WO2019170040A1

WO2019170040A1 - Control method and device for multi-terminal direct current power transmission system during inter-station communication fault

Info

Publication number: WO2019170040A1
Application number: PCT/CN2019/076737
Authority: WO
Inventors: 卢东斌; 侍乔明; 田杰; 王俊生; 黄志岭; 张翔
Original assignee: 南京南瑞继保电气有限公司; 南京南瑞继保工程技术有限公司
Priority date: 2018-03-05
Filing date: 2019-03-01
Publication date: 2019-09-12
Also published as: CN108418237A; CN108418237B

Abstract

The present application provides a control method and device for a multi-terminal direct current power transmission system during an inter-station communication fault, used for a multi-terminal direct current power transmission system. The method comprises the following steps: when a fault occurs in the communication of the converters at the rectification side of the multi-end direct current power transmission system and the converters at the inversion side, the inversion side reduces a direct current voltage to operate; when the inversion side detects that the direct current or alternating current flowing through the converters at the inversion side is greater than a rated current or an overload allowable current, the inversion side increases the direct current voltage to operate; moreover, the rectification side limits the direct current by using a high-voltage current-limiting function until the direct current or alternating current of the converters at the inversion side is reduced to the rated current or the overload allowable current. According to the technical solution provided by the present application, the whole multi-terminal direct current system can be effectively prevented from being turned off when an inter-station communication fault occurs in the multi-terminal direct current system, thereby reducing the impact on an alternating current power grid, and improving the stability of the system.

Description

Method and device for controlling communication failure between stations in multi-terminal direct current transmission system

Technical field

The invention belongs to the field of high voltage direct current transmission, and particularly relates to a control method and device for communication failure between stations in a multi-terminal direct current transmission system.

Background technique

A multi-terminal direct current (MTDC) transmission system refers to a direct current transmission system containing three or more converter stations. Compared with DC transmission at both ends, multi-terminal DC transmission provides a more economical and flexible transmission mode, which can achieve multi-power supply and multi-drop power reception, and has good development potential and application prospects in China. From the perspective of control protection, the generalized multi-terminal DC transmission system also refers to a DC transmission system in which two or more inverters are connected in parallel on the rectification side or the inverter side.

The structure of the multi-terminal DC transmission system is basically divided into parallel and series. In the parallel structure, the power adjustment range of each converter station is large, the expansion of the converter station is flexible, the whole system is easy to cooperate with insulation, and the operation economy is high. It is the preferred method for multi-terminal DC transmission engineering.

In a parallel multi-terminal DC system, since there are multiple rectification-side converter stations or multiple inverter-side converter stations at the same time, it is usually necessary to set a communication between the multi-terminal controller and each station control to realize multi-terminal DC stations. Coordinated control to balance power or current commands between the various converter stations. The commutation station and the multi-terminal controller need to be connected through the inter-station communication channel, and the normality of the inter-station communication has a great influence on the stable operation of the whole system.

In a multi-terminal direct current (MTDC) transmission system, the type of converter station may include a conventional grid commutated inverter (LCC) type and a voltage source converter (VSC) type. Among them, the multi-terminal DC system including only the LCC type converter station is called a multi-terminal conventional DC system, and the multi-terminal DC system including the LCC type and the VSC type converter station is called a multi-terminal hybrid DC system, and only includes the multi-end of the VSC type converter station. The DC system is called a multi-terminal flexible DC system.

Figure 1 shows a typical structure of a main circuit of a parallel type four-terminal conventional HVDC transmission system. The four-terminal DC transmission system comprises two rectifier stations and two inverter stations, namely a rectifier station I 1 , a rectifier station II 2 , an inverter station I 3 and an inverter station II 4 . The four converter stations are all LCC type converter stations, and different converter stations are connected to different AC grids 5, and different converter stations are connected in parallel by DC lines 6. Each converter station includes symmetrical two poles, and the two pole neutral busbars 15 are connected to the grounding poles 17 via grounding leads 16 . Each pole includes a high-side inverter 13 and a low-end inverter 14 which are six-pulse or twelve-pulse bridge circuits, which are respectively connected to the AC grid 5 through a high-side converter transformer 11 and a low-side converter transformer 12.

Figure 2 shows the main circuit structure of a parallel type three-terminal hybrid DC transmission system. The three-terminal hybrid DC transmission system comprises a rectifier station and two inverter stations, wherein the rectifier station I 1 and the inverter station I 3 are both LCC type converter stations, and the inverter station II 7 is a VSC type converter station. Each converter station is connected to a different AC grid 5, and different converter stations are connected in parallel via a DC line 6. The configuration of the LCC type converter station is the same as that in Fig. 1. Each pole of the VSC type converter station is composed of a modular multi-level converter (MMC) 71, and the MCC type converter is coupled. The transformer 72 is connected to the AC grid 5.

Figure 3 shows a hybrid DC converter comprising a grid commutated inverter 31 in series with a voltage source converter on the inverter side, wherein the series branch of the voltage source converter comprises two parallel modules. Multilevel voltage source inverters 71 and 73. The grid commutating inverter 31, the modular multilevel voltage source inverter 71 and the modular multilevel voltage source converter 73 pass through the converter transformer 32, the coupling converter 72 and the coupling converter 74, respectively. AC grid 5 connection. The grid commutating inverter 31, the modular multilevel voltage source inverter 71 and the modular multilevel voltage source converter 73 can be distributed in the same inverter station, or the grid commutating converter 31, the module The multi-level voltage source inverter 71 is in one inverter station, the modular multi-level voltage source converter 73 is in another inverter station, or the grid commutated inverter 31 is in an inverter station, modular The multi-level voltage source inverter 71 and the modular multi-level voltage source converter 73 are at another inverter station, or three are distributed among three different inverter stations.

When the multi-terminal DC system is in normal operation, the power or current balance control between different stations is realized through multi-level control at the system level. 4 and 5 are two typical configuration diagrams of inter-station communication in a parallel type four-terminal direct current transmission system. In FIG. 4, a four-terminal controller is disposed in both the rectifier station I 1 and the inverter station I 3 , wherein the four-terminal controller configured by the rectifier station I 1 is a master controller, and the four terminals of the inverter station I 3 are configured. Control is the standby controller. The four converter stations are connected to the two four-terminal control through the inter-station communication channel, and the two four-terminal controls are also connected by the inter-station communication. When the communication between stations is normal, the four-terminal main controller of the rectifier station 1 simultaneously receives the voltage, current, power and other state values of the two rectifier stations and the two inverter stations, and at the same time, the converters issue control commands such as voltage and current. Achieve balanced and stable control of the entire multi-terminal DC. In Figure 5, the converter stations realize two-to-two interconnections through the inter-station communication channel. Each station transmits state information such as voltage, current, and power to each other. At the same time, the four commutations are all equipped with multi-end coordination controllers. The multi-end coordinated control of one station is in an active state, and the multi-end coordinated control of other stations is in a standby state.

Generally, two rectification-side converter stations in four-terminal DC operate in current or power control mode. In the two inverter-side converter stations, the larger capacity operates in voltage control mode, and the smaller capacity operates in current or Power control mode. When a converter station exits due to fault lockout, the multi-terminal control can detect the running status of the converter station in time, and simultaneously adjust the operation mode and voltage and current control commands of other converter stations in time to realize the whole multi-terminal DC. System rebalance control. Taking the inverter side voltage control station fault lockout operation as an example, during the normal operation of the four-terminal DC, when the inverter side voltage control station exits due to the fault lockout, the multi-end control firstly controls the operation mode of the other inverter station by current. The mode is adjusted to the voltage control mode to ensure the stability of the DC voltage. At the same time, according to the transmission capacity of the inverter station, the current commands of the two converter stations on the rectification side are adjusted in time to ensure the balance between the power of the transmitting and receiving ends, and the inverter station is prevented from being overloaded for a long time.

Due to the long distance between the converter stations, the communication channel between stations is long, and communication failure between stations is inevitable. When the inter-station communication fails due to the communication channel, the communication between the inverter-side converter station and the rectifier-side converter station is lost. The multi-terminal control will not be able to detect the running status of the inverter station in real time, and the correct control cannot be transmitted to the rectifier station. instruction. At this point, the multi-terminal controller can only exit the operation, and each converter station will be in independent operation state. During the period, if an inverter-side converter station is blocked due to a fault, it will cause overload operation of other inverter-side converter stations that are in normal operation. At present, in order to avoid the long-term overload state of the inverter-side converter station, the usual control strategy is that when the converter station is detected to lose communication with the multi-terminal control, the overload capacity of the inverter beyond the converter station is blocked. The flow station is coordinated by the multi-terminal converter to control the operation status of other normally operating converter stations. When all the communication stations on the inverter side are lost, the entire multi-terminal DC transmission system can only be blocked.

When the inter-station communication between the inverter-side converter stations is lost, if the entire multi-terminal DC transmission system is blocked due to the overload of the inverter-side converter station, it will bring a big impact to the AC system of the transmission and reception, affecting the stable operation of the AC grid. .

Summary of the invention

The object of the present invention is to provide a control method for communication failure between stations in a multi-terminal direct current transmission system. When the communication station on the rectification side of the multi-terminal direct current transmission system and the converter station on the inverter side have communication failure, the rectification side of the transmission end is The active regulation of the inverter-side converter avoids the active latching of the entire multi-terminal DC system or avoids the latching of the entire multi-terminal DC transmission system due to the latching of a certain terminal converter; and provides a multi-terminal DC transmission system under the communication failure between stations. Control device for controlling a multi-terminal DC converter.

An embodiment of the present invention provides a multi-terminal direct current transmission system control method for communication between stations, which is used in a multi-terminal direct current transmission system, and the method includes the following steps: commutation of a rectifier side of a multi-terminal direct current transmission system When the inverter and the converter on the inverter side are in communication failure, the inverter side reduces the DC voltage operation; the inverter side detects that the DC current or the AC current flowing through the inverter on the inverter side is greater than the rated current When the overload current is allowed, the inverter side increases the DC voltage operation, and the rectifier side uses the high voltage current limiting function to limit the DC current until the DC current or the AC current of the inverter on the inverter side falls to the rated state. Current or overload allows current.

Further, the inverter side includes at least two inverter stations or at least two inverters in parallel, and when the inverter side includes at least two inverter stations, two or more of the inverter stations Sharing the same DC bus, the inverter station is composed of a grid commutation converter or a voltage source converter, but at least one of the inverter stations is composed of a grid commutation converter; the inverter When the side comprises at least two inverters connected in parallel, the parallel converters are composed of a network commutating converter or consist of a voltage source converter, but at least one parallel converter is commutated by the grid. Streamer composition.

Further, the converter on the rectification side of the multi-terminal direct current transmission system and the converter communication fault on the inverter side include: all of the converters on the rectification side and all inverters on the inverter side are lost Communicating, or part of the inverter-side converter loses communication with all of the rectifying-side converters, or part of the rectifying-side converters and all of the inverter-side commutations The device loses communication, or part of the rectifier side converter loses communication with a portion of the inverter side inverter.

Further, the inverter side reduces the DC voltage operation, including: the inverter that controls the DC voltage of the inverter side reduces the DC voltage, and if the DC voltage converter is the grid commutation converter, Reducing the DC voltage by changing the converter transformer tap of the grid commutating converter to reduce the valve side phase voltage or increasing the arc extinction angle of the grid commutating converter; if the DC voltage converter is The voltage source converter reduces the valve side phase voltage by changing the junction transformer tap of the voltage source converter, or controls the voltage source converter voltage, or reduces the number of sub-module inputs, or reduces the sub-module voltage. To achieve a reduction in DC voltage;

The inverter side increases the DC voltage operation, including: the inverter that controls the DC voltage of the inverter side increases the DC voltage, and if the converter of the DC voltage is the grid commutation converter, The converter transformer tap of the grid commutating converter increases the valve side phase voltage or reduces the arc extinction angle of the grid commutating converter to increase the DC voltage; if the DC voltage converter is a voltage source The flow device can improve the valve side phase voltage by changing the junction transformer tap of the voltage source converter, or control the voltage source converter voltage, or increase the number of submodule inputs, or increase the submodule voltage to improve DC voltage.

Further, in the operation of reducing the DC voltage in the inverter side, the reduction of the DC voltage is preset; other converters in the current control mode or the power control mode maintain a DC current during the DC voltage reduction process. The command value or DC power command value does not change.

Further, the inverter side detects that a direct current or an alternating current flowing through the inverter on the inverter side is greater than a rated current or an overload allowable current, including: flowing through an inverter of the inverter side The DC current is greater than the rated DC current or the overload allows the DC current, or the AC current flowing through the inverter on the inverter side is greater than the rated AC current or the overload allowed AC current, including the inverter on the inverter side or The rectifier station raises the DC power to cause a DC current or an AC current overcurrent; the overload allows the DC current or the overload allows the AC current to be operated by the inverter on the inverter side, considering that the main circuit device is overcurrent Pressure level, according to the temperature of the valve hall, with or without redundant cooling, the maximum operating current allowed by the temperature of the inlet and outlet water, different overload allowable current levels correspond to different allowable operating times. The above-mentioned inverter side detects that the DC current or the AC current flowing through the inverter is greater than the rated current or the overload current is triggered by the delay opening.

Further, the rectifying side adopting a high voltage current limiting function includes: the rectifying side reduces a DC current command when a DC voltage is higher than an allowable DC voltage in a communication fault condition; and the DC voltage is higher, the DC current is higher The smaller the instruction. The above-mentioned allowable DC voltage is preset by the converter on the rectification side, and is a linear function of a constant value or a direct current, which is determined by the inverter voltage on the inverter side and the line voltage drop. The above high voltage current limiting function is introduced when the communication between stations is faulty.

Further, the inverter side increases the DC voltage operation, including: if the inverter on the inverter side of the fault lockout is in the current control mode or the power control mode before the lock, the converter on the inverter side in the voltage control mode After detecting that the DC current or AC current of the station is greater than the rated current or the overload allowable current, the DC voltage of the multi-terminal DC transmission system will be immediately increased, thereby passing the overload signal of the inverter on the inverter side through the DC voltage. The converter that is transmitted to the rectification side; the converter on the rectification side immediately enters the high-voltage current limiting control mode after detecting the rise of the DC voltage, and reduces the DC current of the converter on the rectification side; The inverter on the variable side is in the voltage control mode before blocking, and the inverter on the inverter side in the current control mode or the power control mode will immediately be converted into the voltage control mode for DC boost control.

The embodiment of the present application further provides a multi-terminal direct current transmission system control device for communication failure between stations, which is used in a multi-terminal direct current power transmission system, wherein the device includes a detecting unit and a control unit, wherein: the detecting unit detects the DC current, DC voltage, inter-station communication signal, converter transformer or junction transformer tap of multi-terminal DC transmission system; control unit detects inverter communication failure on inverter side and inverter side of multi-terminal DC transmission system Controlling the inverter on the inverter side to reduce DC voltage operation, when the inverter on the inverter side detects that the DC current or AC current flowing through the inverter on the inverter side is greater than the inverter When the rated current or the overload is allowed, the inverter on the inverter side increases the DC voltage operation, and the converter on the rectification side adopts a high voltage current limiting function to limit the DC of the converter on the rectification side. Current until the DC current or AC current of the inverter on the inverter side drops to the rated current or the overload allowable current.

Further, the detecting unit includes an inverter side detecting module and a rectifying side detecting module, and the inverter side detecting module detects a direct current, a direct current voltage, an inter-station communication signal, a converter transformer or a junction transformer of the inverter side. a rectifier; the rectifier side detection module detects a DC current, a DC voltage, an inter-station communication signal, a converter transformer or a junction transformer tap on the rectification side.

Further, the control unit includes a communication fault control module and an overcurrent control module, and the communication fault control module controls when the inverter on the rectification side of the multi-terminal DC transmission system and the inverter on the inverter side are faulty. The converter on the inverter side reduces the DC voltage operation; the inverter of the inverter side detects that the DC current or the AC current flowing through the inverter on the inverter side is greater than When the rated current of the inverter or the overload allowable current, the inverter on the inverter side increases the DC voltage operation, and the converter on the rectification side adopts a high voltage current limiting function to limit the commutation of the rectification side The DC current of the inverter is reduced until the DC current or AC current of the inverter on the inverter side drops to the rated current or the overload allowable current.

Further, the communication fault control module includes a buck control module and an instruction control module. The buck control module controls the inverter on the inverter side to reduce the DC voltage operation on the inverter side when detecting the communication failure of the inverter on the rectification side of the multi-terminal DC transmission system and the converter on the inverter side, The reduction amplitude of the DC voltage on the inverter side is preset; the inverter in the current control mode or the power control mode on the inverter side of the command control module maintains a DC during the DC voltage reduction process The current command value or DC power command value does not change.

Further, the overcurrent control module includes a boost control module and a rectifier side current limiting module, and the boost control module detects an inverter flowing through the inverter side on the inverter side of the inverter side. When the direct current or the alternating current is greater than the rated current of the inverter or the overload allowable current, the inverter on the inverter side increases the DC voltage operation; the commutation side current limiting module converts the current on the inverter side While increasing the DC voltage operation, the inverter that controls the rectification side adopts a high voltage current limiting function to limit the DC current of the converter on the rectification side until the DC current of the inverter on the inverter side or The AC current drops to the rated current or the overload allows the current.

In the technical solution provided by the embodiment of the present application, when the communication station on the rectification side of the multi-terminal direct current transmission system and the converter station on the inverter side are in communication failure, the inverter side operates by reducing the DC voltage, thereby effectively improving the inverter station pair. Overload current control capability, on the other hand, when the inverter side is locked at the inverter side, when the converters of other converter stations detect that the DC current is greater than the rated current, the inverter will be operated by increasing the DC voltage. The overload signal is transmitted to the rectification side through the DC voltage, so that the rectification side uses the high-voltage current limiting function to limit the DC current, thereby preventing the inverter side from being blocked due to the overload capacity being exhausted, thereby preventing the entire multi-terminal DC transmission system from being shut down. When the communication between stations in the multi-terminal DC system is faulty, the entire multi-terminal DC system is effectively prevented from being locked, thereby reducing the impact on the AC grid and improving the stability of the system.

DRAWINGS

In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings used in the description of the embodiments will be briefly described below. It is obvious that the drawings in the following description are only some embodiments of the present application. Other drawings may also be obtained from those of ordinary skill in the art in light of the inventive work.

1 is a schematic diagram of a main circuit of a parallel type four-terminal DC power transmission system using an LCC type converter station on both the rectification side and the inverter side according to an embodiment of the present application;

2 is a schematic diagram of a main circuit of a parallel type three-terminal direct current transmission system including an LCC and a VSC type converter station on an inverter side according to another embodiment of the present application;

3 is a schematic diagram of a main circuit of a DC transmission system formed by a hybrid DC converter composed of an LCC and a VSC converter in series on an inverter side according to another embodiment of the present application;

4 is a schematic structural diagram of a communication mode between stations of a parallel type four-terminal direct current transmission system according to an embodiment of the present application;

FIG. 5 is a schematic structural diagram of a second inter-station communication mode of a parallel type four-terminal direct current transmission system according to another embodiment of the present application; FIG.

6 is a flow chart of a method for controlling communication failure between stations in a multi-terminal direct current transmission system according to an embodiment of the present application;

7 is a control characteristic diagram of a rectification-side converter station when controlling a communication failure between stations in a multi-terminal direct current transmission system according to an embodiment of the present application;

8 is a schematic structural diagram of a control device for communication failure between stations in a multi-terminal direct current transmission system according to an embodiment of the present application;

FIG. 9 is a schematic structural diagram of a device for controlling communication between stations in a multi-terminal direct current transmission system according to another embodiment of the present application.

Reference numerals: 1, LCC type rectifier station I; 11, high-end converter transformer; 12, low-end converter transformer; 13, high-end inverter; 14, low-end converter; 15, pole neutral bus; , grounding lead; 17, grounding pole; 2, LCC type rectifier station II; 3, LCC type inverter station I; 31, power grid commutation converter; 32, converter transformer; 4, LCC type inverter station II; 5, AC grid; 6, DC line; 7, VSC type inverter station II; 71, modular multi-level voltage source converter; 72, coupling transformer; 73, modular multi-level voltage source converter; 74, coupling transformer; 8, diode valve; 9, multi-terminal DC transmission system communication failure control station; 91, detection unit; 92, control unit; 911, inverter side detection module; 912, rectifier side detection module; , communication fault control module; 922, overcurrent control module; 9211, buck control module; 9212, command control module; 9221, boost control module; 9222, rectifier side current limiting module.

Detailed ways

The specific embodiments of the technical solutions of the present application will be described in more detail and clearly with reference to the accompanying drawings and embodiments. However, the specific embodiments and examples described below are for illustrative purposes only and are not limiting of the application. It is intended to cover a part of the embodiments of the present application, and not all of the embodiments, and other embodiments obtained by those skilled in the art for various changes of the present application are within the scope of the present application.

FIG. 6 is a flowchart of a method for controlling communication failure between stations in a multi-terminal direct current transmission system according to an embodiment of the present invention, and shows a control method for communication failure between stations in a multi-terminal direct current transmission system according to the present invention.

In Fig. 6, when the inter-station communication is normal, the balance control of the system is realized by the multi-terminal controller between the converter stations.

When the communication between the inverter-side converter or the converter station and the rectifier-side converter or converter station is lost, the inverter-side voltage control station will enter the step-down control mode to actively reduce the DC voltage of the system, and the DC voltage. The reduction range is preset by the system, such as reducing the rated DC voltage by 5%; other converter stations in the current control mode or the power control mode maintain the DC current command value or the DC power command value during the DC voltage reduction process. change.

At this point, the entire multi-terminal transmission system enters the buck and power reduction modes, or the buck and constant power modes of operation, wherein if the power is reduced, the power reduction is the same as the voltage reduction. The regulation of the DC voltage of the multi-terminal DC system is realized for the grid commutating converter by adjusting the arc-extinguishing angle of the inverter-side voltage control station or the converter transformer tap. In the actual engineering adjustment process, it is necessary to consider the ability of the inverter station for reactive power compensation and the adjustment capability of the converter transformer tap. Since the adjustment speed of the arc-extinguishing angle is much faster than the tap control, it is usually preferred to use the method of keeping the converter transformer tap position unchanged and increasing the arc-extinguishing angle of the inverter side for buck control; for voltage source commutation To reduce the voltage on the valve side by changing the junction transformer tap of the inverter, or to reduce the voltage of the voltage source converter, or to reduce the number of sub-module inputs, or to reduce the voltage of the sub-module. In the actual engineering adjustment process, it is preferable to reduce the number of sub-module inputs.

During the inter-station communication failure, the converter on the rectification side introduces a high voltage current limiting function. If the operating power of the system is large and the inverter on one inverter side is blocked due to failure, the DC current Id of other normally operating inverters will be greater than the rated value IdN or the overload allowable current, or the alternating current. Iac is greater than the rated IacN or overload current, resulting in an overload operation. At this time, the inverter on the inverter side performs boost control, and the inverter on the rectifier side performs high voltage current limiting control to reduce the DC current on the rectifier side, thereby reducing the DC power on the rectifier side.

For the parallel type four-terminal conventional DC transmission system shown in Figure 1, during the inter-station communication failure, if the fault-locked inverter station is in the current control mode before blocking, it is the inverter-side converter station in the voltage control mode. After detecting that the DC current of the station is greater than the rated current, the DC voltage of the system will be raised immediately by raising the tap position or reducing the arc extubation angle of the converter, thereby overloading the inverter side converter station. The signal is transmitted to the rectification side converter station via a DC voltage. After the rectifier side converter station detects the DC voltage rise, it immediately enters the high voltage current limit control mode to reduce the DC current of the rectifier side converter station. Eventually, the rectifier side and inverter side converter stations will again be adjusted to operate at a stable operating point. If the fault-locked inverter station is in the voltage control mode before blocking, the inverter-side converter station in the current control mode will immediately be converted into the voltage control control mode for DC boost control.

For the parallel three-terminal hybrid DC transmission system shown in Figure 2, during the inter-station communication fault, if the fault-locked inverter station is in the current control mode before blocking, the VSC-type converter station performs voltage control. If the fault-locked inverter-side converter station is a VSC-type converter station, the inverter-side converter station in the current control mode detects that the DC current of the station is greater than the rated current, and immediately converts it to a voltage control station. DC boost control.

The hybrid DC converter shown in Figure 3 constitutes a DC transmission system. During the inter-station communication fault, if the faulty latched modular multilevel voltage source converter is in current control mode before blocking, it is in voltage control. The modular multi-level voltage source converter of the mode detects that the DC current flowing through the converter is greater than the rated DC current or the overload allowable current, or the AC current flowing through the converter is greater than the rated AC current or overload. Immediately after the current, the junction transformer tap is raised to raise the valve side phase voltage, or the voltage source converter voltage is increased, or the number of submodule inputs is increased, or the submodule voltage is increased to increase the system DC voltage, thereby The overload signal of the inverter-side converter station is transmitted to the rectifier-side converter station through the DC voltage. After the rectifier side converter station detects the DC voltage rise, it immediately enters the high voltage current limit control mode to reduce the DC current of the rectifier side converter station. Eventually, the rectifier side and inverter side converter stations will again be adjusted to operate at a stable operating point. Modular multilevel voltage source converters in current control mode or power control mode are immediately converted to voltage control if the faulty latched modular multilevel voltage source converter is in voltage control mode prior to latching The mode performs DC boost control.

FIG. 7 is a control characteristic diagram of a rectification-side converter station when a multi-terminal direct current transmission system is controlled under inter-station communication failure according to an embodiment of the present invention, and shows control characteristics of a rectification-side converter station before and after an inter-station communication failure. curve.

In Figure 7, characteristic curve 1 is the rectifier side converter station operating curve before the station communication failure. The curve mainly includes the constant current control curve CD, the low voltage current limiting curve BC and the minimum current limit curve AB; the characteristic curve 2 is the station The running curve of the rectification side converter station after communication failure, the curve mainly includes a constant current control curve GH, a low voltage current limiting curve FG, a minimum current limiting curve EF, a high voltage current limiting characteristic curve HJ, and a high voltage minimum current limiting curve JK.

In Figure 7, before the inter-station communication failure, the rectifier-side converter operates at the operating point 1, the voltage is the rated value UdN, and the current value is the command value Iord transmitted by the multi-terminal controller; after the communication failure between the stations, the rectifier station changes The control characteristic curve of the flow device is shifted to the left as a whole, and the rectifier-side converter operates at the operating point 2, and its voltage value is less than the rated operating value, which is Udo, and its current is maintained as the multi-end controller command value Iord. After the communication failure between stations, during the step-down operation, the converter with the inverter side in the current control mode can keep the power ratio of each converter kept the same if the method of keeping the DC current command constant is adopted. During the step-down operation, after an inverter-side converter exits due to fault lockout, the rectifier-side converter adopts the high-voltage current-limiting characteristic curve HJ of the same slope, which can achieve equal-equal coordination of DC power between different rectifier stations. .

FIG. 8 is a schematic structural diagram of a control device for communication failure between stations in a multi-terminal direct current transmission system according to an embodiment of the present invention, showing a control device 9 for communication failure between stations of a multi-terminal direct current transmission system, the principle structure thereof, including detection Unit 91, control unit 92.

The detecting unit 91 detects a direct current, a direct current voltage, an inter-station communication signal, and a converter transformer tap. When the control unit 92 detects a communication failure, the inverter side reduces the DC voltage operation. When the inverter side detects that the DC current or the AC current is greater than the rated current or the overload allowable current, the inverter side increases the DC voltage operation while the rectifier side The high voltage current limiting function is used to limit the DC current.

FIG. 9 is a schematic structural diagram of a control device according to another embodiment of the present invention, showing a control device 9 for a communication failure between stations of a multi-terminal direct current transmission system, and a schematic structure thereof, specifically including a detecting unit 91 and a control unit 92.

The detecting unit 91 includes an inverter side detecting module 911 and a rectifying side detecting module 912.

The inverter side detection module 911 detects a DC current, a DC voltage, an inter-station communication signal, a converter transformer, or a junction transformer tap on the inverter side. The rectification side detection module 912 detects a DC current, a DC voltage, an inter-station communication signal, a converter transformer, or a junction transformer tap on the rectification side.

The control unit 92 includes a communication failure control module 921 and an overcurrent control module 922.

The communication failure control module 921 controls the inverter on the inverter side to reduce the DC voltage operation when detecting the inverter communication failure on the rectifier side of the multi-terminal DC transmission system and the converter on the inverter side. The overcurrent control module 922 detects the commutation current on the inverter side when the inverter on the inverter side detects that the DC current or the AC current flowing through the inverter on the inverter side is greater than the rated current of the inverter or the overload allowable current. The device increases the DC voltage operation, and the converter on the rectification side adopts a high-voltage current limiting function to limit the DC current of the converter on the rectification side until the DC current or AC current of the inverter on the inverter side drops to the rated current or The load allows current.

The communication failure control module 921 includes a step-down control module 9211 and an instruction control module 9212.

The buck control module 9211 controls the inverter on the inverter side to reduce the DC voltage operation on the inverter side when detecting the inverter communication failure on the rectifier side of the multi-terminal DC transmission system and the converter on the inverter side. The magnitude of the decrease in the DC voltage on the inverter side is set in advance. The command control module 9212 controls the inverter in the current control mode or the power control mode on the inverter side, and keeps the DC current command value or the DC power command value unchanged during the DC voltage reduction process.

The overcurrent control module 922 includes a boost control module 9221 and a rectification side current limiting module 9222.

The boost control module 9221 detects the commutation current on the inverter side when the inverter on the inverter side detects that the DC current or the AC current flowing through the inverter on the inverter side is greater than the rated current or the overload allowable current of the inverter. The device increases the DC voltage operation. The rectifier side current limiting module 9222 increases the DC voltage operation of the inverter on the inverter side, and controls the converter on the rectifier side to adopt a high voltage current limiting function to limit the DC current of the converter on the rectifier side until the inverter side The DC current or AC current of the converter drops to the rated current or the overload allowable current.

In summary, the present invention discloses a control method and apparatus for communication failure between stations of a multi-terminal direct current transmission system, which is used for power coordinated control when a communication failure between stations of a multi-terminal DC system is realized. When the communication between the rectifier side converter station and the inverter side converter station of the multi-terminal DC transmission system fails, the inverter on the inverter side reduces the DC voltage operation, and when the inverter side detects the DC current or AC current flowing through the inverter When the current is greater than the rated current or overload, the DC voltage is increased. At the same time, the inverter on the rectifier side uses high-voltage current limiting control to limit the DC current and prevent the inverter on the inverter side from being overloaded for a long time, thus ensuring multi-terminal DC. The transmission system operates reliably and avoids blocking the entire multi-terminal DC transmission system.

It should be noted that the various embodiments described above with reference to the accompanying drawings are only used to illustrate the scope of the application, and the scope of the present application should be understood by those skilled in the art without departing from the spirit and scope of the application. Modifications or equivalent substitutions to this application are intended to be included within the scope of the present application. In addition, unless the context indicates otherwise, words in the singular include plural and vice versa. In addition, all or a portion of any embodiment can be used in combination with all or a portion of any other embodiment, unless otherwise stated.

Claims

A multi-terminal direct current transmission system control method for communication failure between stations is used for a multi-terminal direct current transmission system, characterized in that the method comprises the following steps:

When the converter on the rectification side of the multi-terminal direct current transmission system and the inverter on the inverter side are in communication failure, the inverter side reduces the DC voltage operation;

When the inverter side detects that the DC current or the AC current flowing through the inverter on the inverter side is greater than the rated current or the overload allowable current, the inverter side increases the DC voltage operation, and the rectification side adopts The high voltage current limiting function limits the DC current until the DC current or AC current of the inverter on the inverter side drops to the rated current or the overload allowable current.
The method of claim 1 wherein said inverting side comprises:

At least two inverter stations, and two or more of the inverter stations share the same DC bus, the inverter station consisting of a network commutating converter or a voltage source converter, but at least One of the inverter stations is composed of a grid commutation converter; or

At least two inverters connected in parallel, the parallel converters being composed of a network commutating converter or consisting of a voltage source converter, but at least one parallel converter consisting of a grid commutating converter .
The method according to claim 1, wherein the converter on the rectification side of the multi-terminal direct current transmission system and the converter on the inverter side have communication faults:

All of the converters on the rectification side lose communication with all inverters on the inverter side, or

Part of the inverter-side inverter loses communication with all of the rectifying-side converters, or

Part of the rectifying side inverter loses communication with all of the inverter side inverters, or

A portion of the rectifying-side inverter loses communication with a portion of the inverter-side inverter.
The method of claim 1 wherein said inverting side reduces DC voltage operation comprises:

The inverter that controls its DC voltage on the inverter side reduces the DC voltage, and if the converter of the DC voltage is a grid commutated converter, the converter transformer is changed by changing the grid commutating converter The connector reduces the valve side phase voltage or increases the arc extinction angle of the grid commutating converter to reduce the DC voltage;

If the DC voltage converter is a voltage source converter, the valve side phase voltage is reduced by changing the junction transformer tap of the voltage source converter, or the voltage source converter voltage is controlled, or the submodule is reduced The number of inputs, or the sub-module voltage is reduced to achieve a reduction in DC voltage;

The inverter side increases DC voltage operation, including:

The inverter that controls its DC voltage on the inverter side increases the DC voltage, and if the converter of the DC voltage is a grid commutator, the converter transformer is changed by changing the grid commutator The joint increases the valve side phase voltage or reduces the arc extinction angle of the grid commutating converter to increase the DC voltage;

If the DC voltage converter is a voltage source converter, increase the valve side phase voltage by changing the junction transformer tap of the voltage source converter, or control the voltage source converter voltage, or add a submodule Increase the DC voltage by increasing the number of inputs or by increasing the sub-module voltage.
The method according to claim 1, wherein in the operation of reducing the DC voltage in the inverter side, the magnitude of the decrease of the DC voltage is preset; and other converters in the current control mode or the power control mode are During the DC voltage reduction process, the DC current command value or the DC power command value is kept unchanged.
The method according to claim 1, wherein the inverter side detects that a direct current or an alternating current flowing through the inverter on the inverter side is greater than a rated current or an overload allowable current, including:

The DC current flowing through the inverter on the inverter side is greater than the rated DC current or the overload allowed DC current, or the AC current flowing through the converter on the inverter side is greater than the rated AC current or the overload allowed AC current , including DC current or AC current overcurrent caused by inverter blocking on the inverter side or DC power boosted by the rectifier station;

The overload allows the direct current or the overload allows the alternating current to be operated by the inverter on the inverter side, taking into account the overcurrent and overvoltage level of the main circuit device, according to the valve hall temperature, with or without redundant cooling, The maximum operating current allowed by the inlet and outlet water temperature. Different overloads allow the current level to correspond to different allowable operating times.
The method of claim 1 wherein said rectifying side employs a high voltage current limiting function comprising:

The rectifying side reduces the DC current command when the DC voltage is higher than the allowable DC voltage when the communication fault is detected; the higher the DC voltage, the smaller the DC current command.
The method of claim 1 wherein said inverting side increases DC voltage operation comprises:

If the inverter on the inverter side of the faulty lockout is in the current control mode or the power control mode before the lockout, the inverter on the inverter side in the voltage control mode detects that the direct current or the alternating current of the own station is greater than the rated current. Or after the overload is allowed, the DC voltage of the multi-terminal DC transmission system will be raised immediately, so that the overload signal of the inverter on the inverter side is transmitted to the converter on the rectification side through the DC voltage; After detecting the rise of the DC voltage, the flow device immediately enters the high voltage current limiting control mode to reduce the DC current of the converter on the rectifier side;

If the converter on the inverter side of the faulty lockout is in the voltage control mode before the lockout, the inverter on the inverter side in the current control mode or the power control mode will immediately be converted into the voltage control mode for DC boost control.
A multi-terminal direct current transmission system communication control device between stations is used for a multi-terminal direct current transmission system, characterized in that the device comprises a detection unit and a control unit, wherein:

a detecting unit, detecting a direct current, a direct current voltage, an inter-station communication signal, a converter transformer or a junction transformer tap of the multi-terminal direct current transmission system;

a control unit, when detecting a communication failure of the inverter on the rectification side of the multi-terminal direct current transmission system and the inverter on the inverter side, controlling the inverter on the inverter side to reduce the DC voltage operation, when the inverter side When the inverter detects that the direct current or the alternating current flowing through the inverter on the inverter side is greater than the rated current of the inverter or the overload allowable current, the converter on the inverter side increases the DC voltage operation, Simultaneously controlling the converter on the rectification side to adopt a high voltage current limiting function, limiting the DC current of the converter on the rectification side until the DC current or the AC current of the inverter on the inverter side is reduced to a rated current or Overload allows current.
The apparatus of claim 9 wherein said inverter side comprises:

At least two inverter stations, and two or more inverter stations share the same DC bus, the inverter station consisting of a network commutation converter or a voltage source converter, but at least one inverse The variable station is composed of a grid commutation converter; or

At least two inverters connected in parallel, the parallel converters being composed of a network commutating converter or consisting of a voltage source converter, but at least one parallel converter consisting of a grid commutating converter .
The apparatus according to claim 9, wherein said detecting unit comprises:

The inverter side detecting module detects a direct current, a direct current voltage, an inter-station communication signal, a converter transformer or a junction transformer tap on the inverter side;

The rectification side detecting module detects a direct current, a direct current voltage, an inter-station communication signal, a converter transformer or a junction transformer tap on the rectification side.
The device of claim 9 wherein said control unit comprises:

The communication fault control module controls the inverter on the inverter side to reduce the DC voltage operation when detecting the communication failure of the converter on the rectifier side of the multi-terminal DC transmission system and the inverter on the inverter side;

An overcurrent control module, when the inverter on the inverter side detects that a direct current or an alternating current flowing through the inverter on the inverter side is greater than a rated current or an overload allowable current of the inverter, The inverter on the inverter side increases the DC voltage operation, and the converter on the rectifier side uses a high voltage current limiting function to limit the DC current of the converter on the rectifier side until the inverter on the inverter side The DC current or AC current drops to the rated current or the overload allowable current.
The device of claim 12, wherein the communication failure control module comprises:

The buck control module controls the inverter on the inverter side to reduce the DC voltage operation on the inverter side when detecting the communication failure of the converter on the rectifier side of the multi-terminal DC transmission system and the inverter on the inverter side The magnitude of the decrease in the DC voltage on the inverter side is preset;

The command control module controls the inverter in the current control mode or the power control mode on the inverter side, and keeps the DC current command value or the DC power command value unchanged during the DC voltage reduction process.
The device of claim 12, wherein the overcurrent control module comprises:

a boost control module, when the inverter on the inverter side detects that a direct current or an alternating current flowing through the inverter on the inverter side is greater than a rated current or an overload allowable current of the inverter, The inverter on the inverter side increases the DC voltage operation;

a rectification-side current limiting module, wherein the inverter on the inverter side increases the DC voltage operation, and controls the inverter on the rectification side to adopt a high-voltage current limiting function to limit the DC current of the converter on the rectification side Until the DC current or AC current of the inverter on the inverter side drops to the rated current or the overload allowable current.