Energy interconnection transformation system used between new energy power station and railway traction power supply system and control method

Abstract

The invention belongs to the technical field of alternating-current electrified railway traction power supply, and particularly relates to an energy interconnection transformation system and a control method used between a new energy power station and a railway traction power supply system. According to the electric energy conversion topology and energy interconnection control method for energy interconnection between the new energy power station and the railway traction power supply system, the new energy power station can supply power to the railway traction power supply system, and high-capacity new energy can provide clean electric energy to the railway traction power supply system; the green level of railway traction power supply energy consumption is improved, and the problem that the power grid absorption capacity is insufficient generally faced by new energy power stations can be solved. Meanwhile, regenerative braking electric energy of the railway traction load can be fed back to the new energy power station, good electric energy quality is guaranteed, and the problems that after the traction load is consumed, remaining new energy is called remaining electricity for short, the quality of electric energy fed back to a power grid through an existing traction substation is poor, and economic benefits are not generated are solved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of AC electrified railway traction power supply, and particularly relates to an energy interconnection conversion system and a control method between a new energy power station and a railway traction power supply system. BACKGROUND

[0002] With the expansion of the construction scale of new energy power stations, the carrying capacity of the power grid is increasingly tested, and the load supplied by the power grid in many areas cannot fully accommodate new energy. Under the current background, it is urgent to explore new measures for large energy consumers to improve new energy consumption and solve the problem of insufficient new energy consumption capacity on the power grid side. Electrified railways play a crucial role in the economic and social development of countries around the world. At present, there are many researches and explorations on the application of new energy power generation technology in the field of rail transit. Distributed photovoltaic and energy storage are connected to the electrified railway traction power supply system, which is in the demonstration application stage. The publicly reported new energy applied to electrified railways, especially the new energy connected to the railway traction power supply system, is mostly built along the railway, such as the roof of the station house, the ground of the station yard, and the railway slope. The construction area of new energy along the railway is limited, so the installed capacity of new energy is generally small, mostly tens of kW to several MW. Therefore, the construction capacity of new energy for the railway traction power supply system is often limited.

[0003] Secondly, the railway traction power supply system is single-phase power supply, and the traction transformer is needed to convert three-phase power into one or two single-phase power. Therefore, the power conversion between the power grid side and the traction side is asymmetric conversion, which will generate a large negative sequence current on the power grid side under the condition that the railway traction load is a single-phase load, thereby increasing the voltage unbalance degree of the power grid side. Therefore, a large amount of regenerative braking electric energy generated by electric locomotives or motor trains is fed back to the power grid in an asymmetric manner, which is not expected by the power grid, and therefore the regenerative braking electric energy fed back does not have economic value.

[0004] The new energy along the railway is generally connected to the traction bus of the railway traction substation and consumed by the traction load. The remaining new energy, referred to as residual power, is stored in expensive energy storage or fed back to the power grid. However, for the reasons mentioned above, the residual power fed back to the power grid will also generate a large negative sequence current on the power grid side, which also does not have economic value.

[0005] In the prior art, for example, a patent for an invention of a multi-energy complementary off-grid traction power supply system based on battery energy storage is disclosed in Chinese Patent No. CN201810934439.X, as shown in FIG. 1. Three-phase wind power generation, three-phase photovoltaic power generation, and energy storage units supply power to a three-phase AC bus, and a traction transformer connected to the three-phase AC bus supplies power to the traction grid. Similarly, a railway traction power supply system based on photovoltaic power generation is disclosed in Chinese Patent No. CN201621211746.8, as shown in FIG. 2. The system comprises a photovoltaic power generation unit, a battery energy storage unit, a traction transformer, and a traction grid. The photovoltaic power generation unit and the battery energy storage unit supply power to the traction transformer, and the traction transformer supplies power to the traction grid. Figure 1 a ​Figure 1 b As shown in the drawings, patent No. CN201621212838.8 discloses a high-efficiency energy-saving railway traction power supply system, as shown in Figure 1 c As shown in the drawings, patent No. CN201720123338.5 discloses a high-speed railway traction power supply system containing a photovoltaic power supply, as shown in Figure 1 d As shown in the drawings, the above-mentioned patent is only applicable to the scene where the three-phase inverter is connected to the traction network through the Vv, Ynd11, Dyn11 different wiring form transformer. The three-phase power supply for new energy access in the above-mentioned patent claim needs to be transformed from the two traction buses of the traction substation through different form transformers to maintain, so the capacity of the three-phase power supply is much smaller than that of the traditional power grid, the accessible new energy capacity is smaller, and the system operation stability is significantly reduced due to the small capacity of the three-phase power supply.

[0006] Patent No. CN201820581706.5 discloses a braking energy recovery traction photovoltaic power generation system, as shown in Figure 2 As shown in the drawings, patent No. CN201820581713.5 discloses a regenerative braking energy recovery railway photovoltaic energy storage system, patent No. CN201721334804.0 discloses a multi-energy complementary grid-connected system applied to electrified railways, and papers such as "Harmonic Interaction and Adaptability Analysis of Photovoltaic Access to Traction Power Supply System" and "Electrified Railway Back-to-Back Photovoltaic Power Generation System and Control Strategy" all disclose or propose different forms of photovoltaic power generation or wind-solar storage power generation systems applied to electrified railway traction substations, which all need to connect an AC / DC / AC converter through two transformers, and the DC end of the AC / DC / AC converter is connected to new energy generation, energy storage, etc. Since the above-mentioned photovoltaic power generation system can only access the DC end of the AC / DC / AC converter, it is suitable for small-capacity distributed new energy access to the railway traction power supply system near the traction substation, but not suitable for large-capacity new energy access to the railway traction power supply system, especially for long-distance new energy access.

[0007] In the field of large-capacity new energy application in electrified railway traction power supply system, the existing technology mainly has the following shortcomings: 1. In the existing technical solutions applied to electrified railway traction power supply system, new energy is mostly accessed to the traction side of the traction power supply, and is accessed through the DC side of the AC / DC / AC converter. Limited by the lack of photovoltaic construction site along the railway, the capacity of new energy accessed by the railway traction power supply system is small, which is not suitable for large-capacity new energy access to the railway traction power supply system, especially for long-distance new energy access.

[0008] 2. In existing technical solutions applied to electrified railway traction power supply systems, some scholars have proposed a scheme to connect new energy sources through three-phase power. However, the three-phase power supply in these schemes requires voltage transformation from two traction busbars at the traction substation by a transformer. Therefore, the capacity of this three-phase power supply is much smaller than that of the traditional power grid, resulting in a smaller capacity of new energy sources that can be connected. Furthermore, the small capacity of the three-phase power supply significantly reduces the stability of the system operation.

[0009] 3. Regarding the feedback of surplus electricity and regenerative braking energy to the grid, both of the above-mentioned schemes involve feeding the remaining renewable energy or regenerative braking energy after the traction load has been absorbed back to the grid through the traction transformers in the traction substation. Because the traction transformers in railway traction substations are asymmetrical transformers, the energy fed back to the grid will generate a large amount of negative sequence current, exacerbating the voltage imbalance on the grid side and adversely affecting the power quality. Furthermore, due to the electricity billing principles on the grid side of the traction substation, the energy fed back to the grid is not included in the electricity billing calculation; therefore, feeding renewable energy back to the grid through the traction substation generally does not generate economic benefits.

[0010] Therefore, in view of the above three technical shortcomings or deficiencies, there is an urgent need for an energy interconnection and conversion system and control method that can enable large-capacity new energy to be connected to the railway traction power supply system, and the surplus power to be fed into the grid without deteriorating the power quality on the grid side, and even generate certain economic benefits. Summary of the Invention

[0011] The purpose of this invention is to provide an energy interconnection and conversion system and control method for connecting a new energy power plant and a railway traction power supply system. The new energy power plant, as a new energy source, supplies power to the railway traction power supply system through the energy interconnection and power conversion system, enabling large-capacity new energy to provide clean electricity to the railway traction power supply system and improving the greening level of energy use in railway traction power supply. Furthermore, surplus electricity can be improved in power quality through three-phase symmetrical conversion and fed back to the grid from the new energy power plant, ensuring both grid-side power quality and generating revenue from surplus electricity fed into the grid.

[0012] The specific technical solution adopted by this invention is as follows: An energy interconnection and conversion system for new energy power plants and railway traction power supply systems includes a main circuit and a control circuit. The main circuit connects the existing new energy power station and the railway traction power supply system; wherein, the main circuit connects to the low-voltage end of the three-phase grid-connected transformer of the existing new energy power station, that is, the new energy generator set side, without requiring any modification to the high-voltage grid-connected side of the existing new energy power station; at the same time, the main circuit connects to the two traction bus ends of the railway traction substation. The control circuit collects information from new energy power plants and railway traction substations. The information from new energy power plants mainly includes the output signals of the voltage transformers and current transformers on the low-voltage side of the three-phase grid-connected transformers, while the information from railway traction substations mainly includes the voltage and current signals on the traction load side.

[0013] A control method for an energy interconnection and conversion system between a new energy power plant and a railway traction power supply system includes the following steps: Step 1: Collect the output signals of the voltage transformer and current transformer of the new energy power station, and calculate the new energy power generation P. ng The calculated new energy power generation P ng The control circuit of the energy interconnection and conversion system is transmitted via wired or wireless transmission. Step 2: Collect the output signals of the voltage transformer and current transformer of phase a of the railway traction substation, and calculate the traction load power P of phase a. ra A positive value indicates that the traction load absorbs electrical energy and the train is in traction mode; a negative value indicates that the traction load generates electrical energy and the train is in regenerative braking mode; the same applies below. Collect the output signals of the voltage transformer and current transformer of phase b in the railway traction substation, and calculate the traction load power P of phase b. rb ; Step 3: Identify the traction load conditions for the traction load power of phase a and phase b respectively. When the load power is greater than 0, it is considered to be the traction condition; when the load power is less than 0, it is considered to be the regenerative braking condition. Step 4: Generate two grid-connected unit power commands for the traction load conditions of phase a and phase b respectively: When the traction load of phase a is traction condition P ra >0, and the power generation of new energy sources P ng When the value is greater than 0, the output power command of the single-phase grid-connected unit of phase a is P×a=Min (P ra P ng S Cona S Reca ); where S Cona and S Reca Converter C ona and three-phase rectifier R ec a is the rated capacity; Min() is the minimum value function, P×a greater than 0 indicates that electrical energy is supplied to the traction load, the same below; When the traction load of phase a is in regenerative braking condition P ra When <0, the output power command of the single-phase grid-connected unit of phase a is P×a=Max(P ra -S Cona -S Reca ); where S Cona and SReca Converter C ona and three-phase rectifier R eca Rated capacity; Max() is the maximum value function; P×a less than 0 indicates that electrical energy is absorbed from the traction load, the same below; When the traction load of phase b is the traction condition P rb >0, and the power generation of new energy sources P ng When the value is greater than 0, the output power command of the b-phase single-phase grid-connected unit is P×b=Min (P rb P ng S Conb S Recb ); where S Conb and S Recb Converter C onb The rated capacity of the three-phase rectifier Recb; When the traction load of phase b is in regenerative braking condition P rb When <0, the output power command of the b-phase single-phase grid-connected unit is P×b=Max(P rb -S Conb -S Recb ); where S Conb and S Recb Converter C onb and three-phase rectifier R ecb Rated capacity; Step 5: Based on the power commands from the two grid-connected units, perform converter C... ona and converter C onb The closed-loop control typically employs a dual closed-loop control system with an outer voltage or power loop and an inner current loop to achieve operation according to the aforementioned power command; simultaneously, the two single-phase rectifiers R eca and R ecb Dual closed-loop control, consisting of an outer voltage loop and an inner current loop, is implemented to stabilize DC voltage and achieve bidirectional power transmission.

[0014] The technical effects achieved by this invention are as follows: This invention solves the problem of insufficient photovoltaic construction sites along railway stations, resulting in a limited capacity of renewable energy for railway traction power supply systems. Existing methods for constructing renewable energy power generation systems around railway stations are limited by site size, with renewable energy, such as photovoltaic power generation, generally not exceeding 6MW. This invention utilizes existing renewable energy power plants as the renewable energy source, no longer limiting itself to constructing renewable energy systems around railway stations. Therefore, it can provide tens or even hundreds of MW of renewable energy to the railway traction power supply system, significantly increasing the renewable energy capacity.

[0015] This invention solves the problem of large negative sequence currents caused by the feedback of surplus electricity from new energy sources and regenerative braking energy to the power grid through railway traction substations, which exacerbates voltage imbalance on the grid side. This patent uses a three-phase rectifier (Reca and Recb) to perform symmetrical energy conversion of surplus electricity or regenerative braking energy, which eliminates the negative sequence component of the grid-side current, thus avoiding any adverse impact on the voltage imbalance on the grid side.

[0016] In this invention, the feedback of surplus electricity from renewable energy sources and regenerative braking energy to the power grid can generate economic benefits. This patent feeds surplus electricity or regenerative braking energy back to the power grid through existing renewable energy power plants, avoiding feedback from traction substations. Since the grid-connected electricity from renewable energy power plants is profitable, the proposed solution of feeding surplus electricity from renewable energy sources and regenerative braking energy back to the power grid through existing renewable energy power plants can also generate economic benefits. Attached Figure Description

[0017] Figure 1 is a schematic diagram of the prior art; Figure 2 This is a schematic diagram of existing technology; Figure 3 This is a connection diagram of the energy interconnection and conversion system of the present invention; Figure 4 This is the main circuit structure of the energy interconnection and conversion system of the present invention; Figure 5 It is a control system block diagram. Detailed Implementation

[0018] 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.

[0019] like Figures 3-5 As shown, an energy interconnection and conversion system for new energy power plants and railway traction power supply systems, such as... Figure 3 As shown, it includes the main circuit and the control circuit; The main circuit connects the existing new energy power station and the railway traction power supply system; wherein, the main circuit connects to the low-voltage end of the three-phase grid-connected transformer of the existing new energy power station, that is, the new energy generator set side, without requiring any modification to the high-voltage grid-connected side of the existing new energy power station; at the same time, the main circuit connects to the two traction bus ends of the railway traction substation. The control circuit collects information from new energy power plants and railway traction substations. The information from new energy power plants mainly includes the output signals of the voltage transformers and current transformers on the low-voltage side of the three-phase grid-connected transformers, while the information from railway traction substations mainly includes the voltage and current signals on the traction load side.

[0020] Preferably, the main circuit includes a three-phase incoming line unit, a three-phase transmission line, a three-phase rectifier unit, a phase a single-phase grid-connected unit, and a phase b single-phase grid-connected unit, such as... Figure 4 As shown; among them, the three-phase incoming line unit is on the side of the new energy power station, and the three-phase rectifier unit, the a-phase single-phase grid-connected unit, and the b-phase single-phase grid-connected unit are on the side of the railway traction substation.

[0021] Preferably, the three-phase incoming line unit includes a circuit breaker and a current transformer, with its input end connected to the low-voltage end of the three-phase grid-connected transformer of the existing new energy power station, and its output end connected to the three-phase transmission line.

[0022] Preferably, the three-phase transmission line can be a three-phase overhead transmission line or a three-phase cable transmission line, enabling the long-distance transmission of electrical energy from the new energy power station to the railway traction substation.

[0023] Preferably, the three-phase rectifier unit includes an input switch, a voltage transformer, a current transformer, and two three-phase rectifiers R. eca and R ecb The input end of the three-phase rectifier unit is connected to the three-phase transmission line, and the output end is connected to the DC bus to realize the conversion of electrical energy between the three-phase AC side and the DC side, and to realize the bidirectional transmission of electrical energy. Among them, the two three-phase rectifiers are connected in parallel on the AC side, and the DC side is connected to a set of DC buses respectively.

[0024] Preferably, the single-phase grid-connected unit of phase a includes circuit breaker II, voltage transformer PTa, current transformer CTa, transformer TTa, and converter C. ona The DC side of the single-phase grid-connected unit is connected to a set of DC buses, and the AC side is connected to the phase a traction bus of the railway traction substation; this realizes the conversion of electrical energy between the DC bus and the phase a traction bus, and achieves bidirectional transmission of electrical energy.

[0025] Preferably, the b-phase single-phase grid-connected unit includes a circuit breaker, a voltage transformer PTb, a current transformer CTb, a transformer TTb, and a converter C. onb The DC side of the b-phase single-phase grid-connected unit is connected to another set of DC buses, and the AC side is connected to the b-phase traction bus of the railway traction substation, realizing the power conversion between the DC bus and the b-phase traction bus and realizing bidirectional power transmission.

[0026] Preferably, the two sets of DC buses can also be connected to one or both of a new energy power generation system and an energy storage system; wherein, the new energy power generation system can be arranged along the railway line and in surrounding stations.

[0027] A control method for an energy interconnection and conversion system between a new energy power plant and a railway traction power supply system includes the following steps: Step 1: Collect the output signals of the voltage transformer and current transformer of the new energy power station, and calculate the new energy power generation P. ng The calculated new energy power generation P ng The control circuit of the energy interconnection and conversion system is transmitted via wired or wireless transmission. Step 2: Collect the output signals of the voltage transformer and current transformer of phase a of the railway traction substation, and calculate the traction load power P of phase a. ra A positive value indicates that the traction load absorbs electrical energy and the train is in traction mode; a negative value indicates that the traction load generates electrical energy and the train is in regenerative braking mode; the same applies below. Collect the output signals of the voltage transformer and current transformer of phase b in the railway traction substation, and calculate the traction load power P of phase b. rb ; Step 3: Identify the traction load conditions for the traction load power of phase a and phase b respectively. When the load power is greater than 0, it is considered to be the traction condition; when the load power is less than 0, it is considered to be the regenerative braking condition. Step 4: Generate two grid-connected unit power commands for the traction load conditions of phase a and phase b respectively: When the traction load of phase a is traction condition P ra >0, and the power generation of new energy sources P ng When the value is greater than 0, the output power command of the single-phase grid-connected unit of phase a is P×a=Min (P ra P ng S Cona S Reca ); where S Cona and S Reca Converter C ona and three-phase rectifier R ec a is the rated capacity; Min() is the minimum value function, P×a greater than 0 indicates that electrical energy is supplied to the traction load, the same below; When the traction load of phase a is in regenerative braking condition P ra When <0, the output power command of the single-phase grid-connected unit of phase a is P×a=Max(P ra -S Cona -S Reca ); where S Cona and S Reca Converter C ona and three-phase rectifier R eca Rated capacity; Max() is the maximum value function; P×a less than 0 indicates that electrical energy is absorbed from the traction load, the same below; When the traction load of phase b is the traction condition P rb >0, and the power generation of new energy sources P ngWhen the value is greater than 0, the output power command of the b-phase single-phase grid-connected unit is P×b=Min (P rb P ng S Conb S Recb ); where S Conb and S Recb Converter C onb The rated capacity of the three-phase rectifier Recb; When the traction load of phase b is in regenerative braking condition P rb When <0, the output power command of the b-phase single-phase grid-connected unit is P×b=Max(P rb -S Conb -S Recb ); where S Conb and S Recb Converter C onb and three-phase rectifier R ecb Rated capacity; Step 5: Based on the power commands from the two grid-connected units, perform converter C... ona and converter C onb The closed-loop control typically employs a dual closed-loop control system with an outer voltage or power loop and an inner current loop to achieve operation according to the aforementioned power command; simultaneously, the two single-phase rectifiers R eca and R ecb The system employs dual closed-loop control with an outer voltage loop and an inner current loop to stabilize the DC voltage and achieve unity power factor operation on the AC side. This allows for bidirectional power transmission of the system based on the operating states of the two converters.

[0028] The working principle of this invention is as follows: The energy interconnection and conversion system structure of this invention connects the renewable energy power station and the railway traction busbar, enabling direct green electricity supply from the large-capacity renewable energy power station to the railway traction load. The energy interconnection and conversion system includes a three-phase incoming line unit, a three-phase transmission line, a three-phase rectifier unit, an a-phase single-phase grid-connected unit, and a b-phase single-phase grid-connected unit. The three-phase incoming line unit is located on the renewable energy power station side, connecting to the low-voltage end of the existing renewable energy power station's three-phase grid-connected transformer, i.e., the renewable energy generator set side. The three-phase rectifier unit, the a-phase single-phase grid-connected unit, and the b-phase single-phase grid-connected unit are located on the railway traction substation side, with two single-phase grid-connected units respectively connecting to the two traction buses of the railway traction substation.

[0029] This invention discloses a control method for an energy interconnection and conversion system. This method comprehensively utilizes the power generation status and traction load status of the renewable energy power station to achieve real-time control of energy interconnection between the renewable energy power station and railway traction power supply. It calculates the renewable energy power generation and the traction load power of phases a and b of the traction substation. Then, based on the magnitude of the traction load power, it identifies whether the traction load is in traction or regenerative braking mode. Next, based on the output power status of the renewable energy power station, the traction load mode, and the equipment capacity, it calculates the output power of the single-phase grid-connected converters for phases a and b, respectively. This allows the photovoltaic power from the existing renewable energy power station to be absorbed by the traction load when there is traction load and it is in traction mode, and to be fed back to the grid when there is no traction load. Furthermore, when the traction load is in regenerative braking mode, the regenerative braking energy can also be fed back to the grid through the renewable energy power station.

[0030] This invention solves the problem of insufficient photovoltaic construction sites along railway stations, resulting in a limited capacity of renewable energy for railway traction power supply systems. Existing methods for constructing renewable energy power generation systems around railway stations are limited by site size, with renewable energy, such as photovoltaic power generation, generally not exceeding 6MW. This invention utilizes existing renewable energy power plants as the renewable energy source, no longer limiting itself to constructing renewable energy systems around railway stations. Therefore, it can provide tens or even hundreds of MW of renewable energy to the railway traction power supply system, significantly increasing the renewable energy capacity.

[0031] This invention solves the problem of large negative sequence currents caused by the feedback of surplus electricity from new energy sources and regenerative braking energy to the power grid through railway traction substations, which exacerbates voltage imbalance on the grid side. This patent uses a three-phase rectifier (Reca and Recb) to perform symmetrical energy conversion of surplus electricity or regenerative braking energy, which eliminates the negative sequence component of the grid-side current, thus avoiding any adverse impact on the voltage imbalance on the grid side.

[0032] In this invention, the feedback of surplus electricity from renewable energy sources and regenerative braking energy to the power grid can generate economic benefits. This patent feeds surplus electricity or regenerative braking energy back to the power grid through existing renewable energy power plants, avoiding feedback from traction substations. Since the grid-connected electricity from renewable energy power plants is profitable, the proposed solution of feeding surplus electricity from renewable energy sources and regenerative braking energy back to the power grid through existing renewable energy power plants can also generate economic benefits.

[0033] 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 power interconnection conversion system for a new energy power station and a railway traction power supply system, as shown in Figure 3, characterized in that: The main circuit and the control circuit are included. The main circuit is connected with both the existing new energy power station and the railway traction power supply system; wherein, the main circuit is connected with the low-voltage end of the three-phase grid-connected transformer of the existing new energy power station, i.e. the new energy generator set side; at the same time, the main circuit is connected with the two traction bus bars of the railway traction substation. The control circuit collects information of the new energy power station and information of the railway traction substation; the information of the new energy power station mainly includes output signals of the low-voltage side voltage transformer and current transformer of the three-phase grid-connected transformer, and the information of the railway traction substation mainly includes voltage and current signals of the traction load side.

2. The energy interconnection conversion system between new energy power station and railway traction power supply system according to claim 1, characterized in that: The main circuit includes a three-phase incoming line unit, a three-phase transmission line, a three-phase rectifier unit, an a-phase single-phase grid-connected unit and a b-phase single-phase grid-connected unit, as shown in FIG. 4; wherein, the three-phase incoming line unit is at the new energy power station side, and the three-phase rectifier unit, the a-phase single-phase grid-connected unit and the b-phase single-phase grid-connected unit are at the railway traction substation side.

3. The energy interconnection conversion system between new energy power station and railway traction power supply system according to claim 2, characterized in that: The three-phase incoming line unit includes a circuit breaker and a current transformer, and the input end is connected to the low-voltage end of the three-phase grid-connected transformer of the existing new energy power station, and the output end is connected to the three-phase transmission line.

4. The energy interconnection conversion system between new energy power station and railway traction power supply system according to claim 3, characterized in that: The three-phase transmission line can be a three-phase overhead transmission line or a three-phase cable transmission line, which realizes long-distance transmission of the electric energy of the new energy power station to the railway traction substation.

5. The energy interconnection conversion system between new energy power station and railway traction power supply system according to claim 4, characterized in that: The three-phase rectifying unit comprises an incoming line switch, a voltage transformer, a current transformer and two three-phase rectifiers R eca and R ecb The input end of the three-phase rectifying unit is connected to a three-phase transmission line, and the output end is connected to a DC bus, so as to realize the electric energy conversion between the three-phase AC side and the DC side and the bidirectional transmission of electric energy; wherein the AC sides of the two three-phase rectifiers are connected in parallel, and the DC sides are respectively connected to a group of DC buses.

6. The energy interconnection conversion system between new energy power station and railway traction power supply system according to claim 5, characterized in that: The a-phase single-phase grid-connected unit comprises a circuit breaker II, a voltage transformer PTa, a current transformer CTa, a transformer TTa and a converter C ona The a-phase single-phase grid-connected unit is connected to a group of DC bus bars at the DC side and connected to an a-phase traction bus bar of a railway traction substation at the AC side, realizes electric energy conversion between the DC bus bar and the a-phase traction bus bar, and realizes bidirectional transmission of electric energy.

7. The energy interconnection conversion system between new energy power station and railway traction power supply system according to claim 6, characterized in that: The b-phase single-phase grid-connected unit comprises a circuit breaker three, a voltage transformer PTb, a current transformer CTb, a transformer TTb and a converter C onb The b-phase single-phase grid-connected unit is connected to another group of DC bus bars at the DC side and to a b-phase traction bus bar of the railway traction substation at the AC side, realizes electric energy conversion between the DC bus bars and the b-phase traction bus bar, and realizes bidirectional transmission of electric energy.

8. The energy interconnection conversion system between new energy power station and railway traction power supply system according to claim 7, characterized in that: The two groups of DC bus bars can also be connected with one or both of the new energy power generation system and the energy storage system; wherein, the new energy power generation system can be arranged along the railway and in the surrounding station yard.

9. The control method of claim 1-8, wherein, The method comprises the following steps: Step 1: collect the output signal of the voltage transformer and the current transformer of the new energy power station, and calculate the new energy power P ng ; the calculated new energy power P ng is transmitted to the control circuit of the energy interconnection conversion system in a wired transmission or wireless transmission manner. Step 2: Collect the output signals of the voltage transformer and the current transformer of the a-phase of the railway traction substation, and calculate the a-phase traction load power P ra ; a positive value indicates that the traction load consumes electric energy, and the train is in a traction working condition; a negative value indicates that the traction load generates electric energy, and the train is in a regenerative braking working condition; the same below. Collecting the output signals of the voltage transformer and the current transformer of phase b of a railway traction substation, calculating the traction load power P of phase b rb ; Step 3: identify the traction load working condition for the a-phase traction load power and the b-phase traction load power respectively; when the load power is greater than 0, it is considered as a traction working condition, and when the load power is less than 0, it is considered as a regenerative braking working condition; Step 4: generate two grid-connected unit power commands for the a-phase and b-phase traction load working conditions respectively: When the a-phase traction load is the traction working condition P ra > 0, and the new energy power generation power P ng > 0, the a-phase single-phase grid-connected unit output power instruction Pxa= Min (P ra , P ng , S Cona , S Reca ); where S Cona and S Reca are the ratings of the converter C ona and the three-phase rectifier R ec respectively; Min() is the minimum function, and P x a is greater than 0, which means that the electric energy is supplied to the traction load, and the same below. When the a-phase traction load is a regenerative braking condition P ra <0, the a-phase single-phase grid-connected unit outputs a power command Pxa=Max(P ra ,-S Cona ,-S Reca ); wherein S Cona and S Reca are the rated capacities of the converter C ona and the three-phase rectifier R eca , respectively; Max() is a maximum function; Pxa<0 indicates that electric energy is absorbed from the traction load, and the same applies below. When the b-phase traction load is the traction working condition P rb > 0, and the new energy power generation power P ng > 0, the b-phase single-phase grid-connected unit output power instruction P x b = Min (P rb , P ng , S Conb , S Recb ) is output; wherein S Conb and S Recb are the rated capacities of the converter C onb and the three-phase rectifier Recb respectively. When the b-phase traction load is a regenerative braking condition P rb <0, the b-phase single-phase grid-connected unit outputs a power command Pxb=Max(P rb ,-S Conb ,-S Recb ); wherein S Conb and S Recb are the rated capacities of the converter C onb and the three-phase rectifier R ecb , respectively. Step 5: According to the power instruction of two grid-connected units, the converter C ona and the closed-loop control of the converter C onb , generally, the double closed-loop control of voltage or power outer loop and current inner loop is adopted to achieve the purpose of running according to the above power instruction; at the same time, the double closed-loop control of voltage outer loop and current inner loop is carried out on two single-phase rectifiers R eca and R ecb to stabilize the DC voltage and realize bidirectional transmission of electric energy.

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