Medium-voltage direct-current traction power supply system simulation experiment platform with distributed new energy access

Abstract

The invention provides a medium-voltage direct-current traction power supply system simulation experiment platform with distributed new energy access. The medium-voltage direct-current traction power supply system simulation experiment platform comprises a simulation traction network, a system control module, and a traction substation simulation device, an energy storage simulation device and a new energy power generation simulation device which are electrically connected with the simulation traction network, the simulation traction network comprises a plurality of network rail impedance simulation devices which are sequentially connected in series, each network rail impedance simulation device comprises a main control module, a stepping motor and an impedance regulator, the locomotive simulation devices are electrically connected with the impedance regulators respectively, and the stepping motors are used for adjusting impedance of the impedance regulators connected into the simulation traction network. Dynamic adjustment of traction network equivalent impedance is realized through the network rail impedance simulation device, so that the experiment platform can reproduce the operation state of a traction power supply system under the combined action of locomotive mobility and new energy fluctuation in an experiment environment; therefore, the method is used for carrying out experimental researches such as system stability analysis, coordination control strategy verification and typical fault condition simulation.

Description

Technical Field

[0001] This invention relates to the field of traction power supply for rail trains, and in particular to a simulation experimental platform for a medium-voltage DC traction power supply system with distributed new energy access. Background Technology

[0002] With the high-speed, high-density, and networked development of railway transportation, existing AC traction power supply systems have exposed inherent defects such as phase separation, poor power quality, and limited power supply distance. More importantly, they suffer from inflexible and unfriendly integration of renewable energy sources. In contrast, medium-voltage DC traction power supply systems, relying on a continuous DC traction network, not only overcome the shortcomings of traditional AC traction power supply but also, due to their high degree of power electronics, simple grid connection, flexible control, and strong support, are more suitable for local integration and consumption of renewable energy and efficient utilization of locomotive regenerative braking energy. Therefore, they are key to building a self-sufficient railway power supply network in the future.

[0003] However, the research and engineering application of medium-voltage DC traction power supply systems still face the following key technical challenges: 1. Locomotives have the characteristic of continuous movement along the line, and their equivalent electrical position changes over time, leading to continuous changes in the equivalent impedance of the traction network, node voltage distribution, and power flow direction. Existing simulation or experimental studies mostly use fixed impedance or static equivalent models, which are difficult to truly reflect the impact of dynamic changes in line electrical parameters on the system's operating state during locomotive operation. 2. The output of new energy power generation simulation devices has significant fluctuations and uncertainties. Under the condition of multiple new energy sources and multiple locomotives operating in parallel, the power fluctuations of new energy sources and the changes in locomotive loads are superimposed, which can easily cause voltage fluctuations and power imbalances in the traction network. Existing research mostly stays at the level of theoretical analysis or offline simulation, lacking a physical experimental platform that can verify the coordinated stability control strategy of new energy sources, energy storage, and traction substations in an experimental environment. 3. The fault conditions of the traction power supply system are characterized by their suddenness and wide impact. Faults such as DC-side short circuits, overvoltage, and sudden voltage drops are difficult to verify experimentally in actual railway systems. Existing experimental platforms cannot conduct controllable and repeatable experimental simulations of typical fault processes and their protective actions while ensuring safety. 4. The operating scenarios of the traction power supply system are significantly diverse. Under different line conditions, train operation methods, and new energy and energy storage configuration schemes, the system topology and operating scale vary considerably. Existing experimental platforms are mostly fixed structures, making it difficult to flexibly adjust the number and capacity of new energy sources, energy storage, and locomotives, and thus unable to support research on system operation mechanisms and verification of control strategies across multiple scenarios and schemes.

[0004] Therefore, there is an urgent need for a medium-voltage DC traction power supply system simulation experimental platform that can simultaneously reflect the locomotive's moving characteristics, the fluctuation characteristics of new energy sources, and the system stability control mechanism, and supports the flexible configuration of fault simulation and operating scenarios, so as to make up for the shortcomings of existing research in experimental verification. Summary of the Invention

[0005] The purpose of this invention is to provide a simulation experimental platform for a medium-voltage DC traction power supply system with distributed renewable energy access. This platform can solve the technical problem that existing experimental platforms cannot reflect the locomotive's moving characteristics and the fluctuation characteristics of renewable energy sources, and can be used for experimental research such as system stability analysis, coordinated control strategy verification, and simulation of typical fault conditions.

[0006] A simulation experimental platform for a medium-voltage DC traction power supply system with distributed new energy access includes a simulated traction network and a system control module, as well as a traction substation simulation device, an energy storage simulation device, and a new energy power generation simulation device that are electrically connected to the simulated traction network.

[0007] The simulated traction network, traction substation simulation device, energy storage simulation device, locomotive simulation device, and new energy power generation simulation device are all signal-connected to the system control module. The simulated traction network includes several track impedance simulation devices connected in series. Each track impedance simulation device includes a main control module, a stepper motor, and an impedance regulator. The main control module is signal-connected to the system control module and the stepper motor. Several locomotive simulation devices are electrically connected to the impedance regulators of several track impedance simulation devices. The stepper motor is used to adjust the impedance of the impedance regulator connected to the simulated traction network.

[0008] Optionally, the impedance regulator is a variable resistor, and the locomotive simulation device is connected to the sliding brush of the variable resistor;

[0009] During impedance adjustment, the system control module transmits control information to the main control module, which controls the stepper motor to rotate. The stepper motor drives the sliding brush to slide, thereby adjusting the impedance of the two ends of the sliding brush connected to the simulated traction network, simulating the movement of the locomotive in the actual system.

[0010] Optionally, the traction substation simulation device, energy storage simulation device, new energy power generation simulation device and locomotive simulation device all include a DC circuit breaker for connecting to the simulated traction network power.

[0011] The traction substation simulation device, energy storage simulation device, new energy power generation simulation device, and locomotive simulation device selectively connect or disconnect the simulated traction network through the switching on and off of the DC circuit breaker.

[0012] Optionally, the simulation steps for the operating characteristics of the medium-voltage DC traction power supply system under the conditions of new energy fluctuations and changes in vehicle load are as follows:

[0013] S1: The system control module selectively engages or disengages the corresponding new energy power generation simulation device, energy storage simulation device, and locomotive simulation device based on the preset traffic density and the output curve of the new energy power generation simulation device, thereby constructing traction power supply system operation scenarios with different new energy penetration ratios, different energy storage configuration scales, and different locomotive load combinations.

[0014] S2: Issue power setting commands and operating mode commands to the simulated devices in operation, and set their power levels and operating states.

[0015] S3: Under different operating scenarios of traction power supply systems with different numbers of new energy access, different energy storage configuration capacities, and different locomotive operating load combinations, the traction power supply system generates different voltage and power distribution states. Experimental verification and effect evaluation are conducted on the system stability control strategy, power flow regulation strategy, and protection control strategy.

[0016] Optionally, in step S3, when considering the impact of output fluctuations and uncertainties in the new energy power generation simulation device, the simulation steps for system stability analysis and control are as follows:

[0017] S3.1.1: The system control module acquires the grid-connected voltage, current, power, line equivalent impedance, and state of charge of the energy storage simulation device uploaded by each simulation device;

[0018] S3.1.2: Analyze the power coupling relationship under the conditions of output fluctuation of new energy power generation simulation device, locomotive load change and multi-source access, and analyze the impact mechanism of output fluctuation and uncertainty of new energy power generation simulation device on system voltage stability and power distribution;

[0019] S3.1.3: When the output of the new energy power generation simulation device fluctuates or the operating status of the simulated traction network changes, the system control module determines the impact of the output of the new energy power generation simulation device on the system stability based on the voltage deviation, power fluctuation amplitude and line equivalent impedance change parameters of the simulated traction network, and issues an operating mode switching command to the new energy power generation simulation device.

[0020] S3.1.4: The system control module sends charging and discharging control commands to the bidirectional DC-DC converter of the energy storage simulation device based on the state of charge, power constraints, and output variation of the new energy power generation simulation device. The energy storage simulation device compensates for the output fluctuations of the new energy power generation simulation device through bidirectional energy regulation, thereby maintaining the stability of the traction grid voltage and system power balance.

[0021] Optionally, the new energy power generation simulation device also includes a grid-connected converter, and the operation mode switching command is used to control the grid-connected converter to switch between maximum power point tracking mode, power limiting mode and DC voltage support mode.

[0022] Optionally, the simulation experiment steps for system power flow control are as follows:

[0023] S3.2.1: The system control module collects real-time operating information uploaded by each simulation device;

[0024] S3.2.2: Calculate the power flow distribution of the system;

[0025] S3.2.3: Issue power regulation commands to the energy storage simulation device and the traction substation simulation device;

[0026] S3.2.4: The energy storage simulation device smooths out power fluctuations in the locomotive simulation device and the new energy power generation simulation device, and the traction substation simulation device makes up for the power shortage.

[0027] Optionally, the specific method for simulating system faults in step S3 is as follows:

[0028] Simulation of overvoltage fault in the system: The locomotive simulation device is controlled to be in regenerative mode, the bidirectional DC-DC converter in the energy storage simulation device is locked, and the grid voltage is forced to rise, thus forming an overvoltage fault simulation.

[0029] Simulation of grid voltage drop fault: disconnect the power simulation module in the new energy power generation simulation device, lock the bidirectional DC-DC converter in the energy storage simulation device, force grid voltage drop, and form grid voltage drop fault simulation.

[0030] Simulation of short-circuit faults in the system: By introducing an external current source, short-circuit current is injected into the outlet of the traction substation, the midpoint of the line, and the power receiving point of the locomotive in the simulated traction network to form a short-circuit fault simulation.

[0031] Optionally, the specific method for simulating system faults in step S3 is as follows:

[0032] Simulation of system overvoltage fault: By limiting the power absorption of the bidirectional DC-DC converter in the traction substation simulation device or switching its operating mode through the system control module, it is prevented from absorbing excess energy from the traction network in time. When the locomotive regenerative braking or the output of new energy is large, the voltage of the traction network will continue to rise, thus forming an overvoltage fault simulation.

[0033] Simulation of sudden voltage drop in the system grid: The system control module controls the locomotive simulation device to quickly switch from coasting or low load conditions to traction conditions, so that the programmable electronic load or fixed load is put into operation instantly, and the output capacity of the energy storage simulation device is locked, causing a sudden increase in the load of the traction grid, thereby forming a sudden voltage drop simulation of the traction grid voltage.

[0034] Simulation of short-circuit faults in the system: By controlling the track impedance simulation device, the equivalent impedance of the corresponding node is adjusted to a minimum value to form an approximate short-circuit state, thereby simulating the occurrence process of short-circuit faults in the DC traction network.

[0035] Optionally, the specific method for simulating system faults in step S3 is as follows:

[0036] Simulation of system overvoltage fault: Under the condition that the new energy power generation simulation device maintains maximum power output and the traction load is small, the power regulation capability of the energy storage device and the traction substation is limited, so that the new energy output cannot be absorbed in time, causing the traction grid voltage to rise, forming a new energy-dominated overvoltage fault simulation.

[0037] Simulation of sudden voltage drop fault in the system grid: By limiting the output power of the simulation device in the traction substation or reducing its voltage setpoint through the system control module, it is unable to provide sufficient power support when the load is present, resulting in a drop in the traction grid voltage and forming a simulation of sudden voltage drop fault in the grid.

[0038] Simulation of system short-circuit faults: Controllable short-circuit branches are set at nodes corresponding to the outlet of traction substation, the midpoint of the line, or the power receiving point of the locomotive. The DC circuit breaker is controlled to close quickly through the system control module, so that the traction network forms a low-impedance path at the designated location, thereby realizing the simulation of DC short-circuit faults at different locations.

[0039] Because of the adoption of the above technical solution, the present invention has the following advantages:

[0040] 1. This application introduces a track impedance simulation device to achieve dynamic adjustment of the equivalent impedance of the traction network, which can effectively simulate the impact of changes in the electrical position of the locomotive on the system's operating status during its operation along the track in an experimental environment.

[0041] 2. This application constructs an experimental system that connects multiple sources in parallel, including new energy, energy storage, traction substation, and locomotive. It achieves centralized coordination control through a system control module, which can be used to study the system operation characteristics under the coupling conditions of output fluctuation of new energy power generation simulation device and locomotive load change.

[0042] 3. This application considers the bidirectional energy flow characteristics and state of charge constraints of energy storage devices, and can verify the effect of new energy and energy storage working together to participate in system power balance and voltage stability control on an experimental platform.

[0043] 4. This application can achieve controllable simulation of typical fault conditions such as overvoltage, sudden voltage drop and short circuit under laboratory conditions, providing support for experimental verification of protection strategies and control methods of traction power supply system.

[0044] 5. This application, through flexible access and capacity configuration of simulation devices such as new energy, energy storage and locomotives, can adapt to the experimental needs of different line conditions and operating scenarios, and has strong scalability and adaptability.

[0045] 6. This application constructs a simulation experimental platform based on the idea of ​​proportional scaling, which reduces experimental risks and implementation costs while maintaining an operating mechanism similar to that of a real medium-voltage DC traction power supply system.

[0046] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0047] The accompanying drawings of this invention are described below.

[0048] Figure 1 This is a structural block diagram of the simulation experimental platform for the medium-voltage DC traction power supply system of the present invention.

[0049] Figure 2 This is a structural block diagram of the traction substation simulation device of the present invention.

[0050] Figure 3 This is a structural block diagram of the energy storage simulation device of the present invention.

[0051] Figure 4 This is a structural block diagram of the locomotive simulation device of the present invention.

[0052] Figure 5 This is a structural block diagram of the system control module of the present invention.

[0053] Figure 6 This is a structural block diagram of the wire track impedance simulation device of the present invention.

[0054] Figure 7 This is a structural block diagram of the new energy power generation simulation device of the present invention. Detailed Implementation

[0055] The present invention will be further described below with reference to the accompanying drawings and embodiments. In the description of the embodiments of the present invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "connected" or "linked" should be interpreted broadly. For example, it can be a fixed connection, a detachable connection, an integral connection, an electrical connection, or a signal connection; it can be a direct connection or an indirect connection through an intermediate medium.

[0056] like Figures 1-7The experimental platform for a distributed new energy access medium-voltage DC traction power supply system includes a simulated traction network and a system control module, as well as a traction substation simulation device, an energy storage simulation device, and a new energy power generation simulation device that are electrically connected to the simulated traction network.

[0057] The simulated traction network, traction substation simulation device, energy storage simulation device, locomotive simulation device, and new energy power generation simulation device are all signal-connected to the system control module. The simulated traction network includes several track impedance simulation devices connected in series. Each track impedance simulation device includes a main control module, a stepper motor, and an impedance regulator. The main control module is signal-connected to the system control module and the stepper motor. Several locomotive simulation devices are electrically connected to the impedance regulators of several track impedance simulation devices. The stepper motor is used to adjust the impedance of the impedance regulator connected to the simulated traction network.

[0058] The impedance regulator is a variable resistor, and the locomotive simulation device is connected to the sliding brush of the variable resistor. During impedance adjustment, the system control module transmits control information to the main control module, and the main control module controls the stepper motor to rotate. The stepper motor drives the sliding brush to slide, so as to adjust the impedance of the two ends of the sliding brush connected to the simulated traction network, thereby simulating the movement of the locomotive in the actual system.

[0059] In this embodiment, the simulation experimental platform is designed based on the principle of proportional scaling. When constructing the experimental system, it uses a theoretical medium-voltage DC traction power supply system as a prototype, selecting key physical quantities such as the traction network voltage level, the power levels of each power supply and load link, and the equivalent impedance of the line as scaling objects. While ensuring that the proportional relationships between these key physical quantities remain unchanged, the relative relationships between voltage, current, power, and loss parameters in the experimental platform are kept consistent with the real system, thereby achieving the reproduction of the actual operating characteristics of the medium-voltage DC traction power supply system. The traction network voltage level is scaled from 24kV to 500V, and the output power of the energy storage simulation device, new energy power generation simulation device, locomotive simulation device, and traction substation simulation device is scaled from several MW to a maximum of ±3kW. This simulates the operating state of the traction power supply system. Based on the relationship between power and voltage, the maximum output current of each simulation device is determined to be 10A.

[0060] 1. System Control Module:

[0061] like Figure 5 As shown, the system control module includes a serial port server and a host computer. The host computer is connected to the serial port server via Ethernet or serial port signals. The serial port server is connected to the main control unit of each simulation device via fieldbus signals. The host computer interacts with each simulation device through the serial port server.

[0062] The system control module is used for centralized monitoring and distributed collaborative control of various simulation devices. The system control module periodically collects the operating information of the traction substation simulation device, energy storage simulation device, locomotive simulation device, and new energy power generation simulation device. The operating information includes voltage, current, power, and state of charge parameters. The host computer generates system-level control strategies based on the collected information and sends corresponding power adjustment commands, DC circuit breaker start / stop commands, operating mode switching commands, voltage control commands, and impedance adjustment commands to each simulation device through the communication link, so as to realize the operation simulation, power flow regulation, stability analysis, and fault protection behavior verification of the medium-voltage DC traction power supply system.

[0063] 2. Traction substation simulation device:

[0064] like Figure 2 As shown, the traction substation simulation device includes a bidirectional power supply simulator (programmable bidirectional DC power supply), a bidirectional DC-DC converter, and a DC circuit breaker. The bidirectional power supply simulator is signal-connected to a serial port server, and is electrically connected to the simulated traction network via the bidirectional DC-DC converter. The traction substation simulation device maintains the DC voltage level of the simulated traction network through the bidirectional DC-DC converter and provides power support during load changes or fluctuations in renewable energy. The rated operating voltage of the traction substation simulation device is DC 500V, and the maximum output current is DC ± 10A.

[0065] The traction substation simulation device interacts with the system control module via a communication link, uploading information on the grid-connected DC voltage, current, and output power at the traction substation side to the system control module, and receiving DC bus voltage setpoint commands, power adjustment commands, and operating mode control commands issued by the system control module. Based on the traction grid voltage deviation, system power balance status, and energy storage regulation capability, the system control module controls the traction substation simulation device to provide or absorb the power required by the system through its bidirectional DC-DC converter, thereby forming a hierarchical coordinated control mode with the traction substation simulation device as the voltage support source and the energy storage simulation device as the fast power regulation unit.

[0066] The bidirectional DC-DC converter of the traction substation simulation device maintains the simulated traction network voltage using a network control method, controlling its output voltage at DC 500V. Combined with droop control, voltage average value adjustment, and output power adjustment, the output voltage on the network side is regulated. The programmable bidirectional DC power supply does not have a power limit, allowing the traction substation simulation device to supplement the power shortage of the line traction network. At this time, the traction substation simulation device is in network construction mode.

[0067] 3. New energy power generation simulation device:

[0068] like Figure 7As shown, the new energy power generation simulation device includes a photovoltaic power generation simulation device (programmable DC power supply), a wind power generation simulation device (wind power simulated programmable AC power supply), a DC-DC converter (grid-connected converter), an AC-DC converter, and a DC circuit breaker. The photovoltaic and wind power generation simulation devices are connected to a serial port server. The photovoltaic power generation simulation device is electrically connected to the simulated traction network via the DC-DC converter and the DC circuit breaker. The wind power generation simulation device is electrically connected to the simulated traction network via the AC-DC converter, DC-DC converter, and DC circuit breaker. This allows for switching between centralized and distributed access modes for the new energy power generation device. The rated operating voltage of the new energy power generation simulation device is DC 500V, and the maximum output current is DC 10A. It can simulate the output characteristics of photovoltaic and wind power generation under different operating conditions under the control of a host computer.

[0069] The photovoltaic power generation simulation device and the wind power generation simulation device interact with the system control module through a communication link. They upload their output power, voltage, and current information to the system control module and receive start / stop control commands, power limit commands, maximum power point tracking control commands, and DC circuit breaker on / off commands from the system control module. This forms a grid-connected control mode where the output of the new energy power generation simulation device is controlled and the access mode can be switched. During the experiment, the capacity, voltage, and current parameters are set in the photovoltaic and wind power simulation programmable power supplies to make them output power curves with photovoltaic and wind power characteristics. The maximum power point tracking command is sent to the DC-DC converter through the host computer to realize the simulation of the working condition where the photovoltaic and wind power simulation programmable power supplies output maximum power to the traction network. The system control module can selectively activate some photovoltaic or wind power simulation units according to experimental requirements and adjust their rated capacity and grid connection mode to simulate the system operation status under different new energy penetration ratios and output fluctuation conditions.

[0070] 4. Energy storage simulation device:

[0071] like Figure 3 As shown, the energy storage simulation device includes a battery simulation power supply (a lithium battery simulation programmable bidirectional DC power supply), a supercapacitor simulation power supply (a supercapacitor simulation programmable bidirectional DC power supply), a bidirectional DC-DC converter, and a DC circuit breaker. The energy storage simulator is connected to a serial port server, and the energy storage simulator is electrically connected to the simulated traction network via the bidirectional DC-DC converter. Under the control of the system control module, energy absorption or release is achieved according to the energy storage state of charge (SOC) and the system operating status. The rated operating voltage of the energy storage simulation device is DC 500V, and the maximum charging and discharging current is DC ± 10A.

[0072] The battery simulation power supply and the supercapacitor simulation power supply are used to simulate the charging and discharging characteristics of lithium battery energy storage and supercapacitor energy storage, respectively. Parameters such as voltage, current, and series / parallel connection number are set in the battery simulation power supply and the supercapacitor simulation power supply to make them have the output characteristics of lithium battery energy storage and supercapacitor energy storage. The DC-DC converter adopts a power outer loop control strategy. The host computer sends the regulated power to the DC-DC converter, and the power output is controlled by controlling the voltage on the battery simulation power supply and the supercapacitor simulation power supply side. When the power output is greater than zero, the energy storage simulation device is in the discharging state; when the power output is less than zero, the energy storage simulation device is in the charging state. The battery simulation power supply and the supercapacitor simulation power supply in the energy storage simulation device can be put into operation independently or jointly. Their capacity ratio and control method can be configured by the system control module to study the impact of different energy storage configuration schemes on system stability.

[0073] 5. Locomotive simulation device:

[0074] like Figure 4 As shown, the locomotive simulation device includes a power simulator (programmable bidirectional DC power supply), an electronic load (programmable electronic load), a DC circuit breaker, and a DC-DC converter. The power simulator and electronic load are signal-connected to a serial port server. The power simulator is electrically connected to the simulated traction network via the DC-DC converter and DC circuit breaker, and the electronic load is also connected to the simulated traction network via the DC-DC converter and DC circuit breaker. Under the control of the host computer, the simulation of various operating conditions such as locomotive traction, coasting, and regenerative braking can be achieved by switching the connection status of the power simulator and electronic load. The rated operating voltage of the locomotive simulation device is DC 500V, and the maximum operating current is DC ± 10A.

[0075] The system includes a programmable DC power supply to simulate energy feedback under regenerative braking conditions, and programmable electronic loads and fixed loads to simulate power demands under traction and coasting conditions. When the locomotive is under regenerative braking, the host computer controls the DC circuit breaker to connect the programmable bidirectional DC power supply to the simulated traction network and sends power adjustment commands to the programmable bidirectional DC power supply to control power output, which is then input to the traction network via a DC-DC converter. When the locomotive is under traction, the host computer controls the DC circuit breaker to connect the high-power fixed load to the traction network, absorbing 80% of the maximum traction load power. When the locomotive is under coasting, the host computer controls the DC circuit breaker to connect the programmable electronic load to the traction network and sends adjustment commands to the programmable electronic load, allowing it to absorb 3% of the maximum traction load power. This allows for continuous switching and unified simulation of locomotive traction, coasting, and regenerative braking conditions on the same experimental platform.

[0076] Meanwhile, the host computer continuously sends impedance adjustment commands to the main control module in the track impedance simulation device according to the preset train running speed curve. The main control module controls the stepper motor to drive the impedance regulator to dynamically adjust the equivalent impedance of the traction network and rail return circuit, so that the equivalent impedance of the line changes continuously with time, thereby simulating the impact of the change in electrical distance on the operating status of the traction power supply system during the locomotive's operation along the line.

[0077] 6. Track impedance simulation device:

[0078] like Figure 6 As shown, the track impedance simulation device consists of two stepper motors, two impedance regulators, and two controllers, forming an integrated impedance regulation system.

[0079] The system control module controls the position, speed, and acceleration of the stepper motor to drive the impedance regulator to dynamically adjust the equivalent impedance of the traction network and the rail return circuit. This simulates the changes in electrical distance corresponding to different operating positions of the train on the traction line. The impedance adjustment command is synchronized with the operating status and power demand curve of the locomotive simulation device to reflect the mutual influence between changes in electrical position and changes in locomotive power status during the locomotive's operation along the line, thus achieving an equivalent simulation of the locomotive's operation process and the impedance distribution of the line.

[0080] The aforementioned simulation devices achieve standardized data transmission through a communication protocol, enabling the system control module to uniformly coordinate and synchronously control the operating status of the multi-source, multi-load traction power supply system at the system level.

[0081] The simulation steps for the operating characteristics of the medium-voltage DC traction power supply system under the conditions of new energy fluctuations and changes in vehicle load are as follows:

[0082] S1: The system control module selectively engages or disengages the corresponding new energy power generation simulation device, energy storage simulation device, and locomotive simulation device based on the preset traffic density and the output curve of the new energy power generation simulation device, thereby constructing traction power supply system operation scenarios with different new energy penetration ratios, different energy storage configuration scales, and different locomotive load combinations.

[0083] S2: Issue power setting commands and operating mode commands to the simulated devices in operation, and set their power levels and operating states.

[0084] S3: Under different operating scenarios of traction power supply systems with different numbers of new energy access, different energy storage configuration capacities, and different locomotive operating load combinations, the traction power supply system generates different voltage and power distribution states. Experimental verification and effect evaluation are conducted on the system stability control strategy, power flow regulation strategy, and protection control strategy.

[0085] Simulation Experiment 1:

[0086] When considering the impact of output fluctuations and uncertainties in a new energy power generation simulation device, the simulation steps for system stability analysis and control are as follows:

[0087] S3.1.1: The system control module acquires the grid-connected voltage, current, power, line equivalent impedance, and state of charge of the energy storage simulation device uploaded by each simulation device;

[0088] S3.1.2: Analyze the power coupling relationship under the conditions of output fluctuation of new energy power generation simulation device, locomotive load change and multi-source access, and analyze the impact mechanism of output fluctuation and uncertainty of new energy power generation simulation device on system voltage stability and power distribution;

[0089] S3.1.3: When the output of the new energy power generation simulation device fluctuates or the operating status of the simulated traction network changes, the system control module determines the impact of the new energy power generation simulation device's output on system stability based on parameters such as the voltage deviation, power fluctuation amplitude, and line equivalent impedance change of the simulated traction network, and issues an operating mode switching command to the new energy power generation simulation device. The operating mode switching command is used to control the grid-connected converter in the new energy power generation simulation device to switch between maximum power point tracking mode, power limiting mode, and DC voltage support mode. The specific method is as follows:

[0090] When the traction power supply system is in stable operation, the grid-connected converter is switched to operate in maximum power point tracking mode to simulate the operation state of new energy sources generating electricity according to their output characteristics.

[0091] When the power output fluctuation of the new energy power generation simulation device or the change in locomotive load causes an increase in the voltage deviation of the simulated traction network, the system control module controls the grid-connected converter to switch from the maximum power point tracking mode to the power limiting mode to limit the range of change in the output power of the new energy.

[0092] When the simulated traction grid voltage fluctuation intensifies or the system stability decreases, the system control module controls the grid-connected converter to switch to DC voltage support mode, enabling the new energy power generation simulation device to participate in the simulated traction grid voltage regulation, thereby reducing the adverse impact of new energy volatility on the stable operation of the traction power supply system.

[0093] S3.1.4: The system control module sends charging and discharging control commands to the bidirectional DC-DC converter of the energy storage simulation device based on the state of charge, power constraints, and output variation of the new energy power generation simulation device. The energy storage simulation device compensates for the output fluctuations of the new energy power generation simulation device through bidirectional energy regulation, thereby maintaining the stability of the traction grid voltage and system power balance.

[0094] In this embodiment, during the grid connection and operation of each simulation device, the host computer collects in real time the bidirectional DC-DC output voltage, current, and power information of the traction substation simulation device, the output power information of the photovoltaic and wind power programmable DC power supplies in the new energy power generation simulation device, and the charging and discharging power and state of charge parameters fed back by the programmable bidirectional DC power supply in the energy storage simulation device through a serial port server. Combined with the equivalent impedance data of the line uploaded by the rail impedance simulation device, the stability analysis of the traction network operation status is performed. When traction network voltage fluctuations or power imbalances are detected due to output fluctuations of the new energy power generation simulation device, locomotive operating condition switching, or changes in line impedance, the host computer sends coordinated control commands to the bidirectional DC-DC converters of the traction substation simulation device, the new energy power generation simulation device, and the energy storage simulation device through the communication link to adjust the output power of the traction substation, the output level of the new energy power generation simulation device, and the charging and discharging power of the energy storage device, so as to suppress system operation fluctuations and maintain traction network voltage stability, thereby simulating and verifying the stable operation of the traction power supply system under multi-source parallel conditions.

[0095] Simulation Experiment 2:

[0096] The simulation experiment steps for system power flow control are as follows:

[0097] S3.2.1: The system control module collects real-time operating information uploaded by each simulation device;

[0098] S3.2.2: Calculate the power flow distribution of the system;

[0099] S3.2.3: Issue power regulation commands to the energy storage simulation device and the traction substation simulation device;

[0100] S3.2.4: The energy storage simulation device smooths out power fluctuations in the locomotive simulation device and the new energy power generation simulation device, and the traction substation simulation device makes up for the power shortage.

[0101] In this embodiment, the power flow regulation process is centered on the system control module and is achieved through the coordinated control of the new energy power generation simulation device, the energy storage simulation device, and the traction substation simulation device. During operation, the photovoltaic and wind power simulation power supplies, the locomotive simulation device, and the energy storage simulation device in the new energy power generation simulation device periodically upload their DC-DC output voltage, current, and power information to the host computer via a communication link. The energy storage simulation device also uploads the state of charge parameters of its programmable bidirectional DC power supply. The host computer calculates the power distribution status of the traction power supply system based on the real-time collected data and line impedance parameters, and generates a power flow regulation strategy accordingly. When the output of the new energy power generation simulation device fluctuates or the locomotive load changes, the host computer prioritizes issuing power adjustment commands to the bidirectional DC-DC converter of the energy storage simulation device to achieve system power balance and voltage stability by controlling its charging and discharging power. When the energy storage capacity or power is limited, the host computer further issues power compensation commands to the traction substation simulation device, which then undertakes the supply or absorption of the system's remaining power.

[0102] Simulation Experiment 3:

[0103] The system faults are simulated, including overvoltage faults, voltage drop faults, and short-circuit faults.

[0104] The simulation of system overvoltage faults includes, but is not limited to, the following methods: 1) Controlling the locomotive simulation device to regenerative mode, locking the bidirectional DC-DC converter in the energy storage simulation device, forcing the grid voltage to rise, and forming an overvoltage fault simulation; 2) Limiting the power absorption of the bidirectional DC-DC converter in the traction substation simulation device or switching its operating mode through the system control module, so that it cannot absorb excess energy from the traction grid in time, causing the traction grid voltage to rise continuously when the locomotive regenerative braking or the new energy output is large, thereby forming an overvoltage fault simulation; 3) Under the condition that the new energy power generation simulation device maintains maximum power output and the traction load is small, limiting the power regulation capability of the energy storage device and the traction substation, so that the new energy output cannot be absorbed in time, causing the traction grid voltage to rise, forming a new energy-dominated overvoltage fault simulation.

[0105] The simulation of grid voltage drop faults in the system includes, but is not limited to, the following methods: 1) Disconnecting the power simulation module in the new energy power generation simulation device and locking the bidirectional DC-DC converter in the energy storage simulation device to force a grid voltage drop, thus simulating a grid voltage drop fault; 2) Controlling the locomotive simulation device to quickly switch from coasting or low load conditions to traction conditions through the system control module, enabling the programmable electronic load or fixed load to be put into operation instantaneously, and locking the output capacity of the energy storage simulation device, causing a sudden increase in traction grid load, thereby simulating a grid voltage drop fault; 3) Limiting the output power of the traction substation simulation device or reducing its voltage setpoint through the system control module, so that it cannot provide sufficient power support when the load exists, resulting in a drop in traction grid voltage, thus simulating a grid voltage drop fault.

[0106] The simulation of short-circuit faults in the system includes, but is not limited to, the following methods: 1) By introducing an external current source, short-circuit current is injected into the traction substation outlet, the midpoint of the line, and the locomotive power receiving point of the simulated traction network to form a short-circuit fault simulation; 2) By controlling the track impedance simulation device, the equivalent impedance of the corresponding node is adjusted to a minimum value to form an approximate short-circuit state, thereby simulating the occurrence process of short-circuit faults in the DC traction network; 3) Controllable short-circuit branches are set at the nodes corresponding to the traction substation outlet, the midpoint of the line, or the locomotive power receiving point, and the DC circuit breaker is controlled to close quickly through the system control module, so that the traction network forms a low-impedance path at the specified location, thereby realizing the simulation of DC short-circuit faults at different locations.

[0107] In this embodiment, fault simulation is achieved through coordinated control of the traction substation simulation device, locomotive simulation device, new energy power generation simulation device, energy storage simulation device, and DC circuit breaker by a host computer. During the fault simulation process, the host computer records the voltage, current, and circuit breaker operation status of each simulation device in real time to analyze the response characteristics and coordination of the system protection actions. In actual medium-voltage DC traction power supply systems, the aforementioned overvoltage, grid voltage drop, and short-circuit faults are difficult to artificially construct and repeatedly verify in actual lines, and the system response characteristics corresponding to different fault locations differ significantly.

[0108] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A simulation experimental platform for a medium-voltage DC traction power supply system with distributed new energy access, characterized in that, It includes a simulated traction network and system control module, as well as a traction substation simulation device, an energy storage simulation device, and a new energy power generation simulation device that are electrically connected to the simulated traction network; The simulated traction network, traction substation simulation device, energy storage simulation device, locomotive simulation device, and new energy power generation simulation device are all signal-connected to the system control module. The simulated traction network includes several track impedance simulation devices connected in series. Each track impedance simulation device includes a main control module, a stepper motor, and an impedance regulator. The main control module is signal-connected to the system control module and the stepper motor. Several locomotive simulation devices are electrically connected to the impedance regulators of several track impedance simulation devices. The stepper motor is used to adjust the impedance of the impedance regulator connected to the simulated traction network.

2. The simulation experimental platform for a medium-voltage DC traction power supply system with distributed new energy access as described in claim 1, characterized in that, The impedance regulator is a variable resistor, and the locomotive simulation device is connected to the sliding brush of the variable resistor; During impedance adjustment, the system control module transmits control information to the main control module, which controls the stepper motor to rotate. The stepper motor drives the sliding brush to slide, thereby adjusting the impedance of the two ends of the sliding brush connected to the simulated traction network, simulating the movement of the locomotive in the actual system.

3. The simulation experimental platform for a medium-voltage DC traction power supply system with distributed new energy access according to claim 2, characterized in that, The traction substation simulation device, energy storage simulation device, new energy power generation simulation device and locomotive simulation device all include a DC circuit breaker for connecting to the simulated traction network power. The traction substation simulation device, energy storage simulation device, new energy power generation simulation device, and locomotive simulation device selectively connect or disconnect the simulated traction network through the switching on and off of the DC circuit breaker.

4. The simulation experimental platform for a medium-voltage DC traction power supply system with distributed new energy access according to any one of claims 1-3, characterized in that, The simulation steps for the operating characteristics of the medium-voltage DC traction power supply system under the conditions of new energy fluctuations and changes in vehicle load are as follows: S1: The system control module selectively engages or disengages the corresponding new energy power generation simulation device, energy storage simulation device, and locomotive simulation device based on the preset traffic density and the output curve of the new energy power generation simulation device, thereby constructing traction power supply system operation scenarios with different new energy penetration ratios, different energy storage configuration scales, and different locomotive load combinations. S2: Issue power setting commands and operating mode commands to the simulated devices in operation, and set their power levels and operating states. S3: Under different operating scenarios of traction power supply systems with different numbers of new energy access, different energy storage configuration capacities, and different locomotive operating load combinations, the traction power supply system generates different voltage and power distribution states. Experimental verification and effect evaluation are conducted on the system stability control strategy, power flow regulation strategy, and protection control strategy.

5. The simulation experimental platform for a medium-voltage DC traction power supply system with distributed new energy access according to claim 4, characterized in that, In step S3, when considering the impact of output fluctuations and uncertainties in the new energy power generation simulation device, the simulation steps for system stability analysis and control are as follows: S3.1.1: The system control module acquires the grid-connected voltage, current, power, line equivalent impedance, and state of charge of the energy storage simulation device uploaded by each simulation device; S3.1.2: Analyze the power coupling relationship under the conditions of output fluctuation of new energy power generation simulation device, locomotive load change and multi-source access, and analyze the impact mechanism of output fluctuation and uncertainty of new energy power generation simulation device on system voltage stability and power distribution; S3.1.3: When the output of the new energy power generation simulation device fluctuates or the operating status of the simulated traction network changes, the system control module determines the impact of the output of the new energy power generation simulation device on the system stability based on the voltage deviation, power fluctuation amplitude and line equivalent impedance change parameters of the simulated traction network, and issues an operating mode switching command to the new energy power generation simulation device. S3.1.4: The system control module sends charging and discharging control commands to the bidirectional DC-DC converter of the energy storage simulation device based on the state of charge, power constraints, and output variation of the new energy power generation simulation device. The energy storage simulation device compensates for the output fluctuations of the new energy power generation simulation device through bidirectional energy regulation, thereby maintaining the stability of the traction grid voltage and system power balance.

6. The simulation experimental platform for a medium-voltage DC traction power supply system with distributed new energy access according to claim 5, characterized in that, The new energy power generation simulation device also includes a grid-connected converter, and the operation mode switching command is used to control the grid-connected converter to switch between maximum power point tracking mode, power limiting mode and DC voltage support mode.

7. The simulation experimental platform for a medium-voltage DC traction power supply system with distributed new energy access according to claim 4, characterized in that, The simulation experiment steps for system power flow control are as follows: S3.2.1: The system control module collects real-time operating information uploaded by each simulation device; S3.2.2: Calculate the power flow distribution of the system; S3.2.3: Issue power regulation commands to the energy storage simulation device and the traction substation simulation device; S3.2.4: The energy storage simulation device smooths out power fluctuations in the locomotive simulation device and the new energy power generation simulation device, and the traction substation simulation device makes up for the power shortage.

8. The simulation experimental platform for a medium-voltage DC traction power supply system with distributed new energy access according to claim 4, characterized in that, The specific method for simulating system faults in step S3 is as follows: Simulation of overvoltage fault in the system: The locomotive simulation device is controlled to be in regenerative mode, the bidirectional DC-DC converter in the energy storage simulation device is locked, and the grid voltage is forced to rise, thus forming an overvoltage fault simulation. Simulation of grid voltage drop fault: disconnect the power simulation module in the new energy power generation simulation device, lock the bidirectional DC-DC converter in the energy storage simulation device, force grid voltage drop, and form grid voltage drop fault simulation. Simulation of short-circuit faults in the system: By introducing an external current source, short-circuit current is injected into the outlet of the traction substation, the midpoint of the line, and the power receiving point of the locomotive in the simulated traction network to form a short-circuit fault simulation.

9. The simulation experimental platform for a medium-voltage DC traction power supply system with distributed new energy access according to claim 4, characterized in that, The specific method for simulating system faults in step S3 is as follows: Simulation of system overvoltage fault: By limiting the power absorption of the bidirectional DC-DC converter in the traction substation simulation device or switching its operating mode through the system control module, it is prevented from absorbing excess energy from the traction network in time. When the locomotive regenerative braking or the output of new energy is large, the voltage of the traction network will continue to rise, thus forming an overvoltage fault simulation. Simulation of sudden voltage drop in the system grid: The system control module controls the locomotive simulation device to quickly switch from coasting or low load conditions to traction conditions, so that the programmable electronic load or fixed load is put into operation instantly, and the output capacity of the energy storage simulation device is locked, causing a sudden increase in the load of the traction grid, thereby forming a sudden voltage drop simulation of the traction grid voltage. Simulation of short-circuit faults in the system: By controlling the track impedance simulation device, the equivalent impedance of the corresponding node is adjusted to a minimum value to form an approximate short-circuit state, thereby simulating the occurrence process of short-circuit faults in the DC traction network.

10. The simulation experimental platform for a medium-voltage DC traction power supply system with distributed new energy access according to claim 4, characterized in that, The specific method for simulating system faults in step S3 is as follows: Simulation of system overvoltage fault: Under the condition that the new energy power generation simulation device maintains maximum power output and the traction load is small, the power regulation capability of the energy storage device and the traction substation is limited, so that the new energy output cannot be absorbed in time, causing the traction grid voltage to rise, forming a new energy-dominated overvoltage fault simulation. Simulation of sudden voltage drop fault in the system grid: By limiting the output power of the simulation device in the traction substation or reducing its voltage setpoint through the system control module, it is unable to provide sufficient power support when the load is present, resulting in a drop in the traction grid voltage and forming a simulation of sudden voltage drop fault in the grid. Simulation of system short-circuit faults: Controllable short-circuit branches are set at nodes corresponding to the outlet of traction substation, the midpoint of the line, or the power receiving point of the locomotive. The DC circuit breaker is controlled to close quickly through the system control module, so that the traction network forms a low-impedance path at the designated location, thereby realizing the simulation of DC short-circuit faults at different locations.

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