A method for implementing a power electronic switch device for a BESS system

Abstract

The present invention provides a method for implementing a power electronic switch device for a BESS system, the method comprising the following steps: step S1, when in use, installing a power electronic switch device for real-time monitoring of the DC current change rate of the battery module on each battery module of the BESS energy storage system; step S2, turning on the power electronic switch device, and the power electronic switch device detecting the DC current change rate dI / dt of the BESS energy storage unit in real time via a DC sensor; when the BESS energy storage unit is normal, the DC current change rate dI / dt does not change; step S3, when a fault occurs in the BESS energy storage unit, the power electronic switch device detecting the DC current change rate dI / dt and the DC loop current I in real time; step S4, judging whether both the DC current change rate dI / dt and the DC loop current I are greater than user-set values; if so, cutting off the current of the power electronic switch device; the present invention can effectively and timely cut off the faulty part when a fault occurs in the BESS energy storage system, thereby ensuring safety performance.

Description

Technical Field

[0001] The present invention relates to the technical field of battery detection in energy storage power stations, and in particular to a method for implementing a power electronic switch device for a BESS system. Background Art

[0002] The battery system of an energy storage station consists of cells forming modules, modules forming battery modules, and finally, battery modules forming a battery energy storage system (BESS). Two topologies are available: low-voltage parallel connection and medium- and high-voltage series connection. Currently, low-voltage parallel connection is the mainstream approach. BESS systems typically operate at 1000V or 1500V, exchanging power with the AC grid via a PCS.

[0003] When a BESS short-circuit occurs, the fault current rises very rapidly. According to measurements provided by leading battery manufacturers, for a single battery module with a capacity of 372.7 kWh, the short-circuit current rises to a peak of 10.65 kA within 0.66 milliseconds. This can cause thermal and electrical damage to BESS equipment in a very short time.

[0004] At present, in terms of BESS protection strategy, most integrators adopt "isolating switch + fuse" for protection. Figure 1 As shown:

[0005] In the diagram, ① is the battery module, ② is the main control box, and ③ is the DC busbar. Component ① consists of several battery cells (BAT) and an internal fuse (F2). Component ② includes disconnect switch QS1, DC contactors K1-K3, pre-charge resistor R1, current transformer TA1, and main circuit fuse F1. Several battery modules connected in parallel form a BESS unit.

[0006] The problems with this solution are as follows:

[0007] The system time constant of F1 and F2 fuses determines the transient current rise time. A smaller time constant (<2.5ms) allows the fuse to open quickly, requiring the fuse material to quickly absorb energy and cool the arc. A larger time constant (>6ms) causes the temperature of the fuse material to rise slowly, and when the arc is finally formed, it cannot be fully cooled by the energy-absorbing material. Currently, fuses with a rated breaking capacity of 250kA, a time constant ≤5ms, and a rated current of 100A to 450A are used. These need to be customized and are relatively expensive.

[0008] The minimum breaking current of this solution is 5 In. For BESS, the current of 1.1 In to 5 In may occur, which cannot be broken. To cope with small currents and load currents, it is necessary to consider the use of fast disconnect switches.

[0009] It cannot provide automatic repower protection. Once a short circuit occurs, all parts must be replaced.

[0010] The parameters of the F1 and F2 fuses in the BESS system and the DC-side fuses of the upper-level PCS are all selected to be consistent, which makes it impossible to form a differential coordination.

[0011] The operating time is in the millisecond range, typically 20 to 50 ms. Before the fuse blows, the short-circuit current continues to increase. The battery cells themselves need to withstand large short-circuit currents, placing high demands on battery equipment. This increases BESS costs and system risks.

[0012] Since the fuse link itself is discrete, it takes a long time to blow when used as the main short-circuit protection device. An internal fuse F2 is also provided inside the module.

[0013] The future development trend of BESS is that the capacity of single battery modules will further increase, which means that the level of short-circuit current will further increase and the rated current will exceed 450A, which means that existing fuse equipment will be difficult to adapt to future development trends. Summary of the Invention

[0014] In view of this, an object of the present invention is to provide a method that can effectively cut off the faulty part in real time and ensure safety performance when a BESS energy storage system fails.

[0015] The present invention is implemented by the following method: a method for implementing a power electronic switch device for a BESS system, the method comprising the following steps:

[0016] Step S1: When in use, a power electronic switch device for real-time monitoring of the DC power change rate of the battery module is installed on each battery module of the BESS energy storage system;

[0017] Step S2: Turn on the power electronic switch device, which detects the DC current change rate dI / dt of the BESS energy storage unit in real time via a DC sensor. When the BESS energy storage unit is normal, the DC current change rate dI / dt does not change;

[0018] Step S3: When a BESS energy storage unit fails, the power electronic switch device detects the DC current change rate dI / dt and the DC loop current I in real time;

[0019] Step S4: Determine whether the DC current change rate dI / dt and the DC loop current I are both greater than the user set value. If yes,

[0020] The power electronic switch device will cut off the current, thereby cutting off the faulty battery module in real time.

[0021] Furthermore, several battery modules are connected in parallel to form a BESS energy storage system. The power electronic switch device is connected to the DC bus. The power electronic switch device consists of a power electronic switch DC, a DC sensor TA2 and a fuse F3. The output end of the power electronic switch DC is connected to the fuse F3, and the input end of the power electronic switch DC is connected to the positive and negative poles of the DC bus. The fuse F3 is connected to the battery module via the DC sensor TA2.

[0022] Furthermore, the user set value in step S3 is further specified as follows: the set value of the DC current change rate dI / dt needs to be selected according to the measured short-circuit current curve provided by the BESS energy storage unit, and the set value of the DC loop current I ranges from 2 to 4 amperes.

[0023] Furthermore, the current cut-off time in step S3 needs to be controlled within 0.005ms to 0.01ms.

[0024] Furthermore, the power electronic switch device is provided with a communication interface, so that it is electrically connected to the battery module of the BESS energy storage system through the function of the communication interface.

[0025] The beneficial effects of the present invention are as follows: after the power electronic switch is installed inside the BESS energy storage system, the overall fault clearing time is controlled between 0.2ms and 0.3ms. If there is no energy absorption circuit, it is controlled between 0.1ms and 0.15ms, which is much improved compared with the existing "isolating switch + fuse" protection action time of 20 to 50ms. The short-circuit fault is quickly removed, the battery cell itself does not need to withstand a large short-circuit current, the requirements for battery equipment are reduced, the cost of the battery body of the BESS energy storage system is reduced, and the risk of the system is greatly reduced; only a backup fuse is configured inside the power electronic switch as a backup for action refusal (the probability is basically 0); the backup fuse only considers the fault requirements within the area, and a fuse with a rated breaking current of 20kA can be selected; the fuse in the battery module of the BESS energy storage system is cancelled, and the number and cost of the fuse part are greatly reduced; the DC / DC composed of power electronic devices (such as IGBT) inside the power electronic switch can be fully current and voltage. The power electronic switch is equipped with a communication interface to maintain communication with the battery BMS. According to the instructions of the battery BMS, it meets the BESS system pre-charging requirements, overload detection and other functions, without the need for additional pre-charging circuits. The power electronic switch is self-recovering and can provide automatic repowering protection, avoiding the disadvantage of using fuses as the main short-circuit action scheme, which requires complete replacement in the event of a short circuit, greatly reducing the workload of on-site operation and maintenance. The action of the power electronic switch is entirely based on the sudden change of DC current. The maximum current flowing through the BESS system does not exceed 4In. Since each battery module is equipped with a power electronic switch, the fault can be cut off in real time for both internal and external faults. There is no linkage requirement, no need for additional communication settings, and no level coordination requirement. In the future development trend of the BESS energy storage system, the capacity of the single battery module will be further increased, and the levels of short-circuit current and rated current will also be further increased. The internal parameters of the device can be adjusted to well adapt to the future development of BESS energy storage system equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of DC protection of BESS energy storage system in the prior art.

[0027] Figure 2 Schematic diagram of the method of the present invention.

[0028] Figure 3 This is a schematic diagram of the power electronic switch in use.

[0029] Figure 4 Schematic diagram of the power electronic switch operation logic. DETAILED DESCRIPTION

[0030] The present invention will be further described below with reference to the accompanying drawings.

[0031] See also Figure 2 As shown, the present invention provides a method for implementing a power electronic switch device for a BESS system, the method comprising the following steps:

[0032] Step S1: When in use, a power electronic switch device for real-time monitoring of the DC power change rate of the battery module is installed on each battery module of the BESS energy storage system;

[0033] Step S2: Turn on the power electronic switch device, which detects the DC current change rate dI / dt of the BESS energy storage unit in real time via a DC sensor. When the BESS energy storage unit is normal, the DC current change rate dI / dt does not change;

[0034] Step S3: When a BESS energy storage unit fails, the power electronic switch device detects the DC current change rate dI / dt and the DC loop current I in real time;

[0035] Step S4: Determine whether the DC current change rate dI / dt and the DC loop current I are both greater than the user set value. If yes,

[0036] The power electronic switch device will cut off the current, thereby cutting off the faulty battery module in real time.

[0037] The present invention will be further described below by a specific embodiment:

[0038] See also Figure 3 and Figure 4 As shown, several battery modules 1 are connected in parallel to form a BESS energy storage system. The power electronic switch device 2 is connected to the DC bus 3. The power electronic switch device 2 consists of a power electronic switch DC-4, a DC sensor TA2-5 and a fuse F3-6. The output end of the power electronic switch DC-4 is connected to the fuse F3-6, and the input end of the power electronic switch DC-4 is connected to the positive and negative poles of the DC bus 3. The fuse F3-6 is connected to the battery module 1 via the DC sensor TA2-5.

[0039] The power electronic switch device based on DC current mutation consists of a DC / DC power electronic switch, a TA2 DC sensor, and a backup fuse F3. The power electronic switch device detects the DC current change rate dI / dt in real time, with a sampling frequency of no less than 10kHz.

[0040] Under normal circumstances, when the BESS system has no faults, the DC current change rate dI / dt is very small or even unchanged, and the power electronic switching device does not start.

[0041] In the event of a fault, the power electronic switchgear monitors the DC current rate of change (dI / dt) and the DC loop current (I) in real time. When both dI / dt > (dI / dt)set (set value) and I > Iset (set value), the power electronic switchgear switches on all power electronic components to interrupt the current. (dI / dt)set (set value) can be selected based on the measured short-circuit current curve provided by the BESS. Depending on the capabilities of the selected power electronic components, Iset (set value) can be set between 2 and 4 In. The time required for the power electronic switchgear to determine operation is controlled within 0.1 to 0.15 ms.

[0042] The DC current change rate dI / dt at the moment of a fault will have different polarities depending on the fault location. For example, assuming the BESS charging current is positive, the discharge current is negative. When a fault occurs outside the area where the power electronic switchgear is installed (from the power electronic switchgear to the DC bus, and by extension, to the energy storage converter PCS), the short-circuit current flows from the battery cluster to the short-circuit point, in the same direction as the discharge current, and dI / dt is negative. When a fault occurs within the area where the power electronic switchgear is installed (from the inside of the battery module to the power electronic switchgear), the short-circuit current flows from the non-short-circuited battery cluster to the short-circuited battery cluster, in the same direction as the charging current, and dI / dt is positive. Therefore, the polarity can be used to determine whether the short-circuit fault is external or internal, without the need for a separate directional element to assist in the determination.

[0043] After the judgment criteria are met and the power electronic switch device is divided into internal and external faults, different response measures are taken. In the event of an internal fault, the power electronic switch device will force the DC / DC composed of the power electronic devices (such as insulated gate bipolar transistors IGBTs) in this circuit to open and cut off the current. The time required for current cutting is controlled within 0.005ms to 0.01ms. In the event of an external fault, the power electronic switch devices in front of all battery modules connected to the DC bus will operate simultaneously, forcing the DC / DC composed of the power electronic devices (such as IGBTs) in their respective circuits to open and cut off the current. The time required for current cutting is controlled within 0.005ms to 0.01ms.

[0044] The energy absorption circuit inside the DC / DC converter, which is composed of power electronic devices (such as IGBTs) within the power electronic switch device, is selected based on the calculated energy amount. The time required for the energy absorption process is controlled within 0.1ms to 0.15ms.

[0045] The operation of the power electronic switch device is completely based on the sudden change of DC current. The maximum current flowing through the BESS system does not exceed 4In. Since each battery module is equipped with this power electronic switch device, the fault can be cut off in real time for both internal and external faults. There is no linkage requirement, no need to add additional communication settings, and no level coordination requirement.

[0046] After installing this power electronic switch device inside the BESS, the overall fault clearing time is controlled between 0.2ms and 0.3ms. If there is no energy absorption circuit, it is controlled between 0.1ms and 0.15ms, which is significantly improved compared to the existing "isolating switch + fuse" protection action time of 20 to 50ms.

[0047] The DC / DC composed of power electronic devices (such as IGBT) inside the power electronic switch device is a fully controlled device, so the current and voltage can be adjusted within the full range. The power electronic switch device is equipped with a communication interface to maintain communication with the battery BMS. According to the BMS instructions, it meets the BESS system pre-charging requirements, overload detection and other functions.

[0048] Power electronic switchgear is equipped with a backup fuse as a backup in the event of a failed operation (with a probability of essentially zero). The backup fuse only considers the requirements for internal faults and can be selected with a rated breaking current of 20kA.

[0049] In summary, the present invention can ensure that faults can be quickly and effectively cut off through the power electronic switch device, thereby improving the safety level of the BESS energy storage system.

[0050] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. A method for implementing a power electronic switch device for a BESS system, characterized in that: A plurality of battery modules are connected in parallel to form a BESS energy storage system. The power electronic switch device is connected to the DC bus. The power electronic switch device is composed of a power electronic switch DC, a DC sensor TA2, and a fuse F3. The output end of the power electronic switch DC is connected to the fuse F3, and the input end of the power electronic switch DC is connected to the positive and negative poles of the DC bus. The fuse F3 is connected to the battery module via the DC sensor TA2. The method includes the following steps: Step S1: When in use, a power electronic switch device for real-time monitoring of the DC power change rate of the battery module is installed on each battery module of the BESS energy storage system; Step S2: Turn on the power electronic switch device, which detects the DC current change rate dI / dt of the BESS energy storage unit in real time via a DC sensor. When the BESS energy storage unit is normal, the DC current change rate dI / dt does not change; Step S3: When a BESS energy storage unit fails, the power electronic switch device detects the DC current change rate dI / dt and the DC loop current I in real time; Step S4: determine whether the DC current change rate dI / dt and the DC loop current I are both greater than the user-set value. If yes, the power electronic switch device cuts off the current, thereby cutting off the faulty battery module in real time.

2. The method for implementing a power electronic switch device for a BESS system according to claim 1, characterized in that: The user setting value in step S3 is further specified as follows: the setting value of the DC current change rate dI / dt needs to be selected according to the measured short-circuit current curve provided by the BESS energy storage unit, and the setting value of the DC loop current I ranges from 2 to 4 amperes.

3. The method for implementing a power electronic switch device for a BESS system according to claim 1, characterized in that: The current cut-off time in step S3 needs to be controlled within 0.005ms to 0.01ms.

4. The method for implementing a power electronic switch device for a BESS system according to claim 1, characterized in that: The power electronic switch device is provided with a communication interface, so that it is electrically connected to the battery module of the BESS energy storage system through the function of the communication interface.

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