Braking energy recovery system and rail transit operation system

Abstract

The utility model provides a brake energy recovery system and a rail transit operation system, the brake energy recovery system comprises: a first DC-DC converter, the first end of which is configured to be electrically connected to a DC traction power transmission line; the energy storage unit is connected to the second end of the first DC-DC converter; and a DC-AC converter, the first end of the DC-AC converter is connected to the second end of the first DC-DC converter, and the second end of the DC-AC converter is configured to be electrically connected to electric equipment except the DC traction power transmission line.

Description

Technical Field

[0001] The utility model belongs to the technical field of rail transit, and particularly relates to a braking energy recovery system and a rail transit operation system. Background Technique

[0002] The statements in this part are only for providing background information related to the utility model to help understand the utility model. These background information do not necessarily constitute the prior art.

[0003] Rail transit is a transportation mode that uses tracks to guide vehicle operation, mainly including railways, subways, light rails, tramways, etc., and has the advantages of strong carrying capacity, high transportation efficiency, low energy consumption, good safety, and small environmental pollution. Among them, urban rail transit (such as subways, light rails, tramways, etc.) is an important part of the urban public transportation system.

[0004] In the application of urban rail transit such as subways, the direct current (DC) traction power line of the vehicle is usually powered by a high voltage (HV) alternating current (AC) power grid of, for example, 10 kV to 35 kV. In a specific application, the high-voltage alternating current from the high-voltage AC power grid is converted into low-voltage (LV) alternating current, and then the low-voltage alternating current is converted into direct current of, for example, 750 V to 1500 V to be supplied to the DC traction power line of the vehicle.

[0005] However, during the operation of the subway, when the vehicle starts and runs, there will be a large amount of power consumption on the DC traction power line, and when the vehicle brakes, there will be a large amount of power injection into the DC traction power line. Therefore, the voltage of the DC traction power line will fluctuate. In particular, when the vehicle brakes, the voltage of the DC traction power line increases rapidly. When the voltage is higher than the voltage upper limit, the system will shut down due to overvoltage faults. Therefore, an energy absorption scheme is needed to solve the problem of braking power injection. In addition, since a large amount of braking energy is generated when the subway vehicle frequently leaves and arrives at the platform, for the purpose of green energy conservation and environmental protection, it is necessary to recycle and reuse the braking energy.

[0006] For the braking energy of the subway, the currently commonly used treatment solutions include the braking resistor solution, the energy feedback solution, and the energy storage solution. Among them, the braking resistor solution wastes all the braking energy and also generates a large amount of heat, thus increasing the burden on the in-station air conditioning system; the energy feedback solution changes the one-way transmission subway power supply system into a two-way transmission system, and feeds the braking energy from the DC traction transmission line back to the high-voltage AC power grid, which requires changing the original in-station power supply system, with low reliability and poor operability; while the energy storage solution uses a supercapacitor to absorb the braking energy from the DC traction transmission line and then provides the absorbed energy to the DC traction transmission line when the vehicle departs. This solution is limited by the capacity of the supercapacitor and has a low rated power. In addition, this solution requires the supercapacitor to quickly absorb energy during vehicle braking and quickly release energy during vehicle startup. This "fast charge and fast discharge" will seriously affect the life of the supercapacitor. Summary of the Invention

[0007] Therefore, the purpose of the present utility model is to overcome the defects of the above-mentioned prior art and provide a braking energy recovery system, including:

[0008] A first DC-DC converter, whose first end is configured to be electrically connectable to the DC traction transmission line;

[0009] An energy storage unit, which is connected to the second end of the first DC-DC converter; and

[0010] A DC-AC converter, the first end of the DC-AC converter is connected to the second end of the first DC-DC converter, and the second end of the DC-AC converter is configured to be electrically connected to electrical equipment other than the DC traction transmission line.

[0011] According to the braking energy recovery system of the present utility model, preferably, it further includes a first DC bus, wherein the energy storage unit is connected to the second end of the first DC-DC converter through the first DC bus, and the first end of the DC-AC converter is connected to the second end of the first DC-DC converter through the first DC bus.

[0012] According to the braking energy recovery system of the present utility model, preferably, the energy storage unit includes a supercapacitor or an energy storage battery.

[0013] According to the braking energy recovery system of the present utility model, preferably, the energy storage unit includes a supercapacitor and an energy storage battery.

[0014] According to the braking energy recovery system of the present utility model, preferably, it further includes a second DC-DC converter, wherein the supercapacitor or the energy storage battery is connected to the second end of the first DC-DC converter through the second DC-DC converter.

[0015] According to the braking energy recovery system of the present utility model, preferably, the DC-AC converter is connected to the second end of the first DC-DC converter through the second DC-DC converter.

[0016] According to the braking energy recovery system of the present utility model, preferably, it further includes an AC power grid, wherein the second end of the DC-AC converter is configured to be electrically connected to the electrical equipment through the AC power grid.

[0017] According to the braking energy recovery system of the present utility model, preferably, it includes the following working modes:

[0018] The first working mode, wherein the energy storage unit absorbs energy from the DC traction power line, and the DC-AC converter absorbs energy from the DC traction power line and supplies it to the AC power grid; and

[0019] The second working mode, the energy storage unit releases the absorbed energy to the AC power grid through the DC-AC converter.

[0020] According to the braking energy recovery system of the present utility model, preferably, the energy storage unit includes an energy storage battery, and the energy storage battery is configured to release the absorbed energy to the AC power grid during a specific time period.

[0021] According to the braking energy recovery system of the present utility model, preferably, the AC power grid supplies all the absorbed energy to the electrical equipment.

[0022] According to the braking energy recovery system of the present utility model, preferably, it further includes a third working mode, wherein the DC-AC converter absorbs energy from the AC power grid and supplies it to the DC traction power line.

[0023] According to the braking energy recovery system of the present utility model, preferably, it further includes a fourth working mode, wherein the energy storage unit absorbs energy from the AC power grid via the DC-AC converter.

[0024] According to the braking energy recovery system of the present utility model, preferably, the energy storage unit includes an energy storage battery, and the energy storage unit is configured to absorb energy from the AC power grid during a first specific time period and release the absorbed energy to the AC power grid during a second specific time period, wherein the electricity price during the second specific time period is higher than the electricity price during the first specific time period.

[0025] According to the braking energy recovery system of the present utility model, preferably, the AC power grid includes an electricity meter for measuring the amount of recovered braking energy.

[0026] The present utility model also provides a rail transit operation system, which includes a braking energy recovery system according to the present utility model.

[0027] Compared with the prior art, the braking energy recovery system of the present utility model has high reliability, fast response speed, low cost, and significant benefits. The recovery of braking energy is not limited by the capacity of the supercapacitor. The use of regenerated power is flexible and has a high utilization rate. In addition, the braking energy recovery system of the present utility model can continuously supply power to in-station electrical equipment. The discharge process of the supercapacitor is slow and its service life is long. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The following further describes the embodiments of the present utility model with reference to the drawings, where:

[0029] Figure 1 FIG. is a schematic diagram of a subway operation system according to an embodiment of the present utility model;

[0030] Figure 2 is Figure 1 The equivalent circuit topology of the part including the DC-DC converter, the supercapacitor, and the DC-AC converter in the shown embodiment;

[0031] Figure 3 FIG. is a schematic diagram of a subway operation system according to another embodiment of the present utility model;

[0032] Figure 4 FIG. is a schematic diagram of a subway operation system according to yet another embodiment of the present utility model;

[0033] Figure 5 FIG. is a schematic diagram of a subway operation system according to another embodiment of the present utility model; and

[0034] Figure 6 FIG. is a schematic diagram of a subway operation system according to another embodiment of the present utility model. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0035] In order to make the objectives, technical solutions, and advantages of the present utility model clearer, the following further details the present utility model through specific embodiments with reference to the drawings. It should be understood that the specific embodiments described herein are only used to explain the present utility model and are not used to limit the present utility model.

[0036] The embodiment of the present utility model provides a braking energy recovery system, especially a braking energy recovery system for urban rail transit. See Figure 1Schematic diagram of a subway operation system according to an embodiment of the present invention, which includes a power supply system 1 and a braking energy recovery system 2. The power supply system 1 is arranged between the high-voltage AC power grid 101 and the DC traction power transmission line 102, and the braking energy recovery system 2 is arranged between the DC traction power transmission line 102 and the low-voltage AC power grid 103. In the embodiment of the present invention, the voltage of the high-voltage AC power grid 102 is preferably 10 kV to 35 kV; the voltage of the DC traction power transmission line 102 is preferably 750 V to 1500 V, which is used to supply power to the vehicle; the voltage of the low-voltage AC power grid 103 is preferably 380 V to 450 V, for example, to supply power to electrical equipment such as air conditioners and lighting in the subway station.

[0037] The power supply system 1 includes a transformer T1 and a rectifier 104. The transformer T1 steps down the voltage from the high-voltage AC power grid 101 and supplies it to the rectifier 104. The rectifier 104 converts the input alternating current into direct current and supplies it to the DC traction power transmission line 102. Preferably, the rectifier 104 is a diode rectifier.

[0038] In a further embodiment, a circuit breaker and a disconnecting switch are arranged in the power supply system 1 to achieve circuit protection. For example, a first circuit breaker K1 is arranged between the high-voltage AC power grid 101 and the transformer T1, and the first circuit breaker K1 is a high-voltage AC circuit breaker; a second circuit breaker K2 is arranged between the transformer T1 and the rectifier 104, and the second circuit breaker K2 is, for example, a low-voltage AC circuit breaker; a third circuit breaker K3 and a first disconnecting switch ISO1 are arranged between the rectifier 104 and the DC traction power transmission line 102. Preferably, the third circuit breaker K3 is a DC circuit breaker, which is arranged between the positive pole of the DC output end of the rectifier 104 and the positive pole of the DC traction power transmission line 102; the first disconnecting switch ISO1 is arranged between the negative pole of the DC output end of the rectifier 104 and the negative pole of the DC traction power transmission line 102.

[0039] The braking energy recovery system 2 includes a DC-DC converter 105, a supercapacitor SC, and a DC-AC converter 106. The first end of the DC-DC converter 105 is connected to the DC traction power transmission line 102, and the second end is connected to both ends of the supercapacitor SC. It is used to convert the voltage of the DC traction power transmission line 102 and supply it to the supercapacitor SC to charge the supercapacitor SC; the first end (DC end) of the DC-AC converter 106 is connected to both ends of the supercapacitor SC, and the second end (AC end) is connected to the low-voltage AC power grid 103, which is used to invert the electrical energy from the supercapacitor SC and supply it to the low-voltage AC power grid 103. In addition, see Figure 2As can be seen from the equivalent circuit topology of the part including the DC-DC converter 105, the supercapacitor SC, and the DC-AC converter 106 of this embodiment shown, the first end of the DC-AC converter 106 is connected to the second end of the DC-DC converter 105, so that the voltage output by the DC-DC converter 105 can be directly inverted and supplied to the low-voltage AC power grid 103.

[0040] The electric energy received by the low-voltage AC power grid 103 can be stored in the energy storage module in the power grid or directly supply power to the in-station electrical equipment (such as the low-voltage load L). Those skilled in the art can understand that the power grid, also known as the electrical grid or power system, is a complex system composed of power generation facilities, transmission lines, substations, distribution networks, and related control and protection equipment. Its main function is to generate, transmit, distribute, and control electric energy. The low-voltage AC power grid 103 of the embodiment of the present utility model can store electric energy and can also supply power to electrical equipment other than vehicles. The electrical equipment other than vehicles includes in-station electrical equipment. Those skilled in the art can understand that the in-station electrical equipment includes air-conditioning equipment, lighting equipment, ticket-checking equipment, ventilation equipment, monitoring equipment, broadcasting equipment, elevators, escalators, advertising display screens, vending machines, communication equipment, ticket-selling equipment, security inspection equipment, charging equipment, office equipment, cleaning equipment, fire-fighting equipment, etc.

[0041] Preferably, a circuit breaker and a disconnecting switch are provided in the braking energy recovery system 2 to achieve circuit protection. For example, a fourth circuit breaker K4 and a second disconnecting switch ISO2 are provided between the DC-DC converter 105 and the DC traction transmission line 102. More preferably, the fourth circuit breaker K4 is a DC circuit breaker, which is provided between the positive pole of the first end of the DC-DC converter 105 and the positive pole of the DC traction transmission line 102; the second disconnecting switch ISO2 is provided between the negative pole of the first end of the DC-DC converter 105 and the negative pole of the DC traction transmission line 102.

[0042] In one embodiment, when the vehicle is running, the high-voltage AC power grid 101 supplies power to the DC traction transmission line 102 through the power supply system 1 to tow the vehicle; when the vehicle brakes, the vehicle braking energy is charged from the DC traction transmission line 102 to the supercapacitor SC via the DC-DC converter 105. If the captured vehicle braking energy is greater than the capacity of the supercapacitor SC, the energy from the DC traction transmission line 102 can also be directly supplied to the low-voltage AC power grid 103 via the DC-DC converter 105 and the DC-AC converter 106, bypassing the supercapacitor SC in this process. Therefore, the braking energy recovery of the embodiment of the present utility model is not limited by the capacity of the supercapacitor SC.

[0043] In another embodiment, when the vehicle brakes, most of the braking energy (e.g., 80%) is supplied to the supercapacitor SC via the DC traction power line 102 through the DC-DC converter 105 to charge the supercapacitor, while another part of the braking energy (e.g., 20%) is directly supplied to the low-voltage AC power grid 103 via the DC-DC converter 105 and the DC-AC converter 106 to supply power to the on-station electrical equipment; and during the interval between two brakings of the vehicle (including the vehicle startup process and the vehicle operation process), the supercapacitor SC continuously supplies stable power to the on-station electrical equipment through the DC-AC converter 106. Therefore, the braking energy recovery system of the embodiment of the present utility model can continuously supply power to the on-station electrical equipment. In addition, since the DC-AC converter 106 can provide a stable power output, the on-station electrical equipment can be continuously and stably powered by the braking energy recovery system. Thus, the recovery and utilization rate of the braking energy is greatly improved, and the cost is further saved.

[0044] In the embodiment of the present utility model, the voltage of the low-voltage AC power grid 103 is lower than the voltage of the DC traction power line 102, and the discharge of the supercapacitor SC occurs during the vehicle startup and operation processes, and the discharge duration is long. Therefore, the discharge of the supercapacitor is a "slow discharge" process. Therefore, the embodiment of the present utility model extends the service life of the supercapacitor.

[0045] In summary, the embodiment of the present utility model sets up an independent braking energy recovery system to recover the braking energy of the vehicle, without changing the existing subway traction system, with high reliability, fast response speed, low cost, and significant benefits; the recovery of the braking energy is not limited by the capacity of the supercapacitor, the use of the regenerative power is flexible and the utilization rate is high; the braking energy recovery system can continuously supply power to the on-station electrical equipment; the discharge process of the supercapacitor is slow and the service life is long.

[0046] Another embodiment of the present utility model provides another braking energy recovery system. Refer to Figure 3 the schematic diagram of the subway operation system according to another embodiment of the present utility model as shown. The braking energy recovery system 2 of this embodiment adds another DC-DC converter 107 and an energy storage battery B on the basis of the Figure 1 braking energy recovery system as shown. Among them, the second end of the DC-DC converter 105 is also connected to the charging port of the energy storage battery B through the DC-DC converter 107.

[0047] In this embodiment, the supercapacitor SC and the energy storage battery B constitute an energy storage unit. When the vehicle is running, the high-voltage AC power grid 101 supplies power to the DC traction power line 102 through the power supply system 1 to drive the vehicle; when the vehicle brakes, the braking energy of the vehicle can be divided into three parts. The first part charges the supercapacitor SC from the DC traction power line 102 through the DC-DC converter 105. The second part charges the energy storage battery B through the DC-DC converters 105 and 107. The third part directly bypasses the supercapacitor SC and the energy storage battery B and is supplied to the low-voltage AC power grid 103 through the DC-AC converter 106. In the embodiment of the present utility model, the energy storage battery B can absorb a part of the braking energy, thereby further reducing the capacity of the supercapacitor. In addition, the energy storage battery B can also be used as a backup power source during power outages. In one embodiment, the energy storage battery B is controlled to supply power to the in-station electrical equipment during the peak period of in-station power consumption (such as the peak period of going to and from work), so as to achieve peak shaving and valley filling and further save the power consumption cost. Preferably, during the interval between two brakings of the vehicle, if the energy storage battery B is undercharged, the supercapacitor SC also charges the energy storage battery B through the DC-DC converter 107.

[0048] Compared with Figure 1 the embodiment shown, the braking energy recovery system of this embodiment can provide a backup power source, transfer peak loads, further improve the utilization rate of braking energy and further save costs.

[0049] Another embodiment of the present utility model provides another braking energy recovery system. Refer to Figure 4 the schematic diagram of the subway operation system according to another embodiment of the present utility model shown. The difference from the Figure 3 embodiment shown is that the DC-DC converter 107 is connected between the supercapacitor SC and the DC-DC converter 105, rather than between the energy storage battery B and the DC-DC converter 105. Those skilled in the art can understand that the position of the DC-DC converter 107 depends on the matching degree between the output voltage range of the DC-DC converter 105 and the voltage of the supercapacitor or the energy storage battery.

[0050] In one embodiment of the present utility model, the DC-AC converter 106 supplies power to the in-station electrical equipment through the low-voltage AC power grid. In another embodiment of the present utility model, the second end of the DC-AC converter 106 is directly connected to the in-station electrical equipment to supply power to the in-station electrical equipment.

[0051] Another embodiment of the present utility model provides a braking energy recovery system, especially for the braking energy recovery system of urban rail transit. Refer to Figure 5Schematic diagram of a subway operation system according to an embodiment of the present invention, which includes a power supply system 1 and a braking energy recovery system 2. Among them, the structure of the power supply system 1 is the same as that of the power supply system in the previous embodiment. The braking energy recovery system 2 of this embodiment includes a first DC-DC converter 105, a DC-AC converter 106, a second DC-DC converter 107, a supercapacitor SC, and an energy storage battery B. Among them, the positive electrode of the first end of the first DC-DC converter 105 is connected to the positive electrode of the DC traction transmission line 102 through the fourth circuit breaker K4, and the negative electrode of the first end of the first DC-DC converter 105 is connected to the negative electrode of the DC traction transmission line 102 through the second DC isolator ISO2. The second end of the first DC-DC converter is electrically connected to the DC bus 108; the supercapacitor SC is connected to the DC bus 108; the energy storage battery B is connected to the DC bus 108 through the second DC-DC converter 107; and the first end of the DC-AC converter 106 is connected to the DC bus 108, and the second end is connected to the low-voltage AC power grid 103 through the fifth circuit breaker K5. The low-voltage AC power grid 103 is used to supply power to the in-station electrical equipment L.

[0052] Illustratively rather than restrictively, the voltage of the high-voltage AC power grid 101 is 35 kV; the voltage of the DC traction transmission line 102 is 1500 V; the voltage of the DC bus 108 is 300 V to 1000 V, preferably 650 V to 1000 V or 300 V to 850 V or 500 V to 1000 V; the voltage of the low-voltage AC power grid 103 is 400 V.

[0053] In this example, when the vehicle is running, the high-voltage AC power grid 101 supplies power to the DC traction transmission line 102 through the power supply system 1 to tow the vehicle. When the vehicle brakes, the braking energy of the vehicle is provided to the DC bus 108 after being stepped down and converted by the DC-DC converter 105 from the 1500 V DC traction transmission line 102. The DC bus 108 can charge the supercapacitor SC, charge the energy storage battery B through the DC-DC converter 107, and supply power to the low-voltage AC power grid 103 through the DC-AC converter 106. During the interval between two brakings of the vehicle, the supercapacitor SC supplies power to the low-voltage AC power grid 103 through the DC-AC converter 106, and can also charge the energy storage battery B through the DC-DC converter 105 when the energy storage battery B is undercharged. The energy storage battery B is used as an emergency backup power supply and can also be configured to supply power to the in-station load during a specific period to achieve peak shaving and valley filling.

[0054] Taking subway operation as an example, generally, the subway operation time is from 6:30 am to 10:30 pm. During the operation, on average, a vehicle enters the station every 3 minutes, and the effective braking time of the vehicle is 18 seconds. Assume that each time the vehicle brakes, 13 kWh of energy is released to the DC traction power line. In one example, 10 kWh of the 13 kWh of braking energy is absorbed by the supercapacitor SC, and the other 3 kWh is directly released to the low-voltage AC power grid 103 through the DC-AC converter 106. In another example, 8 kWh of the braking energy is absorbed by the supercapacitor SC, 2 kWh of the braking energy is absorbed by the energy storage battery B, and the other 3 kWh of the braking energy is directly released to the low-voltage AC power grid 103 through the DC-AC converter 106. The distribution of the braking energy can be set according to actual needs. As is well known to those skilled in the art, the energy (E) stored in a capacitor can be expressed as where C is the capacitance of the capacitor (in farads F), and V is the voltage across the capacitor (in volts V). The more energy the capacitor needs to absorb, the higher the requirement for the capacitance of the capacitor. Therefore, the setting of the low-voltage AC power grid enables the braking energy recovery to be not limited by the capacity of the supercapacitor, and the setting of the energy storage battery B can further reduce the requirement for the capacity of the supercapacitor.

[0055] In one embodiment, the first DC-DC converter 105, the supercapacitor SC, the second DC-DC converter 107, and the DC-AC converter 106 are connected to different ports of the DC bus 108. In another embodiment, the energy storage battery B is directly connected to the DC bus 108 while the supercapacitor SC is connected to the DC bus 108 through the second DC-DC converter 107. In another embodiment, the braking energy recovery system 2 does not include the energy storage battery B and the second DC-DC converter 107. In another embodiment, the braking energy recovery system only includes the energy storage battery B as the energy storage unit, and the energy storage battery B is directly connected to the DC bus 108.

[0056] Another embodiment of the present invention provides a braking energy recovery system, especially for the braking energy recovery system of urban rail transit, see Figure 6Schematic diagram of a subway operation system according to an embodiment of the present invention, which includes a power supply system 1 and a braking energy recovery system 2. Among them, the structure of the power supply system 1 is the same as that of the power supply system in the foregoing embodiment, and will not be described herein again. The braking energy recovery system 2 of this embodiment includes a first DC-DC converter 105, a DC-AC converter 106, a second DC-DC converter 107, a supercapacitor SC, and an energy storage battery B. Among them, the positive pole of the first end of the first DC-DC converter 105 is connected to the positive pole of the DC traction power line 102 through a fourth circuit breaker K4, and the negative pole of the first end of the first DC-DC converter 105 is connected to the negative pole of the DC traction power line 102 through a second DC isolator ISO2. The second end of the first DC-DC converter 105 is electrically connected to the first DC bus 108; the supercapacitor SC is connected to the first DC bus 108; the first end of the second DC-DC converter 107 is connected to the first DC bus 108, and the second end is connected to the second DC bus 109; the energy storage battery B is connected to the second DC bus 109; the first end of the DC-AC converter 106 is connected to the second DC bus 109, and the second end is connected to the low-voltage AC power grid 103 through a fifth circuit breaker K5. The low-voltage AC power grid 103 is used to supply power to the in-station electrical equipment L. The difference between this embodiment and Figure 5 the embodiment shown is that the DC-AC converter 106 for providing stable power to the low-voltage AC power grid 103 obtains a voltage signal from the second DC bus 109. The voltage of the second DC bus 109 is the voltage after the voltage of the first DC bus 108 is transformed by the second DC-DC converter 107, which further improves the conversion efficiency and stability and further improves the electromagnetic compatibility.

[0057] Schematically and non-limitingly, the voltage of the first DC bus 108 is 500V to 1000V, and the voltage of the second DC bus 109 is 630V to 810V.

[0058] In one embodiment, the braking energy recovery system 2 does not include the energy storage battery B.

[0059] The DC-AC converter of the braking energy recovery system in the embodiment of the present invention absorbs energy and performs DC-AC conversion on it and then provides it to the in-station electrical equipment.

[0060] The DC-AC converter of the braking energy recovery system in the embodiment of the present invention absorbs energy and performs DC-AC conversion on it and then provides it to the in-station electrical equipment through the AC power grid.

[0061] The braking energy recovery system in one embodiment of the present invention includes at least the following two working modes:

[0062] The first operating mode, in which the energy storage unit absorbs energy from the DC traction power line, and the DC-AC converter absorbs energy from the DC traction power line and supplies it to the AC power grid; and

[0063] The second operating mode, in which the energy storage unit releases the absorbed energy to the AC power grid through the DC-AC converter. Preferably, the energy storage unit includes an energy storage battery, and the energy storage battery is configured to release the absorbed energy to the AC power grid during a specific time period to supply power to the in-station electrical equipment, for example, release the absorbed energy during a time period with a higher electricity price. In another embodiment, the braking energy recovery system further includes a third operating mode, in which the DC-AC converter is a bidirectional converter and the energy is transmitted in reverse, that is, the DC-AC converter absorbs energy from the AC power grid and supplies it to the DC traction power line. For example, in Figure 1 the embodiment shown, the DC-AC converter 106 absorbs energy from the low-voltage AC power grid 103 and supplies it to the DC traction power line 102 through the DC-DC converter 105.

[0064] In yet another embodiment, the braking energy recovery system further includes a fourth operating mode, in which the energy storage unit absorbs energy from the AC power grid via the DC-AC converter. Also for example Figure 1 as shown, the DC-AC converter 106 absorbs energy from the low-voltage AC power grid 103 and charges the supercapacitor SC. Preferably, the energy storage unit includes an energy storage battery, and the energy storage unit is configured to absorb energy from the AC power grid during a first specific time period, and release the absorbed energy to the AC power grid during a second specific time period, where the electricity price during the second specific time period is higher than that during the first specific time period. For example, during the low electricity consumption valley period with a lower electricity price, the energy storage battery stores energy, while during the high electricity consumption peak period with a higher electricity price, the energy storage battery releases energy, so as to achieve peak shaving and valley filling.

[0065] In the embodiment of the present utility model, the braking energy of the rail transit vehicle can be entirely absorbed by the AC power grid, and then the AC power grid distributes the absorbed energy. An electricity meter can be set on the AC power grid side to measure the amount of the recovered braking energy. Since the voltage of the AC power grid is relatively low, this method of measuring braking energy is economical, reliable and low-cost. In one embodiment, the AC power grid supplies all the energy to the in-station low-voltage load. In another embodiment, the AC power grid supplies a part of the absorbed energy to the in-station load, and the other part is fed back to the DC traction power line.

[0066] The in-station electrical equipment in the embodiment of the present utility model is an AC load and receives the AC signal from the DC-AC converter. Those skilled in the art can understand that the AC signal from the DC-AC converter can also be supplied to the DC load through the AC-DC converter.

[0067] The braking energy recovery system of the embodiment of the present utility model provides braking energy to electrical equipment other than the DC traction power line instead of feeding back the braking energy to the DC traction power line. Thus, the braking energy recovery system quickly absorbs energy during vehicle braking, and can release energy during vehicle braking, starting, and running. Therefore, continuous slow discharge of the braking energy recovery system is achieved, realizing "fast charge and slow discharge" of the energy storage unit, effectively prolonging the service life of the energy storage unit. In addition, the continuous discharge of the braking energy recovery system can stably supply power to in-station electrical equipment, improving the recovery utilization rate of braking energy and saving costs.

[0068] According to other embodiments of the present utility model, the energy storage unit for absorbing vehicle braking energy is not limited to supercapacitors and energy storage batteries, and other energy storage devices well-known in the art can also be used, such as flywheels, capacitors, inductors, etc. In the embodiments of the present utility model, the energy storage battery can be a lithium-ion battery, a lead-acid battery, etc.

[0069] According to other embodiments of the present utility model, in the circuit, fuses are provided between, for example, supercapacitors, energy storage batteries, DC-AC converters and the DC bus for circuit protection.

[0070] According to other embodiments of the present utility model, the power grid for consuming the recovered braking energy is not limited to the low-voltage power grid, and any power grid that can supply power to in-station electrical equipment is applicable to the present utility model.

[0071] The embodiments of the present utility model are described by taking the subway as an example. Those skilled in the art can understand that any rail transit vehicle well-known in the art is applicable to the present utility model.

[0072] Although the present utility model has been described through preferred embodiments, the present utility model is not limited to the embodiments described herein, and various changes and variations are also included without departing from the scope of the present utility model.

Claims

1. A braking energy recovery system, comprising: A first DC-DC converter, a first end of which is configured to be electrically connectable to a DC traction power line; An energy storage unit, which is connected to a second end of the first DC-DC converter; And A DC-AC converter, a first end of the DC-AC converter is connected to the second end of the first DC-DC converter, and a second end of the DC-AC converter is configured to be electrically connected to an electrical device other than the DC traction power line.

2. The braking energy recovery system according to claim 1, wherein, It further includes a first DC bus, wherein the energy storage unit is connected to the second end of the first DC-DC converter through the first DC bus, and the first end of the DC-AC converter is connected to the second end of the first DC-DC converter through the first DC bus.

3. The braking energy recovery system according to claim 1, wherein The energy storage unit includes a supercapacitor or an energy storage battery.

4. The braking energy recovery system according to claim 1, wherein The energy storage unit includes a supercapacitor and an energy storage battery.

5. The braking energy recovery system according to claim 4, wherein, It further includes a second DC-DC converter, wherein the supercapacitor or the energy storage battery is connected to the second end of the first DC-DC converter through the second DC-DC converter.

6. The braking energy recovery system according to claim 5, wherein, The DC-AC converter is connected to the second end of the first DC-DC converter through the second DC-DC converter.

7. The braking energy recovery system according to any one of claims 1-6, wherein, It further includes an AC power grid, wherein the second end of the DC-AC converter is configured to be electrically connected to the electrical device through the AC power grid.

8. The braking energy recovery system according to claim 7, wherein, It includes the following operating modes: A first operating mode, wherein the energy storage unit absorbs energy from the DC traction power line, and the DC-AC converter absorbs energy from the DC traction power line and supplies it to the AC power grid; and A second operating mode, the energy storage unit releases the absorbed energy to the AC power grid through the DC-AC converter.

9. The braking energy recovery system according to claim 8, wherein, The energy storage unit includes an energy storage battery, and the energy storage battery is configured to release the absorbed energy to the AC power grid during a specific time period.

10. The braking energy recovery system according to claim 8 or 9, wherein, The AC power grid supplies all the absorbed energy to the electrical device.

11. The braking energy recovery system according to claim 8, wherein, It further includes a third operating mode, wherein the DC-AC converter absorbs energy from the AC power grid and supplies it to the DC traction power line.

12. The braking energy recovery system according to claim 8, wherein, It further includes a fourth operating mode, wherein the energy storage unit absorbs energy from the AC power grid via the DC-AC converter.

13. The braking energy recovery system according to claim 12, wherein, The energy storage unit includes an energy storage battery, and the energy storage unit is configured to absorb energy from the AC power grid during a first specific time period and release the absorbed energy to the AC power grid during a second specific time period, wherein the electricity price during the second specific time period is higher than the electricity price during the first specific time period.

14. The braking energy recovery system according to claim 8 or 9, wherein, The AC power grid includes an electricity meter for measuring the amount of recovered braking energy.

15. A rail transit operation system, which includes the braking energy recovery system according to any one of claims 1-14.

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