Battery impedance online monitoring system and method

Abstract

The invention discloses a battery impedance online monitoring system and method. The system comprises a sinusoidal signal generation circuit, a voltage-current conversion circuit, a signal processing module and an impedance calculation module, the sinusoidal signal generation circuit generates a frequency-controllable sinusoidal signal through direct digital frequency synthesis (DDS) and is used for controlling a battery disturbance signal; the voltage-to-current conversion circuit realizes the adjustment of the output current of the voltage-to-current conversion circuit by controlling the input voltage of the voltage-to-current conversion circuit; the signal processing module collects a voltage response signal of a battery to be detected, carries out signal processing of direct current removal and noise removal, converts an analog signal into a digital signal through an AD sampling circuit, and inputs the digital signal to the impedance calculation module. And the impedance calculation module is used for calculating the impedance of the battery by identifying the amplitude and the phase of the acquired signal. According to the invention, the direct current superposed with sine disturbance is extracted from the battery through the voltage-current conversion circuit, and the device can be used for the online measurement of the impedance of the battery under the working conditions of battery offline, constant-current charging and discharging and the like.

Description

Technical Field

[0001] The present invention relates to the field of battery status monitoring, and in particular to a battery impedance online monitoring system and method, which are used to realize online monitoring of battery impedance information. Background Art

[0002] Lithium-ion batteries are widely used in new energy vehicles and new energy storage due to their superior power density and current efficiency. In order to ensure the safety of lithium-ion batteries and extend their service life, accurate and convenient battery status monitoring is particularly necessary. Online monitoring of the impedance of lithium-ion batteries can reflect the internal status of the battery, including the internal temperature, state of charge, and aging status of the battery.

[0003] The existing method of achieving disturbance based on the PWM duty cycle of the DC-DC converter limits the freedom of converter design; the method of achieving disturbance based on special instruments such as electrochemical workstations, frequency response analyzers and external excitation source injection of bipolar AC power supplies cannot accurately measure the impedance when the battery is loaded. Therefore, it is necessary to develop a method that can monitor the battery impedance in real time and use it as the basis for battery state estimation to ensure battery performance and monitor the battery state. Summary of the invention

[0004] In order to overcome the defects of the above-mentioned prior art, the present invention provides a battery impedance online monitoring system and method. The method extracts a direct current superimposed with a sinusoidal disturbance from the battery through a voltage-to-current conversion circuit. Therefore, it can be used for online measurement of battery impedance under conditions such as battery offline and constant current charging and discharging.

[0005] The technical solution adopted by the present invention is:

[0006] A battery impedance online monitoring system, the system comprising:

[0007] Sinusoidal signal generating circuit, voltage-current conversion circuit, signal processing module, impedance calculation module;

[0008] The sinusoidal signal generating circuit is connected to the voltage-current conversion circuit, the voltage-current conversion circuit is connected to the battery to be tested, the battery to be tested is connected to the signal processing module, and the signal processing module is connected to the impedance calculation module;

[0009] The sinusoidal signal generating circuit generates a frequency-controllable sinusoidal voltage signal through direct digital frequency synthesis DDS, which is used to control the battery disturbance signal;

[0010] By controlling the input voltage of the voltage-to-current conversion circuit, the output current of the voltage-to-current conversion circuit is regulated;

[0011] The signal processing module collects the voltage response signal of the battery to be tested, performs signal processing to remove DC and noise, converts the analog signal into a digital signal through an AD sampling circuit, and inputs the digital signal to the impedance calculation module;

[0012] The impedance calculation module collects the amplitude and phase of the signal through the signal processing module to perform identification to calculate the battery impedance.

[0013] The sinusoidal signal generating circuit is connected to a host computer, and the host computer is used to control the frequency of the sinusoidal signal in the sinusoidal signal generating circuit.

[0014] The sinusoidal signal generating circuit is connected to the battery management system BMS. The program control of the battery management system BMS can realize the frequency regulation of the sinusoidal signal in the sinusoidal signal generating circuit based on DDS to cope with the signal frequency required by different monitoring objects: temperature, SOC, SOH, etc.

[0015] The voltage-current conversion circuit includes resistors R2 and R S , capacitor C6, operational amplifier OP1, operational amplifier OP2, NPN transistor;

[0016] One end of the resistor R2 is connected to the output port VOUT of the DDS, and the other end of the resistor R2 is connected to one end of the capacitor C6 and the negative port of the operational amplifier OP1 respectively; the other end of the capacitor C6 is connected to the AGND terminal;

[0017] The output port of the operational amplifier OP1 is connected to one end of the switch ST, and the other end of the switch ST is connected to the negative port of the operational amplifier OP2 and the positive port of the operational amplifier OP1 respectively;

[0018] The positive port of the operational amplifier OP2 is connected to the resistor R S One end of the NPN transistor is connected to the emitter; the resistor R S The other end of the pin is connected to AGND.

[0019] Based on the voltage-to-current conversion circuit, the frequency-adjustable voltage signal generated by the sinusoidal signal generating circuit is used as the input. According to the virtual short characteristic of the operational amplifier, the positive terminal of the operational amplifier OP2 is connected to the emitter of the NPN transistor to control the emitter voltage of the NPN transistor. A resistor R is connected to the emitter of the NPN transistor. S , by adjusting the emitter voltage of the NPN transistor and the resistor R S , generating a predetermined disturbance current signal for monitoring.

[0020] Based on the voltage-to-current conversion circuit with adjustable sinusoidal signal, the battery disturbance current frequency can be set within the range of 1Hz to 1MHz. The system takes 1kHz as an example and uses it as the disturbance signal frequency.

[0021] The signal processing module includes a resistor R6, a resistor R7, a capacitor C9, a capacitor C 10 , operational amplifier OP5, operational amplifier OP6;

[0022] The positive port of the operational amplifier OP5 is connected to the positive electrode of the single battery, and the negative port of the operational amplifier OP5 is connected to the negative electrode of the single battery; the output port of the operational amplifier OP5 is connected to one end of the resistor R6, and the other end of the resistor R6 is connected to one end of the capacitor C9;

[0023] The other end of the capacitor C9 is connected to the capacitor C 10 One end of the resistor R7 and the negative port of the operational amplifier OP6 are connected;

[0024] The capacitor C 10 The other end of is respectively connected to the other end of the resistor R7 and the output port of the operational amplifier OP6; the positive port of the operational amplifier OP6 is connected to the AGND terminal.

[0025] A battery impedance online monitoring method is disclosed. A sinusoidal signal generating circuit based on DDS generates a frequency-controllable sinusoidal voltage signal. A voltage-to-current conversion circuit is used to extract a DC current signal with a superimposed sinusoidal disturbance from the battery. Then, an AC impedance calculation is performed to realize online measurement of the battery impedance under conditions such as offline battery operation and constant current charge and discharge.

[0026] The following steps are involved:

[0027] Step 1: The host computer controls the sinusoidal signal generating circuit to generate a voltage disturbance signal of a predetermined frequency. The value of the disturbance signal frequency should be set according to the monitoring object: temperature, SOC, SOH. The correlation frequency of battery thermal runaway is 30Hz~90Hz, the correlation frequency of battery state of charge is 0.1Hz~800Hz, the correlation frequency of battery health status is 0.01Hz~1kHz, and the correlation frequency of battery internal temperature is 30Hz~2kHz;

[0028] Step 2: The voltage-to-current conversion circuit converts the applied disturbance voltage signal into a disturbance current signal, and extracts the disturbance current signal from the battery or injects the disturbance current signal into the battery;

[0029]

[0030] Where: I S is the disturbance current, U S is the disturbance voltage, RS It is a variable resistor that adjusts the disturbance current.

[0031] Step 3: The signal processing module collects the voltage response signal of the battery to be tested and removes DC and noise. The disturbance current signal does not need to be collected and can be processed by U S , R S After calculation, the processed analog signal is converted into a digital signal and input into the impedance calculation module.

[0032] Step 4: After the disturbance signal is applied, the impedance calculation module measures the impedance characteristics of the battery under charging and discharging conditions according to the impedance calculation formula. The impedance calculation formula is:

[0033]

[0034] Where: |Z| is the impedance amplitude of the battery; ∠θ is the impedance phase angle, u(t) is the response voltage across the battery after DC removal and noise removal, i(t) is the applied perturbed sinusoidal current, ∠θ u is the phase angle of the voltage response at both ends of the battery, ∠θ i is the phase angle of the disturbed sinusoidal current, |U| is the amplitude of the voltage response at both ends of the battery after DC removal and noise removal, and |I| is the amplitude of the disturbed sinusoidal current;

[0035] Impedance can also be calculated by the dq change method, and the implementation idea is as follows:

[0036] S1: Filter out the DC component of the battery current and voltage and establish an α-β coordinate system. This step eliminates the DC component by using a bandpass filter (BPF), with the output of the BPF as the α axis, and an all-pass filter (APF), with the output of the APF as the β axis. The APF passes all frequencies with the same gain but only provides a 90° phase shift at the pass frequency. The BPF and APF coefficient calculation formulas are as follows:

[0037]

[0038]

[0039] Where: H BPF(S) is the bandpass filter transfer function; H APF(S) is the all-pass filter transfer function; S is a complex variable; ω b is the center frequency; is the pass frequency; B is the band frequency,

[0040] S2: Using dq transformation, the α-β coordinate system is mapped to the dual-axis synchronous rotating reference system. The values ​​of current and voltage under dq transformation are as follows:

[0041]

[0042]

[0043] Where: v d is the voltage value on the d-axis of the dq coordinate system; i d is the current value on the d-axis of the dq coordinate system; v q is the voltage value on the q axis of the dq coordinate system; i q is the current value on the q axis of the dq coordinate system; v α is the voltage value on the α-axis of the α-β coordinate system; i α is the current value on the α-axis of the α-β coordinate system; v β is the voltage value on the β axis of the α-β coordinate system; i β is the current value on the β axis of the α-β coordinate system; θ is v d Angle of the lead datum;

[0044] S3: Calculate the ripple power, impedance amplitude and phase angle. The calculation formula is as follows:

[0045]

[0046]

[0047]

[0048]

[0049]

[0050] Where: P is active power, Q is reactive power, S is apparent power, |Z| is impedance amplitude, θ is impedance phase angle;

[0051] Through the above method, the impedance amplitude and impedance phase angle of the battery are calculated.

[0052] Under the three working conditions of charging, discharging and offline, the battery is allowed to continuously output a sinusoidal current through small current disturbances, and the voltage response signal of the battery to be tested is collected and de-DC and de-noised. The analog signal is converted into a digital signal through an AD sampling circuit and input into the impedance calculation module to calculate the real-time impedance under the three working conditions.

[0053] The present invention provides a battery impedance online monitoring system and method, the technical effects are as follows:

[0054] 1) Controllable excitation: The frequency and amplitude of the disturbance signal are controllable. The frequency is controlled by the host computer program, and the amplitude is controlled by the resistor Rs and the sinusoidal voltage. Generally, large current (tens of amperes) excitation signals are applied to large-capacity batteries (small internal resistance), and small current (milliampere level) excitation signals are applied to small-capacity batteries (large internal resistance). The method of the present invention can easily achieve adjustable excitation signal amplitude by selecting appropriate resistors, so as to be applied to batteries of different capacities.

[0055] 2) High reliability: The voltage-type disturbance method requires the battery voltage to remain unchanged, and its practicality and reliability are low. However, the sinusoidal signal of the present invention has a high signal-to-noise ratio, and the sinusoidal current disturbance method simplifies the sampling of the current signal while improving the anti-interference ability of the system.

[0056] 3) High degree of freedom: The circuit structure of the monitoring system of the present invention is simple, and the DC-DC converter matched with the battery is completely decoupled when in use, which expands the degree of freedom of DC-DC converter design and is superior to the traditional DC-DC converter PWM duty cycle perturbation method.

[0057] 4) Real-time online: The monitoring method of the present invention realizes the extraction of direct current superimposed with sinusoidal disturbance from the battery through a voltage-to-current conversion circuit based on sinusoidal voltage. It can be used for online measurement of battery impedance under conditions such as battery offline and constant current charging and discharging, which is superior to the traditional external excitation source injection method based on special instruments.

[0058] 5) The impedance of the present invention can also be calculated by the dq variation method: the dq framework can separate system components, identify the real and imaginary parts of the impedance, as well as the magnitude and phase angle of the impedance. Compared with traditional signal processing methods, the dq variation method has more computational advantages. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 The system structure diagram of a battery impedance online monitoring system and method of the present invention.

[0060] Figure 2 The present invention is a circuit diagram of a battery impedance online monitoring system and method.

[0061] Figure 3 This is the circuit structure diagram of the charging state impedance measurement in MATLAB simulation.

[0062] Figure 4 This is the circuit structure diagram of the discharge state impedance measurement in MATLAB simulation.

[0063] Figure 5 This is the circuit structure diagram of offline impedance measurement in MATLAB simulation.

[0064] Figure 6The waveforms of disturbance current, battery current and back-end voltage of filter under charging state.

[0065] Figure 7 The waveforms of disturbance current, battery current and back-end voltage of filter in discharge state.

[0066] Figure 8 The waveforms of disturbance current, battery current and filtered back-end voltage in offline state. DETAILED DESCRIPTION

[0067] The present invention is described in detail below with reference to the accompanying drawings and specific examples:

[0068] like Figure 1 As shown, the present invention provides a battery impedance online monitoring system and method, the implementation circuit of the method includes a host computer, a sinusoidal voltage generating circuit, a voltage-current conversion circuit, a constant current charging and discharging circuit, a signal processing module, and an impedance calculation module.

[0069] The functions of each component are described as follows:

[0070] (1) Host computer: used to control the frequency of the sinusoidal signal in the sinusoidal signal generating circuit;

[0071] (2) Sinusoidal signal generating circuit: Generates a frequency-controllable sinusoidal voltage signal through direct digital frequency synthesis (DDS) for controlling the battery disturbance signal;

[0072] (3) Voltage-to-current conversion circuit: Based on the virtual short and virtual break characteristics of the op amp, this structure converts the voltage into current through the sinusoidal voltage and the resistor R s Control the current flowing through the battery;

[0073] (4) Constant current charging and discharging circuit: It is composed of an external constant current charging device and a constant current load, so that the battery is in a constant current charging or constant current discharging condition;

[0074] (5) Signal processing module: collects the current excitation and voltage response signals of the battery to be tested and removes DC and noise, converts the analog signals into digital signals through AD sampling circuits and inputs them into the impedance calculation module;

[0075] (6) Impedance calculation module: calculates the battery impedance by identifying the amplitude and phase of the collected signal.

[0076] Through the battery impedance online monitoring method, the specific example operation includes the following steps:

[0077] 1) Generate a voltage disturbance signal of a predetermined frequency through a sinusoidal signal generating circuit in the circuit, and the frequency in this example is 1kHz;

[0078] 2) Through the voltage-current conversion circuit, the output of the sinusoidal signal generating circuit is used as the input of the operational amplifier, and through the ideal operational amplifier, transistor, resistor R s To control the size of the battery disturbance current, the applied small signal voltage disturbance is converted into a current disturbance, so as to continuously extract a sinusoidal current signal from the battery.

[0079] 3) Disconnect the constant current source and the constant current load branch to put the battery in an offline state, collect the voltage signal at both ends of the battery through the signal processing module, perform signal processing on the battery voltage, filter out the DC signal and noise, and calculate the impedance value in the offline state;

[0080] 4) Close the constant current source branch and disconnect the constant current load branch to put the battery in a charging state. Collect the voltage signal at both ends of the battery through the signal processing module, perform signal processing on the battery voltage, filter out the DC signal and noise, and calculate the impedance value in the charging state;

[0081] 5) Close the constant current load branch and disconnect the constant current source branch to put the battery in a discharge state. Collect the voltage signal at both ends of the battery through the signal processing module, perform signal processing on the battery voltage, filter out the DC signal and noise, and calculate the impedance value in the discharge state;

[0082] Example:

[0083] In this embodiment, a battery impedance online monitoring model is built in MATLAB, such as Figure 3 , Figure 4 , Figure 5 As shown, the impedance calculation module structure is omitted in the simulation of this embodiment, and the host computer, sinusoidal signal generating circuit and signal processing module structure are simplified. Figure 3 , Figure 4 , Figure 5 The parameters of the relevant simulation components are shown in Table 1 below.

[0084] Table 1 Simulation component parameters

[0085] Sinusoidal voltage 0.3V DC voltage source 0.33V Battery voltage 12V Battery capacity 10Ah Battery internal resistance 0.1Ω Transistor amplification factor β 100 Constant current source 5A Resistor R0 10Ω Resistor Rs 5Ω Resistor R1 100Ω Resistor R2 100Ω Capacitor C1 3μF Capacitor C2 1μF

[0086] In the simulation circuit of MATLAB, the impedance of the battery is set as shown in the table. The impedance is only set to the internal resistance without considering the inductance and capacitance. This example is only for verifying the feasibility of applying a predetermined disturbance signal to the battery under three predetermined working conditions and collecting the corresponding response signal to obtain the impedance. It is verified that through this circuit, this method can monitor the impedance of the battery under the three predetermined working conditions of the battery.

[0087] like Figure 6 , Figure 7 , Figure 8It can be seen that under the three predetermined working conditions, the value of the disturbance current will not change with the change of the battery working state. The total current value is the superposition of the disturbance current and the charging current or the discharging current. The terminal voltage of the battery is also the superposition of the response voltage of the disturbance current and the response voltage of other currents. The disturbance current of the battery is the same under the three working conditions. The current is determined by U S , R S After removing DC and denoising the battery terminal voltage signal, it can be seen from the simulation diagram that the battery response voltage to the disturbance current under the three working conditions is the same, and the calculated impedance is also the same, so this method is feasible for online measurement of battery impedance.

Claims

1. A battery impedance online monitoring system, characterized in that: The system includes: Sinusoidal signal generating circuit, voltage-current conversion circuit, signal processing module, impedance calculation module; The sinusoidal signal generating circuit is connected to the voltage-current conversion circuit, the voltage-current conversion circuit is connected to the battery to be tested, the battery to be tested is connected to the signal processing module, and the signal processing module is connected to the impedance calculation module; The sinusoidal signal generating circuit generates a frequency-controllable sinusoidal signal through direct digital frequency synthesis DDS, which is used to control the battery disturbance signal; The signal processing module collects the voltage response signal of the battery to be tested, performs signal processing to remove DC and noise, converts the analog signal into a digital signal through an AD sampling circuit, and inputs the digital signal to the impedance calculation module; The impedance calculation module collects the amplitude and phase of the signal through the signal processing module to perform identification to calculate the battery impedance.

2. According to claim 1, a battery impedance online monitoring system is characterized in that: The sinusoidal signal generating circuit is connected to a host computer, and the host computer is used to control the frequency of the sinusoidal signal in the sinusoidal signal generating circuit.

3. According to claim 1, a battery impedance online monitoring system is characterized in that: The sinusoidal signal generating circuit is connected to a battery management system BMS, and program control of the battery management system BMS can achieve frequency regulation of the sinusoidal signal in the sinusoidal signal generating circuit based on DDS.

4. The battery impedance online monitoring system according to claim 1, characterized in that: The voltage-current conversion circuit includes resistors R2 and R S , capacitor C6, operational amplifier OP1, operational amplifier OP2, NPN transistor; One end of the resistor R2 is connected to the output port VOUT of the DDS, and the other end of the resistor R2 is connected to one end of the capacitor C6 and the negative port of the operational amplifier OP1 respectively; the other end of the capacitor C6 is connected to the AGND terminal; The output port of the operational amplifier OP1 is connected to one end of the switch ST, and the other end of the switch ST is connected to the negative port of the operational amplifier OP2 and the positive port of the operational amplifier OP1 respectively; The positive port of the operational amplifier OP2 is connected to the resistor R S One end of the NPN transistor is connected to the emitter; the resistor R S The other end of the pin is connected to AGND.

5. The battery impedance online monitoring system according to claim 1, characterized in that: Based on the voltage-to-current conversion circuit, the frequency-adjustable voltage signal generated by the sinusoidal signal generating circuit is used as the input. According to the virtual short characteristic of the operational amplifier, the positive terminal of the operational amplifier OP2 is connected to the emitter of the NPN transistor to control the emitter voltage of the NPN transistor. A resistor R is connected to the emitter of the NPN transistor. S , by adjusting the emitter voltage of the NPN transistor and the resistor R S , generating a predetermined disturbance current signal for monitoring.

6. The battery impedance online monitoring system according to claim 1, characterized in that: The signal processing module includes a resistor R6, a resistor R7, a capacitor C9, a capacitor C 10 , operational amplifier OP5, operational amplifier OP6; The positive port of the operational amplifier OP5 is connected to the positive electrode of the single battery, and the negative port of the operational amplifier OP5 is connected to the negative electrode of the single battery; the output port of the operational amplifier OP5 is connected to one end of the resistor R6, and the other end of the resistor R6 is connected to one end of the capacitor C9; The other end of the capacitor C9 is connected to the capacitor C 10 One end of the resistor R7 and the negative port of the operational amplifier OP6 are connected; The capacitor C 10 The other end of is respectively connected to the other end of the resistor R7 and the output port of the operational amplifier OP6; the positive port of the operational amplifier OP6 is connected to the AGND terminal.

7. A method for online monitoring of battery impedance using the online monitoring system for battery impedance according to any one of claims 1 to 6, characterized in that: A frequency-controllable sinusoidal voltage signal is generated by a DDS-based sinusoidal signal generating circuit. A DC current signal with a superimposed sinusoidal disturbance is extracted from the battery through a voltage-to-current conversion circuit. Then, through AC impedance calculation, online measurement of battery impedance under conditions such as offline battery and constant current charge and discharge is achieved.

8. A battery impedance online monitoring method according to claim 7, characterized in that The following steps are involved: Step 1: The host computer controls the sinusoidal signal generating circuit to generate a voltage disturbance signal of a predetermined frequency. The value of the disturbance signal frequency should be set according to the monitoring object: temperature, SOC, SOH; Step 2: The voltage-to-current conversion circuit converts the applied disturbance voltage signal into a disturbance current signal, and extracts the disturbance current signal from the battery or injects the disturbance current signal into the battery; Where: I is the disturbance current, U is the disturbance voltage, and R is the variable resistor for adjusting the disturbance current; Step 3: The signal processing module collects the voltage response signal of the battery to be tested and removes DC and noise. The disturbance current signal does not need to be collected and can be calculated by U and R. The processed analog signal is converted into a digital signal and input into the impedance calculation module; Step 4: After the disturbance signal is applied, the impedance calculation module measures the impedance characteristics of the battery under charging and discharging conditions according to the impedance calculation formula. The impedance calculation formula is: Where: |Z| is the impedance amplitude of the battery; ∠θ is the impedance phase angle, u(t) is the response voltage across the battery after DC removal and denoising, i(t) is the applied perturbed sinusoidal current, ∠θ is the phase angle of the response voltage across the battery, ∠θ is the phase angle of the perturbed sinusoidal current, |U| is the amplitude of the voltage response across the battery after DC removal and denoising, and |I| is the amplitude of the perturbed sinusoidal current.

9. A battery impedance online monitoring method according to claim 8, characterized in that: The impedance can be calculated by the dq variation method, which includes the following steps: S1: Filter out the DC component of the battery current and voltage and establish an α-β coordinate system. This step eliminates the DC component by using a bandpass filter (BPF), with the output of the BPF as the α axis, and an all-pass filter (APF), with the output of the APF as the β axis. The APF passes all frequencies with the same gain but only provides a 90° phase shift at the pass frequency. The BPF and APF coefficient calculation formulas are as follows: Where: H BPF(S) is the bandpass filter transfer function; H APF(S) is the all-pass filter transfer function; S is a complex variable; ω b is the center frequency; is the pass frequency; B is the band frequency, S2: Using dq transformation, the α-β coordinate system is mapped to the dual-axis synchronous rotating reference system. The values ​​of current and voltage under dq transformation are as follows: Where: v d is the voltage value on the d-axis of the dq coordinate system; i d is the current value on the d-axis of the dq coordinate system; v q is the voltage value on the q axis of the dq coordinate system; i q is the current value on the q axis of the dq coordinate system; v α is the voltage value on the α-axis of the α-β coordinate system; i α is the current value on the α-axis of the α-β coordinate system; v β is the voltage value on the β axis of the α-β coordinate system; i β is the current value on the β axis of the α-β coordinate system; θ is v d Angle of the lead datum; S3: Calculate the ripple power, impedance amplitude and phase angle. The calculation formula is as follows: Where: P is active power, Q is reactive power, S is apparent power, |Z| is impedance amplitude, θ is impedance phase angle; Through the above method, the impedance amplitude and impedance phase angle of the battery are calculated.

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