Non-isolated Bidirectional Soft-switching Equalization Circuit and Its Method for Battery EIS Detection

Abstract

The present invention provides a non-isolated bidirectional soft-switching equalization circuit and a method for battery EIS detection. The equalization circuit is based on a bidirectional chopper circuit, which can achieve bidirectional energy transfer. By adding auxiliary switches, capacitors and inductors, soft switching is realized to reduce switching losses. And this equalization circuit is applied to the detection of battery electrochemical impedance spectroscopy. The method for using this equalization circuit to detect battery electrochemical impedance spectroscopy includes: injecting multi-frequency periodic signals into the equalization control loop; exciting the battery under test with the output current and collecting battery voltage and current data; processing the data using fast Fourier transform to obtain impedance information at multiple frequencies, and further obtaining the battery electrochemical impedance spectroscopy. The solution of the present invention provides an equalization circuit, and can realize the function integration of active equalization and battery electrochemical impedance spectroscopy detection. The equalization circuit is adopted and no additional power supply is required. Integrated in the battery management system, it can also be applied to battery fault diagnosis, etc.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery management, and particularly relates to a non-isolated bidirectional soft-switching equalization circuit and a method for battery EIS detection using the same. Background Art

[0002] Lithium-ion batteries are widely used in energy storage, new energy vehicles, and electronic devices. Currently, the applications of lithium-ion batteries are becoming increasingly rich, but battery management still faces many problems. The Electrochemical Impedance Spectroscopy (EIS) of a battery is one of the important means for battery monitoring, which can provide relevant information about the battery performance and reflect the capacity of a single battery cell; during the normal use of a lithium-ion battery, the impedance change range is small, but after a certain number of charge-discharge cycles, the impedance will change significantly. Therefore, EIS can be used to predict the battery life; for a lithium-ion battery pack, selecting lithium-ion batteries with relatively consistent impedance for combination can extend the service life of the battery pack; in addition, battery fault diagnosis can also be performed through the change of battery EIS. Currently, many methods for detecting the electrochemical impedance spectrum of a battery rely on expensive instrument equipment and require off-line measurement in a laboratory environment. The measurement results are mainly used for precise research in the field of electrochemistry, and more attention is paid to the measurement accuracy, but there are great limitations and deficiencies in terms of measurement speed and convenience.

[0003] Active equalization is a technology that uses various equalization topologies to ensure the consistency of the State of Charge (SOC) among batteries. Improving the equalization topology is an important research direction in battery active equalization technology. Improving the equalization topology can effectively improve the speed and efficiency of battery equalization, reduce circuit losses, and lower the equalization cost.

[0004] Both of the above two technologies achieve their respective functions by supplying electrical energy to the battery. Therefore, it is considered to combine the perturbation injection method in a new equalization circuit to detect the battery EIS online. Summary of the Invention

[0005] To solve the problems of defects and deficiencies existing in the prior art, the present invention proposes a non-isolated bidirectional soft-switching equalization circuit and a method for battery EIS detection using the same. It provides an equalization topology circuit and is applied to an online battery EIS detection system based on active equalization, which can realize the functional integration of active equalization and battery electrochemical impedance spectrum detection. It innovatively uses the equalization circuit to complete the excitation of the battery, expands the functions and applications of the equalization topology circuit; makes full use of the original software and hardware of the battery management system, reduces the cost of the EIS detection system; the battery can be conveniently detected for EIS online without being disconnected from the working state.

[0006] The equalization circuit is based on a bidirectional chopper circuit, which can achieve bidirectional energy transfer; by adding auxiliary switches, capacitors and inductors, soft switching is realized to reduce switching losses; and this equalization circuit is applied to the detection of the electrochemical impedance spectrum of the battery. The method for using this equalization circuit to detect the electrochemical impedance spectrum of the battery includes: injecting multi-frequency periodic signals into the equalization control loop; exciting the battery under test with the output current, and collecting battery voltage and current data; processing the data using the fast Fourier transform to obtain impedance information at multiple frequencies, and then obtaining the electrochemical impedance spectrum of the battery. The solution of the present invention provides an equalization circuit, which can realize the functional integration of active equalization and the detection of the electrochemical impedance spectrum of the battery, adopts the equalization circuit and does not require an additional power supply; integrated in the battery management system, it can also be applied to battery fault diagnosis, etc.

[0007] The technical solution adopted by the present invention to solve its technical problems is:

[0008] The present invention first provides a non-isolated bidirectional soft-switching equalization circuit, which is based on a non-isolated bidirectional chopper circuit, and includes two switching tubes V1 and V2 with anti-parallel diodes, auxiliary switching tubes Va1 and Va2 with anti-parallel diodes, resonant capacitors Cr1 and Cr2, capacitor C1, resonant inductor Lr, inductors L1, L2 and L3, and both ends of the equalizer are respectively connected to two battery cells;

[0009] Among them, the resonant capacitor Cr1 is connected in parallel at both ends of the switching tube V1, and is respectively connected to the battery B1 through the inductors L1 and L2. After passing through the capacitor C1, it is connected in parallel with the series-connected auxiliary switching tube Va1, resonant inductor Lr and auxiliary switching tube Va2, and the parallel inductor L3, and the parallel series-connected switching tube V2 and battery B2; the resonant capacitor Cr2 is connected in parallel at both ends of the switching tube V2;

[0010] This equalization circuit is used to achieve bidirectional energy transfer between the two end batteries. When applied as an active equalizer ICE (Individual Cell Equalizer), it equalizes the SOC between the batteries, and realizes soft switching through the auxiliary switches, so that the main switches V1, V2 and the auxiliary switches Va1, Va2 are turned on and off according to a given switching timing, ensuring that the main switches achieve zero-voltage switching and the auxiliary switches achieve zero-current switching during the equalization process, and reducing the switching losses during the equalization process.

[0011] The SOC information of a single cell is obtained through relevant methods for SOC estimation. When the SOC of the cell connected to one end of the equalization circuit is higher than that of the cell at the other end, the SOC difference is used as the equalization criterion. When the difference is higher than the set threshold, equalization is enabled; the end with the higher SOC is used as the input end, and the end with the lower SOC is used as the load end. The on / off of the switching tube is controlled by the PWM signal output by the equalization control circuit, causing the battery at the input end to discharge and the equalization current to charge the battery at the output end; when the SOC difference converges within the equalization threshold, the SOC equalization between the batteries ends.

[0012] This type of equalization circuit can be applied to the detection of the electrochemical impedance spectrum of the battery and provide excitation to the battery as a power circuit.

[0013] When the direction of energy transfer in the equalization circuit is different, the batteries connected to its two ends may be at the input end or the load end. Among them, the discharging battery at the input end supplies power to provide excitation to the battery under test at the load end. Therefore, when applied to the detection of the battery electrochemical impedance spectrum, the equalization circuit does not require an additional power source.

[0014] The control of the equalization current can adopt equalization-related control methods such as fuzzy control, PID control, and adaptive control. Here, the equalization topology structure is mainly introduced, and the relevant equalization control methods and equalization strategies will not be elaborated.

[0015] Most of the relevant schemes for detecting EIS use DC converters, and the active equalization function is realized by the equalization circuit, both of which can provide excitation to the battery. Therefore, it is considered to transform the active equalization circuit to realize the detection of battery EIS. Then the equalization circuit can not only equalize the battery SOC, but also provide excitation energy to the battery under test, realizing function integration and hardware circuit sharing, and expanding the application scope of the equalization circuit.

[0016] Based on the above circuit design, the present invention provides a method for detecting battery EIS using a non-isolated bidirectional soft-switching equalization circuit. According to the non-isolated bidirectional soft-switching equalization circuit described above, it is based on a signal conditioning circuit, a battery string combination, a battery management system sampling module, a PWM (Pulse Width Modulation) driving circuit, a digital controller, and a battery management system;

[0017] The non-isolated bidirectional soft-switching equalization circuit is connected to the battery string combination; the voltage and current signal terminals of the battery string are connected to the signal conditioning circuit; the output terminal of the signal conditioning circuit is connected to the ADC (Analog to Digital Converter) pin of the battery management system sampling module; the PWM output terminal of the digital controller is connected to the input terminal of the PWM driving circuit; the output terminal of the PWM driving circuit is connected to the gate of the switching tube in the non-isolated bidirectional soft-switching equalization circuit.

[0018] As an alternative, in this EIS detection method, the equalization circuit can be other types of equalization circuits in addition to the non-isolated bidirectional soft-switching equalization circuit described above. These include: an equalization circuit capable of bidirectional or unidirectional energy transfer between adjacent cells; an equalization circuit capable of bidirectional or unidirectional energy transfer between any two cells; and an equalization circuit capable of bidirectional or unidirectional energy transfer between a cell and a battery pack.

[0019] The number of batteries that can be detected by this application method is determined by the number of batteries connected in the equalization circuit, which includes X cells, where X ≥ 2; multiple batteries in the equalization circuit can be simultaneously in an excited state, and by obtaining the voltage and current data of the excited batteries, the EIS can be detected. Therefore, this detection method can detect the EIS of multiple batteries simultaneously.

[0020] The signal conditioning circuit separates the AC and DC signals of the battery voltage and current, removes the influence of DC and high-frequency noise interference, and amplifies the AC signal.

[0021] The function of collecting the battery voltage and current signals is realized by the sampling module in the battery management system without the need for additional hardware circuits. Considering the sampling accuracy and the frequency range of the disturbance signals, the sampling module of the battery management system is preferably an analog front-end chip with a relatively high sampling frequency. The realization of the detection function also includes other necessary software and hardware of the battery management system.

[0022] The PWM drive circuit amplifies the PWM control pulse output by the digital controller to a level sufficient to drive the switching tube, provides sufficient driving ability, and avoids overvoltage and overcurrent of the power device.

[0023] The digital controller is used for system control, signal processing, and calculating the impedance spectrum, and can be the digital controller in the battery management system or a microcomputer.

[0024] In actual operation, this method includes the following steps:

[0025] Step S1: Establish an active equalization circuit, use the cell at the input end of the equalizer as the power supply DC source, and use the cell at the load end as the battery to be measured;

[0026] Step S2: Control the switching tube in the equalizer to output current to the load end. After the equalization current reaches a steady state, inject multi-frequency periodic signals into the current reference value of the current control loop, and then use the superimposed current to excite the battery to be measured connected to the load end;

[0027] Step S3: After injecting the superimposed signal, separate the AC and DC of the voltage across the battery and the battery current in the signal conditioning circuit, remove the influence of DC and high-frequency noise interference, and amplify the AC signal; at the same time, the sampling module of the battery management system samples at a frequency f SSynchronously collect the conditioned battery voltage and current signals, and the sampling frequency f S is at least 5 to 10 times the highest disturbance frequency f n ;

[0028] Step S4: Perform a fast Fourier transform on the obtained voltage and current information in the digital controller or microcomputer of the battery management system, and calculate the battery impedance information at each disturbance frequency by an algorithm, and further obtain the battery EIS within a certain frequency range.

[0029] Furthermore, step S1 specifically includes the following steps:

[0030] Establish the non-isolated bidirectional soft-switching equalization circuit as the active equalizer ICE, and connect one such active equalizer ICE between two series-connected batteries to achieve the mutual transfer and mutual excitation of energy between the two batteries;

[0031] By controlling the on and off of different switching tubes, among the two batteries connected by the equalizer ICE, the battery with a high SOC discharges and the battery with a low SOC charges; the battery discharging at the input end is used as the power supply DC source, and the battery charging at the load end is used as the battery under test; the equalization control loop in the digital controller makes the equalization current stable at the reference current value by tracking the magnitude of the reference current.

[0032] Furthermore, step S2 specifically includes the following steps:

[0033] The detection of the battery electrochemical impedance spectrum requires the battery to be in a stable DC polarization condition, and then perturbations and excitations are performed. Therefore, this technical solution adopts a constant current detection mode;

[0034] After starting the detection, the battery under test at the load end is excited. After the current reaches a steady state, a sine signal is injected into the reference current of the control loop, and then the duty cycle output by the control circuit is superimposed with the duty cycle D dc corresponding to the perturbation on the basis of the DC part D ac , and the duty cycle for controlling the switching tube is obtained as:

[0035] D = D dc + D ac (1)

[0036] After obtaining the duty cycle for controlling the switching tube, a PWM control pulse with a duty cycle of D is output through the PWM module of the digital controller, and then the PWM control pulse is amplified by the switching tube drive circuit to be sufficient to drive the switching tube; the current output by the equalization circuit excites the battery under test at the load end, and the excitation current for the battery is obtained by superimposing the DC current I dc with the AC perturbation current I m sin(ωt), expressed as:

[0037] I dc +I m sin(ωt)(2)

[0038] The frequency of the perturbation signal is selected to have the same number of frequency components per decade to reduce the noise interference in detection.

[0039] In addition, since the EIS detection and the battery management system share a sampling module to collect voltage and current information, the perturbation frequency range needs to consider the limitation of the sampling frequency of the analog front-end chip in the battery management system. At the same time, considering the sampling theorem and the requirements of engineering practice, it is necessary to comprehensively determine the upper and lower limits of the perturbation frequency.

[0040] Furthermore, step S3 specifically includes the following steps:

[0041] After injecting multi-frequency periodic signals into the equalization circuit, the directly sampled battery voltage and current are the superposition of a large DC component and a small AC component, and contain high-frequency noise interference signals, resulting in a large sampling error.

[0042] Separate the AC and DC signals of the voltage and current in the signal conditioning circuit; use the method of inverting and adding the effective values to obtain the AC voltage and AC current, remove the influence of the DC and high-frequency noise interference signals, and amplify the voltage and current signals by the same multiple;

[0043] Subtract the DC signal from the mixed signal to obtain the required small AC signal; the mixed signal is amplified by the differential circuit for the useful signal and the high-frequency interference is removed through a low-pass filter; one path of the mixed signal is used for signal following, and the other path extracts the effective value of the mixed signal through an effective value chip and is inverted by an inverter, and finally the two paths of signals are superimposed to obtain the small AC signal;

[0044] The sampling module in the battery management system synchronously collects the time-domain voltage and current information of the battery at a frequency f S ;

[0045] According to the Nyquist sampling theorem, the sampling frequency f s higher than twice the highest frequency of the frequency band to be measured is sufficient.

[0046] However, in engineering practice, considering the sampling accuracy and frequency aliasing problems, the sampling frequency f s is selected to be 5 to 10 times or more of the highest frequency of the frequency band to be measured, and the sampling can be carried out for a duration of more than 2 times the lowest frequency period.

[0047] Furthermore, step S4 specifically includes the following steps:

[0048] The periodic function is represented by the Fourier series as the sum of an infinite series composed of a DC component and sine functions:

[0049]

[0050] Where A n is the amplitude of the sine vector with a frequency of nf 0 ; is its phase angle; A 0 is the DC bias;

[0051] After the system obtains voltage and current information, in the digital controller of the battery management system, the sampled voltage and current information is subjected to FFT (Fast Fourier Transform) decomposition to obtain the signal corresponding to the disturbance frequency, that is, complex voltage and current information containing real and imaginary parts is obtained;

[0052] The signal of the current peak point above a given amplitude is selected, and the voltage peak point signal corresponding to the frequency of this current peak point is selected; processing operations are performed on this voltage and current signal, and the complex impedance information at this frequency is obtained:

[0053]

[0054] Where θ(f) is the phase difference between voltage and current at this frequency; V p (f) is the amplitude of the voltage peak point at this frequency; I p (f) is the amplitude of the current peak point at this frequency. R is the real part of the complex impedance, and X is the imaginary part of the complex impedance;

[0055] The complex impedance information at multiple disturbance frequencies is obtained at one time through the algorithm, and the electrochemical impedance spectrum of the battery within a certain frequency range is plotted.

[0056] Compared with the prior art, the beneficial effects of the present invention and its preferred solutions include:

[0057] 1. The present invention adopts a non-isolated bidirectional soft-switching equalization circuit, realizes soft switching through an auxiliary switch, reduces the switching loss in long-term equalization, and applies this topology to battery EIS detection as a power circuit for providing excitation.

[0058] 2. The present invention can realize the functional integration of battery active equalization and battery electrochemical impedance spectrum detection, share the equalization circuit to charge and excite the battery, and expands the function and application range of the equalization circuit;

[0059] 3. The present invention adopts the sampling module, digital controller of the battery management system and other necessary components of the battery management system, makes full use of the original software and hardware of the battery management system, and reduces the cost of battery EIS detection.

[0060] 4. By injecting a multi-frequency periodic signal, such as a sine signal, into the charging current of the battery, the present invention can obtain complex impedance information at multiple frequencies within a certain acquisition period, and obtain an electrochemical impedance spectrum within a certain frequency range; moreover, the battery can be conveniently detected online for EIS without being disconnected from the working state; furthermore, it can be applied to battery fault diagnosis. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] The present invention will be further described in detail below in conjunction with the drawings and specific embodiments:

[0062] Figure 1 Schematic diagram of the system architecture and balancing circuit of the embodiment of the present invention;

[0063] Figure 2 Schematic diagram of the principle of injecting a perturbation into the non-isolated bidirectional soft-switching balancing circuit in the embodiment of the present invention;

[0064] Figure 3 Electrochemical impedance spectrum within a certain frequency range obtained from the simulation data of the embodiment of the present invention under the FFT algorithm. The solid line part is the theoretical impedance spectrum of the battery Randles impedance model in the simulation, and the dotted line and circle part are the impedance spectra obtained by the method of the embodiment in the simulation. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0065] In order to make the features and advantages of this patent more obvious and understandable, specific embodiments are given below and described in detail as follows:

[0066] It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used in this specification have the same meaning as commonly understood by those of ordinary skill in the technical field to which this application belongs.

[0067] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0068] The solution provided in this embodiment uses a non-isolated bidirectional soft-switching balancing circuit as the equalizer ICE and applies it to the battery EIS online detection system.

[0069] As Figure 1As shown, it is the online detection hardware architecture of the battery EIS based on the equalization circuit, including the battery active equalization circuit, the signal conditioning circuit, the battery string combination, the battery management system sampling module, the PWM drive circuit, the digital controller, and other various necessary software and hardware of the battery management system. The battery active equalization circuit is connected to the battery string combination, and an active equalizer ICE is connected between two adjacent batteries; the voltage and current signal terminals of the battery string are connected to the signal conditioning circuit; the output terminal of the signal conditioning circuit is connected to the ADC pin of the battery management system sampling module; the PWM output terminal of the battery management system digital controller is connected to the input terminal of the PWM drive circuit; the output terminal of the PWM drive circuit is connected to the gate of each switching tube in the active equalization circuit.

[0070] As Figure 1 Shown in the upper block diagram, it is the schematic diagram of the equalization topology circuit in this embodiment. This non-isolated bidirectional soft-switching equalization circuit includes two switching tubes V1 and V2 with anti-parallel diodes, auxiliary switching tubes Va1 and Va2, resonant capacitors Cr1 and Cr2, capacitor C1, resonant inductor Lr, inductors L1, L2, and L3. Both ends of the equalizer are respectively connected to two battery cells.

[0071] This equalization circuit can realize the bidirectional transfer of energy between the two end batteries. As an equalizer, it can perform the equalization of the SOC between the batteries.

[0072] When the EIS detection is started, the equalization circuit serves as the power circuit to provide excitation. When B1 is used as the input terminal battery to provide excitation energy; the battery under test B2 is placed at the load terminal. In the equalizer ICE, keep the switching tube V2 off, and only control the high-frequency on-off of the switching tube V1, so that the battery B1 charges the battery B2. The auxiliary switching tubes Val and Va2 are turned on and off in a specific switching sequence to ensure soft switching during the equalization process and reduce the switching loss during the equalization process.

[0073] After starting the EIS detection, perform closed-loop control on the current output by the equalizer, and control the current magnitude at the set current reference value. When the equalization current reaches a steady state, the battery forms a stable DC polarization condition, reaching the constant current state required for electrochemical impedance detection.

[0074] As Figure 2 Shown, after the current reaches a steady state, add sine superposition signals of multiple frequencies to the current reference value of the current closed-loop control loop through the digital controller. Then the duty cycle output by the controller will superimpose the duty cycle D corresponding to the perturbation on the basis of the DC corresponding duty cycle D dc , obtaining the duty cycle for controlling the switching tube V1 as: ac

[0075] D = D dc + D ac (1)

[0076] Then, the PWM module of the digital controller outputs a PWM control signal with a duty cycle of D, and a sufficient driving voltage is generated through the driving circuit to reliably drive the switching transistor V1. The excitation current for the battery is composed of a DC current I dc superimposed with an AC perturbation current I m sin(ωt), which is expressed as:

[0077] I dc +I m sin(ωt) (2)

[0078] At this time, the current and voltage signals of the battery contain the AC impedance information.

[0079] Similarly, when detecting the EIS of battery B1, control the switching transistor V2 to turn on and off at a high frequency, so that battery B2 charges battery B1, and other processes are the same as those in the above embodiment.

[0080] After injecting the perturbation signal, the method of inverting and superimposing the effective values is used to separate the AC and DC signals, obtain the AC voltage and current, remove the influence of the DC and high-frequency noise interference signals, and amplify the AC signal. Then, the sampling module in the battery management system synchronously samples the voltage and current signals of the battery at a frequency f S to obtain the time-domain voltage and current information.

[0081] Theoretically, according to the Nyquist sampling theorem, the sampling frequency f S higher than twice the highest frequency of the frequency band to be measured is sufficient. However, in engineering practice, considering the sampling accuracy and frequency aliasing problems, the sampling frequency f S is usually 5 to 10 times higher than the highest frequency of the frequency band to be measured.

[0082] The sampling function of the present invention is implemented by the sampling module of the battery management system. Considering that the sampling frequency of the commonly used analog front-end chip in the battery management system is usually not very high, the highest frequency of the perturbation signal in this embodiment is taken as 300 Hz; the information acquisition period is selected to be more than twice the period of the lowest perturbation frequency for sampling.

[0083] Periodic functions can all be expressed as an infinite series sum of a DC component and sine functions through Fourier series:

[0084]

[0085] where A n is the amplitude of the sine vector with a frequency of nf 0 ; is its phase angle; A 0 is the DC bias.

[0086] Therefore, in the digital controller of the battery management system, fast Fourier transform (FFT) is performed on the sampled battery voltage and current signals to obtain voltage and current signals with real and imaginary parts at different disturbance frequencies.

[0087] Through the algorithm, current peak point signals above a certain amplitude are selected, and the voltage peak point signals corresponding to the frequencies of these current peak points are selected. Processing operations are performed on the complex signals of the voltage and current peak points at this frequency, and the complex impedance information at this frequency is obtained:

[0088]

[0089] where θ(f) is the phase difference between the voltage and current at this frequency; V p (f) is the amplitude of the voltage peak point at this frequency; I p (f) is the amplitude of the current peak point at this frequency. R is the real part of the complex impedance, and X is the imaginary part of the complex impedance.

[0090] By solving the impedance information corresponding to each disturbance frequency, the algorithm can draw the electrochemical impedance spectrum information of the battery to be tested within the disturbance frequency range.

[0091] As Figure 3 shown, it is the impedance spectrum obtained from the simulation experiment of the embodiment under the FFT algorithm. An isolated bidirectional soft-switching equalization circuit and a first-order battery impedance Randles model are built in the Simulink software. A multi-frequency periodic sine superposition signal is injected into the current reference value of the current closed-loop controller, with the highest frequency being 300 Hz and the lowest frequency being 0.1 Hz. The battery voltage and current information obtained by sampling forms a data set, and the battery EIS information within the disturbance frequency range shown in the figure is obtained through processing by the FFT algorithm program.

[0092] The above are only the preferred embodiments of the present invention, and it is not a limitation to the present invention in other forms. Any person skilled in the art may use the disclosed technical content to make changes or modifications into equivalent embodiments with equivalent changes. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the technical solution content of the present invention still fall within the protection scope of the technical solution of the present invention.

[0093] This patent is not limited to the above best implementation manner. Anyone inspired by this patent can obtain various other forms of non-isolated bidirectional soft-switching equalization circuits and methods for their use in battery EIS detection. All equal changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope covered by this patent.

Claims

1. A method for battery EIS detection using a non-isolated bidirectional soft-switching equalization circuit, characterized in that, the non-isolated bidirectional soft-switching equalization circuit includes: Based on a non-isolated bidirectional chopper circuit, which includes two switching transistors V1 and V2 with anti-parallel diodes, auxiliary switching transistors Va1 and Va2 with anti-parallel diodes, resonant capacitors Cr1 and Cr2, capacitor C1, resonant inductor Lr, inductors L1, L2 and L3. The two ends of the equalizer are respectively connected to two battery cells; Resonant capacitor Cr1 is connected in parallel across the two ends of switching transistor V1, and is respectively connected to battery B1 through inductors L1 and L2. After passing through capacitor C1, it is connected in parallel with the series-connected auxiliary switching transistor Va1, resonant inductor Lr and auxiliary switching transistor Va2, and parallel inductor L3, and parallel with the series-connected switching transistor V2 and battery B2; Resonant capacitor Cr2 is connected in parallel across the two ends of switching transistor V2; This equalization circuit is used to realize the bidirectional transfer of energy between the two end batteries. When applied as an active equalizer, it equalizes the SOC between the batteries, and realizes soft switching through the auxiliary switches, so that the main switches V1, V2 and the auxiliary switches Va1, Va2 are turned on and off according to a given switching sequence, ensuring that the main switches achieve zero-voltage switching and the auxiliary switches achieve zero-current switching during the equalization process, reducing the switching losses during the equalization process; Obtain the SOC information of the single battery through relevant methods of SOC estimation. When the SOC of the battery connected to one end of the equalization circuit is higher than that of the battery at the other end, use the SOC difference as the equalization criterion. When the difference is higher than the set threshold, start the equalization; The end with the higher SOC is used as the input end, and the end with the lower SOC is used as the load end. Control the on and off of the switching transistors through the PWM signal output by the equalization control circuit, so that the battery at the input end discharges, and the equalization current charges the battery at the output end; When the SOC difference converges within the equalization threshold, end the SOC equalization between the batteries; Based on a signal conditioning circuit, a battery string combination, a battery management system sampling module, a PWM drive circuit, a digital controller, and a battery management system; The non-isolated bidirectional soft-switching equalization circuit is connected to the battery string combination; the voltage and current signal terminals of the battery string are connected to the signal conditioning circuit; the output terminal of the signal conditioning circuit is connected to the ADC pin of the battery management system sampling module; the PWM output terminal of the digital controller is connected to the input terminal of the PWM drive circuit; The output terminal of the PWM drive circuit is connected to the gate of the switching transistor in the non-isolated bidirectional soft-switching equalization circuit; A method for battery EIS detection includes the following steps: Step S1: Establish an active equalization circuit, use the single cell currently at the input end of the equalizer as the power supply DC source, and use the single cell at the load end as the battery under test; Step S2: Control the switching transistor in the equalizer to output current to the load end. After the equalization current reaches a steady state, inject a multi-frequency periodic signal into the current reference value of the current control loop, and then use the superimposed current to excite the battery under test connected to the load end; Step S3: After injecting the superimposed signal, the voltage across the battery and the battery current are separated into AC and DC in the signal conditioning circuit to remove the influence of DC and high-frequency noise interference and amplify the AC signal; at the same time, the sampling module of the battery management system synchronously collects the conditioned battery voltage and current signals at a frequency f S which is at least 5 to 10 times the highest disturbance frequency f S where the f n is at least 5 to 10 times the highest disturbance frequency f Step S4: Perform a fast Fourier transform on the obtained voltage and current information in the digital controller or microcomputer of the battery management system, calculate the battery impedance information at each perturbation frequency through the algorithm, and further obtain the battery EIS within a certain frequency range.

2. The method according to claim 1, wherein: Step S2 specifically includes the following steps: Adopt a constant current detection mode; After starting the detection, the battery under test at the load end is excited. After the current reaches a steady state, a multi-frequency sine superposition signal is injected into the reference current of the control loop, and then the duty cycle output by the control circuit is superimposed with the duty cycle D dc corresponding to the perturbation on the basis of the DC part D ac , and the duty cycle for controlling the switching transistor is obtained as follows: D = D dc + D ac (1) After obtaining the duty cycle of the control switch tube, a PWM control pulse with a duty cycle of D is output through the PWM module of the digital controller, and then the PWM control pulse is amplified by the switch tube drive circuit to be sufficient to drive the switch tube; the current output by the equalization circuit excites the battery under test at the load end, where the excitation current for the battery is composed of a DC current I dc superimposed with an AC perturbation current I m sin(ωt), expressed as: I dc +I m sin(ωt) (2) The frequency of the perturbation signal is selected to contain the same number of frequency components per decade to reduce noise interference in the detection.

3. The method according to claim 1, wherein: Step S1 specifically includes the following steps: Establish the non-isolated bidirectional soft-switching equalization circuit as the active equalizer ICE, connect one such active equalizer ICE between two series-connected batteries to achieve the mutual transfer and mutual excitation of energy between the two batteries; By controlling the on / off of different switching tubes, among the two batteries connected by the equalizer ICE, the battery with a high SOC discharges and the battery with a low SOC charges; the battery discharging at the input end is used as the power supply DC source, and the battery charging at the load end is used as the battery under test; the equalization control loop in the digital controller makes the equalization current stable at the reference current value by tracking the magnitude of the reference current.

4. The method according to claim 1, wherein: Step S3 specifically includes the following steps: Separate the AC and DC signals of the voltage and current in the signal conditioning circuit; use the method of inverting and adding the effective values to obtain the AC voltage and AC current, remove the influence of DC and high-frequency noise interference signals, and amplify the voltage and current signals by the same multiple; Subtract the DC signal from the mixed signal to obtain the required small AC signal; the mixed signal is amplified by the differential circuit for the useful signal and passes through a low-pass filter to remove high-frequency interference; one path of the mixed signal is used for signal following, and the other path extracts the effective value of the mixed signal through an effective value chip and takes the inverse through an inverter, and finally the two paths of signals are superimposed to obtain the small AC signal; The sampling module in the battery management system synchronously acquires the time-domain voltage and current information of the battery at a frequency f S ​ 5. The method according to claim 1, wherein: Step S4 specifically includes the following steps: The periodic function is represented by the Fourier series as the sum of an infinite series composed of a DC component and sine functions: ; where, A n is the amplitude of a sine vector with a frequency of nf 0 ; is its phase angle; A 0 is the DC bias; After the system obtains the voltage and current information, in the digital controller of the battery management system, perform an FFT fast Fourier decomposition on the sampled voltage and current information to obtain the signals corresponding to the perturbation frequencies, that is, obtain the complex voltage and current information containing real and imaginary parts; Select the current peak point signal above a given amplitude, and select the voltage peak point signal corresponding to the frequency of this current peak point; perform processing operations on this voltage and current signal, that is, obtain the complex impedance information at this frequency: ; where θ(f) is the phase difference between voltage and current at this frequency; V p (f) is the amplitude of the voltage peak point at this frequency; I p (f) is the amplitude of the current peak point at this frequency; R is the real part of the complex impedance, and X is the imaginary part of the complex impedance; Obtain the complex impedance information at multiple perturbation frequencies at one time through the algorithm, and draw the battery electrochemical impedance spectrum within a certain frequency range.

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