Apparatus and method for locomotive regenerative braking

Abstract

An apparatus for regenerative braking is provided. In one embodiment, the apparatus includes a traction motor, a battery, and a DC bus. The traction motor is configured for regenerative braking such that power generated from braking can be used to charge the battery. Excess power generated from regenerative braking is diverted to a resistor grid for dissipation as heat. In another embodiment, the apparatus includes a first traction motor and a second traction motor. The first traction motor is configured for regenerative braking, and is coupled to the one or more batteries via the DC bus, such that power generated from the first traction motor is fed to the one or more batteries for charging thereof. The second traction motor is configured for dynamic braking, and is coupled to the resistor grid, such that power generated from braking of the second traction motor is dissipated at the resistor grid.

Description

APPARATUS AND METHOD FOR LOCOMOTIVE REGENERATIVE BRAKINGBENEFIT OF EARLIER APPLICATIONS

[0001] This application claims priority from US provisional application 63 / 623,096, filed January 19, 2024.TECHNICAL FIELD

[0002] The present invention relates to locomotives in general, and apparatus and methods for locomotive braking in particular.BACKGROUND

[0003] Locomotives may have traction motors configured to brake via dynamic braking. In dynamic braking systems of the prior art, the traction motor generates an electrical field that is directed to a resistor grid for dissipation. In this manner, the locomotive traction motors may be used to slow the train, at least reducing the need to use air brakes. Dynamic braking may be initiated by the train operator (e.g., locomotive engineer) by moving a dynamic braking handle to a "setup" position on the control stand. Braking effort can be increased by moving the handle between notches, e.g., with higher notches corresponding to higher braking effort. When increasing braking effort, more current from the armature of the traction motor may be passed into the dynamic braking resistor grids. In locomotives of the prior art, power generated from dynamic braking is only used for braking, and excess power is generally passed through resistor grids and dissipated as heat.

[0004] When the dynamic braking handle is initially moved to the "setup" notch, initiating dynamic braking, contactors in the dynamic braking circuit close, allowing current to flow from the armature of the traction motors into the resistor grid, while power from a DC bus excites the motor field current. These contactors may not open until the operator moves the handle to "off1or "idle."

[0005] When the locomotive is powered by electricity, such as via batteries or fuel cells, a regenerative braking system is sometimes proposed. Compared to dynamic braking, regenerative braking uses the electrical energy from braking to charge the batteries, instead of dissipating it at the resistor grid. However, when using the traction motors for regenerative braking, the batteries may become fully charged and opening / closing contactors during high current events may resultin welded contactors. A welded contactor may result in difficulty or inability to exit or re-enter braking, and may give rise to unsafe conditions, such as fire. Ultimately, in locomotive braking systems using traction motors, considerations are required to avoid locomotive malfunction and safety incidents.SUMMARY OF INVENTION

[0006] In accordance with a broad aspect of the present invention, there is provided an apparatus for regenerative braking, comprising: a DC bus coupled to one or more batteries; a first traction motor configured for regenerative braking, coupled to the one or more batteries via the DC bus, such that power generated from braking of the first traction motor is fed to the one or more batteries for charging thereof; and a second traction motor configured for dynamic braking, coupled to a resistor grid, such that power generated from braking of the second traction motor is dissipated at the resistor grid.

[0007] In accordance with another broad aspect of the present invention, there is provided an apparatus for regenerative braking, comprising: a traction motor; a battery; a DC bus; a regenerative braking circuit connecting the traction motor to the battery via the DC bus; a bidirectional DC / DC converter connected in the regenerative braking circuit between the DC bus and the batteries; a resistor grid; a connection between the resistor grid and the traction motors for dissipating to the resistor grid excess power from braking the traction motor; and a DC chopper in the connection between the traction motor and the resistor grid.

[0008] It is to be understood that other aspects of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein various embodiments of the invention are shown and described by way of illustration. As will be realized, the invention is capable of other and different embodiments and its several details are capable of modification in various other respects, all within the present invention. Furthermore, the various embodiments described may be combined, mutatis mutandis, with other embodiments described herein. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not as restrictive.BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Referring to the drawings, several aspects of the present invention are illustrated by way of example, and not by way of limitation, in detail in the figures, wherein:(a) Fig. 1 is a schematic diagram of a locomotive regenerative braking apparatus, according to one embodiment of the present invention;(b) Fig. 2 is a schematic diagram of a locomotive regenerative braking apparatus, according to another embodiment of the present invention;(c) Fig. 3 is a schematic diagram of a locomotive regenerative braking apparatus, according to yet another embodiment of the present invention; and(d) Fig. 4 is a schematic diagram of a locomotive regenerative braking apparatus, according to yet another embodiment of the present invention.DETAILED DESCRIPTION OF EMBODIMENTS

[0010] The detailed description set forth below in connection with the appended drawings is intended as a description of various embodiments of the present invention and is not intended to represent the only embodiments contemplated by the inventor. The detailed description includes specific details for the purpose of providing a comprehensive understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced without these specific details.

[0011] A low (e.g., zero) emissions locomotive for use on railways may be powered by electricity. For example, as shown in Fig. 1, electricity may be used to power one or more electric traction motors 130.

[0012] The electricity can be from a power supply such as on-board batteries 420, possibly in combination with hydrogen fuel cells 425 or other power generators or power sources.

[0013] A locomotive may employ alternating current (AC) traction motors or direct current (DC) traction motors, e.g., depending on the level of power required. In Fig. 1, a locomotive with a DC power system, including a DC traction motor, is illustrated. The power from batteries 420 and fuel cells 425 may be supplied and regulated through a set of independent DC / DC converters 110 to a common DC link / bus 912. The common DC bus connects the power supply (e.g., one or more hydrogen fuel cells and / or batteries) to independent DC choppers 120, which regulate the generated power to the DC traction motors 130.

[0014] ADC / DC converter is a device that can selectively convert an input DC voltage to a desired output DC voltage. ADC chopper is a device that can convert a fixed DC input voltage to a pulse width DC output voltage.

[0015] A plurality of sensors, switches, controllers and managers 900 are in communication with the equipment and control the system.

[0016] In a locomotive that uses alternating current (AC) traction motors, the DC choppers 120 are replaced by inverters, to convert power to be input into the AC traction motors.

[0017] The locomotive can employ the traction motors 130 to affect braking, e.g., when operating on descending grades, that is, declining slopes. While regenerative braking is of interest to direct electrical power generated during braking into battery recharge operations, care should be taken to avoid the problems that may occur when batteries become fully charged, such as welding of contacts and other safety-related incidents. For example, in regenerative braking, once batteries are full, high voltages may cause contactors to weld. Alternatively, if regenerative braking is exited once batteries are full (and before contactors weld), regenerative braking effort is lost. Accordingly, there is a demand for means to maintain braking effort even after batteries are full.

[0018] As noted, braking may be initiated by the train operator, e.g., by moving a braking handle to a "setup" position on the control stand. Braking effort can be increased, e.g., by moving the handle up to notches beyond the "setup" position, e.g., with higher notches corresponding to higher braking effort. When increasing braking effort, more current from the armature of the traction motors may be generated. Braking via the traction motors may be discontinued, e.g., when the braking handle is set to "idle" or "off."

[0019] In one embodiment, a selective traction motor braking apparatus and a selective traction motor braking method are provided, and described with reference to Fig. 2. It is noted that a locomotive generally has at least one truck, and typically two trucks. In this embodiment, (i) one or more traction motors 1130 of at least one truck T1 of the locomotive may be configured for regenerative braking and connected via wiring connection 1132 to DC bus 1912, where generated power from braking is fed to the traction batteries 1420 for recharging thereof, and (ii) the one or more traction motors 1130' of at least one other truck T2 of the locomotive may be configured for dynamic braking, where they are connected 1134 such that generated power is directed to a resistor grid 1250.

[0020] In the illustrated embodiment, all the traction motors in a truck have the same braking configuration, either regenerative or dynamic. In another embodiment, a truck may have motors that are of different braking configurations, i.e., a truck may have a traction motor configured for regenerative braking and a second traction motor configured for dynamic braking.

[0021] This configuration may be advantageous on certain terrain or depending on other factors. A device, such as a switch, may be provided to adjust the extent to which the regenerative motor and the dynamic motor are engaged, or such adjustments may be automated. For example, the regenerative motor may be caused to exert 90% of overall braking force, and the dynamic motor may be caused to exert 10% of overall braking force. It is to be appreciated that one motor could exert 100% of the overall braking force, or 50% of the overall braking force, or 0% of the overall braking force, or any other amount of the overall braking force.

[0022] For reference, Fig. 2 also illustrates a simplified electrical architecture of an electric locomotive, wherein strings of batteries 1420 are each coupled to a DC / DC converter 1110 and each converter is coupled to DC bus 1912. Having the DC / DC converter 1110 between the battery and the DC bus allows for electrical regulation of the batteries onto and from the DC bus 1912.

[0023] In a preferred embodiment, there is a DC chopper 1120 for each traction motor. Each DC chopper 1120, 1120' is coupled between the DC bus and one of the traction motors 1130, 1130'. In a DC traction system, DC choppers 1120, 1120' flow current to excite the motors 1130, 1130'.

[0024] It is also possible for multiple traction motors to share a DC chopper. This is not the preferred embodiment because, for example, if the shared DC chopper fails, multiple motors will lose power.

[0025] As noted, the traction motors of each truck may be used separately to perform either regenerative braking or dynamic braking. The particular configuration as between regenerative and dynamic braking is determined by the circuit to which the truck motors are connected. In particular, first truck T1 may be used for regenerative braking, such as by connecting 1132 the motor armatures of motors 1130 back to DC bus 1912 and thereby to batteries 1420. Also, second truck T2 may perform dynamic braking methods, such as by passing current from the motor armatures of motors 1130' through connection 1134 to resistor grid 1250. To be clear, the motors of truck T2 direct all power generated during dynamic braking to the resistor grid, without any power going to the batteries.

[0026] Contactor 1252 controls (i.e., opens and closes) the connection of the motor armature of each motor 1130' to the resistor grid 1250.

[0027] Contactor 1253 in wiring connection 1132 controls (i.e., opens and closes) the connection of the motor armature of each motor 1130 in truck T1 to DC bus 1912. This connection 1132 may include a DC / DC drive 1002 (which may also be referred to as a DC / DC regenerative convertor, a DC / DC boost converter, and / or other terms) to drive and control the recharging process. The DC / DC drive is configured to boost the voltage input from the motors 1130 to exceed the DC bus voltage. This enables power to flow into the batteries 1420 and the DC choppers 1120, 1120' which are exciting the motors. In the event that a battery manager 1900 coupled to the batteries determines that the batteries reach a state of charge beyond a certain threshold, e.g., beyond 80% charged or beyond 90% charged, such as is considered to be a fully recharged state, the DC / DC drive 1002 is configured to no longer boost the voltage preventing power from flowing into the batteries. When this voltage reduction occurs, the motors 1130 are then controlled to spin freely and exert no braking effort, or motors 1130 will continue to be used for braking but generated power from such motors is directed via a connection 1136 to the resistor grid and dissipated as heat. The decision between continuing regenerative braking or diverting power to the resistor grid is made by a controller, such as battery manager 1900. Achopper 1138 may be used in association with contact 1253 and connection 1136 to permit ramping up and ramping down of power to the resistor grid. As such, there may be a transition from regenerative braking to dynamic braking while still maintaining a braking effect.

[0028] Even when braking operations are shut down in truck Tl, the other truck T2 continues to maintain dynamic braking with generated power dissipated through the resistor grid 1250.

[0029] All braking via motors 1130, 1130', both regenerative braking and dynamic braking, is discontinued when the operator moves the braking handle to "off or "idle." In particular, movement of the dynamic braking handle to "off or "idle" opens the contactors 1252, 1253. If the system is configured to shut down the braking effort of motors 1130 once the batteries are full, the contactor 1253 may open with no power load and thus cannot become welded. If contactor 1253 does become welded, dynamic braking is still available via motors 1130' of the second truck T2.

[0030] A system where each truck may be used separately to perform either regenerative braking or dynamic braking, may facilitate seamless operation, from an operator perspective. Putdifferently, dynamic braking and regenerative braking may be available simultaneously. Thus, the system offers the benefits of regenerative braking, but once the batteries are fully charged, the operator does not lose the ability to brake via the traction motors. Instead, dynamic braking can continue via the motors dedicated to dynamic breaking (i.e., second truck T2), with current being directed only to the resistor grid, while the regenerative motors (i.e., Tl) can spin freely and exert no braking effect.

[0031] When the batteries are fully charged, i.e., the state of charge of the batteries is greater than 80%, greater than 90% or substantially 100%, regenerative braking cannot typically be used to slow the train. However, dynamic braking through the motors dedicated to dynamic braking, may still be maintained or used even in the event batteries reach a state of charge beyond a certain threshold, such as the fully recharged state.

[0032] While Fig. 2 illustrates a DC traction system, this approach may also be employed in AC drive locomotives.

[0033] In another embodiment, illustrated in Fig. 3, there is another solution to permit regenerative braking from at least some and possibly all the truck motors, without at least some of the problems previously noted. In this embodiment, DC choppers are employed in the circuit instead of contactors to regulate power into the resistor grids. Thus, in the event regenerative braking brings the batteries to a fully recharged threshold, the electrical current from braking the traction motors is then diverted to the resistor grid through a DC chopper. Again, power contactors, when opened, can be welded due to the high voltage. This welding failure may leave the locomotive traction motors in a permanent state of braking. Using a DC chopper in the connection to the resistor grid, as an alternative to a contactor, avoids the problem of contactor welding altogether, and the DC chopper can regulate power into the resistor grids.

[0034] As illustrated in Fig. 3 for example, all of the traction motors 2130 and 2130' of the locomotive are electrically coupled for regenerative braking, with the option to feed generated power at least in excess of what is needed for battery recharge to a resistor grid 2250. Therefore, unlike the system of Fig. 2, all of the traction motors 2130 of truck Tl' and all of the one or more traction motors 2130' of at least one other truck T2' of the locomotive are configured for regenerative braking.

[0035] Fig. 3 illustrates an embodiment with AC traction motors. Strings of batteries 2420 are each coupled to a DC / DC converter 2110 and each converter is coupled to DC bus 2912. Motors 2130 and 2130' are all connected via AC inverters 2120, 2120' to DC bus 2912. A resistor grid 2250 is connected 2136 to DC bus 2912. A DC chopper 2138 is positioned in circuit 2136 between DC bus 2912 and resistor grid 2250. DC / DC converters 2110 may be bidirectional converters, e g., buck-boost converters. This allows power to flow from batteries 2420 to DC bus 1912 and vice versa, via bidirectional DC / DC converters 2110. For example, it is also noted that there is no unidirectional diode between the batteries 2420 and DC bus 2912.

[0036] When powering the traction motors, AC inverters 2120, 2120' condition and regulate power from DC bus 2912 into each traction motor 2130 and 2130'. When the traction motors are used for braking, alternating current from the AC motors 2130, 2130' is converted into direct current by AC inverters 2120, 2120' before flowing into DC bus 2912.

[0037] Thus, power generated from braking at motors 2130 and 2130' is converted into direct current and fed to the batteries 2420 for recharging thereof.

[0038] AC inverters 2120, 2120' flow power from the motors into the DC bus 2912 during braking via the traction motors. Once the DC bus voltage exceeds the DC bus voltage being provided by the batteries 2420, power is enabled to flow into the batteries 2420. DC chopper 2138 is configured to increase its duty cycle once batteries reach a state of charge limit. In one embodiment, a controller such as a battery manager 2900, coupled to the batteries, determines that the batteries reach a state of charge beyond a certain threshold, e.g., beyond 80% charged or beyond 90% charged, such as is considered to be a fully recharged state, the DC chopper 2138 is operated to increase duty cycle to flow power into the resistor grid 2250. Motors 2130, 2130' can continue to be used for braking, but generated power from such motors is directed via the DC chopper 2138 to the resistor grid 2250 and dissipated as heat. Specifically, DC chopper 2138 is employed in connection 2136 to regulate power into the resistor grid 2250.

[0039] By employing DC chopper 2138, excess power can be absorbed through connection 2136 to resistor grid 2250. In the event the batteries reach a fully charged state, DC chopper 2138, which is between the braking output of the traction motors and resistor grid 2250, enables excess power to pass into the resistor grid. DC choppers are configured to flow increasing amounts of power.When the battery state of charge lowers, DC chopper 2138 can reduce the duty cycle to allow flow of power back into batteries 2420.

[0040] As noted, DC / DC converters 2110 may be bidirectional converters, which allows power to flow from batteries 2420 to DC bus 1912 and vice versa. This configuration allows batteries 2420 to keep the voltage of the DC bus stable, as the traction motors may provide unstable power to the DC bus 2912. In other words, if the power from the traction motors does not meet the power demands of the DC bus, the batteries can provide the difference in power needed. If the traction motors are generating more power than the DC bus requires, such excess power can be used to recharge the batteries or, if the batteries are fully charged, such excess power from the traction motors can be passed to the resistor grid and dissipated as heat. This allows the locomotive to use regenerative braking continuously, without destabilizing voltage of the DC bus. Independent of speed, for example even down to 0.5 mph (approximately 0.80 km / h), DC bus voltage can be maintained stable while regenerative braking is used.

[0041] DC chopper 2138 is arranged in parallel to the DC / DC converters 2110, which allows them to operate independently of each other. DC chopper 2138 is connected via circuitry between DC bus 2912 and resistor grid 2250, and DC / DC converters 2110 are connected via circuitry between batteries 2420 and DC bus 2912. DC chopper 2138 does not affect power flowing into DC bus 2912. In other words, power can flow independently into the DC chopper and into and out of the batteries

[0042] It is to be appreciated that a DC traction motor system can also be configured such that all motors are operable for regenerative braking. In such an embodiment as shown in Fig. 4, DC traction motors 1130, 1130' are connected via a circuit 1132 to the batteries 1420 for regenerative braking and an electrical connection 1133 also extends from the circuit to the resistor grid 1250 for dissipation of excess power from braking. Specifically, circuit 1132 connects the traction motors 1130, 1130' via drive 1002 to bus 1219, and the DC bus is connected to the batteries. Bidirectional DC / DC converters 1110 are in the connection between the bus and batteries, which allows power to flow from the batteries to the DC bus and vice versa. In addition, a DC chopper 1138 is electrically coupled in the connection between circuit 1132 and resistor grid 1250. Because DC chopper 1138 acts to ramp up and down power being diverted to the resistor grid depending on the power generated by regenerative braking, i.e., to allow excess power to be absorbed intothe resistor grid, contact 1253 (Fig 2) is not required. ADC traction system has benefits similar to those noted above for the AC system. For example, even down to 3 mph (approximately 4.83 km / h), DC bus voltage can be maintained stable while regenerative braking is used and risk of welding and fires is mitigated.Clauses

[0043] Clause 1. An apparatus for regenerative braking, comprising: a DC bus coupled to one or more batteries; a first traction motor configured for regenerative braking, coupled to the one or more batteries via the DC bus, such that power generated from braking of the first traction motor is fed to the one or more batteries for charging thereof; and a second traction motor configured for dynamic braking, coupled to a resistor grid, such that power generated from braking of the second traction motor is dissipated at the resistor grid.

[0044] Clause 2. The apparatus of any one or more of clauses 1-6, further comprising: a first contactor between the first traction motor and the DC bus for opening and closing connection therebetween.

[0045] Clause 3. The apparatus of any one or more of clauses 1-6, further comprising: a battery manager coupled to the one or more batteries, the battery manager configured to monitor a state of charge of the one or more batteries; and a DC / DC drive between the first contactor and the DC bus, wherein, if the battery manager detects that the one or more batteries have a state of charge beyond a tolerable threshold, the DC / DC drive is configured to reduce voltage flowing into the one or more batteries from the first traction motor and directing excess power to the resistor grid.

[0046] Clause 4. The apparatus of any one or more of clauses 1-6, further comprising: a DC chopper between the first contactor and the resistor grid, configured to permit ramping up and ramping down of power to the resistor grid.

[0047] Clause 5. An apparatus for regenerative braking, comprising: a traction motor; a battery; a DC bus; a regenerative braking circuit connecting the traction motor to the battery via the DC bus; a bidirectional DC / DC converter connected in the regenerative braking circuit between the DC bus and the batteries; a resistor grid; a connection between the resistor grid and the traction motors for dissipating to the resistor grid excess power from braking the traction motor; and a DC chopper in the connection between the traction motor and the resistor grid.

[0048] Clause 6. The apparatus of any one or more of clauses 1-6, wherein: the traction motor is an AC traction motor; the DC chopper is electrically coupled between the DC bus and the resistor grid; and wherein the connection passes power from the traction motor, through the inverter to be converted into direct current, to the DC bus and then to the resistor grid.Interpretation

[0049] References in the specification to "one embodiment," "an embodiment," etc., indicate that the embodiment described may include a particular aspect, feature, structure, or characteristic, but not every embodiment necessarily includes that aspect, feature, structure, or characteristic. Moreover, such phrases may, but do not necessarily, refer to the same embodiment referred to in other portions of the specification. Further, when a particular aspect, feature, structure, or characteristic is described in connection with an embodiment, it is within the knowledge of one skilled in the art to affect or connect such module, aspect, feature, structure, or characteristic with other embodiments, whether or not explicitly described. In other words, any module, element or feature may be combined with any other element or feature in different embodiments, unless there is an obvious or inherent incompatibility, or it is specifically excluded.

[0050] It is further noted that the claims may be drafted to exclude any optional element or step. As such, this statement is intended to serve as antecedent basis for the use of exclusive terminology, such as "solely," "only," and the like, in connection with the recitation of claim elements or use of a "negative" limitation. The terms "preferably," "preferred," "prefer," "optionally," "may," and similar terms are used to indicate that an item, condition or step being referred to is an optional (not required) feature of the invention.

[0051] The singular forms "a," "an," and "the" include the plural reference unless the context clearly dictates otherwise. The term "and / or" means any one of the items, any combination of the items, or all of the items with which this term is associated. The phrase "one or more" is readily understood by one of skill in the art, particularly when read in context of its usage.

[0052] The term "about" can refer to a variation of ± 5%, ± 10%, ± 20%, or ± 25% of the value specified. For example, "about 50" percent can in some embodiments carry a variation from 45 to 55 percent. For integer ranges, the term "about" can include one or two integers greater than and / or less than a recited integer at each end of the range. Unless indicated otherwise herein, the term"about" is intended to include values and ranges proximate to the recited range that are equivalent in terms of the functionality of the composition, or the embodiment.

[0053] As will be understood by one skilled in the art, for any and all purposes, particularly in terms of providing a written description, all ranges recited herein also encompass any and all possible sub-ranges and combinations of sub-ranges thereof, as well as the individual values making up the range, particularly integer values. A recited range includes each specific value, integer, decimal, or identity within the range. Any listed range can be easily recognized as sufficiently describing and enabling the same range being broken down into at least equal halves, thirds, quarters, fifths, or tenths. As a non-limiting example, each range discussed herein can be readily broken down into a lower third, middle third and upper third, etc.

[0054] As will also be understood by one skilled in the art, all language such as "up to," "at least," "greater than," "less than," "more than," "or more," and the like, include the number recited and such terms refer to ranges that can be subsequently broken down into sub-ranges as discussed above. In the same manner, all ratios recited herein also include all sub-ratios falling within the broader ratio.

[0055] The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to those embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein, but is to be accorded the full scope consistent with the claims. All structural and functional equivalents to the elements of the various embodiments described throughout the disclosure that are known or later come to be known to those of ordinary skill in the art are intended to be encompassed by the elements of the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. No claim element is to be construed under the provisions of 35 USC 112, sixth paragraph, unless the element is expressly recited using the phrase "means for" or "step for."

Claims

CLAIMS1. An apparatus for regenerative braking, comprising: a DC bus coupled to one or more batteries; a first traction motor configured for regenerative braking, coupled to the one or more batteries via the DC bus, such that power generated from braking of the first traction motor is fed to the one or more batteries for charging thereof; and a second traction motor configured for dynamic braking, coupled to a resistor grid, such that power generated from braking of the second traction motor is dissipated at the resistor grid.

2. The apparatus of claim 1, further comprising: a first contactor between the first traction motor and the DC bus for opening and closing connection therebetween.

3. The apparatus of claim 2, further comprising: a battery manager coupled to the one or more batteries, the battery manager configured to monitor a state of charge of the one or more batteries; and a DC / DC drive between the first contactor and the DC bus, wherein, if the battery manager detects that the one or more batteries have a state of charge beyond a tolerable threshold, the DC / DC drive is configured to reduce voltage flowing into the one or more batteries from the first traction motor and directing excess power to the resistor grid.

4. The apparatus of claim 3, further comprising: a DC chopper between the first contactor and the resistor grid, configured to permit ramping up and ramping down of power to the resistor grid.

5. An apparatus for regenerative braking, comprising: a traction motor; a battery; a DC bus;a regenerative braking circuit connecting the traction motor to the battery via the DC bus; a bidirectional DC / DC converter connected in the regenerative braking circuit between the DC bus and the batteries; a resistor grid; a connection between the resistor grid and the traction motors for dissipating to the resistor grid excess power from braking the traction motor; and a DC chopper in the connection between the traction motor and the resistor grid.

6. The apparatus of claim 5, wherein: the traction motor is an AC traction motor; the DC chopper is electrically coupled between the DC bus and the resistor grid; and wherein the connection passes power from the traction motor, through the inverter to be converted into direct current, to the DC bus and then to the resistor grid.

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