A method and related device for suppressing transient overvoltage at a direct current sending end

Abstract

The application discloses a direct-current sending end transient overvoltage suppression method and related devices. After commutation failure, the application calculates the reactive power that needs to be provided by a wind farm to control the voltage of a wind farm grid connection point within a reasonable range, distributes the reactive power that needs to be provided by the wind farm, changes the working mode of the wind turbine according to the current wind speed of the wind turbine and the distributed reactive power, controls the reactive power output of the wind turbine through active power reduction, plays the power regulation role of the wind power in a wind and fire bundled direct-current external sending system, and suppresses the transient overvoltage of the direct-current sending end.

Description

TECHNICAL FIELD

[0001] The application relates to a direct-current sending-end transient overvoltage suppression method and a related device, and belongs to the technical field of wind farm group control. BACKGROUND

[0002] At present, large-scale wind power bases are mainly developed in the direction of long-distance power transmission by taking the advantages of large capacity and long-distance transmission through extra-high voltage direct-current (EHV DC) transmission. However, the randomness, volatility and intermittence of wind power bring higher requirements and challenges to the power transmission system. When the system encounters commutation failure, the random fluctuation characteristics caused by high proportion of wind power access are superimposed on the DC side, which aggravates the transient fluctuation of the DC system. If no timely and correct measures are taken, continuous commutation failure may occur, and the system DC may be locked, which may interrupt power transmission and seriously threaten the safety of power electronic devices of the internal converter station of the DC transmission system and the power grid near the sending end, and may cause large-scale wind farms to be disconnected from the grid due to transient overvoltage. How to suppress the voltage out-of-limit of the sending end caused by commutation failure of the wind-thermal bundled DC transmission system has become a problem to be solved in the system control.

[0003] At present, the suppression of the transient overvoltage of the DC sending end mainly focuses on the DC system side, and is inclined to use reactive power compensation devices for overvoltage suppression. For the DC transmission system with large-scale wind power access, the utilization of the reactive power regulation capability of the wind turbine itself is lacking. SUMMARY

[0004] The application provides a DC sending-end transient overvoltage suppression method and a related device, which solves the problems disclosed in the background art.

[0005] In order to solve the above technical problems, the technical scheme adopted by the application is as follows:

[0006] A DC sending-end transient overvoltage suppression method, comprising the following steps:

[0007] According to the operation electrical data of the wind-thermal bundled DC transmission system, if it is determined that the wind-thermal bundled DC transmission system has commutation failure, the power flow analysis is performed on an equivalent model of a wind farm access power grid, and the reactive power required to be provided by the wind farm to control the voltage at the grid connection point of the wind farm within a preset reasonable range is calculated; wherein the reactive power required to be provided by the wind farm is the reactive power required to be provided by the wind farm in the recovery stage of the wind-thermal bundled DC transmission system;

[0008] According to the ultra-short-term predicted wind speed of the wind turbine, the reactive power required to be provided by the wind farm is distributed to obtain the reactive power distributed to each wind turbine of the wind farm;

[0009] According to the current wind speed of the wind turbine and the distributed reactive power, the working mode of the wind turbine is changed, and the DC sending-end transient overvoltage suppression is performed.

[0010] The operation electrical data of the wind-fire-bundling HVDC transmission system includes a DC transmission power P d , an inverter-side arc-extinction angle γ, and a reactive power consumption Q d and a DC bus voltage U d .

[0011] According to the operation electrical data of the wind-fire-bundling HVDC transmission system, whether the wind-fire-bundling HVDC transmission system fails to commutate is detected, including:

[0012] If and U d <U d0 , it is determined that the wind-fire-bundling HVDC transmission system fails to commutate; wherein t is time, γ min is a limit arc-extinction angle at the inverter side, and U d0 is a critical commutation failure DC bus voltage.

[0013] After detecting that the wind-fire-bundling HVDC transmission system fails to commutate, before performing a power flow analysis, the reactive power required to be provided by the wind farm in a recovery stage of the wind-fire-bundling HVDC transmission system is reduced by adjusting an inverter-side DC current instruction.

[0014] The reactive power required to be provided by the wind farm to control the voltage at a wind farm grid connection point within a preset reasonable range is calculated, and a formula is as follows:

[0015]

[0016] Wherein Q demand is the reactive power required to be provided by the wind farm, Q L is a reactive power output at the wind farm grid connection point, U dc is the DC bus voltage, U dem is a DC bus voltage instruction value, k2 is a transformer ratio, X is a sum of a tie-line reactance and a transformer reactance, P w is a total active power output by the grid-connected wind farm, P L is an active power at the wind farm grid connection point, and R is a sum of a tie-line resistance and a transformer resistance.

[0017] According to an ultra-short-term predicted wind speed of a wind turbine, the reactive power required to be provided by the wind farm is distributed to obtain the reactive power distributed to each wind turbine of the wind farm, including:

[0018] According to the ultra-short-term predicted wind speed of the wind turbine, an ultra-short-term active power prediction value of the wind turbine is calculated.

[0019] According to the ultra-short-term active power prediction value of the wind turbine, an upper limit and a lower limit of an ultra-short-term reactive power capacity of the wind turbine are calculated.

[0020] According to the upper limit and the lower limit of the ultra-short-term reactive power capacity of the wind turbine, the reactive power required to be provided by the wind farm is distributed to obtain the reactive power distributed to each wind turbine of the wind farm.

[0021] The reactive power of the fan is provided by the grid-side converter, and the upper and lower limits of the ultra-short-term reactive power capacity of the fan are calculated, and the formula is:

[0022]

[0023] Q i max is the upper limit of the ultra-short-term reactive power capacity of the i th fan, Q i min is the lower limit of the ultra-short-term reactive power capacity of the i th fan, S g is the capacity of the grid-side converter, P i,f is the ultra-short-term active power prediction value of the i th fan.

[0024] The reactive power allocated to each fan of the wind farm is obtained, and the formula is:

[0025]

[0026] Q is the reactive power allocated to the i th fan, δ i is the reactive power allocation coefficient of the i th fan, Q demand is the reactive power required by the wind farm, is the maximum ultra-short-term reactive power prediction value of the i th fan, n is the number of fans of the wind farm, is the sum of the maximum reactive power generated by the n fans.

[0027] According to the current wind speed of the fan and the allocated reactive power, the working mode of the fan is changed, and the DC sending end transient overvoltage suppression is carried out, including:

[0028] If the current wind speed of the fan does not reach the rated wind speed, the fan is controlled to enter the reactive power compensator mode, the fan rectifier is used as a reactive power compensator, and the DC sending end transient overvoltage suppression is carried out;

[0029] If the reactive power compensation capacity of the fan cannot meet the allocated reactive power, the fan is controlled to enter the active power reduction mode, the reactive power capacity is increased by reducing the active power of the fan, and the DC sending end transient overvoltage suppression is carried out;

[0030] If the reactive power compensation capacity of the fan can meet the allocated reactive power instruction, the fan is controlled to enter the adaptive droop control mode, the reactive power of the fan is controlled by the reactive power droop coefficient adapted to the allocated reactive power, and the DC sending end transient overvoltage suppression is carried out.

[0031] In the active power reduction mode, the fan reduces the active power according to the priority; wherein the active power reduction priority is determined according to the following formula:

[0032]

[0033]

[0034] wherein P i is the active power output of the i-th wind turbine, ΔP i is the first active power reduction of the i-th wind turbine, S i is the rated capacity of the i-th wind turbine, n is the number of wind turbines, ΔQ i is the reactive power capacity increment of the i-th wind turbine after active power reduction, j is the number of the wind turbine with the highest active power reduction priority.

[0035] The reactive power droop coefficient adapted to the allocated reactive power is:

[0036]

[0037] wherein, is the reactive power droop coefficient of the i-th wind turbine at time t, n is the number of wind turbines in the wind farm, is the maximum reactive power capacity of the i-th wind turbine at time t, and a is a coefficient adjusted according to the allocated reactive power.

[0038] A direct current sending end transient overvoltage suppression device, comprising:

[0039] A reactive power demand module, according to the operating electrical data of a wind-thermal bundled direct current external sending system, if it is determined that the wind-thermal bundled direct current external sending system fails to commutate, performing power flow analysis on an equivalent model of a wind farm connected to a power grid, and calculating the reactive power required to be provided by the wind farm to control the voltage at the wind farm grid connection point within a preset reasonable range; wherein the reactive power required to be provided by the wind farm is the reactive power required to be provided by the wind farm during the recovery stage of the wind-thermal bundled direct current external sending system.

[0040] A reactive power allocation module, according to the ultra-short-term predicted wind speed of the wind turbine, allocating the reactive power required to be provided by the wind farm to obtain the reactive power allocated to each wind turbine of the wind farm.

[0041] An output control module, according to the current wind speed of the wind turbine and the allocated reactive power, changing the operating mode of the wind turbine, and performing direct current sending end transient overvoltage suppression.

[0042] A computer readable storage medium storing one or more programs, the one or more programs including instructions that, when executed by a computing device, cause the computing device to perform a direct current sending end transient overvoltage suppression method.

[0043] A computing device, comprising one or more processors, one or more memories, and one or more programs, wherein the one or more programs are stored in the one or more memories and configured to be executed by the one or more processors, the one or more programs including instructions for performing a direct current sending end transient overvoltage suppression method.

[0044] The application achieves the beneficial effects that after the commutation failure, the reactive power provided by the wind farm to control the voltage of the wind farm grid connection point in a reasonable range is calculated, the reactive power provided by the wind farm is distributed, the working mode of the wind turbine is changed according to the current wind speed of the wind turbine and the distributed reactive power, the DC sending end transient overvoltage is suppressed, and the reactive power regulation capability of the wind power in the wind and fire bundled DC external transmission system is fully utilized. BRIEF DESCRIPTION OF DRAWINGS

[0045] Figure 1 Flow chart of the DC sending end transient overvoltage suppression method;

[0046] Figure 2 Control block diagram for suppressing continuous commutation failure;

[0047] Figure 3 Equivalent model of the wind farm connected to the power grid;

[0048] Figure 4 Control block diagram of the adaptive droop control;

[0049] Figure 5 Overall control structure of the wind turbine. DETAILED DESCRIPTION

[0050] The application will be further described below with reference to the drawings. The following examples are only used to more clearly illustrate the technical solutions of the application, and cannot be used to limit the protection scope of the application.

[0051] As shown in Figure 1 A DC sending end transient overvoltage suppression method, comprising the following steps:

[0052] Step 1, according to the operation electrical data of the wind and fire bundled DC external transmission system, if it is determined that the wind and fire bundled DC external transmission system has commutation failure, the power flow analysis is performed on the equivalent model of the wind farm connected to the power grid, and the reactive power provided by the wind farm to control the voltage of the wind farm grid connection point in a predetermined reasonable range is calculated; wherein the reactive power provided by the wind farm is the reactive power provided by the wind farm in the recovery stage of the wind and fire bundled DC external transmission system;

[0053] Step 2, according to the super-short-term predicted wind speed of the wind turbine, the reactive power provided by the wind farm is distributed to obtain the distributed reactive power of each wind turbine of the wind farm.

[0054] Step 3, according to the current wind speed of the wind turbine and the distributed reactive power, the working mode of the wind turbine is changed to suppress the DC sending end transient overvoltage.

[0055] After commutation failure, the above method calculates the reactive power required by the wind farm to keep the grid connection voltage within a reasonable range, allocates the reactive power required by the wind farm, and changes the wind turbine's operating mode according to the current wind speed and the allocated reactive power to suppress transient overvoltage at the DC transmission end, thus giving full play to the reactive power regulation capability of wind power in the wind-thermal bundled DC transmission system.

[0056] The analysis of the overvoltage mechanism at the DC transmitting end caused by commutation failure reveals that the electrical quantity changes in the DC power transmission system (hereinafter referred to as "the system") under commutation failure can be divided into three stages: Stage 1 corresponds to the initial stage of the system encountering commutation failure, where the system's DC transmission power P... d With DC bus voltage U d A significant drop occurred, with the inverter-side extinction angle γ decreasing to the inverter-side limiting extinction angle γ. min The following is the system reactive power consumption Q. d Increase; Phase two corresponds to the system recovery phase, the system DC transmission power P d With DC bus voltage U d Gradually recovering, the inverter-side arc extinction angle γ returns to normal, and the system feeds back reactive power to the sending end; stage three corresponds to the continuous commutation failure stage, and the DC transmission power P d DC bus voltage U d The second drop caused the inverter-side arc extinction angle γ to decrease to γ ​​a second time. min Under these conditions, the system's reactive power consumption Q d Increase.

[0057] Therefore, the DC transmission power P of the system can be obtained in real time. d Inverter-side arc extinction angle γ, system reactive power consumption Q d and DC bus voltage U d When these operating electrical data change significantly and fall below the stability threshold, it can be determined that the system has encountered a commutation failure, which can be expressed by the formula:

[0058]

[0059] In other words, as long as the real-time acquired operating electrical data satisfies the above formula, it can be determined that the system has failed to commutate.

[0060] To address the risk of consecutive commutation failures after a commutation failure, the DC transmission power can be reduced by adjusting the DC current command on the inverter side. Based on the coupling relationship between active power transmission and reactive power consumption at the DC sending end, the reactive power demand during the system recovery phase can be reduced, i.e., the reactive power that the wind farm needs to provide, as detailed below:

[0061] The electrical equations on the inverter side of the system can be expressed as:

[0062]

[0063]

[0064]

[0065] wherein, is the power factor, U is the DC voltage of the system, U0 is the no-load voltage of the system, P d is the DC transmission power of the system, Q d is the reactive power consumption of the system, S d is the apparent power of the system, β is the triggering angle of the rectifier side;

[0066] The coupling relationship between the active transmission power and the reactive power consumption of the system is obtained from the above formula:

[0067]

[0068] Generally, the reactive power consumption of the system accounts for 50% to 60% of the DC transmission power, and after the commutation failure occurs, the DC transmission power is reduced, thereby reducing the system reactive power consumption;

[0069] The DC current is related to the arc extinction angle:

[0070]

[0071] wherein, I d is the DC current of the system, X is the commutation reactance (all reactances in series with the commutation voltage in the commutation circuit);

[0072] The coupling relationship between the DC transmission power and the arc extinction angle of the inverter side is:

[0073]

[0074] After the system encounters the commutation failure, according to the coupling relationship between the active transmission power and the reactive power consumption of the DC system, the DC transmission power of the system is reduced to raise the arc extinction angle of the inverter side, thereby avoiding continuous commutation failure of the system.

[0075] The control strategy for suppressing continuous commutation failure of the DC system is shown in FIG. Figure 2 CORDER is the DC current command of the control system of the inverter side, CMRS is the actual measured current of the inverter side, CERRR is the current deviation obtained by subtracting the two, and the triggering advance angle β of the inverter side is obtained through the PI correction link. After β is subtracted by π, the triggering delay angle command AOR is obtained. After the commutation failure is encountered, the DC current command is adjusted, the current deviation CERRR is increased, the triggering advance angle β is increased, the triggering delay angle of the inverter side is further reduced, the reactive power consumption of the converter station is reduced during operation, and the system reactive power demand during the system fault period is improved.

[0076] If the DC power is reduced by the DC power drop method, the active power of the DC system is reduced ΔP dc , the reactive power consumption of the DC system is reduced ΔQ dc = ΔP dc tanφ dc .

[0077]

[0078] wherein X dc is the reactance of the DC transmission line, and U dc is the voltage of the DC sending end.

[0079] Further, the equivalent model of the wind farm connected to the power grid shown in Figure 3 is subjected to power flow analysis to obtain the voltage of the wind farm grid connection point, and the reactive power required to be provided by the wind farm to control the voltage of the wind farm grid connection point within a reasonable range is calculated.

[0080] The voltage calculation formula of the wind farm grid connection point is as follows:

[0081]

[0082] wherein U dc is the DC bus voltage, U pcc is the voltage of the wind farm grid connection point, k2 is the voltage ratio of the transformer, P T is the active power measured on the transformer, Q T is the reactive power measured on the transformer, R is the sum of the resistance of the tie line and the resistance of the transformer, and X is the sum of the reactance of the tie line and the reactance of the transformer.

[0083] Neglecting the active component, the total reactive power output of the wind turbine is represented as:

[0084]

[0085] wherein P L is the active power of the wind farm grid connection point, Q L is the reactive power of the wind farm grid connection point, P w is the total active power output of the grid-connected wind farm, and Q w is the total reactive power output of the grid-connected wind farm.

[0086] To control the voltage of the grid connection point within a reasonable range, i.e. 90% to 110% of the rated voltage, the total reactive power required to be provided by the wind farm is:

[0087]

[0088] wherein Q demand is the reactive power required to be provided by the wind farm, and Udem is a direct current bus voltage instruction value.

[0089] Further, the ultra-short-term active power prediction value of the fan can be calculated according to the ultra-short-term predicted wind speed of the fan, and the formula can be represented as:

[0090]

[0091] wherein, P i,f is the ultra-short-term active power prediction value of the i th fan, V i,f is the ultra-short-term predicted wind speed of the i th fan, ρ is the air density, A is the fan blade area, C p is the wind energy utilization coefficient, λ is the tip speed ratio, and β is the pitch angle.

[0092] For direct-drive fans, the reactive power of the fan is provided by the grid-side converter, and according to the ultra-short-term active power prediction value of the fan, the upper and lower limits of the ultra-short-term reactive power capacity of the fan can be calculated, and the formula can be represented as:

[0093]

[0094] wherein, is the upper limit of the ultra-short-term reactive power capacity of the i th fan, Q i min is the lower limit of the ultra-short-term reactive power capacity of the i th fan, S g is the capacity of the grid-side converter.

[0095] According to the upper and lower limits of the ultra-short-term reactive power capacity of the fan, the reactive power required to be provided by the wind farm is distributed, and the reactive power allocated to each fan of the wind farm can be obtained, and the formula can be represented as:

[0096]

[0097] wherein, Q demand is the reactive power required to be provided by the wind farm, is the reactive power allocated to the i th fan, δ i is the reactive power allocation coefficient of the i th fan, is the maximum ultra-short-term reactive power prediction value of the i th fan, and n is the number of fans in the wind farm, is the sum of the maximum reactive power generated by the n fans.

[0098] Further, the working mode of the fan can be changed according to the current wind speed of the fan and the allocated reactive power, and the working mode of the fan includes a reactive power compensator mode, an active power reduction mode, and an adaptive droop control mode.

[0099] If the current wind speed of the wind turbine does not reach the rated wind speed, the wind turbine is controlled to enter the reactive power compensator mode, the wind turbine rectifier is used as a reactive power compensator, and the DC sending end transient overvoltage is suppressed; when the wind turbine works in the reactive power compensator mode, when the wind speed does not reach the rated wind speed, the wind turbine is cut off from the power grid, the capacity of the wind turbine inverter is used as a static reactive power compensator, and the reactive power is compensated in real time according to the dynamic reactive power change in the system; when an emergency occurs, the wind turbine inverter is fully put into the system to maintain the stability of the bus voltage. If the reactive power compensation capacity of the wind turbine cannot meet the allocated reactive power, the wind turbine is controlled to enter the active power reduction mode, the active power of part of the wind turbine is reduced to increase the reactive power, and the DC sending end transient overvoltage is suppressed.

[0100] When the wind farm grid-connected point voltage is out of limit and the reactive power demand Q demand is greater than the maximum reactive power output Q max of the wind turbine, active power reduction control is adopted. By reducing the active power of part of the wind turbine, more reactive power is absorbed to provide reactive power support for the grid-connected point. According to the improved wind turbine margin allocation strategy, the reactive power allocation instructions of each wind turbine are determined, and the active power of the corresponding wind turbine is reduced.

[0101] The specific calculation method of the active power reduction evaluation parameter is as follows:

[0102] After active power reduction, the voltage change of the grid-connected point is as follows:

[0103]

[0104] Where, ΔU2 is the voltage of the grid-connected point of the wind turbine group, Figure 3 the voltage change at BUS2, ΔU is the voltage of the power grid, Figure 3 the voltage at BUS4, ΔP W is the active power reduction amount of the wind turbine group, ΔQ W is the reactive power increase amount of the wind turbine group, and X L is the impedance of the tie line between the wind farm and the DC grid.

[0105] In the active power reduction mode, the wind turbine reduces the active power according to the priority; wherein the active power reduction priority is determined according to the following formula:

[0106] The relationship between the reactive power ΔQ i increased by the i-th wind turbine and the active power reduction amount ΔP i is as follows:

[0107]

[0108]

[0109] Where, P i is the active power output by the i-th wind turbine, and ΔP iS represents the active power reduction of the i-th wind turbine. i Let ΔQ be the rated capacity of the i-th fan, n be the number of fans, and ΔQ be the rated capacity of the i-th fan. i Let j be the reactive capacity increment after the active power reduction of the i-th wind turbine, and j be the number of the wind turbine with the highest priority for active power reduction. The wind turbine number j is given priority for reduction when the reactive power increase per unit of active power reduction (5% of apparent power) is the largest.

[0110] After quantitative active power reduction, the effect of transient high voltage suppression is evaluated. The grid-connected voltage of the wind farm should not exceed 110% of the rated voltage. An evaluation parameter ξ for active power reduction effect is proposed to assess the effect of active power reduction of the wind turbine, expressed as:

[0111]

[0112] Where U2 is the grid connection voltage of the wind turbine group, U rating This refers to the rated voltage at the grid connection point of the wind turbine group.

[0113] When ξ is greater than 10%, active power reduction continues to suppress transient high voltage; when ξ is less than 10%, active power reduction stops to maintain the existing output of the wind turbine.

[0114] If the reactive power compensation capacity of the wind turbine can meet its allocated reactive power command, the wind turbine is controlled to enter the adaptive droop control mode. The reactive power output of the wind turbine is controlled by the reactive power droop coefficient that is adapted to the allocated reactive power, so as to suppress the transient overvoltage at the DC sending end.

[0115] Due to weather conditions and geographical location, the input wind speed to wind turbines varies over time, resulting in differences in reactive power capacity among the turbines in a wind farm. Traditional control methods use a fixed droop control coefficient, uniformly allocating the same reactive power margin regardless of turbine capacity differences. However, to address the varying turbine capacity characteristics, an adaptive droop control mode is adopted during normal turbine operation. (See...) Figure 4 Specifically, the allocated reactive power will be used as the reactive power reference quantity for the droop control loop.

[0116] The output of the droop control loop is defined as follows:

[0117]

[0118] in, This is the output of the droop control loop for the i-th fan. U is the reactive power droop coefficient of the i-th wind turbine at time t. ref Given a reference voltage, U pcc This is the voltage at the grid connection point of the wind farm.

[0119] The reactive power droop factor that matches the allocated reactive power is:

[0120]

[0121] Wherein, n is the number of wind turbines in the wind farm, is the maximum reactive power capacity of the i th wind turbine at time t, and a is a coefficient according to the allocated reactive power regulation.

[0122] Delta Q i and are added to obtain the reactive power instruction Q out , and the current instruction I qref is obtained through a PI correction link.

[0123] As Figure 5 the overall control structure of the wind turbine, the controller is divided into a left machine side control part and a right grid side control part. The machine side control module includes active power outer loop control, current inner loop control and pulse width modulation control. In the active power outer loop control module in the machine side module, different working modes are selected according to different situations, and the reactive power compensator mode, the active power reduction mode or the adaptive droop control mode can be selected. The controller inputs the active current reference value to the current inner loop according to the algorithm corresponding to the selected mode. In the grid side control, the given voltage reference value is subtracted from the rated voltage value, and the reactive power adjustment value is generated through adaptive droop control. The reactive power reference value obtained from the reactive power adjustment value and the wind speed prediction is subtracted to obtain the reactive power instruction. The reactive power outer loop inputs the current inner loop after the PI controller, and the current reference value outputs the voltage reference value after the control link. Finally, the PWM driving signal required by the converter is output through the space vector modulation, realizing the active and reactive control.

[0124] The above method can reduce the transmission of direct current active power by adjusting the direct current instruction after the commutation failure, can reduce the reactive power demand of the system in the late recovery stage after the fault, can avoid the occurrence of continuous commutation failure, and can fully play the reactive power regulation role of the wind turbine. The working mode of the wind turbine is changed according to different reactive power conditions, the active power of part of the wind turbine is preferentially reduced to meet the reactive power demand of the system, the influence of the surplus reactive power of the system on the direct current voltage after the direct current power speed is reduced can be reduced, and the stability of the direct current transmission system can be maintained.

[0125] Based on the same technical solution, the application also discloses a software device of the above method, a direct current sending end transient overvoltage suppression device, which comprises:

[0126] A reactive power demand module, according to the operation electrical data of the wind-fire bundled direct current external transmission system, if it is determined that the wind-fire bundled direct current external transmission system commutation failure, first, the direct current current instruction of the inverter side is adjusted to reduce the reactive power required by the wind farm in the recovery stage of the wind-fire bundled direct current external transmission system, and then the power flow analysis is carried out on the wind farm grid connection equivalent model to calculate the reactive power required by the wind farm to control the voltage at the wind farm grid connection point within a preset reasonable range. The reactive power required by the wind farm is the reactive power required by the wind farm in the recovery stage of the wind-fire bundled direct current external transmission system.

[0127] The operation electrical data of the wind-fire bundled HVDC transmission system can specifically include the DC transmission power P d , the extinction angle γ of the inverter side, the reactive power consumption Q d , and the DC bus voltage U d .

[0128] According to the operation electrical data of the wind-fire bundled HVDC transmission system, it is determined that the wind-fire bundled HVDC transmission system has a commutation failure, including if and U d <U d0 , it is determined that the wind-fire bundled HVDC transmission system has a commutation failure; wherein t is time, γ min is the limit extinction angle of the inverter side, and U d0 is the critical commutation failure DC bus voltage.

[0129] The wind farm needs to provide reactive power to specifically control the voltage at the wind farm grid connection point within a preset reasonable range, and the formula can be:

[0130]

[0131] wherein Q demand is the reactive power that the wind farm needs to provide, Q L is the reactive power output at the wind farm grid connection point, U dc is the DC bus voltage, U dem is the DC bus voltage command value, k2 is the transformer ratio, X is the sum of the tie line reactance and the transformer reactance, P w is the total active power output by the grid-connected wind farm, P L is the active power at the wind farm grid connection point, and R is the sum of the tie line resistance and the transformer resistance.

[0132] The reactive power distribution module distributes the reactive power that the wind farm needs to provide according to the ultra-short-term predicted wind speed of the wind turbine, to obtain the reactive power allocated to each wind turbine of the wind farm.

[0133] The process of specifically obtaining the reactive power allocated to each wind turbine of the wind farm can be:

[0134] A1) According to the ultra-short-term predicted wind speed of the wind turbine, the ultra-short-term active power prediction value of the wind turbine is calculated.

[0135] A2) According to the ultra-short-term active power prediction value of the wind turbine, the upper and lower limits of the ultra-short-term reactive power capacity of the wind turbine are calculated.

[0136] The reactive power of the wind turbine is provided by the grid-side converter, and the upper and lower limits of the ultra-short-term reactive power capacity of the wind turbine are calculated, and the formula can be:

[0137]

[0138] wherein, is the upper limit of the ultra-short-term reactive power capacity of the i-th wind turbine, is the lower limit of the ultra-short-term reactive power capacity of the i-th wind turbine, g is the capacity of the grid-side converter, P i,f is the ultra-short-term active power prediction value of the i-th wind turbine.

[0139] A3) According to the upper and lower limits of the ultra-short-term reactive power capacity of the wind turbine, the reactive power provided by the wind farm is allocated to obtain the reactive power allocated to each wind turbine of the wind farm.

[0140] The formula for obtaining the reactive power allocated to each wind turbine of the wind farm can be:

[0141]

[0142] wherein, is the reactive power allocated to the i-th wind turbine, δ i is the reactive power allocation coefficient of the i-th wind turbine, Q demand is the reactive power provided by the wind farm, is the maximum ultra-short-term reactive power prediction value of the i-th wind turbine, n is the number of wind turbines of the wind farm, is the sum of the maximum reactive power of the n wind turbines.

[0143] The output control module changes the operating mode of the wind turbine according to the current wind speed and the allocated reactive power, and performs DC sending end transient overvoltage suppression.

[0144] The specific process can be:

[0145] B1) If the current wind speed of the wind turbine does not reach the rated wind speed, control the wind turbine to enter the reactive power compensator mode, and use the wind turbine rectifier as a reactive power compensator to perform DC sending end transient overvoltage suppression.

[0146] B2) If the reactive power compensation capacity of the wind turbine cannot meet the allocated reactive power, control the wind turbine to enter the active power reduction mode, increase the reactive power capacity by reducing the active power of the wind turbine, and perform DC sending end transient overvoltage suppression.

[0147] In the active power reduction mode, the wind turbine reduces the active power according to the priority; wherein the active power reduction priority can be determined according to the following formula:

[0148]

[0149]

[0150] wherein, P i is the active power output by the i-th wind turbine, ΔP i is the first active power reduction amount of the i-th wind turbine, S iQi is the rated capacity of the i-th wind turbine, n is the number of wind turbines, and AQ is the reactive power increment of the i-th wind turbine. i Qi is the rated capacity of the i-th wind turbine, n is the number of wind turbines, and AQ is the reactive power increment of the i-th wind turbine.

[0151] B3) If the reactive power compensation capacity of the wind turbine can meet the allocated reactive power instruction, the wind turbine is controlled to enter an adaptive droop control mode, the wind turbine is controlled to output reactive power through a reactive power droop coefficient matched with the allocated reactive power, and transient overvoltage suppression of a DC sending end is performed.

[0152] wherein the reactive power droop coefficient matched with the allocated reactive power is:

[0153]

[0154] wherein, Qi is the reactive power droop coefficient of the i-th wind turbine at the t time, n is the number of wind turbines in the wind farm, Qi is the maximum reactive power capacity of the i-th wind turbine at the t time, and a is a coefficient adjusted according to the allocated reactive power.

[0155] Based on the same technical solution, the application further discloses a computer readable storage medium storing one or more programs, the one or more programs including instructions that, when executed by a computing device, cause the computing device to perform the transient overvoltage suppression method of the DC sending end.

[0156] Based on the same technical solution, the application further discloses a computing device including one or more processors, one or more memories, and one or more programs, wherein the one or more programs are stored in the one or more memories and configured to be executed by the one or more processors, and the one or more programs include instructions for performing the transient overvoltage suppression method of the DC sending end.

[0157] Those skilled in the art will understand that embodiments of the application can be provided as methods, systems, or computer program products. Therefore, the application can take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects. Moreover, the application can take the form of a computer program product implemented on one or more computer usable storage media (including, but not limited to, disk storage, CD-ROMs, optical storage devices, etc.) containing computer usable program code.

[0158] The computer program instructions can also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart or flows and / or block diagram block or blocks. Figure 1 one or more flow or flows and / or block diagram block or blocks. Figure 1 one or more flow or flows and / or block diagram block or blocks.

[0159] These computer program instructions can also be stored in a computer readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer readable memory produce an article of manufacture including instructions which implement the function specified in the flowchart or flows and / or block diagram block or blocks. Figure 1 one or more flow or flows and / or block diagram block or blocks. Figure 1 one or more flow or flows and / or block diagram block or blocks.

[0160] The computer program instructions can also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart or flows and / or block diagram block or blocks. Figure 1 one or more flow or flows and / or block diagram block or blocks. Figure 1 one or more flow or flows and / or block diagram block or blocks.

[0161] The above merely provides an embodiment of the present application, but is not intended to limit the present application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall fall within the scope of the claims of the present application.

Claims

1. A method of suppressing a transient overvoltage at a DC sending end, characterized by, Comprising: According to the operation electrical data of the wind-fire-bundling HVDC transmission system, if it is determined that the wind-fire-bundling HVDC transmission system commutation failure, the power flow analysis is performed on the equivalent model of the wind farm connected to the power grid, and the reactive power required to be provided by the wind farm to control the voltage at the wind farm grid-connected point within a preset reasonable range is calculated; wherein the reactive power required to be provided by the wind farm is the reactive power required to be provided by the wind farm during the recovery stage of the wind-fire-bundling HVDC transmission system; According to the ultra-short-term predicted wind speed of the wind turbine, an ultra-short-term active power predicted value of the wind turbine is calculated, according to the ultra-short-term active power predicted value of the wind turbine, an upper limit and a lower limit of the ultra-short-term reactive power capacity of the wind turbine are calculated, according to the upper limit and the lower limit of the ultra-short-term reactive power capacity of the wind turbine, the reactive power required to be provided by the wind farm is distributed to obtain the reactive power distributed to each wind turbine of the wind farm; wherein the reactive power distributed to each wind turbine of the wind farm is obtained, the formula is: , is the reactive power distributed to the i th wind turbine, is the reactive power distribution coefficient of the i th wind turbine, is the reactive power required to be provided by the wind farm, is the ultra-short-term maximum reactive power predicted value of the i th wind turbine, and n is the number of wind turbines of the wind farm, is the sum of the maximum reactive power emitted by the n wind turbines. If the current wind speed of the wind turbine does not reach the rated wind speed, the wind turbine is controlled to enter the reactive power compensator mode, the wind turbine rectifier is used as a reactive power compensator, and the transient overvoltage suppression of the DC sending end is performed; if the reactive power compensation capacity of the wind turbine cannot meet the allocated reactive power, the wind turbine is controlled to enter the active power reduction mode, the reactive power capacity is increased by reducing the active power of the wind turbine, and the transient overvoltage suppression of the DC sending end is performed; if the reactive power compensation capacity of the wind turbine can meet the allocated reactive power instruction, the wind turbine is controlled to enter the adaptive droop control mode, the reactive power output of the wind turbine is controlled through the reactive power droop coefficient adapted to the allocated reactive power, and the transient overvoltage suppression of the DC sending end is performed.

2. The method of claim 1, wherein the method comprises: The operation electrical data of the wind-fire-bundling HVDC transmission system includes DC transmission power P of the wind-fire-bundling HVDC transmission system d , inverter side arc extinguishing angle , reactive power consumption Q d and DC bus voltage U d ; According to the operation electrical data of the wind-fire-bundling HVDC transmission system, it is determined that the wind-fire-bundling HVDC transmission system commutation failure, comprising: If , it is determined that the commutation failure of the wind-thermal bundled direct current transmission system occurs; wherein t is time, is the limit extinction angle of the inverter side, is the critical commutation failure DC bus voltage.

3. The method of claim 1, wherein the method comprises: Before detecting the wind-fire-bundling HVDC transmission system commutation failure and performing power flow analysis, the DC current instruction on the inverter side is adjusted to reduce the reactive power required to be provided by the wind farm during the recovery stage of the wind-fire-bundling HVDC transmission system.

4. The method of claim 1, wherein the method comprises: The formula for calculating the reactive power required to be provided by the wind farm to control the voltage at the wind farm grid-connected point within a preset reasonable range is: ； wherein, is the reactive power required by the wind farm, is the reactive power output at the point of common coupling (PCC) of the wind farm, is the DC bus voltage, is the DC bus voltage command, is the transformer ratio, X is the sum of the tie-line reactance and the transformer reactance, is the total active power output of the wind farm, is the active power at the PCC of the wind farm, R is the sum of the tie-line resistance and the transformer resistance.

5. The method of claim 1, wherein the method further comprises: The reactive power of the wind turbine is provided by the grid-side converter, and the upper and lower limits of the wind turbine ultra-short-term reactive power capacity are calculated, and the formula is: ； wherein, is the upper limit of the ultra-short-term reactive power capacity of the i-th wind turbine, is the lower limit of the ultra-short-term reactive power capacity of the i-th wind turbine, is the capacity of the grid-side converter, is the ultra-short-term active power forecast value of the i-th wind turbine.

6. The method of claim 1, wherein the method further comprises: In the active power reduction mode, the wind turbine reduces the active power according to the priority; wherein the active power reduction priority is determined according to the following formula: ； ； wherein P i is the active power output of the i-th wind turbine, is the first active power reduction of the i-th wind turbine, S i is the rated capacity of the i-th wind turbine, and n is the number of wind turbines, is the reactive power capacity increment of the i-th wind turbine after active power reduction, and j is the number of the wind turbine with the highest active power reduction priority.

7. The method of claim 1, wherein the method further comprises: The reactive power droop coefficient adapted to the allocated reactive power is: ； wherein, is the reactive droop coefficient of the i-th wind turbine at time t, n is the number of wind turbines in the wind farm, is the maximum reactive power capacity of the i-th wind turbine at time t, is the coefficient according to the reactive power regulation assigned.

8. A DC sending end transient overvoltage suppression device, characterized by, Comprising: The reactive power required to be provided by the wind farm is the reactive power required to be provided by the wind farm during the recovery stage of the wind-fire-bundling HVDC transmission system; The reactive power distribution module calculates the ultra-short-term active power prediction value of the wind turbine according to the ultra-short-term prediction wind speed of the wind turbine, calculates the upper and lower limits of the ultra-short-term reactive power capacity of the wind turbine according to the ultra-short-term active power prediction value of the wind turbine, distributes the reactive power required to be provided by the wind farm according to the upper and lower limits of the ultra-short-term reactive power capacity of the wind turbine, and obtains the reactive power distributed to each wind turbine of the wind farm; wherein the formula for obtaining the reactive power distributed to each wind turbine of the wind farm is: , is the reactive power distributed to the i th wind turbine, is the reactive power distribution coefficient of the i th wind turbine, is the reactive power required to be provided by the wind farm, is the ultra-short-term maximum reactive power prediction value of the i th wind turbine, and n is the number of wind turbines in the wind farm, is the sum of the maximum reactive power generated by the n wind turbines. The output control module, if the current wind speed of the wind turbine does not reach the rated wind speed, controls the wind turbine to enter the reactive power compensator mode, the wind turbine rectifier is used as a reactive power compensator, and the transient overvoltage suppression of the DC sending end is performed; if the reactive power compensation capacity of the wind turbine cannot meet the allocated reactive power, the wind turbine is controlled to enter the active power reduction mode, the reactive power capacity is increased by reducing the active power of the wind turbine, and the transient overvoltage suppression of the DC sending end is performed; if the reactive power compensation capacity of the wind turbine can meet the allocated reactive power instruction, the wind turbine is controlled to enter the adaptive droop control mode, the reactive power output of the wind turbine is controlled through the reactive power droop coefficient adapted to the allocated reactive power, and the transient overvoltage suppression of the DC sending end is performed.

9. A computer-readable storage medium storing one or more programs, the one or more programs comprising instructions for: The one or more programs include instructions that, when executed by a computing device, cause the computing device to perform any of the methods of claims 1-7.

10. A computing device, comprising: Comprising: One or more processors, one or more memories, and one or more programs, wherein the one or more programs are stored in the one or more memories and configured to, with the one or more processors, perform any of the methods of claims 1-7. One or more processors, one or more memories, and one or more programs, wherein the one or more programs are stored in the one or more memories and configured to, with the one or more processors, perform any of the methods of claims 1-7. One or more processors, one or more memories, and one or more programs, wherein the one or more programs are stored in the one or more memories and configured to, with the one or more processors, perform any of the methods of claims 1-7. One or more processors, one or more memories

Images