CN110601249A

CN110601249A - Voltage source converter unit, online switching method and voltage source converter valve

Info

Publication number: CN110601249A
Application number: CN201910860119.9A
Authority: CN
Inventors: 鲁江; 董云龙; 黄如海; 邱德锋; 卢宇; 田杰; 胡兆庆; 张庆武; 张君君
Original assignee: NR Electric Co Ltd; NR Engineering Co Ltd
Current assignee: NR Electric Co Ltd; NR Engineering Co Ltd
Priority date: 2019-09-11
Filing date: 2019-09-11
Publication date: 2019-12-20
Also published as: WO2021047460A1

Abstract

The present application relates to a method of online commissioning of a voltage source converter unit comprising a voltage source converter and a bypass switch connected in parallel to a dc side of the voltage source converter, wherein the bypass switch is in a closed state before the voltage source converter unit is commissioned online, the method comprising: superimposing a harmonic voltage quantity on a direct current voltage reference value of the voltage source converter; the bypass switch is opened when a zero crossing occurs in the current through the bypass switch that meets a predetermined requirement.

Description

Voltage source converter unit, online switching method and voltage source converter valve

Technical Field

The invention belongs to the technical field of direct current transmission, and particularly relates to an online input method of a voltage source converter unit, the voltage source converter unit, a voltage source converter valve and electronic equipment.

Background

In order to meet the power transmission requirement of long distance and large capacity, the conventional direct current power transmission project adopts the technology of connecting two or more thyristor converter valves in series to improve the direct current voltage level and the transmission capacity of a direct current power transmission system, and a plurality of thyristor converter valve series-connected direct current power transmission projects are built and put into operation at present. At present, a series hybrid direct-current transmission technology that thyristor converter valves are connected in series in a converter station at one end and voltage source converter valves are connected in series in a converter station at the other end and a series flexible direct-current transmission technology that voltage source converter valves are connected in series at both ends are still in a research stage.

For a direct-current power transmission system adopting a converter valve series connection technology, the basic requirement of a main loop topological structure and a control system is that the online investment of a converter valve in the operation process of a direct-current pole can be realized so as to meet the following requirements when the direct-current pole is connected in series by two or more converter valves: 1) after the maintenance of a single converter valve is finished, the converter valve can be put into operation continuously on line; 2) the normal operation of other converter valves is not influenced by the online investment of a single converter valve, and the flexibility and the reliability of the operation of the series direct-current transmission system can be ensured by the requirement.

The inventor of the application finds that the existing online input method of the voltage source converter valve in the series hybrid direct-current power transmission system and the series flexible direct-current power transmission system has the problems of complex topological structure, poor economy and the like.

Disclosure of Invention

It is an object herein to provide a voltage source converter cell and an online commissioning method of a voltage source converter cell.

One embodiment of the present application provides a method of online commissioning of a voltage source converter cell comprising a voltage source converter and a bypass switch connected in parallel to a dc side of the voltage source converter, wherein the bypass switch is in a closed state prior to online commissioning of the voltage source converter cell, the method comprising: superimposing a harmonic voltage quantity on a direct current voltage reference value of the voltage source converter; the bypass switch is opened when a zero crossing occurs in the current through the bypass switch that meets a predetermined requirement.

Another embodiment of the application provides a method of online commissioning of a voltage source converter cell comprising a voltage source converter and a bypass switch connected in parallel to a dc side of the voltage source converter, wherein the bypass switch is in a closed state before online commissioning of the voltage source converter cell, the method comprising: superimposing a first current signal on the bypass switch such that a zero crossing of the current flowing through the bypass switch occurs; the bypass switch is opened when a zero crossing occurs in the current through the bypass switch that meets a predetermined requirement.

Another embodiment of the present application also provides a voltage source converter cell comprising: a voltage source converter; the bypass switch is connected to the direct current side of the voltage source converter in parallel and controls whether the voltage source converter unit is put into operation or not; a control module connected to the bypass switch and the voltage source converter, respectively, and configured to: superimposing an amount of harmonic voltage on a dc voltage reference value of the voltage source converter before controlling the bypass switch to open, and controlling the bypass switch to open when a zero crossing of the current through the bypass switch occurs that meets a predetermined requirement.

Another embodiment of the present application further provides a voltage source converter valve comprising at least two voltage source converter cells of any of the above mentioned types.

Yet another embodiment of the present application provides an electronic device comprising a processor, a memory, and the processor-executable program stored in the memory,

when the program is executed, the processor performs any one of the methods described above.

By using the voltage source converter unit online input method, the voltage source converter unit and the converter valve, before the voltage source converter unit is input (namely before the bypass switch is closed), a current amount is superposed on the bypass switch, so that the current flowing through the bypass switch has a plurality of zero-crossing points. One of the plurality of zero-crossing points can be used for cutting off the bypass switch, so that the action process of the bypass switch is safe and reliable. In other words, the online input of the voltage source converter unit can be safely and reliably controlled.

Meanwhile, the voltage source converter unit and the voltage source converter valve which utilize the voltage source converter unit method can generate the current zero crossing point of the bypass switch without introducing extra hardware at a strong current end. The zero-crossing point can thus be used to safely and reliably open the bypass switch online. Thereby, the voltage source converter cells can be safely and reliably put in-line in the voltage source converter valves. Therefore, the topological structures of the voltage source converter valve and the voltage source converter unit are relatively simple, and the economical efficiency is relatively good.

Drawings

Fig. 1A shows a topology diagram of a hybrid dc power transmission system in the prior art.

Fig. 1B shows a topology diagram of a flexible dc power transmission system in the prior art.

Fig. 1C shows a topology diagram of a prior art voltage source converter.

Fig. 2A shows a schematic flow chart of an online commissioning method of a voltage source converter cell according to an embodiment of the present application.

Fig. 2B shows a schematic diagram of a voltage source converter valve to be fed into a converter cell.

Fig. 2C shows an equivalent circuit schematic of the circuit shown in fig. 2B.

Fig. 2D shows a waveform diagram of the harmonic voltage amount.

Fig. 2E shows a waveform diagram of a current flowing through the bypass switch.

Fig. 3 shows a schematic flow chart of an online commissioning method of a voltage source converter cell according to another embodiment of the present application.

Fig. 4A shows a schematic diagram of a voltage source converter cell according to another embodiment of the present application.

Fig. 4B shows a schematic diagram of the composition of the voltage source converter in the voltage source converter cell shown in fig. 4A.

Fig. 4C shows a schematic composition of the controller in the voltage source converter cell shown in fig. 4A.

Fig. 4D shows a partial circuit schematic of the voltage source converter cell of fig. 4A.

Detailed Description

The following is a description of the embodiments of the present disclosure relating to "a voltage source converter cell online commissioning method, a voltage source converter cell and a voltage source converter valve" by specific embodiments, and those skilled in the art can understand the advantages and effects of the present disclosure from the disclosure of the present disclosure. The invention is capable of other and different embodiments and its several details are capable of modification in various other respects, all without departing from the spirit and scope of the present invention. The drawings of the present invention are for illustrative purposes only and are not intended to be drawn to scale. The following embodiments will further explain the related art of the present invention in detail, but the disclosure is not intended to limit the scope of the present invention.

In order to better understand the technical solution, the following further explains the application environment and the background art of the embodiments of the present application.

Currently, high voltage direct current transmission systems can be divided into two types: a conventional direct current transmission system based on thyristor converter valves (LCC-HVDC) and a flexible direct current transmission system based on fully controlled voltage source converter valves (VSC-HVDC). The conventional direct-current transmission system is low in cost, small in loss and mature in operation technology, most direct-current transmission systems in operation in the world are LCC-HVDC systems at present, but the conventional direct-current transmission system has the defects that commutation failure is easy to occur on an inversion side, the dependence on an alternating-current system is strong, a large amount of reactive power needs to be absorbed, the occupied area of a converter station is large and the like; the new generation of flexible direct current transmission system has the advantages of capability of realizing active power and reactive power decoupling control, capability of supplying power to a passive network, compact structure, small occupied area, no problem of commutation failure and the like, but also has the defect of higher cost.

Therefore, by combining the advantages of the conventional direct current transmission and the flexible direct current transmission, the hybrid direct current transmission technology that the thyristor converter valve is adopted in the converter station at one end and the voltage source converter valve is adopted in the converter station at the other end has good engineering application prospect. In a long term, with the reduction of the price of the full-control device used by the voltage source converter valve, the flexible direct-current transmission technology of the voltage source converter valve adopted by the converter stations at two ends can be more and more widely applied.

Fig. 1A shows a topology diagram of a hybrid dc power transmission system in the prior art. Fig. 1B shows a topology diagram of a flexible dc power transmission system in the prior art. Fig. 1C shows a topology diagram of a prior art voltage source converter.

As shown in fig. 1A, the hybrid dc transmission system 1000 performs ac-dc conversion at a power transmission end (i.e., rectifying side) by using a thyristor converter valve 10, and performs dc-ac conversion at a power reception end (i.e., inverting side) by using a voltage source converter valve 11. As shown in fig. 1B, a voltage source converter valve is used at both ends of the flexible dc power transmission system to perform ac-dc conversion and dc-ac conversion, respectively.

As shown in fig. 1A, the voltage source converter valves 11 may be composed of at least two voltage source converter cells 111. Wherein each voltage source converter cell 111 may comprise a dc side and an ac side. The at least two voltage source converter units are connected in series on the dc side, and the ac side of each voltage source converter unit is connected to an ac bus via a different transformer. The voltage source converter unit may be a three-phase ac terminal connected to a three-phase ac line.

The voltage source converter unit 111 may comprise a voltage source converter 1110 and a bypass switch 1111 connected in parallel to the dc side of the voltage source converter 1110. Wherein voltage source converter 1110 may be used for either ac-to-dc conversion or dc-to-ac conversion. The bypass switch 1111 may be used to control online commissioning and online retirement of the voltage source converter unit 111. When the bypass switch 1111 is closed, the voltage source converter 1110 is in a short-circuit state, and the voltage source converter unit 111 cannot normally operate; after the bypass switch 1111 is disconnected online, the voltage source converter 1110 may enter a normal operating state, that is, the online switching of the voltage source converter unit 111 is realized.

The voltage source converter unit 111 may further comprise a plurality of isolation switches 1112 for performing maintenance operations during system maintenance. For example, it is possible to adapt the state of the individual isolation switches such that the voltage source converter unit 111 is switched into the converter valves 11 or such that the voltage source converter unit 111 is disconnected from the converter valves 11 when the voltage source converter valves are not in operation.

As shown in fig. 1C, the voltage source converter may include a dc side lead terminal U_p、U_nAnd an AC side lead terminal U_a、U_b、U_c. At the direct current side lead terminal U_p、U_nAnd AC side lead terminal U_a、U_bAnd U_cMay include 6 converter valve sub-module strings, respectively: u shape_ap、U_bp、U_cp、U_an、U_bnAnd U_cn. Wherein each converter valve sub-module string may be made up of a plurality of converter valve sub-modules connected in series, such as SM in FIG. 1C₁……SM_N. Wherein each converter valve sub-module may be one of a full bridge sub-module (FBSM), a half bridge sub-module (HBSM), and a full bridge like sub-module (SFBSM).

As shown in fig. 1A, prior to online commissioning of the voltage source converter unit 111 to the voltage source converter valves 11, the voltage source converter unit 111 in the voltage source converter valves 11 is in an inactive state, i.e. the bypass switch 1111 is in a closed state, while typically at least one other voltage source converter unit is now in a normal operating state. Therefore, in this case, the bypass switch 1111 generally flows a large dc current, which is a dc side operating current of the voltage source converter valve 11.

When the voltage source converter cells 111 are brought online to the voltage source converter valves 11, the bypass switches 1111 have to be opened online. In a state where a large direct current flows through the bypass switch 1111, if the bypass switch 1111 is forcibly opened, an arc is easily generated between the contacts of the bypass switch 1111. This arc may still keep current passing between the contacts of the bypass switch 1111 even though the contacts of the bypass switch 1111 have been fully separated, i.e., the arc may make it difficult to reliably open the switch 1111. At the same time, the arc poses a threat to the safety of equipment and personnel.

The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are some, but not all, embodiments of the present application. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.

It should be understood that the terms "first," "second," "third," and "fourth," etc. in the claims, description, and drawings of the present application are used for distinguishing between different objects and not for describing a particular order. The terms "comprises" and "comprising," when used in the specification and claims of this application, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

It is also to be understood that the terminology used in the description of the present application herein is for the purpose of describing particular embodiments only, and is not intended to be limiting of the application. As used in the specification and claims of this application, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It should be further understood that the term "and/or" as used in the specification and claims of this application refers to any and all possible combinations of one or more of the associated listed items and includes such combinations.

Fig. 2A shows a schematic flow chart of an online commissioning method of a voltage source converter cell according to an embodiment of the present application. Fig. 2B shows a schematic diagram of a voltage source converter valve to be fed into a converter cell. Fig. 2C shows an equivalent circuit schematic of the circuit shown in fig. 2B. Fig. 2D shows a waveform diagram of the harmonic voltage amount. Fig. 2E shows a waveform diagram of a current flowing through the bypass switch.

As shown in fig. 2B, the voltage source converter valve 20 may comprise two voltage source converter cells 21 and 22 connected in series on the dc side. Wherein the voltage source converter unit 22 has been put into operation while the voltage source converter 21 is in a ready-to-put state.

According to an exemplary embodiment, the voltage source converter unit 21 comprises a voltage source converter 211, and a bypass switch S1 connected in parallel to the dc side of the voltage source converter 211. Optionally, the voltage source converter unit 21 may further comprise isolation switches D1, D2, D3. The inverter unit 22 and the inverter unit 21 have the same structure, and are not described in detail.

As shown in fig. 2B, the voltage source converter unit 21 is in a ready-to-be-put into operation state, i.e. the bypass switch S1 of the voltage source converter unit 21 is closed. While the converter cell 22 is in the open bypass switch already in operation. At this time, the current I flowing through the bypass switch S1_ds1Equal to the operating current I of the voltage source converter valve 20_d。

The method 2000 shown in fig. 2A may be performed when an on-line commissioning of the converter cell 21 is required. As shown in fig. 2A, method 2000 includes: s230 and S240.

In S230, the dc voltage reference U to be input to the voltage source converter 211 may be_dV-refUpper superimposed harmonic voltage U_Harm. Harmonic voltage quantity U_HarmResulting in the DC side of the voltage source converter 211 appearing with harmonic voltage U_HarmThe voltage component of the same waveform that is applied to the voltage source inverter 211 generates a harmonic current. This harmonic current may be superimposed on the bypass switch S1 such that the current flowing through the bypass switch produces a zero crossing.

Optionally, the harmonic voltage amount U_HarmContains harmonic components, at least one of which has a frequency that is an integer multiple of the ac-side voltage frequency of the voltage source converter 211.

In S240, the current I may be flowing through the bypass switch S1 to be injected into the voltage source converter cell 211_ds1When a zero-crossing point satisfying a preset condition occurs, the bypass switch S1 is turned off. Alternatively, the components associated with bypass switch S1 may be actuated to disconnect bypass switch S1 by sending a command to open bypass switch S1. Further, the method comprisesMay be set when a current I flows through the bypass switch S1 to be injected into the voltage source converter cell 211_ds1The continuous time of the continuous occurrence of alternate positive and negative zero-crossing points reaches a predetermined time interval T_setAt this point, a command to disconnect the bypass switch S1 to be put into the voltage source converter unit 211 is issued.

According to an example embodiment, method 2000 may further include S220 before S230. In S220, first, the dc-side voltage U to be input to the voltage source converter 211 may be unlocked and the output thereof may be controlled_dVIs 0, wherein unlocking the voltage source converter 211 sends a pulse to unlock the control terminal of each semiconductor device to be put into the voltage source converter 211, and controls each semiconductor device in the voltage source converter 211 to enter a switching state. For example: the reference value U of the direct current voltage can be controlled firstly_dV-refIs zero; the retransmission pulse unlocks the voltage source inverter 211.

Then, the dc-side voltage to be input to the output of the voltage source converter 211 may be controlled such that the voltage gradually decreases or gradually increases from zero. Further, the direct current I flowing through the cell bypass switch S1 can be made to flow_ds1Gradually decreases until it approaches zero. For example: when the voltage source converter 211 is installed at the power transmission end, the positive voltage output from the dc side is gradually increased so that the dc current I flowing through the cell bypass switch S1 flows_ds1Gradually decreases until it approaches zero. When the voltage source converter 211 is installed at the receiving end, the negative voltage output from the dc side is gradually decreased so that the dc current I flowing through the cell bypass switch S1_ds1Gradually decreases until it approaches zero.

Further, in S230, the current I of the switch S1 may be bypassed_ds1Less than threshold I_TH1When the DC voltage reference value U of the voltage source converter 211 is to be input_dV-refUpper superimposed harmonic voltage U_Harm。

For the voltage source converter valve to be put into the unlocked state, the following operation formula is satisfied:

u_pj＝0.5U_dV-ref-u_j (1)

u_nj＝0.5U_dV-ref+u_j (2)

U_dV＝u_pj+u_nj＝U_dV-ref (3)

wherein u is_pjAnd u_njThe upper and lower bridge arm voltages u of j phase (j ═ a, b and c) of the voltage source converter valve to be put into are respectively_jFor the AC voltage to be fed out of the converter valve of the voltage source, U_dVFor a DC voltage to be supplied to the converter valve output of the voltage source, U_dV-refIs the DC voltage reference value to be put into the voltage source converter valve.

As can be seen from the equations (1) to (3), if the DC voltage reference value U of the converter valve is applied to the voltage source to be applied_dV-refUpper active superposition of harmonic voltage U as shown in FIG. 2D_HarmCan make the DC voltage output by the converter valve of the voltage source to be input generate harmonic voltage variation and superpose the harmonic voltage U_HarmThe operation formula of the voltage source converter valve to be put into later is as follows:

u_pj＝0.5(U_dV-ref+U_Harm)-u_j (4)

u_nj＝0.5(U_dV-ref+U_Harm)+u_j (5)

U_dV＝u_pj+u_nj＝U_dV-ref+U_Harm (6)

the harmonic voltage U_HarmHarmonic currents may be generated in the dc-side loop of the voltage source converter cell to be placed as shown in fig. 2C, thereby causing a current I flowing through the bypass switch S1 of the voltage source converter cell to be placed_dS1Resulting in constantly alternating positive and negative zero crossings as shown in fig. 2E, satisfying the turn-off condition of the voltage source converter unit bypass switch S1 to be thrown in.

Further, S210 may also be included before S220. In S210, the converter transformer ac incoming switch S2 corresponding to the voltage source converter unit 21 to be switched may be turned on, and the voltage source converter valve to be switched may be ac-uncontrollably charged first. And then starting a charging controller to charge the capacitor voltage of each bridge arm submodule of the voltage source converter valve to be input to be close to the rated value of the capacitor voltage.

OptionallyAfter S240, S250 may also be included. In S250, a tap signal of the bypass switch S1 may be detected, and the tap signal may be used to determine whether the bypass switch S1 is effectively turned off; after the occurrence of the tap signal of the bypass switch S1 of the voltage source converter unit 21 to be switched in, the reference value U of the dc voltage to be switched in to the voltage source converter 211_dV-refHarmonic voltage U superimposed on the upper part_HarmAnd (4) removing. The divide signal of the bypass switch S1 can be used to detect whether the bypass switch S1 is effectively turned off. Alternatively, in S250, it may be determined whether the bypass switch S1 is effectively open in other ways; and removing the harmonic voltage amount U after determining that the bypass switch S1 is effectively turned off_Harm。

Fig. 3 shows a schematic flow chart of an online commissioning method of a voltage source converter cell according to an embodiment of the present application. Applied in converter valves 20 to be thrown into a voltage source converter unit as shown in fig. 2B.

As shown in fig. 3, method 3000 may include: s310 and S320.

As shown in fig. 3 and 2C, in the method S310, the current I may be superimposed on the bypass switch S1_dVSo that a current I flowing through the bypass switch S1_ds1Satisfies the following formula:

I_ds1＝I_d-I_dV (7)

wherein, I_dIs the operating current of the converter valve 20.

Alternatively, the current I_ds1The current may be either a direct current or an alternating current, or may be a current including a direct current component and an alternating current component. Further, the waveform of the ac component may be a sine wave, a square wave, or other waveform. Alternatively the frequency of the ac component may be an integer multiple of the frequency of the ac side voltage of the voltage source converter 211. Further, among the harmonic components included in the ac component, at least one of the harmonic components has a frequency that is an integer multiple of the frequency of the ac-side voltage of the voltage source converter 211.

Optionally, S310 may include, adjusting the current I_dVIs zero, the direct current component becomes gradually larger from zero, so thatCurrent I flowing through bypass switch S1_ds1Gradually reducing until the zero is approached; retainment of I_dVIs not changed, the amplitude of the alternating current component is gradually increased, so that the current I flowing through the bypass switch S1_ds1Zero crossings occur.

As shown in FIG. 3, in S320, the current I may be measured_ds1Controls the bypass switch S1 to open at the zero crossing point. Alternatively, the current I can be measured_ds1May turn off the bypass switch S1 at the positive zero crossing point of the bypass switch S1, or may turn off the bypass switch S1 at the negative zero crossing point of the bypass switch S1. Further, the current I can be measured_ds1After a predetermined number of zero crossings have occurred continuously and steadily, at a current I_ds1Controls the bypass switch S1 to open at the zero crossing point. Alternatively, the current I can also be measured_ds1After continuously generating a plurality of zero-crossing states stably and keeping the states for a preset time interval, at a current I_ds1Controls the bypass switch S1 to open at the zero crossing point.

As shown in fig. 3 and 2B, optionally, in S310, the voltage U may be output on the dc side by controlling the voltage source converter 211_dV. Voltage U_dVActing on the equivalent resistance R and the equivalent reactance L of the voltage source converter 211 to generate a current I_dV. As shown in fig. 3, further, S310 may include: converting the voltage input from the AC side 23 to the voltage U from the DC side by the inverter 211_dV. Further, when the voltage source converter valve 20 is used as an ac-to-dc converter for the supply side, the ac side 23 of the converter 211 is the input side. The voltage U on the DC side can be generated by using the input voltage on the AC side of the inverter 211_dV. When the voltage source converter valve 20 is used as a dc-to-ac converter at the receiving side, the ac side 23 of the converter 211 is the output side. Although the inverter unit 21 is not in the on state at this time, electric energy may be temporarily introduced from the ac bus and used to generate the voltage U on the dc side_dVTo assist in opening the bypass switch S1.

Alternatively, in S310, a first power source connected to the voltage source converter 211 may be used to act on the voltage source converter 211 to generate the current I_dV. Wherein the first oneThe power source may be either a voltage source or a current source. The first power source may be included in the voltage source converter unit 21 or may be hardware independent of the voltage source converter unit 21. The first power source may be directly connected to the voltage source converter 211 or may be coupled to the voltage source converter 211.

As shown in fig. 2C, the voltage between Y1 and Y2 may be always maintained at zero due to the short-circuit action of the bypass switch S1 when the bypass switch S1 is closed. Likewise, current I is due to the short-circuiting action of bypass switch S1_dVWithout affecting the dc side current I of the voltage source converter valve 20_d. That is, when the bypass switch S1 is closed, the voltage U_dVNeither the voltage nor the current to the voltage source converter valve 20 is affected.

However, after the bypass switch S1 is turned off, the current I is not bypassed by the bypass switch S1_dVWill have an influence on the dc side of the voltage source converter valve 20. If the current I is_dVIs formed by a voltage U_dVGenerated due to voltage U_dVCan be small, so that the voltage U_dVThe generated noise may be small and have a limited effect on the operating state of the voltage source converter valve 20.

Optionally, the method 3000 may further include: and S330. In S330, after determining that the bypass switch S1 is effectively turned off, the inverter 211 may be controlled to stop superimposing the current I on the bypass switch S1_dVAnd controls the inverter 211 to enter a normal operation state. To reduce the current I containing AC component_dVThe operating state of the inverter 211. The normal operating state may include a rectified (ac-dc) state and an inverted (dc-ac) state. Alternatively, it may be determined whether the bypass switch S1 is effectively open by detecting the divide signal of the bypass switch S1.

Fig. 4A shows a schematic diagram of a voltage source converter cell according to another embodiment of the present application. Fig. 4B shows a schematic diagram of the composition of the voltage source converter in the voltage source converter cell shown in fig. 4A. Fig. 4C shows a schematic composition of the controller in the voltage source converter cell shown in fig. 4A. Fig. 4D shows a partial circuit schematic of the voltage source converter cell of fig. 4A.

As shown in fig. 4A, the voltage source converter cell 4000 comprises: a voltage source converter 41, a bypass switch 42 and a controller 43. Wherein:

the voltage source converter 41 is a basic functional component of the voltage source converter unit 4000 and may be used for performing an ac-to-dc conversion or a dc-to-ac conversion. That is, the voltage source converter 41 may convert the dc input between the dc sides Z1 and Z2 into the ac output of the ac side Z3, or may convert the ac input of the ac side Z3 into the dc output between the dc sides Z1 and Z2. Wherein the ac side Z3 may be a three-phase terminal. The ac side Z3 of the voltage source converter 41 is also the ac side of the voltage source converter cell 4000.

Voltage source converter 41 may also convert the energy input on ac side Z3 to a first voltage output on dc sides Z1-Z2. This first voltage, acting on the voltage source converter cell 4000, may weaken the current through the bypass switch 42, resulting in a zero crossing of the current of the bypass switch 42. By using the zero-crossing current, the bypass switch 42 is turned off, and the bypass switch 42 is turned off online with safety and reliability. That is, the voltage source converter cells 21 can be safely and reliably put into the voltage source converter valves 20 on-line.

The voltage source converter 41 may be controllably switched between a rectifying (ac-dc) state, an inverting (dc-ac) state and a first voltage output state.

The bypass switch 42 is connected in parallel across the dc side of the voltage source converter 41Z 1 and Z2. X1 and X2 are the dc side terminals of the voltage source converter cell 4000. When the bypass switch 42 is closed, the voltage source converter 41 is in a short-circuit state and cannot be normally put into operation; when the bypass switch 42 is open, the voltage source converter 41 can operate normally. The voltage source converter cell 4000 may be brought online by opening the bypass switch 42 online.

The controller 43 is connected to the voltage source converter 41 and the bypass switch 42, respectively. The voltage source converter 41 may be controlled to switch between different operating states, including: a rectifying (ac-dc) state, an inverting (dc-ac) state, and a first voltage output state. The controller 43 may also control the bypass switch 42 to open/close.

Controller 43 may be configured to: superimposing an amount of harmonic voltage on the dc voltage reference value of the voltage source converter 41 before controlling the bypass switch 42 to open, so that the voltage source converter 41 outputs a first voltage on the dc side; and controlling the bypass switch 42 to be turned off when a zero-crossing point satisfying a predetermined requirement occurs in the current flowing through the bypass switch 42.

Further, the amount of harmonic voltage superimposed on the dc voltage reference of the voltage source converter 41 can be adjusted by the controller 43.

The contact position of the bypass switch 42 may also be sensed by the controller 43 to determine whether the bypass switch 42 is effectively open. And after determining that the bypass switch 42 is effectively turned off, the controller 43 stops superimposing the harmonic voltage amount on the dc voltage reference value of the voltage source converter 41, and controls the voltage source converter 41 to enter a rectifying state or an inverting state.

As shown in fig. 4B, the voltage source converter 41 may optionally comprise a converter controller 411, a converter reference source 412, a stack of converter valve sub-modules 413 and a converter feedback 414. Wherein:

as shown in fig. 4B, the converter valve sub-module stack 413 is a basic functional component of the voltage source converter cell 4000, which may be used for ac-to-dc conversion, dc-to-ac conversion. The ac side of the voltage source converter unit 4000 may be connected to a three-phase ac current, in which case the converter valve sub-module stack 413 may be composed of a plurality of converter valve sub-module strings, each comprising a plurality of converter valve sub-modules connected in series. Each converter valve submodule string is connected with one of three-phase alternating currents.

As shown in fig. 4B, the inverter reference source 412 is connected to the inverter controller 411, and outputs a dc voltage reference value to the inverter controller 411. The dc voltage reference may be used as a reference input to inverter controller 411, and the output waveform of voltage source inverter 41 may be adjusted by adjusting the waveform of the dc voltage reference. The dc voltage reference may be a dc signal or an ac signal. The inverter reference source 412 may also output a dc voltage reference that includes both a dc component and an ac component. The dc voltage reference value of the ac component output by the inverter reference source 412 may be a sine wave, a square wave, or other waveforms. The inverter reference source 412 may controllably adjust the waveform of the dc voltage reference.

As shown in fig. 4B, converter feedback 414 is connected to converter valve sub-module stack 413 and converter controller 411, respectively. The converter feedback 414 collects the voltage output of the converter valve sub-module stack 413 and feeds the collected results back to the converter controller 411 in real time. The converter feedback 414 may detect the voltage output on the dc side of the converter valve sub-module stack 413 or the voltage output on the ac side of the converter valve sub-module stack 413.

As shown in fig. 4B, the converter controller 411 is connected to a converter reference source 412, a converter valve sub-module stack 413 and a converter feedback 414, respectively. Converter valve submodule 413 can be controlled to convert ac power input on the ac side to dc power output on the dc side based on the dc voltage reference output from converter reference 412 and the feedback input from converter feedback 414. The converter controller 411 may also control the converter valve submodule stack 413 to convert the dc power input at the dc side to ac power output at the ac side according to the dc voltage reference output from the converter reference source 412 and the feedback input of the converter feedback 414.

As shown in fig. 4B, the converter reference source 412 may be controlled to output the first dc voltage reference value, such that the converter controller 411 controls the converter valve submodule stack 413 to convert the ac power input at the ac side into the first power output at the dc side according to the first dc voltage reference value output by the converter reference source 412 and the feedback input of the converter feedback 414, where the first power may be the first voltage or the first current. Wherein the first dc voltage reference may be a dc signal having an ac component. Both the first voltage and the first current may be used to weaken the current flowing through the bypass switch 42 and to ensure the safety and reliability of the online disconnection of the bypass switch 42, i.e. the online commissioning of the voltage source converter cell 4000.

Alternatively, the controller 43 may be directly electrically connected to the bypass switch 42, or may be coupled to the bypass switch 42. The controller 43 may be optically coupled to the bypass switch 42 or may be coupled to the bypass switch 42 via a transformer.

Alternatively, the controller 43 may be directly electrically connected to the voltage source converter 41, or may be coupled to the voltage source converter 41. The controller 43 may be optically coupled to the voltage source converter 41, or may be coupled to the voltage source converter 41 via a transformer.

As shown in fig. 4C, optionally, the controller 43 may include: a bypass switch current detector 431, a bypass switch position detector 432, and a bypass switch current controller 433.

As shown in fig. 4C, the bypass switch controller 433 may be connected to the converter reference source 412 of the voltage source converter 41, and adjust the waveform of the dc voltage reference outputted from the converter reference source 412, thereby controlling the output waveform of the voltage source converter 41 and further controlling the current of the bypass switch.

As shown in fig. 4C, a bypass switch current detector 431 is connected to the bypass switch 42 for detecting the current passing through the bypass switch 42. When the bypass switch current detector 431 detects that the current of the bypass switch 42 is less than the threshold I_TH1The controller 43 may superimpose an amount of harmonic voltage on the dc voltage reference of the voltage source converter 41 to attenuate the current flowing through the bypass switch 42 to produce zero-crossings of the current of the bypass switch 42. And the bypass switch current detector 431 may be utilized to detect the zero crossing of the current of the bypass switch 42.

A bypass switch position detector 432 is connected to the bypass switch 42 for detecting whether the bypass switch 42 is effectively open. Alternatively, the bypass switch position detector 432 may determine whether the bypass switch 42 is effectively turned off by detecting a distance between contacts of the bypass switch 42, that is, may detect whether the bypass switch 42 is effectively turned off by detecting a tap signal of the bypass switch 42. When the bypass switch position detector 432 detects that the switch 42 is effectively disconnected, the controller 43 may control the voltage source converter 41 to stop outputting the first voltage and enter a normal operation state.

As shown in fig. 4C, controller 43 may also include an inverter controller 434. Wherein: the converter controller 434 is connected to the voltage source converter 41. The converter controller 434 may control the voltage source converter 41 into different states, such as a rectifying (ac-dc) state, an inverting (dc-ac) state and a first voltage output state.

As shown in fig. 4C, controller 43 may also include a processor 435. The processor 435 is connected to a bypass switch current detector 431, a bypass switch position detector 432, a bypass switch current controller 433, and an inverter controller 434, respectively. For coordinating the bypass switch current detector 431, the bypass switch position detector 432, the bypass switch current controller 433 and the inverter controller 434, and for controlling the bypass switch 42 to open.

As shown in fig. 4D, the voltage source converter cell 4000 may further include isolation switches D1, D2, D3. Wherein:

the isolation switches D1 and D2 are respectively connected in series with the two ends Y1 and Y2 of the circuit composed of the voltage source converter 41 and the bypass switch.

The isolation disconnecting link D3 is connected in parallel between the two ends X1 and X2 of the circuit composed of the isolation disconnecting links D1 and D2, the voltage source converter 41 and the bypass switch.

The isolation switches D1, D2, D3 are used to switch the voltage source converter cell 4000 into a converter valve comprised in the voltage source converter cell 4000 or to disconnect the voltage source converter cell 4000 from the converter valve when the voltage source converter cell 4000 is not operating.

The present application further provides an embodiment of a voltage source converter valve comprising at least two voltage source converter cells of any of the above mentioned types. Wherein the at least two voltage source converter cells of any of the above mentioned types are connected in series on the dc side.

The present application further provides an embodiment, an electronic device comprising a processor, a memory, and a program executable by the processor and stored in the memory, wherein when the program is executed, the processor performs any one of the methods described above.

In the foregoing embodiments, the descriptions of the respective embodiments have respective emphasis, and for parts that are not described in detail in a certain embodiment, reference may be made to related descriptions of other embodiments. The technical features of the embodiments may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments are not described, but should be considered as the scope of the present specification as long as there is no contradiction between the combinations of the technical features.

The foregoing detailed description of the embodiments of the present application has been presented to illustrate the principles and implementations of the present application, and the description of the embodiments is only intended to facilitate the understanding of the methods and their core concepts of the present application. Meanwhile, a person skilled in the art should, according to the idea of the present application, change or modify the embodiments and applications of the present application based on the scope of the present application. In view of the above, the description should not be taken as limiting the application.

Claims

1. A method of online commissioning of a voltage source converter unit comprising a voltage source converter and a bypass switch connected in parallel to a dc side of the voltage source converter, wherein the bypass switch is in a closed state prior to online commissioning of the voltage source converter unit, the method comprising:

superimposing a harmonic voltage quantity on a direct current voltage reference value of the voltage source converter;

the bypass switch is opened when a zero crossing occurs in the current through the bypass switch that meets a predetermined requirement.

2. The method of claim 1, wherein the harmonic voltage amount includes at least one harmonic component having a frequency that is an integer multiple of an ac side voltage frequency of the voltage source converter.

3. The method of claim 1, wherein said opening the bypass switch when a zero crossing occurs in the current through the bypass switch that meets a predetermined requirement comprises:

and sending a command for opening the bypass switch when the duration of the alternating positive and negative zero-crossing points of the current flowing through the bypass switch continuously reaches a set value.

4. The method of claim 1, further comprising, prior to superimposing an amount of harmonic voltage on the dc voltage reference of the voltage source converter:

unlocking the voltage source converter and controlling the voltage of the direct current side output by the voltage source converter to be zero;

and controlling the voltage on the direct current side output by the voltage source converter to gradually decrease or gradually increase, so that the current flowing through the bypass switch is gradually decreased.

5. The method of claim 1, wherein said superimposing an amount of harmonic voltage on a dc voltage reference value of the voltage source converter comprises:

superimposing an amount of harmonic voltage on a DC voltage reference of the voltage source converter when the current flowing through the bypass switch is less than a first threshold.

6. The method of claim 4, wherein said unlocking said voltage source converter and controlling said voltage source converter output to zero before said direct side voltage further comprises:

carrying out alternating-current uncontrolled charging on the voltage source converter by utilizing the alternating-current side voltage of the voltage source converter;

starting a charge controller to charge the plurality of capacitors with an AC side voltage of the voltage source converter such that the voltage of the plurality of capacitors approaches a voltage rating of the capacitors.

7. The method of claim 1, after opening the bypass switch, further comprising: removing the harmonic voltage amount.

8. The method of claim 7, wherein said rejecting said harmonic voltage amount comprises:

detecting a tap signal of the bypass switch;

and after the occurrence of the sub-bit signal of the bypass switch, removing the harmonic voltage quantity.

9. A method of online commissioning of a voltage source converter unit comprising a voltage source converter and a bypass switch connected in parallel to a dc side of the voltage source converter, wherein the bypass switch is in a closed state prior to online commissioning of the voltage source converter unit, the method comprising:

superimposing a first current signal on the bypass switch such that a zero crossing of the current flowing through the bypass switch occurs;

10. The method of claim 9, wherein,

superimposing a first current signal on the bypass switch, comprising:

superimposing a direct current signal on the bypass switch;

and superposing an alternating current signal on the bypass switch.

11. The method of claim 9, wherein superimposing a first current signal on the bypass switch comprises:

generating a first voltage signal on a direct current side of the voltage source converter using the voltage source converter, the first voltage signal being used to generate the first current signal; and/or

Generating the first current signal with a first power source connected to a DC side of the voltage source converter.

12. A voltage source converter cell comprising:

a voltage source converter;

the bypass switch is connected to the direct current side of the voltage source converter in parallel and controls whether the voltage source converter unit is put into operation or not;

a control module connected to the bypass switch and the voltage source converter, respectively, and configured to: superimposing an amount of harmonic voltage on a dc voltage reference value of the voltage source converter before controlling the bypass switch to open, and controlling the bypass switch to open when a zero crossing of the current through the bypass switch occurs that meets a predetermined requirement.

13. The converter cell of claim 12 wherein the control module controls the bypass switch to open by sending a command to open the bypass switch.

14. The converter cell of claim 12, wherein the control module comprises:

a bypass switch current controller for superimposing an amount of harmonic voltage on a dc voltage reference value of the voltage source converter such that a zero crossing of current through the bypass switch occurs;

a bypass switch current detector to detect a current flowing through the bypass switch.

15. The converter cell of claim 12, wherein the control module comprises:

and a bypass switch position detector for detecting the branch signal of the bypass switch.

16. The converter cell of claim 12, wherein the control module comprises:

and the controller processor controls the bypass switch to be switched off.

17. The converter cell of claim 13, further comprising:

the first isolation disconnecting link and the second isolation disconnecting link are respectively connected in series at two ends of the direct current side of the voltage source converter;

and two ends of the third isolation switch are respectively and electrically connected with the first isolation switch and the second isolation switch.

18. Voltage source converter valve comprising at least two voltage source converter cells according to at least one of the claims 13-18 connected in series.

19. An electronic device comprising a processor, a memory, and the processor-executable program stored in the memory,

when the program is executed, the processor performs the method of at least one of claims 1-8, or

When the program is executed, the processor performs the method of at least one of claims 9-11.