Apparatus

Abstract

A power management system for an electrically powered aircraft comprises an electrical power source 110-119, a propulsion unit 142, 144 arranged to generate propulsion from electrical power, a busbar

Description

Technical Field The present invention is concerned with electrical propulsion systems and the configuration and arrangement of electrical propulsion systems within aircrafts. Electrical distribution systems connect power sources to electrical loads. There are several alternative power sources options (that are much more environmentally friendly than typical combustion of fossil fuels) but these are not widespread. Moreover, such systems are not at present used in commercial-sized aircraft (e.g. 48 or 96 passenger aircraft and / or CS-25 related aircraft). Power systems in aircraft are designed to include fault mitigation. In modern systems, aircraft power components are designed and sized for worst case safety scenarios. This has the impact that, while highly safe, the components are oversized for the vast majority of flying time. Such components are heavier, bulkier and less efficient. In the search for high levels of safety, this has become the accepted trade-off position. This oversizing applies to primary and supporting components. A typical fuel cell in a typical electrical power arrangement for a smaller aircraft could be run at 250 kW however due to the worst case safety position, typical fuel cells are run at around 300 kW and must be capable of running at this output rate. A result is that the fuel cell stack is overrated alongside the pumps, compressors, cables which have to be overrated to provide the function required of them from the overrated fuel cell stack. With this approach to safety being consistent across the full aircraft, this leads to significant weight gain and therefore inefficiencies. The arrangement disclosed herein provides a solution to the above that has a reduction in weight, a reduction in size and a gain in efficiency when implemented in an electrical propulsion. This provides a significant improvement over modern systems, allowing environmentally friendly fuels to be used on large scale aircraft. Electrical propulsion systems have many benefits over combustion propulsion systems, particularly in relation to chemical emissions and the like. It is widely seen that electrical propulsion systems may render transport as more viable in a long term perspective. There are however a number of problems inherent in the use of electrical propulsion over traditional combustion propulsion systems. In an attempt to increase the viability of electrical propulsion, attempts have been made to overcome such problems. We provide herein a further advancement in this area. Summary of the Invention Aspects of the invention are set out in the accompanying claims. In accordance with some embodiments described herein, there is provided a power management system for an electrically powered aircraft, the system comprising: at least one electrical power source; at least one propulsion source arranged to generate propulsion from electrical power; a busbar arrangement comprising a plurality of busbars, wherein each busbar is connected to at least one electrical power source and at least one propulsion source and wherein each busbar has a connection to at least one other busbar; a re-configuration element arranged to controllably re-configure connections between the plurality of busbars; a controller arrangement arranged to: control electrical power delivery via the busbar arrangement from the at least one electrical power source to the at least one propulsion source; detect an operating failure state; detect propulsive power requirement; and, provide a signal to the reconfiguration element based on the operating failure state and the propulsive power requirement. The present management system provides excellent redundancy in response to a lack of operation of certain elements within the system. For example, this may occur during a safety event or the like. Moreover, the present system provides this excellent redundancy without requiring significant oversizing as per modern solutions. Use of the re-configuration element to adjust connections between busbars based on information from the controller arrangement allows a highly reactive system that provides excellent redundancy. This arrangement also allows for the significant reduction in weight and cost over modern systems. In use, when a fault occurs that limits the power of one of the busbars, the re-configuration device will alter connections and the power from an adjacent busbar will be routed through the connections to the original busbar. In examples, the re-configuration element is arranged to re-configure at least one connection in response to a re-configure signal provided from the controller arrangement. In this way, there is at least one alteration of the power route from a power source to a propulsion source. In these examples, the system is able to re-route power provision through the management system and account for losses in specific areas of the system by relying more heavily on other areas. This load sharing is enabled by the structure of the management system. In examples, the system further comprises a secondary energy user arrangement connected to the busbar arrangement, wherein the secondary energy user arrangement comprises at least one of: surface controls and / or avionics; environmental control systems; navigation systems; communication systems; weather radar systems; thermal management systems; and, air delivery systems. In examples, the controller arrangement is further arranged to: in response to detecting an operating failure state, detect a power requirement for the secondary energy user arrangement; and, provide a signal to the re-configuration element based on the operating failure state, the propulsive power requirement and the power requirement of the secondary energy user arrangement. In examples, the controller arrangement is arranged to: calculate a priority for power allocation based on the operating failure state, the propulsive power requirement and the power requirement of the secondary energy user arrangement; and, provide a signal to the reconfiguration element based on the calculated priority. Each of these systems require a power load from the power management system. As such, each are relevant for consideration of how to allocate power throughout the system. For example, depending on the severity of the safety event (or other event that provides a difference from normal functioning power provision), the system will prioritise certain power load users and may deprioritise other power load users. For example, television sets for passengers in aircrafts may be deprioritised while navigation systems may be prioritised. The systems provide the information to the controller, the selection of prioritising and deprioritising can be made on a reactive and therefore highly relevant basis. Modern systems may be programmed with simpler instructions noting which systems to notoperate in response to a safety event (or the like). The present system is more advanced by virtue of offering bespoke power management based on the severity of the power loss from normal operation. Indeed, in response to a minor power loss, the system may be able to reconfigure connections without loss of any function from the aircraft. The reactive aspect of this system is highly advantageous. In examples, the system further comprises a plurality of power distribution centres arranged to receive electrical power from the at least one electrical power source and provide electrical power to electrical power users in response to signals from the re-configuration element. The power management system may include power distribution centres from where power can be provided to power users (such as avionics systems or internal conditioning or entertainment systems or the like). Increasing the complexity of the system may seem counterintuitive however using the present controller arrangement this complexity is advantageous in providing alternative source points of power. This can be integrated into the system and controlled by the controller arrangement. In examples, the re-configuration element comprises a closeably openable switch, arranged to be closed or opened in response to signals from the controller arrangement. Advantageously, this system provides a robust and easy to manufacture re-configuration element wherein the controller arrangement can open or close the switch in response to power provision and power demands. In examples, the re-configuration element further comprises a plurality of closeably openable switches, each arranged to be closed or opened in response to signals from the controller arrangement, wherein each busbar is electrically connected to every other busbar via at least one of the switches to form busbar pairs. Advantageously, this provides a great level of redundancy in the power management system. Such high levels of redundancy is particularly advantageous in mitigating power loss from various power sources within the system. While this greater flexibility provides greater complexity, the controller arrangement is able to account for this and this provides robust defence against power loss. In examples, the re-configuration element further comprises a plurality of closeably openable switches, each arranged to be closed or opened in response to signals from the controller arrangement, wherein each busbar is electrically connected to one fewer than every other busbar via at least one of the switches to form busbar pairs. Advantageously, in the event of a failure of a busbar, at least one busbar is isolated from the failure of that busbar. As such, there is redundancy provided in the case of large failure events that cause failures in multiple busbars. In examples, at least one propulsion source comprises a propulsor. Such a propulsion source are suitable for provision of thrust from the power sources within the power management system. Such propulsion sources are particularly suitable for provision of thrust in electrically powered aircraft. In examples, at least one electrical power source is a uni-directional power source. In examples, at least one electrical power source is a fuel cell. In specific examples discussed herein, the power sources may be fuel cells or the like. Fuel cells may be seen as uni-directional power sources. Fuel cells are highly advantageous for use in power generation for aircraft. Fuel cells also offer sustainable power generation and are therefore beneficial from an environmental viewpoint. In examples, each of the plurality of busbars are electrically, thermally and magnetically isolated from one another, and wherein each connection between the plurality of busbars and other components is independently controllable by the controller arrangement and the reconfiguration element. Advantageously, the busbars do not interact with each other in parasitic electrical behaviours. Such behaviours would include eddy currents and the like. In accordance with some embodiments described herein, there is provided an at least partially electrically powered aircraft comprising a power management system according to any of above examples or embodiments. Such an aircraft may comprise fuel cells as well as e.g. a gas turbine power generator. Combined power propulsion may be advantageous for further power redundancy. Similarly, combined power propulsion may provide advantageous thrust benefits considering differing requirements of thrust at different stages of flight. In accordance with some embodiments described herein, there is provided a method of controlling a power management system in an aircraft, the method comprising: i) receive signals indicative of power flow, at a controller, from at least one of: an electrical power source; a propulsion source; a busbar arrangement comprising a plurality of busbars, wherein each busbar is connected to at least one electrical power source and at least one propulsion source; ii) receive, at the controller, indications of an operating failure state; iii) calculate, by the 5 controller, propulsive power requirement; and, iv) send signals, by the controller, to a reconfiguration element based on the power flow, operating failure state and the propulsive power requirement. With this use, the method provides a robust and reactive approach for power loss mitigation. 10 This method provides improvement over previous systems as per the above discussion particularly in light of the reduction of overall weight and size of components alongside lack of any unnecessary impact on power using systems within the aircraft. In examples, the method further comprises (v) actuating the re-configuration element, in 15 response to a re-configure signal provided from the controller, to re-configure at least one connection between at least one of the plurality of busbars. In examples, wherein actuating the re-configuration element comprises actuating a switch between busbars. Brief Description of the Drawings One or more embodiments of the invention will now be described, by way of example only, and with reference to the following figures in which: Figure 1 shows a schematic view of a power management system according to an example of the present disclosure; Figure 2 shows a schematic view of a power management system according to an example of the present disclosure; Figure 3 shows a schematic view of a power management system according to an example of the present disclosure; Figure 4 shows a flow diagram of a method according to an example of the present disclosure; and, Figure 5 shows a schematic view of a power management system according to an example of the present disclosure. Any reference to prior art documents in this specification is not to be considered an admission that such prior art is widely known or forms part of the common general knowledge in the field. As used in this specification, the words “comprises”, “comprising”, and similar words, are not to be interpreted in an exclusive or exhaustive sense. In other words, they are intended to mean “including, but not limited to”. The invention is further described with reference to the following examples. It will be appreciated that the invention as claimed is not intended to be limited in any way by these examples. It will also be recognised that the invention covers not only individual embodiments but also combination of the embodiments described herein. The various embodiments described herein are presented only to assist in understanding and teaching the claimed features. These embodiments are provided as a representative sample of embodiments only, and are not exhaustive and / or exclusive. It is to be understood that advantages, embodiments, examples, functions, features, structures, and / or other aspects described herein are not to be considered limitations on the scope of the invention as defined by the claims or limitations on equivalents to the claims, and that other embodiments may be utilised and modifications may be made without departing from the spirit and scope of the claimed invention. Various embodiments of the invention may suitably comprise, consist of, or consist essentially of, appropriate combinations of the disclosed elements, components, features, parts, steps, means, etc, other than those specifically described herein. In addition, this disclosure may include other inventions not presently claimed, but which may be claimed in future. Detailed Description An invention described herein relates to power management within an electrical powered aircraft. A particular system for this invention may be an aircraft with an electrically drivable motor or a drivable motor that is at least partially electrically driven. For example, a propulsion source in the arrangements discussed may be fully or partially electrically powered. Partially powered aircraft may use thrust provided in part by electrical means and in part by combustion means. Figure 1 shows a simple schematic view of a power management system 100. The power management system 100 may be for an electrically powered aircraft. The system 100 comprises at least one electrical power source 110. The at least one electrical power source may be e.g. a series of fuel cells 111, 112, 113, 114, 116, 117, 118, 119. The at least one electrical power source 110 may be arranged to provide energy to different sections of the system 100. The system 100 comprises at least one propulsion source 142, 144 arranged to generate propulsion from electrical power. The electrical power from the at least one electrical power source 110 is channelled to the at least one propulsion source 142, 144 for provision of thrust for the aircraft. In the example shown, there are two propulsion sources 142, 144. The system 100 further comprises a busbar arrangement 120 comprising a plurality of busbars 122, 124 wherein each busbar is connected to at least one electrical power source 111, 112, 113, 114, 116, 117, 118, 119 and at least one propulsion source 142, 144 and wherein each busbar has a connection 131 to at least one other busbar. The busbar arrangement 120 allows for power from the power sources to be controllably provided to the propulsion sources. In this way, the busbar arrangement 120 provides a controllable and alterable pathway from the power provider 110 (the power source) to the power user (propulsion source) 142, 144. The propulsion source 142, 144 acts to provide thrust from electrical power. The system 100 further comprises a re-configuration element 130 arranged to controllably reconfigure connections 131 between the plurality of busbars 120. The re-configuration element 130 controls the status of the connection 131 between the busbars 120. In the example shown, there are two busbars 122, 124 with a connection 131 between the busbars 122, 124. In an example, the connection 131 is open as a default and therefore electrical energy cannot pass between one busbar 122 to the other busbar 124. However, where there is a desire for this to occur, the re-configuration element 130 changes the status of the connection 131 to closed such that electrical energy can pass between the busbars 122, 124. Changing the status of the connections 131 re-configures the architecture of the power management system such that faults can be accounted for. In an example, the power sources 111, 112 may become faulty or not operational or the like. In this example, the sources 111, 112 are not providing the amount of electrical energy expected of them. The busbar 122 connected to the power sources 113, 114 would have fewer power sources 110 connected to it. In modern systems, the power sources 111, 112, 113, 114, 116, 117, 118, 119 are simply highly overrated such that very high amounts of redundancy are built into their sizing and operational capacity. This is inefficient for reasons mentioned above. In the present system, the re-configuration element may close the connection 131 to allow power sources 113, 114, 116, 117, 118,119 to provide power to both busbars 122, 124 and therefrom onto propulsion sources 142, 144. The system 100 further comprises a controller arrangement 135 arranged to: control electrical power delivery via the busbar arrangement 120 from the at least one electrical power source 110 to the at least one propulsion source 142, 144; detect an operating failure state; detect propulsive power requirement; and, provide a signal to the re-configuration element 130 based on the operating failure state and the propulsive power requirement. The controller arrangement 135 provides a level of responsiveness to the system 100. In response to detecting an operating failure state and a propulsive power requirement, the controller arrangement 135 provides signals to the re-configuration element 130 to alter connections between the busbars such that power distribution can be altered. The signal from the controller arrangement 135 to the re-configuration element 130 occurs in response to an operating failure state. As mentioned above, a failure state may be a reduction of power from any one power source 110 and does not only refer to a total failure of that specific power source. Considering a specific worked example now, we may have total failures in power sources 111, 112. In this example, the propulsion requires e.g. 80 kW. Without a connection, the remaining power sources 113, 114 are to provide the same power as a fully functioning arrangement without the flight mission being compromised. In this instance, therefore the rating of the power sources 113, 114 is necessarily 100 kW and the associated balance of plant is also rated at 20 kW. The balance of plant may require different power levels at different stages of flight. In contrast, the present system allows for a reactive response to such failures. By enabling the power sources on the full busbar 124 to provide some power to the half-powered busbar 122, the power sources only require overrating to 250 kW, with each of the power sources 116, 117, 118, 119 sharing the power deficit from the failed power sources 111, 112. This is supported by the controller arrangement 135 detecting the failure from the power sources 111, 112 and signalling for the re-configuration element 130 to close the previously open connection 131. In other words, in the present arrangement while the total power requirement is assumed to remain constant during any events (such as safety events or the like), the power drawn from each individual remaining power source is more evenly shared. As such, the maximum rating of each power source - i.e. the maximum power that a power source can reliably provide -may be significantly lower in the present disclosed arrangement than is possible in modern systems. Furthermore and advantageously, the present invention still provides redundancy and segregation during normal operation while offering an increased number of reactive response options during safety events (or the like). Specifically, by increasing the output from power sources 116, 117, 118, 119 by around 15 kW each, the load on the power sources decreases by around 30 kW each. This allows all the power sources in the arrangement to be lighter and less complex to manufacture as each will be overrated far less than in modern systems. Furthermore, overrating power sources such as fuel cells is known to damage the fuel cell and therefore reduce the lifetime of the power source. As such, this system 100 also provides a longer lifetime for the thrust arrangement of the aircraft. As noted above, this solution is also lighter and smaller due to less overrating required for each electrical element within the arrangement 100. The re-configuration element 130, connection 131 and controller arrangement 135 weigh far less than the gains on the other electrical equipment, thereby leading to greater overall efficiencies from the present system 100 over modern solutions. Closing the connection 131 reduces further redundancy of the system (i.e. from two busbars to one in the example of Figure 1). While this is counterintuitive, this solution provides great advantages at larger scale aircraft with multiple busbars where redundancy is only proportionally reduced. The reduction in redundancy may be somewhat mitigated by inclusion of greater numbers of busbars 122, 124 within the busbar arrangement 120. In an example of the larger scale aircraft, there may be e.g. 24 fuel cells and 4 independent busbars. As such, the loss of redundancy from the closed connection 131 is more than accounted for in the larger system. The requirement for intelligent control over this system is also unusual in the field and therefore the combination of these unusual steps provides for an improved solution over the modern systems. In an example, the re-configuration element 130 is arranged to re-configure at least one connection 131 in response to a re-configure signal provided from the controller arrangement 135. As described above in the use example, the system 100 notes power status changes from default (normal fully operating status) and then handles this by considerations of overrating the remaining power sources 110 and / or altering the connections 131 within the power management system 100. Referring now to Figure 2, there is shown an example of a simple schematic view of a power management system 200. The power management system 200 of Figure 2 has a number of elements in common with the system 100 of Figure 1, these will not be discussed again in detail for expediency. Elements with numerals increased by 100 relate to elements with the same or similar function. For example, system 100 has the same function as system 200, and power sources 110 of Figure 1 provide power for propulsion as per the power sources 210 of Figure 2. The system 200 of Figure 2 has a series of power sources 210, a series of busbars 220, and two propulsion sources 242, 244. The power delivery is controlled via connection 231 between the busbars 220 and a re-configuration element 230 alongside a controller arrangement 235. The controller arrangement 235 detects changes in the power status of the system 200 and may control alteration of the status of the connection 231 accordingly. Figure 2 also shows two energy storage systems 252, 254. The energy storage systems 252, 254 may be electrical power stores such as batteries, capacitors or super capacitors or the like. The power from the power sources 210 may also be compensated or conditioned or the like by the two energy storage systems 252, 254. In a use example, while the system is fully operational and there is an excess power provision from the sources 210, power from the sources 210 may be directed to the energy storage systems 252, 254 for storing. When the system is no longer in a fully operational capacity, energy from the energy storage systems 252, 254 may be used to assist in accounting for a loss in electrical power provision elsewhere in the arrangement 200. Alternatively, the energy storage systems 252, 254 may be provided with electrical power prior to take off such that the energy may be used in intensive thrust requirement stages of flight such as take off and climb. Such elements therefore assist in the provision of redundancy and increase the overall safety of the system 200. Referring now to Figure 3, there is shown an example of a simple schematic view of a power management system 300. As for Figure 2, similar or identical elements are shown with numerals increased by 100. Not all elements of Figure 3 will be discussed in detail for efficiency. Figure 3 shows a power management system 300. In the example of Figure 3, the system further one secondary aircraft system 362, 364 connected to one of the busbars 322, 324. In the arrangement shown, busbar 322 is connected to secondary aircraft system 362 while busbar 324 is connected to secondary aircraft system 364. The secondary aircraft systems (SAS) 362, 364 comprise for example a plurality of SAS interfaces and a plurality SAS distribution centres, wherein each busbar is electrically connected to at least two of the SAS interfaces, and wherein each SAS interface is arranged to provide an SAS electrical channel. In an example, each SAS distribution centre is powered by at least two of the SAS electrical channels, and each SAS electrical channel is arranged to form a unique SAS interface-to-distribution centre channel. In any of the examples discussed herein, the aircraft system may also have a series of energy or power users, i.e. elements that use power provided by the power sources. The energy users may vary in significance. In a stark example, the power for the entertainment system in the aircraft is less significant than the avionics of the aircraft, at least from the view of safety. As such, the power management system may take into consideration the requirements on power for the whole aircraft. While propulsion may be a primary power user, secondary power users may include surface controls and / or avionics; environmental control systems; navigation systems; communication systems; weather radar systems; thermal management systems; and, air delivery systems. As discussed these may be ranked by the controller arrangement 335 and prioritised accordingly in response to a change in the operational status of the power sources 310. The operational status of the sources 310 may be failed (fully or partially) or not failed (fully operational). This may be detected by the controller arrangement 335 in either power output or in any other reasonable manner. The operational status of any part of the network or aircraft may also be provided to the controller arrangement 335 for consideration as to how to account for the power load requirements in the system 300. The controller arrangement 335 may be arranged to detect power usage in the immediacy. In this way, the controller arrangement 335 detects the power load needs of the network and organises connections to account for these based on the operational status of the power sources 310. In this way, the controller arrangement 335 provides a reactive and robust solution to power management. The controller arrangement 335 may additionally or alternatively be arranged to detect power usage based on historic power usage. This may be used to provide an expected power load from aspects of the network. In this way, the controller arrangement 335 may provide a proactive and robust solution to power management. Changes in power load that occur repeatedly (e.g. at take off and during climb) can be better accounted for in the moment by predictive power load handling. During use, the controller arrangement 335 may receive signals from various detectors and sensors or the like to indicate the status of the elements within the power management system 300. This allows controller arrangement 335 to detect when power requirements or power provision has changed within the system 300. The controller arrangement 335 therefore detects the condition of elements in the system 300. This detection may be continuous or may be intermittent. This detection may be in response to detection of a change such as a detection in a change of electrical load from a specific power source, e.g. power source 311. In response to detecting an operating failure state, the controller arrangement may detect a power requirement for the secondary energy user arrangement and provide a signal to the reconfiguration element based on the operating failure state, the propulsive power requirement and the power requirement of the secondary energy user arrangement. In this way, the controller arrangement 335 has sufficient information to provide a robust power solution for the requirements and the present power output from the sources 310. As mentioned above, this may be performed with a consideration of priority for more important aspects of the network. In this example, the controller arrangement 335 may calculate a priority for power allocation based on the operating failure state, the propulsive power requirement and the power requirement of the secondary energy user arrangement and provide a signal to the re-configuration element based on the calculated priority. This provides for a robust response that can be tailored to particular scenarios of power requirement in light of the power source failure. As mentioned above, if the power source failure is small, all power usage may continue with a somewhat shared load across a few busbars. In the power source failure is large, high priority systems continue to function while low priority systems may not be provided with power. In some examples, the systems may therefore include a plurality of power distribution centres arranged to receive electrical power from the at least one electrical power source and provide electrical power to electrical power users in response to signals from the re-configuration element. The distribution centres may control the delivery of power from e.g. the ESS. The electrical power users may be any of the propulsion sources alongside e.g. any of the secondary energy user arrangement. In the examples shown, there may be greater than two busbars and therefore more than one connection. Each of the connections may be controlled by the controller arrangement shown. The propulsion source may comprise a propulsor for converting electrical energy into kinetic energy. The busbars may be electrically, thermally and magnetically isolated from one another to reduce the likelihood of failure cascade from one busbar to another in the arrangement. For example, if an arc occurs in one busbar it is preferable for the distance between the busbars to be sufficient to prevent the arc from crossing to other busbars. The arrangement therefore benefits from sufficient segregation between the busbars. This also allows the connection to provide the only communication between the busbars. This connection is state controlled by the re-configuration element and the controller arrangement. The present system may be used in any vehicle. The present system may be highly advantageous in aircraft where redundancy, weight and size of system are of high importance. Referring now to Figure 4, a method 400 according to an example of the present disclosure is shown as a flow diagram. The method 400 has four steps 405, 410, 415, 420. In a first step 405, a controller receives signals indicative of power flow from at least one of an electrical power source, a propulsion source, and, a busbar arrangement. In this step, the controller (or controller arrangement) notes the flow of power from the power source to the propulsion source and in particular is able to detect both normal activity and abnormal activity. In a second step 410, the controller receives indications of an operating failure state. In this step, the controller is able to detect an operating “failure” state. This may be failure of a power source or the like. This may relate to e.g. a failure of one or more fuel cells in the system. In a third step 415, the controller calculates a propulsive power requirement. In this step, the controller is able to communicate with the propulsion systems and access an energy requirement for the propulsion system to continue with functioning as desired. Desired functioning may be continued functioning, for example where the aircraft is in cruise stage of flight and the aircraft does not requirement greater propulsion than was being provided prior to the operating failure state. Desired functioning may not be continued functioning but instead involve additional thrust being provided from the propulsion system in response to an operating failure stage. This may be the case e.g. where additional manoeuvres are required from the aircraft in response to a failure stage, such as an emergency go around (aborted or delayed landing) at an airport or the like. In a fourth step 420, the controller sends signals to a re-configuration element based on the power flow, operating failure state and the propulsive power requirement. With the data received by the controller, the controller is able to provide an optimal instruction to the reconfiguration element in relation to the connections that are to be closed. As noted above, by closing connections the system shares a power load between a series of power sources. In this way, the power sources need not be overrated so highly in comparison to arrangements wherein these controlled reactive connections do not. Gains are therefore provided in the present system in relation to all of weight, size and robustness of function. In an example, there is a further step of the method wherein the re-configuration element is actuated. This actuation occurs in response to a re-configure signal from the controller. The actuation of the re-configuration element re-configures at least one connection between at least one of the plurality of busbars. The device herein has excellent weight and size properties while reducing overall redundancy only slightly. The size of aircraft arrangements envisaged will be benefitted by the present systems. Such systems use green propulsion (by virtue of being at least partially electric) and are therefore more beneficial for the environment over present systems that utilise gas turbine and combustion of fuels. As such, the present system is more environmentally friendly alongside being lighter and smaller (which have a further impact on the reduction of fuel required to propel the aircraft). Referring now to Figure 5, there is shown an example of a simple schematic view of a power management system 500. In the arrangement shown, there are four busbars 520a, 520b, 520c, and 520d. Furthermore, in the arrangement shown, there are two propulsors 542, 544, wherein each busbar provides one electrical power channel to each propulsor. Each electrical power channel in the propulsor may be electrically, thermally and magnetically isolated from one another - this provides segregation between busbars in case of arcs or other similar failures. In the arrangement shown, each busbar may have one or more power sources 510a, 510b, 510c, 510d. In an example, each busbar is electrically connected to almost every other busbar via at least one of the switches to form busbar pairs - every busbar is specifically not electrically connected to at least one other busbar. In Figure 5 specifically, it can be seen that busbar 520b is connected to busbar 510a via connection 531a of re-configuration unit 530a, and is connected to busbar 510c via connection 531b of re-configuration unit 530b, wherein the re-configuration units 530a, 530b receive control signals from controller arrangements 535a, 535b respectively. In contrast to aforementioned embodiments wherein each busbar is electrically connected to every other busbar, the arrangement in Figure 5 permits the re-configuration units 530a, 530b to circumvent a failure in the controller arrangements 535a, 535b. For example, if one or both of the controller arrangements 535a, 535b fail and send signals to close connection 531a, 531b, and busbar 520d were instead electrically connected to busbar 520b as well, a common cause failure may result the hypothetical connection between busbars 520b, 520d being closed also, cascading the failure. In the arrangement 500 shown, there are two propulsors 542, 544 arranged symmetrically around a centre line. Each propulsor connects to every busbar. As such, the starboard propulsor connects to both starboard and port side busbars and the same for the port propulsor. This redundancy is useful for the reasons noted above. A feature of this arrangement is that, relative to one propulsion bus, a propulsion bus can interconnect to two other propulsion busses (e.g. bus 520d can connect to both 5520c and 520a). The optional connection relates to the open or closed state of the switches in the arrangement 500. This network 500 arrangement means any failure in the command to re-configuration will always mean one power channel remains isolated. Therefore there is no single point failure associated with the loss of any one incorrectly re-configured position. There is therefore always some safety redundancy built into the system proposed. Further feature combinations are outlined below in the following clauses: First Set of Clauses 1. A re-configurable electrical network for an electrical powered aircraft, the reconfigurable electrical network comprising: a busbar arrangement comprising two or more busbars, wherein each busbar is arranged to provide at least two propulsion electrical channels; a plurality of uni-directional electrical power sources, wherein each busbar is powered by at least one of the electrical power sources; and, at least two propulsors, wherein each propulsor is powered by at least two of the propulsion electrical channels, and, wherein each busbar is electrically connected to every other busbar via a respective re-configuration switch to form busbar pairs. Second Set of Clauses 1. A re-configurable electrical network for an electrical powered aircraft , the reconfigurable electrical network comprising: a busbar arrangement comprising two or more busbars, wherein each busbar is arranged to provide at least two propulsion electrical channels; a plurality of uni-directional electrical power sources, wherein each busbar is powered by at least one of the electrical power sources; at least two propulsors, wherein each propulsor is powered by at least two of the propulsion electrical channels; and, a reconfiguration unit comprising a controller and a plurality of controllable switches, wherein each busbar is electrically connected to every other busbar via at least one of the switches to form busbar pairs. 2. A re-configurable electrical network according to clause 1 wherein each propulsion electrical channel is arranged to form a unique busbar-to-propulsor channel. 3. A re-configurable electrical network according to clauses 1 or 2 further comprising: a plurality of bi-directional energy storage systems (ESSs), wherein each busbar is electrically connected to at least one of the ESSs. 4. A re-configurable electrical network according to any preceding clause further comprising: a secondary aircraft system (SAS) comprising a plurality of SAS interfaces and a plurality SAS distribution centres, wherein each busbar is electrically connected to at least two of the SAS interfaces, and wherein each SAS interface is arranged to provide an SAS electrical channel, wherein each SAS distribution centre is powered by at least two of the SAS electrical channels, and, wherein each SAS electrical channel is arranged to form a unique SAS interface-to-distribution centre channel. 5. A re-configurable electrical network according to any preceding clause, wherein in operation the controller is arranged to operate in: a normal operation, wherein the controller maintains all switches open, and simultaneously detects for a fault in all devices of the re-configurable electrical network; and, a fault operation upon detection of a fault, wherein the controller closes at least one of the switches. 6. A re-configurable electrical network according to clause 5, wherein in fault operation the controller is arranged to perform the following steps: i) determine which of the devices has partially or wholly failed; ii) calculate the optimum switch or switches to close to maintain the required power in each of the remaining devices; iii) close the optimum switch or switches . Third Set of Clauses 1. A re-configurable electrical network for an electrical powered aircraft , the reconfigurable electrical network comprising: an electrical power source arrangement comprising two or more electrical power sources; a busbar arrangement comprising two or more busbars, wherein each busbar is electrically connected to every other busbar to form busbar pairs via a respective reconfiguration switch; and, an at least one propulsor, wherein each busbar is arranged to receive electrical power from a distinct subset of the electrical power sources, and, wherein the propulsor is arranged to receive electrical power from the busbars; and, wherein the re-configurable electrical network further comprises a controller, wherein the controller is arranged to controllably open and close the re-configuration switches.

Claims

1. A power management system for an electrically powered aircraft, the system comprising:at least one electrical power source;at least one propulsion source arranged to generate propulsion from electrical power;a busbar arrangement comprising a plurality of busbars, wherein each busbar is connected to at least one electrical power source and at least one propulsion source and wherein each busbar has a connection to at least one other busbar;a re-configuration element arranged to controllably re-configure connections between the plurality of busbars;a controller arrangement arranged to:control electrical power delivery via the busbar arrangement from the at least one electrical power source to the at least one propulsion source;detect an operating failure state;detect propulsive power requirement; and, provide a signal to the re-configuration element based on the operating failure state and the propulsive power requirement.

2. A power management system according to claim 1, wherein the re-configuration element is arranged to re-configure at least one connection in response to a re-configure signal provided from the controller arrangement.

3. A power management system according to claim 1 or 2, further comprising a secondary energy user arrangement connected to the busbar arrangement,wherein the secondary energy user arrangement comprises at least one of:surface controls and / or avionics;environmental control systems;navigation systems;communication systems;weather radar systems;thermal management systems; and, air delivery systems.

4. A power management system according to claim 3, wherein the controller arrangement is further arranged to:in response to detecting an operating failure state, detect a power requirement for the secondary energy user arrangement; and,provide a signal to the re-configuration element based on the operating failure state, the propulsive power requirement and the power requirement of the secondary energy user arrangement.

5. A power management system according to claim 4, wherein the controller arrangement is arranged to:calculate a priority for power allocation based on the operating failure state, the propulsive power requirement and the power requirement of the secondary energy user arrangement; and,provide a signal to the re-configuration element based on the calculated priority.

6. A power management system according to any of claims 1-5, further comprising: a plurality of power distribution centres arranged to receive electrical power from the at least one electrical power source and provide electrical power to electrical power users in response to signals from the re-configuration element.

7. A power management system according to any of claims 1-6, wherein the reconfiguration element comprises a closeably openable switch, arranged to be closed or opened in response to signals from the controller arrangement.

8. A power management system according to claim 7, wherein the re-configuration element further comprises a plurality of closeably openable switches, each arranged to be closed or opened in response to signals from the controller arrangement, wherein each busbar is electrically connected to every other busbar via at least one of the switches to form busbar pairs.

9. A power management system according to claim 7, wherein the re-configuration element further comprises a plurality of closeably openable switches, each arranged to be closed or opened in response to signals from the controller arrangement, wherein each busbar is electrically connected to one fewer than every other busbar via at least one of the switches to form busbar pairs.

10. A power management system according to any of claims 1-9, wherein at least one propulsion source comprises a propulsor.

11. A power management system according to any of claims 1-10, wherein at least one electrical power source is a uni-directional power source.

12. A power management system according to any of claims 1-11, wherein at least one electrical power source is a fuel cell.

13. A power management system according to any of claims 1-12, wherein each of the plurality of busbars are electrically, thermally and magnetically isolated from one another, and wherein each connection between the plurality of busbars and other components is independently controllable by the controller arrangement and the re-configuration element.

14. An at least partially electrically powered aircraft comprising a power management system according to any of claims 1-13.

15. A method of controlling a power management system in an aircraft, the method comprising:i) receive signals indicative of power flow, at a controller, from at least one of:an electrical power source;a propulsion source; and,a busbar arrangement comprising a plurality of busbars, wherein each busbar is connected to at least one electrical power source and at least one propulsion source;ii) receive, at the controller, indications of an operating failure state;iii) calculate, by the controller, propulsive power requirement; and,iv) send signals, by the controller, to a re-configuration element based on the power flow, operating failure state and the propulsive power requirement.

16. A method according to claim 15, further comprising:(v) actuating the re-configuration element, in response to a re-configure signal provided from the controller, to re-configure at least one connection between at least one of the plurality of busbars.

17. A method according to claim 16, wherein actuating the re-configuration element comprises actuating a switch between busbars.

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