CN113193558A - Coordinated start control method and system suitable for multi-terminal direct current system fault recovery - Google Patents

Coordinated start control method and system suitable for multi-terminal direct current system fault recovery Download PDF

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CN113193558A
CN113193558A CN202110604840.9A CN202110604840A CN113193558A CN 113193558 A CN113193558 A CN 113193558A CN 202110604840 A CN202110604840 A CN 202110604840A CN 113193558 A CN113193558 A CN 113193558A
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converter station
voltage
mmc1
mmc
controller
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解大
王西田
王晨磊
张鑫林
潘明杰
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Shanghai Jiaotong University
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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
    • H02J3/001—Methods to deal with contingencies, e.g. abnormalities, faults or failures
    • 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
    • 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 coordinated start control method and a coordinated start control system suitable for multi-terminal direct current system fault recovery. The invention realizes the starting of the main converter station, the synchronous pre-charging of the slave converter stations and the coordinated starting control of coordinating and merging the main converter station and the slave converter stations into the direct current network, greatly reduces the energy transient impact in the starting process, and changes the energy loss and the time extension of the system restarting after the system is stopped after the original fault.

Description

Coordinated start control method and system suitable for multi-terminal direct current system fault recovery
Technical Field
The invention relates to the technical field of starting control of a multi-terminal direct-current system, in particular to a coordinated starting control method and system suitable for fault recovery of the multi-terminal direct-current system.
Background
Different from the existing traditional Direct Current transmission project, a Multi-Terminal Direct Current (MTDC) transmission system based on the MMC is more suitable for the requirement of modern power systems for developing new potentials. A plurality of multi-terminal direct-current transmission projects based on MMC are continuously built and operated, and an MMC-MTDC system is a new research hotspot in the field of direct-current transmission. There are many problems to be optimized with regard to the topology, modulation technique, capacitance grading control technique, and circulating current suppression technique of MMC systems. In aspects of starting control, master-slave control, shutdown control, redundancy control, protection control and the like of the MMC-MTDC system, a plurality of key problems are still to be solved.
In the starting process of the multi-terminal direct current system, various faults may occur to influence the starting of the system, the fault which can be recovered after a short time after the fault occurs is a temporary fault, and the fault which cannot be recovered after the short time after the fault occurs is a permanent fault. The recovery start-up process of the multi-terminal direct current system after the temporary fault is generally slower or directly enters the shutdown discharge. If the start-up is to be re-implemented, a large amount of energy is already lost and the start-up time is extended, reducing the efficiency of the system.
Patent document CN104578187B (application number: CN201510006777.3) discloses a multi-terminal flexible dc transmission system-level coordination control device, which includes a data acquisition module, a data processing module, a control function processing module, a communication management module and a redundancy control module, wherein the data acquisition module is responsible for acquiring process data, sampling analog data such as state signals and voltage and current, and generating input data required by the control function processing module; the control function processing module comprises an active control module, a reactive control module, a direct current voltage control module, a VF control module and the like, finally generates reference value signals of voltage, active, reactive, frequency and the like of the converter station, and sends the reference value signals to the converter station unit controller through the communication management module to complete the control target of the system.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide a coordinated start control method and a coordinated start control system suitable for multi-terminal direct current system fault recovery.
The coordinated starting control method suitable for the fault recovery of the multi-terminal direct-current system provided by the invention comprises the following steps:
step 1: selecting a single-ended MMC1 converter station of a multi-ended direct current system to carry out single-ended pre-charging to reach 70% of a pre-charging target value;
step 2: starting control of constant direct-current voltage and constant reactive power is carried out on the single-ended MMC1 converter station, and starting of the MMC1 converter station and capacitor charging to a target value are completed;
and step 3: when the single-ended MMC1 converter station is started, the MMC is merged into a direct current bus from the converter station;
and 4, step 4: starting the MMC slave converter station under the control of constant active power and constant reactive power to realize the pre-charging and starting of the whole multi-terminal direct-current system;
and 5: and when a fault occurs in the starting process, judging the fault type, adjusting the controller and completing the recovery starting of the multi-terminal direct current system.
Preferably, the step 3 comprises:
calculating whether the charging of the slave converter station exceeds the upper and lower voltage limits, obtaining the upper and lower limits of a submodule voltage feasible interval of the MMC slave converter station according to the charging requirement and the uncontrollable charging capacity, and judging the feasibility of a coordinated pre-charging mode according to the upper limit of the feasible interval;
the upper limit of the feasible interval includes: the maximum voltage value of the local converter station to the capacitance of the uncontrollable charging submodule of the remote converter station, the maximum voltage value of the direct current bus to the secondary converter station to be charged after the MMC1 converter station is started, the maximum voltage value of the secondary converter station to be charged from the capacitance of the converter station submodule in the MMC1 converter station starting process and the voltage of the secondary converter station capacitance after the secondary converter station is started are expressed by the corresponding formula and the relation:
Figure BDA0003093804680000021
in the formula of UphFor AC system phase voltages, UdcrefSpecifying the value of u for the DC-side bus voltagevalidThe voltage effective value of the direct current side in the transient process is obtained; n denotes the number of converter stations.
Preferably, the transient process dc-side voltage is represented by:
Udc(t)＝A1sin(B1x+C1)+D1+A2sin(B2x+C2)+D2+...+An sin(Bnx+Cn)+Dn………(2)
in the formula, A1、B1、C1、D1、A2、B2、C2、D2...An、Bn、Cn、DnCoefficients of the associated sine function;
the effective value expression of the voltage at the direct current side is as follows:
Figure BDA0003093804680000022
starting of the single-ended MMC1 converter station of the multi-end direct current system is completed, and each MMC is charged to u from a submodule of the converter stationvalidAnd after 2N, starting control of constant active power and constant reactive power is carried out on the MMC slave converter station.
Preferably, the step 5 comprises:
after the short-circuit fault is recovered, voltage is controlled again through a voltage controller, and the expression of the output quantity of the controller is as follows:
Outcontroller＝Kp·Δx+Ki∫Δxdt………(4)
where Δ x is the interpolation of the actual value from the reference value, KpAnd KiProportional coefficient and integral coefficient in PI control;
the MMC1 converter station controller varies as follows:
Figure BDA0003093804680000031
in the formula,. DELTA.id1、Δiq1For the current change quantity of d and q axes of the MMC1 converter station, delta Udc、ΔQ1Is the DC voltage and reactive power variation, delta u, of the MMC1 converter stationcd1、Δucq1For the controller to output the variation of the control quantity, kp1、ki1、kp2、ki2、kp3、ki3、kp4、ki4The corresponding proportional and integral parameters for the MMC1 converter station controller.
Preferably, the MMC is changed from the converter station controller by the following equation:
Figure BDA0003093804680000032
in the formula,. DELTA.id2、Δiq2For MMC slave converter station d, q axis current change, delta P2、ΔQ2Active and reactive power variations, Deltau, for MMC slave converter stationscd2、Δucq2For the controller to output the variation of the control quantity, kp1'、ki1'、kp2'、ki2'、kp3'、ki3'、kp4'、ki4' are the corresponding proportional and integral parameters of the MMC from the converter station controller.
The coordinated starting control system suitable for the fault recovery of the multi-terminal direct-current system provided by the invention comprises the following components:
module M1: selecting a single-ended MMC1 converter station of a multi-ended direct current system to carry out single-ended pre-charging to reach 70% of a pre-charging target value;
module M2: starting control of constant direct-current voltage and constant reactive power is carried out on the single-ended MMC1 converter station, and starting of the MMC1 converter station and capacitor charging to a target value are completed;
module M3: when the single-ended MMC1 converter station is started, the MMC is merged into a direct current bus from the converter station;
module M4: starting the MMC slave converter station under the control of constant active power and constant reactive power to realize the pre-charging and starting of the whole multi-terminal direct-current system;
module M5: and when a fault occurs in the starting process, judging the fault type, adjusting the controller and completing the recovery starting of the multi-terminal direct current system.
Preferably, the module M3 includes:
calculating whether the charging of the slave converter station exceeds the upper and lower voltage limits, obtaining the upper and lower limits of a submodule voltage feasible interval of the MMC slave converter station according to the charging requirement and the uncontrollable charging capacity, and judging the feasibility of a coordinated pre-charging mode according to the upper limit of the feasible interval;
the upper limit of the feasible interval includes: the maximum voltage value of the local converter station to the capacitance of the uncontrollable charging submodule of the remote converter station, the maximum voltage value of the direct current bus to the secondary converter station to be charged after the MMC1 converter station is started, the maximum voltage value of the secondary converter station to be charged from the capacitance of the converter station submodule in the MMC1 converter station starting process and the voltage of the secondary converter station capacitance after the secondary converter station is started are expressed by the corresponding formula and the relation:
Figure BDA0003093804680000041
in the formula of UphFor AC system phase voltages, UdcrefSpecifying the value of u for the DC-side bus voltagevalidThe voltage effective value of the direct current side in the transient process is obtained; n denotes the number of converter stations.
Preferably, the transient process dc-side voltage is represented by:
Udc(t)＝A1sin(B1x+C1)+D1+A2sin(B2x+C2)+D2+...+Ansin(Bnx+Cn)+Dn………(2)
in the formula, A1、B1、C1、D1、A2、B2、C2、D2...An、Bn、Cn、DnIs a phase ofThe coefficients of the sine function are turned off;
the effective value expression of the voltage at the direct current side is as follows:
Figure BDA0003093804680000042
starting of the single-ended MMC1 converter station of the multi-end direct current system is completed, and each MMC is charged to u from a submodule of the converter stationvalidAnd after 2N, starting control of constant active power and constant reactive power is carried out on the MMC slave converter station.
Preferably, the module M5 includes:
after the short-circuit fault is recovered, voltage is controlled again through a voltage controller, and the expression of the output quantity of the controller is as follows:
Outcontroller＝Kp·Δx+Ki∫Δxdt………(4)
where Δ x is the interpolation of the actual value from the reference value, KpAnd KiProportional coefficient and integral coefficient in PI control;
the MMC1 converter station controller varies as follows:
Figure BDA0003093804680000051
in the formula,. DELTA.id1、Δiq1For the current change quantity of d and q axes of the MMC1 converter station, delta Udc、ΔQ1Is the DC voltage and reactive power variation, delta u, of the MMC1 converter stationcd1、Δucq1For the controller to output the variation of the control quantity, kp1、ki1、kp2、ki2、kp3、ki3、kp4、ki4The corresponding proportional and integral parameters for the MMC1 converter station controller.
Preferably, the MMC is changed from the converter station controller by the following equation:
Figure BDA0003093804680000052
in the formula,. DELTA.id2、Δiq2For MMC slave converter station d, q axis current change, delta P2、ΔQ2Active and reactive power variations, Deltau, for MMC slave converter stationscd2、Δucq2For the controller to output the variation of the control quantity, kp1'、ki1'、kp2'、ki2'、kp3'、ki3'、kp4'、ki4' are the corresponding proportional and integral parameters of the MMC from the converter station controller.
Compared with the prior art, the invention has the following beneficial effects:
the invention realizes the starting of the main converter station, the synchronous pre-charging of the slave converter stations and the coordinated starting control of coordinating and merging the main converter station and the slave converter stations into the direct current network, greatly reduces the energy transient impact in the starting process, and changes the energy loss and the time extension of the system restarting after the system is stopped after the original fault.
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Other features, objects and advantages of the invention will become more apparent upon reading of the detailed description of non-limiting embodiments with reference to the following drawings:
FIG. 1 is a schematic diagram of a master and slave controller of the system of the present invention;
FIG. 2 is a flow chart of the system coordination start-up of the present invention;
FIG. 3 is a flowchart illustrating the system failure recovery initiation process of the present invention.
Detailed Description
The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the invention, but are not intended to limit the invention in any way. It should be noted that it would be obvious to those skilled in the art that various changes and modifications can be made without departing from the spirit of the invention. All falling within the scope of the present invention.
Example (b):
as shown in fig. 1, the coordinated start control method adapted to multi-terminal dc system fault recovery provided by the present invention includes:
step S1: selecting a single-ended MMC1 converter station of a multi-end direct current system, and carrying out independent uncontrollable pre-charging on the single-ended MMC system to enable sub-modules of the single-ended MMC system to reach 70% of a pre-charging target value;
step S2: after the pre-charging of the MMC1 converter station is completed, starting control of constant direct-current voltage and constant reactive power is carried out on the single-ended MMC1 converter station, and the starting of the MMC1 converter station and the charging of the sub-module capacitor to a target value are completed;
step S3: simultaneously when the single-ended MMC1 converter station starts to start, other MMC converter stations are simultaneously merged into a direct current bus;
step S4: the MMC is started under the control of constant active power and constant reactive power from the converter station, so that the pre-charging and starting of the whole MMC-MTDC system are realized;
step S5: and when a fault occurs in the starting process, judging the fault type, and adjusting the controller to finish the recovery starting of the MMC-MTDC.
Specifically, as shown in fig. 2, the coordinated pre-charging and start-up control method for the multi-terminal dc system includes the following steps:
(1) at the same time as the single-ended MMC1 converter station starts to start, other MMC converter stations are simultaneously incorporated into the dc bus. The MMC1 converter station can generate larger voltage fluctuation in the starting process, the brought energy impact can charge other MMC from the converter station, the charging process can exceed the uncontrollable charging capability of an alternating current system to the slave converter station, and pre-charging is realized in advance. According to the coordination pre-charging mode, whether charging exceeds the upper and lower voltage limits or not is calculated from the converter station, the upper and lower limits of the submodule voltage feasible interval of the MMC from the converter station can be obtained according to the requirement of submodule charging and the uncontrollable charging capacity, and the feasibility of the coordination pre-charging mode is judged according to the upper limit of the feasible interval and is expressed as follows:
A. the local converter station charges the maximum voltage value of the sub-module capacitor uncontrollably of the far-end converter station;
B. after the MMC1 converter station is started, the direct current bus has the maximum voltage value capable of being charged to a submodule of the slave converter station;
C. the maximum voltage value charged from a converter station submodule capacitor in the starting process of the MMC1 converter station;
D. and (4) the submodule capacitor voltage after the start of the slave converter station is completed.
The corresponding formula for the four cases is expressed as:
Figure BDA0003093804680000071
in the formula of UphFor AC system phase voltages, UdcrefSpecifying the value of u for the DC-side bus voltagevalidFor the transient process direct-current side voltage effective value, N represents the number of converter stations.
The transient dc-side voltage is expressed as:
Udc(t)＝A1sin(B1x+C1)+D1+A2sin(B2x+C2)+D2+...+Ansin(Bnx+Cn)+Dn………(2)
in the formula, A1、B1、C1、D1、A2、B2、C2、D2...An、Bn、Cn、DnCoefficients of the associated sine function;
the effective value of the voltage on the direct current side is as follows:
Figure BDA0003093804680000072
(2) at the MMC1 converter station start-up of the multi-terminal DC system, each MMC is charged from a submodule of the converter station to uvalidAnd after 2N, starting control of constant active power and constant reactive power is carried out on the MMC slave converter station.
Specifically, as shown in fig. 3, the MMC-MTDC fault recovery fast start control method includes the following steps:
various faults have different influences on related control quantities of various phase controllers, direct current side voltage is 0 due to direct current side short circuit faults, the fixed direct current voltage controller can be greatly impacted, the fixed direct current voltage controller is used for realizing the control over the direct current side voltage again after the short circuit faults are recovered, the capacitor voltage of the sub-module is started to have certain requirements after the faults, and the capacitor voltage of the sub-module needs a sensitive protection device to act immediately so as to ensure that the sub-module capacitor has certain voltage. And adjusting or clearing the fixed direct-current voltage controller and other related controllers according to the situation requirement, and restarting the whole system after the fault. The alternating current system fault affects the reactive power control quantity of the system controller, directly affects the reference value of the constant reactive power, and reflects the change of the control quantity of the q axis actually, so that the control quantity of the constant reactive power controller is out of limit.
Because the controller contains a plurality of PI controllers, each controller has different parameters and limit values, and higher requirements are put on restarting.
Outcontroller＝Kp·Δx+Ki∫Δxdt………(4)
In the formula, OutcontrollerFor the controller output, Δ x is the interpolation of the actual value from the reference value, KpAnd KiProportional coefficient and integral coefficient in PI control.
The main converter station MMC1 controller varies as follows:
Figure BDA0003093804680000081
in the formula,. DELTA.id1、Δiq1For the current change quantity of d and q axes of the MMC1 converter station, delta Udc、ΔQ1Is the DC voltage and reactive power variation, delta u, of the MMC1 converter stationcd1、Δucq1For the controller to output the variation of the control quantity, kp1、ki1、kp2、ki2、kp3、ki3、kp4、ki4The corresponding proportional and integral parameters for the MMC1 converter station controller.
From the converter station MMC controller the following formula is changed:
Figure BDA0003093804680000082
in the formula,. DELTA.id2、Δiq2For MMC slave converter station d, q axis current change, delta P2、ΔQ2Active and reactive power variations, Deltau, for MMC slave converter stationscd2、Δucq2For the controller to output the variation of the control quantity, kp1'、ki1'、kp2'、ki2'、kp3'、ki3'、kp4'、ki4' are the corresponding proportional and integral parameters of the MMC from the converter station controller. The slave station MMC3 is controlled in the same way as MMC 2.
As can be seen from equations (5) and (6), a system fault has a great influence on the control quantity of the controller, one control quantity may cause the control quantity of the whole system to exceed the limit, and in the actual system operation, after a plurality of PI controllers inside under the action of different controllers are stably operated, the controller output quantity may be stabilized at a value and within the limit range.
Those skilled in the art will appreciate that, in addition to implementing the systems, apparatus, and various modules thereof provided by the present invention in purely computer readable program code, the same procedures can be implemented entirely by logically programming method steps such that the systems, apparatus, and various modules thereof are provided in the form of logic gates, switches, application specific integrated circuits, programmable logic controllers, embedded microcontrollers and the like. Therefore, the system, the device and the modules thereof provided by the present invention can be considered as a hardware component, and the modules included in the system, the device and the modules thereof for implementing various programs can also be considered as structures in the hardware component; modules for performing various functions may also be considered to be both software programs for performing the methods and structures within hardware components.
The foregoing description of specific embodiments of the present invention has been presented. It is to be understood that the present invention is not limited to the specific embodiments described above, and that various changes or modifications may be made by one skilled in the art within the scope of the appended claims without departing from the spirit of the invention. The embodiments and features of the embodiments of the present application may be combined with each other arbitrarily without conflict.

Claims (10)

1. A coordinated starting control method suitable for multi-terminal direct current system fault recovery is characterized by comprising the following steps:
step 1: selecting a single-ended MMC1 converter station of a multi-ended direct current system to carry out single-ended pre-charging to reach 70% of a pre-charging target value;
step 2: starting control of constant direct-current voltage and constant reactive power is carried out on the single-ended MMC1 converter station, and starting of the MMC1 converter station and capacitor charging to a target value are completed;
and step 3: when the single-ended MMC1 converter station is started, the MMC is merged into a direct current bus from the converter station;
and 4, step 4: starting the MMC slave converter station under the control of constant active power and constant reactive power to realize the pre-charging and starting of the whole multi-terminal direct-current system;
and 5: and when a fault occurs in the starting process, judging the fault type, adjusting the controller and completing the recovery starting of the multi-terminal direct current system.
2. The coordinated start-up control method adapted to multi-terminal dc system fault recovery according to claim 1, wherein the step 3 comprises:
calculating whether the charging of the slave converter station exceeds the upper and lower voltage limits, obtaining the upper and lower limits of a submodule voltage feasible interval of the MMC slave converter station according to the charging requirement and the uncontrollable charging capacity, and judging the feasibility of a coordinated pre-charging mode according to the upper limit of the feasible interval;
the upper limit of the feasible interval includes: the maximum voltage value of the local converter station to the capacitance of the uncontrollable charging submodule of the remote converter station, the maximum voltage value of the direct current bus to the secondary converter station to be charged after the MMC1 converter station is started, the maximum voltage value of the secondary converter station to be charged from the capacitance of the converter station submodule in the MMC1 converter station starting process and the voltage of the secondary converter station capacitance after the secondary converter station is started are expressed by the corresponding formula and the relation:
Figure FDA0003093804670000011
in the formula of UphFor AC system phase voltages, UdcrefSpecifying the value of u for the DC-side bus voltagevalidThe voltage effective value of the direct current side in the transient process is obtained; n denotes the number of converter stations.
3. The coordinated start-up control method adapted to multi-terminal dc system fault recovery according to claim 2, wherein the transient process dc side voltage is expressed as:
Udc(t)＝A1sin(B1x+C1)+D1+A2sin(B2x+C2)+D2+...+An sin(Bnx+Cn)+Dn………(2)
in the formula, A1、B1、C1、D1、A2、B2、C2、D2...An、Bn、Cn、DnCoefficients of the associated sine function;
the effective value expression of the voltage at the direct current side is as follows:
Figure FDA0003093804670000021
starting of the single-ended MMC1 converter station of the multi-end direct current system is completed, and each MMC is charged to u from a submodule of the converter stationvalidAnd after 2N, starting control of constant active power and constant reactive power is carried out on the MMC slave converter station.
4. The coordinated start-up control method adapted to multi-terminal dc system fault recovery according to claim 1, wherein the step 5 comprises: after the short-circuit fault is recovered, voltage is controlled again through a voltage controller, and the expression of the output quantity of the controller is as follows:
Outcontroller＝Kp·Δx+Ki∫Δxdt………(4)
where Δ x is the interpolation of the actual value from the reference value, KpAnd KiProportional coefficient and integral coefficient in PI control;
the MMC1 converter station controller varies as follows:
Figure FDA0003093804670000022
in the formula,. DELTA.id1、Δiq1For the current change quantity of d and q axes of the MMC1 converter station, delta Udc、ΔQ1Is the DC voltage and reactive power variation, delta u, of the MMC1 converter stationcd1、Δucq1For the controller to output the variation of the control quantity, kp1、ki1、kp2、ki2、kp3、ki3、kp4、ki4The corresponding proportional and integral parameters for the MMC1 converter station controller.
5. The coordinated start-up control method adapted to multi-terminal dc system fault recovery according to claim 4, wherein the MMC is changed from the converter station controller as follows:
Figure FDA0003093804670000023
in the formula,. DELTA.id2、Δiq2For MMC slave converter station d, q axis current change, delta P2、ΔQ2Active and reactive power variations, Deltau, for MMC slave converter stationscd2、Δucq2For the controller to output the variation of the control quantity, kp1'、ki1'、kp2'、ki2'、kp3'、ki3'、kp4'、ki4' are the corresponding proportional and integral parameters of the MMC from the converter station controller.
6. A coordinated start-up control system adapted for multi-terminal dc system fault recovery, comprising:
module M1: selecting a single-ended MMC1 converter station of a multi-ended direct current system to carry out single-ended pre-charging to reach 70% of a pre-charging target value;
module M2: starting control of constant direct-current voltage and constant reactive power is carried out on the single-ended MMC1 converter station, and starting of the MMC1 converter station and capacitor charging to a target value are completed;
module M3: when the single-ended MMC1 converter station is started, the MMC is merged into a direct current bus from the converter station;
module M4: starting the MMC slave converter station under the control of constant active power and constant reactive power to realize the pre-charging and starting of the whole multi-terminal direct-current system;
module M5: and when a fault occurs in the starting process, judging the fault type, adjusting the controller and completing the recovery starting of the multi-terminal direct current system.
7. The coordinated start-up control system adapted to multi-terminal dc system fault recovery according to claim 6, wherein the module M3 includes:
calculating whether the charging of the slave converter station exceeds the upper and lower voltage limits, obtaining the upper and lower limits of a submodule voltage feasible interval of the MMC slave converter station according to the charging requirement and the uncontrollable charging capacity, and judging the feasibility of a coordinated pre-charging mode according to the upper limit of the feasible interval;
the upper limit of the feasible interval includes: the maximum voltage value of the local converter station to the capacitance of the uncontrollable charging submodule of the remote converter station, the maximum voltage value of the direct current bus to the secondary converter station to be charged after the MMC1 converter station is started, the maximum voltage value of the secondary converter station to be charged from the capacitance of the converter station submodule in the MMC1 converter station starting process and the voltage of the secondary converter station capacitance after the secondary converter station is started are expressed by the corresponding formula and the relation:
Figure FDA0003093804670000031
in the formula of UphFor AC system phase voltages, UdcrefSpecifying the value of u for the DC-side bus voltagevalidThe voltage effective value of the direct current side in the transient process is obtained; n denotes the number of converter stations.
8. The coordinated start-up control system adapted for multi-terminal dc system fault recovery of claim 7, wherein the transient process dc side voltage is expressed as:
Udc(t)＝A1sin(B1x+C1)+D1+A2sin(B2x+C2)+D2+...+An sin(Bnx+Cn)+Dn………(2)
in the formula, A1、B1、C1、D1、A2、B2、C2、D2...An、Bn、Cn、DnCoefficients of the associated sine function;
the effective value expression of the voltage at the direct current side is as follows:
Figure FDA0003093804670000041
starting of the single-ended MMC1 converter station of the multi-end direct current system is completed, and each MMC is charged to u from a submodule of the converter stationvalidAnd after 2N, starting control of constant active power and constant reactive power is carried out on the MMC slave converter station.
9. The coordinated start-up control system adapted to multi-terminal dc system fault recovery according to claim 6, wherein the module M5 includes: after the short-circuit fault is recovered, voltage is controlled again through a voltage controller, and the expression of the output quantity of the controller is as follows:
Outcontroller＝Kp·Δx+Ki∫Δxdt………(4)
where Δ x is the interpolation of the actual value from the reference value, KpAnd KiFor proportional coefficients and integral systems in PI controlCounting;
the MMC1 converter station controller varies as follows:
Figure FDA0003093804670000042
in the formula,. DELTA.id1、Δiq1For the current change quantity of d and q axes of the MMC1 converter station, delta Udc、ΔQ1Is the DC voltage and reactive power variation, delta u, of the MMC1 converter stationcd1、Δucq1For the controller to output the variation of the control quantity, kp1、ki1、kp2、ki2、kp3、ki3、kp4、ki4The corresponding proportional and integral parameters for the MMC1 converter station controller.
10. The coordinated start-up control system adapted for multi-terminal dc system fault recovery of claim 9, wherein MMC is changed from the converter station controller by the following formula:
Figure FDA0003093804670000043
in the formula,. DELTA.id2、Δiq2For MMC slave converter station d, q axis current change, delta P2、ΔQ2Active and reactive power variations, Deltau, for MMC slave converter stationscd2、Δucq2For the controller to output the variation of the control quantity, kp1'、ki1'、kp2'、ki2'、kp3'、ki3'、kp4'、ki4' are the corresponding proportional and integral parameters of the MMC from the converter station controller.
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