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CN-115877241-B - Electric automobile fills electric pile of integrated broadband impedance measurement

CN115877241BCN 115877241 BCN115877241 BCN 115877241BCN-115877241-B

Abstract

The invention discloses an electric vehicle charging pile integrating broadband impedance measurement, which designs an intelligent charging pile topological structure integrating broadband impedance measurement aiming at the problem that the internal state information of a battery can not be effectively known in the charging process of the electric vehicle by the traditional charging pile, besides realizing the functions of constant current and constant voltage of a bicycle and pulse charging, the design cost of the AC/DC converter is reduced and the service life of the AC/DC converter is prolonged by optimizing the phases of disturbance signals and pulse charging current when two bicycles are charged simultaneously. The invention also provides a method for rapidly acquiring the broadband impedance of the lithium battery in real time aiming at the charging mode with the topological structure, optimizes the pulse charging frequency based on the broadband impedance, realizes the health diagnosis of the battery pack of the electric automobile, and provides health detection information. The invention relieves the anxiety of the endurance mileage of the electric automobile to a certain extent, and simultaneously prevents the safety problem caused by the inconsistent expansion of the battery cells of the electric automobile.

Inventors

  • HU HAITAO
  • GENG ANQI
  • PENG YUANZHEN
  • CHEN YANYU

Assignees

  • 西南交通大学

Dates

Publication Date
20260512
Application Date
20221204

Claims (8)

  1. 1. The electric automobile charging pile integrating broadband impedance measurement is characterized in that the primary side of an isolation transformer is connected with a power grid, and the secondary side of the isolation transformer is connected to the input end of an AC/DC converter; the input end of the first bidirectional DC/DC converter is connected with the first supporting capacitor in parallel and then is connected to the output end of the AC/DC converter, and the output end of the first bidirectional DC/DC converter is connected to the first interaction bus; the system comprises a data interaction center module, a broadband impedance identification module and a central controller, wherein the data interaction center module is connected to a first interaction bus through a data interconnecting wire; The broadband impedance recognition module is also connected to the central controller.
  2. 2. The electric vehicle charging pile integrated with broadband impedance measurement according to claim 1, further comprising a second bidirectional DC/DC converter having an input connected in parallel with the second supporting capacitor and connected to an output of the AC/DC converter, and an output connected to a second interaction bus, the second interaction bus being connected to the data interaction center module via a data link.
  3. 3. A control method of an electric vehicle charging pile integrating broadband impedance measurement is characterized by comprising the steps of charging a first electric vehicle in a pulse mode, when the voltage of the first electric vehicle is smaller than a charging cut-off voltage V m-1 of the first electric vehicle, controlling a first DC/DC converter to output pulse current with frequency f b-1 and amplitude I p to charge the first electric vehicle, and stopping charging when the voltage of the first electric vehicle is equal to V m-1 ; The frequency f b-1 is obtained by the following steps: step time identification, namely sampling battery current every time the battery charge state of the first electric automobile rises by x%, and extracting a current step point; Extracting the broadband impedance, and calculating the optimal pulse frequency, including: Step 1, respectively calculating a wavelet coefficient W U,i,j (a,k j T s ) of a voltage U i (k j T s ) of a battery core in a first electric automobile battery pack at a current step moment and a wavelet coefficient W I,i,j (a,k j T s ) of a current I i (k j T s ), wherein I represents an ith battery core, k j represents the number of sampling points of a jth current step point, T s represents a sampling period, and a is the scale of wavelet transformation; Step 2, calculating broadband impedance of the ith battery cell at current step moment k j T s ; Step 3, calculating the average value of broadband impedance of the ith battery cell at all current step moments as the impedance of the ith battery cell, taking a mode of the impedance of the ith battery cell, and obtaining the frequency corresponding to the mode minimum value as the optimal pulse frequency of the ith battery cell; And 4, calculating the average value of the optimal pulse frequencies of all the battery cells of the first electric automobile, and taking the average value as the optimal pulse frequency f op-1 of the battery pack of the first electric automobile, so that f b-1 ＝f op-1 is realized.
  4. 4. The method for controlling the electric vehicle charging pile integrating broadband impedance measurement according to claim 3, wherein the method is further characterized by charging the second electric vehicle by pulse, when the voltage of the second electric vehicle is smaller than the charging cut-off voltage V m-2 , controlling the second DC/DC converter to output pulse current with the frequency f b-2 and the amplitude I p to charge the second electric vehicle, and when the voltage of the second electric vehicle is equal to V m-2 , stopping charging, wherein the pulse current for charging the first electric vehicle is 180 DEG different from the pulse current for charging the second electric vehicle; the method for obtaining the optimal pulse frequency f op-2 of the second electric vehicle battery pack is the same as the method for obtaining the optimal pulse frequency f op-1 of the first electric vehicle battery pack; Taking the average of f op-1 and f op-2 , f d-op , let f b-1 ＝f b-2 ＝f d-op .
  5. 5. The method for controlling the electric vehicle charging pile integrating broadband impedance measurement according to claim 3, wherein the method further comprises the steps of controlling the output current I s of the second DC/DC converter to charge the second electric vehicle at constant current and constant voltage when the voltage of the second electric vehicle is smaller than the charging cut-off voltage V m-2 of the second electric vehicle, controlling the output voltage V m-2 of the second DC/DC converter to charge the second electric vehicle at constant voltage when the voltage of the second electric vehicle is equal to V m-2 of the second electric vehicle, and stopping charging until the charging current is smaller than a preset value I m .
  6. 6. The method for diagnosing the health state of the battery pack of the electric automobile is characterized in that the electric automobile is charged in a pulse mode; Step 1, step time identification, namely, sampling battery current every time the battery charge state of the electric automobile rises by x%, and extracting a current step point; step2, extracting broadband impedance, including: 2.1, respectively calculating the wavelet coefficient W U,i,j (a,k j T s ) of the voltage U i (k j T s ) of the battery core at the current step moment in the battery pack of the electric automobile and the wavelet coefficient W I,i,j (a,k j T s ) of the current I i (k j T s ), wherein I represents the ith battery core, k j represents the number of sampling points of the jth current step point, T s represents the sampling period; 2.2, calculating broadband impedance of the ith battery cell at current step moment k j T s ; 2.3, calculating the average value of broadband impedance of the ith battery cell at all current step moments, and taking the average value as the impedance of the ith battery cell; step 3, establishing a diagnosis model for diagnosis, which comprises the following steps: 3.1, establishing a dual-polarized fractional order equivalent circuit model; 3.2, establishing a frequency domain impedance equation of the dual-polarized fractional order equivalent circuit model according to each element in the model; 3.3, establishing an adaptability function according to the frequency domain impedance equation; 3.4 adopting a particle swarm optimization to optimize and solve the fitness function to respectively obtain ohmic impedance R 0,i , SEI film resistance R SEI,i , charge transfer impedance R CT,i , fractional order alpha i of constant phase angle element CPE 1 , fractional order beta i of constant phase angle element CPE 2 , coefficient C 1,i of constant phase angle element CPE 1 and coefficient C 2,i of constant phase angle element CPE 2 of the ith electric core of the electric automobile; 3.5 calculating the variance of ohmic resistance R 0 , the variance of SEI film resistance R SEI and the variance of charge transfer resistance R CT of all the battery cores of the electric automobile according to R 0,i 、R SEI,i 、R CT,i 、α i 、β i 、C 1,i 、C 2,i ; and 4, judging the degree of inconsistent battery cells of the electric automobile by using the total variance and a preset threshold value.
  7. 7. A method for diagnosing the health state of a battery pack of an electric automobile is characterized in that, The electric automobile is a first electric automobile, and is subjected to constant-current and constant-voltage charging, wherein when the voltage of the first electric automobile is smaller than a charging cut-off voltage V m-1 of the first electric automobile, the first DC/DC converter is controlled to output a current I s to perform constant-current charging on the first electric automobile; Step 0, disturbance signal injection, namely, in the constant current charging process, each time the battery charge state of the first electric automobile rises by x%, square wave disturbance with the amplitude of 0.1 xI s , the duty ratio of 0.5 and the step interval time of t a is superimposed on the basis of the charging current I s , T a is a constant greater than 0, the number of cycles of the injection disturbance is a preset value n, n is an integer greater than 0; step 1, step time identification, namely sampling the battery current of a first electric automobile and extracting a current step point; step2, extracting broadband impedance, including: 2.1 respectively calculating the wavelet coefficient W U,i,j (a,k j T s ) of the voltage U i (k j T s ) of the battery core at the current step moment in the battery pack of the first electric automobile and the wavelet coefficient W I,i,j (a,k j T s ) of the current I i (k j T s ), wherein I represents the ith battery core, k j represents the number of sampling points of the jth current step point, T s represents the sampling period, and a is the scale of wavelet transformation; 2.2, calculating broadband impedance of the ith battery cell at current step moment k j T s ; 2.3, calculating the average value of broadband impedance of the ith battery cell at all current step moments, and taking the average value as the impedance of the ith battery cell; step 3, establishing a diagnosis model for diagnosis, which comprises the following steps: 3.1, establishing a dual-polarized fractional order equivalent circuit model; 3.2, establishing a frequency domain impedance equation of the dual-polarized fractional order equivalent circuit model according to each element in the model; 3.3, establishing an adaptability function according to the frequency domain impedance equation; 3.4 adopting a particle swarm optimization to optimally solve the fitness function to respectively obtain ohmic impedance R 0,i , SEI film resistance R SEI,i , charge transfer impedance R CT,i , fractional order alpha i of constant phase angle element CPE 1 , fractional order beta i of constant phase angle element CPE 2 , coefficient C 1,i of constant phase angle element CPE 1 and coefficient C 2,i of constant phase angle element CPE 2 of the ith electric core of the first electric automobile; 3.5 calculating the variance of ohmic resistance R 0 , the variance of SEI film resistance R SEI and the variance of charge transfer resistance R CT of all the battery cores of the first electric automobile according to R 0,i 、R SEI,i 、R CT,i 、α i 、β i 、C 1,i 、C 2,i ; and 4, judging the degree of inconsistent battery cells of the first electric automobile by using the total variance and a preset threshold value.
  8. 8. The method for diagnosing the health state of the battery pack of the electric automobile as set forth in claim 7, further comprising the step of charging the second electric automobile with constant current and constant voltage, wherein when the voltage of the second electric automobile is smaller than the charging cut-off voltage V m-2 , the second DC/DC converter is controlled to output the current I s to charge the second electric automobile with constant current, and when the voltage of the second electric automobile is equal to V m-2 , the second DC/DC converter is controlled to output the voltage V m-2 to charge the second electric automobile with constant voltage until the charging current is smaller than the preset value I m ; The step 0 is replaced by complementary injection of disturbance signals, namely, in the constant current charging process, each time the state of charge of the first electric automobile or the second electric automobile rises by x percent, square wave disturbance with the amplitude of 0.1 xI s , the duty cycle of 0.5 and the step interval time of t a is superimposed on the basis of the charging current I s of the first electric automobile, and meanwhile, square wave disturbance with the amplitude of 0.1 xI s , the duty cycle of 0.5 and the step interval time of t a is superimposed on the basis of the charging current I s of the second electric automobile, the phase of the square wave disturbance is different from the phase of the square wave disturbance of the first electric automobile by 180 degrees, t a is a constant larger than 0, the period number of the injection disturbance is a preset value n, and n is an integer larger than 0; And (3) respectively judging the inconsistent degree of the battery cores of the first electric automobile and the second electric automobile according to the methods of the steps 1-4.

Description

Electric automobile fills electric pile of integrated broadband impedance measurement Technical Field The invention relates to the technical field of electric automobile charging, in particular to an electric automobile charging pile integrating broadband impedance measurement. Background In order to relieve the anxiety of the endurance mileage of the electric automobile, the electric automobile needs to be equipped with a battery with larger capacity, however, as the energy density of the lithium battery is continuously improved, the safety problem of the electric automobile is increasingly outstanding. Therefore, in order to avoid battery safety accidents of the electric automobile as much as possible and simultaneously alleviate the anxiety of the endurance mileage of the electric automobile, the charging speed of the electric automobile needs to be actively monitored and managed at the same time. The charging method mainly used at present is still constant-current constant-voltage (CCCV) charging, the aging of the battery can be accelerated by increasing the charging current in the constant-current stage, and the constant-voltage stage has long duration and small charging quantity. In order to eliminate the polarization phenomenon of the battery due to charging, a pulse charging mode is gradually used for rapid charging of an electric vehicle, which has obvious advantages in terms of charging speed, energy efficiency, and improved battery life. The pulse charging frequency has obvious influence on the charging effect, and the pulse charging frequency is optimized through the impedance of the lithium battery, so that the charging loss is greatly reduced, and the charging efficiency is improved. The state of charge, temperature, and remaining life all affect the broadband impedance of the lithium battery, resulting in poor adaptability to the pulse charging frequency. However, the existing charging pile cannot acquire the charging state of the lithium battery in real time in the charging process, and with the continuous penetration of the rapid charging technology, monitoring the battery state is also important for optimizing the charging performance. The broadband impedance of the lithium battery can reflect the internal working state of the lithium battery, and further, the identification and diagnosis of a specific fault mode can be performed through the broadband impedance. The traditional EIS method is a quasi-steady state measurement method, the battery needs to be fully kept still before measurement, the battery is guaranteed to be in a stable state, the measurement is performed in a sweep frequency mode, the speed is low, and the method is difficult to be used for controlling a site in real time. Therefore, how to obtain the broadband impedance of the lithium battery in real time and rapidly aiming at different charging scenes so as to monitor the health state of the electric automobile has important significance. Disclosure of Invention The invention aims to provide an electric vehicle charging pile integrating broadband impedance measurement, which aims at providing real-time acquisition of broadband impedance of a lithium battery according to different charging modes, optimizes pulse charging frequency based on the broadband impedance, realizes health diagnosis of a battery pack of the electric vehicle and provides health detection information. The technical scheme for realizing the purpose of the invention is as follows: The electric automobile charging pile integrating broadband impedance measurement comprises an electric network connected to the primary side of an isolation transformer, an AC/DC converter connected to the secondary side of the isolation transformer, a first bidirectional DC/DC converter connected to the output end of the AC/DC converter after being connected in parallel with a first supporting capacitor, a data interaction center module, a broadband impedance identification module and a central controller, wherein the data interaction center module is connected to the first interaction bus through a data connecting wire, the data interaction center module is also connected to the broadband impedance identification module and the central controller respectively, and the broadband impedance identification module is also connected to the central controller. The system further comprises a second bidirectional DC/DC converter, wherein the input end of the second bidirectional DC/DC converter is connected with a second supporting capacitor in parallel and then connected to the output end of the AC/DC converter, the output end of the second bidirectional DC/DC converter is connected to a second interaction bus, and the second interaction bus is connected to the data interaction center module through a data interconnection line. The control method of the electric vehicle charging pile integrating the broadband impedance measurement comprises the steps of controlling the first DC/DC