A system and method for composite utilization of regenerative braking energy on long and steep slopes of high-speed railways

Abstract

The present invention provides a system and method for composite utilization of regenerative braking energy on long and steep slopes of high-speed railways. The system includes an on-board energy storage unit, a power integration unit, and a ground energy storage unit. The method includes on-board energy storage, train traction consumption, ground energy storage, and brake resistor consumption. The on-board energy storage unit realizes the storage and release of regenerative braking energy. The power integration unit is used to construct an energy interaction channel to realize the transmission of regenerative braking energy on out-of-phase power supply arms. The ground energy storage unit is connected to the high-speed railway traction power supply system through the power integration unit to realize the storage and release of regenerative braking energy. The present invention adds converters and energy storage equipment to the high-speed railway traction power supply system and the train traction transmission system, realizes the composite utilization of regenerative braking energy on long and steep slope lines, improves the utilization rate of regenerative braking energy, and is conducive to promoting the green and low-carbon development of high-speed railways.

Description

Technical Field

[0001] The present invention relates to the field of rail transportation technology, and in particular to a system and method for composite utilization of regenerative braking energy on a high-speed railway long and steep slope. Background Art

[0002] my country's terrain is high in the west and low in the east. The railway network in the central and western regions is characterized by a large design slope and long slope lines. When a high-speed train runs in a long and steep slope section in the downhill direction, it is preferred to use regenerative braking to slow down. At this time, the traction motor works in the power generation state to generate regenerative braking energy and return it to the traction network. The regenerative braking energy generated by the train on the long and steep slope line can reach 10%~30% of the traction energy. However, the regenerative braking energy that is not effectively utilized and returned to the traction network will cause the network voltage to rise, endangering driving safety. In addition, since the regenerative braking energy contains a large number of harmonics and negative sequence components, the power department imposes punitive charges on the regenerative braking energy returned to the external power grid, which increases the operating burden of the railway department. Therefore, through the composite utilization of regenerative braking energy on the long and steep slope of high-speed railways, the effective utilization of regenerative braking energy in the traction power supply system is promoted, which is conducive to promoting energy conservation and consumption reduction in the railway department and has economic benefits. Summary of the invention

[0003] The purpose of the present invention is to solve the above-mentioned problems and to provide a system and method for composite utilization of regenerative braking energy on long and steep slopes of high-speed railways.

[0004] To achieve the above object, the technical solution adopted by the present invention is:

[0005] According to one aspect of the present invention, a high-speed railway long and steep slope regenerative braking energy composite utilization system is provided, comprising: an on-board energy storage unit, a power financing unit, and a ground energy storage unit. The on-board energy storage unit is connected in parallel to both ends of a DC side support capacitor of a traction drive system of a high-speed train, the power financing unit is connected in parallel to two out-of-phase power supply arms at the outlet of a traction substation or a substation, and the ground energy storage unit is connected in parallel to both ends of a DC side support capacitor of the power financing unit.

[0006] Furthermore, the on-board energy storage unit includes a three-port bidirectional DC / DC converter, a supercapacitor, and a lithium battery. The supercapacitor and the lithium battery serve as energy storage media and are respectively connected to two low-voltage DC ports of the three-port bidirectional DC / DC converter. The high-voltage DC port of the three-port bidirectional DC / DC converter is connected in parallel to both ends of the DC side support capacitor of the high-speed train traction drive system.

[0007] Furthermore, the ground energy storage unit includes a three-port bidirectional DC / DC converter, a supercapacitor, and a lithium battery. The supercapacitor and the lithium battery serve as energy storage media and are respectively connected to two low-voltage DC ports of the three-port bidirectional DC / DC converter. The high-voltage DC port of the three-port bidirectional DC / DC converter is connected in parallel to both ends of the DC side support capacitor of the power financing unit.

[0008] Furthermore, the supercapacitor is a double-layer supercapacitor, and the lithium battery is a ternary lithium battery or a lithium iron phosphate battery.

[0009] A method for composite utilization of regenerative braking energy on a high-speed railway long and steep slope according to the present invention is based on the above system and comprises the following steps:

[0010] Step 1: On-board energy storage, the on-board energy storage unit of the braking train stores the regenerative braking energy;

[0011] Step 2: Train traction consumption, which is consumed by trains in traction condition on the same or adjacent power supply arm;

[0012] Step 3: Ground energy storage, which is stored by ground energy storage units connected to the same or adjacent power supply arms;

[0013] Step 4: The braking resistor is consumed by the braking resistor of the braking condition train.

[0014] Furthermore, the system power satisfies the relationship:

[0015]

[0016] in, P regen Output power for train regenerative braking; P ESS is the power transferred through the energy storage unit; P t is the power consumed by the traction train; P r is the power consumed by the braking resistor; P ESS,onb is the power of the on-board energy storage unit; P ESS,way is the power of the ground energy storage unit; P tract The power required for train traction; P TSS The power provided for traction substation.

[0017] Furthermore, the on-board energy storage comprises the following steps:

[0018] S1, when the braking train generates regenerative braking energy, it is determined whether the onboard energy storage unit of the braking train is fully charged;

[0019] S2. If the onboard energy storage unit of the braking train is not fully charged, the regenerative braking energy is stored through the onboard energy storage unit;

[0020] S3. If the onboard energy storage unit of the braking train is fully charged, the train traction consumption is performed.

[0021] Furthermore, the train traction consumption comprises the following steps:

[0022] S1. After the on-board energy storage is completed, there is still residual regenerative braking energy in the system, or when the on-board energy storage unit of the braking train is fully charged during the on-board energy storage stage, it is determined whether there is a traction working train in the same power supply section;

[0023] S2. If there is a traction train in the same power supply section, the remaining regenerative braking energy is directly transferred to the train for traction consumption;

[0024] S3. If there is no traction train in the same power supply section, determine whether there is a traction train in the adjacent power supply section;

[0025] S4. If there is a traction train in the adjacent power supply section, the remaining regenerative braking energy is transferred to the train for traction consumption through the power financing unit;

[0026] S5. If there is no traction train in the adjacent power supply section, ground energy storage is performed.

[0027] Furthermore, the ground energy storage comprises the following steps:

[0028] S1. After the train traction consumption phase is completed, if there is still residual regenerative braking energy in the system, or if there is no traction working train in the adjacent power supply section during the train traction consumption phase, determine whether there is a ground energy storage unit in the same power supply section;

[0029] S2. If there is a ground energy storage unit in the same power supply section, the remaining regenerative braking energy is directly transferred to the ground energy storage unit for storage;

[0030] S3. If there is no ground energy storage unit in the same power supply interval, determine whether there is a ground energy storage unit in the adjacent power supply interval;

[0031] S4. If there is a ground energy storage unit in the adjacent power supply section, the remaining regenerative braking energy is transferred to the ground energy storage unit for storage through the power financing unit;

[0032] S5. If there is no ground energy storage unit in the adjacent power supply section, the braking resistor is consumed.

[0033] Furthermore, the braking resistor is consumed, and when there is still residual regenerative braking energy in the system after the ground energy storage is completed, or when there is no ground energy storage unit in the adjacent power supply interval in the ground energy storage step, the residual regenerative braking energy is dissipated in the form of heat energy through the braking resistor of the braking condition train.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] 1. The present invention fully considers the characteristics of regenerative braking energy on long and steep slopes of high-speed railways, and according to the load complementarity of slope braking trains and traction trains, adds converters and energy storage equipment to the existing high-speed railway traction power supply system and high-speed train traction transmission system, and designs a regenerative braking energy composite utilization system and method, which has a reasonable design and is feasible for popularization and application.

[0036] 2. The power integration unit used in the present invention is connected in parallel to two out-of-phase power supply arms at the outlet of the traction substation or substation, constructing an energy interaction channel, realizing the transfer of active power, and facilitating the access of the energy storage unit, avoiding large-scale transformation of the existing high-speed railway traction power supply system, which is in line with engineering practice.

[0037] 3. The present invention adopts a three-port bidirectional DC / DC converter to replace two independent DC / DC converters, which is connected to the DC side of the high-speed train traction drive system or the power integration unit. The system layout is compact, and flexible access to energy storage equipment is achieved. It has modular and portable characteristics, is easy to control, and is convenient to maintain.

[0038] 4. The vehicle-mounted energy storage unit and ground energy storage unit used in the present invention both contain supercapacitors and lithium batteries, which take advantage of the high power density of supercapacitors and the high energy density of lithium batteries to meet the needs of high-power, large-capacity regenerative braking energy storage. Supercapacitor and lithium battery energy storage technologies are mature, widely used in the market, and have cost advantages. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a structural schematic diagram of the regenerative braking energy composite utilization system of the present invention;

[0040] Figure 2 It is a structural schematic diagram of the vehicle-mounted energy storage unit of the present invention connected to the traction drive system;

[0041] Figure 3 is a circuit structure diagram of a three-port bidirectional DC / DC converter of the present invention;

[0042] Figure 4 is a circuit structure diagram of the power fusion unit of the present invention;

[0043] Figure 5It is a flow chart for implementing the method for composite utilization of regenerative braking energy of the present invention. DETAILED DESCRIPTION

[0044] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the present invention is further explained below in conjunction with specific implementation methods.

[0045] like Figure 1 As shown, the present invention provides a high-speed railway long and steep slope regenerative braking energy composite utilization system, including an on-board energy storage unit, a power integration unit, and a ground energy storage unit. The on-board energy storage unit is connected in parallel to both ends of the DC side support capacitor of the high-speed train traction transmission system, the power integration unit is connected in parallel to two out-of-phase power supply arms at the outlet of the traction substation or substation, and the ground energy storage unit is connected in parallel to both ends of the DC side support capacitor of the power integration unit.

[0046] The ground energy storage unit includes a three-port bidirectional DC / DC converter, a super capacitor, and a lithium battery. The super capacitor and the lithium battery are used as energy storage media and are respectively connected to two low-voltage DC ports of the three-port bidirectional DC / DC converter, and the high-voltage DC port of the three-port bidirectional DC / DC converter is connected in parallel to the two ends of the DC side support capacitor of the power integration unit.

[0047] When the ground energy storage unit is charging, the regenerative braking energy is transmitted to the power financing unit through the traction power supply arm where the braking train is located, and then flows to the three-port bidirectional DC / DC converter through the DC side of the power financing unit, and then flows to the supercapacitor and lithium battery from the three-port bidirectional DC / DC converter; when the ground energy storage unit is discharging, the energy stored in the supercapacitor and lithium battery flows to the three-port bidirectional DC / DC converter, and then flows from the three-port bidirectional DC / DC converter to the DC side of the power financing unit, and then is transmitted to the traction power supply arm where the traction working train is located through the power financing unit.

[0048] like Figure 2 As shown, the on-board energy storage unit includes a three-port bidirectional DC / DC converter, a super capacitor, and a lithium battery. The super capacitor and the lithium battery are used as energy storage media and are respectively connected to the two low-voltage DC ports of the three-port bidirectional DC / DC converter, and the high-voltage DC port of the three-port bidirectional DC / DC converter is connected in parallel to the two ends of the DC side support capacitor of the high-speed train traction drive system.

[0049] When the on-board energy storage unit is charging, the regenerative braking energy flows from the traction motor to the traction inverter, flows to the three-port bidirectional DC / DC converter through the DC side of the high-speed train traction drive system, and flows from the three-port bidirectional DC / DC converter to the supercapacitor and lithium battery; when the on-board energy storage unit is discharging, the energy stored in the supercapacitor and lithium battery flows to the three-port bidirectional DC / DC converter, flows from the three-port bidirectional DC / DC converter to the DC side of the high-speed train traction drive system, and flows to the traction motor through the traction inverter.

[0050] like Figure 3 As shown, the three-port bidirectional DC / DC converter consists of three H-bridge units and three power transmission inductors L 1 , L 2 , L 3 Connected to the three-winding high-frequency transformer T, the H-bridge unit port is connected to the filter capacitor C 1 , C 2 , C 3 Ports a1-a2 and b1-b2 are the low-voltage side, connected to supercapacitors and lithium batteries respectively; ports c11-c21 are the high-voltage side, connected to the DC side support capacitors of the high-speed train traction drive system or power integration unit.

[0051] Each H-bridge unit in the three-port bidirectional DC / DC converter includes two bridge arms, and each bridge arm is composed of two switch tubes connected in series.

[0052] In the H-bridge unit where the low-voltage side port a1-a2 is located, the first bridge arm is connected in series with the switch tube S 1 With switch tube S 2 , the midpoint of the first bridge arm is connected to the power transfer inductor L 1 The first end of the power transfer inductor L 1 The second end of the bridge arm is connected to the first end of one of the windings of the three-winding high-frequency transformer T, and the second bridge arm is connected in series with the switch tube S 3 With switch tube S 4 The midpoint of the second bridge arm is connected to the second end of one of the windings of the three-winding high-frequency transformer T, and the filter capacitor C 1 In parallel with the two bridge arms.

[0053] In the H-bridge unit where the low-voltage side port b1-b2 is located, the first bridge arm is connected in series with the switch tube S 5 With switch tube S 6 , the midpoint of the first bridge arm is connected to the power transfer inductor L 2 The first end of the power transfer inductor L 2 The second end of the bridge arm is connected to the first end of one of the windings of the three-winding high-frequency transformer T, and the second bridge arm is connected in series with the switch tube S 7 With switch tube S 8The midpoint of the second bridge arm is connected to the second end of one of the windings of the three-winding high-frequency transformer T, and the filter capacitor C 2 In parallel with the two bridge arms.

[0054] In the H-bridge unit where the high-voltage side ports c11-c21 are located, the first bridge arm is connected in series with the switch tubes S 9 With switch tube S 10 , the midpoint of the first bridge arm is connected to the power transfer inductor L 3 The first end of the power transfer inductor L 3 The second end of the bridge arm is connected to the first end of one of the windings of the three-winding high-frequency transformer T, and the second bridge arm is connected in series with the switch tube S 11 With switch tube S 12 The midpoint of the second bridge arm is connected to the second end of one of the windings of the three-winding high-frequency transformer T, and the filter capacitor C 3 In parallel with the two bridge arms.

[0055] When the three-port bidirectional DC / DC converter is working, each H-bridge unit will form a high-frequency square wave voltage on the corresponding transformer winding. When the phase shift angle and positive and negative of each square wave voltage are adjusted, the power size and direction transmitted between the three ports can be controlled.

[0056] like Figure 4 As shown, the power transfer unit consists of two single-phase step-down transformers T a With T b Through the phase modulation inductor L a With L b Connected to the AC side of two H-bridge units, the two H-bridge units are symmetrical in structure and have a common DC side, and the common DC side is connected in parallel with a supporting capacitor C s High-voltage DC ports c21-c22 are reserved for connecting a three-port bidirectional DC / DC converter.

[0057] Each H-bridge unit in the power integration unit includes two bridge arms, and each bridge arm is composed of two switch tubes connected in series.

[0058] In the left H-bridge unit, the first bridge arm is connected in series with the switch tube V 1 With V 2 , the midpoint of the first bridge arm is connected to the phase-modulating inductor L a The first end of the phase inductor L a The second end is connected to the single-phase step-down transformer T a The first end of the low-voltage side winding and the second bridge arm are connected in series with the switch tube V 3 With V 4 The midpoint of the second bridge arm is connected to a single-phase step-down transformer T a The second end of the low voltage side winding, single-phase step-down transformer T aThe high-voltage side winding is connected to the left power supply arm of the traction substation or substation outlet.

[0059] In the right H-bridge unit, the first bridge arm is connected in series with the switch tube V 5 With V 6 The midpoint of the first bridge arm is connected to a single-phase step-down transformer T b The second end of the low-voltage side winding and the second bridge arm are connected in series with the switch tube V 7 With V 8 The midpoint of the second bridge arm is connected to the phase-modulating inductor L b The first end of the phase inductor L b The second end is connected to the single-phase step-down transformer T b The first end of the low voltage side winding, single-phase step-down transformer T b The high-voltage side winding is connected to the right power supply arm of the traction substation or substation outlet.

[0060] When the power integration unit is working, by controlling the output power of the H-bridge units on both sides, the active power transfer and reactive negative sequence dynamic compensation between the out-of-phase traction power supply arms connected to the single-phase transformers on the left and right sides are realized, and a stable DC voltage is provided for the access of the ground energy storage unit.

[0061] In this embodiment, after the three-port bidirectional DC / DC converter is connected to the energy storage medium, it can be connected to the high-speed railway traction power supply system through the reserved ports c21-c22 of the power financing unit.

[0062] In this embodiment, the supercapacitor is a double-layer supercapacitor, and the lithium battery is a ternary lithium battery or a lithium iron phosphate battery.

[0063] like Figure 5 As shown, the present invention provides a method for composite utilization of regenerative braking energy on a high-speed railway long slope, and the system power satisfies the relationship:

[0064]

[0065] in, P regen Output power for train regenerative braking; P ESS is the power transferred through the energy storage unit; P t is the power consumed by the traction train; P r is the power consumed by the braking resistor; P ESS,onb is the power of the on-board energy storage unit; P ESS,way is the power of the ground energy storage unit; P tract The power required for train traction; PTSS The power provided for traction substation.

[0066] The method for composite utilization of regenerative braking energy on a high-speed railway long and steep slope comprises the following steps:

[0067] Step 1: On-board energy storage, the regenerative braking energy generated by the braking condition train is first stored through its own on-board energy storage unit;

[0068] Step 2: Train traction consumption: the remaining regenerative braking energy is consumed by the traction train on the same power supply arm, and the unused regenerative braking energy flows across the phase separation area to the adjacent power supply arm through the power transfer unit to be consumed by the traction train;

[0069] Step 3: Ground energy storage: the remaining regenerative braking energy is stored in the ground energy storage unit. If the ground energy storage unit is not connected to the power supply arm, the regenerative braking energy flows across the phase separation area to the adjacent power supply arm through the power transfer unit and then stored in the ground energy storage unit.

[0070] Step 4: The braking resistor is consumed, and the remaining regenerative braking energy is dissipated in the form of heat energy through the braking resistor of the braking train.

[0071] Furthermore, the on-board energy storage comprises the following steps:

[0072] S1. When the braking train generates regenerative braking energy, the charge state of the onboard energy storage unit of the braking train is determined according to the charge state of the onboard energy storage unit of the braking train at that moment;

[0073] S2. If the onboard energy storage unit of the braking train is not fully charged, the amount of electricity available for storage is calculated based on the output power of the regenerative braking energy and the charge state of the onboard energy storage unit, and stored in the onboard energy storage unit;

[0074] S3. If the onboard energy storage unit of the braking train is fully charged, the train traction consumption is performed.

[0075] Furthermore, the train traction consumption comprises the following steps:

[0076] S1. After the on-board energy storage is completed, there is still residual regenerative braking energy in the system, or when the on-board energy storage unit of the braking train is fully charged during the on-board energy storage stage, it is determined whether there is a traction working train in the same power supply section according to the real-time load data of the traction substation;

[0077] S2. If there is a traction train in the same power supply section, the remaining regenerative braking energy is returned to the traction power supply arm through the train traction drive system and directly transmitted to the train traction consumption;

[0078] S3. If there is no traction train in the same power supply section, determine whether there is a traction train in the adjacent power supply section based on the real-time load data of the traction substation;

[0079] S4. If there is a traction train in the adjacent power supply section, the remaining regenerative braking energy is transferred to the adjacent power supply arm through the power transfer unit to be consumed by the train traction on the adjacent power supply arm;

[0080] S5. If there is no traction train in the adjacent power supply section, ground energy storage is performed.

[0081] Furthermore, the ground energy storage comprises the following steps:

[0082] S1. After the train traction consumption phase is completed, there is still residual regenerative braking energy in the system, or when there is no traction working train in the adjacent power supply section during the train traction consumption phase, determine whether there is a ground energy storage unit in the same power supply section according to the traction power supply system structure;

[0083] S2. If there is a ground energy storage unit in the same power supply section, the remaining regenerative braking energy is directly transferred to the ground energy storage unit for storage through the power transfer unit connected to the power supply arm;

[0084] S3. If there is no ground energy storage unit in the same power supply section, determine whether there is a ground energy storage unit in the adjacent power supply section according to the traction power supply system structure;

[0085] S4. If there is a ground energy storage unit in the adjacent power supply section, the remaining regenerative braking energy is transferred to the adjacent power supply arm through the power integration unit connected to the power supply arm, and then transferred to the ground energy storage unit for storage through the power integration unit connected to the power supply arm;

[0086] S5. If there is no ground energy storage unit in the adjacent power supply section, the braking resistor is consumed.

[0087] Furthermore, the braking resistor is consumed, and when there is still residual regenerative braking energy in the system after the ground energy storage is completed, or when there is no ground energy storage unit in the adjacent power supply interval in the ground energy storage step, the residual regenerative braking energy is dissipated in the form of heat energy through the braking resistor of the braking condition train.

[0088] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

[0089] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A method for composite utilization of regenerative braking energy based on a high-speed railway long and steep slope system, characterized in that: The system includes an on-board energy storage unit, a power financing unit, and a ground energy storage unit. The on-board energy storage unit is connected in parallel to both ends of the DC side support capacitor of the high-speed train traction drive system. The power financing unit is connected in parallel to two out-of-phase power supply arms at the exit of the traction substation or substation. The ground energy storage unit is connected in parallel to both ends of the DC side support capacitor of the power financing unit. The system power satisfies the following relationship: Where Pregen is the train regenerative braking output power; PESS is the power transferred through the energy storage unit; Pt is the power consumed by the traction train; Pr is the power consumed by the braking resistor; PESS,onb is the power of the on-board energy storage unit; PESS,way is the power of the ground energy storage unit; Ptract is the power required for train traction; PTSS is the power provided by the traction substation; The specific steps include: Step 1: On-board energy storage, the on-board energy storage unit of the braking train stores the regenerative braking energy. The specific steps are as follows: S1, when the braking train generates regenerative braking energy, it is determined whether the onboard energy storage unit of the braking train is fully charged; S2. If the onboard energy storage unit of the braking train is not fully charged, the regenerative braking energy is stored through the onboard energy storage unit; S3. If the onboard energy storage unit of the braking train is fully charged, the train traction consumption is performed; Step 2: Train traction consumption is consumed by trains in traction condition on the same or adjacent power supply arm. The specific steps are as follows: S1. After the on-board energy storage is completed, there is still residual regenerative braking energy in the system, or when the on-board energy storage unit of the braking train is fully charged during the on-board energy storage stage, it is determined whether there is a traction working train in the same power supply section; S2. If there is a traction train in the same power supply section, the remaining regenerative braking energy is directly transferred to the train for traction consumption; S3. If there is no traction train in the same power supply section, determine whether there is a traction train in the adjacent power supply section; S4. If there is a traction train in the adjacent power supply section, the remaining regenerative braking energy is transferred to the train for traction consumption through the power financing unit; S5. If there is no traction train in the adjacent power supply section, ground energy storage is performed; Step 3: Ground energy storage, which is stored by ground energy storage units connected to the same or adjacent power supply arms. The specific steps are as follows: S1. After the train traction consumption phase is completed, if there is still residual regenerative braking energy in the system, or if there is no traction working train in the adjacent power supply section during the train traction consumption phase, determine whether there is a ground energy storage unit in the same power supply section; S2. If there is a ground energy storage unit in the same power supply section, the remaining regenerative braking energy is directly transferred to the ground energy storage unit for storage; S3. If there is no ground energy storage unit in the same power supply interval, determine whether there is a ground energy storage unit in the adjacent power supply interval; S4. If there is a ground energy storage unit in the adjacent power supply section, the remaining regenerative braking energy is transferred to the ground energy storage unit for storage through the power financing unit; S5. If there is no ground energy storage unit in the adjacent power supply section, the braking resistor is consumed; Step 4: Braking resistor consumption, which is consumed by the braking resistor of the braking condition train. The specific contents are as follows: When there is still residual regenerative braking energy in the system after the ground energy storage is completed, or when there is no ground energy storage unit in the adjacent power supply interval during the ground energy storage step, the residual regenerative braking energy is dissipated in the form of heat energy through the braking resistor of the braking train.

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