CN110994663B - Direct current converter station and control method and control system thereof - Google Patents
Direct current converter station and control method and control system thereof Download PDFInfo
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- CN110994663B CN110994663B CN201911254165.0A CN201911254165A CN110994663B CN 110994663 B CN110994663 B CN 110994663B CN 201911254165 A CN201911254165 A CN 201911254165A CN 110994663 B CN110994663 B CN 110994663B
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- 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
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- 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
- H02J3/12—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load
- H02J3/16—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load by adjustment of reactive power
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- 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
- Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
- Y02E40/30—Reactive power compensation
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- 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]
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Abstract
The invention provides a direct current converter station and a control method and a control system thereof, wherein the control method of the direct current converter station comprises the steps of controlling a sending end converter station by adopting a fixed direct current voltage control method; controlling a receiving end converter station by adopting an active-reactive control method; the method for controlling the receiving end converter station by adopting the active-reactive control method comprises the following steps: adding an input power adjusting module at the input end of an active-reactive power control power loop, wherein the input power adjusting module is connected with the active-reactive power control power loop; and the input power regulating module regulates an input power instruction of active-reactive power control according to the receiving end power grid voltage and the receiving end direct current bus voltage. By using the invention, reactive power can be continuously provided for the power grid when the voltage of the receiving-end power grid drops, the overcurrent phenomenon cannot occur in the converter station, the system can stably operate after the fault is recovered, the direct-current bus voltage can be stabilized when the voltage of the transmitting-end power grid drops, and the system can stably operate after the fault is recovered.
Description
Technical Field
The invention relates to the technical field of power transmission and distribution of a power system, in particular to a direct current converter station and a control method and a control system thereof.
Background
With the continuous adjustment of energy structures in China, flexible direct current transmission (HVDC) is used as a novel power transmission mode, and has the characteristics of small line loss, low harmonic level, capability of independently adjusting active power and reactive power and the like, so that the flexible direct current transmission (HVDC) is widely applied to medium-distance and long-distance transmission, particularly long-distance transmission of renewable energy sources and interconnection of power grids.
The Low Voltage Ride Through (LVRT) capability means that when a grid-connected point is subjected to voltage drop, a grid-connected converter system can keep a grid-connected state, and after a power grid recovers to be in fault, the system can recover to work normally.
Disclosure of Invention
In view of the above-mentioned drawbacks of the prior art, an object of the present invention is to provide a dc converter station, a control method and a control system thereof, which can realize low voltage ride through of a flexible dc transmission converter station without communication establishment of the converter station.
To achieve the above and other related objects, the present invention provides a method for controlling a dc converter station, including:
controlling a sending end converter station by adopting a constant direct current voltage control method to stabilize direct current bus voltage;
controlling a receiving end converter station by adopting an active-reactive control method;
the step of controlling the receiving end converter station by adopting the active-reactive control method comprises the following steps:
adding an input power adjusting module at the input end of an active-reactive power control power loop, wherein the input power adjusting module is connected with the active-reactive power control power loop;
and the input power regulating module regulates an input power instruction of active-reactive power control according to the receiving end power grid voltage and the receiving end direct current bus voltage.
In an embodiment, the step of controlling the receiving end converter station by using the active-reactive control method further includes:
acquiring a current instruction under a rotating coordinate system according to the adjusted active-reactive power control input power instruction;
and forming a modulation wave by using the acquired current instruction as input through current loop control and nearest level approximation control so as to control the receiving end converter station.
In an embodiment, the receiving-end grid voltage and the receiving-end dc bus voltage are obtained by voltage monitoring devices disposed at the receiving-end grid and the receiving-end dc bus, respectively.
In one embodiment, the input power regulation module comprises a selector switch and a dc bus voltage compensation branch, wherein the dc bus voltage compensation branch is connected with the active-reactive power control power loop through the selector switch;
when the voltage of the receiving end direct current bus is normal, the input power instruction of active-reactive power control is correspondingly adjusted through the selection switch and the direct current bus voltage compensation branch;
when the voltage of the receiving end direct current bus falls, the selection switch switches the active instruction of the active-reactive control to zero, and meanwhile, the direct current converter station performs reactive compensation on a power grid.
In one embodiment, the step of adjusting the input power command of the active-reactive power control through the selection switch and the dc bus voltage compensation branch comprises:
when the receiving end direct current bus voltage and the receiving end grid voltage are normal, the direct current bus voltage compensation branch does not adjust the input power instruction of the active-reactive power control;
when the receiving end power grid voltage is normal and the direct current bus voltage deviates, the direct current bus voltage compensation branch adds an additional power instruction as the input power instruction of active-reactive power control on the basis of the active instruction in normal operation.
To achieve the above and other related objects, the present invention also provides a dc converter station control system, including:
the sending end converter station control module is used for controlling the sending end converter station by adopting a constant direct current voltage control method so as to stabilize direct current bus voltage;
and the receiving end converter station control module is used for controlling the receiving end converter station by adopting an active-reactive control method, and comprises an input power adjusting module which is used for adjusting an input power instruction of active-reactive control according to the receiving end power grid voltage and the receiving end direct current bus voltage.
In an embodiment, the receiving end converter station control module includes:
the power controller module is used for acquiring a current instruction under a rotating coordinate system according to the adjusted input power instruction of the active-reactive control;
a modulation wave control module which takes the obtained current instruction as input and forms a modulation wave through current loop control and nearest level approximation control so as to control the receiving end converter station;
in an embodiment, the control system further includes a voltage monitoring device, which is respectively disposed at the receiving-end power grid and the receiving-end dc bus, and is configured to obtain the receiving-end power grid voltage and the receiving-end dc bus voltage.
In one embodiment, the input power regulation module comprises a selector switch and a dc bus voltage compensation branch, wherein the dc bus voltage compensation branch is connected with the active-reactive power control power loop through the selector switch; and the receiving end converter station control module correspondingly adjusts the input power instruction of the active-reactive power control through the selector switch and the direct-current bus voltage compensation branch.
In order to achieve the above objects and other related objects, the present invention further provides a dc converter station, which is controlled by any one of the above control methods, so as to implement low voltage ride through of a flexible dc transmission converter station under the condition that the converter station does not establish communication.
By using the invention, when the voltage of the receiving-end power grid drops, the reactive power can be continuously provided for the power grid, the overcurrent phenomenon cannot occur in the converter station, and the system can stably run after the fault is recovered;
by using the invention, the DC bus voltage can be stabilized when the voltage of the power grid at the sending end drops, and the normal and stable operation can be realized after the fault is recovered.
Drawings
Fig. 1 shows a schematic diagram of the basic structure of a flexible dc transmission converter station according to the invention.
Fig. 2 is a flow chart illustrating a control method of the dc converter station according to the present invention.
Fig. 3 is a flow chart illustrating a process of controlling a receiving end converter station using a PQ control method according to the present invention.
Fig. 4 shows a control block diagram of the HVDC converter station low voltage ride through control strategy of the present invention.
Fig. 5 shows a control block diagram of the PQ control of the present invention.
FIG. 6 shows a U-based scheme of the present inventiondcA detected power disturbance control block.
Fig. 7 is a block diagram showing the structure of the dc converter station control system of the present invention.
Fig. 8 is a block diagram illustrating a control module structure of a receiving end converter station in the dc converter station control system according to the present invention.
Fig. 9 is a control flow diagram of the input power adjustment module of the present invention.
Detailed Description
The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention.
Please refer to fig. 1-9. It should be noted that the drawings provided in the present embodiment are only for illustrating the basic idea of the present invention, and the components related to the present invention are only shown in the drawings rather than drawn according to the number, shape and size of the components in actual implementation, and the type, quantity and proportion of the components in actual implementation may be changed freely, and the layout of the components may be more complicated.
Fig. 1 shows a basic topology of a flexible direct current transmission (HVDC) converter station according to the present invention, where a hardware portion of the flexible direct current transmission system specifically includes a double-ended MMC-HVDC system including two Modular Multilevel converters (Modular Multilevel converters)er, MMC) MMC converter station, concretely including sending end converter station MMC1 and receiving end converter station MMC2, sending end converter station MMC1 and receiving end converter station MMC2, sending end converter station MMC1 and receiving end converter station MMC2 link to each other with electric wire netting Grid1 and Grid2 respectively, sending end converter station MMC1 can adopt the constant direct current voltage control method for example, stabilize HVDC system direct current bus voltage UdcThe MMC2 of the receiving end converter station independently controls the active power and the reactive power of an MMC2 system of the receiving end converter station by adopting a PQ control method so as to realize power balance between the two converter stations. The direct current converter station has double-end fault ride-through capability, and can realize low-voltage ride-through of the HVDC converter station without communication between two stations.
Referring to fig. 4, each phase of the receiving-end circulating station MMC2 of the present invention has an upper bridge arm and a lower bridge arm, and each bridge arm has n submodules SM 1-SMn; two current-limiting reactors are connected in series between the upper bridge arm and the lower bridge arm, and each submodule consists of two switching devices, 2 anti-parallel diodes and 1 voltage-stabilizing capacitor; the sending end converter station MMC1 and the receiving end circulating station MMC2 are similar in structure and are not described in detail again. It should be noted that, in other embodiments, the sending end converter station MMC1 and the receiving end converter station MMC2 may also adopt other structures, and are not limited to the structure shown in fig. 3.
Fig. 2 shows a flow chart of a control method of a direct current transmission (HVDC) converter station according to the present embodiment, referring to fig. 2, the control method includes: step S10, controlling the sending end converter station MMC1 by adopting a constant direct current voltage control method, and stabilizing the direct current bus voltage U of the HVDC systemdc(ii) a And step S20, controlling the receiving end converter station by adopting an active-reactive control method. Fig. 3 shows a schematic flow chart of controlling a receiving end converter station by using a PQ control method in a direct current transmission (HVDC) converter station according to the present embodiment. Referring to fig. 2, the method for controlling the receiving end converter station by using the PQ control method includes the steps of executing step S21, and adjusting an input power command of the PQ control according to the receiving end grid voltage and the receiving end dc bus voltage; executing step S22, and acquiring a current instruction in a rotating coordinate system according to the adjusted input power instruction of the PQ control; step S23 is executed, the obtained current instruction is used as input, and a modulation wave is formed through current loop control and nearest level approximation control so as to control the current receiving partThe end converter station performs control.
In step S21, please refer to fig. 3 and 9, the input power adjusting module 3 may be added to the input end of the active-reactive power loop, and the input power adjusting module 3 is connected to the active-reactive power loop; the receiving grid voltage (u in fig. 3) is obtained by means of voltage monitoring devices arranged at the receiving grid and at the receiving dc busa、ub、ucCorresponding to step S211) in fig. 9 and the receiving-end dc bus voltage Udc(corresponding to step S213 in fig. 9), the input power adjusting module 3 adjusts the input power command for active-reactive control according to the receiving-end grid voltage and the receiving-end dc bus voltage.
Specifically, in step S21, referring to fig. 3 and 9, the input power regulating module 3 includes a selection switch S and a dc bus voltage compensation branch 31, where the dc bus voltage compensation branch 31 is connected to the active-reactive power control power loop through the selection switch S; when the input power command is adjusted, firstly, whether the receiving-end power grid voltage is normal is judged (step S212), when the receiving-end power grid voltage is normal, the receiving-end power grid voltage is divided into two conditions, which respectively correspond to a control mode 1 and a control mode 2, and the input power command of the active-reactive power control can be correspondingly adjusted through the selector switch S and the direct-current bus voltage compensation branch 31, wherein details are shown in the following; when the voltage of the receiving-end power grid drops, corresponding to the control mode 3, the selection switch S switches the active instruction of the active-reactive control to zero, and meanwhile, the direct current converter station performs reactive compensation on the power grid (step S216 and step S219).
Specifically, in step S21, referring to fig. 3 and 9, when the voltage of the receiving end grid is normal, it may be determined whether the dc bus voltage is normal (step S214), and when the voltage of the dc bus is normal, corresponding to the control mode 1, the dc bus voltage compensation branch 31 does not adjust the input power command of the active-reactive power control, specifically, see the following description of relevant parts (step S217 and step S219); when the DC bus voltage is deviated, corresponding to the control mode 2, the DC bus voltage is deviated, and the control mode is startedThe DC bus voltage compensation branch 31 adds an additional power instruction P on the basis of an active instruction in normal operationoutAnd as an input power instruction of the active-reactive power control (step S218 and step S219), the additional power value is generated by the direct current bus voltage through a hysteresis control link.
A method of controlling a direct current transmission (HVDC) converter station will now be described with reference to FIGS. 2-6, in which FIG. 4 shows a control block diagram for a low voltage ride through control strategy for an HVDC converter station, FIG. 5 shows a control block diagram for PQ control, and FIG. 6 shows a control block diagram for U-based controldcA detected power disturbance control block.
Referring to fig. 2 and fig. 3, a basic scheme of the method for controlling a dc power transmission converter station of this embodiment includes that a sending-end converter station MMC1 in a double-end HVDC flexible dc converter station controls a stable dc bus voltage with a constant dc voltage, an additional input power adjusting module 3 (including a selector switch S and a dc bus voltage compensation branch 31) is added to a receiving-end converter station MMC2 (shown as reference numeral 1 in fig. 4) based on an original PQ control, an input power instruction of PQ control in different control modes is obtained through the input power adjusting module 3, and a current instruction i in a rotating coordinate system is obtained by using a PQ power controller 4 according to a PQ control principled_ref，iq_refThe voltage instruction u under the rotating coordinate system is obtained through the control of the current loop module 5d_ref，uq_refAt the moment, the receiving end power grid obtains a phase angle theta of coordinate change under a rotating coordinate system through a PLL (phase locked loop) 2, and a Park inverse transformation module 6 is utilized to transform a voltage instruction under the rotating coordinate system into a voltage instruction u under a three-phase coordinate systemabc_refAnd finally, the control of the flexible direct current converter station under the fault ride-through condition is realized through a nearest level approximation modulation mode of a nearest level approximation module 7(NLM module).
FIG. 5 is a block diagram of PQ control strategy of MMC2 of a receiving end converter station, and reference commands i of d-axis and q-axisd_ref、iq_refRespectively by active commands P input to PQ power controller 4ref *And reactive instruction QrefThe real active power P and the real reactive power Q are obtained by calculation of a PI regulator, and the formula can be expressed as follows:
in the formula kp1，ki1，kp2，ki2Respectively, a proportional gain and an integral gain in the PI regulator.
The actual values of the active power P and the reactive power Q are expressed as follows:
in the formula ud，uqDirect and quadrature axis voltages, i, output for a receiving end converter station MMC2d，iqThe direct and quadrature currents output by the receiving end converter station MMC 2.
Under the condition of voltage balance of a three-phase power grid, the vector direction of the power grid is taken as the direction of a d axis, and u is taken asdU (U is the ac system voltage amplitude), UqAnd (5) simplifying to obtain an active calculation formula and a reactive calculation formula:
obtaining a current instruction i of an outer ringd_ref，iq_refAnd as an input, the MMC2 system of the receiving end converter station is controlled through a current inner loop and the nearest level approximation modulation, and the direct current is converted into alternating current and is transmitted to a power grid.
Based on id_ref，iq_refCarrying out current inner loop control through a current loop module 5 under a rotating coordinate system to obtain a modulated wave instruction ud_ref，uq_refAnd a modulation wave is formed through Park inverse transformation of the Park inverse transformation module 6 and nearest level approximation control of the nearest level approximation module 7, so that control over the receiving end converter station MMC2 is achieved, and direct current is converted into alternating current and is sent to a power grid. The control equation of the current inner loop is as follows:
wherein u isd_refIndicating that the current inner loop control obtains the direct-axis modulated wave command uq_refIndicating that the current inner loop control obtains a quadrature-axis modulated wave command, id_refIndicating the direct-axis current command, iq_refRepresenting quadrature axis current command, idRepresenting the direct component of the grid output current, iqRepresenting the quadrature component of the grid output current, omega representing the mechanical angular velocity, LsRepresenting the synchronous inductance, kp3Proportional gain, k, representing the proportional integral element of the current inner loop control direct axisi3Integral gain, k, of a proportional-integral element representing the direct axis of the current inner loop controlp4Proportional gain, k, representing the proportional integral element of the current inner loop control quadrature axisi4And the integral gain of a proportional integral link of a current inner loop control quadrature axis is shown.
FIG. 6 is based on UdcA block diagram of detected hysteresis control. U shape1And U2Upper and lower limit voltages, U, of the voltage hysteresis loop, respectivelydc_puIs the DC bus voltage P of HVDC system in normal operationrefFor active commands in normal operation of the system, PoutAn additional instruction (namely an additional power value) of active input when the voltage of the MMC1 of the sending end converter station falls, PrefThe active command input to the PQ power controller by the system.
The invention detects the voltage output by the direct current bus of the MMC2 of the receiving end converter station, and according to the hysteresis control principle and the voltage value of the direct current bus, the original power instruction P is carried outrefIs added with a new power PoutObtaining an active power instruction P when the selector switch is at the 0 positionref *. The basic principle of hysteresis control is as follows: when the DC bus voltage is lower than U1At this time, the power P of the output is controlled by the hysteresis loopoutis-PrefI.e. active power command P of the receiving end converter station MMC2ref *Is 0; when the voltage is from U1Rise to U2Time-lag control output power PoutIs still-PrefIs receivingActive power instruction P of end converter station MMC2ref *Is still 0; when the voltage rises to U2Time-lag control output power PoutTo become 0, the active power instruction P of the receiving end converter station MMC2ref *Go back to P againref(ii) a When the voltage is from U2Falls back to U1Time-lag control output power PoutKeeping 0 constant until U is reduced1When it is changed to-P againref。
Referring to fig. 4 and 9, the specific situation of the additional control link before PQ control provided in this embodiment is as follows: by adding voltage monitoring devices at the receiving end power grid and the receiving end direct current bus (u in figure 4)a、ub、ucBlack dots at (b) show voltage monitoring devices on the receiving grid for obtaining said receiving grid voltage value (u in fig. 4)a、ub、uc) And the receive side dc bus voltage; the voltage monitoring device on the receiving end power grid is connected with the selection switch S, the voltage monitoring device can transmit the acquired voltage signal to the selection switch S, and the selection switch S can adjust the position of the selection switch S according to the voltage value of the receiving end power grid. Specifically, when the voltage of the receiving-end power grid is normal, the switch S is located at the position 0, when the voltage of the receiving-end power grid drops, the switch S is located at the position 1, and the voltage of the direct-current bus is U when the system works normallydc_pu. When direct current bus voltage and receiving end grid voltage are all normal, for normal operating condition, receiving end converter station MMC 2's control mode defines for control mode 1 this moment, when direct current bus voltage takes place to squint, when receiving end grid voltage is normal, for sending end grid voltage drops, receiving end converter station MMC 2's control mode defines for control mode 2 this moment, when receiving end grid voltage drops, receiving end converter station MMC 2's control mode defines for control mode 3 this moment. Referring to fig. 4, the specific operation of the three control modes is as follows: the control mode 1 is the condition of normal operation of the system, the selection switch S is at the position 0, and the direct-current bus voltage compensation branch 31 has no influence on the operation of the system; in the control mode 2, when the voltage of the sending-end converter station MMC1 drops, the selector switch S is still at the position 0, and the voltage of the dc bus generates an additional voltage through a hysteresis control linkPower PoutTo maintain the voltage stability of the DC bus; the control mode 3 is the condition that the voltage of the receiving end converter station MMC2 drops, and at this time, the selector switch S is switched to the position 1, so that reactive compensation is provided for the receiving end power grid.
Specifically, referring to fig. 4 and fig. 9, during normal operation, the selection switch detects that the voltage of the receiving end converter station MMC2 is not abnormal, the selection switch S is placed at the position 0, the system is in the control mode 1, the active power output by the hysteresis control is 0, and the active command of the receiving end converter station MMC2 is PrefThe idle command is 0.
Referring to fig. 4 and 9, when the voltage of the sending-end converter station MMC1 drops, the selection switch S detects that the voltage of the receiving-end converter station MMC2 is not abnormal, the selection switch S is still located at the position 0, the system is in the control mode 2, due to the action of the current limiting device, the active power output by the sending-end converter station MMC1 is smaller than the active power required by the receiving-end converter station MMC2, at this time, the sending-end converter station MMC1 cannot provide enough voltage to stabilize the voltages of the converter station submodule and the dc bus, and the voltage of the dc bus drops. When the sensor (the voltage monitoring device mentioned above) detects the DC bus voltage UdcLower than hysteresis lower limit voltage U1Time lag control outputs additional power Poutis-PrefAt this time, the receiving end converter station MMC2 active instruction Pref *At 0, the receiving end converter station MMC2 supplies power to the sending end converter station MMC1 to stabilize the dc bus voltage and raise the dc bus voltage, when a sensor (the voltage monitoring device mentioned above) detects the dc bus voltage UdcHigh lower than hysteresis upper limit voltage U2Time lag controlling output additional power PoutAnd then becomes 0, at this moment, the active command P of the receiving end converter station MMC2ref *Is PrefThe sending end converter station MMC1 can not provide corresponding active power, the direct current bus voltage can start to drop, and finally the direct current bus voltage can be in U1And U2The voltage of the direct current bus can return to the U after the fault is recovereddc_puAnd the system quickly recovers stable operation.
Referring to fig. 4 and 9, when the receiving end converter stationWhen MMC2 has voltage drop, selector switch S detects that receiving end converter station MMC2 voltage takes place unusually, selector switch S arranges position 1 department in, the system is under control mode 3, neglect the line loss, the active power of sending end converter station MMC1 output is greater than the active power of receiving end converter station MMC2, in order to avoid receiving end converter station MMC2 to appear overcurrent state, will receive end converter station MMC 2' S active power P through selector switch Sref *Switching to 0, reactive power to QrefAt the moment, overcurrent of the MMC2 of the receiving end converter station is avoided, and the reactive compensation requirement of a low-penetration power grid can be met, wherein the dynamic reactive current I of the power grid is injected into the grid by the grid-connected inverterqThe voltage change of the grid-connected point should be tracked in real time, and the following formula is satisfied:
wherein U isGIs the per unit value of the voltage of the grid-connected point, INIs the rated current of the grid side, IqIs a reactive current, UdIs the ac fault voltage of the straight axis.
After the fault is recovered, the selection switch S detects that the voltage of the MMC2 of the receiving end converter station is recovered to be normal, the switch is switched back to the position 0, and the system is rapidly recovered to a stable running state under the condition that the system works and the control mode 1 again.
Referring to fig. 7, the present embodiment further provides a dc converter station control system 100, which includes a sending-end converter station control module 101 and a receiving-end converter station control module 102. Referring to fig. 4 and 8, the receiving-end converter station control module 102 includes an input power adjusting module 3, a PQ power controller module 4, a current loop module 5, a Park inverse transformation module 6, and a nearest level approximation module 7, which are connected in sequence; the nearest level approximation module 7 is connected with a receiving end converter station MMC 2; the input power adjusting module 3 comprises a selector switch S and a dc bus voltage compensation branch 31, the dc bus voltage compensation branch 31 is connected to the active-reactive power control power loop (i.e. the PQ power controller module 4) through the selector switch S, and the receiving-end converter station control module performs corresponding adjustment on the active-reactive power control input power command through the selector switch and the dc bus voltage compensation branch, wherein the current loop adjusting module 5, the Park inverse transformation module 6 and the nearest level approximation module 7 together form a modulation wave control module; and for coordinate transformation, the receiving end converter station control module 102 further includes a phase-locked loop 2, and the phase-locked loop 2 is connected with the Park inverse transformation module 6. It should be noted that the functions of the above module units are described in detail in the relevant parts of the above description, and are not described herein again.
It should be noted that the PLL phase-locked loop 2, the input power adjusting module 3, the PQ power controller 4, the current loop module 5, the Park inverse transformation module 6, and the level approximation module 7 are, for example, modules divided according to logic functions, and may be wholly or partially integrated into a physical entity or physically separated in actual implementation. And these modules can be realized in the form of software called by processing element; or may be implemented entirely in hardware; and part of the modules can be realized in the form of calling software by the processing element, and part of the modules can be realized in the form of hardware. In addition, all or part of the modules can be integrated together or can be independently realized. The processing element described herein may be an integrated circuit having signal processing capabilities. In implementation, each step of the above method or each module above may be implemented by an integrated logic circuit of hardware in a processor element or an instruction in the form of software.
For example, the above modules may be one or more integrated circuits configured to implement the above methods, such as: one or more Application Specific Integrated Circuits (ASICs), or one or more microprocessors (DSPs), or one or more Field Programmable Gate Arrays (FPGAs), among others. For another example, when one of the above modules is implemented in the form of a Processing element scheduler code, the Processing element may be a general-purpose processor, such as a Central Processing Unit (CPU) or other processor capable of calling program code. For another example, these modules may be integrated together and implemented in the form of a system-on-a-chip (SOC).
It should be noted that, the control system and the control method of the direct current converter station of the present invention can continuously provide reactive power to the grid when the voltage of the receiving end grid drops, the over-current phenomenon does not occur in the converter station, and the system can stably operate after the fault is recovered; when the voltage of the power grid at the sending end drops, the direct-current bus voltage can be stabilized, and the normal and stable operation can be realized after the fault is recovered.
In the description herein, numerous specific details are provided, such as examples of components and/or methods, to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that an embodiment of the invention can be practiced without one or more of the specific details, or with other apparatus, systems, assemblies, methods, components, materials, parts, and/or the like. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of embodiments of the invention.
Reference throughout this specification to "one embodiment", "an embodiment", or "a specific embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment, and not necessarily all embodiments, of the present invention. Thus, respective appearances of the phrases "in one embodiment", "in an embodiment", or "in a specific embodiment" in various places throughout this specification are not necessarily referring to the same embodiment. Furthermore, the particular features, structures, or characteristics of any specific embodiment of the present invention may be combined in any suitable manner with one or more other embodiments. It is to be understood that other variations and modifications of the embodiments of the invention described and illustrated herein are possible in light of the teachings herein and are to be considered as part of the spirit and scope of the present invention.
It will also be appreciated that one or more of the elements shown in the figures can also be implemented in a more separated or integrated manner, or even removed for inoperability in some circumstances or provided for usefulness in accordance with a particular application.
Additionally, any reference arrows in the drawings/figures should be considered only as exemplary, and not limiting, unless otherwise expressly specified. Further, as used herein, the term "or" is generally intended to mean "and/or" unless otherwise indicated. Combinations of components or steps will also be considered as being noted where terminology is foreseen as rendering the ability to separate or combine is unclear.
As used in the description herein and throughout the claims that follow, "a", "an", and "the" include plural references unless otherwise indicated. Also, as used in the description herein and throughout the claims that follow, unless otherwise indicated, the meaning of "in …" includes "in …" and "on … (on)".
The above description of illustrated embodiments of the invention, including what is described in the abstract of the specification, is not intended to be exhaustive or to limit the invention to the precise forms disclosed herein. While specific embodiments of, and examples for, the invention are described herein for illustrative purposes only, various equivalent modifications are possible within the spirit and scope of the present invention, as those skilled in the relevant art will recognize and appreciate. As indicated, these modifications may be made to the present invention in light of the foregoing description of illustrated embodiments of the present invention and are to be included within the spirit and scope of the present invention.
The systems and methods have been described herein in general terms as the details aid in understanding the invention. Furthermore, various specific details have been given to provide a general understanding of the embodiments of the invention. One skilled in the relevant art will recognize, however, that an embodiment of the invention can be practiced without one or more of the specific details, or with other apparatus, systems, assemblies, methods, components, materials, parts, and/or the like. In other instances, well-known structures, materials, and/or operations are not specifically shown or described in detail to avoid obscuring aspects of embodiments of the invention.
Thus, although the present invention has been described herein with reference to particular embodiments thereof, a latitude of modification, various changes and substitutions are intended in the foregoing disclosures, and it will be appreciated that in some instances some features of the invention will be employed without a corresponding use of other features without departing from the scope and spirit of the invention as set forth. Thus, many modifications may be made to adapt a particular situation or material to the essential scope and spirit of the present invention. It is intended that the invention not be limited to the particular terms used in following claims and/or to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include any and all embodiments and equivalents falling within the scope of the appended claims. Accordingly, the scope of the invention is to be determined solely by the appended claims.
Claims (7)
1. A method for controlling a dc converter station, comprising:
controlling a sending end converter station by adopting a constant direct current voltage control method;
controlling a receiving end converter station by adopting an active-reactive control method;
the step of controlling the receiving end converter station by adopting the active-reactive control method comprises the following steps:
adding an input power adjusting module at an input end of an active-reactive power control power loop, wherein the input power adjusting module is connected with the active-reactive power control power loop and comprises a selector switch and a direct current bus voltage compensation branch, and the direct current bus voltage compensation branch is connected with the active-reactive power control power loop through the selector switch;
the input power regulating module regulates an input power instruction of active-reactive power control according to the receiving end power grid voltage and the receiving end direct current bus voltage;
acquiring a current instruction under a rotating coordinate system according to the adjusted active-reactive power control input power instruction;
the obtained current instruction is used as input, and a modulation wave is formed through current loop control and nearest level approximation control so as to control the receiving end converter station;
the input power regulating module regulates the input power instruction of active-reactive power control according to the receiving end power grid voltage and the receiving end direct current bus voltage, and the input power regulating module comprises the following steps:
when the receiving end direct current bus voltage and the receiving end grid voltage are normal, the direct current bus voltage compensation branch does not adjust the input power instruction of the active-reactive power control;
when the receiving end power grid voltage is normal and the direct current bus voltage deviates, the direct current bus voltage compensation branch adds an additional power instruction as an input power instruction of active-reactive power control on the basis of an active instruction in normal operation, wherein the additional power instruction is generated by the direct current bus voltage through a hysteresis control link.
2. The direct current converter station control method according to claim 1, characterized in that the receiving end grid voltage and the receiving end direct current bus voltage are obtained by voltage monitoring devices arranged at a receiving end grid and a receiving end direct current bus, respectively.
3. The dc converter station control method according to claim 1 or 2, wherein the step of adjusting the input power command of the active-reactive control by the input power adjusting module according to the receiving-end grid voltage and the receiving-end dc bus voltage further comprises switching the active command of the active-reactive control to zero by the selector switch when the receiving-end dc bus voltage drops, and performing reactive compensation on the grid by the dc converter station.
4. A direct current converter station control system, comprising:
the sending end converter station control module is used for controlling the sending end converter station by adopting a constant direct current voltage control method so as to stabilize direct current bus voltage;
a receiving end converter station control module for controlling a receiving end converter station by adopting an active-reactive control method, wherein the receiving end converter station control module comprises an input power adjusting module, the input power adjusting module comprises a selector switch and a direct current bus voltage compensation branch, the direct current bus voltage compensation branch is connected with the active-reactive control power loop through the selector switch, the input power adjusting module is used for adjusting an active-reactive control input power instruction according to receiving end grid voltage and receiving end direct current bus voltage, wherein when the receiving end direct current bus voltage and the receiving end grid voltage are normal, the direct current bus voltage compensation branch does not adjust the active-reactive control input power instruction, and when the receiving end grid voltage is normal, the direct current bus voltage is deviated, the direct current bus voltage compensation branch adds an additional power instruction as an input power instruction of the active-reactive power control on the basis of an active instruction during normal operation, wherein the additional power instruction is generated by a direct current bus voltage through a hysteresis control link;
the receiving end converter station control module further comprises:
the power controller is used for acquiring a current instruction under a rotating coordinate system according to the adjusted active-reactive power control input power instruction;
and the modulation wave control module is used for forming a modulation wave by taking the acquired current instruction as input and controlling through current loop control and nearest level approximation control so as to control the receiving end converter station.
5. The DC converter station control system according to claim 4, further comprising voltage monitoring devices respectively disposed at a receiving end grid and a receiving end DC bus for obtaining the receiving end grid voltage and the receiving end DC bus voltage.
6. The direct current converter station control system according to any one of claims 4 or 5, wherein when the voltage of the receiving end direct current bus falls, the input power regulating module switches an active instruction of the active-reactive power control to zero through the selection switch, and the direct current converter station performs reactive power compensation on a power grid.
7. A direct current converter station controlled by the control method of claim 1.
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