Flexible through-type traction power supply system and control method thereof

Abstract

The embodiment of the application discloses a flexible through traction power supply system and a control method thereof, the system comprising: n traction substations and one power flow control station, the power flow control station comprising: a Scott transformer, two groups of voltage source converters VSC, two groups of DC-DC bidirectional converters DDC, a photovoltaic array, a super capacitor SC, a three-phase grid-connected inverter TGI, a three-phase step-up transformer TT and a measurement and control unit; the measurement and control unit is used for collecting electrical data and then controlling the two groups of voltage source converters VSC, the three-phase grid-connected inverter TGI and the two groups of DC-DC bidirectional converters DDC. The application eliminates all electric phase separation in the traction network, reduces the risk of train passing through the phase separation, guarantees the safety of train operation, solves the power quality problems such as negative sequence, reactive power and harmonic, and creates favorable conditions for further high-speed and heavy-load operation of the train.

Description

Technical Field

[0001] The present invention relates to the technical field of electrified railway traction power supply systems, and in particular to a flexible through-type traction power supply system and a control method thereof. Background Art

[0002] At present, AC electrified railways have become an indispensable part of people's livelihood. However, there are still a series of problems to be solved, which hinder the further high-speed and heavy-load development of electrified railways. At present, AC electrified railways are of industrial frequency single-phase AC standard, which will inject negative sequence current into the external power grid at the point of common coupling (PCC). AC-DC-AC trains have high power factor and low harmonic content, but as the power of trains is further increased, the negative sequence problem becomes more and more obvious. In addition, some lines are still AC-DC locomotive lines, which have problems such as low power factor and high harmonic content.

[0003] This section is intended to provide a background or context to the embodiments of the invention that are recited in the claims. No statement herein is admitted to be prior art by virtue of its inclusion in this section. Summary of the Invention

[0004] In order to solve at least one technical problem in the above-mentioned background technology, the present invention proposes a flexible through-type traction power supply system and a control method thereof.

[0005] To achieve the above object, according to one aspect of the present invention, a flexible through-type traction power supply system is provided, comprising: n traction substations and a power flow control station, where n is an integer greater than 1, and the n traction substations and the primary side of the power flow control station have the same common connection point;

[0006] The power flow control station includes: a Scott transformer, two groups of voltage source converters VSC, two groups of DC-DC bidirectional converters DDC, a photovoltaic array, a supercapacitor SC, a three-phase grid-connected inverter TGI, a three-phase step-up transformer TT, and a measurement and control unit; the Scott transformer includes: a first transformer and a second transformer; the two groups of voltage source converters include: a first voltage source converter VSC1 and a second voltage source converter VSC2; the two groups of DC-DC bidirectional converters DDC include: a first DC-DC bidirectional converter DDC1 and a second DC-DC bidirectional converter DDC2;

[0007] The primary side of the first transformer is connected to two-phase AC busbars of the traction substation, and the secondary side of the first transformer is connected to the AC side of the first voltage source converter VSC1; one end of the primary side of the second transformer is connected to one-phase AC busbar of the traction substation, and the other end of the primary side of the second transformer is connected to the center tap position of the first transformer, and the secondary side of the second transformer is connected to the AC side of the second voltage source converter VSC2; the DC side of the first voltage source converter VSC1 and the DC side of the second voltage source converter VSC2 are connected to the DC bus;

[0008] One side of the first DC-DC bidirectional converter DDC1 is connected to the photovoltaic array, and the other side of the first DC-DC bidirectional converter DDC1 is connected to the DC bus; one side of the second DC-DC bidirectional converter DDC2 is connected to the super capacitor SC, and the other side of the second DC-DC bidirectional converter DDC2 is connected to the DC bus;

[0009] The AC side of the three-phase grid-connected inverter TGI is connected to the primary side of the three-phase step-up transformer TT, and the DC side of the three-phase grid-connected inverter TGI is connected to the DC bus; the secondary side of the three-phase step-up transformer TT is connected to the railway power distribution network;

[0010] The measurement and control unit is configured to collect electrical data and control the two groups of voltage source converters VSC, the three-phase grid-connected inverter TGI and the two groups of DC-DC bidirectional converters DDC.

[0011] In order to achieve the above-mentioned purpose, according to another aspect of the present application, a control method of a flexible through-type traction power supply system is also provided, the control method is applied to the flexible through-type traction power supply system, and the control method comprises the following steps:

[0012] determining the power threshold P of the three-phase grid-connected inverter TGI T_MAX , the power threshold P of the first DC-DC bidirectional converter DDC1 D1_MAX , the power threshold P of the second DC-DC bidirectional converter DDC2 D2_MAX , the upper threshold SOC of the state of charge SOC of the super capacitor SC MAX and the lower threshold SOC of the state of charge SOC of the super capacitor SC MIN , the maximum charge and discharge power P of the super capacitor SC SC_MAX and the DC bus voltage reference value U DC_REF ;

[0013] calculating the total active power P of the n traction substations ACL , the total reactive power Q of the n traction substations ACL , the harmonic current i h , the active power P of the railway power distribution network load TL , the active power P of the photovoltaic array PV and the state of charge SOC of the super capacitor SC;

[0014] Obtaining the active power reference value P of the three-phase grid-connected inverter TGI connected to the DC bus side port T_REF , the active power reference value P of the first DC-DC bidirectional converter DDC1 connected to the DC bus side port D1_REF , the active power reference value P of the second DC-DC bidirectional converter DDC2 connected to the DC bus side port D2_REF , the reference current i of the first voltage source converter VSC1 on the AC side 1,REF , and the reference current i of the second voltage source converter VSC2 on the AC side 2,REF ;

[0015] According to P T_REF , P D1_REF , P D2_REF , i 1,REF , and i 2,REF , and through the measurement and control unit, the two groups of voltage source converters VSC, the three-phase grid-connected inverter TGI and the two groups of DC-DC bidirectional converters DDC are controlled.

[0016] The beneficial effects of the present application are:

[0017] The flexible through-type traction power supply system of the present application comprises: n traction substations and 1 power flow control station, the power flow control station comprises: a Scott transformer, two groups of voltage source converters VSC, two groups of DC-DC bidirectional converters DDC, a photovoltaic array, a super capacitor SC, a three-phase grid-connected inverter TGI, a three-phase step-up transformer TT and a measurement and control unit, through the special setting of the power flow control station, the power quality problems such as negative sequence, reactive power and harmonics of the flexible through-type traction power supply system are improved, and photovoltaic access and recycling of regenerative braking energy are realized. BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor. In the drawings:

[0019] Figure 1 is an electrical structure schematic diagram of the flexible through-type traction power supply system of the embodiment of the present application;

[0020] Figure 2 is a general flow schematic diagram of the control method of the flexible through-type traction power supply system of the embodiment of the present application;

[0021] Figure 3 is a flow schematic diagram of the control method of the embodiment of the present application. DETAILED DESCRIPTION

[0022] In the following, the technical solutions in the embodiments of the present application will be described clearly and completely with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all the other embodiments obtained by a person of ordinary skill in the art without creative effort should belong to the protection scope of the present application.

[0023] Those skilled in the art should understand that the embodiments of the present application can be provided as a method, a system, or a computer program product. Therefore, the present application can adopt a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present application can adopt a computer program product implemented on one or more computer usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer usable program codes.

[0024] It should be noted that the terms "comprising" and "having" and any variations thereof in the specification and claims of the present application and the above-described drawings are intended to cover non-exclusive inclusion, for example, a process, a method, a system, a product, or an apparatus containing a series of steps or units does not have to be limited to the clearly listed steps or units, but can include other steps or units that are not clearly listed or inherent to the process, the method, the product, or the apparatus.

[0025] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The present application will be described in detail below with reference to the drawings and in combination with the embodiments.

[0026] At present, AC electrified railway has become an important part of people's livelihood. However, there are still a series of problems to be solved, which hinder the further development of high-speed and heavy-load electrified railway:

[0027] 1) At present, the AC electrified railway is a single-phase AC system of power frequency. In order to reduce the negative sequence influence on the external power grid, the scheme of alternating phase sequence and separate-phase partition power supply is adopted, and an electric phase break is set at the traction network separate-phase partition. The train needs to be powered off and coasting when passing through the electric phase break, which may cause accidents such as slope stop and slope slow-down, and affect the operation safety of electrified railway. In addition, the electric phase break will block the energy interaction between the traction loads of different power supply arms, and reduce the utilization rate of regenerative braking energy of electrified railway;

[0028] 2) Currently, AC electrified railways use a single-phase AC system with industrial frequency, which injects negative sequence current into the external grid at the point of common coupling (PCC). AC / DC / AC trains have a high power factor and low harmonic content, but as train power increases, negative sequence issues become increasingly apparent. Furthermore, some lines currently still use AC / DC locomotives, which suffer from low power factor and high harmonic content.

[0029] 3) The electrified railway traction power supply system relies primarily on coal-fired power, with a small proportion of new clean energy sources such as photovoltaics, hindering support for the dual-carbon development strategy. Power is drawn from a single power source, resulting in poor flexibility and resiliency in the traction power supply system.

[0030] How to solve the problems of electrified railway operation safety caused by phase separation, power quality problems such as negative sequence reactive harmonics caused by single-phase traction load, and energy structure problems with coal-fired power as the main consumption and a small proportion of clean energy has become a current research hotspot and brought challenges to relevant scientific researchers.

[0031] The purpose of the present invention is to provide a flexible through-type traction power supply system and its control method, aiming to eliminate the phase separation of the traction grid, eliminate power quality problems such as negative sequence, reactive power, harmonics, etc., and realize the absorption of photovoltaic power in the traction power supply system and the efficient utilization of regenerative braking energy.

[0032] In order to solve the above technical problems, the present invention, in one aspect of the present invention, Figure 1 As shown, a flexible through-type traction power supply system is provided, which includes: n traction substations and 1 flow control station, where n is an integer greater than 1, and the n traction substations and the primary side of the flow control station have the same common connection point.

[0033] In the present invention, the main function of the traction substation is to provide electric energy to the traction load. g , g = 1, 2, …, n. A single-phase traction transformer is installed in the traction substation. The primary side of the traction transformer is connected to the two phases of the AC busbar of the power substation, and the secondary side is connected to the traction grid, providing power to the traction grid. No phase separation is required at the traction grid substation or at the substation exit, achieving full power supply.

[0034] In this invention, the main function of the flow control station is to improve the power quality issues of the flexible through-type traction power supply system, such as negative sequence, reactive power, and harmonics, and to achieve photovoltaic access and the recovery and utilization of regenerative braking energy. The primary side of the flow control station draws power from the main substation.

[0035] In the application, the tidal current control station comprises a Scott transformer, two groups of voltage source converters (VSC), two groups of DC-DC converters (DDC), a photovoltaic array, a super capacitor (SC), a three-phase grid-connected inverter (TGI), a three-phase transformer (TT), and a measurement and control unit.

[0036] The Scott transformer is composed of two transformers perpendicular to each other in structure, that is, the Scott transformer comprises a first transformer (also referred to as transformer 1 in the application) and a second transformer (also referred to as transformer 2 in the application). The two groups of voltage source converters comprise a first voltage source converter VSC1 and a second voltage source converter VSC2; the two groups of DC-DC converters DDC comprise a first DC-DC converter DDC1 and a second DC-DC converter DDC2.

[0037] The primary side of the first transformer is connected to a two-phase AC bus of which power is taken by the traction substation, and the secondary side is connected to the AC side of the first voltage source converter VSC1; one end of the primary side of the second transformer is connected to a single-phase AC bus of which power is not taken by the traction substation, and the other end is connected to the center tap position of the first transformer, and the secondary side of the second transformer is connected to the AC side of the second voltage source converter VSC2. The DC sides of the first voltage source converter VSC1 and the second voltage source converter VSC2 are connected to a DC bus.

[0038] One side of the first DC-DC converter DDC1 is connected to the photovoltaic array, and the other side is connected to the DC bus; one side of the second DC-DC converter DDC2 is connected to the super capacitor SC, and the other side is connected to the DC bus.

[0039] The AC side of the three-phase grid-connected inverter TGI is connected to the primary side of the three-phase transformer TT, and the DC side of the three-phase grid-connected inverter TGI is connected to the DC bus. The primary side of the three-phase transformer TT is connected to the AC side of the three-phase grid-connected inverter TGI, and the secondary side of the three-phase transformer TT is connected to the railway power distribution network.

[0040] In an optional embodiment of the application, the railway power distribution network is specifically a railway 10kV power distribution network.

[0041] The measurement and control unit is used to collect electrical data and control the two groups of voltage source converters VSC, the three-phase grid-connected inverter TGI, and the two groups of DC-DC converters DDC.

[0042] In the present invention, the traction substation includes: a traction transformer; the primary side of the traction transformer is connected to the AC bus, the secondary side of the traction transformer is connected to the traction network, and the traction network completely eliminates electrical phase separation; the AC bus is connected to the power supply network.

[0043] In one embodiment of the present invention, the traction substation is used to provide electric energy to the traction load; and the power flow control station is used to achieve photovoltaic access and recovery and utilization of regenerative braking energy.

[0044] In one embodiment of the present invention, the measurement and control unit includes a voltage transformer, a current transformer, an optical fiber network, and a terminal controller. The unit transmits the detected voltage and current of the traction substation, load data of the railway's 10kV distribution network, the state of charge (SOC) of the SC, and the power of the photovoltaic array to the terminal controller. The terminal controller processes the transmitted data and, based on a predetermined energy management strategy, calculates power and current reference values. It then controls the power electronic devices to track these reference power and current values ​​in real time, thereby completing control of the flexible through-type traction power supply system.

[0045] In another aspect of the present invention, Figure 2 As shown, a control method for a flexible through-type traction power supply system is also provided, and the control method is applied to the flexible through-type traction power supply system described in the above embodiment. Figure 2 As shown, in one embodiment of the present invention, the control method of the flexible through-type traction power supply system of the present invention specifically includes the following steps:

[0046] Step 1: Determine the power threshold of the power electronic device: Assume that the power thresholds of TGI, DDC1, and DDC2 are P T_MAX 、P D1_MAX 、P D2_MAX , the upper and lower thresholds of SOC are respectively, MAX , SOC MIN , the maximum charge and discharge power of SC is P SC_MAX , DC bus voltage reference value U DC_REF .

[0047] Step 2: Take phase A voltage as the reference to obtain SS h The voltage and current on the primary side, the load power of the railway 10kV distribution network, the state of charge (SOC) of the SC, and the power of the photovoltaic array. Calculate the total active power P of n traction substations. ACL , the reactive power is Q ACL , harmonic current i h , stipulate P ACL , Q ACL 、i h The positive direction is: the flow from the traction substation to the traction load is positive, and the reverse direction is negative; the load active power P of the railway 10kV distribution network is obtainedTL , it is stipulated that the energy obtained from the 10kV distribution network is positive; the active power of the photovoltaic array is P PV , it is stipulated that the power transmitted from the photovoltaic array into the DC bus is positive; the state of charge SOC of the supercapacitor is obtained. Figure 1 The direction marked by the arrow of the corresponding quantity is the positive direction.

[0048] Step 3: Obtain the power and current reference values ​​of the power electronic device according to the established energy management strategy. Obtain the active power reference value P of the ports connected to the DC bus side of TGI, DDC1, and DDC2. T_REF 、P D1_REF 、P D2_REF , specifies the positive direction: P D1_REF The positive direction is when it flows into the DC bus, and the negative direction is when it flows into the DC bus. T_REF 、P D2_REF The positive direction is when the DC bus flows out, and the negative direction is when the DC bus flows out. 1,REF 、i 2,REF , the positive direction is defined as the flow from the PCC point to the AC side of VSC1 and VSC2. Figure 1 The direction marked by the arrow of the corresponding quantity is the positive direction.

[0049] 3.1 Calculating P D1_REF =min{P D1_MAX ,P PV}; Set the intermediate value P L =P ACL –P D1_REF ;

[0050] 3.2 According to P L , SOC determines the system working mode, and calculates P under each working mode T_REF 、P D2_REF :

[0051] 1) Idle mode: P L ≥0 and SOC≤SOC MIN , P T_REF =0,P D2_REF =0;

[0052] 2) Energy release mode: P L ≥0 and SOC>SOC MIN , P T_REF =max{0,-P D2_REF -P L},

[0053] P D2_REF =-min{P L +P TL ,P SC_MAX ,PL +P T_MAX};

[0054] 3) Transfer mode: P L <0 and SOC≥SOC MAX , P T_REF =0,P D2_REF =

[0055] min{P T_MAX ,P TL ,-P L};

[0056] 4) Energy storage mode: P L <0 and SOC < SOC MAX , P T_REF =min{P T_MAX ,P TL ,

[0057] -P L},

[0058] P D2_REF =min{-P L –P T_REF ,P SC_MAX};

[0059] 3.3 Finding i 1_REF ,i 2_REF :

[0060]

[0061] Where: is the permissible value of negative sequence power, Q′ is the permissible value of reactive power, is the actual value of negative sequence power, Wherein, j is a complex unit. are the vectors of the AC side voltages u1 and u2 of the first and second groups of voltage source converters, respectively; ψ1 and ψ2 are the connection angles of u1 and u2 (the phase of the lagging A phase voltage); [] * It means taking the conjugate of the variables in [], and k1 is the transformation ratio of transformer 1.

[0062] Step 4: Input the calculated power / current reference value into the power electronic device control terminal, coordinate the power / current of the power electronic device port to track the reference power in real time, and complete the control of the flexible traction power supply system at that moment. The specific power electronic device control method is as follows:

[0063] 1) VSC: Taking VSC1 control method as an example, VSC2 control method is the same. It adopts voltage and current dual closed-loop control strategy, stabilizes DC side voltage through voltage outer loop, and tracks VSC1 AC side current reference value in real time through current inner loop control, outputs compensation current quickly and accurately. Detects the actual value of DC bus voltage U DC , will U DC_REF with U DC The difference is adjusted by the proportional-integral controller to obtain the output I DC_REF . Obtain u1 synchronization signal sin(ωt-ψ1) through the phase-locked loop, and I DC_REF Multiply by sin(ωt-ψ1) and add 1_REF The sum is added, and the difference between the sum result and the actual value i1 of the VSC1 AC measured current is made. After adjustment by the proportional-integral controller, it is input into the PWM module for modulation to generate a control signal to drive the VSC1, thereby completing the control of the VSC1.

[0064] 2) DDC1: Adopt voltage closed-loop control strategy, collect PV array voltage and current, obtain PV array reference voltage, and control DDC1.

[0065] 3) DDC2: adopts current closed-loop control strategy to collect supercapacitor voltage and current, and uses P D2_REF Divide the supercapacitor voltage to obtain the supercapacitor reference current, subtract it from the actual supercapacitor current, and input the result into the PWM module for modulation to generate the control signal that drives DDC2, thereby completing the control of DDC2.

[0066] 4) TGI: The closed-loop control of the inverter output side current is adopted with capacitor current feedforward, and the phase is locked based on the 10kV distribution network phase A voltage. The dq0 coordinate system components of the 10kV distribution system voltage, 10kV distribution system current, filter capacitor current, inverter input side current and P are respectively converted into T_REF The input is input to the controller, and after being adjusted by the controller, it is subjected to Park inverse transformation, and finally input into the PWM module for modulation to generate the control signal for driving the TGI, thereby completing the control of the TGI.

[0067] In an optional embodiment of the present invention, other control methods in the prior art may be used to control VSC, DDC and TGI.

[0068] Compared with the existing technology, the beneficial effects of the present invention are: 1) it completely eliminates the phase separation of the traction network, ensures the safety of train operation, and improves the utilization rate of regenerative braking energy; 2) it solves the power quality problems such as negative sequence, reactive power, and harmonics, creating favorable conditions for further high-speed and heavy-load operation of trains; 3) it realizes the access of photovoltaic power to the traction power supply system, increases the proportion of clean energy, and increases the power supply flexibility and flexibility of the system.

[0069] As Figure 3 shown, in one embodiment of the present application, the control method of the flexible through-type traction power supply system of the present application specifically includes steps S101 to S104, and it should be noted that the control method of the flexible through-type traction power supply system of the following embodiments of the present application is applied to the measurement and control unit, that is, the execution subject of the control method of the following embodiments of the present application is the measurement and control unit.

[0070] Step S101, determine the power threshold P T_MAX of the three-phase grid-connected inverter TGI, the power threshold P D1_MAX of the first DC-DC bidirectional converter DDC1, the power threshold P D2_MAX of the second DC-DC bidirectional converter DDC2, the upper threshold SOC MAX and the lower threshold SOC MIN of the state of charge SOC of the super capacitor SC, the maximum charge and discharge power P SC_MAX of the super capacitor SC, and the DC bus voltage reference value U DC_REF .

[0071] Step S102, calculate the total active power P ACL of the n traction substations, the total reactive power Q ACL of the n traction substations, the harmonic current i h , the active power P TL of the railway distribution network load, the active power P PV of the photovoltaic array, and the state of charge SOC of the super capacitor SC.

[0072] Step S103, obtain the active power reference value P T_REF of the three-phase grid-connected inverter TGI connected to the DC bus side port, the active power reference value P D1_REF of the first DC-DC bidirectional converter DDC1 connected to the DC bus side port, the active power reference value P D2_REF of the second DC-DC bidirectional converter DDC2 connected to the DC bus side port, the reference current i 1,REF of the first voltage source converter VSC1, and the reference current i 2,REF of the second voltage source converter VSC2.

[0073] Step S104, according to P T_REF , P D1_REF , P D2_REF , i 1,REF , and i 2,REF , and through the measurement and control unit, control the two groups of voltage source converters VSC, the three-phase grid-connected inverter TGI, and the two groups of DC-DC bidirectional converters DDC.

[0074] In one embodiment of the present invention, the controlling of the two groups of voltage source converters VSC in step S104 specifically includes:

[0075] Detect the actual value of DC bus voltage U DC , will U DC_REF with U DC The difference is adjusted by the proportional-integral controller to obtain the output I DC_REF ;

[0076] The u1 synchronization signal sin(ωt-ψ1) is obtained through the phase-locked loop, and I DC_REF Multiply by sin(ωt-ψ1) and add 1_REF Add the two, and subtract the result from the actual value i1 of the AC current measured by the first voltage source converter VSC1. The result is regulated by the proportional-integral controller and then input into the PWM module for modulation to generate a control signal for driving the first voltage source converter VSC1, thereby completing the control of the first voltage source converter VSC1. u1 is the AC side voltage of the first voltage source converter VSC1, and ψ1 is the connection angle of u1.

[0077] The u2 synchronization signal sin(ωt-ψ2) is obtained through the phase-locked loop, and I DC_REF Multiply by sin(ωt-ψ2) and add 2_REF The two currents are added together, and the difference between the addition result and the actual value i2 of the AC measured current of the second voltage source converter VSC2 is made. The result is adjusted by the proportional-integral controller and then input into the PWM module for modulation to generate a control signal for driving the second voltage source converter VSC2, thereby completing the control of the second voltage source converter VSC2. u2 is the AC side voltage of the second voltage source converter VSC2, and ψ2 is the connection angle of u2.

[0078] In one embodiment of the present invention, the control of the two groups of DC-DC bidirectional converters DDC in step S104 specifically includes:

[0079] A voltage closed-loop control strategy is adopted to collect the voltage and current of the photovoltaic array, obtain the reference voltage of the photovoltaic array, and control the first DC-DC bidirectional converter DDC1.

[0080] In one embodiment of the present invention, the control of the two groups of DC-DC bidirectional converters DDC in step S104 specifically includes:

[0081] Adopt current closed loop control strategy, collect voltage and current of super capacitor SC, use P D2_REFThe supercapacitor reference current is obtained by dividing the voltage of the supercapacitor SC, and the result is subtracted from the actual current value of the supercapacitor SC. The result is input into the PWM module for modulation to generate a control signal for driving the second DC-DC bidirectional converter DDC2, thereby completing the control of the second DC-DC bidirectional converter DDC2.

[0082] In one embodiment of the present invention, the control of the three-phase grid-connected inverter TGI in step S104 specifically includes:

[0083] The closed-loop control of the inverter output side current with capacitor current feedforward is adopted, and the phase-locking is performed based on the phase A voltage of the railway distribution network. The dq0 coordinate system components of the distribution system voltage, distribution system current, filter capacitor current, inverter input side current and P are respectively converted into T_REF The input is input to the controller, and after being adjusted by the controller, it is subjected to Park inverse transformation, and finally input into the PWM module for modulation to generate a control signal to drive the three-phase grid-connected inverter TGI, thereby completing the control of the three-phase grid-connected inverter TGI.

[0084] In one embodiment of the present invention, the active power reference value P of the DC bus side port of the three-phase grid-connected inverter TGI is obtained in step S103. T_REF The first DC-DC bidirectional converter DDC1 is connected to the DC bus side port active power reference value P D1_REF The second DC-DC bidirectional converter DDC2 is connected to the DC bus side port active power reference value P D2_REF , specifically including:

[0085] Find P D1_REF =min{P D1_MAX ,P PV};

[0086] Find the intermediate quantity P L =P ACL –P D1_REF ;

[0087] According to the intermediate quantity P L The state of charge SOC of the supercapacitor SC determines the system working mode, and the P under each working mode is obtained. T_REF and P D2_REF .

[0088] In one embodiment of the present invention, the above steps are performed according to the intermediate quantity P L The state of charge SOC of the supercapacitor SC determines the system working mode, and the P under each working mode is obtained. T_REF and P D2_REF , specifically including:

[0089] When P L≥ 0 and SOC ≤ SOC MIN , the system operating mode is determined as idle mode, in which P T_REF = 0, P D2_REF = 0.

[0090] When P L ≥ 0 and SOC > SOC MIN , the system operating mode is determined as discharging mode, in which P T_REF = max{0, -P D2_REF -P L}, P D2_REF = -min{P L + P TL , P SC_MAX , P L + P T_MAX}.

[0091] When P L < 0 and SOC ≥ SOC MAX , the system operating mode is determined as transfer mode, in which P T_REF = 0, P D2_REF = min{P T_MAX , P TL , -P L}.

[0092] When P L < 0 and SOC < SOC MAX , the system operating mode is determined as energy storage mode, in which P T_REF = min{P T_MAX , P TL , -P L}, P D2_REF = min{-P L -P T_REF , P SC_MAX}.

[0093] In one embodiment of the present application, the first voltage source converter VSC1 AC side reference current i 1,REF and the second voltage source converter VSC2 AC side reference current i 2,REF in the step S103 are calculated, specifically including:

[0094] According to the negative sequence power allowable value, the reactive power allowable value, the negative sequence power actual value, the total reactive power Q ACL of the n traction substations, the vector of the first voltage source converter VSC1 AC side voltage u1, the connection angle of the first voltage source converter VSC1 AC side voltage u1, the transformation ratio of the first transformer and the harmonic current i h , the i 1,REF is calculated.

[0095] According to the negative sequence power allowable value, reactive power allowable value, negative sequence power actual value, total reactive power Q of n traction substations ACL , the vector of the AC side voltage u2 of the second voltage source converter VSC2 and the connection angle of the AC side voltage u2 of the second voltage source converter VSC2, and calculate i 2,REF .

[0096] In one embodiment of the present invention, find i 1,REF and i 2,REF Specifically, it can be expressed by the following formula:

[0097]

[0098]

[0099] Where: is the permissible value of negative sequence power, Q′ is the permissible value of reactive power, is the actual value of negative sequence power, Wherein, j is a complex unit. are the vectors of the AC side voltages u1 and u2 of the first and second voltage source converters, respectively; ψ1 and ψ2 are the connection angles of u1 and u2 (the phase of the lagging A phase voltage); [] * It represents taking conjugate of the variables in [], and k1 is the transformation ratio of the first transformer.

[0100] It can be seen from the above embodiments that the present invention completely eliminates the phase separation of the traction network, greatly ensuring the safety of train operations and improving the utilization rate of regenerative braking energy; relying on high-power power electronic devices to solve the power quality problems such as negative sequence, reactive power, and harmonics, creating favorable conditions for further high-speed and heavy-load operation of trains; the introduction of the DC bus provides an interface for the photovoltaic array, realizing the connection of photovoltaics to the traction power supply system, increasing the proportion of clean energy, and increasing the flexibility and toughness of the system's power supply. It provides a reference for further optimizing the economic and technical efficiency of electrified railways.

[0101] It should be noted that the steps in the above embodiments of the present invention and the steps shown in the flowcharts of the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowcharts, in some cases, the steps shown or described may be executed in an order different from that shown here.

[0102] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A flexible through-type traction power supply system, characterized in that: include: n traction substations and one power flow control station, where n is an integer greater than 1, and the n traction substations and the primary side of the power flow control station have the same common connection point; The power flow control station includes: a Scott transformer, two groups of voltage source converters VSC, two groups of DC-DC bidirectional converters DDC, a photovoltaic array, a supercapacitor SC, a three-phase grid-connected inverter TGI, a three-phase step-up transformer TT, and a measurement and control unit; the Scott transformer includes: a first transformer and a second transformer; the two groups of voltage source converters include: a first voltage source converter VSC1 and a second voltage source converter VSC2; the two groups of DC-DC bidirectional converters DDC include: a first DC-DC bidirectional converter DDC1 and a second DC-DC bidirectional converter DDC2; The primary side of the first transformer is connected to the two-phase AC busbar that draws power from the traction substation, and the secondary side is connected to the AC side of the first voltage source converter VSC1. One end of the primary side of the second transformer is connected to the one-phase AC busbar that does not draw power from the traction substation, and the other end is connected to the center tap position of the first transformer. The secondary side of the second transformer is connected to the AC side of the second voltage source converter VSC2. The DC sides of the first voltage source converter VSC1 and the second voltage source converter VSC2 are connected to the DC busbar. One side of the first DC-DC bidirectional converter DDC1 is connected to the photovoltaic array, and the other side is connected to the DC bus; one side of the second DC-DC bidirectional converter DDC2 is connected to the super capacitor SC, and the other side is connected to the DC bus; The AC side of the three-phase grid-connected inverter TGI is connected to the primary side of the three-phase step-up transformer TT, and the DC side of the three-phase grid-connected inverter TGI is connected to the DC bus; the secondary side of the three-phase step-up transformer TT is connected to the railway distribution network; The measurement and control unit is used to control two groups of voltage source converters VSC, three-phase grid-connected inverters TGI and two groups of DC-DC bidirectional converters DDC after collecting electrical data; The control method of the flexible through-type traction power supply system includes: Determine the power threshold P of the three-phase grid-connected inverter TGI T_MAX , the power threshold P of the first DC-DC bidirectional converter DDC1 D1_MAX , the power threshold P of the second DC-DC bidirectional converter DDC2 D2_MAX , the upper limit threshold SOC of the state of charge SOC of the supercapacitor SC MAX and lower threshold SOC MIN 、The maximum charge and discharge power P of supercapacitor SC SC_MAX And the DC bus voltage reference value U DC_REF ; The total active power P of n traction substations is calculated ACL , the total reactive power Q of n traction substations ACL , harmonic current i h , Railway distribution network load active power P TL , the active power P of the photovoltaic array PV and the state of charge SOC of the supercapacitor SC; Obtain the active power reference value P of the three-phase grid-connected inverter TGI connected to the DC bus side port T_REF The first DC-DC bidirectional converter DDC1 is connected to the DC bus side port active power reference value P D1_REF The second DC-DC bidirectional converter DDC2 is connected to the DC bus side port active power reference value P D2_REF , AC side reference current i of the first voltage source converter VSC1 1,REF and the AC side reference current i of the second voltage source converter VSC2 2,REF ; According to P T_REF 、P D1_REF 、P D2_REF 、i 1,REF and i 2,REF and controlling two groups of voltage source converters VSC, three-phase grid-connected inverters TGI and two groups of DC-DC bidirectional converters DDC through the measurement and control unit; The AC side reference current i of the first voltage source converter VSC1 1,REF and the AC side reference current i of the second voltage source converter VSC2 2,REF It is determined by the following formula: Where: is the permissible value of negative sequence power, is the allowable value of reactive power, is the actual value of negative sequence power, j is a complex unit, 、 are the vectors of the AC side voltages u1 and u2 of the first and second groups of voltage source converters, respectively. 、 are the connection angles of u1 and u2 respectively, Express The intermediate variables are conjugate, and k1 is the transformation ratio of the first transformer.

2. The flexible through-type traction power supply system according to claim 1, characterized in that: The traction substation includes: a traction transformer; The primary side of the traction transformer is connected to the AC busbar, and the secondary side of the traction transformer is connected to the traction network. The traction network completely eliminates electrical phase separation; the AC busbar is connected to the power supply network.

3. A control method for a flexible through-type traction power supply system, characterized in that: Applied to the flexible through-type traction power supply system according to claim 1 or 2, the method comprises: Determine the power threshold P of the three-phase grid-connected inverter TGI T_MAX , the power threshold P of the first DC-DC bidirectional converter DDC1 D1_MAX , the power threshold P of the second DC-DC bidirectional converter DDC2 D2_MAX , the upper limit threshold SOC of the state of charge SOC of the supercapacitor SC MAX and lower threshold SOC MIN 、The maximum charge and discharge power P of supercapacitor SC SC_MAX And the DC bus voltage reference value U DC_REF ; The total active power P of n traction substations is calculated ACL , the total reactive power Q of n traction substations ACL , harmonic current i h , Railway distribution network load active power P TL , the active power P of the photovoltaic array PV and the state of charge SOC of the supercapacitor SC; Obtain the active power reference value P of the three-phase grid-connected inverter TGI connected to the DC bus side port T_REF The first DC-DC bidirectional converter DDC1 is connected to the DC bus side port active power reference value P D1_REF The second DC-DC bidirectional converter DDC2 is connected to the DC bus side port active power reference value P D2_REF , AC side reference current i of the first voltage source converter VSC1 1,REF and the AC side reference current i of the second voltage source converter VSC2 2,REF ; According to P T_REF 、P D1_REF 、P D2_REF 、i 1,REF and i 2,REF The two groups of voltage source converters VSC, the three-phase grid-connected inverter TGI and the two groups of DC-DC bidirectional converters DDC are controlled through the measurement and control unit.

4. The control method of the flexible through-type traction power supply system according to claim 3, characterized in that: Controlling two groups of voltage source converters (VSCs) includes: Detect the actual value of DC bus voltage U DC , will U DC_REF with U DC The difference is adjusted by the proportional-integral controller to obtain the output I DC_REF ; Get u1 synchronization signal through phase-locked loop , will I DC_REF and Multiply and add to i 1_REF The sum is added, and the difference between the summed value and the actual value i1 of the AC current measured by the first voltage source converter VSC1 is calculated. After being adjusted by the proportional-integral controller, it is input into the PWM module for modulation to generate a control signal to drive the first voltage source converter VSC1, thereby completing the control of the first voltage source converter VSC1. u1 is the AC side voltage of the first voltage source converter VSC1. is the connection angle of u1; Get u2 synchronization signal through phase-locked loop , will I DC_REF and Multiply and add to i 2_REF The sum is added, and the difference between the summed value and the actual value i2 of the AC current measured by the second voltage source converter VSC2 is calculated. After being adjusted by the proportional-integral controller, it is input into the PWM module for modulation to generate a control signal to drive the second voltage source converter VSC2, thereby completing the control of the second voltage source converter VSC2. u2 is the AC side voltage of the second voltage source converter VSC2. is the connection angle of u2.

5. The control method of the flexible through-type traction power supply system according to claim 3, characterized in that: Controlling two sets of DC-DC bidirectional converters DDC, specifically including: A voltage closed-loop control strategy is adopted to collect the voltage and current of the photovoltaic array, obtain the reference voltage of the photovoltaic array, and control the first DC-DC bidirectional converter DDC1.

6. The control method of the flexible through-type traction power supply system according to claim 3, characterized in that: Controlling two sets of DC-DC bidirectional converters DDC, specifically including: Adopt current closed loop control strategy, collect voltage and current of super capacitor SC, use P D2_REF The supercapacitor reference current is obtained by dividing the voltage of the supercapacitor SC, and the result is subtracted from the actual current value of the supercapacitor SC. The result is input into the PWM module for modulation to generate a control signal for driving the second DC-DC bidirectional converter DDC2, thereby completing the control of the second DC-DC bidirectional converter DDC2.

7. The control method of the flexible through-type traction power supply system according to claim 3, characterized in that: Control the three-phase grid-connected inverter TGI, including: The closed-loop control of the inverter output side current with capacitor current feedforward is adopted, and the phase-locking is performed based on the phase A voltage of the railway distribution network. The dq0 coordinate system components of the distribution system voltage, distribution system current, filter capacitor current, inverter input side current and P are respectively converted into T_REF The input is input to the controller, and after being adjusted by the controller, it is subjected to Park inverse transformation, and finally input into the PWM module for modulation to generate a control signal to drive the three-phase grid-connected inverter TGI, thereby completing the control of the three-phase grid-connected inverter TGI.

8. The control method of the flexible through-type traction power supply system according to claim 3, characterized in that: The active power reference value P of the three-phase grid-connected inverter TGI connected to the DC bus side port is obtained. T_REF The first DC-DC bidirectional converter DDC1 is connected to the DC bus side port active power reference value P D1_REF The second DC-DC bidirectional converter DDC2 is connected to the DC bus side port active power reference value P D2_REF , specifically including: Find P D1_REF = min{P D1_MAX , P PV }; Find the intermediate quantity P L = P ACL – P D1_REF ; According to the intermediate quantity P L The state of charge SOC of the supercapacitor SC determines the system working mode, and the P under each working mode is obtained. T_REF and P D2_REF .

9. The control method of the flexible through-type traction power supply system according to claim 8, characterized in that: The intermediate quantity P L The state of charge SOC of the supercapacitor SC determines the system working mode, and the P under each working mode is obtained. T_REF and P D2_REF , specifically including: when and When the system working mode is determined to be idle mode, in idle mode P T_REF = 0, P D2_REF = 0; when and When the system working mode is determined to be the energy release mode, in the energy release mode P T_REF = max{0, -P D2_REF -P L }, P D2_REF = -min{P L +P TL , P SC_MAX , P L +P T_MAX }; when and When the system working mode is determined to be transfer mode, in transfer mode P T_REF = 0, P D2_REF = min{P T_MAX , P TL , -P L }; when and When the system working mode is determined to be energy storage mode, in energy storage mode P T_REF = min{P T_MAX , P TL , -P L }, P D2_REF = min{-P L – P T_REF , P SC_MAX }.

10. The control method of the flexible through-type traction power supply system according to claim 3, characterized in that: The AC side reference current i of the first voltage source converter VSC1 is obtained. 1,REF and the AC side reference current i of the second voltage source converter VSC2 2,REF , specifically including: According to the negative sequence power allowable value, reactive power allowable value, negative sequence power actual value, total reactive power Q of n traction substations ACL , the vector of the AC side voltage u1 of the first voltage source converter VSC1, the connection angle of the AC side voltage u1 of the first voltage source converter VSC1, the transformation ratio of the first transformer and the harmonic current i h , find i 1,REF ; According to the negative sequence power allowable value, reactive power allowable value, negative sequence power actual value, total reactive power Q of n traction substations ACL , the vector of the AC side voltage u2 of the second voltage source converter VSC2 and the connection angle of the AC side voltage u2 of the second voltage source converter VSC2, and calculate i 2,REF .

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