CN111404190B - Control method and system for enhancing power output capability of MMC converter station under power grid fault - Google Patents
Control method and system for enhancing power output capability of MMC converter station under power grid fault Download PDFInfo
- Publication number
- CN111404190B CN111404190B CN202010309131.3A CN202010309131A CN111404190B CN 111404190 B CN111404190 B CN 111404190B CN 202010309131 A CN202010309131 A CN 202010309131A CN 111404190 B CN111404190 B CN 111404190B
- Authority
- CN
- China
- Prior art keywords
- voltage
- mmc
- current
- axis
- phase
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Active
Links
Images
Classifications
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]
Landscapes
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Inverter Devices (AREA)
Abstract
The invention discloses a control method for enhancing the power sending-out capability of an MMC converter station under the power grid voltage asymmetric drop fault, which aims at the problem that the power sending-out capability of the MMC converter station under the power grid asymmetric drop fault is obviously reduced due to the existence of zero sequence and negative sequence current, realizes the inhibition of zero sequence current components through a second-order generalized integrator, can be combined with the existing positive and negative sequence decoupling control method, fully inhibits the zero sequence component and the negative sequence component in the current when the power grid voltage asymmetric drop occurs, effectively improves the power sending-out capability of the MMC converter station, reduces the input times of DC choppers and can realize the fault ride-through operation of a system even under the condition of not needing to input the DC choppers when the fault is light. The improved control strategy provided by the invention is very simple to realize and has strong practicability.
Description
Technical Field
The invention relates to a control method and a control system for enhancing the power output capability of an MMC converter station under the condition of power grid faults, and is suitable for the technical field of power electronics.
Background
With the increasing severity of global environmental pollution and energy crisis problems, the rapid development of renewable energy has become a common consensus of the development of all countries in the world. The flexible direct current transmission technology has very good application prospect in the collection and transmission process of large-scale renewable energy sources, and has gained wide attention. Especially for long-distance offshore wind farms, the flexible direct current transmission technology has become the optimal choice for accessing the onshore large power grid. Compared with the flexible direct-current transmission technology based on the two-level or three-level topology, the flexible direct-current transmission technology based on the Modular Multilevel Converter (MMC) topology has the advantages of low manufacturing difficulty, high waveform quality, low operation loss and the like, so that the flexible direct-current transmission technology is widely applied.
However, when a large grid connected to the grid fails, the flexible dc transmission system is also severely affected. Take the gentle direct delivery system of marine wind-powered electricity generation as an example, when the voltage drop accident takes place for land big electric wire netting, the power delivery ability of land MMC converter station will seriously reduce, and because the output power of fan can't attenuate in the short time, the input power of marine MMC converter station also hardly attenuates at the very first time, surplus power will make the direct current bus voltage of flexible direct current transmission system rise rapidly, if do not take effective measure, will lead to whole direct current system to be off-network, seriously influence the safety and stability of generating efficiency and local electric wire netting. Therefore, the research on the fault ride-through strategy of the MMC converter station under the grid fault has important significance.
At present, research on a fault ride-through strategy of an MMC converter station under the fault of an alternating current power grid is limited, existing research mainly focuses on inputting DC chopper to consume surplus power when the fault occurs, the effectiveness of the method depends on the capacity of an energy consumption resistor, for a high-power direct current transmission system, the cost is high, and the method can be input only in a short intermittent mode.
In fact, the faults of the large alternating-current power grid are asymmetric faults such as single-phase short-circuit faults, and when the asymmetric faults occur, the MMC converter station still has certain power transmission capacity. At this time, how to enhance the power sending capability of the MMC converter station when the power grid has an asymmetric fault by adopting a proper control strategy is considered, the investment time of the DC chopper can be effectively shortened, and even the fault ride-through operation of the system is realized under the condition that the DC chopper is not needed, so that the method has important significance.
Aiming at the asymmetric fault of the power grid, a control strategy for respectively controlling the positive sequence component and the negative sequence component of the current under a positive and negative rotation synchronous coordinate system is developed, so that the negative sequence current can be effectively inhibited. However, for the MMC converter station, when a large power grid has voltage asymmetric drop fault such as single-phase grounding and the like, the fault point is connected with the MMC by the connecting transformer, and when the connecting transformer adopts Y0/Y0When the connection is carried out, an additional zero sequence loop is generated. At this time, the output current of the MMC current converter will contain a large amount of zero sequence components, which further causes the distortion of current waveform and seriously affects the power output capability of the current converter.
Disclosure of Invention
Aiming at the existing problems, a control method and a control system for enhancing the power sending capability of the MMC converter station under the power grid fault are provided, so that the power sending capability of the MMC converter station is effectively improved when the fault occurs, and the input times of the DC chopper are reduced.
The technical scheme adopted by the invention is as follows: a control method for enhancing the power output capability of an MMC converter station under the power grid fault is characterized by comprising the following steps: the suppression of zero sequence current components is realized through a second-order generalized integrator, and the zero sequence current components and the negative sequence components in the current are fully suppressed when the voltage of a power grid falls asymmetrically by combining with a positive-negative sequence decoupling control method, so that the power output capacity of the MMC converter station is improved.
The method comprises the following steps:
acquisition of three-phase voltage U of MMC alternating current network sidesabcThree-phase current IsabcAnd three-phase current I on valve side of connecting transformervabcMMC upper and lower bridge arm current IpabcAnd InabcAnd a DC-side DC bus voltage Udc；
Acquiring three-phase voltage U on power grid side by using phase-locked loopsabcPhase angle thetavAnd angular frequency ωv(ii) a According to the MMC upper and lower bridge arm current IpabcAnd InabcCalculating to obtain MMC three-phase internal circulation Icabc(ii) a According to three-phase voltage and current U at power grid sidesabcAnd IsabcCalculating reactive power Q output by MMCs；
To three-phase voltage and current U of power grid sidesabcAnd IsabcPerforming Park conversion to correspondingly obtain a voltage vector U under a synchronous rotation d-q-0 coordinate systemsdq0Sum current vector Ivdq0；
Zero-sequence current component I by using second-order generalized integratorv0Performing individual control, setting its reference value to zero; the output of the second-order generalized integrator is used as a zero-sequence component U of the MMC reference differential mode voltagedifref0；
Direct current bus voltage U using PI controllerdcAnd reactive power QsControl is performed so as to respectively follow a given reference value UdcrefAnd QsrefThe outputs of the two PI controllers are respectively used as reference values I of the d axis and the q axis of the positive sequence currentvdqref+(ii) a Reference value UdcrefReference value Q for rated DC bus voltage of systemsrefGiven by an upper controller according to a system instruction; reference value QsrefAccording to the system instruction, the unit power factor is set to be 0 during operation, and corresponding reactive compensation can be performed on the power grid according to the reactive requirement of the power grid.
For voltage current vector UsdqI of (A)vdqPositive and negative sequence separation is carried out on the d-axis component and the q-axis component to obtain a positive sequence component U of the positive sequence component U in a positive rotation synchronous coordinate systemsdq+And Ivdq+And a negative sequence component U in a reverse synchronous coordinate systemsdq-And Ivdq-(ii) a Respectively aligning positive sequence current I and negative sequence current I under a positive rotation coordinate system and a negative rotation coordinate system through two sets of PI controllersvdq+、Ivdq-Control is carried out, wherein the positive sequence current reference value is Ivdqref+And the negative sequence current reference value is zero to obtain the positive sequence component U of the MMC reference differential mode voltagedifrefdq+And a negative sequence component Udifrefdq-；
Will Udifrefdq-Transformation into a forward synchronous coordinate system, with Udifrefdq+Adding to obtain MMC reference differential mode voltage d and q axis components UdifrefdqAnd then with the zero sequence component U of the MMC reference differential mode voltagedifref0Combining to obtain MMC reference differential mode voltage Udifrefdq0；
Three-phase internal circulation I by using Park conversioncabcConversion to at-2 thetavD for rotation-2-q-2Obtaining internal circulation I in rotating coordinate systemcdq(ii) a At d-2-q-2Adopting PI controller to carry out internal circulation I under a coordinate systemcdqControl is performed, the d and q axes reference values IcdqrefAre all given as zero, and the output of the PI controller is used as the MMC reference common mode voltage Ucomrefdq；
MMC reference differential mode voltage U by utilizing inverse Park conversiondifrefdq0And MMC reference common mode voltage UcomrefdqTransforming to a stationary three-phase coordinate system to obtain UdifrefabcAnd UcomrefabcObtaining the reference voltage U of the upper bridge arm and the lower bridge arm of the MMC through calculationprefabcAnd UnrefabcAnd modulating by using a nearest level approximation method to realize the control of the MMC.
Three-phase voltage and current U on power grid sidesabcAnd IsabcAccording to the following equationObtaining a voltage vector U by row Park conversionsdq0Sum current vector Ivdq0：
Wherein: u shapesa、UsbAnd UscAre respectively a voltage UsabcCorresponding to A, B, C voltage on three phases, Isa、IsbAnd IscAre respectively current IsabcCorresponding to currents on three phases, U of A, B, Csd、UsqAnd Us0Corresponding to a voltage vector Usdq0D-, q-and 0-axis components of (I)vd、IvqAnd Iv0Corresponding to a current vector Ivdq0The d-axis, q-axis and 0-axis components of (1).
Zero sequence component U of MMC reference differential mode voltagedifref0Obtained according to the following method:
Udifref0＝FSOGI(s)(0-Iv0)
wherein: fSOGI(s) is the transfer function of a second-order generalized integrator, kgIs the gain coefficient, omega, of a second-order generalized integratorcTo cut-off frequency, ωrIs the resonant frequency.
The resonance frequency omegarSelecting 50Hz and cut-off frequency omegac12Hz was chosen.
The MMC refers to differential mode voltage Udifrefdq0Obtained according to the following method:
wherein, Udifrefd+、Udifrefq+Corresponding to a positive sequence voltage vector Udifrefdq+D-axis, q-axis components of (U)difrefd-、Udifrefq-Corresponding to a negative sequence voltage vector Udifrefdq-D-axis, q-axis components.
The MMC refers to differential mode voltage Udifrefdq0And MMC reference common mode voltage UcomrefdqCarrying out inverse Park conversion according to the following formula to obtain UdifrefabcAnd Ucomrefabc：
Wherein, Udifrefd、UdifrefqAnd Udifref0Corresponding to a voltage vector Udifrefdq0D-, q-and 0-axis components of (1), Udifrefa、UdifrefbAnd UdifrefcCorresponding to a voltage vector UdifrefabcA-axis, b-axis and c-axis components of, Ucomrefd、UcomrefqCorresponding to a voltage vector UcomrefdqD-axis, q-axis components of (U)comrefa、UcomrefbAnd UcomrefcCorresponding to a voltage vector UcomrefabcThe a-axis, b-axis and c-axis components of (a).
Calculating the reference voltage U of the upper and lower bridge arms of the MMC according to the following methodprefabcAnd Unrefabc：
Wherein, Uprefa、UprefbAnd UprefcCorresponding to a voltage vector UprefabcA-axis, b-axis and c-axis components of, Unrefa、UnrefbAnd UnrefcCorresponding to a voltage vector UprefabcThe a-axis, b-axis and c-axis components of (a).
A control system based on the control method is characterized by comprising the following steps:
a voltage sensor for detecting three-phase voltage U at power grid sidesabc；
A current sensor I for detecting three-phase current I on the side of the power gridsabc；
A current sensor II for detecting the three-phase current I on the valve side of the connecting transformervabc；
A phase-locked loop module for obtaining three-phase voltage U at power grid sidesabcPhase angle thetavAnd angular frequency ωv；
A power calculation module for calculating the three-phase voltage and current U according to the power grid sidesabcAnd IsabcCalculating reactive power Q output by MMCs；
A coordinate transformation and positive-negative sequence separation module for three-phase voltage and current U on the power grid sidesabcAnd IsabcPerforming Park conversion to correspondingly obtain a voltage vector U under a synchronous rotation d-q-0 coordinate systemsdq0Sum current vector Ivdq0(ii) a For circulating three-phase internal currents I by means of Park conversioncabcConversion to at-2 thetavD for rotation-2-q-2Obtaining internal circulation I in rotating coordinate systemcdq；
A zero sequence current suppression module for using a second-order generalized integrator to correct the zero sequence current component Iv0Performing individual control, setting its reference value to zero; the output of the second-order generalized integrator is used as a zero-sequence component U of the MMC reference differential mode voltagedifref0；
A DC bus voltage and reactive power controller for using PI controller to DC bus voltage UdcAnd reactive power QsControl is performed so as to respectively follow a given reference value UdcrefAnd QsrefThe outputs of the two PI controllers are respectively used as reference values I of the d axis and the q axis of the positive sequence currentvdqref+；
Positive and negative sequence current controllers for respectively aligning positive sequence current I and negative sequence current I under positive and negative coordinate systems via two sets of PI controllersvdq+、Ivdq-Control is carried out, wherein the positive sequence current reference value is Ivdqref+And the negative sequence current reference value is zero to obtain the positive sequence component U of the MMC reference differential mode voltagedifrefdq+And a negative sequence component Udifrefdq-；
A reference differential mode voltage calculation module for calculating Udifrefdq-Transformation into a forward synchronous coordinate system, with Udifrefdq+Adding to obtain MMC reference differential mode voltage d and q axis components UdifrefdqAnd then with the zero sequence component U of the MMC reference differential mode voltagedifref0Combining to obtain MMC reference differential mode voltage Udifrefdq0And the MMC is referenced to the differential mode voltage U by utilizing inverse Park conversiondifrefdq0Transforming to a stationary three-phase coordinate system to obtain Udifrefabc；
Internal loop controller for controlling the flow at d-2-q-2Adopting PI controller to carry out internal circulation I under a coordinate systemcdqControl is performed, the d and q axes reference values IcdqrefAre all given as zero, and the output of the PI controller is used as the MMC reference common mode voltage UcomrefdqAnd the MMC is referenced to the common-mode voltage U by utilizing inverse Park conversioncomrefdqTransforming to a stationary three-phase coordinate system to obtain Ucomrefabc；
A bridge arm voltage calculation module for calculating the voltage according to UdifrefabcAnd UcomrefabcObtaining the reference voltage U of the upper bridge arm and the lower bridge arm of the MMC through calculationprefabcAnd Unrefabc；
A modulation module for modulating the reference voltage U according to the MMC upper and lower bridge armsprefabcAnd UnrefabcAnd outputting a switch on-off signal by adopting a recent level approximation method to realize the control of the MMC.
The invention has the beneficial effects that: when the voltage of a power grid has an asymmetric drop fault, the zero sequence component and the negative sequence component in the current are restrained, so that the power sending capacity of the MMC converter station can be effectively improved, the input times of the DC chopper are reduced, and the fault ride-through operation of a system can be realized even under the condition of not inputting the DC chopper when the fault is light.
The invention realizes the inhibition of zero sequence current components through a second-order generalized integrator, has very simple realization mode, combines the method with the existing positive and negative sequence decoupling control method, verifies the compatibility of the improved control method and the existing research in the field, and shows that the method can be widely applied to the existing control strategy and has stronger practicability.
Drawings
Fig. 1 is a schematic diagram of a structure of an MMC converter station.
Fig. 2 is a schematic diagram of a system implementation principle of the control method in the embodiment.
FIG. 3 is a diagram of a model structure based on a PSCAD/EMTDC simulation environment for verifying effectiveness of an embodiment.
Fig. 4 shows a simulation waveform using a conventional control strategy.
Fig. 5 is a simulation waveform of the strategy for controlling the power output capability of the enhanced MMC current converter according to the present invention.
Detailed Description
As shown in fig. 1 and fig. 2, this embodiment is a control system for enhancing the power output capability of an MMC converter station under a power grid voltage asymmetric drop fault, where the system includes the MMC converter station 1 and a connection group Y0/Y0The system comprises a connecting transformer 2, a voltage sensor 3 for detecting three-phase voltage at the side of a power grid, a current sensor I4 for detecting three-phase current at the side of the power grid and a current sensor II 5 for detecting three-phase current at the side of a valve of the connecting transformer, wherein a control link of the system comprises a phase-locked loop module 6, a coordinate transformation and positive-negative sequence separation module 7, a power calculation module 8, a zero-sequence current suppression module 9, a direct-current bus voltage and reactive power controller 10, a positive-negative sequence current controller 11, a reference differential mode voltage calculation module 12, an internal loop controller 13, a bridge arm voltage calculation module 14 and a modulation module 15.
The control method of the control system in the embodiment includes the following steps:
acquisition of three-phase voltage U on MMC alternating current network side by using voltage sensor 3sabc(ii) a Three-phase current I is collected by current sensor 4sabcCollecting and connecting three-phase current I on the transformer valve side by using a current sensor 5vabcAcquiring the upper and lower bridge arms of the MMC by using a sensor inside the MMC converter stationCurrent IpabcAnd InabcAnd a DC-side DC bus voltage UdcAnd all of them are converted into per unit values.
Obtaining a voltage phase angle theta by means of a phase locked loop 6vAnd angular frequency ωvAccording to the MMC upper and lower bridge arm current IpabcAnd InabcAnd calculating to obtain the MMC three-phase internal circulation IcabcThe calculation method is as follows:
wherein: i ispa、Ipb、IpcRespectively is an upper bridge arm current IpabcCorresponding to the currents on the A, B and C phases, Ina、Inb、IncRespectively, the lower bridge arm current InabcCorresponding to the currents on the A, B and C phases, Ica、Icb、IccRespectively three-phase internal circulation IcabcCorresponding to the current on the A phase, the B phase and the C phase.
According to three-phase voltage and current U at power grid sidesabcAnd IsabcAnd the active power P output by the MMC is calculated by using the power calculation module 7sAnd reactive power Qs(ii) a The calculation method is as follows:
wherein: u shapesa，UsbAnd UscAre respectively a voltage UsabcCorresponding to voltages on A, B and C phases, Isa，IsbAnd IscAre respectively current IsabcCorresponding to the current on the A phase, the B phase and the C phase.
Three-phase voltage U is respectively measured by using coordinate transformation and positive and negative sequence separation modules 8sabcAnd three-phase current IvabcPerforming Park conversion to correspondingly obtain a voltage vector U under a synchronous rotation d-q-0 coordinate systemsdq0Sum current vector Ivdq0The calculation method is as follows:
wherein: u shapesd、UsqAnd Us0Corresponding to a voltage vector Usdq0D-, q-and 0-axis components of (I)vd、IvqAnd Iv0Corresponding to a current vector Ivdq0D-axis, q-axis, and 0-axis components of (a);
then positive and negative sequence separation is carried out on the d-axis and q-axis components to obtain a positive sequence component U of the positive sequence component U in a positive rotation synchronous coordinate systemsdq+And Ivdq+And a negative sequence component U in a reverse synchronous coordinate systemsdq-And Ivdq-。
In the zero sequence current suppression module 9, a second-order generalized integrator is adopted to correct the zero sequence current component Iv0Performing independent control, setting the reference value to be zero to realize the suppression of zero-sequence current, and taking the output of the second-order generalized integrator as the zero-sequence component U of the MMC reference differential mode voltagedifref0The controller is as follows:
Udifref0＝FSOGI(s)(0-Iv0)
wherein: fSOGI(s) is the transfer function of a second-order generalized integrator, kgIs the gain coefficient, omega, of a second-order generalized integratorcTo cut-off frequency, ωrFor the resonance frequency, in the embodiment, the resonance frequency is selected to be ± 50Hz, and the cutoff frequency is selected to be 12 Hz.
DC bus voltage U is controlled by DC bus voltage and reactive power controller 10dcAnd reactive power QsControl is performed so as to respectively follow a given reference value UdcrefAnd QsrefTwo controlsThe outputs of the generators are used as reference values I of the d-axis and q-axis of the positive sequence current respectivelyvdqref+。
The positive and negative sequence current controllers 11 are adopted to align the sequence current Ivdq+And negative sequence current Ivdq-Control is carried out, wherein the positive sequence current reference value adopts a reference value Ivdqref+The negative sequence current reference value is zero, and the output of the controller is used as the positive sequence component U of the MMC reference differential mode voltagedifrefdq+And a negative sequence component Udifrefdq-。
In the reference differential mode voltage calculation module 12, U is calculateddifrefdq-Transformation into a forward synchronous coordinate system, with Udifrefdq+Adding to obtain MMC reference differential mode voltage d and q axis components UdifrefdqZero sequence component U of MMC reference differential mode voltagedifref0Combining to obtain the final reference differential mode voltage Udifrefdq0The calculation process is as follows:
wherein, Udifrefd+,Udifrefq+Corresponding to a positive sequence voltage vector Udifrefdq+D-axis, q-axis component, Udifrefd-,Udifrefq-Corresponding to a negative sequence voltage vector Udifrefdq-D-axis, q-axis component.
Transforming U with inverse Parkdifrefdq0Transforming to a stationary three-phase coordinate system to obtain UdifrefabcThe calculation method is as follows:
wherein, Udifrefd,UdifrefqAnd Udifref0Corresponding to a voltage vector Udifrefdq0D-axis, q-axis and 0-axis components of (1), Udifrefa,UdifrefbAnd UdifrefcCorresponding to a voltage vector UdifrefabcThe a-axis, b-axis and c-axis components of (a).
Three-phase internal circulation by using coordinate transformation and positive-negative sequence separation module 8IcabcConversion to at-2 thetavD for rotation-2-q-2Obtaining an internal circulation vector I in a rotating coordinate systemcdqThen at d-2-q-2Using internal circulation controllers 13 for internal circulation I in a coordinate systemcdqControl is performed, the d and q axes reference values IcdqrefAll given as zero, the output of the controller is taken as the MMC reference common mode voltage Ucomrefdq。
Transforming U with inverse ParkcomrefdqTransforming to a stationary three-phase coordinate system to obtain UcomrefabcThe calculation method is as follows:
wherein, Ucomrefd，UcomrefqCorresponding to a voltage vector UcomrefdqD-axis, q-axis component, Ucomrefa,UcomrefbAnd UcomrefcCorresponding to a voltage vector UcomrefabcThe a-axis, b-axis and c-axis components of (a).
Obtaining the reference voltage U of the upper and lower bridge arms of the MMC by using the bridge arm voltage calculation module 14prefabcAnd UnrefabcAnd then, outputting a switch on-off signal by using a modulation module 15 adopting a nearest level approximation method to realize the control of the MMC, wherein the calculation method of the reference voltages of the upper bridge arm and the lower bridge arm is as follows:
wherein, Uprefa,UprefbAnd UprefcCorresponding to a voltage vector UprefabcA-axis, b-axis and c-axis components of (1), Unrefa,UnrefbAnd UnrefcCorresponding to a voltage vector UprefabcThe a-axis, b-axis and c-axis components of (a).
FIG. 3 is a model structure diagram of a PSCAD/EMTDC simulation environment based on verifying the effectiveness of the present invention. In the simulation process, the marine MMC converter sends constant power to the onshore side, the onshore alternating current power grid has single-phase voltage short-circuit fault within 3s, the fault lasts for 1s, and the alternating current power grid recovers to be normal within 4 s.
Fig. 4 shows a simulation waveform using a conventional control strategy. In fig. 4(a), the active power waveform, the voltage waveform, and the current waveform sent from the MMC converter station to the ac power grid are from top to bottom, respectively; fig. 4(b) shows an operation signal of the DC chopper. From simulation results, after the voltage drop fault occurs to the grid voltage, the output power of the MMC converter station is limited, and drops from 930MW to 850MW, and in order to prevent the system from being disconnected due to the excessive rise of the DC bus voltage caused by the excessive power, a part of energy needs to be consumed by the input of the DC chopper, and 4 times of input of the DC chopper is performed in 1 s.
Fig. 5 is a simulation waveform of the strategy for enhancing the power sending capability of the MMC converter according to this embodiment. In fig. 5(a), the active power waveform, the voltage waveform, and the current waveform sent from the MMC converter station to the ac power grid are from top to bottom, respectively; fig. 5(b) shows an operation signal of the DC chopper. According to simulation results, when the stable state is achieved after the fault occurs, the output power capability of the MMC converter station is not obviously reduced, and compared with the traditional method, the output power capability of the MMC converter station is obviously improved, so that the fault ride-through operation of the system can be realized only by putting DC chopper once at the initial stage of the fault within 1s of fault time. The zero sequence component in the output current is effectively inhibited when the improved method is adopted, and when the current reaches a current limiting value, the proportion of the effective current is increased, so that the power output capability of the system is enhanced.
In summary, by using the control method for enhancing the power sending capability of the MMC converter station in the embodiment, when an asymmetric voltage drop fault occurs in a power grid, the zero sequence component in the output current can be effectively inhibited, and the output power capability of the MMC converter station is enhanced, so that the input times of the DC chopper can be reduced, and even the fault ride-through operation of a system can be realized under the condition that the DC chopper is not required to be input; the improved control strategy provided by the embodiment is very simple to implement and has strong practicability.
Claims (8)
1. A control method for enhancing the power output capability of an MMC converter station under the power grid fault is characterized by comprising the following steps: the suppression of zero sequence current components is realized through a second-order generalized integrator, and the zero sequence current components are combined with a positive-negative sequence decoupling control method, so that the zero sequence components and the negative sequence components in the current are fully suppressed when the voltage of a power grid falls asymmetrically, and the power output capacity of the MMC converter station is improved;
the control method for enhancing the power sending capability of the MMC converter station under the power grid fault comprises the following steps:
acquisition of three-phase voltage U of MMC alternating current network sidesabcThree-phase current IsabcAnd three-phase current I on valve side of connecting transformervabcMMC upper and lower bridge arm current IpabcAnd InabcAnd a DC-side DC bus voltage Udc；
Acquiring three-phase voltage U on power grid side by using phase-locked loopsabcPhase angle thetavAnd angular frequency ωv(ii) a According to the MMC upper and lower bridge arm current IpabcAnd InabcCalculating to obtain MMC three-phase internal circulation Icabc(ii) a According to three-phase voltage and current U at power grid sidesabcAnd IsabcCalculating reactive power Q output by MMCs；
To three-phase voltage and current U of power grid sidesabcAnd IsabcPerforming Park conversion to correspondingly obtain a voltage vector U under a synchronous rotation d-q-0 coordinate systemsdq0Sum current vector Ivdq0；
Zero-sequence current component I by using second-order generalized integratorv0Performing individual control, setting its reference value to zero; the output of the second-order generalized integrator is used as a zero-sequence component U of the MMC reference differential mode voltagedifref0；
Direct current bus voltage U using PI controllerdcAnd reactive power QsControl is performed so as to respectively follow a given reference value UdcrefAnd QsrefThe outputs of the two PI controllers are respectively used as reference values I of the d axis and the q axis of the positive sequence currentvdqref+(ii) a Reference value UdcrefReference value Q for rated DC bus voltage of systemsrefGiven by an upper controller according to a system instruction;
vector of voltage and currentQuantity UsdqI of (A)vdqPositive and negative sequence separation is carried out on the d-axis component and the q-axis component to obtain a positive sequence component U of the positive sequence component U in a positive rotation synchronous coordinate systemsdq+And Ivdq+And a negative sequence component U in a reverse synchronous coordinate systemsdq-And Ivdq-(ii) a Respectively aligning positive sequence current I and negative sequence current I under a positive rotation coordinate system and a negative rotation coordinate system through two sets of PI controllersvdq+、Ivdq-Control is carried out, wherein the positive sequence current reference value is Ivdqref+And the negative sequence current reference value is zero to obtain the positive sequence component U of the MMC reference differential mode voltagedifrefdq+And a negative sequence component Udifrefdq-；
Will Udifrefdq-Transformation into a forward synchronous coordinate system, with Udifrefdq+Adding to obtain MMC reference differential mode voltage d and q axis components UdifrefdqAnd then with the zero sequence component U of the MMC reference differential mode voltagedifref0Combining to obtain MMC reference differential mode voltage Udifrefdq0；
Three-phase internal circulation I by using Park conversioncabcConversion to at-2 thetavD for rotation-2-q-2Obtaining internal circulation I in rotating coordinate systemcdq(ii) a At d-2-q-2Adopting PI controller to carry out internal circulation I under a coordinate systemcdqControl is performed, the d and q axes reference values IcdqrefAre all given as zero, and the output of the PI controller is used as the MMC reference common mode voltage Ucomrefdq；
MMC reference differential mode voltage U by utilizing inverse Park conversiondifrefdq0And MMC reference common mode voltage UcomrefdqTransforming to a stationary three-phase coordinate system to obtain UdifrefabcAnd UcomrefabcObtaining the reference voltage U of the upper bridge arm and the lower bridge arm of the MMC through calculationprefabcAnd UnrefabcAnd modulating by using a nearest level approximation method to realize the control of the MMC.
2. The method for controlling the power output capacity of the MMC converter station under the power grid fault according to claim 1, characterized in that the three-phase voltage and current U on the power grid sidesabcAnd IsabcPerforming Park conversion according to the following formula to obtain a voltage vectorUsdq0Sum current vector Ivdq0：
Wherein: u shapesa、UsbAnd UscAre respectively a voltage UsabcCorresponding to A, B, C voltage on three phases, Isa、IsbAnd IscAre respectively current IsabcCorresponding to currents on three phases, U of A, B, Csd、UsqAnd Us0Corresponding to a voltage vector Usdq0D-, q-and 0-axis components of (I)vd、IvqAnd Iv0Corresponding to a current vector Ivdq0The d-axis, q-axis and 0-axis components of (1).
3. The method for controlling power delivery capability of an MMC converter station under grid fault according to claim 1, wherein the second order generalized integrator has the following function:
Udifref0＝FSOGI(s)(0-Iv0)
wherein: fSOGI(s) is the transfer function of a second-order generalized integrator, kgIs the gain coefficient, omega, of a second-order generalized integratorcTo cut-off frequency, ωrIs the resonant frequency.
4. The method for controlling the power take-off capability of the MMC converter station under the grid fault according to claim 3, characterized in that: the resonance frequency omegarSelecting 50Hz and cut-off frequency omegac12Hz was chosen.
5. The method for controlling power delivery capability of an MMC converter station in case of power grid failure according to claim 1, wherein the MMC is referenced to a differential mode voltage Udifrefdq0Obtained according to the following method:
wherein, Udifrefd+、Udifrefq+Corresponding to a positive sequence voltage vector Udifrefdq+D-axis, q-axis components of (U)difrefd-、Udifrefq-Corresponding to a negative sequence voltage vector Udifrefdq-D-axis, q-axis components.
6. The method for controlling the power take-off capability of the MMC converter station under the grid fault according to claim 1, characterized in that: the MMC refers to differential mode voltage Udifrefdq0And MMC reference common mode voltage UcomrefdqCarrying out inverse Park conversion according to the following formula to obtain UdifrefabcAnd Ucomrefabc：
Wherein, Udifrefd、UdifrefqAnd Udifref0Corresponding to a voltage vector Udifrefdq0D-, q-and 0-axis components of (1), Udifrefa、UdifrefbAnd UdifrefcCorresponding to a voltage vector UdifrefabcA-axis, b-axis and c-axis components of, Ucomrefd、UcomrefqCorresponding to a voltage vector UcomrefdqD-axis, q-axis components of (U)comrefa、UcomrefbAnd UcomrefcCorresponding to a voltage vector UcomrefabcThe a-axis, b-axis and c-axis components of (a).
7. The method for controlling the power take-off capability of the MMC converter station under the grid fault according to claim 6, characterized in that: calculating the reference voltage U of the upper and lower bridge arms of the MMC according to the following methodprefabcAnd Unrefabc：
Wherein, Uprefa、UprefbAnd UprefcCorresponding to a voltage vector UprefabcA-axis, b-axis and c-axis components of, Unrefa、UnrefbAnd UnrefcCorresponding to a voltage vector UprefabcThe a-axis, b-axis and c-axis components of (a).
8. A control system based on the control method according to any one of claims 1 to 7, characterized by comprising:
a voltage sensor for detecting three-phase voltage U at power grid sidesabc；
A current sensor I for detecting three-phase current I on the side of the power gridsabc；
A current sensor II for detecting the three-phase current I on the valve side of the connecting transformervabc；
A phase-locked loop module for obtaining three-phase voltage U at power grid sidesabcPhase angle thetavAnd angular frequency ωv；
A power calculation module for calculating the three-phase voltage and current U according to the power grid sidesabcAnd IsabcCalculating reactive power Q output by MMCs；
A coordinate transformation and positive-negative sequence separation module for three-phase voltage and current U on the power grid sidesabcAnd IsabcPerforming Park conversion to correspondingly obtain a voltage vector U under a synchronous rotation d-q-0 coordinate systemsdq0Sum current vector Ivdq0(ii) a For circulating three-phase internal currents I by means of Park conversioncabcTo change to-2θvD for rotation-2-q-2Obtaining internal circulation I in rotating coordinate systemcdq；
A zero sequence current suppression module for using a second-order generalized integrator to correct the zero sequence current component Iv0Performing individual control, setting its reference value to zero; the output of the second-order generalized integrator is used as a zero-sequence component U of the MMC reference differential mode voltagedifref0；
A DC bus voltage and reactive power controller for using PI controller to DC bus voltage UdcAnd reactive power QsControl is performed so as to respectively follow a given reference value UdcrefAnd QsrefThe outputs of the two PI controllers are respectively used as reference values I of the d axis and the q axis of the positive sequence currentvdqref+；
Positive and negative sequence current controllers for respectively aligning positive sequence current I and negative sequence current I under positive and negative coordinate systems via two sets of PI controllersvdq+、Ivdq-Control is carried out, wherein the positive sequence current reference value is Ivdqref+And the negative sequence current reference value is zero to obtain the positive sequence component U of the MMC reference differential mode voltagedifrefdq+And a negative sequence component Udifrefdq-；
A reference differential mode voltage calculation module for calculating Udifrefdq-Transformation into a forward synchronous coordinate system, with Udifrefdq+Adding to obtain MMC reference differential mode voltage d and q axis components UdifrefdqAnd then with the zero sequence component U of the MMC reference differential mode voltagedifref0Combining to obtain MMC reference differential mode voltage Udifrefdq0And the MMC is referenced to the differential mode voltage U by utilizing inverse Park conversiondifrefdq0Transforming to a stationary three-phase coordinate system to obtain Udifrefabc；
Internal loop controller for controlling the flow at d-2-q-2Adopting PI controller to carry out internal circulation I under a coordinate systemcdqControl is performed, the d and q axes reference values IcdqrefAre all given as zero, and the output of the PI controller is used as the MMC reference common mode voltage UcomrefdqAnd the MMC is referenced to the common-mode voltage U by utilizing inverse Park conversioncomrefdqTransforming to a stationary three-phase coordinate system to obtain Ucomrefabc；
A bridge arm voltage calculation module for calculating the voltage according to UdifrefabcAnd UcomrefabcObtaining the reference voltage U of the upper bridge arm and the lower bridge arm of the MMC through calculationprefabcAnd Unrefabc；
A modulation module for modulating the reference voltage U according to the MMC upper and lower bridge armsprefabcAnd UnrefabcAnd outputting a switch on-off signal by adopting a recent level approximation method to realize the control of the MMC.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202010309131.3A CN111404190B (en) | 2020-04-19 | 2020-04-19 | Control method and system for enhancing power output capability of MMC converter station under power grid fault |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202010309131.3A CN111404190B (en) | 2020-04-19 | 2020-04-19 | Control method and system for enhancing power output capability of MMC converter station under power grid fault |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CN111404190A CN111404190A (en) | 2020-07-10 |
| CN111404190B true CN111404190B (en) | 2021-09-03 |
Family
ID=71437005
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN202010309131.3A Active CN111404190B (en) | 2020-04-19 | 2020-04-19 | Control method and system for enhancing power output capability of MMC converter station under power grid fault |
Country Status (1)
| Country | Link |
|---|---|
| CN (1) | CN111404190B (en) |
Citations (18)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103986357A (en) * | 2013-02-13 | 2014-08-13 | 韩国电气研究院 | Method for suppressing circulating current in modular multilevel converter for high voltage direct-current transmission |
| CN104181374A (en) * | 2014-08-08 | 2014-12-03 | 合肥工业大学 | Method for detecting and separating positive and negative sequence components of grid voltage of three-phase neutral-line-free system |
| CN104811067A (en) * | 2015-04-30 | 2015-07-29 | 山东大学 | PR (proportional resonant) controller-based NMC-HVDC (modular multilevel converter-high voltage direct current) circulating current suppression method |
| CN105406484A (en) * | 2015-12-29 | 2016-03-16 | 湖南大学 | Power grid voltage regulation method of angle form cascade synchronous compensator |
| CN105425171A (en) * | 2015-12-18 | 2016-03-23 | 南京南瑞继保电气有限公司 | Method for detecting voltage drop of low voltage ride-through power source of frequency converter |
| CN105743371A (en) * | 2016-04-13 | 2016-07-06 | 上海交通大学 | Manufacturing method of MMC controller suitable for unbalanced voltage |
| CN106208054A (en) * | 2016-09-22 | 2016-12-07 | 湘潭大学 | The apparatus and method of synchronous inverter negative-sequence current are suppressed under the conditions of unbalanced power supply |
| CN108448660A (en) * | 2018-03-22 | 2018-08-24 | 太原理工大学 | Alternating current-direct current mixing micro-capacitance sensor parallel inverter circulation inhibition method based on hierarchical control |
| CN108711861A (en) * | 2018-05-08 | 2018-10-26 | 深圳供电局有限公司 | A kind of voltage dip generator control method |
| CN108964500A (en) * | 2017-05-09 | 2018-12-07 | 徐州润泽电气有限公司 | It is a kind of can be to the method that zero-sequence current control effectively |
| CN109038658A (en) * | 2018-07-24 | 2018-12-18 | 全球能源互联网研究院有限公司 | Off-lying sea wind-powered electricity generation flexible direct current transmitting system and land AC single phase ground fault traversing method |
| CN109164352A (en) * | 2018-09-19 | 2019-01-08 | 武汉中原电子信息有限公司 | A kind of three-phase synchronous method of distribution system fault indicator acquisition unit |
| CN109510223A (en) * | 2018-12-14 | 2019-03-22 | 山东鲁能智能技术有限公司 | A kind of three-phase current unbalance administers controller, device and control method |
| CN109709409A (en) * | 2019-01-16 | 2019-05-03 | 中南大学 | A kind of three-phase imbalance detection method and system based on Second Order Generalized Integrator |
| CN109950925A (en) * | 2019-03-14 | 2019-06-28 | 华南理工大学 | No phase-locked loop photovoltaic DC-to-AC converter control method under unbalanced power grid based on SOGI |
| CN110198050A (en) * | 2019-07-01 | 2019-09-03 | 南瑞集团有限公司 | DFIG virtual synchronous control method based on the idle Collaborative Control of torque-under a kind of unbalanced power grid |
| CN110460276A (en) * | 2019-07-12 | 2019-11-15 | 淮阴工学院 | A kind of few rare-earth permanent-magnet electric machine drive system inhibiting zero-sequence current |
| CN110474350A (en) * | 2018-05-11 | 2019-11-19 | 华为技术有限公司 | A kind of control method of virtual synchronous generator, apparatus and system |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN106208127A (en) * | 2016-08-19 | 2016-12-07 | 华北电力大学 | The HVDC transmission system emulation modelling method analyzed for sub-synchronous oscillation |
-
2020
- 2020-04-19 CN CN202010309131.3A patent/CN111404190B/en active Active
Patent Citations (18)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103986357A (en) * | 2013-02-13 | 2014-08-13 | 韩国电气研究院 | Method for suppressing circulating current in modular multilevel converter for high voltage direct-current transmission |
| CN104181374A (en) * | 2014-08-08 | 2014-12-03 | 合肥工业大学 | Method for detecting and separating positive and negative sequence components of grid voltage of three-phase neutral-line-free system |
| CN104811067A (en) * | 2015-04-30 | 2015-07-29 | 山东大学 | PR (proportional resonant) controller-based NMC-HVDC (modular multilevel converter-high voltage direct current) circulating current suppression method |
| CN105425171A (en) * | 2015-12-18 | 2016-03-23 | 南京南瑞继保电气有限公司 | Method for detecting voltage drop of low voltage ride-through power source of frequency converter |
| CN105406484A (en) * | 2015-12-29 | 2016-03-16 | 湖南大学 | Power grid voltage regulation method of angle form cascade synchronous compensator |
| CN105743371A (en) * | 2016-04-13 | 2016-07-06 | 上海交通大学 | Manufacturing method of MMC controller suitable for unbalanced voltage |
| CN106208054A (en) * | 2016-09-22 | 2016-12-07 | 湘潭大学 | The apparatus and method of synchronous inverter negative-sequence current are suppressed under the conditions of unbalanced power supply |
| CN108964500A (en) * | 2017-05-09 | 2018-12-07 | 徐州润泽电气有限公司 | It is a kind of can be to the method that zero-sequence current control effectively |
| CN108448660A (en) * | 2018-03-22 | 2018-08-24 | 太原理工大学 | Alternating current-direct current mixing micro-capacitance sensor parallel inverter circulation inhibition method based on hierarchical control |
| CN108711861A (en) * | 2018-05-08 | 2018-10-26 | 深圳供电局有限公司 | A kind of voltage dip generator control method |
| CN110474350A (en) * | 2018-05-11 | 2019-11-19 | 华为技术有限公司 | A kind of control method of virtual synchronous generator, apparatus and system |
| CN109038658A (en) * | 2018-07-24 | 2018-12-18 | 全球能源互联网研究院有限公司 | Off-lying sea wind-powered electricity generation flexible direct current transmitting system and land AC single phase ground fault traversing method |
| CN109164352A (en) * | 2018-09-19 | 2019-01-08 | 武汉中原电子信息有限公司 | A kind of three-phase synchronous method of distribution system fault indicator acquisition unit |
| CN109510223A (en) * | 2018-12-14 | 2019-03-22 | 山东鲁能智能技术有限公司 | A kind of three-phase current unbalance administers controller, device and control method |
| CN109709409A (en) * | 2019-01-16 | 2019-05-03 | 中南大学 | A kind of three-phase imbalance detection method and system based on Second Order Generalized Integrator |
| CN109950925A (en) * | 2019-03-14 | 2019-06-28 | 华南理工大学 | No phase-locked loop photovoltaic DC-to-AC converter control method under unbalanced power grid based on SOGI |
| CN110198050A (en) * | 2019-07-01 | 2019-09-03 | 南瑞集团有限公司 | DFIG virtual synchronous control method based on the idle Collaborative Control of torque-under a kind of unbalanced power grid |
| CN110460276A (en) * | 2019-07-12 | 2019-11-15 | 淮阴工学院 | A kind of few rare-earth permanent-magnet electric machine drive system inhibiting zero-sequence current |
Non-Patent Citations (5)
| Title |
|---|
| Arm Current Balancing Control for Modular Multilevel Converters Under Unbalanced Grid Conditions;Jinyu Wang,etc.;《IEEE TRANSACTIONS ON POWER ELECTRONICS》;20200331;第35卷(第3期);第2467-2479页 * |
| MMC-HVDC 换流站电流波动抑制策略研究与仿真分析;陈继开，等;《电网技术》;20181231;第42卷(第12期);第3842-3849页 * |
| 基于对零轴矢量构造坐标系的电流控制方法;赵岩 等;《电力电子技术》;20180731;第52卷(第7期);第41-43页 * |
| 新型牵引供电系统直流侧二次波动分析与抑制;宋平岗 等;《电工技术学报》;20170531;第32卷(第9期);第80-91页 * |
| 海上风电场谐振分析的实用计算方法;孙长江，等;《广东电力》;20180630;第31卷(第6期);第75-83页 * |
Also Published As
| Publication number | Publication date |
|---|---|
| CN111404190A (en) | 2020-07-10 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| CN110504711B (en) | New energy grid-connected control system and method based on new energy synchronous machine | |
| CN103904635B (en) | A kind of topological structure of multiport direct current transformer station and control method thereof | |
| CN111404191B (en) | MMC converter station low-voltage ride through method and system based on resonance controller | |
| CN105429183A (en) | Permanent magnetic direct-drive type offshore wind power plant grid-connected system topology structure and control method thereof | |
| CN107895962B (en) | Current source type high-voltage direct-current transmission system and operation method thereof | |
| Pan et al. | Hybrid multi-terminal HVDC system for large scale wind power | |
| CN112653171A (en) | Hybrid converter topology suitable for offshore wind power transmission and control strategy thereof | |
| CN111969641A (en) | Fault current suppression method for sending-end MMC of flexible direct-current power transmission system | |
| CN108923450B (en) | Control and operation method of current source type high-voltage direct-current transmission system | |
| CN113949089A (en) | Electrochemical energy storage commutation system and method with harmonic suppression capability | |
| CN106712084A (en) | Wind power generation system for direct current (DC) series connection of offshore wind farm | |
| CN110729909A (en) | Multi-port railway power regulator system and comprehensive control method thereof | |
| CN111600334B (en) | Alternating current fault diagnosis and ride-through control method for four-terminal wind power direct current power grid | |
| CN114629136A (en) | Offshore wind power soft direct-sending system based on super capacitor and inertia coordination method thereof | |
| CN115603372A (en) | New energy sending system and control method thereof | |
| CN110752762A (en) | Control method for parallel virtual capacitor of grid-connected converter | |
| CN112086988B (en) | Smooth switching method for control strategy of voltage source type converter | |
| CN113922410A (en) | Hybrid Direct Current (DC) sending system and low voltage fault ride-through method thereof | |
| Bernal-Perez et al. | Connection of off-shore wind power plants to VSC-MTdc networks using HVdc diode-rectifiers | |
| CN112670970A (en) | Overvoltage suppression method for power grid at delivery end of offshore wind field flexible direct current transmission system | |
| CN105140961A (en) | Hybrid direct-current power transmission device used for new energy grid connection and power transmission method thereof | |
| CN117117886A (en) | Offshore large-scale wind power transmission system and control method thereof | |
| CN111404190B (en) | Control method and system for enhancing power output capability of MMC converter station under power grid fault | |
| CN116632902A (en) | Multi-port flexible direct current transmission system based on PWM current source converter | |
| CN114421498A (en) | Medium-voltage wind power system fluctuation power stabilizing method and system based on energy router |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PB01 | Publication | ||
| PB01 | Publication | ||
| SE01 | Entry into force of request for substantive examination | ||
| SE01 | Entry into force of request for substantive examination | ||
| GR01 | Patent grant | ||
| GR01 | Patent grant |