CN109888814B - Continuous commutation failure direct current blocking suppression method based on sound direct current emergency support - Google Patents

Continuous commutation failure direct current blocking suppression method based on sound direct current emergency support Download PDF

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CN109888814B
CN109888814B CN201910218580.4A CN201910218580A CN109888814B CN 109888814 B CN109888814 B CN 109888814B CN 201910218580 A CN201910218580 A CN 201910218580A CN 109888814 B CN109888814 B CN 109888814B
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欧阳金鑫
肖超
熊小伏
魏碧桧
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Chongqing University
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Abstract

The invention discloses a continuous commutation failure direct current blocking restraining method based on sound direct current emergency support, aiming at the influence of power sag on the stability of a sending end power grid during direct current continuous commutation failure, a rolling calculation method of a sending end system power angle difference and an acceleration area variable quantity in the direct current continuous commutation failure process is established through continuous commutation failure direct current commutation failure signals and receiving end alternating current commutation voltage detection, and sound direct current emergency power control instructions are obtained through the relative size rolling calculation of acceleration and deceleration areas so as to implement control. The method provided by the invention can effectively reduce the direct current blocking risk of continuous phase commutation failure, reduce the machine switching amount of a direct current sending end power grid, and improve the running stability and economy of the alternating current and direct current power grid.

Description

Continuous commutation failure direct current blocking suppression method based on sound direct current emergency support
Technical Field
The invention relates to the technical field of power system protection and control, in particular to a continuous commutation failure direct current blocking restraining method based on sound direct current emergency support.
Background
With the rapid development of high-capacity extra-high voltage direct-current transmission technology and the accelerated construction of direct-current engineering, an alternating-current and direct-current series-parallel power grid forms a running pattern with multiple direct currents in parallel, strong direct currents and weak alternating currents. For a large-scale direct current asynchronous interconnection system, the influence of the dynamic response of a direct current system on an alternating current power grid is more and more obvious due to the fact that the transmission capacity of a direct current project is continuously increased. The power grid disturbance easily causes the phase commutation failure of the extra-high voltage direct current system, the transmission power of the direct current system is greatly reduced in a short time during the phase commutation failure, the stability margin of the alternating current power grid is influenced, and the safe operation of the power system is seriously threatened.
If the receiving end system is weak or the fault duration is long, the inverter controller lacks enough turn-off angle adjusting capacity, and continuous phase commutation failure of the direct current system can be caused. The power sag caused by continuous commutation failure has the characteristics of short time, large amplitude, uncertain commutation failure times and the like, continuous power transient quantity is difficult to accurately calculate, and an effective quantitative control method is lacked in emergency control in the continuous commutation failure process. In order to avoid the instability of an alternating current system under the condition of continuous phase commutation failure, the current main means is to implement different phase switching schemes according to the frequency of the continuous phase commutation failure, when the phase commutation failure reaches a certain frequency, a direct current system with the continuous phase commutation failure is locked, and a corresponding phase switching measure of direct current locking is adopted. However, blocking dc systems may cause grid frequency problems, resulting in large scale tripping, load shedding. Large scale generator cut-out will result in long system recovery start-up procedures, resulting in economic losses and other negative effects.
Therefore, how to provide a technical scheme for avoiding the instability of an alternating current system under the failure of continuous commutation and without large-scale generator tripping and load shedding becomes a problem which needs to be solved urgently by technical personnel in the field.
Disclosure of Invention
Therefore, the problem to be solved by the present invention is how to provide a technical scheme for avoiding the instability of the ac system under the failure of continuous commutation without large-scale load shedding.
In order to solve the technical problems, the invention adopts the following technical scheme:
a continuous commutation failure direct current blocking suppression method based on sound direct current emergency support comprises the following steps:
step 1: solving the steady state value delta of the power angle difference corresponding to the steady state operation point a1Power angle difference delta corresponding to critical stable operation point hhWhen a commutation failure signal is detected, the commutation failure frequency k is 1, delta T is set as the duration of 1 commutation failure power sag, the equivalent mechanical power and electromagnetic power change process caused by 1 commutation failure power sag is divided into n periods according to step length delta T for piecewise linearization processing, and the obtained discrete sampling point sequence is [ T1,t2,t3,…,tn]Where n is Δ T/Δ T, Tn＝t1+ (n-1) delta t, and the equivalent power angle difference value change sequence of the sending end system corresponding to each sampling point is [ delta ]1,δ2,…,δm,…,δn]Wherein, deltamSetting i to 1 for the maximum value of the power angle difference in the acceleration process of the system, wherein the equivalent mechanical power and the electromagnetic power corresponding to the ith sampling point are P'miAnd PemaxsinδiAnd then:
Figure BDA0002002853440000021
executing the step 2;
step 2: comparing the acceleration area A in the ith periodaiAnd a deceleration area AdiThe relative magnitude of (d) is obtained as the emergency power control quantity Δ Pem_iIf A isai≤AdiThen robust DC emergency power control is not initiated, i.e. Δ Pem_iIf A is equal to 0ai＞AdiThen, the emergency power control amount Δ P is calculated based on the following formulaem_i，
Figure BDA0002002853440000022
Wherein A isaiFor the cumulative acceleration area in the ith cycle:
Figure BDA0002002853440000023
the estimated acceleration area value of the kth commutation failure is as follows:
Figure BDA0002002853440000024
section (delta)n,δh) Inner deceleration area AdIs divided intomI equal parts, deceleration area A per unit perioddi：
Figure BDA0002002853440000025
The healthy DC maximum power support amount is 1.2-1.5 times of rated operation power, if healthy DC maximum power support amount PDC_maxGreater than or equal to Δ Pem_iThen order the DC control command value PDC_compIs DeltaPem_iControl the command value P by DCDC_compPerforming healthy direct current emergency power control; if PDC_maxLess than Δ Pem_iSupporting the quantity P with the maximum powerDC_maxPerforming healthy direct current emergency power control; executing the step 3;
and step 3: if i is m, finishing the current direct current blocking suppression; if i is less than m, executing the step 4;
and 4, step 4: novel calculation testAfter the ith control period is finished after the robust direct current emergency power control is considered, the power angle difference change sequence [ delta ] is obtained1′,δ2′,…,δ′m,…,δn′]Accelerated area A 'accumulated in ith sampling period after robust DC emergency control is applied'aiComprises the following steps:
Figure BDA0002002853440000031
therefore, considering the effect of robust DC emergency power control, the uncompensated acceleration area Δ A in the ith periodaiComprises the following steps:
Figure BDA0002002853440000032
let i equal i +1, the acceleration area a of the i-th cycle is calculated based on the following equationai：
Figure BDA0002002853440000033
The deceleration area is divided into m-i equal parts to obtain the deceleration area A in the unit perioddiComprises the following steps:
Figure BDA0002002853440000034
recalculating Δ Pem_i、A′aiAnd Δ AaiAnd returns to step 2.
Preferably, the power angle steady state value δ is solved based on the following formula1：
Figure BDA0002002853440000035
Figure BDA0002002853440000036
Figure BDA0002002853440000037
Figure BDA0002002853440000038
In the formula: theta1And theta2Are respectively a bus B1、B2The phase angle of (a) is,
Figure BDA0002002853440000039
for the sum of active power transmitted by all direct current systems, delta is the power angle difference of equivalent generators in the sub-region S1 and the sub-region S2, S1 and S2 are two synchronous interconnection sub-regions with weak electrical connection in the end grid respectively, and delta is equal to deltas1-δs2，δs1Equivalent generator power angle, δ, for sub-region S1s2Equivalent generator power angle for sub-region S2, t represents time, PmTo equivalent mechanical power, PemaxIs the peak value of the equivalent electromagnetic power, PG1And PG2Output mechanical power, M, of equivalent generators of sub-zone S1 and sub-zone S2, respectively1And M2Equivalent generator inertia time constants, P, for sub-region S1 and sub-region S2, respectivelyL1And PL2Respectively is a load L1And load L2Expressed power value, PDC1、PDC2Respectively being a direct current transmission system DC1And a direct current transmission system DC2For transmitting DC power, U1And U2Are respectively a bus B1And bus B2Voltage amplitude of (x)12Is a bus B1And bus B2The tie line reactance in between.
Preferably, P is calculated based on the following formulaDC1And PDC2：
Figure BDA0002002853440000041
Wherein, z is 1 or 2, t0At the commutation failure occurrence time, k is the number of consecutive commutation failures, and k is 1, 2, 3, …, N. Delta T1For a duration of time, Δ T, during which the output power of the inverter station is zero in the event of a failure of the DC commutation2Time required for recovery from dc power to power before failure, Δ T ═ Δ T1+ΔT2；
Output power P of inverter station under steady state operation conditiond0Comprises the following steps:
Figure BDA0002002853440000042
maximum value P of DC power in phase commutation failure recovery staged1Comprises the following steps:
Figure BDA0002002853440000043
in the formula: n is the number of 6 pulse current converters in each pole of the inverter station; u shapeBThe effective value of the voltage of the valve side line of the converter transformer of the inverter station is obtained; i isdIs direct current; gamma is the turn-off angle of the inverter station; xcThe equivalent commutation reactance is reduced to the valve side of the converter transformer; u'BAnd the voltage is the fault voltage of the alternating current side of the inverter station at the initial moment of the fault.
Preferably, the accumulated acceleration area of the commutation failure is as follows:
Figure BDA0002002853440000044
the uncompensated acceleration area after the phase commutation failure is as follows:
Figure BDA0002002853440000045
the maximum speed reduction area which can be compensated by the sound direct-current emergency power control after the phase change failure power sag is finished is as follows:
ΔAcomp＝PDC_max(δh-δn′)
when Δ Acomp＜AremainIn step 2, the maximum power support P is usedDC_maxWhen the direct current emergency power control is carried out, the stability requirement is met by adopting the control measure of the generator tripping of the power grid at the sending end, and the minimum generator tripping quantity
Figure BDA0002002853440000046
Preferably, if the next commutation failure signal is detected, let k be k +1, and accelerate the maximum power angle difference δ in the last commutation failure processn' initial power angle difference delta as acceleration process of this commutation failure1And step 1 is executed in which the calculation of the deceleration area minus the accumulation of the acceleration area A caused by the occurrence of the commutation failurea′。
In summary, the invention discloses a continuous commutation failure dc blocking suppression method based on robust dc emergency support, which establishes a rolling calculation method for power angle difference and accelerated area variation of a sending end system in a dc continuous commutation failure process through a continuous commutation failure dc commutation failure signal and ac voltage detection aiming at the influence of power sag on the stability of the sending end power grid during the dc continuous commutation failure, and obtains a robust dc emergency power control instruction through the relative size rolling calculation of the accelerated and decelerated areas to implement control. The method provided by the invention can effectively reduce the direct current blocking risk of continuous phase commutation failure, reduce the machine switching amount of a direct current sending end power grid, and improve the running stability and economy of the alternating current and direct current power grid.
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For purposes of promoting a better understanding of the objects, aspects and advantages of the invention, reference will now be made in detail to the present invention as illustrated in the accompanying drawings, in which:
FIG. 1 shows the output power characteristics of a DC inverter station in case of continuous commutation failure;
FIG. 2 is an equivalent model of an AC/DC interconnection system;
FIG. 3 is a power characteristic curve of a sending-end system in the case of a DC continuous commutation failure;
FIG. 4 is a simulation verification diagram of control effects under different control methods; (a) a sound direct current inversion station output power waveform, (b) a generator 1-2 power angle difference change curve;
fig. 5 is a schematic diagram of an implementation of emergency power control based on robust dc.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings.
As shown in fig. 5, the present invention discloses a continuous commutation failure dc blocking suppression method based on robust dc emergency support, which includes the following steps:
step 1: solving a power angle difference steady-state value delta 1 corresponding to a steady-state operation point a and a power angle difference value delta h corresponding to a critical stable operation point h, when a commutation failure signal is detected, recording the commutation failure frequency k as 1, setting delta T as 1 commutation failure power temporary reduction duration, dividing the equivalent mechanical power and electromagnetic power change process caused by 1 commutation failure power temporary reduction into n periods according to step length delta T for piecewise linearization processing, and obtaining a discrete sampling point sequence of [ T [ [ T ] T1,t2,t3,…,tn]Where n is Δ T/Δ T, Tn＝t1+ (n-1) delta t, and the equivalent power angle difference value change sequence of the sending end system corresponding to each sampling point is [ delta ]1,δ2,…,δm,…，δn]Wherein, deltamSetting i to 1 for the maximum value of the power angle difference in the acceleration process of the system, wherein the equivalent mechanical power and the electromagnetic power corresponding to the ith sampling point are P'miAnd PemaxsinδiAnd then:
Figure BDA0002002853440000051
executing the step 2;
step 2: comparing the acceleration area A in the ith periodaiAnd a deceleration area AdiThe relative magnitude of (d) is obtained as the emergency power control quantity Δ Pem_iIf A isai≤AdiThen robust DC emergency power control is not initiated, i.e. Δ Pem_iIf A is equal to 0ai＞AdiThen, the emergency power control amount Δ P is calculated based on the following formulaem_i，
Figure BDA0002002853440000061
Wherein A isaiFor the cumulative acceleration area in the ith cycle:
Figure BDA0002002853440000062
the estimated acceleration area value of the kth commutation failure is as follows:
Figure BDA0002002853440000063
section (delta)n,δh) Inner deceleration area AdDivided into m-i equal parts and the deceleration area A of unit perioddi：
Figure BDA0002002853440000064
The healthy DC maximum power support amount is 1.2-1.5 times of rated operation power, if healthy DC maximum power support amount PDC_maxGreater than or equal to Δ Pem_iThen order the DC control command value PDC_compIs DeltaPem_iControl the command value P by DCDC_compPerforming healthy direct current emergency power control; if PDC_maxLess than Δ Pem_iSupporting the quantity P with the maximum powerDC_maxPerforming healthy direct current emergency power control; executing the step 3;
and step 3: if i is m, finishing the current direct current blocking suppression; if i is less than m, executing the step 4;
and 4, step 4: the new calculation considers the power angle difference change sequence [ delta ] after the ith control period is finished after the healthy direct current emergency power control1′,δ2′,…,δ′m,…,δn′]Accelerated area A 'accumulated in ith sampling period after robust DC emergency control is applied'aiComprises the following steps:
Figure BDA0002002853440000065
therefore, considering the effect of robust DC emergency power control, the uncompensated acceleration area Δ A in the ith periodaiComprises the following steps:
Figure BDA0002002853440000066
let i equal i +1, the acceleration area a of the i-th cycle is calculated based on the following equationai：
Figure BDA0002002853440000067
The deceleration area is divided into m-i equal parts to obtain the deceleration area A in the unit perioddiComprises the following steps:
Figure BDA0002002853440000071
recalculating Δ Pem_i、A′aiAnd Δ AaiAnd returns to step 2.
The invention discloses a continuous commutation failure direct current blocking restraining method based on sound direct current emergency support, aiming at the influence of power sag on the stability of a sending end power grid during direct current continuous commutation failure, a rolling calculation method of a sending end system power angle difference and an acceleration area variable quantity in the direct current continuous commutation failure process is established through continuous commutation failure direct current commutation failure signals and alternating current voltage detection, and sound direct current emergency power control instructions are obtained through the relative size rolling calculation of acceleration and deceleration areas so as to implement control. The method provided by the invention can effectively reduce the direct current blocking risk of continuous phase commutation failure, reduce the machine switching amount of a direct current sending end power grid, and improve the running stability and economy of the alternating current and direct current power grid.
In specific implementation, the power angle steady state value delta is solved based on the following formula1：
Figure BDA0002002853440000072
Figure BDA0002002853440000073
Figure BDA0002002853440000074
Figure BDA0002002853440000075
In the formula: theta1And theta2Are respectively a bus B1、B2The phase angle of (a) is,
Figure BDA0002002853440000076
for the sum of active power transmitted by all direct current systems, delta is the power angle difference of equivalent generators in the sub-region S1 and the sub-region S2, S1 and S2 are two synchronous interconnection sub-regions with weak electrical connection in the end grid respectively, and delta is equal to deltas1-δs2，δs1Equivalent generator power angle, δ, for sub-region S1s2Equivalent generator power angle for sub-region S2, t represents time, PmTo equivalent mechanical power, PemaxIs the peak value of the equivalent electromagnetic power, PG1And PG2Output mechanical power, M, of equivalent generators of sub-zone S1 and sub-zone S2, respectively1And M2Equivalent generator inertia time constants, P, for sub-region S1 and sub-region S2, respectivelyL1And PL2Respectively is a load L1And load L2Expressed power value, PDC1、PDC2Respectively being a direct current transmission system DC1And a direct current transmission system DC2For transmitting DC power, U1And U2Are respectively a bus B1And bus B2Voltage amplitude of (x)12Is a bus B1And bus B2The tie line reactance in between.
Fig. 2 is a schematic diagram of a 4-zone ac/dc interconnection system. Under steady state operation, the sending end power grid transmits power to the area 3 and the area 4 through two-circuit direct current, and two synchronous interconnection sub-areas S1 and S2 with weak electrical connection exist in the sending end power grid. In FIG. 2, Es1∠δs1、Es2∠δs2Internal potential and rotor angle of equivalent generators G1 and G2, respectively; u shape1、U2And theta1、θ2The voltage amplitude and phase angle of the bus bars B1, B2, respectively; x is the number of1、x2Generators G1 and G2, respectivelyThe equivalent reactance of (1); x is the number of12Is a tie line reactance between bus B1 and bus B2; pG1、PG2Regions S1 and S2, respectively, equal the output mechanical power of the generator; pL1、PL2Load power represented by L1 and L2, respectively; pDC1、PDC2Is a direct current DC1And DC2Transmitting direct current power.
The interior of the power grid at the transmitting end is weak interconnection, namely when the reactance x12 of the tie line is far greater than the reactance of the equivalent generator, the reactance x12 of the tie line can be approximated to theta1≈δs1，θ2≈δs2。
In specific embodiments, P is calculated based on the following formulaDC1And PDC2：
Figure BDA0002002853440000081
Wherein, z is 1 or 2, t0At the commutation failure occurrence time, k is the number of consecutive commutation failures, and k is 1, 2, 3, …, N. Delta T1For a duration of time, Δ T, during which the output power of the inverter station is zero in the event of a failure of the DC commutation2Time required for recovery from dc power to power before failure, Δ T ═ Δ T1+ΔT2；
Output power P of inverter station under steady state operation conditiond0Comprises the following steps:
Figure BDA0002002853440000082
maximum value P of DC power in phase commutation failure recovery staged1Comprises the following steps:
Figure BDA0002002853440000083
in the formula: n is the number of 6 pulse current converters in each pole of the inverter station; u shapeBThe effective value of the voltage of the valve side line of the converter transformer of the inverter station is obtained; i isdIs direct current; gamma is the turn-off angle of the inverter station; xcThe equivalent commutation reactance is reduced to the valve side of the converter transformer; u'BFor the AC side of the inverter station at the initial moment of the faultA fault voltage.
According to a control equation of the DC converter station, the DC voltage U of the inverter stationdAnd the output power Pd0Can be represented as:
Figure BDA0002002853440000084
Figure BDA0002002853440000085
in the formula: n is a radical ofcThe number of 6 pulse converters in each pole of the inverter station is; u shapeBThe effective value of the voltage of the valve side line of the inversion station is obtained; i isdIs direct current; gamma is the turn-off angle of the inverter station; xcIs the equivalent commutation reactance reduced to the valve side of the converter transformer.
The maximum value of the direct current power in the phase change failure recovery stage is determined by the alternating current fault voltage and the direct current. During a dip in the ac voltage, the dc current is determined by the low voltage current limiting controller:
Figure BDA0002002853440000091
in the formula: i isdlAnd IdhRespectively outputting a minimum direct current instruction and a maximum direct current instruction by the low-voltage current-limiting controller; u shapedlAnd UdhRespectively starting voltage threshold values of the low-voltage current-limiting controller.
The continuous commutation failure often occurs in the recovery stage of commutation failure, and according to the formula (1), when the off-angle γ is zero, the dc power obtains the maximum value Pd1：
Figure BDA0002002853440000092
Wherein, U'BThe effective value of the line voltage collected by the valve side of the inversion station after the fault.
Because the commutation failure recovery process is short in time and large in power change rate, the power recovery process can be approximately linear, and the change process of the output power of the direct current inverter station under continuous commutation failure is shown in fig. 1.
Figure BDA0002002853440000093
In specific implementation, the acceleration area accumulated by the commutation failure is as follows:
Figure BDA0002002853440000094
the uncompensated acceleration area after the phase commutation failure is as follows:
Figure BDA0002002853440000095
the maximum speed reduction area which can be compensated by the sound direct-current emergency power control after the phase change failure power sag is finished is as follows:
ΔAcomp＝PDC_max(δh-δn′)
when Δ Acomp＜AremainIn step 2, the maximum power support P is usedDC_maxWhen the direct current emergency power control is carried out, the stability requirement is met by adopting the control measure of the generator tripping of the power grid at the sending end, and the minimum generator tripping quantity
Figure BDA0002002853440000096
In specific implementation, if a next commutation failure signal is detected, k is made to be k +1, and the maximum power angle difference delta in the process of accelerating the last commutation failure is acceleratedn' initial power angle difference delta as acceleration process of this commutation failure1And step 1 is executed in which the calculation of the deceleration area minus the accumulation of the acceleration area A caused by the occurrence of the commutation failurea′。
The following is a specific simulation verification example of the present invention:
an alternating current-direct current interconnection system shown in fig. 2 is built based on MATLAB/SIMULINK, the system reference capacity is 100MW, and the alternating current system line voltage is 220 kV. Region 1(G1) represents 4 parallel synchronous generators, of which 2 output powers are 10.0pu and 2 output powers are 2.0 pu; the region 2(G2) includes 1 output powerThe generator is a 10.0pu synchronous generator, and the inertia time constants of the single unit in the area 1 and the area 2 are both 3.2 s. S3 and S4 adopt equivalent models of voltage source and series impedance, and load L1And L22.2pu and 11.8pu, respectively. The sending end system is connected with the two-circuit direct current transmission system DC through a bus B11And DC2The direct current system adopts a high-voltage direct current transmission model of a 12-pulse current converter, each time the direct current transmission power is 10.0pu, the rectifying station adopts constant current control, and the inverter station adopts constant turn-off angle control and constant current control. Low voltage current limiting control parameter IdlAnd Idh0.5pu and 1.0pu, U, respectivelydlAnd Udh0.5pu and 0.9pu, respectively. In normal operation, the power transmitted from the region 1 to the region 2 is 180MW, and the bus B1And bus B2Reactance X of cross-connecting lineLAnd 300 omega. The system equivalent impedances of S3 and S4 are both 5.4+ j22.8 omega. In order to avoid that the AC side voltage of the converter station is not obviously influenced in the DC power boosting process, the compensation quantity P of single-circuit DC isDC_compThe maximum single-loop direct-current emergency power control amount is limited to be 1.2 times of the rated transmission power, namely 12.0pu, and the maximum single commutation failure recovery process time delta T is 160 ms.
When t is 15s, direct current DC1Three-phase short circuit occurs to the AC bus B3 of the inverter station, the voltage of the bus drops to 0.92pu, the fault is continuously cleared for 0.4s, and the short-circuit fault causes direct current DC1And continuous phase commutation failure occurs in the inversion station. In order to verify the effectiveness of the proposed control method, different emergency power control methods are used for comparison against the above failures. Conventional control methods at direct current DC1Calculating and implementing emergency control quantity after continuous commutation failure disturbance is generated, and improving healthy direct current DC2The power control amount of the power system is 12pu, the power system is used for assisting a generator tripping machine 4pu in the power grid area 1 of the transmitting end, in addition, the control is implemented by adopting the emergency power control method for comparison, and the exit time of the sound direct current emergency power control is taken as 1.5s after the fault. FIG. 4 shows a robust DC under two different control measures2The emergency power control quantity and the power angle difference change curve of the sending end generator. According to the simulation result, based on the calculation method of the emergency control quantity, the stability margin of the system is calculated in real time, and the 2 nd time is detectedStarting a robust DC when commutation fails2And emergency power control, wherein the direct current power control quantity is adjusted to 12pu, so that the stability of a sending end system can be ensured. After the continuous commutation failure is finished, the system stability margin is small, and after the continuous commutation failure, the emergency power control cannot meet the system stability control target, so that the power angle of the power grid at the transmitting end is unstable.
Compared with the conventional control method, the provided control method can be used for putting into sound direct-current emergency power control in advance according to the calculation and comparison of the variation of the acceleration area and the deceleration area, and the problem of insufficient system stability margin caused by overlarge variation of a power angle after the continuous commutation failure is finished is solved.
Finally, it is noted that the above-mentioned embodiments illustrate rather than limit the invention, and that, while the invention has been described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims (5)

1. The continuous commutation failure direct current blocking suppression method based on sound direct current emergency support is characterized by comprising the following steps of:
step 1: solving the steady state value delta of the power angle difference corresponding to the steady state operation point a1Power angle difference delta corresponding to critical stable operation point hhWhen a commutation failure signal is detected, the commutation failure frequency k is 1, delta T is set as the duration of 1 commutation failure power sag, the equivalent mechanical power and electromagnetic power change process caused by 1 commutation failure power sag is divided into n periods according to step length delta T for piecewise linearization processing, and the obtained discrete sampling point sequence is [ T1,t2,t3,…,tn]Where n is Δ T/Δ T, Tn＝t1+ (n-1) delta t, and the equivalent power angle difference value change sequence of the sending end system corresponding to each sampling point is [ delta ]1,δ2,…,δm,…,δn]Wherein, deltamMaking i equal to 1 for the maximum value of the power angle difference in the acceleration process of the system, and making the corresponding equivalent of the ith sampling pointThe mechanical power and the electromagnetic power are respectively P'miAnd Pemaxsinδi，PemaxThe peak value of the equivalent electromagnetic power is then:
Figure FDA0002481071980000011
executing the step 2;
step 2: comparing the acceleration area A in the ith periodaiAnd a deceleration area AdiThe relative magnitude of (d) is obtained as the emergency power control quantity Δ Pem_iIf A isai≤AdiThen robust DC emergency power control is not initiated, i.e. Δ Pem_iIf A is equal to 0ai＞AdiThen, the emergency power control amount Δ P is calculated based on the following formulaem_i，
Figure FDA0002481071980000012
Wherein A isaiFor the cumulative acceleration area in the ith cycle:
Figure FDA0002481071980000013
the estimated acceleration area value of the kth commutation failure is as follows:
Figure FDA0002481071980000014
section (delta)n,δh) Inner deceleration area AdDivided into m-i equal parts and the deceleration area A of unit perioddi：
Figure FDA0002481071980000015
PmThe healthy DC maximum power support amount is 1.2-1.5 times of rated operation power, and if the healthy DC maximum power support amount is equal to the equivalent mechanical power, the healthy DC maximum power support amount P is equal to the rated operation powerDC_maxIs greater than or equal toIs equal to Δ Pem_iThen order the DC control command value PDC_compIs DeltaPem_iControl the command value P by DCDC_compPerforming healthy direct current emergency power control; if PDC_maxLess than Δ Pem_iSupporting the quantity P with the maximum powerDC_maxPerforming healthy direct current emergency power control; executing the step 3;
and step 3: if i is m, finishing the current direct current blocking suppression; if i is less than m, executing the step 4;
and 4, step 4: new calculation considers the power angle difference change sequence [ delta 'after the ith control period is finished after robust direct current emergency power control'1,δ′2,…,δ′m,…,δ′n]Accelerated area A 'accumulated in ith sampling period after robust DC emergency control is applied'aiComprises the following steps:
Figure FDA0002481071980000021
therefore, considering the effect of robust DC emergency power control, the uncompensated acceleration area Δ A in the ith periodaiComprises the following steps:
Figure FDA0002481071980000022
let i equal i +1, the acceleration area a of the i-th cycle is calculated based on the following equationai：
Figure FDA0002481071980000023
The deceleration area is divided into m-i equal parts to obtain the deceleration area A in the unit perioddiComprises the following steps:
Figure FDA0002481071980000024
recalculating Δ Pem_i、A′aiAnd Δ AaiAnd returns to step 2.
2. The successive commutation failure dc blocking suppression method based on robust dc emergency support as claimed in claim 1, wherein the power angle steady state value δ is solved based on the following formula1：
Figure FDA0002481071980000025
Figure FDA0002481071980000026
Figure FDA0002481071980000027
Figure FDA0002481071980000031
In the formula: theta1And theta2Are respectively a bus B1、B2The phase angle of (a) is,
Figure FDA0002481071980000032
for the sum of active power transmitted by all direct current systems, delta is the power angle difference of equivalent generators in the sub-region S1 and the sub-region S2, S1 and S2 are two synchronous interconnection sub-regions with weak electrical connection in the end grid respectively, and delta is equal to deltas1-δs2，δs1Equivalent generator power angle, δ, for sub-region S1s2Equivalent generator power angle for sub-region S2, t represents time, PmTo equivalent mechanical power, PemaxIs the peak value of the equivalent electromagnetic power, PG1And PG2Output mechanical power, M, of equivalent generators of sub-zone S1 and sub-zone S2, respectively1And M2Equivalent generator inertia time constants, P, for sub-region S1 and sub-region S2, respectivelyL1And PL2Respectively is a load L1And load L2Expressed power value, PDC1、PDC2Respectively being a direct current transmission system DC1And DC power transmission systemSystem DC2For transmitting DC power, U1And U2Are respectively a bus B1And bus B2Voltage amplitude of (x)12Is a bus B1And bus B2The tie line reactance in between.
3. The successive commutation failure dc blocking suppression method based on robust dc emergency support as claimed in claim 2, wherein P is calculated based on the following equationDC1And PDC2：
Figure FDA0002481071980000033
Wherein, z is 1 or 2, t0K is the number of successive commutation failures occurring at the commutation failure occurrence time, k is 1, 2, 3, …, N, Δ T1For a duration of time, Δ T, during which the output power of the inverter station is zero in the event of a failure of the DC commutation2Time required for recovery from dc power to power before failure, Δ T ═ Δ T1+ΔT2；
Output power P of inverter station under steady state operation conditiond0Comprises the following steps:
Figure FDA0002481071980000034
maximum value P of DC power in phase commutation failure recovery staged1Comprises the following steps:
Figure FDA0002481071980000035
in the formula: n is a radical ofcThe number of 6 pulse converters in each pole of the inverter station is; u shapeBThe effective value of the voltage of the valve side line of the converter transformer of the inverter station is obtained; i isdIs direct current; gamma is the turn-off angle of the inverter station; xcThe equivalent commutation reactance is reduced to the valve side of the converter transformer; u'BAnd the voltage is the fault voltage of the alternating current side of the inverter station at the initial moment of the fault.
4. The method of claim 1The continuous commutation failure direct current blocking restraining method based on sound direct current emergency support is characterized in that the accumulated acceleration area of the current commutation failure is as follows:
Figure FDA0002481071980000041
the uncompensated acceleration area after the phase commutation failure is as follows:
Figure FDA0002481071980000042
the maximum speed reduction area which can be compensated by the sound direct-current emergency power control after the phase change failure power sag is finished is as follows:
ΔAcomp＝PDC_max(δh-δ′n)
when Δ Acomp＜AremainIn step 2, the maximum power support P is usedDC_maxWhen the direct current emergency power control is carried out, the stability requirement is met by adopting the control measure of the generator tripping of the power grid at the sending end, and the minimum generator tripping quantity
Figure FDA0002481071980000043
5. The method as claimed in claim 1, wherein the method further comprises, when a next commutation failure signal is detected, setting k to k +1, and accelerating a maximum power angle difference δ 'during a previous commutation failure'nAs the initial power angle difference delta of the phase change failure acceleration process1And step 1 is executed in which the calculation of the deceleration area minus the accumulation of the acceleration area A 'caused by the occurrence of the commutation failure'a。
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