Hybrid charging and discharging device for energy storage system of tramcar

Abstract

A hybrid charging and discharging device of a tramcar energy storage system comprises a super capacitor, a lithium battery and a bidirectional DC / DC device. One end of the super capacitor and one end of the bidirectional DC / DC device are electrically connected with a main circuit bus of the tramcar, and the other end of the bidirectional DC / DC device is electrically connected with the lithium battery. The bidirectional DC / DC device comprises two bidirectional DC / DC units which are connected in parallel, and each bidirectional DC / DC subunit comprises two bidirectional DC / DC circuits which are connected in parallel. Compared with the prior art, the energy storage type tramcar comprehensively utilizes the advantages of large charge-discharge multiplying power of the super capacitor and large energy storage of the lithium battery, and solves the problems that the endurance mileage of an existing energy storage type tramcar with the super capacitor as an energy storage element is short, and if the lithium battery is used as the energy storage element, the power requirement of large ramp running of the tramcar cannot be met. Therefore, the vehicle is short in charging time, long in endurance mileage, high in gradeability and high in running speed.

Description

Technical Field

[0001] The utility model relates to the technical field of trams, and in particular to a hybrid charging and discharging device of a tram energy storage system. Background Art

[0002] Existing energy storage trams use supercapacitors as energy storage elements for power supply. Supercapacitors have a large charge and discharge rate but store less energy. They have the characteristics of fast charge and fast discharge, but the vehicle's range is short. Using supercapacitors as a tram energy storage system alone cannot give full play to the tram's operating capacity, affecting the average driving speed and passengers' riding experience.

[0003] Lithium batteries have a low charge and discharge rate but can store large amounts of energy, which can increase the vehicle's range. However, they take a long time to charge and cannot meet the power requirements of the vehicle when operating on steep slopes. Summary of the invention

[0004] The invention of this application aims to solve the problem that the existing energy storage type tram has a short cruising range if it uses supercapacitors as energy storage elements, and cannot meet the power requirements of the vehicle running on a steep slope if it uses lithium batteries as energy storage elements.

[0005] In order to achieve the above-mentioned purpose, this application adopts the following technical solution.

[0006] Provided is a hybrid charging and discharging device for a tram energy storage system, comprising a supercapacitor, a lithium battery and a bidirectional DC / DC device; one end of the supercapacitor and the bidirectional DC / DC device are electrically connected to the main circuit bus of the tram respectively, and the other end of the bidirectional DC / DC device is electrically connected to the lithium battery;

[0007] The bidirectional DC / DC device includes two bidirectional DC / DC units connected in parallel with each other, each of the bidirectional DC / DC subunits includes two bidirectional DC / DC circuits connected in parallel with each other, a fuse is connected in series between each bidirectional DC / DC circuit and the supercapacitor, and a contactor is connected in series between each bidirectional DC / DC circuit and the lithium battery.

[0008] Therefore, on the basis of retaining the power supply of supercapacitors, by adding a bidirectional DC / DC device between the output end of the lithium battery and the main circuit bus of the vehicle, the electric energy of the lithium battery is converted into DC / DC and then used together with the supercapacitor to power the vehicle load, and the advantages of the large charge and discharge rate of the supercapacitor and the large energy storage of the lithium battery are comprehensively utilized, thereby solving the problem that the existing energy storage trams have a short range when using supercapacitors as energy storage elements, and cannot meet the power requirements of the vehicle running on large slopes if lithium batteries are used as energy storage elements, so that the vehicle has a short charging time, a long range, a strong climbing ability, and a fast driving speed. Secondly, a redundant solution is set for the bidirectional DC / DC device to reduce the probability of vehicle degradation due to failure of the bidirectional DC / DC device and improve the reliability of normal operation of the vehicle.

[0009] In some embodiments, a main contactor, a pre-charging contactor and a pre-charging resistor are provided between each of the bidirectional DC / DC sub-units and the supercapacitor; the main contactor is connected in series between each of the bidirectional DC / DC sub-units and the supercapacitor, and the pre-charging contactor and the pre-charging resistor are connected in series to form a branch connected in parallel with the main contactor.

[0010] In some embodiments, a voltage detection device is provided between each of the bidirectional DC / DC subunits and the supercapacitor, and between each of the bidirectional DC / DC subunits and the lithium battery.

[0011] In some embodiments, the bidirectional DC / DC circuit is formed by three buck-boost circuits connected in parallel.

[0012] This application has at least the following technical effects or advantages:

[0013] 1. Comprehensively utilizing the advantages of large charge and discharge rate of supercapacitors and large energy storage of lithium batteries, the problem of short mileage of existing energy storage trams using supercapacitors as energy storage elements and inability to meet the power requirements of vehicles running on large slopes if lithium batteries are used as energy storage elements is solved, making the vehicle have short charging time, long mileage, strong climbing ability and fast driving speed.

[0014] 2. A redundancy scheme is set up for the bidirectional DC / DC device to reduce the probability of vehicle degradation due to failure of the bidirectional DC / DC device and improve the reliability of normal vehicle operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a schematic structural diagram of a hybrid charging and discharging device for a tram energy storage system in one embodiment of the present application;

[0016] Figure 2 This is a schematic diagram of the structure of a bidirectional DC / DC device in an embodiment of the present application;

[0017] Figure 3 Schematic diagram of the structure of a bidirectional DC / DC circuit in one embodiment of the present application. DETAILED DESCRIPTION

[0018] In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0019] Embodiment 1

[0020] See also Figure 1 A hybrid charging and discharging device for a tram energy storage system includes a super capacitor 1, a lithium battery 2, and a bidirectional DC / DC device 3. One end of the super capacitor 1 and the bidirectional DC / DC device 3 are electrically connected to the main circuit bus of the tram, and the other end of the bidirectional DC / DC device 3 is electrically connected to the lithium battery 2.

[0021] like Figure 2 As shown, the bidirectional DC / DC device 3 includes two bidirectional DC / DC units connected in parallel, and each bidirectional DC / DC subunit includes two bidirectional DC / DC circuits 311 connected in parallel. A fuse is connected in series between each bidirectional DC / DC circuit 311 and the supercapacitor 1. The fuses connected in series with the four bidirectional DC / DC circuits 311 are FU1, FU2, FU3, and FU4 respectively. When an overcurrent or short circuit fault occurs in a branch, the corresponding fuse will immediately blow to cut off the branch to prevent the fault from expanding. A contactor is connected in series between each bidirectional DC / DC circuit 311 and the lithium battery 2. The contactors connected in series with the four bidirectional DC / DC circuits 311 are KM12, KM13, KM22, and KM23 respectively. When a branch fails, the corresponding contactor is disconnected, and the branch is out of operation without affecting the normal operation of other branches.

[0022] The two bidirectional DC / DC units are respectively a first bidirectional DC / DC unit 31 and a second bidirectional DC / DC unit 32. A first main contactor KM11, a first pre-charging contactor KM1 and a first pre-charging resistor R1 are provided between the first bidirectional DC / DC unit 31 and the supercapacitor 1, wherein the first main contactor KM11 is connected in series between the first bidirectional DC / DC unit 31 and the supercapacitor 1, and the first pre-charging contactor KM1 and the first pre-charging resistor R1 are connected in series to form a branch in parallel with the first main contactor KM11. A second main contactor KM21, a second pre-charging contactor KM2 and a second pre-charging resistor R2 are provided between the second bidirectional DC / DC unit 32 and the supercapacitor 1, wherein the second main contactor KM21 is connected in series between the second bidirectional DC / DC unit 32 and the supercapacitor 1, and the second pre-charging contactor KM2 and the second pre-charging resistor R2 are connected in series to form a branch in parallel with the second main contactor KM21. When a bidirectional DC / DC unit fails, the corresponding main contactor and pre-charging contactor can be disconnected to cut off the failed unit.

[0023] A first voltage detection device U1 is provided between the first bidirectional DC / DC unit 31 and the supercapacitor 1, a second voltage detection device U2 is provided between the second bidirectional DC / DC unit 32 and the supercapacitor 1, a third voltage detection device U3 is provided between the first bidirectional DC / DC unit 31 and the lithium battery 2, and a fourth voltage detection device U4 is provided between the second bidirectional DC / DC unit 32 and the lithium battery 2.

[0024] like Figure 3 As shown, the bidirectional DC / DC circuit 311 is composed of three buck-boost circuits in parallel. When the circuit is running in the forward direction, the lower tube IGBT is continuously turned off, the diode acts as a freewheeling current, the upper tube is controlled by pulses, and the capacitor, IGBT, and reactor form a buck circuit topology to achieve a step-down chopping function. The right side (battery) voltage is always lower than the left side (supercapacitor) voltage. When the circuit is running in the reverse direction, the upper tube IGBT is continuously turned off, the diode acts as a freewheeling current, the lower tube is controlled by pulses, and the reactor, IGBT, and capacitor form a boost circuit topology to achieve a step-up chopping function. The left side (supercapacitor) voltage is always higher than the right side (battery) voltage.

[0025] The pulse phase-shifting control of the three IGBTs, the current sensors BC1, BC2, and BC3 monitor the chopping current of the three IGBTs respectively, and make the average current of each reactor (L1-L3) equal and close to the target value by slightly adjusting the pulse width. The discharge resistor R is used to reduce the high voltage on the chopping capacitors C1 and C2 to less than 50V within 5 minutes after the high voltage power is cut off.

[0026] In order to quickly respond to the energy transfer of supercapacitors and lithium titanate batteries, as long as the supercapacitors and batteries are not over-voltage, the on-board DC / DC will start to the pre-pulse preparation state. Taking the first branch as an example, the first pre-charge contactor KM1 is closed, and the chopper capacitors C1 and C2 are pre-charged to a voltage close to that of the supercapacitor. Then the first pre-charge contactor KM1 is disconnected, and contactors KM11 and KM12 are closed. At this time, the IGBT is in the off state, and the current of all reactors is 0.

[0027] When running on the positive line, the supercapacitor will be used to power the vehicle first. If the supercapacitor has insufficient energy, the lithium battery will be put into use to convert the output voltage of the lithium battery to be consistent with the main circuit bus voltage, thereby mixing with the supercapacitor to power the vehicle load; when the vehicle is charging, the bidirectional DC / DC charges the lithium battery through step-down chopping.

[0028] Specifically, when charging a lithium battery, the pulse duty cycle of the upper tube of the IGBT gradually increases from 0, and the battery current rises from 0 to 700A, and then charges at a constant 700A. When the tram needs to leave the station, the pulse duty cycle is reduced to 0, and the charging current is correspondingly reduced to 0, and then the contactor remains in a closed state.

[0029] When the vehicle leaves the platform or the supercapacitor energy is insufficient under other working conditions, the lithium battery needs to be discharged to charge the supercapacitor. The pulse duty cycle of the lower tube of the IGBT component gradually increases from 0, and the voltage of the chopper capacitor is slightly higher than the supercapacitor voltage. The battery energy is transmitted to the supercapacitor, traction inverter, and 24V charger to provide sufficient energy for vehicle traction assistance.

[0030] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the utility model, rather than to limit it. Although the utility model has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the utility model.

Claims

1. A hybrid charging and discharging device for a tram energy storage system, characterized in that: It comprises a super capacitor, a lithium battery and a bidirectional DC / DC device; one end of the super capacitor and the bidirectional DC / DC device are electrically connected to the main circuit bus of the tram respectively, and the other end of the bidirectional DC / DC device is electrically connected to the lithium battery; The bidirectional DC / DC device includes two bidirectional DC / DC units connected in parallel with each other, each of the bidirectional DC / DC subunits includes two bidirectional DC / DC circuits connected in parallel with each other, a fuse is connected in series between each bidirectional DC / DC circuit and the supercapacitor, and a contactor is connected in series between each bidirectional DC / DC circuit and the lithium battery.

2. The hybrid charging and discharging device for the tram energy storage system according to claim 1, characterized in that: A main contactor, a pre-charging contactor and a pre-charging resistor are provided between each of the bidirectional DC / DC sub-units and the supercapacitor; the main contactor is connected in series between each of the bidirectional DC / DC sub-units and the supercapacitor, and the pre-charging contactor and the pre-charging resistor are connected in series to form a branch connected in parallel with the main contactor.

3. The hybrid charging and discharging device of the tram energy storage system according to claim 1 or 2, characterized in that: A voltage detection device is provided between each of the bidirectional DC / DC subunits and the supercapacitor, and between each of the bidirectional DC / DC subunits and the lithium battery.

4. The hybrid charging and discharging device for a tram energy storage system according to claim 1 or 2, characterized in that: The bidirectional DC / DC circuit is formed by connecting three buck-boost circuits in parallel.

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