CN114977159B - Line coordination recovery method after alternating current fault of receiving end of simultaneous transmission and receiving system - Google Patents
Line coordination recovery method after alternating current fault of receiving end of simultaneous transmission and receiving system Download PDFInfo
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- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
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Abstract
The invention discloses a line coordination recovery method after an alternating current fault of a receiving end of a simultaneous transmission and receiving system, which modifies parameters of a low-voltage current-limiting controller in a direct current control link according to recovery indexes to ensure that each line outputs different direct current values under the same voltage level, reactive power consumption of a receiving end converter station of each line is positively correlated with a direct current instruction value, and lower current output enables reactive power to flow into the alternating current system to support reactive voltage so as to accelerate the recovery speed of the voltage of an alternating current power grid of the receiving end, thereby realizing coordinated and orderly recovery of the voltage of each line and further improving the recovery speed and transient stability of the alternating current voltage after the receiving end of the simultaneous transmission and receiving system is in fault.
Description
Technical Field
The invention belongs to the technical field of electric power, and particularly relates to a line coordination recovery method after an alternating current fault of a receiving end of a synchronous transmission and receiving system.
Background
The characteristics of power resources and load distribution in China determine the western electric east power transmission network structure of China based on ultra-high voltage direct current transmission. In 2020, after part of extra-high voltage direct current engineering is put into operation, a typical concurrent transmission and concurrent reception multi-terminal direct current transmission system is formed with the original extra-high voltage direct current transmission system. Although the system expands the capacity of clean energy coordination and digestion, the near-interval electrical distance of the sending end is smaller, the electrical connection of the receiving end converter stations is tight, and the interaction influence between the alternating current and direct current systems is more serious than that of a multi-feed direct current system. During the fault recovery period of the direct current system, a plurality of lines are recovered at the same time, and the strong coupling effect among the lines makes the voltage stability of the receiving end alternating current system difficult to maintain. Therefore, the interaction of the synchronous transmission and the direct current system and the recovery strategy are urgently needed to be studied.
Currently, research on ultra-high voltage direct current transmission engineering is still focused on correction of interaction factor (multi-infeed interaction factor, MIIF) and receiving ac system strength (multi-infeed effective short circuit ratio, miecr) precision of the receiving converter station under a multi-feed structure. The multi-feed dc system may have problems of continuous commutation failure, excessive reactive power demand, slow recovery of dc active power, etc. after ac failure, and even affect the system stability. Therefore, part of the research further defines a multi-feed power recovery factor (multi-infeed power recovery factor, MIPRF) and a multi-feed direct voltage power recovery intensity index (multi-infeed DC voltage power recovery intensity indicator, DRI) based on MIIF and MIESCR, and establishes a strategy for recovering each DC peak by peak in sequence according to MIPRF and DRI. The recovery strategy focuses on improving the transient performance of the direct current system and the power coordination among the direct current systems so as to weaken bad interaction, and can reduce the reactive power consumption of the converter bus of the receiving-end inverter station and accelerate the recovery speed of alternating voltage in the fault transient process of the multi-feed system.
At present, research on recovery strategies after the AC faults of the receiving end of the synchronous transmission and synchronous receiving system is still deficient, and the synchronous transmission and synchronous receiving DC transmission system with multi-feed and multi-feed structures directly applied to MIPRF and DRI derived based on MIIF and MIESCR ignores the influence of the electric coupling characteristics of the AC and DC systems of the transmitting end, which may cause the AC systems of the transmitting end to break down, damage the stability of the system and greatly influence the electric networks of the two ends.
Disclosure of Invention
The invention aims to overcome the defects of the prior art, and provides a line coordination recovery method after the alternating current fault of the receiving end of the same-sending and same-receiving system, which modifies the parameters of a low-voltage current-limiting controller in a direct-current control link according to recovery indexes, so that each line outputs different direct-current values under the same voltage level, reactive power consumption of a receiving end converter station of each line is positively correlated with a direct-current command value, reactive power flows into the alternating current system to support reactive voltage, the recovery speed of the alternating current power grid voltage of the receiving end is accelerated, and the coordination orderly recovery of the voltages of each line is realized, so that the recovery speed and transient stability of the alternating current voltage after the receiving end fault of the same-sending and same-receiving system are further improved.
In order to achieve the purpose of the invention, the invention relates to a line coordination recovery method after the communication fault of the receiving end of a synchronous transmission and synchronous receiving system, which is characterized by comprising the following steps:
(1) Calculating the voltage recovery intensity factor of the simultaneous transmission and simultaneous receiving system according to the impedance network structure of the system and the alternating current operation working condition of the receiving end;
(1.1) calculating a multi-feed-out interaction factor and a multi-feed-in interaction factor under the structure of the synchronous transmission and synchronous receiving system according to the impedance network of the alternating current system at the rectification side of the synchronous transmission and synchronous receiving system and the impedance network of the alternating current system at the inversion side of the receiving end:
wherein MOVIF ji Multi-feed-out interaction factor, MIIF, representing feed-side commutation buses i and j ji Representing multi-feed interaction factors of the receiving end converter buses i and j; z is Z Rij 、Z Rii Z is the transimpedance and self-impedance of the impedance network of the alternating current system at the transmitting end rectifying side Iij 、Z Iii Is the trans-impedance and the self-impedance of the impedance network of the alternating current system at the inversion side of the receiving end, delta U Ri 、ΔU Rj For the voltage of the system feed-side commutation buses i and j, deltaU Ii 、ΔU Ij The voltage of the current converting buses i and j at the receiving end of the system;
(1.2) calculating a transmitting end action coefficient alpha and a receiving end action coefficient beta of the simultaneous transmitting and receiving system;
wherein DeltaU acR Representing maximum voltage offset, deltaU, allowed by corresponding sending end rectifying side converter bus when receiving end converter bus fails acI The maximum voltage offset allowed by the inversion side converter bus of the receiving end is represented when the converter bus of the receiving end fails;
(1.3) calculating a voltage interaction factor between the receiving end converter buses of the synchronous transmission and receiving system:
MOMI_IF ji ＝αMOVIF ji +βMIIF ji
wherein MOMI_IF ji Representing the voltage interaction factor between the receiving end converter buses i and j;
(1.4) calculating the effective short-circuit ratio of the receiving end converter bus of the synchronous transmission and receiving system:
wherein MOMI_ESCR is as follows i Representing the effective short-circuit ratio of the receiving end converter bus i, S aci Short-circuit capacity at the receiving-end converter bus i; q (Q) ci The reactive compensation capacity of the capacitor, the alternating current filter and the reactive compensation device at the receiving end converter bus i; p (P) dNj Rated direct current power at the receiving end converter bus j; n is the number of bus bars;
(1.5) calculating the voltage recovery intensity factor of each bus in the simultaneous transmission and reception system;
wherein MOMI_VRIF i Represents the voltage recovery strength factor, MOMI_ESCR, of the receiving-end converter bus i i Representing the effective short-circuit ratio of the receiving end converter bus i, P dmax Representing the maximum value of active power transmitted by a direct current circuit connected with each converter bus;
(2) Orderly recovering each converter bus by utilizing the improved low-voltage current-limiting control characteristic curve;
(2.1) acquiring the recovery priority of each converter bus;
the voltage recovery intensity factors of the converter buses are arranged in ascending order, and the ordered order is used as the recovery order of the converter buses;
(2.2) completing orderly recovery of the converter bus according to the priority;
(2.2.1) two turning coordinate points of the traditional low-voltage current-limiting control curve of the converter bus i are set asAnd
(2.2.2), atIs->Two turning points are additionally arranged between the two points>
(2.2.3), determinationAnd->Coordinate values of (2);
first destabilizing the systemCritical maximum and->The critical minimum value is taken as an initial value;
when (when)Taking the critical minimum stable value as +.>An initial value;
after the initial values of the coordinates at the two ends are determined, the initial values of the coordinates of the added turning points are determined by adopting the following steps:
after the initial value is determined, each direct current is kept unchanged, whenIn a step of 0.01p.u +.>Takes the value of the element which can minimize the reactive consumption overshoot of the converter bus during the fault recovery as +.>Is a final value of (a); in determining->After that, at->Is determined within the value range of +.>The specific method is as follows: order theThen let->From->Beginning at->In a step of 0.01p.u +.>Takes the value of the element which can minimize the reactive consumption overshoot of the converter bus during the fault recovery as +.>Is a final value of (a);
at the position ofSearching for an element value which stabilizes the system and minimizes the reactive power consumption overshoot of the line converter bus during the fault recovery as +.>Is a final value of (a); in determining->After that, at->Is determined within the value range of +.>The specific method is as follows: let->Then let->From->Beginning at->In a step of 0.01p.u +.>Takes the value of the element capable of minimizing the reactive consumption overshoot of the converter bus during the fault recovery as the value ofIs a final value of (a);
(2.2.4), constructing an improved low-voltage current-limiting control characteristic curve of the converter bus i:
wherein,representing the DC voltage of the DC line to which the converter bus I is connected, I i DC current of DC line connected with converting bus i, U i The input voltage of the direct current line low-voltage current-limiting control connected with the converter bus i;
and (2.2.5) orderly recovering each converter bus according to the respective improved low-voltage current-limiting control characteristic curve.
Meanwhile, the line coordination recovery method after the communication fault of the receiving end of the simultaneous transmission and simultaneous receiving system has the following beneficial effects:
(1) The invention combines the voltage coupling interaction effect on the transmission end alternating current system in the co-transmission co-reception ultra-high voltage direct current transmission system on the basis of the original multi-feed interaction factor, defines the co-transmission co-reception interaction factor evaluationElectromagnetic coupling characteristics of the receiving end alternating current near zone; compared with MIIF ji The method is directly applied to the concurrent transmission and concurrent reception direct current transmission system, the evaluation result is more accurate, and the method has a certain guiding effect on the research of the concurrent transmission and concurrent reception of the commutation failure of the novel power system topological structure.
(2) The invention constructs MOMI_VRIF i The impact of the voltage stability of the system on the integral synchronous transmission after the current conversion bus and faults is shown, so that the impact is more intuitively estimated; when an alternating current system at a system converter bus with a multi-feed structure fails, reactive power is injected into the converter bus of the failed converter station through a connecting line adjacent to the converter buses of other converter stations.
(3) The invention realizes the advanced or retarded recovery of each converter bus after the fault by changing the control characteristic curve of the VDCOL, and no novel control equipment is added in the secondary side control system, thereby reducing the requirements on a hardware measuring circuit, a converting circuit, an input circuit and an output circuit and being easier to realize in engineering.
Drawings
FIG. 1 is a flow chart of a method for recovering line coordination after communication failure of a receiving end of a simultaneous transmission and reception system;
fig. 2 is an equivalent topology of a certain common-transmission and common-reception multi-circuit extra-high voltage direct current transmission system;
FIG. 3 is a graph of VDCOL control characteristics employed by the invention;
fig. 4 is a simulation diagram of commutation voltages of each converter station after a fault of a certain dc-to-ac system;
FIG. 5 is a simulation diagram of the commutation voltage after a fault of a DC-DC receiving AC system;
fig. 6 is a simulation diagram of reactive power consumption of a converter station after a fault of a certain two direct current receiving end alternating current system;
FIG. 7 is a schematic diagram of the commutation voltage of a DC/DC low-level AC/DC receiver in the event of a DC/AC fault;
fig. 8 is a reactive power consumption simulation diagram of a certain dc and a certain dc low-level receiving-end converter station when a certain two dc receiving-end ac fails;
fig. 9 is a graph of reactive power consumption versus simulation for each recovery method after a certain dc receiver ac fault.
Detailed Description
The following description of the embodiments of the invention is presented in conjunction with the accompanying drawings to provide a better understanding of the invention to those skilled in the art. It is to be expressly noted that in the description below, detailed descriptions of known functions and designs are omitted here as perhaps obscuring the present invention.
Examples
In this embodiment, as shown in fig. 2, the simultaneous transmission and simultaneous reception dual-circuit extra-high voltage direct current transmission system in fig. 2 is taken as an example for explanation, and a model is built based on PSCAD/EMTDC electromagnetic transient simulation software, and is formed by equivalently simplifying the detailed operation parameters of a certain extra-high voltage direct current project and a certain two extra-high voltage direct current transmission projects of a power grid and a near-region alternating current power grid.
The following describes in detail a method for recovering line coordination after communication failure at the receiving end of a co-transmitting and co-receiving system by combining with a model of fig. 2, as shown in fig. 1, and comprises the following steps:
in this embodiment, as shown in fig. 1, the method for recovering line coordination after the communication fault of the receiving end of the co-sending and co-receiving system of the present invention includes the following steps:
s1, calculating a voltage recovery intensity factor of a simultaneous transmission and simultaneous reception system according to a system impedance network structure and a receiving end alternating current operation condition;
s1.1, calculating a multi-feed-out interaction factor and a multi-feed-in interaction factor under the structure of the synchronous transmission and synchronous receiving system according to a transmission end rectifying side alternating current system impedance network and a receiving end inversion side alternating current system impedance network of the synchronous transmission and synchronous receiving system:
wherein MOVIF ji Multi-feed-out interaction factor, MIIF, representing feed-side commutation buses i and j ji Representing multi-feed interaction factors of the receiving end converter buses i and j; z is Z Rij 、Z Rii Z is the transimpedance and self-impedance of the impedance network of the alternating current system at the transmitting end rectifying side Iij 、Z Iii Is the trans-impedance and the self-impedance of the impedance network of the alternating current system at the inversion side of the receiving end, delta U Ri 、ΔU Rj For the voltage of the system feed-side commutation buses i and j, deltaU Ii 、ΔU Ij The voltage of the current converting buses i and j at the receiving end of the system;
in this embodiment, according to the power network structure of the transmitting and receiving ends of the co-transmitting and receiving double-circuit extra-high voltage direct current transmission system shown in fig. 2, the equivalent impedance network Z of the transmitting-end alternating current power grid is solved R Equivalent impedance network Z for receiving end alternating current power grid I . The two DC receiving ends adopt a layered access structure, only the high-level system and one DC are used as analysis and explanation, after admittance matrix inversion, the Z of the co-transmission co-reception extra-high voltage DC transmission system shown in figure 2 R12 ＝55.17∠85.58°Ω、Z R11 ＝17.14∠84.00°Ω、Z R22 ＝15.56∠84.00°Ω、Z I12 ＝39.00∠84.99°Ω、Z I11 ＝6.87∠76.00°Ω、Z I22 =9.15 +.84.99 Ω. MOVIF for calculating co-transmission and co-reception ultra-high voltage direct current transmission structure 12 MIIF (Mobile industry if) 12 ；
S1.2, calculating a transmitting end action coefficient alpha and a receiving end action coefficient beta of the simultaneous transmitting and receiving system;
wherein DeltaU acR Representing maximum voltage offset, deltaU, allowed by corresponding sending end rectifying side converter bus when receiving end converter bus fails acI The maximum voltage offset allowed by the inversion side converter bus of the receiving end is represented when the converter bus of the receiving end fails;
s1.3, calculating a voltage interaction factor between the receiving end converter buses of the synchronous transmission and receiving system:
MOMI_IF ji ＝αMOVIF ji +βMIIF ji
wherein MOMI_IF ji The voltage interaction factor between the receiving-end current-converting buses i and j is expressed as the voltage fluctuation percentage of the receiving-end current-converting bus j when the voltage fluctuation of the receiving-end current-converting bus i of the same-transmission and same-receiving system is 1%;
in the present embodiment, ΔU acR ＝0.1080，ΔU acI = 0.2907, α=0.271, β=0.729. Substituting MOMI_IF 12 The expression of (2) is obtained by: MOMI_IF 12 ＝0.1731。
S1.4, calculating an effective short circuit ratio of a receiving end converter bus of the synchronous transmission and receiving system:
wherein MOMI_ESCR is as follows i Representing the effective short-circuit ratio of the receiving end converter bus i, S aci Short-circuit capacity at the receiving-end converter bus i; q (Q) ci The reactive compensation capacity of the capacitor, the alternating current filter and the reactive compensation device at the receiving end converter bus i; p (P) dNj Rated direct current power at the receiving end converter bus j; n is the number of bus bars;
s1.5, calculating a voltage recovery intensity factor of each bus in the simultaneous transmission and reception system;
in the multi-feed system, a multi-feed power recovery factor and a multi-feed dc voltage power recovery strength index are proposed based on the multi-feed interaction factor, which is defined as follows:
wherein MIRRF i The power recovery factor of the receiving-end converter bus i is represented, and DRI represents the voltage power recovery strength index of the receiving-end converter bus i. MIPRF (MIPRF) i Considering the relative reactive voltage supporting capacity of the ac system connected to the converter bus i to the line i, DRI i The reactive voltage supporting capability of the alternating current system connected with the converter buses i on the other lines is considered, so that the multi-feed system determines the recovery sequence of the direct current systems connected with the converter buses according to the values of the two factors at the positions of the multi-feed system and the converter buses, adverse interaction among the direct current systems of the multi-feed direct current transmission system is weakened, staggered recovery of the direct current power is realized, reactive power consumption of the direct current systems is consistent to a certain extent, and system instability accidents are reduced.
At present, research on a multi-feed system is mature, and a multi-feed interaction factor and a multi-feed effective short circuit ratio are respectively provided in the evaluation of voltage interaction influence and voltage stability of a receiving end. The multi-feed interaction factor is defined as the voltage variation of the receiving-end converter bus j when the three-phase reactor is connected in parallel on the receiving-end converter bus i of the multi-feed system so that the voltage drops by 1%. At the moment, the influence of the transmitting end structure on the interaction of the receiving end converter stations is ignored, namely, the electric distance between the transmitting end converter stations is considered to be large at the moment, a plurality of single-feed-out structures are formed, and voltage fluctuation caused by reactive power flow due to coupling characteristics during transient state is ignored. However, in the simultaneous sending and receiving system, the electrical distance of the sending end converter station is smaller, the sending end converter station also has an interaction coupling effect, the voltage rise of the sending end converter bus i can simultaneously cause the voltage rise of the sending end converter bus j, the direct current system connected with the converter bus j outputs different direct current gas amounts through the control system, the change can further be embodied on the voltage change of the receiving end converter bus j, and the receiving end converter bus j can change the receiving end converter bus i through the interaction influence of the receiving end. It is apparent that the definition of multi-feed interaction factors ignores this process, which is no longer applicable in co-feed co-receiving systems.
The simultaneous sending and receiving system can be understood as that the sending end forms a multi-feeding structure on the basis of the multi-feeding system, so that the consideration of the interaction influence on the converter station of the sending end is needed to be taken into consideration, and the order index is restored under the simultaneous sending and receiving structure. When the synchronous sending and synchronous receiving interaction factors are used for evaluating the interactive influence of the synchronous sending and synchronous receiving system on the receiving end converter station, the voltage interactive size of the receiving end inversion station can be accurately evaluated according to the coupling characteristic of the receiving end converter station, and the reactive voltage supporting capability of the receiving end alternating current system on the converter station can be effectively evaluated based on the synchronous sending and synchronous receiving effective short circuit ratio obtained by the synchronous sending and synchronous receiving interaction factors. The reactive voltage supporting capability of the receiving end alternating current system on the direct current line connected with the converting bus and the supporting capability of the receiving end alternating current system on the direct current line during the fault transient period of the converting station connected with the direct current line are integrated, and the voltage recovery strength factor of the line is defined:
wherein MOMI_VRIF i Represents the voltage recovery strength factor, MOMI_ESCR, of the receiving-end converter bus i i Representing the effective short-circuit ratio of the receiving end converter bus i, P dmax Representing the maximum value of active power transmitted by a direct current circuit connected with each converter bus;
in the present embodiment, MOMI_VRIF is used 2 For purposes of illustration, the same MOMI_IF 21 Calculating MOMI_IF by calculation method of (2) 23 Substituting MOMI_VRIF 2 In the expression of (2), MOMI_VRIF can be obtained 2 = 5.2015. The same can be used to obtain MOMI_VRIF 1 ＝4.5937，MOMI_VRIF 3 ＝33.1008。
S2, orderly recovering each converter bus by utilizing an improved low-voltage current-limiting control characteristic curve;
s2.1, acquiring recovery priority of each converter bus;
in the present embodiment, the MO of the dc linkMI_VRIF i The larger the voltage fluctuation of the converter bus i is, the larger the impact of the same-current and same-current voltage stability of the system is, and the larger the supporting capacity of the rest converter buses on the converter bus i is. The former shows that if the voltage recovery of the converter bus i is enhanced at the initial stage of the fault, the voltage recovery speed of the converter buses of other systems is increased due to the strong coupling characteristic among the converter stations of the same-sending and same-receiving systems, and at the moment, a large amount of reactive power is insufficient for the converter stations to flow from the alternating current system to the converter stations, so that the reactive power is insufficient in reactive support of the alternating current system, the alternating current voltage drops, the fault is further worsened, the larger the value is, the larger the impact of the voltage fluctuation of the same-sending and same-receiving systems on the voltage stability is, the greater the risk of system instability is, and the voltage recovery of the converter bus i needs to be delayed by the voltage recovery of the other converter buses; the latter indicates that the larger the value is, the stronger the reactive power supporting capability of the rest of the converter buses on the converter buses i in the fault recovery period is, namely, the converter buses i can not only absorb reactive power from the alternating current system thereof, but also receive reactive power on other converter buses from the connecting lines, so that the resource coordination between the systems is realized, if the voltage recovery of the converter buses i is accelerated in the initial stage of the fault, only the alternating current system connected with the converter buses i provides reactive voltage support for the converter buses, the higher the requirement on the capacity of reactive compensation equipment is generated, meanwhile, the supporting capability of the converter buses on the rest of the converter buses is relatively smaller, and the rest of the converter buses cannot receive the reactive voltage support of the enough converter buses i through the connecting lines, so that the resource waste is caused, and the larger the value is, the more the recovery of the rest of the converter buses i should be delayed. Therefore, the voltage recovery intensity factor synthesizes the impact of each converter bus on the overall voltage stability of the system and the recovery order index after the resource cooperation between the systems, when the voltage recovery intensity factor of a certain converter bus is larger, the voltage recovery speed of the converter bus is lagged by the voltage recovery speed of the converter bus smaller than the voltage recovery intensity factor, so that the coordination recovery between the systems can be realized, and the MOMI_VRIF is avoided i And absorbing a large amount of reactive power from the near alternating current area in the process of recovering the faults of the larger system to damage reactive power balance and voltage stability of the alternating current power grid.
Therefore, the voltage recovery intensity factors of the converter buses are arranged in an ascending order, and the ordered order is used as the recovery order of the converter buses, so that the recovery priority of the converter buses is obtained;
s2.2, orderly recovering the converter bus according to the priority;
in order to realize coordinated and orderly recovery of the voltages of all the converter buses of the same receiving system, a delay link is added in a direct current control link or a control characteristic curve for adjusting low-voltage current limiting control is generally adopted for realizing. The former changes the magnitude of the delay constant by serially connecting the delay links after the output value of the relevant electric quantity of the direct current control link according to the recovery order index, thereby changing the recovery speed of the direct current electric quantity and further changing the voltage recovery speed of the direct current connected converter bus. The latter is based on the control method of low-voltage current-limiting control, i.e. limiting the output of current when the voltage is low, and setting different current output command values under the same voltage level, so as to control the transmission power of each direct-current line, thereby controlling the reactive power consumption of each converter station connected with the direct-current line and indirectly controlling the recovery speed of each converter bus. The added delay link increases engineering complexity, and the setting of the delay time constant is not unified at present, so the invention adopts the improvement of the control characteristic curve of low-voltage current-limiting control, so that the direct-current circuit connected with the converter bus which is required to be recovered in advance has higher current output under the same voltage level, thereby more reactive power flows into the converter bus, more reactive voltage support is provided for the converter bus, and further the accelerated recovery of the voltage of the converter bus is realized, and the specific operation is as follows:
s2.2.1 two turning coordinate points of the traditional low-voltage current-limiting control curve of the converter bus i are set asAndI.e. when the DC voltage is less than or equal to the threshold +.>When the controller outputs a DC command value of +.>When the DC current is +.>In the range of->Is a function of +.>Is->Is a straight line of (2); when the DC voltage is more than or equal to the threshold value +.>When the controller outputs a DC command value of +.>The control function is as follows:
wherein,representing the DC voltage of the DC line to which the converter bus I is connected, I i DC current of DC line connected with converting bus i, U i The input voltage of the direct current line low-voltage current-limiting control connected with the converter bus i;
s2.2.2 changing two turning coordinate pointsIs->The control characteristic of the low-voltage current limiting control can be changed, namely, the current command value which is different from the original current command value is output under the same voltage level. By setting different turning point coordinate values, the fault recovery speed of each converter bus is limited, so that coordinated and orderly recovery after faults is realized. However, the traditional low-voltage current-limiting control curve is only determined by two turning points, and the recovery speed cannot be adjusted in time according to the fault recovery degree, so that the utilization rate of resources is low. In the fault recovery period, the voltage continuously rises, the compensation capacity of the reactive compensation equipment is continuously increased, the reactive demand of the converter station on the alternating current power grid is gradually reduced, the reactive compensation of the system can accept a faster voltage recovery speed than the initial fault period, a larger reactive power deficiency can not be generated, a large amount of reactive power can be effectively prevented from flowing from the alternating current power grid to the converter station, and the alternating current voltage is further deteriorated. Therefore, the recovery speed of the DC system is increased, the voltage stability of the AC power grid is not affected, and the recovery of the overall voltage stability of the system is facilitated, so as shown in figure 3, we are inIs->Two turning points are additionally arranged between the two points>
S2.2.3, determination ofAnd->Coordinate values of (2);
first destabilizing the systemCritical maximum and->The critical minimum value is taken as an initial value;
when (when)Taking the critical minimum stable value as +.>An initial value;
after the initial values of the coordinates at the two ends are determined, the initial values of the coordinates of the added turning points are determined by adopting the following steps:
after the initial value is determined, each direct current is kept unchanged, whenIn a step of 0.01p.u +.>Takes the value of the element which can minimize the reactive consumption overshoot of the converter bus during the fault recovery as +.>Is a final value of (a); in determining->After that, at->Is determined within the value range of +.>The specific method is as follows: order theThen let->From->Beginning at->In a step of 0.01p.u +.>Takes the value of the element which can minimize the reactive consumption overshoot of the converter bus during the fault recovery as +.>Is a final value of (a);
at the position ofSearching for an element value which stabilizes the system and minimizes the reactive power consumption overshoot of the line converter bus during the fault recovery as +.>Is a final value of (a); in determining->After that, at->Is determined within the value range of (a)The specific method is as follows: let->Then let->From->Beginning at->In a step of 0.01p.u +.>Takes the value of the element which can minimize the reactive consumption overshoot of the converter bus during the fault recovery as +.>Is a final value of (a);
s2.2.4, constructing an improved low-voltage current-limiting control characteristic curve of a converter bus i:
wherein,representing the DC voltage of the DC line to which the converter bus I is connected, I i DC current of DC line connected with converting bus i, U i The input voltage of the direct current line low-voltage current-limiting control connected with the converter bus i;
in the present embodiment, as shown in FIG. 3, curve 0 represents a conventional control curve, and curves a, b, and c represent MOMI_VRIF a <MOMI_VRIF b <MOMI_VRIF c VDCOL control curve selection at that time.
S2.2.5, each converter bus is orderly recovered according to the respective improved low-voltage current-limiting control characteristic curve.
In combination with the co-transmission and co-reception extra-high voltage direct current transmission model actually built according to engineering, under the structure that a certain two direct current converter stations at a receiving end are connected into an alternating current power grid in a layering manner, turning point value results of a low-voltage current-limiting control curve formulated according to the magnitude of the voltage recovery strength factor value of each converter bus are shown in table 1:
TABLE 1
| DC name | A certain direct current | Some two direct currents |
| V L | 0.4 | 0.40/0.40/0.30 |
| V M1 | 0.75 | 0.60/0.63/0.69 |
| V M2 | 0.898 | 0.80/0.85/0.88 |
| V H | 0.97 | 0.90/0.96/1.00 |
| I L | 0.4 | 0.55/0.35/0.30 |
| I M1 | 0.69 | 0.73/0.54/0.52 |
| I M2 | 0.881 | 0.91/0.83/0.72 |
| I H | 1 | 1.00/1.00/1.00 |
As can be seen from fig. 4, when a certain two direct-current high-rise receiving-end converter bus fails, the measured value of the voltage fluctuation ratio of the available receiving-end converter bus is 0.1857 according to the voltage waveform ratio; and MIIF obtained by calculation 12 = 0.1335, with large error, using momi_if ji After the calculation method of (2) obtaining MOMI_IF 12 As can be seen from 0.1730, in the co-sending and co-receiving structure, the method of the invention uses the momi_if as the evaluation index of the voltage cross coupling characteristic of the converter bus at the receiving end of the co-sending and co-receiving system, so that the co-sending and co-receiving system fault recovery order index obtained based on the momi_if has higher accuracy than the index obtained based on the MIIF. Meanwhile, as can be seen from fig. 5, when the coordinated recovery method based on the momi_vrif is not adopted, the recovery time of the voltage of the commutated bus of a certain two-direct-current high-level converter station is 1.078s, after the coordinated recovery method is adopted, the recovery time is advanced by 0.03s, and the recovery time is restored to 90% of the operation level before the fault at 1.075 s. And the maximum voltage drop is reduced by a small extent when the barrier occurs. The coordination recovery method based on MOMI_VRIF makes VDCOL more sensitive to fault detection, limits direct current more rapidly after faults occur, reduces reactive power consumption of a converter station in time, and provides more reactive voltage support for the voltage of a converter bus compared with the traditional recovery method. As can be seen from FIG. 6, the reactive power consumption during the fault period is effectively reduced by the coordination recovery strategy proposed by the present invention, and the peak value is reduced by 0.729p.uAs small as 0.696pu, the reactive overshoot is reduced from 21.5% to 16%, the maximum reactive power demand of two direct currents is reduced, the reactive power of the alternating current system flowing to the converter station is reduced, and the reactive support capability of the voltage of the receiving end system is improved. Fig. 7 and 8 show the reactive power consumption of the non-fault converter bus voltage and the converter station where the non-fault converter bus voltage is located, and the reactive power consumption is consistent with that of the fault converter bus voltage in fig. 5 and 6, the maximum dropping degree of the converter bus voltage is reduced in the fault transient process, the recovery speed of the converter bus voltage is accelerated, as shown in fig. 7, the dropping speed of a certain receiving-end converter bus voltage is reduced by 0.020pu compared with the conventional recovery method at the moment of fault removal (1.05 s), and the voltage is recovered before the fault removal, because the transmission power of the system is rapidly reduced when the voltage drops, and the reactive power shortage of the alternating current system is reduced. In addition, a certain commutation bus voltage reaches the rated operating level at 1.102s, while under the uncoordinated recovery strategy, the commutation bus voltage recovers less than 0.99pu at 1.102 s. In the aspect of reactive power balance, after the coordination recovery strategy provided by the invention is adopted, the demand of the non-fault converter bus in the converter station in the transient process for reactive power is reduced, so that surplus reactive power flows to the alternating current power grid and the converter station in which the fault converter bus is positioned, the establishment of new reactive power balance is further accelerated, as shown in fig. 8, the minimum reactive power consumption of the converter station in the fault recovery period is reduced from 0.416pu to 0.279pu, secondary overshoot of reactive power consumption is avoided, the recovery speed of reactive power balance of the system is accelerated, the reactive power consumption is recovered to a stable operation state in 1.218s, and the reactive power consumption is 0.670pu in the normal recovery mode at the same time, which is higher than the stable operation level, and the balance steady state is not recovered yet. Therefore, under the coordination recovery strategy, the recovery speed of reactive power balance of the non-fault line is accelerated.
Fig. 9 shows the reactive consumption of the faulty converter station during the fault transient period of the recovery strategy based on the different recovery order indexes, and it is obvious from fig. 9 that the reactive consumption overshoot of the converter station during the fault recovery is reduced by 0.649pu at the maximum and 0.070pu and 0.062pu compared with the DRI mode in the recovery mode using the momi_vrif compared with the recovery mode using the DRI and MIPRF. At the same time, the strategies hereinIn the mode, the reactive balance recovery speed of the system is about 0.5s faster than that of the DRI recovery mode, and the recovery strategy based on MIPRF has an unstable state after 2s, further embodying the superiority of the method of the invention, so that the simultaneous transmission and reception system is based on MOMI_VRIF i Is greater than the MIPRF established based on the multi-feed system i And DRI i The method has more remarkable effect on reactive power consumption inhibition, and the feasibility and effectiveness of the method are verified.
While the foregoing describes illustrative embodiments of the present invention to facilitate an understanding of the present invention by those skilled in the art, it should be understood that the present invention is not limited to the scope of the embodiments, but is to be construed as protected by the accompanying claims insofar as various changes are within the spirit and scope of the present invention as defined and defined by the appended claims.
Claims (1)
1. A method for recovering line coordination after communication faults of a receiving end of a simultaneous transmission and simultaneous receiving system is characterized by comprising the following steps:
(1) Calculating the voltage recovery intensity factor of the simultaneous transmission and simultaneous receiving system according to the impedance network structure of the system and the alternating current operation working condition of the receiving end;
(1.1) calculating a multi-feed-out interaction factor and a multi-feed-in interaction factor under the structure of the synchronous transmission and synchronous receiving system according to the impedance network of the alternating current system at the rectification side of the synchronous transmission and synchronous receiving system and the impedance network of the alternating current system at the inversion side of the receiving end:
wherein MOVIF ji Multi-feed-out interaction factor, MIIF, representing feed-side commutation buses i and j ji Representing multi-feed interaction factors of the receiving end converter buses i and j; z is Z Rij 、Z Rii Z is the transimpedance and self-impedance of the impedance network of the alternating current system at the transmitting end rectifying side Iij 、Z Iii Is the trans-impedance and the self-impedance of the impedance network of the alternating current system at the inversion side of the receiving end, delta U Ri 、ΔU Rj For the voltage of the system feed-side commutation buses i and j, deltaU Ii 、ΔU Ij The voltage of the current converting buses i and j at the receiving end of the system;
(1.2) calculating a transmitting end action coefficient alpha and a receiving end action coefficient beta of the simultaneous transmitting and receiving system;
wherein DeltaU acR Representing maximum voltage offset, deltaU, allowed by corresponding sending end rectifying side converter bus when receiving end converter bus fails acI The maximum voltage offset allowed by the inversion side converter bus of the receiving end is represented when the converter bus of the receiving end fails;
(1.3) calculating a voltage interaction factor between the receiving end converter buses of the synchronous transmission and receiving system:
MOMI_IF ji ＝αMOVIF ji +βMIIF ji
wherein MOMI_IF ji Representing the voltage interaction factor between the receiving end converter buses i and j;
(1.4) calculating the effective short-circuit ratio of the receiving end converter bus of the synchronous transmission and receiving system:
wherein MOMI_ESCR is as follows i Representing the effective short-circuit ratio of the receiving end converter bus i, S aci Short-circuit capacity at the receiving-end converter bus i; q (Q) ci The reactive compensation capacity of the capacitor, the alternating current filter and the reactive compensation device at the receiving end converter bus i; p (P) dNj Rated direct current power at the receiving end converter bus j; n is the number of bus bars;
(1.5) calculating the voltage recovery intensity factor of each bus in the simultaneous transmission and reception system;
wherein MOMI_VRIF i Represents the voltage recovery strength factor, MOMI_ESCR, of the receiving-end converter bus i i Representing the effective short-circuit ratio of the receiving end converter bus i, P dmax Representing the maximum value of active power transmitted by a direct current circuit connected with each converter bus;
(2) Orderly recovering each converter bus by utilizing the improved low-voltage current-limiting control characteristic curve;
(2.1) acquiring the recovery priority of each converter bus;
the voltage recovery intensity factors of the converter buses are arranged in ascending order, and the ordered order is used as the recovery order of the converter buses;
(2.2) completing orderly recovery of the converter bus according to the priority;
(2.2.1) two turning coordinate points of the traditional low-voltage current-limiting control curve of the converter bus i are set asAnd
(2.2.2), atIs->Two turning points are additionally arranged between the two points>
(2.2.3), determinationAnd->Coordinate values of (2);
first destabilizing the systemCritical maximum and->The critical minimum value is taken as an initial value;
when (when)Taking the critical minimum stable value as +.>An initial value;
after the initial values of the coordinates at the two ends are determined, the initial values of the coordinates of the added turning points are determined by adopting the following steps:
after the initial value is determined, each direct current is kept unchanged, whenIs changed in a step of 0.01p.u within the value rangeTakes the value of (1) to minimize the reactive consumption overshoot of the converter bus during fault recoveryThe prime value is->Is a final value of (a); let->In the same way->Is determined within the value range of +.>Is a value of (2);
at the position ofSearching for an element value which stabilizes the system and minimizes the reactive power consumption overshoot of the line converter bus during the fault recovery as +.>Is a final value of (a); let->In the same way->In the same way +.>Is a value of (2);
(2.2.4), constructing an improved low-voltage current-limiting control characteristic curve of the converter bus i:
wherein,representing the DC voltage of the DC line to which the converter bus I is connected, I i DC current of DC line connected with converting bus i, U i The input voltage of the direct current line low-voltage current-limiting control connected with the converter bus i;
and (2.2.5) orderly recovering each converter bus according to the respective improved low-voltage current-limiting control characteristic curve.
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