CN112103984B - Control method for inhibiting continuous commutation failure of hybrid double-feed-in direct-current power transmission system - Google Patents

Control method for inhibiting continuous commutation failure of hybrid double-feed-in direct-current power transmission system Download PDF

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CN112103984B
CN112103984B CN202010954854.9A CN202010954854A CN112103984B CN 112103984 B CN112103984 B CN 112103984B CN 202010954854 A CN202010954854 A CN 202010954854A CN 112103984 B CN112103984 B CN 112103984B
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CN112103984A (en
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毛炽祖
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Maintenance and Test Center of Extra High Voltage Power Transmission Co
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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
    • 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
    • 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
    • H02J3/18—Arrangements for adjusting, eliminating or compensating reactive power in networks
    • 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
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]
    • 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
    • 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 discloses a control method for inhibiting continuous commutation failure of a hybrid double-feed-in direct-current transmission system, which is characterized by establishing an inversion side reactive power balance model for the hybrid double-feed-in direct-current transmission system, designing an MMC (modular multilevel converter) switching control strategy according to the inversion side reactive power balance model, solving a minimum direct-current limit value for inhibiting LCC (lower control limit) continuous commutation failure according to a commutation voltage-time area theory, determining an MMC reactive power reference value according to the minimum direct-current limit value, effectively inhibiting the fluctuation of commutation bus voltage, avoiding the occurrence of LCC subsequent commutation failure and having important significance for inhibiting the continuous commutation failure of the inversion side of the multi-feed-in direct-current transmission system.

Description

Control method for inhibiting continuous commutation failure of hybrid double-feed-in direct-current power transmission system
Technical Field
The invention relates to the technical field of high-voltage direct-current power transmission, in particular to a control method for inhibiting continuous commutation failure of a hybrid double-fed direct-current power transmission system.
Background
In the converter, if the converter valve which is out of conduction fails to recover the blocking capability within a period of time when a reverse voltage is applied, or if the phase change process is not completed during the period of time when the reverse voltage is applied, the phase of the valve which is out of conduction is changed to the original valve which is scheduled to be out of conduction when the valve voltage is changed to the positive direction, and the condition is called phase change failure. Since the rectifier converter valve is under reverse voltage for a long time after the current is turned off, the rectifier will fail to change phase only when the trigger circuit fails. Most of phase commutation failures of the direct current system occur on the inversion side, and the phase commutation failures are one of the most common failure types on the inversion side. Therefore, the research on commutation failure mainly focuses on the interaction between the dc system and the inverter-side ac system.
A high-voltage direct-current transmission (LCC-HVDC) system based on the power grid phase-change type converter has obvious advantages in the aspects of long-distance large-capacity power transmission and power grid interconnection, but also has the defects of phase-change failure, large reactive power consumption in operation and the like. With the rapid development of the direct current transmission technology, a voltage source converter-based high-voltage direct current transmission (VSC-HVDC) system is widely applied by virtue of the advantages of independent decoupling control of active power and reactive power, small short-circuit capacity, no commutation failure and the like. When 2 types of dc transmission systems are fed into the same ac grid, a hybrid dual feed dc transmission system is formed. Under the condition that a receiving end alternating current power grid has a short-circuit fault or the voltage of the power grid is distorted, the LCC-HVDC inverter station is easy to have phase commutation failure. During the phase commutation failure period, LCC-HVDC direct current is increased for a short time, and direct current voltage and direct current power are reduced to zero within a certain time. If the commutation failure is not effectively inhibited, subsequent commutation failure may be caused, so that the direct-current system operates in a reduced power mode. If multiple phase conversion failures occur, the converter valve can be locked, the direct current transmission channel is interrupted, and the safe and stable operation of the alternating current system is seriously influenced.
Disclosure of Invention
Aiming at the problems, the invention provides a control method for inhibiting continuous commutation failure of a hybrid double-feed-in direct-current power transmission system, which is characterized in that voltage-reactive power characteristics under the alternating-current fault of an inversion side are analyzed for the hybrid double-feed-in direct-current power transmission system, an MMC switching control strategy for inhibiting the continuous commutation failure of the hybrid double-feed-in direct-current power transmission system is designed, and a method for determining an MMC reactive power reference value according to a commutation voltage-time area theory is provided.
In order to solve the technical problems, the technical scheme of the invention is as follows:
a control method for inhibiting continuous commutation failure of a hybrid double-feed-in direct-current power transmission system comprises the following three parts: firstly, establishing a voltage-reactive characteristic model under an alternating current fault of an inverter side of a hybrid double-feed-in direct current transmission system; secondly, suppressing an MMC switching control strategy of a multi-feed-in direct-current power transmission system in continuous commutation failure; and thirdly, a determination method of the MMC reactive power reference value.
The invention has the beneficial effects that: the direct current limit value for inhibiting the LCC continuous commutation failure is obtained according to the commutation voltage-time area theory, and the MMC reactive power reference value is determined according to the direct current limit value, so that the fluctuation of the commutation bus voltage can be effectively inhibited, the occurrence of the LCC subsequent commutation failure is avoided, and the method has important significance for inhibiting the continuous commutation failure of the inversion side of the multi-feed-in direct current transmission system.
Drawings
FIG. 1 is a block diagram of a control system on the inverter side of LCC-HVDC;
fig. 2 is a topological structure diagram of a parallel hybrid double-feed-in direct-current power transmission system;
FIG. 3 is a schematic diagram of inverter side reactive power exchange;
fig. 4 is a block diagram of the fast reactive-voltage droop control disclosed in the embodiment of the present invention;
fig. 5 is a comparison diagram of the preceding and following simulations of the MMC switching control strategy disclosed in the embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention clearer and clearer, the following detailed description of the present invention is provided with reference to the accompanying drawings and detailed description. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and are not limiting of the invention. It should be further noted that, for the convenience of description, only some but not all of the relevant aspects of the present invention are shown in the drawings.
Before a suitable control method is provided, an LCC-HVDC continuous commutation failure mechanism needs to be analyzed:
1.1LCC-HVDC inversion side control system
The traditional direct current transmission system adopts layered control and comprises a main control level, a pole control level and a valve group control level from top to bottom. When an alternating current system on the inversion side has a fault, the fault recovery characteristic of the direct current system is mainly related to the pole control level. CIGRE HVDC the controller in the standard model is a pole control stage, and its specific structure is shown in fig. 1. In the figure, the first-order inertia element is used for simulating the measurement process of direct current voltage and direct current. The low-voltage current-limiting controller (VDCOL) is used for limiting a direct current instruction value when an alternating current system on the inverter side fails and reducing the reactive power requirement of a converter station on the alternating current system in the failure process. The output of the constant current and the output of the constant turn-off angle controller are compared to generate an advanced trigger angle instruction beta, and then corresponding trigger pulses are generated through the valve group control stage. The current deviation control (CEC) can achieve smooth switching between the constant current control and the constant off angle control.
And under a normal operation condition, the operation state of the inverter is closed-loop regulated by the constant turn-off angle control, so that the turn-off angle gamma is kept at a setting value, once the inverter side alternating current system fails to cause phase change failure, the operation state of the inverter is switched to the constant current control, and is recovered to the operation point of the failure state under the action of the low-voltage current-limiting control, and finally switched to the constant turn-off angle control. In the recovery process, mutual switching of constant current control, current deviation control and constant turn-off angle control exists, and continuous commutation failure is likely to be caused.
1.2 commutation failure recovery Process analysis
When an alternating current system on the inversion side has a fault, the pole control stage of the direct current transmission system can quickly respond, the direct current after the fault runs to a new stable running point, and the fault recovery process is under the combined action of a plurality of controllers on the rectification side and the inversion side. In order to clearly depict the process, the process is divided into three stages according to the state switching of the inverter side controller, and the functions of the controllers in different stages are analyzed one by one. When the direct current system operates in a rated state, the direct current is determined by constant current control on the rectifying side, and the direct current voltage is determined by constant turn-off angle control on the inverting side. When an inverter side alternating current system fails and causes a commutation failure, the fault recovery process can be divided into three stages:
(1) stage 1: the phase change failure occurs, and the operating point of the inverter side system shifts
After the phase change failure caused by the fault of the inverter side alternating current system, the upper bridge arm converter valve and the lower bridge arm converter valve of the inverter are quickly short-circuited, so that the direct current voltage of the inverter side is greatly reduced, the direct current of the inverter side is increased, the operating point of the inverter side system is deviated, the target point deviation between the direct current of the inverter side and the constant current control is increased at the moment, the current deviation control is started, and the inverter side is switched to the constant current control from the constant turn-off angle control.
(2) And (2) stage: low-pressure flow-limiting function, normal commutation of converter valve
When the system operating point is under the action of a low-voltage current limiting link in constant current control, the direct current on the inversion side is greatly reduced, the converter valve realizes normal phase conversion, and the direct voltage on the inversion side is increased, so that the system operating point can continuously move to a control target point under the action of constant current control. In the movement process, the direct current of the inversion side is continuously increased, so that the direct current voltage of the inversion side is continuously increased, and a control target point moves on the low-voltage current limiting curve of the inversion side.
(3) And (3) stage: the operating point of the inversion side system is coincided with the target point of the constant current control, and the current deviation control is carried out
The system operating point will gradually approach to its target point under the action of the control system until meeting. At this time, the difference value between the direct current at the inverting side and the target current at the rectifying side is 0.1pu, and the inverter enters current deviation control.
1.3 continuous commutation failure mechanism analysis
First, in phase 1 and phase 2, the low voltage current limit control plays a crucial role. The larger the slope of the characteristic curve of the low-voltage current-limiting control is, the faster the recovery speed of the direct-current system is, the higher the recovery level of the direct current is, and the higher the possibility of continuous phase commutation failure is. Therefore, as long as the rationality of the setting of the low-voltage current-limiting parameter is ensured, the recovery speed and level of the direct current can be ensured, and meanwhile, the fault recovery type continuous phase change failure cannot occur in the stage 1 and the stage 2. Therefore, it can be known that the fault recovery type continuous commutation failure occurs in phase 3, i.e., the current deviation control section.
The main function of the current deviation control is that when the slope of the characteristic curve of the inverter constant turn-off angle control is larger than the rectifier constant alphaminThe slope of the controlled characteristic curve, and at the moment, no stable operation point exists between the fixed values of the two-end current regulators, and the direct current oscillates back and forth between the two values. In order to avoid this, a current deviation control is designed in a practical control system, and when a dc current is between an inverter-side current fixed value and a rectifier-side current fixed value, an external characteristic of an inverter is changed to a straight line with a positive slope, that is, a straight line with a positive slope
γ＝γref+K(Id0-Id)/Id0 (1-1)
In the formula, gammarefFor the inverse side turn-off angle setting value, Id0For setting the rectified side current, IdThe value of K is a constant value for the current value of the inversion side, and the slope of the external characteristic of the current deviation control can be a positive value by properly selecting the value of K. The current deviation control can realize smooth switching of constant current control and constant turn-off angle control at the same time. When the current margin between the rectifying side and the inverting side is 0.1pu, the larger the slope of the external characteristic of the current deviation control is, the longer the process of the stage 3 is, which may cause the inverting side to operate in the current deviation control, rather than smoothly switching from the constant current control to the constant off angle control. Therefore, the slope of the outer characteristic curve of the current deviation control needs to be kept at a low level, and the fixed-lead trigger angle control can be adopted, and the formula of the voltage-current characteristic of the current deviation control is as follows:
Figure BDA0002678245440000041
although the two current deviation control implementation schemes are different, the functions are the same, and the characteristic curves keep positive slopes. It can be considered that in the current deviation control process, in any implementation, the control target can be approximately considered to keep the inversion side leading firing angle β constant. The DC current on the inversion side is gradually increased in the 3 rd stage by the increment delta IdMore than 0.1pu, which can be obtained by the commutation voltage-time area theory, and the commutation area can be divided into the commutation required area SneedAnd commutation supply area SsupplyOf the formula
Figure BDA0002678245440000042
In the formula, XcThe value is equal commutation inductance, E is effective value of commutation voltage, omega is alternating current system frequency, alpha is trigger delay angle.
The formula (1-3) is developed to obtain:
Figure BDA0002678245440000043
as can be seen from the formulae (1-4), in stage 3, IdIf the area is continuously increased, the area S required by commutation is increasedneedContinuously increasing, in order to ensure successful commutation, the commutation supply area SsupplyIt should also be continuously increased, however, since the advance firing angle should be closer to the command value in phase 3, in order to determine the change of β to SsupplyBy calculating the partial derivative of beta from the formula (1-4), the influence of (2)
Figure BDA0002678245440000044
The value ranges of the formula (1-5) and β and μ
Figure BDA0002678245440000045
Then SsupplyDecreases with decreasing β. Simulation analysis shows that in the stage 3, the advance trigger angle beta is in a descending trend, approaches to a target value, and has a small variation range. It can thus be seen that in stage 3, the required area S for commutation isneedA continuous increase, with a slight decrease of the advance firing angle beta, results in SsupplyDecrease, S is guaranteed only if the commutation angle μ continues to increase in order to maintain successful commutationsupplyContinuously increase and with SneedAre equal. When beta is slightly reduced and mu is gradually increased, the turn-off angle gamma is gradually reduced in the stage 3, and when the turn-off angle gamma is smaller than the inherent limit turn-off angle gammaminWhen the phase change failure occurs, the phase change failure will occur, which is the root cause of the occurrence of the phase change failure.
However, as can be seen from the above analysis, the occurrence of the LCC-HVDC continuous commutation failure has a great relationship with the severity of the fault, which often occurs in a non-severe fault scenario, because in the non-severe fault scenario, the dc system has a high dc current recovery degree after the first commutation failure, which increases the risk of the occurrence of the continuous commutation failure when the inverter side enters the current deviation control.
According to the above analysis process, the present embodiment provides a control method for suppressing a continuous phase commutation failure of a hybrid dual-infeed direct-current power transmission system, which is divided into three parts: firstly, establishing a voltage-reactive characteristic model under an alternating current fault of an inverter side of a hybrid double-feed-in direct current transmission system; secondly, suppressing an MMC control strategy of a multi-feed-in direct-current power transmission system in continuous commutation failure; and thirdly, a determination method of the MMC reactive power reference value.
1. Establishing a voltage-reactive characteristic model under an AC fault of an inverter side of a hybrid double-feed-in DC power transmission system
The topology of the parallel hybrid dual-feed-in dc transmission system is shown in fig. 2. In the figure LCC-HVDC and MMC-HVDC are fed to the same AC system, Z, via a common coupling buss1、Zs2And Zs3Respectively representing thevenin equivalent impedance, T, of an AC system1、T2、T3And T4Is a converter transformer. LCC-HVDC adopts a thyristor without self-turn-off capability as a converter device, so that a phase-change voltage needs to be provided by a phase difference between two valve side windings of a three-winding transformer.
The reactive power absorbed by the high-voltage direct-current transmission system is related to the alternating-current pressure. When an alternating current system fault occurs on the inversion side of the hybrid double-feed direct current transmission system, a large short-circuit current flows through the LCC converter valve, the reactive demand of a converter station on the alternating current system is increased, the voltage of an alternating current bus is further reduced, and even a phase change failure occurs. FIG. 3 is a schematic diagram of inverter side reactive power exchange of a hybrid dual-feed-in DC power transmission system, wherein U isd1、Ud2Direct current voltage of LCC and MMC, QLCCRepresenting reactive power absorbed by the LCC converter station, QcRepresenting reactive power, Q, emitted by reactive-load compensation meansMMCRepresenting reactive power, Q, emitted by the MMCacReactive power, U, flowing into the bus for the receiving ac systemPCCFor common coupling of bus voltage, BcIs the susceptance of the reactive power compensation device. From fig. 3, an inverter-side reactive power balance model can be established as follows:
QLCC＝Qac-Qc-QMMC (2-1)
wherein:
Figure BDA0002678245440000051
when an alternating current system fault occurs on the inversion side, the voltage drop of the public coupling bus can reduce the reactive power sent by the reactive power compensation device, and the voltage of the alternating current bus is further reduced. The reactive power consumed by the LCC converter station can be calculated by adopting the following formula:
Figure BDA0002678245440000052
where phi is the power factor angle of the LCC converter station. According to the reactive power balance model, the reactive power consumption of the LCC converter station can be compensated by controlling the reactive power output of the MMC, the fluctuation of the voltage of a converter bus is reduced, and the occurrence of subsequent commutation failure is avoided.
2. MMC control strategy for inhibiting continuous commutation failure of multi-feed-in direct-current power transmission system
According to above-mentioned contravariant side reactive power balance model design MMC switches control strategy, MMC switches control strategy and includes: when the hybrid double-feed-in direct current transmission system stably operates, an inversion side MMC active control loop adopts constant direct current voltage control, and an inversion side MMC reactive control loop adopts constant reactive power control. When an inverter side alternating current system breaks down, the control mode of the MMC traditional reactive control loop has a slow response speed to the fault, and the MMC output reactive power is easy to be unstable. In order to overcome the disadvantage that the MMC adopts single constant reactive power control and constant alternating voltage control, after the voltage drop of the alternating bus is detected, the inverter side MMC is switched from the constant reactive power control to the fast reactive-voltage droop control, and a control block diagram of the fast reactive-voltage droop control is shown in fig. 4. After the MMC adopts the rapid reactive-voltage droop control, the outer characteristic of an outer ring q axis is not a straight line with zero slope, but a straight line with specific slope including the alternating-current bus voltage and reactive power characteristics.
Determination method of MMC reactive power reference value
LCC (lower control carrier) switching caused by serious alternating current fault on the inversion sideIf the voltage drop of the public coupling bus cannot be compensated in time, continuous phase conversion failure is easily caused, so that the converter valve is locked, and the system is broken down. After the voltage of the alternating current bus is detected to drop, the MMC on the inversion side is switched from constant reactive power control to rapid reactive power-voltage droop control, wherein the voltage reference value U of the public coupling busPCCrefSet to a value slightly above 1. In the process of phase change failure of the LCC, a converter station needs to consume a large amount of reactive power, and the compensation capability of the reactive compensation device is reduced due to the drop of the voltage of the alternating-current bus, so that the MMC is required to bear more reactive power. Therefore, the inverter-side MMC reactive reference value should be determined in consideration of the transient characteristics of the LCC during a commutation failure.
According to the theory of phase-change voltage-time area, the phase-change area can be divided into the phase-change required area S in the phase-change process of LCCneedAnd commutation supply area SsupplyCalculated by respectively adopting the formulas (1-3). The minimum direct current limit value I for avoiding the subsequent commutation failure of the LCC can be obtained by making the commutation required area equal to the commutation supply aread_min：
Figure BDA0002678245440000061
Wherein the triggering angle alpha is a rated value, and gamma is an inherent limit cut-off angle gammaminCommon coupling bus voltage UPCCAnd (6) taking a rated value.
In order to inhibit continuous commutation failure of the LCC-HVDC subsystem by means of the capability of independently adjusting the reactive power of the MMC, the relationship between the reactive power generated by the MMC and the LCC-HVDC direct current needs to be established. When the hybrid double-feed-in direct-current transmission system operates, the reactive power consumed by the LCC at the inverter side can be calculated by adopting the following formula:
Figure BDA0002678245440000062
finishing to obtain:
Figure BDA0002678245440000063
wherein tan φ can be calculated using the following formula:
Figure BDA0002678245440000071
the relation between the MMC reactive power reference value and the LCC-HVDC direct current can be obtained:
Figure BDA0002678245440000072
from the above analysis, Id_minIs a direct current limit value for preventing LCC from subsequent commutation failured_minAnd substituting the formula (4-5) to obtain a reference value of the reactive power of the MMC after the MMC adopts the rapid reactive-voltage droop control. The voltage value of the public coupling bus is adjusted by controlling the reactive power generated by the MMC, and the increase of direct current in the first commutation failure fault recovery process is limited, so that the effect of restraining the subsequent commutation failure of the LCC is achieved.
Fig. 5 is a simulation comparison diagram before and after the inverter side MMC switches the control mode when the inverter side of the hybrid double-feed-in dc power transmission system fails to change the phase due to an ac fault. And setting a fault in 2s, dropping the voltage of the alternating-current bus by 32%, switching the control mode by the MMC after 10ms of time delay, and keeping the fault for 0.5 s. Wherein, the control mode 1: when LCC-HVDC phase commutation failure occurs due to voltage drop of an alternating current bus at an inverter side, the control mode of the MMC is not adjusted; control mode 2: when the LCC-HVDC is detected to have commutation failure, the MMC is switched to fast reactive-voltage droop control, the voltage reference value of the public coupling bus is set to be 1.1, and the reactive power reference value is calculated according to a formula (4-5). As can be seen from fig. 5, a phase commutation failure of the LCC-HVDC subsystem causes a large-amplitude drop of the dc voltage and a rapid increase of the dc current, and a continuous phase commutation failure of the LCC-HVDC subsystem is caused by a continuous fluctuation of the phase commutation voltage due to an increase of the reactive power consumed by the converter station. When the LCC is detected to have phase commutation failure due to the voltage drop of the alternating-current bus, the MMC is switched into fast reactive power-voltage droop control, and a reactive power reference value is calculated according to a formula (4-5), so that the increase of direct current in the phase commutation failure recovery process can be effectively limited, and the occurrence of subsequent phase commutation failure is prevented.
The above embodiments are only for illustrating the technical concept and features of the present invention, and the purpose thereof is to enable those skilled in the art to understand the contents of the present invention and implement the present invention accordingly, and not to limit the protection scope of the present invention accordingly. All equivalent changes or modifications made in accordance with the spirit of the present disclosure are intended to be covered by the scope of the present disclosure.

Claims (1)

1. A control method for inhibiting continuous commutation failure of a hybrid double-feed-in direct-current power transmission system is characterized by comprising the following steps of establishing an inversion side reactive power balance model, and designing an MMC (modular multilevel converter) switching control strategy according to the inversion side reactive power balance model, wherein the MMC switching control strategy comprises the following steps: when the hybrid double-feed-in direct current transmission system stably operates, an inversion side MMC active control loop adopts constant direct current voltage control, and an inversion side MMC reactive control loop adopts constant reactive power control; after the voltage of the alternating current bus is detected to drop, the MMC on the inversion side is switched from constant reactive power control to rapid reactive power-voltage droop control;
the inversion side reactive power balance model specifically comprises the following steps:
QLCC＝Qac-Qc-QMMC
wherein Q isLCCFor reactive power, Q, absorbed by LCC converter stations on the inverter sideacReactive power, Q, flowing into the bus for the receiving ac systemcRepresenting reactive power, Q, emitted by reactive-load compensation meansMMCReactive power generated for the MMC;
the fast reactive-voltage droop control comprises the steps of,
step one, making the area S required by commutationneedEqual to the commutation supply area SsupplyCalculating the minimum direct current limit value I for avoiding the subsequent commutation failure of the LCCd_min；
Step two, establishing reactive power Q absorbed by the LCC convertor station at the inversion sideLCCA relation model with LCC-HVDC direct current;
step three, limiting the minimum direct current Id_minSubstituting the relation model to obtain the MMC reactive power reference value Q after the rapid reactive-voltage droop controlMMCrefBy controlling the MMC reactive power reference value QMMCrefAdjusting voltage value U of public coupling busPCC；
The calculation method of the step one is as follows:
Figure FDA0003221721250000011
wherein, XcThe value is equivalent commutation inductance, alpha is a trigger delay angle, and gamma is an off angle;
the relationship model of the second step is as follows:
reactive power Q absorbed by LCC converter station at inversion side when hybrid double-feed-in direct current transmission system operatesLCCComprises the following steps:
Figure FDA0003221721250000012
wherein, Ud1Is LCC DC voltage, IdThe value of the current on the inversion side is phi, the power factor angle of the LCC converter station is phi, and K is a constant;
finishing to obtain:
Figure FDA0003221721250000021
calculating to obtain the MMC reactive power reference value QMMCrefRelation to LCC-HVDC direct current:
Figure FDA0003221721250000022
wherein, BcIs the susceptance of the reactive power compensation device.
CN202010954854.9A 2020-09-11 2020-09-11 Control method for inhibiting continuous commutation failure of hybrid double-feed-in direct-current power transmission system Active CN112103984B (en)

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