CN115663876B - Main loop parameter design method and system for hybrid cascade extra-high voltage direct current system - Google Patents
Main loop parameter design method and system for hybrid cascade extra-high voltage direct current system Download PDFInfo
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Abstract
The invention relates to the field of direct current transmission, and provides a method and a system for designing main loop parameters of a hybrid cascade extra-high voltage direct current system, wherein the method comprises the following steps: determining the operation mode of the mixed cascade extra-high voltage direct current system; determining a basic control mode of a receiving end VSC and an LCC, a voltage distribution mode of the VSC and the LCC and a current distribution mode among the VSCs, and constructing a steady-state mathematical model of the hybrid cascade system under the obtained constraint equation; calculating the port direct current voltage variation range of the VSC under each operation mode, and designing the modulation ratio range under each operation mode; based on constraint conditions of the PQ operation interval of the VSC, solving the PQ operation interval of the VSC, and determining a gear range; determining the maximum operating power of the hybrid cascade extra-high voltage direct current system in the operating mode; and solving a steady-state mathematical model of the hybrid cascade system based on the maximum operating power and the VSC reactive power of the system to obtain steady-state operating parameters of the system.
Description
Technical Field
The invention relates to a method and a system for designing main loop parameters of a hybrid cascade extra-high voltage direct current system, and relates to the field of direct current transmission.
Background
In order to realize long-distance large-capacity power transmission and multi-drop point power supply and solve the problem of short-circuit ratio reduction of the receiving end multi-feed-in, a mixed cascade extra-high voltage direct current transmission technology, namely a technical scheme of cascade connection of a conventional direct current converter and a plurality of flexible direct current converters, can be adopted, combines the advantages of the conventional direct current and the flexible direct current, can effectively improve the stability of an alternating current power grid of the receiving end, is high in reliability, flexible in operation mode, has a wide application prospect, and is a key technology for constructing the future energy Internet.
The main loop parameter design of the hybrid cascade extra-high voltage direct current system aims at determining key parameters of direct current main equipment, defining steady-state operation parameters of the direct current system under various operation conditions, being the premise and the foundation of the construction of the hybrid cascade direct current system, and directly determining the temporary steady-state operation performance of the system.
The prior art does not relate to the problems of how to design the parameters of the main circuit of the hybrid cascade extra-high voltage direct current transmission, complete the type selection of the parameters of the main equipment of the hybrid cascade system, acquire the steady-state operation characteristics and the like.
Disclosure of Invention
Aiming at the problems, the invention aims to provide a method, a system, equipment and a medium for designing main loop parameters of a hybrid cascade extra-high voltage direct current system, which can determine direct current main equipment parameters and steady-state operation parameters.
In order to solve the technical problems, the invention adopts the following technical scheme:
in a first aspect, the method for designing the main loop parameters of the hybrid cascade extra-high voltage direct current system provided by the invention comprises the following steps:
determining the operation mode of the mixed cascade extra-high voltage direct current system;
determining a basic control mode of a receiving end VSC and an LCC, a voltage distribution mode of the VSC and the LCC and a current distribution mode among the VSCs, and constructing a steady-state mathematical model of the hybrid cascade system under the obtained constraint equation;
calculating the port direct current voltage variation range of the VSC under each operation mode, and designing the modulation ratio range under each operation mode;
based on constraint conditions of a PQ operation interval of the VSC, solving the PQ operation interval of the VSC, and determining a gear range to be configured by the soft direct converter;
determining the maximum operating power of the hybrid cascade extra-high voltage direct current system in the operating mode;
and solving a steady-state mathematical model of the hybrid cascade system based on the maximum operating power and the VSC reactive power of the system to obtain steady-state operating parameters of the system.
Further, the voltage distribution manner of the VSC and the LCC includes:
VSC and LCC follow equal direct currentThe voltage is distributed in a mode, and the corresponding constraint equation isU dcvsc =U dclcc ，U dcvsc AndU dclcc the port direct current voltages of the VSC and the LCC respectively;
the VSC does not consider the fluctuation of the direct current voltage, and the LCC bears the line voltage drop, and the corresponding constraint equation is thatU dcvsc =U setvsc ，U dcvsc Is the port dc voltage of the VSC,U setvsc is a set value.
Further, a current distribution method between VSCs includes:
and each VSC is distributed in a mode of equal current, and a constraint equation is as follows:I vsc1 =I vsc2 =...I vscn =I dc /n，I vsc1 ，...I vscn the direct current of the 1 st to n th VSCs respectively,I dc for the total current flowing into the VSC valve block;
and independently appointing the running power among the VSCs, and then the constraint equation is as follows:I vsc1 =P vsc1 /U setvsc ，I vsc2 =P vsc2 /U setvsc ， ... I vscn =I dc -I vsc1 -I vsc2... I vsc（n-1） ，P vsc1 andP vsc2 active power for VSC1 and VSC 2.
Further, the method for determining the modulation ratio range in each operation mode comprises the following steps:
according to the principle of maximum line resistance, calculating the flexible and straight minimum port voltage under the running modeU dcinit ；
Traversing working conditions requiring VSC power transfer under various faults, calculating port voltage after VSC power transfer under each working condition, and determining minimum port voltage under each working conditionU dcfinal ；
Determining a maximum modulation ratio that ensures that the VSC output voltage is nevertheless modulatedM absmax Calculating the maximum modulation ratio under each operation modeM max ，M max =U dcfinal ×M absmax /U dcinit ；
Designing minimum modulation ratio according to level number capable of meeting system harmonic requirementM min 。
Further, solving the PQ operating interval of the VSC includes:
a. determining limiting conditions of a PQ operation interval of the VSC, wherein the limiting conditions comprise a port direct current voltage change range, a modulation ratio range, an alternating current voltage change range, bridge arm current limit and transformer capacity limit of the VSC;
b. based on constraint conditions, solving a PQ operation interval, wherein the PQ operation interval takes intersections under different direct-current voltage and alternating-current voltage combinations;
c. judging whether the power interval meets the set requirement of the system on power exchange, if so, determining a PQ running interval and a VCS gear, and if not, entering d;
d. if reactive power deficiency is generated or bridge arm current leads to power limitation, negative gear configuration is increased; if the absorption reactive power is insufficient, adding the positive gear configuration, and entering the step b.
Further, the PQ operation interval is designed according to the union of the PQ operation intervals under all gear positions, when a single gear position cannot meet the system requirement, the configuration range of the gear position is gradually increased to increase the PQ operation interval until the gear position configuration meets the requirement of the system on the VSC exchange capacity under the operation mode, or the change power of the VSC and the system cannot be increased any more by increasing the gear position, so that the PQ operation interval under the operation mode is obtained, and the union of the gear positions obtained under each operation mode is the gear position designed by the VSC.
Further, the method for increasing the configuration range of the gear comprises the following steps: when the current limit of the bridge arm causes insufficient active power or reactive power to be absorbed or emitted, negative gear configuration is added, and when the modulation ratio limit causes insufficient reactive power to be absorbed, positive gear configuration is added; when the modulation ratio limitation results in insufficient reactive power being emitted, a negative gear configuration is increased.
In a second aspect, the invention provides a main loop parameter design system of a hybrid cascade extra-high voltage direct current system, which comprises:
the operation mode determining unit is configured to determine the operation mode of the hybrid cascade extra-high voltage direct current system;
the model construction unit is configured to determine a basic control mode of the receiving end VSC and the LCC, a voltage distribution mode of the VSC and the LCC and a current distribution mode among the VSCs, and construct a steady-state mathematical model of the hybrid cascade system under a set constraint equation;
the parameter determining unit is configured to calculate the port direct current voltage variation range of the VSC in each operation mode and design the modulation ratio range in each operation mode; based on constraint conditions of a PQ operation interval of the VSC, solving the PQ operation interval of the VSC, and determining a gear range to be configured by the soft direct converter; determining the maximum operating power of the hybrid cascade extra-high voltage direct current system in the operating mode;
and the model calculation unit is configured to solve a steady-state mathematical model of the hybrid cascade system based on the system running power and the VSC reactive power to obtain steady-state running parameters of the system.
In a third aspect, the present invention provides an electronic device, including computer program instructions, where the program instructions, when executed by a processor, are configured to implement the method for designing main loop parameters of a hybrid cascaded extra-high voltage dc system.
In a fourth aspect, the present invention provides a computer readable storage medium, where a computer program instruction is stored on the computer readable storage medium, where the program instruction is used to implement the method for designing a main loop parameter of a hybrid cascaded uhv dc system when the program instruction is executed by a processor.
The invention adopts the technical proposal and has the following characteristics:
1. according to the invention, the steady-state mathematical model of the hybrid cascade system is established, and the steady-state operation parameters of the hybrid cascade system are obtained by solving the steady-state mathematical model of the hybrid cascade system in the determined system operation power and VSC reactive power, so that the main loop design scheme provided by the invention can ensure that the system still has full power operation capability after a single flexible direct current converter exits, thereby reducing the forced capability unavailability rate of the hybrid cascade system from 0.5% of the conventional direct current to 0.375%, and effectively improving the reliability of the system.
2. The invention provides a differential design method for modulation ratios of different operation modes for the first time, and effectively solves the problem of limited power transfer caused by insufficient voltage reduction operation capability of the VSC of the hybrid cascade system.
In conclusion, the invention provides a main loop design scheme of the hybrid cascade direct current system for the first time, fills the blank of the prior art, and can be widely applied to main loop parameters of the hybrid cascade extra-high voltage direct current system.
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Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the invention. Like parts are designated with like reference numerals throughout the drawings. In the drawings:
fig. 1 is an overall flow chart of a mixed cascaded extra-high voltage direct current main loop parameter design in an embodiment of the invention.
Fig. 2 is a flow chart of a mixed cascaded extra-high voltage direct current VSC modulation ratio range design according to an embodiment of the present invention.
Fig. 3 is a flow chart of a design of an operation interval and a gear of the hybrid cascade extra-high voltage direct current VSC according to an embodiment of the present invention.
Fig. 4 is a topological structure diagram of a hybrid cascade extra-high voltage direct current system according to an embodiment of the invention.
Fig. 5 is a block diagram of an electronic device according to an embodiment of the present invention.
Detailed Description
It is to be understood that the terminology used herein is for the purpose of describing particular example embodiments only, and is not intended to be limiting. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms "comprises," "comprising," "includes," "including," and "having" are inclusive and therefore specify the presence of stated features, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and/or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order described or illustrated, unless an order of performance is explicitly stated. It should also be appreciated that additional or alternative steps may be used.
For ease of description, spatially relative terms, such as "inner," "outer," "lower," "upper," and the like, may be used herein to describe one element or feature's relationship to another element or feature as illustrated in the figures. Such spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures.
The main loop parameter design method of the hybrid cascade extra-high voltage direct current has great difference with the conventional direct current and flexible direct current engineering, the operation capacity of the hybrid cascade extra-high voltage direct current main loop parameter design method is limited by various factors such as a conventional direct current converter valve, a flexible direct current converter valve, the number of flexible direct current operation, the system fault ride through capacity and the like, and the system operation capacity under hundreds of modes considering different flexible direct current operation numbers needs to be obtained by integrating the transient steady state operation characteristics of the system. In addition, the flexible direct current first presents the wide range fluctuation of the direct current voltage of 0.7-1 pu, the design of the power operation interval needs to consider the factor of the wide range fluctuation of the direct current voltage, and the single active power-reactive power circular graph (PQ circular graph) is difficult to adapt to various operation modes. Meanwhile, the configuration of the voltage regulating switch of the flexible direct current is also an important point of the parameter design of the main loop, and the combination design of the voltage regulating switch and the modulation ratio is required to ensure the operation capability of the direct current voltage under the wide fluctuation range.
Based on the design thought, the main loop parameter design method of the hybrid cascade extra-high voltage direct current system provided by the embodiment comprises the following steps: determining the operation mode of the mixed cascade extra-high voltage direct current system; determining a basic control mode of a receiving end VSC and an LCC, a voltage distribution mode of the VSC and the LCC and a current distribution mode among the VSCs, and constructing a steady-state mathematical model of the hybrid cascade system under the obtained constraint equation; calculating the port direct current voltage variation range of the VSC under each operation mode, and designing the modulation ratio range under each operation mode; based on constraint conditions of a PQ operation interval of the VSC, solving the PQ operation interval of the VSC, and determining a gear range to be configured by the soft direct converter; determining the maximum operating power of the hybrid cascade extra-high voltage direct current system in the operating mode; and solving a steady-state mathematical model of the hybrid cascade system in the determined system running power and VSC reactive power to obtain steady-state running parameters of the system.
Exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. While exemplary embodiments of the present invention are shown in the drawings, it should be understood that the present invention may be embodied in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.
As shown in fig. 1, the method for designing main loop parameters of the hybrid cascade extra-high voltage direct current system provided in this embodiment includes:
s1, determining an operation mode of the hybrid cascade extra-high voltage direct current system according to system requirements and topological characteristics of the hybrid cascade extra-high voltage direct current.
In this embodiment, the operation modes of the hybrid cascade extra-high voltage direct current are classified, firstly, according to a conventional extra-high voltage direct current operation mode classification method, a combination of bipolar/monopolar earth/monopolar metal, a double valve group/single valve group and a valve group is considered, wherein the number of VSC (voltage source converter) valve groups is 45 according to an integrated consideration method, further, the different operation numbers of VSC with different positive and negative poles and the operation VSC valves with different operation are considered, and the operation modes included under each subclass of operation can be determined in a combined manner.
Furthermore, because the voltage cannot be turned over and the current cannot be turned over respectively when the power flows of the VSC and the LCC (grid converter) are turned over, the topological characteristic of the hybrid cascade determines that the hybrid cascade extra-high voltage direct current does not consider power back transmission. And configuring a power mutual-aid mode among a plurality of VSCs according to system requirements, namely, part of the VSCs operate in a rectifying state, part of the VSCs operate in an inversion state, and the inversion-operated VSCs receive power of the transmitting end LCC and the VSCs in the rectifying state. The step-down operation is realized by converting the operation into half-voltage operation, the double-valve-group step-down operation realized by normal-straight and soft-straight asymmetric step-down is avoided, on one hand, the configuration and the action frequency of the tap switch are reduced, the equipment safety risk caused by frequent actions of the tap switch is greatly reduced, and on the other hand, the problem that the power transfer caused by LCC exit is severely limited during asymmetric step-down is avoided.
S2, determining a basic control mode of the receiving end VSC and the LCC, a voltage distribution mode of the VSC and the LCC and a current distribution mode among the VSCs according to the topological structure of the hybrid cascade, and setting out a constraint equation to construct a steady-state mathematical model of the hybrid cascade system.
In this embodiment, the voltage distribution manners of the VSC and the LCC include two types:
the first way is: the VSC and LCC are distributed in a mode of equal direct current voltage, and the corresponding constraint equation is thatU dcvsc =U dclcc ，U dcvsc AndU dclcc the port direct current voltages of the VSC and the LCC respectively;
the second way is: the VSC does not consider the fluctuation of the direct current voltage, and the LCC bears the line voltage drop, and the corresponding constraint equation is thatU dcvsc =U setvsc ，U dcvsc Is the port dc voltage of the VSC,U setvsc is a set value.
In the first mode, the port voltage fluctuation amplitude of the VSC is larger, and the VSC needs to be configured with more gears. In the second mode, the port voltage fluctuation of the LCC is 2 times of the original voltage fluctuation, the LCC gear is configured more, when the gear is regulated to the limit in a mode that the voltage drop such as monopole metal return is larger, the closing angle is required to be increased, the reactive power of the converter valve is increased, and because the LCC and the VSC are operated asymmetrically, if the LCC is out of fault, the voltage difference between the voltage of the transmitting end and the voltage of the receiving end is huge, and the power transfer capability is severely limited. According to the principle of being friendly to the system, when the VSC gear configuration is not limited, a first mode is adopted.
In this embodiment, the current distribution manner between VSCs includes two types:
first modeThe method comprises the following steps: and each VSC is distributed in a mode of equal current, and a constraint equation is as follows:I vsc1 =I vsc2 =...I vscn =I dc /n，I vsc1 ，...I vscn the direct current of the 1 st to n th VSCs respectively,I dc for the total current flowing into the VSC valve block;
the second way is: and independently appointing the running power among the VSCs, and then the constraint equation is as follows:I vsc1 =P vsc1 /U setvsc ，I vsc2 =P vsc2 /U setvsc ， ... I vscn =I dc -I vsc1 -I vsc2... I vsc（n-1） ，P vsc1 andP vsc2 active power for VSC1 and VSC 2.
S3, solving the port direct current voltage variation range of the VSC in each operation mode according to the maximum line resistance, the maximum operation current, the minimum line resistance and the minimum operation current, calculating the VSC voltage speed reduction requirement meeting the requirements of various transfer power in each operation mode, and designing the modulation ratio range in each operation mode.
In this embodiment, the port DC voltage variation range of the VSC in each operation mode is solved as [U dcmin 、U dcmax ]。
In this embodiment, as shown in fig. 2, the method for determining the modulation ratio range in each operation mode is as follows:
according to the principle of maximum line resistance, calculating the flexible and straight minimum port voltage under the running modeU dcinit ；
Traversing working conditions requiring VSC power transfer under various faults, calculating port voltage after VSC power transfer under each working condition, and determining minimum port voltage under each working conditionU dcfinal ；
Determining a maximum modulation ratio that ensures that the VSC output voltage is nevertheless modulatedM absmax Calculating the maximum modulation ratio under each operation modeM max ，M max =U dcfinal ×M absmax /U dcinit Wherein, the method comprises the steps of, wherein,U dcfinal direct current voltage after fault under the working condition of maximum voltage drop caused by the power transfer,U dcinit the direct current voltage before failure under the working condition of maximum voltage drop caused by the power transfer,M absmax in order to ensure the maximum modulation ratio of the flexible direct current output voltage without modulation, if third harmonic injection is adopted, the ratio is generally 1.05-1.15.
Designing minimum modulation ratio according to level number capable of meeting system harmonic requirementM min Generally, 0.7 to 0.85 is taken.
Further, different modulation ratio ranges can be designed for each operation mode, in order to simplify the control protection strategy, the 45 operation modes can be further divided into 2-3 types according to the modulation ratio range required by the power transfer, and each type meets the modulation ratio range required by the power transfer according to all operation modes to determine a uniform modulation ratio range.
S4, based on the determined port direct current voltage and direct current of the LCC and the VSC, respectively and independently calculating equipment parameters such as converter transformer rated voltage, rated capacity, short circuit impedance and the like of the LCC and the VSC according to a main equipment parameter selection method of the LCC and the VSC.
S5, solving the PQ operation interval of the VSC based on the constraint condition of the PQ operation interval of the VSC, and determining a gear range to be configured by the soft direct converter;
in this embodiment, as shown in fig. 3, solving the PQ operation interval of the VSC includes:
s51, determining limiting conditions of a PQ operation interval of the VSC, wherein the limiting conditions comprise a port direct current voltage change range, a modulation ratio range, an alternating current voltage change range, bridge arm current limit, transformer capacity limit and the like of the VSC;
s52, solving a PQ operation interval based on constraint conditions, wherein the PQ operation interval takes intersections under different direct-current voltage and alternating-current voltage combinations;
s53, judging whether the power interval meets the set requirement of the system on power exchange, if so, determining a PQ running interval and a VCS gear, and if not, entering S54;
s54, if insufficient reactive power is generated or bridge arm current causes power limitation, increasing negative gear configuration; if the absorption is insufficient, the positive shift configuration is increased, and the process advances to step S52.
Further, the PQ operation interval is designed according to the union of the PQ operation intervals under all gears, and when the single gear cannot meet the system requirement, the configuration range of the gear is gradually increased to increase the PQ operation interval. And (3) obtaining a PQ running interval under the running mode until the gear configuration meets the requirement of the system on the VSC exchange capacity under the running mode, or when the exchange power between the VSC and the system cannot be increased by adding the gears, wherein the union of the gears obtained under each running mode is the gear designed by the VSC.
Further, different PQ operation intervals can be designed for each operation mode, in order to simplify the control protection policy, 45 operation modes can be further divided into 2-3 classes, each class gives a unified PQ operation interval meeting all operation modes in the class, and each unified PQ operation interval is an intersection of PQ operation intervals of all operation modes in the class.
Further, the method for increasing the configuration range of the gear is as follows: when the current limit of the bridge arm causes insufficient active power or reactive power to be absorbed or emitted, negative gear configuration is added, and when the modulation ratio limit causes insufficient reactive power to be absorbed, positive gear configuration is added; when the modulation ratio limitation results in insufficient reactive power being emitted, a negative gear configuration is increased.
S6, determining the maximum operating power corresponding to the VSC according to the PQ operating intervalP vscmax1 Calculating the corresponding maximum operating power of the rectifying side under the maximum operating power, namely the maximum operating power of the systemP max1 According to the minimum line resistance during calculation.
S7, establishing an electromagnetic transient simulation model of the hybrid cascade system based on PSCAD/EMTDC software, and simulating, scanning and calculating that the maximum operating power of the system meeting the alternating current fault ride through requirement under each operating mode isP max2 During calculation, firstly, the system power is set as a system rated value, and the overvoltage of a converter valve and the energy of a controllable self-recovery energy dissipation device when an alternating current system fails are calculated in a simulation mode, if the energy is not out of limit, the maximum power is obtainedP max2 I.e. the rated power of the system, otherwise gradually decreasingP max2 Until the requirements of the converter valve overpressure and the energy of the energy dissipater can be met.
In this embodiment, a detailed controllable self-recovery energy dissipation device model is built in PSCAD/EMTDC software, and the principle of meeting the fault ride-through requirement of an alternating current system is as follows: the module voltage does not exceed the overvoltage protection fixed value of the unlocking operation of the converter valve, the bridge arm current does not reach the protection fixed value, and the energy of the energy dissipation device is within the maximum design energy. The lightning arrester of the energy dissipation device has large characteristics and small characteristics, and simulation needs to be carried out respectively.
S8, determining the maximum operation power of the system in the operation modeP max =max(P max1 ，P max2 ). If the maximum operating power is smaller than the rated operating power of the system, the work rate is limited, or IGBT devices with larger through current capacity, the number of modules and the capacitance of the modules are increased, and the like are adopted to further increaseP max1 AndP max2 until the system power requirements are met.
And S9, solving a steady-state mathematical model of the constructed hybrid cascade system in the finally determined system running power and VSC reactive power, and calculating the running characteristic of the running power from 0.1pu to 1pu under each running mode to form a steady-state running parameter of the system.
In this embodiment, the steady state mathematical model is solved by newton-raphson method under each operation mode.
The application of the main loop parameter design method of the hybrid cascade extra-high voltage direct current system provided by the invention is described in detail below through a specific embodiment.
As shown in fig. 4, a transmission end of the hybrid cascade extra-high voltage direct current transmission system adopts a conventional extra-high voltage direct current topology, and each pole is formed by cascade connection of 2 twelve-pulse conventional direct current converters; the receiving end adopts a hybrid cascade extra-high voltage direct current topology, each pole is formed by cascading a plurality of (3 are shown in the figure) parallel flexible direct current converters of a high-voltage end (namely 800 kV-400 kV) twelve-pulse conventional direct current converter and a low-voltage end (400 kV-neutral line), the flexible direct current converters adopt half-bridge modularized multi-level converters, and the receiving end conventional direct current converter and each flexible direct current converter are fed into different alternating current buses.
The invention is further described in detail below with the specific embodiment of main loop parameters design of a + -800 kV/8000MW, receiving end by single LCC and 3 VSC mixed cascade extra-high voltage direct current transmission system.
1. Firstly, determining the operation mode of the hybrid cascade extra-high voltage direct current system according to the system requirements and the topological characteristics of the hybrid cascade extra-high voltage direct current.
Specifically, the operation modes of the mixed cascade extra-high voltage direct current are divided into 7 major categories and 45 minor categories according to the conventional extra-high voltage direct current, the number of the operation modes of the VSC with different positive poles and negative poles is considered to be 1, 2 or 3, and the total 621 operation modes included in each minor category are determined in a combined mode.
2. And determining a basic control mode, a voltage distribution mode and a current distribution mode of the receiving end VSC and the LCC according to the topological structure of the hybrid cascade, and constructing a steady-state mathematical model of the hybrid cascade system.
Specifically, the transmitting end LCC adopts a constant direct current control, the receiving end LCC adopts a constant direct current voltage control, and among the receiving end 3 VSCs, 1 adopts a constant direct current voltage control, and 2 adopts a constant active power control.
The voltage distribution modes of the VSC and the LCC are determined, for example, a mode of high-low voltage equalization is adopted.
The current distribution pattern between the VSCs is determined, for example in terms of 3 VSC current sharing.
And further obtaining a constraint equation:I dc =I set ，U dcvsc =U dclcc =U set ，I vsc1 =I vsc2 =I vsc3 and finally, constructing a steady-state mathematical model of the hybrid cascade system:
in the method, in the process of the invention,U dR andU dI between-end electricity of single converter for transmitting end and receiving end LCCThe pressure is applied to the pressure-sensitive adhesive,R eq is the equivalent resistance of the direct current loop,U di0R andU di0I ideal no-load dc voltage for each 6-ripple converter on the rectifying side and the inverting side respectively,U di0NR andU di0NI the ideal no-load dc voltage rating for each 6-ripple converter on the rectifying side and the inverting side respectively,αfor the rectifying side firing angle, γ is the inverting side Guan Duanjiao,d xR andd xI the inductance voltage drops at the rectifying side and the inverting side are normalized,d rR andd rI the values of the resistance drops at the rectifying side and the inverting side,I dN for the direct current rating of the power supply,U T is the inherent voltage drop of a 6-pulse inverter,P vscn andQ vscn for the active and reactive power of the nth VSC,M n for the modulation ratio of the nth VSC,U sn andU cn for the ac busbar voltage of the nth VSC and the converter output voltage,Xis the equivalent reactance between the ac busbar of the VSC and the converter,δn is the phase angle difference between the ac busbar voltage of the nth VSC and the converter output voltage.
3. Solving the port direct current voltage variation range of the VSC under each operation mode according to the maximum line resistance, the maximum operation current, the minimum line resistance and the minimum operation current respectively, and designing the maximum modulation ratio under each operation modeM max Minimum modulation ratioM min 。
In this embodiment, the rated resistance is 10Ω, the maximum resistance is 12Ω, the minimum line resistance is 8Ω, the maximum operating current is 5kA, and the minimum short-circuit current is 0.5kA. In the case of monopolar metal return operation, the voltage range of the port of the VSC is [340, 396] kV in the mode, and in the mode, under various rotating belt working conditions, the working condition of the maximum voltage drop which is possible to be flexible and straight is that the single valve group exits, and the voltage of the VSC needs to be reduced from 340kV to 280kV. Considering that the maximum modulation ratio of the overmodulation is guaranteed to be 1.05, the maximum modulation ratio in this manner is further determined to be 0.86.
4. Based on the determined port direct current voltage and direct current of the LCC and the VSC, according to a main equipment parameter selection method of the LCC and the VSC, equipment parameters such as converter transformer rated voltage, rated capacity, short circuit impedance and the like of the LCC and the VSC are independently calculated respectively.
In the embodiment, under the rated working condition, the direct current voltage of the port of the LCC at the transmitting end is 400kV, and the direct current is 5kA; the direct current voltage of the port of the receiving end LCC is 375kV, and the direct current is 5kA; the direct current voltage of the port of the receiving end VSC is 375kV, the direct current is 5kA, and basic equipment parameters of the LCC and the VSC are calculated according to a traditional method.
5. And (3) based on constraints such as a port direct-current voltage change range, a modulation ratio range, an alternating-current voltage change range, bridge arm current limit, transformer capacity limit and the like of the VSC, and solving a PQ operation section of the VSC.
The PQ operation interval is designed according to the union of the PQ operation intervals under all gears, and when a single gear cannot meet the system requirement, the configuration range of the gear is gradually increased to enlarge the PQ operation interval. And (3) obtaining a PQ running interval under the running mode until the gear configuration meets the requirement of the system on the VSC exchange capacity under the running mode, or when the exchange power between the VSC and the system cannot be increased by adding the gears, wherein the union of the gears obtained under each running mode is the gear designed by the VSC.
The maximum operating power of the VSC is determined as: when the VSC valve group is operated at full voltage and the current is symmetrical to the current of the other pole, the maximum operating power of a single VSC (single pole) is 1000MW; when the VSC valve group is operated at full voltage and is asymmetric to the current of the other pole or the VSC valve group is operated at half voltage and is symmetric to the current of the other pole, the maximum operating power of a single VSC (single pole) is 960MW; when the VSC valve set is operated at half-voltage and is asymmetric with the other pole, the maximum operating power of a single VSC (monopolar) is 800MW. The gear that the VSC should design is +24, -6.
6. Then the maximum operating power corresponding to the VSC is determined according to the PQ operating intervalP vscmax1 Calculating the corresponding maximum operating power of the rectifying side under the maximum operating power, namely the maximum operating power of the systemP max1 According to the minimum line resistance during calculation.
In this embodiment, when the number of VSCs is 3, the maximum operating power of the system is the same as that of the conventional dc; when the number of the operation of the VSC is 2, the maximum operation power of the system is the same as that of the conventional direct current in most modes, and only one condition is limited, namely the unipolar half-voltage operation containing the VSC is limited, and the maximum operation power of the system is 1730MW.
7. Establishing a PSCAD simulation model of the hybrid cascade system, and performing simulation scanning to calculate that the maximum operating power of the system meeting the alternating current fault ride-through requirement in each operating mode isP max2 In this embodiment, by optimally configuring the parameters of the energy dissipater,P max2 is consistent with the conventional direct current engineering.
8. Determining the maximum operating power of the system in this operating modeP max =max(P max1 ，P max2 ). For limited unipolar half-voltage operation with a VSC operating number of 2, the maximum operating power is limited.
9. And solving a steady-state mathematical model of the constructed hybrid cascade system in the finally determined system running power and VSC reactive power, and calculating the running characteristic of the running power from 0.1pu to 1pu under each running mode to form a steady-state running parameter of the system. Tables 1 and 2 show the steady-state operation parameters in the bipolar full pressure 1+3 operation mode in this example.
TABLE 1 normally straight section
Table 2 straight and soft part
Embodiment two: the first embodiment provides a method for designing main loop parameters of a hybrid cascade extra-high voltage direct current system, and correspondingly, the embodiment provides a system for designing main loop parameters of a hybrid cascade extra-high voltage direct current system. The system provided by the embodiment can implement the method for designing the main loop parameters of the hybrid cascade extra-high voltage direct current system of the embodiment, and the system can be realized by software, hardware or a combination of software and hardware. For convenience of description, the present embodiment is described while being functionally divided into various units. Of course, the functions of the units may be implemented in the same piece or pieces of software and/or hardware. For example, the system may include integrated or separate functional modules or functional units to perform the corresponding steps in the methods of embodiment one. Because the system of the embodiment is basically similar to the method embodiment, the description process of the embodiment is simpler, and the relevant parts can be referred to the part of the description of the first embodiment.
Specifically, the main loop parameter design system of the hybrid cascade extra-high voltage direct current system provided by the embodiment comprises:
the operation mode determining unit is configured to determine the operation mode of the hybrid cascade extra-high voltage direct current system;
the model construction unit is configured to determine a basic control mode of the receiving end VSC and the LCC, a voltage distribution mode of the VSC and the LCC and a current distribution mode among the VSCs, and construct a steady-state mathematical model of the hybrid cascade system under a set constraint equation;
the parameter determining unit is configured to calculate the port direct current voltage variation range of the VSC in each operation mode and design the modulation ratio range in each operation mode; based on constraint conditions of a PQ operation interval of the VSC, solving the PQ operation interval of the VSC, and determining a gear range to be configured by the soft direct converter; determining the maximum operating power of the hybrid cascade extra-high voltage direct current system in the operating mode;
and the model calculation unit is configured to solve a steady-state mathematical model of the hybrid cascade system based on the system running power and the VSC reactive power to obtain steady-state running parameters of the system.
Embodiment III: the present embodiment provides an electronic device corresponding to the method for designing a main loop parameter of a hybrid cascade extra-high voltage direct current system provided in the first embodiment, where the electronic device may be an electronic device for a client, for example, a mobile phone, a notebook computer, a tablet computer, a desktop computer, etc., so as to execute the method in the first embodiment.
As shown in fig. 5, the electronic device includes a processor, a memory, a communication interface, and a bus, where the processor, the memory, and the communication interface are connected by the bus to complete communication with each other. The bus may be an industry standard architecture (ISA, industry Standard Architecture) bus, an external device interconnect (PCI, peripheralComponent) bus, or an extended industry standard architecture (EISA, extended Industry Standard Component) bus, among others. The memory stores a computer program that can be run on the processor, and when the processor runs the computer program, the method for designing the main loop parameters of the hybrid cascade extra-high voltage direct current system provided by the embodiment is executed. Those skilled in the art will appreciate that the architecture shown in fig. 5 is merely a block diagram of some of the architecture relevant to the present application and is not limiting of the computing devices to which the present application may be applied, and that a particular computing device may include more or fewer components than shown, or may combine some of the components, or have a different arrangement of components.
In some implementations, the logic instructions in the memory described above may be implemented in the form of software functional units and stored in a computer-readable storage medium when sold or used as a stand-alone product. Based on such understanding, the technical solution of the present application may be embodied essentially or in a part contributing to the prior art or in a part of the technical solution, in the form of a software product stored in a storage medium, including several instructions for causing a computer device (which may be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the methods described in the embodiments of the present application. And the aforementioned storage medium includes: a U-disk, a removable hard disk, a Read-Only Memory (ROM), a random access Memory (RAM, random Access Memory), an optical disk, or other various media capable of storing program codes.
In other implementations, the processor may be a Central Processing Unit (CPU), a Digital Signal Processor (DSP), or other general-purpose processor, which is not limited herein.
Embodiment four: the method for designing the main loop parameters of the hybrid cascading extra-high voltage direct current system according to the first embodiment may be implemented as a computer program product, and the computer program product may include a computer readable storage medium on which computer readable program instructions for executing the method for designing the main loop parameters of the hybrid cascading extra-high voltage direct current system according to the first embodiment are loaded.
The computer readable storage medium may be a tangible device that retains and stores instructions for use by an instruction execution device. The computer readable storage medium may be, for example, but not limited to, an electronic storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any combination of the preceding.
In this specification, each embodiment is described in a progressive manner, and identical and similar parts of each embodiment are all referred to each other, and each embodiment mainly describes differences from other embodiments. In particular, for system embodiments, since they are substantially similar to method embodiments, the description is relatively simple, as relevant to see a section of the description of method embodiments. In the description of the present specification, reference to the terms "one embodiment," "some implementations," and the like, means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the embodiments of the present specification. In this specification, schematic representations of the above terms are not necessarily directed to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, the different embodiments or examples described in this specification and the features of the different embodiments or examples may be combined and combined by those skilled in the art without contradiction.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flowchart illustrations and/or block diagrams, and combinations of flows and/or blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention, and are not limiting; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present invention.
Claims (9)
1. A design method of main loop parameters of a hybrid cascade extra-high voltage direct current system is characterized by comprising the following steps:
determining the operation mode of the mixed cascade extra-high voltage direct current system;
determining a basic control mode of a receiving end VSC and an LCC, a voltage distribution mode of the VSC and the LCC and a current distribution mode among the VSCs, and constructing a steady-state mathematical model of the hybrid cascade system under the obtained constraint equation;
calculating the port direct current voltage variation range of the VSC under each operation mode, and designing the modulation ratio range under each operation mode, wherein the modulation ratio range under each operation mode is designed as follows:
calculating the maximum modulation ratio under each operation modeM max =U dcfinal ×M absmax /U dcinit ，U dcfinal Direct current voltage after fault under the working condition of maximum voltage drop caused by the power transfer,U dcinit the direct current voltage before failure under the working condition of maximum voltage drop caused by the power transfer,M absmax to ensure a maximum modulation ratio of the flexible dc output voltage over modulation; designing minimum modulation ratio according to level number capable of meeting system harmonic requirementM min ；
Based on constraint conditions of a PQ operation interval of the VSC, solving the PQ operation interval of the VSC, and determining a gear range to be configured by the soft direct converter;
determining the maximum operating power of the hybrid cascade extra-high voltage direct current system in the operating mode;
and solving a steady-state mathematical model of the hybrid cascade system based on the maximum operating power and the VSC reactive power of the system to obtain steady-state operating parameters of the system.
2. The method for designing main loop parameters of a hybrid cascade extra-high voltage direct current system according to claim 1, wherein the voltage distribution mode of the VSC and the LCC comprises:
the VSC and LCC are distributed in a mode of equal direct current voltage, and the corresponding constraint equation is thatU dcvsc =U dclcc ，U dcvsc AndU dclcc the port direct current voltages of the VSC and the LCC respectively;
the VSC does not consider the fluctuation of the direct current voltage, and the LCC bears the line voltage drop, and the corresponding constraint equation is thatU dcvsc =U setvsc ，U dcvsc Is the port dc voltage of the VSC,U setvsc is a set value.
3. The method for designing main loop parameters of a hybrid cascade extra-high voltage direct current system according to claim 2, wherein the current distribution manner among the VSCs comprises:
and each VSC is distributed in a mode of equal current, and a constraint equation is as follows:I vsc1 =I vsc2 =...I vscn =I dc /n，I vsc1 ，...I vscn the direct current of the 1 st to n th VSCs respectively,I dc for the total current flowing into the VSC valve block;
and independently appointing the running power among the VSCs, and then the constraint equation is as follows:I vsc1 =P vsc1 /U setvsc ，I vsc2 =P vsc2 /U setvsc …I vscn =P vscn /U setvsc and is also provided withI vscn =I dc -I vsc1 -I vsc2 …I vsc（n-1） ，P vsc1 、P vsc2 …P vscn Active power for VSC1, VSC2 … VSCn.
4. The method for designing main loop parameters of a hybrid cascading extra-high voltage direct current system according to claim 1, wherein solving the PQ operation interval of the VSC comprises:
a. determining limiting conditions of a PQ operation interval of the VSC, wherein the limiting conditions comprise a port direct current voltage change range, a modulation ratio range, an alternating current voltage change range, bridge arm current limit and transformer capacity limit of the VSC;
b. based on constraint conditions, solving a PQ operation interval, wherein the PQ operation interval takes intersections under different direct-current voltage and alternating-current voltage combinations;
c. judging whether the power interval meets the set requirement of the system on power exchange, if so, determining a PQ running interval and a VCS gear, and if not, entering d;
d. if reactive power deficiency is generated or bridge arm current leads to power limitation, negative gear configuration is increased; if the absorption reactive power is insufficient, adding the positive gear configuration, and entering the step b.
5. The method for designing main loop parameters of a hybrid cascade extra-high voltage direct current system according to claim 1, wherein the PQ operation section is designed according to a union of PQ operation sections under all gear positions, when a single gear position cannot meet system requirements, the configuration range of the gear position is gradually increased to increase the PQ operation section until the gear position configuration meets the requirements of the system on VSC exchange capacity under the operation mode, or when the gear position cannot be increased any more to increase the exchange power of the VSC and the system, the PQ operation section under the operation mode is obtained, and the union of the gear positions obtained under each operation mode is the gear position of the VSC design.
6. The method for designing main loop parameters of a hybrid cascade extra-high voltage direct current system according to claim 4 or 5, wherein the method for increasing the configuration range of gears comprises the following steps: when the current limit of the bridge arm causes insufficient absorption or emission of active power or reactive power, increasing negative gear configuration; when the modulation ratio is limited so as to cause insufficient reactive power absorption, adding a positive gear configuration; when the modulation ratio limitation results in insufficient reactive power being emitted, a negative gear configuration is increased.
7. The utility model provides a mixed cascade extra-high voltage direct current system main loop parameter design system which characterized in that includes:
the operation mode determining unit is configured to determine the operation mode of the hybrid cascade extra-high voltage direct current system;
the model construction unit is configured to determine a basic control mode of the receiving end VSC and the LCC, a voltage distribution mode of the VSC and the LCC and a current distribution mode among the VSCs, and construct a steady-state mathematical model of the hybrid cascade system under a set constraint equation;
the parameter determining unit is configured to calculate the port direct current voltage variation range of the VSC in each operation mode and design the modulation ratio range in each operation mode; based on constraint conditions of a PQ operation interval of the VSC, solving the PQ operation interval of the VSC, and determining a gear range to be configured by the soft direct converter; determining the maximum operating power of the hybrid cascade extra-high voltage direct current system in the operating mode; the modulation ratio range under each operation mode is designed as follows: calculating the maximum modulation ratio under each operation modeM max =U dcfinal ×M absmax /U dcinit ，U dcfinal Direct current voltage after fault under the working condition of maximum voltage drop caused by the power transfer,U dcinit the direct current voltage before failure under the working condition of maximum voltage drop caused by the power transfer,M absmax to ensure a maximum modulation ratio of the flexible dc output voltage over modulation; designing minimum modulation ratio according to level number capable of meeting system harmonic requirementM min ；
And the model calculation unit is configured to solve a steady-state mathematical model of the hybrid cascade system based on the maximum running power and the VSC reactive power of the system to obtain steady-state running parameters of the system.
8. An electronic device comprising computer program instructions, wherein the program instructions, when executed by a processor, are configured to implement the method for designing main loop parameters of a hybrid cascaded uhv dc system according to any one of claims 1-6.
9. A computer readable storage medium, wherein computer program instructions are stored on the computer readable storage medium, and when the program instructions are executed by a processor, the program instructions are used to implement the method for designing main loop parameters of the hybrid cascade extra-high voltage direct current system according to any one of claims 1 to 6.
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