A short-circuit impedance regulation device and method for an MMC converter transformer

Abstract

The present application discloses a short-circuit impedance adjustment device and method for an MMC converter transformer. The short-circuit impedance adjustment device includes a short-circuit impedance adjustment circuit electrically connected to the secondary winding of the converter transformer. The short-circuit impedance adjustment circuit is a three-phase short-circuit impedance adjustment sub-circuit, and the short-circuit impedance adjustment sub-circuit includes a first bidirectional IGBT component, a second bidirectional IGBT component, a third bidirectional IGBT component, a first adjustment inductor, and a second adjustment inductor. According to different operating states of the MCC, the conduction states of the three IGBT components are controlled. When the MMC is operating normally, the short-circuit impedance is adjusted to a smaller value, so that the system reduces the consumption of reactive power and at the same time meets the control response requirements. When a short-circuit fault occurs on the DC side of the MMC, it instantaneously switches to the large-impedance mode of operation to limit the rise of the short-circuit current. According to different operating modes, the inductance value input is flexibly switched, improving the stability of the system.

Description

Technical Field

[0001] The present application relates to the technical field of flexible direct current transmission equipment, and in particular to a short-circuit impedance adjustment device and method for an MMC converter transformer. Background Art

[0002] With the rapid development of flexible DC transmission technology, the advantages of modular multilevel converters are becoming more and more obvious compared to two-level and three-level converters. The six bridge arms of modular multilevel converters (MMC) are not composed of multiple switching devices in series, but are cascaded in submodules. Using several submodules to build a large-capacity DC converter has the advantages of reduced manufacturing difficulty, good waveform quality, reduced step voltage, exponentially reduced losses, and strong fault handling capabilities.

[0003] The short-circuit impedance of the converter transformer affects the short-circuit impact current borne by the faulty converter and the reactive power consumed by the converter during a DC fault. When a short-circuit fault occurs on the DC side of the MMC, in order to limit the excessive short-circuit current from damaging the switch devices and freewheeling diodes in the power module, the converter transformer should have a sufficiently large short-circuit impedance. However, if the short-circuit impedance is too large, the reactive power consumed by the MMC will increase, and the speed at which the MMC output AC current tracks the grid-side AC current will slow down. Summary of the invention

[0004] In order to solve the above technical problems, this application proposes the following technical solutions:

[0005] In a first aspect, an embodiment of the present application provides a short-circuit impedance adjustment device for an MMC converter transformer, comprising: a short-circuit impedance adjustment circuit electrically connected to a secondary winding of a converter transformer, the short-circuit impedance adjustment circuit being a three-phase short-circuit impedance adjustment sub-circuit, the short-circuit impedance adjustment sub-circuit comprising a first bidirectional IGBT component, a second bidirectional IGBT component, a third bidirectional IGBT component, a first adjustment inductor, and a second adjustment inductor, wherein: a first end of the first bidirectional IGBT component is electrically connected to the secondary winding of the converter transformer and a first end of the first adjustment inductor, respectively, a second end of the first bidirectional IGBT component is electrically connected to a first end of the second adjustment inductor and a first end of the second bidirectional IGBT component, respectively, a second end of the first adjustment inductor and a second end of the second adjustment inductor are both electrically connected to a first end of the third bidirectional IGBT component, and a second end of the third bidirectional IGBT component and a second end of the second bidirectional IGBT component are both electrically connected to a bridge arm reactor cabinet.

[0006] Adopting the above implementation method, according to different operating states of the MCC, the conduction states of three IGBT components are controlled. When the MMC is operating normally, the short-circuit impedance is adjusted to a small value, so that the system reduces the consumption of reactive power and meets the control response requirements at the same time. When a short-circuit fault occurs on the DC side of the MMC, it instantaneously switches to the large-impedance mode of operation to limit the rise of the short-circuit current. The inductance value input is flexibly switched according to different operating modes, improving the stability of the system.

[0007] Combined with the first aspect, in the first possible implementation manner of the first aspect, the bidirectional IGBT component includes a first IGBT and a second IGBT, and the first IGBT and the second IGBT are reversely connected in parallel. Since the signal passing through the bidirectional IGBT component is an alternating current signal, the direction of the current will change at a certain frequency. Therefore, two IGBTs are reversely connected in parallel to ensure the conduction of the alternating current signal.

[0008] Combined with the first aspect or the first possible implementation manner of the first aspect, in the second possible implementation manner of the first aspect, the regulating inductor is a multi-tap regulating inductor, and the inductance values corresponding to different taps are different. The inductance values between the outgoing terminals and the incoming terminal of different taps of the multi-tap regulating inductor are different, and the rapid adjustment of the inductance value can be realized by adopting different outgoing taps.

[0009] Combined with the second possible implementation manner of the first aspect, in the third possible implementation manner of the first aspect, three arm reactor groups are arranged in the arm reactor cabinet. The arm reactor group includes a first reactor and a second reactor. The first end of the first reactor is electrically connected to the upper arm cabinet of the MMC, the second end of the first reactor is electrically connected to the first end of the second reactor, the second end of the second reactor is electrically connected to the lower arm cabinet of the MMC, and the second end of the third bidirectional IGBT component and the second end of the second bidirectional IGBT component are electrically connected to the second end of the first reactor.

[0010] Combined with the third possible implementation manner of the first aspect, in the fourth possible implementation manner of the first aspect, the upper arm cabinet of the MMC and the lower arm cabinet of the MMC include a plurality of cascaded sub-modules, and the sub-modules include half-bridge sub-modules and full-bridge sub-modules.

[0011] Combined with the fourth possible implementation manner of the first aspect, in the fifth possible implementation manner of the first aspect, the first end of the first reactor is electrically connected to the first sub-module in the upper arm cabinet, and the second end of the second reactor is electrically connected to the second sub-module in the lower arm cabinet.

[0012] Combined with the fourth or fifth possible implementation manners of the first aspect, in the sixth possible implementation manner of the first aspect, the half-bridge sub-module includes two IGBT modules and a capacitor. The two IGBT modules are connected in series, and after the two IGBT modules are connected in series, they are connected in parallel with the capacitor.

[0013] Combined with the fourth or fifth possible implementation manners of the first aspect, in the seventh possible implementation manner of the first aspect, the full-bridge sub-module includes four IGBT modules and a capacitor. The four IGBT modules are divided into two groups and connected in series, and then respectively connected in parallel with the capacitor.

[0014] Combined with the first aspect, in the eighth possible implementation manner of the first aspect, a switching electronic switch is provided on the regulating inductor. The regulating inductor is switched by the electronic switch, and the response speed is fast, realizing fast switching of the inductance value of the adjustable inductor.

[0015] In a second aspect, an embodiment of the present application provides a method for regulating the short-circuit impedance of an MMC commutation transformer, adopting the MMC commutation transformer short-circuit impedance regulating device described in the first aspect or any possible implementation manner of the first aspect. The method includes: obtaining the operating state of the MMC; if the MMC operates normally, controlling the first bidirectional IGBT component and the third bidirectional IGBT component to conduct, and closing the second bidirectional IGBT component; or, if multiple faults occur on the DC side of the MMC, closing the first bidirectional IGBT component and the third bidirectional IGBT component, and controlling the second bidirectional IGBT component to conduct; after the switching is completed, adjusting the reactance of the first regulating inductor and the second regulating inductor according to different MMC device parameters. Description of the Drawings

[0016] Figure 1 It is a schematic structural diagram of an MMC commutation transformer short-circuit impedance regulating device provided by an embodiment of the present application;

[0017] Figure 2 It is an application schematic diagram of the MMC commutation transformer short-circuit impedance regulating device provided by an embodiment of the present application;

[0018] Figure 3 It is a schematic structural diagram of a half-bridge sub-module provided by an embodiment of the present application;

[0019] Figure 4 It is a schematic structural diagram of a full-bridge sub-module provided by an embodiment of the present application;

[0020] Figure 5 It is a schematic flow diagram of a method for regulating the short-circuit impedance of an MMC commutation transformer provided by an embodiment of the present application;

[0021] Figures 1-5Among them, the symbols are represented as: T1 - the first bidirectional IGBT component, T2 - the second bidirectional IGBT component, T3 - the third bidirectional IGBT component, L1 - the first regulating inductor, L2 - the second regulating inductor, L3 - the first reactor, L4 - the second reactor, SM - the sub-module. Detailed implementation manners

[0022] The following combines the accompanying drawings with the detailed implementation manners to elaborate on this solution.

[0023] Figure 1 It is a schematic structural diagram of an MMC converter transformer short-circuit impedance regulation device provided by an embodiment of the present application. Refer to Figure 1 , the MMC converter transformer short-circuit impedance regulation device in this embodiment includes: a short-circuit impedance regulation circuit electrically connected to the secondary winding of the converter transformer, and the short-circuit impedance regulation circuit is a three-phase short-circuit impedance regulation sub-circuit.

[0024] The short-circuit impedance regulation sub-circuit includes a first bidirectional IGBT component T1, a second bidirectional IGBT component T2, a third bidirectional IGBT component T3, a first regulating inductor L1, and a second regulating inductor L2. Among them: the first end of the first bidirectional IGBT component T1 is electrically connected to the secondary winding of the converter transformer and the first end of the first regulating inductor L1 respectively, and the second end of the first bidirectional IGBT component T1 is electrically connected to the first end of the second regulating inductor L2 and the first end of the second bidirectional IGBT component T2 respectively. The second ends of the first regulating inductor L1 and the second regulating inductor L2 are both electrically connected to the first end of the third bidirectional IGBT component T3. The second end of the third bidirectional IGBT component T3 and the second end of the second bidirectional IGBT component T2 are both electrically connected to the arm reactor cabinet.

[0025] The bidirectional IGBT component includes a first IGBT and a second IGBT, and the first IGBT and the second IGBT are reversely connected in parallel. Since the signal passing through the bidirectional IGBT component is an alternating current signal, the direction of the current will change according to a certain frequency. Therefore, two IGBTs are reversely connected in parallel to ensure the conduction of the alternating current signal.

[0026] In this embodiment, the regulating inductor is a multi-tap regulating inductor, and the inductance values corresponding to different taps are different. The inductance values between the different tap output terminals and the input terminal of the multi-tap regulating inductor are different, and the inductance value can be quickly adjusted by using different output taps. The regulating inductor is provided with a switching electronic switch. The regulating inductor is switched by the electronic switch, and the response speed is fast, realizing the quick switching of the inductance value of the adjustable inductor.

[0027] Refer to Figure 2, three arm reactor groups are arranged in the arm reactor cabinet. Each arm reactor group includes a first reactor L3 and a second reactor L4. The first end of the first reactor L3 is electrically connected to the MMC upper arm cabinet. The second end of the first reactor L3 is electrically connected to the first end of the second reactor L4. The second end of the second reactor L4 is electrically connected to the MMC lower arm cabinet. The second end of the third bidirectional IGBT component T3 and the second end of the second bidirectional IGBT component T2 are electrically connected to the second end of the first reactor L3.

[0028] The MMC upper arm cabinet and the MMC lower arm cabinet include a plurality of cascaded sub-modules SM. The sub-module SM includes a half-bridge sub-module and a full-bridge sub-module. The first end of the first reactor L3 is electrically connected to the first sub-module in the upper arm cabinet. The second end of the second reactor L4 is electrically connected to the second sub-module in the lower arm cabinet.

[0029] See Figure 3 , the half-bridge sub-module includes two IGBT modules and a capacitor. The two IGBT modules are connected in series, and after the two IGBT modules are connected in series, they are connected in parallel with the capacitor.

[0030] See Figure 4 , the full-bridge sub-module includes four IGBT modules and a capacitor. The four IGBT modules are divided into two groups and connected in series, and then are respectively connected in parallel with the capacitor.

[0031] As can be seen from the above embodiments, the present embodiment provides an MMC commutation transformer short-circuit impedance adjustment device, which controls the conduction states of three IGBT components according to different operating states of the MCC. When the MMC is operating normally, the short-circuit impedance is adjusted to a smaller value, so that the system reduces the consumption of reactive power and at the same time meets the control response requirements. When a short-circuit fault occurs on the DC side of the MMC, it instantaneously switches to the large-impedance mode of operation to limit the rise of the short-circuit current. The inductance value input is flexibly switched according to different operating modes, improving the stability of the system.

[0032] For the embodiment of an MMC commutation transformer short-circuit impedance adjustment device provided in the above embodiment, the present application also provides an embodiment of an MMC commutation transformer short-circuit impedance adjustment method. See Figure 5 , the method includes:

[0033] S101, obtain the operating state of the MMC.

[0034] S102, if the MMC is operating normally, control the first bidirectional IGBT component and the third bidirectional IGBT component to conduct, and turn off the second bidirectional IGBT component.

[0035] Assume that the leakage inductance of the commutation transformer is L0. When the MMC operates normally, to reduce the reactive power consumption of the system, control the first bidirectional IGBT component T1 and the third bidirectional IGBT component T3 to conduct, and at the same time turn off the second bidirectional IGBT component T2, so that the first regulating inductor L1 and the second regulating inductor L2 are in parallel, and the short-circuit impedance regulating device operates at a smaller impedance value, and its value satisfies the minimum value of system operation after being connected in series with the short-circuit impedance of the commutation transformer, that is, the equivalent impedance of the commutation transformer ωL = ω(L0+(L1 + L2) / 2).

[0036] S103, if a short-circuit fault occurs on the DC side of the MMC, turn off the first bidirectional IGBT component and the third bidirectional IGBT component, and control the second bidirectional IGBT component to conduct.

[0037] When a short-circuit fault occurs on the DC side of the MMC, at the same moment, control the first bidirectional IGBT component T1 and the third bidirectional IGBT component T3 to turn off, and the second bidirectional IGBT component T2 conducts immediately, so that the first regulating inductor L1 and the second regulating inductor L2 are in series, and the short-circuit impedance regulating device operates at a maximum value, that is, the equivalent impedance of the commutation transformer ωL = ω(L0 + L1 + L2). The larger impedance value can suppress the rise of the short-circuit fault current.

[0038] S104, after the switching is completed, adjust the reactance of the first regulating inductor and the second regulating inductor according to the different MMC device parameters.

[0039] When it is necessary to increase the equivalent impedance of the commutation transformer due to the change of MMC device parameters, change the connection tap of the regulating inductor to a larger value to meet the usage requirements. Conversely, change the connection tap of the regulating inductor to a smaller value. In this embodiment, switching electronic switches are arranged for each tap of the corresponding regulating inductor, and the regulating inductor is switched by the electronic switch, with a fast response speed, realizing the rapid switching of the inductance value of the adjustable inductor.

[0040] 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 actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "including a..." does not exclude the existence of additional identical elements in the process, method, article or device including the element.

[0041] Of course, the above description is not limited to the above examples. The technical features not described in this application can be implemented by or adopted from the prior art, and will not be elaborated here. The above embodiments and the accompanying drawings are only used to illustrate the technical solutions of this application and are not intended to limit this application. Instead, this application is only described in detail by combining and referring to the preferred embodiments. Those of ordinary skill in the art should understand that any changes, modifications, additions, or substitutions made by those of ordinary skill in the art within the scope of the essence of this application do not depart from the purpose of this application and should also fall within the scope of protection of the claims of this application.

Claims

1. A method for adjusting the short-circuit impedance of an MMC converter transformer, characterized in that, The following MMC converter transformer short-circuit impedance adjustment device is adopted, including: a short-circuit impedance adjustment circuit electrically connected to the secondary winding of the converter transformer. The short-circuit impedance adjustment circuit is a three-phase short-circuit impedance adjustment sub-circuit, and the short-circuit impedance adjustment sub-circuit includes a first bidirectional IGBT component, a second bidirectional IGBT component, a third bidirectional IGBT component, a first adjustment inductor, and a second adjustment inductor, where: the first end of the first bidirectional IGBT component is electrically connected to the secondary winding of the converter transformer and the first end of the first adjustment inductor respectively, the second end of the first bidirectional IGBT component is electrically connected to the first end of the second adjustment inductor and the first end of the second bidirectional IGBT component respectively, the second ends of the first adjustment inductor and the second adjustment inductor are both electrically connected to the first end of the third bidirectional IGBT component, and the second end of the third bidirectional IGBT component and the second end of the second bidirectional IGBT component are both electrically connected to the arm reactor cabinet; The method includes: Obtaining the operating state of the MMC; If the MMC operates normally, controlling the first bidirectional IGBT component and the third bidirectional IGBT component to conduct, and turning off the second bidirectional IGBT component; Or, If multiple faults occur on the DC side of the MMC, turning off the first bidirectional IGBT component and the third bidirectional IGBT component, and controlling the second bidirectional IGBT component to conduct; After the switching is completed, adjusting the reactance of the first adjustment inductor and the second adjustment inductor according to different MMC device parameters.

2. The short-circuit impedance regulation method of the MMC converter transformer according to claim 1, wherein The bidirectional IGBT component includes a first IGBT and a second IGBT, and the first IGBT and the second IGBT are connected in reverse parallel.

3. The method for regulating the short-circuit impedance of the MMC converter transformer according to claim 1 or 2, characterized in that, The adjustment inductor is a multi-tap adjustment inductor, and the inductance values corresponding to different taps are different.

4. The method for regulating the short-circuit impedance of the MMC converter transformer according to claim 3, wherein Three arm reactor groups are arranged in the arm reactor cabinet. The arm reactor group includes a first reactor and a second reactor. The first end of the first reactor is electrically connected to the upper arm cabinet of the MMC, the second end of the first reactor is electrically connected to the first end of the second reactor, the second end of the second reactor is electrically connected to the lower arm cabinet of the MMC, and the second end of the third bidirectional IGBT component and the second end of the second bidirectional IGBT component are electrically connected to the second end of the first reactor.

5. The short-circuit impedance regulation method of the MMC converter transformer according to claim 4, characterized in that, The upper arm cabinet and the lower arm cabinet of the MMC include a plurality of cascaded sub-modules, and the sub-modules include half-bridge sub-modules and full-bridge sub-modules.

6. The method for adjusting the short-circuit impedance of the MMC converter transformer according to claim 5, characterized in that, The first end of the first reactor is electrically connected to the first sub-module in the upper arm cabinet, and the second end of the second reactor is electrically connected to the second sub-module in the lower arm cabinet.

7. The method for adjusting the short-circuit impedance of the MMC converter transformer according to claim 5 or 6, characterized in that The half-bridge sub-module includes two IGBT modules and a capacitor. The two IGBT modules are connected in series, and after the two IGBT modules are connected in series, they are connected in parallel with the capacitor.

8. The method for adjusting the short-circuit impedance of the MMC converter transformer according to claim 5 or 6, characterized in that, The full-bridge sub-module includes four IGBT modules and a capacitor. The four IGBT modules are divided into two groups and connected in series and then connected in parallel with the capacitor respectively.

9. The short-circuit impedance regulation method of the MMC converter transformer according to claim 1, wherein The adjustment inductor is provided with a switching electronic switch.

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