An electric vehicle charging pile integrated with wideband impedance measurement

Abstract

The application discloses an electric vehicle charging pile integrated with wideband impedance measurement, and aims at the problem that the internal state information of a battery cannot be effectively obtained in the charging process of a traditional charging pile. The application discloses an electric vehicle charging pile integrated with wideband impedance measurement, and aims at the problem that the internal state information of a battery cannot be effectively obtained in the charging process of a traditional charging pile. The application discloses an electric vehicle charging pile integrated with wideband impedance measurement, and aims at the problem that the internal state information of a battery cannot be effectively obtained in the charging process of a traditional charging pile. The application discloses an electric vehicle charging pile integrated with wideband impedance measurement, and aims at the problem that the internal state information of a battery cannot be effectively obtained in the charging process of a traditional charging pile. The application discloses an electric vehicle charging pile integrated with wideband impedance measurement, and aims at the problem that the internal state information of a battery cannot be effectively obtained in the charging process of a traditional charging pile. The application discloses an electric vehicle charging pile integrated with wideband impedance measurement, and aims at the problem that the internal state information of a battery cannot be effectively obtained in the charging process of a traditional charging pile. The application discloses an electric vehicle charging pile integrated with wideband impedance measurement, and aims at the problem that the internal state information of a battery cannot be effectively obtained in the charging process of a traditional charging pile. The application discloses an electric vehicle charging pile integrated with wideband impedance measurement, and aims

Description

Technical Field

[0001] This invention relates to the field of electric vehicle charging technology, and in particular to an electric vehicle charging pile that integrates wideband impedance measurement. Background Technology

[0002] To alleviate range anxiety in electric vehicles (EVs), larger capacity batteries are needed. However, as the energy density of lithium batteries continues to increase, safety issues in EVs are becoming increasingly prominent. Therefore, to minimize battery safety incidents and alleviate range anxiety, it is necessary to actively monitor and manage EVs while simultaneously improving charging speed.

[0003] Currently, the primary charging method is constant current constant voltage (CCCV) charging. Increasing the charging current during the constant current phase accelerates battery aging, and the constant voltage phase lasts a long time with limited charge. To eliminate battery polarization during charging, pulse charging is increasingly being used for fast charging of electric vehicles, offering significant advantages in charging speed, energy efficiency, and battery lifespan. The frequency of pulse charging significantly impacts charging performance; optimizing the pulse charging frequency through lithium battery impedance can greatly reduce charging losses and improve charging efficiency. State of charge, temperature, and remaining battery life all affect the wideband impedance of lithium batteries, resulting in poor adaptability to pulse charging frequencies. However, existing charging stations cannot acquire real-time lithium battery charging status during the charging process, and with the continuous advancement of fast charging technology, monitoring battery status becomes increasingly crucial for optimizing charging performance.

[0004] The wideband impedance of a lithium battery can reflect its internal operating state, thus enabling the identification and diagnosis of specific fault modes. Traditional EIS (Electrical Inductively coupled Block) methods are quasi-steady-state measurement methods. Before measurement, the battery needs to be allowed to settle sufficiently to ensure a stable state, and the measurement is performed in a frequency sweep mode, which is slow and difficult to use for real-time control. Therefore, it is of great significance to find a way to obtain the wideband impedance of lithium batteries in real time and quickly for different charging scenarios to monitor the health status of electric vehicles. Summary of the Invention

[0005] The purpose of this invention is to provide an electric vehicle charging pile that integrates wideband impedance measurement. It proposes to acquire the wideband impedance of lithium batteries in real time for different charging modes, optimize the pulse charging frequency based on this impedance, and realize the health diagnosis of electric vehicle battery packs, providing health detection information.

[0006] The technical solution for achieving the objective of this invention is as follows:

[0007] An electric vehicle charging pile integrating wideband impedance measurement includes an isolation transformer whose primary side is connected to the power grid and whose secondary side is connected to the input of an AC / DC converter; a first bidirectional DC / DC converter, whose input is connected in parallel with a first supporting capacitor and then connected to the output of the AC / DC converter, and whose output is connected to a first interactive bus; it also includes a data interaction center module, a wideband impedance identification module, and a central controller; the data interaction center module is connected to the first interactive bus via a data link; the data interaction center module is also connected to the wideband impedance identification module and the central controller; the wideband impedance identification module is also connected to the central controller.

[0008] Furthermore, it also includes a second bidirectional DC / DC converter, whose input terminal is connected in parallel with a second supporting capacitor and then connected to the output terminal of the AC / DC converter, and whose output terminal is connected to a second interactive bus; the second interactive bus is connected to the data interactive center module through a data communication line.

[0009] A control method for an electric vehicle charging pile integrating wideband impedance measurement, wherein the first electric vehicle is pulse-charged: when the voltage of the first electric vehicle is less than its charging cut-off voltage V m-1 At that time, control the output frequency f of the first DC / DC converter. b-1 Amplitude I p A pulsed current is used to charge the first electric vehicle; when the voltage of the first electric vehicle equals V... m-1 When charging stops, the charging process will cease.

[0010] The frequency f b-1 It is obtained through the following steps:

[0011] Step time identification: For each x% increase in the battery state of charge of the first electric vehicle, sample the battery current and extract the current step point; extract the wideband impedance and calculate the optimal pulse frequency, including:

[0012] Step 1: Calculate the voltage U of each cell in the first electric vehicle battery pack at the moment of current step change. i (k j T s The wavelet coefficients W U,i,j (a,k j T s ), and current I i (k j T s The wavelet coefficients W I,i,j (a,k j T s ); where i represents the i-th cell; k j T represents the number of sampling points at the j-th current step point. s The sampling period is represented by ; 'a' is the scale of the wavelet transform.

[0013] Step 2, calculate k at the current step time of the i-th cell. j T s Wideband impedance;

[0014] Step 3: Calculate the average broadband impedance of the i-th cell at all current step moments, and use it as the impedance of the i-th cell; take the modulus of the impedance of the i-th cell, and find the frequency corresponding to the minimum modulus value, and use it as the optimal pulse frequency of the i-th cell; Step 4: Calculate the average of the optimal pulse frequencies of all cells in the first electric vehicle, and use it as the optimal pulse frequency f of the first electric vehicle battery pack. op-1 , let f b-1 =f op-1 .

[0015] Furthermore, a pulse charge is applied to the second electric vehicle: when the voltage of the second electric vehicle is less than its charging cutoff voltage V. m-2 At that time, control the output frequency f of the second DC / DC converter. b-2 Amplitude I p A pulsed current is used to charge the second electric vehicle; when the voltage of the second electric vehicle equals V... m-2 When charging stops, the pulse current charging the first electric vehicle and the pulse current charging the second electric vehicle are 180° out of phase.

[0016] The optimal pulse frequency f of the second electric vehicle battery pack is obtained. op-2 The method, and obtaining the optimal pulse frequency f of the first electric vehicle battery pack. op-1 The method is the same;

[0017] Take f op-1 and f op-2 The mean f d-op , let f b-1 =f b-2 =f d-op .

[0018] Furthermore, the second electric vehicle is charged under constant current and constant voltage: when the voltage of the second electric vehicle is less than its charging cutoff voltage V... m-2 At that time, control the output current I of the second DC / DC converter. s The second electric vehicle is charged with a constant current; when the voltage of the second electric vehicle equals V... m-2 At that time, control the output voltage V of the second DC / DC converter. m-2 The second electric vehicle is charged with constant voltage until the charging current is less than the preset value I. m When the time is right, stop charging.

[0019] A method for diagnosing the health status of an electric vehicle battery pack, wherein the electric vehicle is pulse-charged;

[0020] Step 1, Step Time Identification: For every x% increase in the state of charge of the electric vehicle's battery, sample the battery current and extract the current step point;

[0021] Step 2, extract the broadband impedance, including:

[0022] 2.1 Calculate the voltage U of each cell in the electric vehicle battery pack at the moment of current step change. i (k j T s The wavelet coefficients W U,i,j (a,k j T s ), and current I i (k j T s The wavelet coefficients W I,i,j (a,k j T s ); where i represents the i-th cell; k j T represents the number of sampling points at the j-th current step point. s The sampling period is represented by ; 'a' is the scale of the wavelet transform.

[0023] 2.2 Calculate k at the current step time of the i-th cell. j T s Wideband impedance;

[0024] 2.3 Calculate the average broadband impedance of the i-th cell at all current step moments, and use it as the impedance of the i-th cell;

[0025] Step 3: Establish a diagnostic model for diagnosis, including:

[0026] 3.1 Establish a fractional-order equivalent circuit model for dual-polarization;

[0027] 3.2 Based on each component in the dual-polarization fractional-order equivalent circuit model, establish the frequency domain impedance equation of the model;

[0028] 3.3 Establish the fitness function based on the frequency domain impedance equation;

[0029] 3.4 The fitness function is optimized using the particle swarm optimization algorithm to obtain the ohmic impedance R of the i-th cell in the electric vehicle. 0,i SEI film resistance R SEI,i Charge transfer impedance R CT,i The fractional order α of the constant phase angle element CPE1 i The fractional order β of the constant phase angle element CPE2 i The coefficient C of the constant phase angle element CPE1 1,i The coefficient C of the constant phase angle element CPE2 2,i ;

[0030] 3.5 According to R 0,i R SEI,i R CT,i α i β i C 1,i C 2,i Calculate the variance of the ohmic impedance R0 and the SEI film resistance R of all battery cells in the electric vehicle. SEI variance and charge transfer impedance R CT Calculate the variance of the three variances mentioned above; calculate the total variance of the three variances mentioned above.

[0031] Step 4: Use the total variance and a preset threshold to determine the degree of inconsistency in the battery cells of the electric vehicle.

[0032] Another method for diagnosing the health status of an electric vehicle battery pack, wherein the electric vehicle is a first electric vehicle, and the first electric vehicle is charged with constant current and constant voltage: when the voltage of the first electric vehicle is less than its charging cut-off voltage V m-1 At that time, control the output current I of the first DC / DC converter. s The first electric vehicle is charged with a constant current; when the voltage of the first electric vehicle equals V... m-1 At that time, control the output voltage V of the first DC / DC converter. m-1 The first electric vehicle is charged with constant voltage until the charging current is less than the preset value I. m When charging stops, the charging process will cease.

[0033] Step 0, Disturbance signal injection: During constant current charging, for every x% increase in the battery state of charge of the first electric vehicle, the charging current I... s Based on this, an amplitude of 0.1×I is superimposed. s The duty cycle is 0.5 and the step interval is t. a Square wave disturbance, t a It is a constant greater than 0; the number of cycles for injecting perturbation is a preset value n, where n is an integer greater than 0;

[0034] Step 1, Step Time Identification: Sample the battery current of the first electric vehicle and extract the current step point;

[0035] Step 2, extract the broadband impedance, including:

[0036] 2.1 Calculate the voltage U of each cell in the first electric vehicle battery pack at the moment of current step change. i (k j T s The wavelet coefficients W U,i,j (a,k j T s ), and current I i (k jT s The wavelet coefficients W I,i,j (a,k j T s ); where i represents the i-th cell; k j T represents the number of sampling points at the j-th current step point. s The sampling period is represented by ; 'a' is the scale of the wavelet transform.

[0037] 2.2 Calculate k at the current step time of the i-th cell. j T s Wideband impedance;

[0038] 2.3 Calculate the average broadband impedance of the i-th cell at all current step moments, and use it as the impedance of the i-th cell;

[0039] Step 3: Establish a diagnostic model for diagnosis, including:

[0040] 3.1 Establish a fractional-order equivalent circuit model for dual-polarization;

[0041] 3.2 Based on each component in the dual-polarization fractional-order equivalent circuit model, establish the frequency domain impedance equation of the model;

[0042] 3.3 Establish the fitness function based on the frequency domain impedance equation;

[0043] 3.4 The fitness function is optimized using the particle swarm optimization algorithm to obtain the ohmic impedance R of the i-th cell in the first electric vehicle. 0,i SEI film resistance R SEI,i Charge transfer impedance R CT,i The fractional order α of the constant phase angle element CPE1 i The fractional order β of the constant phase angle element CPE2 i The coefficient C of the constant phase angle element CPE1 1,i The coefficient C of the constant phase angle element CPE2 2,i ;

[0044] 3.5 According to R 0,i R SEI,i R CT,i α i β i C 1,i C 2,i Calculate the variance of the ohmic impedance R0 and the SEI film resistance R of all cells in the first electric vehicle. SEI variance and charge transfer impedance R CT Calculate the variance of the three variances mentioned above; calculate the total variance of the three variances mentioned above.

[0045] Step 4: Use the total variance and a preset threshold to determine the degree of inconsistency in the battery cells of the first electric vehicle.

[0046] Furthermore, it also includes a second electric vehicle, which is charged with constant current and constant voltage: when the voltage of the second electric vehicle is less than its charging cutoff voltage V m-2 At that time, control the output current I of the second DC / DC converter. s The second electric vehicle is charged with a constant current; when the voltage of the second electric vehicle equals V... m-2 At that time, control the output voltage V of the second DC / DC converter. m-2 The second electric vehicle is charged with constant voltage until the charging current is less than the preset value I. m When charging stops, the charging process will cease.

[0047] Step 0 is replaced by complementary perturbation signal injection: during constant current charging, for every x% increase in the state of charge of the first electric vehicle or the second electric vehicle, the charging current I of the first electric vehicle... s Based on this, an amplitude of 0.1×I is superimposed. s The duty cycle is 0.5 and the step interval is t. a The square wave disturbance; simultaneously, the charging current I of the second electric vehicle s Based on this, an amplitude of 0.1×I is superimposed. s The duty cycle is 0.5 and the step interval is t. a The square wave disturbance has a phase that differs from the phase of the square wave disturbance of the first electric vehicle by 180°; t a The number of cycles for which the disturbance is injected is a constant greater than 0, and n is a preset value, where n is an integer greater than 0.

[0048] Following the methods in steps 1-4, determine the degree of inconsistency between the battery cells of the first electric vehicle and the second electric vehicle.

[0049] The beneficial effects of this invention are that, addressing the problem of traditional charging piles' inability to effectively obtain internal battery status information during electric vehicle charging, a smart charging pile topology integrating wideband impedance measurement is designed. Besides achieving constant current and constant voltage for a single vehicle and pulse charging functions, it also reduces the design cost of the AC / DC converter and improves its lifespan by optimizing the phase of the disturbance signal and pulse charging current when two vehicles are charging simultaneously. Furthermore, this invention proposes a method for real-time and rapid acquisition of the wideband impedance of the lithium battery to address the charging modes present in the aforementioned topology. Based on this, the pulse charging frequency is optimized to achieve health diagnosis of the electric vehicle battery pack and provide health monitoring information. This invention alleviates range anxiety for electric vehicles to a certain extent and prevents safety issues caused by the increased inconsistency of electric vehicle battery cells. Attached Figure Description

[0050] Figure 1This invention relates to a topology for an electric vehicle charging station that integrates wideband impedance measurement.

[0051] Figure 2 This is a schematic diagram of the control method of the present invention.

[0052] Figure 3 This is the current waveform after disturbance injection in the constant current and constant voltage mode of this invention.

[0053] Figure 4 This is the current waveform under the pulse charging mode of the present invention.

[0054] Figure 5 This is a schematic diagram of the dual-polarization fractional-order equivalent circuit model structure established in this invention. Detailed Implementation

[0055] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0056] like Figure 1 As shown, an electric vehicle charging pile topology integrating wideband impedance measurement includes:

[0057] The primary side of the isolation transformer T is connected to the public power grid, and the secondary side is connected to the AC / DC converter. The AC / DC converter is connected in series with bidirectional DC / DC converter-1 and bidirectional DC / DC converter-2, respectively, and bidirectional DC / DC converter-1 and bidirectional DC / DC converter-2 are connected in parallel. The input terminal of bidirectional DC / DC converter-1 is connected to a supporting capacitor C1, and its output terminal is connected to electric vehicle-1 through an interactive bus to transfer energy. The input terminal of bidirectional DC / DC converter-2 is connected to a supporting capacitor C2, and its output terminal is connected to electric vehicle-2 through an interactive bus to transfer energy.

[0058] The data interaction center module is the hub for data interaction between the smart charging pile, mobile terminal, and electric vehicle. It transmits data wirelessly with mobile terminal-1 and mobile terminal-2, and obtains voltage and current data from the battery energy management systems of electric vehicle-1 and electric vehicle-2 in real time through data communication lines.

[0059] The wideband impedance identification module processes the electric vehicle voltage and current data obtained from the data interaction center, identifies the wideband impedance of each battery, optimizes the frequency of pulse charging based on the impedance, and completes the health status detection of the electric vehicle.

[0060] The central controller is used to control the operation of the AC / DC converter, DC / DC converter-1 and bidirectional DC / DC converter-2, and to complete the charging conditions preset in the mobile terminal. At the same time, it responds to the pulse charging frequency optimized by the wideband impedance identification module.

[0061] like Figure 2 A control method for an electric vehicle charging pile integrating broadband impedance measurement, comprising:

[0062] S1. Charging Mode Selection: When only one electric vehicle needs to be charged, select charging mode 3 (constant voltage and constant current charging for one electric vehicle) or charging mode 5 (pulse charging for one electric vehicle) according to the charging mode information in mobile terminal-1 or mobile terminal-2; when two electric vehicles need to be charged simultaneously, select charging mode 1 (pulse charging for both electric vehicles), charging mode 2 (constant voltage and constant current charging for both electric vehicles), or charging mode 4 (constant voltage and constant current charging for one electric vehicle, and pulse charging for the other electric vehicle) according to the charging mode information in mobile terminal-1 and mobile terminal-2.

[0063] S2.A1, Charging Mode 1 (Pulse Charging of Both Electric Vehicles): Sets the initial pulse charging frequency f of electric vehicle -1. b =1 / t b , t b A constant greater than 0; set the initial pulse charging frequency f of electric vehicle -2 to be... b =1 / t b , t b The value is a constant greater than 0, and its phase differs from the pulse current of electric vehicle-1 by 180°. The amplitude of the pulse current is set to a preset value I. p I p A constant greater than 0, specifically as follows: Figure 3 As shown. Setting the phase difference to 180° can effectively reduce the maximum output current of the AC / DC converter, while also reducing its DC-side ripple, improving operating efficiency and service life. When the electric vehicle's -1 voltage is less than its charging cut-off voltage V... m-1 At that time, the output frequency of the control DC / DC converter is f b The amplitude is I p A pulsed current is applied to charge electric vehicle -1; otherwise, charging stops. Charging is stopped when the voltage of electric vehicle -2 is lower than its charging cutoff voltage V. m-2 At that time, the output frequency of the control DC / DC converter is f b The amplitude is I p A pulsed current is used to charge the electric vehicle-2; otherwise, charging is stopped.

[0064] S2.A2, Charging Mode 2 (Both electric vehicles are charged under constant voltage and constant current): The charging current during the constant current phase is set to a preset value I. s I s It is a constant; when the voltage of electric vehicle -1 is less than V m-1 At that time, the output current of the control DC / DC converter-1 is I. sCharge electric vehicle -1; when the voltage of electric vehicle -1 equals V m-1 At that time, the output voltage of the control DC / DC converter-1 is V. m-1 Charge the electric vehicle until the charging current of electric vehicle-1 is less than the preset value I. m Stop charging, I m It is a constant; when the voltage of electric vehicle -2 is less than V m-2 At that time, the output current of the control DC / DC converter-2 is I. s Charge electric vehicle -2; when the voltage of electric vehicle -2 equals V m-2 At that time, the output voltage of the control DC / DC converter-2 is V. m-2 Charge electric vehicle-2 until the charging current of electric vehicle-2 is less than I. m Stop charging.

[0065] S2.A3, Charging Mode 3 (Constant Voltage and Constant Current Charging of One Electric Vehicle): When the voltage of electric vehicle-1 or electric vehicle-2 is less than V... m-1 or V m-2 At that time, the output current of either DC / DC converter-1 or DC / DC converter-2 is I. s Charge electric vehicle-1 or electric vehicle-2; when the voltage of electric vehicle-1 or electric vehicle-2 is equal to V m-1 or V m-2 At that time, the output voltage of either DC / DC converter-1 or DC / DC converter-2 is V. m-1 or V m-2 Charge electric vehicle-1 or electric vehicle-2 until the charging current of electric vehicle-1 or electric vehicle-2 is less than I. m Stop charging.

[0066] S2.A4, Charging Mode 5 (Pulse Charging of One Electric Vehicle): When the voltage of electric vehicle-1 or electric vehicle-2 is less than or equal to V m-1 or V m-2 At that time, the output frequency of either DC / DC converter-1 or DC / DC converter-2 is f. b-1 or f b-2 The amplitude is I p A pulsed current charges electric vehicle-1 or electric vehicle-2. This occurs when the voltage of electric vehicle-1 or electric vehicle-2 equals V. m-1 or V m-2 When the time is right, stop charging.

[0067] S2.A5, Charging Mode 4 (One electric vehicle is charged with constant voltage and constant current, and the other electric vehicle is charged with pulse): Control one of the two electric vehicles to execute step S2.A3, and the other electric vehicle to execute step S2.A4.

[0068] S3.A1, Disturbance Signal Injection: During constant current charging, every 10% increase in the electric vehicle's state of charge (i.e., the electric vehicle's battery state of charge increases by 10%, or other battery state of charge increase ratios can be set), the charging pile will inject a disturbance signal at the original charging current I. s Based on this, an amplitude of 0.1×I is superimposed. s The duty cycle is 0.5 and the step interval is t. a Square wave disturbance, t a It is a constant greater than 0, and the specific operating current is as follows: Figure 4 As shown. To ensure the accuracy of subsequent impedance identification and to minimize the measurement time that could affect the normal operation of the system, the number of cycles of the injected disturbance is a preset value n, where n is an integer greater than 0.

[0069] S3.A2, Complementary Injection of Disturbance Signal: When both electric vehicles are undergoing constant current and constant voltage charging, during the constant current charging phase, if the state of charge of electric vehicle-1 or electric vehicle-2 increases by 10%, DC / DC converter-1 will maintain the original charging current I... s Based on this, an amplitude of 0.1×I is superimposed. s The duty cycle is 0.5 and the step interval is t. a The square wave disturbance has a disturbance period of n. Meanwhile, the DC / DC converter-2 operates at the original charging current I... s Based on this, an amplitude of 0.1×I is superimposed. s The duty cycle is 0.5 and the step interval is t. a The square wave disturbance has n cycles, and its phase differs from the output disturbance of DC / DC converter-1 by 180°. The output current waveform of the above converter is as follows. Figure 4 As shown, the disturbances of the two converters are 180° out of phase, which effectively avoids DC-side current ripple without increasing the maximum output current of the AC / DC converter. This can effectively reduce the design cost of the AC / DC converter and improve its service life.

[0070] For constant current and constant voltage charging, perturbation signal injection or complementary perturbation signal injection is used to extract wideband impedance to perform battery pack health status diagnosis. If battery pack health status diagnosis is not required and only constant current and constant voltage charging is performed, perturbation signal injection is not necessary.

[0071] S4, Step Time Identification: When the battery current... Then, the kth sampling time is defined as the current step point, and the step time t = kTs Among them, T s I(k+1) represents the sampling time; I(k+1) represents the battery current at the (k+1)th sampling time; I(k) represents the battery current at the kth sampling time; A e This is a preset constant; a value that is too large will prevent the identification of step points, while a value that is too small will lead to misidentification of step points. For steps S2.A2, S2.A3, and S2.A5, a disturbance signal is injected every 10% state of charge of the electric vehicle, and the number of cycles is n. At this time, a set of data with 2n step points can be extracted. For steps S2.A1, S2.A4, and S2.A5, after every 10% state of charge of the electric vehicle, a set of step points is extracted, and the number of step points is also 2n.

[0072] S5. Wideband Impedance Extraction: Based on the step points extracted in step S4, calculate the voltage U of the i-th cell in the electric vehicle battery pack at different step times. i (k j T s ), current I i (k j T s The wavelet coefficients W U,i,j (a,k j T s W I,i,j (a,k j T s The wavelet coefficients are obtained by performing Morse wavelet transforms on the voltage and current, respectively. Low-frequency impedance information of the battery is particularly important for battery state monitoring; therefore, the Morse wavelet, which has better low-frequency performance, is selected. Finally, the impedance at different step times is calculated, and its average value is used as the broadband impedance of the i-th cell in the electric vehicle battery pack in the current state.

[0073] The specific calculation process is as follows:

[0074] Step 1. Calculate the voltage and current of electric vehicle-1 or electric vehicle-2 at step time k. j T s wavelet coefficients:

[0075]

[0076] In the formula, a is the scale of the wavelet transform; U i (t) represents the current of the i-th cell; I i (t) represents the current of the i-th cell; For Morse wavelet ψ a,b The complex conjugate of (t), where Morse wavelet ψ a,b (t) can be represented as:

[0077]

[0078] In the formula, ω is the angular frequency; Ψ β,γ (ω) is the Fourier transform of the Morse wavelet, and its expression is:

[0079]

[0080] In the formula, e is the natural constant; γ and γ are constants. In order to make the Morse wavelet have the highest time-frequency resolution, γ = 3 is taken.

[0081] Step 2. Calculate the step time k of the i-th battery. j T s Wideband impedance:

[0082]

[0083] In the formula, The unit is Hz.

[0084] Step 3. Calculate the mean broadband impedance of the i-th cell at all step points:

[0085]

[0086] Step 4. Establish a bipolar fractional-order equivalent circuit model, including a series power supply, resistors R0 and R... SEI and R CT It also includes R SEI The parallel constant phase angle element CPE1, and R CT The parallel constant phase angle element CPE2, see the specific structure for details. Figure 5 , Figure 5 Middle,U oc U is the open-circuit voltage. L The voltage at the battery terminals is represented by ; I represents the current flowing through the entire circuit. The frequency domain impedances of CPE1 and CPE2 are shown below:

[0087]

[0088] In the formula, α and β are the fractional orders of the constant phase angle elements CPE1 and CPE2, respectively; C1 and C2 are the capacitance values ​​of CPE1 and CPE2, respectively; and ω is the angular frequency.

[0089] Simultaneously, based on the components in the dual-polarization fractional-order equivalent circuit model, the frequency domain impedance equation of the model is established:

[0090]

[0091] In the formula, Z TZ1(jω) is the frequency domain impedance of the dual-polarization equivalent circuit model; Z2(jω) is the frequency domain impedance of the constant phase angle element CPE1; and Z2(jω) is the frequency domain impedance of the constant phase angle element CPE2.

[0092] Based on the frequency domain impedance equation of the dual-polarization fractional-order equivalent circuit model, the following fitness function is established:

[0093]

[0094] In the formula, This represents the magnitude of the model's frequency domain impedance after dividing it by the impedance obtained in step 3; The phase angle, expressed as rad, is the result of dividing the model's frequency domain impedance by the impedance obtained in step 3. e This represents the weighting coefficient, which is typically set to 2.2222.

[0095] The particle swarm optimization algorithm is used to optimize the fitness function to obtain the impedance model parameter R1 of the i-th battery in electric vehicle-1 or electric vehicle-2. 0,i R2 0,i R1 SEI,i R2 SEI,i R1 CT,i R2 CT,i α1 i α2 i β1 i β2 i C1 1,i C2 1,i C1 2,i C2 2,i R0 and RSEI represent the ohmic impedance R0 and SEI film resistance R2 for electric vehicle-1 and electric vehicle-2, respectively. SEI Charge transfer impedance R CT The fractional order α of constant phase angle element CPE1, the fractional order β of constant phase angle element CPE2, the coefficient C1 of constant phase angle element CPE1, and the coefficient C2 of constant phase angle element CPE2.

[0096] S6. Optimal Pulse Frequency Calculation: Establish an objective function for the optimal pulse frequency of the i-th battery for either electric vehicle-1 or electric vehicle-2:

[0097]

[0098] In the formula, f p,i,min This represents the pulse frequency when the above objective function is minimized.

[0099] The optimized pulse charging frequency for either electric vehicle-1 or electric vehicle-2 was ultimately determined as follows:

[0100]

[0101] In the formula, m is the number of battery cells in the electric vehicle.

[0102] Set the initial set frequency f of S2.A4 or S2.A5 b =f d-op This achieves optimal pulse frequency charging.

[0103] S7. Calculation of Optimal Average Pulse Frequency: Calculate the optimal pulse frequency f for electric vehicle-1 and electric vehicle-2 respectively according to step 6. op-1 f op-2 Finally, the optimized average pulse frequency f was determined. d-op for:

[0104]

[0105] Let the initial set frequency f of S2.A1 be... b =f d-op This achieves optimal pulse frequency charging.

[0106] S8. Battery Pack Health Status Diagnosis: By calculating the resistance parameter variance of electric vehicle-1 and electric vehicle-2 using the parameters obtained in step S5, the inconsistency of the battery cells in the battery pack can be obtained, as detailed below:

[0107]

[0108]

[0109]

[0110]

[0111]

[0112]

[0113] The total variance of electric vehicle-1 or electric vehicle-2 can be expressed as:

[0114]

[0115]

[0116] S9. Health Status Information Release: In step 6... and This indicates the degree of inconsistency between the battery cells in electric vehicle-1 and electric vehicle-2. If it exceeds a set value h, where h is a constant greater than 0, information needs to be sent to the mobile terminal through the data interaction center to remind the user to maintain and service the electric vehicle battery pack, thereby preventing the inconsistency from escalating and causing a safety accident.

[0117] The above description is only a preferred embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the embodiments of the present invention should be included within the protection scope of the present invention.

Claims

1. An electric vehicle charging pile with integrated wideband impedance measurement, characterized in that, The primary side of the isolation transformer is connected to the power grid, and the secondary side is connected to the input terminal of the AC / DC converter; the first bidirectional DC / DC converter has its input terminal connected in parallel with a first supporting capacitor and then connected to the output terminal of the AC / DC converter, and its output terminal is connected to the first interactive bus; it also includes a data interaction center module, a wideband impedance identification module, and a central controller; the data interaction center module is connected to the first interactive bus through a data link line; the data interaction center module is also connected to the wideband impedance identification module and the central controller respectively; The wideband impedance identification module is also connected to the central controller.

2. The electric vehicle charging pile with integrated wideband impedance measurement as described in claim 1, characterized in that, It also includes a second bidirectional DC / DC converter, whose input is connected in parallel with a second supporting capacitor and then connected to the output of the AC / DC converter, and whose output is connected to a second interactive bus; the second interactive bus is connected to the data interactive center module through a data communication line.

3. A control method for an electric vehicle charging pile integrating wideband impedance measurement, characterized in that, Pulse charging of the first electric vehicle: when the voltage of the first electric vehicle is less than its charging cutoff voltage V m-1 At that time, control the output frequency f of the first DC / DC converter. b-1 Amplitude I p A pulsed current is used to charge the first electric vehicle; when the voltage of the first electric vehicle equals V... m-1 When charging stops, the charging process will cease. The frequency f b-1 It is obtained through the following steps: Step time identification: For every x% increase in the state of charge of the battery of the first electric vehicle, sample the battery current and extract the current step point; Extracting the broadband impedance and calculating the optimal pulse frequency includes: Step 1: Calculate the voltage U of each cell in the first electric vehicle battery pack at the moment of current step change. i (k j T s The wavelet coefficients W U,i,j (a,k j T s ), and current I i (k j T s The wavelet coefficients W I,i,j (a,k j T s ); where i represents the i-th cell; k j T represents the number of sampling points at the j-th current step point. s The sampling period is represented by ; 'a' is the scale of the wavelet transform. Step 2, calculate k at the current step time of the i-th cell. j T s Wideband impedance; Step 3: Calculate the average broadband impedance of the i-th cell at all current step moments, and use it as the impedance of the i-th cell; take the modulus of the impedance of the i-th cell, and find the frequency corresponding to the minimum modulus value, and use it as the optimal pulse frequency of the i-th cell. Step 4: Calculate the average of the optimal pulse frequencies of all cells in the first electric vehicle, and use this average as the optimal pulse frequency f of the first electric vehicle battery pack. op-1 , let f b-1 =f op-1 .

4. The control method for an electric vehicle charging pile with integrated wideband impedance measurement as described in claim 3, characterized in that, Also provide pulse charging for the second electric vehicle: when the voltage of the second electric vehicle is less than its charging cutoff voltage V. m-2 At that time, control the output frequency f of the second DC / DC converter. b-2 Amplitude I p A pulsed current is used to charge the second electric vehicle; when the voltage of the second electric vehicle equals V... m-2 When charging stops, the pulse current charging the first electric vehicle and the pulse current charging the second electric vehicle are 180° out of phase. The optimal pulse frequency f of the second electric vehicle battery pack is obtained. op-2 The method, and obtaining the optimal pulse frequency f of the first electric vehicle battery pack. op-1 The method is the same; Take f op-1 and f op-2 The mean f d-op , let f b-1 =f b-2 =f d-op .

5. The control method for an electric vehicle charging pile with integrated wideband impedance measurement as described in claim 3, characterized in that, The second electric vehicle is also charged using a constant current and constant voltage method: when the voltage of the second electric vehicle is less than its charging cutoff voltage V. m-2 At that time, control the output current I of the second DC / DC converter. s The second electric vehicle is charged with a constant current; when the voltage of the second electric vehicle equals V... m-2 At that time, control the output voltage V of the second DC / DC converter. m-2 The second electric vehicle is charged with constant voltage until the charging current is less than the preset value I. m When the time is right, stop charging.

6. A method for diagnosing the health status of an electric vehicle battery pack, characterized in that, The electric vehicle pulse charging; Step 1, Step Time Identification: For every x% increase in the state of charge of the electric vehicle's battery, sample the battery current and extract the current step point; Step 2, extract the broadband impedance, including: 2.1 Calculate the voltage U of each cell in the electric vehicle battery pack at the moment of current step change. i (k j T s The wavelet coefficients W U,i,j (a,k j T s ), and current I i (k j T s The wavelet coefficients W I,i,j (a,k j T s ); where i represents the i-th cell; k j T represents the number of sampling points at the j-th current step point. s The sampling period is represented by ; 'a' is the scale of the wavelet transform. 2.2 Calculate k at the current step time of the i-th cell. j T s Wideband impedance; 2.3 Calculate the average broadband impedance of the i-th cell at all current step moments, and use it as the impedance of the i-th cell; Step 3: Establish a diagnostic model for diagnosis, including: 3.1 Establish a fractional-order equivalent circuit model for dual-polarization; 3.2 Based on the components in the dual-polarization fractional-order equivalent circuit model, establish the frequency domain impedance equation of the model; 3.3 Establish the fitness function based on the frequency domain impedance equation; 3.4 The fitness function is optimized using the particle swarm optimization algorithm to obtain the ohmic impedance R of the i-th cell in the electric vehicle. 0,i SEI film resistance R SEI,i Charge transfer impedance R CT,i The fractional order α of the constant phase angle element CPE1 i The fractional order β of the constant phase angle element CPE2 i The coefficient C of the constant phase angle element CPE1 1,i The coefficient C of the constant phase angle element CPE2 2,i ; 3.5 According to R 0,i R SEI,i R CT,i α i β i C 1,i C 2,i Calculate the variance of the ohmic impedance R0 and the SEI film resistance R of all battery cells in the electric vehicle. SEI variance and charge transfer impedance R CT Calculate the variance of the three variances mentioned above; calculate the total variance of the three variances mentioned above. Step 4: Use the total variance and a preset threshold to determine the degree of inconsistency in the battery cells of the electric vehicle.

7. A method for diagnosing the health status of an electric vehicle battery pack, characterized in that, The electric vehicle is a first electric vehicle, and it is charged with constant current and constant voltage: when the voltage of the first electric vehicle is less than its charging cutoff voltage V m-1 At that time, control the output current I of the first DC / DC converter. s The first electric vehicle is charged with a constant current; when the voltage of the first electric vehicle equals V... m-1 At that time, control the output voltage V of the first DC / DC converter. m-1 The first electric vehicle is charged with constant voltage until the charging current is less than the preset value I. m When charging stops, the charging process will cease. Step 0, Disturbance signal injection: During constant current charging, for every x% increase in the battery state of charge of the first electric vehicle, the charging current I... s Based on this, an amplitude of 0.1×I is superimposed. s The duty cycle is 0.5 and the step interval is t. a Square wave disturbance, t a It is a constant greater than 0; the number of cycles for injecting perturbation is a preset value n, where n is an integer greater than 0; Step 1, Step Time Identification: Sample the battery current of the first electric vehicle and extract the current step point; Step 2, extract the broadband impedance, including: 2.1 Calculate the voltage U of each cell in the first electric vehicle battery pack at the moment of current step change. i (k j T s The wavelet coefficients W U,i,j (a,k j T s ), and current I i (k j T s The wavelet coefficients W I,i,j (a,k j T s ); where i represents the i-th cell; k j T represents the number of sampling points at the j-th current step point. s The sampling period is represented by ; 'a' is the scale of the wavelet transform. 2.2 Calculate k at the current step time of the i-th cell. j T s Wideband impedance; 2.3 Calculate the average broadband impedance of the i-th cell at all current step moments, and use it as the impedance of the i-th cell; Step 3: Establish a diagnostic model for diagnosis, including: 3.1 Establish a fractional-order equivalent circuit model for dual-polarization; 3.2 Based on the components in the dual-polarization fractional-order equivalent circuit model, establish the frequency domain impedance equation of the model; 3.3 Establish the fitness function based on the frequency domain impedance equation; 3.4 The fitness function is optimized using the particle swarm optimization algorithm to obtain the ohmic impedance R of the i-th cell in the first electric vehicle. 0,i SEI film resistance R SEI,i Charge transfer impedance R CT,i The fractional order α of the constant phase angle element CPE1 i The fractional order β of the constant phase angle element CPE2 i The coefficient C of the constant phase angle element CPE1 1,i The coefficient C of the constant phase angle element CPE2 2,i ; 3.5 According to R 0,i R SEI,i R CT,i α i β i C 1,i C 2,i Calculate the variance of the ohmic impedance R0 and the SEI film resistance R of all cells in the first electric vehicle. SEI variance and charge transfer impedance R CT Calculate the variance of the three variances mentioned above; calculate the total variance of the three variances mentioned above. Step 4: Use the total variance and a preset threshold to determine the degree of inconsistency in the battery cells of the first electric vehicle.

8. The method for diagnosing the health status of an electric vehicle battery pack as described in claim 7, characterized in that, It also includes a second electric vehicle, which is charged with constant current and constant voltage: when the voltage of the second electric vehicle is less than its charging cutoff voltage V m-2 At that time, control the output current I of the second DC / DC converter. s The second electric vehicle is charged with a constant current; when the voltage of the second electric vehicle equals V... m-2 At that time, control the output voltage V of the second DC / DC converter. m-2 The second electric vehicle is charged with constant voltage until the charging current is less than the preset value I. m When charging stops, the charging process will cease. Step 0 is replaced by complementary perturbation signal injection: during constant current charging, for every x% increase in the state of charge of the first electric vehicle or the second electric vehicle, the charging current I of the first electric vehicle... s Based on this, an amplitude of 0.1×I is superimposed. s The duty cycle is 0.5 and the step interval is t. a The square wave disturbance; simultaneously, the charging current I of the second electric vehicle s Based on this, an amplitude of 0.1×I is superimposed. s The duty cycle is 0.5 and the step interval is t. a The square wave disturbance has a phase that differs from the phase of the square wave disturbance of the first electric vehicle by 180°; t a The number of cycles for which the disturbance is injected is a constant greater than 0, and n is a preset value, where n is an integer greater than 0. Following the methods in steps 1-4, determine the degree of inconsistency between the battery cells of the first electric vehicle and the second electric vehicle.

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