A battery impedance spectrum in-situ online measurement system and measurement method

Abstract

The present invention provides an in-situ online measurement system and method for battery impedance spectrum, which belongs to the field of battery impedance spectrum detection. Considering the working scenario of a battery system connected to a converter, a parallel current disturbance generating circuit is bypassed in the battery system, and then a cell impedance spectrum time-sharing multiplexing measurement circuit is installed in each battery pack. Under the coordinated control of the host computer control system, the disturbance current and response voltage of each cell at each characteristic frequency point set are detected to achieve the measurement of the impedance spectrum of each single cell in the battery system. Compared with the prior art, the measurement system proposed by the present invention can achieve in-situ online detection without affecting the normal charging and discharging operation of the battery system; and the current disturbance energy is generated by reactive power to reduce active power consumption; it can achieve impedance spectrum detection of each single cell in the battery system at a lower cost, higher accuracy and in a patrol inspection manner.

Description

Technical Field

[0001] The present invention belongs to the field of battery impedance spectrum detection, and more specifically, relates to an in-situ online measurement system and a measurement method for battery impedance spectrum. Background Art

[0002] The safe and stable operation of batteries mainly depends on the battery management system (BMS). The battery management system monitors the status of the battery in real time. Its main functions include battery voltage and current monitoring, surface temperature monitoring, state of charge (SOC) estimation, and state of health (SOH) estimation. However, in most current applications, the battery management system only monitors external voltage and current information, and cannot obtain the internal characteristic parameters of the battery, especially the temperature inside the battery, and cannot identify the potential defects of the battery, resulting in the phenomenon of battery fire and spontaneous combustion still occurring from time to time.

[0003] As a non-destructive parameter determination and effective battery kinetic behavior determination method, electrochemical impedance spectroscopy is widely used in the evaluation and prediction of battery status information such as SOC, SOH and internal temperature. It can describe and fit battery characteristics, and thereby control the operating conditions of the battery system to avoid failures.

[0004] In the laboratory, an electrochemical workstation or other dedicated impedance measurement equipment can be used to collect impedance spectrum data of the battery in the full frequency range. However, in actual engineering environments, dedicated impedance measurement equipment has defects such as large size, easy damage, and high cost, and is not suitable for real-time detection of battery systems. In addition, the battery system is composed of multiple single cells connected in series and parallel in a certain way, and instruments such as electrochemical workstations are mostly designed for single cell impedance spectrum measurement, which is not suitable for actual engineering measurement of battery systems.

[0005] In order to solve the above problems, a variety of battery impedance spectrum measurement technologies have been proposed in the prior art. However, most of the impedance spectrum measurement technologies in the prior art are used for offline detection, and most of them are detection technologies for single cells. Although there are technologies for impedance spectrum detection for each cell in a series-parallel battery system in the prior art, they use active excitation current sources to excite the battery system with current. For large battery systems, this will require a lot of active excitation energy and increase system losses. There are also schemes in the prior art that control the switch array to perform current excitation on each battery series branch to ensure sufficient excitation energy for impedance spectrum detection. This scheme also ignores a problem. To excite each battery series branch separately, a switch array is required to cut each series branch out of the system for excitation and detection. However, if the battery series branch is cut into the system after the measurement, it is easy to generate circulating current and burn the battery. This is because the battery has polarization phenomenon. The terminal voltage of the same battery is different under different charging, discharging and static states. The polarization phenomenon will cause a voltage difference between the battery series branch in the charge and discharge operation state and the battery series branch cut out for impedance spectrum detection. The internal resistance of the battery is very small. If it is cut in forcibly, the small voltage difference may also cause a large circulation in the battery branch and burn the battery. In addition, when the battery system is working normally, cutting in and out of its series branch will inevitably affect the system operation state. Summary of the invention

[0006] In view of the defects of the prior art, the purpose of the present invention is to provide an in-situ online measurement system and method for battery impedance spectrum, aiming to solve the problem that the prior art is unable to use reactive power energy to generate current disturbance without affecting the normal charging and discharging operation of the battery system, and to achieve in-situ online detection of the impedance spectrum of each battery cell in the battery system.

[0007] To achieve the above-mentioned object, in a first aspect, the present invention provides an in-situ online measurement system for a battery impedance spectrum, comprising: a current disturbance generating circuit, a switch, a control unit and a measurement circuit;

[0008] The current disturbance generating circuit is connected in parallel with the battery system through a switch; the battery system includes one battery branch or at least two battery branches connected in parallel; each battery branch includes at least one battery pack or at least two battery packs connected in series, and each battery pack includes at least one battery cell;

[0009] The current disturbance generating circuit is used to generate a disturbance current with a preset frequency and amplitude;

[0010] The measuring circuit is used to measure the voltage and current of each battery cell;

[0011] When measuring the battery impedance spectrum, the control unit controls the switch to close, controls the current disturbance generating circuit to generate a disturbance current of preset frequency and amplitude, and controls the measuring circuit to measure the voltage and current of each battery cell; the control unit determines the impedance of each battery cell at a preset frequency based on the voltage and current of each battery cell; the control unit controls the current disturbance generating circuit to generate disturbance currents at different frequencies, and obtains the impedance of each battery cell at different frequencies through the measuring circuit, so as to determine the impedance spectrum of each battery cell based on the impedance at different frequencies.

[0012] In an optional example, the current disturbance generating circuit includes: a full-bridge inverter, a capacitor and a filter circuit;

[0013] The DC side of the full-bridge inverter is connected to the capacitor, and the AC side is connected to the input end of the filter circuit;

[0014] The output end of the filter circuit is connected in parallel with the battery system;

[0015] The control unit determines a preset value of the disturbance current and a preset value of the capacitor voltage, and collects a current value of the capacitor voltage and a current value output by the filter circuit; determines a first error between the preset value of the capacitor voltage and the current value of the capacitor voltage, and a second error between the preset value of the disturbance current and the current value output by the filter circuit; generates a corresponding switch signal according to the first error and the second error;

[0016] The power devices in the full-bridge inverter are turned on and off under the action of the switching signal, so that the filter circuit outputs the disturbance current of the preset value.

[0017] In an optional example, each battery pack is connected to a measurement circuit;

[0018] The measuring circuit comprises: a programmable multiplexing switch, a current sensor, a current sampling circuit, a voltage sampling circuit and a sampling controller;

[0019] The current sensor is connected in series with the battery pack;

[0020] The programmable multiplexing switch connects the voltage sampling circuit to both ends of each battery cell in the battery pack;

[0021] The sampling controller controls the programmable multiplexing switch to be turned on in time division to measure the voltage of each battery cell respectively;

[0022] While the voltage sampling circuit measures the voltage of each battery cell, the sampling controller controls the current sampling circuit to respectively collect the current value of the current sensor as the current value of each battery cell.

[0023] In an optional example, the control unit determines each frequency sweep characteristic frequency point of the disturbance current according to the impedance spectrum measurement requirement;

[0024] During a period when the battery system is stably charged, stably discharged, or in a static state, the control unit controls the switch to connect the current disturbance generating circuit to the battery system; thereafter, the control unit sends a detection instruction and a corresponding current disturbance setting value to the current disturbance generating circuit according to each determined sweep characteristic frequency point, so as to control the current disturbance generating circuit to output a disturbance current of a corresponding frequency to the battery system at each characteristic frequency point, and then in each battery pack, the measurement circuit measures the terminal voltage and current of each battery cell under the disturbance at each characteristic frequency point, and uploads the data to the control unit;

[0025] The control unit calculates the impedance of each battery cell in the battery system at each characteristic frequency point, and then obtains the impedance spectrum of each battery cell. After completing the impedance spectrum measurement of all battery cells in the battery system, the switch is disconnected and the measurement ends. The entire measurement process is carried out without affecting the normal operation of the battery system, realizing in-situ online detection.

[0026] In a second aspect, the present invention provides an in-situ online measurement method for a battery impedance spectrum, comprising the following steps:

[0027] A disturbance current of preset frequency and amplitude is input to a battery system in normal operation through a current disturbance generating circuit; the battery system comprises one battery branch or at least two battery branches connected in parallel; each battery branch comprises at least one battery pack or at least two battery packs connected in series, and each battery pack comprises at least one battery cell; the current disturbance generating circuit is connected in parallel with the battery system;

[0028] Measuring the voltage and current of each battery cell under the preset frequency disturbance current to determine the impedance of each battery cell at the preset frequency;

[0029] A disturbance current at different preset frequencies is input into the battery system to measure the impedance of each battery cell at different frequencies, so as to determine the impedance spectrum of each battery cell based on the impedance at different frequencies.

[0030] In an optional example, the current disturbance generating circuit includes: a full-bridge inverter, a capacitor and a filter circuit;

[0031] The DC side of the full-bridge inverter is connected to the capacitor, and the AC side is connected to the input end of the filter circuit;

[0032] The output end of the filter circuit is connected in parallel with the battery system;

[0033] The disturbance current of the preset frequency and amplitude is determined by the following steps:

[0034] Determining a preset value of a disturbance current and a preset value of a capacitor voltage;

[0035] Collecting the current value of the capacitor voltage and the current value output by the filter circuit;

[0036] Determine a first error between a preset value of the capacitor voltage and a current value of the capacitor voltage, and a second error between a preset value of the disturbance current and a current value output by the filter circuit;

[0037] generating a corresponding switching signal according to the first error and the second error;

[0038] The switching signal is input to the full-bridge inverter, and the power devices in the full-bridge inverter are turned on and off under the action of the switching signal, so that the filter circuit outputs the disturbance current of the preset value.

[0039] In an optional example, the voltage and current of each battery cell under a preset frequency disturbance current are measured, specifically:

[0040] The voltage of each battery cell in the same battery pack is measured in time by the same voltage sampling circuit, and while measuring the voltage of each battery cell, the current value of the current sensor connected in series with the battery pack is collected as the current value of each battery cell.

[0041] In an optional example, the method further includes the following steps:

[0042] According to the impedance spectrum measurement requirements, determine each frequency sweep characteristic frequency point of the disturbance current;

[0043] During a period when the battery system is stably charged, stably discharged or in a static state, a detection instruction and a corresponding current disturbance setting value are sent to the current disturbance generating circuit according to each determined sweep characteristic frequency point, so as to control the current disturbance generating circuit to output a disturbance current of a corresponding frequency to the battery system at each characteristic frequency point, and then respectively measure the terminal voltage and current of each battery cell under the disturbance at each characteristic frequency point;

[0044] The impedance of each battery cell at each characteristic frequency point is calculated according to the terminal voltage and current of each battery cell under the disturbance of each characteristic frequency point, and then the impedance spectrum of each battery cell is obtained;

[0045] After measuring the impedance spectra of all cells in the battery system, the current disturbance generating circuit is disconnected and the measurement is completed; the entire measurement process is carried out without affecting the normal operation of the battery system, realizing in-situ online detection.

[0046] In general, the above technical solution conceived by the present invention has the following beneficial effects compared with the prior art:

[0047] The present invention provides an in-situ online measurement system and method for battery impedance spectrum, which can be performed without affecting the normal charging and discharging operation of the battery system, taking into account the working scenario of the battery system connected to the converter, to achieve in-situ online detection. The DC side of the full-bridge inverter of the current disturbance generation circuit is connected to the capacitor, so that the current disturbance energy uses reactive power and reduces active power consumption.

[0048] The present invention provides an in-situ online measurement system and method for battery impedance spectrum, which can realize impedance spectrum detection of each single cell in the energy storage system at a low cost and with high accuracy and in a patrol inspection manner. It is convenient for the host computer control system of the energy storage system to monitor the real-time status of the battery system, which is helpful for early warning of faults and improving system reliability and safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 It is a schematic structural diagram of the in-situ online measurement system for battery impedance spectrum provided by the present invention;

[0050] Figure 2 It is a schematic diagram of a current disturbance generating circuit in the present invention;

[0051] Figure 3 is a block diagram of a control loop of a current disturbance generating circuit in the present invention;

[0052] Figure 4 This is a schematic diagram of a time-division multiplexing measurement circuit for a cell impedance spectrum in the present invention;

[0053] Figure 5 It is a program control flow chart of the measuring system and the measuring method in the present invention;

[0054] Figure 6 It is a flow chart of the in-situ online measurement method of battery impedance spectrum provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0055] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0056] The present invention provides an in-situ online measurement system and method for battery impedance spectrum. The present invention can be applied to energy storage power stations to perform status monitoring and safety warning on the battery system of energy storage power stations by detecting and analyzing the impedance spectrum of each battery cell. The present invention can also be applied to status monitoring of power batteries of electric vehicles. It can also be applied to health assessment, sorting and other cascade utilization-related technologies of retired battery packs to evaluate the characteristic status of each single-core battery in the retired battery pack.

[0057] The following three application scenarios are introduced through three embodiments.

[0058] Embodiment 1,

[0059] The current lithium-ion energy storage battery system faces technical bottlenecks in improving safety and lacks active safety defense technology. It is necessary to improve the safety of lithium-ion energy storage battery systems to meet the growing demand for large-scale energy storage.

[0060] The safety performance of lithium-ion batteries depends on the competitive process of heat generation and dissipation inside the battery cell. When high current discharge, overcharging and internal short circuit occur during battery operation, a large amount of heat will be generated inside the battery. If this heat cannot be released in time, the battery system will reach a high temperature, and further "thermal runaway" may occur.

[0061] The mechanism of battery "thermal runaway" is generally similar. When the battery starts to heat up abnormally, its internal temperature rises slowly. After a period of time, the temperature rises sharply, eventually causing the electrolyte to spray out and burn. The thermal runaway is further transmitted from the single cell to the battery module and system, causing fire and explosion. At present, energy storage power stations mostly use a combination of series and parallel to assemble and use multiple single cells, and the heat generation and heat dissipation of each single cell are different. Inaccurate and untimely fault detection of abnormal single cells and estimation of the status of the energy storage battery system are prone to frequent safety accidents of the energy storage battery system. Passive protection cannot fundamentally solve safety problems. Therefore, it is necessary to monitor at the cell level to block or reduce the risk of thermal runaway.

[0062] In existing battery systems, there are generally only three directly monitored quantities: the terminal voltage of each single cell, the external surface temperature of each single cell or the temperature inside the battery pack, and the current of each battery pack. Because the cells in the battery pack are connected in series, it is equivalent to the measured cell current. Other quantities such as SOC and SOH are calculated in the background based on the measured voltage and current and historical operating data.

[0063] However, at the beginning of the "thermal runaway" process of the battery, the thermocouple installed on the surface of the battery can hardly accurately detect abnormal changes in the internal temperature of the battery, and before the surface thermocouple detects the temperature abnormality, the "thermal runaway" accident may have occurred.

[0064] In the prior art, there is a method of combining the surface temperature of the battery cell with the equivalent thermal model of the lithium battery for temperature estimation. However, the estimation accuracy of the semi-empirical thermal equivalent model is limited, the model construction calculation is complex, and the surface temperature measurement is easily disturbed by the ambient temperature. In addition, in the prior art, there is a method of pre-embedded thermocouples or optical fibers inside the battery cell to directly detect the temperature inside the battery. However, if accurate safety status detection of all battery cells is to be achieved, thermocouples or optical fibers must be pre-embedded in each battery cell in the entire energy storage power station, which will lead to a significant increase in the production cost of the battery cell.

[0065] Based on the electrochemical impedance spectroscopy (EIS), a non-destructive parameter determination and effective battery kinetic behavior determination method, a small amplitude current disturbance signal of a specific frequency is applied to the battery cell, and the battery cell generates a voltage response. Based on the measurement results, the impedance and phase shift value of the battery cell at the characteristic frequency can be calculated. The complete impedance spectrum of the battery cell can be obtained by sweeping the frequency of the battery cell. Then, in the host computer control system, the impedance spectrum measurement results can be calculated and analyzed.

[0066] In the prior art, there are experiments based on EIS impedance spectrum, which do not use the battery equivalent circuit model, and directly obtain the mapping relationship between the impedance or phase shift value in a specific frequency segment of the battery impedance spectrum and the temperature inside the battery. After obtaining the measurement results of the specific frequency segment of the impedance spectrum, the temperature inside the battery cell is determined by calculation or table lookup.

[0067] In order to apply this measurement principle, i.e., the mapping relationship between the impedance or phase shift value in a specific frequency segment of the battery impedance spectrum and the temperature inside the battery, to the temperature detection inside the battery cell of an energy storage power station without affecting the normal operation of the battery system, thereby improving the safety of the energy storage battery system, an embodiment of the present invention proposes an in-situ online measurement system and a measurement method for a battery impedance spectrum.

[0068] It should be noted that Example 1 of the present invention discusses from the perspective of measuring the temperature inside the battery cell, just to be closer to the actual engineering needs of the safety status assessment of the energy storage power station. The in-situ online battery cell impedance spectrum detection achieved by the technical solution of the present invention can provide accurate impedance spectrum data for each battery cell in the battery system. Based on the battery cell impedance spectrum data, a variety of data analysis methods in the prior art can be used to perform real-time online evaluation of various characteristic parameters of the battery cell and the battery system, including battery cell SOC, SOH, internal temperature, etc.

[0069] Referring to the structure and specifications currently widely used in the construction of energy storage power stations, the battery container of the energy storage power station has a cell specification of 3.2V / 280Ah and adopts a 16×1P400S arrangement, that is, 20 cells are connected in series to form a battery plug-in box, and then 20 battery plug-in boxes are connected in series to form a battery cabinet, and finally 16 battery cabinets are connected in parallel to form a battery container. The battery container is connected to the PCS energy storage converter.

[0070] Example 1 is to apply the present invention to an energy storage power station, and to perform status monitoring and safety assessment on the battery system of the energy storage power station by detecting and analyzing the impedance spectrum of each battery cell. Figure 1 As shown, in Example 1 of the present invention, Figure 1 The "inverter" corresponds to the PCS energy storage inverter in the energy storage power station, the "battery box" corresponds to the battery container, and the "battery pack" corresponds to the battery plug-in box. In Example 1 of the present invention, each battery plug-in box has 20 battery cells.

[0071] like Figure 1 As shown, a battery impedance spectrum in-situ online measurement system and measurement method, comprising:

[0072] The current disturbance generating circuit can use reactive power energy to generate disturbance currents of specific frequency and amplitude on each parallel battery branch in the battery box while the battery system is working normally in charge and discharge;

[0073] A switch for connecting or disconnecting the current disturbance generating circuit from the battery system;

[0074] The cell impedance spectrum time-division multiplexing measurement circuit is installed in each battery pack. It can detect the current and voltage of each single cell and upload the measurement results to the host computer control system.

[0075] The host computer control system is used to control the operation of the current disturbance generating circuit, so that each battery branch generates a disturbance current of a specific frequency and amplitude, controls the on-off of the switch, receives the current and voltage detection results of the battery cell impedance spectrum time-sharing multiplexing measurement circuit, calculates the impedance spectrum of each single battery cell according to the detection results, and is also used to communicate with the converter to determine the best detection time, and coordinate the control of the entire measurement system.

[0076] like Figure 1 , Figure 2 As shown, the integrated current disturbance generating circuit performs current disturbance on all cells in the battery system, and the disturbance current energy is generated using reactive power. The current disturbance generating circuit uses an inverter full-bridge and filter circuit topology, and controls the generation of disturbance current with controllable frequency and amplitude through the designed control loop. Because each battery branch is connected in parallel, each battery branch shunts the disturbance current output by the current disturbance generating circuit to obtain current disturbance while connecting to the converter for normal charging and discharging, and does not interfere with each other. The entire battery system is only connected to one current disturbance generating circuit, that is, the entire system has only one disturbance signal source, which avoids the situation where multiple disturbance signals interfere with each other.

[0077] like Figure 2 , Figure 3As shown in FIG. 1 , the mechanism of the current disturbance generating circuit generating the current disturbance is as follows: the current disturbance generating circuit uses the inverter full bridge and filter circuit topology structure, and the DC side of the inverter full bridge is connected to the capacitor C d The AC side of the inverter full bridge is connected to the filter circuit, and the filter circuit is connected to the battery system through the output terminal. The host control system sends the required current disturbance command to the disturbance generation controller, and the disturbance generation controller detects the capacitor voltage u on the DC side of the inverter full bridge through the voltage sensor. dc , the current sensor detects the output current i of the current disturbance generating circuit c , and in Figure 3 Under the control loop shown, a switch signal is generated to control the power devices of the inverter full bridge to turn on and off. After the inverter full bridge output current passes through the filter circuit, the disturbance current i with the frequency and amplitude set by the host control system is obtained. c , sent to the battery system as a current disturbance.

[0078] like Figure 3 The control loop block diagram shown in FIG. 1 shows a specific control principle: the amplitude and frequency of the AC current disturbance to be generated in the battery system are set, and the amplitude and frequency are used as the given value of the AC disturbance current output by the current disturbance generating circuit. is an unbiased AC quantity. The DC component is added to make the DC side capacitor of the inverter full bridge transmit energy to the battery system in the form of the DC component of the output current of the current disturbance generating circuit to stabilize the DC side capacitor voltage. The DC side capacitor voltage detection feedback value u dc The capacitor voltage error signal is output by the regulator as an additional DC component to stabilize the DC side capacitor voltage. Add together to obtain the real current disturbance generating circuit output current given signal, which contains AC disturbance component and DC component. The given signal and the detection feedback quantity i of the current disturbance generating circuit output current are c The error signal is adjusted to generate a PWM signal, which is then amplified by the driver to control the power devices in the inverter full bridge to turn on and off. After the inverter full bridge output current passes through the filter circuit, the disturbance current i with the frequency and amplitude set by the host control system is obtained. c , sent to the battery system as a current disturbance.

[0079] The current disturbance generated by the current disturbance generating circuit in each battery branch must ensure the accuracy of the disturbance frequency, but the amplitude of the disturbance can have a certain error relative to the set value, which does not affect the measurement, because the battery cell current and voltage detection is carried out in the battery cell impedance spectrum time-sharing multiplexing measurement circuit, and the impedance spectrum is calculated based on the voltage and current detection results obtained by real-time measurement.

[0080] The current disturbance generating circuit is connected to the battery system through a switch. The switch can be closed for a long time, or it can be closed only when measurement is needed. This avoids the impact of the long-term connection of the current disturbance generating circuit to the battery system on the system operation stability and reduces the risk that abnormal fluctuations in the battery system may damage the current disturbance generating circuit.

[0081] like Figure 4 As shown, the cell impedance spectrum time-division multiplexing measurement circuit is installed in each battery pack, and the current sensor is used to collect the cell current. Because all the cells in a battery pack are connected in series, the current measurement of each cell is sampled at the current sensor, and the separate detection of each cell voltage is achieved through a programmable multiplexing switch. The voltage and current are sampled synchronously to improve the measurement accuracy. During the measurement process, the sampling controller starts the measurement after receiving the command from the host control system, and communicates with the host control system in real time during the measurement process. The sampling controller realizes the separate measurement of each cell voltage by controlling the programmable multiplexing switch, and the voltage and current measurement results are uploaded to the host control system in real time.

[0082] According to the actual situation, the programmable multiplexing switch can use relays, semiconductor devices, multiplexing switch chips, etc. During measurement, the measurement port and each battery cell are sequentially selected through program control. The battery cell impedance spectrum time-division multiplexing measurement circuit can be combined with the BMS circuit in the battery pack to achieve cost reduction and efficiency improvement.

[0083] It should be noted that the GND reference ground potential of the cell impedance spectrum time-division multiplexing measurement circuit installed in each battery pack needs to be independent and cannot be shared, otherwise it will introduce greater interference and affect the accuracy of the cell impedance spectrum measurement. Accordingly, when each cell impedance spectrum time-division multiplexing measurement circuit communicates with the host control system, isolation communication measures such as optical coupler isolation should be taken.

[0084] like Figure 5 As shown, the measuring system and the measuring method are divided into the following steps:

[0085] (1) The host control system determines the characteristic frequency points of the impedance spectrum sweep, the number of characteristic frequency points a, and the number of cells b in each battery pack according to the measurement requirements and the actual situation of the battery system.

[0086] (2) The host control system establishes communication with the inverter. When the battery system is stably charging, stably discharging, or in a static state, the control switch connects the current disturbance generating circuit to the battery system for impedance spectrum measurement to minimize the impact of the polarization phenomenon of the battery during unstable charging and discharging on the measurement results.

[0087] (3) The host computer control system sends a detection command to control the switch to close, setting j=1.

[0088] (4) Prepare to measure the impedance spectrum of the j-th battery cell in each battery pack, and let i=1.

[0089] (5) The host computer control system controls the current disturbance generating circuit to generate the current disturbance at the i-th characteristic frequency point.

[0090] (6) In each battery pack, the cell impedance spectrum time-division multiplexing measurement circuit measures the voltage and current of the j-th cell in each battery pack and uploads the data to the host computer control system.

[0091] (7) The host computer control system calculates the impedance of the j-cell in each battery pack at frequency point i and records the data.

[0092] (8) The host computer control system waits for each cell impedance spectrum time-division multiplexing measurement circuit to complete the detection of the i-th characteristic frequency point of the j-th cell in the battery pack.

[0093] (9) If i<a, the host computer control system determines that i=i+1, and returns to "step (5)" to loop; if i≥a, it means that the impedance spectrum detection of the j-th battery cell in all battery packs is completed, and proceeds to the next step.

[0094] (10) The host computer control system calculates the impedance spectrum of the j-cell in each battery pack.

[0095] (11) The host computer control system determines that if j < b, then j = j + 1, and returns to "step (4)" to loop; if j ≥ b, it means that the impedance spectrum detection of all cells in the battery system is completed, and proceeds to the next step.

[0096] (12) Disconnect the switch, end the measurement, and analyze and process the data.

[0097] The entire measurement process can be carried out without affecting the normal charging and discharging operation of the battery system, realizing in-situ online detection.

[0098] For the selection of characteristic frequency points, during the measurement, the state quantity of the battery cell to be detected is determined, such as the battery cell SOC, SOH and internal temperature, etc. According to the mapping relationship between the state quantity of the battery cell to be detected and the impedance spectrum, the characteristic frequency section of the sweep frequency measurement is selected in the complete impedance spectrum of the battery cell, and the sweep frequency characteristic frequency point is further selected in the characteristic frequency section, considering that harmonic interference may be generated on the battery system side when the converter is running, thereby affecting the measurement accuracy of the impedance spectrum of the battery cell. Therefore, in the characteristic frequency section, non-fundamental and non-harmonic frequencies are selected as characteristic frequency points. During the measurement process, the DC component, fundamental component and harmonic component of the voltage and current detection results are filtered out in the upper computer control system through the program algorithm, and only the selected characteristic frequency point frequency component is retained for impedance spectrum calculation, thereby eliminating the interference of converter ripple and normal battery charge and discharge reaction on the measurement.

[0099] Embodiment 2,

[0100] Embodiment 2 of the present invention applies the present invention to a power battery pack of an electric vehicle. Accordingly, the "inverter" in Embodiment 2 of the present invention corresponds to a drive inverter, the "battery box" corresponds to a vehicle-mounted power battery box, and the "battery pack" corresponds to a vehicle-mounted power battery pack.

[0101] Similar to the battery system of an energy storage power station, the battery management system in existing electric vehicles can monitor the status of the on-board power battery in real time. However, the monitoring system cannot obtain the internal electrochemical parameters of the power battery, cannot identify potential defects in the battery, and cannot obtain the temperature inside the battery, resulting in electric vehicle fires and spontaneous combustion still occurring from time to time.

[0102] The technical solution of the present invention can also be applied to the impedance spectrum detection of single cells in the power battery pack of electric vehicles to realize in-situ online detection and provide accurate impedance spectrum data for monitoring and evaluation of various characteristic parameters of the power battery pack.

[0103] The relevant technical solution is the same as that in Example 1 and will not be described in detail here.

[0104] Embodiment 3,

[0105] Embodiment 3 of the present invention applies the present invention to retired battery pack health status assessment, sorting and other cascade utilization related technologies to assess the characteristic status of each battery cell in the retired battery pack.

[0106] It should be noted that breakthroughs in the rapid detection of energy storage battery cycle life and aging status evaluation technology, and the development of retired battery health assessment, sorting, repair and other cascade utilization related technologies, have attracted great attention from all walks of life. The peak of retirement of power batteries for electric vehicles in my country is coming. Compared with new batteries, retired batteries have poor consistency, high performance dispersion, and great safety hazards. In addition, in the process of layer-by-layer integration from battery cells, modules, battery clusters to energy storage systems, the above problems will be superimposed and amplified, resulting in increased uncertainty in the overall performance of the system. Large quantities of power batteries are continuously retired, and their cascade utilization is expected to maximize the value of the battery's full life cycle.

[0107] According to the battery degradation mechanism and combined with the internal characteristic parameters, by analyzing the impedance response evolution mechanism of special frequency bands in the cascade utilization stage, the characteristic frequency segments of the impedance spectrum that can characterize the health and aging states of the battery are identified.

[0108] In Example 3 of the present invention, the characteristic frequency point is selected in the characteristic frequency section based on the above principle. Because it is an assessment of the health status and aging status of the retired battery pack, the impedance spectrum measurement can be performed when the converter is not working or when the battery box is not connected to the converter. The measurement process can be relatively simplified compared to Example 1 and Example 2.

[0109] The rest of the related technical solutions are the same as those in Example 1 and will not be described in detail here.

[0110] It should be noted that, from the perspective of battery recycling, the cell impedance spectrum time-sharing multiplexing measurement circuit in the present invention can be integrated and installed in the BMS circuit in the battery pack during the battery pack production stage, and then in the electric vehicle power battery pack application stage described in Example 2, the retired battery pack health status assessment and sorting application stage described in Example 3, and the energy storage power station application stage described in Example 1, the battery impedance spectrum can be measured in situ online in combination with the switch outside the battery pack, the current disturbance generating circuit, and the host computer control system. That is, the battery impedance spectrum in situ online measurement system and measurement method proposed by the present invention can be used throughout the life cycle of the battery to achieve cost reduction and efficiency improvement to the greatest extent.

[0111] Figure 6 is a flow chart of the in-situ online measurement method of battery impedance spectrum provided by an embodiment of the present invention, such as Figure 6 As shown, the following steps are included:

[0112] S101, inputting a disturbance current of preset frequency and amplitude to a battery system in normal operation through a current disturbance generating circuit; the battery system comprises one battery branch or at least two battery branches connected in parallel; each battery branch comprises at least one battery pack or at least two battery packs connected in series, and each battery pack comprises at least one battery cell; the current disturbance generating circuit is connected in parallel with the battery system;

[0113] S102, measuring the voltage and current of each battery cell under the preset frequency disturbance current to determine the impedance of each battery cell under the preset frequency;

[0114] S103, inputting disturbance currents at different preset frequencies into the battery system to measure the impedance of each battery cell at the different frequencies, so as to determine the impedance spectrum of each battery cell based on the impedance at the different frequencies.

[0115] It should be noted that Figure 6 The detailed functional implementation of each step in the above system embodiment can be found in the introduction, which will not be repeated here.

[0116] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A battery impedance spectrum in-situ online measurement system, characterized in that: include: Current disturbance generating circuit, switch, control unit and measuring circuit; The current disturbance generating circuit is connected in parallel with the battery system through a switch; the battery system includes one battery branch or at least two battery branches connected in parallel; each battery branch includes at least one battery pack or at least two battery packs connected in series, and each battery pack includes at least one battery cell; The current disturbance generating circuit is used to generate a disturbance current with a preset frequency and amplitude; The current disturbance generating circuit includes: a full-bridge inverter, a capacitor and a filter circuit; the DC side of the full-bridge inverter is connected to the capacitor, so that the current disturbance energy uses reactive power and reduces active power consumption, and the AC side is connected to the input end of the filter circuit; the output end of the filter circuit is connected in parallel with the battery system; the control unit determines the preset value of the disturbance current and the preset value of the capacitor voltage, and collects the current value of the capacitor voltage and the current value output by the filter circuit; determines a first error between the preset value of the capacitor voltage and the current value of the capacitor voltage, and a second error between the preset value of the disturbance current and the current value output by the filter circuit; generates a corresponding switching signal according to the first error and the second error; the power device in the full-bridge inverter is turned on and off under the action of the switching signal, so that the filter circuit outputs the disturbance current of the preset value; the measurement circuit is used to measure the voltage and current of each battery cell; When measuring the battery impedance spectrum, the control unit controls the switch to close, controls the current disturbance generating circuit to generate a disturbance current of preset frequency and amplitude, and controls the measuring circuit to measure the voltage and current of each battery cell; the control unit determines the impedance of each battery cell at a preset frequency based on the voltage and current of each battery cell; the control unit controls the current disturbance generating circuit to generate disturbance currents at different frequencies, and obtains the impedance of each battery cell at different frequencies through the measuring circuit, so as to determine the impedance spectrum of each battery cell based on the impedance at different frequencies.

2. The system according to claim 1, characterized in that Each battery pack is connected to a measurement circuit; The measuring circuit comprises: a programmable multiplexing switch, a current sensor, a current sampling circuit, a voltage sampling circuit and a sampling controller; The current sensor is connected in series with the battery pack; The programmable multiplexing switch connects the voltage sampling circuit to both ends of each battery cell in the battery pack; The sampling controller controls the programmable multiplexing switch to conduct in time division to measure the voltage of each battery cell respectively; While the voltage sampling circuit measures the voltage of each battery cell, the sampling controller controls the current sampling circuit to respectively collect the current value of the current sensor as the current value of each battery cell.

3. The system according to claim 1 or 2, characterized in that: The control unit determines each frequency sweep characteristic frequency point of the disturbance current according to the impedance spectrum measurement requirement; During a period when the battery system is stably charged, stably discharged, or in a static state, the control unit controls the switch to connect the current disturbance generating circuit to the battery system; thereafter, the control unit sends a detection instruction and a corresponding current disturbance setting value to the current disturbance generating circuit according to each determined sweep characteristic frequency point, so as to control the current disturbance generating circuit to output a disturbance current of a corresponding frequency to the battery system at each characteristic frequency point, and then in each battery pack, the measurement circuit measures the terminal voltage and current of each battery cell under the disturbance at each characteristic frequency point, and uploads the data to the control unit; The control unit calculates the impedance of each battery cell in the battery system at each characteristic frequency point, and then obtains the impedance spectrum of each battery cell. After completing the impedance spectrum measurement of all battery cells in the battery system, the switch is disconnected and the measurement ends. The entire measurement process is carried out without affecting the normal operation of the battery system, realizing in-situ online detection.

4. A method for in-situ online measurement of battery impedance spectrum, characterized in that: The steps include: A disturbance current of preset frequency and amplitude is input to a battery system in normal operation through a current disturbance generating circuit; the battery system comprises one battery branch or at least two battery branches connected in parallel; each battery branch comprises at least one battery pack or at least two battery packs connected in series, and each battery pack comprises at least one battery cell; The current disturbance generating circuit is connected in parallel with the battery system; The current disturbance generating circuit comprises: a full-bridge inverter, a capacitor and a filter circuit; the DC side of the full-bridge inverter is connected to the capacitor so that the current disturbance energy uses reactive power and reduces active power consumption, and the AC side is connected to the input end of the filter circuit; the output end of the filter circuit is connected in parallel with the battery system; the disturbance current of the preset frequency and amplitude is determined by the following steps: determining a preset value of the disturbance current and a preset value of the capacitor voltage; collecting the current value of the capacitor voltage and the current value output by the filter circuit; determining a first error between the preset value of the capacitor voltage and the current value of the capacitor voltage, and a second error between the preset value of the disturbance current and the current value output by the filter circuit; generating a corresponding switching signal according to the first error and the second error; inputting the switching signal to the full-bridge inverter, and the power devices in the full-bridge inverter are turned on and off under the action of the switching signal, so that the filter circuit outputs the disturbance current of the preset value; Measuring the voltage and current of each battery cell under the preset frequency disturbance current to determine the impedance of each battery cell at the preset frequency; A disturbance current at different preset frequencies is input into the battery system to measure the impedance of each battery cell at different frequencies, so as to determine the impedance spectrum of each battery cell based on the impedance at different frequencies.

5. The method according to claim 4, characterized in that Measure the voltage and current of each cell under the preset frequency disturbance current, specifically: The voltage of each battery cell in the same battery pack is measured in time by the same voltage sampling circuit, and while measuring the voltage of each battery cell, the current value of the current sensor connected in series with the battery pack is collected as the current value of each battery cell.

6. The method according to claim 4 or 5, characterized in that: The following steps are also included: According to the impedance spectrum measurement requirements, determine each frequency sweep characteristic frequency point of the disturbance current; During a period when the battery system is stably charged, stably discharged or in a static state, a detection instruction and a corresponding current disturbance setting value are sent to the current disturbance generating circuit according to each determined sweep characteristic frequency point, so as to control the current disturbance generating circuit to output a disturbance current of a corresponding frequency to the battery system at each characteristic frequency point, and then respectively measure the terminal voltage and current of each battery cell under the disturbance at each characteristic frequency point; The impedance of each battery cell at each characteristic frequency point is calculated according to the terminal voltage and current of each battery cell under the disturbance of each characteristic frequency point, and then the impedance spectrum of each battery cell is obtained; After measuring the impedance spectra of all cells in the battery system, the current disturbance generating circuit is disconnected and the measurement is completed; the entire measurement process is carried out without affecting the normal operation of the battery system, realizing in-situ online detection.

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