Detection system and method for separation of storage battery pack from DC bus

Abstract

The invention discloses a detection system and method for separation of a storage battery pack from a DC bus, and belongs to the technical field of storage battery pack operation and maintenance detection. The system comprises a direct current bus, a storage battery pack, a measuring module, a single battery management module and a control module, and a positive bus of the direct current bus is connected with a positive electrode of the storage battery pack to form a positive electrode circuit; a negative bus of the direct-current bus is connected with the cathode of the storage battery pack to form a cathode circuit; the storage battery pack comprises a plurality of single batteries, and the single battery management module is connected with any single battery in parallel; the measurement module is connected with the DC bus, the storage battery pack, the positive line and the negative line. The control module is connected with the measurement module and the single battery management module, and the control module is used for controlling the on-off state of the single battery management module and detecting the connection state of the storage battery pack and the direct current bus according to the output result of the measurement module. The embodiment of the invention can improve the accuracy of detecting whether the storage battery pack is separated from the DC bus.

Description

Technical Field

[0001] The present application relates to the technical field of battery pack operation and maintenance detection, and in particular to a detection system and method for a battery pack being disconnected from a DC bus. Background Art

[0002] Ensuring normal power supply is an important foundation for the stable development of all industries. Since the industrial power grid may not be able to supply power normally under special circumstances, it will cause the DC system to lose power and make important equipment unable to work. Therefore, in addition to the normal power supply of the industrial power grid, a backup power supply system is required. The battery pack is the core component of the backup power supply system, which can provide real-time backup power supply for each circuit and equipment and provide power support for the substation. When the AC power fails, the battery pack disconnects from the DC bus, which may cause the entire system to lose power, threatening the safe operation of the substation and causing significant losses. Therefore, it is very important to detect whether the battery pack is disconnected from the DC bus. Summary of the invention

[0003] The purpose of the embodiments of the present application is to provide a system and method for detecting whether a battery pack is disconnected from a DC bus, which can improve the accuracy of detecting whether a battery pack is disconnected from a DC bus and improve the reliability and safety of a power supply system.

[0004] To achieve the above-mentioned purpose, a first aspect of an embodiment of the present application provides a detection system for a battery pack being separated from a DC bus, the system comprising a DC bus, a battery pack, a measurement module, a single battery management module and a control module, wherein:

[0005] The positive busbar of the DC busbar is connected to the positive electrode of the battery pack to form a positive electrode circuit;

[0006] The negative busbar of the DC busbar is connected to the negative electrode of the battery pack to form a negative electrode circuit;

[0007] The battery pack includes a plurality of single cells, and the single cell management module is connected in parallel with any of the single cells;

[0008] The measuring module is respectively connected to the DC bus, the battery pack, the positive line and the negative line;

[0009] The control module is connected to the measurement module and the single battery management module respectively. The control module is used to control the switch state of the single battery management module and detect the connection state between the battery pack and the DC bus according to the output result of the measurement module.

[0010] Compared with the prior art, the embodiment of the present application provides a detection system for battery packs being separated from the DC bus, and its beneficial effects are: the DC bus is connected to the battery pack through positive and negative lines, the single battery management module is connected in parallel with a single battery in the battery pack, and the measurement module is respectively connected to the DC bus, the battery pack, and the positive and negative lines, and the output data of each part can be collected in real time and accurately. The control module is connected to the measurement module on the one hand to obtain the output data, and on the other hand to control the switch state of the single battery management module, and can efficiently and accurately detect the connection state of the battery pack and the DC bus through the switch state of the single battery management module and the output data of the measurement module, that is, improve the accuracy of detecting whether the battery pack is separated from the DC bus, and improve the reliability and safety of the power supply system.

[0011] In some embodiments, the measurement module includes a first amplifying unit connected in parallel with the DC bus and a second amplifying unit connected in parallel with the battery pack, and the first amplifying unit and the second amplifying unit are respectively connected to the control module.

[0012] In some embodiments, the measurement module also includes a first Hall current sensor surrounding the negative pole circuit and a first differential amplifier unit connected to the output end of the first Hall current sensor, a second Hall current sensor surrounding the positive pole circuit and a second differential amplifier unit connected to the output end of the second Hall current sensor, and the first differential amplifier unit and the second differential amplifier unit are respectively connected to the control module.

[0013] In some embodiments, the single battery management module includes:

[0014] a first switch, wherein one end of the first switch is connected to the negative electrode of the single battery, and the other end of the first switch is connected to the switch control end of the control module;

[0015] A first resistor, one end of the first resistor is connected to the other end of the first switch, and the other end of the first resistor is connected to the positive electrode of the single battery.

[0016] In some embodiments, the control module includes:

[0017] A signal unit, wherein the signal unit is used to generate and send out a fault alarm signal according to the disconnection state of the battery pack and the DC bus.

[0018] To achieve the above object, a second aspect of an embodiment of the present application provides a method for detecting that a battery pack is disconnected from a DC bus, which is applied to the system as described in the first aspect, and comprises the following steps:

[0019] Obtaining an output result of the measurement module;

[0020] The control module controls the switch state of the single battery management module, and detects the connection state between the battery pack and the DC bus according to the output result of the measurement module.

[0021] In some embodiments, the method further comprises:

[0022] When the battery pack is normally charged, the first switch is in an open state, and the output current of the second differential amplifier unit is less than a preset small current, the control module switches the first switch from an open state to a closed state;

[0023] When the first switch is closed, the output current of the second differential amplifier unit is less than a preset small current, and it is detected that the battery pack is disconnected from the DC bus;

[0024] When the first switch is closed, the output current of the second differential amplifier unit is greater than the preset small current, and it is detected that the battery pack and the DC bus are in a connected state.

[0025] In some embodiments, the method further comprises:

[0026] When the battery pack is normally charged at a preset voltage, the first switch is in an off state, and the output current of the first differential amplifier unit is greater than a preset high current;

[0027] If the output current of the first differential amplifier unit suddenly changes to zero, the output voltage of the first amplifier unit is the same as the preset voltage, and the output voltage of the first amplifier unit is greater than the output voltage of the second amplifier unit, it is detected that the battery pack is disconnected from the DC bus.

[0028] In some embodiments, the method further comprises:

[0029] When the battery pack is normally charged at a preset voltage, the first switch is in an off state, and the output current of the first differential amplifier unit is greater than a preset high current;

[0030] If the output voltage of the first amplifying unit is greater than the output voltage of the second amplifying unit, and the output voltage difference between the first amplifying unit and the second amplifying unit is less than a preset value, it is detected that the battery pack is in a connected state with the DC bus.

[0031] In some embodiments, the method further comprises:

[0032] When it is detected that the battery pack is disconnected from the DC bus, the signal unit generates and sends a fault alarm signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1It is a structural schematic diagram of a detection system for a battery pack being disconnected from a DC bus in an embodiment of the present application;

[0034] Figure 2 It is another structural schematic diagram of a detection system for a battery pack being disconnected from a DC bus in an embodiment of the present application. DETAILED DESCRIPTION

[0035] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0036] In the description of the present application, it should be understood that the terms "center", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0037] The terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, unless otherwise specified, "plurality" means two or more.

[0038] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0039] First, some nouns involved in this application are analyzed:

[0040] Charger: An electrical device that converts alternating current into direct current suitable for battery charging and adjusts the output voltage and current according to the characteristics and charging status of the battery to achieve safe and efficient charging.

[0041] Ensuring normal power supply is an important foundation for the stable development of all industries. Since the industrial power grid may not be able to supply power normally under special circumstances, it will cause the DC system to lose power and make important equipment unable to work. Therefore, in addition to the normal power supply of the industrial power grid, a backup power supply system is required. The battery pack is the core component of the backup power supply system, which can provide real-time backup power supply for each circuit and equipment and provide power support for the substation. When the AC power fails, the battery pack disconnects from the DC bus, which may cause the entire system to lose power, threatening the safe operation of the substation and causing significant losses. Therefore, it is very important to detect whether the battery pack is disconnected from the DC bus.

[0042] See also Figure 1 , is a structural schematic diagram of a detection system for a battery pack disconnected from a DC bus provided in an embodiment of the present application. The detection system for a battery pack disconnected from a DC bus includes a DC bus, a battery pack, a measurement module, a single battery management module, and a control module. Among them, the positive bus HM+ of the DC bus is connected to the positive electrode of the battery pack to form a positive electrode circuit; the negative bus HM- of the DC bus is connected to the negative electrode of the battery pack to form a negative electrode circuit; the battery pack includes a number of single cells, and the single battery management module is connected in parallel with any single cell; the measurement module is respectively connected to the DC bus, the battery pack, the positive electrode circuit, and the negative electrode circuit; the control module is respectively connected to the measurement module and the single battery management module, and the control module is used to control the switch state of the single battery management module, and detect the connection state of the battery pack and the DC bus according to the output result of the measurement module.

[0043] Compared with the prior art, the embodiment of the present application provides a detection system for battery packs being separated from the DC bus, and its beneficial effects are: the DC bus is connected to the battery pack through positive and negative lines, the single battery management module is connected in parallel with a single battery in the battery pack, and the measurement module is respectively connected to the DC bus, the battery pack, and the positive and negative lines, and the output data of each part can be collected in real time and accurately. The control module is connected to the measurement module on the one hand to obtain the output data, and on the other hand to control the switch state of the single battery management module, and can efficiently and accurately detect the connection state of the battery pack and the DC bus through the switch state of the single battery management module and the output data of the measurement module, that is, improve the accuracy of detecting whether the battery pack is separated from the DC bus, and improve the reliability and safety of the power supply system.

[0044] See also Figure 2 , is another structural schematic diagram of a detection system for a battery pack disconnected from a DC bus provided in an embodiment of the present application.

[0045] The charger is connected in parallel with the battery pack through the DC bus, and is used to charge the battery pack. In the battery charging process, there are two important charging stages: equalizing charging and floating charging. Equalizing charging and floating charging play a key role in maintaining the performance of the battery and extending its service life.

[0046] Equalization charging usually refers to balanced charging, and its charging current is set to 1 / 10H of the battery capacity. Here, "H" represents the hour rate. For example, if the battery capacity is 100Ah (ampere-hour), according to the equalization current requirement of 1 / 10H, the equalization current is 10A. The purpose of equalization charging is to ensure that each single cell in the battery pack can be fully charged, to avoid the charging difference between each single cell during use, resulting in some batteries being in a long-term undercharged state, thereby affecting the performance and life of the entire battery pack. During the equalization charging stage, the charging equipment will charge the battery with a relatively large and stable current, causing the battery voltage to gradually rise until it reaches the set equalization voltage value.

[0047] Floating charge is a charging method that maintains the battery power, which aims to compensate for the power loss caused by the self-discharge of the battery and keep the battery in a fully charged state at all times. In the embodiment of the present application, when the charging current is less than 2A, the battery can be considered to be in the floating charge stage. The current in the floating charge stage is relatively small. It can not only replenish the power consumed by the self-discharge of the battery, but also will not cause overcharging of the battery, thereby effectively extending the service life of the battery. In the floating charge state, the battery is basically in a fully charged standby state, ready to provide electrical energy to the load at any time. In the embodiment of the present application, when the charging current is 1 / 10H of the battery capacity, the battery pack is in an equalized charge state. When the charging current is less than 2A, the battery pack is in a floating charge state.

[0048] The measuring module comprises a first amplifying unit connected in parallel with the DC bus and a second amplifying unit connected in parallel with the battery pack. The first amplifying unit and the second amplifying unit are respectively connected with the control module.

[0049] It should be noted that the measurement module can be a battery management module BMU, the measurement result of the first amplification unit is the voltage value of the DC bus, the measurement result of the second amplification unit is the voltage value of the battery pack, and the control module includes multiple signal input terminals, which can directly obtain the voltage value of the DC bus and the voltage value of the battery pack. The first amplification unit and the second amplification unit can both include a chip with model HT7017, and the first amplification unit and the second amplification unit are both amplification circuits centered on the chip model HT7017. When the voltage is collected, after the voltage signal is input, the HT7017 adjusts the internal circuit and outputs an amplified or processed voltage signal, thereby realizing the collection and amplification functions of the input voltage.

[0050] The measurement module also includes a first Hall current sensor HR1 surrounding the negative pole circuit and a first differential amplifier unit connected to the output end of the first Hall current sensor HR1, a second Hall current sensor HR2 surrounding the positive pole circuit and a second differential amplifier unit connected to the output end of the second Hall current sensor HR2, and the first differential amplifier unit and the second differential amplifier unit are respectively connected to the control module.

[0051] It should be noted that the battery pack can be a lead-acid battery. The lead-acid battery itself has a large self-discharge. Generally speaking, its floating charge current range is between 200mA-2A, and the specific value will vary according to the capacity of different battery packs. In view of this, the embodiment of the present application adopts a high-precision second Hall current sensor HR2 for floating charge current detection, and its sensor range can be selected to be around 2A. The second Hall current sensor HR2 is a Hall sensor that only cuts the top but is not damaged when the range is exceeded. It has a super overload characteristic to ensure that it will not be damaged in the case of equalized charging with large current. At the same time, this solution is also equipped with a first Hall current sensor HR1, which is used to measure the charging current during equalized charging. This combination realizes the accurate monitoring and control of the current of the lead-acid battery at different charging stages.

[0052] It should be noted that based on Kirchhoff's current law, in a closed loop, the current flowing into a node is equal to the current flowing out of the node. Therefore, the current through the negative line is equal to the current through the positive line, but in the opposite direction.

[0053] It should be noted that the Hall current sensor works based on the Hall effect principle, that is, when current passes through a conductor, a Hall voltage is generated in a direction perpendicular to the current and the magnetic field. The sensor determines the magnitude and direction of the current by detecting this Hall voltage. Generally, the positive direction of the current of the second Hall current sensor HR2 points to the battery, and the negative direction points to the charger. If the collected current is positive, it indicates that it is a charging current; if the collected current is negative, it indicates that it is a discharging current.

[0054] For the second Hall current sensor HR2 wrapped around the positive line, ensure that the charging current flows in from the front side (usually the side with the mark) of the second Hall current sensor HR2 and flows out from the back side. In this way, according to the polarity regulations of the sensor and the internal circuit design, the output current signal will be positive. Generally speaking, the current in the negative line flows out from the negative pole of the battery pack and returns to the negative pole of the charger. At this time, the current in the negative line should flow in from the back side of the first Hall current sensor HR1 and out from the front side, so that the output is positive.

[0055] It should be noted that the first differential amplifier unit connected to the output end of the first Hall current sensor HR1 and the second differential amplifier unit connected to the output end of the second Hall current sensor HR2 both include a differential amplifier circuit centered around the chip model OPA2188.

[0056] The OPA2188 chip is a high-performance operational amplifier with low noise, high precision, high bandwidth and other characteristics. It is very suitable for amplifying weak signals, which is critical for amplifying weak voltage signals converted after current acquisition. After the Hall current sensor is connected to the differential amplifier circuit based on OPA2188, the output signal is usually a voltage signal, but the first differential amplifier unit and the second differential amplifier unit of the embodiment of the present application also include a voltage-current conversion circuit or a V / I conversion chip, which can first convert the output voltage signal into a current signal and then output it to the control module.

[0057] The single battery management module includes a first switch K1 and a first resistor R1, one end of the first switch K1 is connected to the negative electrode of the single battery, and the other end of the first switch K1 is connected to the switch control end of the control module; one end of the first resistor R1 is connected to the other end of the first switch K1, and the other end of the first resistor R1 is connected to the positive electrode of the single battery.

[0058] The control module includes a signal unit (not shown in the figure), which is used to generate and send a fault alarm signal according to the disconnection state of the battery pack and the DC bus. The control module can be an MCU, and the control module includes a comparison circuit inside, which can compare the output result of the measurement module and output the detection result.

[0059] An embodiment of the present application also discloses a method for detecting when a battery pack is disconnected from a DC bus, which is applied to a system as described above and includes the following steps: obtaining the output result of a measurement module; a control module controls the switching state of a single battery management module, and detects the connection state between the battery pack and the DC bus according to the output result of the measurement module.

[0060] It should be noted that the output result of the measurement module includes the output current of the first differential amplifier unit (equalizing current I1), the output current of the second differential amplifier unit (floating current I2), the output voltage of the first amplifier unit (bus voltage U1) and the output voltage of the second amplifier unit (battery group terminal voltage U2). The embodiment of the present application can compare the two voltage values ​​of the bus voltage U1 and the battery group terminal voltage U2, analyze the comparison results, and promptly determine whether the battery group is disconnected from the bus, thereby ensuring the safe and stable operation of the DC system and safeguarding the safe operation of other equipment.

[0061] However, because the floating charge current is small, it is difficult to identify from the voltage dimension alone, and additional current is required for identification.

[0062] Exemplarily, in one embodiment, when the battery pack is normally charged (floating charge), the first switch is in the disconnected state, and the output current I2 of the second differential amplifier unit is generally in the range of 200mA-2A. When the output current I2 of the second differential amplifier unit is less than the preset small current, the preset small current can be tens of milliamperes, which is close to zero current. When I2 is less than the preset small current, it is preliminarily identified as a bus abnormality. At this time, the embodiment of the present application can first measure the voltage of each single cell in the battery pack, and then connect the single cell management module in parallel with the single cell with the highest voltage, and the control module then switches the first switch K1 from the disconnected state to the closed state. After closing, the battery is discharged (the discharge current is less than 2A).

[0063] It should be noted that switching the first switch K1 from an open state to a closed state can be achieved by the control module, or by the measurement module (BMU) sending a passive balancing command to the single battery management module of the highest voltage cell in the battery pack, but is not limited thereto.

[0064] When the first switch is closed, the output current of the second differential amplifier unit (floating charge current I2) is still smaller than the preset small current or the floating charge current I2 does not change and is still very small, and the battery pack is detected to be disconnected from the DC bus. When the battery pack is detected to be disconnected from the DC bus, the signal unit generates a fault alarm signal and sends it out.

[0065] When the first switch is closed, the output current I2 of the second differential amplifier unit is greater than the preset small current, and I2 recovers to several hundred mA (less than 2 A), and it is detected that the battery pack is in a connected state with the DC bus.

[0066] In another embodiment, when the battery pack is normally charged at a preset voltage (equalized charging), the first switch is in an off state, and the output current I1 of the first differential amplifier unit is greater than the preset high current;

[0067] It should be noted that the preset voltage is the set voltage of the charger, and the set voltage of the charger is generally slightly greater than or equal to the output voltage of the charger (ie, the bus voltage U1); the preset large current can be 1A or other preset values, and this application does not make specific limitations on this.

[0068] When the output current I1 of the first differential amplifier unit is greater than 1A, for example, I1 is several amperes or tens of amperes, if the output voltage U1 of the first amplifier unit is greater than the output voltage U2 of the second amplifier unit, and the output voltage difference ΔU (ΔU=U1-U2) between the first amplifier unit and the second amplifier unit is within the preset value (preset value=I*R=current*line impedance) range (that is, ΔU is less than the preset value), then it is detected that the battery pack is in a connected state with the DC bus.

[0069] Under normal circumstances of the charger, if the output current I1 of the first differential amplifier unit suddenly changes from a state greater than the preset large current to zero, the output voltage U1 of the first amplifier unit is the same as or close to the preset voltage (the set voltage of the charger), the output voltage U1 of the first amplifier unit is greater than the output voltage U2 of the second amplifier unit and the output voltage difference ΔU (ΔU=U1-U2) is large, then the battery pack is detected to be disconnected from the DC bus. When the battery pack is detected to be disconnected from the DC bus, the signal unit generates a fault alarm signal and sends it out.

[0070] The embodiment of the present application sets different detection methods for different states of the battery pack during equalization charging or floating charging, and can identify DC bus disconnection from two dimensions of voltage and current, which is more accurate than the traditional voltage comparison method and current judgment method.

[0071] A person skilled in the art can understand that all or part of the processes in the above-mentioned embodiments can be implemented by instructing the relevant hardware through a computer program, and the program can be stored in a computer-readable storage medium, and when the program is executed, it can include the processes of the embodiments of the above-mentioned methods. The storage medium can be a disk, an optical disk, a read-only memory (ROM) or a random access memory (RAM), etc.

[0072] The above is a preferred embodiment of the present application. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present application. These improvements and modifications are also considered to be within the scope of protection of the present application.

Claims

1. A detection system for a battery pack being disconnected from a DC bus, characterized in that: The system includes a DC bus, a battery pack, a measurement module, a single battery management module and a control module, wherein: The positive busbar of the DC busbar is connected to the positive electrode of the battery pack to form a positive electrode circuit; The negative busbar of the DC busbar is connected to the negative electrode of the battery pack to form a negative electrode circuit; The battery pack includes a plurality of single cells, and the single cell management module is connected in parallel with any of the single cells; The measuring module is respectively connected to the DC bus, the battery pack, the positive line and the negative line; The control module is connected to the measurement module and the single battery management module respectively. The control module is used to control the switch state of the single battery management module and detect the connection state between the battery pack and the DC bus according to the output result of the measurement module.

2. The detection system for battery pack disconnection from the DC bus as claimed in claim 1, characterized in that: The measuring module comprises a first amplifying unit connected in parallel with the DC bus and a second amplifying unit connected in parallel with the battery pack. The first amplifying unit and the second amplifying unit are respectively connected with the control module.

3. The detection system for battery pack disconnection from the DC bus as claimed in claim 1, characterized in that: The measurement module also includes a first Hall current sensor surrounding the negative pole circuit and a first differential amplifier unit connected to the output end of the first Hall current sensor, a second Hall current sensor surrounding the positive pole circuit and a second differential amplifier unit connected to the output end of the second Hall current sensor, and the first differential amplifier unit and the second differential amplifier unit are respectively connected to the control module.

4. The detection system for battery pack disconnection from the DC bus as claimed in claim 1, characterized in that: The single battery management module comprises: a first switch, wherein one end of the first switch is connected to the negative electrode of the single battery, and the other end of the first switch is connected to the switch control end of the control module; A first resistor, one end of the first resistor is connected to the other end of the first switch, and the other end of the first resistor is connected to the positive electrode of the single battery.

5. The detection system for battery pack disconnection from the DC bus as claimed in claim 1, characterized in that: The control module comprises: A signal unit, wherein the signal unit is used to generate and send out a fault alarm signal according to the disconnection state of the battery pack and the DC bus.

6. A method for detecting when a battery pack is disconnected from a DC bus, applied to a system as claimed in any one of claims 1 to 5, characterized in that: The steps include: Obtaining an output result of the measurement module; The control module controls the switch state of the single battery management module, and detects the connection state between the battery pack and the DC bus according to the output result of the measurement module.

7. The method for detecting battery pack disconnection from a DC bus as claimed in claim 6, characterized in that: The method further comprises: When the battery pack is normally charged, the first switch is in an open state, and the output current of the second differential amplifier unit is less than a preset small current, the control module switches the first switch from an open state to a closed state; When the first switch is closed, the output current of the second differential amplifier unit is less than a preset small current, and it is detected that the battery pack is disconnected from the DC bus; When the first switch is closed, the output current of the second differential amplifier unit is greater than the preset small current, and it is detected that the battery pack and the DC bus are in a connected state.

8. The method for detecting battery pack disconnection from a DC bus as claimed in claim 6, characterized in that: The method further comprises: When the battery pack is normally charged at a preset voltage, the first switch is in an off state, and the output current of the first differential amplifier unit is greater than a preset high current; If the output current of the first differential amplifier unit suddenly changes to zero, the output voltage of the first amplifier unit is the same as the preset voltage, and the output voltage of the first amplifier unit is greater than the output voltage of the second amplifier unit, it is detected that the battery pack is disconnected from the DC bus.

9. The method for detecting battery pack disconnection from a DC bus as claimed in claim 8, characterized in that: The method further comprises: When the battery pack is normally charged at a preset voltage, the first switch is in an off state, and the output current of the first differential amplifier unit is greater than a preset high current; If the output voltage of the first amplifying unit is greater than the output voltage of the second amplifying unit, and the output voltage difference between the first amplifying unit and the second amplifying unit is less than a preset value, it is detected that the battery pack is in a connected state with the DC bus.

10. The method for detecting battery pack disconnection from a DC bus as claimed in claim 6, characterized in that: The method further comprises: When it is detected that the battery pack is disconnected from the DC bus, the signal unit generates and sends a fault alarm signal.

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