CN1556417A - Judging method of electromobile car battery discharging termination bused on small wave transformation - Google Patents

Abstract

In the invention, using method of fixed final voltage and slope method of discharge curve synthetically carries out judgment of discharge off. Using method of fixed final voltage carried out prejudgment. When load voltage is lower then fixed final voltage, wavelet analysis module is started up. Using wavelet transform analyzes signal of load voltage on batteries to pick up catastrophe point of slope. When catastrophe point of slope occurs, discharge is stopped. The invention possesses strong adaptability. The method determines final state of discharge in self-adapting under different environment in use and different kinds of batteries. Moreover, the method overcomes influence of measuring noise.

Description

Decision method based on the battery of electric vehicle discharge off state of wavelet transformation

Technical field

Decision method based on the battery of electric vehicle discharge off state of wavelet transformation relates to electric automobile intelligent information processing technology field.

Background technology

Day by day strong along with human environmental consciousness, increasing people has thrown into sight on the electric vehicle of zero-emission in the automotive field.Battery is the key components of electric automobile as the main or auxiliary power source of electric automobile.How rationally to use battery, make full use of the energy in the electric battery, be the problem that institute must solution during electric automobile and hybrid vehicle further developed the serviceable life that prolongs battery.For the energy that makes full use of battery prevents arbitrary battery over-discharge in the electric battery again, must be in good time and accurately to the judgement of discharging ending status of battery.

At present the method for the judgement discharge off state that uses of electric automobile power battery mainly contains 3 kinds: fixedly final voltage method, discharge curve slope method and capacity accumulative.Though fixedly the final voltage method is simple, final discharging voltage difference under different discharge currents, the standard that neither one is unified, and the discharge current of actual power battery of electric vehicle is a random variation, does not have certain rule.If set unified final discharging voltage, for preventing battery overdischarge under any operating mode, this voltage must be tending towards conservative (higher), influences making full use of of the energy content of battery.When being the constant-current discharge test, discharge curve slope method uses maximum a kind of methods.From the battery discharge curve, can see in the battery discharge later stage, the slope catastrophe point (being called " flex point ") that obviously has a discharge curve (V～t curve), the capacity that battery can be emitted after this point seldom, and this discharge and use in future for battery is also very uneconomical, can be decided to be this flex point the terminating point of battery discharge.Generally flex point is decided to be its slope equals the point that 10 times of voltage-time curve plateau slopes are located now.Battery is when low discharging current, and the slope of the plateau that its voltage descends is very little, and slope is the obviously local and actual discharge off point wide apart of 10 times of plateaus in the discharge curve.And during heavy-current discharge, the slope of the plateau that its voltage descends is bigger, and slope is plateau 10 times place in the discharge curve, and voltage descends very fastly, has surpassed the stop value of actual discharge.It is very big that The noise is measured in the calculating of discharge curve slope simultaneously.The capacity accumulative promptly writes down the electric weight that battery charges into and emits, and when in a charge and discharge cycles, both equate, think that battery discharge stops.This method constantly writes down discharging and recharging the historical data of battery except that need, also will carry out corrections such as discharge current, cell degradation, self discharge to capacity, and the process complexity is generally seldom used.

Summary of the invention

At the deficiencies in the prior art part, the present invention proposes decision method based on the battery of electric vehicle discharge off state of wavelet transformation.The advantage of this method is to have very strong adaptivity, promptly can determine the discharge off state adaptively for different environments for use and this method of different types of battery; This method can overcome the measurement The noise effectively simultaneously.

The present invention fully utilizes fixedly final voltage method and discharge curve slope method and carries out discharge off and judge.At first utilize fixedly the final voltage method to judge in advance, when being lower than fixedly final voltage, load voltage starts the wavelet analysis module, utilize wavelet transformation that the load voltage signal of battery is analyzed, be used to extract slope catastrophe point, when the slope catastrophe point occurring, just stop discharge through level and smooth back voltage signal.

This method is characterised in that it contains the following steps by the control of the central processing unit in battery management system operation:

1) initialization: the fixedly final voltage threshold value V of given battery ₀

The threshold value WT of given load voltage signal extreme point behind wavelet transformation _Valve

2) obtain the load voltage signal V (t) of battery cell;

3) judge whether V (t) is lower than threshold value V ₀, as V (t)＜V ₀Shi Ze carries out wavelet transformation, otherwise continues step 2);

4) V (t) is carried out wavelet transformation by following formula:

$\mathrm{WTx}(a,t)=\frac{1}{{}_{}a}{\∫}_{R}x\left(t\right)\mathrm{\ψ}\left(\frac{t-\mathrm{\τ}}{a}\right)\mathrm{d\τ}$

Wherein R is a limit of integration, for beginning to carry out the initial moment of wavelet analysis to the zone between the current sampling instant;

Following formula is abbreviated as: WT _aX (t)=x (t) * ψ _a(t);

X (t)=V (t), a is a scale factor, a=2 ^j, j is a natural number, its scope is 2～5;

Wherein: ${\mathrm{\ψ}}_a\left(t\right)=\frac{1}{a}\frac{d{\mathrm{\θ}}_a\left(t\right)}{\mathrm{dt}}$

${\mathrm{\θ}}_a\left(t\right)=\frac{1}{a}\mathrm{\θ}\left(\frac{t}{a}\right)$

θ (t) is Gauss's lowpass function, $\mathrm{\θ}\left(t\right)=\frac{1}{\sqrt{2\mathrm{\π}}}\exp (-\frac{t^2}{2})$

5) obtain the extreme point WT of figure signal _Max:

${\mathrm{WT}}_{\max }=\underset{a,t}{\max }\left\{W{T}_{a}x\left(t\right)\right\}$

6) judge WT _MaxWhether surpass threshold value WT _Valve, WT _ValveScope be 0.2～0.4, work as WT _Max＞WT _ValveThe time then battery stop discharge, otherwise continue step 2).

Prove that by experiment method proposed by the invention has very strong adaptivity, can determine the discharge off state adaptively for different environments for use and this method of different types of battery; Simultaneously can overcome the measurement The noise effectively, reach its intended purposes.

Description of drawings

Fig. 1 is the FB(flow block) based on the decision method of the battery of electric vehicle discharge off state of wavelet transformation.

Sparking voltage signal V (t) when Fig. 2 is 80A for discharge current in the inventive embodiments.

The wavelet transformation result (yardstick a=8) of sparking voltage signal V (t) when Fig. 3 is 80A for discharge current in the inventive embodiments.

Fig. 4 is for realizing battery management system block diagram of the present invention.

Embodiment

Accompanying drawings the specific embodiment of the present invention.

Describe in conjunction with Fig. 1, wherein the load voltage signal V (t) of battery cell is the data acquisition module acquisition from battery management system.When utilizing that fixedly the final voltage method is judged in advance, threshold value V ₀Choose and can utilize the fixedly experiment of final voltage method (constant-current discharge experiment) conclusion to select the conservative value of a final voltage as V ₀For example for Ni-MH battery thresholding V ₀=1.1V is for lithium ion battery thresholding V ₀=2.9V.

When V (t) is lower than threshold value V ₀After, start small echo load voltage V (t) is analyzed.

The continuous wavelet transform of signal x (t) is defined as:

$\mathrm{WTx}(a,t)=\frac{1}{a}{\∫}_{R}x\left(t\right)\mathrm{\ψ}\left(\frac{t-\mathrm{\τ}}{a}\right)\mathrm{d\τ}----\left(1\right)$

X in this method (t) corresponds to load voltage signal V (t); The following formula brief note is WT _aX (t)=x (t) * ψ _a(t), wherein * is a convolution, and a is a scale factor, a=2 ^j, j is a natural number, j=2～5; ${\mathrm{\ψ}}_a\left(t\right)=\frac{1}{a}\mathrm{\ψ}\left(\frac{t}{a}\right)$ Be basic small echo ψ (t) stretching on yardstick.

Definition θ (t) is Gauss's lowpass function, and basic small echo ψ (t) elects the first order derivative of θ (t) as, order ${\mathrm{\θ}}_a\left(t\right)=\frac{1}{a}\mathrm{\θ}\left(\frac{t}{a}\right),$ Then

$\mathrm{\θ}\left(t\right)=\frac{1}{\sqrt{2\mathrm{\π}}}\exp (-\frac{t^2}{2})----\left(2\right)$

${\mathrm{\ψ}}_a\left(t\right)=\frac{1}{a}\frac{d{\mathrm{\θ}}_a\left(t\right)}{\mathrm{dt}}----\left(3\right)$

${\mathrm{WT}}_{a}x\left(t\right)=x\left(t\right)*\frac{1}{a}\frac{d{\mathrm{\θ}}_a\left(t\right)}{\mathrm{dt}}=a\frac{d}{\mathrm{dt}}[x\left(t\right)*{\mathrm{\θ}}_a\left(t\right)]----\left(4\right)$

By above-mentioned several formulas as seen, the wavelet transformation of x (t) is equivalent to and x (t) is carried out low-pass filtering, differentiate then, WT earlier _aThe extreme point of x (t) is corresponding to the flex point of level and smooth back signal, and according to discharge curve slope method, the corresponding battery of this flex point stops point of discharge.

${\mathrm{WT}}_{\max }=\underset{a,t}{\max }\left\{{\mathrm{WT}}_{a}x\left(t\right)\right\}----\left(5\right)$

Judge WT _MaxWhether surpass threshold value WT _Valve, WT _ValveScope be 0.2～0.4, work as WT _Max＞WT _ValveThe time then battery management system send warning message, the prompting driver operation makes battery stop discharge, otherwise continues the deterministic process of the load voltage that next time records.

Flow process according to Fig. 1 is carried out 1C discharge l-G simulation test to 80Ah Ni-MH battery monomer, puts an electric current and is the load voltage V (t) of 80A. Fig. 2 for beginning from discharge to gather to discharge off, and the final voltage threshold value is got conservative value V ₀The threshold value WT of=1.1V, load voltage signal extreme point behind wavelet transformation _Valve=0.3, wavelet transform dimension factor a=8 (j=3); Detailed process is: begin promptly in real time to gather the voltage signal V (t) of battery from discharge, whenever collect a voltage promptly with final voltage threshold value V ₀=1.1V compares, as V (t) 〉=V ₀Next collection constantly of Shi Jixu is as V (t)＜V ₀In time, then start the wavelet analysis module V (t) carried out wavelet analysis, and wavelet analysis carries out scale factor a=8 according to following three formulas.

$\mathrm{\θ}\left(t\right)=\frac{1}{\sqrt{2\mathrm{\π}}}\exp (-\frac{t^2}{2})----\left(6\right)$

${\mathrm{\ψ}}_a\left(t\right)=\frac{1}{a}\frac{d{\mathrm{\θ}}_a\left(t\right)}{\mathrm{dt}}----\left(7\right)$

${\mathrm{WT}}_{a}x\left(t\right)=x\left(t\right)*\frac{1}{a}\frac{d{\mathrm{\θ}}_a\left(t\right)}{\mathrm{dt}}=a\frac{d}{\mathrm{dt}}[x\left(t\right)*{\mathrm{\θ}}_a\left(t\right)]----\left(8\right)$

X in the formula (t) corresponds to load voltage signal V (t), asks for the extreme point of wavelet transformation under this yardstick then according to following formula,

${\mathrm{WT}}_{\max }=\underset{a,t}{\max }\left\{{\mathrm{WT}}_{a}x\left(t\right)\right\}----\left(9\right)$

Judge WT _MaxWhether surpass threshold value WT _Valve=0.3, work as WT _Max＞WT _ValveThe time then battery management system send warning message, the prompting driver operation makes battery stop discharge, otherwise continues next sampling and wavelet analysis constantly, up to the WT that satisfies condition _Max＞WT _ValveTill then discharge finish.Fig. 3 is the wavelet transformation result, WT when V (t)=1.0V _Max＞WT _Valve, discharge finishes, and emulation experiment of the present invention is carried out wavelet transformation with Matlab software, can realize with the C Programming with Pascal Language during practical application.Fig. 4 is for realizing battery management system block diagram of the present invention.For the present invention, data acquisition module in the battery management system is implemented the collection of load voltage signal V (t), CPU implements wavelet algorithm, discharging ending status of battery is calculated and judges, calculate and judge that required parameter is stored in the memory module, battery management system sends warning message by alarm module when reaching the discharge off state, and the prompting driver operation makes battery stop discharge.

The invention has the advantages that combining fixedly final voltage method and discharge curve slope method carries out discharge off and judge.Overcome that fixedly the final voltage method is more conservative, be unfavorable for giving full play to the shortcoming of battery performance, the analysis that utilizes wavelet transformation to discharge latter stage simultaneously, and discharge just, only judge with fixing final voltage method mid-term.So both made that this method had very strong adaptivity, promptly can determine the discharge off state adaptively for different environments for use and this method of different types of battery, also overcome the measurement The noise effectively, partly reduced the big inferior position of wavelet transformation operand again.The cycle of data processing is second that level gets final product in battery management system, so this invention can directly apply to existing battery management system and not need to improve the hardware index, and central processing unit generally adopts 16 single-chip microcomputers can realize (for example C167CR).

Claims (1)

1. Based on the decision method of the battery of electric vehicle discharge off state of wavelet transformation, it is characterized in that 1, it contains the following steps by the control of the central processing unit in battery management system operation:

   1) initialization: the fixedly final voltage threshold value V of given battery ₀The threshold value WT of given load voltage signal extreme point behind wavelet transformation _Valve

   2) obtain the load voltage signal V (t) of battery cell;

   3) judge whether V (t) is lower than threshold value V ₀, as V (t)＜V ₀Shi Ze carries out wavelet transformation, otherwise continues step 2);

   4) V (t) is carried out wavelet transformation by following formula:

   $\mathrm{WTx}(a,t)=\frac{1}{a}{\∫}_{R}x\left(t\right)\mathrm{\ψ}\left(\frac{t-\mathrm{\τ}}{a}\right)\mathrm{d\τ}$

   Wherein R is a limit of integration, for beginning to carry out the initial moment of wavelet analysis to the zone between the current sampling instant;

   Following formula is abbreviated as: WT _aX (t)=x (t) * ψ _a(t);

   X (t)=V (t), α is a scale factor, α=2 ^j, j is a natural number, its scope is 2～5;

   Wherein: ${\mathrm{\ψ}}_a\left(t\right)=\frac{1}{a}\frac{d{\mathrm{\θ}}_a\left(t\right)}{\mathrm{dt}}$

   ${\mathrm{\θ}}_a\left(t\right)=\frac{1}{a}\mathrm{\θ}\left(\frac{t}{a}\right)$

   θ (t) is Gauss's lowpass function, $\mathrm{\θ}\left(t\right)=\frac{1}{\sqrt{2\mathrm{\π}}}\exp (-\frac{t^2}{2})$

   5) obtain the extreme point WT of figure signal _Max:

   ${\mathrm{WT}}_{\max }=\underset{a,t}{\max }\left\{{\mathrm{WT}}_{a}x\left(t\right)\right\}$

   6) judge WT _MaxWhether surpass threshold value WT _Valve, WT _ValveScope be 0.2～0.4, work as WT _Max＞WT _ValveThe time then battery stop discharge, otherwise continue step 2).

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