CN104795857A - Lithium ion battery energy balance system and implementation method thereof - Google Patents

Abstract

The invention discloses a lithium-ion battery energy balance system and its realization method. The system comprises: a lithium-ion battery pack, n voltage detection circuits, n DCDC converters, n main control chips, data processing chips, CAN communication Module and current detection circuit, the lithium-ion battery pack is composed of n lithium-ion battery cells in series, the input terminal of the kth voltage detection circuit is connected to the positive and negative electrodes of the k-th lithium-ion battery cell, and voltage detection is performed when necessary Sampling starts at the beginning of time, and the sampled value is transmitted to the kth group of main control chips after isolation. Each DCDC converter controls the switch of the MOS tube to directly charge and discharge each lithium-ion battery cell in the lithium-ion battery pack, and at the same time By adjusting the balance current through the switching frequency, the invention uses the second-order RC model to simulate the lithium-ion battery chemical model, and uses the SOC generated by linear regression as the judgment basis for the balance of the lithium-ion battery to achieve the purpose of balance.

Description

Lithium-ion battery energy balance system and its realization method

technical field

The invention relates to a lithium-ion battery energy balance system and its implementation method, in particular to a battery SoC-based lithium-ion battery energy balance system and its implementation method.

Background technique

The key to the development of pure electric vehicles is the battery. In recent years, lithium battery technology has made great progress. Lithium iron phosphate, lithium manganese oxide, lithium cobalt oxide and other batteries have significantly improved the performance of lithium batteries; but the inconsistency between single cells in lithium battery packs is naturally widespread. The parameters of lithium batteries inevitably produce some slight differences in the mass production process, mainly manifested in inconsistencies in the internal resistance, capacity, and open circuit voltage of lithium batteries. With the increasing use of lithium batteries, long-term self-discharge and the influence of large temperature differences in automobiles, these differences will become larger and larger, so that the performance differences between lithium battery packs will become larger and larger. Both overcharging and overdischarging will cause irreversible damage to the battery. At the same time, since the capacity of the series battery pack is determined by the capacity of the lowest single battery in the pack, once a battery in the battery pack is deeply discharged or overcharged, The entire battery pack must stop the original charging and discharging state, otherwise the battery life will be severely reduced, and even cause a major safety hazard. The most extreme situation is that some of the single cells of the lithium battery pack have been fully charged, and some of the single cells have been discharged. At this time, the entire battery pack can neither be charged nor discharged.

The balance function of the lithium-ion battery balance management system mainly solves the inconsistency in the lithium battery pack and reduces the difference between batteries, which is of great significance for extending battery life and reducing costs, and can also increase the discharge capacity. At present, the equalization methods are mainly active equalization and passive equalization, and the equalization judgment criteria are divided into voltage equalization and SOC equalization. Fundamentally speaking, battery equalization is the balance of power stored among the individual cells in the battery pack. The voltage value is only an external characteristic of the battery and cannot reflect the battery SOC. Therefore, the equalization method based on voltage as a discrimination cannot be very effective. Therefore, how to obtain the SOC of lithium-ion batteries has become a key part of the balance system, and it is also an important problem in the world. How to control the equalization circuit is also a relatively complicated problem. Due to the highly nonlinear characteristics of lithium-ion batteries, there is no more accurate mathematical model. Therefore, it is difficult to determine the control strategy, such as the factors of input and output, how to effectively control them, etc.

Contents of the invention

In order to overcome the deficiencies in the above-mentioned prior art, the object of the present invention is to provide a lithium-ion battery energy balance system and its implementation method, through the estimation of the SOC of the lithium-ion battery in the process of energy balance transfer, based on this SOC By controlling DCDC to achieve equalization, the system avoids false equalization caused by voltage equalization, and has higher reliability.

In order to achieve the above and other purposes, the present invention proposes a lithium-ion battery energy balance system, including:

Lithium-ion battery pack, the lithium-ion battery pack is composed of n lithium-ion battery cells connected in series, and each lithium-ion battery cell is connected to a voltage detection circuit and a DCDC converter;

n voltage detection circuits, the input terminals of the kth voltage detection circuit are respectively connected to the positive pole and negative pole of the kth lithium-ion battery cell, and sampling is started when voltage detection is required, and the sampled value is transmitted to the kth after isolation K group of main control chips;

n DCDC converters, each DCDC converter directly charges and discharges each lithium-ion battery cell in the lithium-ion battery pack by controlling the switch of the MOS tube, and at the same time adjusts the balance current through the switching frequency;

n main control chips, each main control chip reads the voltage information of the lithium ion battery in the voltage detection circuit corresponding to each lithium ion battery cell, and then transmits the data to the data processing chip 60 through the CAN bus;

The data processing chip calculates the SOC of each lithium-ion battery cell through linear regression, and at the same time decides whether to balance the lithium-ion battery pack according to the fuzzy control algorithm. The data processing chip 60 sends the balanced signal to each main control unit through the CAN communication module Chip, each main control chip sends the balance enable control signal to each lithium-ion battery cell for balance control;

A CAN communication module is responsible for realizing the communication between the main control chip and the data processing chip;

The current detection circuit is connected to the lithium-ion battery pack and the data processing chip, and is used to detect the balanced current of the battery pack to turn on or off the primary and secondary switch tubes.

Further, the DCDC converter adopts a bidirectional synchronous flyback DCDC converter, each DCDC converter is independent of other DCDCs, one end of each DCDC converter is connected to a lithium-ion battery cell, and the other end is connected to a lithium-ion battery pack .

Further, the kth bidirectional synchronous flyback DCD converter includes a high-frequency transformer (Tk), a primary switch (Qkp), a secondary switch (Qks), and the source of the primary switch (Qkp) is connected to the lithium-ion The negative pole of the battery cell (Cellk), the drain of the primary switch tube (Qkp) is connected to one end of the primary of the high-frequency transformer (Tk), and the other end of the primary of the high-frequency transformer (Tk) is connected to the lithium-ion battery cell ( Cellk), the source of the secondary switching tube (Qks) is connected to the negative pole of the lithium-ion battery pack, and the drain of the secondary switching tube (Qks) is connected to the secondary end of the high-frequency transformer (Tk), high The other end of the secondary of the frequency transformer (Tk) is connected to the positive terminal of the Li-ion battery pack.

In order to achieve the above object, the present invention also provides a method for realizing energy balance of lithium-ion batteries, comprising the following steps:

Step 1, collecting information on the voltage and current of each battery in the lithium-ion battery pack multiple times;

Step 2, input the voltage and current information of each battery and the nonlinear curve relationship information of battery capacity, service life, open circuit voltage and SOC into the data processing chip;

Step 3: discretize the battery voltage signal measured multiple times according to the second-order RC model of the battery, and process the data through linear regression to obtain useful matrix information, and calculate the lithium-ion battery voltage through the matrix. Corresponding open circuit voltage;

Step 4, according to the calculated open circuit voltage of the battery, interpolate the SOC of the lithium ion battery through the open circuit voltage of the lithium ion battery and the SOC relationship curve, and calculate the average SOC of the battery pack;

Step 5, according to the method of fuzzy control, the calculated SOC of the lithium-ion battery is used to determine the equalization current and equalization time required by the battery;

Step 6, control the bidirectional flyback DCDC converter, by detecting that the current on the DCDC reaches a certain peak value, control the switching MOS tube of the bidirectional flyback DCDC to realize the on-off of the current in the lithium-ion battery pack, thereby realizing the lithium-ion battery energy transfer.

Further, after step four, the following steps are also included:

Calculating cell dispersion for Li-ion battery packs;

judging whether the degree of dispersion of the battery is greater than a predetermined threshold;

If the degree of dispersion of the battery is less than the predetermined threshold, then enter step one and continue to start from detecting the voltage of the lithium-ion battery; if the degree of dispersion of the lithium-ion battery is greater than the predetermined threshold, then enter step five.

Further, in step 1, the battery voltage and current information of the lithium-ion battery is extracted more frequently, and the interval time of the voltage and current information is shorter.

Further, step three includes the following steps: .

According to the voltage and current information measured multiple times, the SOC is estimated by discretizing the second-order RC model of the lithium-ion battery;

Model the lithium-ion battery, take the current passing through the model as the excitation I, and the difference between the terminal voltage and the open-circuit voltage of the lithium-ion battery as the response, and obtain the transfer function of the model;

When the sampling frequency is very high, the transfer function is discretized with bilinear transformation method to obtain the difference equation, and the difference is converted into the value of terminal voltage and open circuit voltage at the same time.

Further, in step 4, according to the information matrix calculated in step 3, through the open circuit voltage value of the lithium-ion battery, according to the relationship between the open circuit voltage and the SOC curve stored in step 2, through the graph, and using the calculated open circuit voltage value , interpolation to obtain the SOC of the lithium-ion battery at this time.

Further, in step five, the bidirectional flyback DCDC converter is controlled, one end is connected to a lithium-ion battery cell, and the other end is connected to a lithium-ion battery pack formed by lithium ions connected by multiple lithium-ion batteries, through the MOS The switching of the tube realizes the energy transfer of the lithium-ion battery, and the current transferred by the lithium-ion battery is measured through the precision resistance on the coil, and the current control for the energy transfer of the lithium-ion battery is realized. At the same time, the energy of the lithium-ion battery is realized through time control. The length of the transfer time realizes the control of the current size and time of the lithium-ion battery through the switching frequency and the length of time.

Further, the time for controlling the energy transfer of the lithium-ion battery is determined by a fuzzy controller, which is a single-variable two-dimensional fuzzy controller.

Compared with the prior art, the present invention provides a lithium-ion battery energy balance system and its implementation method. In the process of energy balance transfer, the SOC of the lithium-ion battery is estimated, and the SOC is used as a basis to achieve balance by controlling DCDC, so that The system avoids the false balance caused by the voltage balance method, and has higher reliability.

Description of drawings

Fig. 1 is the system structural diagram of a kind of lithium-ion battery energy balance system of the present invention;

Fig. 2 is a schematic structural view of a bidirectional synchronous flyback DCDC converter in a preferred embodiment of the present invention;

Fig. 3 is a flow chart of steps of a method for realizing energy balance of a lithium-ion battery in the present invention;

Fig. 4 is the discretization schematic diagram to the second-order RC model of lithium-ion battery in the preferred embodiment of the present invention;

Fig. 5 is the graph that the SOC of calculating lithium-ion battery utilizes in the preferred embodiment of the present invention;

Fig. 6 is a schematic diagram of the triangular membership function selected by the fuzzy controller in a preferred embodiment of the present invention;

FIG. 7 is a flow chart of a specific embodiment of a method for realizing energy balance of a lithium-ion battery according to the present invention.

Detailed ways

The implementation of the present invention is described below through specific examples and in conjunction with the accompanying drawings, and those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific examples, and various modifications and changes can be made to the details in this specification based on different viewpoints and applications without departing from the spirit of the present invention.

Fig. 1 is a system structure diagram of a lithium-ion battery energy equalization system according to the present invention. As shown in FIG. 1 , a lithium-ion battery energy balance system of the present invention includes: a lithium-ion battery pack 10, n voltage detection circuits 20, n DCDC converters 30, n main control chips 40, and a current detection circuit 50 , data processing chip 60 and CAN communication module

The lithium-ion battery pack 10 is composed of n lithium-ion battery cells (Cell1, Cell2, ... Celln) connected in series, each lithium-ion battery cell is connected to a voltage detection circuit 20, and the voltage detection circuit 20 is used to collect lithium-ion battery cells The voltage of each lithium-ion battery cell in the battery cell, and the sampled value is sent to each main control chip 40, that is, the input terminal of the kth voltage detection circuit 20 is respectively connected to the positive pole and the negative pole of the k-th lithium-ion battery cell, and Sampling starts when voltage detection is required, and the sampled value is transmitted to the kth group of main control chips after isolation; each lithium-ion battery cell is also connected to a DCDC converter 30, and each DCDC converter 30 controls the MOS tube The switch can directly charge and discharge each lithium-ion battery cell in the lithium-ion battery pack, and at the same time adjust the balance current through the switching frequency. Each DCDC converter is independent of other DCDCs. One end of each DCDC converter is connected to the lithium-ion battery. An ion battery cell, and the other end is connected to a lithium-ion battery pack.

In a preferred embodiment of the present invention, the DCDC converter 30 adopts a bidirectional synchronous flyback DCDC converter. FIG. 2 is a schematic structural diagram of a bidirectional synchronous flyback DCDC converter in a preferred embodiment of the present invention. Specifically, the k-th bidirectional synchronous flyback DCDC includes a high-frequency transformer Tk, a primary switching tube Qkp, and a secondary switching tube Qks. The source of the primary switching tube Qkp is connected to the negative pole of the lithium-ion battery cell Cellk, and the primary switch The drain of the tube Qkp is connected to one end of the primary of the high-frequency transformer Tk, the other end of the primary of the high-frequency transformer Tk is connected to the positive pole of the lithium-ion battery cell Cellk, and the source of the secondary switching tube Qks is connected to the lithium-ion battery pack The negative pole of the secondary switching tube Qks is connected to one end of the secondary side of the high-frequency transformer Tk, and the other end of the secondary side of the high-frequency transformer Tk is connected to the positive pole of the lithium-ion battery pack.

Taking the discharge of the first lithium-ion battery as an example, when the primary switch is turned on, the current (the current passing through the winding is calculated by measuring the voltage on the winding) ramps up in the DCDC primary winding until the current is twice the average current until the time. The primary switch is then turned off and the energy stored in the DCDC is transferred to the secondary winding causing current to flow in the secondary winding of the DCDC. Turning on the secondary switch transfers the energy stored in the secondary winding in the DCDC to the Li-ion battery pack until the current through the winding drops to 0A. Once the secondary current is zero, the secondary switch is turned off and the primary switch is turned back on, repeating the cycle just described. Repeating the cycle, energy will be transferred from the Li-ion battery cells to all the Li-ion battery packs connected between the top and bottom of the secondary winding, thereby charging the Li-ion battery packs.

The main control chip 40 reads the voltage information of the lithium-ion battery in the voltage detection chip corresponding to each lithium-ion battery cell, and then transmits the data to the data processing chip 60 through the CAN bus, and the data processing chip 60 calculates the voltage information of each lithium-ion battery through a linear regression method. The SOC (State of Charge, state of charge) of the lithium-ion battery cell, and at the same time decide whether to balance the lithium-ion battery pack according to the fuzzy control algorithm, and the data processing chip 60 will communicate whether and how to balance the signal through CAN communication The module 70 is sent to each main control chip 40, and each main control chip 40 sends an equalization enable control signal to each lithium-ion battery cell for equalization control, thereby charging and balancing the lithium-ion battery cell with a lower SOC, and adjusting the SOC Higher lithium-ion battery cells carry out discharge equalization; the CAN communication module is mainly responsible for realizing the communication between the main control chip 40 and the data processing chip 60; the current detection circuit 50 is connected to the lithium-ion battery pack 10 and the data processing chip 60 for detecting battery The equalizing current of the group turns on or off the primary and secondary switch tubes.

FIG. 3 is a flow chart of the steps of a method for realizing energy balance of a lithium-ion battery according to the present invention. As shown in Figure 3, a method for realizing energy balance of a lithium-ion battery of the present invention comprises the following steps:

Step 301, collecting information on the voltage and current of each battery in the lithium-ion battery pack multiple times. Preferably, the battery voltage and current information of the lithium-ion battery is extracted at a relatively high frequency, and the interval between the voltage and current information is relatively short, such as 100 Hz.

Step 302, input the voltage and current information of each battery, battery capacity, service life, nonlinear curve relationship between open circuit voltage and SOC, etc. into the data processing chip. Preferably, the voltage and current information of the lithium-ion battery measured multiple times is input into the data processing chip, and read out after comparing with the data (such as the relationship between open circuit voltage and SOC) stored in advance and the battery information open circuit voltage.

Step 303, discretize the battery voltage signals measured multiple times according to the second-order RC model of the battery, and process the data through linear regression to obtain useful matrix information, and calculate the lithium-ion battery voltage through the matrix. Corresponding other information, etc., the most important one is the open circuit voltage of the lithium-ion battery.

Specifically, step 303 includes:

First, according to the voltage and current information measured multiple times, the SOC is estimated by discretizing the second-order RC model of the lithium-ion battery, as shown in Figure 4.

Then the lithium-ion battery is modeled, and the current passing through the model is used as the excitation I, and the difference between the terminal voltage and the open circuit voltage of the lithium-ion battery is used as the response, then the lithium-ion battery can be used as a transfer function:

$\mathrm{<span\; class="notranslate">\; E.</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; I</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; \&Omega;</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; I</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; /</span><span\; class="notranslate">\; /</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\text{<span class="notranslate"> the s</span>}{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; I</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; /</span><span\; class="notranslate">\; /</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; the\; s</span>}{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; )</span>$

Among them, E is the difference between the battery lithium ion terminal circuit and the open circuit voltage, I is the current through the winding, R _Ω is the ohmic resistance, R ₁ , R ₂ , C ₁ , and C ₂ are the resistance and capacitance of the second-order RC in the model.

The transfer function of the model is obtained as:

$\mathrm{<span\; class="notranslate">\; G</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; E.</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; I</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; \&Omega;</span>}}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; the\; s</span>}}$

Among them, E is the difference between the battery lithium ion terminal circuit and the open circuit voltage, I is the current passing through the battery, R _Ω is the ohmic resistance, R ₁ , R ₂ , C ₁ , and C ₂ are the resistance and capacitance of the second-order RC in the model

When the sampling frequency is high, the above transfer function is discretized by the bilinear transformation method to obtain the difference equation:

E(k)＝a ₁ E(k-1)+a ₂ E(k-2)+a ₃ I(k)+a ₄ I(k-1)+a ₅ I(k-2)

E is the difference between the battery lithium ion terminal circuit and the open circuit voltage, I is the current passing through the battery, a1, a2, a3, a4, a5 are the coefficients after discretization.

At the same time, the difference is converted to the value of the terminal voltage and the open circuit voltage. Since the sampling time is fast, the open circuit voltage is approximate, and it can be obtained:

V(k)＝θ ₁ V(k-1)+θ ₂ V(k-2)+θ ₃ I(k)+θ ₄ I(k-1)+θ ₅ I(k-2)+θ ₆

make:

$\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; =</span>{\left[\begin{array}{cccccc}{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}& {\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}& {\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}& {\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}& {\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 5</span>}}& {\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 6</span>}}\end{array}\right]}^{\mathrm{<span\; class="notranslate">\; T</span>}}$

$\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\left[\begin{array}{cccccc}\mathrm{<span\; class="notranslate">\; V</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>& \mathrm{<span\; class="notranslate">\; V</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>& \mathrm{<span\; class="notranslate">\; I</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>& \mathrm{<span\; class="notranslate">\; I</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>& \mathrm{<span\; class="notranslate">\; I</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>& \mathrm{<span\; class="notranslate">\; 1</span>}\end{array}\right]$

Then the above formula can be written in the form of multivariate matrix multiplication:

V(k)=X ^T (k)θ

the above $\mathrm{\&theta;}={\left[\begin{array}{cccccc}{\mathrm{\&theta;}}_1& {\mathrm{\&theta;}}_2& {\mathrm{\&theta;}}_3& {\mathrm{\&theta;}}_4& {\mathrm{\&theta;}}_5& {\mathrm{\&theta;}}_6\end{array}\right]}^T$ The calculation of the value is in the form of multivariate matrix multiplication, and the matrix is calculated by multiple linear regression method, that is, if Y=XZ, then Z=(X ^T X) ^-1 X ^T Y.

After calculating the information matrix through linear regression, and through the calculation of the formula, the open circuit voltage OCV of the lithium-ion battery is mainly calculated, and other information about the lithium-ion battery is obtained at the same time:

OCV(k)=θ ₆ /[1-(a ₁ +a ₂ )+a ₁ a ₂ ]=θ ₆ /(1-θ ₁ -θ ₂ )

${\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>\sqrt{{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 4</span>}{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}$

${\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>\sqrt{{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 4</span>}{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}$

${\mathrm{<span\; class="notranslate">\; b</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 5</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; /</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; b</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 5</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; /</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>$

_RΩ ＝ _-θ3

R ₁ =b ₁ /(1-a ₁ )

C ₁ ＝-T/(R ₁ lna ₁ )

R ₂ =b ₂ /(1-a ₂ )

Among them, OCV is the open circuit voltage, θ ₁ -θ ₆ is the value of the θ matrix obtained by the regression just now, a1, a2, a3, a4, a5 are the coefficients after discretization, R _Ω is the ohmic resistance, R ₁ , R ₂ , C ₁ , C ₂ are the resistance and capacitance of the second-order RC in the model.

Step 304 , according to the calculated open circuit voltage of the battery, the SOC of the lithium ion battery is interpolated through the relationship curve between the open circuit voltage and the SOC of the lithium ion battery, and the average SOC of the battery pack is calculated.

Specifically, according to the information matrix calculated in step 303, through the open circuit voltage value of the lithium ion battery, according to the relationship between the open circuit voltage and the SOC curve stored in step 302, through the graph shown in Figure 5, using the calculated open circuit voltage Voltage value, interpolation can get the SOC of the lithium-ion battery at this time.

Step 305, control the bidirectional flyback DCDC converter, by detecting that the current on the DCDC reaches a certain peak value, control the switching MOS tube of the bidirectional flyback DCDC to realize the on-off of the current in the lithium-ion battery pack, thereby realizing the lithium-ion battery energy transfer.

Specifically, to control the bidirectional flyback DCDC converter, one end is connected to a lithium-ion battery cell, and the other end is connected to a lithium-ion battery pack formed by lithium ions connected by multiple lithium-ion batteries, through the disconnection of the MOS tube Realize the transfer of lithium-ion battery energy, and measure the current transferred by the lithium-ion battery through the precise resistance on the coil, realize the current control for the energy transfer of lithium-ion batteries, and realize the timing of the energy transfer time of lithium-ion batteries through time control The length, through the switching frequency and the length of the time, realize the control of the current size and time of the lithium-ion battery.

Step 306, according to the method of fuzzy control, the calculated SOC of the lithium-ion battery is used to determine the equalization current and equalization time required by the battery, and finally the balanced DCDC balanced lithium-ion battery is controlled through step 305 until the battery equalization is finally completed, that is, all lithium-ion batteries The battery sample difference of the ion battery is less than 2%, otherwise continue to start from step 301 .

The time for controlling the energy transfer of the lithium-ion battery is mainly determined by fuzzy control, and the fuzzy controller used in the present invention is a single-variable two-dimensional fuzzy controller, that is, two inputs and one output. The input of the fuzzy controller needs to be able to accurately reflect the relationship between the battery pack and the battery to be balanced. Therefore, the input of the fuzzy controller selected according to the actual situation is the difference between the average SOC of the battery pack and the SOC of the battery pack to be balanced. The average SOC of is taken as input. A larger difference means that a longer equalization time is required to achieve the purpose of equalization, and a smaller one means the opposite. When the average SOC is close to the charging or discharging state, the equalization time is long to achieve fast equalization effect and prevent the battery from overcharging and over-discharging. When the average SOC is in the middle state, slow equalization can be used to achieve better equalization effect. Through the fuzzy control knowledge base shown in Table 1 below, a triangle is selected as the shape of the membership function (as shown in Figure 6). The output of the fuzzy controller is to control the equalization time T and the equalization current I in the equalization circuit, and to control the DCDC conversion Switching time of the switch to achieve the control balance effect.

Table 1 Fuzzy control knowledge base

FIG. 7 is a flow chart of a specific embodiment of a method for realizing energy balance of a lithium-ion battery according to the present invention. As shown in FIG. 7 , the present invention collects the voltage and current of the lithium ion battery by charging and discharging the lithium ion battery. Study the voltage characteristics and SOC characteristics of lithium-ion batteries. Including the relationship curve between OCV (open circuit voltage) and SOC, the relationship curve between the internal resistance of the battery and the SOC of the battery, and observe the performance curve of the lithium-ion battery. Then the lithium-ion battery voltage and current data are transmitted to the data processing board. Through the differential equation of the second-order RC model, the open circuit voltage of the lithium-ion battery at that time is calculated through the linear regression equation, and the SOC of the lithium-ion battery at that time is calculated by the interpolation method. Then calculate the average SOC of the lithium-ion battery pack. Calculate the battery dispersion degree of the lithium-ion battery pack, and judge whether the battery dispersion degree is greater than 2%. If the battery dispersion is less than 2%, continue to start from detecting the lithium-ion battery voltage. If the dispersion of lithium-ion batteries is greater than 2%, the balance current and balance time are judged by the fuzzy control method. After obtaining the balance current and balance time of the lithium-ion battery pack, the balance of the lithium-ion battery is controlled by controlling the DCDC converter until the battery dispersion is less than 2%.

In summary, the present invention provides a lithium-ion battery energy balance system and its implementation method. In the process of energy balance transfer, the SOC of the lithium-ion battery is estimated, and the SOC is used as a basis to achieve balance by controlling DCDC, so that the system avoids The misbalance caused by the voltage equalization method is eliminated, and the reliability is higher.

The above-mentioned embodiments only illustrate the principles and effects of the present invention, but are not intended to limit the present invention. Any person skilled in the art can modify and change the above-mentioned embodiments without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention should be listed in the claims.

Claims (10)

1. a lithium ion battery balancing energy system, comprising:

Li-ion batteries piles, described Li-ion batteries piles is composed in series by n block lithium-ion battery monomer, and each lithium-ion battery monomer connects a voltage detecting circuit and a DC-DC converter;

N voltage detecting circuit, the input of a kth voltage detecting circuit connects positive pole and the negative pole of a kth lithium-ion battery monomer respectively, and when needs carry out voltage detecting, start sampling, and its sampled value is transferred into kth group main control chip after isolation;

N DC-DC converter, each DC-DC converter, by controlling the switch of metal-oxide-semiconductor, directly carries out charging and discharging to lithium-ion battery monomer each in Li-ion batteries piles respectively, simultaneously by switching frequency adjustment electric current;

N main control chip, each main control chip reads the information of voltage of lithium ion battery in voltage detecting circuit corresponding to each lithium-ion battery monomer, is then delivered in data processing chip 60 by data by CAN;

Data processing chip, the SOC of each lithium-ion battery monomer is calculated by the method for linear regression, determine whether equilibrium is carried out to Li-ion batteries piles according to FUZZY ALGORITHMS FOR CONTROL simultaneously, equalizing signal is sent to each main control chip through CAN communication module by data processing chip 60, and enable for equilibrium control signal sends to each lithium-ion battery monomer to carry out Balance route by each main control chip;

CAN communication module, is responsible for the communication realizing described main control chip and described data processing chip;

Current detection circuit, connects described Li-ion batteries piles and data processing chip, for detecting the euqalizing current of battery pack to open or to turn off the switching tube of primary and secondary.

2. a kind of lithium ion battery balancing energy system as claimed in claim 1, it is characterized in that: described DC-DC converter adopts bi-directional synchronization inverse-excitation type DC-DC converter, each DC-DC converter other DCDC all independent, one end of each DC-DC converter connects lithium-ion battery monomer, and the other end connects Li-ion batteries piles.

3. a kind of lithium ion battery balancing energy system as claimed in claim 2, it is characterized in that: a kth bi-directional synchronization inverse-excitation type DCD transducer comprises high frequency transformer (Tk), primary switch pipe (Qkp), secondary switch pipe (Qks), the source electrode of primary switch pipe (Qkp) is connected to the negative pole of lithium-ion battery monomer (Cellk), the drain electrode of primary switch pipe (Qkp) is connected to elementary one end of high frequency transformer (Tk), the elementary other end of high frequency transformer (Tk) is connected to the positive pole of lithium-ion battery monomer (Cellk), the source electrode of secondary switch pipe (Qks) is connected to the negative pole of this Li-ion batteries piles, the drain electrode of secondary switch pipe (Qks) is connected to secondary one end of high frequency transformer (Tk), the secondary other end of high frequency transformer (Tk) is connected to the positive pole of Li-ion batteries piles.

4. an implementation method for lithium ion battery balancing energy, comprises the steps:

Step one, the information of every block cell voltage and electric current in multi collect Li-ion batteries piles;

Step 2, is input in data processing chip by the nonlinear curve relation information of the information of the voltage and current of every block battery and battery capacity, life-span, open circuit voltage and SOC;

Step 3, repeatedly measured battery voltage signal is carried out discretization according to the Order RC model of battery, and by the method for linear regression, data are processed, draw useful matrix information, and calculate the open circuit voltage corresponding to lithium ion battery by matrix;

Step 4, according to the open circuit voltage of calculated battery, is gone out the SOC of lithium ion battery, and calculates the average SOC of battery pack by the open circuit voltage of lithium ion battery and SOC relation curve interpolation;

Step 5, according to the method for fuzzy control, judges the euqalizing current required for battery and time for balance by the SOC of calculated lithium ion battery;

Step 6, controls two-way inverse-excitation type DC-DC converter, and reach certain peak value by the electric current detected on DCDC, the switch MOS pipe controlling two-way inverse-excitation type DCDC realizes the break-make of the electric current in Li-ion batteries piles, thus realizes lithium ion battery energy trasfer.

5. the implementation method of a kind of lithium ion battery balancing energy as claimed in claim 4, is characterized in that, after step 4, also comprise the steps:

Calculate the battery decentralization of Li-ion batteries piles;

Judge whether battery decentralization is greater than predetermined threshold;

If when battery decentralization is less than this predetermined threshold, then enters step one and continue to press off the beginning from detection lithium ion battery battery; If when lithium ion battery decentralization is greater than this predetermined threshold, then enter step 5.

6. the implementation method of a kind of lithium ion battery balancing energy as claimed in claim 5, is characterized in that: in step one, and extract frequency to the cell voltage of lithium ion battery and current information higher, the voltage and current information interval time is shorter.

7. the implementation method of a kind of lithium ion battery balancing energy as claimed in claim 6, it is characterized in that, step 3 comprises the steps:.

According to repeatedly measured electric current and voltage information by obtaining the estimation to SOC to the Order RC model discretization of lithium ion battery;

By Li-ion battery model, using the electric current by model as excitation I, the terminal voltage of lithium ion battery and the difference of open circuit voltage responsively, draw the transfer function of model;

When sample frequency is very high time, this transfer function Bilinear transformation method is carried out discretization, draws difference equation, difference is converted to the value of terminal voltage and open circuit voltage simultaneously.

8. the implementation method of a kind of lithium ion battery balancing energy as claimed in claim 6, it is characterized in that: in step 4, according to the information matrix that step 3 calculates, by the open-circuit voltage values of lithium ion battery, the open circuit voltage stored according to step 2 and SOC curved line relation, by curve chart, and utilize the open-circuit voltage values calculated, interpolation draws lithium ion battery SOC now.

9. the implementation method of a kind of lithium ion battery balancing energy as claimed in claim 6, it is characterized in that: in step 5, control this two-way inverse-excitation type DC-DC converter, a lithium-ion battery monomer of ining succession, in succession the Li-ion batteries piles that lithium ion that polylith lithium ion battery links up is formed in other end, the transfer realizing lithium ion battery energy is cut-off by metal-oxide-semiconductor, and measure by the precision resistance on coil the electric current that lithium ion battery shifts, realize the Current Control for lithium ion battery energy trasfer, pass through time controling simultaneously, realize the length of the time of lithium ion battery energy trasfer, by the length to switching frequency and time, realize the size of current of lithium ion battery and the control of time.

10. the implementation method of a kind of lithium ion battery balancing energy as claimed in claim 9, is characterized in that: the time controlling lithium ion battery energy trasfer is determined by fuzzy controller, and this fuzzy controller is single argument two-dimensional fuzzy controller.