target braking torque in Embodiment 1 of the present invention;

4 is a flowchart of step S14 in Embodiment 1 of the present invention;

5 is a schematic diagram of the three-dimensional relationship between the battery SOC value, the battery temperature T and the battery influence factor k _soc in Embodiment 1 of the present invention;

6 is a flow chart of Embodiment 2 of the present invention;

[Corrected 14.01.2021 in accordance with Rule 91]
FIG. 7 is a block diagram of the braking energy recovery system of the electric vehicle in the present invention.

FIG. 8 is a comparison diagram of driving range in the present invention.

Detailed ways

The method for recovering braking energy of _an electric vehicle of the present invention will be described in further detail below with reference to the accompanying drawings and specific embodiments. The first speed threshold is n ₁ , the second speed threshold is n ₂ , the third speed threshold is n ₃ , the maximum speed of the motor is _n _max , the rated braking torque of the motor is Te, and the motor braking torque command T _eb ^{* *} , the target braking torque command T _eb ^* , the current braking torque command T _eb , the battery temperature is T, and the maximum battery charging power is P _{chg_max} .

Example 1:

Please refer to FIG. 1, the electric vehicle braking energy recovery method of this embodiment specifically includes the following steps:

Step S11: Acquire the brake button signal, motor speed, current battery SOC, temperature, and battery maximum charging power.

Specifically, the driving parameters of the electric vehicle are obtained by sampling: including the brake button signal, the motor speed n, the SOC value of the current battery, etc., and the device parameters are obtained: including the temperature of the battery, the maximum charging power P _{chg_max} of the battery, etc., where the brake button The signal is determined by the level state of the button detected by the controller; if the motor speed is measured by the motor Hall sensor, the sampling frequency is 62.5us, and the calculation formula of the motor speed n is:

Among them, SixHallTimeSum is the count value of the six Hall commutation time, and p is the number of pole pairs of the motor, which is obtained from the actual motor parameters;

The SOC value and battery temperature of the battery can be determined by sampling the controller, which reflects the actual remaining power of the battery and the working state of the battery; the maximum battery charging power P _{chg_max} can be described as the battery nominal voltage U _dc × the battery maximum charging current I _dc , which is determined by the power The battery characteristics are determined.

Specifically, it is determined whether the brake button is pressed, and if it is pressed, the energy recovery enable flag F ₁ is set, and the electronic braking (energy recovery) mode is entered, and the operation of step S12 is performed, otherwise the energy recovery enable flag F is cleared. ₁ .

Step S12: Calculate the motor braking torque command according to the braking time and gradually approach the motor rated torque.

Specifically, in order to conform to the usual braking habits, the vehicle does not produce obvious braking shock and frustration during the energy recovery process, so that the motor braking torque command T _eb ^** increases linearly with the braking time count value, and It is gradually approached to the rated braking torque _Te of the motor, namely:

Among them, T _eb ^** is the motor braking torque command, K _t is the change step size of the command (which needs to be calibrated according to the control time), and T _e is the rated braking torque of the motor, which corresponds to the electronic braking force in the program. Step S13: Calculate the target braking torque command according to the motor speed and the maximum charging power of the battery. The specific flowchart is shown in FIG. 2 .

The target braking torque command T _eb ^* is calculated according to the motor speed n. Specifically, the permanent magnet synchronous motor has a similar characteristic curve to its driving during braking, so the motor should be able to recover the vehicle from coasting within a reasonable range. Therefore, the motor braking intensity must be adjusted according to the motor speed, that is, a constant torque is output below the base speed, and a constant power is output above the base speed. The output torque decreases with the increase of the speed, and the schematic diagram of the relationship between the motor speed and the target braking torque is shown in Figure 3.

In S131, it is necessary to preset a first rotational speed threshold value n ₁ , a second rotational speed threshold value n ₂ and a third rotational speed threshold value n ₃ , where n ₁ <n ₂ <n ₃ <n _max , n _max is the maximum rotational speed value of the motor, and the rotational speed The threshold value needs to be calibrated according to the actual parameters of the motor.

In S132, it is judged whether the motor speed n is less than the first speed threshold n ₁ , if it is not less than the threshold, step S133 is executed; if it is less than the threshold, since the motor is braking at low speed, the feedback braking energy does not exceed The copper loss, iron loss and inverter loss of the motor itself, so at low speed, the motor feedback braking is basically not used, and the target braking torque command T _eb ^* is 0 at this time.

In S133, it is judged whether the motor speed n is less than the second speed threshold n ₂ , if it is not less than the threshold, step S134 is executed; if it is less than the threshold, the motor regenerative braking is started, and the target braking torque command T _eb ^* follows As the motor speed n increases, the target braking torque command T _eb ^* can be calculated by the following formula:

Wherein, T _eb ^* is the target braking torque command, n is the speed of the motor, n ₁ is the first speed threshold, n ₂ is the second speed threshold, and T _eb ^** is the motor braking torque command.

In S134, it is determined whether the motor speed n is less than the third speed threshold n ₃ , if it is less than the threshold, the target braking torque command T _eb ^* is the motor braking torque command T _eb ^** , and the motor outputs torque at this time otherwise, the target braking torque command T _eb ^* decreases as the motor speed n increases, and the motor output power is constant at this time, and the target braking torque command T _eb ^* can be calculated by the following formula:

Wherein, T _eb ^* is the target braking torque command, n is the rotational speed of the motor, n ₃ is the third rotational speed threshold, and T _eb ^** is the motor braking torque command.

In S135, the target braking torque command T _eb ^* is calculated according to the maximum charging power P _{chg_max} of the battery. Specifically, since the actual charging capacity of the battery is limited, during the regenerative braking process, the actual regenerative power P _{reg_chg} provided by the motor to the battery It should be within the maximum battery charging power P _{chg_max} . After considering the motor stator and rotor resistance, copper loss, heat loss and other factors to lose a part of the electric energy, the actual feedback power P _{reg_chg} of the motor is:

Among them, T _eb ^* is the target braking torque command, n is the rotational speed of the motor, and η (0.7~0.9) is the motor feedback braking power generation efficiency after considering the loss of the motor.

Therefore, in the regenerative braking process, the target braking torque command T _eb ^* needs to be limited, and the limited target braking torque command T _eb ^* is:

Among them, T _eb ^* is the target braking torque command, n is the rotational speed of the motor, η is the motor feedback braking power generation efficiency after considering the loss of the motor, and P _{chg_max} is the maximum charging power of the battery.

Step S14: Calculate the target braking torque command according to the battery SOC value and the battery temperature. The specific flowchart is shown in FIG. 4 .

Specifically, in the process of regenerative braking of the electric vehicle, considering the safety of the energy storage system, when the SOC value of the battery is small, the braking force of the motor can be appropriately increased at this time to recover more braking energy. When the SOC value of the battery is high (generally designed to take SOC>0.9), it indicates that the battery capacity is close to saturation. In order to avoid the shortening of its life due to overcharging of the battery, regenerative braking is not performed at this time, and only mechanical braking is used. Generally speaking, the working temperature of the battery has a safe range. If the battery temperature is too high or too low, it may cause the protection of the energy storage system and make it impossible to charge and discharge. Therefore, when it is detected that the battery temperature is outside the safe range, it should be reduced. The braking force of the motor protects the battery. In order to achieve these requirements, it is necessary to introduce the battery influence factor k _soc to correct the target braking torque command T _eb ^* . The schematic diagram of the three-dimensional relationship between the battery SOC value, the battery temperature T and the battery influence factor k _soc is shown in Figure 5.

In S141, look up a table according to the battery SOC value and the battery temperature T, such as Table 1 (the data in Table 1 is not unique according to different battery characteristics) to obtain the battery influence factor k _soc . In particular, when the battery SOC value and the battery temperature T are between two thresholds, linearization can be performed to obtain the current battery influence factor k _soc . For example, when the battery SOC value is 0.56 and the battery temperature T is 13°C, The current battery impact factor k _soc is 0.902.

Table 1 Relation table of battery impact factor k _soc

In S142, the target braking torque command T _eb ^* is modified according to the obtained battery influence factor k _soc to obtain the current braking torque command T _eb , and the current braking torque command T _eb can be calculated by the following formula:

Among them, T _eb ^* is the target braking torque command, k _soc is the battery influence factor, and T _eb is the current braking torque command.

In S143, the motor is controlled to transition from the current torque to the target torque according to the current braking torque command. Specifically, according to the current braking torque command T _eb obtained in S142, the motor is controlled from the current actual torque to the target torque. The smooth transition allows the motor to complete the energy recovery work.

Embodiment 2:

Referring to FIG. 6 , the method for recovering braking energy of an electric vehicle in this embodiment specifically includes the following steps.

Step S21: Acquire the brake lever signal, the motor speed, the current battery SOC, the temperature, and the maximum battery charging power.

Specifically, the driving parameters and equipment parameters of the electric vehicle are obtained by sampling, among which, the brake handle signal is determined by detecting the level state of the brake handle by the controller; other parameters have been described in detail above, so they will not be repeated here.

Specifically, it is determined whether the brake handle signal is triggered, and if so, the energy recovery enable flag F1 is set, and the electronic braking (energy recovery) mode is entered, and the operation _of step S22 is performed, otherwise, the energy recovery enable flag F1 is _cleared .

Step S22: Calculate the motor braking torque command according to the braking time and gradually approach the rated torque of the motor. Please refer to the first embodiment, which has been described in detail above, so it will not be repeated here.

Step S23 : Calculate the target braking torque command according to the rotational speed of the motor and the maximum charging power of the battery. Please refer to the first embodiment, which has been described in detail above, so it will not be repeated here.

Step S24: Calculate the target braking torque command according to the battery SOC value and the battery temperature. Please refer to the first embodiment, which has been described in detail above, so it will not be repeated here.

In addition, the electric vehicle braking energy recovery method of the present invention can adopt the electric vehicle braking energy recovery system as shown in 7. It can be seen from FIG. 7 that the system includes:

The acquisition module 11 is used to acquire the driving parameters of the electric vehicle: including the brake signal (button signal or brake lever signal), the motor speed n, the SOC value of the current battery, etc., and obtain the equipment parameters of the electric vehicle: including the temperature of the battery, the maximum charge of the battery Power P _{chg_max} and other parameters.

The judgment module 12 is used for judging whether to enter the electronic braking (energy recovery) mode according to the driving parameters and the equipment parameters.

The calculation module 13 is configured to calculate the motor braking torque command T _eb ^** , the target braking torque command T _eb ^* and the current braking torque command T _eb according to the driving parameters and the equipment parameters.

The control module 14 is used to control the motor to smoothly transition from the current actual torque to the target braking torque without sudden change in the braking torque.

It works as follows:

By obtaining the driving parameters and equipment parameters of the electric vehicle, including the braking signal, the motor speed n, the current SOC value of the battery, the temperature of the battery and the maximum charging power P _{chg_max} of the battery, etc.; the motor braking torque command T is calculated according to the braking time _eb ^** ; Motor speed n and battery maximum charging power P _{chg_max to} calculate motor braking torque command target braking torque command T _eb ^* ; Calculate current braking torque command T according to battery SOC value and battery temperature T _eb ; The motor is controlled by the current braking torque command T _eb to transition from the current actual torque to the target torque.

In addition, according to GB/T 24157 "Electric Motorcycles and Electric Mopeds Test Method for Driving Range and Residual Power Indication", the working condition method in the driving range test is tested. It can be seen from the chart comparison that the energy recovery of the present invention is adopted. The method makes the cruising range reach 108.85%, and the battery performance has also been greatly improved. It has been verified that when the braking feedback energy is carried out, it is controlled by combining the actual external characteristics (power generation capacity) of the motor to maximize the range of the motor capacity. The effect is obvious to carry out energy recovery and improve the recovered energy.

Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by those skilled in the art within the essential scope of the present invention should also belong to the present invention. the scope of protection of the invention.

Claims

A method for recovering braking energy of an electric vehicle, comprising the following steps:

S11, obtaining the driving parameters and equipment parameters of the electric vehicle;

S12. Calculate the motor braking torque command according to the braking time, so that the motor braking torque command T eb ** increases linearly with the braking time count value, and approaches the motor rated braking torque T e ;

S13. Calculate the target braking torque command according to the motor speed and the maximum charging power of the battery;

S14: Calculate the current braking torque command according to the battery SOC value and the battery temperature.
The braking energy recovery method for an electric vehicle according to claim 1, characterized in that: in said step S11, the driving parameters and equipment parameters include braking signal, motor speed n, current battery SOC value, battery temperature and battery maximum charge Power P chg_max .
The braking energy recovery method for an electric vehicle according to claim 2, wherein the formula for calculating the motor speed n is:

The battery SOC value and battery temperature are determined by sampling by the controller, and reflect the actual remaining power of the battery and the working state of the battery; the maximum battery charging power P chg_max is the battery nominal voltage U dc × the battery maximum charging current I dc .
The method for recovering braking energy of an electric vehicle according to claim 2, wherein in the step S12, the braking signal is a braking lever signal or a braking button signal.
The braking energy recovery method for an electric vehicle according to claim 1, characterized in that: in the step S12, the motor braking torque command T eb ** is linearly increased with the braking time count value, and is adjusted to the rated value of the motor. The dynamic torque T e is approximated, namely:
The braking energy recovery method for an electric vehicle according to claim 1, characterized in that: the specific flow method of the step S13 is as follows:

S131, preset motor parameters: a first rotational speed threshold n 1 , a second rotational speed threshold n 2 and a third rotational speed threshold n 3 , where n 1 <n 2 <n 3 <n max , and n max is the maximum rotational speed value of the motor;

S132, determine whether the motor speed n is less than the first speed threshold n 1 , if not less than the threshold, execute step S133; if it is less than the threshold, the motor does not perform regenerative braking, and the target braking torque command T eb * is 0;

S133, determine whether the motor speed n is less than the second speed threshold n 2 , if it is not less than the threshold, execute step S134; if it is less than the threshold, start the motor regenerative braking, and the target braking torque command T eb * follows the motor The speed n increases and increases;

S134, determine whether the motor speed n is less than the third speed threshold n 3 , if it is less than the threshold, the target braking torque command T eb * is the motor braking torque command T eb ** , and the motor output torque is constant at this time; Otherwise, the target braking torque command T eb * decreases as the motor speed n increases, and the motor output power is constant at this time;

S135: Calculate the target braking torque command T eb * according to the maximum charging power P chg_max of the battery. During the regenerative braking process, the actual feedback power P reg_chg provided by the motor to the battery is within the maximum charging power P chg_max of the battery, and the actual feedback power of the motor is within the maximum charging power P chg_max of the battery. P reg_chg is:

During the regenerative braking process, the target braking torque command T eb * is limited, and the limited target braking torque command T eb * is:
The braking energy recovery method for an electric vehicle according to claim 6, characterized in that: in the step S133, the target braking torque command T eb *

It is calculated by the following formula:
The braking energy recovery method for an electric vehicle according to claim 6, characterized in that: in the step S134, the target braking torque command T eb * is calculated by the following formula:
The electric vehicle braking energy recovery method according to claim 2, characterized in that: the process operation method of step S14 is as follows:

S141, look up a table according to the battery SOC value and the battery temperature T, such as obtaining the battery influence factor k soc ;

S142, correcting the target braking torque command T eb * according to the obtained battery influence factor k soc to obtain the current braking torque command T eb ;

S143 , controlling the motor to transition from the current torque to the target torque according to the current braking torque command.