Multi-port new energy conversion device for electrified railway traction power supply system and direct-current voltage balance control method

Abstract

The invention belongs to the technical field of alternating-current electrified railway traction power supply, and particularly relates to a multi-port new energy conversion device for an electrified railway traction power supply system and a direct-current voltage balance control method, and the multi-port new energy conversion device comprises a transformer, a single-phase rectification system, a direct-current bus system, an energy conversion system and the like. The requirement for the number of windings on the low-voltage side of a transformer is lowered through cascade operation of the alternating current sides of the two AC / DC rectification modules, multiple direct current buses are constructed through parallel operation of the direct current sides of the AC / DC rectification modules at the relative positions of the single-phase rectification system, and each direct current bus is connected with a new energy power generation and energy storage converter. On the basis of direct-current voltage balance control of a traditional cascade converter, active power adjustment can be carried out between the AC / DC rectification modules connected in parallel on the direct-current side, and balance control over the direct-current voltage is further achieved.

Description

Technical Field

[0001] This invention belongs to the field of AC electrified railway traction power supply technology, specifically relating to a multi-port new energy conversion device and a DC voltage equalization control method for electrified railway traction power supply systems. Background Technology

[0002] Electrified railways play a crucial role in economic and social development. Currently, there is considerable research and exploration into the application of renewable energy power generation technologies in the rail transit sector, but much of the focus is on photovoltaic power generation for station lighting and new energy electric vehicles. For trunk railways, due to factors such as the massive network scale, high traction power supply voltage levels, and strong train traction load impacts, the application of new energy technologies is currently limited to powering non-traction loads. Currently, the use of station canopies for photovoltaic power generation is quite widespread, with many stations already equipped with photovoltaic modules, providing power for station lighting and communication equipment.

[0003] In existing technologies, most current AC traction power supply systems for new energy applications require connecting two traction power supply arms, or traction buses, between the traction substation or section substation via AC-DC-AC converters. This does not allow for flexible selection of any single traction power supply arm or traction bus. Furthermore, the traditional multi-layered structure, where each H-bridge converter needs to be connected to a transformer's low-voltage winding, results in a large number of low-voltage windings and a complex transformer structure.

[0004] Some improved solutions employ cascaded AC-DC-AC converters and multi-winding transformers to form a new multiplexing structure, which can reduce the number of low-voltage windings in the transformer. However, these solutions have several drawbacks: 1: The high-voltage side windings of the transformer are connected in series. If any one winding fails, the other windings will not work, which reduces reliability and availability, and also increases the difficulty of electrical insulation and stable operation. 2: Different AC-DC-AC converters cannot be connected to each other because of the different potentials on their DC sides. The capacity of each DC terminal interface is very small, which is not conducive to the connection of large-capacity DC sources. 3: The power of the DC source on each DC side is different, which exacerbates the imbalance of DC voltages, making voltage balance control more difficult and reducing system stability.

[0005] Therefore, the present invention provides a multi-port new energy conversion device and a DC voltage equalization control method for an electrified railway traction power supply system. Summary of the Invention

[0006] The purpose of this invention is to provide a multi-port renewable energy conversion device and a DC voltage balancing control method for electrified railway traction power supply systems. This involves parallel operation of the DC side of AC / DC rectifier modules in a single-phase rectifier system, constructing multiple DC buses. Each DC bus connects a renewable energy generator and an energy storage converter. Building upon traditional cascaded converter DC voltage balancing control, the parallel-connected AC / DC rectifier modules on the DC side can adjust active power, further achieving balanced DC voltage control.

[0007] The specific technical solution adopted by this invention is as follows: A multi-port new energy conversion device for an electrified railway traction power supply system is characterized by comprising a transformer, a single-phase rectifier system, a DC bus system, and an energy conversion system, wherein the primary side of the transformer is connected to the traction network as an AC grid-connected port, which can be any location in the traction substation, sectioning station, or contact network; the energy conversion system is connected to one or both of a new energy power generation and energy storage system. By cascading two AC / DC rectifier modules on the AC side of the single-phase rectifier system, the requirement for the number of low-voltage windings of the transformer is reduced. Multiple DC buses are constructed by paralleling the DC sides of the AC / DC rectifier modules in relative positions within the single-phase rectifier system. These multiple DC buses form a DC bus system, and each DC bus in the system connects to the new energy generation and energy storage converter in the energy converter system. Based on the traditional DC voltage balancing control of cascaded converters, active power regulation is performed among the parallel AC / DC rectifier modules on the DC side of the single-phase rectifier system to achieve DC voltage balancing control.

[0008] The transformer has an AC grid connection port on its high-voltage side, which is connected to the grid connection point of the railway traction power supply system. The grid connection point is the traction bus of the traction substation, the traction bus of the sectioning substation, or the power supply line of the contact network. The transformer has one high-voltage winding and j low-voltage windings; j is a positive integer not less than 1. The high-voltage winding is connected to the grid connection point, and each low-voltage winding is connected to the AC side of a subunit in the single-phase rectifier system.

[0009] The single-phase rectifier system comprises j sub-units, where j is a positive integer not less than 1. Each sub-unit consists of i cascaded AC / DC rectifier modules; the i AC / DC rectifier modules are such as Con1_1, Con1_x, ..., Con1_i; i is a positive integer not less than 2, and x is a positive integer between 1 and i; a filter reactor Lk is connected in series on the AC side of each sub-unit, and at least one supporting capacitor is connected in parallel on the DC side of each AC / DC rectifier module; such as Ck_1 and Ck_2.

[0010] Each AC / DC rectifier module includes a left bridge arm and a right bridge arm. The cascaded structure is such that the middle output terminal of the right bridge arm of the first AC / DC rectifier module is connected to the middle output terminal of the left bridge arm of the second AC / DC rectifier module. A reactor is connected in series at the middle output terminal of the left bridge arm of the first AC / DC rectifier module.

[0011] The DC bus system comprises i groups of DC buses, each group consisting of a positive bus and a negative bus, with each group of DC buses isolated from the others. The first group of DC buses connects to the DC terminal of the first AC / DC rectifier module in each subunit of the single-phase rectifier system; similarly, the m-th group of DC buses connects to the DC terminal of the m-th AC / DC rectifier module in each subunit of the single-phase rectifier system. Furthermore, each group of DC buses is connected to the energy conversion system.

[0012] The energy conversion system includes multiple sets of DC / DC converters and DC / AC converters. Each set of DC buses is connected to one or both of the DC / DC converters and DC / AC converters. Each set of DC buses is connected to the same number of DC / DC converters and the same number of DC / AC converters. The output terminal of each DC / DC converter and DC / AC converter is connected to one or more of the photovoltaic power generation system, wind power generation system, or energy storage system.

[0013] A DC voltage equalization control method for a multi-port renewable energy converter for an electrified railway traction power supply system: The multi-port renewable energy converter is connected to the DC terminals of AC / DC rectifier modules at the same position in different sub-units of a single-phase rectifier system via a DC bus. Therefore, energy exchange between AC / DC rectifier modules at the same position in different sub-units can be realized through the DC bus, that is, energy exchange between multiple cascaded converters can be realized, providing another energy equalization channel for DC voltage equalization control, thereby accelerating DC voltage equalization control. Based on the traditional DC voltage equalization control of cascaded converters, cross-unit DC voltage equalization control between multiple cascaded converters is added. Specifically, the power adjustment amount of cross-unit DC voltage equalization control is superimposed on the active power command of each rectifier module of each cascaded converter.

[0014] Preferably, in the power regulation generation method of the cross-unit DC voltage equalization control, all AC / DC rectifier modules at the same position in each subsystem of the single-phase rectifier system are subjected to cross-unit DC voltage equalization control. Since each subsystem has i AC / DC rectifier modules, a total of i sets of cross-unit DC voltage equalization control are required. Specifically, the average DC voltage of all AC / DC rectifier modules at the same location in the single-phase rectifier system is calculated. Then, this average DC voltage is subtracted from the DC voltage of each AC / DC rectifier module at that location to obtain the differences. Each difference is passed through a regulator, and the output of each regulator is multiplied by the steady-state value of the active power Ps on the AC side to obtain the power regulation amount for cross-unit DC voltage equalization control of each AC / DC rectifier module at that location.

[0015] The technical effects achieved by this invention are as follows: This invention allows for connection to a single traction power supply arm, with flexible connection location. The AC grid connection port on the high-voltage side of the transformer in the multi-port renewable energy conversion device is a single-phase port, connected to the traction network. Specifically, it can be connected to any location in the traction substation, sectioning station, or overhead contact line, allowing for the selection of any traction power supply arm for connection. It does not require connection to two adjacent traction power supply arms in the traction substation or sectioning station, thus making the connection to the traction network more flexible.

[0016] This invention reduces the number of low-voltage windings in traction transformers. The AC / DC rectifier modules of each subsystem in the single-phase rectifier system are cascaded, with each subsystem connecting only one low-voltage winding of the transformer. Therefore, the number of low-voltage windings in the transformer is significantly reduced, lowering the difficulty and cost of transformer manufacturing.

[0017] This invention features a large number of DC buses with high capacity. Multiple sets of DC buses connect AC / DC rectifier modules at the same location within each subsystem of a single-phase rectifier system, enabling parallel operation of multiple AC / DC rectifier modules on the DC side. This increases the capacity of the DC buses and facilitates the integration of large-capacity renewable energy generation and storage systems. Furthermore, multiple sets of DC buses can operate independently, connecting the same or different renewable energy generation and storage systems, thus providing greater flexibility in operation and control.

[0018] This invention relates to cross-unit DC voltage equalization control. Energy exchange can be achieved between AC / DC rectifier modules at the same location in different sub-units via the DC bus, i.e., energy exchange between multiple cascaded converters, thereby accelerating DC voltage equalization control. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the main circuit structure of the multi-port renewable energy conversion device in this invention; Figure 2 This is a schematic diagram of the single-phase rectifier system subunit and its external connections in this invention; Figure 3 This is a schematic diagram of a single-phase rectifier system subunit using a two-level converter as an example in this invention; Figure 4 This is the main circuit of the DC bus system in this invention; Figure 5 This is a schematic diagram of the main circuit structure of a multi-port renewable energy conversion device, taking two-stage cascade as an example, in this invention. Figure 6 This is a block diagram of DC voltage balancing control for a traditional cascaded converter. Figure 7 This is a control block diagram of the cross-unit DC voltage equalization control added in this invention; Figure 8 This is a schematic diagram of the method for generating the power regulation amount in this invention; Figure 9 This is an example of the energy flow diagram illustrating the application of the multi-port new energy conversion device in the new energy application scenario of the electrified railway traction power supply system. Figure 10 This is a schematic diagram of the circuit structure of a back-to-back AC-DC-AC average value converter. Detailed Implementation

[0020] To make the objectives and advantages of this invention clearer, the invention will be specifically described below with reference to embodiments. It should be understood that the following text is merely used to describe one or more specific embodiments of the invention and does not strictly limit the scope of protection specifically claimed by the invention.

[0021] Example 1: like Figure 1-10 As shown, a multi-port new energy conversion device for an electrified railway traction power supply system is characterized by comprising a transformer, a single-phase rectifier system, a DC bus system, and an energy conversion system, such as... Figure 1 As shown; where the primary side of the transformer is connected to the traction network as an AC grid-connected port, it can be any location in the traction substation, sectioning station, or contact network; the energy conversion system connects to one or both of the new energy power generation and energy storage systems; By cascading two AC / DC rectifier modules on the AC side of the single-phase rectifier system, the requirement for the number of low-voltage windings of the transformer is reduced. Multiple DC buses are constructed by paralleling the DC sides of the AC / DC rectifier modules in relative positions within the single-phase rectifier system. These multiple DC buses form a DC bus system, and each DC bus in the system connects to the new energy generation and energy storage converter in the energy converter system. Based on the traditional DC voltage balancing control of cascaded converters, active power regulation is performed among the parallel AC / DC rectifier modules on the DC side of the single-phase rectifier system to achieve DC voltage balancing control.

[0022] The transformer has an AC grid connection port on its high-voltage side, which is connected to the grid connection point of the railway traction power supply system. The grid connection point is the traction bus of the traction substation, the traction bus of the sectioning substation, or the power supply line of the contact network. The transformer has one high-voltage winding and j low-voltage windings; j is a positive integer not less than 1. The high-voltage winding is connected to the grid connection point, and each low-voltage winding is connected to the AC side of a subunit in the single-phase rectifier system.

[0023] The single-phase rectifier system comprises j sub-units, where j is a positive integer not less than 1. Each sub-unit consists of i cascaded AC / DC rectifier modules; the i AC / DC rectifier modules are such as Con1_1, Con1_x, ..., Con1_i; i is a positive integer not less than 2, and x is a positive integer between 1 and i; a filter reactor Lk is connected in series on the AC side of each sub-unit, and at least one supporting capacitor is connected in parallel on the DC side of each AC / DC rectifier module; such as Ck_1 and Ck_2.

[0024] Taking a sub-unit with two cascaded AC / DC rectifier modules as an example, i.e., i=2, the circuit structure of the y-th sub-unit is as follows: Figure 2 As shown; y is a positive integer from 1 to j. Taking a two-level converter as an example, Figure 3 The diagram shows the cascaded connection of the sub-units. Each AC / DC rectifier module includes a left bridge arm and a right bridge arm. The cascaded structure is such that the middle output terminal of the right bridge arm of the first AC / DC rectifier module is connected to the middle output terminal of the left bridge arm of the second AC / DC rectifier module. A reactor is connected in series at the middle output terminal of the left bridge arm of the first AC / DC rectifier module.

[0025] The DC bus system comprises i groups of DC buses, each group consisting of a positive bus (+) and a negative bus (-), with each group of DC buses isolated from the others. The first group of DC buses connects to the DC terminal of the first AC / DC rectifier module in each subunit of the single-phase rectifier system; similarly, the m-th group of DC buses connects to the DC terminal of the m-th AC / DC rectifier module in each subunit of the single-phase rectifier system. Furthermore, each group of DC buses is connected to the energy conversion system. Taking two sets of DC buses (i.e., i=2) as an example, the DC bus system and its external connections are as follows: Figure 4 As shown.

[0026] The energy conversion system includes multiple sets of DC / DC converters and DC / AC converters. Each set of DC buses is connected to one or both of the DC / DC converters and DC / AC converters. To facilitate DC voltage balancing between the two cascaded AC / DC rectifier modules, each set of DC buses is connected to the same number of DC / DC converters and the same number of DC / AC converters. The output of each DC / DC converter and DC / AC converter is connected to one or more of the following: a photovoltaic power generation system, a wind power generation system, or an energy storage system. To more clearly describe the main circuit structure of the multi-port renewable energy conversion device, we take an example where each subunit has two cascaded AC / DC rectifier modules; that is, i=2. The main circuit structure is as follows: Figure 5 As shown; The circuit structure of the multi-port renewable energy conversion device proposed in this invention has the following advantages: It can connect to one traction power supply arm, and the connection location is flexible. The AC grid connection port on the high-voltage side of the transformer of the multi-port new energy conversion device is a single-phase port, which connects to the traction network. Specifically, it can be connected to any location of the traction substation, sectioning station, or contact network. Any traction power supply arm can be selected for connection, without needing to connect to two adjacent traction power supply arms of the traction substation or sectioning station. Therefore, the connection method to the traction network is more flexible.

[0027] The number of low-voltage windings in the traction transformer is reduced. The AC / DC rectifier modules of each subsystem in the single-phase rectifier system are cascaded, and each subsystem is connected to only one low-voltage winding of the transformer. Therefore, the number of low-voltage windings in the transformer is significantly reduced, which reduces the difficulty and cost of transformer manufacturing.

[0028] The system features numerous and high-capacity DC buses. Multiple sets of DC buses connect AC / DC rectifier modules at the same location within each subsystem of a single-phase rectifier system, enabling parallel operation of multiple AC / DC rectifier modules on the DC side. This increases the capacity of the DC buses and facilitates the integration of large-capacity renewable energy generation and storage systems. Furthermore, multiple sets of DC buses can operate independently, connecting the same or different renewable energy generation and storage systems, thus providing greater flexibility in operation and control.

[0029] Example 2: Traditional cascaded converter DC-side voltage equalization control, such as Figure 6 As shown, based on a double closed-loop design with an outer DC voltage loop and an inner AC current loop, the difference between the DC voltage of each rectifier module and its average DC voltage is calculated. This difference is then processed by the DC voltage equalization regulator of each rectifier module to obtain the adjustment amount for each module. The DC voltage equalization regulator, such as a traditional proportional regulator or a proportional-integral regulator, is superimposed on the output of the DC voltage averaging regulator to obtain the active power command for each rectifier module. This enables balanced control of the DC-side voltage of cascaded converters.

[0030] In the multi-port new energy conversion device proposed in this invention, each transformer low-voltage winding is connected to a cascaded converter, i.e., a sub-unit of a single-phase rectifier system, and each sub-unit adopts traditional DC-side voltage equalization control. This invention discloses a DC voltage equalization control method for a multi-port renewable energy conversion device in an electrified railway traction power supply system. The multi-port renewable energy conversion device is connected to the DC terminals of AC / DC rectifier modules at the same position in different sub-units of a single-phase rectifier system via a DC bus. Therefore, energy exchange between AC / DC rectifier modules at the same position in different sub-units can be realized through the DC bus, that is, energy exchange between multiple cascaded converters can be realized, providing another energy equalization channel for DC voltage equalization control, thereby accelerating DC voltage equalization control. Based on traditional cascaded converter DC voltage balancing control, cross-unit DC voltage balancing control between multiple cascaded converters is added. Specifically, the power regulation amount of cross-unit DC voltage balancing control is superimposed on the active power command of each rectifier module in each cascaded converter; the active power command of each rectifier module is as follows: The power regulation amount of cross-unit DC voltage equalization control is as follows: ;like Figure 7 As shown.

[0031] In the power regulation generation method for cross-unit DC voltage equalization control, all AC / DC rectifier modules at the same location in each subsystem of the single-phase rectifier system undergo cross-unit DC voltage equalization control. Since each subsystem has i AC / DC rectifier modules, a total of i sets of cross-unit DC voltage equalization control are required. Figure 8 As shown; Specifically, the average DC voltage of all AC / DC rectifier modules at the same location in the single-phase rectifier system is calculated. Then, this average DC voltage is subtracted from the DC voltage of each AC / DC rectifier module at that location to obtain individual differences. Each difference is processed by a regulator; the regulator is either a proportional regulator or a proportional-integral regulator. The output of each regulator is multiplied by the steady-state value of the active power Ps on the AC side to obtain the power regulation amount for cross-unit DC voltage equalization control of each AC / DC rectifier module at that location. Figure 8 As shown in the figure. The steady-state value of active power Ps on the AC side is calculated from the voltage and current signals on the AC side.

[0032] Specifically, to describe in detail the power regulation generation method for cross-unit DC voltage equalization control, the first sub-unit of each single-phase rectifier system is used as an example. Figure 8 The first group and the xth one Figure 8 Let's take the xth group of AC / DC rectifier modules as an example for explanation: Example 1 of the method for generating power regulation; that is Figure 8 Group 1: First: Calculate the average DC voltage of the first AC / DC rectifier module in all sub-units of the single-phase rectifier system:

[0033] Then, the average DC voltage is subtracted one by one from the DC voltage of the first AC / DC rectifier module of each subsystem to obtain the individual differences, and each difference is passed through a regulator:

[0034] In the formula, For regulator function, This is the output value of the regulator.

[0035] Next, calculate the steady-state value of active power on the AC side (P). s ):

[0036] In the formula, This is the load power factor on the AC side.

[0037] Finally, the output of each regulator is compared with the steady-state value of the active power on the AC side (P). s Multiplying these together, we obtain the power regulation amount for cross-unit DC voltage equalization control of the first AC / DC rectifier module in all sub-units: .

[0038] Example 2 of the method for generating power regulation; that is Figure 8 Group x: First, calculate the average DC voltage of the x-th AC / DC rectifier module in all sub-units of the single-phase rectifier system.

[0039] Then, the average DC voltage is subtracted one by one from the DC voltage of the xth AC / DC rectifier module in each subsystem to obtain the individual differences, and each difference is passed through a regulator:

[0040] In the formula, For regulator function, This is the output value of the regulator.

[0041] Next, calculate the steady-state value of active power on the AC side (P). s ):

[0042] In the formula, This is the load power factor on the AC side.

[0043] Finally, the output of each regulator is compared with the steady-state value of the active power on the AC side (P). s Multiplying these together, we obtain the power regulation amount for cross-unit DC voltage equalization control of the x-th AC / DC rectifier module in all sub-units: .

[0044] Examples of applications of multi-port renewable energy conversion devices: Examples of multi-port renewable energy conversion devices applied in renewable energy application scenarios of electrified railway traction power supply systems. Figure 9 As shown, for simplicity, the example uses a two-stage cascaded system with i=2, a dual-stage system with j=2, and two sets of DC buses. The AC side of the multi-port renewable energy conversion device is connected to the traction bus with a rated voltage of 27.5kV at the traction substation, enabling energy feeding to the traction network. The DC / DC converter and DC / AC converter connected to each set of DC buses are connected to the renewable energy power generation and energy storage system.

[0045] like Figure 5 As shown, the first set of DC bus DC / DC converters is connected to the photovoltaic power generation system, and the DC / AC converter is connected to the flywheel energy storage system. The second set of DC bus DC / DC converters is connected to the battery energy storage system, and the DC / AC converter is connected to the wind power generation system.

[0046] When the system is running, the AC power of the first-stage converter equals the sum of the power generated by photovoltaic power generation and the power of the flywheel energy storage system, and the AC power of the second-stage converter equals the sum of the power generated by wind power generation and the power of the battery energy storage system, i.e., P bj1 =P PV +P ESS1 P bj2 =P WT +P ESS2 Among them, the energy storage system can store the fluctuating electrical energy from photovoltaic power generation and wind power generation, that is, smooth out the output power of new energy power generation.

[0047] The AC power of the two cascaded converters is fed back to the traction bus of the traction substation through the high-voltage side of the transformer, forming the total grid-connected power P. bj That is, P bj =P bj1 +P bj2 The existing traction substation and multi-port renewable energy conversion unit work together to supply the train's traction load P. L Provide electrical energy, i.e., P L =P s +P bjThis enables new energy sources, such as photovoltaic power generation and wind power generation, to provide clean energy to traction loads.

[0048] In this invention, the multi-port renewable energy conversion device includes a transformer, a single-phase rectifier system, a DC bus system, and an energy conversion system. The low-voltage side of the transformer includes multiple low-voltage windings, each connected to multiple cascaded AC / DC rectifier modules. Multiple sets of DC buses are provided, with each set connecting AC / DC rectifier modules at the same location within each subsystem of the single-phase rectifier system, enabling parallel operation of multiple AC / DC rectifier modules on the DC side.

[0049] This invention, based on traditional cascaded converter DC voltage balancing control, adds cross-unit DC voltage balancing control between multiple cascaded converters. Specifically, the power regulation amount of cross-unit DC voltage balancing control is further superimposed on the active power command of each rectifier module in each cascaded converter group. Specifically, the average DC voltage of all AC / DC rectifier modules at the same location in the single-phase rectifier system is calculated. Then, this average DC voltage is subtracted one by one from the DC voltage of each AC / DC rectifier module at that location to obtain various differences. Each difference is output by a regulator and then multiplied by the steady-state value of the AC side active power to obtain each power regulation amount.

[0050] It should be noted that the circuit structures of back-to-back and AC-DC-AC average value converters convey the same meaning, and the circuit structures are as follows: Figure 10 As shown.

[0051] The above description is merely a preferred embodiment of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention. Structures, devices, and operating methods not specifically described or explained in this invention are implemented according to conventional methods in the art unless otherwise specified or limited.

Claims

1. A multi-port new energy conversion device for an electrified railway traction power supply system, characterized in that: The single-phase rectifier system, the DC bus system, and the energy conversion system, wherein the primary side of the transformer is connected to the traction network as an AC grid connection port, and is any position of the traction substation, the substation, or the overhead line; the energy conversion system is connected to one or both of the new energy generation and the energy storage system; The two AC / DC rectifier modules in the single-phase rectifier system are connected in series to reduce the number of low-voltage winding of the transformer, and the DC sides of the AC / DC rectifier modules in the single-phase rectifier system are connected in parallel to build multiple DC buses, which form the DC bus system, and each DC bus in the DC bus system is connected to the new energy generation and the energy storage converter in the energy conversion system; on the basis of the traditional cascade converter DC voltage balance control, the active power between the DC side parallel AC / DC rectifier modules in the single-phase rectifier system is adjusted to complete the balance control of the DC voltage. 2.The multi-port new energy conversion device for electrified railway traction power supply system according to claim 1, characterized in that: The transformer has one AC grid connection port at the high-voltage end, which is connected to the grid connection point of the railway traction power supply system; the grid connection point is the traction bus of the traction substation, the traction bus of the substation, or the power supply line of the overhead line; the transformer has one high-voltage winding and j low-voltage windings; j is a positive integer not less than 1, the high-voltage winding is connected to the grid connection point, and each low-voltage winding is connected to the AC input side of the subunit in the single-phase rectifier system.

3. The multi-port new energy conversion device for electrified railway traction power supply system according to claim 2, characterized in that: The single-phase rectifier system includes j subunits, j is a positive integer not less than 1, and each subunit is composed of i AC / DC rectifier modules in series; i AC / DC rectifier modules such as Con1_1, Con1_x,..., and Con1_i; i is a positive integer not less than 2, and x is a positive integer between 1 and i; each subunit has one filter reactor Lk connected in series at the AC side, and at least one support capacitor such as Ck_1 and Ck_2 connected in parallel at the DC side of each AC / DC rectifier module; Each AC / DC rectifier module includes a left bridge arm and a right bridge arm, and the cascade structure is that the middle output end of the right bridge arm of the first AC / DC rectifier module is connected to the middle output end of the left bridge arm of the second AC / DC rectifier module; the middle output end of the left bridge arm of the first AC / DC rectifier module is connected in series with the reactor.

4. The multi-port new energy conversion device for electrified railway traction power supply system according to claim 3, characterized in that: The DC bus system includes i groups of DC buses, each group of DC buses includes a positive bus and a negative bus, and each group of DC buses is isolated from each other; the first group of DC buses is connected to the DC end of the first AC / DC rectifier module of each subunit of the single-phase rectifier system; similarly, the mth group of DC buses is connected to the DC end of the mth AC / DC rectifier module of each subunit of the single-phase rectifier system; in addition, each group of DC buses is connected to the energy conversion system.

5. The multi-port new energy conversion device for electrified railway traction power supply system according to claim 4, characterized in that: The energy conversion system comprises multiple groups of DC / DC converters and DC / AC converters, and each group of DC bus is connected with one or both of the DC / DC converter and the DC / AC converter; wherein the number of DC / DC converters connected to each group of DC bus is the same, and the number of DC / AC converters connected to each group of DC bus is the same; the output end of each DC / DC converter and DC / AC converter is connected with one or several of the photovoltaic power generation system, the wind power generation system or the energy storage system.

6. The DC voltage equalization control method for the multi-port new energy conversion device of the electrified railway traction power supply system according to any one of claims 1-5, characterized in that: The multi-port new energy conversion device connects the DC ends of the AC / DC rectifier modules at the same position of different sub-units of the single-phase rectification system through the DC bus, so that the energy exchange between the AC / DC rectifier modules at the same position of different sub-units can be realized through the DC bus, that is, the energy exchange between the multiple groups of cascaded converters is realized, another energy equalization channel is provided for the DC voltage equalization control, and the equalization control of the DC voltage is accelerated. On the basis of the traditional DC voltage equalization control of the cascaded converter, the cross-unit DC voltage equalization control between the multiple groups of cascaded converters is added, and specifically, the power adjustment amount of the cross-unit DC voltage equalization control is superimposed on the active power instruction of each rectifier module of each group of cascaded converters. 7.The DC voltage equalization control method for the multi-port new energy conversion device of the electrified railway traction power supply system according to claim 6, characterized in that: In the power adjustment amount generation method of the cross-unit DC voltage equalization control, all the AC / DC rectifier modules at the same position of each subsystem of the single-phase rectification system are subjected to the cross-unit DC voltage equalization control, and since each subsystem has i AC / DC rectifier modules, i groups of cross-unit DC voltage equalization control are needed in total. Specifically, the average DC voltage of all the AC / DC rectifier modules at the same position of the single-phase rectification system is calculated, and then the average DC voltage is subtracted from the DC voltage of each AC / DC rectifier module at the position to obtain each difference value, each difference value passes through a regulator; the output of each regulator is multiplied by the steady-state value Ps of the active power on the AC side, and the power adjustment amount of the cross-unit DC voltage equalization control of each AC / DC rectifier module at the position is obtained.

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