CN110723134A

CN110723134A - Working condition prediction-based range-increasing type electric automobile self-adaptive thermostat control method

Info

Publication number: CN110723134A
Application number: CN201910998697.9A
Authority: CN
Inventors: 顾琰浩; 吴晓东; 张光洲
Original assignee: Shanghai Jiaotong University
Current assignee: Shanghai Jiaotong University
Priority date: 2019-10-21
Filing date: 2019-10-21
Publication date: 2020-01-24
Anticipated expiration: 2039-10-21
Also published as: CN110723134B

Abstract

The invention discloses a working condition prediction-based self-adaptive thermostat control method for a range-extended electric vehicle, relates to the field of range-extended electric vehicle control, and aims to integrate the fuel consumption rate J of a power system by considering the operation state of an APU (auxiliary Power Unit)_zAnd battery current I_bAnd determining an objective function, and solving the objective function to obtain the optimal working power of the APU. The method provided by the invention has the following technical effects: (1) has working condition self-adaptive capacity(ii) a (2) The service life of the power battery is prolonged; (3) less noise and vibration.

Description

Working condition prediction-based range-increasing type electric automobile self-adaptive thermostat control method

Technical Field

The invention relates to the field of range-extending electric vehicle control, in particular to a range-extending electric vehicle self-adaptive thermostat control method based on working condition prediction.

Background

At present, the national increasingly stricter automobile energy-saving indexes and test conditions are, and on the premise that the efficiency of an engine and the capacity of a power battery are difficult to break through, the hybrid electric vehicle becomes an effective scheme for meeting the energy-saving indexes in a short term. An Extended Range Electric Vehicle (EREV) is additionally provided with a Range extender on the basis of a pure Electric Vehicle, so that the working condition and the efficiency of an engine can be effectively improved.

The hybrid vehicles can be divided into series, parallel, hybrid and complex types in structural form. The extended range electric vehicle system structure is generally a series connection (as shown in fig. 1). The series hybrid power has a simpler structure, wheels are directly driven by a driving motor, and an Auxiliary power generation unit (also called an Auxiliary Power Unit (APU)) consisting of an engine and a generator is not directly connected with the driving wheels and is only used for power generation.

The energy distribution strategy should be determined prior to studying the extended range electric vehicle energy control strategy. Energy distribution strategies for extended range electric vehicles can be broadly divided into two categories: a Charge-Depleting and Charge-Sustaining, CDCS, and a mixed strategy (Blended). Wherein, the exhaustion maintenance strategy is more in line with the conventional recognition of extended range electric vehicles in the industry.

The present invention employs a depletion maintenance strategy. FIG. 2 is a schematic diagram of a depletion maintenance strategy, the basic concepts of which are: the power battery is used for pure electric driving at the beginning stage, namely a Charge-depletion (CD) stage; when the state of Charge (SOC) of the battery is reduced to a certain limit, the APU is started to generate power, and the SOC is maintained above a minimum allowable limit, namely a Charge-Sustaining (CS) stage.

Scholars at home and abroad have already conducted relevant research on energy control strategies of extended range electric vehicles, and the energy control strategies are mainly divided into two directions of rule-based control strategies and optimization-based control strategies at present, and the rule-based control strategies mainly used in practical engineering mainly comprise thermostat control strategies, power following control strategies and the like.

The thermostat control strategy is also known as a single point control strategy. After the range extender is started, the engine outputs constant power at a preset working point, the output power does not change along with the change of the working condition, and the power point is the optimal power point and can also be the optimal power pointThe minimum oil consumption point is ensured on the premise of ensuring the dynamic property, and the selection of the working point is in consideration of the fuel consumption, the power and the rotating speed of the engine. In a traditional thermostat control strategy, the working condition (such as NEDC) of the extended range electric vehicle is predetermined in a CDCS mode, the driving power requirement of the whole vehicle is calculated after the weight, the wind resistance and the rolling optimization of the whole vehicle are combined, and the optimal working power of the APU is set according to the working condition. The NEDC refers to New European Driving Cycle, a New European Cycle test, and an automobile operating condition. When the SOC is sufficient, the APU does not work, pure electric driving is carried out, the automobile is zero emission, and the automobile is in a CD stage at the moment. When the SOC is lower than the SOC_csminWhen the system is started, the APU starts and sets the engine to work at a fixed optimal working point, part of the output power is transmitted to the driving motor, and the surplus power is stored in the battery until the SOC rises to the SOC_csmaxThen, the APU is turned off, the battery outputs power to the driving motor again, and the SOC is kept at the SOC_csminAnd SOC_csmaxIn the CS phase at this time.

The power following control strategy, i.e. the operation of the engine is changed along a fixed curve, can continuously change the power value of the engine, and generally selects the power curve of the engine at the time of the best fuel economy as the target following curve. The control strategy is determined by the running condition of the vehicle, the characteristic of the engine is known, and the required power of the vehicle under a certain working condition at a certain moment determines the value of the lowest fuel consumption rate point at the power. When the SOC reaches the minimum value, the APU system is turned on and runs along the lowest fuel consumption curve.

Both the conventional thermostat control strategy and the power follow control strategy of the prior art have some drawbacks, among them the drawbacks of the conventional thermostat control strategy are:

(1) in a traditional thermostat control strategy, an APU operates at a set constant power point, and the constant power point is designed according to a certain working condition. When the vehicle working condition changes, the APU working power point can not change because of no working condition self-adaptive capacity, the vehicle can not adapt to the new working condition, and the energy efficiency of the whole vehicle is reduced.

(2) In a conventional thermostat control strategy, in order to ensure that a vehicle can keep a vehicle speed in an electric quantity maintaining state, a set constant power point has a high power. And the high working power ensures that the power battery is charged with high power when the APU operates and discharged with high power when the APU is closed, so that the service life of the battery is reduced.

(3) In conventional thermostat control strategies, the constant power point power is high, resulting in large noise and vibration when the APU is running.

The disadvantages of the power-following control strategy are:

(1) under the power following control strategy, the engine operates along a set interval of the high efficiency curve. The engine works at a non-maximum efficiency point most of the time, and the comprehensive efficiency is low.

(2) Under the power following control strategy, the output power of the engine changes according to the required power, and the output power switching can cause the sudden change of the rotating speed and the torque of the engine, so that the working state of the engine is unstable, the efficiency of the engine is reduced, and the pollutant emission of the engine is increased.

(3) The APU has long running time, the engine has large noise and the sound volume is unstable.

Accordingly, those skilled in the art have endeavored to develop a new adaptive thermostat control method for extended range electric vehicles that overcomes the above-mentioned shortcomings of the conventional thermostat control strategy and power follow control strategy.

Disclosure of Invention

The invention is used for the APU control strategy of the range-extended electric locomotive. In view of the above-mentioned drawbacks of the prior art, the present invention provides an adaptive thermostat control strategy based on operating condition prediction. Specifically, the technical problems to be solved by the present invention are:

(1) the problem that the working power point of the APU in the traditional thermostat control strategy can not be adjusted along with the actual working condition is solved, and the dynamic adjustment of the working power point of the APU is realized by predicting the required power in a short time in the future, so that the control strategy in the invention has the self-adaptive capacity of the working condition.

(2) The problem that the service life of a battery is influenced by overlarge charging and discharging current under the working power of an APU in a traditional thermostat control strategy is solved, the fuel consumption rate and the battery current of a power system are comprehensively considered in the calculation of the working power point of the APU, the obtained working power point of the APU is smaller than that of the traditional thermostat control strategy, and factors such as low speed, braking energy recovery and the starting and stopping interval of the APU are comprehensively added into a control rule, so that the oil consumption of an engine is reduced and the service life of the battery is protected.

In the self-adaptive thermostat control strategy, on the basis of predicting the required power of a vehicle in a short time, an optimization equation taking the fuel consumption rate and the battery current of a power system as objective functions is designed, meanwhile, factors such as noise and vibration, engine emission, the service life of a power battery and the like are comprehensively considered, and the working efficiency of the APU is adjusted, so that the APU and the power battery always work in an efficient interval under different working conditions of the vehicle, and the service life of the power battery is prolonged.

In order to achieve the purpose, the invention provides a working condition prediction-based self-adaptive thermostat control method for an extended-range electric vehicle, which considers the comprehensive fuel consumption rate J of a power system when an APU is in an operating state_zAnd battery current I_bDetermining an objective function, and solving the objective function to obtain the optimal working power of the APU;

the objective function is as shown in equation (1):

min J＝J_z+αJ_i(1)

wherein, J_zCan be represented by formula (2):

the molecular moiety of said formula (2) is represented by the formula₀To t₀Fuel consumption of the engine during + T time, where P_APUIs the output power of the APU and,

represents the output power of the APU as P_APUThe optimal fuel consumption rate of the APU is obtained;

the denominator part of the equation (2) represents the active power output by the APU; the output power of the APU flows in common to two parts, the firstPart of the required power flows to the motor, and the second part flows to the power battery; the second part flowing to the power battery generates a part of power loss due to the internal resistance of the power battery; wherein, I_bIs the charging and discharging current of the power battery, R_bIs the internal resistance of the power battery;

wherein, alpha is a weight coefficient in the objective function;

wherein, J_iRepresents from t₀To t₀And the sum of the charges charged and discharged by the power battery in the + T time.

Further, the

Can be represented by formula (3):

wherein, b_eThe fuel consumption rate of the engine in the APU under the torque Te and the rotating speed ne; eta_gIs the generator in the APU is at torque T_eRotational speed n_eEfficiency of the process.

Further, the I_bCan be represented by formula (4):

wherein E is_bIs the open circuit voltage of the power battery; r_bIs the internal resistance of the power battery; p_mThe effective power for supplying power to the power battery or the power provided by the outside during charging.

Further, the α may be optimized according to specific vehicle parameters; the higher the alpha setting, the more the preference is to reducing the average current, and prolonging the service life of the battery; the lower the alpha setting, the more preferred the APU is to operate in the high efficiency region.

Further, the J is_iCan be represented by integrating the formula (4), as shown in formula (5):

wherein, P_dRepresenting a prediction of future required power.

Further, the current time is set to t in the above equation (5)₀The current required power is

With said t₀Time forward T₁For recording the time domain, backward T₂Is a prediction time domain; predicting T using linear means₂The required power in time is formula (6):

further, the APU may also be in an OFF state.

Further, the APU is transitionable between an operating state and an off state; t is_onIs a single run duration, T, of the APU in run state_offIs a single run off duration in which the APU is in an off state.

Further, SOC_csmaxAnd SOC_csminAnd the upper limit and the lower limit of the normal operation of the APU in the CS stage.

Further, when the SOC is lower than the SOC_lowWhen the APU is started, the APU is started; when SOC < SOC_csminStarting the APU when SOC is more than SOC_csmaxTurning off the APU; when the SOC is at SOC_csminAnd SOC_csmaxAnd in between, the switch state of the APU is kept unchanged.

The invention provides a working condition prediction-based range-extending type electric automobile self-adaptive thermostat control method which has the following technical effects:

(1) the method has the working condition self-adaptive capacity:

in the control strategy of the invention, the APU working power point is not a fixed value any more, but a variable value which is solved according to a demand power prediction system and an optimization equation which takes the fuel consumption rate and the battery current of a power system as objective functions. When the vehicle working condition changes, the system modifies the APU working power point correspondingly.

(2) The service life of the power battery is prolonged:

the fuel economy and the charging and discharging current of the vehicle are comprehensively considered by the optimization equation taking the fuel consumption rate of the power system and the battery current as the objective function, and compared with the traditional thermostat control strategy, the battery current is not considered at all.

(3) Less noise, vibration:

factors such as low-speed APU closing, brake energy recovery closing, APU starting and stopping interval setting and the like are added into the control rule, and noise and vibration of the vehicle are reduced in a low-speed environment.

The conception, the specific structure and the technical effects of the present invention will be further described with reference to the accompanying drawings to fully understand the objects, the features and the effects of the present invention.

Drawings

FIG. 1 is a schematic diagram of the basic structure and energy flow of an extended range electric vehicle;

FIG. 2 is a schematic diagram of a CDCS policy;

fig. 3 is a flow chart of a control strategy in a charge sustaining phase;

fig. 4 is a diagram of predicted required power.

Detailed Description

The technical contents of the preferred embodiments of the present invention will be more clearly and easily understood by referring to the drawings attached to the specification. The present invention may be embodied in many different forms of embodiments and the scope of the invention is not limited to the embodiments set forth herein.

The strategy adopted by the invention is a rule-based APU power control strategy, and factors such as fuel consumption, noise, power battery service life and the like are comprehensively considered, so that the following control rules are established in the electric quantity maintaining stage:

(1) when the speed of the vehicle is less than V, the requirements of vibration and noise of the vehicle are met_lowWhen the APU is started, the APU is not started; however, there are some cases, such as a case where the vehicle is in a congested or low-speed running state for a long time, so that the vehicle speed is at V for a long time_lowThe following; in order to prevent the SOC from being too low due to the fact that the APU does not work for a long time, additional provisions are needed;

(2) when the SOC is lower than the SOC_lowWhen the data is read, the APU is started; SOC_lowIt can be appreciated that a relatively dangerous charge level, once the SOC falls below it, the APU must start unconditionally.

(3) In order to protect the engine and reduce the number of engine starts, the APU must have each on duration and off duration greater than T_limit；

(4) In a braking energy recovery state, in order to prevent the battery charging current from being overlarge, the APU is required to be closed, and the service life of the battery is protected;

(5) setting the electric quantity maintaining interval SOC < SOC_csminWhen the APU is started, SOC is more than SOC_csmaxThe APU is turned off, and the switch state of the APU is kept unchanged between the APU and the APU.

Fig. 3 is a control flow chart of the extended range electric vehicle in the electric quantity maintaining stage. SOC_lowA threshold value for the APU forced start; SOC_csmaxAnd SOC_csminIs the upper and lower limits of normal operation of the APU in the power maintenance mode. T is_onIs the duration of this operation of the APU, T_offIs the duration of the APU turning off this time; s_APUThe operating or off state of the APU. P_APUAPU output power given for system control strategy.

Under the control of a traditional thermostat, the generated power of the APU is calculated by predetermining the working condition (such as NEDC) of the extended range type electric automobile, combining the weight of the whole automobile, the wind resistance and the rolling optimization, and then the driving power requirement of the whole automobile is set according to the working condition. The self-adaptive thermostat strategy does not need to know the working condition in advance, but when the APU is in the running state, the comprehensive fuel consumption rate J of the power system is considered_zAnd battery current I_bDetermining an objective function, and solving the objective function to obtain the optimal working power of the APU;

the objective function is shown in equation (1):

min J＝J_z+αJ_i(1)

wherein, J_zCan be represented by formula (2):

the molecular moiety of formula (2) is represented by the formula₀To t₀Fuel consumption of the engine during + T time, where P_APUIs the output power of the APU and,

indicating that the output power of the APU is P_APUThe optimal fuel consumption rate of the APU is obtained;

the denominator part of equation (2) represents the active power output by the APU; the output power of the APU flows to two parts in common, the first part flows to the required power of the motor, and the second part flows to the power battery; the second part flowing to the power battery generates a part of power loss due to the internal resistance of the power battery; wherein, I_bIs the charging and discharging current of the power battery, R_bIs the internal resistance of the power battery;

wherein, alpha is a weight coefficient in the objective function;

Wherein the content of the first and second substances,can be represented by formula (3):

wherein, b_eFor engine in APU at torque T_eRotational speed n_eLower fuel consumption rate; eta_gIs the generator in the APU at torque T_eRotational speed n_eEfficiency of the process.

Wherein, I_bCan be represented by formula (4):

wherein E is_bIs the open circuit voltage of the power battery; r_bIs the internal resistance of the power battery; p_mAvailable power for supplying power to the power battery or externally supplied power during charging.

Wherein α can be optimized according to specific vehicle parameters; the higher the alpha setting, the more the preference is to reduce the average current, and the service life of the battery is prolonged; the lower the setting of α is, the more preferred the APU is to operate in the high efficiency region.

Wherein, J_iCan be expressed by integrating equation (4), as equation (5):

wherein, P_dRepresenting a prediction of future required power.

As shown in fig. 4, the current time is set to t in equation (5)₀The current required power is

With t₀Time forward T₁For recording the time domain, backward T₂Is a prediction time domain; predicting T using linear means₂The required power in time is formula (6):

therefore, the optimal output power P under the current working condition can be obtained by calculating the minimum value J in the formula (1)_APU。

Critical vehicle speed V for starting APU (auxiliary Power Unit) in invention_lowMinimum duration of APU startup and shutdown_on，T_offAnd the weight coefficient alpha in the objective function can be optimized according to specific vehicle parameters, so that the method has very good universality. Such as in daily use V_lowCan be set to 20km/h to avoid the APU starting belt in the low-speed stateThe noise problem of (2). T is_on，T_offMay be set to 20s to avoid the reduction in engine life caused by frequent starting and shutting down of the APU. The higher the setting of α, the more preferred is to reduce the average current and extend the battery life, and the lower the setting, the more preferred is to operate the APU in the high efficiency region.

Additionally, the APU may also be in an OFF state. The APU may transition between an on state and an off state.

The foregoing detailed description of the preferred embodiments of the invention has been presented. It should be understood that numerous modifications and variations could be devised by those skilled in the art in light of the present teachings without departing from the inventive concepts. Therefore, the technical solutions available to those skilled in the art through logic analysis, reasoning and limited experiments based on the prior art according to the concept of the present invention should be within the scope of protection defined by the claims.

Claims

1. A method for controlling a range-extended electric vehicle self-adaptive thermostat based on working condition prediction is characterized in that when an APU is in an operating state, the comprehensive fuel consumption rate J of a power system is considered_zAnd battery current I_bDetermining an objective function, and solving the objective function to obtain the optimal working power of the APU;

the objective function is as shown in equation (1):

minJ＝J_z+αJ_i(1)

wherein, J_zCan be represented by formula (2):

the molecular moiety of said formula (2) is represented by the formula₀To t₀Fuel consumption of the engine during + T time, where P_APUIs the output power of the APU and,represents the output power of the APU as P_APUWhen the fuel is optimal for the APUA consumption rate;

the denominator part of the equation (2) represents the active power output by the APU; the output power of the APU flows to two parts in common, the first part flows to the required power of the motor, and the second part flows to the power battery; the second part flowing to the power battery generates a part of power loss due to the internal resistance of the power battery; wherein, I_bIs the charging and discharging current of the power battery, R_bIs the internal resistance of the power battery;

wherein, alpha is a weight coefficient in the objective function;

2. The method of claim 1, wherein the method comprises controlling the adaptive thermostat of the extended-range electric vehicle based on the prediction of operating conditions

Can be represented by formula (3):

wherein, b_eAt torque T for the engine in the APU_eRotational speed n_eLower fuel consumption rate; eta_gIs the generator in the APU is at torque T_eRotational speed n_eEfficiency of the process.

3. The method of claim 1, wherein I is the operating condition prediction-based adaptive thermostat control method for the extended-range electric vehicle_bCan be represented by formula (4):

wherein E is_bIs the open circuit voltage of the power battery; r_bIs the power batteryInternal resistance of (d); p_mThe effective power for supplying power to the power battery or the power provided by the outside during charging.

4. The extended-range electric vehicle adaptive thermostat control method based on operating condition prediction as claimed in claim 1, wherein α can be optimized according to specific vehicle parameters; the higher the alpha setting, the more the preference is to reducing the average current, and prolonging the service life of the battery; the lower the alpha setting, the more preferred the APU is to operate in the high efficiency region.

5. The method of claim 1, wherein J is the adaptive thermostat control method for extended range electric vehicles based on operating condition prediction_iCan be represented by integrating the formula (4), as shown in formula (5):

wherein, P_dRepresenting a prediction of future required power.

6. The extended-range electric vehicle adaptive thermostat control method based on operating condition prediction according to claim 5, characterized in that the current time is set to t in the formula (5)₀The current required power is

7. the extended-range electric vehicle adaptive thermostat control method based on operating condition prediction as claimed in claim 1, wherein the APU may also be in an off state.

8. The extended-range electric vehicle adaptive thermostat control method based on operating condition prediction of claim 7, wherein the APU is switchable between an on state and an off state; t is_onIs a single run duration, T, of the APU in run state_offIs a single run off duration in which the APU is in an off state.

9. The extended-range electric vehicle adaptive thermostat control method based on operating condition prediction as claimed in claim 8, wherein SOC_csmaxAnd SOC_csminAnd the upper limit and the lower limit of the normal operation of the APU in the CS stage.

10. The extended-range electric vehicle adaptive thermostat control method based on operating condition prediction as claimed in claim 9, wherein when SOC is lower than SOC_lowWhen the APU is started, the APU is started; when SOC < SOC_csminStarting the APU when SOC is more than SOC_csmaxTurning off the APU; when the SOC is at SOC_csminAnd SOC_csmaxAnd in between, the switch state of the APU is kept unchanged.