Description:A REGENERATIVE BRAKING SYSTEM FOR LOCOMOTIVE AND DC TRACTION SYSTEMS
TECHNICAL FIELD:
[001] The present invention relates to the technical field of large-power electronics applied to rail transport, and in particular, to a locomotive regenerative braking system. The present invention particularly relates to development of IGBT(Insulated Gate Bipolar Transistor) based regenerative braking system for WAG7 locomotive and other DC traction systems.
BACKGROUND OF THE INVENTION:
[002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
[003] Presently Indian railways is using large number of locomotives like WAG7 which are using DC motors for propulsion. For braking locomotives use dynamic braking and pneumatic braking. During dynamic braking the motors are converted into generators and feed the power to resistances. This results in conversion of kinetic energy to heat energy.
[004] Insulated Gate Bipolar Transistor (IGBT) is power switching device for medium to high power application. IGBT is suitable for high frequency application, high di/dt capacity and its simple gate driver and low consumption of gate power and accordingly provides very high-power gain during turn on as well as turn off.
[005] There is a requirement to recover heat energy and feed it to the grid to save energy and environment.
PRIOR ART
[006] CN Publication No. CN104802646B discloses a method and a system for recovering regenerative brake energy of an energy storage type urban rail based on a supercapacitor. The system comprises the chopping unit, the supercapacitor unit, a chopping control module and a direct current isolation switch unit, wherein the chopping unit comprises the two bidirectional chopping module units which are connected in series or parallel, and each bidirectional chopping module unit comprise one or more than one bidirectional DC/DC (direct current/direct current) chopping module which is connected in parallel.
[007] US Patent No. US7304445B2 discloses about controlling various prime power, energy storage and/or regenerative braking systems for powering a variety of off road vehicular (e.g., locomotive) transmission and traction motor combinations providing auxiliary power for the vehicle (e.g., for the locomotive and trailing cars).
[008] Railways are under increasing pressure to reduce emissions and fuel consumption. A key component to reduce fuel consumption and emissions is the use of regenerative braking systems which can recover a significant portion of the kinetic energy of a train during braking. Especially in a hybrid locomotive, a successful regenerative braking system requires proper management of a large energy storage system and a specific control strategy for utilizing traction motors as generators during braking.
[009] There therefore remains a need for specific operating and control strategies to recover energy from regenerative braking, compatible with the use of traction motors with IGBT(insulated-gate bipolar transistor) based regenerative braking system for WAG7 locomotive and other DC traction systems. Also, there is a need to provide a system that is economically competitive with or superior to conventional locomotives.
OBJECTS OF THE INVENTION:
[0010] It is therefore an object of the present subject matter to overcome the aforementioned and other drawbacks in the solutions available in state-of-the-art.
[0011] The principal objective of the present subject matter is to provide an Insulated Gate Bipolar Transistor (IGBT) based regenerative braking system.
[0012] Another objective of the present subject matter is to provide IGBT based regenerative braking for WAG7 locomotive which can be used along with DC link capacitors.
[0013] Another objective of the present subject matter is to provide IGBT based regenerative braking for WAG7 locomotive which produces controlled rate of rise of output voltage.
[0014] Another objective of the present subject matter is to recover the energy from motors of the locomotive in the form of current and voltage and feed to grid of 25KV AC line at near unity power factor from where the locomotive draws power during motoring.
[0015] These and other objects and advantages of the present subject matter will be apparent to a person skilled in the art after consideration of the following detailed description taken into consideration with accompanying drawings in which preferred embodiments of the present subject matter are illustrated.

SUMMARY OF THE INVENTION:
[0016] Solution to one or more drawbacks of existing technology, and additional advantages are provided through the present subject matter. Additional features and advantages are realized through the technicalities of the present subject matter. Other embodiments and aspects of the subject matter are described in detail herein and are considered to be a part of the claimed subject matter.
[0017] The present invention relates to a regenerative braking system for locomotive and DC traction systems, comprises a power circuit block having IGBT module, a plurality of AC contactors, a pair of inductors, a front-end converter with DC link capacitors, a plurality of DC contactor and at least one boost chopper circuit connected with one set of three motors. The front-end converter is connected to transformer secondaries via pair of inductors and the plurality of AC contactors and the at least one boost chopper circuit connected with one set of three motors via the DC contactor. A step-down chopper circuit is connected to field windings of all six motors in series via the DC contactor. Back emf of all three motors of each set connected in series is maintained to a nominal value by controlling the motor field current through the step-down chopper circuit connected to fields of the motors. when speed goes down the field current increases and if the field is saturated and reaches maximum value, DC link voltage is maintained by the booster circuit connected with each set of three motors and the DC link voltage is converted into single phase AC voltage at transformer secondaries and active power is pumped into the line at near unity power factor through the front-end converter. Regeneration process occurs by each of the motors of the locomotive in the form of current and voltage and active power is feed to grid at near unity power factor from where the locomotive draws power during motoring.
[0018] In an aspect of the invention, nominal value of constant DC to be maintained is in the range of 1600 to 1800 V.
[0019] In an aspect of the invention, regeneration is up to a speed of approximately 15 KPH.
[0020] In an aspect of the invention, an average power feedback is 1.5MW.
[0021] In an aspect of the invention, the transformer secondary voltage which is connected to front-end converter is kept at approximately. 1000 V RMS at suitable notch.
[0022] In an aspect of the invention, maximum braking effort at 100KPH is approximately 7 Ton and at 15KPH is approximately 30 Ton.
[0023] In an aspect of the invention, the power and the braking are adjusted within the motor by the front-end converters, the step-down chopper and the boost chopper.
[0024] In an aspect of the invention, each booster circuit are used to connect each set of three motors.
[0025] In an aspect of the invention, the boost chopper circuit is a step-up circuit.
[0026] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.
BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS:
[0027] It is to be noted, however, that the appended drawings illustrate only typical embodiments of the present subject matter and are therefore not to be considered for limiting of its scope, for the invention may admit to other equally effective embodiments. The detailed description is described with reference to the accompanying figures. In the figures, a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the figures to reference like features and components. Some embodiments of system or methods or structure in accordance with embodiments of the present subject matter are now described, by way of example, and with reference to the accompanying figures, in which:
[0028] FIG. 1 illustrates a schematic circuit of an Insulated Gate Bipolar Transistor (IGBT) based regenerative braking system with three motors (M1, M2 and M3) connected in series according to the present invention;
[0029] FIG. 2 illustrates a schematic circuit of an Insulated Gate Bipolar Transistor (IGBT) based regenerative braking system with three motors (M4, M5 and M6) connected in series and field windings of all six motors connected in series according to the present invention;
[0030] FIG.3 shows a waveform with grid voltage, grid current and DC voltage of the regenerative braking system during regenerative braking 100kmph to 15kmph during unloaded condition in accordance with present invention; and
[0031] FIG.4 shows waveform with grid voltage, grid current and DC voltage of the regenerative braking system during regenerative braking 80kmph to 15kmph during loaded condition (loco with wagons) in accordance with present invention.
[0032] The figures depict embodiments of the present subject matter for the purposes of illustration only. A person skilled in the art will easily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the subject matter described herein.
DETAILED DESCRIPTION OF THE INVENTION:
[0033] While the embodiments of the subject matter are subject to various modifications and alternative forms, specific embodiment thereof have been shown by way of example in the figures and will be described below. It should be understood, however, that it is not intended to limit the subject matter to the particular forms disclosed, but on the contrary, the subject matter is to cover all modifications, equivalents, and alternative falling within the scope of the subject matter.
[0034] The terms “comprises”, “comprising”, or any other variations thereof used in the subject matter, are intended to cover a non-exclusive inclusion, such that a device, system, assembly that comprises a list of components does not include only those components but may include other components not expressly listed or inherent to such system, or assembly, or device. In other words, one or more elements in a system or device proceeded by “comprises… a” does not, without more constraints, preclude the existence of other elements or additional elements in the system or device.
[0035] The regenerative braking system (100) based on FIG. 1 & FIG. 2 is based on Insulated Gate Bipolar Transistor (IGBT) (102) based module for WAG7 locomotive has two main distinct functional blocks in power circuit. The first part comprises power rectifier (104,106), transformers (108,110), single phase inverter (128), DC link capacitor (130) and filter (132) and the second part comprises a plurality of AC Contactors (112, 114, 116, 118), a plurality of DC Contactors (120, 122, 124, 126), boost chopper (134), buck chopper (136) along with a motoring circuit (138) and plurality of motors (M1, M2, M3, M4, M5, and M6).
[0036] Referring to FIG.1 illustrates a schematic of an Insulated Gate Bipolar Transistor (IGBT) (102) based regenerative braking system (100) with three motors (M1, M2 and M3) connected in series. In a preferred embodiment the power circuit for regeneration consists of AC contactor (112,114), inductor (L1), front-end converter (128) with DC link capacitors (130), booster circuit (134) and DC contactor (120). The front-end converters (128) are connected to transformer secondaries (108) via the inductor (L1) and the AC contactors (112,114), the booster circuit (134) is connected to all the three motors in series (M1, M2 and M3) via the DC contactor (120). The traction circuit remains similar to the WAG7 locomotive.
[0037] FIG. 2 illustrates a schematic circuit of an Insulated Gate Bipolar Transistor (IGBT) (102) based regenerative braking system (100) with three motors (M4, M5 and M6) connected in series. In a preferred embodiment the power circuit for regeneration consists of AC contactor (116,118), inductor (L2), front-end converter (128) with DC link capacitors (130), booster circuit (134) and DC contactor (122). The front-end converters (128) are connected to transformer secondaries (110) via Inductor (L2) and AC Contactors (116,118), the booster circuit (134) is connected to all the three motors in series (M4, M5 and M6) via DC Contactor (122). The step-down chopper circuit (136) is connected to field windings (F1, F2, F3, F4, F5, F6) of all six motors (M1, M2, M3, M4, M5, and M6) in series via DC Contactor (124,126). The traction circuit remains similar to the WAG7 locomotive. With reference to FIG. 1, back emf of all three motors (M1, M2 and M3) connected in series is maintained to a value in the range of 1600 to 1800 V constant DC by controlling the motor field current through step-down chopper circuit (136) connected to fields of the motors (M1, M2, M3, M4, M5 and M6). When speed goes down the field current increases. If the field is saturated and reaches its maximum value, DC link voltage is maintained by the booster circuit (134) connected as shown in FIG. 1 and FIG. 2. The DC link voltage is converted into single phase ac voltage at transformer secondary (108, 110) and active power is pumped into the line at near unity power factor through front-end converter (128). Similarly for remaining three motors M4, M5 and M6 the conversion of voltage is achieved.
[0038] With reference to FIG. 1 & FIG. 2, transformer secondary voltage which is connected to front-end converter (128) is kept at approx. 1000 V RMS at suitable notch. The magnitude of power feed back into the line is controlled by the IGBT (102) switching of the front-end converter (128). Regeneration to a speed of approximately 15 KPH is possible using the regenerative braking system (100). Average power feedback is 1.5MW (which could be increased to 2.5MW and the energy remains the same during one braking cycle because at higher braking power, braking duration is less so energy remains almost same) during braking from 100KPH to 15KPH. Maximum braking effort at 100KPH is approximately 7 Ton and at 15KPH is approximately 30 Ton achieved through IGBT (102) based front -end converter (128) and booster (134). The power and the braking efforts are adjusted within the motors (M1, M2, M3, M4, M5, and M6) through the regenerative braking system (100). The regenerative braking system (100) recover the energy from motors (M1, M2, M3, M4, M5, and M6) of the locomotive in the form of current and voltage and feed active power to grid of 25KV AC line at near unity power factor from where the locomotive draws power during motoring.
[0039] In the present invention the regenerative braking system (100) is used in DC locomotives. The IGBT (102) based regenerative braking produce controlled rate of rise of output voltage. Also, the regenerative braking system (100) is used in other DC traction EMU and locomotive systems thereby saving lot of energy and saves valuable resources. The regenerative braking system (100) is used in large-power electronics such as rail transport. The regenerative braking system (100) is used particularly in WAG7 locomotive and DC traction systems.
WORKING OF THE INVENTION:
[0040] In a preferred embodiment when locomotive (Loco) is running and driver operate the master controller lever to braking side for applying the regenerative braking system (100). Post applying the regenerative braking system (100) tap change automatically move to 28th notch. Then Convert traction fields (CTF1, CTF2 & CTF3) move towards braking position. Post to that armature of one set of three motors ((M1, M2, M3) of bogie1 gets connected in series and armature of other set of three motors (M4, M5,M6) of bogie2 gets connected in series. Then field of all 6 motors (M1, M2, M3, M4, M5, and M6) gets connected in series. Inductor cooling fan, pump and blower of heat exchanger system gets in on condition. Water pressure built up is of approx. 4Kg/cm2. In the regenerative braking system (100) brake controller automatically apply regenerative brake and regenerative power start feeding the 25kV line which in turn speed starts reducing. This regenerative brake operation continues to operate between 100 kmph to 15 kmph. Below 15 kmph regenerative braking system (100) stop functioning and driver apply pneumatic brake.

TECHNICAL ADVANTAGES:
[0041] The present disclosure proposes a regenerative braking system which lead to recovery of 15-28 % of energy consumed by the locomotive for motoring.
[0042] The present disclosure proposes the regenerative braking system in which saved energy is very large when the loaded goods trains are placed to regenerative braking.
[0043] The present disclosure proposes the regenerative braking system in which a locomotive produce energy worth approximately Rs 25 to 40 lakhs in one year period.
[0044] The present disclosure proposes the regenerative braking system which is environment friendly as heat produced is reduced to 5% as compared to Dynamic braking system (DBR) based systems.
[0045] The present disclosure proposes the regenerative braking system in which maintenance costs due to wear and tear of mechanical braking is reduced substantially.
[0046] The present disclosure proposes the regenerative braking system in which maintenance of the DBR system due to heat generation and burning of elements is eliminated.
TEST RESULT
[0047] FIG.3 shows a waveform with grid voltage, grid current and DC voltage of the regenerative braking system during regenerative braking 100kmph to 15kmph during unloaded condition. FIG.3 waveforms showing current voltage and duration in load trial. In an example field trial done without Load (LOCO only, weight of LOCO is 123Tonn).
• Regenerative Braking applied at 100kmph, 80kmph, 60kmph.
• Maximum Regenerative Power : 1.51 MW @ 1070 V AC at secondary of transformer.
• The regenerative braking system took 32 to 40 Sec. to bring loco from 100 kmph to 15 kmph, regenerated energy is 13kWh to16.8 kWh depending on track profile.

[0048] FIG.4 shows waveform with grid voltage, grid current and DC voltage of the regenerative braking system during regenerative braking 80kmph to 15kmph during loaded condition (loco with wagons). FIG.4 waveforms showing current voltage and duration in load trial. Field trial done with Load (58 Wagons + 1 WAG9 LOCO, Total load: 1582Tonn )
• Regenerative braking applied at 80kmph, 70kmph, 60kmph
• Maximum regenerative power : 1.51 MW @ 1070 V AC at secondary of transformer
• Loco took 90 to 100 Sec. to bring loco from 80 kmph to 15 kmph, regenerated energy is 39 kWh.

[0049] The exemplary embodiment above includes examples of one or more embodiments. It is, of course, not possible to describe every conceivable combination of components or methodologies for purposes of describing the aforementioned embodiments, but one of ordinary skill in the art may recognize that many further combinations and permutations of various embodiments can be possible. Accordingly, the described embodiments can be intended to embrace all such alterations, modifications and variations that fall within the spirit and scope of the appended claims. Furthermore, to the extent that the term “includes” can be used in either the detailed description or the claims, such term can be intended to be inclusive in a manner similar to the term “comprising” as “comprising” can be interpreted when employed as a transitional word in a claim.
[0050] It will be further appreciated that functions or structures of a plurality of components or steps may be combined into a single component or step, or the functions or structures of one-step or component may be split among plural steps or components. The present invention contemplates all of these combinations. Unless stated otherwise, dimensions and geometries of the various structures depicted herein are not intended to be restrictive of the invention, and other dimensions or geometries are possible. In addition, while a feature of the present invention may have been described in the context of only one of the illustrated embodiments, such feature may be combined with one or more other features of other embodiments, for any given application. It will also be appreciated from the above that the fabrication of the unique structures herein and the operation thereof also constitute methods in accordance with the present invention. The present invention also encompasses intermediate and end products resulting from the practice of the methods herein. The use of “comprising” or “including” also contemplates embodiments that “consist essentially of” or “consist of” the recited feature.
[0051] Further, the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. It will be appreciated that several of the above-disclosed and other features and functions, or alternatives thereof, may be combined into other systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may subsequently be made by those skilled in the art without departing from the scope of the present disclosure as encompassed by the following claims.
[0052] The claims, as originally presented and as they may be amended, encompass variations, alternatives, modifications, improvements, equivalents, and substantial equivalents of the embodiments and teachings disclosed herein, including those that are presently unforeseen or unappreciated, and that, for example, may arise from applicants/patentees and others.
[0053] It will be appreciated that variants of the above-disclosed and other features and functions, or alternatives thereof, may be combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.
, Claims:We Claim:
1. A regenerative braking system (100) for locomotive and DC traction systems, comprising:
a power circuit block having IGBT module (102), a plurality of AC contactors (112,114,116,118), a pair of inductors (L1,L2), a front-end converter (128) with DC link capacitors (130), a plurality of DC contactor (120, 122, 124, 126) and at least one boost chopper circuit (134) connected with one set of three motors (M1, M2, M3 and M4, M5, M6);
the front-end converter (128) is connected to transformer secondaries (108,110) via pair of inductors (L1,L2) and the plurality of AC contactors (112,114,116,118), and the at least one boost chopper circuit (134) connected with one set of three motors (M1, M2, M3 and M4, M5, M6) via the DC contactor (120,122);
a step-down chopper circuit (136) is connected to field windings (F1, F2, F3, F4, F5, F6) of all six motors (M1, M2, M3, M4, M5, and M6) in series via the DC contactor (124,126);
wherein back emf of all three motors of each set (M1, M2, M3 and M4,M5,M6) connected in series is maintained to a nominal value by controlling the motor field current through the step-down chopper circuit (136) connected to fields of the motors (M1, M2, M3, M4, M5 and M6);
when speed goes down the field current increases and if the field is saturated and reaches maximum value, DC link voltage is maintained by the booster circuit (134) connected with each set of three motors (M1, M2, M3 and M4, M5, M6) and the DC link voltage is converted into single phase AC voltage at transformer secondaries (108, 110) and active power is pumped into the line at near unity power factor through the front-end converter (128); and
regeneration process occurs by each of the motors (M1, M2, M3, M4, M5, and M6) of the locomotive in the form of current and voltage and active power is feed to grid at near unity power factor from where the locomotive draws power during motoring.
2. The regenerative braking system (100) for locomotive and DC traction systems as claimed in claim 1, wherein nominal value of constant DC to be maintained is in the range of 1600 to 1800 V.
3. The regenerative braking system (100) for locomotive and DC traction systems as claimed in claim 1, wherein regeneration is up to a speed of approximately 15 KPH.
4. The regenerative braking system (100) for locomotive and DC traction systems as claimed in claim 1, wherein an average power feedback is 1.5MW.
5. The regenerative braking system (100) for locomotive and DC traction systems as claimed in claim 1, wherein the transformer (108, 110) secondary voltage which is connected to front end converters (128) is kept at approximately 1000 V RMS at suitable notch.
6. The regenerative braking system (100) for locomotive and DC traction systems as claimed in claim 1, wherein maximum braking effort at 100KPH is approximately 7 Ton and at 15KPH is approximately 30 Ton.
7. The regenerative braking system (100) for locomotive and DC traction systems as claimed in claim 1, wherein the power and the braking are adjusted within the motor (M1, M2, M3, M4, M5, and M6) by front end converters (128), step-down chopper (136) and boost chopper (134).
8. The regenerative braking system (100) for locomotive and DC traction systems as claimed in claim 1, wherein each booster circuit (134) are used to connect each set of three motors (M1, M2, M3 & M4, M5, M6)
9. The regenerative braking system (100) for locomotive and DC traction systems as claimed in claim 1,wherein the boost chopper (134) circuit is a step-up circuit.