阅读说明：本技术 模块化多电平转换器中的dc偏移补偿 (DC migration in modular multilevel converter ) 是由 I·科莱克 柯新花 于 2017-04-05 设计创作，主要内容包括：本公开涉及一种补偿来自包括至少一个相支路的模块化多电平转换器(MMC)的高压AC输出的DC偏移的方法。MMC经由电网变压器被连接到三相高压AC电网。该方法包括,在至少一个DC偏移校正装置(10)中,通过以下在至少一个DC偏移校正装置的每个DC偏移校正装置中测量DC偏移：在MMC中获得高压AC信号,通过无源高阶滤波器(11)从获得的高压AC信号中去除高压AC分量以获得模拟滤波信号,通过模拟-数字转换器将模拟滤波信号转换为数字信号,通过数字滤波器(12)从数字信号中去除剩余的AC分量以获得DC偏移,以及在控制器(13)中将获得的偏移与参考值进行比较,并基于所述比较形成控制信号。该方法还包括将控制信号从至少一个DC偏移校正装置的每个DC偏移校正装置传送到MMC的控制装置(20)。该方法还包括,控制装置将来自至少一个DC偏移校正装置的控制信号映射到至少一个相支路。该方法还包括,基于映射,控制装置向至少一个相支路的每个相支路中的MMC单元的半导体开关发送切换命令以补偿DC偏移。(This disclosure relates to a kind of method of the DC offset of high pressure AC output of compensation from the modular multilevel converter (MMC) for including at least one phase branch.MMC is connected to three-phase high-voltage AC power grid via network transformer.This method includes, in at least one DC offset correction device (10), by the way that DC offset is measured in each DC offset correction device of at least one DC offset correction device below: obtaining voltage in MMC, high pressure AC component is removed from the voltage obtained by passive higher order filter (11) to obtain analog filtering signal, analog filtering signal is converted into digital signal by analogue-to-digital converters, remaining AC component is removed from digital signal by digital filter (12) to obtain DC offset, and the offset of acquisition is compared with reference value in controller (13), and control signal is formed based on the comparison.This method further includes the control device (20) that control signal is transmitted to MMC from each DC offset correction device of at least one DC offset correction device.This method further includes that the control signal from least one DC offset correction device is mapped at least one phase branch by control device.This method further includes, and based on mapping, the semiconductor switch of MMC unit of the control device into each phase branch of at least one phase branch sends switching command to compensate DC offset.)

1. a kind of method of compensation from the high pressure AC of modular multilevel converter MMC (1) the DC offset exported, the MMC At least one phase branch (9) including at least one AC phase (8), wherein each phase branch packet at least one described phase branch Multiple cascade converter units (2) are included, each unit includes multiple semiconductor switch and forms intermediate DC in the unit The energy accumulator of circuit, wherein the MMC is connected to three-phase high-voltage AC power grid via network transformer (3a), the side Method includes:

It is inclined at least one described DC in the following manner at least one DC offset correction device (10) of the MMC (1) The DC offset is measured in each DC offset correction device in shift correction device:

Voltage is obtained in the MMC,

High pressure AC component is removed from voltage obtained by passive higher order filter (11), to obtain analog filtering Signal,

The analog filtering signal is converted into digital signal by analogue-to-digital converters,

Remaining AC component is removed from the digital signal by digital filter (12), to obtain the DC offset, and

In controller (13), offset obtained is compared with reference value, and believes based on the comparison to form control Number；

The control signal is transmitted from each DC offset correction device at least one described DC offset correction device (10) To the control device (20) of the MMC；

The control signal from least one DC offset correction device is mapped to described by the control device (20) At least one phase branch (9)；And

Based on the mapping, institute of the control device (20) in each phase branch at least one described phase branch (9) The semiconductor switch for stating unit (2) sends switching command, to compensate the DC offset.

2. according to the method described in claim 1, wherein, the high pressure AC power grid is three phase network, and wherein the MMC is also The second high pressure AC power grid is connected to via the second network transformer (3b) and/or feed(er) reactor.

3. according to the method described in claim 2, wherein, the second high pressure AC power grid is single-phase power grid, thus the MMC (1) there are double Y shape topologys.

4. the method according to any one of the preceding claims, wherein the voltage is from the MMC's (1) Output terminal obtains.

5. according to the method described in claim 4, wherein, the first DC at least one described DC offset correction device (10) is inclined Shift correction device is connected to the three-phase output end of the MMC, to be connected to first network transformer (3a).

6. method described in any one of -3 according to claim 1, wherein the voltage crosses over the MMC (1) Phase branch (9) obtains.

7. according to the method described in claim 6, wherein, for each phase branch in the phase branch (9) of the MMC, A DC offset correction device at least one described DC offset correction device (10) is connected across the phase branch.

8. the method according to any one of the preceding claims, wherein at least one described DC offset correction device (10) each DC offset correction device in is powered inside the MMC (1) via power supply.

9. according to the method described in claim 8, wherein, the power supply includes being connected to institute via step-down transformer (5) State the AC-DC converter of the output terminal of MMC (1).

10. according to the method described in claim 8, wherein, the power supply includes the unit (2) for being connected to (1) the MMC The DC-DC converter of the intermediate DC circuit.

11. the method according to any one of the preceding claims, wherein the control signal via optical cable (21) and by Transmission.

12. a kind of modular multilevel converter MMC (1), at least one phase branch (9) including at least one AC phase (8), Described in each phase branch at least one phase branch include multiple cascade converter units (2), each unit includes more A semiconductor switch and the energy accumulator that intermediate DC circuit is formed in the unit, wherein the MMC is via power grid transformation Device (3a) and be connected to three-phase high-voltage AC power grid, the MMC includes:

At least one DC offset correction device (10) is configured as filling at least one described DC offset correction in the following manner The DC offset is measured in each DC offset correction device set:

Voltage is obtained in the MMC,

High pressure AC component is removed from voltage obtained by passive higher order filter (11), to obtain analog filtering Signal,

The analog filtering signal is converted into digital signal by analogue-to-digital converters,

Remaining AC component is removed from the digital signal by digital filter, to obtain the DC offset,

In controller (13), offset obtained is compared with reference value, and form control signal based on the comparison, And

The control signal is transmitted from each DC offset correction device at least one described DC offset correction device (10) To the control device (20) of the MMC；And

Control device (20) is configured as the control signal being mapped to from least one described DC offset correction device described At least one phase branch (9), and it is based on the mapping, the institute in each phase branch at least one described phase branch (9) The semiconductor switch for stating unit (2) sends switching command, to compensate the DC offset.

Technical field

This disclosure relates to a kind of high pressure (HV) alternating current (AC) for correcting from modular multilevel converter (MMC) The method and apparatus of direct current (DC) offset of output.

Background technique

In many applied power electronics, transformer is used for the one or both sides of converter, power grid or load at this Voltage amplitude be different from converter input and/or output voltage.When intentional or unintentional between the semiconductor in converter Between lag certain inexactness is shown on its switching time.Therefore, it is possible that asymmetric or uneven in converter Even operation.This may result in the undesirable DC current for flowing through transformer winding.Since system feedback is not any The DC current or system cannot be sensed in the case where measuring device not by current control, therefore DC component leads to magnetization electricity Stream increases, and makes core saturation, increases heat, and therefore lead to the increase of the loss of transformer.

Although DC offset is very small (such as several volts or its score), and DC is inclined compared with the amplitude of AC output voltage Shifting can be such that transformer is saturated.This greatly reduces the power wait be transmitted, or even becoming operation can not.

It has attempted to measure by expensive high-precision DC electric current transformer and school positive dc offset.However, this same production Raw unsatisfactory offset correction, and control correspondingly complicated and expensive.

US 5,870,297 discloses the use of low-pass filter, followed by DC measuring unit to generate measuring signal School positive dc offset can be used for the low pressure less than 3.6kV into the application of middle pressure.

Summary of the invention

The object of the present invention is to provide one kind to have for measuring and compensating more than 3.6kV, such as the output of up to 36kV The method and apparatus of DC drift current in the output of the high pressure MMC power converter of voltage.

The output voltage of MMC include very big (HV) AC component and it is very small (for example, be less than 1V or be less than 100mV) DC component, DC component herein are referred to as DC offset.In order to correctly measure DC offset, need to remove from output voltage enough HV AC component with allow DC component be detected and measurement.Inventor is it has now been realized that this can be filtered by passive high-order Wave device (having the filter higher than second order) simultaneously follows the combination of digital filter behind to realize.

According to aspects of the present invention, a kind of method of the DC offset of high pressure AC output of the compensation from MMC, the MMC are provided At least one phase branch including at least one AC phase.Each phase branch of at least one phase branch includes multiple cascaded inverters Unit.Each unit includes multiple semiconductor switch and forms the energy accumulator of intermediate DC circuit in the cells.MMC is via electricity Net transformer is connected to three-phase HV AC power grid.This method includes, at least one DC offset correction device of MMC (1), By the way that DC offset is measured in each DC offset correction device of at least one DC offset correction device below: being obtained in MMC Voltage removes high pressure AC component from the voltage obtained by passive higher order filter to obtain analog filtering Analog filtering signal is converted to digital signal by analogue-to-digital converters by signal, by digital filter from digital signal The middle remaining AC component of removal is to obtain DC offset, and in the controller, the offset of acquisition is compared with reference value, and Control signal is formed based on the comparison.This method further includes that will control signal from each of at least one DC offset correction device DC offset correction device is transmitted to the control device of MMC.This method further includes that control device will deviate school from least one DC The control signal of equipment is mapped at least one phase branch, and based on mapping, and control device is at least one phase branch The semiconductor switch of unit in each phase branch sends switching command to compensate DC offset.

According to another aspect of the present invention, a kind of MMC is provided comprising at least one phase branch of at least one AC phase. Each phase branch of at least one phase branch includes multiple cascaded inverters units.Each unit include multiple semiconductor switch and The energy accumulator of intermediate DC circuit is formed in the cells.MMC is connected to three-phase HV AC power grid via network transformer.MMC Including at least one DC offset correction device, it is configured as by below in each DC of at least one DC offset correction device DC offset is measured in offset correction device: obtaining voltage in MMC, by passive higher order filter from the high pressure obtained High pressure AC component is removed in AC signal to obtain analog filtering signal, is turned analog filtering signal by analogue-to-digital converters It is changed to digital signal, removes remaining AC component from digital signal by digital filter to obtain DC offset, in controller (13) in, the offset of acquisition is compared with reference value, and based on the comparison formed control signal, will control signal to Each DC offset correction device of a few DC offset correction device is transmitted to the control device of MMC.MCC further includes control dress It sets, is configured as the control signal from least one DC offset correction device being mapped at least one phase branch, and The semiconductor switch of unit based on from mapping to each phase branch of at least one phase branch sends switching command to compensate DC Offset.

It should be noted that any feature of any aspect can be applied to any other aspect in appropriate circumstances. Equally, any advantage of any aspect can be applied to any other aspect.From disclosure below, from appended appurtenance In benefit requirement and attached drawing, other purposes of appended embodiment, feature and advantage be will become obvious.

In general, unless in addition explicitly define herein, otherwise by according to its ordinary meaning in technical field come power of interpretation All terms used in benefit requirement.Unless expressly stated otherwise, all to " one/mono-/element, equipment, component, dress Set, step etc. " reference should be construed at least one situation of reference element, equipment, component, device, step etc. with being opened. Unless explicitly stated, otherwise any method disclosed herein the step of not necessarily according to disclosed exact order execute.For this Disclosed different characteristic/component, the use of " first ", " second " etc. are only intended to features/components and other similar feature/groups Part distinguishes, and does not assign any sequence of features/components or level.

Detailed description of the invention

Embodiment will be described in an illustrative manner by referring to accompanying drawing, in which:

Fig. 1 is the signal sexual function of the embodiment for the DC offset correction device that the control according to the present invention with MMC communicates Block diagram.

Fig. 2 a is the schematic block diagram of the embodiment of the MMC according to the present invention including DC offset correction device.

Fig. 2 b is the signal of the embodiment for the DC offset correction device that the control according to the present invention with the MMC of Fig. 2 a communicates Sexual function block diagram.

Fig. 3 a is the schematic block diagram of another embodiment of the MMC according to the present invention including DC offset correction device.

Fig. 3 b is the signal of the embodiment for the DC offset correction device that the control according to the present invention with the MMC of Fig. 3 a communicates Sexual function block diagram.

Fig. 3 c is another embodiment for the DC offset correction device that the control according to the present invention with the MMC of Fig. 3 a communicates Functional block diagram.

Specific embodiment

Embodiment is described more fully with hereinafter with reference to attached drawing now, specific embodiment is shown in the attached drawings. However, within the scope of this disclosure, many various forms of other embodiments are also possible.On the contrary, following embodiment passes through Exemplary mode is provided, so that the disclosure will be thorough and complete, and will sufficiently convey this public affairs to those skilled in the art The range opened.Throughout the specification, identical label indicates identical element.

Any kind of MMC that the embodiment of the present invention can be used to have any topology.Herein, for three-phase MMC between AC power grid and single phase AC power net, also referred to as double Y (Y) topology of double star is by as example.Implementation of the invention The other examples for the MMC topology that example can be used include the MMC that the MMC of triangle connection is connected with (list) Y shape.

According to suitable topology, MMC generally includes any number of phase branch of at least one phase branch, this at least one Phase branch includes multiple converter units that (also referred to as cascade or chain link) is connected in series.Each converter unit includes more A semiconductor switch forms such as full-bridge (the also referred to as H- bridge) topology for bipolarity unit or is directed to unipolarity unit Half-bridge topology.Each converter unit further includes energy accumulator, forms one for being herein referred to as intermediate DC circuit Point.Energy accumulator can be for example including battery, or preferably includes any amount capacitor of at least one capacitor Capacitor device.

AC voltage herein is usually provided by square root voltage, can also be represented as V_rmsOr V_AC。

Referring to Fig.1, it illustrates include multiple DC offset correction devices 10₁To 10_nDC offset correction device overall wheel It is wide.The scheme for the DC component in HV output that the object of the present invention is to provide a kind of for inhibiting MMC to apply.This is by using suitable The DC measured by the DC offset voltage in somewhere in DC offset correction device 10 (according to application) measurement MMC of quantity, the processing is inclined It moves and the output of DC offset correction device is applied to converter phase branch to complete.This method and dress for realizing this method Set preferably should it is as simple as possible, operation is reliable, needs least external module (such as voltage grading resistor, high voltage cable, insulation Portion, power supply etc.) to realize cheaply.

Each DC offset correction device 10 includes measurement input terminal, with for obtaining high pressure from the somewhere in MMC, such as HV AC signal.HV AC signal has the voltage (V higher than 3.6kV_rms), for example, at least 4kV or at least 10kV, up to 36kV are all Such as within the scope of 4-36kV.HV AC signal is handled by passive higher order filter 11, to remove HV AC component.Filter is nothing The expression in source its there is no offset.Passive filter may, for example, be low-pass filter, and it is more than pre- for being designed to decaying Determine the component of the HV AC signal of cutoff frequency.Passive filter 11 can for example be designed to cascade resistance and capacitor (RC) The form of element, such as the three-stage cascade of the RC element for third-order low-pass filter.

In high-voltage applications, passive filter 11 is not sufficient enough to the AC component removed in HV AC signal and obtains HV AC The DC offset component of signal.Therefore, after having applied passive filter 11, signal (analog signal) passes through analog to digital Converter (ADC) is converted into digital signal, and is handled by digital filter 12.Therefore, AC component is adequately suppressed To allow precisely enough to measure DC offset by controller 13.Then, controller 13 can by the DC of measurement deviate with it is described The reference value (usually 0) of offset is compared, and the difference between the offset of the DC based on measurement and reference will control signal output To the control device 20 of MMC.Controller 13 may, for example, be P (ratio) controller and I (integral) controller or PI (ratio Integral) controller.Since DC offset correction device 10 usually may be at controlling 20 different potentials from MMC, between Control signaling preferably can optically be executed via optical cable/optical fiber 21.

MMC control 20 passes through the phase branch for mapping and being applied to MMC, considers from the received control of DC offset correction device 10 Signal controls the semiconductor switch of MMC.This control can control 20 by MMC to realize, MMC control 20 is connected to MMC Each phase branch converter unit semiconductor switch respective driving circuit.Such as it can be by according to inclined from DC The voltage control signal of shift correction device 10 postpones the order switched on and off, carrys out school positive dc offset.For example, if positive DC is inclined Shifting is measured to, then may be delayed by for connecting the switch of positive half-wave, until measurement in a period of time can not be again Determine any DC offset.In the case where negative DC offset, the order for connecting negative half-wave may be delayed by.

Fig. 2 a illustrates the MMC of double Y shapes topology with the three-phase 8 including phase branch 9₁Embodiment.Phase 8_A、8_BWith 8_C In each phase include upper phase branch 9_UWith lower phase branch 9_L, so that a total of six phase branch 9 in MMC.Each phase branch 9 includes Multiple N cascaded inverters units 2 and phase branch reactor (coil is schematically illustrated as in figure).MMC₁Via each Power transformer 3 is connected between two HV AC power grids, and the first network transformer 3a is connected to the first HV in its primary side AC power grid, and secondarily grade side is connected to MMC₁, the second network transformer 3b is connected to the 2nd HV AC electricity in its primary side Net, and secondarily grade side is connected to MMC₁.In the example of Fig. 2 a, the first HV AC power grid is three phase network, such as common electrical Net (such as basic frequency with 50Hz).First HV AC power grid can have higher than 36kV, such as higher than 100kV or be higher than 200kV, such as the voltage of 220kV.In the example of Fig. 2 a, the 2nd HV AC power grid is single-phase power grid, such as track power grid (example Such as with the basic frequency of 16.7Hz or 50/3Hz).2nd HV AC power grid can have higher than 36kV, such as higher than 100kV, Such as 132kV, or the voltage higher than 200kV.As described above, each voltage in the primary side of transformer 3a and 3b, i.e., MMC₁Output voltage, be higher than 3.6kV, for example, at least 4kV or at least 10kV, up to 36kV.It should be noted that transformer 3a With the necessarily phase of each voltage (being respectively facing the MMC output voltage of the first and second HV AC power grids) in the primary side of 3b Together, although they can be identical in some applications.Since HV phase branch 9 is usually located in valve chamber, phase branch can be through The outside of valve chamber is connected to by the bushing 7 by valve chamber wall.

In the embodiment of Fig. 2 a, DC offset correction device 10 is connected to MMC via bushing 7 and voltage grading resistor 6₁Respectively A output terminal, one is connected to three-phase output end, and one is connected to single-phase output terminal, to allow DC offset correction to fill It sets 10 and obtains its each HV AC signal from the output terminal.DC offset correction device 10 is via AC-DC converter 4 and transformation Device 5 (such as step-down transformer) is powered inside MMC, the HV of each output terminal is converted into low pressure (LV), such as hundreds of Volt, such as in the range of 200-500V, for the power supply of DC offset correction device 10.All low-voltage equipments can be installed in Enough required insulation distances are given on the platform of isolation, and between low pressure components and high-tension apparatus.

In the embodiment shown in Fig. 2 a, MMC₁Via the first network transformer 3a to be connected to three-phase public for the first side Power grid, and second side of MMC is connected to single-phase power grid via the second network transformer 3b.However, in the present invention, MMC₁'s Many other selections of second side can be relevant.For example, second side of MMC can via feed(er) reactor rather than via Transformer 3b is connected to single-phase HV power grid, in this case, can not need DC offset correction device in second side of MMC 10.In another example, second side of MMC can not be connected to power grid, and MMC is only connected to three-phase in its first side HV power grid.In yet another example, MMC₁Second side usually can be connected to the second three-phase HV via the second transformer 3b Power grid, thus MMC₁Be connected between two different three phase networks (or may be in two differences in identical three phase network Point between).Certainly, MMC₁Topology be adapted accordingly, when MMC is connected between three phase network and single-phase power grid, It is used as exemplary double Y shape topologys in figure to be typically used.

Fig. 2 b illustrates the embodiment of the DC offset correction device used in the MMC example of Fig. 2 a.In the device It is middle to use two DC offset correction devices 10, one in the primary side of three-phase transformer 3a, and another is in single-phase transformer In the primary side of 3b.First DC means for correcting 10₁It is connected to three-phase output end, the 2nd DC correction dress in fig. 2 a herein Set 10₂It is connected to single-phase output terminal in fig. 2 a herein.

As described above, DC deviates (mV) from high pressure AC (up to 36kV) by passive filter 11 and digital filter 12 In be filtered off.

Upper and lower phase branch 9_UWith 9_LBetween and adjacent phase branch between balanced voltage and system MMC control 20 The current controller of middle implementation makes the DC component of transformer secondary especially low, but it still may be sufficiently large so that power grid transformation Device 3 is saturated.

The HV AC signal of measurement MMC output terminal may be advantageous, because signal will have power grid basic frequency (example Such as 50Hz) and lesser DC offset.In order to filter out DC, then only one AC frequency must be attenuated, to provide simple filtering Device design.In the sample application of double Y shapes topology as shown in figure 2b, two different passive filter 11a and 11b are set Meter is with decay public electric wire net frequency (usually 50Hz), and track mains frequency (usually 16.7Hz) deviates school in individual DC It is attenuated in equipment.

The output of controller 13 can be transferred to other MMC controls 20 via optical fiber 21.There, firstly, DC is deviated The output of means for correcting 10 will be mapped to that phase branch 9.For example, in the example of double Y shape topologys, DC offset correction device 10 Three outputs are mapped to six phase branches.Mapping is carried out so that being applied to the compensation DC component of phase branch not by MMC's Other controllers are eliminated.Second, be applied to phase branch compensation DC component can be added to phase branch set point or including Modify the form of the DC offset of its equivalent scheme of firing pulse.

On each DC offset correction device 10, it can have two independent Measurement channels.For three-phase side, two logical Road all be used to measure two signals, and (one in phase 8_AWith phase 8_CBetween be measured, and another is in phase 8_BWith phase 8_CBetween be tested Amount).Therefore, two passive filter 11a and 11b are shown and for three-phase means for correcting 10₁Two controller 13a and 13b.For single-phase side, only one signal can be measured.Therefore, a channel is used only.Another channel can also be there But it is not used by, is not shown.

Fig. 3 a illustrates MMC₁Embodiment, wherein DC offset correction device, which is spanned, is connected to each phase branch 9, without It is to be connected to output terminal in the embodiment such as Fig. 2 a.

For the embodiment of Fig. 2 a, Fig. 3 a shows the MMC for illustrating double Y shapes topology with the three-phase 8 including phase branch 9₁ Embodiment.Phase 8_A、8_BWith 8_CIn each phase include upper phase branch 9_UWith lower phase branch 9_L, so that a total of six phase branch in MMC Road 9.Each phase branch 9 includes that multiple N cascaded inverters units 2 and phase branch reactor (are schematically illustrated in figure For coil).MMC₁It is connected between two HV AC power grids via each power transformer 3, the first network transformer 3a is at it Primary side is connected to the first HV AC power grid, and secondarily grade side is connected to MMC₁, and the second network transformer 3b is at it Primary side is connected to the 2nd HV AC power grid, and secondarily grade side is connected to MMC₁.In the example of Fig. 2 a, the first HV AC power grid is three phase network, such as public electric wire net (such as basic frequency with 50Hz).First HV AC power grid can have height In 36kV, such as higher than 100kV or higher than the voltage of 200kV, such as 220kV.In the example of Fig. 2 a, the 2nd HV AC power grid It is single-phase power grid, such as track power grid (such as basic frequency with 16.7Hz or 50/3Hz).2nd HV AC power grid can have Have higher than 36kV, such as higher than 100kV, such as 132kV, or the voltage higher than 200kV.As described above, in transformer 3a and 3b Primary side on each voltage, i.e. MMC₁Output voltage, be higher than 3.6kV, for example, at least 4kV or at least 10kV, up to 36kV. It should be noted that each voltage in the primary side of transformer 3a and 3b (is respectively facing the first and second HV AC power grids MMC output voltage) it is necessarily identical, although they can be identical in some applications.Since HV phase branch 9 is usually located at valve chamber In, therefore phase branch can be connected to the outside of valve chamber via the bushing 7 by valve chamber wall.

In the embodiment of figure 3a, DC offset correction device 10 is spanned and is connected to via casing 7 and voltage grading resistor 6 MMC₁Each phase branch 9, in this example, generate a total of six DC offset correction device 10, with allow DC offset correction fill It sets 10 and obtains its each HV AC signal from the phase branch of leap.In this case, DC offset correction device 10 also exists It is powered inside MMC, but here can be via the DC-DC converter 4 for the intermediate DC circuit for being connected to converter unit 2 Power supply, rather than it is necessarily required to any transformer 5 (such as step-down transformer), for the power supply of DC offset correction device 10.It is all Low-voltage equipment can be installed on the platform of isolation, and be given between low pressure components and high-tension apparatus enough required exhausted Edge distance.

When across the measurement of converter phase branch, the survey on the contrary, DC offset correction device 10 is measured in output terminal Amount input terminal is connected to phase branch terminal across converter phase branch 9.The program provides the power supply for using converter unit Chance.Therefore, step-down type transformer 5 and the AC/DC converter with high-insulativity are not needed.However, it may be needed Extremely low power DC/DC power supply, between the semiconductor gate pole unit of isolated location switch and DC offset correction device ground connection Earth potential.On the other hand, in this embodiment, it is possible to not need long high voltage cable, because voltage grading resistor 6 will be assigned to Phase branch.

For upper and lower phase branch 9_UWith 9_LOffset correction device 10 can be physically integrated into each other as shown in Figure 3c Tool there are two a devices of Measurement channel, or two individual devices as shown in Figure 3b.For the former, DC biasing is filled Redundant power may be had in this case by setting.

Similar to the embodiment of Fig. 2 a and 2b, DC offset component (mV) must be filtered from high pressure AC component (up to 36kV) Out.DC component to be measured is expected to be greater than the DC component in the embodiment of Fig. 2 a and 2b.However, more challenging, at this In the case of kind, the signal to DC offset correction device 10 may include more than one basic frequency.With the embodiment of Fig. 2 a and 2b It compares, this may be unfavorable (filter design may be challenged more).In the sample application of double Y shapes topology as shown in Figure 3a In, the basic frequency of basic frequency (usually 50Hz) and single phase tracks power grid from three-phase public electric wire net is (usually It 16.7Hz) all will appear in the measurement of DC offset correction device 10, and the two frequency components must pass through filter 11 Acceptable level is attenuated to 12.

The output of controller 13 can be transferred to MMC control 20 via optical fiber 21.There, firstly, DC offset correction The output of device 10 will be mapped to that phase branch 9.In the sample application of double Y shape MMC topologys, six of DC offset correction device Output will be mapped to that six phase branches.This embodiment to a certain extent than Fig. 2 a and 2b is more direct, because in Fig. 3 a-c Embodiment in, each phase branch 9 have dedicated DC offset correction device 10.However, concern mapping mechanism to be applied to The compensation DC component of phase branch will not be eliminated by other controllers in MMC.Similarly, compensation DC points of phase branch are applied to Amount can be added to the form of the DC offset of phase branch set point or its equivalent scheme including modifying firing pulse.

The embodiment of the present invention can be used together with any MMC topology.However, in some embodiments of the invention, HV AC power grid is three-phase (such as public) power grid.Additionally or alternatively, in some embodiments, MMC is also via the second power grid Transformer 3b and/or the 2nd HV AC power grid is connected to via feed(er) reactor.In some embodiments, the 2nd HV AC power grid It is single-phase power grid (such as track power grid), thus MMC can have double Y shape topologys.In other embodiments, the 2nd HV AC electricity Net is the second three-phase (such as public) power grid.

In some embodiments of the invention, voltage is by from MMC₁Output terminal obtain.In some embodiments In, the first DC offset correction device 10 is connected to three-phase output end of MMC, to be connected to the first network transformer 3a.Such as Fruit MMC is connected to single-phase HV AC power grid, then the 2nd DC offset correction device 10 may be connected to the single-phase output end of MMC Son, to be connected to the second network transformer 3b or feed(er) reactor.

In some other embodiments, voltage is spanned MMC₁Phase branch 9 obtain.In some embodiments, For each phase branch 9 of MMC, a DC offset correction device at least one DC offset correction device 10 is spanned described The connection of phase branch.

In some embodiments of the invention, each DC offset correction device warp of at least one DC offset correction device 10 By power supply in MMC₁It is middle by in-line power.Power supply may include being connected to MMC via step-down transformer 5₁Output terminal AC-DC converter, or it is connected to MMC₁Converter unit 2 intermediate DC circuit DC-DC converter.

In some embodiments of the invention, control signal is transmitted via optical cable 21 from each DC offset correction device 10 To MMC control device 20.

The disclosure is described referring especially to some embodiments above.However, as readily understood by the skilled person, In In the scope of the present disclosure being defined by the following claims, the other embodiments other than embodiments disclosed above are equally It is possible.