CN115092012A - Equivalent state-of-charge estimation method considering multiple working modes of hybrid power supply system - Google Patents

Abstract

The present invention provides a method for estimating an equivalent state of charge considering multiple operating modes of a vehicle composite power supply system, which is specifically completed by a method based on a comprehensive weight factor. Including steps: S1. Obtain the maximum discharge capacity of the battery pack and the supercapacitor, as well as the output power of the battery pack and the supercapacitor; S2. Determine the working mode state of the vehicle according to the output power of the battery pack and the supercapacitor; S3. Calculate the battery The value of the state of charge SOC _bat of the group and the state of charge SOC _uc of the supercapacitor in the equivalent state of charge ESOC weighting factors λ _bat and λ _uc in the working mode state; S4. Calculate the equivalent state of charge ESOC , where: ESOC=λ _bat SOC _bat +λ _uc SOC _uc . The process of the method is simple, the algorithm is not complicated, and it is easy to be embedded in the vehicle composite power management system to realize the equivalent state of charge estimation of the vehicle composite power system in different working modes, and at the same time, it can provide accurate prediction of the driving distance of electric vehicles. Data support, thereby having many beneficial effects that are not available in the prior art.

Description

An Equivalent State of Charge Estimation Method Considering Multiple Operating Modes of a Composite Power System

technical field

The invention relates to the technical field of vehicle composite power supply system management, in particular to an equivalent state-of-charge estimation method considering multiple operating modes of a composite power supply and a system.

Background technique

The composite power system composed of lithium-ion batteries and supercapacitors can meet the dual requirements of electric vehicles for high specific energy and high specific power, and has become one of the important development directions of the automotive industry. In the prior art, the state of charge (State of Charge, SOC) estimation method for a single energy storage system, especially a power battery/supercapacitor, is relatively mature. However, the technology to estimate the equivalent state of charge (ESOC) of the composite power system as a whole is still lacking. ESOC is also an important parameter. This value can provide data support for the accurate prediction of the driving distance of electric vehicles. At the same time, drivers can reasonably arrange travel according to the value of this value. If the ESOC estimation is inaccurate, it may cause the vehicle to break down on the road due to insufficient energy supply, and may even cause a traffic accident.

At the same time, in the face of complex vehicle operating conditions, each energy storage element in the composite power system needs to be turned on or off according to different optimization goals, and the composite power system will also be in different working modes to give full play to the battery and super power. The advantages of capacitors meet the power requirements of the system. However, the flexible working mode of the composite power system makes it difficult for the existing battery/supercapacitor state-of-charge estimation techniques to reflect the remaining energy and power output capability of the composite power system as a whole in the current working mode.

SUMMARY OF THE INVENTION

In view of this, the present invention provides an equivalent state-of-charge estimation method considering multiple operating modes of a composite power system. The method has a simple process and an uncomplicated algorithm, and is easy to embed into a vehicle composite power management system to realize a composite power system. Equivalent state-of-charge estimation in different working modes can provide data support for accurate prediction of the driving distance of electric vehicles, which has many beneficial effects that are not available in the prior art, and is suitable for the composition of battery packs and super capacitors of composite power vehicles. The method includes the steps:

S1. Obtain the maximum discharge capacity of the battery pack and supercapacitor, as well as the output power of the battery pack and supercapacitor;

S2. Determine the working mode state of the vehicle according to the output power of the battery pack and the super capacitor;

S3. Calculate the value of the state of charge SOC _bat of the battery pack and the state of charge SOC _uc of the supercapacitor in the equivalent state of charge ESOC weighting factors λ _bat and λ _uc in the working mode state;

S4. Calculate the equivalent state of charge ESOC, where:

ESOC=λ _bat SOC _bat +λ _uc SOC _uc .

Further, the step S2 specifically includes:

S21. Define symbolic functions m ₁ , m ₂ , m ₃ and m ₄ , specifically:

Among them, P _ave and P _batmax represent the average output power and maximum output power of the battery pack, respectively; P _bat and P _uc represent the output power of the battery pack and super capacitor pack, respectively;

S22. According to the sign function, determine the current working mode state of the composite power supply system, specifically:

If m ₁ =1, m ₂ =0, m ₃ ≤ 0 and m ₄ <0, it is in working mode 1;

If 0<m ₁ <1, 0<m ₂ <1, m ₃ =0 and m ₄ <0, it is in working mode 2;

If 0<m ₁ <1, 0<m ₂ <1, m ₃ >0 and m ₄ =0, it is in working mode 3;

If m ₁ ≤ 0, m ₂ ≤ 0, m ₃ <0 and m ₄ <0, it is in working mode 4;

Others are in working mode 5.

Further, the step S3 specifically includes:

If the working state of the vehicle composite power system is in mode 1, then:

In the formula, λ _bat1 and λ _uc1 respectively represent the weights of SOC _bat and super SOC _uc when the composite power system is in working mode 1;

If the working state of the vehicle composite power system is in mode 2, then:

In the formula, λ _bat2 and λ _uc2 respectively represent the weight of SOC _bat and SOC _uc when the composite power system is in working mode 2; C _C is the ratio of the maximum available capacity of the battery pack to the maximum available total capacity of the composite power system; i represents the vehicle Driving condition, i=1 indicates driving condition 1; _ni is the capacity change probability function under driving condition i.

If the working state of the vehicle composite power system is in mode 3, the calculation method is the same as that in mode 2;

If the working state of the vehicle composite power system is in mode 4, then:

In the formula, λ _bat4 and λ _uc4 represent the weights of SOC _bat and SOC _uc when the composite power system is in working mode 4, respectively; C _bat and C _uc represent the maximum usable capacity of the battery pack and supercapacitor pack, respectively;

If the working state of the vehicle composite power system is in mode 5, the calculation method is the same as that in mode 4.

Further, when the working state of the vehicle composite power system is in mode 2, the ratio C _C of the maximum available capacity of the battery pack to the maximum available total capacity of the composite power system, and the calculation of the capacity change probability function n _i under the driving condition i The method is:

t ₂ =t ₂₁ +t ₂₂ +...+t _2i , i=1, 2, 3, 4,....

Among them, C _bat and C _uc represent the maximum usable capacity of the battery pack and supercapacitor pack, respectively; t _2i , C _a2i and C _b2i respectively represent the duration of the composite power system in mode 2 under driving condition i, and the battery pack The capacity change rate of , and the capacity change rate of the supercapacitor group; t ₂ is the total duration of all operating conditions in mode 2.

Description of drawings

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

Fig. 1 is a flowchart of an equivalent state-of-charge estimation method considering multiple operating modes of a composite power system;

Figure 2 is the equivalent circuit model of the established vehicle composite power system;

Figure 3 shows the specific working mode of the vehicle composite power system and its operating state transition path;

Fig. 4 is a simulation verification effect diagram of the ESOC index of the equivalent state of charge of the composite power system in different working modes when the vehicle is in a comprehensive driving condition.

Detailed ways

The present invention provides an equivalent state-of-charge estimation method considering multiple operating modes of a composite power system, which is suitable for a composite power vehicle composed of a battery pack and a super capacitor, comprising the steps of:

S1. Obtain the maximum discharge capacity of the battery pack and supercapacitor, as well as the output power of the battery pack and supercapacitor;

S2. Determine the working mode state of the vehicle according to the output power of the battery pack and the super capacitor;

S3. Calculate the value of the state of charge SOC _bat of the battery pack and the state of charge SOC _uc of the supercapacitor in the equivalent state of charge ESOC weighting factors λ _bat and λ _uc in the working mode state;

S4. Calculate the equivalent state of charge ESOC, where:

ESOC=λ _bat SOC _bat +λ _uc SOC _uc .

In this embodiment, an equivalent circuit model of the vehicle composite power supply system is established. As shown in FIG. 2 , the equivalent circuit consists of a voltage source U _oc , an ohmic internal resistance R ₀ , and a parallel polarization resistance R _b and The polarized capacitors C _b are formed in series in sequence, and the specific performance is as follows:

In the formula, i ₀ represents the charging and discharging current; U _oc , U _b and U _t represent the open-circuit voltage, polarization voltage and output voltage, respectively;

In this embodiment, the transmission model of the vehicle is established, and its specific expression is as follows:

In the formula, _Preq represents the required power of the vehicle _; va represents the driving speed of the vehicle, the unit of which is km/h; _α represents the slope of the road surface of the vehicle; Drivetrain efficiency, full-load mass, rolling resistance coefficient, air resistance coefficient, windward area, and rotating mass correction coefficient; g stands for gravitational acceleration.

In this embodiment, the step S2 specifically includes:

S21. Define symbolic functions m ₁ , m ₂ , m ₃ and m ₄ , specifically:

Among them, P _ave and P _batmax represent the average output power and maximum output power of the battery pack, respectively; P _bat and P _uc represent the output power of the battery pack and super capacitor pack, respectively;

S22. According to the sign function, determine the current working mode state of the composite power supply system, specifically:

If m ₁ =1, m ₂ =0, m ₃ ≤ 0 and m ₄ <0, it is in working mode 1;

If 0<m ₁ <1, 0<m ₂ <1, m ₃ =0 and m ₄ <0, it is in working mode 2;

If 0<m ₁ <1, 0<m ₂ <1, m ₃ >0 and m ₄ =0, it is in working mode 3;

If m ₁ ≤ 0, m ₂ ≤ 0, m ₃ <0 and m ₄ <0, it is in working mode 4;

Others are in working mode 5.

In this embodiment, the specific working mode and its operating state transition path are shown in Figure 3. The mode 1 refers to: 0<P _req ≤P _ave . At this time, P _req is small, and the battery pack can independently and continuously satisfy the driving motor Power and energy requirements, ie P _bat =P _req , P _uc =0;

The mode 2 refers to: 0<P _ave <P _{req ≤P batmax} , and P _req is divided into two parts, wherein the battery pack continuously outputs P _ave , and the super capacitor pack outputs the remaining power, that is, P _bat =P _ave , P _uc =P _req -P _bat ;

The mode 3 refers to: 0<P _batmax <P _req , the battery pack outputs P _batmax , and the excess part is borne by the supercapacitor pack, that is, P _bat =P _batmax , P _uc =P _req -P _bat ;

The mode 4 refers to: P _req <0; in this case, the feedback power generated by vehicle braking is preferentially absorbed by the supercapacitor until the SOC _uc reaches its upper limit value, and then the battery pack is charged according to its peak charging power. Recycling residual energy;

The mode 5 refers to: _Preq = 0; in this mode, the vehicle is in a standby state, at this time, neither the battery pack nor the super capacitor pack outputs/recovers any power and energy to the drive motor, that is, P _bat =0, P _uc = 0;

In this embodiment, the step S3 specifically includes:

If the working state of the vehicle composite power system is in mode 1, then:

In the formula, λ _bat1 and λ _uc1 respectively represent the weights of SOC _bat and super SOC _uc when the composite power system is in working mode 1;

If the working state of the vehicle composite power system is in mode 2, then:

In the formula, λ _bat2 and λ _uc2 respectively represent the weight of SOC _bat and SOC _uc when the composite power system is in working mode 2; C _C is the ratio of the maximum available capacity of the battery pack to the maximum available total capacity of the composite power system; i represents the vehicle Driving condition, i=1 indicates driving condition 1; _ni is the capacity change probability function under driving condition i.

If the working state of the vehicle composite power system is in mode 3, at this time, _Preq is also shared by the battery pack and the supercapacitor pack. Therefore, the calculation method is the same as that of mode 2;

If the working state of the vehicle composite power system is in mode 4, then:

In the formula, λ _bat4 and λ _uc4 represent the weights of SOC _bat and SOC _uc when the composite power system is in working mode 4, respectively; C _bat and C _uc represent the maximum usable capacity of the battery pack and supercapacitor pack, respectively;

If the working state of the vehicle composite power supply system is in mode 5, at this time, the vehicle is in a standby state, and the calculation method is the same as that in mode 4.

In this embodiment, when the working state of the vehicle composite power system is in mode 2, the ratio C _C of the maximum available capacity of the battery pack to the maximum available total capacity of the composite power system, and the capacity change probability function n under driving condition i The calculation method of _i is:

t ₂ =t ₂₁ +t ₂₂ +...+t _2i , i=1, 2, 3, 4,....

Among them, C _bat and C _uc represent the maximum usable capacity of the battery pack and supercapacitor pack, respectively; t _2i , C _a2i and C _b2i respectively represent the duration of the composite power system in mode 2 under driving condition i, and the battery pack The capacity change rate of , and the capacity change rate of the supercapacitor group; t ₂ is the total duration of all operating conditions in mode 2.

In this embodiment, the duration t _2i of the composite power system in mode 2 of the vehicle under different driving conditions, as well as the capacity change rate C a2i of the battery pack and the capacity change rate C _b2i of the super capacitor _pack are obtained through simulation Obtained by software; in this embodiment, three different typical vehicle driving conditions are selected: UDDS (urban operating conditions), WVUSUB (suburban operating conditions), and HWFET (high-speed operating conditions).

In this embodiment, in the step S4, the ampere-hour integration method is adopted as the estimation method of SOC _bat and SOC _uc , and the calculation formula is as follows:

In the formula, SOC ₀ is the initial nuclear power state of the battery pack/supercapacitor pack; _Cn is the maximum available capacity of the battery pack/ _{supercapacitor} pack; it is the current value of the battery pack/supercapacitor pack at the current moment.

In this embodiment, the simulated operation data of the composite power system in different working modes when the _vehicle is in a comprehensive driving condition is shown in Figure 4; Moreover, when only the battery pack outputs power, the vehicle composite power system is in working mode 1, the equivalent state of charge ESOC and the battery pack state of charge SOC _bat curve show a downward trend, and the super capacitor state of charge SOC _uc does not change; demand; When the power is provided by the battery pack and the supercapacitor pack together, and the complex power supply system is in the mode 2 or mode 3 state, the battery pack state of charge SOC _bat , the super capacitor state of charge SOC _uc and the equivalent state of charge ESOC curve are all in the same state. It shows a downward trend; when the demand power is negative, the composite power system is in mode 4, the super capacitor group recovers the braking energy, the super capacitor state of charge SOC _uc curve rises rapidly, and the equivalent state of charge ESOC increases slowly, because the super capacitor group The working principle is to assist the battery pack to complete the power requirements of the load. Therefore, the ESOC index of the equivalent state of charge obtained by the method provided by the present invention can reflect the change of the actual available capacity caused by the switching of different working modes of the composite power system as a whole, and at the same time, the driving distance of the electric vehicle can be predicted. The stable operation of the power system is very meaningful.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be Modifications or equivalent substitutions without departing from the spirit and scope of the technical solutions of the present invention should be included in the scope of the claims of the present invention.

Claims (4)

1. An equivalent state-of-charge estimation method considering multiple working modes of a hybrid power system is suitable for a hybrid power vehicle consisting of a battery pack and a super capacitor, and is characterized in that: the method comprises the following steps:

s1, acquiring the maximum discharge capacity of a battery pack and a super capacitor and the output power of the battery pack and the super capacitor;

s2, determining the working mode state of the vehicle according to the output power of the battery pack and the output power of the super capacitor;

s3, calculating the state of charge (SOC) of the battery pack _bat And state of charge SOC of super capacitor _uc At equivalent state of charge ESOC weight factor λ _bat And λ _uc Taking values in the working mode state;

s4, calculating an equivalent state of charge (ESOC), wherein:

ESOC＝λ _bat SOC _bat +λ _uc SOC _uc 。

2. the method of claim 1, wherein the method comprises: the step S2 specifically includes:

s21, defining a symbolic function m ₁ 、m ₂ 、m ₃ And m ₄ The method specifically comprises the following steps:

wherein, P _ave And P _batmax Respectively representing the average output power and the maximum output power of the battery pack; p _bat And P _uc Respectively representing the output power of the battery pack and the output power of the super capacitor pack;

s22, judging the current working mode state of the composite power supply system according to the sign function, specifically:

if m is ₁ ＝1、m ₂ ＝0、m ₃ M is less than or equal to 0 ₄ If the number is less than 0, the working mode is 1;

if 0 < m ₁ ＜1、0＜m ₂ ＜1、m ₃ 0 and m ₄ If the value is less than 0, the working mode is 2;

if 0 < m ₁ ＜1、0＜m ₂ ＜1、m ₃ > 0 and m ₄ If 0, the working mode is 3;

if m is ₁ ≤0、m ₂ ≤0、m ₃ < 0 and m ₄ If the value is less than 0, the working mode is 4;

otherwise, it is in the operation mode 5.

3. The method of claim 1, wherein the method comprises: the step S3 specifically includes:

if the working state of the vehicle hybrid power supply system is in the mode 1, the following steps:

in the formula, λ _bat1 And λ _uc1 Respectively represents the SOC when the hybrid power system is in the working mode 1 _bat And super SOC _uc The size of the weight of (c);

if the working state of the vehicle hybrid power supply system is in the mode 2, the following steps are carried out:

in the formula, λ _bat2 And λ _uc2 Respectively represents the SOC when the hybrid power system is in the working mode 2 _bat And SOC _uc The size of the weight of (c); c _C The ratio of the maximum available capacity of the battery pack to the maximum available total capacity of the hybrid power system is obtained; i represents a vehicle driving condition, and i-1 represents a driving condition 1; n is _i Is a capacity change probability function under the driving condition i.

If the working state of the vehicle composite power supply system is in the mode 3, the calculation method is the same as that in the mode 2;

if the working state of the vehicle hybrid power supply system is in the mode 4, the following steps:

in the formula, λ _bat4 And λ _uc4 Respectively represents the SOC when the hybrid power system is in the working mode 4 _bat And SOC _uc The size of the weight of (c); c _bat And C _uc Respectively representing the maximum available capacity of the battery pack and the super capacitor pack;

if the operating state of the hybrid power supply system of the vehicle is in the mode 5, the calculation method is the same as that in the mode 4.

4. The method of claim 3, wherein the method comprises: when the working state of the vehicle composite power supply system is in the mode 2, the ratio C of the maximum available capacity of the battery pack to the maximum available total capacity of the composite power supply system _C And a capacity change probability function n under the driving condition i _i The calculating method comprises the following steps:

t ₂ ＝t ₂₁ +t ₂₂ +...+t _2i ,i＝1,2,3,4,....

wherein, C _bat And C _uc Respectively representing the maximum available capacity of the battery pack and the super capacitor pack; t is t _2i 、C _a2i And C _b2i Respectively representing the duration of the composite power supply system in the mode 2, the capacity change rate of the battery pack and the capacity change rate of the super capacitor pack under the driving working condition i; t is t ₂ The total duration that all operating conditions last in mode 2.

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