Control method, system and device for false blocking of high voltage direct current transmission system

Abstract

The application discloses a control method, system and device for false blocking of a high-voltage direct-current power transmission system, and relates to the technical field of high-voltage direct-current power transmission. The control method comprises the following steps: reading a direct-current voltage value of the high-voltage direct-current power transmission system measured by a control protection device; if the direct-current voltage value is less than a starting voltage value of low-voltage current limiting protection, determining whether the starting of the low-voltage current limiting protection is caused by measurement abnormality after short-time loss of voltage of a low-voltage arm of a direct-current transformer; if the result of the determination is that the starting of the low-voltage current limiting protection is caused by the measurement abnormality after short-time loss of voltage of the low-voltage arm of the direct-current transformer, performing adjustment control of the low-voltage current limiting protection; or if the result of the determination is that the starting of the low-voltage current limiting protection is not caused by the measurement abnormality after short-time loss of voltage of the low-voltage arm of the direct-current transformer, shielding the adjustment control of the low-voltage current limiting protection. The application solves the problem of false blocking of the high-voltage direct-current power transmission system caused by short-time loss of voltage of a low-voltage arm of a direct-current voltage divider of the high-voltage direct-current power transmission system due to lightning disturbance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high-voltage direct current transmission, and more particularly, it relates to a control method, system and device for false blocking of a high-voltage direct current transmission system. BACKGROUND

[0002] The basic principle of high-voltage direct current transmission is that the power transmission end of a direct current transmission system uses a converter to rectify three-phase alternating current into direct current, the electric energy is transmitted through a high-voltage direct current transmission line, and then the power receiving end uses a converter to invert the direct current into three-phase alternating current, and the electric energy is sent to the alternating current system of the power receiving end.

[0003] At present, in the case of lightning-caused ground potential disturbance of a converter station, the low-voltage arm of the direct current voltage divider of the high-voltage direct current transmission system may lose voltage for a short time, resulting in abnormal voltage measurement (i.e. the measured voltage rapidly decreases while the actual voltage does not change), which may further cause control misadjustment and thus trigger low-voltage false blocking of the system. SUMMARY

[0004] The purpose of the present application is to provide a control method, system and device for false blocking of a high-voltage direct current transmission system, which solves the problem of false blocking of a high-voltage direct current transmission system caused by lightning disturbance leading to short-time loss of voltage of the low-voltage arm of the direct current voltage divider of the high-voltage direct current transmission system when a pressure-sensitive resistor is additionally installed in the direct current voltage divider part of the high-voltage direct current transmission system.

[0005] The above technical purpose of the present application is achieved by the following technical scheme:

[0006] In a first aspect, the present application provides a control method for false blocking of a high-voltage direct current transmission system, which is applied to a control and protection device of the high-voltage direct current transmission system, wherein the high-voltage direct current transmission system is equipped with a pressure-sensitive resistor in the direct current voltage divider part, and the method comprises:

[0007] reading a direct current voltage value of the high-voltage direct current transmission system measured by the control and protection device;

[0008] if the direct current voltage value is less than the starting voltage value of the low-voltage current limiting protection, determining whether the starting of the low-voltage current limiting protection is caused by abnormal measurement after short-time loss of voltage of the low-voltage arm of the direct current transformer;

[0009] if the determination result is that the starting of the low-voltage current limiting protection is caused by abnormal measurement after short-time loss of voltage of the low-voltage arm of the direct current transformer, performing adjustment control of the low-voltage current limiting protection; or if the determination result is that the starting of the low-voltage current limiting protection is not caused by abnormal measurement after short-time loss of voltage of the low-voltage arm of the direct current transformer, shielding the adjustment control of the low-voltage current limiting protection.

[0010] In an implementation, it is determined whether the starting of the low-voltage current limiting protection is caused by the measurement abnormality after the short-time loss of voltage of the low-voltage arm of the DC transformer, specifically:

[0011] reading a DC current value of the HVDC power transmission system measured by the control protection device;

[0012] calculating an absolute value of a current difference value between the DC current value and a DC current rated value;

[0013] if the absolute value of the current difference value is greater than a first threshold value, the starting of the low-voltage current limiting protection is caused by the measurement abnormality after the short-time loss of voltage of the low-voltage arm of the DC transformer; or

[0014] if the absolute value of the current difference value is not greater than the first threshold value, the starting of the low-voltage current limiting protection is not caused by the measurement abnormality after the short-time loss of voltage of the low-voltage arm of the DC transformer.

[0015] In an implementation, the first threshold value is determined by a DC voltage rated value, the DC voltage rated value and a starting voltage value of the low-voltage current limiting protection.

[0016] In an implementation, an expression of the first threshold value is: M1=k*I dn (U dn -U d_high ) / U dn , wherein M1 is the first threshold value, k is a constant, U dn is the DC voltage rated value, I dn is the DC current rated value, and U d_high is the starting voltage value of the low-voltage current limiting protection.

[0017] In an implementation, if the absolute value of the difference value is not greater than the first threshold value, a first interval time is waited for, a plurality of DC current values measured by the control protection device are read again, an absolute value of a current difference value between each read DC current value and the DC current rated value is calculated, and if the absolute value of the current difference value between each read DC current value and the DC current rated value is not greater than the first threshold value, the regulation control of the low-voltage current limiting protection is shielded.

[0018] In an implementation, after the low-voltage current limiting protection is shielded, the method further comprises:

[0019] reading a DC voltage value measured by the control protection device at a current time;

[0020] calculating an absolute value of a voltage difference value between the DC voltage value and a DC voltage rated value;

[0021] if the absolute value of the voltage difference value is less than a second threshold value, the regulation control of the low-voltage current limiting protection is opened; or

[0022] If the absolute value of the voltage difference is not less than the second threshold value, waiting for a preset second interval time, re-reading the DC voltage value measured by the control protection device, until the absolute value of the voltage difference between the DC voltage value and the DC voltage rated value is less than the second threshold value, opening the regulation control of the low-voltage current limiting protection.

[0023] In an implementation, the second threshold value is determined by the DC voltage rated value and the starting voltage value of the low-voltage current limiting protection.

[0024] In an implementation, the expression of the second threshold value is: M2=k* (U (U dn -U d_high ), wherein M2 is the second threshold value, k is a constant, U dn is the DC voltage rated value, and U d_high is the starting voltage value of the low-voltage current limiting protection.

[0025] In the second aspect, the application provides a control system for false blocking of a high-voltage direct-current power transmission system, applied to a control protection device of the high-voltage direct-current power transmission system, wherein the high-voltage direct-current power transmission system is equipped with a voltage-dependent resistor in a DC voltage divider part, and the system comprises:

[0026] a data reading module, configured to read a DC voltage value of the high-voltage direct-current power transmission system measured by the control protection device;

[0027] a judging module, configured to judge whether the starting of the low-voltage current limiting protection is caused by measurement abnormality after short-time voltage loss of a low-voltage arm of a DC transformer, if the DC voltage value is less than the starting voltage value of the low-voltage current limiting protection;

[0028] a control module, configured to execute the regulation control of the low-voltage current limiting protection, if the result of the judgment is that the starting of the low-voltage current limiting protection is caused by measurement abnormality after short-time voltage loss of the low-voltage arm of the DC transformer; or, configured to shield the regulation control of the low-voltage current limiting protection, if the result of the judgment is that the starting of the low-voltage current limiting protection is not caused by measurement abnormality after short-time voltage loss of the low-voltage arm of the DC transformer.

[0029] In the third aspect, the application provides a control protection device applied to a high-voltage direct-current power transmission system, configured to execute the steps of the control method for false blocking of a high-voltage direct-current power transmission system provided in the first aspect.

[0030] Compared with the prior art, the application has the following beneficial effects:

[0031] The control method provided by the application, based on the characteristics of high coupling between the DC voltage and the DC current of the high-voltage DC power transmission system, further judges whether the DC current value is abnormal in the state of abnormal DC voltage value, so as to confirm again whether the voltage abnormality is caused by real voltage change or caused by measurement abnormality after short-time voltage loss of the low-voltage arm of the DC transformer; after confirming that it is voltage measurement abnormality, the source link (VDCOL, i.e. low-voltage current limiting protection) of the control misadjustment is shielded, and the prevention control for the subsequent mislock is simply and efficiently realized, and the smooth transition of the high-voltage DC power transmission system to the normal state is ensured. BRIEF DESCRIPTION OF DRAWINGS

[0032] The accompanying drawings, which are included to provide a further understanding of the embodiments of the application and constitute a part of this application, illustrate embodiments of the application and are used to explain the embodiments of the application. In the drawings:

[0033] Figure 1 It is a structural schematic diagram of the DC voltage divider;

[0034] Figure 2 It is an equivalent circuit diagram of the DC voltage divider;

[0035] Figure 3 It is a basic control characteristic diagram of the high-voltage DC power transmission system;

[0036] Figure 4 It is a low-voltage current limiting control characteristic diagram;

[0037] Figure 5 It is a voltage loss process schematic diagram of the low-voltage arm of the DC voltage divider;

[0038] Figure 6 It is a variation diagram of the system operating point after voltage loss of the low-voltage arm of the DC voltage divider (the low-voltage arm voltage is higher than UD_High);

[0039] Figure 7 It is a variation diagram of the system operating point after voltage loss of the low-voltage arm of the DC voltage divider (the low-voltage arm voltage is slightly lower than UD_High);

[0040] Figure 8 It is a variation diagram of the system operating point after voltage loss of the low-voltage arm of the DC voltage divider (the low-voltage arm voltage is significantly lower than UD_High);

[0041] Figure 9 It is a schematic diagram of the DC voltage, DC current and trigger angle waveforms of the low-voltage arm of the DC voltage divider of pole I;

[0042] Figure 10 It is a schematic diagram of the DC voltage, DC current and trigger angle waveforms of the low-voltage arm of the DC voltage divider of pole II;

[0043] Figure 11A flowchart of a control method for a high-voltage direct-current power transmission system false blocking provided by an embodiment of the present application is shown.

[0044] Figure 12 A principle block diagram of a control system for a high-voltage direct-current power transmission system false blocking provided by an embodiment of the present application is shown. DETAILED DESCRIPTION

[0045] In order to make the objectives, technical solutions, and advantages of the present application clearer, further detailed descriptions will be given to the present application in combination with embodiments and drawings, and the illustrative embodiments of the present application and their descriptions are only used to explain the present application, and not as a limitation to the present application.

[0046] It should be noted that the term "include" or "may include" used in various embodiments of the present application indicates the existence of the claimed function, operation, or element, and does not limit the addition of one or more functions, operations, or elements. In addition, as used in various embodiments of the present application, the terms "include", "have", and their synonyms only mean to indicate specific features, numbers, steps, operations, elements, components, or combinations of the foregoing, and should not be understood as first excluding the existence or addition of one or more other features, numbers, steps, operations, elements, components, or combinations of the foregoing, or as first excluding the possibility of adding one or more features, numbers, steps, operations, elements, components, or combinations of the foregoing.

[0047] It should be understood that terms such as "first", "second", etc. are only used for description purposes, and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined with "first", "second" can explicitly or implicitly include one or more of the features. In the description of the present application, the meaning of "multiple" is two or more, unless otherwise specifically limited.

[0048] The DC voltage divider is a key device for real-time monitoring of line voltage in an ultra-high voltage direct-current power transmission system, and its measurement result directly affects the reliability of the control and protection system. Its structure is shown in Figure 1 The DC voltage divider realizes two-stage voltage transformation using the principle of resistance-capacitance voltage division, the first stage reduces 800kV primary voltage to 70V and introduces a balance module. In the subsequent voltage division module, the 70V input voltage is changed to 5V, and after passing through an isolation amplifier, it is input to the control and protection system.

[0049] In combination with the actual operating parameters of the converter station, the equivalent circuit of the DC voltage divider is shown in Figure 2 Figure 2 ​It can be seen that the DC voltage divider adopts the principle of resistance-capacitance voltage division, and the high-voltage arm is composed of resistor R1 and capacitor C1, and the low-voltage arm is composed of resistor R2 and capacitor C2, which jointly complete the measurement of DC voltage. At the same time, the resistors and capacitors of the high-voltage and low-voltage arms satisfy the following matching principle, that is: The function of the discharge gap is to rapidly conduct and discharge the surge energy after lightning impulse occurs, thereby limiting the voltage amplitude and preventing the equipment from being damaged due to overvoltage. The varistor is connected in series in the protection gap circuit to ensure that a certain voltage exists in the circuit after the discharge gap is broken down. The analysis of the response characteristics of the low-voltage arm of the DC voltage divider of the HVDC transmission system after short circuit is as follows: assuming that there is no varistor, the circuit analysis is performed. Under normal operating conditions, once the discharge gap is broken down due to lightning disturbance, etc., the air gap is restored. Figure 2

[0050] Considering that the DC voltage U1 maintains an amplitude of V D during the entire process, and C3 is ignored, the transient response of U2 satisfies: It can be seen from the above formula that, at the moment of recovery of the short circuit of the low-voltage arm of the DC voltage divider, due to the charging process of the capacitor of the low-voltage arm, the voltage of U2 still remains 0, and gradually changes to the steady-state value through a first-order dynamic response, and the time constant satisfies: .

[0051] The current margin control characteristic is a common control method for maintaining the stable operation of the HVDC transmission system, as shown in Figure 3 . The rectifier side characteristic is composed of two straight lines of constant current and minimum trigger angle; the inverter side characteristic is composed of two characteristics of constant DC current and constant off angle or constant DC voltage. In order to avoid the simultaneous operation of the current regulators at both ends, causing unstable regulation, the constant value of the inverter side current regulator is generally 0.1 pu smaller than that of the DC side, which is the current margin. During normal operation, the rectifier side operates in the constant current mode, and the inverter side operates in the constant off angle or constant DC voltage mode. When the AC voltage of the rectifier side decreases or the AC voltage of the inverter side increases significantly, the rectifier enters the minimum trigger angle limit, and the DC current is less than 0.1 pu of the steady-state value, and the inverter will automatically switch to the constant DC current control. The combination of the control characteristics of the rectifier and the inverter is the current margin control characteristic, so that the DC current transmitted by the HVDC transmission system will not fluctuate greatly due to the change of the voltage of the connected AC system, thereby ensuring the stable transmission of the DC power.

[0052] ​For the low-voltage current limiting control of UHVDC transmission system, the control objectives of rectifier side and inverter side are DC current and voltage respectively. However, if the steady-state control strategy is still adopted after system fault, the voltage drop will lead to a significant reduction of arc extinction angle γ of inverter side, and the serious risk of commutation failure of converter, and the DC current surge will bring serious impact on system equipment. Therefore, the low-voltage current limiting (VDCOL) link is added in the control strategy design of rectifier side and inverter side, and its external characteristic curve is shown in FIG. 1. Figure 4 In the VDCOL link, the input variable is DC line midpoint voltage U dc_middle , and the output variable is constant current control instruction value I dcref , and the minimum value between the two is taken as the input current reference value of subsequent PI link. According to the curve characteristics in the figure, when the system fault leads to abnormal drop of DC voltage, VDCOL will automatically reduce the DC line current instruction value according to the drop degree of voltage, and reduce the reactive power absorbed by the converter, which is beneficial to the recovery of subsequent AC voltage, and ensures the uninterrupted and stable power transmission when the DC voltage is abnormal; after the fault disappears, the current instruction value increases slowly under the control of VDCOL link, which improves the transient characteristics of AC and DC voltages in the fault recovery process.

[0053] The voltage loss process of low-voltage arm of DC voltage divider is divided into complete voltage loss (without pressure-sensitive resistor) and partial voltage loss (with pressure-sensitive resistor). For complete voltage loss, according to the above transient response expression and time constant expression, it can be known that this transient process is in the time scale of hundreds of milliseconds. It takes 68.5 milliseconds to recover to 0.35pu (higher than the setting value of low-voltage protection), 256 milliseconds to recover to 0.8pu (higher than the upper limit setting value of VDCOL), and 477 milliseconds to end the transient process. For partial voltage loss, i.e. under the condition of assembling pressure-sensitive resistor, the dynamic process after the breakdown of discharge gap is more complex. Firstly, under the voltage condition of discharge gap breakdown, the resistance of pressure-sensitive resistor will quickly decrease to ohm level or even lower, but it is not 0, at this time, the voltage of low-voltage arm cannot be equivalent to instant drop to 0, but needs to go through a very fast transient discharge process. Secondly, in the process of capacitor discharge and rapid reduction of low-voltage arm voltage, the resistance of pressure-sensitive resistor is also dynamically changing, and after the voltage decreases, the resistance will quickly increase, which makes the time constant of discharge loop increase sharply, resulting in the rapid slowing down of the descending speed of low-voltage arm voltage, and even the beginning of reverse charging, until the discharge gap is restored, and the capacitor charging process starts again with the current state as the initial state.

[0054] After the lightning impulse causes the instantaneous change of ground grid potential, the high potential difference leads to the short-time breakdown of discharge gap, and the dynamic process of voltage loss of DC voltage divider low-voltage arm is shown in FIG. 2. Figure 5As shown, although the discharge gap is broken, the discharge gap-varistor path is not the main energy discharge path caused by the ground potential change (the ground potential can naturally drop even if it is not broken, and the energy is discharged through the ground), therefore, the voltage loss process of the low-voltage arm of the DC voltage divider can be approximately equivalent to that the low-voltage arm is only connected with a variable resistor Rc whose resistance value first decreases and then increases, and the resistance value is only related to the absolute value of the voltage across the resistor. At the moment of the discharge gap breakdown, the varistor withstands overvoltage, and the resistance value decreases to the ohmic level or even lower. At this time, R2||Rc≈Rc, and the time constant RcC2 is in the microsecond level. Although the time constant is very small, it cannot be ignored in the lightning disturbance analysis scenario. With the recovery of the resistance value of the varistor, the discharge time constant R2||Rc·C2 of C2 increases rapidly, and the voltage of the low-voltage arm decreases and even rises. Until the discharge gap is restored, C2 continues to charge slowly with the time constant R2C2, and the voltage is restored.

[0055] During the voltage loss and charging recovery process of the low-voltage arm of the DC voltage divider, the primary electrical parameters of the DC system are normal. However, during this process, the secondary measurement deviation may cause abnormal operation of the control system, and even trigger the protective shutdown of the DC system. The following will analyze in detail in combination with the DC system operating characteristic curve. After the voltage loss of the low-voltage arm of the DC voltage divider, the actual operating point of the system does not change, but the operating point observed by the secondary system on the rectifier side instantaneously decreases. According to the different decrease amplitudes, three types of consequences can be caused. The first is that the electrical quantities on the DC primary side of the system are not disturbed at all. The second is that the system is slightly disturbed, but the overall process is controlled. The third is that the system is significantly disturbed and there is a loss of control process.

[0056] For the first type, it is assumed that under the action of the varistor, the discharge gap is broken, but the voltage loss of the low-voltage arm is not serious, and the voltage is still higher than the VDCOL start voltage UD_High. The electrical quantities on the DC primary side will not be disturbed at all, and the change of the operating point of the system is as shown in Figure 6 As shown, under the normal operating state of the system, the control on the rectifier side is stable in the constant current state. After the voltage loss of the low-voltage arm of the DC voltage divider, the operating point of the system observed by the secondary system on the rectifier side decreases from the red point to the yellow point in the figure. At this time, the measured current does not change, VDCOL is not started, and the current command also does not change, so the rectifier side will not perform additional control adjustment. In addition, the electrical quantities and the secondary system on the inverter side are normal, so the inverter side will not perform additional control adjustment. With the charging of the low-voltage arm, the measured voltage of the secondary system on the rectifier side gradually recovers to the correct value, as shown by the gray arrow in the figure. During the entire process, the real electrical quantities of the DC system are not disturbed at all.

[0057] Assuming the system experiences a slight disturbance but the overall process remains under control, and that the low-voltage arm experiences significant voltage loss after the discharge gap breaks down, with the voltage slightly below the VDCOL start-up voltage UD_High, the DC primary side electrical quantities will be slightly disturbed, but the overall process will remain under control. The changes in the system operating point are as follows: Figure 7 As shown, the system operating point observed by the rectifier-side secondary system drops from the red point to the yellow point. Although the measured current remains unchanged, VDCOL starts, and the control system increases the rectifier-side firing angle (reducing the DC voltage) in an attempt to reduce the DC current, shifting the observed operating point, which has deviated from the operating characteristic curve, towards one side of the curve (leftward). Consequently, the actual operating point deviates from the steady-state operating point and also moves to the lower left. After detecting the actual operating point shifting to the lower left (reduced voltage and current), the inverter side, due to the small deviation, can use constant turn-off angle control to maintain the operating point near the operating characteristic curve, and may also switch to constant current control mode. Subsequently, as the low-voltage arm charges, the measured voltage of the rectifier-side secondary system gradually rises and recovers, and the system operating point smoothly returns to the steady-state operating point. Throughout this process, the rectifier-side control makes a misjudgment due to measurement issues, but this can be mitigated by appropriate adjustments to the inverter-side control during the low-voltage arm charging process, ensuring a smooth system recovery. The operating point is controlled throughout and moves only within the green area shown in the figure.

[0058] Assuming the system is subjected to significant disturbances and experiences a runaway process, and that the low-voltage arm suffers severe voltage loss after the discharge gap breaks down, with the voltage significantly lower than the VDCOL start-up voltage UD_High, the DC primary side electrical quantities will be significantly disturbed and experience a runaway process. The changes in the system operating point are as follows: Figure 8 As shown, the system operating point observed by the rectifier-side secondary system drops sharply from the red point to the yellow point, VDCOL is activated, and the control system continuously increases the rectifier-side firing angle (reducing the DC voltage) in an attempt to quickly reduce the DC current. This causes the actual operating point to deviate from the steady-state operating point, continuously moving to the lower left. After the inverter side switches from constant turn-off angle control to constant current control, the rectifier side continues to reduce the current. Once the current drops below the inverter-side current command value, the control trend on the inverter side changes to increasing the DC current by reducing the DC voltage. Subsequently, both the rectifier-side and inverter-side controls exhibit a voltage-reducing trend, resulting in mutual amplification and non-convergence of control effects. The system deviates further and further from the steady-state operating point, and the DC voltage becomes uncontrolled and drops rapidly. In summary, the magnitude of the instantaneous voltage loss on the low-voltage arm of the DC voltage divider determines the subsequent control system response. The more severe the voltage loss, the more difficult it is for the system to regulate and recover, and it may even trigger DC voltage runaway, leading to a series of consequences such as low-voltage protection activation.

[0059] On this basis, the response characteristics of the system under the condition of low-voltage arm voltage loss caused by discharge gap breakdown of the DC voltage divider low-voltage arm are simulated and analyzed. Considering that the low-voltage arm voltage is 70 V under normal operating conditions, the remaining voltage Uremof the low-voltage arm after voltage loss is set to decrease from 65 V to 0 V by 5 V intervals. The remaining voltage U rem The five conditions with a voltage greater than or equal to 45 V belong to case one analyzed above (no disturbance to electrical quantities). After the low-voltage arm of the DC voltage divider loses voltage, its voltage decreases from the corresponding U rem begins to recover smoothly, during which the trigger angle has no adjustment process. U rem The two conditions with voltages of 40 V and 35 V belong to case two analyzed above (slightly disturbed but the overall process is controlled), and the trigger angle has an adjustment process, but control convergence can be achieved. The trigger angle deviates briefly before returning to the normal operating value, after which the DC voltage recovers smoothly. The remaining voltage U rem The seven conditions with voltages less than or equal to 30 V belong to case three analyzed above (significantly disturbed and out of control), and the DC voltage measurement value experiences a short recovery process after voltage loss, after which the system loses the steady-state operating point and the voltage begins to accelerate downward. At the same time, the more serious the low-voltage arm voltage loss, the shorter the normal voltage recovery process (i.e., the earlier the out-of-control inflection point), the faster the voltage drops, and the deeper the voltage drop. In general, the more serious the low-voltage arm voltage loss caused by the discharge gap breakdown of the DC voltage divider low-voltage arm, the more obvious the disturbance to the system, and the more difficult the voltage recovery. The simulation results show that, under the condition of single voltage loss, considering that the start value of the Jin-Su DC low-voltage protection is 0.35 pu, if the remaining voltage of the Jinping station low-voltage arm after voltage loss still exceeds 30 V, the low-voltage protection can be ensured not to act. In combination with the above analysis, under the condition of single lightning disturbance, if no pressure-sensitive resistor is installed, the remaining voltage of the low-voltage arm after voltage loss is 0 V, and under the combined action of low-voltage arm voltage charging recovery and control out of control, the voltage is still negative 80 ms after voltage loss, and the voltage value is recovered to about 0 V after 150 ms, which is far lower than the low-voltage protection action value of 0.35 pu, and the low-voltage protection will act; after the installation of the pressure-sensitive resistor, the low-voltage arm remaining voltage corresponding to the first lightning in this event is 50 V and 52.5 V (pole I and pole II), and the low-voltage protection will not act. The final action of the low-voltage protection of pole I is due to three lightning disturbances in a short period of time, and each voltage loss has a large amplitude, which synchronously causes more difficult recovery, and the voltage gradually decreases and eventually loses control when the low-voltage arm charging is not completed. Pole II did not cause the low-voltage protection to act because the second voltage loss had a lighter amplitude, and the voltage recovered to a higher degree before the third voltage loss, so the third voltage loss did not cause the system DC voltage to lose control.

[0060] In summary, the above-described analysis process is as follows:

[0061] 1) The low-voltage arm voltage loss is essentially caused by the rapid recovery of the resistance value of the voltage-dependent resistor, which leads to the "fast discharge and slow charging" phenomenon of capacitor C2. During this process, the time constant of the RC discharge circuit changes by several orders of magnitude.

[0062] 2) The rapid discharge process of the capacitor is synchronized with the recovery of the resistance value of the voltage-dependent resistor. The final voltage loss amplitude depends on the inflection point of C2 "from discharge to charge", which is not only affected by the parameters of the voltage-dependent resistor, but also by the complex effects of the peak value, shape, and duration of the lightning disturbance waveform, and has certain randomness.

[0063] 3) After the low-voltage arm loses voltage, the voltage measurement value of the DC voltage changes, which is not only related to the voltage loss of the low-voltage arm, but also related to the actual DC voltage. In this incident, the control action caused the actual DC voltage to continuously decrease, and the low-voltage arm lost voltage multiple times, resulting in a "step-like" drop in the measured voltage.

[0064] 4) Without the voltage-dependent resistor, the complete loss of voltage in the low-voltage arm of the DC voltage divider is equivalent to the variable resistor Rc directly jumping between "high resistance" and "short circuit" states.

[0065] Based on the above analysis of the low-voltage arm voltage loss mechanism and the dynamic response characteristics of the DC control system after voltage loss, in the actual scene, multiple lightning strikes caused the station grounding grid voltage to rise multiple times, resulting in multiple breakdowns of the discharge gap of the low-voltage arm of the DC voltage divider of pole I and pole II, leading to the instantaneous voltage loss of the low-voltage arm of the DC voltage divider.

[0066] As shown in Figure 9 and 10 , the Figure 9 and Figure 10In terms of the vertical coordinates of the three parts from top to bottom, the vertical coordinates are direct current voltage, direct current and triggering angle in sequence. In the time period in which the measured value of the direct current voltage of pole I falls from 800 kV to 0 kV in the event, the waveforms of the direct current voltage, the direct current and the triggering angle of the PCP control host of pole I and pole II are given. It can be seen that the discharge gap breakdown causes the low-voltage arm to lose voltage three times, and the voltage gradually decreases. Finally, the measured voltage of pole I is lower than the under-voltage protection threshold of the direct current line after the third voltage loss, and the protection action sends a restart signal after 80 ms delay; the measured voltage of pole II is still higher than the under-voltage protection threshold of the direct current line after the third voltage loss, and the protection does not act. In summary, compared with the bipolar blocking event caused by the voltage loss of the low-voltage arm of the direct current voltage divider of the converter station without the pressure-sensitive resistor, the low-voltage arm in this event suffers three obvious voltage losses before the restart of the direct current system, and the disturbance times are more. However, due to the fact that the pressure-sensitive resistor is connected in series in the discharge gap circuit, there is still a certain residual voltage in the circuit after the discharge gap breakdown, and the value of the residual voltage has a certain randomness. Until the low-voltage protection of pole I triggers the restart logic after the third voltage loss, and the low-voltage protection of pole II does not act, therefore, although the pressure-sensitive resistor can effectively prevent the low-voltage protection action caused by the voltage loss of the low-voltage arm due to a single lightning strike after being installed. However, if the low-voltage arm suffers multiple lightning disturbances in a short time, and each voltage loss has a large amplitude, and the voltage loss is superimposed again when the charging of the low-voltage arm has not been completed, it is easy to cause the voltage to gradually decrease and finally lose control, thereby causing the false blocking phenomenon.

[0067] Therefore, in order to solve the problem of false blocking control, the embodiment of the present application provides a control method for false blocking of a high-voltage direct current power transmission system. The method is based on the characteristics of high coupling between the direct current voltage and the direct current of the high-voltage direct current power transmission system, and further judges whether the direct current value is abnormal under the condition of abnormal direct current voltage value, so as to further confirm whether the voltage abnormality is caused by real voltage change or caused by measurement abnormality after the low-voltage arm of the direct current transformer loses voltage for a short time. After confirming that the voltage measurement is abnormal, the source link (VDCOL, i.e. low-voltage current limiting protection) of false regulation is shielded, and the prevention and control of subsequent false blocking is simply and efficiently realized, and the stable transition of the high-voltage direct current power transmission system to the normal state is ensured.

[0068] The control method for false blocking of a high-voltage direct current power transmission system provided by the embodiment of the present application will be described in detail below in combination with specific implementation manners. It should be noted that the method is applied to a control and protection device of a high-voltage direct current power transmission system, and the high-voltage direct current power transmission system is provided with a pressure-sensitive resistor in the direct current voltage divider part, as shown in FIG. 1. Figure 11 The method comprises the following steps.

[0069] S1101, reading the direct current voltage value of the high-voltage direct current power transmission system measured by the control and protection device.

[0070] In the embodiment, first, the control and protection device of the HVDC transmission system is responsible for accurate monitoring, regulation and protection of the converter stations (rectifier stations and inverter stations) and DC transmission lines under normal and fault conditions, to ensure reliable transmission of electric energy according to the established target, which is the common knowledge in the technical field. Therefore, the embodiment does not make redundant description of the control and protection device.

[0071] Generally, the measurement frequency of the control and protection device is 0.1 ms / time, so the DC voltage value measured every 0.1 ms is also read in the embodiment.

[0072] S1102, if the DC voltage value is less than the starting voltage value of the low-voltage current limiting protection, it is judged whether the starting of the low-voltage current limiting protection is caused by the measurement abnormality after the short-time loss of voltage of the low-voltage arm of the DC transformer.

[0073] In the embodiment, the read DC voltage value is detected to judge whether the starting of the low-voltage current limiting protection is caused by the measurement abnormality after the short-time loss of voltage of the low-voltage arm of the DC transformer. Specifically, the DC current value of the HVDC transmission system measured by the control and protection device is read; the current difference absolute value of the DC current value and the DC current rated value is calculated; if the current difference absolute value is greater than a first threshold value, the starting of the low-voltage current limiting protection is caused by the measurement abnormality after the short-time loss of voltage of the low-voltage arm of the DC transformer; or if the current difference absolute value is not greater than the first threshold value, the starting of the low-voltage current limiting protection is not caused by the measurement abnormality after the short-time loss of voltage of the low-voltage arm of the DC transformer. The first threshold value is determined by the DC voltage rated value, the DC voltage rated value and the starting voltage value of the low-voltage current limiting protection. Specifically, |I d -I dn |>M1(1),M1=k*I dn (U dn -U d_high ) / U dn , wherein M1 is the first threshold value, k is a constant, U dn is the DC voltage rated value, I dn is the DC current rated value, and U d_high is the starting voltage value of the low-voltage current limiting protection. It should be noted that k is 0.3 in actual calculation.

[0074] S1103, if the judgment result is that the starting of the low-voltage current limiting protection is caused by the measurement abnormality after the short-time loss of voltage of the low-voltage arm of the DC transformer, the regulation control of the low-voltage current limiting protection is executed; or if the judgment result is that the starting of the low-voltage current limiting protection is not caused by the measurement abnormality after the short-time loss of voltage of the low-voltage arm of the DC transformer, the regulation control of the low-voltage current limiting protection is shielded.

[0075] Specifically, if formula (1) is established, it is considered that the direct current also changes after the direct voltage changes, the VDCOL starts and is not caused by measurement abnormality, and then the normal VDCOL adjustment control is entered.

[0076] If formula (1) is not established, it is considered that the direct current does not change after the direct voltage changes, the VDCOL start may be caused by measurement abnormality after the low-voltage arm short-time voltage loss, and after waiting for a first interval time, the measured multiple direct current values are repeatedly read, the current difference absolute value of each read direct current value and the direct current rated value is calculated, and if the current difference absolute value of each read direct current value and the direct current rated value is not greater than the first threshold value, the low-voltage current limiting protection adjustment control is shielded.

[0077] If the judgment of formula (1) is not established for multiple times, it is considered that the low-voltage current limiting protection start is not caused by measurement abnormality after the low-voltage arm short-time voltage loss of the direct current transformer, and the low-voltage current limiting protection adjustment control can be shielded. It should be noted that the first interval time can be 1 ms, 2 ms, etc.

[0078] In some embodiments, after shielding the low-voltage current limiting protection, the method further comprises:

[0079] reading the direct voltage value measured by the control protection device at the current time;

[0080] calculating the voltage difference absolute value of the direct voltage value and the direct voltage rated value;

[0081] If the voltage difference absolute value is less than a second threshold value, the low-voltage current limiting protection adjustment control is opened; or

[0082] If the voltage difference absolute value is not less than the second threshold value, the low-voltage current limiting protection adjustment control is opened until the voltage difference absolute value of the direct voltage value and the direct voltage rated value is less than the second threshold value after waiting for a preset second interval time and re-reading the direct voltage value measured by the control protection device.

[0083] Specifically, the second threshold value is determined by the direct voltage rated value and the start voltage value of the low-voltage current limiting protection. The expression of the second threshold value is: M2=k* (U (U dn -U d_high ), wherein M2 is the second threshold value, k is a constant, U dn is the direct voltage rated value, and U d_high is the start voltage value of the low-voltage current limiting protection.

[0084] It should be noted that the second interval time can be 10 ms, 20 ms, etc.

[0085] Figure 12The principle block diagram of the control system of the high-voltage direct current transmission system false blocking provided by the embodiment of the present application, the embodiment of the present application further provides a control system of a high-voltage direct current transmission system false blocking, which is applied to a control protection device of a high-voltage direct current transmission system, wherein the high-voltage direct current transmission system is provided with a voltage-dependent resistor in a direct current voltage divider part, and the system comprises:

[0086] The data reading module 1201 is configured to read a direct current voltage value of the high-voltage direct current transmission system measured by the control protection device.

[0087] The judgment module 1202 is configured to judge whether the start of the low-voltage current limiting protection is caused by the measurement abnormality after the short-time voltage loss of the low-voltage arm of the direct current transformer if the direct current voltage value is less than the start voltage value of the low-voltage current limiting protection.

[0088] The control module 1203 is configured to perform the adjustment control of the low-voltage current limiting protection if the judgment result is that the start of the low-voltage current limiting protection is caused by the measurement abnormality after the short-time voltage loss of the low-voltage arm of the direct current transformer, or to shield the adjustment control of the low-voltage current limiting protection if the judgment result is that the start of the low-voltage current limiting protection is not caused by the measurement abnormality after the short-time voltage loss of the low-voltage arm of the direct current transformer.

[0089] In the control system provided by the present application, under the condition of the abnormal direct current voltage value, based on the characteristics that the direct current voltage and the direct current of the high-voltage direct current transmission system are highly coupled, it is further judged whether the direct current value is abnormal, so as to confirm again whether the voltage abnormality is caused by the real primary voltage change or the measurement abnormality after the short-time voltage loss of the low-voltage arm of the direct current transformer; after confirming that it is the voltage measurement abnormality, the source link (VDCOL, i.e., the low-voltage current limiting protection) of the false adjustment is shielded, and the prevention control of the subsequent false blocking is simply and efficiently realized, and the high-voltage direct current transmission system is smoothly and stably transitioned to the normal state.

[0090] The embodiment of the present application further provides a control protection device applied to a high-voltage direct current transmission system, which is used to execute the steps of the control method of the high-voltage direct current transmission system false blocking as described in the above embodiment.

[0091] The above specific embodiments further specifically describe the purposes, technical solutions and beneficial effects of the present application, and it should be understood that the above description is only the specific embodiments of the present application, and is not used to limit the protection scope of the present application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A control method for erroneous blocking in a high-voltage direct current (HVDC) transmission system, applied to the control and protection device of a HVDC transmission system, wherein, A high-voltage direct current (HVDC) transmission system is equipped with a varistor in the DC voltage divider section. The method is characterized by comprising: Read the DC voltage value of the high-voltage direct current transmission system measured by the control and protection device; If the DC voltage value is less than the starting voltage value of the low-voltage current limiting protection, it is determined whether the start of the low-voltage current limiting protection is caused by a measurement abnormality after a short-term loss of voltage in the low-voltage arm of the DC transformer. Specifically, determining whether the start of the low-voltage current limiting protection is caused by a measurement abnormality after a short-term loss of voltage in the low-voltage arm of the DC transformer involves: reading the DC current value of the high-voltage DC transmission system measured by the control and protection device; calculating the absolute value of the current difference between the DC current value and the rated DC current value; if the absolute value of the current difference is greater than a first threshold, then the start of the low-voltage current limiting protection is caused by a measurement abnormality after a short-term loss of voltage in the low-voltage arm of the DC transformer; or if the absolute value of the current difference is not greater than the first threshold, then the start of the low-voltage current limiting protection is not caused by a measurement abnormality after a short-term loss of voltage in the low-voltage arm of the DC transformer. If the judgment result is that the activation of the low-voltage current limiting protection is caused by the measurement abnormality after a short-term loss of voltage in the low-voltage arm of the DC transformer, then the regulation and control of the low-voltage current limiting protection shall be executed; or, if the judgment result is that the activation of the low-voltage current limiting protection is not caused by the measurement abnormality after a short-term loss of voltage in the low-voltage arm of the DC transformer, then the regulation and control of the low-voltage current limiting protection shall be disabled. If the absolute value of the difference is not greater than the first threshold, then wait until the preset first interval time, reread the multiple DC current values ​​measured by the control and protection device, calculate the absolute value of the current difference between the DC current value read each time and the rated DC current value, and if the absolute value of the current difference between the DC current value read each time and the rated DC current value is not greater than the first threshold, then the adjustment control of the low voltage current limiting protection is disabled.

2. The method according to claim 1, characterized in that, The first threshold is determined by the rated DC voltage, the rated DC voltage, and the starting voltage value of the low-voltage current limiting protection.

3. The method according to claim 2, characterized in that, The expression for the first threshold is: M1 = k * I dn (U dn -U d_high ) / U dn Where M1 is the first threshold, k is a constant, and U dn For DC voltage rating, I dn U is the rated DC current. d_high This is the starting voltage value for low-voltage current limiting protection.

4. The method according to any one of claims 1 to 3, characterized in that, After shielding the low-voltage current limiting protection, the method further includes: Read the DC voltage value measured by the control and protection device at the current moment; Calculate the absolute value of the voltage difference between the DC voltage value and the rated DC voltage value; If the absolute value of the voltage difference is less than the second threshold, then the low-voltage current limiting protection regulation control is activated; or If the absolute value of the voltage difference is not less than the second threshold, wait until the preset second interval time, reread the DC voltage value measured by the control and protection device, until the absolute value of the voltage difference with the rated DC voltage is less than the second threshold, and then open the adjustment control of the low voltage current limiting protection.

5. The method according to claim 4, characterized in that, The second threshold is determined by the rated DC voltage and the starting voltage of the low-voltage current limiting protection.

6. The method according to claim 5, characterized in that, The expression for the second threshold is: M2=k*(U dn -U d_high ), where M2 is the second threshold, k is a constant, and U dn U is the rated DC voltage. d_high This is the starting voltage value for low-voltage current limiting protection.

7. A control system for erroneous blocking in a high-voltage direct current (HVDC) transmission system, applied to the control and protection device of a HVDC transmission system, wherein, The high-voltage direct current (HVDC) transmission system is equipped with a varistor in the DC voltage divider section, characterized in that the system includes: The data reading module is used to read the DC voltage value of the high-voltage direct current transmission system measured by the control and protection device; The judgment module is used to determine whether the activation of the low-voltage current limiting protection is caused by a measurement anomaly after a short-term loss of voltage in the low-voltage arm of the DC transformer if the DC voltage value is less than the activation voltage value of the low-voltage current limiting protection. Specifically, determining whether the activation of the low-voltage current limiting protection is caused by a measurement anomaly after a short-term loss of voltage in the low-voltage arm of the DC transformer involves: reading the DC current value of the high-voltage DC transmission system measured by the control and protection device; calculating the absolute value of the current difference between the DC current value and the rated DC current value; if the absolute value of the current difference is greater than a first threshold, then the activation of the low-voltage current limiting protection is caused by a measurement anomaly after a short-term loss of voltage in the low-voltage arm of the DC transformer; or if the absolute value of the current difference is not greater than the first threshold, then the activation of the low-voltage current limiting protection is not caused by a measurement anomaly after a short-term loss of voltage in the low-voltage arm of the DC transformer. The control module is used to perform the adjustment control of the low-voltage current limiting protection if the judgment result is that the start of the low-voltage current limiting protection is caused by the measurement abnormality after a short-term loss of voltage in the low-voltage arm of the DC transformer; or, if the judgment result is that the start of the low-voltage current limiting protection is not caused by the measurement abnormality after a short-term loss of voltage in the low-voltage arm of the DC transformer, then the adjustment control of the low-voltage current limiting protection is disabled. If the absolute value of the difference is not greater than the first threshold, then wait until the preset first interval time, reread the multiple DC current values ​​measured by the control and protection device, calculate the absolute value of the current difference between the DC current value read each time and the rated DC current value, and if the absolute value of the current difference between the DC current value read each time and the rated DC current value is not greater than the first threshold, then the adjustment control of the low voltage current limiting protection is disabled.

8. A control and protection device for a high-voltage direct current transmission system, characterized in that, The steps are for performing a control method for erroneous blocking of a high-voltage direct current transmission system as described in any one of claims 1 to 6.

Images