CN110323776B - SC-based L CC-HVDC receiving end direct current system feedforward control method, system and medium - Google Patents
SC-based L CC-HVDC receiving end direct current system feedforward control method, system and medium Download PDFInfo
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Abstract
The invention discloses an SC-based L CC-HVDC receiving end direct currentThe invention discloses a system feedforward control method, a system and a medium, and the implementation steps of the invention comprise the following steps of according to the exciting current I of a synchronous phase modulator SC after the power grid failurefGenerating a feedforward angle delta β, and subtracting the feedforward angle delta β from the initial firing angle β of the control strategy output to obtain the firing angle α of the inverter1The invention can obviously improve L CC-HVDC resistance to commutation failure, effectively reduce the probability of commutation failure or continuous commutation failure of the system, and is beneficial to quick recovery of an AC/DC system, improves the problem of low adjustment speed of an initial trigger angle β output by a control strategy of L CC-HVDC, simultaneously improves the stability of the system, and has the advantages of good compatibility and convenient technical upgrading and reconstruction.
Description
Technical Field
The invention relates to a high-voltage direct-current transmission technology, in particular to an SC-based L CC-HVDC receiving end direct-current system feedforward control method, system and medium, which are used for realizing the suppression of the probability of the occurrence of commutation failure through the synergistic effect of a synchronous phase modulator and a direct-current control system in a receiving end converter station under a fault.
Background
L CC-HVDC (high voltage direct current transmission system based on power grid commutation) has the characteristics of long transmission distance, large capacity, rapid and controllable transmission power, etc., but because of the use of a large number of semi-controlled devices, when in operation, system disturbance or failure can cause commutation failure and consume a large amount of reactive power.
The traditional control strategies mainly comprise an actual measurement type gamma control strategy of SIEMENS and a prediction type gamma control strategy of ABB. Although the actual measurement type γ control strategy of SIEMENS can improve the control accuracy of γ, when a fault occurs, the dc current Id suddenly increases and the dc voltage U increasesdA sharp drop, or both, may cause the arc-extinguishing angle to decrease so much suddenly that the controller fails to respond in time to a commutation failure. Although the response speed of the ABB prediction type gamma control strategy is high, the gamma angle is not obtained through measurement, and the deviation between the calculated angle and the actual angle under the fault is large; moreover, variations in the electrical quantities during commutation, e.g. DC current I, cannot be expecteddWith continued increase, the commutation angle may be larger than expected, making the actual gamma angle less than the minimum. When the receiving end is provided with the synchronous phase modulator, the effective short-circuit ratio of the system can be improved, and the voltage stability of the system is improved to a certain extent.
In summary, two commonly used shutdown angle control strategies based on the ABB and SIEMENS routes have defects, the reactive power consumption is increased due to the fact that the ABB prediction type gamma control strategy is forcibly reduced by α greatly, the risk of gamma overcompensation exists, the economical efficiency of system operation is reduced, and the SIEMENS actual measurement type gamma control strategy adopts PI regulation when a fault occurs, the speed is low, and the controller possibly fails to respond in time and then commutation fails.
Disclosure of Invention
The invention aims to solve the technical problems in the prior art, and provides a feedforward control method, a system and a medium for an SC-based L CC-HVDC receiving-end direct current system, which can obviously improve the resistance of L CC-HVDC to commutation failure, effectively reduce the probability of commutation failure or continuous commutation failure of the system, and facilitate the rapid recovery of an alternating current and direct current system, improve the problem of low regulation speed of an initial trigger angle β output by a L CC-HVDC control strategy, improve the stability of the system, and have the advantages of good compatibility and convenience in technical upgrading and reconstruction.
In order to solve the technical problems, the invention adopts the technical scheme that:
an SC-based L CC-HVDC receiving end direct current system feedforward control method comprises the implementation steps of:
1) detecting L whether an AC power grid connected with the CC-HVDC is in fault, and jumping to execute the next step when the fault occurs;
2) according to the excitation current I of the synchronous phase-modifier SCfGenerating a feed forward angle Δ β;
3) subtracting the feedforward angle delta β from the initial firing angle β of the control strategy output of L CC-HVDC to obtain the firing angle α of the inverter1；
4) According to the firing angle α1Generating a trigger pulse and transmitting to a valve side of L CC-HVDC;
5) and (6) judging L whether the bus voltage of the CC-HVDC is recovered to be within a second threshold value range, ending and exiting if the bus voltage is recovered to be within the second threshold value range, otherwise, skipping to execute the step 2).
Optionally, step 1) is preceded by a step of detecting L a busbar voltage of CC-HVDC, and step 1) is continued only if L a busbar voltage of CC-HVDC is not within a preset first threshold range).
Optionally, the fault detected L when the ac power grid connected to the CC-HVDC in step 1) has a fault includes a single-phase fault, and the single-phase fault is determined under the condition that a zero-sequence component occurs in the ac bus voltage of L CC-HVDC, and the zero-sequence component is greater than a set value.
Optionally, the fault which occurs when detecting L CC-HVDC connected AC power grid fault in step 1) includes three-phase fault, and the three-phase fault determining step is that the AC bus voltage of L CC-HVDC is converted by abc- αβ to obtain two components on α - β plane respectively corresponding to α axis and β axis, and a vector u rotating at angular speed is calculated according to the two components on corresponding α axis and β axisabIf the vector uabAnd the vector u before the faultabIf the difference between the normal values is larger than the set value, the three-phase fault is judged to occur.
Optionally, the excitation current I according to the synchronous phase modulator SC in step 2)fGenerating the feed forward angle Δ β specifically refers to phase modulating the synchronizationExcitation current I of machine SCfThe feedforward angle delta β is obtained through first-order low-pass filtering, gain, amplitude limiting and ascending/descending rate limiting in sequence.
Optionally, a gain factor G of the gainfThe value is 0.15.
Optionally, the lower limit and the upper limit of the clipping are 0 ° and 45 °.
Optionally, the detailed steps of L CC-HVDC control strategy output initial firing angle β in step 3) include:
s1) converting the direct current into a reference value IdrefThe output result of VDCO L and DC current I are controlled by low-voltage current-limitingdThe difference between the two output results after first-order low-pass filtering;
s2) passing the difference obtained in the step S1) through the output result of the current deviation control CEC and the direct current voltage reference value UdrefSumming the two, calculating the sum and DC voltage UdObtaining a voltage variation amount DeltaU by a difference between output results of the first-order low-pass filteringd(ii) a Subtracting the preset threshold value from the difference value obtained in the step S1) to obtain the current variation delta Id(ii) a According to the turn-off angle reference value gammarefAnd a turn-off angle gamma in one periodmeaObtaining the variation quantity delta gamma of the turn-off angle by the difference value between the minimum values;
s3) from the voltage change amount Δ UdAnd the current change amount delta IdAnd the variation delta gamma of the turn-off angle takes the maximum value;
s4) limiting the maximum value by the PI controller, and outputting the result as an initial firing angle β.
Furthermore, the present invention also provides an SC-based L CC-HVDC received dc system feedforward control system comprising a computer device programmed or configured to perform the steps of the L CC-HVDC received dc system feedforward control method, or a computer program stored on a storage medium of the computer device and programmed or configured to perform the L CC-HVDC received dc system feedforward control method.
In addition, the invention also provides a computer readable medium, and the computer readable medium stores the computer program of the L CC-HVDC receiving end direct current system feedforward control method.
Compared with the prior art, the invention has the following advantages:
1. the method can remarkably improve the resistance of L CC-HVDC to commutation failure, effectively reduce the probability of commutation failure or continuous commutation failure of the system, and is favorable for the rapid recovery of an AC/DC system.
2. Compared with the conventional ABB and SIEMENS control strategies for controlling the turn-off angle, the invention adds the following IfThe variable feedforward angle delta β output can improve the problem that overcompensation exists when an ABB strategy forcibly increases a fixed turn-off angle, and the feedforward strategy provided by the invention can output the feedforward control quantity delta β without PI regulation under a fault, so that the problem that the regulation speed is slow in the initial trigger angle β output by the L CC-HVDC control strategy is solved, and the stability of the system is improved.
3. According to the invention, the feedforward angle delta β is subtracted from the initial firing angle β output by the control strategy of L CC-HVDC to obtain the firing angle α of the inverter1According to the firing angle α1The trigger pulse is generated and transmitted to the valve side of L CC-HVDC, the control strategy of the L CC-HVDC can be compatible, and the control strategy has the advantages of good compatibility and convenience in technical upgrading and reconstruction.
Drawings
FIG. 1 is a schematic diagram of a basic flow of a method according to an embodiment of the present invention.
Fig. 2 is a detailed flowchart of a feedforward control strategy of a receiving-end dc system according to an embodiment of the present invention.
Fig. 3 is a control block diagram of a control strategy in which an embodiment of the present invention attaches a feedforward controller to L CC-HVDC.
FIG. 4 shows gain G in an embodiment of the present inventionfCurve of the effect of transmitting active power to the system.
Fig. 5 shows the single-phase-to-ground fault current waveforms for three cases in the embodiment of the present invention.
Fig. 6 is a α versus gamma curve for three cases of single-phase ground fault in an embodiment of the present invention.
Detailed Description
As shown in fig. 1, the implementation steps of the SC-based L CC-HVDC receiving end direct current system feedforward control method in this embodiment include:
1) detecting L whether an AC power grid connected with the CC-HVDC is in fault, and jumping to execute the next step when the fault occurs;
2) according to the excitation current I of the synchronous phase-modifier SCfGenerating a feed forward angle Δ β;
3) subtracting the feedforward angle delta β from the initial firing angle β of the control strategy output of L CC-HVDC to obtain the firing angle α of the inverter1；
4) According to the firing angle α1Generating a trigger pulse and transmitting to a valve side of L CC-HVDC;
5) and judging L whether the bus voltage of the CC-HVDC is recovered to the second threshold range, ending and exiting if the bus voltage is recovered to the second threshold range, otherwise, skipping to execute the step 2).
As shown in fig. 2, step 1) is preceded by a step of detecting a bus voltage of L CC-HVDC, and step 1) is continuously executed only when the bus voltage of L CC-HVDC is not within a preset first threshold range, in this embodiment, the first threshold range means that the bus voltage is between 500kV and 550kV, and when the high-voltage bus is within this range, the feedforward control link is not functional.
In the embodiment, the pass enable signal SENTo mark L whether the CC-HVDC has a fault, which results in the SC exciting current IfImmediately upon sudden increase, by the excitation current I of the synchronous phase-modulator SCfGenerating a feedforward control quantity Δ β to be added to an existing control strategy, e.g.As shown in fig. 3. Judging whether the bus voltage is within a first threshold range, if not, entering a fault detection link, and if no fault occurs, enabling a signal SENIf the value is 0, the control link is quitted; enable signal S for determining occurrence of failureENEntering a feedforward control link, exiting the feedforward control link when the bus voltage is restored to be within a second threshold range,
in this embodiment, the fault detected in step 1) to determine whether the ac power grid connected to L CC-HVDC has a fault includes a single-phase fault, and the single-phase fault is determined under the condition that a zero-sequence component occurs in the ac bus voltage of L CC-HVDC, and the zero-sequence component is greater than a set value EN1 is ═ 1; otherwise SENAnd (5) exiting the control strategy when the value is 0.
In the embodiment, the fault which is generated when detecting L CC-HVDC connected with the AC power grid in the step 1) includes a three-phase fault, and the three-phase fault is judged by converting the AC bus voltage of L CC-HVDC through abc- αβ to obtain two components which are respectively corresponding to a α shaft and an β shaft on a α - β plane, and calculating a vector u rotating at an angular speed according to the two components corresponding to the α shaft and the β shaftabIf the vector uabAnd the vector u before the faultabIf the difference between the normal values is larger than the set value, the three-phase fault is judged to occur. The measured three-phase alternating voltage ua、ubAnd ucTwo components U corresponding to α axis and β axis on the α - β plane are obtained through abc- αβ coordinate transformationαAnd UβTransformed to produce a vector u rotating at an angular velocity ωαβCan be represented as
If uαβIf the difference between the current value and the current value is larger than the set value during normal operation, the three-phase fault is judged to occur, and the enable signal S EN1 is ═ 1; otherwise SENAnd (5) exiting the control strategy when the value is 0.
In this embodiment, the exciting current I according to the synchronous phase modulator SC in step 2)fGenerating the feed forward angle Δ β specifically refers to modulating the excitation current I of the synchronous phase modulator SCfThe feedforward angle delta β is obtained by sequentially performing first-order low-pass filtering, gain, amplitude limiting and rising/falling rate limiting, in the embodiment, the lower limit of the amplitude limiting is 0 DEG, the upper limit of the amplitude limiting is 45 DEG, the amplitude overshoot of the turn-off angle gamma is prevented, the rising/falling rate limiting can limit the change rate of the feedforward angle delta β, and the influence of too fast change rate on the system operation stability is prevented, wherein the rising/falling rate limiting can limit the change rate of the feedforward angle delta β, and the system operation stability can be improved.
Referring to fig. 3, the detailed steps of L CC-HVDC control strategy output initial firing angle β in step 3) include:
s1) converting the direct current into a reference value IdrefThe output result of VDCO L and DC current I are controlled by low-voltage current-limitingdThe difference between the two output results after first-order low-pass filtering;
s2) passing the difference obtained in the step S1) through the output result of the current deviation control CEC and the direct current voltage reference value UdrefSumming the two, calculating the sum and DC voltage UdObtaining a voltage variation amount DeltaU by a difference between output results of the first-order low-pass filteringd(ii) a Subtracting the preset threshold value from the difference value obtained in the step S1) to obtain the current variation delta Id(ii) a According to the turn-off angle reference value gammarefAnd a turn-off angle gamma in one periodmeaObtaining the variation quantity delta gamma of the turn-off angle by the difference value between the minimum values;
s3) from the voltage change amount Δ UdAnd the current change amount delta IdAnd the variation delta gamma of the turn-off angle takes the maximum value;
s4) limiting the maximum value by the PI controller, and outputting the result as an initial firing angle β.
In FIG. 3, VDCO L is low voltage current limit control, CEC is current offset control, Idref、Udref、γrefRespectively a direct current reference value, a direct voltage reference value and a turn-off angle reference value, IfmTo excite electric fieldAfter the current measured value and the inversion side AC fault occur, the gamma angle is reduced rapidly, the gamma angle controller is enabled, the output turn-off angle change delta gamma generates an advanced trigger angle β through the PI link, the feedforward control is enabled, IfmAfter filtering, gain, clipping and rise/fall rate limiting, a delta β output is generated, reducing the firing angle α value.
In this embodiment, the gain factor G of the gainfThe value is 0.15. FIG. 4 shows the gain factor G of the gainfTaking three cases, G, of 0.05, 0.15 and 0.25 respectivelyfFor feedforward control of gain, G is increasedfThe output delta β value can be increased, and analysis and comparison are carried out on the active power P transmitted by the system in the fault occurrence and removal processesdCurve of variation of (G), gain factor GfThe value of the variable-frequency-ratio variable-frequency converter is increased, the falling amplitude of the inverter α after a feedforward control link is started can be increased, and the corresponding inverter station operates at a higher gamma value when in fault
The reduction, i.e. the reduction of the inverter transmission activity during a fault. Gain factor GfWhen the power is increased from 0.15 to 0.25, although the system is less prone to phase commutation failure, the transmission power of the system is greatly sacrificed, and the transmission power is reduced by about 0.48pu, namely 768 MW; gain factor GfWhen the value is reduced from 0.15 to 0.05, the transmission active power decline of the system is small, but the capability of resisting commutation failure is weakened. Gain coefficient G obtained by a large number of simulation testsfWhen the value is 0.15, the probability of phase commutation failure of the system can be effectively reduced, and meanwhile, the active transmission of the system cannot be greatly influenced, namely, the risk of over-compensation of the turn-off angle is greatly reduced by the value.
As shown in FIG. 5, Ivta、IvtbAnd IvtcRespectively, the valve side A, B, C three-phase line current, IdIs a direct current. The three cases in the figure are: case 1 only employs the SIEMENS control strategy; in case 2, on the basis of case 1, the receiving end is additionally provided with the SC, and the SC play roles independently; case 3 on the basis of case 2, the feedforward control strategy proposed by the invention is added. Inversion at 1.5sThe AC bus of the station is provided with an A-phase grounding fault through a transition resistor Rf70 Ω, the fault duration is 250ms (same fault settings). Case 1 had two commutation failures after a failure under the SIEMENS control strategy; in case 2, a receiving end is additionally provided with a synchronous phase modulator SC, so that the recovery characteristic of the system is improved to a certain extent, and only one phase commutation failure occurs; case 3 of adding feed-forward control, bus voltage drop when fault occurs leads to IfFig. 6 is a curve comparison of a shutdown angle gamma and a trigger angle α during fault, case 3 adopting a feed-forward control strategy instantly reduces the value of α to 90 DEG after fault, and the reduction amplitude is larger than that of cases 1 and 2 without feed-forward control, the case 1 is operated at a lower α angle during the fault continuous process, cases 1 and 2 both have the time when gamma is 0, compared with the case 3, a higher shutdown angle is maintained during fault, and the phase change failure is avoided, wherein case 1 respectively has two successive phase change failures at the moment of fault occurrence and at the moment of 1.70s, the moment of phase change failure occurrence is under the action of a direct current control system, a trigger angle command is reduced through PI regulation, so that α is reduced, case 2 only has one phase change failure at the moment of fault occurrence, and the higher trigger angle is maintained after the value of α is reduced.
In summary, the feedforward control method of the SC-based L CC-HVDC receiving end dc system of the present embodiment is implemented by using IfA feedforward control quantity delta β is generated to be added to a control link, the control strategy can ensure that an inversion side α is rapidly reduced after a fault, corresponding gamma is increased, the resistance capability of L CC-HVDC to commutation failure can be obviously improved, and rapid recovery of an AC/DC system is facilitated, a single-phase earth fault occurs at a receiving end through changing the resistance value of an earth resistor and analyzing by a large number of simulation experiments, when the severity of the fault is not high, commutation failure does not occur under a feedforward control strategy, commutation failure under an additional feedforward control strategy can be well inhibited, when the severity of the fault is high, the direct current system is difficult to be effectively recovered by a feedforward control strategy due to excessive voltage bus amplitude drop, but the generation of the direct current system can be effectively inhibitedAnd the continuous phase change fails, so that the damage to the system is reduced.
Furthermore, the present invention also provides an SC-based L CC-HVDC received dc system feedforward control system, comprising a computer device programmed or configured to perform the steps of the aforementioned L CC-HVDC received dc system feedforward control method, or a computer program stored on a storage medium of the computer device and programmed or configured to perform the aforementioned L CC-HVDC received dc system feedforward control method.
In addition, the SC-based L CC-HVDC receiving end direct current system feedforward control system further comprises an ultra-high voltage direct current protection system and a synchronous phase modulator SC which are connected with each other, the ultra-high voltage direct current protection system and the synchronous phase modulator SC which are connected with each other are respectively connected with computer equipment, and the synchronous phase modulator SC is used for providing excitation current I for the computer equipmentfThe invention also provides a computer readable medium, which stores the computer program of the feedforward control method of the L CC-HVDC receiving end DC system.
The above description is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiments, and all technical solutions belonging to the idea of the present invention belong to the protection scope of the present invention. It should be noted that modifications and embellishments within the scope of the invention may occur to those skilled in the art without departing from the principle of the invention, and are considered to be within the scope of the invention.
Claims (10)
1. An SC-based L CC-HVDC receiving end direct current system feedforward control method is characterized by comprising the following implementation steps:
1) detecting L whether an AC power grid connected with the CC-HVDC is in fault, and jumping to execute the next step when the fault occurs;
2) according to the excitation current I of the synchronous phase-modifier SCfGenerating a feed forward angle Δ β;
3) subtracting the feedforward angle delta β from the initial firing angle β of the control strategy output of L CC-HVDC to obtain the firing angle α of the inverter1；
4) According to the firing angle α1Generating a trigger pulse and transmitting to a valve side of L CC-HVDC;
5) and (6) judging L whether the bus voltage of the CC-HVDC is recovered to be within a second threshold value range, ending and exiting if the bus voltage is recovered to be within the second threshold value range, otherwise, skipping to execute the step 2).
2. The SC-based L CC-HVDC receive end dc system feedforward control method according to claim 1, further comprising a step of detecting a bus voltage of L CC-HVDC before step 1), and continuing to perform step 1) only when the bus voltage of L CC-HVDC is not within a preset first threshold range.
3. The feedforward control method for the SC-based L CC-HVDC receiving end DC system according to claim 1, wherein the fault detected in step 1) as whether the AC power grid connected with L CC-HVDC has a fault includes a single-phase fault, and the single-phase fault is determined under the condition that a zero-sequence component occurs in the AC bus voltage of L CC-HVDC, and the zero-sequence component is greater than a set value.
4. The feedforward control method of SC-based L CC-HVDC receiving end DC system according to claim 3, wherein the fault detected in step 1) when the AC power grid connected with L CC-HVDC has a fault includes a three-phase fault, and the step of determining the three-phase fault is that the AC bus voltage of L CC-HVDC is converted by abc- αβ to obtain two components on the a- β plane respectively corresponding to the a axis and the β axis, and a vector u rotating at an angular speed is calculated according to the two components on the corresponding a axis and the β axisabIf the vector uabAnd the vector u before the faultabIf the difference between the normal values is larger than the set value, the three-phase fault is judged to occur.
5. The feedforward control method for the SC-based L CC-HVDC receiving-end direct-current system according to claim 1, wherein the step 2) is performed according to an excitation current I of a synchronous phase modulator SCfGeneration of feed forward angle Δ β refers specifically to excitation of synchronous phase modulator SCCurrent IfThe feedforward angle delta β is obtained through first-order low-pass filtering, gain, amplitude limiting and ascending/descending rate limiting in sequence.
6. The SC-based L CC-HVDC receiving end direct current system feedforward control method according to claim 5, wherein the gain coefficient G of the gainfThe value is 0.15.
7. The SC-based L CC-HVDC receiving end direct current system feedforward control method according to claim 5, wherein the lower limit and the upper limit of the amplitude limiting are respectively 0 ° and 45 °.
8. The SC-based L CC-HVDC receiving end direct current system feedforward control method according to claim 5, wherein, the detailed step of L CC-HVDC control strategy output initial firing angle β in step 3) includes:
s1) converting the direct current into a reference value IdrefThe output result of VDCO L and DC current I are controlled by low-voltage current-limitingdThe difference between the two output results after first-order low-pass filtering;
s2) passing the difference obtained in the step S1) through the output result of the current deviation control CEC and the direct current voltage reference value UdrefSumming the two, calculating the sum and DC voltage UdObtaining a voltage variation amount DeltaU by a difference between output results of the first-order low-pass filteringd(ii) a Subtracting the preset threshold value from the difference value obtained in the step S1) to obtain the current variation delta Id(ii) a According to the turn-off angle reference value gammarefAnd a turn-off angle gamma in one periodmeaObtaining the variation quantity delta gamma of the turn-off angle by the difference value between the minimum values;
s3) from the voltage change amount Δ UdAnd the current change amount delta IdAnd the variation delta gamma of the turn-off angle takes the maximum value;
s4) limiting the maximum value by the PI controller, and outputting the result as an initial firing angle β.
9. An SC-based L CC-HVDC received dc system feedforward control system comprising a computer device, characterized in that the computer device is programmed or configured to perform the steps of the L CC-HVDC received dc system feedforward control method of any of claims 1-8, or a storage medium of the computer device has stored thereon a computer program programmed or configured to perform the L CC-HVDC received dc system feedforward control method of any of claims 1-8.
10. A computer readable medium having stored therein a computer program for the L CC-HVDC receive dc system feedforward control method of any of claims 1-8.
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