An Online Detection Method for the Internal Resistance of Lithium Batteries Based on PCS

Abstract

The present invention provides an on-line detection method for the internal resistance of a lithium battery in the technical field of lithium battery detection, including: Step S1, obtaining three-phase voltage U abc and the second DC bus voltage U dc2 and the second DC current I dc2 ; Step S2, performing grid phase-locking on U abc to obtain the 6th harmonic frequency f b3 and the 12th harmonic frequency f b4 ; Step S3, calculating the filtering parameters of the band-pass filter based on f b3 and f b4 ; Step S4, filtering U dc2 and I dc2 based on each filtering parameter to obtain the third DC bus voltage U dc3 and the third DC current I dc3 and the fourth DC bus voltage U dc4 and the fourth DC current I dc4 ; Step S5, calculating the integration parameters of the second-order generalized integrator based on f b3 and f b4 ; Step S6, performing orthogonal phase-locking on U dc3 and I dc3 and U dc4 and I dc4 based on each integration parameter to obtain the corresponding amplitude and phase angle; Step S7, calculating the battery internal resistance and polarization capacitance based on the amplitude and phase angle. The advantages of the present invention are: greatly improving the real-time performance, accuracy and convenience of lithium battery internal resistance detection.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium battery detection, and in particular to a PCS-based lithium battery internal resistance online detection method. Background Art

[0002] The research and development of renewable energy has become a common concern of the world. With the large-scale grid connection of renewable energy such as wind power generation and photovoltaic power generation, the installed capacity of synchronous generators in the power grid has gradually decreased. The inherent randomness and volatility of renewable energy make it difficult for it to provide reliable frequency support for the power grid, and the power system faces severe frequency regulation pressure.

[0003] Configuring energy storage devices on the grid side is an effective means to improve the grid's renewable energy absorption capacity and maintain grid frequency stability. Lithium batteries have been widely used in the field of energy storage due to their high energy density, good power characteristics, long cycle life, good environmental adaptability, and no memory effect. However, lithium batteries are energy carriers after all. During use, improper use or harsh conditions of use may cause thermal runaway and cause safety accidents. Therefore, lithium batteries must be tested for health status during use to ensure their safety. The health status of lithium batteries is determined by many performance parameters, among which internal resistance is an important feature reflecting the health status. Real-time detection of the internal resistance of lithium batteries is of great significance.

[0004] Patent CN105738815B discloses a method for online detection of the health status of lithium-ion batteries. According to a simplified energy balance model and the real-time operating condition curve of the lithium-ion battery, the battery internal resistance is calculated through a series of numerical fitting methods. On the one hand, it is necessary to control a fixed charge and discharge current, which makes it inflexible. On the other hand, the test time exceeds 6 hours and the test data cannot be updated in real time; Patent CN105759124A discloses a method for online detection of the internal resistance of a power battery. By controlling the on and off of the charging switch KC, and detecting the charging current of the power battery pack and the terminal voltage of each single cell in the power battery pack before and after the charging switch KC is turned on and before and after the charging switch KC is turned off, the terminal voltage change is divided by the charging current change to obtain the DC internal resistance of each single cell. This method can only be tested when the battery is offline, and the measurement signal is the instantaneous voltage and current, and the error is large; Patent CN 111722135A discloses a detection circuit that can measure the internal resistance of a power battery online. A weak AC signal is injected into the charging port of an electric vehicle, and a phase-locked amplification method is used to detect the voltage drop of the AC line on the internal resistance of the battery, thereby detecting the internal resistance of the battery. Although this method has high accuracy during offline testing, it is very difficult to inject small AC signals in real time during the charging and discharging process of a high-voltage and high-current lithium battery.

[0005] Therefore, how to provide a method for on-line detection of the internal resistance of a lithium battery based on PCS to improve the real-time performance, accuracy and convenience of the internal resistance detection of the lithium battery has become a technical problem to be solved urgently. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a method for on-line detection of the internal resistance of a lithium battery based on PCS to improve the real-time performance, accuracy and convenience of the internal resistance detection of the lithium battery.

[0007] The present invention is implemented as follows: A method for on-line detection of the internal resistance of a lithium battery based on PCS includes the following steps:

[0008] Step S1: Perform AD sampling through the DSP of the control unit to obtain the three-phase voltage U of the power grid abc , the second DC bus voltage U dc2 and the second DC current I dc2 ;

[0009] Step S2: Perform power grid phase locking on the three-phase voltage U abc through a synchronous rotating coordinate system phase-locked loop to obtain the 6th harmonic frequency f b3 and the 12th harmonic frequency f b4 ;

[0010] Step S3: Based on the 6th harmonic frequency f b3 and the 12th harmonic frequency f b4 , calculate the filtering parameters of the first band-pass filter, the second band-pass filter, the third band-pass filter and the fourth band-pass filter;

[0011] Step S4: Filter the second DC bus voltage U dc2 and the second DC current I dc2 based on each of the filtering parameters to obtain the third DC bus voltage U dc3 , the third DC current I dc3 , the fourth DC bus voltage U dc4 and the fourth DC current I dc4 ;

[0012] Step S5: Based on the 6th harmonic frequency f b3 and the 12th harmonic frequency f b4 , calculate the integral parameters of the first second-order generalized integrator, the second second-order generalized integrator, the third second-order generalized integrator and the fourth second-order generalized integrator;

[0013] Step S6: Based on each of the integral parameters, for the third DC bus voltage U dc3 , the third DC current I dc3 , the fourth DC bus voltage U dc4and the fourth DC current I dc4 Perform orthogonal phase-locking to obtain the corresponding amplitude and phase angle;

[0014] Step S7: Calculate the battery internal resistance and polarization capacitance based on each of the amplitudes and phase angles;

[0015] Step S8: After performing validity verification on each of the battery internal resistances and polarization capacitances, calculate the corresponding mean value for lithium battery state of health monitoring.

[0016] Furthermore, in the step S1, the second DC bus voltage U dc2 is obtained as follows:

[0017] Collect the DC bus voltage U dc of the power grid, extract the first AC weak signal through a Butterworth second-order high-pass filter circuit with a cut-off frequency of 50 Hz to obtain the first DC bus voltage U dc1 , and then amplify the extracted first AC weak signal through an operational amplifier circuit with a gain of 100 to obtain the second DC bus voltage U dc2 ;

[0018] The acquisition process of the second DC current I dc2 is as follows:

[0019] Collect the DC current I dc of the power grid, extract the second AC weak signal through a Butterworth second-order high-pass filter circuit with a cut-off frequency of 50 Hz to obtain the first DC current I dc1 , and then amplify the extracted second AC weak signal through an operational amplifier circuit with a gain of 100 to obtain the second DC current I dc2 .

[0020] Furthermore, the step S2 is specifically:

[0021] Perform grid phase-locking on the three-phase voltage U abc through a synchronous rotating coordinate system phase-locked loop to obtain the grid frequency f b , multiply the grid frequency f b by 6 to obtain the 6th harmonic frequency f b3 , multiply the grid frequency f b by 12 to obtain the 12th harmonic frequency f b4 .

[0022] Furthermore, in the step S3, the calculation formula for the filtering parameters is:

[0023]

[0024] where G bpf(s) represents the filtering parameter; B represents the passband of the band-pass filter; ω c represents the center frequency; s represents the complex frequency of the transfer function;

[0025] For the first band-pass filter and the second band-pass filter, B = 20π, ω c = 2πf b3 ; For the third band-pass filter and the fourth band-pass filter, B = 20π, ω c = 2πf b4 .

[0026] Furthermore, the specific step S4 is as follows:

[0027] The first band-pass filter filters the second DC bus voltage U dc2 to obtain the third DC bus voltage U dc3 ;

[0028] The second band-pass filter filters the second DC current I dc2 to obtain the third DC current I dc3 ;

[0029] The third band-pass filter filters the second DC bus voltage U dc2 to obtain the fourth DC bus voltage U dc4 ;

[0030] The fourth band-pass filter filters the second DC current I dc2 to obtain the fourth DC current I dc4 .

[0031] Furthermore, the specific step S6 is as follows:

[0032] The first second-order generalized integrator performs orthogonal phase-locking on the third DC bus voltage U dc3 to obtain the amplitude r dc3 and the phase angle θ udc3 of the third DC bus voltage U udc3 ;

[0033] The second second-order generalized integrator performs orthogonal phase-locking on the third DC current I dc3 to obtain the amplitude r dc3 and the phase angle θ Idc3 of the third DC current I Idc3 ;

[0034] The third second-order generalized integrator performs orthogonal phase-locking on the fourth DC bus voltage U dc4 to obtain the amplitude r dc4The amplitude r udc4 and the phase angle θ udc4 ;

[0035] The fourth second-order generalized integrator performs orthogonal phase-locking on the fourth DC current I dc4 to obtain the amplitude r dc4 and the phase angle θ Idc4 of the fourth DC current I Idc4 .

[0036] Further, the step S7 is specifically as follows:

[0037] Based on the r udc3 , θ udc3 , r Idc3 and θ Idc3 calculate the battery internal resistance R b3 corresponding to the 6th harmonic frequency f in_6 and the polarization capacitance C po_6 :

[0038]

[0039] Based on the r udc4 , θ udc4 , r Idc4 and θ Idc4 calculate the battery internal resistance R b4 corresponding to the 12th harmonic frequency f in_12 and the polarization capacitance C po_12 :

[0040]

[0041] Further, the step S8 is specifically as follows:

[0042] Judge whether the error between the R in_6 and the R in_12 is less than 10%. If not, the validity check of R in_6 , C po_6 , R in_12 and C po_12 fails, and the process ends; if so, the validity check of R in_6 , C po_6 , R in_12 and C po_12 passes, calculate the average value R in of the battery internal resistance and the average value C po of the polarization capacitance, and monitor the health state of the lithium battery based on the R in and C po :

[0043]

[0044] The advantages of the present invention are as follows:

[0045] By using the characteristic harmonics of the inherent voltage and current output on the DC side of the PCS as the input signal, the 6th harmonic frequency f b3 and the 12th harmonic frequency f b4 can be calculated, which can be directly realized in the control unit of the PCS without injecting additional voltage signals or current signals, and the detection of the battery internal resistance can be completed without adding additional measuring equipment; since the 6th harmonic frequency f b3 and the 12th harmonic frequency f b4 are high-frequency AC signals, it greatly reduces the influence of the DC bias of the sampling channel on the measurement accuracy; by setting the frequencies used by the band-pass filter and the second-order generalized integrator to the real-time grid frequency measured by the phase-locked loop (f b3 and f b4 ), it effectively overcomes the influence of the grid frequency offset on the measurement accuracy; by calculating the corresponding mean values after validating the effectiveness of each battery internal resistance and polarization capacitance, that is, detecting the battery internal resistance using the voltage and current signals of two independent frequencies, the battery internal resistances obtained by the two solutions can be mutually corrected, further improving the detection accuracy; and the present invention can perform real-time detection during the charging and discharging process of the lithium battery, discover the abnormalities of the lithium battery in real time, avoid causing safety accidents, and ultimately greatly improve the real-time performance, accuracy and convenience of the lithium battery internal resistance detection. Description of the Drawings

[0046] The present invention will be further described below with reference to the accompanying drawings in conjunction with the embodiments.

[0047] Figure 1 is the flow chart of a method for online detection of the internal resistance of a lithium battery based on a PCS according to the present invention.

[0048] Figure 2 is the schematic diagram of the energy storage system according to the present invention.

[0049] Figure 3 is the circuit principle block diagram of the PCS according to the present invention.

[0050] Figure 4 is the hardware architecture diagram according to the present invention.

[0051] Figure 5 is the software architecture diagram according to the present invention.

[0052] Figure 6 is the schematic diagram of the quadrature phase-locked loop according to the present invention. Detailed Embodiments

[0053] The overall idea of the technical solution in the embodiments of the present application is as follows:

[0054] In the first-order RC model of the lithium battery, it includes the battery internal resistance Rin , the polarization capacitance C po and the polarization resistance R po These three parameters, the physical meaning is that the polarization capacitance C po and the polarization resistance R po are in parallel, and then in series with the internal resistance R of the battery in The formula for the first-order impedance Z of the lithium battery bat is as follows:

[0055]

[0056] where j represents the imaginary part symbol of the complex number; / / represents the circuit parallel symbol; f represents the frequency of the detection signal. If the frequency of the detection signal is relatively high, for the lithium battery, the capacitive reactance of the polarization capacitance is much smaller than the impedance of the polarization resistance, and the parallel connection of the polarization capacitance and the polarization resistance can be approximately equivalent to the impedance effect of a simple polarization capacitance 1 / j2πfC po , then the formula for the high-frequency simplified first-order impedance Z bat1 of the lithium battery is as follows:

[0057]

[0058] In the application scenario of grid-side energy storage, lithium batteries are generally connected to the three-phase AC grid through a power conversion system (PCS). The PCS is generally a three-phase inverter topology, and the main circuit is divided into two interfaces, the AC side and the DC side. The DC side is connected to the lithium battery, and the AC side is connected to the three-phase AC grid.

[0059] For a PCS with a three-phase inverter topology, the fundamental frequency at which the PCS is incorporated into the AC grid is defined as f b , then during the normal operation of the PCS, there will be a certain content of characteristic harmonics in the DC side current, especially the 6th and 12th harmonics are more prominent. Among them, the 6th harmonic corresponding frequency is defined as f b3 , and the 12th harmonic corresponding frequency is defined as f b4 . If the PCS can extract the voltage and current content of the 6th and 12th harmonic frequencies in real time during operation, the high-frequency simplified first-order impedance parameter Z bat1 of the lithium battery can be calculated in real time, and the internal resistance and polarization capacitance of the battery can be monitored in real time to monitor the health status of the lithium battery in real time.

[0060] Therefore, the 6th characteristic harmonic and the 12th characteristic harmonic inherent in the normal operation of the PCS are used for detection. The collected DC bus voltage and DC current are high-pass filtered and amplified to obtain the second DC bus voltage and the second DC current, and then enter the DSP of the control unit for AD conversion and calculation. In the DSP, the second DC bus voltage and the second DC current are band-pass filtered with a center frequency of the 6th harmonic frequency to obtain the third DC bus voltage and the third DC current; the second DC bus voltage and the second DC current are band-pass filtered with a center frequency of the 12th harmonic frequency to obtain the fourth DC bus voltage and the fourth DC current; the third DC bus voltage and the third DC current are orthogonally phase-locked and then the battery internal resistance and polarization capacitance corresponding to the 6th harmonic frequency are calculated; the fourth DC bus voltage and the fourth DC current are orthogonally phase-locked and then the battery internal resistance and polarization capacitance corresponding to the 12th harmonic frequency are calculated.

[0061] Please refer to Figures 1 to 6 As shown, the energy storage system of the present invention, such as Figure 2 shown, includes three parts: a lithium battery, a PCS, and an AC power grid; among them, the PCS is used to realize the conversion between the DC electrical energy of the battery and the AC electrical energy of the power grid, and externally includes two interfaces, an AC side and a DC side. The DC side is connected to the lithium battery through P dc+ and P dc- , and the AC side is connected to the three-phase AC power grid through P acA , P acB , and P acC .

[0062] The circuit principle block diagram of the PCS is as Figure 3 shown, and includes two parts: a main circuit and a control unit; the PCS generally adopts vector control technology, which is realized by the control unit; the three-phase grid voltage U abc , the three-phase current I abc , the DC bus voltage U dc , and the DC current I dc are collected by the control unit, and the three-phase PWM signal S PWM is output to the three-phase power unit to complete vector control.

[0063] The hardware architecture is as Figure 4 shown. The DSP is the core of the control unit and realizes all control methods; in order to complete the vector control of the PCS, the collected signals include the three-phase grid voltage U abc , the three-phase current I abc , the DC bus voltage U dc , and the DC current I dc .

[0064] In order to realize the detection of the battery internal resistance, on the basis of the original PCS control unit hardware, a DC bus voltage AC weak signal extraction, amplification circuit and an AD channel to the DSP are added, asFigure 5 as shown

[0065] A preferred embodiment of an online lithium battery internal resistance detection method based on PCS of the present invention includes the following steps:

[0066] Step S1: Perform AD sampling through the DSP of the control unit to obtain the three-phase voltage U of the power grid abc , the second DC bus voltage U dc2 and the second DC current I dc2 ;

[0067] Step S2: Perform power grid phase locking on the three-phase voltage U abc through a synchronous rotating coordinate system phase-locked loop (SRF-PLL, Synchronous Reference Frame PLL) to obtain the 6th harmonic frequency f b3 and the 12th harmonic frequency f b4 ;

[0068] Step S3: Based on the 6th harmonic frequency f b3 and the 12th harmonic frequency f b4 , calculate the filtering parameters of the first band-pass filter, the second band-pass filter, the third band-pass filter, and the fourth band-pass filter;

[0069] The first band-pass filter, the second band-pass filter, the third band-pass filter, and the fourth band-pass filter are preferably second-order infinite impulse response filters, referred to as second-order IIR filters. When using a second-order IIR filter, the bilinear transformation equation is used to transform the transfer function in the s domain to the transfer function in the z domain for digital solution in the DSP;

[0070] Step S4: Filter the second DC bus voltage U dc2 and the second DC current I dc2 based on the respective filtering parameters to obtain the third DC bus voltage U dc3 , the third DC current I dc3 , the fourth DC bus voltage U dc4 and the fourth DC current I dc4 ;

[0071] Step S5: Based on the 6th harmonic frequency f b3 and the 12th harmonic frequency f b4 , calculate the integration parameters of the first second-order generalized integrator, the second second-order generalized integrator, the third second-order generalized integrator, and the fourth second-order generalized integrator;

[0072] Step S6: Based on the respective integration parameters, the third DC bus voltage U dc3 , the third DC current Idc3 and the fourth DC bus voltage U dc4 as well as the fourth DC current I dc4 are orthogonally phase-locked to obtain the corresponding amplitude and phase angle;

[0073] Step S7: Calculate the battery internal resistance and polarization capacitance based on each of the amplitudes and phase angles;

[0074] Step S8: After performing validity verification on each of the battery internal resistances and polarization capacitances, calculate the corresponding mean values for lithium battery state of health monitoring.

[0075] In the said step S1, the process of obtaining the second DC bus voltage U dc2 is as follows:

[0076] Collect the DC bus voltage U of the power grid dc , extract the first AC weak signal through a Butterworth second-order high-pass filter circuit with a cut-off frequency of 50 Hz to obtain the first DC bus voltage U dc1 , and then amplify the extracted first AC weak signal through an operational amplifier circuit with a gain of 100 to obtain the second DC bus voltage U dc2 ;

[0077] The process of obtaining the second DC current I dc2 is as follows:

[0078] Collect the DC current I of the power grid dc , extract the second AC weak signal through a Butterworth second-order high-pass filter circuit with a cut-off frequency of 50 Hz to obtain the first DC current I dc1 , and then amplify the extracted second AC weak signal through an operational amplifier circuit with a gain of 100 to obtain the second DC current I dc2 .

[0079] The said step S2 is specifically:

[0080] Perform power grid phase-locking on the three-phase voltage U abc through a synchronous rotating coordinate system phase-locked loop to obtain the power grid frequency f b , multiply the power grid frequency f b by 6 to obtain the 6th harmonic frequency f b3 , multiply the power grid frequency f b by 12 to obtain the 12th harmonic frequency f b4 .

[0081] In the said step S3, the calculation formula for the filtering parameters is:

[0082]

[0083] where Gbpf (s) represents the filtering parameter; B represents the passband of the band - pass filter; ω c represents the center frequency; s represents the complex frequency of the transfer function;

[0084] For the first band - pass filter and the second band - pass filter, B = 20π, ω c = 2πf b3 ; For the third band - pass filter and the fourth band - pass filter, B = 20π, ω c = 2πf b4 .

[0085] The specific step S4 is as follows:

[0086] The first band - pass filter filters the second DC bus voltage U dc2 to obtain the third DC bus voltage U dc3 ;

[0087] The second band - pass filter filters the second DC current I dc2 to obtain the third DC current I dc3 ;

[0088] The third band - pass filter filters the second DC bus voltage U dc2 to obtain the fourth DC bus voltage U dc4 ;

[0089] The fourth band - pass filter filters the second DC current I dc2 to obtain the fourth DC current I dc4 .

[0090] That is, extract the 6 - th harmonic frequency components of the second DC bus voltage U dc2 and the second DC current I dc2 to obtain the third DC bus voltage U dc3 and the third DC current I dc3 ; Extract the 12 - th harmonic frequency components of the second DC bus voltage U dc2 and the second DC current I dc2 to obtain the fourth DC bus voltage U dc4 and the fourth DC current I dc4 .

[0091] The specific step S6 is as follows:

[0092] The first second - order generalized integrator performs orthogonal phase - locking on the third DC bus voltage U dc3 to obtain the amplitude r dc3 of the third DC bus voltage U udc3 and the phase angle θ udc3;

[0093] The second second-order generalized integrator performs orthogonal phase-locking on the third DC current I dc3 to obtain the amplitude r dc3 and phase angle θ Idc3 of the third DC current I Idc3 ;

[0094] The third second-order generalized integrator performs orthogonal phase-locking on the fourth DC bus voltage U dc4 to obtain the amplitude r dc4 and phase angle θ udc4 of the fourth DC bus voltage U udc4 ;

[0095] The fourth second-order generalized integrator performs orthogonal phase-locking on the fourth DC current I dc4 to obtain the amplitude r dc4 and phase angle θ Idc4 of the fourth DC current I Idc4 .

[0096] In the step S6, the orthogonal phase-locking includes two parts: a second-order generalized integrator (SOIG, Second-Order General Integrator) and a Cartesian to Polar converter (C2P, Cartesian to Polar), as Figure 6 shown;

[0097] The transfer function of the second-order generalized integrator is as follows:

[0098]

[0099] where k = 0.707; ω0 represents the angular frequency of the processed signal, and in the first and second orthogonal phase-locking calculations, ω0 = 2πf b3 , and in the third and fourth orthogonal phase-locking calculations, w0 = 2πf b4 ; V represents the input signal; V d represents the d-axis component of V; V q represents the q-axis component of v; D(s) and Q(s) respectively represent the d-axis transfer function and q-axis transfer function of the second-order generalized integrator.

[0100] The equation of the Cartesian to Polar converter is as follows:

[0101]

[0102] where r v represents the amplitude of the signal; θ v represents the phase angle of the signal; atan() is the arctangent function.

[0103] When orthogonally phase-locked, the input signal v passes through a second-order generalized integrator to obtain ∨ d and ∨ q , and then passes through a Cartesian-to-polar coordinate converter to obtain r v and θ v , as Figure 6 shown; the input signal ∨ corresponds to U dc3 , I dc3 , U dc4 , I dc4 .

[0104] The specific content of the step S7 is as follows:

[0105] Based on the r udc3 , θ udc3 , r Idc3 and θ Idc3 calculate the internal resistance R b3 of the battery corresponding to the 6th harmonic frequency f in_6 and the polarization capacitance C po_6 :

[0106]

[0107]

[0108] Based on the r udc4 , θ udc4 , r Idc4 and θ Idc4 calculate the internal resistance R b4 of the battery corresponding to the 12th harmonic frequency f in_12 and the polarization capacitance C po_12 :

[0109]

[0110] The specific content of the step S8 is as follows:

[0111] Judge whether the error between the R in_6 and R in_12 is less than 10%. If not, the validity check of R in_6 , C po_6 , R in_12 and C po_12 fails, and the process ends; if so, the validity check of R in_6 , C po_6 , R in_12 and C po_12 passes, calculate the average value R in of the battery internal resistance and the average value C po of the polarization capacitance, and based on the R in and C poMonitoring the health state of lithium batteries:

[0112]

[0113] In summary, the advantages of the present invention are as follows:

[0114] By using the characteristic harmonics of the inherent voltage and current at the DC side output of the PCS as input signals, the 6th harmonic frequency f b3 and the 12th harmonic frequency f b4 can be calculated. This can be directly implemented in the control unit of the PCS without the need to inject additional voltage or current signals, and the detection of the battery internal resistance can be completed without adding additional measurement equipment. Since the 6th harmonic frequency f b3 and the 12th harmonic frequency f b4 are high-frequency AC signals, the influence of the DC offset of the sampling channel on the measurement accuracy is greatly reduced. By setting the frequencies used by the band-pass filter and the second-order generalized integrator to the real-time grid frequency (f b3 and f b4 ) measured by the phase-locked loop, the influence of grid frequency offset on the measurement accuracy is effectively overcome. By calculating the corresponding mean values after validating the effectiveness of each battery internal resistance and polarization capacitance, that is, by using the voltage and current signals at two independent frequencies to detect the battery internal resistance, the battery internal resistances obtained by the two solutions can be mutually corrected, further improving the detection accuracy. Moreover, the present invention can perform real-time detection during the charging and discharging process of lithium batteries, discover lithium battery anomalies in real time, avoid causing safety accidents, and ultimately greatly improve the real-time performance, accuracy, and convenience of lithium battery internal resistance detection.

[0115] Although the specific embodiments of the present invention have been described above, those skilled in the art of this technology should understand that the specific embodiments we described are illustrative rather than used to limit the scope of the present invention. Equivalent modifications and variations made by those skilled in the art in accordance with the spirit of the present invention should be covered by the scope protected by the claims of the present invention.

Claims

1. An online detection method for the internal resistance of a lithium battery based on PCS, characterized in that: It includes the following steps: Step S1: Perform AD sampling through the DSP of the control unit to obtain the three-phase voltage U of the power grid abc , the second DC bus voltage U dc2 and the second DC current I dc2 ; Step S2: Perform grid phase locking on the three-phase voltage U through a synchronous rotating coordinate system phase-locked loop abc to obtain the 6th harmonic frequency f b3 and the 12th harmonic frequency f b4 ; Step S3: Based on the 6th harmonic frequency f b3 and the 12th harmonic frequency f b4 , calculate the filtering parameters of the first band-pass filter, the second band-pass filter, the third band-pass filter, and the fourth band-pass filter; Step S4. Filter the second DC bus voltage U dc2 and the second DC current I dc2 to obtain the third DC bus voltage U dc3 , the third DC current I dc3 , the fourth DC bus voltage U dc4 and the fourth DC current I dc4 ; Step S5: Based on the 6th harmonic frequency f b3 and the 12th harmonic frequency f b4 , calculate the integration parameters of the first second-order generalized integrator, the second second-order generalized integrator, the third second-order generalized integrator, and the fourth second-order generalized integrator; Step S6: Based on each of the integral parameters, perform orthogonal phase-locking on the third DC bus voltage U dc3 , the third DC current I dc3 , the fourth DC bus voltage U dc4 , and the fourth DC current I dc4 to obtain the corresponding amplitude and phase angle; Step S7: Calculate the battery internal resistance and polarization capacitance based on each of the amplitudes and phase angles; Step S8: After performing validity verification on each of the battery internal resistances and polarization capacitances, calculate the corresponding mean value for lithium battery health state monitoring.

2. The online detection method for the internal resistance of a lithium battery based on PCS according to claim 1, characterized in that: In the step S1, the acquisition process of the second DC bus voltage U dc2 is as follows: Collect the DC bus voltage U of the power grid dc , extract the first weak AC signal through a Butterworth second-order high-pass filter circuit with a cut-off frequency of 50 Hz to obtain the first DC bus voltage U dc1 , then amplify the extracted first weak AC signal through an operational amplifier circuit with a gain of 100 to obtain the second DC bus voltage U dc2 ; The acquisition process of the second DC current I dc2 is as follows: Collect the DC current I of the power grid dc , extract the second weak AC signal through a Butterworth second-order high-pass filter circuit with a cut-off frequency of 50 Hz to obtain the first DC current I dc1 , then amplify the extracted second weak AC signal through an operational amplifier circuit with a gain of 100 to obtain the second DC current I dc2 .

3. The online detection method for the internal resistance of a lithium battery based on PCS according to claim 1, characterized in that: The specific content of Step S2 is as follows: Synchronously rotating coordinate system phase-locked loop is used to perform grid phase-locking on the three-phase voltage U abc to obtain the grid frequency f b , multiply the grid frequency f b by 6 to obtain the 6th harmonic frequency f b3 , multiply the grid frequency f b by 12 to obtain the 12th harmonic frequency f b4 .

4. The online detection method for the internal resistance of a lithium battery based on PCS according to claim 1, characterized in that: In Step S3, the calculation formula for the filtering parameter is: Among them, G bpf (s) represents the filtering parameter; B represents the passband of the band-pass filter; ω c represents the center frequency; s represents the complex frequency of the transfer function; For the first band-pass filter and the second band-pass filter, B = 20π, ω c = 2πf b3 ; for the third band-pass filter and the fourth band-pass filter, B = 20π, ω c = 2πf b4 .

5. The online detection method for the internal resistance of a lithium battery based on PCS according to claim 1, characterized in that: The specific content of Step S4 is as follows: The first band-pass filter filters the second DC bus voltage U dc2 to obtain a third DC bus voltage U dc3 ; The second band-pass filter filters the second DC current I based on the filtering parameter dc2 to obtain a third DC current I dc3 ; The third band-pass filter filters the second DC bus voltage U dc2 to obtain a fourth DC bus voltage U dc4 ; The fourth band-pass filter filters the second DC current I based on the filtering parameter dc2 to obtain a fourth DC current I dc4 .

6. The online detection method for the internal resistance of a lithium battery based on PCS according to claim 1, characterized in that: The specific content of Step S6 is as follows: The first and second order generalized integrator performs orthogonal phase locking on the third DC bus voltage U dc3 to obtain the amplitude r dc3 and phase angle θ udc3 of the third DC bus voltage U udc3 ; The second second-order generalized integrator performs orthogonal phase locking on the third DC current I dc3 to obtain the amplitude r dc3 and the phase angle θ Idc3 of the third DC current I Idc3 ; The third second-order generalized integrator performs orthogonal phase locking on the fourth DC bus voltage U dc4 to obtain the amplitude r dc4 and phase angle θ udc4 of the fourth DC bus voltage U udc4 ; The fourth second-order generalized integrator performs quadrature phase locking on the fourth DC current I dc4 to obtain the amplitude r dc4 and phase angle θ Idc4 of the fourth DC current I Idc4 .

7. A method for online detection of the internal resistance of a lithium battery based on PCS, characterized in that: The specific content of Step S7 is as follows: Based on the said r udc3 , θ udc3 , r Idc3 and θ Idc3 calculate the battery internal resistance R b3 corresponding to the 6th harmonic frequency f in_6 and the polarization capacitance C po_6 : Based on the said r udc4 , θ udc4 , r Idc4 and θ Idc4 calculate the 12th harmonic frequency f b4 corresponding battery internal resistance R in_12 and polarization capacitance C po_12 :

8. A method for online detection of the internal resistance of a lithium battery based on PCS according to claim 7, characterized in that: The specific content of Step S8 is as follows: Determine the R in_6 and R in_12 Whether the error is less than 10%. If not, then R in_6 , C po_6 , R in_12 and C po_12 The validity check fails and the process ends; if so, then R in_6 , C po_6 , R in_12 and C po_12 The validity check passes, calculate the average value of the battery internal resistance R in and the average value of the polarization capacitance C po , and monitor the health state of the lithium battery based on the R in and C po :

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