A method and system for insulation monitoring of cascaded battery energy storage systems

Abstract

This invention discloses an insulation monitoring method and system for cascaded battery energy storage systems. The monitoring method includes the following steps: constructing a signal acquisition module, with a switch and bias resistor connected in series between the positive and negative busbars and ground; acquiring the voltages of the positive busbar to ground and the negative busbar to ground of the battery clusters when the first and second switches are in different on / off states; calculating the insulation resistance values ​​of the positive and negative busbars to ground based on the voltages of the positive and negative busbars to ground, and sending them to a fault diagnosis module; judging the insulation performance of each battery cluster based on the insulation resistance values, and sending the data to a control and protection module; and controlling the corresponding battery cluster to take control and protection actions based on the insulation performance data. The monitoring method proposed in this invention has a simple structure and can detect double-point grounding faults, unaffected by the equal or similar decrease in the insulation resistance of the positive and negative busbars to ground.

Description

Technical Field

[0001] This invention belongs to the field of energy storage system monitoring technology, and specifically relates to a method and system for insulation monitoring of cascaded battery energy storage systems. Background Technology

[0002] In recent years, with the rapid development of human society, the continuous demand for fossil fuel resources has triggered an increasingly severe energy crisis. At the same time, the multifaceted environmental pollution problems caused by the large-scale use of fossil fuels have become increasingly prominent, posing a serious threat to human survival. Currently, countries around the world are adjusting their domestic energy policies and actively carrying out research and development of new energy sources in an attempt to solve the energy crisis and environmental pollution problems through this approach. The development of new energy sources has become an important strategic move for most countries in the global energy sector, striving to provide a sustainable and clean energy supply for the future.

[0003] Due to the challenges of new energy power generation, such as supply randomness, unstable power output, and grid connection difficulties, the development of battery energy storage technology is particularly important. For battery energy storage systems, increasing storage capacity places higher demands on safety and lifespan. Distributing low-voltage battery modules on the DC side of each power module in a multilevel converter allows current battery technology to meet the needs of large-capacity battery energy storage systems, becoming the future direction for large-capacity energy storage system development. Cascaded H-bridge energy storage systems typically use cascaded power modules to boost voltage and then connect to the grid in a star or delta configuration. In this system, the battery system is divided into multiple battery modules, each connected to the DC side of each power module in the cascaded system. Due to the modular structure, the battery system has a higher equivalent voltage, resulting in a larger capacity, while the internal circulating current is relatively small, making it suitable for large-capacity battery systems. With the increase in capacity and cascading levels, especially in high-voltage battery integrated systems, insulation issues have become a key factor to consider in the design and application of battery energy storage systems. External intrusive high-voltage electrical faults can easily lead to the breakdown of the system's external insulation. Meanwhile, AC overvoltage transmission, common-mode interference, and converter failures can all trigger DC overvoltage and leakage current problems in battery systems, leading to internal insulation damage. Therefore, it is necessary to develop a DC insulation monitoring scheme for cascaded battery energy storage systems to ensure safe operation and meet the needs of new energy storage technologies.

[0004] Chinese invention patent application CN110794321A discloses a method and system for monitoring the insulation resistance of a battery energy storage device. The method acquires the actual insulation impedance between the casing and the battery module and the sinusoidal signal after replacing it with a standard resistor. The signal acquired in the time domain is Fourier transformed to obtain the frequency domain signal. A linear calibration method is used to obtain the linear relationship between the frequency domain amplitude and the impedance value of the sampled signal under the standard resistor and to obtain the slope, offset and unit of the relationship. The actual insulation impedance value and unit are obtained based on the frequency domain amplitude of the signal obtained under the actual insulation impedance, as well as the slope and offset.

[0005] This scheme provides a method for monitoring the insulation resistance of battery energy storage devices by injecting low-frequency AC signals. However, it is mainly aimed at the insulation detection of electric vehicle platforms with a battery system voltage platform of up to 800V. It lacks targeted design and applicability when facing large-capacity battery energy storage systems. Moreover, its structure and calculation are complex, and it cannot detect insulation faults when there are double-point grounding faults on the positive and negative busbars or when the insulation resistance of the positive and negative busbars to ground decreases equally or is similar. Summary of the Invention

[0006] This invention provides an insulation monitoring method and system for cascaded battery energy storage systems, aiming to solve the problems of existing technologies having complex structures and calculations, and being unable to detect insulation faults when there are double-point grounding faults on the positive and negative busbars or when the insulation resistance of the positive and negative busbars to ground decreases equally or is similar.

[0007] To solve the above-mentioned technical problems, the present invention proposes an insulation monitoring method, which includes the following steps:

[0008] S1: Construct a signal acquisition module, wherein a first switch and a bias resistor are connected in series between the positive bus and ground, and a second switch and a bias resistor are connected in series between the negative bus and ground.

[0009] S2: The signal acquisition module acquires the voltage to ground of the positive busbar and the voltage to ground of the battery cluster when the first switch and the second switch are in different on / off states;

[0010] S3: The signal acquisition module calculates the insulation resistance value of the positive bus to ground and the insulation resistance value of the negative bus to ground based on the voltage of the positive bus to ground and the voltage of the negative bus to ground, and sends them to the fault diagnosis module.

[0011] S4: The fault diagnosis module determines the insulation performance of each battery cluster based on the received signal and sends the battery cluster and its corresponding insulation performance data to the control and protection module.

[0012] S5: The control and protection module controls the corresponding battery cluster to take control and protection actions based on the received insulation performance data.

[0013] Preferably, step S2 specifically comprises:

[0014] S21: Close the first switch, open the second switch, and collect the voltage of the first positive bus to ground and the voltage of the first negative bus to ground;

[0015] S22: Disconnect the first switch, close the second switch, and collect the voltage to ground of the second positive bus and the voltage to ground of the second negative bus.

[0016] Preferably, the calculation method for the insulation resistance value of the positive busbar to ground and the insulation resistance value of the negative busbar to ground is as follows:

[0017] When the first switch is closed and the second switch is opened, the measured voltages of the first positive busbar to ground and the first negative busbar to ground should satisfy the following formula:

[0018]

[0019] When the first switch is opened and the second switch is closed, the measured voltages of the second positive busbar to ground and the second negative busbar to ground should satisfy the following formula:

[0020]

[0021] In the formula, V1 is the voltage of the first positive bus to ground, V2 is the voltage of the first negative bus to ground, R0 is the resistance of the bias resistor, and R + R is the insulation resistance value of the positive busbar to ground. - V′1 is the insulation resistance value of the negative busbar to ground, V′2 is the voltage of the second positive busbar to ground, and V′2 is the voltage of the second negative busbar to ground.

[0022] By solving the two equations simultaneously, the insulation resistance value R of the positive busbar to ground can be calculated. + and the insulation resistance value R of the negative busbar to ground - .

[0023] Preferably, the first switch and the second switch are one of an optocoupler switch, an opto-MOS relay, and a MOSFET.

[0024] Preferably, the insulation performance includes four levels:

[0025] Excellent, the measured insulation resistance value is greater than 1000Ω / V;

[0026] Good, the measured insulation resistance value range is (800, 1000] Ω / V;

[0027] Generally, the measured insulation resistance value ranges from 300 to 800 Ω / V;

[0028] Poor, the measured insulation resistance value is less than or equal to 300Ω / V.

[0029] Preferably, the control and protection actions include warning and disconnecting the battery cluster, warning, and taking no action.

[0030] Preferably, the acquisition and calculation cycle of the signal acquisition module is 10 seconds.

[0031] Preferably, the communication method between the signal acquisition module, the fault diagnosis module and the control and protection module is RS485.

[0032] Accordingly, the present invention also proposes an insulation monitoring system for cascaded battery energy storage systems, the system being configured to perform the above-described monitoring method, comprising:

[0033] The signal acquisition module has a first switch and a bias resistor connected in series between the positive bus and ground, and a second switch and a bias resistor connected in series between the negative bus and ground. It also acquires the voltage of the positive bus to ground and the voltage of the negative bus to ground of the battery cluster when the first switch and the second switch are in different on / off states. Based on the acquired voltage data, it calculates the insulation resistance values ​​of the positive bus and the negative bus to ground and sends them to the fault diagnosis module.

[0034] The fault diagnosis module determines the insulation performance of each battery cluster based on the received insulation resistance value to ground, and sends the battery cluster and its corresponding insulation performance data to the control and protection module.

[0035] The control and protection module controls the corresponding battery cluster to take control and protection actions based on the received insulation performance data.

[0036] Preferably, the system further includes a main control protection module, which communicates with other control protection modules via a serial port.

[0037] Compared with the prior art, the present invention has the following technical effects:

[0038] 1. The insulation monitoring method proposed in this invention calculates the insulation resistance to ground by adjusting the connection of the bias resistor. It has a simple structure and can detect double-point grounding faults in the positive and negative busbars. At the same time, it is not affected by the equal or similar decrease in the insulation resistance to ground of the positive and negative busbars.

[0039] 2. The insulation monitoring method proposed in this invention can cover a wide measurement range from low to high resistance values ​​by adjusting the bias resistor value, and is suitable for various resistance detection needs.

[0040] 2. The insulation monitoring method proposed in this invention can convert changes in the measured resistance into significant changes in the voltage signal. Even if the measured resistance changes slightly, a clear reading can be obtained at the output of the bridge, thus improving the sensitivity of the measurement.

[0041] 3. The insulation monitoring method proposed in this invention uses an optical MOS relay to control the connection of the bias resistor and controls the conduction and disconnection of the circuit through optical signals to achieve electrical isolation, which can effectively prevent leakage current from affecting the measurement accuracy. Attached Figure Description

[0042] Figure 1 This is a flowchart of the monitoring method described in this invention;

[0043] Figure 2 This is a schematic diagram of the detection circuit of the signal acquisition module according to an embodiment of the present invention;

[0044] Figure 3 This is a schematic diagram of the detection system structure described in this invention. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments of the present application and with reference to the accompanying drawings.

[0046] Example 1

[0047] like Figure 1 , 2 As shown, an insulation monitoring method for a cascaded battery energy storage system includes the following steps:

[0048] S1: Construct a signal acquisition module. The positive bus of the signal acquisition module is connected to ground via a first switch K1 and a bias resistor R0 in series, and the negative bus is connected to ground via a second switch K2 and a bias resistor R0 in series. The bias resistors R0 connected in series on the positive and negative bus have the same resistance value. Since the detection accuracy is directly related to the ratio of the bias resistor R0 to the resistance to be measured, the detection error is minimized when the bias resistor R0 is much smaller than the insulation resistance. However, an excessively low bias resistor R0 will significantly reduce the insulation resistance of the energy storage system, leading to additional failure risks. Therefore, the value of the bias resistor R0 is generally chosen to be in the MΩ range.

[0049] To reduce the impact on the circuit under test, a higher input impedance is selected. In this embodiment, the first switch K1 and the second switch K2 are optical MOS relays. In other embodiments of the present invention, the first switch K1 and the second switch K2 can also be optocouplers or MOSFETs. Using optical MOS relays or optocouplers, electrical isolation between the input and output can be achieved optically, preventing potential high voltage or interference signals from being transmitted back to the measuring equipment from the circuit under test, protecting the safety of the equipment and operators, and improving the accuracy of the measurement.

[0050] S2: The signal acquisition module acquires the voltage between the positive busbar and the ground of the battery cluster and the voltage between the negative busbar and the ground when the first switch K1 and the second switch K2 are in different on / off states.

[0051] Specifically, first, close the first switch K1 and open the second switch K2, and collect the voltage V1 of the first positive bus to ground and the voltage V2 of the first negative bus to ground.

[0052] Then disconnect the first switch K1, close the second switch K2, and collect the voltage V′1 of the second positive bus to ground and the voltage V′2 of the second negative bus to ground.

[0053] S3: The signal acquisition module calculates the insulation resistance values ​​of the positive bus to ground and the negative bus to ground based on the voltage of the positive bus to ground and the voltage of the negative bus to ground, and sends them to the fault diagnosis module.

[0054] The calculation methods for the insulation resistance values ​​(V1, V′1) of the positive busbar to ground and the insulation resistance values ​​(V2, V′2) of the negative busbar to ground are as follows:

[0055] When the first switch K1 is closed and the second switch K2 is opened, the measured voltage V1 of the first positive bus to ground and the voltage V2 of the first negative bus to ground should satisfy the following formula:

[0056]

[0057] When the first switch K1 is opened and the second switch K2 is closed, the measured voltage V′1 of the second positive bus to ground and the voltage V′2 of the second negative bus to ground should satisfy the following formula:

[0058]

[0059] In the formula, V1 is the voltage of the first positive bus to ground, V2 is the voltage of the first negative bus to ground, R0 is the resistance of the bias resistor, and R + R is the insulation resistance value of the positive busbar to ground. - V'1 is the insulation resistance value of the negative busbar to ground, V'2 is the voltage of the second positive busbar to ground, and R0 / / R + This indicates that the bias resistor is connected in parallel with the insulation resistance of the positive busbar to ground, R0 / / R - This indicates that the bias resistor is connected in parallel with the insulation resistance of the negative busbar to ground;

[0060] By combining the two equations above, the insulation resistance value R of the positive busbar to ground can be calculated. + and the insulation resistance value R of the negative busbar to ground - In this embodiment, the signal acquisition module has an acquisition and calculation cycle of 10 seconds, that is, it acquires V1, V2, V′1, and V′2 every 10 seconds and calculates the corresponding R.+ R - .

[0061] This calculation method can detect double-point grounding faults in both positive and negative busbars, and is not affected by the equal or similar decrease in the insulation resistance to ground of both positive and negative busbars.

[0062] S4: The fault diagnosis module determines the insulation performance of each battery cluster based on the received signal and sends the battery cluster and its corresponding insulation performance data to the control and protection module.

[0063] In this embodiment, the fault diagnosis module, according to the battery cluster insulation performance requirements specified in GB / T 36276-2018 Lithium-ion Batteries for Power Storage, stipulates that the insulation resistance between the positive and negative electrodes of the battery cluster and external conductive parts should not be less than 1000Ω / V. Therefore, this can be used to set the fault diagnosis threshold and classify the insulation level. Different insulation levels send corresponding signals to the control and protection module to achieve different control operations. The insulation performance includes four levels:

[0064] Excellent, the measured insulation resistance value is greater than 1000Ω / V;

[0065] Good, the measured insulation resistance value range is (800, 1000] Ω / V;

[0066] Generally, the measured insulation resistance value ranges from 300 to 800 Ω / V;

[0067] Poor, the measured insulation resistance value is less than or equal to 300Ω / V.

[0068] S5: The control and protection module controls the corresponding battery cluster to take control and protection actions based on the received insulation performance data.

[0069] In this embodiment, the control and protection actions include issuing a warning and disconnecting the battery cluster, issuing a warning, and taking no action. Details are shown in Table 1 below:

[0070] Table 1 Threshold settings and function implementation of the fault diagnosis module

[0071]

[0072] The fault diagnosis module determines the corresponding insulation performance and insulation level based on the insulation resistance value. The control and protection module then controls the corresponding battery cluster to take control and protection actions based on the received insulation performance data. If the insulation resistance value received by the fault diagnosis module is greater than 1000Ω / V, the insulation performance is determined to be excellent, and the insulation level is no insulation fault; accordingly, the control and protection module does not take any measures. If the insulation resistance value received by the fault diagnosis module is greater than 800Ω / V and less than or equal to 1000Ω / V, the insulation performance is determined to be good, and the insulation level is Class I; accordingly, the control and protection module issues a warning. If the insulation resistance value received by the fault diagnosis module is greater than 300Ω / V and less than or equal to 800Ω / V, the insulation performance is determined to be average, and the insulation level is Class II; accordingly, the control and protection module issues a warning and controls the relevant circuit of the battery cluster to disconnect from the battery cluster. If the insulation resistance value received by the fault diagnosis module is less than or equal to 300Ω / V, the insulation performance is determined to be poor, and the insulation level is Class III; accordingly, the control and protection module issues a warning and controls the relevant circuit of the battery cluster to disconnect from the battery cluster.

[0073] In this embodiment, after the fault diagnosis module issues a warning message, it notifies the operation and maintenance personnel to conduct troubleshooting.

[0074] In this embodiment, the communication method between the signal acquisition module, the fault diagnosis module and the control and protection module is RS485. In other embodiments of the present invention, RS232, Ethernet, CAN bus, I2C and other solutions may also be used.

[0075] The monitoring method in this embodiment can monitor the insulation resistance values ​​to ground of the positive and negative busbars of the battery cluster DC system. The voltage measurement range of the positive and negative busbars to ground is 100V to 1500V, and the calculated resistance value to ground ranges from 0Ω to 10MΩ. Compared with the existing technology for battery system insulation monitoring of electric vehicles, where the voltage platform of existing electric vehicles is at most 800V, the insulation monitoring method proposed in this invention has better applicability when used in energy storage systems with voltages higher than 800V.

[0076] Example 2

[0077] like Figure 3 As shown, an insulation monitoring system for a cascaded battery energy storage system is configured to perform a monitoring method as described in Embodiment 1, comprising:

[0078] A signal acquisition module (or signal acquisition device) is provided. The positive busbar of the signal acquisition module is connected in series with a first switch and a bias resistor, and the negative busbar is connected in series with a second switch and a bias resistor. The module also acquires the voltage to ground of the positive busbar and the negative busbar of the battery cluster when the first and second switches are in different on / off states. Based on the acquired voltage data, the insulation resistance values ​​to ground of the positive and negative busbars are calculated and sent to the fault diagnosis module. Each battery cluster has one signal acquisition module, with circuits leading from the positive and negative terminals of the battery cluster to the positive and negative busbars of the signal acquisition module. The positive and negative busbars are connected to the ground of the signal acquisition module through these circuits.

[0079] The fault diagnosis module determines the insulation performance of each battery cluster based on the received insulation resistance value to ground, and sends the battery cluster and its corresponding insulation performance data to the control and protection module.

[0080] The control and protection module controls the corresponding battery cluster to take control and protection actions based on the received insulation performance data. When it is necessary to disconnect the battery cluster, the control and protection module controls the switches on the positive and negative terminals of the corresponding battery cluster. If a grounding fault is detected in battery cluster 1, the connection of battery cluster 1 needs to be disconnected until maintenance personnel check and troubleshoot the fault and then reconnect it. At this time, the control and protection module will disconnect switches 11 and 12 controlling battery cluster 1, and reset and reconnect them after maintenance personnel troubleshoot the fault.

[0081] The signal acquisition module, fault diagnosis module, and control and protection module are connected in groups, that is, each battery cluster includes a signal acquisition module, a fault diagnosis module, and a control and protection module.

[0082] In this embodiment, the sampling period of the signal acquisition module is 10s. In other embodiments of the present invention, the sampling period can be set according to actual needs, and the setting range is 1 to 1000s.

[0083] In this embodiment, the communication between the signal acquisition module, the fault diagnosis module, and the control and protection module is via serial communication, specifically RS485 or RS232. In other embodiments of the present invention, Ethernet, CAN bus, I2C, or other similar communication methods may also be used.

[0084] The system also includes a main control protection module, which communicates with other control protection modules via a serial port.

[0085] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several modifications and improvements without departing from the inventive concept of the present invention, and these all fall within the protection scope of the present invention.

Claims

1. A method for monitoring insulation of a cascaded battery energy storage system, characterized by, The method comprises the following steps: S1: a signal acquisition module is constructed, a first switch and a bias resistor are connected in series between a positive bus of the signal acquisition module and the ground, and a second switch and a bias resistor are connected in series between a negative bus and the ground; S2: the signal acquisition module collects the positive bus-to-ground voltage and the negative bus-to-ground voltage of the battery cluster when the first switch and the second switch are in different on-off states; the specific method is: S21: the first switch is closed, the second switch is opened, and the first positive bus-to-ground voltage and the first negative bus-to-ground voltage are collected; S22: the first switch is opened, the second switch is closed, and the second positive bus-to-ground voltage and the second negative bus-to-ground voltage are collected; S3: the signal acquisition module calculates the positive bus-to-ground insulation resistance value and the negative bus-to-ground insulation resistance value according to the positive bus-to-ground voltage and the negative bus-to-ground voltage, and sends the values to a fault diagnosis module; the calculation method is: when the first switch is closed and the second switch is opened, the measured first positive bus-to-ground voltage and the first negative bus-to-ground voltage should satisfy the following formula: when the first switch is opened and the second switch is closed, the measured second positive bus-to-ground voltage and the second negative bus-to-ground voltage should satisfy the following formula: wherein, is the voltage of the first positive bus to ground, is the voltage of the first negative bus to ground, is the resistance value of the bias resistor, is the insulation resistance value of the positive bus to ground, is the insulation resistance value of the negative bus to ground, is the voltage of the second positive bus to ground, is the voltage of the second negative bus to ground; Simultaneously solving the two equations, the positive bus-to-ground insulation resistance value and the negative bus-to-ground insulation resistance value are calculated; S4: the fault diagnosis module judges the insulation performance of each battery cluster according to the received signals, and sends the battery cluster and the corresponding insulation performance data to a control protection module; S5: the control protection module controls the corresponding battery cluster to take control protection actions according to the received insulation performance data.

2. The method for monitoring insulation of a cascade battery energy storage system according to claim 1, wherein, The first switch and the second switch are one of a photoelectric coupling switch, a photo MOS relay and a MOSFET.

3. The method for monitoring insulation of a cascaded battery energy storage system according to claim 1, wherein, The insulation performance includes four levels: excellent, the measured insulation resistance value is greater than 1000Ω / V; good, the measured insulation resistance value ranges from 800 to 1000Ω / V; general, the measured insulation resistance value ranges from 300 to 800Ω / V; poor, the measured insulation resistance value is less than or equal to 300Ω / V.

4. The method for monitoring insulation of a cascaded battery energy storage system according to claim 1, wherein, The control protection actions include warning and disconnecting the battery cluster, warning, and taking no measures.

5. The method for monitoring insulation of a cascaded battery energy storage system according to claim 1, wherein, The collection and calculation period of the signal acquisition module is 10s.

6. The method for monitoring insulation of a cascaded battery energy storage system of claim 1, wherein, The communication mode between the signal acquisition module, the fault diagnosis module and the control protection module adopts RS485.

7. An insulation monitoring system for a cascaded battery energy storage system, characterized by The system is configured to perform the monitoring method according to any one of claims 1-6, comprising: a signal acquisition module, a first switch and a bias resistor connected in series between a positive bus of the signal acquisition module and the ground, and a second switch and a bias resistor connected in series between a negative bus and the ground; the signal acquisition module also collects the positive bus-to-ground voltage and the negative bus-to-ground voltage of the battery cluster when the first switch and the second switch are in different on-off states, and sends the positive bus-to-ground insulation resistance value and the negative bus-to-ground insulation resistance value calculated according to the collected voltage data to a fault diagnosis module; a fault diagnosis module, which judges the insulation performance of each battery cluster according to the received ground insulation resistance value, and sends the battery cluster and the corresponding insulation performance data to a control protection module; a control protection module, which controls the corresponding battery cluster to take control protection actions according to the received insulation performance data.

8. An insulation monitoring system for a cascaded battery energy storage system according to claim 7, characterized in that The system further comprises a master protection module, which communicates with other control protection modules through a serial port.

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