A single-inductor multi-input single-output DC-DC system for lithium battery EIS detection and its control method

Abstract

The present invention discloses a single-inductor multi-input single-output DC-DC system for lithium battery EIS detection and its control method. By coordinating the switch control of (2N+2) MOS tubes in the A and B levels of the DC-DC system and setting the dead time, the four modes of N battery cells are prevented from interfering with each other, so as to repeatedly control the charge and discharge of the single inductor. At the same time, two NMOS switches S are used in the B level of the SI-MISO circuit to control the charge and discharge of the single inductor. l and S u By inputting an additional duty cycle disturbance signal, the AC impedance values ​​of multiple lithium batteries to be tested at different frequencies can be quickly and simultaneously obtained. In addition to reducing hardware costs, the present invention can avoid the reduction in power quality caused by adding a disturbance signal while detecting the impedance of the lithium-ion battery. Therefore, the normal working output of the circuit is not affected while the lithium-ion battery impedance is tested.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium battery detection, and more specifically, relates to a single-inductor multi-input single-output DC-DC system for lithium battery EIS detection and a control method thereof. Background Art

[0002] Lithium batteries are an important energy source for modern electronic devices and electric vehicles, so monitoring their health and performance is crucial. Non-destructive testing of battery impedance is a key technology for evaluating battery health, providing important information on battery aging, degradation, and internal chemical changes. In battery performance evaluation, the non-destructive testing technology of electrochemical impedance spectroscopy (EIS) is an important means of assessing battery health and is widely used in multiple disciplines such as materials science, electrochemistry, electrical engineering, control theory and methods, etc. EIS can non-destructively measure the impedance characteristics of materials or electrochemical systems, and detect the properties of battery materials or the status of the system by analyzing changes in impedance.

[0003] Currently, there are two main methods for measuring battery impedance: offline measurement and online measurement.

[0004] Offline impedance measurement techniques typically involve applying a small sinusoidal alternating current (AC) perturbation voltage or current to a battery in equilibrium and measuring the system's response in a laboratory setting using precision instruments such as an electrochemical workstation and frequency response analyzer. The amplitude of the perturbation signal is typically very small to ensure it does not interfere with the system's natural state. The test frequency range is typically in the kilohertz to millihertz range.

[0005] The current main method for online impedance measurement involves applying a small current perturbation to the battery using a special circuit, and then calculating the battery's impedance using relevant signal processing methods. Because the perturbation circuit and the external circuit are connected in parallel, and the perturbation voltage and current are only 1% of the original voltage and current, it does not affect the battery's normal charging and discharging. In their paper, "Depernet D, Ba O, Berthon A, et al. Online impedance spectroscopy of leadacid batteries for storage management of a standalone power plant [J]. Journal of Power Sources, 2012: 65-74," Depernet et al. employed a PI control method, controlling a boost converter circuit through pulse width modulation, to achieve a small sinusoidal current perturbation of the battery, thereby achieving practical and low-cost measurement of battery impedance. Huang et al. proposed a related control algorithm in the paper "Huang W, Qahouq J A. An Online Battery Impedance Measurement Method Using DC–DC Power Converter Control [J]. IEEE Transactions on Industrial Electronics, 2014, 61(11): 5987-5995.". By controlling the duty cycle of the power converter, a small sinusoidal current disturbance is generated in the battery, thereby achieving the purpose of practical and low-cost online measurement of battery impedance.

[0006] However, the above-mentioned lithium-ion battery impedance measurement methods can all measure the impedance of lithium-ion batteries, but they have certain defects. The related equipment used in the battery impedance offline testing technology, such as the electrochemical workstation, is expensive, only supports impedance measurement in an offline state, and the test time is long, and the test environment requirements are harsh. Most application scenarios are limited to laboratories, and are not capable of meeting the needs of rapid impedance measurement in more complex environments during operation, making it difficult to promote and apply. For the above-mentioned online impedance measurement methods, there are two disadvantages: the first disadvantage is that these methods can only measure the impedance of a certain frequency of a battery at a time. This means that measuring the impedance spectrum of multiple batteries within a certain frequency range needs to be completed sequentially and requires an extended time, but the battery status (such as temperature, SOC, current and voltage, etc.) cannot be controlled, and it is often difficult to effectively measure the battery impedance for a long time. The second disadvantage is that the existing circuit is mainly combined with a single battery through a DC / DC converter topology, and only one battery cell impedance value can be measured at the same time, and there are certain defects in the impedance test efficiency.

[0007] Therefore, there is an urgent need to design a single-inductor multi-input single-output DC-DC system and its control method for lithium battery EIS detection, so as to detect the impedance values ​​of multiple battery cells in a short time and within a certain frequency range, and reliably obtain the electrochemical impedance spectrum curves of multiple batteries. Summary of the Invention

[0008] (1) Technical issues to be resolved

[0009] Based on the defects mentioned in the above background technology, the present invention discloses a single-inductor multi-input single-output DC-DC system for EIS detection of lithium batteries and its control method, which can be used to simultaneously realize online detection of power output and AC impedance, and can quickly measure the impedance values ​​of multiple battery cells in a short time and within a certain frequency range. The hardware cost is low and it has great practical application value. It is conducive to early fault diagnosis of the service life of lithium batteries and improves their reliability and efficiency.

[0010] (2) Technical solution

[0011] The present invention discloses a single-inductor multi-input single-output DC-DC system for lithium battery EIS detection, wherein the DC-DC system consists of two parts, Class A and Class B;

[0012] The A stage consists of N battery cells V bat1 ~V batN , N input capacitors C1~C N and 2N NMOS switches (S 11 ,S 12 ),(S 21 ,S 22 ),…,(S N1 ,S N2 ) constitutes N parallel input circuits, where the battery unit V bati With input capacitor C i Parallel connection, battery cells V bati The positive electrode is connected through two back-to-back series NMOS switches S i1 and S i2 Connect in parallel with the positive terminals of the output terminals of the other N-1 parallel input circuits, and the battery cell to be tested V bati The negative electrode of the N-1 battery cells is connected in parallel to the negative electrode of the other N-1 battery cells to serve as the negative electrode of the output end of the parallel input circuit. The output ends of the N parallel input circuits of level A are connected to the input end of level B, and the i-th group of NMOS switches S i1 and S i2 The gate is driven by the same signal P i Drive, i ranges from 1 to N and N ≥ 2;

[0013] The B-level synchronous Boost circuit includes an inductor L, two NMOS switches S with complementary duty cycle signals, and a l and S u and output capacitor C out , output capacitor C out With the output voltage V out The load is connected in parallel, the NMOS switch S l The drain is connected to the negative terminal of the load, S l The source of the NMOS switch S u The source of the NMOS switch S is connected to one end of the inductor L. u The drain of the load is connected to the positive electrode, and N NMOS switches S i2 The drain of the battery cell V bati The negative electrode of the load and the negative electrode of S l The drains are connected to the common ground.

[0014] Preferably, S l and S u The two NMOS switches input a mixed-frequency AC duty cycle disturbance signal to complete the impedance detection of each battery cell at various frequencies.

[0015] Preferably, the 2N NMOS switches of class A complete an alternating conduction operation cycle T0 and meet the following conditions:

[0016] T0=T1+T2+…+T N +(N-1)T d =NT1+(N-1)T d

[0017] Where T1=T2=…=T N =mT s , at this time each driving signal P i The conduction time T when the voltage is continuously high i equal to achieve battery cell V bati Connection between Class B, T d is the adjacent conduction time T i The dead zone interval between the two periods is m, which is the inductance L in period T. s The total number of continuous charge and discharge times, T s It is the time it takes for the inductor to complete one charge and discharge cycle.

[0018] Preferably, the DC-DC system drives the signal P at each level A. i The conduction time T i It includes the following four modes 1-4:

[0019] Mode 1: Class A switch Si1 、S i2 In the on state, the other 2 (N-1) switches are in the off state, and the switch S of class B is l In the on state and S u In the disconnected state, the battery cell V bati Provide energy to charge the inductor L, the inductor current increases, and the voltage of battery cell i is V i , the load output voltage is V out , the inductor current changes to Δi L , then in mode 1 V i 、V out and Δi L The relationship is given by the following formula

[0020] V i ·(t i1 -t i0 )=Δi L ·L

[0021] Mode 2: Class A switch S i1 、S i2 In the on state, the other 2(N-1) switches are in the off state, and the switch S of B is l In the disconnected state and S u In the on state, the current of the inductor L decreases through the output capacitor and the load discharge. In mode 2, V i 、V out and Δi L The relationship is given by the following formula

[0022] (V out -V i )·(t i2 -t i1 )=Δi L ·L

[0023] Mode 3: Class A switch S i1 、S i2 Continue to conduct, the other 2 (N-1) switches are in the off state, at T i In the last one or several switching cycles, before turning off the switch S i1 、S i2 Before, switch S l and S u All are turned off, and the inductor current is reset to 0 to avoid interfering with the measurement work of other battery cells;

[0024] Mode 4: 2N+2 switches (S 11 ,S 12 ),(S 21 ,S 22),…,(S N1 ,S N2 ), S l and S u Both are in the off state, and the adjacent conduction time T i Set the dead zone interval T between d .

[0025] In another aspect, the present invention further discloses a control method for the single-inductor multi-input single-output DC-DC system for lithium battery EIS detection as described above, the control method comprising the following steps:

[0026] Step 1: Connect N lithium-ion batteries to be tested as battery cells in parallel at the input of a single-inductor multiple-input single-output DC-DC system. Use a time-division multiplexing control method to add multi-frequency disturbances to each battery cell, thereby achieving AC impedance testing of multiple battery cells at the same time.

[0027] Step 2: By S l and S u The two NMOS switches input mixed-frequency AC duty cycle disturbance signals to control their on and off;

[0028] Step 3: Then measure the AC voltage / current response of each battery cell to the injected AC current / voltage signal to detect the impedance of the lithium-ion battery at various frequencies;

[0029] Step 4: Use FFT to analyze the peak-to-peak values ​​of the lithium-ion battery voltage and current at each frequency under multi-frequency disturbance, and calculate the impedance value at that frequency according to the following formula;

[0030]

[0031] where Z fr 、V fr and I fr Respectively represent the frequency f r The impedance, voltage and current values ​​of the battery cell when θ fr Indicates frequency f r The phase difference between the lithium-ion battery voltage and current;

[0032] Step 5: Calculate the impedance value within the required frequency range as needed to draw the EIS curve.

[0033] Preferably, in step 2, the duty cycle disturbance signals at multiple frequencies are mixed and added together and input into the synchronous Boost circuit of Class B to achieve simultaneous and efficient multi-frequency impedance detection, and the amplitude of the added AC duty cycle disturbance signal must not exceed 3% of the DC duty cycle signal amplitude.

[0034] Preferably, in step 2, assuming that N battery cells V bat1 ~V batN The input voltage is V1, V2, ..., V N , and applying the volt-second balance principle, we get the following formula, where D r When the switch in the A class (S r1 , S r2 ) is turned on, the synchronous Boost circuit switch S in stage B l Duty cycle, and r = 1, 2, ..., N

[0035]

[0036] By solving the above formula, we can get the output voltage V of the load out satisfy

[0037]

[0038] In the discharge mode, there is an output voltage control loop whose input is the reference output voltage V out_ref And the output voltage V measured after the i-th battery cell is connected outr The difference between the two, the output of the voltage compensator is the DC duty cycle D dc , continuous transfer function G c_vol (s) or discrete transfer function G c_vol (z) is the proportional integral compensator, and the output voltage control loop generates a switch S l The DC duty cycle of D1 to D N , the DC duty cycle of each battery cell D1 to D N It is given by the following formula;

[0039]

[0040] In level B, two switches S l and S u Input duty cycle disturbance signal, which is DC D dc and AC duty cycle disturbance signals D at various frequencies ac The superposition is shown below;

[0041] D(t)=D dc +D ac

[0042] D ac =D ac-f1 +D ac-f2 +…+D ac-fn

[0043] The added disturbance signal is shown below;

[0044]

[0045] Where D(t) represents the total duty cycle of the Class B driver, D dc Indicates the added DC duty cycle signal, D ac represents the added AC duty cycle disturbance signal, n refers to the number of frequency components, D ac-f1 represents the disturbance signal at frequency f1, D ac-f2 represents the disturbance signal at frequency f2, D ac-fn Indicates the frequency at f n The disturbance signal under p1 is the disturbance signal D ac-f1 The amplitude, D p2 is the disturbance signal D ac-f2 The amplitude, D pn is the disturbance signal D ac-fn The amplitude, f n >…>f2>f1.

[0046] Preferably, step 4 further specifically includes sampling the voltage and current of the battery cell by an analog-to-digital converter, and calculating the voltage V of the measured i-th battery cell. bati and current I bati Perform fast Fourier transform analysis to obtain the voltage frequency component (V ac (f1), V ac (f2),…V ac (f n )), current frequency component (I ac (f1), I ac (f2),…I ac (f n )) and the corresponding phase shifts (θ(f1), θ(f2), …θ(f n )), and calculate different frequencies f r The impedance value under is used to draw the EIS curve.

[0047] (3) Beneficial effects

[0048] 1. The present invention avoids the reduction of power quality caused by adding a disturbance signal while detecting the impedance of the lithium-ion battery. Therefore, the normal working output of the circuit is not affected while the lithium-ion battery impedance is tested.

[0049] 2. The present invention can prevent the four modes of the N battery cells from interfering with each other by coordinating the switch control of the (2N+2) MOS tubes of the A and B levels in the single-inductor multi-input single-output DC-DC system and setting the dead time, so as to repeatedly charge and discharge the inductor L, and at the same time, the two NMOS switches S in the B level of the SI-MISO circuit are used. l and Su By inputting an additional duty cycle disturbance signal, the AC impedance values ​​of multiple lithium batteries to be tested at different frequencies can be quickly and simultaneously obtained.

[0050] 3. In addition, the present invention does not require any testing of lithium-ion batteries and can test the impedance of multiple lithium-ion batteries online in real time. Because the output end of the multi-input switch stage of level A shares the single-inductor synchronous Boost circuit of level B, the hardware cost is relatively low, which can save hardware cost while improving detection efficiency. Moreover, by using the alternating time-sharing multiplexing control method of the inductor L, AC small signal disturbances can be performed on multiple batteries at the same time, thereby fully utilizing each hardware.

[0051] 4. The present invention adds duty cycle disturbance signals of multiple frequencies to the DC-DC converter at the same time, which can realize impedance detection of multiple frequencies at the same time and has high efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] In order to more clearly illustrate the technical solutions of the present invention or the prior art, the following briefly introduces the drawings required for the embodiments:

[0053] Figure 1 This is a schematic structural diagram of a single-inductor multi-input single-output DC-DC system for lithium battery EIS detection according to the present invention;

[0054] Figure 2 This is a flow chart of a control method for measuring the EIS impedance spectrum of a lithium-ion battery using a single-inductor multi-input single-output DC-DC system according to the present invention;

[0055] Figure 3 This is a control timing diagram of each switch tube in the process of the single inductor time-division multiplexing control method used in the present invention;

[0056] Figure 4 : This is the equivalent circuit of the main operating modes of the dual-input SI-MISO circuit of the present invention (the last four operating modes are similar to the first four Mode 1 to Mode 4 and will not be described in detail);

[0057] Figure 5 A block diagram of a voltage control loop for the output DC duty cycle of the inductor of the present invention in a discharge operation mode;

[0058] Figure 6 This is a schematic diagram of the FFT of the current and voltage disturbance of the lithium-ion battery of the present invention;

[0059] Figure 7 The Bode diagram of the lithium battery in the frequency range of 10Hz to 100Hz tested by the present invention;

[0060] Figure 8This is an EIS curve diagram of the lithium battery tested in the frequency range of 10 Hz to 100 Hz in the present invention. DETAILED DESCRIPTION

[0061] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0062] Aiming at the defects of low efficiency and high cost in the prior art of batch lithium battery impedance EIS testing, the present invention proposes a single-inductor multi-input single-output DC-DC system for lithium battery EIS testing and its control method.

[0063] The following will describe in detail the single-inductor multi-input single-output DC-DC system for lithium battery EIS detection of the present invention. Figure 1 As shown, the system of the present invention uses a synchronous Boost circuit as a framework structure. The system consists of two parts, Class A and Class B. Class A (the input stage in the lithium battery discharge mode) is a multi-input switch stage that can accommodate multiple battery cell inputs coupled to the same switch node. Each battery cell is switched on or off by back-to-back n-channel metal oxide semiconductor field effect transistors (MOSFETs) (S 11 ,S 12 ),(S 21 ,S 22 ),…,(S N1 ,S N2 ) connects or disconnects stage B, thereby controlling the bidirectional flow of energy to manage the charging and discharging of the battery cells. Stage B, as the power conversion stage, is a typical synchronous boost circuit, but it lacks input capacitors. In discharge mode, energy flows from stage A to stage B, while in charge mode, energy flows from stage B to stage A. Stages A and B work together to implement the circuit's time-sharing control algorithm.

[0064] Specifically, the A stage as a multi-input switch stage includes N battery cells V bat1 ~V batN , N input capacitors C1~C N and 2N NMOS switches (S 11 ,S 12 ),(S 21 ,S 22 ),…,(S N1 ,S N2) constitutes N parallel input circuits, where the battery unit V bati With capacitor C i Parallel connection, battery cells V bati The positive electrode is connected through two back-to-back series NMOS switches S i1 and S i2 Connect in parallel with the positive terminals of the output terminals of the other N-1 parallel input circuits, and the battery cell to be tested V bati The negative electrode of the N-1 battery cells is connected in parallel to the negative electrode of the other N-1 battery cells to serve as the negative electrode of the output end of the parallel input circuit. The output ends of the N parallel input circuits of level A are connected to the input end of level B, and the i-th group of NMOS switches S i1 and S i2 The gate is driven by the same signal P i Drive, i ranges from 1 to N and N ≥ 2.

[0065] Specifically, the synchronous Boost circuit of Class B includes an inductor L, two NMOS switches S with complementary duty cycle signals. l and S u and output capacitor C out , where the output capacitor C out With the output voltage V out The load is connected in parallel, the NMOS switch S l The drain is connected to the negative terminal of the load, S l The source of the NMOS switch S u The source of the NMOS switch S is connected to one end of the inductor L. u The drain of the load is connected to the positive electrode. In order to realize the bidirectional flow of energy between class A and class B, N NMOS switches S i2 The drain of each battery cell is connected to the other end of the single filter inductor L. bati The negative electrode of the load and the negative electrode of S l The drains of the MOSFETs are connected to the ground to serve as the output stage in discharge mode.

[0066] In order to overcome the shortcomings of the above-mentioned lithium-ion battery impedance detection method, such as the inability to detect online, low detection efficiency and reduced power quality, Figure 1 Based on medium- and low-cost hardware, the present invention provides a control method for a single-inductor multi-input single-output DC-DC system for lithium battery EIS detection, and a method for online multi-frequency impedance detection of multiple lithium-ion batteries. By utilizing the designed single-inductor multi-input single-output DC-DC system and simultaneously adding multiple-frequency duty cycle disturbances to it, it can achieve efficient online multi-frequency AC impedance detection of multiple lithium-ion batteries at the same time without affecting the normal operation and output of the battery power unit.

[0067] The flow chart of the control method of the present invention is as follows Figure 2 As shown, the following steps are included:

[0068] Step 1: Connect N lithium-ion batteries to be tested as battery cells in parallel at the input of a single-inductor multiple-input single-output DC-DC system. Use a time-division multiplexing control method to add multi-frequency disturbances to each battery cell, thereby achieving AC impedance testing of multiple battery cells at the same time.

[0069] Step 2: By S l and S u The two NMOS switches input mixed-frequency AC duty cycle disturbance signals to control their on and off;

[0070] Step 3: Then measure the AC voltage / current response of each battery cell to the injected AC current / voltage signal to detect the impedance of the lithium-ion battery at various frequencies;

[0071] Step 4: Use FFT to analyze the peak-to-peak values ​​of the lithium-ion battery voltage and current at each frequency under multi-frequency disturbance, and calculate the impedance value at that frequency according to the following formula;

[0072]

[0073] where Z fr 、V fr and I fr Respectively represent the frequency f r The impedance, voltage and current values ​​of the battery cell when θ fr Indicates frequency f r The phase difference between the lithium-ion battery voltage and current;

[0074] Step 5: Calculate the impedance value within the required frequency range as needed to draw the EIS curve.

[0075] Specifically, in step 2, the duty cycle disturbance signals at multiple frequencies are mixed and added together and input into the synchronous boost circuit of Class B, enabling simultaneous and efficient multi-frequency impedance detection. The amplitude of the added duty cycle disturbance signal must not exceed 3% of the DC duty cycle value to avoid excessive energy loss in the SI-MISO circuit.

[0076] Specifically, in step 4, the calculated multi-frequency impedance values ​​are the impedance values ​​of the added disturbance signal at each frequency, thereby obtaining the impedance values ​​of the lithium-ion battery at various frequencies.

[0077] In order to reduce the mutual interference between the disturbance inputs of multiple lithium batteries to be tested at multiple frequencies and the EIS detection signals, the present invention further makes the following design.

[0078] Assuming that the current of the shared inductor L is in continuous conduction mode (CCM), the N groups of NMOS switches (S 11 ,S 12 ), (S 21 ,S 22 ),…(S N1 ,S N2 ) and the two NMOS switches S of stage B u and S l Some driving signals such as Figure 3 As shown. According to the driving signal (P1, P2, ..., P N ), N groups of Class A switches are alternately turned on / off for the same time (T1=T2=…=T N ), connects / disconnects each input battery to / from the Class B power converter. In continuous conduction mode (CCM) operation, the switch S u and S l Complementary drive signal P conv Before the end of the time interval between the closing of each input switch of class A, the inductor current is reset to 0. There is a short time delay between the closing of one set of switches in class A and the closing of another set of switches, such as Figure 3 This process ensures that the inputs are decoupled from each other and prevents voltage spikes from occurring on the same switch node when one input is disconnected and the other is connected.

[0079] also, Figure 3 The N groups of A-level switches in the circuit complete an alternating conduction cycle T0 that meets the following conditions: T0 = T1 + T2 + ... + T N +(N-1)T d =NT1+(N-1)T d , where T1=T2=…=T N =mT s , at this time each driving signal P i The conduction time T of the continuous high level is i equal to achieve battery cell V bati Connection between Class B, T d is the adjacent conduction time T i The dead zone interval between the two periods is m, which is the inductance L in period T. s The total number of continuous charge and discharge times, T s is the length of time it takes for the inductor to complete a charge and discharge cycle, that is, Figure 3 Middle t 10 -t 12 The duration is T s , t 12 -t 13 The duration is (m-1)T s .

[0080] In order to simplify the description of the working mode, Figure 4 As shown, the present invention takes the dual-input SI-MISO single inductor-multiple-input single-output system as an example, that is, when N=2, the system working state is analyzed and the working mode is specifically subdivided into 8 modes. At this time, each A-level drive signal P i The conduction time T i It includes four modes: Mode1 to Mode4.

[0081] The conduction time T1 includes modes 1 to 4:

[0082] Mode 1(t 10 -t 11 ):Right now Figure 4 Mode1 state, switch S 11 、S 12 In the on state, switch S 21 、S 22 In the off state, that is, the switch S i1 、S i2 is in the on state, the other 2(N-1) switches are in the off state, and switch S l In the on state and S u In disconnected state. Battery cell V bat1 Provide energy to charge the inductor L, the inductor current increases, and the voltage of battery i is V i , the output voltage is V out , the inductor current changes to Δi L , then in mode 1 V i 、V out and Δi L The relationship is given by the following formula, at this time i=1

[0083] V i ·(t i1 -t i0 )=Δi L ·L

[0084] Mode 2 (t 11 -t 12 ):Right now Figure 4 Mode2 state, switch S 11 、S 12 In the on state, switch S 21 、S 22 In the off state, that is, the switch S i1 、S i2 In the on state, the other 2 (N-1) switches are in the off state, switch S l In the disconnected state and S uIn the on state. The current of the inductor L decreases through the output capacitor and the load discharge. In mode 2, V i 、V out and Δi L The relationship is given by the following formula, at this time i=1

[0085] (V out -V i )·(t i2 -t i1 )=Δi L ·L

[0086] In addition, if Figure 3 As shown, at T1 t 12 -t 13 In the time, the present invention repeats mode 1 and mode 2 (m-1) times, so that in t 10 -t 13 The inductor continuously charges and discharges m times in total within the time, i.e., Mode 1 and Mode 2 are repeated m times before Mode 3.

[0087] Mode 3 (t 13 -t 14 ):Right now Figure 4 Mode3 state, in this mode, switch S 11 、S 12 Continue to conduct, switch S 21 、S 22 In the off state, in the last or several switching cycles of T1, before turning off the switch S 11 、S 12 Before, switch S l and S u All are turned off and the inductor current is reset to 0 to avoid interfering with the measurement work of other battery cells.

[0088] Mode 4 (t 14 -t 20 ):Right now Figure 4 In Mode 4, in order to prevent two batteries from being connected to the same switch node at the same time and to avoid voltage spikes, all switches are closed, i.e. 2N+2 switches (S 11 ,S 12 ),(S 21 ,S 22 ),…,(S N1 ,S N2 ), S l and S u are all turned off, so in Figure 3 There is a T d Indicates the deadband interval.

[0089] The conduction time T2 includes modes 5 to 8. As can be seen from the above, mode 5 (t 20 -t 21 ), Mode 6(t 21 -t 22 ), Mode 7(t 23 -t 24 ) and Mode 8(t 24 -t 30 ) is similar to mode 1-4, except that the battery cell V bat2 Through back-to-back bidirectional NMOS switches S 21 、S 22 Connected to Class B, so no further description is given.

[0090] It should also be pointed out that although the above description of the various modes and their switching methods under the multi-input stage is based on the example of N=2, when the value of the number of lithium batteries N is large, the consistent multi-mode control method is more effective, and it can only be implemented in a synchronous Boost circuit with two signal complementary NMOS switches.

[0091] The following will further introduce the details of adding duty cycle disturbance signals at multiple frequencies at the same time. Figure 1 Impedance detection method of DC-DC converter:

[0092] Assume that there are N battery cells V bat1 ~V batN The input voltage is V1, V2, ..., V N , and applying the volt-second balance principle, we get the following formula, where D r When the switch in the A class (S r1 , S r2 ) is turned on, the synchronous Boost circuit switch S in stage B l Duty cycle, and r = 1, 2, ..., N

[0093]

[0094] By solving the above formula, we can get the output voltage V of the load out satisfy

[0095]

[0096] In the discharge working mode, there is a closed-loop control loop: the output voltage control loop. Figure 5 The output voltage control loop shown is implemented by a voltage compensator, whose input is the reference output voltage V out_ref And the output voltage V measured after the i-th battery cell is connected outr The output of the voltage compensator is the DC duty cycle D dc, continuous transfer function G c_vol (s) or discrete transfer function G c_vol (z) can be a proportional integral (PI) compensator, and the output voltage control loop generates a switch S l The DC duty cycle of D1 to D N , in order to adjust the discharge rate of each battery cell, the DC duty cycle of each battery cell D1 to D N It is given by the following formula.

[0097]

[0098] In order to quickly obtain the AC impedance values ​​of multiple lithium batteries under different frequencies at the same time, two switches S l and S u Input duty cycle disturbance signal, which is DC D dc and AC duty cycle disturbance signals D at various frequencies ac The superposition is shown below.

[0099] D(t)=D dc +D ac

[0100] D ac =D ac-f1 +D ac-f2 +…+D ac-fn

[0101] These frequencies should be able to reflect the charge state and health status of lithium-ion batteries in different frequency bands, and the amplitude of the disturbance signal should not cause excessive energy loss to the lithium-ion battery. Figure 6 The added disturbance signal is shown in the following equation.

[0102]

[0103] Where D(t) represents the total duty cycle of the Class B driver, d dc Indicates the added DC duty cycle signal, D ac Represents the total AC disturbance signal added. This total AC disturbance signal is composed of the superposition of multiple frequency disturbance signal components in the duty cycle disturbance signal. n refers to the number of frequency components, D ac-f1 represents the disturbance signal at frequency f1, D ac-f2 represents the disturbance signal at frequency f2, D ac-fn Indicates the frequency at f n The disturbance signal under p1 is the disturbance signal D ac-f1 The amplitude, D p2 is the disturbance signal Dac-f2 The amplitude, D pn is the disturbance signal D ac-fn The amplitude, D ac The signal amplitude does not exceed D dc 3% of the signal amplitude to avoid affecting the normal working output of the circuit.

[0104] Figure 7 The impedance value measured is in the frequency band of 10Hz-100Hz. The duty cycle signal injected by the present invention is the duty cycle signal superimposed and injected at frequencies of 10, 20, 30, ..., 90, 100. At this time, the value of n is 10.

[0105] The voltage and current of the battery cell are sampled by the analog-to-digital converter (ADC). bati and current I bati Perform fast Fourier transform (FFT) analysis to obtain the voltage frequency component (V ac (f1), V ac (f2),…V ac (f n )), current frequency component (I ac (f1), I ac (f2),…I ac (f n )) and the corresponding phase shifts (θ(f1), θ(f2), …θ(f n )), and calculate the impedance value at different frequencies according to the following formula and draw the EIS curve;

[0106]

[0107] Where r = 1, 2, ..., n, f n >…>f2>f1.

[0108] according to Figure 2 The flowchart shown completes the injection of a mixed multi-frequency signal. The injection duration is 1s. The last 0.1s is taken for FFT analysis to obtain the Bode diagram of the battery impedance spectrum of 10Hz to 100Hz. The EIS curve is as follows Figure 7 and Figure 8 As shown in the figure, it can be seen that the measured battery impedance closely tracks its actual value in both the amplitude-frequency and phase-frequency curves of the Bode plot. Furthermore, the resulting EIS curve is also quite accurate, achieving the desired effect.

[0109] In summary, compared with the existing technology, the characteristics and innovations of the present invention are:

[0110] (1) The present invention can simultaneously perform AC small signal disturbance on multiple batteries by using a time-division multiplexing control method in a DC-DC system;

[0111] (2) The present invention adds duty cycle disturbance signals of multiple frequencies to the DC-DC converter simultaneously, which can realize impedance detection of multiple frequencies at the same time and has high efficiency;

[0112] (3) While testing the impedance of the lithium-ion battery, it does not affect the normal working output of the circuit.

[0113] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A single-inductor multi-input single-output DC-DC system for lithium battery EIS detection, characterized in that: The DC-DC system consists of two parts, Class A and Class B; The A stage consists of N battery cells V bat1 ~V batN , N input capacitors C1~C N and 2N NMOS switches (S 11 ,S 12 ),(S 21 ,S 22 ),…,(S N1 ,S N2 ) constitutes N parallel input circuits, where the battery unit V bati With input capacitor C i Parallel connection, battery cells V bati The positive electrode is connected through two back-to-back series NMOS switches S i1 and S i2 Connect in parallel with the positive terminals of the output terminals of the other N-1 parallel input circuits, and the battery cell to be tested V bati The negative electrode of the N-1 battery cells is connected in parallel to the negative electrode of the other N-1 battery cells to serve as the negative electrode of the output end of the parallel input circuit. The output ends of the N parallel input circuits of level A are connected to the input end of level B, and the i-th group of NMOS switches S i1 and S i2 The gate is driven by the same signal P i Drive, i ranges from 1 to N and N ≥ 2; The B-level synchronous Boost circuit includes an inductor L, two NMOS switches S with complementary duty cycle signals, and a l and S u and output capacitor C out , output capacitor C out With the output voltage V out The load is connected in parallel, the NMOS switch S l The drain is connected to the negative terminal of the load, S l The source of the NMOS switch S u The source of the NMOS switch S is connected to one end of the inductor L. u The drain of the load is connected to the positive electrode, and N NMOS switches S i2 The drain of the battery cell V bati The negative electrode of the load and the negative electrode of S l The drains are connected to the common ground; To S l and S u The two NMOS switches input mixed-frequency AC duty cycle disturbance signals to detect the impedance of each battery cell at various frequencies; The 2N NMOS switches of level A complete an alternating conduction operation cycle T0 and meet the following conditions: T0=T1+T2+…+T N +(N-1)T d =NT1+(N-1)T d Where T1=T2=…=T N =mT s , at this time each driving signal P i The conduction time T when the voltage is continuously high i equal to achieve battery cell V bati Connection between Class B, T d is the adjacent conduction time T i The dead zone interval between the two periods is m, which is the inductance L in period T. s The total number of continuous charge and discharge times, T s It is the time it takes for the inductor to complete one charge and discharge cycle.

2. The single-inductor multi-input single-output DC-DC system for lithium battery EIS detection according to claim 1, characterized in that: The DC-DC system drives the signal P at each level A. i The conduction time T i It includes the following four modes 1-4: Mode 1: Class A switch S i1 、S i2 In the on state, the other 2 (N-1) switches are in the off state, and the switch S of class B is l In the on state and S u In the disconnected state, the battery cell V bati Provide energy to charge the inductor L, the inductor current increases, and the voltage of battery cell i is V i , the load output voltage is V out , the inductor current changes to Δi L , then in mode 1 V i 、V out and Δi L The relationship is given by the following formula V i ·(t i1 -t i0 )=Δi L ·L Mode 2: Class A switch S i1 、S i2 In the on state, the other 2 (N-1) switches are in the off state, and the switch S of class B is l In the disconnected state and S u In the on state, the current of the inductor L decreases through the output capacitor and the load discharge. In mode 2, V i 、V out and Δi L The relationship is given by the following formula (V out -V i )·(t i2 -t i1 )=Δi L ·L Mode 3: Class A switch S i1 、S i2 Continue to conduct, the other 2 (N-1) switches are in the off state, at T i In the last one or several switching cycles, before turning off the switch S i1 、S i2 Before, switch S l and S u All are turned off, and the inductor current is reset to 0 to avoid interfering with the measurement work of other battery cells; Mode 4: 2N+2 switches (S 11 ,S 12 ),(S 21 ,S 22 ),…,(S N1 ,S N2 ), S l and S u Both are in the off state, and the adjacent conduction time T i Set the dead zone interval T between d .

3. A control method for a single-inductor multi-input single-output DC-DC system for lithium battery EIS detection according to any one of claims 1-2, characterized in that: The control method comprises the following steps: Step 1: Connect N lithium-ion batteries to be tested as battery cells in parallel at the input of a single-inductor multiple-input single-output DC-DC system. Use a time-division multiplexing control method to add multi-frequency disturbances to each battery cell, thereby achieving AC impedance testing of multiple battery cells at the same time. Step 2: By S l and S u The two NMOS switches input mixed-frequency AC duty cycle disturbance signals to control their on and off; Step 3: Then measure the AC voltage or current response of each battery cell to the injected AC current or voltage signal to detect the impedance of the lithium-ion battery at various frequencies; Step 4: Use FFT to analyze the peak-to-peak values ​​of the lithium-ion battery voltage and current at each frequency under multi-frequency disturbance, and calculate the impedance value at that frequency according to the following formula; where Z fr 、V ac (f r ) and I ac (f r ) represent the frequency f r The impedance, voltage and current values ​​of the battery cell when θ fr Indicates frequency f r The phase difference between the lithium-ion battery voltage and current; Step 5: Calculate the impedance value within the required frequency range as needed to draw the EIS curve.

4. The control method of the single-inductor multi-input single-output DC-DC system for lithium battery EIS detection according to claim 3, characterized in that: In step 2, the duty cycle disturbance signals at multiple frequencies are mixed and added together and input into the synchronous Boost circuit of Class B to achieve simultaneous and efficient multi-frequency impedance detection. The amplitude of the added AC duty cycle disturbance signal must not exceed 3% of the DC duty cycle signal amplitude.

5. The control method of the single-inductor multi-input single-output DC-DC system for lithium battery EIS detection according to claim 3, characterized in that: In step 2 Assume that there are N battery cells V bat1 ~V batN The input voltage is V1, V2, ..., V N , and applying the volt-second balance principle, we get the following formula, where D r When the switch in the A class (S r1 , S r2 ) is turned on, the synchronous Boost circuit switch S in stage B l Duty cycle, and r = 1, 2, ..., N By solving the above formula, we can get the output voltage V of the load out satisfy In the discharge mode, there is an output voltage control loop whose input is the reference output voltage V out_ref And the output voltage V measured after the i-th battery cell is connected outr The difference between the two, the output of the voltage compensator is the DC duty cycle D dc , continuous transfer function G c_vol (s) or discrete transfer function G c_vol (z) is the proportional integral compensator, and the output voltage control loop generates a switch S l The DC duty cycle of D1 to D N , the DC duty cycle of each battery cell D1 to D N It is given by the following formula; In level B, two switches S l and S u Input duty cycle disturbance signal, which is DC D dc and AC duty cycle disturbance signals D at various frequencies ac The superposition is shown below; D(t)=D dc +D ac D ac =D ac-f1 +D ac-f2 +…+D ac-fn The added disturbance signal is shown below; Where D(t) represents the total duty cycle of the Class B driver, D dc Indicates the added DC duty cycle signal, D ac represents the added AC duty cycle disturbance signal, n refers to the number of frequency components, D ac-f1 represents the disturbance signal at frequency f1, D ac-f2 represents the disturbance signal at frequency f2, D ac-fn Indicates the frequency at f n The disturbance signal under p1 is the disturbance signal D ac-f1 The amplitude, D p2 is the disturbance signal D ac-f2 The amplitude, D pn is the disturbance signal D ac-fn The amplitude, f n >…>f2>f1.

6. The control method of the single-inductor multi-input single-output DC-DC system for lithium battery EIS detection according to claim 5, characterized in that: Step 4 also specifically includes sampling the voltage and current of the battery cell by an analog-to-digital converter, and calculating the voltage V of the measured i-th battery cell. bati and current I bati Perform fast Fourier transform analysis to obtain the voltage frequency component (V ac (f1), V ac (f2),…V ac (f n )), current frequency component (I ac (f1), I ac (f2),…I ac (f n )) and the corresponding phase shifts (θ(f1), θ(f2), …θ(f n )), and calculate different frequencies f r The impedance value under is used to draw the EIS curve.

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