A method for reactive power control of a high voltage direct current transmission system and related apparatus

Abstract

The application discloses a high-voltage direct current power transmission system reactive power control method and related devices, comprising: first, establishing a reactive power calculation model of the high-voltage direct current system, then calculating the reactive power exchange value Qdc1 of the high-voltage direct current system under each working condition and the alternating current system, then calculating the new reactive power exchange value Qdc2 of the high-voltage direct current system under each working condition and the alternating current system after a group of alternating current filters are switched at the converter station, finally, statistically analyzing the change amount AQ of the reactive power exchanged by the high-voltage direct current system under each working condition and the alternating current system after a group of alternating current filters are switched, obtaining the maximum value of the absolute value of the reactive power change amount AQ, and taking the maximum value as the reactive power exchange limit range when the high-voltage direct current system is controlled in the reactive power, so that the frequent switching of the alternating current filter can be avoided. The high-voltage direct current system reactive power control dead zone range obtained by the method avoids the problem of frequent switching of the alternating current filter, and improves the stable operation level of the high-voltage direct current system.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high-voltage direct current transmission, in particular to a reactive power control method for a high-voltage direct current transmission system and related devices. BACKGROUND

[0002] High-voltage direct current transmission technology plays an important role in China's west-to-east power transmission and clean energy consumption. China has put into operation dozens of high-voltage direct current projects, and many high-voltage direct current projects are currently being planned and constructed. The stable operation of high-voltage direct current projects has an increasing impact on China's energy security. When high-voltage direct current is normally operated, due to its own working characteristics, it will transmit certain harmonic currents and inductive reactive power to the alternating current grid. In order to ensure the voltage quality of the alternating current grid, a plurality of alternating current filters need to be configured on the alternating current side of the converter station. By controlling the switching of the alternating current filters, the harmonics generated by the converter can be filtered out, and the reactive power exchanged between the converter station and the alternating current grid can be ensured to be within the allowable range, and the alternating current bus voltage of the converter station can also be maintained at a reasonable level.

[0003] At present, the switching control of the alternating current filter of the high-voltage direct current project mainly has two modes of constant reactive power control and constant voltage control, among which the constant reactive power control mode is more commonly used. According to the operation experience of domestic direct current projects, the alternating current filter in the converter station will appear abnormal situation of frequent switching under certain conditions, which endangers the safety of the equipment and even causes direct current power limiting or even locking, affecting the normal operation of the direct current. Related research shows that the main reason for the frequent switching of the alternating current filter is that the reactive power fluctuation caused by the switching of the filter exceeds the reactive dead zone range of the constant reactive power control. Therefore, in order to avoid the frequent switching of the alternating current filter, the reactive dead zone range of the constant reactive power control can be increased. However, the increase of the reactive dead zone range will increase the reactive power and voltage fluctuation of the alternating current grid. Therefore, a scientific and reasonable reactive control dead zone range is very important for the stable operation of the high-voltage direct current system and the alternating current system. SUMMARY

[0004] The present application provides a reactive power control method for a high-voltage direct current transmission system and related devices, which is used to solve the problem of frequent switching of the alternating current filter and the oscillation adjustment of the converter transformer tap, and the voltage impact and surge harmonic current interference generated by the alternating current and direct current system.

[0005] Therefore, the first aspect of the present application provides a reactive power control method for a high-voltage direct current transmission system, which comprises:

[0006] S1, determining initial basic input parameters according to the engineering parameters of the high-voltage direct current system and initializing, respectively assigning, increasing the step size and analyzing and processing the alternating current system short-circuit capacity, alternating current voltage and direct current power in the initial basic input parameters;

[0007] S2, when the values of the AC system short-circuit capacity, the AC voltage and the DC power after the increase step are all less than the corresponding preset values, calculating the reactive power Q consumed by the converter under the condition that the AC system short-circuit capacity, the AC voltage and the DC power are current values according to the preset first reactive power calculation model of the HVDC system dc1 ;

[0008] S3, calculating the reactive power Q consumed by the converter after the switching of a group of AC filters according to the preset second reactive power calculation model of the HVDC system under the condition that the AC system short-circuit capacity, the AC voltage and the DC power are current values dc2 ;

[0009] S4, calculating the change amount ΔQ of the reactive power exchanged between the HVDC system and the AC system after the switching of a group of AC filters under each working condition according to the reactive power Q dc1 and the reactive power Q dc2 , and determining the maximum value of the absolute value of the change amount ΔQ according to the change amount ΔQ, taking the maximum value as the reactive power exchange limit range for the HVDC system fixed reactive power control, so as to avoid the frequent switching of AC filters.

[0010] Optionally, step S1 specifically comprises:

[0011] S11, determining initial basic input parameters according to the engineering parameters of the HVDC system and initializing;

[0012] S12, assigning an initial value S k to the AC system short-circuit capacity S k0 in the initial basic input parameters, increasing the value of the AC system short-circuit capacity S k by a small step S kstep , and judging whether the value of the AC system short-circuit capacity S k is less than S kmax , if yes, executing step S13, otherwise ending the process;

[0013] S13, assigning an initial value U ac to the AC voltage U ac0 in the initial basic input parameters, increasing the value of the AC voltage U ac by a small step U acstep , and judging whether the value of the AC voltage U ac is less than U acmax , if yes, executing step S14, otherwise returning to step S12;

[0014] S14, assigning an initial value P dcr to the DC power P dcr0 in the initial basic input parameters, increasing the value of the DC power P dcrThe value increases by a small step P dcstep Then, determine the DC power P. dcr Is the value less than P? dcmax If yes, proceed to step S2; otherwise, proceed to step S4.

[0015] Optionally, the step of determining the maximum value of the absolute value of the change ΔQ based on the change ΔQ, and using the maximum value as the reactive power exchange limit range during constant reactive power control of the high-voltage DC system, thereby avoiding frequent switching of AC filters, includes:

[0016] S41. Store the change ΔQ into matrix Q. c And jump to S14 to transfer DC power P dcr The value increases by a small step P dcstep Continue execution;

[0017] S42, take Q c Maximum absolute value Q cmax Q cmax That is, the short-circuit capacity and AC voltage are respectively the short-circuit capacity S of the AC system. k and AC voltage U ac At that time, after a set of AC filters is switched on / off in the high-voltage direct current system at various DC power levels, the converter station absorbs the maximum value of the reactive power change from the system and converts Q... cmax Store in matrix Q cm Clear Q c ;

[0018] S43, Take matrix Q cm Maximum value Q cmmax Q cmmax That is, within the traversed short-circuit capacity range (S) kmin S kmax AC voltage range (U) acmin U acmax ) and DC power range (P dcrmin P dcrmax Within the system, after switching on / off a set of AC filters in the high-voltage DC system, the converter station absorbs the maximum value of the reactive power change from the system, and the process ends.

[0019] Optionally, the first reactive power calculation model includes:

[0020]

[0021] in,

[0022]

[0023]

[0024]

[0025] P = P0 (1 - a) (1) dcr P is the DC power output by the rectifier station, a is the firing angle, U dci Ud is the DC voltage of the inverter station, d xi d is the inverter-side proportion of the commutation voltage drop inductive component, d ri D is the inverter-side proportion of the commutation voltage drop resistive component, I dc I is the DC current, I dcN I is the DC current rated value, U dioNI Ud is the inverter-side rated no-load DC voltage, U dioI1 Ud is the inverter-side rated no-load DC voltage, u 2Ni1 Un is the inverter-side converter transformer network-side voltage, n tapi T is the converter transformer tap, T step2 Q is the inverter-side converter transformer tap range.

[0026] Optionally, the second reactive power calculation model comprises:

[0027]

[0028] wherein,

[0029]

[0030]

[0031]

[0032] u 2Ni2 = u 2Ni1 - Δu 2Ni ;

[0033]

[0034] P = P0 (1 - a) (1) dcr P is the DC power output by the rectifier station, a is the firing angle, U dioI2 Ud is the inverter station converter no-load DC voltage, U dci Ud is the DC voltage of the inverter station, d xi d is the inverter-side proportion of the commutation voltage drop inductive component, d ri D is the inverter-side proportion of the commutation voltage drop resistive component, I dc I is the DC current, I dcN I is the DC current rated value, U dioNI Ud is the inverter-side rated no-load DC voltage, u 2Ni2 Un is the inverter-side converter transformer network-side voltage, n tapi T is the converter transformer tap, T step2 Q is the inverter-side converter transformer tap range, Q acfsThe rated capacity of a group of AC filters, positive when filters are switched in and negative when filters are switched out.

[0035] Optionally, the reactive power Q dc1 and the reactive power Q dc2 The formula expression for calculating the change amount ΔQ of the reactive power exchanged between the high-voltage direct-current system and the alternating-current system after a group of AC filters are switched in / out under each working condition is:

[0036] ΔQ = Q dc2 - Q dc1 - ΔQ acfi ;

[0037] In the formula, ΔQ acfi is the reactive power increment provided by the AC filters in the station after a group of AC filters are switched in / out.

[0038] Optionally, the initial basic input parameters include: direct-current power, direct-current voltage, direct-current current, direct-current line resistance, alternating-current system short-circuit capacity, alternating-current grid voltage, converter transformer ratio, converter transformer tap stage, converter transformer tap distance, converter transformer short-circuit impedance, and converter transformer resistive voltage drop.

[0039] The second aspect of the present application provides a high-voltage direct-current power transmission system reactive power control system, the system comprising:

[0040] An initialization processing unit is configured to determine initial basic input parameters according to engineering parameters of the high-voltage direct-current system and perform initialization, and sequentially perform value assignment, step increment, and analysis processing on the alternating-current system short-circuit capacity, alternating-current voltage, and direct-current power in the initial basic input parameters.

[0041] A first calculation unit is configured to, when the values of the alternating-current system short-circuit capacity, alternating-current voltage, and direct-current power after the step increment are all less than the corresponding preset values, calculate the reactive power Q dc1 consumed by the converter when the alternating-current system short-circuit capacity, alternating-current voltage, and direct-current power are current values according to a preset first reactive power calculation model of the high-voltage direct-current system.

[0042] A second calculation unit is configured to, according to a preset second reactive power calculation model of the high-voltage direct-current system, calculate the reactive power Q dc2 consumed by the converter after a group of AC filters are switched in / out when the alternating-current system short-circuit capacity, alternating-current voltage, and direct-current power are current values.

[0043] An analysis unit is configured to, according to the reactive power Q dc1 and the reactive power Q dc2, the variation of the reactive power exchanged between the high voltage direct current system and the alternating current system under each working condition after a group of alternating current filters are switched on / off is calculated, so that the maximum value Q of the absolute value of the variation of the reactive power is obtained band The maximum value Q band The maximum value Q is used as the range of the limit value of the reactive power exchange when the high voltage direct current system is controlled to be constant reactive power, so that the frequent switching on / off of the alternating current filter is avoided.

[0044] The third aspect of the present application provides a high voltage direct current transmission system reactive power control device, the device comprising a processor and a memory:

[0045] The memory is used for storing program code and transmitting the program code to the processor;

[0046] The processor is used for executing the steps of the high voltage direct current transmission system reactive power control method according to the instructions in the program code.

[0047] The fourth aspect of the present application provides a computer readable storage medium, the computer readable storage medium is used for storing program code, and the program code is used for executing the high voltage direct current transmission system reactive power control method.

[0048] From the above technical solutions, the present application has the following advantages:

[0049] The present application provides a high voltage direct current transmission system reactive power control method, which firstly establishes a reactive power calculation model of the high voltage direct current system, then calculates the reactive power exchange value Qdc1 between the high voltage direct current system and the alternating current system under each working condition, then calculates the new reactive power exchange value Qdc2 between the high voltage direct current system and the alternating current system after a group of alternating current filters are switched on / off, finally, the variation of the reactive power exchanged between the high voltage direct current system and the alternating current system under each working condition after a group of alternating current filters are switched on / off is calculated, so that the maximum value of the absolute value of the variation of the reactive power is obtained, and the maximum value is used as the range of the limit value of the reactive power exchange when the high voltage direct current system is controlled to be constant reactive power, so that the frequent switching on / off of the alternating current filter is avoided. Through the method, a scientific and reasonable dead zone range of the high voltage direct current system reactive power control can be obtained, the problem of frequent switching on / off of the alternating current filter is avoided, and the stable operation level of the high voltage direct current system is improved.

[0050] Compared with the prior art:

[0051] The application can comprehensively calculate and evaluate the reactive power characteristics of the high-voltage direct current system under various working conditions, obtain a scientific and reasonable reactive power control dead zone range, and ensure that the reactive power exchange value between the converter station and the alternating current system is within the dead zone range when the alternating current filter is normally switched or the converter transformer tap is normally adjusted, or even when the alternating current filter switching and the converter transformer tap adjustment occur simultaneously under various direct current power levels, various alternating current voltage conditions and various alternating current grid conditions. Therefore, the application can first reliably avoid the problem of frequent switching of the alternating current filter and back-and-forth oscillation adjustment of the converter transformer tap, reduce the operation frequency of the alternating current filter circuit breaker and the converter transformer tap, improve the service life of the equipment, and reduce the equipment operation workload and cost; in addition, the application can also avoid the voltage impact, surge harmonic current and other interferences generated by the frequent switching of the alternating current filter on the alternating current and direct current system, and improve the stable operation level of the alternating current and direct current system. At the same time, since the method provided by the application is based on the precise quantitative calculation of the reactive dead zone range of the alternating current and direct current system under various working conditions, the blind expansion of the dead zone range is avoided, and the influence of the reactive power and voltage fluctuation on the alternating current system is also minimized, that is, the normal and reasonable operation of the alternating current filter and the converter transformer tap is realized at the minimum reactive power fluctuation cost, the contradiction between the normal operation demand of the alternating current filter and the converter transformer tap and the stability of the alternating current system is balanced, the reactive power control level of the high-voltage direct current system is effectively improved, and the safe and stable operation of the high-voltage direct current system and the near-zone alternating current system is effectively ensured. BRIEF DESCRIPTION OF DRAWINGS

[0052] Figure 1 A flowchart of a high-voltage direct current power transmission system reactive power control method provided in an embodiment of the application is shown in the figure;

[0053] Figure 2 A high-voltage direct current system reactive power exchange diagram provided in an embodiment of the application is shown in the figure;

[0054] Figure 3 A high-voltage direct current system reactive power control design flowchart provided in an embodiment of the application is shown in the figure;

[0055] Figure 4 A Qdc1 calculation flowchart provided in an embodiment of the application is shown in the figure;

[0056] Figure 5 A Qdc2 calculation flowchart provided in an embodiment of the application is shown in the figure;

[0057] Figure 6 Typical waveforms of reactive power changes after switching a group of filters provided in an embodiment of the application are shown in the figure;

[0058] Figure 7 Typical waveforms of reactive power changes after switching a group of filters provided in an embodiment of the application are shown in the figure;

[0059] Figure 8 This is a schematic diagram of the reactive power control system of a high-voltage direct current transmission system provided in the embodiments of this application. Detailed Implementation

[0060] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present application.

[0061] The following is a design description of the reactive power control in this application:

[0062] The current reactive power exchange diagram of the high-voltage direct current system is attached. Figure 2 As shown.

[0063] Appendix Figure 2 The diagram shows a typical reactive power exchange system of a high-voltage direct current (HVDC) system, which consists of three parts: the rectifier side, the inverter side, and the DC line. The rectifier side and the inverter side have similar structures, mainly including: the AC grid, the converter transformer, the converter valve, and the AC filter.

[0064] The main parameters on the rectifier side are as follows: S kr Q represents the short-circuit capacity of the AC power grid. acr Q represents the capacitive reactive power supplied by the AC power grid to the converter station. dcr Q represents the reactive power absorbed by the converter from the grid side. acfr U represents the reactive power supplied by the station's AC filter to the AC system. acr n is the converter bus voltage. tapr For the commutator tap, P dcr U represents the DC power output of the rectifier station. dcr I is the DC voltage of the rectifier station. dc It is direct current.

[0065] The main parameters on the inverter side are as follows: S ki Q represents the short-circuit capacity of the AC power grid. aci Q represents the capacitive reactive power supplied by the AC power grid to the converter station. dci Q represents the reactive power absorbed by the converter from the grid side. acfi U represents the reactive power supplied by the station's AC filter to the AC system. aci n is the converter bus voltage. tapi For the commutator tap, P dci U represents the DC power received by the inverter station. dci I is the DC voltage of the inverter station.dc is direct current.

[0066] The following takes an inverter station as an example to introduce the reactive power control method of the application. The reactive power balance equation of the inverter station is as follows:

[0067] Q aci = Q dci -Q acfi

[0068] Under the constant reactive power control, when Q aci <Q bandmin , a group of filters is cut off; when Q aci >Q bandmax , a group of filters is put in, wherein Q bandmin and Q bandmax are the lower limit and the upper limit of the dead zone Q band of the reactive power control.

[0069] As can be known from the filter switching logic above, the size of Q band is the key to affect the filter switching. The larger Q band is, the larger the allowed reactive power fluctuation range of the constant reactive power control is, and the relatively lower the filter switching frequency is, but the greater the reactive power and voltage impact on the alternating current grid will be; the smaller Q band is, the smaller the allowed reactive power fluctuation range of the constant reactive power control is, and the smaller the reactive power and voltage impact on the alternating current grid will be, but the relatively higher the filter switching frequency is, and sometimes even there will be the situation of frequent back-and-forth oscillation switching of the filters. Therefore, the selection of Q band needs to balance the filter switching frequency and the alternating current grid reactive power fluctuation two aspects, and try to reduce the reactive power impact on the grid and avoid unnecessary frequent switching of the filters. The application proposes a new reactive power control design method based on the above consideration, and the reactive power control design is performed based on the flow and the method, which can minimize the reactive power impact on the alternating current grid and avoid unnecessary frequent oscillation action of the alternating current filters and the converter transformer taps.

[0070] Please refer to Figure 1 , the reactive power control method of the high-voltage direct current transmission system provided in the embodiment of the application comprises:

[0071] Step 101, determine the initial basic input parameters according to the engineering parameters of the high-voltage direct current system and initialize, respectively, assign values to the alternating current system short-circuit capacity, alternating current voltage and direct current power in the initial basic input parameters, increase the step size and analyze and process.

[0072] Step 102, when the values of the AC system short-circuit capacity, the AC voltage and the DC power after being increased by the step are all less than the corresponding preset values, the reactive power Q consumed by the converter under the condition that the AC system short-circuit capacity, the AC voltage and the DC power are the current values is calculated according to the preset first reactive power calculation model of the HVDC system dc1 .

[0073] Step 103, the reactive power Q consumed by the converter after a group of AC filters are switched on / off under the condition that the AC system short-circuit capacity, the AC voltage and the DC power are the current values is calculated according to the preset second reactive power calculation model of the HVDC system dc2 .

[0074] Step 104, the change amount ΔQ of the reactive power exchanged between the HVDC system and the AC system after a group of AC filters are switched on / off under each working condition is calculated according to the reactive power Q dc1 and the reactive power Q dc2 , so as to determine the maximum value of the absolute value of the change amount ΔQ according to the change amount ΔQ, and take the maximum value as the reactive power exchange limit range when the HVDC system is controlled in the reactive power mode, so as to avoid the frequent switching on / off of the AC filters.

[0075] Please refer to Figure 3 , in one embodiment, the high-voltage direct-current power transmission system reactive power control method provided in the embodiments of the present application specifically includes the following steps:

[0076] S11, initial basic input parameters are determined according to the engineering parameters of the HVDC system and are initialized; wherein the initial basic input parameters include: DC power, DC voltage, DC current, DC line resistance, AC system short-circuit capacity, AC grid voltage, converter transformer ratio, converter transformer tap stage, converter transformer tap distance, converter transformer short-circuit impedance and converter transformer resistive voltage drop.

[0077] S12, the AC system short-circuit capacity S k in the initial basic input parameters is assigned an initial value S k0 , the value of the AC system short-circuit capacity S k is increased by a small step S kstep , and it is judged whether the value of the AC system short-circuit capacity S k is less than S kmax , if yes, step S13 is executed, otherwise the process is ended.

[0078] S13, the AC voltage U ac in the initial basic input parameters is assigned an initial value U ac0 , the value of the AC voltage U ac is increased by a small step U acstep , and it is judged whether the value of the AC voltage U acwhether the value of P acmax is less than U dcr , if yes, step S14 is executed, otherwise, step S12 is returned.

[0079] S14, the DC power P dcr in the initial basic input parameter is initialized. dcr0 , the value of DC power P dcr is increased by a small step P dcstep , and then it is judged whether the value of DC power P dcr is less than P dcmax , if yes, step S15 is executed, otherwise, step S19 is executed.

[0080] S15, according to the preset first reactive power calculation model of the high-voltage DC system, the reactive power Q dc1 consumed by the converter when the AC system short-circuit capacity, AC voltage and DC power are the current values is calculated. Figure 4 .

[0081] The first reactive power calculation model includes:

[0082]

[0083] wherein,

[0084]

[0085]

[0086]

[0087] wherein, P dcr is the DC power output by the rectifier station, a is the firing angle, U dci is the DC voltage of the inverter station, d xi is the inverter-side proportional commutation voltage drop inductance component, d ri is the inverter-side proportional commutation voltage drop resistance component, I dc is the DC current, I dcN is the DC current rated value, U dioNI is the inverter-side rated no-load DC voltage, U dioI1 is the inverter-side rated no-load DC voltage, u 2Ni1 is the inverter-side converter transformer grid-side voltage, n tapi is the converter transformer tap, and T step2 is the inverter-side converter transformer tap distance.

[0088] S16, according to the preset second reactive power calculation model of the high-voltage DC system, the reactive power Q dc1 consumed by the converter when the AC system short-circuit capacity, AC voltage and DC power are the current values and a group of AC filters are switched on / off is calculated.dc2 The calculation process is shown in Figure 5 .

[0089] The second reactive power calculation model comprises:

[0090]

[0091] The second reactive power calculation model comprises:

[0092]

[0093]

[0094]

[0095] u 2Ni2 = u 2Ni1 - Δu 2Ni ;

[0096]

[0097] In the formula, P dcr is the output DC power of the rectifier station, a is the firing angle, U dioI2 is the no-load DC voltage of the inverter station converter, U dci is the DC voltage of the inverter station, d xi is the inverter side proportional commutation voltage drop inductance component, d ri is the inverter side proportional commutation voltage drop resistance component, I dc is the DC current, I dcN is the DC current rating, U dioNI is the inverter side rated no-load DC voltage, u 2Ni2 is the inverter side converter transformer side voltage, n tapi is the converter transformer tap, T step2 is the inverter side converter transformer tap pitch, Q acfs is the rated capacity of a group of AC filters, which is positive when the filter is cut and negative when the filter is put.

[0098] S17, calculate the reactive power increment ΔQ provided by the AC filter in the station after a group of AC filters are put / cut acfi ; calculate the reactive power increment ΔQ absorbed by the converter station from the system after a group of filters are put / cut, ΔQ is the increment of the reactive power absorbed by the converter station from the system after a group of AC filters are put / cut when the short-circuit capacity, AC voltage and DC power are S k , U ac and P dcr .

[0099] Wherein, ΔQ = Q dc2 - Q dc1 - ΔQ acfi ;

[0100] where ΔQ acfi is the reactive power increment provided by the AC filter set after the AC filter set is switched in / out.

[0101] S18, store the change amount ΔQ c in the matrix Q dcr , and jump to S14 to increase the value of the DC power P dcstep by a small step P c , and continue execution.

[0102] S19, take the maximum value Q cmax of the absolute value, and Q cmax is the maximum value of the reactive power change absorbed by the converter station from the system after the AC filter set is switched in / out at each DC power level when the short-circuit capacity and the AC voltage are the short-circuit capacity S k and the AC voltage U ac of the AC system respectively, and store Q cmax in the matrix Q cm , and clear Q c .

[0103] S20, take the maximum value Q cm of the matrix Q cmmax , and Q cmmax is the maximum value of the reactive power change absorbed by the converter station from the system after the AC filter set is switched in / out in the range of the short-circuit capacity (S kmin , S kmax ), the range of the AC voltage (U acmin , U acmax ), and the range of the DC power (P dcrmin , P dcrmax ) that are traversed, and end the flow.

[0104] Through the above flow, the theoretical maximum range Q cmmax of the reactive power exchange fluctuation between the converter station and the AC system after the normal switching of the AC filter and the normal regulation of the converter transformer tap are considered during the normal operation of the HVDC system can be obtained.

[0105] The following is a specific application example:

[0106] Please refer to the figure, Figure 6 which is the reactive power change related waveform after a set of filters is switched in / out when the DC power varies from 0.1 p.u. to 1.2 p.u. in a certain typical mode for a certain DC project.

[0107] The following Figure 7 is the reactive power change related waveform after a set of filters is switched in / out when the DC power varies from 0.1 p.u. to 1.2 p.u. in a certain typical mode for a certain DC project.

[0108] Depend on Figure 6 and Figure 7 The results show that the maximum reactive power exchange fluctuation between the DC system and the AC grid under this method is approximately 175 Mvar. Figure 3 The process allows the value of 175Mvar to be stored in Q. cm Then continue with calculations using other methods. Through iterative calculations, Q can be obtained. cm The maximum value is approximately 240 Mvar.

[0109] Depend on Figure 6 and Figure 7 It is known that the absolute value of ΔQ increases with the increase of DC power level, that is, ΔQ is the largest at the maximum DC power. Considering that when the DC power is at its maximum, all AC filters in the converter station are usually in operation, after switching one set of filters, the AC voltage will fluctuate slightly. The total reactive power provided by all existing AC filters will also fluctuate slightly due to the AC voltage fluctuation. Although the relative proportion of the fluctuation is small, the total reactive power provided by all AC filters is large. For the sake of conservatism, the reactive power fluctuation ΔQ provided by all existing AC filters should also be included. acfall Taking this into account, its expression is as follows:

[0110]

[0111] Q acf0 For the rated capacity of a single AC filter bank, this case uses 170 Mvar, n f The expression is as follows:

[0112] n f =n max -1

[0113] Where n max This represents the total number of AC filter groups; in this case, we take 12.

[0114] u 2Ni2 and u 2Ni1 The value is taken based on the maximum voltage fluctuation, i.e., S ki Taking the minimum value and the maximum value for AC voltage, ΔQ can be calculated. acfall The maximum absolute value is approximately 50 Mvar.

[0115] Considering certain margins and engineering errors, the reactive power exchange limit range Q during constant reactive power control of a high-voltage direct current system can be defined. band Take the value according to the following formula.

[0116] Q band =k(Q cmmax +|ΔQ acfall |)

[0117] wherein k is a margin coefficient, which can be set as required, such as about 1.05, and Q band The final value can be 304 Mvar, which is the minimum value of the reactive power exchange limit that can avoid frequent switching of the AC filter, and the value is used as the dead zone range of the reactive power regulation in the constant reactive power control of the HVDC system, thereby solving the problem of frequent switching of the AC filter in normal switching of the AC filter and regulation of the converter transformer tap, and simultaneously minimizing the reactive power and voltage disturbance to the AC system.

[0118] The scheme provided in the application can achieve scientific optimization design of the reactive power control system of the HVDC system, provide theoretical support for reasonable selection of the dead zone range of the constant reactive power control, and improve the efficiency and precision of the design of the reactive power control system of the HVDC system.

[0119] The application mainly aims at the HVDC transmission system, but can also be used in other occasions where a thyristor converter is used, that is, the scheme is also considered to be within the protection scope of the application when used in other places than the HVDC project.

[0120] The above is a reactive power control method of a HVDC transmission system provided in an embodiment of the application, and the following is a reactive power control system of a HVDC transmission system provided in the embodiment of the application.

[0121] Please refer to Figure 8 The reactive power control system of the HVDC transmission system provided in the embodiment of the application comprises:

[0122] The initialization processing unit 201 is configured to determine initial basic input parameters according to engineering parameters of the HVDC system and perform initialization, and sequentially perform value assignment, step length increase and analysis processing on the AC system short-circuit capacity, AC voltage and DC power in the initial basic input parameters.

[0123] The first calculation unit 202 is configured to, when the values of the AC system short-circuit capacity, AC voltage and DC power after the step length increase are all less than the corresponding preset values, calculate the reactive power Q dc1 consumed by the converter under the condition that the AC system short-circuit capacity, AC voltage and DC power are current values according to a preset first reactive power calculation model of the HVDC system.

[0124] The second calculation unit 203 is configured to calculate the reactive power Q dc2 consumed by the converter after switching in / out a group of AC filters under the condition that the AC system short-circuit capacity, AC voltage and DC power are current values according to a preset second reactive power calculation model of the HVDC system.

[0125] The analysis unit 204 is configured to, according to the reactive power Qdc1 and reactive power Q dc2 , calculate the variation of the reactive power exchanged between the high voltage direct current system and the alternating current system after the group of alternating current filters is switched on / off under each working condition, so as to obtain the maximum value Q of the absolute value of the variation of the reactive power band , and the maximum value Q band is taken as the range of the reactive power exchange limit value when the high voltage direct current system is controlled in the constant reactive power mode, so as to avoid the frequent switching of the alternating current filters.

[0126] Further, the embodiment of the present application further provides a high voltage direct current power transmission system reactive power control device, the device comprises a processor and a memory:

[0127] The memory is used for storing program codes and transmitting the program codes to the processor.

[0128] The processor is used for executing the steps of the high voltage direct current power transmission system reactive power control method according to the instructions in the program codes.

[0129] Further, the embodiment of the present application further provides a computer readable storage medium, the computer readable storage medium is used for storing program codes, and the program codes are used for executing the method described in the above method embodiment.

[0130] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working process of the system and the unit described above can refer to the corresponding process in the above method embodiment, and will not be repeated here.

[0131] The terms "first", "second", "third", "fourth" and the like (if any) in the specification of the present application and the above drawings are used to distinguish similar objects, and do not necessarily indicate a specific order or sequence. It should be understood that the data thus used can be interchanged under appropriate circumstances, so that the embodiments of the present application described herein can be implemented in an order other than that illustrated or described herein. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion, for example, a process, method, system, product or device including a series of steps or units does not necessarily limit to the clearly listed steps or units, but can include other steps or units not clearly listed or inherent to the process, method, product or device.

[0132] It should be understood that in this application, "at least one (item)" means one or more, and "more than" means two or more. "And / or" is used to describe the relationship between related objects, indicating that three relationships can exist. For example, "A and / or B" can represent three cases: only A exists, only B exists, and both A and B exist simultaneously, where A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship. "At least one (item) of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, at least one (item) of a, b, or c can represent: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", where a, b, and c can be single or multiple.

[0133] In the several embodiments provided in this application, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be an indirect coupling or communication connection between apparatuses or units through some interfaces, and may be electrical, mechanical, or other forms.

[0134] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0135] Furthermore, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0136] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this application. The aforementioned storage medium includes: USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, optical disks, and other media capable of storing program code.

[0137] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A method of reactive power control in a high voltage direct current power transmission system, characterized by, Comprise: S1, determine initial basic input parameters according to engineering parameters of high voltage direct current system and initialize, respectively, AC system short circuit capacity, AC voltage, DC power in the initial basic input parameters are in turn assigned, increase step and analysis processing; S2, when the values of the AC system short-circuit capacity, the AC voltage and the DC power after the increase step are all less than the corresponding preset values, calculating the reactive power Q consumed by the converter under the condition that the AC system short-circuit capacity, the AC voltage and the DC power are the current values according to the preset first reactive power calculation model of the high-voltage DC system dc1 ; S3, according to the preset second reactive power calculation model of the high-voltage direct-current system, calculating the reactive power Q consumed by the converter after the switching of the set of alternating-current filters under the condition that the alternating-current system short-circuit capacity, alternating-current voltage and direct-current power are current values dc2 ; S4, according to the reactive power Q dc1 and the reactive power Q dc2 , calculate the change amount ΔQ of the reactive power exchanged between the high-voltage direct-current system and the alternating-current system after a group of alternating-current filters are put in or cut off under each working condition, so as to determine the maximum value of the absolute value of the change amount ΔQ according to the change amount ΔQ, take the maximum value as the reactive power exchange limit range when the high-voltage direct-current system is controlled, so as to avoid frequent putting in and cutting off of the alternating-current filter.

2. The method of claim 1, wherein, Step S1, specifically comprising: S11, determine initial basic input parameters according to engineering parameters of high voltage direct current system and initialize; S12, judging whether the value of the AC system short-circuit capacity S in the initial basic input parameter is less than S k initially setting the value of the AC system short-circuit capacity S k0 , increasing the value of the AC system short-circuit capacity S k by a small step S kstep , judging whether the value of the AC system short-circuit capacity S k is less than S kmax , if yes, executing step S13, otherwise ending the flow; S13, increasing the value of the AC voltage U ac by a small step U ac0 , and assigning the value U ac to the initial base input parameter U acstep ; then, in step S14, determining whether the value of the AC voltage U ac is less than U acmax ; if so, proceeding to step S15, otherwise returning to step S12. S14, the value of the direct current power P dcr is initialized dcr0 , the value of the direct current power P dcr is increased by a small step P dcstep , and then it is determined whether the value of the direct current power P dcr is less than P dcmax . If yes, step S2 is executed, otherwise step S4 is executed.

3. The method of claim 2, wherein, The maximum value of the absolute value of the change amount ΔQ is determined according to the change amount ΔQ, and the maximum value is used as the reactive power exchange limit range when the high voltage direct current system is controlled, thereby avoiding the frequent switching of AC filter, comprising: S41, store the change amount ΔQ into the matrix Q c and jump to S14 to increase the value of the direct current power P dcr by a small step P dcstep and continue execution; S42, take Q c Maximum value of absolute value Q cmax , Q cmax That is, the short-circuit capacity and the AC voltage are respectively the short-circuit capacity S k and the AC voltage U ac of the AC system, the maximum value of the change of the reactive power absorbed by the converter station from the system after a group of AC filters is put in / out at each DC power level of the high-voltage DC system, and Q cmax is stored in the matrix Q cm , and Q c is emptied; S43, take the matrix Q cm Maximum value Q cmmax , Q cmmax That is, in the range of the short-circuit capacity (S kmin , S kmax ), the range of the alternating voltage (U acmin , U acmax ) and the range of the direct current power (P dcrmin , P dcrmax ) traversed, the maximum value of the change in the reactive power absorbed by the converter station from the system after a group of alternating filters is put in or cut out in the high-voltage direct current system, and the process ends.

4. The method of claim 1, wherein, The first reactive power calculation model comprises: ； Wherein, ； ； ； wherein P dcr is the DC power output from the rectifier station, is the firing angle, U dci is the DC voltage at the inverter station, is the inverter-side proportional commutation voltage drop inductance component, is the inverter-side proportional commutation voltage drop resistance component, I dc is the DC current, is the DC current rating, is the inverter-side rated no-load DC voltage, is the inverter-side rated no-load DC voltage, is the inverter-side converter transformer tap, tapi1 is the converter transformer tap, is the inverter-side converter transformer tap span.

5. The method of claim 1, wherein, The second reactive power calculation model comprises: ； Wherein, ； ； ； ； ； where P dcr is the DC power output from the rectifier station, is the firing angle, is the inverter station converter no-load DC voltage, U dci is the inverter station DC voltage, is the inverter side proportional commutation voltage drop inductance component, is the inverter side proportional commutation voltage drop resistance component, I dc is the DC current, is the DC current rating, is the inverter side rated no-load DC voltage, is the inverter side converter transformer side voltage, n tapi2 is the converter transformer tap, is the inverter side converter transformer tap span, S ki is the AC grid short circuit capacity, is the rated capacity of a group of AC filters, positive when filters are switched out and negative when filters are switched in.

6. The method of claim 1, wherein, The reactive power Q dc1 and the reactive power Q dc2 The formula expression for calculating the change amount ΔQ of the reactive power exchanged between the high-voltage direct-current system and the alternating-current system after the group of alternating-current filters is switched on / off under each working condition is: ； In the formula, The reactive power increment provided by the AC filter after the set of AC filters is thrown / cut.

7. The method of claim 2, wherein, The initial basic input parameters include: DC power, DC voltage, DC current, DC line resistance, AC system short circuit capacity, AC grid voltage, converter transformer ratio, converter transformer tap stage, converter transformer tap distance, converter transformer short circuit impedance and converter transformer resistive voltage drop.

8. A reactive power control system for a high voltage direct current power transmission system, characterized by Comprise: Initialization processing unit, for determining initial basic input parameters according to engineering parameters of high voltage direct current system and initializing, respectively, AC system short circuit capacity, AC voltage, DC power in the initial basic input parameters are in turn assigned, increase step and analysis processing; The first calculation unit is configured to, when the values of the AC system short-circuit capacity, the AC voltage and the DC power after the increase step are all less than the corresponding preset values, calculate the reactive power Q consumed by the converter under the condition that the AC system short-circuit capacity, the AC voltage and the DC power are the current values according to the preset first reactive power calculation model of the HVDC system. dc1 ; The second computing unit is configured to calculate, according to a preset second reactive power calculation model of the HVDC system, the reactive power Q consumed by the converter after the group of AC filters is switched on / off when the AC system short-circuit capacity, the AC voltage and the DC power are current values dc2 ; Analysis unit, used to analyze reactive power Q dc1 and reactive power Q dc2 Calculate the change in reactive power ΔQ between the HVDC system and the AC system after switching on / off a set of AC filters under various operating conditions, and thus obtain the maximum absolute value Q of the reactive power change ΔQ. band , the maximum value Q band This serves as the reactive power exchange limit range for constant reactive power control in high-voltage DC systems, thereby avoiding frequent switching of AC filters.

9. A high voltage direct current power transmission system reactive power control device, characterised in that, The device comprises a processor and a memory: The memory is used for storing program code and transmitting the program code to the processor; The processor is used for executing the high voltage direct current transmission system reactive power control method according to the instructions in the program code.

10. A computer-readable storage medium, characterized in that, The computer readable storage medium is used for storing program code, and the program code is used for executing the high voltage direct current transmission system reactive power control method. The computer readable storage medium is used for storing program code, and the program code is used for executing the high voltage direct current transmission system reactive power control method.

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