Rail transit braking energy recovery system and rail transit operation system

Abstract

The utility model provides a rail transit braking energy recovery system and a rail transit operation system. The rail transit braking energy recovery system is arranged between a direct-current traction power grid and an alternating-current power grid and comprises a first direct-current converter and an inverter. Wherein the input end of the first direct-current converter is connected to a direct-current traction power grid, and the first direct-current converter is configured to be an isolated converter based on a semiconductor switching device to achieve electrical isolation and convert braking direct current of the direct-current traction power grid into first direct current. The input end of the inverter is connected with the output end of the first direct-current converter, the output end of the inverter is connected to an alternating-current power grid, and the inverter is configured to convert the first direct current into alternating current. According to the system, excess energy generated in the rail transit braking process can be effectively converted into available electric energy, energy loss is reduced, and the energy utilization efficiency is improved. And the direct current converter adopted by the utility model can realize electrical isolation, so that the electrical isolation performance of the system is enhanced, and the safety and reliability of the system are improved.

Description

TECHNICAL FIELD

[0001] The utility model relates to rail transit technical field, concretely relates to a rail transit braking energy recovery system and rail transit operation system. BACKGROUND

[0002] The statements in this section merely provide background information related to the utility model and can not constitute the prior art.

[0003] Rail transit is a kind of traffic mode using rail to guide vehicle operation, mainly including railway, subway, light rail, tramcar etc., with the advantages of strong carrying capacity, high transportation efficiency, low energy consumption, good safety, small environmental pollution etc..Among them, urban rail transit (such as subway, light rail, tramcar etc.) is an important part of urban public transport system.

[0004] In the urban rail transit application such as subway, the direct current (DC) traction power grid of train is usually powered by high voltage (HV) alternating current (AC) power grid such as 10kV~35kV.In addition to high voltage AC power grid, urban rail transit system also includes 400V low voltage (LV) AC power grid, which is the power supply of station lighting, air conditioning and other electrical appliances, and is powered by high voltage AC power grid through transformer step-down.In specific application, high voltage AC power is stepped down through transformer, and then AC power is converted into DC power input to DC traction power grid for train use.In operation process, the start and braking of train will cause voltage fluctuation on traction power supply line.Especially when train brakes, a large amount of braking energy is generated, which will cause the rapid rise of DC traction line voltage.If the voltage exceeds the upper limit voltage designed by system, it may cause system to shut down due to overvoltage failure.Therefore, corresponding energy recovery scheme must be provided to ensure the stable operation of power supply system. SUMMARY

[0005] To solve the above problems, the utility model provides a rail transit braking energy recovery system and rail transit operation system.

[0006] According to the first aspect, the utility model provides a rail transit braking energy recovery system, which is arranged between DC traction power grid and AC power grid, comprising: first DC converter, its input end is connected to the DC traction power grid, the first DC converter is configured to realize electrical isolation and convert braking DC power of the DC traction power grid into first DC power by using isolation type converter based on semiconductor switching device;And inverter, its input end is connected with the output end of the first DC converter, its output end is connected to the AC power grid, the inverter is configured to convert the first DC power into AC power.

[0007] Preferably, the first DC converter comprises: a first current conversion unit configured to convert the braking DC power into first AC power; the semiconductor switching device based isolation type converter configured to achieve electrical isolation and convert the first AC power into second AC power; and a second current conversion unit configured to convert the second AC power into the first DC power.

[0008] Preferably, the first current conversion unit and the second current conversion unit are full-bridge topology, half-bridge topology or multi-stage cascade topology.

[0009] Preferably, the semiconductor switching device based isolation type converter is a magnetic element.

[0010] Preferably, the semiconductor switching device based isolation type converter is a solid state transformer.

[0011] Preferably, the first DC converter adopts a dual active bridge topology or a resonant converter topology to achieve DC-DC conversion.

[0012] Preferably, the rail transit braking energy recovery system further comprises an energy storage unit connected between the DC traction power grid and the first DC converter, wherein the energy storage unit comprises an energy storage medium and a second DC converter, the second DC converter is configured to convert the braking DC power of the DC traction power grid into second DC power, and the energy storage medium is configured to collect the energy of the second DC power and provide the collected energy to a load and / or the first DC converter.

[0013] Preferably, the rail transit braking energy recovery system further comprises an energy storage unit connected between the first DC converter and the inverter, and configured to collect the energy output by the first DC converter and provide the collected energy to a load and / or the inverter.

[0014] Preferably, the rail transit braking energy recovery system further comprises: a DC circuit protection unit connected between the DC traction power grid and the first DC converter; and / or an AC circuit protection unit connected between the AC power grid and the inverter.

[0015] According to a second aspect, the utility model provides a rail transit operation system, comprising a rail transit power supply system and the rail transit braking energy recovery system as any one of the first aspect. Wherein, the rail transit power supply system comprises: a transformer configured to transform the voltage from the AC power grid and provide to the rectifier; and a rectifier configured to convert the input AC power into DC power and provide to the DC traction power grid.

[0016] The utility model discloses can effectively convert the surplus energy produced in the rail transit braking process into usable electric energy, reduce energy loss, improve energy utilization efficiency. Moreover, the utility model discloses removes the traditional low-frequency transformer in the braking energy recovery system, places an isolation type converter based on high-frequency transformer in the system to realize isolation and voltage conversion function enhancement electrical isolation performance of system, improve the security and reliability of system. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 It is a braking energy recovery system's structural diagram of prior art;

[0018] Figure 2 It is the structural diagram of rail transit braking energy recovery system according to an embodiment of the utility model;

[0019] Figure 3 It is the structural diagram of the first direct current converter according to an embodiment of the utility model;

[0020] Figure 4 It is the structural diagram of the first rail transit braking energy recovery system including energy storage unit according to an embodiment of the utility model;

[0021] Figure 5 It is the structural diagram of the second rail transit braking energy recovery system including energy storage unit according to an embodiment of the utility model;

[0022] Figure 6 It is the structural diagram of the rail transit braking energy recovery system including protection unit according to an embodiment of the utility model. DETAILED DESCRIPTION

[0023] The specific embodiments of the utility model will be described in detail below, and it should be noted that the embodiments herein are only used for example and do not limit the utility model. In the following description, a large number of specific details are set forth in order to provide a thorough understanding of the utility model. However, it is obvious to those skilled in the art that the specific details are not necessarily used to implement the utility model. In other examples, in order to avoid obscuring the utility model, well-known procedures, materials or methods are not specifically described.

[0024] Figure 1A schematic diagram of a prior art regenerative braking system is shown, which mainly includes an inverter and a transformer. DC power output from the DC traction grid is sequentially converted by the inverter and transformer before being connected to the AC grid to reuse braking energy. Since the voltages at both ends of the regenerative braking system are different and both are grounded (typically grounded via the negative terminal (rail) on the DC side and via the neutral line on the AC side), electrical isolation is necessary. The transformer in this system is typically a low-frequency transformer, a device used for electrical isolation and voltage conversion, with an operating frequency usually below 20kHz. Low-frequency transformers typically consist of copper windings and a magnetic core, making them bulky and heavy due to their physical characteristics. Furthermore, as a passive component, low-frequency transformers lack self-control or monitoring capabilities, making online monitoring and control difficult. In this system, the equipment between the DC traction grid and the primary side of the transformer needs to withstand very high voltages, requiring additional costs to upgrade device specifications to meet isolation and voltage stress design requirements, ensuring the safety and reliability of the equipment under high-voltage conditions.

[0025] This utility model provides a rail transit braking energy recovery system, which is installed between a DC traction power grid and a low-voltage AC power grid. In this embodiment, the voltage of the low-voltage AC power grid is preferably 380V~450V, which can power the facilities within the station; the voltage of the high-voltage AC power grid is preferably 10kV~35kV; and the voltage of the DC traction power grid is preferably 750V~1500V, used to power the train. Figure 2 The schematic diagram shown is of a rail transit braking energy recovery system according to an embodiment of the present invention. The rail transit braking energy recovery system includes a first DC converter 201 and an inverter 202. The input terminal of the first DC converter 201 is connected to the DC traction power grid and is configured to achieve electrical isolation based on a high-frequency transformer and to convert the braking DC power from the DC traction power grid into first DC power. In this embodiment of the present invention, high frequency refers to an operating frequency above 20kHz. Preferably, the high-frequency transformer is an isolated converter based on semiconductor switching devices. The input terminal of the inverter 202 is connected to the output terminal of the first DC converter 201, and its output terminal is connected to a low-voltage AC power grid, configured to convert the first DC power into AC power. This embodiment of the present invention can effectively convert excess energy generated during rail transit braking into usable electrical energy, reducing energy loss and improving energy utilization efficiency. Utilizing the small size, high efficiency, and intelligent monitoring characteristics of the isolated converter based on the high-frequency transformer, the performance of the braking energy recovery system can be further improved.

[0026] In some embodiments, the rail transit braking energy recovery system is arranged between a direct current traction power grid and a high-voltage alternating current power grid, and the output end of the inverter 202 can be connected to the high-voltage alternating current power grid.

[0027] In some embodiments, the inverter includes a low-voltage inverter and a high-voltage inverter. The low-voltage inverter refers to an inverter with an output voltage of 380V-450V, and the high-voltage inverter refers to an inverter with an output voltage of 10kV-35kV. The output end of the low-voltage inverter is connected to a low-voltage alternating current power grid, and the output end of the high-voltage inverter is connected to a high-voltage alternating current power grid. In this way, energy can be flexibly output to different alternating current power grids, adapting to different voltage requirements and improving the applicability and flexibility of the system. The inverter can adopt a cascaded topology composed of semiconductor elements, without the need for magnetic elements, to optimize energy conversion efficiency and reduce harmonic distortion. The output end of the inverter is connected to an alternating current power grid, which can be an industrial power grid or a public power grid, so that the recovered energy can be used by other users in the power grid.

[0028] As Figure 3The structure diagram of the first direct current converter according to one embodiment of the utility model is shown, the first direct current converter 201 includes the first current conversion unit 301, the high frequency transformer 302 and the second current conversion unit 303 connected in turn. Among them, the first current conversion unit 301 can convert the braking direct current of the direct current traction power grid into the first alternating current. The high frequency transformer 302 can realize electrical isolation and convert the first alternating current into the second alternating current. Preferably, the high frequency transformer 302 is an isolated converter based on semiconductor switching devices. The isolated converter based on semiconductor switching devices is realized by using magnetic elements, which can be magnetic transformers, such as magnetic transformers with inductors or magnetic transformers with capacitors. The diversified selection of magnetic elements provides flexibility to adapt to different electrical parameters and application scenarios. The isolated converter based on semiconductor switching devices can also be a solid-state transformer. The second current conversion unit 303 can convert the second alternating current into the first direct current. Among them, the first alternating current can refer to high-frequency alternating current with a frequency higher than 20 kHz. In the embodiment of the utility model, the high frequency transformer needs to be used in cooperation with the power electronic topology on both sides (i.e. the first current conversion unit and the second current conversion unit). Because the power electronic topology on both sides can control the high frequency transformer to realize electrical energy conversion, the power frequency signal is converted into a high frequency signal through the power electronic topology, and then the voltage is converted through the intermediate high frequency transformer, and the high frequency signal is restored to the power frequency signal through the power electronic topology. The reasonable topology structure cooperates with the power electronic conversion to optimize the waveform, frequency, voltage and other parameters of the direct current converter, thereby improving the power quality and efficiency of the direct current converter during operation. The power electronic topology can have functions such as reactive and harmonic compensation, reactive control, and power factor correction, which can significantly improve the power quality, and its application can also improve the system operation reliability, efficiency and operation performance. Through the cooperation of the power electronic topology and the high frequency transformer, the hardware cost can be reduced, the structure compactness can be improved, and the engineering difficulty can be reduced. In some application scenarios, the cooperation of the high frequency transformer and the power electronic topology can realize power mutual assistance between different transformers, improve the power supply reliability, and realize flexible interconnection of AC and DC sides and power mutual assistance. In summary, the high frequency transformer is used in cooperation with the power electronic topology on both sides, in order to realize effective conversion and isolation of electrical energy, optimize power quality, provide AC and DC interfaces, harmonic and reactive compensation, improve operation reliability and efficiency, and reduce cost and engineering difficulty. By using high-frequency alternating voltage as an intermediate step, the conversion efficiency can be improved, and the addition of magnetic elements enhances the electrical isolation performance of the system and improves the safety and reliability of the system.

[0029] In some embodiments, the first current conversion unit 301 and the second current conversion unit 303 adopt the circuit structure of full-bridge topology, half-bridge topology or multi-stage cascade topology. Different topology structures can optimize system performance according to different requirements and conditions.

[0030] In some embodiments, the first DC-DC converter 201 can implement DC-DC conversion using a dual active bridge topology (i.e., a DAB converter) or a resonant converter topology. The resonant converter can include an LLC converter or a CLLC converter. A DAB converter is a DC-DC converter that provides bidirectional power flow and electrical isolation. It features flexible design characteristics, can be optimized for specific voltage and power requirements, and can achieve high efficiency and high power density, making it suitable for applications requiring bidirectional power transfer and modular structures. An LLC converter is a DC-DC converter based on the resonant principle, consisting of a resonant inductor, a resonant capacitor, and a load inductor, forming a three-stage resonant network. Due to its resonant characteristics, it can achieve zero-voltage switching under specific conditions by controlling the frequency, reducing switching losses and improving system efficiency. A CLLC converter is a bidirectional full-bridge resonant converter, developed from the LLC converter by adding an additional inductor, enabling bidirectional energy transfer. CLLC converters are commonly used in applications requiring bidirectional DC / DC conversion, such as on-board chargers and portable energy storage. This converter achieves bidirectional energy flow by controlling the switching frequency and duty cycle, making it suitable for applications requiring optimized switching losses, reduced EMI, and higher frequency operation. Its symmetrical full-bridge structure allows for different primary and secondary resonant networks in both forward and reverse operating modes, increasing design flexibility. Both dual active bridge topologies and resonant converters are highly efficient DC-DC conversion technologies, improving energy conversion efficiency and reducing energy losses. Furthermore, resonant converters can reduce switching losses and improve overall system performance.

[0031] In some embodiments, the rail transit braking energy recovery system may further include an energy storage unit. The energy storage unit can collect excess braking energy from the DC traction grid and provide the collected energy to the load. The load may refer to electrical equipment within the subway station, such as lighting equipment, cleaning equipment, elevators, and air conditioning, or it may refer to electrical equipment or facilities in buildings outside the station.

[0032] like Figure 4 As shown, in some embodiments, the energy storage unit 203 is connected between the first DC-DC converter 201 and the inverter 202. The energy storage unit may include an energy storage medium for storing the first DC current and providing the collected energy to the load and / or the inverter 202. The energy storage unit 203 not only stores temporarily unused energy but also acts as a buffer between the first DC-DC converter and the inverter, further optimizing energy flow and improving system flexibility and energy utilization.

[0033] like Figure 5As shown, in some embodiments, the energy storage unit 203 can be connected between the DC traction grid and the first DC converter 201. The energy storage unit includes an energy storage medium and a second DC converter. The second DC converter converts the braking DC power from the DC traction grid into a second DC power, and the energy storage medium stores the energy of the second DC power, providing the collected energy to the load and / or the first DC converter 201. The addition of the energy storage unit 203 enables the system to store energy that is not currently needed for use when required, which helps balance the grid load and improve energy utilization efficiency.

[0034] In some embodiments, the energy storage medium may be a supercapacitor, a battery, or a flywheel energy storage device. The energy storage medium can store recovered energy in a battery energy storage system or other types of energy storage devices for unforeseen needs, such as providing additional power support during peak grid demand periods or supporting other electrical loads inside or outside subway stations.

[0035] In some embodiments, the rail transit braking energy recovery system may also be equipped with an intelligent energy management unit that can automatically adjust the energy recovery strategy according to the needs of the DC traction grid and / or AC grid and the operating status of the vehicle.

[0036] like Figure 6 As shown, in some embodiments, the rail transit braking energy recovery system may further include a DC circuit protection unit 204, which is connected between the DC traction power grid and the DC converter 201 to protect the energy recovery system. The DC circuit protection unit 204 may be a circuit breaker. The addition of the DC circuit protection unit can prevent damage to the system from abnormal conditions such as overvoltage and overcurrent, ensuring the stable operation and long-term reliability of the system.

[0037] Please refer to this again. Figure 6 In some embodiments, the rail transit braking energy recovery system may further include an AC circuit protection unit 205, which is connected between the AC power grid and the inverter 202 to protect the energy recovery system. The AC circuit protection unit 205 may be a circuit breaker. The AC circuit protection unit can protect the inverter and the AC power grid from abnormal currents and voltages, improving the safety and stability of the system.

[0038] In some embodiments, semiconductor switching devices may include IGBTs, MOSFETs, and / or diodes. Using high-performance semiconductor switching devices such as IGBTs, MOSFETs, and diodes can improve the switching speed and efficiency of the system, reduce energy loss, and the high reliability of these devices also helps to improve the stability and lifespan of the entire energy recovery system.

[0039] According to one embodiment of the utility model, provide a kind of rail transit operation system, including rail transit power supply system and rail transit braking energy recovery system in above-mentioned embodiment. Among them, the input end of rail transit power supply system is connected with alternating current network, and output end is direct current traction network. Rail transit power supply system includes transformer and rectifier, transformer provides voltage from alternating current network after voltage reduction conversion, and rectifier is provided with direct current traction network with the input alternating current conversion as direct current.

[0040] The above has described the various embodiments of the utility model, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes are obvious to those skilled in the art without departing from the scope and spirit of the described embodiments. The selection of terms used herein is intended to best explain the principles of the embodiments, practical application or improvement of technology in the market, or to enable other ordinary skilled in the art to understand the embodiments disclosed herein.

Claims

1. A rail transit braking energy recovery system, installed between a DC traction power grid and an AC power grid, characterized in that, include: A first DC-DC converter, the input of which is connected to the DC traction grid, is configured to achieve electrical isolation using an isolation converter based on semiconductor switching devices and to convert the braking DC power from the DC traction grid into the first DC power. as well as An inverter, the input of which is connected to the output of the first DC converter and the output of which is connected to the AC power grid, is configured to convert the first DC power into AC power.

2. The system according to claim 1, characterized in that, The first DC-DC converter includes: A first converter unit is configured to convert the braking direct current into a first alternating current. The isolated converter based on semiconductor switching devices is configured to achieve electrical isolation and convert the first AC power into a second AC power; and The second converter unit is configured to convert the second AC power into the first DC power.

3. The system according to claim 2, characterized in that, The first converter unit and the second converter unit are in a full-bridge topology, a half-bridge topology, or a multi-level cascaded topology.

4. The system according to any one of claims 1-3, characterized in that, The isolated converter based on semiconductor switching devices is a magnetic element.

5. The system according to any one of claims 1-3, characterized in that, The isolated converter based on semiconductor switching devices is a solid-state transformer.

6. The system according to any one of claims 1-3, characterized in that, The first DC-DC converter uses a dual active bridge topology or a resonant converter topology to achieve DC-DC conversion.

7. The system according to any one of claims 1-3, characterized in that, It also includes an energy storage unit, which is connected between the DC traction grid and the first DC converter. The energy storage unit includes an energy storage medium and a second DC-DC converter. The second DC-DC converter is used to convert the braking DC power from the DC traction grid into a second DC power. The energy storage medium is used to collect the energy of the second DC power and provide the collected energy to the load and / or the first DC-DC converter.

8. The system according to any one of claims 1-3, characterized in that, It also includes an energy storage unit connected between the first DC converter and the inverter, and configured to collect energy output from the first DC converter and provide the collected energy to the load and / or the inverter.

9. The system according to any one of claims 1-3, characterized in that, Also includes: A DC circuit protection unit is connected between the DC traction power grid and the first DC converter; and / or An AC circuit protection unit is connected between the AC power grid and the inverter.

10. A rail transit operation system, characterized in that, This includes rail transit power supply systems and rail transit braking energy recovery systems as described in any one of claims 1-9; The rail transit power supply system includes: A transformer, configured to transform voltage from an AC power grid and supply it to a rectifier; and A rectifier is configured to convert input alternating current into direct current to supply the DC traction power grid.

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