Lithium battery impedance spectrum autonomous online detection and power signal composite transmission system

Abstract

The invention discloses a lithium battery impedance spectrum autonomous online detection and power signal composite transmission system based on injection type harmonic modulation, which comprises a bidirectional DC-DC converter, a controller, a sampling and filtering circuit and a lithium battery pack, and is characterized in that one side of the bidirectional DC-DC converter is connected with the lithium battery pack, and the other side of the bidirectional DC-DC converter is connected with a power supply or a load. The characteristics of the switching power supply are fully utilized, harmonic waves are injected through the high-frequency switching action of the DC-DC converter to serve as lithium battery impedance spectrum sweep frequency signals and communication carriers, so that the real-time impedance spectrum of the lithium battery is obtained through analysis, SoC and SoH are estimated on line, meanwhile, the result is modulated to the communication carriers and transmitted to a common direct-current bus, and the real-time impedance spectrum of the lithium battery is obtained. The method is not limited by a DC-DC topological form, and online real-time detection and transmission of the SoC and SoH of the lithium battery can be realized on the premise of not additionally adding hardware circuits and wiring and not normally working the lithium battery pack.

Description

Technical Field

[0001] The present invention belongs to the technical field of power electronic communication, and in particular relates to an autonomous online detection system for lithium battery impedance spectrum and power signal composite transmission based on injected harmonic modulation. Background Art

[0002] With the rapid development of my country's new energy power generation and electric vehicle industries, battery energy storage systems are being used more and more widely. For reasons of safety and efficiency, lithium battery energy storage systems have become mainstream; lithium battery packs are connected to power sources or loads through power electronic converters as interface circuits to achieve efficient and controllable charging and discharging. In order to continuously improve the working efficiency of battery packs, avoid performance loss and safety hazards caused by overcharging and over-discharging, and at the same time not affect the normal operation of the system, it is necessary to conduct real-time status monitoring, life estimation and intelligent control of battery packs online, which requires the system to be able to detect and transmit the status of the battery in real time, mainly including the battery's state of charge (SoC) and the battery's state of health (Stateof Health, SoH).

[0003] On the one hand, traditional battery SoC and SoH detection technologies mainly include voltage method, coulomb counting method and electrochemical impedance spectroscopy (EIS) method. However, the voltage method such as the literature [Q.Yao,D.Lu,G.Lei,“Rapid Open-Circuit Voltage Measurement Method for Lithium-IonBatteries Using One-Cycle Bipolar-Current Pulse,”IEEE Journal of Emerging andSelected Topics in Industrial Electronics,vol.2,no.2,pp.132-141,Apr.2021] is sensitive to temperature and has limited accuracy; the coulomb counting method such as the literature [Y.Ko,K.Cho,M.Kim,and W.Choi,“A NovelCapacity Estimation Method for the Lithium Batteries Using the EnhancedCoulomb Counting Method With Kalman Filter,”IEEE Access,vol.10,pp.38793-38801,Apr.2022] requires a complete charge and discharge process, which is not suitable for real-time applications and has a large impact on battery life; the EIS method such as the literature [Z.Pang,K.Yang,Z.Song,G.Chen,and P.Niu, “Research on SOC Estimation ofLithium Battery Based on Electrochemical Impedance Spectroscopy,” 6 thInternational Conference on Energy, Electrical and Power Engineering (CEEPE), May, 2023] has high accuracy, but the equipment cost is high, and it is difficult to achieve online measurement. Therefore, it is difficult for the existing technology to achieve high-precision online real-time monitoring of the battery status, so it is impossible to achieve real-time feedback and transmission. On the other hand, the traditional battery status transmission mainly adopts an independent communication system, including wired communication technology and wireless communication technology. Wired communication technology such as CAN bus, SPI bus, etc. However, this type of method requires additional communication transmission equipment and lays additional communication lines, which greatly increases the volume, power consumption and cost of the system, and increases the complexity of the system. The difficulty and cost of maintenance are also greatly increased; wireless communication technologies such as Wifi, Zigbee, etc., although they save additional wiring costs and complexity, still require additional signal generation and transmission circuits, and are susceptible to external interference and attacks. In short, the existing battery status detection and status transmission technology uses two independent systems, which have high cost and complexity, and it is difficult to achieve online collection and transmission of real data.

[0004] The power electronic converter is a key component for realizing controlled battery charging and discharging. Its basic principle is to use the high-frequency switching action of the switch tube to achieve the change of the form of electric energy, which is essentially equivalent to a chopper structure. The high-frequency PWM signal drives the switch tube to act, so that the switch tube is alternately turned on and off, thereby obtaining a square wave voltage with the same frequency as the switching action of the switch tube, and finally obtaining the required electric energy output through a passive filter composed of inductors, capacitors, etc. Summary of the invention

[0005] In view of the above, the present invention provides an autonomous online detection system for lithium battery impedance spectrum and power signal composite transmission based on injected harmonic modulation, which can realize online detection and composite transmission of lithium battery pack SoC and SoH by using existing power electronic converters without adding additional hardware circuits and wiring and without affecting the normal operation of the system.

[0006] A lithium battery impedance spectrum autonomous online detection and power signal composite transmission system based on injection harmonic modulation, including a bidirectional DC-DC converter, a current sampling and filtering circuit, a lithium battery pack and a controller, wherein:

[0007] The bidirectional DC-DC converter is connected to a lithium battery pack on one side and to a DC power source or a load via a DC bus on the other side, and is used to convert the electric energy of the DC power source to charge the lithium battery pack, or to convert the electric energy in the lithium battery pack to power the load;

[0008] The current sampling and filtering circuit is used to collect the current signal (i.e., the charging and discharging current) on the connection line between the bidirectional DC-DC converter and the lithium battery pack, and provide the current signal to the controller after filtering and conditioning;

[0009] The controller constructs a switch control signal of the bidirectional DC-DC converter by adjusting the phase shift angle according to the current signal and the harmonic signal to be injected, and detects the spectrum of the current signal at the same time, compares the spectrum of the current signal with the spectrum of the harmonic signal to obtain the electrochemical impedance spectrum of the lithium battery pack and analyzes it, estimates the current SoC and SoH of the lithium battery pack according to the corresponding relationship between the electrochemical impedance spectrum and SoC and SoH, and then performs data modulation on the harmonic signal, and uses the bidirectional DC-DC converter to transmit the information of SoC and SoH together with the electric energy through the DC bus.

[0010] Furthermore, the bidirectional DC-DC converter adopts DAB (Dual Active Bridge) and is controlled by a voltage closed loop.

[0011] Further, the DAB includes 8 power switch tubes w1~w8, two filter capacitors C1 and C2, an isolation transformer T and an inductor L, wherein one end of C1 is connected to one end of w1 and one end of w3, the other end of C1 is connected to one end of w2 and one end of w4, the other end of w1 is connected to the other end of w2 and one end of inductor L, the other end of inductor L is connected to the same phase end of the primary winding of the isolation transformer T, the other end of w3 is connected to the other end of w4 and the opposite phase end of the primary winding of the isolation transformer T, one end of C2 is connected to one end of w5 and one end of w7, the other end of C2 is connected to one end of w6 and one end of w8, the other end of w5 is connected to the other end of w6 and the same phase end of the secondary winding of the isolation transformer T, the other end of w7 is connected to the other end of w8 and the opposite phase end of the secondary winding of the isolation transformer T, and C1 and C2 are respectively connected to a lithium battery pack, a DC power supply or a load at both sides of the DAB.

[0012] Furthermore, when one side of the bidirectional DC-DC converter is connected to a DC power supply and the other side is connected to a lithium battery pack, the lithium battery pack operates in a charging mode, and electric energy is charged from the DC power supply to the lithium battery pack via the bidirectional DC-DC converter; when one side of the bidirectional DC-DC converter is connected to a load and the other side is connected to a lithium battery pack, the lithium battery pack operates in a discharging mode, and electric energy is supplied to the load from the lithium battery pack via the bidirectional DC-DC converter.

[0013] Furthermore, the bidirectional DC-DC converter has the following three operating modes:

[0014] (1) When the bidirectional DC-DC converter only performs energy transmission, the phase shift angle is determined only by the charging and discharging requirements, and the phase shift angle is constant in steady state;

[0015] (2) When the bidirectional DC-DC converter performs energy transmission and battery status detection at the same time, the phase shift angle is determined by the current signal and the harmonic signal to be injected. The average value of the phase shift angle is determined by the charging and discharging requirements, and the average value is constant in the steady state. At the same time, the controller applies a disturbance to the phase shift angle according to the harmonic signal to be injected, thereby injecting harmonics into the voltage signal on the battery side of the bidirectional DC-DC converter. The harmonics are square waves with a duty cycle of 0.5 and a frequency less than 1 / 5 of the switching frequency of the bidirectional DC-DC converter.

[0016] (3) When the bidirectional DC-DC converter transmits energy and battery status information simultaneously, the phase shift angle is determined by the current signal and the harmonic signal to be injected. The average value of the phase shift angle is determined by the charging and discharging requirements, and the average value is constant in steady state. At the same time, the controller perturbs the phase shift angle according to the harmonic signal to be injected, thereby injecting harmonics into the voltage signal on the DC bus side of the bidirectional DC-DC converter. The harmonics are sinusoidal waves with a frequency less than 1 / 5 of the switching frequency of the bidirectional DC-DC converter. Then, the controller modulates the current SoC and SoH information of the lithium battery pack on the frequency, phase or amplitude of the harmonic signal by adjusting the perturbation parameters, thereby realizing the composite transmission of information and energy.

[0017] Furthermore, the charging and discharging demand is characterized by the direction and magnitude of the current signal on the connection line between the bidirectional DC-DC converter and the lithium battery pack.

[0018] Furthermore, the controller adopts DSP (Digital Signal Processing).

[0019] Furthermore, the lithium battery pack is composed of a plurality of lithium battery cells connected in series and parallel.

[0020] The present invention is based on the correspondence between the electrochemical impedance spectrum of lithium batteries and SoC and SoH, makes full use of the characteristics of the switching power supply itself, injects harmonics by using the switching action process of the DC-DC converter, and regulates the harmonic voltage, thereby detecting the output current spectrum and comparing the current spectrum with the voltage spectrum to obtain the electrochemical impedance spectrum of the lithium battery, thereby obtaining the real-time state of charge and health state of the lithium battery according to the correspondence between the electrochemical impedance spectrum and SoC and SoH. In addition, the present invention transmits the real-time SoC / SoH data together with the power flow through the DC power bus by data modulation of the injected harmonic voltage. Therefore, the lithium battery state autonomous online detection and power signal composite transmission system of the present invention can realize the real-time monitoring and composite transmission of the state of charge and health state of the lithium battery by injecting tiny AC voltage harmonics without affecting the normal operation of the lithium battery pack and the battery energy management system, without the need for additional signal injection, data modulation, communication lines and other equipment. This method reduces the volume, power consumption and cost of the system, and improves the safety, reliability and service life of the lithium battery energy storage system, as well as the intelligence level of the system.

[0021] The present invention is mainly used in various DC lithium battery energy storage systems, including DC microgrids, electric vehicles, etc. It is not limited by the topology of power electronic converters. It can inject disturbance signals to both sides of the converter input and output through switching actions without adding additional signal injection, data modulation and communication lines, and detect the current value on the battery side. The electrochemical impedance spectrum of the lithium battery can be obtained by simple calculation, and then the current SoC and SoH of the lithium battery can be obtained. This information can be transmitted and shared by performing data modulation on the sinusoidal disturbance signal, that is, the power signal is compositely transmitted, and the communication signal strength is determined by the strength of the injected disturbance harmonics, which is independent of the parameters and status of the converter and the battery, and the communication signal is stable. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The overall structural block diagram of the lithium battery impedance spectrum autonomous online detection and power signal composite transmission system of the present invention.

[0023] Figure 2 It is a structural diagram of the dual active bridge converter DAB. DETAILED DESCRIPTION

[0024] In order to describe the present invention more specifically, the technical solution of the present invention is described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0025] like Figure 1 As shown, the lithium battery impedance spectrum autonomous online detection and power signal composite transmission system based on injection harmonic modulation of the present invention includes: a bidirectional DC-DC converter, a controller, a current sampling and filtering circuit and a group of lithium batteries, wherein:

[0026] In this embodiment, the bidirectional DC-DC converter is an isolated bidirectional DC-DC converter, which adopts a dual active bridge converter DAB. Figure 2 As shown, one side of the DAB is connected to a power source or load, and the other side is connected to a lithium battery pack. The DAB includes two H-bridges H1 and H2, an inductor L and an isolation transformer T, wherein the left H-bridge H1 includes four MOS tubes w1~w4 and a capacitor C1, and the right H-bridge H2 includes four MOS tubes w5~w8 and a capacitor C2. The d-ends of the upper tubes w1 and w3 of the H1 bridge are connected to point a, and the s-ends of the lower tubes w2 and w4 are connected to point b; the s-end of w1 and the d-end of w2 are connected to point p, and the s-end of w3 and the d-end of w4 are connected to point q; a filter capacitor C1 is connected between points a and b, the left end of the inductor L is connected to point p, and the right end is connected to the primary in-phase end of the isolation capacitor, and the primary inverting end of the isolation transformer is connected to point q. The d-ends of the upper tubes w5 and w7 of the H2 bridge are connected to point m, and the s-ends of the lower tubes w6 and w8 are connected to point n; the s-end of w5 and the d-end of w6 are connected to point x, and the s-end of w7 and the d-end of w8 are connected to point y; the filter capacitor C2 is connected between points m and n, and the in-phase terminal of the secondary side of the isolation transformer is connected to point x, and the inverse terminal is connected to point y. The transformation ratio of the primary and secondary sides of the isolation transformer is 1:N.

[0027] In this embodiment, the dual active bridge converter DAB adopts voltage closed-loop control; when one side of the DAB is connected to a power source and the other side is connected to a lithium battery pack, the lithium battery pack operates in a charging mode, and electric energy is charged from the power source via the DAB to the lithium battery pack; when one side of the DAB is connected to a load and the other side is connected to the lithium battery pack, the lithium battery pack operates in a discharging mode, and electric energy is supplied from the lithium battery pack via the DAB to the load.

[0028] The controller constructs the switch control signal by adjusting the phase shift angle according to the closed-loop feedback signal and the harmonic signal to be injected. Therefore, the DAB converter has the following three working modes:

[0029] (1) When the DAB converter is only performing energy transmission, the phase shift angle of the switch control signal is determined only by the charging and discharging requirements, and the phase shift angle is constant in steady state.

[0030] (2) When the DAB converter performs energy transmission and battery status detection at the same time, the phase shift angle is determined by the charging and discharging requirements and the harmonics injected for lithium battery status detection. Specifically: the average value of the phase shift angle is determined by the charging and discharging requirements, and the average value is constant in steady state; the harmonic signal is injected in the form of perturbation of the phase shift angle. The signal is a square wave signal with a duty cycle of 0.5, so it naturally contains the fundamental frequency and its odd harmonics. The choice of the fundamental frequency is mainly determined by two factors: one is the sweep bandwidth determined by the characteristics of the lithium battery pack, and the other is that in order to inject the signal without distortion, the fundamental frequency of the signal is generally less than 1 / 5 of the DAB switching frequency.

[0031] (3) When the DAB converter transmits energy and battery status information at the same time, the phase shift angle is determined by the charging and discharging requirements and the harmonics injected for communication carrier. Specifically: the average value of the phase shift angle is determined by the charging and discharging requirements, and the average value is constant in steady state; the harmonic signal is injected in the form of perturbation of the phase shift angle, and the signal is a sine wave, that is, when no harmonics are injected, the phase shift angle is a stable value. When harmonics need to be injected, a small sinusoidal component is superimposed on the stable value of the phase shift angle, but the average value of the phase shift angle remains unchanged within a sine cycle. In order to inject the signal without distortion, the lower the frequency of the signal, the better, but too low a frequency will result in an extremely low communication rate. Therefore, generally, the signal frequency is less than 1 / 5 of the switching frequency of DAB. The optional modulation degrees of freedom include frequency, phase and amplitude, which are achieved by adjusting the perturbation parameters; for example, when frequency modulation is performed, the frequency value of the injected sinusoidal perturbation needs to be adjusted accordingly.

[0032] The sampling and filtering circuit collects the current between the lithium battery pack and the DAB connection line, that is, the charging and discharging current of the lithium battery, and provides the current signal to the controller after conditioning and filtering. The controller detects the spectrum of the current signal, compares the spectrum of the current signal with the spectrum of the injected voltage harmonic signal, and draws out the electrochemical impedance spectrum of the lithium battery pack according to Ohm's law and analyzes it, and then estimates the current SoC and SoH of the lithium battery pack according to the corresponding relationship between the electrochemical impedance spectrum and SoC and SoH.

[0033] In this embodiment, the controller adopts DSP, and the lithium battery pack includes a plurality of lithium battery cells, each of which is connected in series; if the power capacity needs to be expanded, a plurality of battery cells with the same number of cells can be connected in parallel.

[0034] The above description of the embodiments is to facilitate the understanding and application of the present invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to the above embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments. Improvements and modifications made by those skilled in the art to the present invention based on the disclosure of the present invention should be within the protection scope of the present invention.

Claims

1. A lithium battery impedance spectrum autonomous online detection and power signal composite transmission system based on injection harmonic modulation, including a bidirectional DC-DC converter, a current sampling and filtering circuit, a lithium battery pack and a controller, characterized in that: The bidirectional DC-DC converter is connected to a lithium battery pack on one side and to a DC power source or a load via a DC bus on the other side, and is used to convert the electric energy of the DC power source to charge the lithium battery pack, or to convert the electric energy in the lithium battery pack to power the load; The current sampling and filtering circuit is used to collect the current signal on the connection line between the bidirectional DC-DC converter and the lithium battery pack, and provide the current signal to the controller after filtering and conditioning; The controller constructs a switch control signal of the bidirectional DC-DC converter by adjusting the phase shift angle according to the current signal and the harmonic signal to be injected, and detects the spectrum of the current signal at the same time, compares the spectrum of the current signal with the spectrum of the harmonic signal to obtain the electrochemical impedance spectrum of the lithium battery pack and analyzes it, estimates the current SoC and SoH of the lithium battery pack according to the corresponding relationship between the electrochemical impedance spectrum and SoC and SoH, and then performs data modulation on the harmonic signal, and uses the bidirectional DC-DC converter to transmit the information of SoC and SoH together with the electric energy through the DC bus.

2. The lithium battery impedance spectrum autonomous online detection and power signal composite transmission system according to claim 1 is characterized by: The bidirectional DC-DC converter adopts DAB and is controlled by a voltage closed loop.

3. The lithium battery impedance spectrum autonomous online detection and power signal composite transmission system according to claim 2 is characterized by: The DAB includes 8 power switch tubes w1~w8, two filter capacitors C1 and C2, an isolation transformer T and an inductor L, wherein one end of C1 is connected to one end of w1 and one end of w3, the other end of C1 is connected to one end of w2 and one end of w4, the other end of w1 is connected to the other end of w2 and one end of inductor L, the other end of inductor L is connected to the same phase end of the primary winding of the isolation transformer T, the other end of w3 is connected to the other end of w4 and the opposite phase end of the primary winding of the isolation transformer T, one end of C2 is connected to one end of w5 and one end of w7, the other end of C2 is connected to one end of w6 and one end of w8, the other end of w5 is connected to the other end of w6 and the same phase end of the secondary winding of the isolation transformer T, the other end of w7 is connected to the other end of w8 and the opposite phase end of the secondary winding of the isolation transformer T, and C1 and C2 are respectively connected to a lithium battery pack, a DC power supply or a load at both sides of the DAB.

4. The lithium battery impedance spectrum autonomous online detection and power signal composite transmission system according to claim 1, characterized in that: When one side of the bidirectional DC-DC converter is connected to a DC power supply and the other side is connected to a lithium battery pack, the lithium battery pack operates in a charging mode, and electric energy is charged from the DC power supply to the lithium battery pack via the bidirectional DC-DC converter; when one side of the bidirectional DC-DC converter is connected to a load and the other side is connected to a lithium battery pack, the lithium battery pack operates in a discharging mode, and electric energy is supplied to the load from the lithium battery pack via the bidirectional DC-DC converter.

5. The lithium battery impedance spectrum autonomous online detection and power signal composite transmission system according to claim 1, characterized in that: The bidirectional DC-DC converter has the following three operating modes: (1) When the bidirectional DC-DC converter only performs energy transmission, the phase shift angle is determined only by the charging and discharging requirements, and the phase shift angle is constant in steady state; (2) When the bidirectional DC-DC converter performs energy transmission and battery status detection at the same time, the phase shift angle is determined by the current signal and the harmonic signal to be injected. The average value of the phase shift angle is determined by the charging and discharging requirements, and the average value is constant in the steady state. At the same time, the controller applies a disturbance to the phase shift angle according to the harmonic signal to be injected, thereby injecting harmonics into the voltage signal on the battery side of the bidirectional DC-DC converter. The harmonics are square waves with a duty cycle of 0.5 and a frequency less than 1 / 5 of the switching frequency of the bidirectional DC-DC converter. (3) When the bidirectional DC-DC converter transmits energy and battery status information simultaneously, the phase shift angle is determined by the current signal and the harmonic signal to be injected. The average value of the phase shift angle is determined by the charging and discharging requirements, and the average value is constant in steady state. At the same time, the controller perturbs the phase shift angle according to the harmonic signal to be injected, thereby injecting harmonics into the voltage signal on the DC bus side of the bidirectional DC-DC converter. The harmonics are sinusoidal waves with a frequency less than 1 / 5 of the switching frequency of the bidirectional DC-DC converter. Then, the controller modulates the current SoC and SoH information of the lithium battery pack on the frequency, phase or amplitude of the harmonic signal by adjusting the perturbation parameters, thereby realizing the composite transmission of information and energy.

6. The lithium battery impedance spectrum autonomous online detection and power signal composite transmission system according to claim 5, characterized in that: The charging and discharging demand is characterized by the direction and magnitude of the current signal on the connection line between the bidirectional DC-DC converter and the lithium battery pack.

7. The lithium battery impedance spectrum autonomous online detection and power signal composite transmission system according to claim 1, characterized in that: The controller adopts DSP.

8. The lithium battery impedance spectrum autonomous online detection and power signal composite transmission system according to claim 1, characterized in that: The lithium battery pack is composed of a plurality of lithium battery cells connected in series and in parallel.

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