CN110481532B - Regenerative braking control method of hybrid electric vehicle based on composite structure dual-rotor motor - Google Patents

Abstract

The invention discloses a regenerative braking control method of a hybrid vehicle based on a dual-rotor motor with a composite structure, which comprises the following steps: 1. judging the required braking intensity of the automobile, wherein the braking intensity Z

Z_{_thres3}When the current time is up, selecting MB; 2. judging the SOC value of the battery, and when the SOC value is the SOC value

SOC_{_high}When the current time is up, selecting MB; 3. judging the current vehicle speed, namely judging the current vehicle speed V

V_{_low}When the current time is up, selecting MB; 4. judging the state of the internal combustion engine, and executing the step 5 when the internal combustion engine is in an opening state, or executing the step 6; 5. when V is

V_{_high}Or Z

Z_{_thres1}Selecting SMB; otherwise, selecting EMCB; 6. when braking intensity Z<Z_{_thres2}Selecting SMB; in contrast, Z

Z_{_thres2}DMB is selected. The EMCB solves the problems of high state switching frequency and poor fuel economy of the internal combustion engine; the DMB solves the problems that the participation frequency of mechanical braking force is high and the energy recovery rate of a regenerative braking system is low.

Description

Regenerative braking control method of hybrid electric vehicle based on composite structure dual-rotor motor

technical field

The invention belongs to the technical field of hybrid electric vehicles, and in particular relates to a regenerative braking control method of a hybrid electric vehicle based on a dual-rotor motor with a composite structure.

Background technique

The regenerative braking function is an important performance index of a hybrid vehicle, and its reasonable optimal control can ensure the stability of the braking system, improve the regenerative braking efficiency and driving comfort, and effectively improve the driving range. The existing hybrid braking method mainly uses the motor connected to the vehicle load to provide regenerative braking force. When the maximum regenerative braking force that the motor can provide is greater than the required braking force of the car, the braking torque is completely provided by the motor; when When the maximum regenerative braking force provided by the electric motor is less than the braking force required by the car, the electric motor provides the maximum regenerative braking torque, and then the insufficient braking torque is provided by the mechanical braking force.

The power transmission topology of hybrid electric vehicle based on composite structure dual-rotor motor is shown in Figure 1. The composite structure dual-rotor motor (CSM) includes an inner motor EM1 and an outer motor EM2. The inner rotor of the inner motor EM1 is connected to the output shaft of the internal combustion engine, and the outer The rotor is used as the common rotor of the inner motor EM1 and the outer motor EM2, and the outer rotor is connected to the main reducer; the inner rotor winding of the inner motor EM1 is connected to the two electrodes of the battery through the slip ring and the first power electronic converter 1, and the outer rotor of the outer motor EM2 is connected to the two electrodes of the battery. The stator windings are connected to the two poles of the battery through the second power electronic converter 2 . The power transmission structure can reasonably control the rotational speed and torque of the inner motor EM1 and the outer motor EM2, so that the internal combustion engine can be decoupled from the road load; It can meet the requirements of road load.

The existing hybrid braking method is applied to a hybrid vehicle with a dual-rotor motor with a composite structure. The fuel economy is poor; 2. The participation frequency of the mechanical braking force is high, and the energy recovery rate of the regenerative braking system is low.

SUMMARY OF THE INVENTION

In view of the problems existing in the prior art, the technical problem to be solved by the present invention is to provide a regenerative braking control method for a hybrid vehicle based on a composite structure dual-rotor motor, which can still maintain the internal combustion engine under the condition of coordinated braking of the internal combustion engine and the motor. Working on the optimal fuel economy curve, reducing the frequency of internal combustion engine state switching and improving the fuel economy of the internal combustion engine, on the other hand, under the condition of dual-motor regenerative braking, it can reduce the frequency of participation of mechanical braking force and improve the regeneration of the car. The energy recovery rate of the braking system.

The technical problem to be solved by this invention is realized through such technical scheme, and it comprises the following steps:

Step 1. Judging the braking intensity of the vehicle demand

When the car receives the braking request signal, when the braking intensity Z ≥ the third intensity threshold Z_thres3, the car is in the emergency braking state, which is the MB mode; when Z<Z_thres3, step 2 is performed;

Step 2. Determine the battery SOC value

Judging the SOC value of the battery, when SOC ≥ the high power threshold SOC_high, the battery is in a non-rechargeable state, and the braking is in MB mode;

When the SOC ≤ the low power threshold SOC_low, the battery energy is not enough to maintain the pure electric driving of the car, and the internal combustion engine needs to be turned on, and then the car will be in a hybrid drive state, and step 3 is performed;

When SOC_low<SOC<SOC_high, execute step 3;

Step 3. Determine the current speed

When the vehicle speed V≤the low speed threshold V_low, the braking is in MB mode, otherwise, step 4 is performed;

Step 4. Judging the state of the internal combustion engine

When the internal combustion engine is on, go to step 5; otherwise, go to step 6;

Step 5. Judge the speed and braking strength of the car

When V≥high-speed threshold V_high or Z≥first intensity threshold Z_thres1, select SMB mode; otherwise, select EMCB mode;

Step 6. Judge the braking strength of the car

When the braking intensity Z≤the second intensity threshold Z_thres2, the SMB mode is selected; on the contrary, if Z>Z_thres2, the DMB mode is selected.

The present invention has the following advantages:

1. The EMCB method of the present invention can still keep the internal combustion engine working on the optimal fuel economy curve under the action of an appropriate braking torque, thereby reducing the state switching frequency of the internal combustion engine and improving its fuel economy;

2. The DMB mode of the present invention can make full use of the regenerative braking force provided by the dual motors, reduce the participation ratio of the mechanical braking force, improve the energy recovery efficiency of the regenerative braking system of the vehicle, and better coordinate the regenerative braking control.

Therefore, the EMCB of the present invention keeps the internal combustion engine working on the optimal fuel economy curve, reduces the frequency of switching states of the internal combustion engine, and improves the fuel economy of the internal combustion engine. The DMB of the present invention reduces the frequency of participation of the mechanical braking force and improves the The energy recovery rate of a car's regenerative braking system.

Description of drawings

The accompanying drawings of the present invention are described as follows:

1 is a topological structure diagram of a hybrid electric vehicle power transmission in the background;

Fig. 2 is the power flow diagram of the coordinated braking of the internal combustion engine motor;

Figure 3 is a power flow diagram of dual-motor braking;

FIG. 4 is a flowchart of the regenerative braking mode switching according to the present invention.

Detailed ways

Below in conjunction with accompanying drawing and embodiment, the present invention will be further described:

Terms related to this application:

1. Internal combustion engine motor coordinated braking (EMCB)

The advantage of engine-motor coordinating braking (EMCB) is that the internal combustion engine can still be kept in the best running state during the regenerative braking process, thereby improving the fuel consumption of the hybrid vehicle based on the composite structure dual-rotor motor. economical.

The power flow diagram of the coordinated braking of the internal combustion engine motor is shown in Figure 2. The relationship between energy and power in this braking state is:

In formula (1), P _ICE is the output power of the internal combustion engine, P _EM1 is the power generated by EM1, P _d is the power transmitted by the magnetic field to drive the outer rotor; T _ICE is the output torque of the internal combustion engine; T _EM1 is the electromagnetic rotation of EM1. Torque, T _EM2 is the regenerative braking torque provided by EM2, T _wheel is the braking torque that needs to act on the driving wheel during the braking process of the vehicle, T _req is the torque acting on the front end of the main reducer during the braking process of the vehicle, and i _single is The final gear reduction ratio, ω _ICE is the rotational speed of the internal combustion engine, and ω _EM2 is the rotational speed of EM2.

The output power P _ICE of the internal combustion engine is divided into two parts: one part of the energy P _d is transmitted through the magnetic field to drive the outer rotor, and the other part of the energy is input to the battery in the form of EM1 power generation, namely P _EM1 . When the power system is in a steady state, the torque T _ICE of the internal combustion engine is equal to the electromagnetic torque _{T EM1} of the _{EM1 ;} /r _wheel , where r _wheel is the tire radius. ω _EM1 is the rotational speed of EM1, which is equal to the difference between the rotational speed ω _ICE of the internal combustion engine and the rotational speed ω _EM2 of EM2, and the relationship is: ω _EM1 =ω _ICE -ω _EM2 .

In this braking situation, the regenerative braking torque T _EM2 provided by the EM2 is equal to the output torque of the internal combustion engine and the demand braking torque T _req of the automobile, that is, the regenerative braking torque T _EM2 of the EM2 at this time should not only provide the demand braking torque for the automobile Dynamic torque, but also to overcome the output torque of the internal combustion engine and convert it into electrical energy.

It can be seen from this that under this braking condition, the output power of the internal combustion engine is stored in the battery through the power generation of the dual-rotor motor with the composite structure during the braking process. However, in the existing regenerative braking control method, the internal combustion engine is in an idling state, all the energy of the internal combustion engine is wasted, and when the braking process of the vehicle ends and the braking process needs to be turned into a hybrid drive state, the internal combustion engine needs to be turned from the idle speed again. The state is switched to the drive state, so the EMCB can reduce the frequency of internal combustion engine state switching and improve the fuel economy of the internal combustion engine.

When the vehicle braking strength Z (the braking strength Z is the ratio of the absolute value of the braking deceleration demanded by the vehicle to the gravitational acceleration g) is greater than or equal to the first strength threshold Z_thres1, the braking torque provided by the EM2 is required to be greater than or equal to the first strength threshold Z_thres1. The maximum value it can provide, so the EMCB mode is not available; when the vehicle speed is greater than or equal to the high-speed threshold V_high, at this time, due to the close speed of the outer motor and the engine, the inner single machine EM1 works in the low-speed non-efficient area, so the EMCB mode is not available. ; When the vehicle speed is less than or equal to the low-speed threshold V_low, the external motor EM2 will work in the low-speed non-efficient area, so the EMCB mode is not available; when the SOC value is greater than or equal to the high power threshold SOC_high, the battery is in a non-rechargeable state, so the EMCB mode unavailable. When the conditions are met: Z<Z_thres1, V_low<V<V_high, SOC<SOC_high, the EMCB method is adopted.

During the braking process in EMCB mode, as the vehicle speed decreases, the speed of EM2 also decreases, and the speed of EM1 increases accordingly (the stator of EM1 is connected to the output shaft of the engine, and the rotor is connected to the rotor of EM2, then the speed of EM1 is The rotational speed is the difference between the rotational speed of the internal combustion engine ω _ICE and the rotational speed of EM2 ω _EM1 =ω _ICE -ω _EM2 , the engine rotational speed remains unchanged, so the rotational speed of EM1 will increase as the rotational speed of EM2 decreases).

Motor regenerative braking is to generate braking torque when the rotor speed is higher than the motor synchronous speed to achieve braking. In order to make the motor work characteristics in the regenerative braking curve, the controller will reduce the stator voltage frequency to make the motor synchronous speed lower than rotor speed, and then use the "half-bridge modulation or full-bridge modulation motor feedback braking method" to realize the braking torque control of the motor. The braking torque of EM1 and EM2 is controlled by the motor controller, so that the regenerative braking torque T _EM2 provided by EM2 is equal to the braking torque T _req required by the vehicle and the output torque T _ICE of the internal combustion engine, and the torque T _EM1 of EM1 is made at the same time. It is equal to the internal combustion engine output torque T _ICE .

2. Dual Motor Brake (DMB)

The advantage of dual motor braking (DMB for short) is: using EM1 to supplement the deficiency of EM2 regenerative braking force, overcoming the defect that the existing hybrid electric vehicle is usually supplemented with insufficient braking torque by mechanical brakes, therefore, DMB It can effectively improve the energy recovery efficiency. Since the motor can respond quickly to torque changes, DMB can also improve the coordination of system operation.

The power flow diagram of dual-motor braking (DMB) is shown in Figure 3. The dynamic relationship in this braking state is:

In the formula (2), T _EM1 is the electromagnetic torque of EM1; T _EM2 is the regenerative braking torque provided by EM2, ω _EM1 is the rotational speed of the inner motor, ω _EM2 is the rotational speed of the outer motor, and T _wheel is the braking process of the vehicle. The braking torque on the driving wheel, T _req is the torque acting on the front section of the main reducer during the braking process of the vehicle, i _single is the reduction ratio of the main reducer. Dual-motor braking DMB is a regenerative braking method when the vehicle is in pure electric drive mode. At this time, the internal combustion engine does not output power, and the output shaft of the internal combustion engine is locked. The rotational speeds of EM1 and EM2 are equal and related to the vehicle speed v, namely: ω _EM1 = ω _EM2 =v×i _single /r _wheel .

When the braking intensity Z is less than or equal to the second intensity threshold Z_thres2, the braking force required by the car can only be provided by EM2, so the DMB method is not available; when the braking intensity is greater than or equal to the third intensity threshold Z_thres3, the braking force required by the car The dynamic strength is set urgently. Since the reliability of the DMB mode is not as good as that of pure mechanical braking, the DMB mode is unavailable; when the vehicle speed is less than or equal to the low-speed threshold V_low, the motor will work in the low-speed non-efficient area, so the DMB mode is unavailable; when When the SOC value is greater than or equal to the high power threshold SOC_high, the DMB mode is unavailable because the battery is in a non-rechargeable state; when the SOC value is less than or equal to the low power threshold SOC_low, the battery power is insufficient to provide pure electric drive energy. The driving state has sufficient driving force, it is necessary to release the lock of the output shaft of the internal combustion engine and open the internal combustion engine, so the DMB method is not available. When the conditions are met: Z_thres2<Z<Z_thres3, V>V_low, SOC_low<SOC<SOC_high, the DMB method is adopted.

The above-mentioned first intensity threshold Z_thres1<second intensity threshold Z_thres2<third intensity threshold Z_thres3.

In the process of regenerative braking under the action of DMB, the internal combustion engine does not work, and its output shaft can be locked by the clutch. At this time, the rotational speeds of EM1 and EM2 are equal and decrease as the vehicle speed decreases during the braking process. The controller performs braking torque control on EM1 and EM2, so that the sum of the braking torques of the dual motors is equal to the required braking torque and ensures that the overall efficiency of the dual-motor braking system is optimal. The equivalent efficiency expression of the system is as follows (3) shows:

In the formula, η _equa is the equivalent efficiency of the dual-motor braking system, η _EM1 is the efficiency of the inner motor EM1, and η _EM2 is the efficiency of the outer motor EM2. To ensure that the overall efficiency of the system is optimal, that is, to control the torques of EM1 and EM2 to maximize η _equa .

3. Single Motor Brake (SMB)

Single motor braking (Single motor braking, referred to as SMB) is that the regenerative braking torque required by the car is provided by the EM2 alone.

Braking is required under the pure electric driving condition of the vehicle. When V>V_low, SOC_low<SOC<SOC_high, regenerative braking in pure electric mode is allowed, and when the braking intensity Z is less than or equal to the second intensity threshold Z_thres2 , when EM2 alone can provide all the regenerative braking force, so the SMB method is used. At this time, EM1 does not work, and the torque of EM2 is controlled by the motor controller to make it equal to the regenerative braking torque required by the car.

Braking is required under the hybrid driving condition of the vehicle. When V>V_low and SOC<SOC_high, regenerative braking in the hybrid driving mode is allowed, and when the braking intensity Z is greater than or equal to the first intensity threshold Z_thres1, SMB is used. Way. At this time, EM1 does not work, that is, EM1 is not energized, and the power transmission between the internal combustion engine and EM2 is temporarily disconnected (part of the output power of the internal combustion engine is transmitted to the outer rotor of EM1 through the magnetic field, and the outer rotor of EM1 and the rotor of EM2 are As a whole, there is power transmission between the internal combustion engine and EM2. When EM1 is not working, since the EM1 motor does not generate a magnetic field, the power of the internal combustion engine cannot be transmitted to EM2). The regenerative braking force is completely provided by EM2 and controlled by the motor. The controller performs braking torque control on EM1 and EM2 to make it equal to the braking torque required by the vehicle.

4. Mechanical brake (MB)

Mechanical braking (MB for short) is the braking torque generated by mechanical brakes. There are four situations when using mechanical braking:

1) When the vehicle speed is low, that is, the vehicle speed is less than or equal to the low speed threshold V_low, the EM2 is in the low-speed non-efficient working area, and the mechanical brake is required to provide the braking torque required by the vehicle;

2) The torque of the motor braking is insufficient, and the mechanical braking torque needs to be supplemented;

3) When the car is in emergency braking, that is, when the braking intensity is greater than or equal to the third intensity threshold Z_thres3, considering the safety of braking, a more reliable mechanical brake is required to provide the required braking force alone;

4) When the battery SOC is greater than the power high threshold SOC_high, the battery is in a non-chargeable state and cannot be charged to the battery through regenerative braking. At this time, the mechanical brake provides the braking torque required by the vehicle.

As shown in Figure 4, the present invention comprises the following steps:

Step 1. Judging the braking intensity of the vehicle demand

When the driver depresses the brake pedal, the sensor detects the pedal force, the car receives the braking request signal, and judges the braking intensity required by the car according to the brake layout principle. When the braking intensity Z ≥ Z_thres3, the car is in emergency braking In the dynamic state, select MB mode at this time; when Z<Z_thres3, go to step 2;

Step 2. Determine the battery SOC value

Judging the SOC value of the battery, when SOC ≥ SOC_high, the battery is in a non-rechargeable state, EMCB, DMB and SMB cannot be started, and the braking is in MB mode;

At this time, if the internal combustion engine is on, the internal combustion engine is switched off, and the subsequent driving process operates in a purely electric drive mode.

When SOC≤SOC_low, the battery energy is not enough to maintain the pure electric driving of the car, and the internal combustion engine needs to be turned on, and then the car will be in a hybrid drive state, and step 3 is executed;

When SOC_low<SOC<SOC_high, execute step 3;

Step 3. Determine the current speed

When the vehicle speed V≤V_low, the braking is in MB mode, otherwise, go to step 4;

Step 4. Judging the state of the internal combustion engine

When the internal combustion engine is in the ON state, step 5 is performed to select between EMCB and SMB; otherwise, step 6 is performed to select DMB and SMB;

Step 5. Judge the speed and braking intensity of the car

When V≥V_high or Z≥Z_thres1, select SMB mode; otherwise, select EMCB mode;

Step 6. Judge the braking strength of the car

When the braking intensity Z<Z_thres2, the SMB mode is selected; on the contrary, if Z≥Z_thres2, the DMB mode is selected.

Claims (1)

1. a hybrid electric vehicle regenerative braking control method based on a composite structure dual-rotor motor, is characterized in that, comprises the following steps: Step 1. Judging the braking intensity of the vehicle demand The car receives the braking request signal, when the braking intensity Z ≥ the third intensity threshold Z_thres3, the car is in an emergency braking state, at this time the mechanical braking MB mode; when Z < Z_thres3, go to step 2; Step 2. Determine the battery SOC value Judging the SOC value of the battery, when the SOC ≥ the high power threshold SOC_high, the battery is in a non-rechargeable state, and the braking is in the mechanical braking MB mode; When the SOC ≤ the low power threshold SOC_low, the battery energy is not enough to maintain the pure electric driving of the car, and the internal combustion engine needs to be turned on, and then the car will be in a hybrid drive state, and step 3 is performed; When SOC_low<SOC<SOC_high, execute step 3; Step 3. Determine the current speed When the vehicle speed V≤the low speed threshold V_low, the braking is in the mechanical braking MB mode, otherwise, step 4 is performed; Step 4. Judging the state of the internal combustion engine When the internal combustion engine is on, go to step 5; otherwise, go to step 6; Step 5. Judge the speed and braking strength of the car When V≥high-speed threshold V_high or Z≥first strength threshold Z_thres1, the single-motor braking SMB mode is selected; otherwise, the internal combustion engine-motor coordinated braking EMCB mode is selected; Step 6. Judge the braking strength of the car When the braking intensity Z≤the second intensity threshold Z_thres2, the single-motor braking SMB mode is selected; on the contrary, if Z>Z_thres2, the dual-motor braking DMB mode is selected.

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