Static synchronous compensator system applied to high-voltage direct-current power transmission and control method thereof

Abstract

The invention discloses a static synchronous compensator system applied to high voltage direct current transmission and a control method thereof, the static synchronous compensator system is connected to a converter transformer valve side, and the static synchronous compensator system comprises a three-phase bridge arm, all phases of bridge arms in the three phases of bridge arms are mutually connected in a star-shaped connection mode or a triangular connection mode to form a three-phase static synchronous compensator system; each phase of bridge arm comprises a converter valve group, a damping valve group and a connecting reactor, the damping valve group is respectively connected with the converter valve group and the connecting reactor, and the input end of the converter valve group is connected to the converter variable valve side. The system can be connected to a converter transformer valve side of a high-voltage direct-current power transmission system, reactive compensation and harmonic suppression of an LCC valve group are achieved on the valve side, overcurrent and overvoltage generated by serious faults can be effectively suppressed, and safe operation of static synchronous compensator equipment is protected.

Description

Technical Field

[0001] The present invention belongs to the field of power systems and power electronics, and in particular relates to a STATCOM (static synchronous compensator) system applied to high-voltage direct current transmission and a control method and a control device thereof. Background Art

[0002] The core equipment of the high-voltage direct current transmission system is the LCC converter valve, which can be used to achieve the conversion from AC to DC. The working principle of the LCC converter valve is to control the thyristor to conduct at a fixed angle within the power frequency cycle, thereby converting AC into DC. In this process, the converter valve absorbs a large amount of reactive power from the power grid and generates a large amount of harmonics that are injected into the power grid, causing harmonic pollution and affecting the safe and stable operation of the power system. Therefore, conventional high-voltage direct current projects need to be equipped with a large number of reactive compensation and AC filtering equipment to reduce the injection of harmonic currents.

[0003] At present, the solution adopted by most converter stations is to install passive reactive compensation and AC filtering equipment on the converter transformer grid side. Active equipment represented by STATCOM has dynamic compensation capability, so some converter stations use active equipment to partially replace passive equipment, and all of them are installed on the converter transformer grid side. In fact, STATCOM can be installed on the converter transformer grid side as well as on the converter transformer valve side, because the source of harmonic generation of LCC converter lies in the LCC converter valve. The principle of reactive compensation and harmonic control is local compensation, that is, compensation from the source, because control from the source can limit reactive power and harmonics to the minimum range, which can reduce the compensation capacity; at the same time, the STATCOM valve group can also share the valve hall with the LCC valve group, making full use of the valve hall area and reducing construction costs.

[0004] However, compared with the grid-side access method, valve-side access to STATCOM is technically more difficult. For STATCOM connected to the grid, the voltage of the converter valve group to the ground is AC voltage. In case of a fault, it is only necessary to lock the STATCOM converter valve group. By taking advantage of the characteristic that the modulation ratio of the STATCOM valve group is less than 1, the total voltage of the DC module is higher than the AC voltage, which can quickly block the fault current. For STATCOM connected to the valve side, the voltage of the converter valve group to the ground is AC voltage superimposed on DC voltage, especially for the high-end valve group, the DC voltage is much higher than the AC voltage. Therefore, even if the STATCOM converter valve group is locked in case of a fault, the fault current cannot be blocked, causing overcurrent and overvoltage damage to the STATCOM valve group. Therefore, there is currently no actual application case of STATCOM access to the converter valve side. Summary of the invention

[0005] The purpose of the present invention is to provide a STATCOM system and a control method thereof for high voltage direct current transmission. The system can be connected to the converter transformer valve side of the high voltage direct current transmission system, realize reactive power compensation and harmonic wave suppression of the LCC valve group on the valve side, and can effectively suppress overcurrent and overvoltage caused by serious faults, thereby protecting the safe operation of the STATCOM equipment.

[0006] In order to achieve the above object, the solution of the present invention is:

[0007] A static synchronous compensator system applied to high-voltage direct current power transmission, the static synchronous compensator system is connected to a converter transformer valve side, the static synchronous compensator system comprises: a three-phase bridge arm, each phase bridge arm in the three-phase bridge arm is connected to each other in a star connection mode or a triangle connection mode to form a three-phase static synchronous compensator system; each phase bridge arm comprises a converter valve group, a damping valve group, and a connecting reactor, wherein the damping valve group is respectively connected to the converter valve group and the connecting reactor, and the input end of the converter valve group is connected to the converter transformer valve side.

[0008] The above-mentioned converter valve group includes N single-phase full-bridge sub-modules connected in series.

[0009] The damping valve group comprises M damping submodules connected in series.

[0010] The above-mentioned connecting reactor is an air-core reactor.

[0011] Each phase bridge arm also includes a lightning arrester, one end of the lightning arrester is connected to the input end of the converter valve group, and the other end of the lightning arrester is connected to the output end of the connection reactor.

[0012] Each phase bridge arm also includes a plurality of lightning arresters, and at least one lightning arrester is connected in parallel at both ends of corresponding components in the converter valve group, the damping valve group, and the connecting reactor.

[0013] Each phase bridge arm also includes a plurality of lightning arresters, and at least one lightning arrester is connected in parallel at both ends of any two connected elements among the converter valve group, the damping valve group and the connecting reactor.

[0014] The above-mentioned lightning arrester is a metal oxide lightning arrester.

[0015] The control method of the static synchronous compensator system applied to high voltage direct current transmission as described above determines whether the converter valve group in the static synchronous compensator system has overcurrent, and if overcurrent occurs, control strategy one is adopted, otherwise control strategy two is adopted;

[0016] The control strategy 1 is to lock the damping valve group and control the damping valve group to be in a damping state;

[0017] The second control strategy is to unlock the damping valve group and control the damping valve group to be in a short-circuit state.

[0018] The control device of the static synchronous compensator system applied to high voltage direct current transmission as mentioned above comprises:

[0019] An overcurrent judging module is used to judge whether an overcurrent occurs in the converter valve group in the static synchronous compensator system, and send the judgment result to the control module; and

[0020] A control module, used to control the static synchronous compensator system by adopting control strategy one or control strategy two according to the judgment result of the overcurrent judgment module;

[0021] When the overcurrent judging module judges that the converter valve group in the static synchronous compensator system has overcurrent, the control module adopts control strategy one to control the static synchronous compensator system; the control strategy one is to lock the damping valve group and control the damping valve group to be in a damping state;

[0022] When the overcurrent judgment module judges that the converter valve group in the static synchronous compensator system does not have overcurrent, the control module adopts control strategy 2 to control the static synchronous compensator system; the control strategy 2 is to unlock the damping valve group and control the damping valve group to be in a short-circuit state.

[0023] After adopting the above scheme, the beneficial effects of the present invention include: STATCOM is connected to the DC system on the converter transformer side, which can solve the reactive power and harmonic wave problems from the source and reduce the capacity of the compensation equipment; the fault overcurrent can be effectively suppressed by connecting the damping valve group in series with the STATCOM converter valve group branch; the fault overvoltage can be effectively suppressed by connecting the arrester in parallel at both ends of the converter valve group, the damping valve group and the connecting reactor, thereby ensuring the equipment safety of STATCOM in the event of a fault, providing safety protection for the use of the converter transformer side access STATCOM solution, and further optimizing and improving the performance of the high-voltage DC transmission system.

[0024] The STATCOM system provided by the present invention has both reactive power compensation and harmonic wave compensation functions, and has good overcurrent and overvoltage suppression capabilities, making it possible for STATCOM to be connected to the converter transformer side, and can effectively improve the performance of the high-voltage direct current transmission system. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is the main circuit schematic diagram of the HVDC transmission system equipped with valve-side STATCOM;

[0026] Figure 2 It is the schematic diagram of modular multi-level STATCOM using star connection;

[0027] Figure 3 It is the schematic diagram of modular multi-level STATCOM using delta connection;

[0028] Figure 4 It is a schematic diagram of the arrangement of lightning arresters in each phase bridge arm;

[0029] Among them, (a) is a method in which the lightning arrester is arranged at both ends of the entire bridge arm, (b) is a method in which the lightning arrester is arranged at both ends of the converter valve group, the damping valve group, and the connecting reactor, (c) is a method in which the lightning arrester is arranged at both ends of the converter valve group and the damping valve group, and (d) is a method in which the lightning arrester is arranged at both ends of the connecting reactor, the connected converter valve group, and the damping valve group. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present application.

[0031] In the description of the present application, it should be noted that, unless otherwise clearly specified and limited, the terms "connected" and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection, or can communicate with each other; it can be directly connected, or indirectly connected through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to the specific circumstances. In the description of the present application, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined. In addition, the terms "first" and "second" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more features.

[0032] The disclosure below provides many different embodiments or examples to realize the different structures of the present application. In order to simplify the disclosure of the present application, the parts and settings of specific examples are described below. Of course, they are only examples, and the purpose is not to limit the present application.

[0033] Since STATCOM is only used on the converter transformer grid side in the existing HVDC transmission system, the supporting effect of STATCOM on the DC system is not obvious. STATCOM installed on the converter transformer valve side can better support the DC system and has better compensation effect on reactive power and harmonics. However, in the event of a serious fault, the STATCOM equipment is difficult to withstand the fault voltage and current. Currently, there is no feasible STATCOM technical solution on the converter transformer valve side.

[0034] In view of this, the present invention proposes a novel STATCOM system solution for high-voltage direct current transmission. By adding a damping valve group in series with the converter valve group, the current of the STATCOM converter valve group can be effectively reduced in the event of a serious fault, preventing the valve group from being damaged by overcurrent; lightning arresters are connected in parallel on both sides of the converter valve group, the damping valve group and the connecting reactor, respectively, to prevent the equipment from being damaged by overvoltage. The present invention provides a reliable STATCOM overcurrent and overvoltage suppression solution, making it possible for STATCOM to be connected to the converter valve side, and can effectively improve the performance of the high-voltage direct current transmission system.

[0035] The present invention provides a static synchronous compensator system applied to high-voltage direct current power transmission, the system is connected to a converter transformer valve side, and comprises a three-phase bridge arm, wherein each phase bridge arm of the three-phase bridge arm adopts a star connection mode or a triangle connection mode to form a three-phase static synchronous compensator system; each phase bridge arm comprises a converter valve group, a damping valve group, and a connecting reactor, wherein the damping valve group is respectively connected to the converter valve group and the connecting reactor, and the input end of the converter valve group is connected to the converter transformer valve side.

[0036] The converter valve group in the STATCOM system adopts a modular multi-level structure, including N single-phase full-bridge sub-modules connected in series, and the single-phase full-bridge sub-module adopts a single-phase full-bridge converter structure.

[0037] Among them, the damping valve group in the STATCOM system adopts a modular multi-level structure, including M damping sub-modules connected in series, and the damping sub-module is composed of a power electronic switch and a resistor in parallel; each phase damping valve group is connected in series with the converter valve group, during normal operation, the damping module switch is turned on, and the resistor bypass is exited; in the event of a fault, the damping module switch is turned off, and the resistor is put into the circuit to suppress the rise of the fault current.

[0038] As a preferred embodiment of the present invention, in order to effectively suppress fault overvoltage, each phase bridge arm also includes a lightning arrester, one end of the lightning arrester is connected to the input end of the converter valve group, and the other end of the lightning arrester is connected to the output end of the reactor.

[0039] As another preferred embodiment of the present invention, in order to effectively suppress fault overvoltage, each phase bridge arm also includes multiple lightning arresters, and at least one lightning arrester is connected in parallel at both ends of the corresponding elements in the converter valve group, the damping valve group, and the connecting inductor.

[0040] As another preferred embodiment of the present invention, in order to effectively suppress fault overvoltage, each phase bridge arm also includes multiple lightning arresters, and at least one lightning arrester is connected in parallel at both ends of any two connected elements in the converter valve group, the damping valve group, and the connecting inductor.

[0041] Wherein, the arrester is a metal oxide arrester.

[0042] like Figure 1 The main circuit schematic diagram of the high-voltage direct current transmission system is shown in the dotted box. An embodiment of the STATCOM system applied to high-voltage direct current transmission in the present invention is shown. The STATCOM is connected to the converter valve side. The STATCOM valve side equipment includes a converter valve group, a damping valve group, a connecting reactor, a lightning arrester 1, a lightning arrester 2, and a lightning arrester 3. The converter valve group, the damping valve group, and the connecting reactor of each phase of the STATCOM are connected in series in sequence. The lightning arrester 1, the lightning arrester 2, and the lightning arrester 3 are respectively connected in parallel at both ends of the converter valve group, the damping valve group, and the connecting reactor.

[0043] The three-phase bridge arms of the STATCOM system can be Figure 2 As shown, a star connection is used, or Figure 3 As shown, a triangle connection is adopted.

[0044] Cooperate again Figure 1 As shown, the STATCOM converter valve group is a voltage source converter valve, which adopts a modular multi-level structure. The converter valve group in each phase bridge arm is composed of N single-phase full-bridge sub-modules connected in series, and each single-phase full-bridge sub-module is composed of 4 fully controlled power electronic switches and capacitors.

[0045] Cooperate again Figure 1 As shown, the damping valve group adopts a modular multi-level structure, and the damping valve group in each phase bridge arm is composed of M damping sub-modules connected in series, and each damping sub-module is composed of a fully controlled power electronic switch and a resistor.

[0046] The connecting reactor is usually an air-core reactor.

[0047] Lightning arrester 1, lightning arrester 2, and lightning arrester 3 use metal oxide lightning arresters, and their respective voltage parameters are configured according to the withstand voltage levels of the converter valve group, the damping valve group, and the connected inductor.

[0048] The layout of lightning arresters is relatively flexible. Depending on the components to be protected, they can be arranged in a centralized or decentralized manner. Commonly used arrangements include: Figure 4 As shown. Figure 4 As shown in (a), only one lightning arrester is set in one phase bridge arm, and the lightning arrester is connected in parallel at both ends of the one phase bridge arm to limit the overvoltage of the entire bridge arm; Figure 4 As shown in (b), three lightning arresters can also be set, which are respectively connected in parallel at both ends of the converter valve group, the damping valve group, and the connecting reactor to limit the overvoltage of each component; the lightning arrester can also be set in two, which are connected in parallel at both ends of any two connected components in the converter valve group, the damping valve group, and the connecting reactor to limit the overvoltage of the two components, for example Figure 4(c) shows the situation where two lightning arresters are connected in parallel at both ends of the converter valve group and the damping valve group. Figure 4 In (d), one arrester is connected in parallel to both ends of the connected reactor, while the other arrester is connected in parallel to both ends of the connected converter valve group and damping valve group. When the voltage of the protected component exceeds the arrester action voltage, the arrester will operate to limit the voltage to a safe range.

[0049] The present invention also provides a control method for the aforementioned static synchronous compensator system applied to high-voltage direct current transmission, which can determine whether a serious fault occurs by whether the converter valve group in the STATCOM system is overcurrent, and select control strategy one or control strategy two according to the situation for processing; during normal operation, control strategy two is adopted, the power electronic switch of the damping valve group is in the on state, the damping valve group is unlocked, the damping valve group is controlled to be in a short-circuit state, the resistor is bypassed, and the voltage of each lightning arrester is lower than the action voltage and is in a high-resistance state. Both do not affect the operation of the converter valve group, and the reactive power and harmonic current output by the STATCOM system can be controlled by adjusting the output voltage of the converter valve group. When a serious fault occurs and causes overcurrent in the converter valve group, control strategy 1 is adopted. The control system quickly shuts down the power electronic switch of the damping valve group, locks the damping valve group, controls the damping valve group to be in a damping state, and connects a resistor in series to the fault circuit to increase the damping of the fault circuit and thus limit the fault current; when the voltage at the converter valve group, the damping valve group and the connected reactor terminals exceeds the operating voltage of the parallel arrester, the arrester operates to limit the overvoltage level of the protected parallel components.

[0050] As a preferred embodiment of the present invention, the present invention further provides a control device for the static synchronous compensator system applied to high voltage direct current transmission, comprising:

[0051] An overcurrent judging module is used to judge whether an overcurrent occurs in the converter valve group in the static synchronous compensator system, and send the judgment result to the control module; and

[0052] A control module, used to control the static synchronous compensator system by adopting control strategy one or control strategy two according to the judgment result of the overcurrent judgment module;

[0053] When the overcurrent judging module judges that the converter valve group in the static synchronous compensator system has overcurrent, the control module adopts control strategy one to control the static synchronous compensator system; the control strategy one is to lock the damping valve group and control the damping valve group to be in a damping state;

[0054] When the overcurrent judgment module judges that the converter valve group in the static synchronous compensator system does not have overcurrent, the control module adopts control strategy 2 to control the static synchronous compensator system; the control strategy 2 is to unlock the damping valve group and control the damping valve group to be in a short-circuit state.

[0055] STATCOM has the ability to output fundamental reactive current and harmonic current, such as Figure 1 As shown, the current of the LCC valve group is approximately a rectangular wave. By controlling STATCOM, the reactive current and harmonic current of the LCC valve group can be compensated, so that the current flowing into the converter transformer and the power grid is a sinusoidal fundamental wave. Therefore, STATCOM can replace conventional passive filters and capacitors.

[0056] In case of a fault, the overcurrent and overvoltage of STATCOM can be suppressed through the protection of the damping valve group and the arrester, ensuring the safety of the STATCOM equipment.

[0057] The above embodiments are only for illustrating the technical idea of ​​the present invention, and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the present invention.

Claims

1. A static synchronous compensator system applied to high voltage direct current transmission, the static synchronous compensator system is connected to the converter valve side, characterized in that: The static synchronous compensator system includes: a three-phase bridge arm, each phase bridge arm of the three-phase bridge arm is connected to each other in a star connection mode or a triangle connection mode to form a three-phase static synchronous compensator system; each phase bridge arm includes a converter valve group, a damping valve group, and a connecting inductor, wherein the damping valve group is respectively connected to the converter valve group and the connecting inductor, and the input end of the converter valve group is connected to the converter transformer valve side.

2. The static synchronous compensator system for high voltage direct current transmission according to claim 1, characterized in that: The converter valve group includes N single-phase full-bridge submodules connected in series.

3. The static synchronous compensator system for high voltage direct current transmission according to claim 1, characterized in that: The damping valve group includes M damping submodules connected in series.

4. The static synchronous compensator system for high voltage direct current transmission according to claim 1, characterized in that: The connecting reactor is an air-core reactor.

5. The static synchronous compensator system for high voltage direct current transmission according to claim 1, characterized in that: Each phase bridge arm also includes a lightning arrester, one end of the lightning arrester is connected to the input end of the converter valve group, and the other end of the lightning arrester is connected to the output end of the connection reactor.

6. The static synchronous compensator system for high voltage direct current transmission according to claim 1, characterized in that: Each phase bridge arm also includes a plurality of lightning arresters, and at least one lightning arrester is connected in parallel at both ends of corresponding components in the converter valve group, the damping valve group, and the connecting reactor.

7. The static synchronous compensator system for high voltage direct current transmission according to claim 1, characterized in that: Each phase bridge arm also includes a plurality of lightning arresters, and at least one lightning arrester is connected in parallel at both ends of any two connected elements among the converter valve group, the damping valve group and the connecting reactor.

8. The static synchronous compensator system for high voltage direct current transmission according to any one of claims 6 to 7, characterized in that: The arrester is a metal oxide arrester.

9. The control method of the static synchronous compensator system applied to high voltage direct current transmission according to claim 1, characterized in that: Determine whether the converter valve group in the static synchronous compensator system has overcurrent. If overcurrent occurs, control strategy 1 is adopted; otherwise, control strategy 2 is adopted. The control strategy 1 is to lock the damping valve group and control the damping valve group to be in a damping state; The second control strategy is to unlock the damping valve group and control the damping valve group to be in a short-circuit state.

10. The control device for a static synchronous compensator system for high voltage direct current transmission according to claim 1, characterized in that: include: An overcurrent judging module is used to judge whether an overcurrent occurs in the converter valve group in the static synchronous compensator system, and send the judgment result to the control module; as well as, A control module, used to control the static synchronous compensator system by adopting control strategy one or control strategy two according to the judgment result of the overcurrent judgment module; When the overcurrent judging module judges that the converter valve group in the static synchronous compensator system has overcurrent, the control module adopts control strategy one to control the static synchronous compensator system; the control strategy one is to lock the damping valve group and control the damping valve group to be in a damping state; When the overcurrent judgment module judges that the converter valve group in the static synchronous compensator system does not have overcurrent, the control module adopts control strategy 2 to control the static synchronous compensator system; the control strategy 2 is to unlock the damping valve group and control the damping valve group to be in a short-circuit state.

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