Method and circuit for preventing HVDC commutation failure

Abstract

The invention belongs to the technical field of commutation, and particularly relates to a method and circuit for preventing HVDC commutation failure. The method comprises the following steps: detecting current in a circuit; judging whether a turn-off condition is met or not according to the current detection result; if the turn-off condition is met, the turn-off action of the IGCT device is executed; after the IGCT device is turned off, energy flowing through the IGCT device is absorbed. By adopting the power module of the high-power IGCT device, the problem of commutation failure of the LCC can be effectively solved, the black-start capability is realized, and the technical requirement of large-scale transmission of energy is met; when the measured current is within the allowable turn-off capability, executing a turn-off instruction, and turning off under the condition of commutation failure; when the measured current exceeds the turn-off capability of the device, the turn-off instruction is not executed, and the device bears large current but is not damaged.

Description

Technical Field

[0001] The present invention belongs to the technical field of commutation, and in particular relates to a method and a circuit for preventing HVDC commutation failure. Background Art

[0002] With the country's proposal of dual carbon goals, high voltage direct current (HVDC) technology has many advantages such as low transmission line loss, small line corridor area, and connection to asynchronous power grids. It has been widely used in the fields of long-distance large-capacity power transmission, renewable energy grid connection, and large-scale power grid interconnection. The HVDC converter is the core of realizing AC / DC or DC / AC conversion of electric energy. At present, the converter mainly includes the line commutated converter (LCC-HVDC) based on thyristor.

[0003] LCC converter valves have the advantages of large transmission capacity and low construction cost. At present, dozens of high-voltage direct current transmission projects have been built in my country. However, LCC uses thyristors as power semiconductor switching devices, and requires an external AC power supply to provide commutation voltage to ensure the normal operation of the converter. Therefore, the operation of the converter has certain limitations, resulting in the following problems: First, there is a risk of commutation failure. Once the AC system fails and the voltage drops, commutation failure will occur, causing transmission power fluctuations, and even the converter valve will be locked, stopping DC power transmission. In severe cases, it will cause commutation failures in multiple DC transmission lines of the multi-fed DC system at the same time, seriously threatening the safety of the receiving power grid. Second, because LCC must rely on the grid voltage for commutation, LCC cannot realize the black start function when supplying power to the passive network, and does not have the ability to connect to the grid and island power supply for renewable energy power generation systems such as wind farms and photovoltaic power stations. Third, as the short-circuit ratio of the power grid system caused by multiple DC drop points decreases, the problem of commutation failure becomes more prominent. Summary of the invention

[0004] In view of the above problems, the present invention provides a method for preventing HVDC commutation failure, the method comprising:

[0005] Detect the current in the circuit;

[0006] Determine whether the shutdown condition is met according to the current detection result;

[0007] If the shutdown condition is met, the shutdown action of the IGCT device is executed;

[0008] After the IGCT device is turned off, the energy flowing through the IGCT device is absorbed.

[0009] Preferably, judging whether the shutdown condition is met according to the current detection result includes:

[0010] When the current detection result exceeds the shutdown capability of the IGCT device, the shutdown condition is not met;

[0011] When the current detection result does not exceed the shutdown capability of the IGCT device, the shutdown condition is met.

[0012] Preferably, the absorbing the energy flowing through the IGCT device comprises:

[0013] The energy flowing through the IGCT device is transferred to the MOV module, driving the MOV to operate and absorb energy.

[0014] The present invention also provides a circuit for preventing HVDC commutation failure, comprising a sending-end system and a receiving-end AC system, wherein an upper bridge arm and a lower bridge arm connected in parallel are arranged between the sending-end AC system and the receiving-end AC system.

[0015] A plurality of shutoff branches are arranged between the upper bridge arm and the lower bridge arm, and the shutoff branches are composed of a plurality of IGCT power modules;

[0016] The IGCT power module includes a first bridge arm and a second bridge arm, an IGCT device connected in series is arranged between the first bridge arm and the second bridge arm, a branch is arranged between the IGCT devices, a buffer module is arranged between the first bridge arm and the second bridge arm and the branch, an energy acquisition module is connected to the buffer module, an output end of the energy acquisition module is connected to a driving module, the driving module is connected to the IGCT device, and an energy absorption module is arranged between the first bridge arm and the second bridge arm.

[0017] Preferably, the buffer module comprises a capacitor Cs and a resistor Rs connected in series.

[0018] Preferably, the number of the energy extraction modules is two, wherein one of the energy extraction modules is connected to the buffer module between the first bridge arm and the branch, and the other of the energy extraction modules is connected to the buffer module between the second bridge arm and the branch.

[0019] Preferably, the number of the driving modules is two, and the two energy extraction modules are connected to the two driving modules.

[0020] Preferably, the energy absorption module comprises an MOV device.

[0021] Preferably, a voltage balancing module is further connected between the first bridge arm and the second bridge arm and the branch, and the voltage balancing module includes a voltage balancing resistor.

[0022] Preferably, the two driving modules are connected to two IGCT devices respectively.

[0023] The present invention has the following beneficial effects:

[0024] The present invention adopts a power module of a high-power IGCT device, which can effectively solve the commutation failure problem of LCC and has a black start capability, meeting the technical requirements of large-scale energy transmission needs; when the measured current is within the allowable shutdown capability, the shutdown command is executed to complete the shutdown in the case of commutation failure; when the measured current exceeds the shutdown capability of the device, the shutdown command is not executed, and the device withstands a large current but is not damaged.

[0025] Other features and advantages of the present invention will be described in the following description, and partly become obvious from the description, or be understood by implementing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0027] Figure 1 A diagram showing a method for preventing HVDC commutation failure in an embodiment of the present invention;

[0028] Figure 2 A circuit diagram for preventing HVDC commutation failure in an embodiment of the present invention is shown;

[0029] Figure 3 Shown is a circuit diagram of an IGCT power module in an embodiment of the present invention;

[0030] Figure 4 A schematic diagram of transition commutation of an IGCT power module in an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] The present invention takes a ±800kV / 8000MW HVDC direct current system as an example. The AC side of the sending-end system is converted and transformed, then passes through a rectifier and then is transmitted through an 800kV busbar. The transmission distance is about 1000 kilometers or more, and then passes through an inverter valve / converter transformer to the receiving-end AC system. The core equipment of this HVDC is a sending-end rectifier converter valve and a receiving-end inverter converter valve. The converter valve core is composed of an integrated gate-commutated transformer (IGCT) submodule.

[0033] The present invention takes a ±800kV / 8000MW HVDC direct current system as an example for explanation. The AC side of the sending end system is converted and transformed, then passes through a rectifier and then is transmitted through an 800kV busbar. The transmission distance is about 1000 kilometers or more, and then passes through an inverse conversion valve / converter transformer to the receiving end AC system. The core equipment of this HVDC is a sending end rectifier converter valve and a receiving end inverse conversion valve. The converter valve core is composed of a reverse resistance IGCT submodule.

[0034] like Figure 1 As shown, the present invention proposes a method for preventing HVDC commutation failure, the method comprising the following steps:

[0035] (1) Detect the current in the circuit;

[0036] (2) judging whether the shutdown condition is met according to the current detection result;

[0037] The determining whether the shutdown condition is met based on the current detection result includes: when the current detection result exceeds the shutdown capability of the IGCT device, the shutdown condition is not met; when the current detection result does not exceed the shutdown capability of the IGCT device, the shutdown condition is met.

[0038] (3) If the shutdown condition is met, the shutdown action of the IGCT device is executed;

[0039] (4) After the IGCT device is turned off, the energy flowing through the IGCT device is absorbed.

[0040] The absorbing of energy flowing through the IGCT device comprises:

[0041] The energy flowing through the IGCT device is transferred to the MOV module, driving the MOV to operate and absorb energy.

[0042] The present invention also proposes a circuit for preventing HVDC commutation failure, such as Figure 2 As shown, it includes a sending end system and a receiving end AC system, an upper bridge arm and a lower bridge arm connected in parallel are arranged between the sending end and the receiving end AC system, and multiple shutdown branches are arranged between the upper bridge arm and the lower bridge arm, and the shutdown branches are composed of multiple IGCT power modules.

[0043] The reverse resistance IGCT submodule topology is Figure 3 As shown in the figure, the converter valve designed based on this topology can effectively solve the commutation failure problem caused by the use of conventional DC multiple drop points when large-scale new energy is connected to the new power system;

[0044] The IGCT power module comprises a first bridge arm and a second bridge arm, an IGCT device connected in series is arranged between the first bridge arm and the second bridge arm, and the IGCT device can withstand not only a forward voltage but also a reverse voltage;

[0045] A branch is provided between the IGCT devices, and a buffer module is provided between the first bridge arm and the second bridge arm and the branch. The buffer module includes a capacitor Cs and a resistor Rs connected in series. The damping absorption circuit formed by the capacitor Cs and the resistor Rs can effectively limit the shutdown overvoltage in the IGCT recovery enhancement working mode;

[0046] The buffer module is connected to an energy extraction module, and the number of the energy extraction modules is two, one of which is connected to the buffer module between the first bridge arm and the branch, and the other is connected to the buffer module between the second bridge arm and the branch;

[0047] The output end of the energy acquisition module is connected to a driving module, which is the core execution unit of the IGCT device. The driver can control the IGCT device to open and close to complete the power conversion. The energy acquisition module constitutes cross-power acquisition. The energy acquisition process is that the energy acquisition power supply takes energy from the main circuit RC and connects it in series to the energy acquisition power supply. The power supply has a full-bridge circuit inside, and the energy is stored in the energy storage capacitor. After the electric energy is taken, the circuit inside the drive is powered. Cross-power acquisition means that the two energy acquisition power supplies shown in the figure provide redundant power to their respective drives.

[0048] There are two driving modules, two energy taking modules are connected to two driving modules, the driving modules are connected to IGCT devices, and the two driving modules are connected to two IGCT devices respectively; the driving modules constitute adjacent communication, that is, if the optical fiber of driver 1 is broken, IGCT1 can be triggered by driver 2, and vice versa.

[0049] An energy absorption module is provided between the first bridge arm and the second bridge arm, and the energy absorption module includes an MOV device. Each IGCT power module includes only one MOV device. The function of the MOV is to absorb the large shutdown energy generated when the IGCT is actively shut down when the commutation fails, so as to ensure the safety of the device;

[0050] A voltage balancing module is also connected between the first bridge arm, the second bridge arm and the branch, and the voltage balancing module includes a voltage balancing resistor Rd. The voltage balancing resistor Rd can ensure uniform voltage distribution of the IGBT under static voltage.

[0051] The IGCT power module adopts the reverse resistance IGCT device design, and its normal operation is similar to the thyristor mode (recovery enhancement mode). When the power module encounters a grid AC fault, the IGCT active shutdown function can be used to solve the problem that the thyristor cannot be shut down due to reverse recovery, thus avoiding commutation failure. The power module is equipped with an MOV lightning arrester, which can absorb the energy during the IGCT active shutdown process and avoid IGCT overvoltage breakdown.

[0052] When commutation failure occurs, through the current detection threshold, if the shutdown condition is met, the IGCT executes the active shutdown instruction. After active shutdown, the energy flowing through the IGCT is commutated to the module MOV, and the MOV operates to complete the energy absorption, thereby completing a complete shutdown process.

[0053] For the active shutdown mode of the converter valve based on the IGCT reverse resistance power module, the converter valve is required to shut down the current. The shutdown capacity of the new reverse resistance device is limited. If it exceeds the shutdown capacity of the device itself and is still shut down, it will cause large-scale damage to the valve and cause serious consequences. Therefore, the bridge arm current measurement is adopted: ① Monitor the current of the converter valve, set the protection point in the valve control, and do not shut down when it is judged that it exceeds the shutdown capacity of the device to protect the safety of the valve; ② Traverse the fault current of the system under various working conditions demonstrated in the early stage, consider reliability, and make up for the defects caused by insufficient shutdown capacity of the device.

[0054] If the device's turn-off capability is strong enough, theoretically, there is no need for a current measurement device. The detailed idea for current measurement is as follows:

[0055] At the moment t before the actual shutdown t4, the measured current I t With the set current I0 (I0 = 6500A), such as I t ≤I0, the shutdown is executed; the actual shutdown current at T4 is: I=I t +(t4-t)×A, where A is the current rise rate, t4-t valve control link delay; I≤7000A.

[0056] like Figure 4 As shown, u L Indicates the corresponding i T4 The AC line voltage value on LN Indicates the rated normal condition corresponding to i T4 The AC line voltage value on the bridge, μ′ represents the commutation angle after the AC voltage drops, γ′ represents the turn-off angle after the AC voltage drops, μ0 represents the rated commutation angle, γ0 represents the rated turn-off angle, a0 represents the trigger angle of the next bridge arm, a0+μ0 represents the time when the trigger angle plus the turn-off angle is added, t a Indicates the moment when the voltage starts to drop, t bIndicates the time when commutation starts (i.e. the time corresponding to a0), t c Indicates the current zero crossing point, t d Indicates the fault voltage zero crossing point, i T4 represents the current of bridge arm No. 4 (it can be any bridge arm, here No. 4 is taken as an example), and the shaded part in the figure represents the commutation voltage area;

[0057] according to Figure 4 It can be seen that when time reaches t a When the AC fault causes the voltage to start to drop, when ωt=a0, t b Phase switching starts at time t c The commutation ends at this moment, and the signal turns off when it crosses zero. The commutation process can be completed in a shorter time, thus avoiding commutation failure.

[0058] The circuit described in the present invention is not limited to reverse-resistance IGCT semiconductor devices, and devices such as reverse-resistance IGBT are also applicable to the present invention; the method described in the present invention is not limited to ultra-high voltage levels, and is also applicable to high voltage and other similar scenarios. The present invention is not limited to the method of connecting two-stage IGCT devices in parallel with one MOV, and is also applicable to connecting multiple-stage IGCT devices in parallel with one MOV. The MOV parameters are changed and the design method is similar.

[0059] It should be noted that, in this article, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0060] Those skilled in the art should understand that although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible to modify the technical solutions described in the aforementioned embodiments, or to make equivalent replacements for some of the technical features therein; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preventing HVDC commutation failure, characterized in that: The method comprises: Detect the current in the circuit; Determine whether the shutdown condition is met according to the current detection result; If the shutdown condition is met, the shutdown action of the IGCT device is executed; After the IGCT device is turned off, the energy flowing through the IGCT device is absorbed.

2. The method for preventing HVDC commutation failure according to claim 1, characterized in that: The determining whether the shutdown condition is met according to the current detection result includes: When the current detection result exceeds the shutdown capability of the IGCT device, the shutdown condition is not met; When the current detection result does not exceed the shutdown capability of the IGCT device, the shutdown condition is met.

3. The method for preventing HVDC commutation failure according to claim 1, characterized in that: The absorbing of energy flowing through the IGCT device comprises: The energy flowing through the IGCT device is transferred to the MOV module, driving the MOV to operate and absorb energy.

4. A circuit for preventing HVDC commutation failure, comprising a sending-end system and a receiving-end AC system, wherein an upper bridge arm and a lower bridge arm connected in parallel are arranged between the sending-end AC system and the receiving-end AC system, characterized in that: A plurality of shutoff branches are arranged between the upper bridge arm and the lower bridge arm, and the shutoff branches are composed of a plurality of IGCT power modules; The IGCT power module includes a first bridge arm and a second bridge arm, an IGCT device connected in series is arranged between the first bridge arm and the second bridge arm, a branch is arranged between the IGCT devices, a buffer module is arranged between the first bridge arm and the second bridge arm and the branch, an energy acquisition module is connected to the buffer module, an output end of the energy acquisition module is connected to a driving module, the driving module is connected to the IGCT device, and an energy absorption module is arranged between the first bridge arm and the second bridge arm.

5. The circuit for preventing HVDC commutation failure according to claim 4, characterized in that: The buffer module includes a capacitor Cs and a resistor Rs connected in series.

6. The circuit for preventing HVDC commutation failure according to claim 4, characterized in that: There are two energy extraction modules, one of which is connected to a buffer module between the first bridge arm and the branch, and the other is connected to a buffer module between the second bridge arm and the branch.

7. The circuit for preventing HVDC commutation failure according to claim 6, characterized in that: The number of the driving modules is two, and the two energy taking modules are both connected to the two driving modules.

8. The circuit for preventing HVDC commutation failure according to claim 4, characterized in that: The energy absorption module includes an MOV device.

9. The circuit for preventing HVDC commutation failure according to claim 4, characterized in that: A voltage balancing module is further connected between the first bridge arm, the second bridge arm and the branch, and the voltage balancing module includes a voltage balancing resistor.

10. The circuit for preventing HVDC commutation failure according to claim 4, characterized in that: The two driving modules are connected to two IGCT devices respectively.

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