CN114050583A - Double-end flexible frequency division power transmission system and cooperative control method - Google Patents

Double-end flexible frequency division power transmission system and cooperative control method Download PDF

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CN114050583A
CN114050583A CN202111259885.3A CN202111259885A CN114050583A CN 114050583 A CN114050583 A CN 114050583A CN 202111259885 A CN202111259885 A CN 202111259885A CN 114050583 A CN114050583 A CN 114050583A
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frequency
power
frequency division
voltage
current
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韩杏宁
彭竹弈
刘沈全
王钢
赵菲菲
张文嘉
万鹭
祁万春
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Economic and Technological Research Institute of State Grid Jiangsu Electric Power Co Ltd
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
    • H02J3/241—The oscillation concerning frequency
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/01—Arrangements for reducing harmonics or ripples
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/04—Circuit arrangements for ac mains or ac distribution networks for connecting networks of the same frequency but supplied from different sources
    • H02J3/06—Controlling transfer of power between connected networks; Controlling sharing of load between connected networks
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/12—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
    • Y02E40/40—Arrangements for reducing harmonics

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Abstract

The invention discloses a double-end flexible frequency division power transmission system and a cooperative control method.A frequency conversion device is arranged at two ends of a power frequency circuit to enable the circuit to work at low frequency.

Description

Double-end flexible frequency division power transmission system and cooperative control method
Technical Field
The invention relates to the field of power supply and distribution of an urban power grid, in particular to a double-end flexible frequency division power transmission system and a cooperative control method.
Background
The vigorous development of renewable energy is an important technical means for promoting the energy revolution in China, the frequency division power transmission technology can obviously improve the economic and technical performance of the energy delivery link, is more suitable for the low-rotating-speed characteristic of a double-fed fan, and is beneficial to simplifying the unit structure and reducing the cost. Therefore, research aiming at the frequency division power transmission system is mainly focused on the field of large-scale delivery of renewable energy sources, low-frequency electric energy is directly output by utilizing the network side control characteristic of a renewable energy source unit, and is transmitted to a receiving end frequency conversion station after current collection and voltage boosting, and the electric energy is converted to 50Hz and then is collected into a power frequency power grid.
On the other hand, with the rapid increase of the electricity load of the central city, the expansion and reconstruction of the urban power grid become a problem which is concerned. The frequency division power transmission technology can fully excavate the power transmission potential of the existing line and grid structure.
However, it is currently directed to flexible frequency division M3The control research of the C converter station is concentrated on the scene of a single-end flexible frequency division power transmission system, and for the M in a double-end scene3And C, the operation control research is less, particularly, a cooperative control method of the transmitting end and the receiving end frequency conversion station has no definite conclusion, and the method is a bottleneck problem of engineering application of the double-end flexible frequency division transmission system.
Disclosure of Invention
In order to overcome the defects and shortcomings of the prior art, the primary object of the present invention is to provide a double-ended flexible frequency-division power transmission system, which enables a line to work at a low frequency (50/3Hz) to improve the capacity and the power transmission efficiency of the line and reduce the voltage fluctuation of a bus caused by the power flow change.
Another object of the present invention is to provide a cooperative controlling methodMethod, in particular to M in a scene of a double-ended flexible frequency division power transmission system3And C, a control strategy of the converter station and an inter-station cooperative control method enable the converter station at the side with stronger power frequency to provide a balance node for the frequency division system, and enable the other converter station to work in a constant power mode, so that the long-term stable operation of the system is realized.
The invention adopts the following technical scheme:
as shown in fig. 1, a two-terminal flexible frequency division power transmission system solves the problem of capacity expansion and transformation of an urban power grid, and specifically, frequency conversion devices are arranged at two ends of a power frequency line, and a point-to-point frequency division power transmission channel is constructed to form the two-terminal flexible frequency division power transmission system. The line operates at a lower frequency, typically 50/3Hz or 20Hz, to increase line capacity and transmission efficiency, reducing bus voltage fluctuations caused by power flow variations.
Further, as shown in fig. 2 and 3, the frequency conversion device employs a modular multilevel matrix converter (M)3C. The current converter) specifically comprises nine bridge arms, wherein the nine bridge arms are divided into three groups, and each group is connected with two three-phase ports of the alternating-current power grids on two sides.
The flexible frequency division power transmission system is constructed by using the modular multilevel matrix converter, so that the controllability, robustness and power quality of the system are improved. Each bridge arm in the M3C includes an inductor L and n full-bridge submodules (FBSM) connected in series. The three phases of the power frequency system are denoted by u, v and w, and the three phases of the frequency division system are denoted by a, b and c. For the purpose of simplifying the description, the subsequent part will refer to any one of the three phases a, b and c on the low frequency side with x, and refer to any one of the three phases u, v and w on the power frequency side with y. Each bridge arm is named by the name of the port to which both ends thereof are connected, and for example, the bridge arm connecting the frequency-dividing side a-phase and the power-frequency side u-phase is referred to as "bridge arm au". Each module consists of a module capacitor and a single-phase full-bridge inverter, and can output + v by changing the switching signals of four converter valves in the full-bridge inverterC，-vCOr 0 three levels (v)CModule capacitance voltage), if the capacitance voltage difference between the modules is ignored, nSMA module can generate a slave-nSMvCTo nSMvCOf (2 n)SM+1) levels.
The full-bridge submodule comprises four converter valves and a submodule capacitor, the four converter valves are respectively a first converter valve, a second converter valve, a third converter valve and a fourth converter valve, the positive electrodes of the submodule capacitor are respectively connected with the collecting electrodes of the first converter valve and the third converter valve, the negative electrodes of the submodule capacitor are respectively connected with the emitting electrodes of the second converter valve and the fourth converter valve, the emitting electrode of the first converter valve and the collecting electrode of the second converter valve are connected to form a first port of the full-bridge submodule, and the emitting electrode of the third converter valve and the collecting electrode of the fourth converter valve are connected to form a second port of the full-bridge submodule.
The invention provides M under the scene of a double-end flexible frequency division power transmission system3C, the converter station on the side with stronger power frequency provides a balance node for the frequency division system, and the converter station works in a constant power mode, and a typical control strategy configuration mode is provided.
A system control method of a double-end flexible frequency division power transmission system is characterized in that a frequency conversion device adopts a three-layer control framework of outer ring-inner ring-modulation, and comprises a voltage/power outer ring control link, a current inner ring control link and a modulation link;
the voltage/power outer loop control link controls M3C overall operating state of M3And C, the system can stably work for a long time and responds to a dispatching instruction issued by a superior. M3The output characteristics of the power frequency/frequency division side of the C are not influenced mutually, and an outer ring control target can be set independently. The selectable control targets of the power frequency or frequency division side active outer ring comprise (1) determining active power, (2) determining average submodule capacitor voltage, and (3) active droop control based on frequency offset and the like. To maintain M3C power in and out balance, at least one side active target should be set to the stator module capacitor voltage. The selectable control targets for the reactive outer loop include (1) fixed reactive power, (2) fixed power factor angle, and (3) reactive droop control based on voltage offset, among others. In addition, if M3C is needed to provide a balanced node for the frequency division system, the outer ring of the frequency division sideThe active and reactive parts must provide active/reactive power relaxation for the frequency division system respectively to ensure the frequency/voltage stability of the frequency division system.
The current inner ring control link is responsible for controlling current instruction values issued by tracking each current component by the outer ring, comprises three parts of power frequency side current control, frequency division side current control and harmonic circulation suppression, and respectively realizes the functions of power frequency/frequency division network side current control and high-order harmonic circulation suppression.
And the modulation link is responsible for receiving a bridge arm voltage instruction issued by the current inner ring, and generating a switching signal of each converter valve by utilizing a sequencing switching method in combination with the requirement of voltage sharing of modules in the bridge arm.
Further, the voltage equalizing of the modules in the bridge arm is obtained by adopting the following method:
firstly, sorting different modules in each bridge arm according to the capacitance voltage, and determining the input priority of the modules according to the instantaneous power flow direction; secondly, determining the number and polarity of the modules required to be put into each bridge arm through a modulation algorithm such as nearest level approximation, and putting the corresponding modules according to the priority order of the modules.
The cooperative configuration is as follows:
(1) for the power frequency side active outer ring, because the disturbance resistance of the power frequency main network is far higher than that of a frequency division system, the power frequency side active outer ring works in a stator module average capacitance voltage mode, and the power balance of M3C is maintained; the stator module capacitor voltage is used for maintaining the sub-module capacitor voltage near the rated value of the sub-module capacitor voltage.
(2) For the active outer ring at the frequency division side, M at the stronger side of the power frequency system3C is operated in a V/f mode of the constant frequency division system to provide a balance node of the frequency division system, and M is arranged on the weaker side of the power frequency system3C, working in a fixed active power mode, and tracking a power instruction issued by a superior dispatching;
(3) for the reactive outer ring at the power frequency/frequency division side, except for the occupied M at the stronger side of the power frequency system3And on the frequency division side of C, the rest of the reactive outer rings can be selected within a safety allowable range according to the requirement.
The power frequency side refers to the angle of the M3C converter, M3C implementationThe frequency conversion from the power frequency of 50Hz to the low frequency of 50/3Hz is respectively called as the power frequency side and the low frequency side,
the power frequency system is based on a large system, and the system is strong, namely, the system is large in capacity and low in short circuit impedance.
The frequency dividing side of the sending end converter station works in a constant frequency dividing system V/f mode, and the frequency dividing side of the receiving end converter station works in a constant active/reactive power mode; the rest of the reactive outer rings work in a constant reactive power mode, and a typical double-end type frequency division power transmission system M is provided3The method for the coordination configuration of the outer loop control strategy of the converter station C is shown in the following table 1:
TABLE 1 outer-loop control target of converter station of double-end flexible frequency division power transmission system
Figure BDA0003325167090000041
The invention has the beneficial effects that:
(1) the invention only needs to transform the transformer substations at two ends of the power frequency circuit into the frequency conversion device, does not relate to the large-scale transformation of the circuit, is convenient for centralized construction, and has better project realizability.
(2) The frequency conversion device adopts the modular multilevel matrix converter, the active/reactive power at the network side is controllable, the electric energy quality is excellent, the response speed is rapid, and the operation flexibility of a power grid is favorably improved. By arranging a certain frequency conversion station to operate in the V/f control of the constant frequency division system, a balance node is provided for the frequency division system, the operation control problem of the full-electric electronic frequency division power transmission system can be effectively solved, and the safe, stable and efficient operation of the system is realized.
Drawings
Fig. 1 is a schematic structural diagram of a two-terminal flexible frequency division power transmission system according to the present invention;
FIG. 2 is a drawing of the invention M3C, a schematic diagram of a circuit structure, main electric quantity and a positive direction of the main electric quantity;
FIG. 3 is the invention M3C, control frame diagram;
FIG. 4 is a detailed block diagram of FIG. 3 of the present invention;
FIG. 5 is a system block diagram of a simulation example of an embodiment of the present invention;
FIGS. 6(a) -6 (l) are waveform diagrams of simulation tests according to the embodiment of the present invention.
Detailed Description
The present invention will be described in further detail with reference to examples and drawings, but the present invention is not limited to these examples.
Examples
The effect of the invention was analyzed by quantitative analysis.
(one) M3Mathematical model of C
M3The mathematical modeling of C is the basis of the control system design. Establishment of M under the double Clarke transform3The mathematical model for C is as follows:
(1) kirchhoff equation of voltage and current
According to the positive direction shown in fig. 2, the voltage equation of each bridge arm can be established by using kirchhoff's voltage law:
Figure BDA0003325167090000051
in the formula, vNThe neutral point voltage difference between the frequency division-power frequency systems can be approximately ignored; u is a 3 × 3 all-1 matrix; eSV, I and ELThe power frequency side voltage matrix, the bridge arm current matrix and the frequency division side voltage matrix are 3 multiplied by 3 structures, each element represents the electric quantity of a corresponding bridge arm, namely:
Figure BDA0003325167090000052
wherein ixyAnd vxyRespectively the current and the output voltage of the bridge arm xy.
According to kirchhoff's current law, we can obtain:
Figure BDA0003325167090000053
in the formula: i.e. ix，iy-line current of the x-phase on the frequency division side, or the y-phase on the power frequency side.
(2) Double Clarke transform
The Clarke transformation is a commonly used mathematical tool for three-phase circuit analysis, and can convert a three-phase alternating current variable into a two-phase static coordinate system so as to extract common mode (namely zero sequence) and differential mode components in three-phase electric quantity. The Clarke transformation has two forms of equal amplitude and equal power transformation, the former is adopted in the text, and the expression is as follows:
Figure BDA0003325167090000054
in the formula, Tαβ0Namely the Clarke transformation matrix.
The corresponding inverse transform matrix is:
Figure BDA0003325167090000055
the double Clarke transformation is M-oriented3The coordinate transformation method proposed by the 3 × 3 circuit structure of C is in the mathematical form: make bridge arm variable matrix multiply T on leftαβ0Then right-handed by Tαβ0The transpose of (a), namely:
Figure BDA0003325167090000061
(3) mathematical model and equivalent circuit under double Clarke coordinate system
Double Clarke transformation is performed on two sides of the equation of the formula (1), and v is ignoredNObtaining the following mathematical model of a double alpha beta 0 coordinate system:
Figure BDA0003325167090000062
in the formula, eSα、eSβAnd eS0Respectively under two-phase stationary coordinate systemThe α, β and 0-axis components of the power frequency system voltage, and eLα、eLβAnd eL0Representing the alpha, beta, and 0 axis components of the divided system voltage, respectively. Equation (6) shows that the power frequency side voltage matrix ESAfter double Clarke transformation mapping, the power frequency system only comprises components of 0 alpha, 0 beta and 00, which respectively correspond to the components of the alpha, beta and 0 axes of the three-phase voltage of the power frequency system; in the same way, the voltage matrix E of the frequency division sideLAfter double Clarke conversion mapping, the frequency division system only comprises components of 0 alpha, 0 beta and 00, which correspond to the components of the axes alpha, beta and 0 of the three-phase voltage of the frequency division system.
Based on the above analysis, the bridge arm voltages and currents under the double α β 0 coordinate system can be classified into 4 types:
1) α 0, β 0 component: influenced by the alpha-beta axis component of the voltage of the power frequency system, the current passes through the power frequency system and the M3C, forming a loop by the bridge arm;
2)0 α, 0 β component: under the influence of the alpha-beta axis component of the voltage of the frequency dividing system, the current passes through the frequency dividing system and M3C, forming a loop by the bridge arm;
3) α α, α β, β α, β β components: without influence of external system, current only passes through M3The C bridge arm forms a loop, namely an internal circulation component;
4)00 component: simultaneously, under the influence of the zero sequence voltage of the two-side system, the current forms a loop through the zero sequence network of the two-side system and the bridge arm, so that M is used for avoiding the penetration influence of 00-component current3And C, the systems on the two sides can not be simultaneously grounded, and the bridge arm voltage with the 00 component is represented as the voltage difference between the frequency division-power frequency systems.
The relation between partial current components and network side current can be deduced based on the bridge arm current boundary constraint of the formula (2):
Figure BDA0003325167090000063
Figure BDA0003325167090000064
Figure BDA0003325167090000071
in the formula iSα(β)、iLα(β)The power frequency side current and the frequency division side current respectively have alpha (beta) axis components.
(4) Network side current equation under synchronous coordinate system
According to the above classification method, independent equations for each type of current can be written according to the columns of equations (6), (7), and (8):
power frequency side current:
Figure BDA0003325167090000072
current on the frequency dividing side:
Figure BDA0003325167090000073
circulating current:
Figure BDA0003325167090000074
the following equations (10) and (11) are mapped to the power frequency and frequency division synchronous coordinate system respectively to obtain:
Figure BDA0003325167090000075
Figure BDA0003325167090000076
in the formula, eSd(q)、eLd(q)D (q) axis components of the power frequency side and the frequency division side power grid voltage respectively; i.e. iSd(q)、iLd(q)The d (q) axis component of the power frequency and frequency division component of the bridge arm voltage is also (v)α0,vβ0) And (v)0α,v0β) Mapping under power frequency and frequency division synchronous coordinate systems respectively; i.e. iSd(q)、iLd(q)D (q) axis components of the net side current, respectively; omegaS、ωLRespectively power frequency and angular frequency of a frequency division system.
As is clear from the formulae (13) and (14), M3The control characteristics of the power frequency side and the frequency division side of the C are the same as those of a voltage source type three-phase inverter, and the equivalent internal impedance is 1/3 of the impedance of a bridge arm.
(5) Equation of power
It is assumed herein that the d-axes of the power frequency side and the frequency division side are both located by the grid voltage vector. At this time, M3The input active and reactive power of the C power frequency side can be expressed as:
Figure BDA0003325167090000077
the output active power and reactive power of the frequency division side are as follows:
Figure BDA0003325167090000081
the average sub-module capacitance voltage approximately satisfies, near its nominal value:
Figure BDA0003325167090000082
in the formula, n, C and vCRespectively representing the number of sub-modules, capacitance values and voltages of the sub-modules contained in each bridge arm; the superscript ref denotes the reference value of the variable, where vC refI.e. vCOf the target value of (c).
(II) control strategy of each link
Based on the established M3C, the mathematical model of the C can be designed into M in the attached figure 23C, detailed feedback control equations of various links such as an outer ring, an inner ring and the like and different control strategies.
(1) Outer loop control equation
The control equations for the different outer loop control strategies are as follows:
1) constant average submodule capacitor voltage control
The power frequency side active parts of the transmitting terminal station and the receiving terminal station work in a constant average submodule capacitor voltage mode, and the control equation is as follows:
Figure BDA0003325167090000083
in the formula, KPAnd KIProportional and integral gains of the PI controller, respectively.
2) Constant active/reactive power control
Taking the outer ring of the frequency division side of the receiving end station as an example, the control equation of the fixed active/reactive power is as follows:
Figure BDA0003325167090000084
in the formula, PL、QLRespectively the active power and the reactive power output by the frequency dividing side. Other outer loop control equations for fixed active/reactive power modes can be approximated.
V/f control for fixed frequency division system
In order to accurately control the amplitude and the frequency of the voltage of the frequency division outlet bus, a parallel capacitor C is required to be arranged at the frequency division outletfAnd further by controlling the flow through CfThe bus voltage is regulated. In order to track the voltage command value of the power grid, the current components of d and q axes flowing through the parallel capacitor branch circuit are as follows:
Figure BDA0003325167090000091
in the formula idCf、iqCfRespectively is flowed through CfThe dq axis component of the current. While
Figure BDA0003325167090000092
In the formula idlAnd iqlFor low-frequency line to flow into balance nodeAnd (4) streaming.
(2) Inner loop control equation
According to the established network side current model, M3The grid side characteristic of the C is consistent with that of a three-phase voltage source type inverter, so that power frequency and frequency division grid side current control can be realized through a classical current control strategy based on grid voltage feedforward and dq axis current cross decoupling. Taking the power frequency side as an example, the control equation is as follows:
Figure BDA0003325167090000093
the structure of the frequency-division current controller is similar to equation (22), and is not described in detail here.
M3The harmonic circulation of C includes 4 frequency components, and the current loops are different from each other, and a common control idea is to use a proportional controller in a dual α β 0 coordinate system to achieve the broad-spectrum harmonic circulation suppression, and the control equation is:
Figure BDA0003325167090000094
the designed control strategy is integrated, and the coordinate transformation link is considered, so that M can be formed3C a complete set of solutions for control. Due to the high degree of similarity of the sending and receiving end station control systems, a detailed block diagram of the sending end station control system is presented herein, as shown in FIG. 4. Compared with the sending end, the receiving end station has the following differences: (1) phase angle omega of frequency divisionLt must be given by the phase locked loop; (2) and the outer ring of the frequency division side adopts constant active/reactive power control.
(III) simulation test
This section verifies the correctness and validity of the proposed control strategy based on MATLAB/Simulink simulation, and the example structure is shown in fig. 5. The arithmetic nominal active power/voltage is 600MW/50Hz, the power transmission distance is 100km, and the positive directions of power and current are defined from a power frequency system A to a power frequency system B. The power frequency sides of the frequency conversion stations A and B work in a constant average submodule capacitor voltage and constant reactive power mode, the frequency division side of the station A works in a constant frequency division system V/f control mode, and the frequency division side of the station B works in a constant active/reactive power mode. The main electrical parameters are shown in table 2:
the simulation waveforms are shown in fig. 6(a) to 6 (l). The system is in an idle state at the initial moment, namely the active power instruction of the frequency division side of the station B is 0; from time t to 0.05s, the active power command is increased to a nominal value of 600MW at a rate of 30GW/s and is held constant for the remaining time. As can be seen from the figure, the whole system has excellent transient response characteristics, can enter steady-state operation within 0.1s when the operation state changes suddenly, and can effectively adapt to the output fluctuation of renewable energy sources and various changes of scheduling instructions.
TABLE 2 simulation example parameters
Figure BDA0003325167090000101
According to fig. 6(a), 6(b), 6(d), 6(e), 6(g) and 6(h), the power frequency side current, the frequency division side voltage and the current waveform all keep good sinusoidal characteristics in the whole simulation test, and the FFT analysis shows that the THD of the alternating current is below 1%. Under the no-load state, the effective values of the line voltages of the buses 2 and 3 are 230.0kV and 230.2kV respectively, and under the full-load state, the effective values are 230.0kV and 220.0kV respectively. Thus, under the control of V/f on the frequency dividing side of station A, M3The voltage of the C frequency division side bus can be kept constant under different transmission powers, and stable operation of a frequency division power transmission system is ensured. The load flow calculation shows that the tail end voltages of the power transmission line in the no-load/full-load state with the same parameters under the power frequency system are 231.5kV and 173.2kV respectively, and the full-load state does not meet the requirement of the power system on the line voltage; at a line end voltage of 220.0kV, the line delivered power was 310.5MW, which is only 51.8% of the frequency division. Therefore, the frequency division power transmission system can remarkably improve the line capacity, reduce the voltage fluctuation caused by active power change and is particularly suitable for a power system with high renewable energy permeability.
M is shown in FIGS. 6(i) to 6(k), respectively3C waveform of key electrical quantity inside the bridge arm current and the sub-module capacitance voltage in sequenceAnd bridge arm loops under a dual α β 0 coordinate system. Due to the symmetry of the frequency translating stations a and B, only the relevant waveform for station a is shown here. As can be seen from the figure, the bridge arm current will contain both power frequency and fundamental frequency components, the sub-module capacitor voltage will also contain ripples of multiple frequencies, and the harmonic frequency spectrum of the both is far more complex than that of the conventional MMC rectifier/inverter. Under the designed electrical parameters and control strategies, the capacitor voltage ripple is restrained within +/-5% in a steady state, the harmonic circulating current amplitude of the bridge arm is restrained within 1%, and the high-quality electric energy output characteristic of the network side is guaranteed.
In conclusion, the designed control system can realize the high-efficiency operation of the double-end flexible frequency division power transmission system, and the system has good transient/steady-state characteristics.
The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.

Claims (10)

1. A double-end flexible frequency division power transmission system is characterized in that frequency conversion devices are arranged at two ends of a power frequency circuit in a power grid, and a point-to-point frequency division power transmission channel is constructed by utilizing an existing three-phase alternating current circuit.
2. The two-terminal flexible power transmission system according to claim 1, wherein the frequency conversion means employs a modular multilevel matrix converter.
3. The two-terminal flexible frequency-division power transmission system according to claim 2, wherein the modular multilevel matrix converter comprises nine bridge arms, the nine bridge arms are divided into three groups, each group is connected with two of three-phase ports of a two-side alternating-current power grid, and each bridge arm comprises an inductor and n full-bridge submodules connected in series.
4. The double-ended flexible frequency-division power transmission system according to claim 3, wherein the full-bridge sub-module comprises four converter valves and a sub-module capacitor, the four converter valves are a first converter valve, a second converter valve, a third converter valve and a fourth converter valve respectively, an anode of the sub-module capacitor is connected to collectors of the first converter valve and the third converter valve respectively, a cathode of the sub-module capacitor is connected to emitters of the second converter valve and the fourth converter valve respectively, an emitter of the first converter valve and a collector of the second converter valve are connected to form a first port of the full-bridge sub-module, and an emitter of the third converter valve and a collector of the fourth converter valve are connected to form a second port of the full-bridge sub-module.
5. A cooperative control method for the double-ended flexible frequency division power transmission system according to any one of claims 1 to 4, wherein the frequency conversion device adopts a three-layer control architecture of outer loop-inner loop-modulation, which comprises a voltage/power outer loop control link, a current inner loop control link and a modulation link;
the voltage/power outer ring control link controls the integral operation state of a power frequency side or a frequency division side by setting an active/reactive control target, so that the converter works stably, responds to a dispatching instruction issued by a superior level, outputs an active/reactive current instruction value of a corresponding side, and inputs the current inner ring control link;
the current inner ring control link is used for controlling current components to track current instruction values issued by an outer ring, the current components comprise three parts of power frequency side current control, frequency division side current control and harmonic circulation suppression, the power frequency/frequency division network side current control and high-order harmonic circulation suppression functions are respectively realized, and the voltage instruction values of bridge arms are output and serve as the input of the modulation link;
and the modulation link is used for receiving the voltage instruction value of each bridge arm, generating a switching signal of each converter valve by combining voltage-sharing requirements of the n full-bridge submodules, obtaining switching pulses of each full-bridge submodule, and providing the switching pulses for the main circuit of the converter.
6. The cooperative control method according to claim 5, wherein the control objectives of the active part include fixed active power, fixed average sub-module capacitance voltage and active droop control based on frequency offset.
7. The cooperative control method according to claim 5, wherein the control targets of the reactive part include constant reactive power, constant power factor leg, and reactive droop control based on voltage offset.
8. The cooperative control method according to claim 5, wherein the voltage equalizing of the modules in the bridge arm is obtained by the following method:
firstly, sorting different modules in each bridge arm according to the capacitance voltage, and determining the input priority of the modules according to the instantaneous power flow direction; secondly, determining the number and polarity of the modules required to be put into each bridge arm through a modulation algorithm such as nearest level approximation, and putting the corresponding modules according to the priority order of the modules.
9. The cooperative control method according to claim 5, wherein if the inverter is required to provide a balance point for the frequency dividing system, the active part and the reactive part of the outer ring on the frequency dividing side respectively provide active/reactive power relaxation for the frequency dividing system, so as to ensure the frequency/voltage stability of the frequency dividing system.
10. The cooperative control method according to claim 6, characterized in that the cooperative configuration is as follows:
the power frequency side active outer ring works in a stator module average capacitance voltage mode, and the power balance of the modular multilevel matrix converter is maintained;
the active outer ring at the frequency division side makes the converter at the stronger side of the power frequency system work in the V/f mode of the constant frequency division system to provide a balance node of the frequency division system, and the M at the weaker side of the power frequency system3C, working in a fixed active power mode, and tracking a power instruction issued by a superior dispatching;
for the reactive outer ring at the power frequency/frequency division side, except the occupied frequency division side of M3C at the stronger side of the power frequency system, other reactive outer rings can be selected within a safe allowable range by self according to the requirement.
CN202111259885.3A 2021-10-28 2021-10-28 Double-end flexible frequency division power transmission system and cooperative control method Pending CN114050583A (en)

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Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN106410870A (en) * 2016-12-02 2017-02-15 浙江大学 Frequency control method of offshore wind power integration multi-terminal flexible DC transmission system
CN107240922A (en) * 2017-06-20 2017-10-10 国网江苏省电力公司信息通信分公司 Marine Fractional Frequency Power Transmission System control method and device
CN108521136A (en) * 2018-04-24 2018-09-11 东南大学 A kind of multiple target cooperative control method based on true bipolar flexible direct current transmission system
CN111382525A (en) * 2020-03-24 2020-07-07 国网河北省电力有限公司沧州供电分公司 Low-frequency power transmission closed loop test system and method
US20200409323A1 (en) * 2019-06-28 2020-12-31 Utilidata, Inc. Utility grid control using a dynamic power flow model
CN112366755A (en) * 2020-11-30 2021-02-12 上海交通大学 Wind field-flexible-straight control method and system based on MMC sub-module energy synchronization

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN106410870A (en) * 2016-12-02 2017-02-15 浙江大学 Frequency control method of offshore wind power integration multi-terminal flexible DC transmission system
CN107240922A (en) * 2017-06-20 2017-10-10 国网江苏省电力公司信息通信分公司 Marine Fractional Frequency Power Transmission System control method and device
CN108521136A (en) * 2018-04-24 2018-09-11 东南大学 A kind of multiple target cooperative control method based on true bipolar flexible direct current transmission system
US20200409323A1 (en) * 2019-06-28 2020-12-31 Utilidata, Inc. Utility grid control using a dynamic power flow model
CN111382525A (en) * 2020-03-24 2020-07-07 国网河北省电力有限公司沧州供电分公司 Low-frequency power transmission closed loop test system and method
CN112366755A (en) * 2020-11-30 2021-02-12 上海交通大学 Wind field-flexible-straight control method and system based on MMC sub-module energy synchronization

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
夏春等: "面向城市电网扩容改造的双端型柔性分频输电系统M3C 换流站建模与控制研究", 浙江电力, vol. 40, no. 40, pages 51 - 59 *

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