CN114336733B

CN114336733B - Economic improvement evaluation method for offshore wind power flexible and straight system energy consumption device

Info

Publication number: CN114336733B
Application number: CN202111403029.0A
Authority: CN
Inventors: 罗代军; 鲁晓军; 胡宗邱; 李梦柏; 邓海峰; 金能; 孙文才; 陈功; 陈飞宇
Original assignee: Changjiang Institute of Survey Planning Design and Research Co Ltd; China Three Gorges Construction Engineering Co Ltd
Current assignee: Changjiang Institute of Survey Planning Design and Research Co Ltd; China Three Gorges Construction Engineering Co Ltd
Priority date: 2021-11-24
Filing date: 2021-11-24
Publication date: 2023-05-26
Anticipated expiration: 2041-11-24
Also published as: CN114336733A

Abstract

The invention discloses an economic improvement evaluation method for an offshore wind power flexible-direct system energy consumption device. It comprises the following steps: step one: inputting characteristic parameters of the offshore wind power flexible-direct system, and preprocessing data; step two: calculating the energy margin of the offshore wind power flexible-direct system; step three: checking the feasibility of energy margin of the offshore wind power flexible straightening system; step four: calculating economic improvement indexes of the energy consumption device under a parallel input strategy; step five: and calculating an economic improvement index of the energy consumption device under the serial input strategy. The method has the advantages that when the alternating current power grid at the receiving end has alternating current faults, the maximum energy margin of the offshore wind power flexible-direct system is quantitatively evaluated, and the situation that the energy consumption device is economically improved by using the parallel input strategy and the serial input strategy of energy absorption and resistance energy consumption of the energy margin is quantitatively compared and analyzed so as to determine what input strategy is adopted.

Description

Economic improvement evaluation method for offshore wind power flexible and straight system energy consumption device

Technical Field

The invention relates to the technical field of power transmission of power systems, in particular to the field of offshore wind power engineering which is connected by flexible direct current power transmission, and more particularly relates to an economical efficiency improvement evaluation method of a direct current energy consumption device of an offshore wind power system which is connected by flexible direct current.

Background

At present, offshore wind power grid connection at open sea adopts a high-voltage flexible direct current transmission (VSC-HVDC) based technology. The modularized multi-level converter (MMC) is a flexible direct current transmission converter which is more suitable for application scenes of high voltage class and large transmission capacity, and therefore has wide application prospect in large-scale grid connection of open sea wind power. The current converter topology of MMC is adopted in Jiangsu, such as the eastern offshore wind power flexible direct current transmission project in China.

The fault of the receiving end alternating current system is a risk factor which must be considered in the design and operation stages of the offshore wind power flexible direct current transmission system. When the alternating current power grid at the receiving end has alternating current faults, the transmitted alternating current power of the onshore converter station is blocked. The offshore wind farm still continuously transmits wind power to the receiving end, so that the power of the alternating current side and the direct current side of the land convertor station is differential, and the differential power continuously charges a plurality of sub-module capacitors of the MMC. Under conventional current vector control, the land-based converter station will lose control over the dc voltage, resulting in a dc overvoltage.

In order to suppress the dc overvoltage caused by the ac fault at the receiving end, a method commonly adopted in engineering is to configure a certain capacity of energy dissipation device in the system to dissipate the differential power, including ac energy dissipation device and dc energy dissipation device. For offshore wind power, the area and the bearing requirement of an offshore platform can be increased by configuring an alternating current energy consumption device on the sea, the engineering construction investment is increased, the operation and maintenance conditions of the offshore platform are harsh, and the requirement on the reliability of a system is extremely high. Therefore, the offshore wind power after the soft direct grid connection is generally provided with a direct current energy consumption device on the direct current side of the onshore converter station, so that surplus power of a system during the onshore alternating current power grid fault is dissipated, and direct current overvoltage is avoided.

For example, a direct current energy consumption valve is arranged on the direct current side of an onshore station in the east-ocean wind power project. When the direct-current voltage exceeds the action threshold value of the direct-current energy consumption device, the direct-current voltage at two ends of the energy consumption resistor is controlled by adjusting the quantity of submodules input by the direct-current energy consumption valve, and the energy consumption power is adjusted, so that the direct-current side overvoltage of the converter station is avoided.

In order to improve the operation economy of the direct current energy consumption valve, the energy margin of the converter valve can be fully excavated, and the surplus power of the system can be temporarily absorbed by utilizing the energy margin of the converter valve during alternating current faults. The invention patent 202010858844.5 discloses a method for controlling active energy under alternating current faults of a soft direct grid-connected system of offshore wind power, which is used for controlling the active energy to cope with the alternating current faults. In the method, the energy consumption device and the active energy control of the onshore converter station are put into operation together, so that the dissipation power of the energy consumption device is shared.

However, not only the converter valve has a certain energy margin, but also a large number of submodule capacitors are arranged in the direct current energy consumption valve, and energy storage elements such as the direct current capacitor of the direct current submarine cable are provided with a certain energy margin, so that the energy margin needs to be utilized. In addition, the surplus power of the system can be carried out by utilizing the capacitor, so that the system can be parallel to the energy consumption device, and a serial control strategy that the surplus power of the system is absorbed by utilizing the capacitor and then the energy consumption device is put into can be adopted. How to quantitatively analyze the maximum energy margin of the offshore wind power flexible straightening system, and compare and evaluate the economic improvement condition of the energy consumption device by using the parallel control strategy and the serial control strategy of energy absorption and resistance energy consumption of the energy margin, and further study is needed.

Therefore, the method for quantitatively evaluating the maximum energy margin of the offshore wind power flexible-direct system when the AC power grid at the receiving end has AC faults is developed, and the situation that the energy consumption of the energy margin, the parallel input strategy for resistance energy consumption and the serial input strategy are utilized for improving the economical efficiency of the energy consumption device is quantitatively compared and analyzed, so that the evaluation method for determining what input strategy is adopted is necessary.

Disclosure of Invention

According to engineering parameters of the flexible direct current converter valve and the direct current energy consumption valve and the statistical characteristics of alternating current fault data of a power grid at a receiving end, the method calculates data such as input time, dissipation power, dissipation energy and the like of the direct current energy consumption valve under different active energy control strategies by the converter valve, and finally converts the data into an index for improving the economy, so that the maximum energy margin of the offshore wind power flexible direct current system is quantitatively evaluated when the alternating current power grid at the receiving end fails, and the situation that the energy consumption device is economically improved by utilizing the parallel input strategy and the serial input strategy of energy margin energy absorption and resistance energy consumption is quantitatively compared and analyzed to determine what input strategy is adopted.

In order to achieve the above purpose, the technical scheme of the invention is as follows: the method for evaluating the economic improvement of the offshore wind power flexible-straight system energy consumption device is characterized by comprising the following steps of:

Step one: inputting characteristic parameters of the offshore wind power flexible-direct system, and preprocessing data;

step two: calculating the energy margin of the offshore wind power flexible-direct system;

step three: checking the feasibility of energy margin of the offshore wind power flexible straightening system;

step four: calculating economic improvement indexes of the energy consumption device under a parallel input strategy;

step five: and calculating an economic improvement index of the energy consumption device under the serial input strategy.

In the above technical solution, in the first step, the characteristic parameters of the offshore wind power flexible direct current system include the characteristic parameters of the converter valve, the characteristic parameters of the direct current energy consumption valve, the characteristic parameters of the direct current sea cable, and the fault characteristic parameters of the receiving end alternating current power grid;

characteristic parameters of the converter valve include: rated DC voltage u _dcN Redundancy ρ of converter valve submodule and rated active power P _N Rated voltage u of converter valve submodule _subN Rated voltage u of converter valve submodule capacitor _cN DC capacitance value C of converter valve submodule _sub Withstand voltage multiple sequence of converter valve submodule capacitors (K _Cmaxp ，p＝1，2，……N _C ，N _C For converter valvesThe total number of voltage withstand multiples in the voltage withstand multiple sequence of the module capacitor is a positive integer and greater than or equal to 1) and the maximum allowable run time sequence (T) at the corresponding voltage withstand multiple _Cmaxp ，p＝1，2，……N _C ，N _C The total number of the withstand voltage multiples in the withstand voltage multiple sequence of the capacitance of the converter valve submodule is a positive integer and is more than or equal to 1);

the characteristic parameters of the direct current energy consumption valve comprise: rated voltage u of DC energy consumption valve sub-module _RsubN Rated voltage u of direct current energy consumption valve submodule capacitor _RcN Capacitance value C of DC energy consumption valve submodule _Rsub Withstand voltage multiple sequence of direct current energy consumption valve submodule capacitor (K _Rmaxq ，q＝1，2，……N _R ，N _R The total number of voltage withstand times in the voltage withstand times sequence of the capacitor of the DC energy consumption valve submodule is positive integer and is more than or equal to 1) and the maximum allowable operation time sequence (T) under the corresponding voltage withstand times _Rmaxq ，q＝1，2，……N _R ，N _R The total number of the withstand voltage multiples in the withstand voltage multiple sequence of the capacitor of the direct current energy consumption valve submodule is a positive integer and is more than or equal to 1);

the characteristic parameters of the direct current submarine cable comprise: maximum allowable DC voltage value u of DC submarine cable _dcmax Equivalent direct-current capacitor C of direct-current submarine cable _cable ；

The fault characteristic parameters of the receiving end alternating current power grid comprise: average number of single-phase earth short-circuit faults and corresponding time sequence of each fault, number of two-phase earth and two-phase short-circuit faults and corresponding time sequence of each fault, number of three-phase short-circuit faults and corresponding time sequence of each fault, the time sequence of all the alternating-current faults forms an alternating-current fault set of the receiving alternating-current power grid, N _F The total number of alternating current faults is concentrated for the alternating current fault accidents of the receiving alternating current power grid, is a positive integer and is more than or equal to 1.

In the above technical solution, in the first step, the data preprocessing operation includes calculating a rated energy storage of the converter valve capacitor, calculating a rated energy storage of the dc energy consumption valve capacitor, and calculating a rated energy storage of the dc sea cable;

rated stored energy W of converter valve capacitor _N The calculation method of (1) is as follows:

in the above formula (1):

indicating the total number of 6 bridge arm sub-modules of the converter valve without considering redundancy, < ->

Representing the capacitance rating energy in each sub-module of the converter valve;

rated energy storage W of direct current energy consumption valve capacitor _RN The calculation method of (1) is as follows:

in the above formula (2):

representing the total number of direct current energy consumption valve bridge arm submodules without considering redundancy, < >>

Representing the capacitance rated energy in each sub-module of the direct current energy consumption valve;

rated energy storage W of direct current submarine cable _caN The calculation method of (1) is as follows:

in the above technical scheme, in the second step, the energy margin of the offshore wind power flexible-direct system includes a converter valve energy margin, a direct current energy consumption valve energy margin and a direct current submarine cable energy margin;

the energy margin of the converter valve is determined according to the withstand voltage multiple of the capacitance of the submodule,

The converter valve energy margin calculation includes the following sub-steps: a value of p=1 is set,

the method comprises the following substeps: selecting withstand voltage multiple K of capacitance voltage of converter valve submodule _Cmaxp The energy margin DeltaW of the converter valve under the pressure-resistant multiple _maxKp The calculation method of (1) is as follows:

in the above formula (4):

the total number of 6 bridge arm sub-modules of the converter valve is shown when redundancy is considered,

k is taken to represent withstand voltage multiple of capacitance of converter valve submodule _Cmaxp The energy stored by the time submodule;

sub-step two: setting p=p+1 when p is not equal to N _C When the calculation process is started, and the calculation process is started;

through the calculation, all N of the capacitance of the converter valve submodule can be obtained _C Energy margin sequence of converter valve under multiple withstand voltage

The calculation of the energy margin of the direct current energy consumption valve comprises the following substeps: setting q=1 and,

the method comprises the following substeps: withstand voltage multiple K of capacitor voltage of direct current energy consumption valve submodule _Rmaxq The energy margin DeltaW of the DC energy consumption valve under the pressure-resistant multiple _RmaxKq The calculation method of (1) is as follows:

/>

in the above formula (5):

representing the total number of dc-dissipative valve leg sub-modules considering redundancy,

k is taken to represent the withstand voltage multiple of the capacitance of the direct current energy consumption valve submodule _Rmaxq The energy stored by the time submodule;

sub-step two: setting q=q+1, when q is not equal to N _R When the calculation process is started, and the calculation process is started;

through the calculation, all N of the capacitance of the direct current energy consumption valve submodule can be obtained _R Energy margin sequence of direct current energy consumption valve under multiple withstand voltage

DC submarine cable energy margin delta W _camx According to the allowable maximum DC voltage value u _dcmax Calculating the energy margin of the direct current submarine cable:

in the above technical solution, in the third step, checking the energy margin feasibility of the offshore wind power straightening system includes the following sub-steps:

the method comprises the following substeps: the DC voltage of the DC sea cable takes the maximum value u _dcmax Setting p=1;

sub-step two: selecting an overvoltage multiple K of the overvoltage of the submodule capacitor voltage from a sequence of the voltage withstand multiples of the submodule capacitor of the converter valve _Cmaxp ；

And a sub-step three: solving the modulation ratio of the converter valve and the numerical value of bridge arm current by utilizing a Newton-Lapherson method according to an algebraic equation set of a steady-state mathematical model of the converter valve;

and a sub-step four: checking whether the modulation ratio of the converter valve and the bridge arm current meet the constraint conditions of the converter valve and the bridge arm current (including the fact that the modulation ratio is in a numerical range required by stable operation of the converter valve, and the bridge arm current meets the tolerance capability of a power electronic device of a bridge arm submodule of the converter valve);

Fifth, the sub-steps are: if the modulation ratio and the bridge arm current meet constraint conditions, the capacitance overvoltage multiple K of the submodule is determined _Cmaxp Feasible, use K _Cmaxp The calculated corresponding converter valve energy margin is feasible; otherwise, consider the sub-module capacitance overvoltage multiple K _Cmaxp It is not possible to delete the withstand voltage multiple K from the sequence of withstand voltage multiples of the capacitance of the converter valve submodule _Cmaxp Deleting the corresponding energy margin DeltaW from the converter valve energy margin sequence _maxKp ；

And step six: setting p=p+1 when p is not equal to N _C When the calculation process is started, and the calculation process is started;

after the calculation flow, a feasible capacitance withstand voltage multiple sequence (K) of the converter valve submodule can be obtained _Cmaxp ，p＝1，……N _COK ，N _COK The total number of the withstand voltage multiples in the withstand voltage multiple sequences of the feasible converter valve submodule capacitor is positive integer and is more than or equal to 1), and the maximum allowable operation time sequence (T) under the corresponding withstand voltage multiples _Cmaxp ，p＝1，……N _COK ) Converter valve energy margin sequence under pressure-resistant multiple

In the above technical solution, in the fourth step, the parallel input strategy means that surplus power is absorbed simultaneously by using the energy margin of the offshore wind power flexible direct system and the energy consumption resistor of the direct current energy consumption valve, and the calculation of the energy consumption device economical efficiency improvement index under the parallel input strategy includes the following substeps, firstly, setting the number i=1, where i is a positive integer and is less than or equal to N _F ：

The method comprises the following substeps: selecting an ith alternating current fault from the alternating current fault accident set of the receiving end alternating current power grid, wherein the duration time of the alternating current fault is t _i ；

Sub-step two:estimating surplus energy W accumulated without taking energy consumption measures in the fault _Fimax The calculation method comprises the following steps:

wherein, the fault coefficient K is set according to the AC fault type of the receiving AC power grid _F For single-phase earth short-circuit fault, K _F =1; for two-phase short circuit or two-phase ground short circuit fault, K _F =2; for three-phase short-circuit fault, K _F ＝3；

And a sub-step three: selecting proper withstand voltage multiple K from feasible capacitance withstand voltage multiple sequences of converter valve submodules _Cmax Satisfy its corresponding maximum allowable run time T _Cmax Not exceeding t _i And is closest to t in the optional maximum allowable run time sequence _i The method comprises the steps of carrying out a first treatment on the surface of the Selecting proper withstand voltage multiple K from capacitor withstand voltage multiple sequences of direct current energy consumption valve submodule _Rmax Satisfy its corresponding maximum allowable run time T _Rmax Not exceeding t _i And is closest to t in the optional maximum allowable run time sequence _i The method comprises the steps of carrying out a first treatment on the surface of the Calculating corresponding withstand voltage multiple K _Cmax Energy margin delta W of lower converter valve _maxK And corresponding withstand voltage multiple K _Rmax Energy margin delta W of lower direct current energy consumption valve _RmaxK ；

And a sub-step four: calculating the maximum surplus power P shared by the direct current energy consumption valve _Cmax The calculation method comprises the following steps:

satisfy P _Cmax max(T _Cmax ,T _Rmax )≤W _Fimax (8)

Wherein max (T _Cmax ,T _Rmax ) The representation taking T _Cmax And T _Rmax Is a larger value of (a);

fifth, the sub-steps are: setting surplus power shared by direct current energy consumption valve to correspondEconomic improvement index k of (2) _P And an economic improvement index k corresponding to the duration of the surplus power shared by the direct current energy consumption valve _t Further calculate the energy consumption valve economical efficiency and promote index E in this trouble _i The calculation method comprises the following steps:

E _i ＝k _P P _Cmax +k _t max(T _Cmax ,T _Rmax ) (9)

and step six: setting i=i+1, confirming whether i reaches the maximum value N _F The method comprises the steps of carrying out a first treatment on the surface of the If i does not reach the maximum value N _F Repeating the sub-steps one to five, selecting the next alternating current fault from the alternating current fault accident set of the receiving end alternating current power grid, and calculating the economic improvement index of the energy consumption valve in the next alternating current fault under the parallel input strategy until the economic improvement index of the alternating current fault in all the alternating current fault sets is calculated;

if i reaches the maximum value N _F Entering a sub-step seven;

seventh, the sub-steps: accumulated economical efficiency improvement index E after alternating current fault set scanning calculation of terminal alternating current power grid of calculation energy consumption device under parallel input strategy _{Parallel arrangement} The calculation formula is as follows:

in the above technical solution, in the fifth step, the serial input strategy indicates that the surplus power is absorbed by using the energy margin of the offshore wind power flexible direct-current system, and the surplus power is absorbed by using the energy consumption resistor of the direct-current energy consumption valve after the energy margin is exhausted, firstly, the number of operations saved by the energy consumption device under the serial input strategy is set to be N, the saved operation time is t, an initial value n=0, t=0, and the numbers j=1, j are positive integers and are less than or equal to N _F Calculating the economic improvement index of the energy consumption device under the serial input strategy comprises the following substeps:

the method comprises the following substeps: selecting the j-th alternating current fault from the alternating current fault set of the receiving end alternating current power grid, wherein the duration time of the alternating current fault is t _j ；

Sub-step two: estimating surplus energy W accumulated without taking energy consumption measures in the fault _Fjmax The calculation method comprises the following steps:

/>

And a sub-step three: selecting the maximum withstand voltage multiple of the capacitance of the converter valve submodule and the corresponding maximum allowable running time T from a feasible withstand voltage multiple sequence of the capacitance of the converter valve submodule _Cmax Calculating the energy margin of the converter valve under the corresponding pressure-resistant multiple; selecting the maximum withstand voltage multiple of the capacitor of the direct current energy consumption valve submodule from the withstand voltage multiple sequence of the capacitor of the direct current energy consumption valve submodule, and calculating the energy margin of the direct current energy consumption valve under the corresponding withstand voltage multiple; adding the energy margin of the converter valve, the energy margin of the direct current energy consumption valve and the energy margin of the direct current sea cable to obtain the maximum energy margin of the offshore wind power flexible-direct system;

And a sub-step four: judging maximum energy margin and W of offshore wind power flexible-direct system _Fjmax Is a relative magnitude relation of (2); when the maximum energy margin of the offshore wind power flexible-direct system is greater than or equal to W _Fjmax When the alternating current fault is generated, the energy consumption device is not needed to be put into, the data of the operation times and the operation time saved by the energy consumption device are updated, and the calculation method is as follows:

when the maximum energy margin of the offshore wind power flexible-straightening system is smaller than W _Fjmax When the alternating current fault needs to be input into the energy consumption device, the data of the operation times and the operation time saved by the energy consumption device are updated, and the calculation method is as follows:

fifth, the sub-steps are: setting j=j+1, confirming whether j reaches the maximum value N _F The method comprises the steps of carrying out a first treatment on the surface of the If j does not reach the maximum value N _F Repeating the sub-step one to the sub-step four, selecting the next alternating current fault from the alternating current fault accident set of the receiving end alternating current power grid, and calculating the operation times and operation time saved by the direct current energy consumption valve under the serial input strategy in the current alternating current fault;

if j reaches the maximum value N _F Then enter the next substep;

and step six: setting an economical efficiency improvement index k corresponding to the number of times of operation of the energy consumption device _N Economic improvement index k corresponding to operation time saved by energy consumption device _T Accumulated economic improvement index E after alternating current fault set scanning calculation of terminal alternating current power grid of calculation energy consumption device under serial input strategy _{Serial connection} The calculation method comprises the following steps:

E _{serial connection} ＝k _N N+k _T t (14)。

The invention has the following advantages:

(1) According to the invention, not only is the energy margin in the converter valve considered, but also the energy margin of the capacitor or equivalent capacitor in the energy consumption valve and the direct current sea cable is considered, the range of an acting object of the existing energy control is enlarged, and the energy margin of the offshore wind power flexible-direct system is further improved;

(2) According to the invention, the feasibility problem of the energy margin of the offshore wind power flexible direct system is considered, the modulation ratio and the bridge arm current of the converter valve under the operating point deviating from the rated operating condition are calculated by utilizing the steady-state mathematical analysis model of the converter valve, so that whether the converter valve meets the constraint condition in engineering or not is checked, and the feasibility of the maximum utilization of the energy margin is enhanced;

(3) The invention fully considers the corresponding relation between the withstand voltage multiple of the capacitor and the maximum allowable running time under the corresponding withstand voltage multiple, and considers the combination of the capacitor overvoltage running allowable time and the duration of the onshore alternating current fault, so that the utilization of the energy margin is more attached to the onshore alternating current fault characteristic;

(4) The invention fully considers two schemes of parallel utilization and serial utilization of energy margin, carries out comprehensive calculation based on the statistics data of the faults of the shore alternating current power grid, quantitatively analyzes the improved characteristics of the direct current energy consumption device in the operation aspect under different schemes, including shared dissipation power, saved operation times and saved operation time, and converts the power consumption device into economic improvement indexes of the energy consumption device, thereby reasonably selecting a proper energy margin utilization scheme according to the different fault statistics characteristics of the shore alternating current power grid and maximally improving the economic efficiency of the energy consumption device.

Drawings

Fig. 1 is a schematic flow chart of the present invention.

FIG. 2 is a schematic diagram of the characteristic parameters and data preprocessing of the offshore wind turbine straightening system in step one of the present invention.

Fig. 3 is a schematic flow chart of calculating the energy margin of the offshore wind power flexible-direct system in the second step of the invention.

Fig. 4 is a schematic flow chart for checking the feasibility of the energy margin of the offshore wind power flexible straightening system in the third step of the invention.

Fig. 5 is a schematic flow chart of calculating an economic improvement index of the energy consumption device under the parallel input strategy in the fourth step of the invention.

Fig. 6 is a schematic flow chart of calculating an economic improvement index of the energy consumption device under the serial input strategy in the fourth step of the invention.

Fig. 7 is a schematic diagram of a relationship between a converter valve energy margin and a maximum allowable operation time according to a corresponding relationship between a withstand voltage multiple of a converter valve submodule capacitor and the maximum allowable operation time in an embodiment of the present invention.

Fig. 8 is a schematic diagram of a relationship between a converter valve energy margin and a maximum allowable operation time according to a corresponding relationship between a withstand voltage multiple of a capacitor of a dc energy consumption valve submodule and the maximum allowable operation time in an embodiment of the present invention.

Fig. 9 is a calculation result of an economic improvement index of an energy consumption device in each ac fault according to a parallel input strategy obtained by calculating a fault set of a receiving ac power grid in the embodiment of the present invention.

Fig. 10 is a calculation result of an economic improvement index of an energy consumption device in each ac fault according to a serial input strategy calculated according to a fault set of a receiving ac power grid in the embodiment of the present invention.

Detailed Description

The following detailed description of the invention is, therefore, not to be taken in a limiting sense, but is made merely by way of example. While making the advantages of the present invention clearer and more readily understood by way of illustration.

The invention discloses an economic improvement evaluation method for an offshore wind power flexible-direct system energy consumption device. According to engineering parameters of the flexible direct current converter valve and the direct current energy consumption valve, by combining with the statistical characteristics of alternating current fault data of a receiving end power grid, calculating the input times, input time, dissipation power and other data of the direct current energy consumption valve under different alternating current fault ride-through control strategies adopted by the converter valve, and changing the data under the alternating current fault ride-through control strategy without the converter valve, and finally converting the data into an index for improving the economy, wherein the index is used for quantitatively evaluating the economic improvement condition of the direct current energy consumption valve by the converter valve under different alternating current fault ride-through control strategies, so that the proper alternating current fault ride-through control strategy is selected in the engineering.

As shown in fig. 1, the present invention includes the steps of:

As shown in FIG. 2, the characteristic parameters of the offshore wind power flexible direct current system comprise the characteristic parameters of a converter valve, the characteristic parameters of a direct current energy consumption valve and the characteristic parameters of a direct current sea cableFault characteristic parameters of the ac-side network. Characteristic parameters of the converter valve include: rated DC voltage u _dcN Redundancy ρ of converter valve submodule and rated active power P _N Rated voltage u of converter valve submodule _subN Rated voltage u of converter valve submodule capacitor _cN DC capacitance value C of converter valve submodule _sub Withstand voltage multiple sequence of converter valve submodule capacitors (K _Cmaxp Where p=1, 2, … … N _C ，N _C The total number of withstand voltage multiples in the withstand voltage multiple sequence of the capacitance of the converter valve submodule is a positive integer and is greater than or equal to 1) and the maximum allowable operation time sequence (T) under the corresponding withstand voltage multiple _Cmaxp Where p=1, 2, … … N _C ，N _C The total number of the withstand voltage multiples in the withstand voltage multiple sequence of the capacitance of the converter valve submodule is a positive integer and is more than or equal to 1). The characteristic parameters of the direct current energy consumption valve comprise: rated voltage u of DC energy consumption valve sub-module _RsubN Rated voltage u of direct current energy consumption valve submodule capacitor _RcN Capacitance value C of DC energy consumption valve submodule _Rsub Withstand voltage multiple sequence of direct current energy consumption valve submodule capacitor (K _Rmaxq Where q=1, 2, … … N _R ，N _R The total number of voltage withstand times in the voltage withstand times sequence of the capacitor of the DC energy consumption valve submodule is positive integer and is more than or equal to 1) and the maximum allowable operation time sequence (T) under the corresponding voltage withstand times _Rmaxq Where q=1, 2, … … N _R ，N _R The total number of the voltage withstand multiples in the voltage withstand multiple sequence of the direct current energy consumption valve submodule capacitor is a positive integer and is more than or equal to 1). The characteristic parameters of the direct current submarine cable comprise: maximum allowable DC voltage value u of DC submarine cable _dcmax Equivalent direct-current capacitor C of direct-current submarine cable _cable . The fault characteristic parameters of the receiving end alternating current power grid comprise: average number of single-phase earth short-circuit faults each year and corresponding time sequence of each fault, number of two-phase earth and two-phase short-circuit faults and corresponding time sequence of each fault, number of three-phase short-circuit faults and corresponding time sequence of each fault, and the time sequence of all the alternating-current faults form a receiving-end alternating-current power grid Ac fault set, N _F The total number of alternating current faults is concentrated for the alternating current fault accidents of the receiving alternating current power grid, is a positive integer and is more than or equal to 1.

The data preprocessing operation comprises the steps of calculating rated energy storage of a converter valve capacitor, calculating rated energy storage of a direct current energy consumption valve capacitor and calculating rated energy storage of a direct current submarine cable.

in the above formula (1): u (u) _dcN Is rated DC voltage; u (u) _subN Rated voltage for the converter valve submodule; c (C) _sub The direct current capacitance value of the converter valve submodule is obtained;

Representing the capacitance rated energy in each sub-module of the converter valve.

in the above formula (2): u (u) _dcN Is rated DC voltage; u (u) _RsubN Rated voltage of the direct current energy consumption valve submodule; c (C) _Rsub The capacitance value of the direct current energy consumption valve submodule is obtained;

Representing the capacitance rated energy in each sub-module of the dc consumer valve.

in the above formula (3): c (C) _cable The equivalent direct current capacitor is used as the direct current submarine cable; u (u) _dcN Is rated DC voltage;

as shown in fig. 3, the energy margin of the offshore wind power flexible-direct system comprises a converter valve energy margin, a direct current energy consumption valve energy margin and a direct current submarine cable energy margin;

the energy margin of the converter valve is determined according to the withstand voltage multiple of the capacitance of the submodule of the converter valve;

in the above formula (4): u (u) _dcN Is rated DC voltage; u (u) _subN Rated voltage for the converter valve submodule; c (C) _sub The direct current capacitance value of the converter valve submodule is obtained; u (u) _cN Rated voltage of the capacitance of the submodule of the converter valve; w (W) _N Rated energy storage for the converter valve capacitor; ρ is the redundancy rate of the converter valve submodule;

k is taken to represent withstand voltage multiple of capacitance of converter valve submodule _Cmax The time submodule stores energy. Similarly, when other withstand voltage multiples of the capacitance voltage of the converter valve submodule are selected, the energy margin of the converter valve under the corresponding withstand voltage multiples can be calculated according to the above formula until all N of the capacitance of the converter valve submodule is calculated _C Energy margin at multiple of withstand voltage.

Sub-step two: setting p=p+1 when p is not equal to N _C When the method is used, the method jumps to the first substep, and otherwise; the calculation flow is ended.

The energy margin of the direct current energy consumption valve is determined according to the withstand voltage multiple of the capacitance of the submodule of the direct current energy consumption valve;

in the above formula (5): u (u) _dcN Is rated DC voltage; u (u) _RsubN Rated voltage of the direct current energy consumption valve submodule; c (C) _Rsub The capacitance value of the direct current energy consumption valve submodule is obtained; u (u) _RcN Rated voltage of the capacitor of the DC energy consumption valve submodule; w (W) _RN Rated energy storage for the direct current energy consumption valve; ρ _R Redundancy rate of the direct current energy consumption valve submodule;

representing the total number of direct current energy consuming valve bridge arm submodules when redundancy is considered, < >>

K is taken to represent the withstand voltage multiple of the capacitance of the direct current energy consumption valve submodule _Rmaxq The time submodule stores energy. Similarly, when other withstand voltage multiples of the capacitor voltage of the DC energy consumption valve submodule are selected, the energy margin of the DC energy consumption valve under the corresponding withstand voltage multiples can be calculated according to the above until all N of the capacitor of the DC energy consumption valve submodule is calculated _R Energy margin at multiple of withstand voltage.

Sub-step two: setting q=q+1, when q is not equal to N _R When the method is used, the first substep is skipped; otherwise, the calculation flow is ended.

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in the above formula (6): c (C) _cable The equivalent direct current capacitor is used as the direct current submarine cable; u (u) _dcmax The maximum allowable direct current voltage value of the direct current submarine cable; w (W) _caN And rated energy storage for the direct current submarine cable.

As shown in fig. 4, in step three, checking the energy margin feasibility of the offshore wind power straightening system includes the following sub-steps:

sub-step two: selecting an overvoltage multiple (i.e. withstand voltage multiple) K of the overvoltage of the submodule capacitor voltage from a sequence of withstand voltage multiples of the submodule capacitor of the converter valve _Cmaxp ；

And a sub-step four: checking whether the modulation ratio of the converter valve and the bridge arm current meet the constraint conditions of the converter valve and the bridge arm current, wherein the constraint conditions comprise that the modulation ratio is in a numerical range required by stable operation of the converter valve, and the bridge arm current meets the tolerance capability of a power electronic device of a bridge arm submodule of the converter valve; the range constraint of the converter valve to the modulation ratio in engineering is generally between 0.7 and 0.95, and the modulation ratio calculated in the last substep needs to be satisfied within the range. Bridge arm current of the converter valve needs to meet current resistance of power electronic devices in the submodules, and the value of the bridge arm current needs to be in a current resistance range;

And step six: setting p=p+1 when p is not equal to N _C When the step is performed, the step I is skipped to the sub-step II; otherwise, the calculation flow is ended.

After the calculation flow, a feasible capacitance withstand voltage multiple sequence (K) of the converter valve submodule can be obtained _Cmaxp Where p=1, … … N _COK ，N _COK The total number of the withstand voltage multiples in the withstand voltage multiple sequences of the feasible converter valve submodule capacitor is positive integer and is more than or equal to 1), and the maximum allowable operation time sequence (T) under the corresponding withstand voltage multiples _Cmaxp Where p=1, … … N _COK ) Converter valve energy margin sequence under pressure-resistant multiple

As shown in fig. 5, in the fourth step, the parallel input strategy represents that surplus power is absorbed simultaneously by using the energy margin of the offshore wind power flexible direct system and the energy consumption resistance of the direct current energy consumption valve, and calculating the economic improvement index of the energy consumption device under the parallel input strategy includes the following substeps, firstly setting the number i=1:

the method comprises the following substeps: selecting an ith alternating current fault from an alternating current fault accident set of a receiving end alternating current power grid, and setting the number as i, wherein i=1, 2 … … and N _F And the duration of the alternating current fault is t _i ；

Sub-step two: estimating surplus energy W accumulated without taking energy consumption measures in the fault _Fimax The calculation method comprises the following steps:

P _N Is rated as active power;

And a sub-step four: calculating the maximum surplus power shared by the direct current energy consumption valveP _Cmax The calculation method comprises the following steps:

satisfy P _Cmax max(T _Cmax ,T _Rmax )≤W _Fimax (8)

in the above formula (8): ΔW (delta W) _maxK Is corresponding to the pressure-resistant multiple K _Cmax An energy margin of the lower converter valve; ΔW (delta W) _RmaxK Is corresponding to the pressure-resistant multiple K _Rmax Energy margin of the lower direct current energy consumption valve; ΔW (delta W) _camx The energy margin of the direct current submarine cable is provided;

Fifth, the sub-steps are: setting an economical efficiency improvement index k corresponding to surplus power shared by a direct current energy consumption valve _P And an economic improvement index k corresponding to the duration of the surplus power shared by the direct current energy consumption valve _t Further calculate the energy consumption valve economical efficiency and promote index E in this trouble _i The calculation method comprises the following steps:

E _i ＝k _P P _Cmax +k _t max(T _Cmax ,T _Rmax ) (9)

in the above formula (9); p (P) _Cmax Maximum surplus power shared by the direct current energy consumption valve; t (T) _Cmax For the capacitance withstand voltage multiple K of the converter valve submodule _Cmax Corresponding maximum allowed run time; t (T) _Rmax The capacitor withstand voltage multiple K of the DC energy consumption valve submodule _Rmax Corresponding maximum allowed run time;

and step six: setting i=i+1, confirming whether i reaches the maximum value N _F ；

If i does not reach the maximum value N _F Repeating the sub-steps one to five, selecting the next alternating current fault from the alternating current fault accident set of the receiving end alternating current power grid, and calculating the economic improvement index of the energy consumption valve in the next alternating current fault under the parallel input strategy until the economic improvement index of the alternating current fault in all the alternating current fault sets is calculatedMarking;

if i reaches the maximum value N _F Entering a sub-step seven;

as shown in fig. 6, in the fifth step, the serial input strategy indicates that the surplus power is absorbed by using the energy margin of the offshore wind power flexible and straight system, and the surplus power is absorbed by using the energy consumption resistor of the dc energy consumption valve after the energy margin is exhausted, firstly, the number of operation times saved by the energy consumption device under the serial input strategy is set to be N, the saved operation time is t, an initial value n=0, t=0, and a number j=1 are set, and the calculation of the economic improvement index of the energy consumption device under the serial input strategy includes the following substeps:

wherein, the fault coefficient K is set according to the AC fault type of the receiving AC power grid _F For single-phase earth short-circuit fault, K _F =1; for two-phase short circuit or two-phase ground short circuit fault, K _F =2; for three-phase short-circuit fault, K _F ＝3；P _N Is rated as active power; t is t _j Duration of time for the ac fault;

and a sub-step three: selecting the most current-converting valve sub-module capacitor from the feasible current-converting valve sub-module capacitor voltage-withstand multiple sequence High withstand voltage multiple and corresponding maximum allowable operating time T _Cmax Calculating the energy margin of the converter valve under the corresponding pressure-resistant multiple; selecting the maximum withstand voltage multiple of the capacitor of the direct current energy consumption valve submodule from the withstand voltage multiple sequence of the capacitor of the direct current energy consumption valve submodule, and calculating the energy margin of the direct current energy consumption valve under the corresponding withstand voltage multiple; adding the energy margin of the converter valve, the energy margin of the direct current energy consumption valve and the energy margin of the direct current sea cable to obtain the maximum energy margin of the offshore wind power flexible-direct system;

in the above formula (12), N is the number of times of operation saved by the energy consumption device under the serial input strategy, and t is the saved operation time; t is t _j Duration of time for the ac fault;

In the above formula (13), the number of times of operation saved by the energy consumption device under the serial input strategy is N, and t is the saved operation time; t (T) _Cmax For the capacitance withstand voltage multiple K of the converter valve submodule _Cmax Corresponding maximum allowed run time;

fifth, the sub-steps are: setting j=j+1, confirming whether j reaches the maximum value N _F ；

If j does not reach the maximum valueN _F Repeating the sub-step one to the sub-step four, selecting the next alternating current fault from the alternating current fault accident set of the receiving end alternating current power grid, and calculating the operation times and operation time saved by the direct current energy consumption valve under the serial input strategy in the current alternating current fault;

if j reaches the maximum value N _F Then enter the next substep;

E _{serial connection} ＝k _N N+k _T t (14)。

Examples

The invention is described in detail by taking the test of the invention for a certain open sea offshore wind power grid-connected project as an embodiment, and the invention has a guiding effect on the control of the invention applied to other offshore wind power systems which are subjected to flexible direct current grid connection.

The present embodiment will be described with reference to the calculation cases in fig. 7 to 10.

In this embodiment, the relation between the overvoltage multiple of the submodule capacitor in the converter valve and the dc-energy-consuming valve and the corresponding maximum allowable operation time is shown in table 1.

Table 1 table of the overvoltage times of the submodule capacitances in the converter valve and the dc-consumer valve versus the corresponding maximum permissible operating times

Capacitor overvoltage multiple	Maximum allowed runtime
		1.15	30 minutes
1.2	For 5 minutes
		1.3	For 1 minute
1.5	30 ms of

Considering the redundancy rate of 8% of the converter valve and the DC energy consumption valve submodule, the invention can calculate the energy margin (shown in figure 7) of the converter valve and the energy margin (shown in figure 8) of the DC energy consumption valve under different capacitance overvoltage multiples and maximum allowable running time data.

According to the fault duration data of 30 times of alternating current faults (10 times of single-phase short circuit faults, 10 times of two-phase short circuit faults and 10 times of three-phase short circuit faults) of the receiving end alternating current power grid, the economic improvement index of each alternating current fault under the parallel input strategy can be calculated respectively by adopting the method, as shown in figure 9, and the economic improvement index of each alternating current fault under the serial input strategy can be calculated, as shown in figure 10. The comparison shows that the serial input strategy has more obvious effect on improving the economy of the energy consumption device when the single-phase grounding short-circuit fault occurs in the receiving-end alternating-current power grid, and the parallel input strategy has more obvious effect on improving the economy of the energy consumption device when the three-phase short-circuit fault occurs in the receiving-end alternating-current power grid.

What is not described in detail in this specification is prior art known to those skilled in the art. It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention also include such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.

Other non-illustrated parts are known in the art.

Claims

1. The method for evaluating the economic improvement of the offshore wind power flexible-straight system energy consumption device is characterized by comprising the following steps of:

in the second step, the energy margin of the offshore wind power flexible-direct system comprises a converter valve energy margin, a direct current energy consumption valve energy margin and a direct current submarine cable energy margin;

in the above formula (4):

representing the total number of 6 bridge arm sub-modules of the converter valve when redundancy is considered, < >>

sub-step two: setting p=p+1 when p is not equal to N _C When the method is used, the first substep is skipped; otherwise, ending the calculation flow;

all N of the capacitance of the converter valve submodule is obtained through the calculation _C Energy margin sequence of converter valve under multiple withstand voltage

in the above formula (5):

all N of the direct current energy consumption valve submodule capacitance is obtained through the calculation _R Energy margin sequence of direct current energy consumption valve under multiple withstand voltage

in the third step, checking the energy margin feasibility of the offshore wind power flexible straightening system comprises the following substeps:

and a sub-step four: checking whether the modulation ratio of the converter valve and the bridge arm current meet the constraint conditions of the converter valve on the modulation ratio and the bridge arm current;

And step six: setting p=p+1 when p is not equal to N _C When the step is performed, the step I is skipped to the sub-step II; otherwise, ending the calculation flow;

after the calculation flow, a feasible capacitance withstand voltage multiple sequence K of the converter valve submodule is obtained _Cmaxp ，p＝1，……N _COK ，N _COK The total number of the withstand voltage multiples in the withstand voltage multiple sequences of the feasible converter valve submodule capacitor is positive integer and is more than or equal to 1, and the maximum allowable operation time sequence T under the corresponding withstand voltage multiples _Cmaxp Where p=1, … … N _COK And converter valve energy margin sequence under pressure-resistant multiple

in the fourth step, the parallel input strategy represents that surplus power is absorbed simultaneously by using the energy margin of the offshore wind power flexible direct system and the energy consumption resistance of the direct current energy consumption valve, and the calculation of the energy consumption device economical efficiency improvement index under the parallel input strategy comprises the following substeps that the serial number i=1 is firstly set:

the method comprises the following substeps: selecting an ith alternating current fault from the alternating current fault sets of the receiving end alternating current power grid, wherein the duration time of the alternating current fault is t _i ；

wherein, the fault coefficient K is set according to the AC fault type of the receiving AC power grid _F For single-phase earth short-circuit fault, K _F =1; for two-phase short circuit fault, K _F =2; for three-phase short-circuit fault, K _F ＝3；

And a sub-step four:calculating the maximum surplus power P shared by the direct current energy consumption valve _Cmax The calculation method comprises the following steps:

satisfy P _Cmax max(T _Cmax ,T _Rmax )≤W _Fimax (8)

fifth, the sub-steps are: setting an economical efficiency improvement index k corresponding to surplus power shared by a direct current energy consumption valve _P And an economic improvement index k corresponding to the duration of the surplus power shared by the direct current energy consumption valve _t Further calculate the economic improvement index E of the energy consumption device in the fault _i The calculation method comprises the following steps:

E _i ＝k _P P _Cmax +k _t max(T _Cmax ,T _Rmax ) (9)

and step six: setting i=i+1, confirming whether i reaches the maximum value N _F The method comprises the steps of carrying out a first treatment on the surface of the If i does not reach the maximum value N _F Repeating the sub-step one to the sub-step five, selecting the next alternating current fault from the alternating current fault set of the receiving end alternating current power grid, and calculating the economic improvement index of the direct current energy consumption valve in the alternating current fault set under the parallel input strategy;

if i reaches the maximum value N _F Entering a sub-step seven;

step five: calculating an economic improvement index of the energy consumption device under a serial input strategy;

in the fifth step, the serial input strategy means that the surplus power is absorbed by using the energy margin of the offshore wind power flexible direct system, and the surplus power is absorbed by using the energy consumption resistor of the direct current energy consumption valve after the energy margin is exhausted, firstly, the operation time saved by the energy consumption device under the serial input strategy is set to be N, the operation time saved is t, an initial value n=0, t=0 and a number j=1 are set, and the calculation of the economic improvement index of the energy consumption device under the serial input strategy comprises the following substeps:

and a sub-step four: judging maximum energy margin and W of offshore wind power flexible-direct system _Fjmax Is a relative magnitude relation of (2); when the maximum energy margin of the offshore wind power flexible-direct system is larger than or equal toEqual to W _Fjmax When the alternating current fault is generated, the energy consumption device is not needed to be put into, the data of the operation times and the operation time saved by the energy consumption device are updated, and the calculation method is as follows:

fifth, the sub-steps are: setting j=j+1, confirming whether j reaches the maximum value N _F The method comprises the steps of carrying out a first treatment on the surface of the If j does not reach the maximum value N _F Repeating the sub-step one to the sub-step four, selecting the next alternating current fault from the alternating current fault accident set of the receiving end alternating current power grid, and calculating the operation times and the operation time saved by the direct current energy consumption valve in the alternating current fault under the serial input strategy;

if j reaches the maximum value N _F Then enter the next substep;

E _{serial connection} ＝k _N N+k _T t (14)。

2. The method for improving and evaluating the economical efficiency of the energy consumption device of the offshore wind power flexible-direct system according to claim 1, wherein in the first step, the characteristic parameters of the offshore wind power flexible-direct system comprise the characteristic parameters of a converter valve, the characteristic parameters of a direct current energy consumption valve, the characteristic parameters of a direct current sea cable and the fault characteristic parameters of a receiving-end alternating current power grid;

characteristic parameters of the converter valve include: rated DC voltage u _dcN Redundancy ρ of converter valve submodule and rated active power P _N Rated voltage u of converter valve submodule _subN Rated voltage u of converter valve submodule capacitor _cN DC capacitance value C of converter valve submodule _sub Withstand voltage multiple sequence K of converter valve submodule capacitor _Cmaxp Where p=1, 2, … … N _C ，N _C A total number of withstand voltage multiples in a withstand voltage multiple sequence of the capacitance of the converter valve submodule, which is a positive integer and is greater than or equal to 1, and a maximum allowable operation time sequence T under the corresponding withstand voltage multiple _Cmaxp Where p=1, 2, … … N _C ，N _C The total number of the withstand voltage multiples in the withstand voltage multiple sequence of the capacitance of the converter valve submodule is a positive integer and is more than or equal to 1;

the characteristic parameters of the direct current energy consumption valve comprise: rated voltage u of DC energy consumption valve sub-module _RsubN Rated voltage u of direct current energy consumption valve submodule capacitor _RcN Capacitance value C of DC energy consumption valve submodule _Rsub Withstand voltage multiple sequence K of direct current energy consumption valve submodule capacitor _Rmaxq Where q=1, 2, … … N _R ，N _R The total number of the withstand voltage multiples in the withstand voltage multiple sequence of the capacitor of the direct current energy consumption valve submodule is positive integer and is more than or equal to 1, and the maximum allowable operation time sequence T under the corresponding withstand voltage multiples _Rmaxq Where q=1, 2, … … N _R ，N _R The total number of the withstand voltage multiples in the withstand voltage multiple sequence of the capacitor of the direct current energy consumption valve submodule is a positive integer and is more than or equal to 1;

The fault characteristic parameters of the receiving end alternating current power grid comprise: average number of single-phase-to-ground short-circuit faults each year and corresponding duration sequence of each fault, two-phase-to-ground and two-phase-to-shortThe number of the road faults and the duration sequence of each corresponding fault, the number of the three-phase short-circuit faults and the duration sequence of each corresponding fault, the duration sequences of all the alternating current faults form an alternating current fault set of the receiving alternating current power grid, N _F The total number of alternating current faults is concentrated for the alternating current fault accidents of the receiving alternating current power grid, is a positive integer and is more than or equal to 1.

3. The method for improving and evaluating the economical efficiency of the offshore wind power flexible and straight system energy consumption device according to claim 2, wherein in the first step, the data preprocessing operation comprises calculating the rated energy storage of the converter valve capacitor, calculating the rated energy storage of the direct current energy consumption valve capacitor and calculating the rated energy storage of the direct current submarine cable;

in the above formula (1):

The rated energy of the capacitor in each sub-module of the converter valve is represented;

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in the above formula (2):

representing the dc-dissipative valve legs without redundancyTotal number of sub-modules>

The rated energy of the capacitor in each sub-module of the direct current energy consumption valve is represented;

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