GB2611343A

GB2611343A - Power system for a railway vehicle

Info

Publication number: GB2611343A
Application number: GB2114083.5A
Authority: GB
Inventors: ROSENGREN Jonas
Original assignee: Hitachi Rail Ltd
Current assignee: Hitachi Rail Ltd
Priority date: 2021-10-01
Filing date: 2021-10-01
Publication date: 2023-04-05
Anticipated expiration: 2041-10-01
Also published as: GB202114083D0; GB2611343B

Abstract

A power system for a railway vehicle has one or more on-board generator units (GUs) 1 which generate electrical power from fuel combustion or oxidation; one or more on-board energy storage systems (OBESSs) 2; one or more first traction motors 4A that drive the vehicle using electrical power generated by the GUs; and one or more second traction motors 4B that drive the vehicle using power from the OBESSs. A control sub-system 11 selectively controls the amount of electrical power generated by the GUs and outputted by the OBESSs. The control sub-system also provides an extended operational mode which increases the respective states of charge of the OBESSs by operating the second traction motor(s) as generators to perform regenerative braking while simultaneously operating the GUs to generate electrical power in excess of that needed to drive the vehicle using the first traction motors. The excess electrical power is converted into kinetic energy of the vehicle and then reconverted, by regenerative braking, into regenerated electrical power which is stored by the OBESSs. In a separate embodiment, the control sub-system controls performance of: regenerative braking, where power generated by a first portion of the traction motors is stored by the OBESSs; rheostatic braking, in which kinetic energy of the vehicle is converted into dissipated heat in brake grid resistors by generator operation of a second portion of the traction motors; and friction braking. On braking the vehicle, the control sub-system prioritises regenerative braking, followed by rheostatic braking, then friction braking.

Description

POWER SYSTEM FOR A RAILWAY VEHICLE

Field of the Invention

The present invention relates to a power system for a railway vehicle comprising one or more on-board generator units and one or more on-board energy storage systems.

Background

Conventional hybrid railway vehicles comprise on-board generator units (GUs), such as diesel engine-powered electricity generators, assisted by on-board energy storage systems (OBESSs), such as batteries. These vehicles can produce less carbon dioxide than vehicles whose motive power derives solely from combustion engines.

For all vehicle types, the acceleration phase of a railway journey is when energy consumption peaks.

Thus in conventional hybrid vehicles, during the acceleration phase GUs consume the most fuel and produce the most carbon dioxide. OBESSs contribute to overall improvements in energy consumption by enabling regenerative braking in which kinetic energy of the vehicle is converted into recovered electrical power for subsequent re-use.

It would be desirable for OBESSs to be able to provide more support to GUs during the acceleration phase, thereby improving overall energy consumption performance and reducing overall carbon dioxide emissions of a hybrid railway vehicle. However, because of inevitable inefficiencies, the regenerated electrical energy from conventional regenerative braking energy is generally less than the energy required for acceleration phases. One option for addressing this problem is to re-charge OBESSs to an ideal state of charge (SoC) using additional external and corresponding on-board power infrastructure. However, such infrastructure can be expensive to install or simply may be unavailable.

Furthermore, many conventional railway vehicles have two types of braking systems: dynamic braking and friction brakes. These two types of brake have different priorities, with dynamic braking being applied first, followed by friction braking if necessary. On conventional hybrid trains, dynamic braking involves a simultaneous combination of regenerative braking and rheostatic braking. In rheostatic braking, unlike regenerative braking, kinetic energy of the railway vehicle is simply dissipated as heat. As such, potential regenerative energy that could be recovered during dynamic braking to support the acceleration phase is lost to heat during rheostatic braking.

The present invention has been devised in light of the above considerations. 30 Summary of the Invention Accordingly, in a first aspect, the present disclosure provides a power system for a railway vehicle comprising: one or more on-board generator units which generate electrical power from combustion or oxidation of a fuel; one or more on-board energy storage systems; one or more first traction motors configured to drive the railway vehicle using electrical power generated by the one or more generator units; one or more second traction motors configured to drive the railway vehicle using electrical power outputted by the one or more on-board energy storage systems; and a control sub-system configured to selectively control the amount of electrical power generated by the one or more generator units and the amount of electrical power outputted by the one or more onboard energy storage systems; and wherein the control sub-system is further configured to provide an extended operational mode which increases the respective states of charge of the one or more on-board energy storage systems by operating the one or more second traction motors as generators to perform regenerative braking while simultaneously operating the one or more generator units to generate electrical power in excess of that needed to drive the railway vehicle using the one or more first traction motors, the excess electrical power being converted into kinetic energy of the railway vehicle and then reconverted by the regenerative braking into regenerated electrical power which is stored by the one or more on-board energy storage systems.

In this way, when the railway vehicle has a lower power demand than the GUs are capable of producing, the GUs can advantageously be used to re-charge the OBESSs. Consequently, the OBESSs can be re-charged by regenerative braking during more stages of a journey, and not just when the vehicle as a whole is braking. Moreover, it is possible to implement this approach to re-charging utilising conventional hybrid vehicle hardware (i.e. OBESSs, GUs and traction motors). Thus the extended operational mode can be implemented in a modified conventional hybrid vehicle by reconfiguring its control sub-system. By having more opportunities for re-charging for longer, the OBESSs are able to contribute more power during the most energy-consuming acceleration phases of a journey, leading to overall improvements in energy consumption performance and reductions in carbon dioxide emissions.

The following optional features are applicable singly or in any combination with the power system of the first aspect.

The control sub-system may be configured to selectively control the amount of electrical power generated by the one or more generator units and the amount of electrical power outputted by the one or more on-board energy storage systems so that the first and second traction motors achieve a target. This may be, for example, a target railway vehicle power or velocity, torques at the traction motors, or target forces at the traction motors. In the extended operational mode, the control sub-system may then be configured to operate the one or more generator units to generate electrical power in excess of that which would be needed to drive the railway vehicle using the one or more first traction motors and achieve the given target in the absence of the regenerative braking by the one or more second traction motors.

Conveniently, the GUs may be positioned on one or more cars of the railway vehicle, and the OBESSs may be positioned on one or more different cars of the railway vehicle. The first tractions motors may then be positioned on the cars having their respective GUs, and the second tractions motors may be positioned on the cars having their respective OBESSs. Preferably any car with an OBESS is no more than one car away from a car with a GU. In this way torque contributions can be relatively evenly spread along the length of the vehicle. However, this does not exclude other arrangements, e.g. whereby individual cars have both a GU and an OBESS and their respective first and second traction motors.

In some embodiments, the performance of regenerative braking, in which kinetic energy of the railway vehicle is converted into regenerated electrical power, may be limited to generator operation of the one or more second traction motors. Alternatively, however, in other embodiments, generator operation of the one or more first traction motors may also be able to contribute to the performance of regenerative braking under the control of the control sub-system. Evidently, a braking mode combining regenerative braking based on generator operation of both the first and second traction motors is distinct from the extended operational mode in which only the second traction motors operate as generators.

The control sub-system can be further configured to monitor the SoC and can optionally increase the SoC under the extended operational mode to achieve a target SoC. Typically said target SoC may be less than the maximum possible SoC of the OBESSs. This leaves capacity in the OBESSs for the SoC to be further increased, for example during regenerative braking on approach to a station, thereby avoiding wasting the vehicle's available kinetic energy at that time by unnecessary use of rheostatic braking and friction braking. In addition, reducing use of the friction brakes decreases brake wear and thus reduces maintenance costs.

The control sub-system may be further configured to provide the extended operational mode only when the SoC is less than the target SoC and when the railway vehicle is coasting, cruising or accelerating (i.e. the vehicle is not actively braking as a whole). Typically use of the extended operational mode may be limited to when the railway vehicle is one of coasting and cruising. Providing the extended operational mode only during these journey stages can ensure that the OBESSs have capacity to increase their respective SoCs further under conventional regenerative braking outside the extended operational mode, for example when the vehicle is actively slowing down on station approach.

The control sub-system may vary the target SoC throughout a given journey of the railway vehicle, e.g. depending on predicted power consumption and recovery by the railway vehicle for the remainder of the journey. The prediction may be based on factors such as: predicted velocity profile of the railway vehicle over the remainder of the journey, taking account of position and timings of stops; topography of the remainder of the journey; air resistance, rolling resistance and other known causes of losses; mass and composition of the railway vehicle, etc. Varying the target SoC allows the amount of kinetic energy recoverable by conventional regenerative braking outside the extended operational mode to be maximised.

The control sub-system may be further configured to cease electrical power generation by the GUs for use by the one or more first traction motors, and to drive the railway vehicle solely using electrical power outputted by the OBESSs. This can be beneficial for temporarily avoiding emissions and noise associated with operating the GUs.

The power system may further comprise an override mechanism operable by a driver of the railway vehicle to compel the control sub-system to provide the extended operational mode. In this way the driver can actively control the SoCs of the OBESSs. For example, this can be useful if the vehicle has to make unforeseen deviations from a scheduled journey plan which includes target SOCs at points along the plan.

The railway vehicle may further comprise brake grid resistors and friction brakes, and the control sub-system may be further configured to control performance of: rheostatic braking in which kinetic energy of the railway vehicle is converted into dissipated heat in the brake grid resistors by generator operation of the one or more first traction motors, and friction braking in which the friction brakes are applied. On braking the railway vehicle, the control sub-system may then be further configured to prioritise regenerative braking, followed by rheostatic braking, and then friction braking, in that order.

Indeed, more generally, in a second aspect, the present disclosure provides a combination of a power system and a brake system for a railway vehicle comprising: brake grid resistors and friction brakes; one or more on-board energy storage systems; one or more traction motors at least a first portion of which are configured to drive the railway vehicle using electrical power outputted by the one or more on-board energy storage systems; and a control sub-system configured to control performance of (i) regenerative braking in which kinetic energy of the railway vehicle is converted into regenerated electrical power by generator operation of at least said first portion of the one or more traction motors, the regenerated electrical power being stored by the one or more on-board energy storage systems to increase a state of charge of the one or more on-board energy storage systems, (ii) rheostatic braking in which kinetic energy of the railway vehicle is converted into dissipated heat in the brake grid resistors by generator operation of at least a second portion of the one or more traction motors, and (Hi) friction braking in which the friction brakes are applied; and wherein on braking the railway vehicle, the control sub-system is configured to prioritise regenerative braking, followed by rheostatic braking, and then friction braking, in that order.

Advantageously, performing regenerative braking as a first priority ensures more kinetic energy can be recovered to re-charge the OBESSs than when regenerative braking and rheostatic braking are prioritised together, as is the case in conventional dynamic braking. In this way, the overall energy efficiency and fuel consumption performance of the railway vehicle can be improved.

The following optional features are applicable singly or in any combination with (i) the power system of the first aspect when its control sub-system is further configured to prioritise regenerative braking, followed by rheostatic braking, and then friction braking, in that order, or (ii) the combination of a power system and a brake system of the second aspect.

The regenerative braking may be performable in isolation on braking the railway vehicle, as a light braking mode, without performing rheostatic braking or friction braking, until a target SoC (which may be the maximum possible SoC of the OBESSs) is reached. In this way it is possible to recover a maximum amount of the kinetic energy of the vehicle. The light braking mode may be automatically selectable by the control sub-system. The power system may further comprise an override mechanism operable by a driver of the railway vehicle to compel the control sub-system to brake the railway vehicle in the light braking mode.

In a third aspect, the present disclosure provides a railway vehicle installed with the power system of the first aspect.

In a fourth aspect, the present disclosure provides a railway vehicle installed with the combination of a power system and a brake system of the second aspect.

In a fifth aspect, the present disclosure provides the control sub-system of the power system of the first aspect. Thus the control sub-system of this aspect is for a railway vehicle power system comprising: one or more on-board generator units which generate electrical power from combustion or oxidation of a fuel; one or more on-board energy storage systems; one or more first traction motors configured to drive the railway vehicle using electrical power generated by the one or more generator units; and one or more second traction motors configured to drive the railway vehicle using electrical power outputted by the one or more on-board energy storage systems; and the control sub-system being configured to: selectively control the amount of electrical power generated by the one or more generator units and the amount of electrical power outputted by the one or more on-board energy storage systems; and provide an extended operational mode which increases the respective states of charge of the one or more on-board energy storage systems by operating the one or more second traction motors as generators to perform regenerative braking while simultaneously operating the one or more generator units to generate electrical power in excess of that needed to drive the railway vehicle using the one or more first traction motors, the excess electrical power being converted into kinetic energy of the railway vehicle and then reconverted by the regenerative braking into regenerated electrical power which is stored by the one or more on-board energy storage systems.

In a sixth aspect, the present disclosure provides the control sub-system of the combination of a power system and a brake system of the second aspect. Thus the control sub-system of this aspect is for a combination of a railway vehicle power system and a railway vehicle brake system comprising: brake grid resistors and friction brakes; one or more on-board energy storage systems; and one or more traction motors at least a first portion of which are configured to drive the railway vehicle using electrical power outputted by the one or more on-board energy storage systems; and the control sub-system being configured to: control performance of: (i) regenerative braking in which kinetic energy of the railway vehicle is converted into regenerated electrical power by generator operation of at least said first portion of the one or more traction motors, the regenerated electrical power being stored by the one or more on-board energy storage systems to increase a state of charge of the one or more on-board energy storage systems, (ii) rheostatic braking in which kinetic energy of the railway vehicle is converted into dissipated heat in the brake grid resistors by generator operation of at least a second portion of the one or more traction motors, and (iii) friction braking in which the friction brakes are applied; and on braking the railway vehicle, prioritise regenerative braking, followed by rheostatic braking, and then friction braking, in that order.

The invention includes the combination of the aspects and preferred features described except where such a combination is clearly impermissible or expressly avoided.

Summary of the Figures

Embodiments and experiments illustrating the principles of the invention will now be discussed with reference to the accompanying figures in which: Figure 1 shows schematically an example architecture of a power system for a railway vehicle; and Figures 2A-H shows schematically relative power output levels for GUs and OBESSs for different power demands and different SoCs.

Detailed Description of the Invention

Aspects and embodiments of the present invention will now be discussed with reference to the accompanying figures. Further aspects and embodiments will be apparent to those skilled in the art. All documents mentioned in this text are incorporated herein by reference.

Figure 1 shows an example architecture of a power system for a hybrid vehicle driven by first 4A and second 4B traction motors using electrical power provided by respectively one or more on-board GUs 1 (only one shown in Figure 1) and one or more OBESSs 2 (only one shown in Figure 1). Typically each GU combines a diesel engine and electricity generator powered by that engine to produce AC electrical power, while each OBESS is a battery system having an associated SoC. However other arrangements are possible. For example, the GUs could be fuel cells in which a fuel, such as hydrogen, is oxidised to generate DC electrical power. The railway vehicle may comprise a series of coupled cars in which some cars contain a GU and its first traction motors, and other cars contain an OBESS and its second traction motors. In such an arrangement each car with an OBESS is functionally coupled (as discussed below) with an adjacent or nearby car with a GU. For example, any car with an OBESS may be no more than one car away from a car with a GU. A car with a GU may thus be functionally coupled to more than one car with an OBESS. In other arrangements individual cars may have both a GU and an OBESS and their respective first and second traction motors.

The (typically) three phase AC electrical power generated by the GUs 1 is supplied to AC/DC-AC converters having respective final stage inverters 6A which provide the three phase AC power required by the first traction motors 4A (only one shown in Figure 1). Similarly, the DC power outputted by the OBESSs 2 is inverted by respective inverters 6B to provide the three phase AC power required by the second traction motors 4B (only one shown in Figure 1).

A control sub-system 11 includes a control unit 3 for the functionally coupled GUs 1 and OBESSs 2. The control unit manages the power generated by the GUs and outputted by the OBESSs, the operation of the inverters 6A, 6B and thereby controls the performance of the traction motors 4A, 4B. The railway vehicle also comprises a brake system including brake grid resistors and friction brakes (not shown in Figure 1) that are under the control of the control sub-system.

The control sub-system 11 may have a master controller 10 operable (e.g. by a driver) to select a target vehicle power or total torque demand. The target power and train resistance information 7 are sent to the control unit 3 and converted into respective target torques (or forces) for the traction motors 4A, 4B. The control unit 3 adjusts the amount of electrical power generated by the GUs 1 and outputted by the OBESSs 2 to achieve the target torques at the first 4A and second 4B traction motors. Another option, however, is for the control sub-system to have a master "set-speed" controller operable to select a speed demand, which is converted by the control unit into respective target torques for the traction motors in order for the train to reach and maintain the speed demand.

In a basic operational mode, the control sub-system 11 is configured to prioritise the generation of power from the GUs 1, with torque being mainly provided by the first traction motors 4A. When the GUs 1 and first traction motors 4A are not sufficient alone to achieve their target torques, the control unit 3 demands power from the OBESSs 2 to provide additional torques from the second traction motors 4B. This is most likely to happen during the acceleration phase of a journey where the GUs 1 operate at full power, assisted by the OBESSs 2. When the railway vehicle reaches a desired velocity, the target total torque demand is reduced and the control unit 3 reduces the power demanded from the OBESSs 2 and then from the GUs 1, and the vehicle enters a "cruising" state. If the target torques reduce further to zero (and there is no active braking of the vehicle), "cruising" becomes "coasting".

When the master controller 10 requests a target power which requires active braking of the railway vehicle (i.e. a negative power), one of its braking options (discussed more fully below) is for the control unit 3 to perform regenerative braking in which the second traction motors 4B operate as generators to produce a negative torque contribution. The second traction motors 48 thus operate as generators and kinetic energy of the railway vehicle is converted into regenerated electrical power which is used to charge the OBESSs 2.

The control sub-system 11 is further configured to provide an extended operational mode in which the railway vehicle is driven at a target power which, all things being equal, would require positive or zero total torque contribution from the traction motors 4A, 4B. However, the vehicle achieves this target while simultaneously recharging the OBESSs 2. More particularly, in the extended operational mode, the control unit 3 increases the power generated by the GUs 1 in excess of that which is required to achieve the target using only the first traction motors. A demand for power from the OBESSs is then adjusted to regulate the total torque contribution by operating the inverters 6B and the second traction motors as generators so that the second traction motors make negative torque contributions. In this way, when the railway vehicle is cruising or coasting with a lower power demand than the GUs are capable of producing, excess power from the GUs can be used to increase the SoC of the OBESSs. Effectively, the OBESSs and the second traction motors are used to perform regenerative braking simultaneously with the excess power generation, whereby chemical energy from the fuel is converted into electrical and then kinetic energy, which is then immediately transformed back into electrical energy and stored in the OBESSs.

In an example scenario, the master controller 10 demands a target requiring a total forward torque effort.

The control unit 3 requests a total of 50 kN at a cruising speed of 100 km/h, but the GUs 1 and the first traction motors 4A can deliver a total of 80 kN at that speed. In the extended operational mode, the control unit increases the torque demands from the GUs and first traction motors to 80 kN, and at the same time it asks the OBESSs 2 and the second traction motors 4B to apply a negative torque of 30 kN. The total available power for recovery to the OBESSs is thus 30 kN x 100 km/h = 833 kW.

The functional coupling of each OBESS 2 with a nearby GU 1 under the extended operational mode helps to ensure that the positive and negative torque contributions are relatively evenly distributed along the length of the vehicle. This therefore helps to avoid situations in which all or most of the positive torque contributions are at one end of the vehicle and the negative torque contributions are at the other end of the vehicle, such situations placing undesirably high stresses on mechanical structures such as car couplings and potentially reducing energy conversion efficiencies.

The extended operational mode allows the OBESSs 2 to be re-charged by regenerative braking during more stages of a journey, and not just when the vehicle as a whole is actively braking. By having more opportunities for re-charging, the OBESSs can then usefully be sized to have higher maximum SoCs, allowing them to contribute more power during the most energy-consuming acceleration phases of a journey. Overall this can lead to improvements in energy consumption performance and reductions in carbon dioxide emissions.

The control sub-system 11 can be configured to manage switching between the basic and extended operational modes by monitoring the actual SoCs of the OBESSs 2. The control unit 3 tests the difference between a stored target SoC 12 and actual SoCs. If an actual SoC is lower than the target SoC, the control sub-system enters the extended operational mode. When the actual SoC is equal to or in excess of the target SoC, the control sub-system enters the basic operational mode. The control sub-system is typically capable of controlling each OBESS separately, such that the extended mode can be applied on an OBESS-by-OBESS basis depending on their respective SOCs. However, in general, because the traction pack formed by the first 4A and second 4B traction motors of each functionally coupled GU and OBESS performs approximately the same amount of work as every other such traction pack, switching between the basic and extended operational modes tends to happen at the same time for all the functionally coupled GUs and OBESSs The stored target SoC 12 may change at points across a journey depending on factors such as the topography and velocity profile of the vehicle for the remainder of the route. Generally, the target SoC is less than the maximum SoC possible for the OBESSs 2 to ensure that the OBESSs have capacity to increase their SoCs further under conventional regenerative braking outside the extended operational mode, for example when the railway vehicle is actively slowing down on station approach. Accordingly, the control sub-system 11 makes use of location information 8 to recalculate the target SoC 12 as necessary during the course of a journey.

An override mechanism operable by a driver of the railway vehicle may be provided to compel the control sub-system 11 to enter the extended operational mode. An example of this operation involves the driver activating a Speed Set function where the driver requests a holding cruise control. When the railway vehicle is accelerating and approaches the requested cruising speed, the target total torque demand calculated by the control unit 3 reduces. If an actual SoC is less than the stored target SoC 12 the control sub-system enters the extended operating mode and the control unit continues to operate the GUs 1 at full power, even if this is greater than that which is required to meet the reduced target torque demand.

Conveniently, the control sub-system 11 may be further configured to actively control braking of the railway vehicle as a whole, for instance, to maintain a target speed on a downhill gradient, or on approach to an area with a lower speed limit, or when approaching a station stop. When a braking demand is requested by the master controller 10, the control sub-system 11 calculates a target braking torque. The control sub-system is configured to prioritise regenerative braking first to achieve the target braking torque. Additional rheostatic braking is applied in addition to the regenerative braking, only when the target braking torque exceeds the level of braking torque that the OBESSs 2 and the second traction motors 4B are capable of providing, or when the SoC of the OBESSs has reached its maximum level. In rheostatic braking, kinetic energy of the railway vehicle is dissipated as heat in the brake grid resistors by generator operation of the first traction motors 4A. Finally, if the braking demand is higher than can be provided by both regenerative and rheostatic braking, the friction brakes are applied. The friction brakes are typically able to provide the highest braking force of the three brake systems. However, friction brakes incur significant maintenance costs since mechanical components such as brake pads, discs and callipers can wear out and need replacing. Performing regenerative braking alone as a first priority ensures more kinetic energy can be recovered to re-charge the OBESSs than when regenerative braking and rheostatic braking are performed together.

When there is time to brake slowly, for instance on a long approach to a station, regenerative braking may be performed in isolation, as a light braking mode, without performing rheostatic braking or friction braking, until a target SoC (which may be the maximum possible SoC of the OBESSs) is reached. The light braking mode may be automatically selectable by the control sub-system 11 or by the driver using an override mechanism provided to compel the control sub-system to brake the railway vehicle in the light braking mode. In this way it is possible to recover more of the kinetic energy of the vehicle.

Figures 2A-H shows schematically typical examples of relative power output levels for the GUs 1 and the OBESSs 2 for different power demands and different SoCs of a railway vehicle having two cars with GUs and two cars with OBESSs. The four power levels (2 x GU and 2 x OBESS) shown in each of the examples when summed produce the net power demand requested in each scenario.

Figures 2A and B show examples when the master controller 10 demands a target power resulting in a high target torque. Both the GUs 1 and first traction motors 4A, and the OBESSs 2 and second traction motors 4B contribute to the generation of torque and the forward acceleration of the railway vehicle. Figure 2C and 2E show examples when the master controller 10 requests respectively cruising and coasting speeds, but the actual SoCs are the same or higher than the target SoC 12 so the control subsystem 11 provides the basic operating mode. Thus the power levels for the GUs are lower than the maximum possible, and the OBESSs 2 are used neither to contribute power nor to perform regenerative braking. In contrast, Figures 2D and 2F show examples when the master controller 10 requests respectively cruising and coasting speeds, but the actual SoCs are lower than the target SoC and so the control sub-system provides the extended operational mode. Therefore, the power levels for the GUs are higher than the corresponding examples of Figures 2C and 2E, and the power levels for the OBESSs are negative to represent a negative torque contribution and power regeneration. Finally, Figure 2G shows an example of the relative power output levels for the OBESSs and GUs in light braking mode in which only regenerative braking is performed, and Figure 2H shows an example of full braking mode in which regenerative and rheostatic braking are performed so that both the OBESSs and GUs have negative power levels.

The features disclosed in the foregoing description, or in the following claims, or in the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for obtaining the disclosed results, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.

For the avoidance of any doubt, any theoretical explanations provided herein are provided for the purposes of improving the understanding of a reader. The inventors do not wish to be bound by any of these theoretical explanations.

Any section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described.

Throughout this specification, including the claims which follow, unless the context requires otherwise, the word "comprise" and "include", and variations such as "comprises", "comprising", and "including" will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

It must be noted that, as used in the specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Ranges may be expressed herein as from "about" one particular value, and/or to "about" another particular value. When such a range is expressed, another embodiment includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by the use of the antecedent "about," it will be understood that the particular value forms another embodiment. The term "about" in relation to a numerical value is optional and means for example +/-10%.

Claims

Claims: 1. A power system for a railway vehicle comprising: one or more on-board generator units (1) which generate electrical power from combustion or oxidation of a fuel; one or more on-board energy storage systems (2); one or more first traction motors (4A) configured to drive the railway vehicle using electrical power generated by the one or more generator units (1); one or more second traction motors (4B) configured to drive the railway vehicle using electrical power outputted by the one or more on-board energy storage systems (2); and a control sub-system (11) configured to selectively control the amount of electrical power generated by the one or more generator units (1) and the amount of electrical power outputted by the one or more on-board energy storage systems (2); and wherein the control sub-system (11) is further configured to provide an extended operational mode which increases the respective states of charge of the one or more on-board energy storage systems by operating the one or more second traction motors (4B) as generators to perform regenerative braking while simultaneously operating the one or more generator units (1) to generate electrical power in excess of that needed to drive the railway vehicle using the one or more first traction motors (4A), the excess electrical power being converted into kinetic energy of the railway vehicle and then reconverted by the regenerative braking into regenerated electrical power which is stored by the one or more on-board energy storage systems (2).
2. The power system of claim 1 wherein the one or more generator units (1) are positioned on one or more cars of the railway vehicle, and the one or more on-board energy storage systems (2) are positioned on one or more different cars of the railway vehicle.
3. The power system of claim 2 wherein any car with an on-board energy storage system (2) is no more than one car away from a car with a generator unit (1).
4. The power system of any of the preceding claims wherein the control sub-system (11) is further configured to monitor the state of charge.
5. The power system of claim 4 wherein the control subsystem (11) is further configured to increase the state of charge under the extended operational mode to achieve a target state of charge (12).
6. The power system of claim 5 wherein the target state of charge (12) is less than the maximum possible state of charge of the one or more on-board energy storage systems (2).
7. The power system of claim 5 or 6 wherein the control sub-system (11) is further configured to provide the extended operational mode only when the state of charge is less than the target state of charge (12), and when the railway vehicle is coasting, cruising or accelerating.
8. The power system of claims 5 to 7 wherein the control sub-system (11) is further configured to vary the target state of charge (12) throughout a given journey of the railway vehicle.
9. The power system of claim 8 wherein the control sub-system (11) is further configured to vary the target state of charge (12) during the given journey depending on predicted power consumption and recovery by the railway vehicle for the remainder of the journey.
10. The power system of any of the preceding claims wherein the control sub-system (11) is further configured to cease electrical power generation by the one or more generator units (1) for use by the one or more first traction motors (4A), and to drive the railway vehicle solely using electrical power outputted by the one or more on-board energy storage systems (2).
11. The power system of any of the preceding claims further comprising an override mechanism operable by a driver of the railway vehicle to compel the control sub-system (11) to provide the extended operational mode.
12. The power system of any of the preceding claims wherein the railway vehicle has brake grid resistors and friction brakes, and the control sub-system (11) is further configured to control performance of: rheostatic braking in which kinetic energy of the railway vehicle is converted into dissipated heat in the brake grid resistors by generator operation of the one or more first traction motors (4A), and friction braking in which the friction brakes are applied; wherein on braking the railway vehicle, the control sub-system (11) is further configured to prioritise regenerative braking, followed by rheostatic braking, and then friction braking, in that order.
13. A combination of a power system and a brake system for a railway vehicle comprising: brake grid resistors and friction brakes; one or more on-board energy storage systems (2); one or more traction motors (4A) at least a first portion of which are configured to drive the railway vehicle using electrical power outputted by the one or more on-board energy storage systems (2); 25 and a control sub-system (11) configured to control performance of: (i) regenerative braking in which kinetic energy of the railway vehicle is converted into regenerated electrical power by generator operation of at least said first portion of the one or more traction motors (4A), the regenerated electrical power being stored by the one or more on-board energy storage systems (2) to increase a state of charge of the one or more on-board energy storage systems, (ii) rheostatic braking in which kinetic energy of the railway vehicle is converted into dissipated heat in the brake grid resistors by generator operation of at least a second portion of the one or more traction motors, and (Hi) friction braking in which the friction brakes are applied; and wherein on braking the railway vehicle, the control sub-system (11) is configured to prioritise regenerative braking, followed by rheostatic braking, and then friction braking, in that order.
14. A railway vehicle installed with the power system of any of claims 1 to 12.
15. A railway vehicle installed with the combination of a power system and a brake system of claim 13.
16. The control sub-system of the railway vehicle power system of any of claims 1 to 12.
17. The control sub-system of the combination of a railway vehicle power system and a railway vehicle brake system of claim 13.