Autonomous Online Detection System for Impedance Spectra of Lithium Batteries and Composite Transmission of Power Signals

Abstract

This invention discloses an autonomous online detection and power signal composite transmission system for lithium-ion battery impedance spectrum based on injection harmonic modulation. The system includes a bidirectional DC-DC converter, a controller, sampling and filtering circuits, and a lithium-ion battery pack. One side of the bidirectional DC-DC converter is connected to the lithium-ion battery pack, and the other side is connected to a power supply or load. This invention fully utilizes the characteristics of the switching power supply itself, injecting harmonics through the high-frequency switching action of the DC-DC converter as a sweep signal for the lithium-ion battery impedance spectrum and a communication carrier. This allows for the analysis of the real-time impedance spectrum of the lithium-ion battery, followed by online estimation of the system oscillation (SoC) and sonic equilibrium (SOH). Simultaneously, the result is modulated onto the communication carrier and transmitted to a common DC bus. This system is not limited by the DC-DC topology and can achieve online real-time detection and transmission of the lithium-ion battery SoC and SOH without adding additional hardware circuitry or wiring, or ensuring the normal operation of the lithium-ion battery pack.

Description

Technical Field

[0001] This invention belongs to the field of power electronics and communication technology, specifically relating to a lithium battery impedance spectrum autonomous online detection and power signal composite transmission system based on injection harmonic modulation. Background Technology

[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. Due to considerations such as safety and efficiency, lithium battery energy storage systems have become mainstream. Lithium battery packs are connected to power sources or loads via power electronic converters, which act as interface circuits, to achieve efficient and controllable charging and discharging. To continuously improve the working efficiency of battery packs, avoid performance losses and safety hazards caused by overcharging and over-discharging, and ensure normal system operation, real-time online status monitoring, lifespan prediction, and intelligent control of the battery packs are required. This necessitates that the system can detect and transmit the battery's status in real time, primarily including the battery's state of charge (SoC) and state of health (SQ). Health, SoH).

[0003] On the one hand, traditional battery SoC and SoH detection technologies mainly include voltage method, coulometric method and electrochemical impedance spectroscopy (EIS) method. However, voltage methods, such as those in the literature [Q. Yao, D. Lu, G. Lei, “Rapid Open-Circuit Voltage Measurement Method for Lithium-Ion Batteries Using One-Cycle Bipolar-Current Pulse,” IEEE Journal of Emerging and Selected Topics in Industrial Electronics, vol. 2, no. 2, pp. 132-141, Apr. 2021], are sensitive to temperature and have limited accuracy; coulomb measurement methods, such as those in the literature [Y. Ko, K. Cho, M. Kim, and W. Choi, “A Novel Capacity Estimation Method for the Lithium Batteries Using the Enhanced Coulomb Counting Method With Kalman Filter,” IEEE Access, vol. 10, pp. 38793-38801, Apr. 2022], require a complete charge-discharge process, making them unsuitable for real-time applications and significantly impacting battery life; EIS methods, such as those in 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 th[International Conference on Energy, Electrical and Power Engineering (CEEPE), May, 2023] While possessing high accuracy, existing technologies suffer from high equipment costs and difficulty in achieving online measurement. Therefore, they struggle to achieve high-precision online real-time monitoring of battery status, thus hindering real-time feedback and transmission. Furthermore, traditional battery status transmission primarily employs independent communication systems, including wired and wireless communication technologies. Wired communication technologies such as CAN bus and SPI bus require additional communication transmitting equipment and wiring, significantly increasing system size, power consumption, and cost, while also increasing system complexity and maintenance difficulty and cost. Wireless communication technologies such as Wi-Fi and Zigbee, while eliminating additional wiring costs and complexity, still require additional signal generation and transmission circuits and are susceptible to external interference and attacks. In summary, existing battery status detection and transmission technologies employ two independent systems, resulting in high costs and complexity, and difficulty in achieving online acquisition and transmission of real data.

[0004] Power electronic converters are a key component for controlling the charging and discharging of batteries. Their basic principle is to change the form of electrical energy using the high-frequency switching action of a switching transistor; essentially, they are equivalent to a chopper structure. A high-frequency PWM signal drives the switching transistor to alternately turn it on and off, thereby obtaining a square wave voltage with the same frequency as the switching action. This voltage is then passed through a passive filter composed of inductors, capacitors, etc., ultimately yielding the desired electrical energy output. Summary of the Invention

[0005] In view of the above, the present invention provides an autonomous online detection and power signal composite transmission system for lithium battery impedance spectrum based on injection harmonic modulation. It can realize online detection and composite transmission of lithium battery pack SoC and SoH 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 includes 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 supply or load on the other side via a DC bus. It is used to convert the electrical energy from the DC power supply to charge the lithium battery pack, or to convert the electrical energy from the lithium battery pack to power the load.

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

[0009] The controller adjusts the phase shift angle to construct the switching control signal of the bidirectional DC-DC converter based on the current signal and the required injected harmonic signal. Simultaneously, it detects the spectrum of the current signal, 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. Based on the correspondence between the electrochemical impedance spectrum and SoC and SoH, it estimates the current SoC and SoH of the lithium battery pack, and then modulates the harmonic signal. The bidirectional DC-DC converter then transmits the SoC and SoH information along with the electrical energy through the DC bus.

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

[0011] Furthermore, the DAB includes eight power switching transistors w1 to w8, two filter capacitors C1 and C2, an isolation transformer T, and an inductor L. One end of C1 is connected to one end of w1 and one end of w3, and 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 non-inverting terminal of the primary winding of the isolation transformer T. The other end of w3 is connected to the other end of w4 and the anti-inverting terminal 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, and 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 non-inverting terminal of the secondary winding of the isolation transformer T. The other end of w7 is connected to the other end of w8 and the anti-inverting terminal of the secondary winding of the isolation transformer T. C1 and C2 serve as two sides of the DAB, connected to a lithium battery pack, a DC power supply, or a load, respectively.

[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 charging mode, and electrical energy is drawn from the DC power supply and charged 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 discharging mode, and electrical energy is drawn from the lithium battery pack and supplied to the load 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 transfer, the phase shift angle is determined only by the charging and discharging demand, and the phase shift angle is constant in steady state;

[0015] (2) When the bidirectional DC-DC converter performs energy transfer and battery status detection at the same time, the phase shift angle is determined by the current signal and the required injected harmonic signal. The average value of the phase shift angle is determined by the charging and discharging demand, and the average value is constant in steady state. At the same time, the controller applies a disturbance to the phase shift angle according to the required injected harmonic signal, thereby injecting harmonics into the voltage signal on the battery side of the bidirectional DC-DC converter. The harmonic is a square wave 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 at the same time, the phase shift angle is determined by the current signal and the required injected harmonic signal. The average value of the phase shift angle is determined by the charging and discharging demand, and the average value is constant in steady state. At the same time, the controller applies a disturbance to the phase shift angle according to the required injected harmonic signal, thereby injecting harmonics into the voltage signal on the DC bus side of the bidirectional DC-DC converter. The harmonic is a sine wave 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 onto the frequency, phase or amplitude of the harmonic signal by adjusting the disturbance parameters, thereby realizing the composite transmission of information and energy.

[0017] Furthermore, the charging and discharging requirements are 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 employs a DSP (Digital Signal Processor).

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

[0020] This invention, based on the correspondence between the electrochemical impedance spectroscopy (EIS) of lithium batteries and their state of charge (SoC) and sonic equilibrium (SOH), fully utilizes the characteristics of the switching power supply itself. It injects harmonics during the switching process of a DC-DC converter and regulates the harmonic voltage. By detecting the output current spectrum and comparing it with the voltage spectrum, the EIS of the lithium battery is obtained. Based on the correspondence between the EIS and SoC and SOH, the real-time state of charge and health of the lithium battery can be determined. Furthermore, this invention modulates the injected harmonic voltage, transmitting the real-time SoC / SOH data along with the power flow through a DC power bus. Therefore, this invention's autonomous online lithium battery state detection and power signal composite transmission system can achieve real-time monitoring and composite transmission of the lithium battery's state of charge and health without affecting the normal operation of the lithium battery pack and battery energy management system, by injecting small AC voltage harmonics, without requiring additional signal injection, data modulation, or communication lines. This method reduces the system's size, power consumption, and cost, while improving the safety, reliability, and lifespan of the lithium battery energy storage system, as well as its intelligence level.

[0021] This invention is primarily applied to various DC lithium battery energy storage systems, including DC microgrids and electric vehicles. It is not limited by the topology of the power electronic converter. Without adding additional signal injection, data modulation, or communication lines, it can inject disturbance signals into both the input and output sides of the converter through switching actions and detect the current value on the battery side. A simple calculation can then be performed to obtain the electrochemical impedance spectroscopy of the lithium battery, thereby determining the current system-on-chip (SoC) and sonic equilibrium (SOH) of the lithium battery. This information can be transmitted and shared through data modulation of the sinusoidal disturbance signal, i.e., power signal composite transmission. Furthermore, the communication signal strength is determined by the strength of the injected disturbance harmonics, independent of the parameters and state of the converter and battery, ensuring stable communication signals. Attached Figure Description

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

[0023] Figure 2 This is a schematic diagram of the structure of a dual active bridge converter (DAB). Detailed Implementation

[0024] To describe the present invention in more detail, the technical solution of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[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 this invention includes: a bidirectional DC-DC converter, a controller, a current sampling and filtering circuit, and a set of lithium batteries, wherein:

[0026] In this embodiment, the bidirectional DC-DC converter is an isolated bidirectional DC-DC converter, employing a dual active bridge converter (DAB), such as... Figure 2 As shown, one side of the DAB is connected to the power supply or load, and the other side is connected to the lithium battery pack. The DAB includes two H-bridges H1 and H2, one inductor L, and one isolation transformer T. The left H-bridge H1 includes four MOSFETs w1-w4 and a capacitor C1, while the right H-bridge H2 includes four MOSFETs w5-w8 and a capacitor C2. The drain terminals (d) of the upper MOSFETs w1 and w3 are connected to point a, and the source terminals (s) of the lower MOSFETs w2 and w4 are connected to point b. The source terminal of w1 is connected to the drain terminal of w2 at point p, and the source terminal of w3 is connected to the drain terminal of w4 at 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 non-inverting input of the primary winding of the isolation capacitor. The inverting input of the primary winding of the isolation transformer is connected to point q. The drain terminals (d) of tubes W5 and W7 on bridge H2 are connected to point m, and the sink terminals (s) of tubes W6 and W8 on bridge H2 are connected to point n. The sink terminal (s) of W5 and the drain terminal (d) of W6 are connected to point x, and the sink terminal (s) of W7 and the drain terminal (d) of W8 are connected to point y. A filter capacitor C2 is connected between points m and n. The non-inverting terminal of the secondary side of the isolation transformer is connected to point x, and the non-inverting terminal is connected to point y. The turns ratio of the primary to secondary side 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 the power supply and the other side is connected to the lithium battery pack, the lithium battery pack operates in charging mode, and electrical energy is supplied from the power supply through the DAB to charge the lithium battery pack. When one side of the DAB is connected to the load and the other side is connected to the lithium battery pack, the lithium battery pack operates in discharging mode, and electrical energy is supplied from the lithium battery pack through the DAB to power the load.

[0028] The controller constructs the switching control signal by adjusting the phase shift angle based on the closed-loop feedback signal and the required injected harmonic signal. Therefore, the DAB converter has the following three operating modes:

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

[0030] (2) When the DAB converter performs both energy transfer and battery status detection, the phase shift angle is determined by the charging and discharging demand and the injected harmonics used for lithium battery status detection. Specifically: the average value of the phase shift angle is determined by the charging and discharging demand, and this average value is constant in steady state; the harmonic signal is injected in the form of perturbation of the phase shift angle. This signal is a square wave signal with a duty cycle of 0.5, and therefore naturally contains the fundamental frequency and its odd harmonics. The selection 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 simultaneously transmits energy and battery status information, the phase shift angle is determined by the charging and discharging demand and the injected harmonics used for the communication carrier. Specifically: the average value of the phase shift angle is determined by the charging and discharging demand, and this average value is constant in steady state; the harmonic signal is injected in the form of a perturbation of the phase shift angle. This 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 sine component is superimposed on this stable value, but the average value of the phase shift angle remains unchanged within one sine cycle. In order to inject the signal without distortion, the lower the frequency of the signal, the better. However, too low a frequency will lead to an extremely low communication rate. Therefore, generally, the frequency of the signal is less than 1 / 5 of the switching frequency of the DAB. The selectable modulation degrees of freedom include frequency, phase, and amplitude, which are achieved by adjusting the perturbation parameters; for example, when performing frequency modulation, the frequency value of the injected sine perturbation needs to be adjusted accordingly.

[0032] The sampling and filtering circuit acquires the current of the lithium battery pack and the DAB connection line, which is the charging and discharging current of the lithium battery. After conditioning and filtering the current signal, it is provided to the controller. 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, plots the electrochemical impedance spectrum of the lithium battery pack according to Ohm's law and analyzes it. Then, based on the correspondence between the electrochemical impedance spectrum and SoC and SoH, the current SoC and SoH of the lithium battery pack are estimated.

[0033] In this embodiment, the controller uses a DSP, and the lithium battery pack includes several lithium battery cells connected in series. If it is necessary to expand the power capacity, several battery cells with the same number of cells can be connected in parallel.

[0034] The above description of the embodiments is provided to enable those skilled in the art to understand and apply the present invention. Those skilled in the art can readily make various modifications to the above embodiments and apply the general principles described herein to other embodiments without creative effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made to the present invention by those skilled in the art based on the disclosure thereof should be within the scope of protection 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, comprising 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 supply or load on the other side via a DC bus. It is used to convert the electrical energy from the DC power supply to charge the lithium battery pack, or to convert the electrical energy from 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 to provide the current signal to the controller after filtering and conditioning. The controller adjusts the phase shift angle to construct the switching control signal of the bidirectional DC-DC converter based on the current signal and the required injected harmonic signal. At the same time, it detects the spectrum of the current signal, 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. Based on the correspondence between the electrochemical impedance spectrum and SoC and SoH, it estimates the current SoC and SoH of the lithium battery pack, and then modulates the harmonic signal. The bidirectional DC-DC converter is used to transmit the SoC and SoH information along with the electrical energy through the DC bus. The bidirectional DC-DC converter uses a DAB and is controlled by a voltage closed loop. The DAB includes eight power switching transistors w1 to w8, two filter capacitors C1 and C2, an isolation transformer T, and an inductor L. 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 non-inverting terminal of the primary winding of the isolation transformer T. The other end of w3 is connected to the other end of w4 and the anti-inverting terminal 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 non-inverting terminal of the secondary winding of the isolation transformer T. The other end of w7 is connected to the other end of w8 and the anti-inverting terminal of the secondary winding of the isolation transformer T. C1 and C2 serve as two sides of the DAB, connected to a lithium battery pack, a DC power supply, or a load, respectively. 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 charging mode, and electrical energy is drawn from the DC power supply and charged 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 discharging mode, and electrical energy is drawn from the lithium battery pack and supplied to the load via the bidirectional DC-DC converter. The bidirectional DC-DC converter has the following three operating modes: (1) When the bidirectional DC-DC converter only performs energy transfer, the phase shift angle is determined only by the charging and discharging demand, and the phase shift angle is constant in steady state; (2) When the bidirectional DC-DC converter performs energy transfer and battery status detection at the same time, the phase shift angle is determined by the current signal and the required injected harmonic signal. The average value of the phase shift angle is determined by the charging and discharging demand, and the average value is constant in steady state. At the same time, the controller applies a disturbance to the phase shift angle according to the required injected harmonic signal, thereby injecting harmonics into the voltage signal on the battery side of the bidirectional DC-DC converter. The harmonic is a square wave 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 at the same time, the phase shift angle is determined by the current signal and the required injected harmonic signal. The average value of the phase shift angle is determined by the charging and discharging demand, and the average value is constant in steady state. At the same time, the controller applies a disturbance to the phase shift angle according to the required injected harmonic signal, thereby injecting harmonics into the voltage signal on the DC bus side of the bidirectional DC-DC converter. The harmonic is a sine wave 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 onto the frequency, phase or amplitude of the harmonic signal by adjusting the disturbance parameters, thereby realizing the composite transmission of information and energy.

2. The lithium battery impedance spectrum autonomous online detection and power signal composite transmission system according to claim 1, characterized in that: The charging and discharging requirements are 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.

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

4. 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 multiple lithium battery cells connected in series and parallel.

Images