Direct-current power transmission system reclosing method based on IGCT converter valve

Abstract

The invention provides a direct-current power transmission system reclosing method based on an IGCT converter valve, and the method comprises the steps: controlling the direct-current side of the converter valve to send out an alternating-current signal with a set frequency, and injecting the alternating-current signal to a fault point after a direct-current circuit breaker DCB at the two ends of a fault line is disconnected when a circuit break / short circuit fault occurs in the direct-current line; collecting and analyzing a fault point feedback voltage signal, and judging a fault type according to the characteristics of the voltage signal; when the fault type is judged to be a permanent fault, DCB breaking is kept, and line maintenance is carried out; and when the fault type is judged to be an instantaneous fault, reclosing is started when deionization of the direct-current line is completed. The reclosing efficiency of the direct-current power transmission system can be effectively improved, the fault recovery time is shortened, and the design and application cost of the direct-current circuit breaker is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of power transmission, and in particular relates to a reclosing method for a direct current transmission system based on an IGCT converter valve. Background Art

[0002] At present, more and more DC transmission projects are being built, and the transmission capacity and voltage level are getting higher and higher, and the requirements for the key equipment converter valve in DC transmission projects are getting higher and higher. The converter valves in existing DC transmission projects mostly use LCC (Line commutated converter, grid phase-commutated converter valve) converter valves. LCC has the advantages of large transmission capacity and low construction cost, but because it uses thyristors as switching devices and relies on grid voltage for phase commutation, when the grid voltage is disturbed due to factors such as faults, phase commutation failure will occur. The power transmission fluctuation or even stop caused by phase commutation failure will seriously affect the safety of the receiving end grid.

[0003] The HCC (Hybrid commutated converter) valve uses a fully controlled switch device. Based on the active shutdown capability of the switch device, the valve can achieve active commutation and bidirectional power transmission, effectively avoiding commutation failure and improving grid operation stability. In addition to solving the commutation failure problem, the HCC DC transmission system also faces the problem of reclosing, and fault type identification is a key link in the reclosing process.

[0004] Most existing projects use secondary closing to identify the type of system fault, that is, when a fault is detected, the reclosing is started after the line is de-ionized. After closing, if the system voltage is established, the fault type is judged to be a transient fault and the system resumes operation; if the voltage cannot be established, it is judged to be a permanent fault, the circuit breaker is opened again, and the line is repaired. This method is easy to implement, but when a permanent fault occurs, it will cause a secondary impact on the system, and the two disconnections have high requirements for the energy dissipation design of the DC circuit breaker, which increases the complexity and application cost of the DC circuit breaker. Summary of the invention

[0005] In view of the above technical problems, the present invention provides a reclosing method for a DC transmission system based on an IGCT converter valve, wherein the method comprises:

[0006] When a DC line breaks or shorts out, after the DC breakers DCB at both ends of the faulty line are disconnected, the DC side of the converter valve is controlled to send an AC signal of a set frequency and inject it into the fault point;

[0007] Collect and analyze the feedback voltage signal of the fault point, and determine the fault type according to the characteristics of the voltage signal;

[0008] When the fault type is determined to be a permanent fault, keep the DCB disconnected and carry out line maintenance;

[0009] When the fault type is determined to be a transient fault, the reclosing circuit breaker is started when the DC line is de-ionized.

[0010] Furthermore, the form of the AC signal is determined by the following formula:

[0011] U inject =Asin(ωt) (1)

[0012] Where U inject is the AC signal, A is the AC signal amplitude, ω is the set frequency, and t represents time.

[0013] Furthermore, when the fault type is determined to be a permanent fault, the feedback voltage at the fault point is U1 determined by the following formula:

[0014] U1=A1sin(ω1t) (2)

[0015] Where A1 and ω1 are the amplitude and frequency of the feedback voltage AC signal when the fault type is a permanent fault.

[0016] Furthermore, when the fault type is determined to be a transient fault, the feedback voltage at the fault point is U2 determined by the following formula:

[0017] U2=A2sin(ω2t) (3)

[0018] Where A2 and ω2 are the amplitude and frequency of the feedback voltage AC signal when the fault type is a transient fault.

[0019] Further, judging the fault type according to the characteristics of the voltage signal includes:

[0020] Through Fourier decomposition, the key characteristic parameters of the voltage signal are extracted to determine the fault type.

[0021] Furthermore, the method further comprises:

[0022] When the system operates normally, the control switching signal is switched to the constant voltage control mode, and the converter valve operates in the constant voltage mode to maintain a constant DC line voltage.

[0023] Furthermore, the method further comprises:

[0024] When a short circuit fault occurs in the line and the fault type needs to be determined, the control switching signal is switched to the active injection signal mode, and the converter valve injects an AC signal U into the DC line. inject ,

[0025] Among them, the active injection signal mode is:

[0026] The control is based on the DC side of the IGCT converter valve sending an AC signal of a set frequency and injecting it into the fault point.

[0027] Furthermore, the system includes a power transmission line and two converter valve circuits, and the two converter valve circuits are connected via a DC transmission line, wherein:

[0028] The DC power transmission line includes a DC power transmission line and a DCB connected to both ends of the DC power transmission line, and two DCBs are connected to two converter valves respectively.

[0029] Furthermore, the DCB includes an energy consumption branch, a switch branch and a current transfer branch connected in parallel, wherein:

[0030] The energy consumption branch includes a metal oxide varistor MOV;

[0031] The switch branch includes a switch S;

[0032] The current transfer branch includes an inductor L, a capacitor C and a power switch module which are connected in series in sequence.

[0033] Furthermore, the power switch module includes two anti-parallel switch devices.

[0034] On the other hand, the present invention also provides a DC power transmission system reclosing system based on an IGCT converter valve, wherein the system comprises:

[0035] A signal injection module is used to control the DC side of the converter valve to send an AC signal of a set frequency and inject it into the fault point when a DC line breaks / short-circuit fault occurs and the DC circuit breakers DCB at both ends of the fault line are disconnected;

[0036] A judgment module is used to collect and analyze the feedback voltage signal of the fault point, and judge the fault type according to the characteristics of the voltage signal;

[0037] The reclosing module is used to start the reclosing when the DC line is de-ionized and the fault type is determined to be a transient fault.

[0038] Furthermore, the form of the AC signal is determined by the following formula:

[0039] U inject =Asin(ωt) (1)

[0040] Where U inject is the AC signal, A is the AC signal amplitude, ω is the set frequency, and t represents time.

[0041] The present invention provides a reclosing method for a DC power transmission system based on an IGCT converter valve. Based on the flexible control and operation capabilities of the IGCT converter valve (i.e., an HCC converter valve formed based on IGCT), the fault type can be accurately determined, and a reclosing scheme can be given according to the fault type, thereby effectively improving the reclosing efficiency of the DC power transmission system, reducing the fault recovery time, and reducing the design and application cost of the DC circuit breaker.

[0042] 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

[0043] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, a brief introduction is given below to 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 any creative work.

[0044] Figure 1 A flow chart of a DC power transmission system reclosing method based on an IGCT converter valve according to an embodiment of the present invention is shown;

[0045] Figure 2 A topological schematic diagram of a double-terminal direct current transmission system according to an embodiment of the present invention is shown;

[0046] Figure 3 A schematic diagram of the topology of a DCB according to an embodiment of the present invention is shown;

[0047] Figure 4 A schematic diagram of a control strategy adopted by a constant voltage station according to an embodiment of the present invention is shown;

[0048] Figure 5 A structural schematic diagram of a DC power transmission system reclosing system based on an IGCT converter valve according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0049] 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.

[0050] In view of the problem of reclosing after a fault in a DC power transmission system, the present invention proposes a reclosing strategy applied to an HCC DC power transmission system based on the flexible operation capability of an HCC converter valve, which is described below.

[0051] like Figure 1 As shown, the present invention provides a reclosing method for a DC transmission system based on an IGCT converter valve, wherein the method comprises: when a DC line has an open circuit / short circuit (i.e., an open circuit or a short circuit) fault, the hybrid DC circuit breakers DCB at both ends of the fault line are disconnected.

[0052] Since the DCB disconnection has the following characteristics: after the DCB is disconnected, the capacitor C, inductor L and series branch of the power switch module in the current transfer branch in the DCB cannot be completely disconnected, and an AC current (i.e., an AC signal) of a specific frequency is still allowed to pass. Therefore, when the DC line is de-ionized, the DC side of the converter valve is controlled to send an AC signal of a specific frequency (i.e., a set frequency: a frequency adjusted according to system characteristics, parameters and fault characteristics) to be injected into the fault point; the feedback voltage signal of the fault point is collected and analyzed, and the fault type is determined according to the characteristics of the voltage signal; when the fault type is determined to be a transient fault, the reclosing switch is started when the DC line is de-ionized; when the fault type is determined to be a permanent fault, the DCB is kept disconnected and line maintenance is carried out.

[0053] In some embodiments of the present invention, the above method may be applied to a double-terminal DC power transmission system. The double-terminal DC power transmission system is described below.

[0054] like Figure 2 As shown, the system (double-terminal DC transmission system) includes a converter valve circuit and a transmission line, and the two converter valve circuits are connected through a DC transmission line (DC line), wherein the DC transmission line includes a DC transmission line and a DCB connected to both ends of the DC transmission line, and the two DCBs are respectively connected to two converter valves.

[0055] The specific structure of the above system can be described as follows:

[0056] The converter valve is an HCC converter valve, that is, Figure 2 There are two DC transmission lines, Pos (positive line) and Neg (negative line). DC transmission lines also include DCBs, and each line includes 2 DCBs. The connection method of each part is as follows:

[0057] For the two DCBs of one DC line: one DCB is connected to HCC1, and the other DCB is connected to HCC2, and the two DCBs are connected through Pos.

[0058] For the two DCBs of another DC line: one DCB is connected to one end of HCC1, and the other DCB is connected to one end of HCC2, and the two DCBs are connected through Neg.

[0059] For two HCCs: one end of HCC1 is connected to three-phase AC power (A, B, C three-phase AC power); one end of HCC2 is connected to three-phase AC power (A, B, C three-phase AC power).

[0060] The DC voltage level of the above-mentioned double-terminal DC transmission system is ±800kV, the switching device in the converter valve adopts an IGCT (Integrated Gate-Commutated Thyristor) device with active shutdown capability, and the DCB adopts a hybrid DC circuit breaker.

[0061] In some embodiments of the present invention, Figure 3 As shown, the DCB includes a parallel energy consumption branch, a switch branch and a current transfer branch, wherein the energy consumption branch includes a metal oxide varistor MOV; the switch branch includes a switch S; the current transfer branch includes an inductor L, a capacitor C and a power switch module connected in series in sequence, wherein the power switch module includes two anti-parallel switch devices.

[0062] A reclosing method for a DC power transmission system based on an IGCT converter valve of the present invention is described in detail below.

[0063] In some embodiments of the present invention, the form of the AC signal is determined by the following formula:

[0064] U inject =Asin(ωt) (1)

[0065] Where U inject is an AC signal, A is the amplitude of the active signal (i.e., AC signal), ω is the set frequency, and t represents time.

[0066] Among them, when the fault type is determined to be a permanent fault, the feedback voltage at the fault point is U1 determined by the following formula:

[0067] U1=A1sin(ω1t) (2)

[0068] Where A1 and ω1 are the feedback voltage signal amplitude and frequency respectively when the fault type is a permanent fault.

[0069] Among them, when the fault type is determined to be a transient fault, the feedback voltage at the fault point is U2 determined by the following formula:

[0070] U2=A2sin(ω2t) (3)

[0071] Where A2 and ω2 are the feedback voltage signal amplitude and frequency respectively when the fault type is instantaneous fault.

[0072] The present invention is described below with reference to a case.

[0073] This case is based on a double-terminal DC transmission system (i.e. Figure 2 In the double-terminal DC transmission system, DCB adopts Figure 3 In the hybrid DC circuit breaker shown, the converter valve adopts the HCC with active shut-off capability mentioned above.

[0074] Constant voltage Figure 4 ( Figure 4 Middle,U ref is the voltage given value, U p.u. is the voltage measurement value, I ref is the current given value, I p.u. is the current measurement value; PI is the proportional-integral controller, also known as the PI controller). The control strategy shown, that is, when the system (double-terminal DC transmission system) works normally, the control Switch signal is switched to the double closed-loop control, that is, the constant voltage control mode, that is, U ref and U p.u. The deviation between them is processed by a PI controller and then output I ref , I ref and I p.u. The deviation between them is processed by another PI controller and then outputs a control signal. The HCC inverter side works in constant voltage mode to maintain the DC line voltage stable.

[0075] When a short circuit fault occurs in the line and the fault type needs to be determined, the switch signal is controlled to switch to the active signal injection mode, and the HCC injects a signal U into the DC line. inject .

[0076] Wherein, judging the fault type according to the characteristics of the feedback voltage signal includes:

[0077] Through Fourier decomposition, the key characteristic parameters of the feedback voltage signal are extracted to determine the fault type.

[0078] Among them, the active injection signal mode is:

[0079] The control is based on the DC side of the IGCT converter valve sending an AC signal of a specific frequency to be injected into the fault point.

[0080] When a short circuit occurs in a DC transmission line, the DCBs at both ends of the line are disconnected in time to isolate the fault point. After the DC line is de-ionized, the Switch signal in the control strategy switches to the active injection signal mode, and the HCC converter valve injects U into the DC line. inject Detect the feedback voltage U1 / U2 at the fault point, and use Fourier transform to decompose U1 / U2. Depending on the type of fault, the decomposed signal will present different frequency characteristics. Determine the fault type based on the specific frequency characteristics and start the reclosing strategy.

[0081] On the other hand, Figure 5 As shown, the present invention also provides a DC power transmission system reclosing system based on an IGCT converter valve, wherein the system comprises:

[0082] The signal injection module 100 is used to control the DC side of the converter valve to send an AC signal of a specific frequency to inject into the fault point after the hybrid DC circuit breakers DCB at both ends of the fault line are disconnected when a DC line breaks / short-circuit fault occurs;

[0083] The judgment module 200 is used to collect and analyze the voltage signal fed back from the fault point, and judge the fault type according to the characteristics of the voltage signal;

[0084] The reclosing module 300 is used to start the reclosing when the DC line is de-ionized and the fault type is determined to be a transient fault.

[0085] The other functions and implementation methods of each module in the reclosing system of a DC power transmission system based on an IGCT converter valve of the present invention correspond to the functions and implementation methods of each step of the reclosing method of a DC power transmission system based on an IGCT converter valve mentioned above of the present invention, and therefore, they are not repeated here.

[0086] The above is only a preferred embodiment of the present invention, and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technician familiar with this profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A reclosing method for a DC transmission system based on an IGCT converter valve, wherein: The method comprises: When a DC line breaks or shorts out, after the DC breakers DCB at both ends of the faulty line are disconnected, the DC side of the converter valve is controlled to send an AC signal of a set frequency and inject it into the fault point; Collect and analyze the feedback voltage signal of the fault point, and determine the fault type according to the characteristics of the voltage signal; When the fault type is determined to be a permanent fault, keep the DCB disconnected and carry out line maintenance; When the fault type is determined to be a transient fault, the reclosing circuit breaker is started when the DC line is de-ionized.

2. A DC power transmission system reclosing method based on IGCT converter valve according to claim 1, wherein: The form of the AC signal is determined by the following formula: U inject =Ain(ωt) (1) Where U inject is the AC signal, A is the AC signal amplitude, ω is the set frequency, and t represents time.

3. A DC power transmission system reclosing method based on IGCT converter valve according to claim 1 or 2, wherein: When the fault type is determined to be a permanent fault, the feedback voltage at the fault point is U1 determined by the following formula: U1=A1sin(ω1t) (2) Where A1 and ω1 are the amplitude and frequency of the feedback voltage AC signal when the fault type is a permanent fault.

4. A DC power transmission system reclosing method based on IGCT converter valve according to claim 1 or 2, wherein: When the fault type is determined to be a transient fault, the feedback voltage at the fault point is U2 determined by the following formula: U2=A2sin(ω2t) (3) Where A2 and ω2 are the amplitude and frequency of the feedback voltage AC signal when the fault type is a transient fault.

5. A DC power transmission system reclosing method based on IGCT converter valve according to claim 4, wherein: Determining the fault type according to the characteristics of the voltage signal includes: Through Fourier decomposition, the key characteristic parameters of the voltage signal are extracted to determine the fault type.

6. A DC power transmission system reclosing method based on IGCT converter valve according to claim 5, wherein: The method further comprises: When the system operates normally, the control switching signal is switched to the constant voltage control mode, and the converter valve operates in the constant voltage mode to maintain a constant DC line voltage.

7. A DC power transmission system reclosing method based on IGCT converter valve according to claim 6, wherein: The method further comprises: When a short circuit fault occurs in the line and the fault type needs to be determined, the control switching signal is switched to the active injection signal mode, and the converter valve injects an AC signal U into the DC line. inject , Among them, the active injection signal mode is: The control is based on the DC side of the IGCT converter valve sending an AC signal of a set frequency and injecting it into the fault point.

8. A DC power transmission system reclosing method based on IGCT converter valve according to claim 6, wherein: The system includes a power transmission line and two converter valve circuits, wherein the two converter valve circuits are connected via a DC transmission line, wherein: The DC power transmission line includes a DC power transmission line and a DCB connected to both ends of the DC power transmission line, and two DCBs are connected to two converter valves respectively.

9. A DC power transmission system reclosing method based on IGCT converter valve according to claim 8, wherein: The DCB includes an energy consumption branch, a switch branch and a current transfer branch connected in parallel, wherein: The energy consumption branch includes a metal oxide varistor MOV; The switch branch includes a switch S; The current transfer branch includes an inductor L, a capacitor C and a power switch module which are connected in series in sequence.

10. A DC power transmission system reclosing method based on IGCT converter valve according to claim 9, wherein: The power switch module includes two anti-parallel switch devices.

11. A DC power transmission system reclosing system based on IGCT converter valve, wherein: The system comprises: A signal injection module is used to control the DC side of the converter valve to send an AC signal of a set frequency and inject it into the fault point when a DC line breaks / short-circuit fault occurs and the DC circuit breakers DCB at both ends of the fault line are disconnected; A judgment module is used to collect and analyze the feedback voltage signal of the fault point, and judge the fault type according to the characteristics of the voltage signal; The reclosing module is used to start the reclosing when the DC line is de-ionized and the fault type is determined to be a transient fault.

12. A DC power transmission system reclosing system based on IGCT converter valve according to claim 11, wherein: The form of the AC signal is determined by the following formula: U inject =Ain(ωt) (1) Where U inject is the AC signal, A is the AC signal amplitude, ω is the set frequency, and t represents time.

Images