Centralized excitation battery module cell impedance measurement method and system

Abstract

The invention discloses a centralized excitation battery module cell impedance measurement method and system, belongs to the field of battery management systems, and aims to solve the problem that current control is difficult when an internal resistance measurement method based on an alternating current injection method is applied to actual engineering. The method comprises the following steps of: 1, generating a current excitation signal with variable amplitude and frequency by an alternating current injection circuit; step 2, after the current excitation signal is injected into the battery pack, generating a weak alternating current voltage signal at a battery core end; step 3, AC voltage signals of m battery cell ends in the battery pack are sampled by a BMS voltage sampling terminal and then are subjected to high-pass filtering; 4, the m battery core end alternating current voltage signals after high-pass filtering are sequentially switched and controlled by a switching network to be output in series, and all the battery core end alternating current voltage signals enter a controller in sequence after being amplified; and step 5, the controller obtains the impedance of all the battery cells in the battery pack according to the AC voltage signal and the current excitation signal of each battery cell end.

Description

Technical Field

[0001] The invention relates to a method and system for measuring impedance of a centralized excitation battery module cell, belonging to the field of battery management systems. Background Art

[0002] Lithium batteries are widely used in power supply fields such as electric vehicles, energy storage power stations, and photovoltaic energy storage systems. Among them, batteries are the core of the battery system, and ensuring their safety is crucial. Battery impedance spectrum is a powerful tool to characterize the battery state, and online measurement of battery impedance is of great significance. Battery impedance spectrum can be used to realize the charge state estimation, health state estimation, and power state estimation of aging batteries. Another important function of battery impedance spectrum is to estimate the internal temperature of the battery, which is a very important safety parameter of the battery. High internal temperature may cause thermal runaway of the battery. At this time, battery impedance spectrum can be used to realize early thermal runaway prediction. In addition, battery impedance spectrum can also be used in other fields, such as battery leakage fault diagnosis. Online measurement of battery impedance is very important.

[0003] The battery internal resistance measurement method based on the AC injection method can obtain the battery impedance value at different frequencies. When an AC current of a set frequency is injected into the battery to be tested, a weak AC voltage signal with the same frequency as the injected current will appear at the battery end. The signal is then amplified and calculated together with the current signal to obtain the impedance value. This team proposed an online battery internal resistance measurement method using SOGI (CN202010606877.0). The battery impedance is measured online through the AC injection method combined with the second-order generalized integrator (SOGI) filtering algorithm. The real and imaginary parts of the battery impedance can be output in real time with high accuracy. This team also proposed a battery module impedance online measurement system and method based on reactive current injection (CN202310542313.9), which solves the problem that the measurement system of the traditional AC signal injection method for online impedance measurement is seriously heated and cannot be applied to the measurement of high-voltage battery modules, and the impedance information measurement is incomplete.

[0004] However, there are still the following problems to be solved for the measurement of cells in the battery module. First, the problem of AC current injection in the battery module needs to be solved. The voltage of the battery module is relatively high, and the frequency and amplitude of the injected current need to change according to the actual measurement requirements. The current controller composed of the traditional PI regulator cannot meet the control performance requirements; then the problem of sampling lines during the project implementation needs to be solved. The voltage of each cell needs to be collected. There are a large number of cells and wiring is difficult; finally, the problem of low-cost signal processing needs to be solved. The AC signal amplitude of the cell voltage is small, requiring a high-performance operational amplifier to achieve signal amplification. Summary of the invention

[0005] In order to solve the problems such as current control difficulties in the application of internal resistance measurement methods based on the AC injection method in actual engineering, the present invention proposes a centralized excitation battery module cell impedance measurement method and system, and provides a detailed engineering implementation plan, so that the AC injection method can be applied in actual engineering projects with high precision and low cost.

[0006] In a first aspect, the present invention provides a method for measuring the impedance of a battery cell in a centralized excitation battery module, the method comprising the following steps:

[0007] Step 1: an AC current injection circuit generates a current excitation signal with variable amplitude and frequency, wherein the amplitude and frequency of the current excitation signal are given by a controller;

[0008] Step 2: After the current excitation signal is injected into the battery pack, a weak AC voltage signal is generated at the battery cell end;

[0009] Step 3: The AC voltage signals of the m battery cells in the battery pack are sampled by the BMS voltage sampling terminal and then high-pass filtered;

[0010] Step 4: The m cell-end AC voltage signals after high-pass filtering are switched and controlled in sequence through a switch network and output in series, and each cell-end AC voltage signal is amplified and then enters the controller in sequence;

[0011] Step 5: The controller obtains the impedance of all cells in the battery pack according to the AC voltage signal and current excitation signal at each cell end.

[0012] In a second aspect, the present invention provides a centralized excitation battery module cell impedance measurement system for implementing the method described in claim 1, characterized in that the system includes an AC current injection circuit, a BMS voltage sampling terminal, a high-pass filter, a switch network, a signal amplification circuit and a controller;

[0013] The controller provides a given sinusoidal current i to the AC current injection circuit. ref , the AC current injection circuit generates a current excitation signal i L After being injected into the battery pack, each cell in the battery pack generates a weak AC voltage signal which is sampled by the BMS voltage sampling terminal. The sampled AC voltage signal is subjected to high-pass filtering by the high-pass filter, which is output to the signal amplification circuit in sequence under the control of the switch network. The amplified AC voltage signal is output to the ADC module of the controller. The controller obtains the cell impedance based on the AC voltage signal at each cell end and the current excitation signal injected into the battery pack.

[0014] Preferably, the controller adopts a hysteresis controller.

[0015] Preferably, the AC current injection circuit includes a power circuit, a capacitor charging relay control circuit, a current control circuit and a voltage control circuit;

[0016] The power circuit generates a current excitation signal i by charging and discharging the capacitor C. L ;

[0017] The capacitor charging relay control circuit is used to limit the capacitor charging current in the power circuit;

[0018] The voltage control circuit is used to control the voltage u across the capacitor C in the power circuit. c Controlled within the set range, when u c When the lower limit is reached, the output bias current i B , when u c When the upper limit is reached, the bias current i B is zero;

[0019] The current control circuit is based on the given sinusoidal current i ref and the bias current i provided by the voltage control circuit B Control power circuit to generate follow i ref The current excitation signal i L .

[0020] Preferably, the power circuit includes a battery pack voltage dividing resistor, a capacitor voltage dividing resistor, an inductor L, a switch tube S1, a switch tube S2, a capacitor C and a current limiting resistor Rs;

[0021] The battery pack voltage resistor is connected in parallel at both ends of the battery pack, and the battery pack voltage resistor is used to output the battery pack voltage VBS+;

[0022] The positive electrode of the battery pack is connected to one end of the inductor L, the other end of the inductor L is connected to the negative electrode of the switch tube S1 and the positive electrode of the switch tube S2 at the same time, the positive electrode of the switch tube S1 is connected to one end of the current limiting resistor Rs, the other end of the current limiting resistor Rs is connected to the positive electrode of the capacitor C, and the negative electrode of the capacitor C is connected to the negative electrode of the switch tube S2 and the negative electrode of the battery pack;

[0023] The capacitor voltage divider resistor is connected in parallel across the capacitor C to output the capacitor voltage divider V C _Set and capacitor voltage divider VCS+.

[0024] Preferably, the capacitor charging relay control circuit includes a relay and a comparator A1, the normally open contact of the relay is connected in parallel to the two ends of the current limiting resistor Rs, one end of the relay coil is connected to the output end of the comparator, the positive input end of the comparator A1 is connected to the battery pack voltage divider VBS+, and the negative input end of the comparator A1 is connected to the capacitor voltage divider V C _Set; The other end of the relay coil is grounded;

[0025] When capacitor C is initially charged, comparator A1 outputs a low level, the relay coil loses power, and the normally open contacts of the relay remain disconnected; the current limiting resistor Rs is connected in series with capacitor C to limit the charging current; when the voltage across capacitor C rises to more than 1.8 times the voltage of the battery pack, comparator A1 outputs a high level, the relay coil is energized, the normally open contacts of the relay are closed, the current limiting resistor Rs is short-circuited, and the capacitor is fully charged.

[0026] Preferably, the voltage control circuit includes a bias current generating circuit, an RS trigger, a comparator A3 and a comparator A4;

[0027] The inverting input terminal of comparator A3 and the non-inverting input terminal of comparator A4 are simultaneously connected to the capacitor voltage divider VCS+, the non-inverting input terminal of comparator A3 is connected to the low voltage given signal Vcal, and the inverting input terminal of comparator A4 is connected to the high voltage given signal Vcah;

[0028] The output end of the comparator A3 is connected to the R pin of the RS trigger, the output end of the comparator A4 is connected to the S pin of the RS trigger, and the Q pin of the RS trigger is connected to the control end of the bias current generating circuit;

[0029] Comparator A3 and comparator A4 are used to determine the voltage u across capacitor C. c Is it within the setting range of 1.8 to 2 times the battery pack voltage? c When the lower limit is reached, the RS trigger controls the bias current generation circuit to output the bias current i B , when u c When the upper limit is reached, the RS trigger controls the bias current generation circuit to turn off, controlling the bias current i B is zero.

[0030] Preferably, the bias current generating circuit includes a switch tube S DC And the voltage divider resistor, switch tube S DC The gate of the RS trigger is connected to the Q foot of the voltage control circuit, and the bias current i is output through the voltage divider resistor. B .

[0031] Preferably, the current control circuit includes an RS trigger, a comparator A2 and an adder;

[0032] Given a sinusoidal current i ref and bias current i B After being added by the adder, it is connected to the inverting input of comparator A2, and the positive input of comparator A2 is connected to the current excitation signal i LThe output end of comparator A2 is connected to the R pin of the RS trigger, the S pin of the RS trigger is connected to the periodic PWM signal, and the Q pin of the RS trigger outputs a driving signal, one of which is connected to the gate of the switch tube S2, and the other is connected to the gate of the switch tube S1 after passing through the inverter. The charging and discharging control of the capacitor C is realized by controlling the complementary conduction of the two switch tubes.

[0033] Preferably, the S pin of the RS trigger in the current control circuit is connected to a periodic PWM signal with a frequency of 200 kHz and a duty cycle of 10%.

[0034] Beneficial effects of the present invention:

[0035] 1. Since the hysteresis controller is used to control the injected current and the voltage of the DC bus capacitor C, stable control can be achieved under the conditions of large current frequency variation range, amplitude range and wide voltage range of the battery module.

[0036] 2. Current control and voltage control of DC bus capacitor C are all implemented using hardware circuits, which have the characteristics of fast control speed and high reliability.

[0037] 3. The voltage sampling terminal is shared with the BMS, and the switch network switches the shared amplifier circuit, which can effectively reduce the complexity and cost of system implementation. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is an overall implementation block diagram of a centralized excitation battery module cell impedance measurement method according to the present invention;

[0039] Figure 2 It is the circuit diagram of AC current injection;

[0040] Figure 3 It is the current loop control circuit diagram;

[0041] Figure 4 It is the waveform diagram of the current loop control circuit principle analysis;

[0042] Figure 5 yes Figure 4 The circuit equivalent process corresponding to the curve in section A;

[0043] Figure 6 yes Figure 4 The circuit equivalent process corresponding to the curve in section B;

[0044] Figure 7 It is the voltage loop control circuit diagram;

[0045] Figure 8 It is a waveform diagram for analyzing the principle of voltage loop control circuit. DETAILED DESCRIPTION

[0046] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0047] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0048] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, but they are not intended to limit the present invention.

[0049] Specific implementation method 1: The following is combined Figure 1 This embodiment describes a method for measuring the impedance of a battery cell in a centralized excitation battery module, the method comprising the following steps:

[0050] Step 1: an AC current injection circuit generates a current excitation signal with variable amplitude and frequency, wherein the amplitude and frequency of the current excitation signal are given by a controller;

[0051] Step 2: After the current excitation signal is injected into the battery pack, a weak AC voltage signal is generated at the battery cell end;

[0052] Step 3: The AC voltage signals of the m battery cells in the battery pack are sampled by the BMS voltage sampling terminal and then high-pass filtered;

[0053] Step 4: The m cell-end AC voltage signals after high-pass filtering are switched and controlled in sequence through a switch network and output in series, and each cell-end AC voltage signal is amplified and then enters the controller in sequence;

[0054] Step 5: The controller obtains the impedance of all cells in the battery pack according to the AC voltage signal and current excitation signal at each cell end.

[0055] Current excitation signal i L And given sinusoidal current i ref is a sinusoidal alternating current, i L The given sinusoidal current i provided by the following controller ref , i.e. i L The amplitude and frequency are given by the controller.

[0056] There are m cells in the battery pack, and the weak AC voltage signals generated at both ends of the m-phase cells are u1, u2, ..., u m , the weak AC voltage signals u1, u2, ..., u are switched in turn by a switch network. mBy connecting to the signal amplification circuit, multiple cells share a set of signal amplification circuits, which can effectively save costs. The amplified signals are output to the ADC module in the controller in turn, converting the analog signals into digital signals.

[0057] Combined with the current excitation signal i collected by the controller L , the cell impedance value can be calculated.

[0058] Specific implementation method 2: The following is combined Figures 1 to 8 This embodiment is described. A centralized excitation battery module cell impedance measurement system described in this embodiment is used to implement the method described in the first embodiment. The system includes an AC current injection circuit, a BMS voltage sampling terminal, a high-pass filter, a switch network, a signal amplification circuit and a controller;

[0059] The controller provides a given sinusoidal current i to the AC current injection circuit. ref ,i ref The DAC module in the controller outputs the AC current injection circuit to generate the current excitation signal i L After being injected into the battery pack, each cell in the battery pack generates a weak AC voltage signal which is sampled by the BMS voltage sampling terminal. The sampled AC voltage signal is subjected to high-pass filtering by the high-pass filter, which is output to the signal amplification circuit in sequence under the control of the switch network. The amplified AC voltage signal is output to the ADC module of the controller. The controller obtains the cell impedance based on the AC voltage signal at each cell end and the current excitation signal injected into the battery pack.

[0060] The controller adopts a hysteresis controller. Since the hysteresis controller is used to control the injected current and the voltage of the DC bus capacitor C, stable control can be achieved under the conditions of large current frequency variation range, amplitude range and wide voltage range of the battery module.

[0061] The current excitation signal i of the present invention L This is the reactive current injection method. For the overall block diagram, see Figure 1 shown.

[0062] The present invention focuses on the current excitation signal i L The control strategy is limited in multiple dimensions. For the specific implementation circuit, see Figure 2 The AC current injection circuit shown.

[0063] The AC current injection circuit includes a power circuit, a capacitor charging relay control circuit, a current control circuit and a voltage control circuit;

[0064] The power circuit generates a current excitation signal i by charging and discharging the capacitor C. L ;

[0065] The capacitor charging relay control circuit is used to limit the capacitor charging current in the power circuit;

[0066] The voltage control circuit is used to control the voltage u across the capacitor C in the power circuit. c Controlled within the set range, when u c When the lower limit is reached, the output bias current i B , when u c When the upper limit is reached, the bias current i B is zero;

[0067] The current control circuit is based on the given sinusoidal current i ref and the bias current i provided by the voltage control circuit B Control power circuit to generate follow i ref The current excitation signal i L .

[0068] The power circuit includes a battery pack voltage divider resistor, a capacitor voltage divider resistor, an inductor L, a switch tube S1, a switch tube S2, a capacitor C and a current limiting resistor Rs; the control signal G of the two switches S1 With G S2 Complementary. The current i of the inductor L L This is the current injected into the battery pack.

[0069] The battery pack voltage resistor is connected in parallel at both ends of the battery pack, and the battery pack voltage resistor is used to output the battery pack voltage VBS+;

[0070] The positive electrode of the battery pack is connected to one end of the inductor L, the other end of the inductor L is connected to the negative electrode of the switch tube S1 and the positive electrode of the switch tube S2 at the same time, the positive electrode of the switch tube S1 is connected to one end of the current limiting resistor Rs, the other end of the current limiting resistor Rs is connected to the positive electrode of the capacitor C, and the negative electrode of the capacitor C is connected to the negative electrode of the switch tube S2 and the negative electrode of the battery pack;

[0071] The capacitor voltage divider resistor is connected in parallel across the capacitor C to output the capacitor voltage divider V C _Set and capacitor voltage divider VCS+.

[0072] The capacitor charging relay control circuit includes a relay and a comparator A1. The normally open contact of the relay is connected in parallel to the two ends of the current limiting resistor Rs. One end of the relay coil is connected to the output end of the comparator. The positive input end of the comparator A1 is connected to the battery pack voltage divider VBS+, and the negative input end of the comparator A1 is connected to the capacitor voltage divider V C _Set; The other end of the relay coil is grounded;

[0073] When capacitor C is initially charged, comparator A1 outputs a low level, the relay coil loses power, and the normally open contacts of the relay remain disconnected; the current limiting resistor Rs is connected in series with capacitor C to limit the charging current; when the voltage across capacitor C rises to more than 1.8 times the voltage of the battery pack, comparator A1 outputs a high level, the relay coil is energized, the normally open contacts of the relay are closed, the current limiting resistor Rs is short-circuited, and the capacitor is fully charged.

[0074] When the entire main circuit is powered on and starts working, the voltage of capacitor C is zero and the voltage of the battery pack is relatively high. Therefore, a current-limiting resistor Rs is required to limit the charging current of capacitor C. When the voltage of capacitor C rises to a larger value (greater than 1.8 times the voltage of the battery pack), the normally open contact of the relay closes, and the current-limiting resistor Rs is short-circuited (except for the initial stage of normal operation when the current-limiting resistor Rs is in a short-circuit state). In the relay control circuit, the battery pack voltage is divided by a suitable resistor, and the voltage of capacitor C is also divided by a suitable resistor. The two voltages are compared to obtain a relay control signal. When capacitor C just starts to charge, when the capacitor voltage V C _Set is smaller than the battery pack voltage VBs+, the relay does not work, and the contact is normally open. At this time, the current charges the capacitor C through the current limiting resistor Rs, and the charging current is limited. As the capacitor voltage rises, when the capacitor voltage V C _Set the ratio of battery pack voltage to V Bs+ When the current is large, the relay is activated, the normally open contact closes to short-circuit the current limiting resistor Rs, the capacitor C is charged, and the main circuit enters normal working state.

[0075] During normal operation, the capacitor C should be kept within a reasonable range higher than the battery pack voltage (1.8 to 2 times the battery pack voltage). Reactive current injection is generally used. L And given sinusoidal current i ref It is a sinusoidal alternating current with the same frequency and amplitude. In the first half cycle of the sinusoidal alternating current, the battery pack charges the capacitor C, and the voltage of the capacitor C increases. In the second half cycle, the capacitor C discharges to the battery pack, and the voltage of the capacitor C decreases.

[0076] Theoretically, the charge amount of capacitor C in one cycle is equal to the discharge amount, and the average voltage of capacitor C remains unchanged. In practice, due to the existence of circuit loss, the average voltage of capacitor C gradually decreases. Therefore, it is necessary to design a voltage loop control strategy for capacitor C. When the voltage of capacitor C drops to a certain value, the current bias is increased on the basis of the given sinusoidal current, so that the charging of capacitor C stops when the voltage is charged to a higher voltage, and the current bias is zero. To this end, the present invention is designed as follows Figure 2 , Figure 7The voltage control circuit shown in the figure is composed of a high voltage given Vcah, a low voltage given Vcal, two comparators A3, A4, an RS trigger and a bias current generation circuit. In the voltage loop control circuit, the capacitor voltage given module is composed of two potentiometers. After the power supply voltage is reduced by the linear regulator, the potentiometer is used to divide the voltage to generate two reference voltages Vcah and Vcal. The voltage across the capacitor is divided by resistors to generate a voltage value VCS+ that can be input to the comparator with a suitable ratio. Use the comparator to compare VCS+ with Vcah, V CS + The output voltage is compared with Vcal to generate two output signals, which are connected to the S pin and R pin of the RS trigger respectively. The Q of the RS trigger is the output pin, and the high and low levels of its output are converted into appropriate current bias signals through the bias current generating circuit. The present invention sets the current bias signal as a DC signal.

[0077] Specifically, the voltage control circuit includes a bias current generating circuit, an RS trigger, a comparator A3 and a comparator A4;

[0078] The inverting input terminal of comparator A3 and the non-inverting input terminal of comparator A4 are simultaneously connected to the capacitor voltage divider VCS+, the non-inverting input terminal of comparator A3 is connected to the low voltage given signal Vcal, and the inverting input terminal of comparator A4 is connected to the high voltage given signal Vcah;

[0079] The output end of the comparator A3 is connected to the R pin of the RS trigger, the output end of the comparator A4 is connected to the S pin of the RS trigger, and the Q pin of the RS trigger is connected to the control end of the bias current generating circuit;

[0080] Comparator A3 and comparator A4 are used to determine the voltage u across capacitor C. c Is it within the setting range of 1.8 to 2 times the battery pack voltage? c When the lower limit is reached, the RS trigger controls the bias current generation circuit to output the bias current i B , when u c When the upper limit is reached, the RS trigger controls the bias current generation circuit to turn off, controlling the bias current i B is zero.

[0081] The bias current generating circuit includes a switch tube S DC And the voltage divider resistor, switch tube S DC The gate of the RS trigger is connected to the Q foot of the voltage control circuit, and the bias current i is output through the voltage divider resistor. B .

[0082] The theoretical waveforms of the voltage loop control circuit are as follows: Figure 6As shown in the figure, when the capacitor voltage is too low, VCS+ is smaller than the set low voltage Vcal. At this time, the comparator is activated, the R pin of the RS trigger receives a high signal, and the S pin receives a low signal. Then the control signal S output by the RS trigger is V is low level, controls the bias current generating circuit to output bias current i B , used to increase the given AC current to charge the capacitor C and increase its voltage; when VCS+ rises to the high voltage given Vcah, the comparator is activated, the R pin of the RS trigger receives a low signal, and the S pin receives a high signal, then the control signal S output by the RS trigger V is high level, controlling the bias current i B It is zero and there is no DC bias. At this time, due to the energy consumption in the circuit, the capacitor voltage will slowly decrease. When it decreases to a level lower than the set low voltage Vcal, the bias voltage circuit will be controlled to give a bias voltage to inject a DC bias current, and a new control cycle begins.

[0083] See also Figures 2 to 4 , the current control circuit includes an RS trigger, a comparator A2 and an adder;

[0084] Given a sinusoidal current i ref and bias current i B After being added by the adder, it is connected to the inverting input of comparator A2, and the positive input of comparator A2 is connected to the current excitation signal i L The output end of comparator A2 is connected to the R pin of the RS trigger, the S pin of the RS trigger is connected to the periodic PWM signal, and the Q pin of the RS trigger outputs a driving signal, one of which is connected to the gate of the switch tube S2, and the other is connected to the gate of the switch tube S1 after passing through the inverter. The charging and discharging control of the capacitor C is realized by controlling the complementary conduction of the two switch tubes.

[0085] There are two ways to process the current signals connected to the two input terminals of the comparator A2: one is to convert the current signals into voltage signals for comparison before entering the comparator A2, and the other is to convert the current signals into voltage signals for comparison after entering the comparator A2.

[0086] The current signals connected to the two input terminals of comparator A2 are: the positive input of A2 is the inductor current i L The voltage value obtained by sampling, the negative input of A2 is obtained by adding the voltage signal representing the given sinusoidal current provided by the controller and the voltage signal representing the bias current. The two input terminals of comparator A2 are both connected to the voltage value representing the current. To simplify the description, the two input terminals of comparator A2 are referred to as the current value below.

[0087] The S pin of the RS trigger in the current control circuit is connected to a periodic PWM signal with a duty cycle of 10%.

[0088] The negative input of comparator A2 is i - ,i - The given sinusoidal current i provided to the controller ref With the bias current i B The positive input of comparator A2 is the current i injected into the battery pack. L The output of comparator A2 is connected to the R pin of the RS trigger. The S pin of the RS trigger is connected to a periodic PWM pulse signal as the driving period of the switch tube. In this embodiment, a PWM pulse signal with a frequency of 200kHz and a duty cycle of 10% is selected. The Q pin of the RS trigger output is connected to the switch tube S2 of the main circuit. The signal of the Q output is inverted and connected to the switch tube S1, so that the switch tubes S1 and S2 achieve complementary conduction. The specific control logic diagram and timing diagram are as follows Figure 4 As shown, given a sinusoidal current i ref A switching cycle is given, and the timing of other components is a small-scale part of the schematic. The PWM pulse signal input to the S pin of the RS trigger determines the switching cycle of the switch tube. When S is high, the RS trigger outputs a high level. At this time, the switch tube S2 is turned on and S1 is turned off. The inductor current i L Starts to rise, the equivalent process of the circuit is shown in Figure 6 As shown; when the inductor current i L Rising given sinusoidal current i ref When , comparator A2 acts and outputs high level, the trigger is reset and outputs low level, and the inductor current starts to decrease. The equivalent process of the circuit is shown in Figure 5 As shown; in the next switching cycle, a high level signal appears at the S pin of the RS trigger, and the inductor current i L starts to rise, and a new cycle begins. ref The following makes the inductor current i L Closely follow the given AC current i ref .

[0089] Although the present invention is described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the present invention. It should therefore be understood that many modifications may be made to the exemplary embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims. It should be understood that the various dependent claims and features described herein may be combined in a manner different from that described in the original claims. It should also be understood that the features described in conjunction with a single embodiment may be used in other described embodiments.

Claims

1. A method for measuring the impedance of a concentrated excitation battery module cell, characterized in that: The method comprises the following steps: Step 1: an AC current injection circuit generates a current excitation signal with variable amplitude and frequency, wherein the amplitude and frequency of the current excitation signal are given by a controller; Step 2: After the current excitation signal is injected into the battery pack, a weak AC voltage signal is generated at the battery cell end; Step 3: The AC voltage signals of the m battery cells in the battery pack are sampled by the BMS voltage sampling terminal and then high-pass filtered; Step 4: The m cell-end AC voltage signals after high-pass filtering are switched and controlled in sequence through a switch network and output in series, and each cell-end AC voltage signal is amplified and then enters the controller in sequence; Step 5: The controller obtains the impedance of all cells in the battery pack according to the AC voltage signal and current excitation signal at each cell end.

2. A centralized excitation battery module cell impedance measurement system, used to implement the method described in claim 1, characterized in that: The system includes an AC current injection circuit, a BMS voltage sampling terminal, a high-pass filter, a switch network, a signal amplification circuit and a controller; The controller provides a given sinusoidal current i to the AC current injection circuit. ref , the AC current injection circuit generates a current excitation signal i L Injected into the battery pack, each cell in the battery pack generates a weak AC voltage signal which is sampled by the BMS voltage sampling terminal; The high-pass filter performs high-pass filtering on the sampled AC voltage signal, which is output to the signal amplification circuit in sequence under the control of the switch network. The amplified AC voltage signal is output to the ADC module of the controller. The controller obtains the cell impedance based on the AC voltage signal at each cell end and the current excitation signal injected into the battery pack.

3. According to claim 2, a centralized excitation battery module cell impedance measurement system is characterized in that: The controller adopts hysteresis controller.

4. According to claim 2, a centralized excitation battery module cell impedance measurement system is characterized in that: The AC current injection circuit includes a power circuit, a capacitor charging relay control circuit, a current control circuit and a voltage control circuit; The power circuit generates a current excitation signal i by charging and discharging the capacitor C. L ; The capacitor charging relay control circuit is used to limit the capacitor charging current in the power circuit; The voltage control circuit is used to control the voltage u across the capacitor C in the power circuit. c Controlled within the set range, when u c When the lower limit is reached, the output bias current i B , when u c When the upper limit is reached, the bias current i B is zero; The current control circuit is based on the given sinusoidal current i ref and the bias current i provided by the voltage control circuit B Control power circuit to generate follow i ref The current excitation signal i L .

5. A centralized excitation battery module cell impedance measurement system according to claim 4, characterized in that: The power circuit includes a battery pack voltage divider resistor, a capacitor voltage divider resistor, an inductor L, a switch tube S1, a switch tube S2, a capacitor C and a current limiting resistor Rs; The battery pack voltage resistor is connected in parallel at both ends of the battery pack, and the battery pack voltage resistor is used to output the battery pack voltage VBS+; The positive electrode of the battery pack is connected to one end of the inductor L, the other end of the inductor L is connected to the negative electrode of the switch tube S1 and the positive electrode of the switch tube S2 at the same time, the positive electrode of the switch tube S1 is connected to one end of the current limiting resistor Rs, the other end of the current limiting resistor Rs is connected to the positive electrode of the capacitor C, and the negative electrode of the capacitor C is connected to the negative electrode of the switch tube S2 and the negative electrode of the battery pack; The capacitor voltage divider resistor is connected in parallel across the capacitor C to output the capacitor voltage divider V C _Set and capacitor voltage divider VCS+.

6. A centralized excitation battery module cell impedance measurement system according to claim 5, characterized in that: The capacitor charging relay control circuit includes a relay and a comparator A1. The normally open contact of the relay is connected in parallel to the two ends of the current limiting resistor Rs. One end of the relay coil is connected to the output end of the comparator. The positive input end of the comparator A1 is connected to the battery pack voltage divider VBS+, and the negative input end of the comparator A1 is connected to the capacitor voltage divider V C _Set; The other end of the relay coil is grounded; When capacitor C is initially charged, comparator A1 outputs a low level, the relay coil loses power, and the normally open contacts of the relay remain disconnected; the current limiting resistor Rs is connected in series with capacitor C to limit the charging current; when the voltage across capacitor C rises to more than 1.8 times the voltage of the battery pack, comparator A1 outputs a high level, the relay coil is energized, the normally open contacts of the relay are closed, the current limiting resistor Rs is short-circuited, and the capacitor is fully charged.

7. A centralized excitation battery module cell impedance measurement system according to claim 5, characterized in that: The voltage control circuit includes a bias current generating circuit, an RS trigger, a comparator A3 and a comparator A4; The inverting input terminal of comparator A3 and the non-inverting input terminal of comparator A4 are simultaneously connected to the capacitor voltage divider VCS+, the non-inverting input terminal of comparator A3 is connected to the low voltage given signal Vcal, and the inverting input terminal of comparator A4 is connected to the high voltage given signal Vcah; The output end of the comparator A3 is connected to the R pin of the RS trigger, the output end of the comparator A4 is connected to the S pin of the RS trigger, and the Q pin of the RS trigger is connected to the control end of the bias current generating circuit; Comparator A3 and comparator A4 are used to determine the voltage u across capacitor C. c Is it within the setting range of 1.8 to 2 times the battery pack voltage? c When the lower limit is reached, the RS trigger controls the bias current generation circuit to output the bias current i B , when u c When the upper limit is reached, the RS trigger controls the bias current generation circuit to turn off, controlling the bias current i B is zero.

8. A centralized excitation battery module cell impedance measurement system according to claim 7, characterized in that: The bias current generating circuit includes a switch tube S DC And the voltage divider resistor, switch tube S DC The gate of the RS trigger is connected to the Q foot of the voltage control circuit, and the bias current i is output through the voltage divider resistor. B .

9. A centralized excitation battery module cell impedance measurement system according to claim 5, characterized in that: The current control circuit includes an RS trigger, a comparator A2 and an adder; Given a sinusoidal current i ref and bias current i B After being added by the adder, it is connected to the inverting input of comparator A2, and the positive input of comparator A2 is connected to the current excitation signal i L The output end of comparator A2 is connected to the R pin of the RS trigger, the S pin of the RS trigger is connected to the periodic PWM signal, and the Q pin of the RS trigger outputs a driving signal, one of which is connected to the gate of the switch tube S2, and the other is connected to the gate of the switch tube S1 after passing through the inverter. The charging and discharging control of the capacitor C is realized by controlling the complementary conduction of the two switch tubes.

10. A centralized excitation battery module cell impedance measurement system according to claim 9, characterized in that: The S pin of the RS trigger in the current control circuit is connected to a periodic PWM signal with a frequency of 200kHz and a duty cycle of 10%.

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