Flexible direct current power transmission system and power grid system

Abstract

The invention relates to a flexible direct-current power transmission system and a power grid system, in the flexible direct-current power transmission system, the alternating-current side of a connection transformer is connected with an alternating-current system, and the connection transformer is connected with a first bus and a second bus in a half-circuit-breaker wiring mode; the resonance eliminator and the connection transformer are connected with the same AC bus connection transformer of the AC power distribution device. The AC side of the connection transformer is connected with an AC system through the AC power distribution device. By connecting the resonance eliminator and the AC side of the connection transformer with the same AC bus of the AC power distribution device and combining the resonance eliminator with the connection transformer in series, the access of the resonance eliminator can be ensured and the safety and stability of the AC system can be improved under multiple working conditions, thereby improving the operation reliability and stability of the flexible DC power transmission system.

Description

Technical Field

[0001] The present application relates to the technical field of flexible direct current transmission, and in particular to a flexible direct current transmission system and a power grid system. Background Art

[0002] Flexible DC transmission is a new type of transmission technology based on voltage source converter, turn-off switching devices and pulse width modulation (PWM) technology. It belongs to the new generation of DC transmission technology and is also the most advanced power electronics technology currently entering engineering applications.

[0003] Compared with conventional DC transmission methods, flexible DC transmission has strong technical advantages and broad application prospects in the fields of large-capacity clean energy grid connection, distributed power generation grid connection, large-area power grid interconnection, island power supply, and capacity expansion and transformation of urban distribution networks. It can solve the safety and stability risks of the receiving power grid caused by multiple DC concentrated landing points.

[0004] At present, with the continuous development of flexible DC transmission technology, flexible DC transmission projects are being built at home and abroad. In actual operation, high-frequency oscillations have occurred many times. One of the reasons is that the impedance characteristics of the flexible DC transmission system and the impedance characteristics of the AC system resonate in certain frequency ranges. Therefore, it is necessary to connect a harmonic elimination device to the AC system to improve the impedance characteristics of the flexible DC transmission system and avoid resonance with the AC system impedance under system harmonics.

[0005] However, the applicant has found that in the traditional solution, there is a problem of detuning failure and the resonance suppression effect is poor. Summary of the invention

[0006] Based on this, it is necessary to provide a flexible direct current transmission system and a power grid system that can improve the reliability of resonance elimination.

[0007] In a first aspect, a flexible direct current transmission system is provided, comprising:

[0008] A connection transformer, wherein the AC side of the connection transformer is connected to the AC system, and the connection transformer is connected to the first busbar and the second busbar in a one-and-a-half circuit breaker connection mode;

[0009] A harmonic eliminator is connected to the same AC bus of the AC power distribution device as the connecting transformer.

[0010] In one embodiment, each of the first busbar and the second busbar has at least one bus section circuit breaker.

[0011] In one embodiment, the system further comprises:

[0012] A station transformer, one side of which is connected to the outgoing line terminals led out from the first busbar and the second busbar.

[0013] In one embodiment, a plurality of leads are bridged between the two first busbars and the second busbars, and a plurality of circuit breakers are arranged on the leads, and an outlet terminal is led out between every two adjacent circuit breakers among the plurality of circuit breakers.

[0014] In one embodiment, three circuit breakers are provided on the leads connecting between the first busbar and the second busbar.

[0015] In one embodiment, there are multiple connection transformers, and the number of segments of the connection transformers, the first busbar, and the second busbar is consistent.

[0016] In one embodiment, at least two detuning devices are connected to the AC bus to which each of the connection transformers is connected.

[0017] In one embodiment, a circuit breaker is connected in series between the detuning device and the connected AC bus.

[0018] In one of the embodiments, a circuit breaker is connected in series between the connection transformer and the connected AC bus.

[0019] In a second aspect, a power grid system is provided, comprising:

[0020] AC system, used to output AC power;

[0021] The flexible DC transmission system as described above.

[0022] In the above-mentioned flexible direct current transmission system and power grid system, the AC side of the connecting transformer is connected by a half-circuit breaker connection method to achieve connection with the double busbar (the first busbar and the second busbar); the double busbar can lead out multiple outlets through devices such as circuit breakers. By connecting the harmonic eliminator to the AC busbar of the AC distribution device of the connecting transformer, that is, the harmonic eliminator and the connecting transformer are connected to the same AC busbar. When the connecting transformer is not connected to the AC system, at this time, the flexible direct current transmission is not affected by the impedance interference of the AC system. When the double busbars (the first busbar and the second busbar) are operating normally and the connecting transformer is connected to the AC system, the load line outputs normally. At this time, the harmonic eliminator is connected to the AC system connected to the connecting transformer through the AC busbar to suppress the generation of resonance. If any one or two of the double busbars fail, the harmonic eliminator can still be connected to the AC busbar to suppress the generation of resonance and avoid the impedance interference of the AC system to the flexible direct current transmission system. Therefore, the flexible direct current transmission system provided in the embodiment of the present application can effectively improve the reliability of resonance elimination under various working conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the conventional technology, the drawings required for use in the embodiments or the conventional technology descriptions are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0024] FIG1 is a schematic structural diagram of a flexible direct current transmission system according to an embodiment. DETAILED DESCRIPTION

[0025] In order to facilitate understanding of the present application, the present application will be described more fully below with reference to the relevant drawings. Embodiments of the present application are provided in the drawings. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present application more thorough and comprehensive.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0027] It can be understood that the “connection” in the following embodiments should be understood as “electrical connection”, etc., if the connected circuits, modules, units, etc. transmit electrical signals to each other.

[0028] It can be understood that “at least one” means one or more, “plurality” means two or more, and “at least part of an element” means part or all of an element.

[0029] When used herein, the singular forms "a", "an", and "said / the" may also include plural forms, unless the context clearly indicates otherwise. It should also be understood that the terms "include / comprise" or "have" etc. specify the presence of stated features, wholes, steps, operations, components, parts or combinations thereof, but do not exclude the possibility of the presence or addition of one or more other features, wholes, steps, operations, components, parts or combinations thereof.

[0030] In an exemplary technology, as shown in FIG1 , a flexible direct current transmission system is provided, including: a first busbar (I busbar) and a second busbar (II busbar), a connecting transformer (which may be one or more, for example, may include a connecting transformer 1 and a connecting transformer 2 as shown in the figure, and the connecting transformer may also be called a converter transformer), and a harmonic eliminator 10. The connecting transformer is connected in a half-circuit breaker connection mode, and is connected to the I busbar and the II busbar to ensure that when the first busbar or the second busbar fails, the AC signal of the connecting transformer can still be connected. The harmonic eliminator and the connecting transformer are connected to the same AC busbar 50 of the AC distribution device. Multiple outlet terminals can be respectively drawn from multiple circuit breakers spanned between the double busbars (the first busbar and the second busbar).

[0031] The connecting transformer is a device that is connected between the converter and the AC system to achieve energy and voltage exchange. The double busbar is used to transmit AC power, which is converted by the connecting transformer and converter valve of the converter station to convert AC power into DC power, which is then transmitted through the DC transmission line to achieve the transmission and distribution of electric energy.

[0032] The AC system is the part of the flexible DC transmission system that is connected to the AC side of the connection transformer. In the flexible DC transmission system, the AC system is connected to the bridge arm reactor, starting circuit, converter valve and other parts through the connection transformer to achieve the conversion and transmission of electric energy.

[0033] The AC side of the connecting transformer adopts a one-and-a-half circuit breaker connection mode, and every two circuits share three circuit breakers, that is, each circuit is assigned to one and a half circuit breakers, forming a multi-ring power supply connection mode. In this connection mode, the middle circuit breaker of each string is called a connecting circuit breaker. Since each circuit is connected to the first bus and the second bus through two circuit breakers, and there is a connecting circuit breaker, when a circuit breaker fails, power can continue to be supplied through other circuit breakers, which improves the reliability of the flexible DC transmission system.

[0034] The double busbar setting makes it easy to expand in two directions without affecting the power supply of the original circuit.

[0035] Specifically, by connecting the detuning device and the connecting transformer to the same AC bus of the AC distribution device, when the connecting transformer is not connected to the AC system, it is not affected by the impedance interference of the AC system and does not need to be detuned. When the dual busbars are operating normally, the connecting transformer is connected to the AC system. Because the detuning device and the connecting transformer are connected to the same AC bus of the AC distribution device, the detuning device is also connected to the AC system to suppress the generation of resonance. If any one or both of the dual busbars fail, the detuning device can still suppress the generation of resonance by connecting to the AC bus of the AC distribution device to which the connecting transformer is connected, thereby avoiding impedance interference of the AC system. Therefore, the flexible direct current transmission system provided in the embodiment of the present application can effectively improve the reliability of resonance elimination under a variety of working conditions.

[0036] In one embodiment, as shown in FIG. 1 , each of the first busbar and the second busbar has at least one bus section circuit breaker 30 .

[0037] Among them, based on the busbar section circuit breaker 30, the first busbar and the second busbar can be managed in sections. Under this setting, the short-circuit current can be limited and the reliability and flexibility of the power supply of the flexible direct current transmission system can be improved.

[0038] Specifically, according to the needs and scale of the flexible DC transmission system, a first busbar and a second busbar with two parallel busbars can be designed. These two busbars can be used as working busbars and standby busbars respectively to improve the reliability of power supply. On the basis of the double busbars, one or more busbar section circuit breakers can be set on the first busbar and the second busbar according to actual needs and electrical parameter requirements. Each section can operate independently or be connected to other sections through busbar section circuit breakers. These circuit breakers can quickly cut off the current when necessary to protect the safe operation of circuits and electrical equipment.

[0039] In addition, the busbar segmentation design enables the flexible DC transmission system to flexibly adjust the power supply mode according to actual needs and realize balanced distribution and transfer of loads. Installing busbar segmentation circuit breakers between busbar segments can facilitate non-stop inspection and maintenance, reducing the impact on the operation of the flexible DC transmission system.

[0040] In one of the embodiments, the flexible direct current transmission system further includes: a station transformer.

[0041] Among them, one side of the station transformer is connected to the outgoing line terminals led out from the first busbar and the second busbar.

[0042] Among them, the outgoing line terminals are used to connect other equipment to realize the connection between other equipment and the connecting transformer and the double busbar. Some outgoing line terminals can be connected to the station transformer in the converter station.

[0043] Station transformers can provide independent and reliable power supply for electrical equipment within the station. Even when a failure occurs in the transmission system, they can ensure the normal operation of equipment within the station, thereby ensuring the safe and stable operation of the power system.

[0044] In one of the embodiments, a plurality of leads are bridged between the double busbars (the first busbar and the second busbar), and a plurality of circuit breakers are arranged on the leads, and an outlet terminal is led out between every two adjacent circuit breakers among the plurality of circuit breakers.

[0045] Specifically, multiple leads are connected across the double busbars according to the planned position and quantity. These leads should have good conductivity and insulation properties. Circuit breakers are installed on each lead according to the planned position and quantity. The circuit breaker should be able to reliably cut off and close the circuit to protect the circuit and equipment from the impact of fault current. Between every two adjacent circuit breakers, lead-out terminals are drawn. These lead-out terminals will be used to connect electrical equipment. By connecting multiple leads across the double busbars and setting up multiple circuit breakers, circuit redundancy and backup can be achieved. When a lead or circuit breaker fails, power supply can be continued by switching to other leads or circuit breakers, thereby improving the reliability of power supply.

[0046] In addition, the configuration of the circuit and the distribution of the load can be flexibly adjusted as needed. For example, the topology of the circuit can be changed by opening or closing different circuit breakers to adapt to different load requirements and fault conditions.

[0047] In addition, since each circuit breaker independently controls a section of the circuit, when maintenance or overhaul of a certain part of the circuit is required, only the circuit breaker related to that part of the circuit can be disconnected without affecting the operation of the entire flexible DC transmission system, which can also improve the efficiency and safety of maintenance.

[0048] In one embodiment, three circuit breakers are provided on the leads connected between the double busbars (the first busbar and the second busbar). In this case, each lead can be wired in a half-circuit breaker wiring mode, and two outlets can be led out on a single lead, which has significant beneficial effects in improving power supply reliability, enhancing system flexibility, improving maintenance efficiency, and optimizing resource utilization.

[0049] In one embodiment, there are multiple connection transformers, and the connection transformers have the same number of segments as the first bus and the second bus. Each bus segment is connected to the AC system using a connection transformer to ensure that the flexible DC transmission system can still operate normally when a connection transformer in any segment fails.

[0050] In one embodiment, at least two harmonic eliminators are connected to the AC busbar of the AC power distribution device connected to each of the connecting transformers. The reliability of each harmonic eliminator is improved by adopting a redundant design. If a group of harmonic eliminators is under maintenance or fails, another group of harmonic eliminators can also be connected in parallel with the connecting transformer.

[0051] In one embodiment, a circuit breaker is connected in series between the harmonic eliminator and the connecting transformer and the connected AC busbar. By controlling the on-off of the circuit breaker, a one-in-one-standby design of the harmonic eliminator can be realized. For example, one of the harmonic eliminators is used as the main harmonic eliminator. When the connecting transformer is connected to the AC system, the circuit breaker connected to the main harmonic eliminator is closed, and the main harmonic eliminator is connected to the AC system to suppress resonance. When the main harmonic eliminator fails, at this time, the circuit breaker connected to the other standby harmonic eliminator is closed to connect the standby harmonic eliminator to the AC system to suppress resonance.

[0052] In one embodiment, a circuit breaker is connected in series between the connection transformer and the AC bus. By connecting the circuit breaker in series, the connection transformer can be switched on and off. When the connection transformer fails, the circuit breaker between the connection transformer and the AC bus, and the circuit breaker between the harmonic elimination device and the connected AC bus can be disconnected immediately.

[0053] To better illustrate the working process of the flexible DC power transmission system provided in the embodiment of the present application, an example is given below:

[0054] The harmonic eliminator is connected to the same AC busbar of the AC power distribution device under a section as the connecting transformer, and is merged into a string and connected to the AC system. The wiring diagram is shown in Figure 1. The wiring method is a half-circuit breaker wiring method, and the double busbar belt adopts a segmented design to adapt to the working conditions of segmented operation. According to the construction scale, 2 connecting transformer incoming lines, 2 station transformer incoming lines, 8 outgoing lines, a total of 6 complete strings, and 22 sets of circuit breakers can be designed. The specific string configuration plan is shown in Table 1 below:

[0055] Table 1

[0056] String number 1M side loop 2M side loop String 1 - Complete String Outlet 1 1Connect the transformer String 2 - Complete String #1 500kV station transformer Outgoing 2 String 3 - Complete String Outgoing line 3 Outgoing 4 String 4 - Complete String Outgoing line 5 Outgoing 6 String 5 - Complete String 7 #2 500kV station transformer String 6 - Complete String 2Connection transformer Outgoing 8

[0057] Each time, one detuning device is used and the other is reserved to improve the reliability of the detuning device. If one set of detuning devices is under maintenance or fails, the other set of detuning devices can also be combined in series with the connecting transformer.

[0058] According to the principle of 500kV AC field wiring, the power line is connected in series with the load line as much as possible, and the first string 1 connecting the transformer and the outgoing line 1 is connected in series.

[0059] Under the bus N-2 operating condition: when both the first bus and the second bus fail or the two side switches in the string fail or are under maintenance, that is, when the connecting transformer and the line are operating out of string, the harmonic eliminator can still be normally connected to the AC distribution device, avoiding the risk of resonance and improving the safety and stability of the AC system.

[0060] Under the bus N-1 condition: if the faulty bus is the 500kV I bus (first bus) or II bus (second bus), the harmonic eliminator can also be connected to the AC distribution device; if the faulty bus is a unit bus with a harmonic eliminator and a connecting transformer connected in parallel, the connecting transformer cannot be connected to the AC system and no power is delivered, and the harmonic eliminator does not need to be connected to the AC distribution device.

[0061] In the wiring diagram of Figure 1, the power source is a 1-connection transformer. Only when the 1-connection transformer is connected to the AC system can the load line deliver power normally. When the 1-connection transformer is connected to the AC system, the harmonic eliminator and the parallel busbars and string devices of the connection transformer circuit are all operating normally. Therefore, the harmonic eliminator can also be connected to the AC system. Therefore, the harmonic eliminator can be connected to various working conditions of normal line operation. At the same time, compared with the existing wiring scheme, this wiring scheme does not increase the number of harmonic eliminators and circuit breakers.

[0062] The flexible direct current transmission system provided in the embodiment of the present application can connect the harmonic eliminator to the AC outgoing line to avoid resonance under various operating conditions of the AC system, thereby improving the safety and stability of the AC system.

[0063] In a second aspect, a power grid system is provided, comprising:

[0064] AC system, used to output AC power;

[0065] The flexible DC transmission system as described above.

[0066] The power grid system equipped with the above-mentioned flexible direct current power transmission system has all the beneficial effects described in the above embodiments, which will not be described in detail here.

[0067] In the description of this specification, the description with reference to the terms "some embodiments", "other embodiments", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic description of the above terms does not necessarily refer to the same embodiment or example.

[0068] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0069] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

Claims

1. A flexible direct current transmission system, characterized in that: include: A connection transformer, wherein the AC side of the connection transformer is connected to the AC system, and the connection transformer is connected to the first busbar and the second busbar in a one-and-a-half circuit breaker connection mode; A harmonic eliminator is connected to the same AC bus of the AC power distribution device as the connecting transformer.

2. The system according to claim 1, characterized in that There is at least one busbar section circuit breaker on each of the first busbar and the second busbar.

3. The system according to claim 1, characterized in that The system further comprises: A station transformer, one side of which is connected to the outgoing line terminals led out from the first busbar and the second busbar.

4. The system according to claim 1, characterized in that A plurality of lead wires are bridged between the first busbar and the second busbar, and a plurality of circuit breakers are arranged on the lead wires. An outlet terminal is led out between every two adjacent circuit breakers among the plurality of circuit breakers.

5. The system according to claim 4, characterized in that Three circuit breakers are arranged on the leads bridged between the first busbar and the second busbar.

6. The system according to claim 2, characterized in that There are multiple connection transformers, and the number of segments of the connection transformers, the first busbar, and the second busbar is consistent.

7. The system according to any one of claims 1 to 6, characterized in that At least two harmonic eliminators are connected to the AC busbar to which each of the connection transformers is connected.

8. The system according to any one of claims 1 to 6, characterized in that: A circuit breaker is connected in series between the detuning device and the connected AC busbar.

9. The system according to claim 8, characterized in that A circuit breaker is connected in series between the connection transformer and the connected AC busbar.

10. A power grid system, characterized in that: include: AC system, used to output AC power; A flexible direct current transmission system as claimed in any one of claims 1 to 9.

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