Patent Description:
System applications with electrical systems having an energy source and energy sinks that perform, at least in some scenarios, safety-critical operations are found in many places, such as spacecraft, aircraft, motor vehicles, drones, alarm systems, power plants, just to name a few. Examples for safety-critical operations, which are sometimes also referred to as mission-critical operations, performed by electrical systems in an aircraft include controlling the aircraft's roll, pitch, yaw, and thrust. A failure of any of these safety-critical operations under certain conditions can potentially lead to an instable motion of the aircraft with life endangering, consequences. Thus, the continued, uninterrupted, fail-safe operation of these electrical systems and thus of the corresponding system application is often required.

In particular, a loss of lift power avoidance is very important for an aircraft's propulsion unit and involves high qualification efforts on an architectural level. For example, the European Union Aviation Safety Agency (EASA) has released a Special Condition for type certification of small vertical take-off and landing (VTOL) aircraft (SC-VTOL-<NUM>) on July, <NUM>nd <NUM>, in which, VTOL aircraft that are certified in the category Enhanced would have to meet requirements for continued safe flight and landing, and be able to continue to the original intended destination or a suitable alternate vertiport after a failure.

In the category Enhanced, failure conditions that would prevent continued safe flight and landing of the aircraft are considered catastrophic. A quantitative safety objective in the category Enhanced determines that catastrophic failure conditions have to occur at a rate that is smaller than or equal to <NUM>-<NUM> occurrences per flight hour.

Regulations such as SC-VTOL-<NUM> have a big impact on the design of electrical energy storage systems and power distribution systems that operate mission-critical electrical energy sinks. In fact, these electrical energy storage systems and power distribution systems have to be designed to guarantee the imposed predetermined failure conditions, and conventional energy storage systems that use a single state-of-the-art energy source may not be adapted in terms of power and energy density for such a mission-critical electrical energy sink.

As a result, electrical energy sources are often oversized to compensate for potential power loss or energy loss failure conditions at the cost of a significant weight increase. For example, a primary power distribution system within a vehicle may have multiple energy sources, which are either electrically segregated from each other during normal operation, or which are connected in parallel during normal operation.

Such primary power distribution systems usually react to emergency conditions (e.g., network failures or energy sink failures), by using switching devices that isolate the failure and continue to supply power to the mission-critical electrical energy sinks. However, both concepts, the electrically segregated energy sources and the energy sources that are connected in parallel, are confronted with different drawbacks.

The electrically segregated energy sources of the power distribution system prevent the electrical energy sources from feeding an overload current or a short circuit current, which may potentially lead to a power interrupt at the corresponding electrical energy sink.

However, in case of a failure at one of the segregated electrical energy sources, a power interrupt at a corresponding mission-critical electrical energy sink may occur. To ensure that mission-critical electrical energy sinks remain operational, a loss of an electrical energy source usually ensues a reconfiguration of the power distribution system. The reconfiguration of the power distribution system is performed using switching devices such as electromechanical contactors or semiconductor switches that connect the mission-critical electrical energy sinks to a backup electrical energy source.

The backup electrical energy source can either be another electrical energy source of the power distribution system or a dedicated independent emergency energy source. In both cases, the backup electrical energy source needs to be dimensioned to cover the power and energy demands of all the mission-critical electrical energy sinks to which it is connected as a result of the reconfiguration. In the worst-case scenario, in which all newly connected electrical energy sinks and all originally connected electrical energy sinks perform mission-critical operations, the backup electrical energy source needs to be dimensioned to cover the power and energy demands of all the newly connected electrical energy sinks in addition to the originally connected electrical energy sinks.

At a nominally connected primary power distribution system, the primary electrical energy sources are connected in parallel during normal operation. This reduces the risk of power interrupts at electrical energy sinks in case of a primary electrical energy source loss. However, very high overload currents or short circuit currents may occur until the failure path is isolated by electrical reconfiguration.

All primary electrical energy sources and the associated interconnections downstream from the respective electrical energy sources to the failure location are exposed to high failure currents until the overload condition has been isolated. Thus, all primary electrical energy sources, the electrical switching devices (e.g. fault current protection switches) and the associated interconnections must be dimensioned to withstand these overload conditions.

Furthermore, all primary electrical energy sources sink their power to the failure location until the segregation between the electrical energy sources is completed, which increases the risk of an electrical power interrupt at mission-critical electrical energy sinks.

The principles of failure management require that the electrical energy sources and the mission-critical electrical energy sinks are qualified against failure scenarios, use monitoring functions to detect failure events, use reconfiguration switching devices with corresponding control mechanisms, are qualified with respect to power interruption times until buffering of backup electrical energy sources and with respect to the performance of the backup electrical sources during emergency conditions.

Thereby, the principles of failure management lead to an increased certification complexity and certification effort. For example, an oversizing of the primary power distribution with a significant weight impact is often required to satisfy the power supply during an emergency condition.

Recent state-of-the-art electrical power train applications use a hybrid electrical energy storage system that combines power optimized sources (e.g., high-power batteries) with energy optimized sources (e.g., gen set). Thereby, the increased complexity of the hybrid electrical energy storage system is traded-off against a reduction in weight and an optimization of performance.

The contribution of the energy optimized sources to the load is often actively steered to optimize the hybrid electrical energy storage system with respect to the overall energy and power density. The active steering of the contribution of the energy optimized sources to the load may be implemented using switching power electronic components and/or a DC/DC converter for each one of the power and energy optimized sources.

However, the increased complexity of hybrid electrical energy storage systems may affect reliability and failure robustness. Therefore, high qualification efforts are often required if mission-critical electrical energy sinks are connected to a hybrid electrical energy storage system.

Document <CIT> describes a hybrid propulsion system for a multirotor rotary wing aircraft that comprises at least one inverter configured to supply power in parallel to multiple electric motors intended to drive the corresponding propellers of the system. In particular, the hybrid propulsion system comprises an internal combustion engine and an electric generator coupled to the internal combustion engine so that, in operation, the internal combustion engine drives the electric generator, a rectifier connected to the electrical generator for converting an alternating current delivered by the electrical generator into a direct current, conversion means configured to convert the direct current to alternating current, and an electrical network connecting the rectifier to the means of conversion, at least a first group of at least two first electric motors connected to the conversion means so that in operation, the conversion means supply the first electric motors with alternating current, and propellers respectively coupled to the first electric motors so that in operation, the first electric motors drive the propellers, characterized in that the conversion means comprise a first inverter configured to supply in parallel the first electric motors.

However, the power management control of the presented hybrid propulsion system has a comparatively high complexity that requires comparatively high qualification efforts. Furthermore, there is no primary source associated with the load. Instead, a single main source supplies all loads. Thus, significant oversizing at the battery level and/or the genset level is required, to either compensate a genset loss, which has a probability of approximately <NUM>-<NUM> occurrences per flight hour, or a buffer battery loss, which has a probability of approximately <NUM>-<NUM> occurrences per flight hour. Either way, it is very likely that the proposed hybrid propulsion system has difficulties to reach the failure rate of less than <NUM>-<NUM> occurrences per flight hour that is required for supplying critical loads like propulsion units.

Documents <CIT>, <CIT>, and <CIT> describe hybrid powertrains that are similar to and have the same disadvantages as the hybrid propulsion system of document <CIT>.

Document <CIT> describes a multirotor aircraft with at least two thrust producing units, the multirotor aircraft being adapted for transportation of passengers and comprising an aircraft operating structure that is adapted for operation of the multirotor aircraft in failure-free operating mode, and a redundant security architecture that is at least adapted for operation of the multirotor aircraft in case of a failure of the aircraft operating structure in operation, the redundant security architecture being provided to comply with applicable authority regulations and certification requirements regarding passenger transportation.

However, the redundant security architecture is lacking a hybrid electrical energy storage system. Thus, an oversizing of the primary power distribution with a significant weight impact is very likely required to satisfy the power supply during an emergency condition.

In summary, conventional energy storage and power distribution systems that use a single type of energy source technology may lack the required power and energy density for supplying mission-critical electrical energy sinks without a significant oversizing of the energy storage modules.

Thus, hybrid electrical energy storage systems that combine energy optimized energy sources with power optimized energy sources were recently introduced. Such hybrid electrical energy storage systems allow to optimize the power distribution working points during power or energy intensive vehicle operation phases such as take-off and landing or cruise flight. However, many state-of-the-art hybrid electrical energy storage systems have a comparatively high complexity and low robustness.

Document <CIT> describes a hybrid power system that comprises a power controller adapted to be in communication with a first power source, a second power source, and a load. The power controller may be configured to detect whether a current drawn by the load exceeds a predetermined threshold, control discharging of the first power source without permitting discharging of the second power source to power the load when the current drawn by the load is less than the predetermined threshold current, and control discharging of the first power source and the second power source to power the load when the current drawn by the load is greater than the predetermined threshold current.

Document <CIT> describes a system for providing regenerative power for an aircraft to sustain flight that includes multiple energy cells disposed within the aircraft, the energy cells being configured to supply power to a propulsion motor and electronics of the aircraft, a fan generator harnessing propeller blast created by an aircraft propeller and converting kinetic energy of the propeller blast into electrical energy, a charger receiving the electrical energy generated by the fan generator and using the electrical energy to recharge one or more of the energy cells, and a power transfer switch selectively connecting one of the energy cells to the propulsion motor and electronics of the aircraft, such that the energy cells are rotated one at a time to power the propulsion motor and electronics. During recharging, the one or more of the energy cells are disconnected by the power transfer switch.

It is, therefore, an objective to provide a new electrical system for an aircraft. The new electrical system should enable simplified working point optimization, have a lower complexity, and require lower qualification efforts than conventional power distribution systems. Furthermore, compared to conventional power distribution systems the new electrical system should be more robust and reliable and offer a simpler and more robust concept to cover energy source failure conditions and overload conditions without risk of interrupts.

The objective is solved by an electrical system comprising the features of claim <NUM>. More specifically, an electrical system for an aircraft may comprise a hybrid energy storage system and one or more energy sinks, wherein each energy sink of the one or more energy sinks comprises a load. The hybrid energy storage system may comprise one or more primary energy sources, a secondary energy source, and a secondary energy source control unit. The one or more primary energy sources may be coupled to the one or more energy sinks and supply power to the one or more energy sinks, wherein each primary energy source of the one or more primary energy sources comprises an energy storage unit that stores electrical energy and supplies power at a predetermined voltage range, and an electrical energy source management unit that collects sensor data from the energy storage unit. The secondary energy source may be coupled to the one or more primary energy sources and adapted to supply power at a variable output voltage to the one or more primary energy sources. The secondary energy source control unit may receive the sensor data from the electrical energy source management unit and send command signals to the secondary energy source to control the variable output voltage based on the sensor data. The secondary energy source control unit may be adapted to directing the secondary energy source to provide the variable output voltage at a value that is smaller or greater than at least one output voltage of all of the one or more primary energy sources when all of the one or more primary energy sources are working normal and are contributing to supply the respective one or more energy sinks.

Illustratively, the electrical system describes a robust way of realizing a hybrid energy storage system. In particular, the electrical system covers the electrical power distribution system principle and the hybrid energy storage principle through interactions between primary energy sources and secondary energy sources.

Thereby, the hybrid energy storage system can be extended from <NUM> to n branches (i.e., <NUM> to n primary energy sources connected to <NUM> to n electrical energy sinks). The <NUM> to n branches may be coupled in parallel to at least one secondary energy source using an electric backbone.

By way of example, dedicated control logic may control each secondary energy source. If desired, each secondary energy source may have its separate dedicated control logic. The dedicated control logic may gather sensor data from the respective source management units (SMU) of the respective primary energy sources within the hybrid energy storage system.

In other words, the electric backbone may have a common voltage potential that enables a connection of the at least one secondary energy source with each primary energy source of the hybrid energy storage system.

By way of example, the primary energy source switching devices may be implemented using power diode modules. If desired, an electrical vehicle may include one or more hybrid energy storage systems. For example, an electrical vehicle may have two independent hybrid energy storage systems.

If desired, the secondary energy source of the hybrid energy storage system may perform buffering tasks. For example, the secondary energy source may allow to optimize the working point of the primary energy sources at different load conditions. Thus, the secondary energy source may enable downsizing and hence weight reduction of the primary energy sources.

Furthermore, the secondary energy source can act as an emergency/backup source that takes over the respective electrical energy sink in case of a primary energy source loss. The secondary energy source may comprise energy optimized batteries, generators driven by combustion engine, fuel cells, a supercapacitor, an ultracapacitor, etc..

Depending on the load profile, the secondary energy source control can actively lower the consumption of the primary energy source (e.g., by setting the output voltage of the secondary energy source to a value that is greater than the bus bar voltage of the primary energy source). Thus, the secondary energy source may act as a range extender, for example in case of power reduced and energy intensive load conditions.

The primary energy source may be dimensioned for its nominal condition. In other words, the primary energy source does not need to be oversized to compensate for other primary energy sources in case of a failure of one or more of these other primary energy sources. Thus, the primary energy source may be downsized compared to state-of-the-art energy sources due to the buffer properties (e.g. lower load peaks) of the secondary energy source.

Furthermore, a potential loss of the secondary energy source can be considered as an emergency load case and as a sizing criterion for the primary energy source. The arrangement of the primary energy sources' switching elements simplifies the control logic of the secondary energy source control and the monitoring and protection logic of the primary energy source.

Thus, a simple and robust hybrid energy storage system can be realized. Such a hybrid energy storage system can be used for safety critical vehicle applications e.g., supplying critical consumers, because it achieves the required reliability figures at a quantitative safety assessment. Moreover, the reduced complexity combined with the increased robustness of the hybrid energy storage system decreases the certification efforts compared to state-of-the-art energy storage systems.

The proposed architecture of the hybrid energy storage system eliminates the need for a dedicated electrical power distribution system (e.g. stand-alone distribution boxes having own intelligence), which is usually required to re-route the remaining power from the energy sources to critical consumers (e.g., by electrical reconfiguration) in case of an energy source loss or malfunction. Thus, as a side effect of the proposed hybrid energy storage system, an overall reduction in complexity of the power distribution system can be achieved.

Furthermore, the voltage-controlled output of the secondary energy source can be combined with an energy management system in a way that the contribution of the secondary energy source to the primary bus is always ideal, e.g. following active energy reduction strategies depending on flight state and remaining capacity of the secondary energy source.

Contrary to state-of-the-art hybrid energy storage systems, the herewith presented hybrid energy storage system comprises one voltage-controlled energy source that is combined with at least one primary energy source, which reduces the complexity of the hybrid energy storage system to a minimum.

Additionally, the hybrid energy storage system allows the implementation of further vehicle operational modes, like auxiliary power supply unit functionalities, e.g. to extent ground operation modes, electrical taxiing, etc..

Furthermore, a dedicated charging mode in which the secondary energy source recharges the primary energy sources (e.g., while on ground) is introduced.

According to one aspect, the secondary energy source further comprises a negative output port and a positive output port, wherein the variable output voltage is supplied between the positive output port and the negative output port.

According to one aspect, the secondary energy source further comprises a buffer that is coupled between the positive and negative output ports.

According to one aspect, the secondary energy source further comprises an energy storage component that comprises at least one of a battery, a supercapacitor, an ultracapacitor, a fuel cell, or an engine-generator set.

According to one aspect, the secondary energy source further comprises a voltage control unit that is coupled between the energy storage component and the positive and negative output ports, wherein the voltage control unit supplies the variable output voltage between the positive and negative output ports based at least in part on the command signals.

According to one aspect, the voltage control unit sends feedback signals to the secondary energy source control unit, and the command signals from the secondary energy source control unit are based at least in part on the feedback signals.

According to one aspect, the voltage control unit comprises at least one of a rectifier, a DC/AC converter, a DC/DC converter, or a stabilizing buffer.

According to one aspect, an energy sink of the one or more energy sinks comprises a three-phase AC machine, and a DC/AC converter that is coupled between a primary energy source of the one or more primary energy sources and the three-phase AC machine.

According to one aspect, each primary energy source of the one or more primary energy sources supplies power to exactly one energy sink of the one or more energy sinks.

According to one aspect, at least one primary energy source of the one or more primary energy sources further comprises a positive input port, a negative input port, wherein the positive and negative input ports are coupled to the secondary energy source, a positive output port, a negative output port, wherein the positive and negative output ports are coupled to at least one of the one or more energy sinks, and a bus bar that is coupled between the energy storage unit and the positive input and output ports.

According to one aspect, the at least one primary energy source of the one or more primary energy sources further comprises a primary switch arrangement that is coupled between the energy storage unit and the bus bar.

According to one aspect, the primary switch arrangement further comprises a primary switch diode that is arranged in forward direction from the energy storage unit to the bus bar, and a primary switch contactor that is arranged in parallel to the primary switch diode between the energy storage unit and the bus bar.

According to one aspect, the at least one primary energy source of the one or more primary energy sources further comprises an input switch that is coupled between the positive input port and the bus bar, wherein the input switch comprises at least one of an electromechanical switch, a semiconductor based switch, or a diode in forward current direction to the bus bar.

According to one aspect, the at least one primary energy source of the one or more primary energy sources further comprises an output switch that is coupled between the bus bar and the positive output port, wherein the output switch comprises at least one of an electromechanical switch or a semiconductor based switch.

According to one aspect, the at least one primary energy source of the one or more primary energy sources further comprises a protection switch that is coupled between the negative input and output ports and the energy storage unit for disconnecting the energy storage unit from the positive and negative input and output ports, wherein the protection switch comprises at least one of an electromechanical switch, a semiconductor based switch, a fuse, or a circuit breaker.

Embodiments are outlined by way of example in the following description with reference to the attached drawings. In these attached drawings, identical or identically functioning components and elements are labelled with identical reference numbers and characters and are, consequently, only described once in the following description.

Exemplary embodiments may be included in any application that includes an electrical energy source and an electrical energy sink that performs safety-critical operations. The electrical energy sink may perform safety-critical operations under predetermined circumstances (e.g., when operating under certain conditions), at predetermined times (e.g., at predetermined time intervals), or exclusively (i.e., under any condition and at all times).

For example, embodiments may be included in transportation vehicles. <FIG> shows an example of a transportation vehicle. A transportation vehicle may be a spacecraft, an aircraft, a car, a bus, a truck, or a train, just to name a few. As shown in <FIG>, the transportation vehicle may be an aircraft <NUM> that is exemplarily illustrated as a rotary-wing aircraft <NUM>.

Rotary-wing aircraft <NUM> may have an aircraft airframe <NUM>. The aircraft airframe <NUM> defines a supporting structure of aircraft <NUM> that is also referred to hereinafter as the fuselage <NUM> of the rotary-wing aircraft <NUM>.

The aircraft airframe <NUM> may be provided with an outer shell <NUM> that defines an internal volume 102a. Illustratively, the internal volume 102a may be adapted for the transportation of passengers, so that the rotary-wing aircraft <NUM> as a whole is adapted for transportation of passengers. The internal volume 102a may be adapted for accommodating operational and electrical equipment, such as e.g. a hybrid energy storage system that is required for operation of the rotary-wing aircraft <NUM>.

It should be noted that exemplary configurations of the internal volume 102a that are suitable for transportation of passengers, but also for accommodation of operational and electrical equipment, are readily available to the person skilled in the art and generally implemented to comply with applicable authority regulations and certification requirements regarding passenger transportation. Thus, these configurations of the internal volume 102a are not described in detail for brevity and conciseness.

By way of example, the rotary-wing aircraft <NUM> comprises a predetermined number of thrust producing units <NUM>. If desired, the predetermined number of thrust producing units <NUM> comprises at least two thrust producing units 103a, 103b. If desired, the predetermined number of thrust producing units <NUM> may be more than two. For example, rotary-wing aircraft may comprise three, four, or more thrust producing units.

It should be noted that the thrust producing units 103a, 103b are all exemplarily arranged laterally with respect to the fuselage <NUM>. In other words, thrust producing units of the predetermined number of thrust producing units <NUM> are exemplarily arranged on the left or right side of the fuselage <NUM> seen in its longitudinal direction. Accordingly, in <FIG> only the thrust producing units 103a, 103b are visible, while other thrust producing units of the predetermined number of thrust producing units <NUM> may be masked by fuselage <NUM>.

If desired, two additional thrust producing units may be embodied in an axially symmetrical manner with respect to the thrust producing units 103a, 103b, wherein a longitudinal center axis in the longitudinal direction of fuselage <NUM> defines the symmetry axis. Accordingly, only the thrust producing units 103a, 103b and their constituent elements are described in more detail hereinafter, while a more detailed description of the additional thrust producing units is omitted for brevity and conciseness.

The thrust producing units 103a, 103b are embodied for producing thrust in a predetermined direction in operation such that the rotary-wing aircraft <NUM> is able to hover in the air as well as to fly in any forward or rearward direction.

Illustratively, the thrust producing units 103a, 103b are structurally connected to a predetermined number of structural supports <NUM>, which may include at least two structural support members. Illustratively, the predetermined number of structural supports and the predetermined number of thrust producing units <NUM> form a thrust producing units arrangement.

By way of example, one or more of the thrust producing units 103a, 103b may comprise an associated shrouding in order to improve underlying aerodynamics and to increase operational safety. By way of example, a plurality of shrouding units <NUM> is shown with two separate shroudings 106a, 106b. Illustratively, the shrouding 106a is associated with the thrust producing unit 103a, and the shrouding 106b with the thrust producing unit 103b.

If desired, the shroudings 106a, 106b may be connected to the predetermined number of structural supports <NUM>. More specifically, the shrouding 106a is preferably connected to the structural support member 104a, and the shrouding 106b to the structural support member 104b.

According to one aspect, at least one and, preferably, each one of the thrust producing units 103a, 103b is equipped with at least one rotor assembly. By way of example, the thrust producing unit 103a is equipped with a rotor assembly 108a, and the thrust producing unit 103b is equipped with a rotor assembly 108b. The rotor assemblies 108a, 108b illustratively define a plurality of rotor assemblies <NUM>, which is preferably mounted to the plurality of shroudings <NUM>.

The plurality of rotor assemblies <NUM> may be powered by an associated plurality of engines 105a, 105b. If desired, rotary wing aircraft may have an electrical system that comprises a hybrid energy storage system and one or more electrical energy sinks. For example, the plurality of engines 105a, 105b may be embodied as electrical engines and thus as electrical energy sinks. Illustratively, rotor assembly 108a may be powered by electrical engine 105a and rotor assembly 108b may be powered by electrical engine 105b.

The plurality of engines 105a, 105b that powers the plurality of rotor assemblies <NUM> are part of the safety-critical components, which are sometimes also referred to as the mission-critical components or mission-critical electrical energy sinks of the rotary-wing aircraft <NUM>. Accordingly, a fail-safe electrical drive unit may implement at least one of electrical engines 105a, 105b. If desired, the fail-safe electrical drive unit may be one of the one or more energy sinks <NUM> of <FIG>.

The mission-critical electrical energy sinks of rotary-wing aircraft <NUM> may be powered by the hybrid energy storage system, if desired. <FIG> is a diagram of an illustrative electrical system <NUM> having a hybrid energy storage system <NUM> with a secondary energy source and two primary energy sources that supply power to two energy sinks in accordance with some embodiments.

As shown, electrical system <NUM> may include energy sinks <NUM>. Energy sinks <NUM> may include any electrical component that transforms electrical energy into some other form of energy, which may include electrical energy, thermal energy, mechanical energy, electromagnetic energy, sound energy, chemical energy, or a combination thereof.

As an example, energy sinks <NUM> may include an electric motor that transforms electrical energy into mechanical energy, sound, and heat. As another example, energy sinks <NUM> may include a light bulb that transforms electrical energy into light and heat. If desired, energy sinks <NUM> may perform mission-critical operations. As an example, energy sinks <NUM> may include electrical engines 105a, 105b that power the plurality of rotor assemblies <NUM> of rotary-wing aircraft <NUM> of <FIG>.

Each energy sink 240a, 240b of energy sinks <NUM> may have one or more loads (e.g., electrical engines 105a, 105b of <FIG>). If desired, each energy sink may include a single load (e.g., energy sink 240a has electrical engine 105a and energy sink 240b has electrical engine 105b of <FIG>).

Energy sink 240a and/or 240b may perform safety-critical operations and/or mission-critical operations. Energy sink 240a and/or 240b may perform safety-critical and/or mission-critical operations under predetermined circumstances (e.g., when operating under certain conditions), at predetermined times (e.g., at predetermined time intervals), or exclusively (i.e., under any condition and at all times).

Illustratively, electrical system <NUM> may include a hybrid energy storage system <NUM>. Hybrid energy storage system <NUM> may include primary energy sources <NUM> that are coupled to energy sinks <NUM> and supply power to energy sinks <NUM>.

If desired, each primary energy source of primary energy sources <NUM> may be coupled to and supply power to energy sinks <NUM>. For example, each primary energy source 210a, 210b of primary energy sources <NUM> may be associated with and supply power to exactly one energy sink of energy sinks <NUM>. As shown, primary energy source 210a is coupled to and supplies power to energy sink 240a and primary energy source 210b to energy sink 240b.

Each primary energy source 210a, 210b contains an electrical energy storage device. The electrical energy storage device may be any apparatus able to store and provide electricity to electrical energy sinks <NUM>. For example, primary energy source 210a, 210b may include a lithium ion rechargeable battery, a nickel cadmium rechargeable battery, a lithium ion polymer rechargeable battery, a nickel metal hydride battery, or any other rechargeable or non-rechargeable battery.

If desired, primary energy source 210a, 210b may include at least one of a supercapacitor, an ultracapacitor, a fuel cell, an engine-generator set, etc. which are sized to provide power to the corresponding energy sink 240a, 240b.

Illustratively, hybrid energy storage system <NUM> may include a single secondary energy source <NUM> that is coupled to primary energy sources <NUM> and adapted to supply power at a variable output voltage to primary energy sources <NUM>. For example, the single secondary energy source <NUM> may supply power at a variable output voltage to at least two primary energy sources 210a, 210b.

By way of example, hybrid energy storage system <NUM> may include more than one secondary energy sources <NUM>, and each secondary energy source <NUM> of the more than one secondary energy sources <NUM> may be associated with one primary energy source. If desired, at least one secondary energy source <NUM> of the more than one secondary energy sources <NUM> may be associated with at least two primary energy sources 210a, 210b.

Secondary energy source <NUM> may have an energy storage component. The energy storage component of secondary energy source <NUM> may include at least one of a battery, a supercapacitor, an ultracapacitor, a fuel cell, an engine-generator set, or any other device suitable to store or supply energy in form of electricity.

Secondary energy source <NUM> may be provided with means for controlling the output voltage. For example, secondary energy source <NUM> may include at least one of a rectifier, an inverter, a DC/DC converter, or any other means suitable to adjust the output voltage of secondary energy source <NUM>.

The selected means for controlling the output voltage may be dependent on the output current type of the energy storage component. As an example, a three-phase AC generator may require means for controlling the output voltage that include a three-phase inverter. As another example, a fuel cell may require means for controlling the output voltage that include a DC/DC converter.

If desired, a buffer that may include a battery, a supercapacitor, or any other suitable buffering device may be installed parallel to the controllable means at the output of the secondary energy source <NUM> (e.g., buffer <NUM> of <FIG>).

Secondary energy source <NUM> may be sized to support primary energy sources <NUM> when defined failure conditions are fulfilled. Illustratively, hybrid energy storage system <NUM> may include a secondary energy source control unit <NUM>.

Secondary energy source control unit <NUM> may receive sensor data 215a, 215b from primary energy sources 210a, 210b, respectively. Secondary energy source control unit <NUM> may send command signals 225a to secondary energy source <NUM> to control the variable output voltage of secondary energy source <NUM> based on sensor data 215a, 215b from primary energy sources 210a, 210b.

Secondary energy source <NUM> may send feedback signals 225b to secondary energy source control unit <NUM>. Feedback signals 225b may form a control loop <NUM> together with command signals 225a. If desired, command signals 225a from the secondary energy source control unit <NUM> may be based at least partially on feedback signals 225b.

Illustratively, secondary energy source control unit <NUM> may control the level of output contribution that secondary energy source <NUM> contributes to the primary energy sources <NUM>. For example, secondary energy source control unit <NUM> may set a constant output voltage at secondary energy source <NUM> independent of the load condition at the respective primary energy sources 210a, 210b.

If desired, a control function within each primary energy source 210a, 210b may monitor and assess the safety of the respective primary energy source 210a, 210b to determine whether the primary energy source 210a, 210b operates within safety margins. For example, the control function may monitor the discharge power, the depth of discharge, and/or the temperature of the respective primary energy source 210a, 210b.

As an example, the control function may determine that the temperature of the respective primary energy source 210a, 210b is outside a safe operating temperature range, and, as a consequence, the primary energy source 210a, 210b may incur the risk of a thermal runaway temperature that can lead to fire. If desired, primary energy source 210a, 210b may generate sensor data 215a, 215b, respectively, to indicate whether primary energy source 210a, 210b is operating in a safe state or whether primary energy source 210a, 210b is at risk of becoming a safety hazard.

If desired, sensor data 215a, 215b may include information related to the power, energy, and health condition of the respective primary energy source 210a, 210b.

Illustratively, hybrid energy storage system <NUM> may include secondary energy source control adjustment data <NUM>, which may be stored in an appropriate memory device, as an example. If desired, secondary energy source control adjustment data <NUM> may be stored within secondary energy source control unit <NUM>.

Secondary energy source control adjustment data <NUM> may provide for the implementation of different control strategies with secondary energy source control unit <NUM>. As an example, based on secondary energy source control adjustment data <NUM>, secondary energy source control unit <NUM> may send command signals 225a to secondary energy source such that hybrid energy storage system <NUM> operates in a floating hybrid mode, in which the secondary energy source <NUM> acts as a buffer for filtering high power demands from energy sinks <NUM> with the goal of providing a power optimized hybrid energy storage system <NUM>. As another example, based on secondary energy source control adjustment data <NUM>, secondary energy source control unit <NUM> may send command signals 225a to secondary energy source such that hybrid energy storage system <NUM> operates in a boosting hybrid mode, in which the secondary energy source <NUM> acts as an energy source to support power-reduced load intervals with the goal of providing an energy optimized hybrid energy storage system <NUM>.

<FIG> is a diagram of an illustrative electrical system <NUM> having a hybrid energy storage system <NUM> with a single secondary energy source <NUM> and n primary energy sources <NUM> that supply power to n energy sinks <NUM> in accordance with some embodiments.

The n primary energy sources <NUM> are labelled 210a to 210n and the n energy sinks <NUM> are labelled 240a to 240n. However, this does not imply that there are exactly <NUM> primary energy sources <NUM> and <NUM> energy sinks <NUM> that correspond to the <NUM> letters of the alphabet between a and n. Instead, there can be any number n of primary energy sources <NUM> and any number n of energy sinks <NUM>.

As shown, each primary energy source 210a to 210n of the n primary energy sources <NUM> is associated and provides power to exactly one energy sink 240a to 240n of the n energy sinks <NUM>. In other words, each energy sink 240a to 240n of the n energy sinks <NUM> is coupled to a single primary energy source 210a to 210n of the n primary energy sources <NUM>.

Each energy sink 240a to 240n of energy sinks <NUM> may have one or more loads (e.g., electrical engines). As an example, energy sink 240a may have loads <NUM>, <NUM>, <NUM>, and <NUM>. Loads <NUM> and <NUM> may be coupled in series and parallel to loads <NUM> and <NUM>. As another example, energy sinks 240b and 240n may each have a single load. Energy sink 240b may have load <NUM>, and energy sink 240n may have load <NUM>. If desired, each energy sink may include a single load.

Each energy sink 240a to 240n of energy sinks <NUM> may have a negative input port and a positive input output. For example, energy sinks 240a, 240b, and 240n may have negative input ports 339a, 339b, and 339n, respectively, and positive input ports 341a, 341b, and 341n, respectively.

Illustratively, at least one primary energy source of the one or more primary energy sources <NUM> may include a positive output port and a negative output port. The positive output port and the negative output port of the at least one primary energy source may be coupled to at least one of the energy sinks <NUM>. If desired, each primary energy source 210a to 210n may have a positive output port and a negative output port.

As an example, primary energy sources 210a, 210b, and 210n may include negative output ports 304a, 304b, and 304n, respectively, and positive output ports 306a, 306b, and 306n, respectively. Negative output ports 304a, 304b, and 304n may be coupled to negative input ports 339a, 339b, and 339n of energy sinks 240a, 240b, and 240n, respectively. Positive output ports 306a, 306b, and 306n may be coupled to positive input ports 341a, 341b, and 341n of energy sinks 240a, 240b, and 240n, respectively.

Illustratively, at least one primary energy source of the one or more primary energy sources <NUM> may include a positive input port and a negative input port. The positive input port and the negative input port of the at least one primary energy source may be coupled to secondary energy source <NUM>. If desired, each primary energy source 210a to 210n may have a positive input port and a negative input port.

As an example, primary energy sources 210a, 210b, and 210n may include negative input ports 305a, 305b, and 305n, respectively, and positive input ports 307a, 307b, and 307n, respectively.

By way of example, the single secondary energy source <NUM> may include a negative output port <NUM> and a positive output port <NUM>. As shown, negative output port <NUM> may be coupled to negative input ports 305a, 305b, and 305n of primary energy sources 210a, 210b, and 210n, respectively, and positive output port <NUM> may be coupled to positive input ports 307a, 307b, and 307n of primary energy sources 210a, 210b, and 210n, respectively.

Illustratively, each primary energy source 210a to 210n of the primary energy sources <NUM> may include an energy storage unit that stores electrical energy and supplies power at a predetermined voltage range. For example, primary energy sources 210a, 210b, and 210n may include energy storage units 314a, 314b, and 314n, respectively, that store electrical energy and supply power at predetermined voltage ranges 308a, 308b, and 308n, respectively.

If desired, each primary energy source 210a to 210n of the primary energy sources <NUM> may include a respective bus bar 312a to 312n that is coupled between the respective energy storage unit 314a to 314n and the respective positive input and output ports 307a to 307n and 306a to 306n. Therefore, the predetermined voltage ranges 308a, 308b, and 308n are sometimes also referred to as bus bar voltages 308a, 308b, and 308n.

Illustratively, at least one primary energy source of primary energy sources <NUM> may include an input switch that is coupled between the positive input port and the bus bar. As shown, primary energy sources 210a, 210b, and 210n of primary energy sources <NUM> include input switches 315a, 315b, and 315n, respectively, that are coupled between positive input ports 307a, 307b, and 307n and bus bars 312a, 312b, and 312n, respectively.

As an example, any one of input switches 315a, 315b, or 315n may include at least one of an electromechanical switch, a semiconductor based switch, or a diode in forward current direction to the bus bar. As another example, any one of input switches 315a, 315b, or 315n may include a gate turn-off thyristor, a power metal-oxide field effect transistor, an insulated-gate bipolar transistor, an analogue switch, a relay, or a solid-state relay.

By way of example, at least one primary energy source of primary energy sources <NUM> may include an output switch that is coupled between the bus bar and the positive output port. As shown, primary energy sources 210a, 210b, and 210n of primary energy sources <NUM> include output switches 316a, 316b, and 316n, respectively, that are coupled between bus bars 312a, 312b, and 312n and positive output ports 306a, 306b, and 306n, respectively.

As an example, any one of output switches 316a, 316b, or 316n may include at least one of an electromechanical switch or a semiconductor based switch. As another example, any one of output switches 316a, 316b, or 316n may include a gate turn-off thyristor, a power metal-oxide field effect transistor, an insulated-gate bipolar transistor, an analogue switch, a relay, or a solid-state relay.

Illustratively, at least one primary energy source of primary energy sources <NUM> may include a primary switch that is coupled between the energy storage unit and the bus bar. As shown, primary energy sources 210a, 210b, and 210n of primary energy sources <NUM> may include primary switch arrangements 313a, 313b, and 313n, respectively, that are coupled between energy storage units 314a, 314b, and 314n and bus bars 312a, 312b, and 312n, respectively.

If desired, at least one primary energy source of primary energy sources <NUM> may include a protection switch that is coupled between the negative input and output ports and the energy storage unit. As shown, primary energy sources 210a, 210b, and 210n of primary energy sources <NUM> may include protection switches 317a, 317b, and 317n, respectively, for disconnecting the respective energy storage unit 314a, 314b, or 314n from the negative input and output ports 305a, 304a, 305b, 304b, and 305n, 304n, respectively.

By way of example, at least one primary energy source of the primary energy sources <NUM> may include an electrical energy source management unit that collects sensor data from the respective energy storage unit. If desired, each primary energy source 210a to 210n of the primary energy sources <NUM> may include an electrical energy source management unit 311a to 311n that collects respective sensor data 215a to 215n from the respective energy storage unit 314a to 314n.

Respective electrical energy source management units 311a, 311b, and 311n may monitor and assess the safety of the respective primary energy sources 210a, 210b, and 210n to determine whether the respective primary energy sources 210a, 210b, and 210n operate within safety margins. For example, the respective electrical energy source management units 311a, 311b, and 311n may monitor the discharge power, the depth of discharge, and/or the temperature of the respective energy storage units 314a, 314b, and 314n of primary energy sources 210a, 210b, and 210n.

As an example, the respective electrical energy source management units 311a, 311b, and 311n may determine that the temperature of the respective primary energy sources 210a, 210b, and/or 210n are outside a safe operating temperature range, and, as a consequence, the corresponding primary energy source 210a, 210b, or 210n may incur the risk of a thermal runaway temperature that can lead to fire. If desired, the respective electrical energy source management units 311a, 311b, or 311n may generate sensor data 215a, 215b, or 215n, respectively, to indicate whether primary energy source 210a, 210b, or 210n is operating in a safe state or whether primary energy source 210a, 210b, or 210n is at risk of becoming a safety hazard.

If desired, sensor data 215a, 215b, and 215n may include information related to the power, energy, and health condition of the respective primary energy source 210a, 210b, or 210n.

As shown, the respective electrical energy source management unit 311a, 311b, and 311n may send the respective sensor data 215a, 215b, and 215n to secondary energy source control unit <NUM>.

The secondary energy source <NUM> is coupled to primary energy sources <NUM> and adapted to supply power at a variable output voltage <NUM> to the primary energy sources <NUM>. For example, secondary energy source <NUM> may include a controlled energy source <NUM> that is adapted to provide the variable output voltage <NUM>. The variable output voltage <NUM> may be supplied between the positive output port <NUM> and the negative output port <NUM> of secondary energy source <NUM>.

Since negative output port <NUM> is coupled to negative input ports 305a, 305b, and 305n of primary energy sources 210a, 210b, and 210n, respectively, and positive output port <NUM> to positive input ports 307a, 307b, and 307n of primary energy sources 210a, 210b, and 210n, respectively, variable output voltage <NUM> is provided as input voltages 309a, 309b, and 309n at primary energy sources 210a, 210b, and 210n, respectively.

If desired, secondary energy source control unit <NUM> may send command signals 225a to the secondary energy source <NUM> to control the variable output voltage <NUM> provided by the controlled energy source <NUM> based on the sensor data 215a to 215n from the respective electrical energy source management units 311a to 311n.

Illustratively, secondary energy source control unit <NUM> may receive feedback signals 225b from controlled energy source <NUM> and send command signals 225a to the secondary energy source <NUM> to control the variable output voltage <NUM> provided by the controlled energy source <NUM> based on the feedback signals 225b.

<FIG> is a more detailed diagram of the illustrative electrical system of <FIG> showing an electrical system <NUM> having a hybrid energy storage system <NUM> with a secondary energy source <NUM> and a primary energy source <NUM> that supplies power to an energy sink <NUM> in accordance with some embodiments.

It should be noted that an electrical system <NUM> with a single primary energy source <NUM> that is coupled to a single secondary energy source <NUM> and a single energy sink <NUM> is described hereinafter, for simplicity and brevity. However, if desired, the electrical system <NUM> may include more than one energy sink <NUM> that is connected to and receives electrical power from primary energy source <NUM>. If there are more than one energy sink, hybrid energy storage system <NUM> may include more than one primary energy source. As an example, hybrid energy storage system <NUM> may have two primary energy sources. As another example, hybrid energy storage system <NUM> may have as many primary energy sources as the electrical system has energy sinks, whereby each primary energy source is associated with and provides electrical power to exactly one energy sink.

In the scenario in which hybrid energy storage system <NUM> includes more than one primary energy source, hybrid energy storage system <NUM> may include more than one secondary energy source. If desired, hybrid energy storage system <NUM> may include as many secondary energy sources as primary energy sources, whereby each secondary energy source is associated with exactly one primary energy source.

Illustratively, energy sink <NUM> may have one or more loads (e.g., electrical engines). As shown, energy sink <NUM> may include a DC/AC converter <NUM>, which is sometimes also referred to as a "DC/AC inverter" or simply an "inverter", and a three-phase machine <NUM>. Energy sink <NUM> may have a negative input port <NUM> and a positive input output <NUM> that are coupled to DC/AC converter <NUM>.

Illustratively, primary energy source <NUM> may include negative output port <NUM> and positive output port <NUM>. Negative output port <NUM> may be coupled to negative input port <NUM> of energy sink <NUM>, and positive output port <NUM> may be coupled to positive input port 341of energy sink <NUM>.

By way of example, primary energy source <NUM> may include a positive input port <NUM> and a negative input port <NUM> that are coupled to secondary energy source <NUM>. By way of example, secondary energy source <NUM> may include negative output port <NUM> and positive output port <NUM>. As shown, negative output port <NUM> may be coupled to negative input port <NUM> of primary energy source <NUM>, and positive output port <NUM> may be coupled to positive input port <NUM> of primary energy source <NUM>.

Illustratively, primary energy source may include energy storage unit <NUM> that stores electrical energy and supplies power at a predetermined voltage range to energy sink <NUM>. If desired, primary energy source <NUM> may include bus bar <NUM> that is coupled to the energy storage unit <NUM>.

By way of example, primary energy source <NUM> may include an input switch <NUM> and an output switch <NUM> that are coupled in series between the positive input port <NUM> and positive output port <NUM>. As an example, input switch <NUM> may include a diode in forward current direction to bus bar <NUM> and output switch <NUM>. As another example, output switch <NUM> may include a contactor that is coupled between bus bar <NUM> and diode <NUM>, and positive output port <NUM>.

Illustratively, primary energy source <NUM> may include a primary switch arrangement <NUM> that is coupled between the energy storage unit <NUM> and the bus bar <NUM>. As shown, primary switch diode 413a that is arranged in parallel with primary switch contactor 413b may implement primary switch arrangement <NUM>.

If desired, primary energy source <NUM> may include a protection switch <NUM> that is coupled between the negative input and output ports <NUM>, <NUM>, and the energy storage unit <NUM>. Protection switch <NUM> may disconnect energy storage unit <NUM> from the negative input and output ports <NUM>, <NUM>.

By way of example, primary energy source <NUM> may include electrical energy source management unit <NUM>. Electrical energy source management unit <NUM> may collect sensor data from primary energy source <NUM>.

For example, electrical energy source management unit <NUM> may collect sensor data from energy storage unit <NUM> to monitor and assess the safety of primary energy source <NUM> and to determine whether primary energy sources <NUM> is operating within safety margins. For example, electrical energy source management unit <NUM> may monitor the discharge power, the depth of discharge, and/or the temperature of primary energy source <NUM>.

As an example, electrical energy source management units <NUM> may determine that the temperature of primary energy source <NUM> is outside a safe operating temperature range, and, as a consequence, primary energy source <NUM> may incur the risk of a thermal runaway temperature that can lead to fire. If desired, electrical energy source management unit <NUM> may generate sensor data 215a to indicate whether primary energy source <NUM> is operating in a safe state or whether primary energy source <NUM> is at risk of becoming a safety hazard.

If desired, sensor data 215a may include information related to the power, energy, and health condition of primary energy source <NUM>. As shown, electrical energy source management unit <NUM> may send sensor data 215a to secondary energy source control unit <NUM>. Secondary energy source control unit <NUM> may receive the sensor data 215a from the electrical energy source management unit <NUM> and, in response, send command signals 225a to the secondary energy source <NUM>.

The secondary energy source <NUM> is coupled to primary energy sources <NUM> and adapted to supply power at a variable output voltage <NUM> to the primary energy sources <NUM>. For example, secondary energy source control unit <NUM> may send command signals 225a to the secondary energy source <NUM> to control the variable output voltage <NUM> based on the sensor data 215a.

Secondary energy source <NUM> may include an energy storage component <NUM>. Energy storage component <NUM> may include at least one of a battery, a supercapacitor, an ultracapacitor, a fuel cell, or an engine-generator set.

Illustratively, secondary energy source <NUM> may include a voltage control unit <NUM>. Voltage control unit <NUM> may include at least one of a rectifier <NUM>, a DC/AC converter, a DC/DC converter <NUM>, or a stabilizing buffer <NUM>. Buffer <NUM> may be coupled between the positive and negative output ports <NUM>, <NUM> of secondary energy source <NUM>.

Voltage control unit <NUM> may be coupled between energy storage component <NUM> and positive and negative output ports <NUM>, <NUM>. Voltage control unit <NUM> may provide variable output voltage <NUM> at positive and negative output ports <NUM>, <NUM> based at least in part on the command signals 225a.

Since negative output port <NUM> is coupled to negative input port <NUM> of primary energy source <NUM>, and positive output port <NUM> to positive input port <NUM> of primary energy source <NUM>, variable output voltage <NUM> is provided as input voltage to primary energy source <NUM>.

By way of example, voltage control unit <NUM> may send feedback signals 225b to the secondary energy source control unit <NUM>. The command signals 225a from the secondary energy source control unit <NUM> may be based at least in part on the feedback signals 225b.

Based on the secondary energy source control adjustment data <NUM>, secondary energy source control unit <NUM> may control the contribution of secondary energy source <NUM> within the hybrid energy storage system <NUM>.

Illustratively, secondary energy source control unit <NUM> of hybrid energy storage system <NUM> may operate independently from the monitoring and/or protection functions of electrical energy source management unit <NUM> and vice versa. Thereby, electrical energy source management unit <NUM> may safeguard primary energy source <NUM> from abusive conditions with strategies that are different and independent from the goals of secondary energy source control unit <NUM>.

As an example, electrical energy source management unit <NUM> may open primary switch contactor 413b and/or protection switch <NUM> to safeguard primary energy source <NUM> from overload, over-voltage, and/or overheating conditions. As another example, electrical energy source management unit <NUM> may open output switch <NUM> to isolate primary energy source <NUM> from overload conditions at energy sink <NUM>.

By way of example, secondary energy source control unit <NUM> may, based on the sensor data 215a from electrical energy source management unit <NUM>, but independently from electrical energy source management unit <NUM>, adjust variable output voltage <NUM> according to the defined energy or power optimization goals (e.g., provided by secondary energy source control adjustment data <NUM>) and considering the boundary conditions of secondary energy source <NUM>.

The hybrid energy storage system <NUM> can be designed in a way that the individual sizing of primary and secondary energy sources <NUM>, <NUM> is correctly considering all possible failure scenarios. As an example, secondary energy, source <NUM> is sized based on a potential loss of primary energy source <NUM>. As another example, primary energy source <NUM> is sized based on a potential loss of secondary energy source <NUM>. As yet another example, sizing of primary and secondary energy sources <NUM>, <NUM> may take into account the power demand for individual over-power and/or over-energy at energy sinks <NUM> (e.g. sizing for emergency power load profiles).

Thus, hybrid energy storage system <NUM> may be realized in a very failure robust and safe way. Robustness and the mutual independency of the electrical energy source management unit <NUM> and the secondary source control unit <NUM>, both contribute to a reduced complexity of hybrid energy storage system <NUM>.

Due to the reduced complexity of the secondary energy source control unit <NUM>, even an analogue control loop <NUM>, based on simple discrete electronic hardware without a need for software may be implemented, thereby further reducing the complexity of hybrid energy storage system <NUM>. A hybrid energy storage system <NUM> with a significantly reduced complexity is easing vehicle certification efforts, reducing development costs, and reducing recurring costs.

In a first scenario, secondary energy source control unit <NUM> may direct secondary energy source <NUM> to act as buffer for filtering high power demands from energy sink <NUM>, thereby decoupling secondary energy source <NUM> from primary energy source <NUM>.

In this first scenario, secondary energy source control unit <NUM> is aiming at providing a power optimized hybrid energy storage system <NUM>, in which secondary energy source <NUM> acts as an emergency or backup energy source for primary energy source <NUM>. For example, secondary energy source <NUM> may ensure an uninterrupted power supply at energy sink <NUM> in case of a degraded performance or loss of primary energy source <NUM>.

Therefore, in this first scenario, secondary energy source control unit <NUM> may direct secondary energy source <NUM> to provide variable output voltage <NUM> at a value, which is the smaller than the output voltage (i.e., the voltage between positive output port <NUM> and negative output port <NUM>) of primary energy source <NUM> or smaller than at least one of the output voltages 308a to 308n of all n primary energy sources 210a to 210n of <FIG> when all n primary energy sources 210a to 210n are working normal and are contributing to supply the respective energy sink 240a to 240n.

If desired, a secondary source minimum limit output voltage for variable output voltage <NUM> may be considered in order to comply with the minimum input voltage range of the connected energy sink <NUM> (or the n energy sinks 240a to 240n of <FIG>). Thus, in this first scenario, the variable output voltage may be set to a first value, which is selected in the interval delimited by secondary source minimum limit output voltage for the variable output voltage and the output voltage of primary energy source <NUM> (or the minimum output voltage of any one of the output voltages 308a to 308n of all n primary energy sources 210a to 210n of <FIG>). Furthermore, a constant forward voltage may be subtracted from the variable output voltage <NUM> to prevent conductivity in case input switch 315a to 315n is implemented by diodes (e.g., input voltage <NUM> of <FIG> may be at least <NUM>. 7V smaller than bus voltage <NUM> to decouple output voltage from input voltage).

In this first scenario, primary energy source <NUM> is electrically decoupled from secondary energy source <NUM> if the output voltage of primary energy source <NUM> is greater than the first value. Similarly, in this first scenario, all primary energy sources 210a to 210n of <FIG>, whose output voltages 308a to 308n are greater that the first value, are electrically decoupled from secondary energy source <NUM>.

<FIG> is a diagram of the illustrative primary energy source <NUM> of <FIG> in this first state in accordance with some embodiments. In this first state, input voltage <NUM> is smaller than output voltage <NUM>, which is sometimes also referred to as bus bar voltage <NUM>.

Thus, primary energy source <NUM> is exclusively contributing to supply power to the assigned energy sink (e.g., energy sink <NUM> of <FIG>) and no current is flowing through diode <NUM>. In other words, output switch <NUM> and protection switch <NUM> are both closed, and a current is flowing from energy storage unit <NUM> via primary switch arrangement <NUM>, output switch <NUM>, positive output port <NUM> through the energy sink and back via negative output port <NUM> and protection switch <NUM> to energy storage unit <NUM> (i.e., primary switch diode current <NUM> is greater than zero and primary switch contactor current <NUM> is greater than zero).

Primary energy source <NUM> operates in this first state in which primary energy source <NUM> is exclusively contributing to supply power to the assigned energy sink. Primary energy source <NUM> also operates in this first state when the secondary energy source of the hybrid energy storage system (e.g., secondary energy source <NUM> of hybrid energy storage system <NUM> of <FIG>) is failing. In other words, the hybrid energy storage system operates as an uninterrupted power supply to the energy sink when the secondary energy source is failing.

In other words, primary energy source <NUM> is independently buffering all secondary energy source transients or continuous power and/or voltage drops. If desired, primary energy source <NUM> may be sized to sustain all secondary energy source failure scenarios for a given emergency time interval.

However, secondary energy source <NUM> may act as a buffer if output voltage <NUM> drops below input voltage <NUM>. For example, energy storage unit <NUM> may be a non-controlled voltage source (e.g., a battery), and a transient high load may cause the output voltage <NUM> to drop below the input voltage <NUM> of primary energy source <NUM>.

In this example, the secondary energy source <NUM> may temporarily take over the power peaks that cause the output voltage drops, thereby buffering the transient high load. As a result, the size of the energy storage unit <NUM>, and thus the size of primary energy source <NUM>, may be reduced,
In a second scenario, a secondary energy source control unit (e.g., secondary energy source control unit <NUM> of <FIG>) may direct the secondary energy source (e.g., secondary energy source <NUM> of <FIG>) to support power-reduced load intervals. In this second scenario, the secondary energy source control unit is aiming at providing an energy optimized hybrid energy storage system (e.g., hybrid energy storage system <NUM> of <FIG>), in which the secondary energy source acts as a range extender for primary energy source <NUM>.

Therefore, in this second scenario, the secondary energy source control unit may direct the secondary energy source to provide a variable output voltage (e.g., variable output voltage <NUM> of <FIG>), and thereby input voltage <NUM> at a value, which is greater than the output voltage <NUM> (i.e., the voltage between positive output port <NUM> and negative output port <NUM>) of primary energy source <NUM> or greater than at least one of the output voltages 308a to 308n of all n primary energy sources 210a to 210n of <FIG> when all n primary energy sources 210a to 210n are working normal and are contributing to supply the respective energy sink 240a to 240n.

If desired, a secondary source maximum limit output voltage for the variable output voltage may be considered in order to comply with the maximum input voltage range of the connected energy sink (e.g., energy sink <NUM> of <FIG> or the n energy sinks 240a to 240n of <FIG>). Thus, in this second scenario, the variable output voltage may be set to a second value, which is selected in the interval delimited by the secondary source maximum limit output voltage for the variable output voltage and the output voltage of primary energy source <NUM> (or the maximum output voltage of any one of the output voltages 308a to 308n of all n primary energy sources 210a to 210n of <FIG>).

Furthermore, a constant forward voltage may be added to the variable output voltage <NUM> to enable conductivity in case input switch 315a to 315n is implemented by diodes (e.g., input voltage <NUM> of <FIG> may be at least <NUM>. 7V higher than bus voltage <NUM> to couple output voltage to input voltage).

In this second scenario, primary energy source <NUM> is electrically coupled to the secondary energy source through diode <NUM> if the output voltage of primary energy source <NUM> is smaller than the second value. Similarly, in this second scenario, all primary energy sources 210a to 210n of <FIG>, whose output voltages 308a to 308n are smaller than the second value, are electrically coupled through input switch 315a to 315n to secondary energy source <NUM>.

<FIG> is a diagram of the illustrative primary energy source of <FIG> in a second state in which the primary energy source implements the second scenario in accordance with some embodiments. In this second state, input voltage <NUM> is greater than output voltage <NUM>, output switch <NUM> and protection switch <NUM> are both closed, and primary switch contactor 413b is open.

Thus, primary energy source <NUM> is not contributing to supply power to the assigned energy sink (e.g., energy sink <NUM> of <FIG>) and no current is flowing through primary switch diode 413a. In other words, a current is flowing from the secondary energy source (e.g., secondary energy source <NUM> of <FIG>) via positive input port <NUM>, input switch <NUM>, output switch <NUM>, positive output port <NUM> through the energy sink and back via negative output port <NUM> and negative input port <NUM> to the secondary energy source (i.e., primary switch diode current <NUM> is zero).

Nevertheless, depending on the load conditions at energy sink <NUM> (e.g., with power transients) and the control loop <NUM> between secondary energy source <NUM> and secondary energy source control unit <NUM> of <FIG>, the output voltage <NUM> of secondary energy source <NUM> may temporarily drop below the output voltage of primary energy source <NUM>. If the output voltage of the secondary energy source drops below the output voltage of primary energy source <NUM>, energy storage unit <NUM> is then able to buffer the energy sink with an additional current that flows from energy storage unit <NUM> via primary switch diode 413a, output switch <NUM>, and positive output port <NUM> to the energy sink, even though the secondary energy source remains the main contributor of power supply to the energy sink.

In a third scenario, primary energy source <NUM> has a weak power and energy condition and primary switch contactor 413b is closed. In this third scenario and depending on the voltage difference between output voltage <NUM> and input voltage <NUM>, a current can flow from secondary energy source <NUM> via positive input port <NUM>, input switch <NUM>, and primary switch contactor 413b into energy storage unit <NUM>.

This third scenario may be beneficial to recover or recharge energy storage unit <NUM> during load and/or discharge operation of hybrid energy storage system <NUM>. This third scenario may also be used to adjust the output voltages 308a to 308n of all primary energy sources 210a to 210n of <FIG> to one common voltage level, which may be beneficial for optimizing the life time of the hybrid energy storage system <NUM>, for harmonising the charge levels at the respective primary energy sources 210a to 210n, and for shortening the recharging times of hybrid energy storage system <NUM>.

<FIG> shows the illustrative primary energy source <NUM> of <FIG> in a third state that implements the third scenario in accordance with some embodiments. In this third state, input voltage <NUM> is greater than output voltage <NUM>, and protection switch <NUM> and primary switch contactor 413b are closed, while output switch <NUM> is open.

Thus, the energy sink is decoupled from primary energy source <NUM> and the secondary energy sink (e.g., energy sink <NUM> of <FIG> is at least temporarily not mission-critical) to relieve power from the charging source and to secure the energy sink (e.g., to prevent undesired consumption). Thus, no current is flowing through primary switch diode 413a. However, a recharging current is flowing from the secondary energy source via positive input port <NUM>, input switch <NUM>, and primary switch contactor 413b to energy storage unit <NUM>, which is charged by this current.

However, the recharging current may be higher than a limiting threshold. The limiting threshold may be defined within the electrical energy source management unit <NUM> of primary energy source <NUM>. As a result, the primary switch contactor 413b may be steered open or temporarily opened by electrical energy source management unit <NUM> to prevent overcharge conditions.

If desired, output switch <NUM> may be closed in the third scenario. For example, energy sink <NUM> of <FIG> may perform a mission-critical operation and the hybrid energy storage system <NUM> is required to supply power to energy sink <NUM>. Thus, energy sink <NUM> may be coupled to primary energy source <NUM> and secondary energy source <NUM>.

As a result, no current is flowing through primary switch diode 413a. However, a current is flowing from the secondary energy source through positive input port <NUM> and input switch <NUM>. A first portion of this current is flowing from input switch <NUM> via primary switch contactor 413b to energy storage unit <NUM>, which is charged by this current. A second portion of this current is flowing from input switch <NUM> via output switch <NUM> and through the energy sink via negative output port <NUM> and negative input port <NUM> to the secondary energy source.

In a fourth scenario, primary energy source <NUM> may be failing. If desired, electrical energy source management unit <NUM> may open primary switch contactor 413b and protection switch <NUM> to isolate energy storage unit <NUM> from the energy sink and the secondary energy source.

<FIG> is a diagram of the illustrative primary energy source of <FIG> in a fourth state that implements the fourth scenario in accordance with some embodiments.

In this fourth scenario, the hybrid energy storage system <NUM> of <FIG> may operate as an uninterrupted power supply to the connected energy sink <NUM>. In particular, the energy sink <NUM> may receive power from the secondary energy source <NUM> of <FIG>.

In other words, a current is flowing from the secondary energy source (e.g., secondary energy source <NUM> of <FIG>) via positive input port <NUM>, input switch <NUM>, output switch <NUM>, positive output port <NUM> through the energy sink and back via negative output port <NUM> and negative input port <NUM> to the secondary energy source (i.e., primary switch diode current <NUM> is zero).

If desired, the secondary energy source may be sized to provide enough power and energy to cover all potential primary energy source <NUM> failure conditions for a given emergency time interval (e.g., until the vehicle is recovering, stabilizing, in a steady state, or has performed an emergency landing).

In a fifth scenario, the energy sink (e.g., energy sink <NUM> of <FIG>) may reach an overload situation. For example, the energy sink may have a short-circuit. In this fifth scenario, the electrical energy source management unit <NUM> may protect primary energy source <NUM> by opening the output switch <NUM>, thereby isolating the failing energy sink and by opening the protection switch <NUM> to prevent overload currents at the energy storage unit <NUM>.

<FIG> is a diagram of the illustrative primary energy source <NUM> of <FIG> in a fifth state that implements the fifth scenario in accordance with some embodiments.

In a sixth scenario, secondary energy source control unit <NUM> may direct secondary energy source <NUM> to provide variable output voltage <NUM> at a value that is greater than the secondary source minimum limit output voltage and greater than the smallest output voltage of any one of the output voltages 308a to 308n of all n primary energy sources 210a to 210n of <FIG>.

In this sixth scenario, a first strong and/or charged primary energy source of primary energy sources 210a to 210n may operate as in the first scenario and be configured as shown in <FIG>, while a second weak and/or discharged primary energy source of primary energy sources 210a to 210n operates as in the second scenario and is configured as shown in <FIG>. In other words, the first strong and/or charged primary energy source may behave as described in <FIG>, while the second weak and/of discharged primary energy source behaves as described in <FIG>.

It should be noted that modifications to the above described embodiments are within the common knowledge of the person skilled in the art and, thus, also considered as being part of the present invention.

For instance, all components of primary and secondary energy sources of <FIG> (i.e., all components of hybrid energy storage system <NUM>) may have an opposite polarity compared to what is shown in <FIG> without changing the functionality of the hybrid energy storage system. As an example, energy storage unit <NUM> of <FIG> may be installed such that its negative pole is connected to input switch <NUM>, bus bar <NUM>, and output switch <NUM> and its positive pole to protection switch <NUM> such that primary energy source <NUM> has positive input port <NUM>, positive output port <NUM>, negative input port <NUM>, and negative output port <NUM>. Furthermore, diodes 413a and <NUM> would be connected in opposite direction.

Moreover, buffer <NUM> of <FIG> is shown as a standalone part of secondary energy source <NUM>. However, buffer <NUM> may be implemented by two or more parallel buffers. Alternatively, or in addition, buffer <NUM> may be implemented as part of voltage control unit <NUM>. If desired, buffer <NUM> may be arranged outside of secondary energy source <NUM> between secondary energy source <NUM> and primary energy source <NUM>.

Claim 1:
An electrical system (<NUM>) for an aircraft (<NUM>), comprising:
one or more energy sinks (<NUM>), wherein each energy sink (240a) of the one or more energy sinks (<NUM>) comprises a load (<NUM>); and
a hybrid energy storage system (<NUM>), comprising:
one or more primary energy sources (<NUM>) that are coupled to the one or more energy sinks (<NUM>) and supply power to the one or more energy sinks (<NUM>), wherein each primary energy source (210a) of the one or more primary energy sources (<NUM>) comprises:
an energy storage unit (314a) that stores electrical energy and supplies power at a predetermined voltage range (308a), and
an electrical energy source management unit (311a) that collects sensor data from the energy storage unit (314a);
a secondary energy source (<NUM>) that is coupled to the one or more primary energy sources (<NUM>) and adapted to supply power at a variable output voltage (<NUM>) to the one or more primary energy sources (<NUM>); and
a secondary energy source control unit (<NUM>) that receives the sensor data (215a) from the electrical energy source management unit (311a) and sends command signals (225a) to the secondary energy source (<NUM>) to control the variable output voltage (<NUM>) based on the sensor data (215a), wherein the secondary energy source control unit (<NUM>) is adapted to directing the secondary energy source (<NUM>) to provide the variable output voltage (<NUM>) at a value that is smaller or greater than at least one output voltage (308a) of all of the one or more primary energy sources (<NUM>) when all of the one or more primary energy sources (<NUM>) are working normal and are contributing to supply the respective one or more energy sinks (<NUM>).