CN114825356A

CN114825356A - Optimization method and device of reactive power exchange limit value, computer equipment and storage medium

Info

Publication number: CN114825356A
Application number: CN202210601761.7A
Authority: CN
Inventors: 黄聪; 郝志杰; 刘彬; 黄松强; 李晓霞; 胡付有; 孙上元; 张越帆; 王靓; 宋阳; 汤安琪; 田越宇; 夏武; 申狄秋; 王荣超; 尹忠葵; 张文鹏; 李洪坤; 荣军; 卢雯兴
Original assignee: Liuzhou Bureau of Extra High Voltage Power Transmission Co
Current assignee: Liuzhou Bureau of Extra High Voltage Power Transmission Co
Priority date: 2022-05-30
Filing date: 2022-05-30
Publication date: 2022-07-29
Anticipated expiration: 2042-05-30
Also published as: CN114825356B

Abstract

The application relates to a reactive power exchange limit optimization method and device, computer equipment and a storage medium. The method comprises the following steps: under the condition that gear adjustment of a converter transformer tap is completed, acquiring bus voltage of an alternating current bus and direct current of a converter station; determining the valve side voltage of the converter transformer according to the bus voltage and the gear after the regulation is finished; determining first reactive power consumed by the converter transformer according to the direct current and the voltage at the valve side; determining second reactive power provided by the alternating current filter according to the bus voltage and the rated reactive power of the alternating current filter; determining a reactive power exchange actual value between the converter station and the alternating current system according to the first reactive power and the second reactive power; and adjusting the initial upper limit value and the initial lower limit value of the reactive power exchange limit value according to the reactive power exchange actual value, and correspondingly obtaining a target upper limit value and a target lower limit value. By adopting the method, the accuracy of the reactive power exchange limit value can be improved, and the service life of equipment in the converter station is prolonged.

Description

Optimization method and device of reactive power exchange limit value, computer equipment and storage medium

Technical Field

The present application relates to the field of power technologies, and in particular, to a method and an apparatus for optimizing a reactive power switching limit, a computer device, and a storage medium.

Background

High voltage direct current transmission systems also need to absorb a large amount of reactive power and emit a large amount of harmonics to alternating current systems while transmitting direct current power. Therefore, a plurality of sets of ac filters are installed in the converter station of the hvdc transmission system (excluding the flexible dc transmission system) to limit the size of the characteristic harmonics in the converter station, and simultaneously provide the reactive power required for converting the dc power into the ac power. Because the reactive power can occupy the capacity of an alternating current system, the larger the reactive power is, the less the alternating current active power is, and the lower the transmission efficiency is. In order to reduce the reactive power transmitted by the ac system, the reactive power needs to be balanced locally. When the converter station transmits different direct current powers, switching control needs to be performed on each group of alternating current filters in the converter station, reactive power exchange between the converter station and an alternating current system is guaranteed within an allowable range, and the requirement of reactive power local balance is met.

At present, when setting the reactive power exchange limit between the converter station and the ac system, the ac system is usually defaulted to a strong ac system, the lower limit of the reactive power exchange limit is usually set to-230, and the upper limit of the reactive power exchange limit is usually set to 0, i.e. reactive power is not absorbed from the ac system, and a certain level of reactive support can be provided for the ac system. When a weak alternating current system (for example, an alternating current system with low reactive power or low power level) is connected to the converter station, if the reactive power is balanced locally by using the set reactive power exchange limit value, frequent switching of equipment in the converter station is easily caused, and the service life of the equipment in the converter station is further reduced.

Disclosure of Invention

In view of the above, it is necessary to provide a method, an apparatus, a computer device and a storage medium for optimizing a reactive power exchange limit that can improve the service life of equipment in a converter station.

In a first aspect, the present application provides a method for optimizing a reactive power switching limit value, which is applied to a power transmission system, where the power transmission system includes a converter station and an ac system, the converter station includes a converter transformer, a converter transformer tap, an ac bus, and an ac filter, and the method includes:

under the condition that gear adjustment of the converter transformer tap is completed, acquiring bus voltage of the alternating current bus and direct current of the converter station;

determining the voltage of the valve side of the converter transformer according to the bus voltage and the gear after the regulation is finished;

determining first reactive power consumed by the converter transformer according to the direct current and the valve side voltage;

determining second reactive power provided by the alternating current filter according to the bus voltage and the rated reactive power of the alternating current filter;

determining a reactive power exchange actual value between the converter station and the alternating current system according to the first reactive power and the second reactive power;

and adjusting the initial upper limit value and the initial lower limit value of the reactive power exchange limit value according to the reactive power exchange actual value, and correspondingly obtaining a target upper limit value and a target lower limit value.

In one embodiment, the adjusting the initial upper limit value and the initial lower limit value of the reactive power exchange limit value according to the actual reactive power exchange value to obtain the target upper limit value and the target lower limit value correspondingly includes:

comparing the reactive power exchange actual value with the initial upper limit value and the initial lower limit value respectively;

under the condition that the reactive power exchange actual value is larger than the initial upper limit value, determining candidate upper limit variation according to the difference value between the reactive power exchange actual value and the initial upper limit value;

under the condition that the reactive power exchange actual value is smaller than the initial lower limit value, determining candidate lower limit variation according to the difference value between the reactive power exchange actual value and the initial lower limit value;

determining a plurality of candidate upper limit variation amounts and a plurality of candidate lower limit variation amounts of the converter station under different direct current conditions;

determining a maximum value of the plurality of candidate upper limit variation amounts as a target upper limit variation amount;

determining a maximum value of the plurality of candidate lower limit variation amounts as a target lower limit variation amount;

determining the sum of the initial upper limit value and the target upper limit variation as a target upper limit value of the reactive power exchange limit value;

and determining the difference between the initial lower limit value and the target lower limit variation as a target lower limit value of the reactive power exchange limit value.

In one embodiment, the target upper limit variation amount and the target lower limit variation amount are less than or equal to 30 MVar.

In one embodiment, the valve side voltage is calculated based on a first formula;

wherein the first formula comprises:

wherein ,U_di0 To the valve side voltage, U _{di0_norm} For rated value of said valve-side voltage, U _{ac_1} For said bus voltage, U _{ac_norm} For the rated value of the bus voltage, T _c And adjusting the finished gear for the tap joint of the converter transformer.

In one embodiment, the first reactive power is calculated based on a second formula;

wherein the second formula comprises:

wherein ,Q_conv Is the first reactive power, I _d Mu is a commutation overlap angle of the converter transformer, and alpha is a trigger angle of a converter valve of the converter transformer for the direct current.

In one embodiment, the determining the second reactive power provided by the ac filter according to the bus voltage and the rated reactive power of the ac filter includes:

acquiring a rated value of the bus voltage, a rated frequency of the alternating current system and an operating frequency of the alternating current system;

and determining the second reactive power according to the bus voltage, the rated value of the bus voltage, the rated reactive power, the rated frequency and the operating frequency.

In one embodiment, the determining an actual value of reactive power exchange between the converter station and the ac system according to the first reactive power and the second reactive power includes:

determining the number of the alternating current filters which are connected into the converter station under the condition of transmitting the direct current;

and determining the reactive exchange actual value according to the product of the number of the alternating current filters and the second reactive power and the first reactive power.

In a second aspect, the present application further provides an apparatus for optimizing a reactive power switching limit value, which is applied to a power transmission system, where the power transmission system includes a converter station and an ac system, the converter station includes a converter transformer, a converter transformer tap, an ac bus, and an ac filter, and the apparatus includes:

the data acquisition module is used for acquiring the bus voltage of the alternating current bus and the direct current of the converter station under the condition that the gear adjustment of the converter transformer tap is finished;

the valve side voltage determining module is used for determining the valve side voltage of the converter transformer according to the bus voltage and the gear after the regulation is finished;

the power determining module is used for determining first reactive power consumed by the converter transformer according to the direct current and the valve side voltage;

the power determination module is further used for determining second reactive power provided by the alternating current filter according to the bus voltage and the rated reactive power of the alternating current filter;

the actual value determining module is used for determining a reactive power exchange actual value between the converter station and the alternating current system according to the first reactive power and the second reactive power;

and the limit value optimization module is used for adjusting the initial upper limit value and the initial lower limit value of the reactive power exchange limit value according to the reactive power exchange actual value to correspondingly obtain a target upper limit value and a target lower limit value.

In a third aspect, the present application further provides a computer device applied to a power transmission system, where the power transmission system includes a converter station and an ac system, and the converter station includes a converter transformer, a converter transformer tap, an ac bus, and an ac filter. The computer device comprises a memory storing a computer program and a processor implementing the following steps when executing the computer program:

In a fourth aspect, the present application further provides a computer readable storage medium for use in a power transmission system comprising a converter station and an ac system, the converter station comprising a converter transformer, converter transformer taps, an ac busbar and an ac filter. The computer-readable storage medium having stored thereon a computer program which, when executed by a processor, performs the steps of:

According to the optimization method, the optimization device, the computer equipment and the storage medium for the reactive power exchange limit value, under the condition that gear adjustment of the tap joint of the converter transformer is completed, the bus voltage of the alternating-current bus and the direct current of the converter station are obtained; determining the voltage of the valve side of the converter transformer according to the bus voltage and the gear after the regulation is finished; determining first reactive power consumed by the converter transformer according to the direct current and the valve side voltage; determining second reactive power provided by the alternating current filter according to the bus voltage and the rated reactive power of the alternating current filter; determining a reactive power exchange actual value between the converter station and the alternating current system according to the first reactive power and the second reactive power; and adjusting the initial upper limit value and the initial lower limit value of the reactive power exchange limit value according to the reactive power exchange actual value, and correspondingly obtaining a target upper limit value and a target lower limit value. According to the characteristics that in a converter station connected with a weak alternating current system, the reactive power provided by an alternating current filter can be influenced by the bus voltage and the power generated by the converter transformer can be influenced by the change of the tap position of the converter transformer, the tap position of the converter transformer and the bus voltage are added as parameters when the reactive power exchange limit value is optimized, so that the reactive power exchange limit value is suitable for the converter station connected with the weak alternating current system, the problems that the alternating current filter is continuously switched and the tap position of the converter transformer is frequently adjusted due to inaccurate calculation of the reactive power exchange limit value are avoided, the service life of equipment in the converter station is prolonged, and the stability of an alternating current and direct current system is maintained.

Drawings

FIG. 1 is a diagram of an exemplary implementation of a method for optimizing reactive power exchange limits;

FIG. 2 is a schematic flow diagram of a method for optimizing reactive power exchange limits in one embodiment;

FIG. 3 is a schematic flow chart of a method for optimizing reactive power exchange limits in another embodiment;

FIG. 4 is a block diagram of an apparatus for optimizing reactive power exchange limits in one embodiment;

FIG. 5 is a diagram illustrating an internal structure of a computer device according to an embodiment.

Detailed Description

In order to make the objects, technical solutions and advantages of the present application more apparent, the present application is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application.

The method for optimizing the reactive power exchange limit value provided by the embodiment of the application can be applied to the application environment shown in fig. 1. The power transmission system comprises a converter station 100 in a dc system and an ac system 200, the converter station 100 comprising a converter transformer 102, converter transformer taps 104, an ac busbar (not shown), an ac filter 106 and a control module 108. Wherein the consumer of reactive power of the converter station 100 is mainly the converter transformer 102 and the provider of reactive power is mainly the ac filter 106. The control module 108 provides a reactive power exchange limit value between the converter station 100 and the ac system 200, and when the actual value of the reactive power exchange between the converter station 100 and the ac system 200 exceeds the upper limit value of the reactive power exchange limit value, reactive power needs to be absorbed from the ac system 200, and at this time, the control module 108 controls to input a group of ac filters 106; if the actual value of reactive power exchange is lower than the lower limit of the reactive power exchange limit, the control module 108 controls to cut off a set of ac filters 106 when it is necessary to transmit reactive power to the ac system 200.

In the prior art, when the reactive power exchange limit value is set, electrical parameters such as bus voltage of an alternating current bus and reactive power of reactive power equipment in a converter station connected with a weak alternating current system are not considered, and the electrical parameters are easy to fluctuate due to changes of running conditions, generating power or electrical loads, so that the set reactive power exchange limit value is inaccurate. When the converter station is connected to the weak ac system, once the transmitted dc power changes, the reactive power consumed by the converter transformer and the bus voltage fluctuate, resulting in frequent switching of the ac filter 106 by the control module 108. If the reactive power exchange limit value is set unreasonably, the ac filter 106 will be switched in and out, that is, after the control module 108 is switched into a group of ac filters 106, the actual reactive power exchange value exceeds the lower limit value, the control module 108 will immediately switch off a group of ac filters 106, after the actual reactive power exchange value exceeds the upper limit value, the control module 108 will switch into a group of ac filters 106. the ac filters 106 will be switched frequently, so that the service life will be reduced rapidly, and even the ac filters will explode easily due to overheating of the equipment. In order to ensure the safety of the equipment, the control module 108 usually needs to be put into operation again after the ac filter 106 is cut off and cooled down for ten minutes. Since the ac filter 106 provides reactive power, once the ac filter 106 has too low a factor to satisfy the reactive power consumption of the converter transformer 102, the control module 108 may reduce the transmission of dc power for the stability of the ac system, resulting in the loss of generated power. Therefore, the influence of the weak ac system needs to be taken into account when calculating the reactive exchange limit between the converter station 100 and the ac system 200.

It should be understood that the strength of the ac system 200 is a relative concept that varies with seasonal variations, thermal and hydraulic plant start-up and shut-down variations, and electrical loads. When considering the effects of a weak ac system, it is necessary to physically find the inherent connection between the reactive power in the converter station 100 and the electrical characteristics of the ac system 200, i.e. to quantify the weak ac system by building a reasonable mathematical model or expression. A large characteristic of weak ac systems is that the voltage varies with the reactive power. For the converter station 100, the converter transformer tap 104 is used as a regulating tool of the high voltage direct current system, and the stability of the transmission power of the high voltage direct current system is reduced due to external disturbance by regulating the trigger angle or the turn-off angle to operate at a reasonable angle value. Once the converter transformer taps 104 are adjusted, the valve side voltage of the converter transformer 102 must change, which is ultimately transferred to the reactive power consumption of the converter transformer 102. Meanwhile, the ac filter 106 acts as a capacitive device that provides reactive power that is directly related to the level of the bus voltage of the ac bus. Therefore, a mathematical expression of the reactive power exchange limit value can be established according to the gear change of the converter transformer tap 104 and the change condition of the bus voltage, so that the setting of the reactive power exchange limit value is more accurate, the operation requirement of a weak alternating current system can be met, and the purpose of dynamically adjusting the reactive power exchange limit value is achieved.

In the embodiment of the application, in the calculation of the reactive power exchange limit, the influence of the gear change of the converter transformer tap 104 on the reactive power consumed by the converter transformer 102 and the influence of the bus voltage of the alternating current bus on the reactive power in the converter station 100 are considered, and the mathematical expressions of the converter transformer tap, the bus voltage and the reactive power are established, so that the reactive power exchange limit is more suitable for the converter station connected with a weak alternating current system, and the problems that the alternating current filter 106 is not switched continuously and the converter transformer tap 104 is not regulated continuously due to inaccurate calculation of the reactive power exchange limit are avoided.

In one embodiment, as shown in fig. 2, a method for optimizing reactive power exchange limit is provided, which is described by taking the method as an example for being applied to the control module 108 in fig. 1, and includes the following steps:

step 201, under the condition that gear adjustment of a converter transformer tap is completed, acquiring bus voltage of an alternating current bus and direct current of a converter station.

The gear range of the converter transformer tap is generally-3-18, and for different high-voltage direct-current projects, the gear of the converter transformer tap may be different, but generally has a positive value and a negative value, and the positive value is more than 15.

Specifically, the bus voltage of the ac bus and the dc current of the converter station may be obtained by a real-time simulation system or by measuring operational data within the converter station. The bus voltage can be adjusted through a formula U after the tap position of the converter transformer is adjusted _{ac_1} ＝U _{ac_0} +△U _ac Is calculated to obtain, wherein, U _{ac_0} For the busbar voltage, DeltaU, before regulation of the tap of the converter transformer _ac For current conversionVariation of bus voltage during dynamic adjustment of transformer taps, U _{ac_1} The bus voltage of the tap joint of the converter transformer after the first gear is adjusted up or reduced down is obtained. The dc current delivered by the converter station will vary with the dc power delivered by the converter station, typically 160A to 5000A.

And step 202, determining the voltage of the valve side of the converter transformer according to the bus voltage and the gear after the regulation is finished.

The converter transformer is a power transformer connected between a converter bridge and an alternating current system, can realize the connection between the converter bridge and an alternating current bus, and provides a three-phase commutation voltage with ungrounded neutral point for the converter bridge. The valve side voltage refers to the voltage at the output side of the transformer.

It will be appreciated that when the tap position of the converter transformer is changed, the valve side voltage of the converter transformer will necessarily change. In a specific implementation, after the gear position after the adjustment is determined and the bus voltage after the adjustment is completed, the valve side voltage of the converter transformer may be calculated according to the bus voltage, the rated value of the valve side voltage of the converter transformer, and the gear position after the adjustment is completed.

And step 203, determining the first reactive power consumed by the converter transformer according to the direct current and the valve side voltage.

Specifically, the first reactive power may be determined in various manners, in one example, the first reactive power may be calculated according to a product of the direct current and the valve side voltage, in another example, a commutation overlap angle of the converter transformer and a firing angle of the converter valve may be obtained, and the first reactive power may be determined jointly according to the direct current, the valve side voltage, the commutation overlap angle, and the firing angle. Because the dynamic adjustment condition of the converter transformer tap and the change of the bus voltage are considered in the calculation, compared with the prior art, the first reactive power consumed by the converter transformer is more accurate.

And step 204, determining second reactive power provided by the alternating current filter according to the bus voltage and the rated reactive power of the alternating current filter.

The rated reactive power of the ac filter may be determined according to the model of the ac filter, and the second reactive power is the reactive power provided by a group of ac filters in the converter station.

Specifically, the second reactive power may be determined in various manners, and in one example, the ratio of the second reactive power to the rated reactive power may be calculated according to the ratio of the bus voltage to the rated value of the bus voltage, the actual operating frequency of the ac system, and the rated frequency, and then the second reactive power may be calculated according to the ratio and the rated reactive power.

And step 205, determining a reactive power exchange actual value between the converter station and the alternating current system according to the first reactive power and the second reactive power.

It should be understood that the first reactive power is the reactive power consumed by the converter transformer, and the second reactive power is the reactive power provided by the group of ac filters, and the actual value of reactive power exchange between the converter station and the ac system may be calculated according to the total reactive power provided by the plurality of groups of ac filters in the converter station and the reactive power consumed by the converter transformer.

And step 206, adjusting the initial upper limit value and the initial lower limit value of the reactive power exchange limit value according to the reactive power exchange actual value, and correspondingly obtaining a target upper limit value and a target lower limit value.

The initial upper limit value of the reactive power exchange limit value refers to a preset upper limit value, the initial lower limit value refers to a preset lower limit value, the lower limit value is usually set to be-230, and the upper limit value is set to be 0, and the reactive power exchange limit value can meet the condition that the converter station does not absorb reactive power from the alternating current system and can provide a certain level of reactive power support for the alternating current system. According to the embodiment, the initial upper limit value and the initial lower limit value are adjusted according to the reactive power exchange actual value, so that the target upper limit value and the target lower limit value of the reactive power exchange limit value can be suitable for a strong alternating current system and a weak alternating current system, and can be dynamically adjusted by matching with the change of the operation mode of the alternating current system, the safe and efficient operation of the whole alternating current-direct current system is facilitated, the input and use of additional reactive power equipment are reduced, and the construction cost of a high-voltage direct current project is indirectly reduced.

According to the characteristic that in the converter station connected with the weak alternating current system, the bus voltage can affect the reactive power provided by the alternating current filter, and the gear change of the tap joint of the converter transformer can affect the power consumption of the converter transformer, the gear of the tap joint of the converter transformer and the bus voltage are added as parameters when the reactive exchange limit value is optimized, so that the reactive exchange limit value is suitable for the converter station connected with the weak alternating current system, the phenomena that the alternating current filter is continuously switched and the tap joint of the converter transformer is frequently adjusted due to inaccurate calculation of the reactive exchange limit value are avoided, the service life of equipment in the converter station is prolonged, and the stability of an alternating current-direct current system is maintained.

In one embodiment, the step of adjusting the initial upper limit value and the initial lower limit value of the reactive power exchange limit value according to the actual reactive power exchange value to correspondingly obtain the target upper limit value and the target lower limit value includes:

comparing the reactive power exchange actual value with an initial upper limit value and an initial lower limit value respectively; under the condition that the reactive power exchange actual value is larger than the initial upper limit value, determining candidate upper limit variable quantity according to the difference value of the reactive power exchange actual value and the initial upper limit value; under the condition that the reactive power exchange actual value is smaller than the initial lower limit value, determining candidate lower limit variation according to the difference value of the reactive power exchange actual value and the initial lower limit value; determining a plurality of candidate upper limit variation amounts and a plurality of candidate lower limit variation amounts of the converter station under different direct current conditions; determining the maximum value of the plurality of candidate upper limit variation amounts as a target upper limit variation amount; determining a maximum value of the plurality of candidate lower limit variation amounts as a target lower limit variation amount; determining the sum of the initial upper limit value and the target upper limit variable quantity as a target upper limit value of the reactive power exchange limit value; and determining the difference between the initial lower limit value and the target lower limit variation as the target lower limit value of the reactive power exchange limit.

Specifically, in the case that the reactive power exchange actual value is greater than the initial upper limit value, a difference between the reactive power exchange actual value and the initial upper limit value may be used as the candidate upper limit variation amount, and the candidate upper limit variation amount may also be determined together according to the margin of the weak ac system and the difference. In one example, assuming that the actual reactive power exchange value is Qexp and the initial upper limit value is Qexp _ up, if Qexp > Qexp _ up, the candidate upper limit variation amount Δ Qexp _ up ═ Qexp _ up-Qexp | (1+ 10%), 10% is a margin applicable to various weak ac systems.

When the reactive power exchange actual value is smaller than the initial lower limit value, a difference between the reactive power exchange actual value and the initial lower limit value may be used as a candidate lower limit variation, or the candidate lower limit variation may be determined together with the difference according to the margin of the weak alternating current system. In one example, assuming that the reactive power exchange actual value is Qexp, the initial lower limit value is Qexp _ down, and if Qexp > Qexp _ down, the candidate lower limit variation amount Δ Qexp _ down is | Qexp _ down-Qexp | (1+ 10%), and 10% is a margin applicable to various weak ac systems.

It should be understood that since the dc current is constantly changing when the converter station is transmitting each dc power, after determining the candidate upper limit variation and the candidate lower limit variation for one dc current, a plurality of candidate upper limit variations and a plurality of candidate lower limit variations for different dc currents may be determined in the same manner, and the maximum values Δ Qexp _ up _ max and Δ Qexp _ down _ max may be selected therefrom as the target upper limit variation and the target lower limit variation, respectively.

The target upper limit value of the reactive power exchange limit value may be calculated by a formula Qexp _ up ═ Qexp _ up +. DELTA.qexp _ up _ max, and the target lower limit value of the reactive power exchange limit value may be calculated by a formula Qexp _ down ═ Qexp _ down-. DELTA.qexp _ down _ max.

It is emphasized that, considering that the weak ac system is sensitive to the change of the reactive power, the change range of the reactive power exchange limit value is not too large, and in one example, the target upper limit change amount and the target lower limit change amount are not more than 30MVar, i.e., Δ Qexp _ up _ max is less than or equal to 30MVar, and Δ Qexp _ down _ max is less than or equal to 30 MVar.

In the embodiment, the initial upper limit value and the initial lower limit value of the reactive power exchange limit value are optimized, so that frequent switching of an alternating current filter and frequent adjustment of taps of a converter transformer caused by disturbance and fine adjustment of a direct current system can be effectively avoided, and the service life of equipment in the converter station is prolonged.

wherein the first formula comprises:

wherein ,U_di0 Is valve side voltage, U _{di0_norm} Rated value for valve-side voltage, U _{ac_1} For bus voltage, U _{ac_norm} Rated value for bus voltage, T _c And adjusting the finished gear for the tap joint of the converter transformer.

In the embodiment, a detailed mathematical calculation process is established by introducing an electrical parameter of the valve side voltage of the converter transformer and by taking a physical phenomenon that how the fluctuation of the bus voltage affects the reactive power of the converter station, so that a relational expression between the reactive power exchange limit value and the bus voltage is established, and a theoretical calculation basis is provided for the dynamic adjustment of the reactive power exchange limit value.

wherein the second formula comprises:

wherein ,Q_conv Is the first reactive power, U _di0 Is the valve side voltage, I _d And mu is the commutation overlap angle of the converter transformer, and alpha is the trigger angle of the converter valve of the converter transformer.

In this embodiment, because factors such as a commutation overlap angle of the converter transformer and a trigger angle of the converter valve are added when the first reactive power is calculated, the accuracy of the first reactive power is further improved.

In one embodiment, determining the second reactive power provided by the ac filter based on the bus voltage and the rated reactive power of the ac filter comprises: acquiring a rated value of bus voltage, a rated frequency of an alternating current system and an operating frequency of the alternating current system; and determining the second reactive power according to the bus voltage, the rated value of the bus voltage, the rated reactive power, the rated frequency and the operating frequency.

Specifically, the second reactive power may be calculated based on a third formula, where the third formula includes:

Q _filt ＝Q _{_norm} *(U _{ac_1} /U _{ac_norm} ) ² *(f/f _n )；

wherein ,Q_filt Is a second reactive power, U _{ac_1} For bus voltage, U _{ac_norm} Rated value of bus voltage, f operating frequency, f _n To rated frequency, Q _{_norm} Rated reactive power is provided for a bank of ac filters.

The embodiment considers that the alternating current filter is taken as a capacitive device, the reactive power provided by the alternating current filter is directly related to the level of the bus voltage, and the parameter of the bus voltage is added when the second reactive power is calculated, so that the accuracy of the second reactive power is improved.

In one embodiment, determining an actual value of reactive power exchange between the converter station and the ac system based on the first reactive power and the second reactive power comprises: determining the number of alternating current filters connected into the converter station under the condition of transmitting direct current; and determining the reactive exchange actual value according to the product of the number of the alternating current filters and the second reactive power and the first reactive power.

Specifically, the actual value of reactive power exchange may be calculated based on a fourth formula, where the fourth formula includes:

Q _exp ＝2*Q _conv -N*Q _filt ；

wherein ,Q_exp For reactive exchange of actual value, Q _conv N is the first reactive power, Q _filt For the second reactive power, N is the direct current I transmitted by the converter station _d The number of ac filters required to be invested.

In the embodiment, the condition that a plurality of groups of alternating current filters exist in the converter station is considered, and the reactive power exchange actual value is determined according to the first reactive power, the second reactive power and the number of the alternating current filters, so that the calculation accuracy of the reactive power exchange actual value is improved.

In one embodiment, as shown in fig. 3, the method for optimizing reactive power exchange limits may include the steps of:

and 301, acquiring the bus voltage of the alternating current bus and the direct current of the converter station under the condition that the gear adjustment of the converter transformer tap is finished.

And step 302, determining the voltage of the valve side of the converter transformer according to the bus voltage and the gear after the regulation is finished.

Step 303, determining a first reactive power consumed by the converter transformer according to the direct current and the valve side voltage.

And step 304, determining second reactive power provided by the alternating current filter according to the bus voltage and the rated reactive power of the alternating current filter.

And 305, determining a reactive exchange actual value between the converter station and the alternating current system according to the first reactive power and the second reactive power.

And step 306, comparing the reactive power exchange actual value with the initial upper limit value and the initial lower limit value respectively, determining a candidate upper limit variable quantity according to the difference value between the reactive power exchange actual value and the initial upper limit value under the condition that the reactive power exchange actual value is greater than the initial upper limit value, and determining a candidate lower limit variable quantity according to the difference value between the reactive power exchange actual value and the initial lower limit value under the condition that the reactive power exchange actual value is less than the initial lower limit value.

In step 307, a plurality of candidate upper limit variation amounts and a plurality of candidate lower limit variation amounts of the converter station under different direct currents are determined.

In step 308, the maximum value of the plurality of candidate upper limit variations is determined as the target upper limit variation, and the maximum value of the plurality of candidate lower limit variations is determined as the target lower limit variation.

Step 309, determining the sum of the initial upper limit value and the target upper limit variation as the target upper limit value of the reactive power exchange limit value, and determining the difference between the initial lower limit value and the target lower limit variation as the target lower limit value of the reactive power exchange limit value.

The converter station is operated at Id of 2950A, the commutation overlap angle mu of the converter transformer is 19 DEG of 0.3316rad, the firing angle alpha of 142.3 DEG of 2.48rad (the numerical values of the commutation overlap angle and the firing angle generally do not change along with the power change), the tap of the converter transformer is one gear, the bus voltage U is connected with the converter station, and the converter station is connected with the converter station through the tap of the converter transformer _ac The present embodiment will be described by taking 542kV as an example, in which 10 ac filters are put in, the rated capacity of each ac filter is 168MVar, the converter transformer tap is adjusted for one step, the bus voltage is changed by about 1kV, the bus voltage is changed by 2kV after the converter transformer tap is adjusted, the period frequency is not changed, the initial lower limit value of the reactive power switching limit is-230, and the initial upper limit value is 0.

When the tap joint of the converter transformer is adjusted from 1 gear to 2 gears due to the disturbance of the direct current system (the control module of the converter station maintains the stability of electrical parameters such as a trigger angle, a commutation overlap angle and the like by adjusting the tap joint of the converter transformer so that the converter valve can operate in the optimal working condition), the bus voltage is changed from 542kV to 544kV, namely U _{ac_0} ＝542kV，U _{ac_1} ＝544kV。

By a first formula

Calculating to obtain the valve side voltage U of the converter transformer after the gear adjustment of the tap of the converter transformer is finished _di0 273.76 kV.

By a second formula

Calculating to obtain first reactive power Q consumed by the converter transformer after the regulation is finished _conv Is 784.07 MVar.

By a third formula Q _filt ＝Q _{_norm} *(U _{ac_1} /U _{ac_norm} ) ² *(f/f _n ) After the bus voltage is calculated to change due to the gear shifting of the tap of the converter transformer, the second reactive power Q provided by each group of alternating current filters _filt Is 180.38 MVar.

By a fourth formula Q _exp ＝2*Q _conv -N*Q _filt And calculating to obtain the reactive power exchange actual value Q of the converter station and the alternating current system _exp Is-235.66 MVar.

Because the actual value of reactive exchange is smaller than the initial lower limit value-230 MVar, the control module cuts off a group of alternating current filters. However, for weak ac systems, when a set of ac filters is cut off, the reactive power varies greatly (about 168MVar), the bus voltage will drop greatly (about 3kV), and the reactive power provided by the ac filters in the converter station will decrease. Meanwhile, the dc voltage and the valve side voltage of the converter station are reduced when the bus voltage is reduced. To maintain the DC power stable, the control module will lower the converter transformer taps to increase the valve side voltage and the DC voltage. At this time, the reactive power consumed by the converter transformer is increased, and on the premise that the reactive power provided by the alternating current filter is reduced as a whole, the actual value of reactive power exchange is easily higher than the set initial upper limit value, so that the dead cycle of frequent back-and-forth adjustment of a tap joint of the converter transformer and frequent switching of the alternating current filter is caused, a safety accident that equipment is overheated and burned out is caused, and the stable operation of an alternating current/direct current system is not facilitated.

Therefore, in the weak ac system, if the reactive power switching limit value can be optimized, for example, the initial lower limit value is adjusted to-230- (-230+235.66) ((1 + 10%)) -237 (taking an integer), it is possible to avoid frequent switching or adjustment of reactive power devices such as an ac filter due to disturbance and fine adjustment of the dc system in the converter station, and improve the service life of the devices.

It should be understood that, although the steps in the flowcharts related to the embodiments are shown in sequence as indicated by the arrows, the steps are not necessarily executed in sequence as indicated by the arrows. The steps are not limited to being performed in the exact order illustrated and, unless explicitly stated herein, may be performed in other orders. Moreover, at least a part of the steps in the flowcharts related to the above embodiments may include multiple steps or multiple stages, which are not necessarily performed at the same time, but may be performed at different times, and the order of performing the steps or stages is not necessarily sequential, but may be performed alternately or alternately with other steps or at least a part of the steps or stages in other steps.

Based on the same inventive concept, the embodiment of the present application further provides an optimization device for the reactive power exchange limit value, which is used for implementing the above-mentioned optimization method for the reactive power exchange limit value. The implementation scheme for solving the problem provided by the apparatus is similar to the implementation scheme described in the above method, so specific limitations in the following embodiments of the optimization apparatus for one or more reactive power exchange limit values may refer to the limitations in the above method for optimizing the reactive power exchange limit values, and are not described herein again.

In one embodiment, as shown in fig. 4, there is provided an apparatus for optimizing a reactive power exchange limit value, which is applied to a power transmission system, the power transmission system including a converter station and an ac system, the converter station including a converter transformer, converter transformer taps, an ac bus and an ac filter, the apparatus for optimizing a reactive power exchange limit value including: a data acquisition module 401, a valve side voltage determination module 402, a power determination module 403, an actual value determination module 404, and a limit optimization module 405, wherein: a data acquisition module 401, configured to acquire a bus voltage of an ac bus and a dc current of a converter station when gear adjustment of a converter transformer tap is completed; a valve side voltage determining module 402, configured to determine a valve side voltage of the converter transformer according to the bus voltage and the adjusted gear; a power determining module 403, configured to determine, according to the direct current and the valve-side voltage, a first reactive power consumed by the converter transformer; the power determining module 403 is further configured to determine a second reactive power provided by the ac filter according to the bus voltage and the rated reactive power of the ac filter; an actual value determining module 404, configured to determine a reactive power exchange actual value between the converter station and the ac system according to the first reactive power and the second reactive power; and a limit optimization module 405, configured to adjust an initial upper limit and an initial lower limit of the reactive power exchange limit according to the actual reactive power exchange value, and correspondingly obtain a target upper limit and a target lower limit.

In one embodiment, the limit value optimizing module 405 is further configured to compare the reactive power exchange actual value with an initial upper limit value and an initial lower limit value, respectively; under the condition that the reactive power exchange actual value is larger than the initial upper limit value, determining candidate upper limit variable quantity according to the difference value of the reactive power exchange actual value and the initial upper limit value; under the condition that the reactive power exchange actual value is smaller than the initial lower limit value, determining candidate lower limit variation according to the difference value of the reactive power exchange actual value and the initial lower limit value; determining a plurality of candidate upper limit variation amounts and a plurality of candidate lower limit variation amounts of the converter station under different direct current conditions; determining the maximum value of the plurality of candidate upper limit variation amounts as a target upper limit variation amount; determining a maximum value of the plurality of candidate lower limit variation amounts as a target lower limit variation amount; determining the sum of the initial upper limit value and the target upper limit variable quantity as a target upper limit value of the reactive power exchange limit value; and determining the difference between the initial lower limit value and the target lower limit variation as the target lower limit value of the reactive power exchange limit.

In one embodiment, the valve side voltage determining module 402 is configured to calculate a valve side voltage based on a first formula; wherein the first formula comprises:

In an embodiment, the power determining module 403 is further configured to calculate a first reactive power based on a second formula; wherein the second formula comprises:

wherein ,Q_conv Is the first reactive power, I _d And the mu is a commutation overlap angle of the converter transformer, and the alpha is a trigger angle of a converter valve of the converter transformer.

In one embodiment, the power determination module 403 is further configured to obtain a rated value of the bus voltage, a rated frequency of the ac system, and an operating frequency of the ac system; and determining the second reactive power according to the bus voltage, the rated value of the bus voltage, the rated reactive power, the rated frequency and the operating frequency.

In one embodiment, the actual value determining module 404 is further configured to determine the number of ac filters that the converter station switches in when transmitting dc current; and determining the reactive exchange actual value according to the product of the number of the alternating current filters and the second reactive power and the first reactive power.

The modules in the reactive power exchange limit optimization device can be wholly or partially realized by software, hardware and a combination thereof. The modules can be embedded in a hardware form or independent from a processor in the computer device, and can also be stored in a memory in the computer device in a software form, so that the processor can call and execute operations corresponding to the modules.

In one embodiment, a computer device is provided, which may be a terminal, and its internal structure diagram may be as shown in fig. 4. The computer device includes a processor, a memory, a communication interface, a display screen, and an input device connected by a system bus. Wherein the processor of the computer device is configured to provide computing and control capabilities. The memory of the computer device comprises a nonvolatile storage medium and an internal memory. The non-volatile storage medium stores an operating system and a computer program. The internal memory provides an environment for the operation of an operating system and computer programs in the non-volatile storage medium. The communication interface of the computer device is used for carrying out wired or wireless communication with an external terminal, and the wireless communication can be realized through WIFI, a mobile cellular network, NFC (near field communication) or other technologies. The computer program is executed by a processor to implement a method of optimizing reactive power exchange limits. The display screen of the computer equipment can be a liquid crystal display screen or an electronic ink display screen, and the input device of the computer equipment can be a touch layer covered on the display screen, a key, a track ball or a touch pad arranged on the shell of the computer equipment, an external keyboard, a touch pad or a mouse and the like.

Those skilled in the art will appreciate that the architecture shown in fig. 4 is merely a block diagram of some of the structures associated with the disclosed aspects and is not intended to limit the computing devices to which the disclosed aspects apply, as particular computing devices may include more or less components than those shown, or may combine certain components, or have a different arrangement of components.

In one embodiment, a computer device is provided, comprising a memory and a processor, the memory having a computer program stored therein, the processor implementing the following steps when executing the computer program:

under the condition that gear adjustment of a converter transformer tap is completed, acquiring bus voltage of an alternating current bus and direct current of a converter station;

determining the valve side voltage of the converter transformer according to the bus voltage and the gear after the regulation is finished;

determining first reactive power consumed by the converter transformer according to the direct current and the voltage at the valve side;

In one embodiment, the processor, when executing the computer program, further performs the steps of:

comparing the reactive power exchange actual value with an initial upper limit value and an initial lower limit value respectively; under the condition that the reactive power exchange actual value is larger than the initial upper limit value, determining candidate upper limit variable quantity according to the difference value of the reactive power exchange actual value and the initial upper limit value; under the condition that the reactive power exchange actual value is smaller than the initial lower limit value, determining candidate lower limit variation according to the difference value of the reactive power exchange actual value and the initial lower limit value; determining a plurality of candidate upper limit variation amounts and a plurality of candidate lower limit variation amounts of the converter station under different direct current conditions; determining a maximum value of the plurality of candidate upper limit variation amounts as a target upper limit variation amount; determining a maximum value of the plurality of candidate lower limit variation amounts as a target lower limit variation amount; determining the sum of the initial upper limit value and the target upper limit variable quantity as a target upper limit value of the reactive power exchange limit value; and determining the difference between the initial lower limit value and the target lower limit variation as the target lower limit value of the reactive power exchange limit.

the target upper limit variation amount and the target lower limit variation amount are less than or equal to 30 MVar.

the valve side voltage is obtained by calculation based on a first formula; wherein the first formula comprises:

the first reactive power is calculated based on a second formula; wherein the second formula comprises:

wherein ,Q_conv Is the first reactive power, I _d And mu is the commutation overlap angle of the converter transformer, and alpha is the trigger angle of the converter valve of the converter transformer.

acquiring a rated value of bus voltage, a rated frequency of an alternating current system and an operating frequency of the alternating current system; and determining the second reactive power according to the bus voltage, the rated value of the bus voltage, the rated reactive power, the rated frequency and the operating frequency.

determining the number of alternating current filters connected into the converter station under the condition of transmitting direct current; and determining the reactive exchange actual value according to the product of the number of the alternating current filters and the second reactive power and the first reactive power.

In one embodiment, a computer-readable storage medium is provided, having a computer program stored thereon, which when executed by a processor, performs the steps of:

In one embodiment, the computer program when executed by the processor further performs the steps of:

wherein ,U_di0 Is valve side voltage, U _{di0_norm} Rated value for valve-side voltage, U _{ac_1} For bus voltage, U _{ac_norm} Rated value of bus voltage, T _c And adjusting the finished gear for the tap joint of the converter transformer.

determining the number of alternating current filters connected into the converter station under the condition of transmitting direct current; and determining a reactive exchange actual value according to the product of the number of the alternating current filters and the second reactive power and the first reactive power.

In one embodiment, a computer program product is provided, comprising a computer program which, when executed by a processor, performs the steps of:

wherein ,U_di0 Is valve side voltage，U _{di0_norm} Rated value for valve-side voltage, U _{ac_1} For bus voltage, U _{ac_norm} Rated value for bus voltage, T _c And adjusting the finished gear for the tap joint of the converter transformer.

It should be noted that, the user information (including but not limited to user device information, user personal information, etc.) and data (including but not limited to data for analysis, stored data, presented data, etc.) referred to in the present application are information and data authorized by the user or sufficiently authorized by each party.

It will be understood by those skilled in the art that all or part of the processes of the methods of the embodiments described above can be implemented by hardware instructions of a computer program, which can be stored in a non-volatile computer-readable storage medium, and when executed, can include the processes of the embodiments of the methods described above. Any reference to memory, database, or other medium used in the embodiments provided herein may include at least one of non-volatile and volatile memory. The nonvolatile Memory may include Read-Only Memory (ROM), magnetic tape, floppy disk, flash Memory, optical Memory, high-density embedded nonvolatile Memory, resistive Random Access Memory (ReRAM), Magnetic Random Access Memory (MRAM), Ferroelectric Random Access Memory (FRAM), Phase Change Memory (PCM), graphene Memory, and the like. Volatile Memory can include Random Access Memory (RAM), external cache Memory, and the like. By way of illustration and not limitation, RAM can take many forms, such as Static Random Access Memory (SRAM) or Dynamic Random Access Memory (DRAM), among others. The databases referred to in various embodiments provided herein may include at least one of relational and non-relational databases. The non-relational database may include, but is not limited to, a block chain based distributed database, and the like. The processors referred to in the embodiments provided herein may be general purpose processors, central processing units, graphics processors, digital signal processors, programmable logic devices, quantum computing based data processing logic devices, etc., without limitation.

The technical features of the above embodiments can be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the above embodiments are not described, but should be considered as the scope of the present specification as long as there is no contradiction between the combinations of the technical features.

The above-mentioned embodiments only express several embodiments of the present application, and the description thereof is specific and detailed, but not construed as limiting the scope of the present application. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the concept of the present application, which falls within the scope of protection of the present application. Therefore, the protection scope of the present application shall be subject to the appended claims.

Claims

1. A method for optimizing reactive power exchange limit values, applied to a power transmission system, is characterized in that the power transmission system comprises a converter station and an alternating current system, the converter station comprises a converter transformer, converter transformer taps, an alternating current bus and an alternating current filter, and the method comprises the following steps:

2. The method according to claim 1, wherein the adjusting the initial upper limit value and the initial lower limit value of the reactive power exchange limit value according to the reactive power exchange actual value to obtain the target upper limit value and the target lower limit value of the reactive power exchange limit value correspondingly comprises:

3. The method of claim 2, wherein the target upper limit variation amount and the target lower limit variation amount are less than or equal to 30 MVar.

4. The method according to any one of claims 1 to 3, wherein the valve side voltage is calculated based on a first formula;

wherein the first formula comprises:

wherein ,U_di0 To the valve side voltage, U _{di0_norm} For rated value of said valve-side voltage, U _{ac_1} For said bus voltage, U _{ac_norm} For the rated value of the bus voltage, T _c For the said converter transformerAnd adjusting the finished gear by a tap of the transformer.

5. The method of claim 4, wherein the first reactive power is calculated based on a second formula;

wherein the second formula comprises:

6. The method of claim 1, wherein determining the second reactive power provided by the ac filter based on the bus voltage and the rated reactive power of the ac filter comprises:

7. The method according to claim 6, wherein said determining an actual value of reactive power exchange between the converter station and the ac system based on the first reactive power and the second reactive power comprises:

8. An apparatus for optimizing reactive power exchange limits for use in a power transmission system, the power transmission system including a converter station and an ac system, the converter station including a converter transformer, converter transformer taps, an ac bus and an ac filter, the apparatus comprising:

9. A computer device comprising a memory and a processor, the memory storing a computer program, characterized in that the processor, when executing the computer program, implements the steps of the method of any of claims 1 to 7.

10. A computer-readable storage medium, on which a computer program is stored, which, when being executed by a processor, carries out the steps of the method of any one of claims 1 to 7.