CN116683548B - MMC-based flexible direct-current traction power supply comprehensive coordination control method - Google Patents

MMC-based flexible direct-current traction power supply comprehensive coordination control method Download PDF

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CN116683548B
CN116683548B CN202310630817.6A CN202310630817A CN116683548B CN 116683548 B CN116683548 B CN 116683548B CN 202310630817 A CN202310630817 A CN 202310630817A CN 116683548 B CN116683548 B CN 116683548B
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voltage
mmc
phase
power supply
coordinate system
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CN116683548A (en
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何晓琼
王东
潘义松
曾理
韩鹏程
林静英
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Southwest Jiaotong University
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60M—POWER SUPPLY LINES, AND DEVICES ALONG RAILS, FOR ELECTRICALLY- PROPELLED VEHICLES
    • B60M3/00—Feeding power to supply lines in contact with collector on vehicles; Arrangements for consuming regenerative power
    • 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
    • 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
    • H02J5/00—Circuit arrangements for transfer of electric power between ac networks and dc 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
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]
    • 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
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]

Abstract

The invention discloses a flexible direct current traction power supply comprehensive coordination control method based on MMC, which comprises the following steps: establishing a mathematical model of the three-phase MMC under a d-q coordinate system; acquiring reference voltage values of voltage outer loop control of each MMC-based flexible direct current traction power supply station; establishing an outer ring voltage control model according to a reference voltage value of voltage outer ring control of the MMC-based flexible direct current traction power supply station; establishing an inner loop current control model according to the outer loop voltage control model; establishing a circulation suppression modulation wave correction quantity model, a three-phase MMC modulation model and a capacitor voltage balance model according to a mathematical model of the three-phase MMC under a d-q coordinate system; and performing MMC-based flexible direct-current traction power supply comprehensive coordination control according to the obtained model. The invention can realize the long-distance and electroless split-phase power supply of the traction network, reduce the number of traction substations along the line, and simultaneously ensure that the traction power supply system is stable in power supply area and supplies power with high quality.

Description

MMC-based flexible direct-current traction power supply comprehensive coordination control method
Technical Field
The invention relates to the technical field of traction power supply, in particular to a flexible direct current traction power supply comprehensive coordination control method based on MMC.
Background
Currently, existing electrified railway traction power supply systems in various countries in the world mostly adopt 25kV power frequency single-phase alternating current power supply systems. The substation is powered down from the three-phase power grid through the traction transformer and then outputs by two power supply arms to supply power for the traction grid. Because the voltage phase, amplitude and frequency of the power supply arms are difficult to be completely consistent, an electric phase separation is required to be arranged among the power supply arms. However, with the large-scale use of such power supply system in the traction power supply field, a plurality of problems are also exposed:
(1) The quality of the electric energy is poor. Firstly, a traction load is used as a single-phase nonlinear impact load, the power is larger in the operation process, and larger negative-sequence current is injected into a power grid, so that the power system operates asymmetrically in three phases. In addition, the traction load is used as a harmonic source, and the harmonic wave caused in the running process has the characteristics of randomness, fluctuation and unbalance, so that the influence on the communication along the line is caused, and even the vehicle network resonance accident occurs.
(2) There is an electrical phase separation. The power frequency single-phase alternating current power supply system is limited by the frequency and phase problems existing in the power frequency single-phase alternating current power supply system, an electric phase separation link exists on the traction network at intervals, the power supply dead zone is needed to be powered off for running of a train, the speed of the train is limited to a certain extent, and meanwhile, the reliability of the electric phase separation device is low.
(3) The power supply capacity is limited. Because of the existence of the electric split phase, each traction substation is provided with a main traction transformer and a standby traction transformer, certain capacity waste is caused, and the power supply capacity of the traction substation is limited.
Disclosure of Invention
Aiming at the defects in the prior art, the MMC-based flexible direct current traction power supply comprehensive coordination control method solves the problems that the existing traction power supply system is poor in power quality and limited in power splitting and power supply capacity.
In order to achieve the aim of the invention, the invention adopts the following technical scheme:
the utility model provides a flexible direct current traction power supply comprehensive coordination control method based on MMC, which comprises the following steps:
s1, acquiring and establishing a mathematical model of the three-phase MMC under a d-q coordinate system according to circuit information of flexible direct current traction power supply based on the MMC;
s2, constructing a cooperative control model among the flexible direct current traction power supply stations based on MMC, and acquiring reference voltage values of voltage outer loop control of each flexible direct current traction power supply station based on MMC;
s3, establishing an outer ring voltage control model according to a reference voltage value of voltage outer ring control of the MMC-based flexible direct current traction power supply station;
s4, an inner loop current control model is established according to the outer loop voltage control model;
s5, establishing a circulation suppression modulation wave correction quantity model, a three-phase MMC modulation model and a capacitor voltage balance model according to a mathematical model of the three-phase MMC in a d-q coordinate system;
s6, performing MMC-based flexible direct current traction power supply comprehensive coordination control based on the model obtained in the steps S2 to S5.
The beneficial effects of the invention are as follows:
1. the invention can realize the long-distance and non-electric split-phase power supply of the traction network, reduce the number of traction substations along the line, ensure that the traction power supply system is stable in power supply area and high-quality power supply, and has the advantages of conveniently accessing new energy, an energy storage system and an urban rail traction power supply system, increasing the power supply distance and reducing the number of traction substations.
2. The invention can ensure the stable operation of a traction power supply system and a traction substation, solve the problems of internal circulation of a modularized multi-level converter (MMC) and unbalanced capacitance and voltage of submodules, and limit the deviation of the output voltage of the traction substation while realizing the balanced distribution of the output power of all-line traction substations as required under the condition of considering the failure exit of the traction substation and the communication failure between the traction substation.
3. The invention is suitable for a 35kV flexible direct current traction power supply system based on a modularized multi-level converter.
Drawings
FIG. 1 is a schematic flow chart of the method;
FIG. 2 is a schematic view of a scenario in an embodiment;
FIG. 3 is a schematic diagram of a modular multilevel converter;
FIG. 4 is a schematic diagram of the upper half of the integrated coordination control method;
fig. 5 is a schematic diagram of the lower half of the integrated coordination control method.
Detailed Description
The following description of the embodiments of the present invention is provided to facilitate understanding of the present invention by those skilled in the art, but it should be understood that the present invention is not limited to the scope of the embodiments, and all the inventions which make use of the inventive concept are protected by the spirit and scope of the present invention as defined and defined in the appended claims to those skilled in the art.
As shown in fig. 1, 4 and 5, the MMC-based flexible direct-current traction power supply comprehensive coordination control method comprises the following steps:
s1, acquiring and establishing a mathematical model of the three-phase MMC under a d-q coordinate system according to circuit information of flexible direct current traction power supply based on the MMC;
s2, constructing a cooperative control model among the flexible direct current traction power supply stations based on MMC, and acquiring reference voltage values of voltage outer loop control of each flexible direct current traction power supply station based on MMC;
s3, establishing an outer ring voltage control model according to a reference voltage value of voltage outer ring control of the MMC-based flexible direct current traction power supply station;
s4, an inner loop current control model is established according to the outer loop voltage control model;
s5, establishing a circulation suppression modulation wave correction quantity model, a three-phase MMC modulation model and a capacitor voltage balance model according to a mathematical model of the three-phase MMC in a d-q coordinate system;
s6, performing MMC-based flexible direct current traction power supply comprehensive coordination control based on the model obtained in the steps S2 to S5.
The expression of the mathematical model of the three-phase MMC in the d-q coordinate system in the step S1 is as follows:
wherein L is the equivalent inductance on the bridge arm in the phase; i.e vd The d-axis component of the alternating side phase current in a d-q coordinate system; u (u) sd Is the d-axis component of the alternating-current side phase voltage under a d-q coordinate system; u (u) diffd The d-axis component of the differential mode voltage of the upper bridge arm and the lower bridge arm under a d-q coordinate system; r is an equivalent resistance on the bridge arm in the phase; omega is the fundamental frequency of the network side alternating voltage; i.e vq Is a crossQ-axis component of the current side phase current in d-q coordinate system; u (u) sq Is the d-axis component of the alternating-current side phase voltage under a d-q coordinate system; u (u) diffq Is the q-axis component of the differential mode voltage of the upper bridge arm and the lower bridge arm in the d-q coordinate system.
The specific method in step S2 comprises the following sub-steps:
s2-1, connecting two adjacent MMC-based flexible direct current traction power supplies through a bidirectional sparse communication network; connecting flexible direct current traction power supply stations based on MMC from beginning to end through a bidirectional sparse communication network;
s2-2, connecting all the intelligent agents through a directed graph by taking each MMC-based flexible direct current traction power supply station as an intelligent agent to obtain a graph G multi-intelligent agent system, wherein the expression is as follows:
graph g= (V, E, D)
Where v= {1,2, …, n } represents a set of respective communication nodes;e represents a set of edges of nodes in graph G; d is a system state transition matrix of the graph G, and D represents connection weights among nodes in the graph G;
s2-3, setting synchronous clocks for all agents;
s2-4, collecting the voltage and power of each intelligent agent in the current clock period, and taking the voltage and power as initial state variables of the corresponding intelligent agents;
s2-5, judging whether the communication network needs to be reconstructed according to the current state variable of the ith intelligent agent, if so, returning the communication network topology to a chain type communication network, reconstructing and calculating the iteration number K required by the convergence of the consistency algorithm according to the system state transition matrix, and entering the step S2-6; otherwise, directly calculating iteration times K required by convergence of the consistency algorithm according to the system state transition matrix and entering a step S2-6;
s2-6, according to the formula:
performing discrete consistency iteration on the ith agent to obtain a state variable x of the ith agent after the (k+1) th iteration i [k+1]The method comprises the steps of carrying out a first treatment on the surface of the Wherein x is j [k]The state variable of the jth agent after the kth iteration; d, d ij The element of the ith row and the jth column in the system state transition matrix;
s2-7, judging whether the current iteration number reaches K, if so, outputting x obtained by the Kth discrete consistency iteration i [K]And enter step S2-8; otherwise, adding 1 to the current iteration number and returning to the step S2-6;
s2-8, according to the formula:
performing voltage compensation and power distribution on the ith intelligent agent through self-adaptive droop control to obtain a reference voltage value U of the voltage outer loop control of the ith intelligent agent i,dcref The method comprises the steps of carrying out a first treatment on the surface of the Wherein U is * dci An output voltage rating for the ith agent; p (P) i The output power of the ith agent; r is (r) d Is a sagging coefficient; k (k) p6 And k p7 The proportional parameter of the PI controller; k (k) i6 And k i7 Integrating parameters of the PI controller; s is S i Rated capacity for the ith agent; p (P) ave Calculating a system output power average value for all the intelligent agents through a discrete consistency algorithm; u (U) dcave Calculating a system output voltage average value for all the intelligent agents through a discrete consistency algorithm; s denotes a differentiation factor in the laplace transform,representing the integral in the laplace transform.
The reference value of the d axis of the output current under the d-q coordinate system can be obtained through the outer ring voltage control of the three-phase modularized multi-level converterTherefore, the outer loop voltage in step S3The expression of the control model is:
wherein k is p3 The proportional parameter of the PI controller; k (k) i3 Integrating parameters of the PI controller; u (u) dc Is a direct current side voltage;and the reference current value is used for external loop control of the voltage of the MMC-based flexible direct current traction power supply station of the d-axis in the d-q coordinate system.
The specific method of the step S4 is as follows:
s4-1, according to the formula:
obtaining the differential mode voltage u of the upper bridge arm and the lower bridge arm of the d axis under the d-q coordinate system diffd And the upper and lower bridge arm differential mode voltage u of the q axis under the d-q coordinate system diffq The method comprises the steps of carrying out a first treatment on the surface of the Wherein i is vq * The reference current value is used for the voltage outer loop control of the MMC-based flexible direct current traction power supply station of the q axis under the d-q coordinate system; k (k) p1 And k p2 Are integral parameters of the PI controller; k (k) i1 And k i2 The proportional parameters of the PI controller;
s4-2, u diffd And u diffq And transforming the three-phase reference modulation waves into a three-phase stationary a-b-c coordinate system to obtain reference modulation waves of the three-phase MMC, and obtaining the output of the inner loop current control model.
The method for establishing the loop-suppressed modulated wave correction quantity model in the step S5 comprises the following steps:
s5-1, according to the formula:
obtaining a control quantity u of a d-axis of each phase circulation suppression strategy under a d-q coordinate system jcird And the control quantity u of q axis of each phase circulation suppression strategy under d-q coordinate system jcirq The method comprises the steps of carrying out a first treatment on the surface of the Wherein m is harmonic frequency, m is more than or equal to 2, and m is even;is the power factor angle; l (L) 0 The bridge arm inductance value is MMC; i.e jcirq A component of the q-axis in the d-q coordinate system for the circulation of each phase; i.e * jcird A reference quantity of d-axis in d-q coordinate system for circulation of each phase; i.e jcird A component of the d-axis in the d-q coordinate system for the circulation of each phase; k (k) p4 And k p5 The proportional parameters of the PI controller; k (k) i4 And k i5 Are integral parameters of the PI controller; i.e * jcirq A reference quantity of q-axis in d-q coordinate system for circulation of each phase;
s5-2, u jcird And u jcirq And transforming the three-phase stationary a-b-c coordinate system to obtain the circulation suppression modulation wave correction quantity of the three-phase MMC, and obtaining the output of the circulation suppression modulation wave correction quantity model.
The expression of the three-phase MMC modulation model in step S5 is:
wherein n is down The number of half-bridge sub-modules is the number of half-bridge sub-modules with lower bridge arms in the input state; n is the number of half-bridge sub-modules of the MMC; f (f) round (. Cndot.) is the nearest rounding function; u (u) ref Is a modulated wave; u (U) c Capacitance voltage for the half-bridge submodule; n is n up The number of the half-bridge sub-modules is equal to the number of the half-bridge sub-modules with the upper bridge arm in the input state.
The method for establishing the capacitor voltage equalization model in the step S6 comprises the following steps: judging the charge and discharge states of the half-bridge submodule capacitors according to the current directions of the upper bridge arm and the lower bridge arm, respectively sequencing the voltages of the half-bridge submodules of the upper bridge arm and the lower bridge arm, and when the capacitors are in the charge state, sequencing the n with the lowest voltage in the upper bridge arm up N with lowest voltage in each half-bridge sub-module and lower bridge arm down Putting in a half-bridge submodule; when the capacitor is in a discharge state, the upper bridge arm is connected with the capacitorN with highest medium voltage up N is the highest voltage in each half-bridge sub-module and the lower bridge arm down Putting in a half-bridge submodule; and obtaining the output of the capacitance-voltage equalization model, namely triggering pulse sequences of all half-bridge submodules with the capacitance-voltage equalization effect.
The method for calculating the iteration number K in the step S2-5 comprises the following steps: according to the formula:
obtaining iteration times K; where ε is a given precision, i.e., a constant; lambda (lambda) 2 Is the second largest feature root of the system state transition matrix.
Element d of the ith row and jth column of the system state transition matrix in step S2-6 ij The calculation method of (1) is as follows: according to the formula:
acquiring element d of ith row and jth column in system state transition matrix ij Is a value of (2); wherein n is i Representing the number of agents connected with the ith agent; n is n j Representing the number of agents connected with the jth agent; n (N) i Representing a collection of agents connected to the ith agent.
In one embodiment of the invention, as shown in fig. 2, the 35kV flexible direct current traction power supply system based on the modularized multi-level converter comprises a three-phase power grid, a plurality of traction substations based on the modularized multi-level converter, a 35kV direct current traction network and steel rails, wherein the input ends of the traction substations based on the modularized multi-level converter are connected with the three-phase power grid, the output ends of the traction substations based on the modularized multi-level converter are connected with the 35kV direct current traction network and the steel rails, and the 35kV direct current traction network is used for supplying power to a train.
As shown in fig. 3, the specific structure of the traction substation based on the modularized multi-level converter is as follows:
the primary side high-voltage side of the step-down transformer is connected with a three-phase power grid, and the secondary side low-voltage side three-phase is respectively connected with an a-phase breaker K1, a b-phase breaker K2 and a c-phase breaker K3. The a-phase breaker K1 is connected with one end of an a-phase input rectifying side inductor La, and the other end of the rectifying side inductor La is connected with the middle points of an a-phase upper bridge arm inductor L0 and a-phase lower bridge arm inductor L0; the b-phase breaker K2 is connected with one end of a b-phase input rectifying side inductor Lb, and the other end of the rectifying side inductor Lb is connected with the middle points of an upper bridge arm and a lower bridge arm of the b-phase, namely, the lower end of a b-phase upper bridge arm inductor L0 and the upper end of a b-phase lower bridge arm inductor L0; the c-phase breaker K1 is connected with one end of a c-phase input rectifying side inductor Lc, and the other end of the rectifying side inductor Lc is connected with the middle points of the upper and lower bridge arms of the c-phase, namely, the lower end of the upper bridge arm inductor L0 of the c-phase and the upper end of the lower bridge arm inductor L0 of the c-phase.
The submodule of the modular multilevel converter consists of two insulated gate bipolar transistors T1, T2, two diodes D1, D2 and a capacitor C. The collector of the insulated gate bipolar transistor T1 is connected with one end of the capacitor C, the emitter of the insulated gate bipolar transistor T1 is connected with the collector of the insulated gate bipolar transistor T2, the emitter electrode of the insulated gate bipolar transistor T1 and the collector of the insulated gate bipolar transistor T2 are jointly used as an external port a of the half-bridge submodule, the emitter of the insulated gate bipolar transistor T2 is connected with the other end of the capacitor C, and the emitter of the insulated gate bipolar transistor T2 and the other end of the capacitor C are jointly used as an external port b of the half-bridge submodule.
The external port a of the first half-bridge sub-module SM1 of the a-phase upper bridge arm is connected with the external port a of the first half-bridge sub-module SM1 of the b-phase upper bridge arm and the external port a of the first half-bridge sub-module SM1 of the c-phase upper bridge arm, and the external ports are used as the first output end of a traction substation based on the modularized multi-level converter, and the first output end of the three-phase modularized multi-level converter is connected with a 35kV direct current traction network.
The external port b of the first half-bridge sub-module SM1 of the a-phase upper bridge arm is connected with the external port a of the second half-bridge sub-module SM2 of the a-phase upper bridge arm, the external ports of the other half-bridge sub-modules are sequentially connected, the external port b of the (n-1) -th half-bridge sub-module SM (n-1) of the a-phase upper bridge arm is connected with the external port a of the half-bridge sub-module SMn of the a-phase upper bridge arm, and the external port b of the n-th half-bridge sub-module SMn of the a-phase upper bridge arm is connected with the upper end of the a-phase upper bridge arm inductance L0. The external port b of the first half-bridge sub-module SM1 of the upper bridge arm of the b-phase is connected with the external port a of the second half-bridge sub-module SM2 of the upper bridge arm of the b-phase, the external ports of the other half-bridge sub-modules are sequentially connected, the external port b of the (n-1) th half-bridge sub-module SM (n-1) of the upper bridge arm of the b-phase is connected with the external port a of the half-bridge sub-module SMn of the upper bridge arm of the b-phase, and the external port b of the n-th half-bridge sub-module SMn of the upper bridge arm of the b-phase is connected with the upper end of the inductance L0 of the upper bridge arm of the b-phase. The external port b of the first half-bridge sub-module SM1 of the upper bridge arm of the c-phase is connected with the external port a of the second half-bridge sub-module SM2 of the upper bridge arm of the c-phase, the external ports of the other half-bridge sub-modules are sequentially connected, the external port b of the (n-1) th half-bridge sub-module SM (n-1) of the upper bridge arm of the c-phase is connected with the external port a of the half-bridge sub-module SMn of the upper bridge arm of the c-phase, and the external port b of the n-th half-bridge sub-module SMn of the upper bridge arm of the c-phase is connected with the upper end of the bridge arm inductance L0 of the upper bridge arm of the c-phase.
The lower end of the inductance L0 of the lower bridge arm of the phase a is connected with the external port a of the first half-bridge submodule SM1 of the lower bridge arm of the phase a, the external port b of the first half-bridge submodule SM2 of the lower bridge arm of the phase a is connected with the external port a of the second half-bridge submodule SM2 of the lower bridge arm of the phase a, the external ports of the other half-bridge submodules are sequentially connected, and the external port b of the (n-1) th half-bridge submodule SM (n-1) of the lower bridge arm of the phase a is connected with the external port a of the n-th half-bridge submodule SMn of the lower bridge arm of the phase a. The lower end of the inductance L0 of the lower bridge arm of the phase b is connected with the external port a of the first half-bridge submodule SM1 of the lower bridge arm of the phase b, the external port b of the first half-bridge submodule SM2 of the lower bridge arm of the phase b is connected with the external port a of the second half-bridge submodule SM2 of the lower bridge arm of the phase b, the external ports of the other half-bridge submodules are sequentially connected, and the external port b of the (n-1) th half-bridge submodule SM (n-1) of the lower bridge arm of the phase b is connected with the external port a of the n-th half-bridge submodule SMn of the lower bridge arm of the phase b. The lower end of the inductance L0 of the lower bridge arm of the c-phase is connected with the external port a of the first half-bridge submodule SM1 of the lower bridge arm of the c-phase, the external port b of the first half-bridge submodule SM2 of the lower bridge arm of the c-phase is connected with the external port a of the second half-bridge submodule SM2 of the lower bridge arm of the c-phase, the external ports of the other half-bridge submodules are sequentially connected, and the external port b of the (n-1) th half-bridge submodule SM (n-1) of the lower bridge arm of the c-phase is connected with the external port a of the n-th half-bridge submodule SMn of the lower bridge arm of the c-phase.
The external port b of the nth half-bridge sub-module SMn of the a-phase lower bridge arm is connected with the external port b of the nth half-bridge sub-module SMn of the b-phase lower bridge arm and the external port b of the nth half-bridge sub-module SMn of the c-phase lower bridge arm, and the external ports are jointly used as the second output end of the traction substation based on the modularized multi-level converter, and the second output end of the traction substation based on the modularized multi-level converter is connected with the steel rail.
In summary, the invention can be used in a 35kV flexible direct current traction power supply system based on a modularized multi-level converter, and solves the problems of the existing power frequency single-phase alternating current traction power supply system. A flexible direct current traction substation based on a modularized multi-level converter is formed by adopting a power electronic device, so that the problem of poor electric energy quality is solved. The 35kV direct current traction network can solve the problem of electric phase separation, and has the advantages of being convenient to access new energy, an energy storage system and an urban rail traction power supply system, increasing the power supply distance and reducing the number of traction substations.
The invention not only can realize the basic control of the flexible traction substation based on the modularized multi-level converter, but also can solve the problems of circulation and unbalanced capacitance voltage of the modularized multi-level converter, and can also ensure the stable operation of a 35kV flexible direct current traction power supply system formed by a plurality of flexible traction power converters under the multi-working condition, ensure the stability of the voltage of a direct current contact network, regulate the output force of each traction power substation, realize the balanced distribution of the output power of each traction power substation of the whole line as required, and limit the deviation of the output voltage of the traction power substation.

Claims (5)

1. The MMC-based flexible direct-current traction power supply comprehensive coordination control method is characterized by comprising the following steps of:
s1, acquiring and establishing a mathematical model of the three-phase MMC under a d-q coordinate system according to circuit information of flexible direct current traction power supply based on the MMC;
s2, constructing a cooperative control model among the flexible direct current traction power supply stations based on MMC, and acquiring reference voltage values of voltage outer loop control of each flexible direct current traction power supply station based on MMC;
s3, establishing an outer ring voltage control model according to a reference voltage value of voltage outer ring control of the MMC-based flexible direct current traction power supply station;
s4, an inner loop current control model is established according to the outer loop voltage control model;
s5, establishing a circulation suppression modulation wave correction quantity model, a three-phase MMC modulation model and a capacitor voltage balance model according to a mathematical model of the three-phase MMC in a d-q coordinate system;
s6, performing MMC-based flexible direct current traction power supply comprehensive coordination control based on the model obtained in the steps S2 to S5;
the expression of the mathematical model of the three-phase MMC in the d-q coordinate system in the step S1 is as follows:
wherein the method comprises the steps ofLIs equivalent inductance on the bridge arm in the phase;the d-axis component of the alternating side phase current in a d-q coordinate system; />Is the d-axis component of the alternating-current side phase voltage under a d-q coordinate system; />The d-axis component of the differential mode voltage of the upper bridge arm and the lower bridge arm under a d-q coordinate system; r is an equivalent resistance on the bridge arm in the phase; />The fundamental frequency of the network side alternating voltage; />Q-axis component of the alternating side phase current in d-q coordinate system; />Is the d-axis component of the alternating-current side phase voltage under a d-q coordinate system; />The q-axis component of the differential mode voltage of the upper bridge arm and the lower bridge arm under a d-q coordinate system;
the specific method in step S2 comprises the following sub-steps:
s2-1, connecting two adjacent MMC-based flexible direct current traction power supplies through a bidirectional sparse communication network; connecting flexible direct current traction power supply stations based on MMC from beginning to end through a bidirectional sparse communication network;
s2-2, connecting all the intelligent agents through a directed graph by taking each MMC-based flexible direct current traction power supply station as an intelligent agent to obtain a graph G multi-intelligent agent system, wherein the expression is as follows:
drawing of the figureG=(V,E,D)
Wherein the method comprises the steps ofV= {1,2, …, n } represents a set of respective communication nodes; ，Erepresenting a set of edges of the nodes in FIG. G;Dfor the system state transition matrix of graph G,Drepresenting the connection weights from node to node in graph G;
s2-3, setting synchronous clocks for all agents;
s2-4, collecting the voltage and power of each intelligent agent in the current clock period, and taking the voltage and power as initial state variables of the corresponding intelligent agents;
s2-5 according to the firstiJudging whether the communication network needs to be reconstructed or not by the current state variables of the intelligent agents, if so, returning the communication network topology to a chain type communication network, reconstructing and calculating iteration times K required by the convergence of a consistency algorithm according to a system state transition matrix, and entering a step S2-6; otherwise, directly switching according to the system stateMoving the matrix to calculate the iteration number K required by the convergence of the consistency algorithm and entering the step S2-6;
s2-6, according to the formula:
for the firstiPerforming discrete consistency iteration on the intelligent agents to obtain the firstiState variable of each agent after the k+1th iterationThe method comprises the steps of carrying out a first treatment on the surface of the Wherein->Is the firstjState variables of the intelligent agent after the kth iteration; />Is the first in the system state transition matrixiLine 1jElements of a column;
s2-7, judging whether the current iteration number reaches K, if so, outputting a K-th discrete consistency iterationAnd enter step S2-8; otherwise, adding 1 to the current iteration number and returning to the step S2-6;
s2-8, according to the formula:
for the firstiThe intelligent agent performs voltage compensation and power distribution through self-adaptive droop control to obtain the first stepiReference voltage value controlled by external ring of intelligent body voltageThe method comprises the steps of carrying out a first treatment on the surface of the Wherein->Is the firstiThe output voltage ratings of the individual agents; />Is the firstiThe output power of the individual agents; />Is a sagging coefficient; />And->The proportional parameter of the PI controller; />And->Integrating parameters of the PI controller; />Is the firstiRated capacity of the individual agents; />Calculating a system output power average value for all the intelligent agents through a discrete consistency algorithm; />Calculating a system output voltage average value for all the intelligent agents through a discrete consistency algorithm;srepresents the differentiation factor in the Laplace transform, < ->Representing an integral in the laplace transform;
the method for establishing the loop-suppressed modulated wave correction quantity model in the step S5 comprises the following steps:
s5-1, according to the formula:
obtaining the control quantity of d-axis of each phase circulation suppression strategy under d-q coordinate systemAnd control amount of q-axis in d-q coordinate system of each phase circulation suppression strategy +.>The method comprises the steps of carrying out a first treatment on the surface of the Wherein m is the harmonic frequency; />Is the power factor angle; />The bridge arm inductance value is MMC;a component of the q-axis in the d-q coordinate system for the circulation of each phase; />A reference quantity of d-axis in d-q coordinate system for circulation of each phase; />A component of the d-axis in the d-q coordinate system for the circulation of each phase; />And->The proportional parameters of the PI controller;and->Are integral parameters of the PI controller; />A reference quantity of q-axis in d-q coordinate system for circulation of each phase;
s5-2, willAnd->Transforming to a three-phase stationary a-b-c coordinate system to obtain a circulation suppression modulation wave correction quantity of the three-phase MMC, and obtaining output of a circulation suppression modulation wave correction quantity model;
the expression of the three-phase MMC modulation model in step S5 is:
wherein the method comprises the steps ofThe number of half-bridge sub-modules is the number of half-bridge sub-modules with lower bridge arms in the input state; n is the number of half-bridge sub-modules of the MMC; />Is a nearest rounding function; />Is a modulated wave; />Capacitance voltage for the half-bridge submodule; />The number of the half-bridge sub-modules is equal to the number of the half-bridge sub-modules with the upper bridge arm in the input state;
the method for establishing the capacitor voltage balance model in the step S5 is as follows:
judging the charge and discharge states of the half-bridge submodule capacitors according to the current directions of the upper bridge arm and the lower bridge arm, respectively sequencing the voltages of the half-bridge submodules of the upper bridge arm and the lower bridge arm, and when the capacitors are in the charge state, sequencing the n with the lowest voltage in the upper bridge arm up N with lowest voltage in each half-bridge sub-module and lower bridge arm down Putting in a half-bridge submodule; when the capacitor is in a discharge state, the highest voltage n in the upper bridge arm up N is the highest voltage in each half-bridge sub-module and the lower bridge arm down Putting in a half-bridge submodule; and obtaining the output of the capacitance-voltage equalization model, namely triggering pulse sequences of all half-bridge submodules with the capacitance-voltage equalization effect.
2. The MMC-based flexible direct-current traction power supply comprehensive coordination control method of claim 1, characterized in that the expression of the outer-loop voltage control model in step S3 is:
wherein the method comprises the steps ofThe proportional parameter of the PI controller; />Integrating parameters of the PI controller; />Is a direct current side voltage; />And the reference current value is used for external loop control of the voltage of the MMC-based flexible direct current traction power supply station of the d-axis in the d-q coordinate system.
3. The MMC-based flexible direct-current traction power supply comprehensive coordination control method of claim 2, characterized in that the specific method of step S4 is as follows:
s4-1, according to the formula:
obtaining the differential mode voltage u of the upper bridge arm and the lower bridge arm of the d axis under the d-q coordinate system diffd And the upper and lower bridge arm differential mode voltage u of the q axis under the d-q coordinate system diffq The method comprises the steps of carrying out a first treatment on the surface of the Wherein the method comprises the steps ofThe reference current value is used for the voltage outer loop control of the MMC-based flexible direct current traction power supply station of the q axis under the d-q coordinate system; />And->Are integral parameters of the PI controller; />And->The proportional parameters of the PI controller;
s4-2, u diffd And u diffq And transforming the three-phase reference modulation waves into a three-phase stationary a-b-c coordinate system to obtain reference modulation waves of the three-phase MMC, and obtaining the output of the inner loop current control model.
4. The MMC-based flexible direct-current traction power supply comprehensive coordination control method according to claim 1, wherein the iteration number K in the step S2-5 is calculated by the following steps:
according to the formula:
obtaining iteration times K; wherein the method comprises the steps ofFor a given precision, i.e. constant; />Is the second largest feature root of the system state transition matrix.
5. The MMC-based flexible direct-current traction power supply comprehensive coordination control method of claim 1, characterized by the following in step S2-6iLine 1jElements of columnsThe calculation method of (1) is as follows:
according to the formula:
acquiring the first of the system state transition matricesiLine 1jElements of columnsIs a value of (2); wherein->Representation and the firstiThe number of the intelligent agents connected with each other; />Representation and the firstjThe number of the intelligent agents connected with each other; />Representation and the firstiAnd the intelligent agents are connected with each other.
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