Patent Description:
Some systems, such as unmanned aerial vehicles (UAV's) or the like often utilize electrical power for propulsion and operation of onboard systems. Some such systems, such as medium-sized UAV's that require power levels in the range of about <NUM> KW to <NUM> KW, have relatively short mission times because the energy density of batteries is far too low to effectively work in this power range, and conventional internal combustion engines and jet engines are very inefficient at these low power levels. One option that has been developed is a tethered UAV system in which the UAV is connected to a power source on the ground by a tether. Use of a tethered UAV allows for an increase in mission duration time, but reduces an operating height and distance in which the UAV may operate, due to the constraint of the tether. An untethered power source that is lightweight with a high power density is greatly desired. <CIT> relates to an electrical power generation system.

As defined in claim <NUM>, an electrical power generation system is provided.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that at least one of the one or more shafts passes through the electric generator.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the electric generator is a permanent magnet alternator.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the rotor element is located radially inward from the stator element.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the one or more shafts further includes a compressor shaft attached or operably connected to the first stage compressor, a turbine shaft attached or operably connected to the at least one turbine, and a coupling assembly operably connecting the turbine shaft to the compressor shaft.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the compressor shaft extends in an aft direction away from the first stage compressor and through the electric generator to operably connect to the coupling assembly.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the compressor shaft is located radially inward of the rotor element.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the micro-turbine alternator further includes an alternator stator cooling heat exchanger configured to utilize the compressed airflow from the first stage compressor to cool the electric generator.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the micro-turbine alternator further includes a third stage compressor located aft of the second stage compressor.

According to another embodiment, a vehicle is provided. The vehicle includes a propulsion system and an electrical power generation system operably connected to the propulsion system. The electrical power generation system includes a micro-turbine alternator. The micro-turbine alternator includes a combustion chamber, at least one turbine driven by combustion gases from the combustion chamber, a first stage compressor, and a second stage compressor located aft of the first stage compressor. The first stage compressor and the second stage compressor being operably connected to the combustion chamber to provide a compressed airflow thereto. The micro-turbine alternator also includes one or more shafts connecting the at least one turbine to the first stage compressor and the second stage compressor such that rotation of the at least one turbine drives rotation of the first stage compressor and the second stage compressor, and an electric generator disposed along the one or more shafts such that electrical power is generated via rotation of the one or more shafts. The electric generator is disposed along the one or more shafts between the first stage compressor and the second stage compressor.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the electric generator further includes a stator element. The stator element includes a hub, a plurality of spokes extending radially inward from the hub, and one or more conductive elements that are wound around the spokes to form windings. The electric generator further includes a rotor element operable connected to and configured to rotate with the one or more shafts. The rotor element further includes an annular base member and an annular array of permanent magnets coupled to the annular base member.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the one or more shafts further include a compressor shaft attached or operably connected to the first stage compressor, a turbine shaft attached or operably connected to the at least one turbine, and a coupling assembly operably connecting the turbine shaft to the compressor shaft.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the vehicle is an unmanned aerial vehicle or an electrically-powered suit.

As previously noted, an untethered, lightweight, high power density power source would allow systems like UAVs to have longer mission times without the height and distance limits of a tether. A prior approach to power generation involves micro-turbine alternator designs that places the electric generator at a forward end of a rotating shaft upstream of the compressor and turbine, which are then both located at an aft end of a rotating shaft. With this type of arrangement, the rotational speed of the compressor is limited by the compressor inlet relative velocity as the inlet diameter of the compress hub is increased to accommodate the rotating shaft that connects the compressor hub to the electric generator. Further, with this type of arrangement the compressor and turbine are overhung on the aft end of the rotating shaft, thus reducing the critical speed of the overall assembly. Embodiments disclosed herein relate to an interstage electric alternator for micro-turbine alternator applications. The micro-turbine alternator according to one or more embodiments may be used in a UAV or electrically-powered suit, as discussed for explanatory purposes, or any electrically-powered system. The design places an electric generator between two stages of the compressor to reduce the inlet diameter of the first stage compressor hub to as close to zero as possible so that the micro-turbine alternator may provide more power and operate with a lower inlet pressure.

Referring to <FIG>, an isometric view of an unmanned aerial vehicle (UAV) <NUM> is illustrated in accordance with an embodiment of the present disclosure. The UAV <NUM> includes a propulsion/lift system <NUM>, for example a plurality of lift rotors <NUM>, operably connected to an electrical power generation system <NUM>, which includes a micro-turbine alternator system <NUM>. In an embodiment, the micro-turbine alternator system <NUM> is a high efficiency Brayton cycle micro-turbine alternator. The UAV <NUM> includes a propulsion system having electric motors <NUM> and lift rotors <NUM> associated with each electric motor <NUM>. Each lift rotor <NUM> is operably connected to the electric motor <NUM> that is configured to rotate the lift rotor <NUM> using electrical power generated by the micro-turbine alternator system <NUM> of the electrical power generation system <NUM>. The micro-turbine alternator system <NUM> is configured to convert fuel to electrical power to power at least the electric motors <NUM> of the lift rotors <NUM>. The fuel is provided from one or more fuel storage tanks <NUM> operably connected to the micro-turbine alternator system <NUM>. In some embodiments, the fuel utilized is JP-<NUM>. The micro-turbine alternator system <NUM> may utilize compressed air provided from a compressed air tank <NUM> at <NUM> kPa (<NUM> psig) and regulated to about <NUM> kPa (<NUM> psig). The compressed air from the compressed air tank <NUM> of <FIG> may be utilized to provide the motive pressure required to drive the liquid fuel through a turbine speed control valve (not shown) and into a combustion chamber. Alternatively, an electric driven pump may be used in place of the compressed air.

Referring now to <FIG>, with continued reference to <FIG>, an isometric view of an electrically-powered suit <NUM> is illustrated in accordance with an embodiment of the present disclosure. While in <FIG>, the micro-turbine alternator system <NUM> is described as utilized in a UAV <NUM>, the micro-turbine alternator system <NUM> disclosed herein may be readily applied to other systems, and may be utilized in, for example, an electrically-powered suit <NUM>, as shown in <FIG>.

The electrically-powered suit <NUM> is operably connected to an electrical power generation system <NUM>, which includes a micro-turbine alternator system <NUM>. The micro-turbine alternator system <NUM> is configured to convert fuel to electrical power to power the electrically-powered suit <NUM>. The fuel is provided from one or more fuel storage tanks <NUM> operably connected to the micro-turbine alternator system <NUM>. In some embodiments, the fuel utilized is JP-<NUM>. The fuel storage tanks <NUM> may be located on legs of the electrically-powered suit <NUM>, as illustrated in <FIG>.

It is understood that the micro-turbine alternator system <NUM> is not limited to a UAV <NUM> and an electrically-powered suit <NUM> application, and the micro-turbine alternator system <NUM> may be applied to other systems not disclosed herein.

Referring now to <FIG>, an isometric cut-away view of the micro-turbine alternator system <NUM> is illustrated, in accordance with an embodiment of the present disclosure. The micro-turbine alternator system <NUM> includes a first stage compressor <NUM>, a second stage compressor <NUM>, a third stage compressor <NUM>, a first stage turbine <NUM>, and a second stage turbine <NUM>. The first stage compressor <NUM>, the second stage compressor <NUM>, the third stage compressor <NUM>, the first stage turbine <NUM>, and the second stage turbine <NUM> are oriented along a central longitudinal axis A of the micro-turbine alternator system <NUM>. The micro-turbine alternator system <NUM> also includes an electric generator <NUM> located between the first stage compressor <NUM> and the second stage compressor <NUM> as measured along the central longitudinal axis A.

Advantageously, by locating the electric generator <NUM> between the first stage compressor <NUM> and the second stage compressor <NUM>, the overall physical size of the micro-turbine alternator system <NUM> is reduced. As a result, the micro-turbine alternator system <NUM> according to one or more embodiments may be used in a UAV <NUM>, an electrically-powered suit <NUM>, or another system that benefits from untethered, lightweight power generation.

The micro-turbine alternator system <NUM> also includes an alternator stator cooling heat exchanger <NUM> configured to utilize airflow from the first stage compressor <NUM> to cool the electric generator <NUM>. The alternator stator cooling heat exchanger <NUM> may encircle or enclose the electric generator <NUM> and may be configured to pass airflow from the first stage compressor <NUM> through or around the electric generator <NUM>. Advantageously, by locating the electric generator <NUM> between the first stage compressor <NUM> and the second stage compressor <NUM>, moderately cool air in the core flow path C from the first stage compressors <NUM> is forced through the alternator stator cooling heat exchanger <NUM> and heat may be drawn out of the electric generator <NUM> and to the airflow within the alternator stator cooling heat exchanger <NUM>.

The electric generator <NUM> may be a permanent magnet alternator, an induction generator, a switched reluctance generator, a wound field generator, a hybrid generator, or any other type of alternator known to one of skill in the art. As illustrated in <FIG>, the electric generator <NUM> may be a permanent magnet alternator that includes a rotor element <NUM> and a stator element <NUM> radially outward from the rotor element. In other words, the rotor element <NUM> is located radially inward from the stator element <NUM> as measured relative to the central longitudinal axis A. It is understood that the embodiments disclosed herein may be applicable to a rotor element <NUM> that is located radially outward from the stator element <NUM>. The rotor element <NUM> may be rotated around the central longitudinal axis A to generate electricity.

The rotor element <NUM> includes an annular base member <NUM>, an annular array of permanent magnets <NUM> that are respectively coupled to an outer diameter of the annular base member <NUM>. The rotor element <NUM> may include a magnet retention band that fits over an outer diameter of the permanent magnet <NUM>, and keeps the permanent magnet <NUM> on the rotating annular base member <NUM>. In accordance with further embodiments, the stator element <NUM> includes a hub <NUM>, a plurality of spokes <NUM> extending radially inward from the hub <NUM> and conductive elements <NUM> that are wound around the spokes <NUM> to form windings. When the rotor element <NUM> is rotated around the central longitudinal axis A a rotating flux field is generated by the permanent magnets <NUM> and this rotating flux field generates an alternating current in the conductive elements <NUM> to generate electricity for use by the UAV <NUM> of <FIG> or the electrically-powered suit <NUM> of <FIG>.

The micro-turbine alternator system <NUM> includes a combustion chamber <NUM>, in which a fuel-air mixture is combusted, with the combustion products utilized to drive an electric generator <NUM>. In some embodiments, the fuel utilized in the combustion chamber <NUM> is JP-<NUM>. The micro-turbine alternator system <NUM> converts the energy of the combustion products into electrical power by urging the combustion products through the first stage turbine <NUM> and the second stage turbine <NUM>, which are operably connected to and configured to rotate the rotor element <NUM> of the electric generator <NUM>. The electrical energy generated by the electric generator <NUM> may then be rectified via a generator rectifier (not shown) and utilized by the propulsion/lift system <NUM> of <FIG> or the electrically-powered suit <NUM> of <FIG>. The compressed air from the compressed air tank <NUM> of <FIG> may be utilized to provide the motive pressure required to drive the liquid fuel through a turbine speed control valve (not shown) and into the combustion chamber <NUM>.

The first stage compressor <NUM> is located forward of the second stage compressor <NUM> and the third stage compressor <NUM> as measured along the central longitudinal axis A, and the second stage compressor <NUM> is located forward of the third stage compressor <NUM> as measured along the central longitudinal axis A. In other words, the second stage compressor <NUM> is located aft of the first stage compressor <NUM> and the third stage compressor <NUM> is located aft of the second stage compressor <NUM> as measured along the central longitudinal axis A. The forward direction D1 and the aft direction D2 are illustrated in <FIG>. The first stage turbine <NUM> is located forward of the second stage turbine <NUM> as measured along the central longitudinal axis A. In other words, the second stage turbine <NUM> is located aft of the first stage turbine <NUM> as measured along the central longitudinal axis A. The first stage compressor <NUM>, the second stage compressor <NUM>, and the third stage compressor <NUM> are located forward of first stage turbine <NUM> and the second stage turbine <NUM> as measured along the central longitudinal axis A.

The micro-turbine alternator system <NUM> includes a compressor shaft <NUM> oriented along and co-axial to the central longitudinal axis A. In an embodiment, the compressor shaft <NUM> is a tie bolt and is used to compress a rotating group of components including the first stage compressor <NUM>, compressor transfer tube <NUM>, the compressor shaft <NUM>, and a second journal bearing <NUM> in the axial direction, causing the multi-segment shaft to act as a single stiff shaft. The compressor shaft <NUM> may be attached or operably connected to the first stage compressor <NUM>. The micro-turbine alternator system <NUM> includes a turbine shaft <NUM> oriented along and co-axial to the central longitudinal axis A. The turbine shaft <NUM> may be attached or operably connected to the first stage turbine <NUM> and the second stage turbine <NUM>.

The micro-turbine alternator system <NUM> includes a coupling assembly <NUM> configured to operably connect the turbine shaft <NUM> to the compressor shaft <NUM>. The coupling assembly <NUM> may be attached or operably connected to the second stage compressor <NUM>. The compressor shaft <NUM> extends in the aft direction D2 away from the first stage compressor <NUM> and through the electric generator <NUM> to operably connect to the coupling assembly <NUM>. In an embodiment, the compressor shaft <NUM> is located radially inward of the rotor element <NUM>.

Advantageously, locating the electric generator <NUM> between the first stage compressor <NUM> and the second stage compressor <NUM> allows the first stage compressor <NUM> to have a reduced inlet hub diameter that is smaller than a diameter of the rotor element <NUM>. Having a reduced inlet hub diameter DIA1 reduces the inlet flow relative velocity, increasing the aerodynamic performance of the first stage compressor <NUM> and increasing the swallowing capacity of the first stage compressor <NUM>. If the electric generator <NUM> was located forward of the first stage compressor <NUM>, then the compressor shaft <NUM> would have to extend forward of the first stage compressor <NUM> and thus the inlet hub diameter DIA1 would have to be increased to a diameter of the compressor shaft <NUM>, thus decreasing the aerodynamic performance of the first stage compressor <NUM> and decreasing the swallowing capacity of the first stage compressor <NUM>.

The turbine shaft <NUM> extends in the forward direction D1 away from the first stage turbine <NUM> to operably connect to the coupling assembly <NUM>. The turbine shaft <NUM>, the coupling assembly <NUM>, and the compressor shaft <NUM> are configured to rotate in unison. Thus, when exhaust <NUM> from the combustion chamber <NUM> drives rotation of the first stage turbine <NUM> and the second stage turbine <NUM>, the rotation of the first stage turbine <NUM> and the second stage turbine <NUM> drives rotation of the turbine shaft <NUM>, which drives rotation of the coupling assembly <NUM> and the compressor shaft <NUM>. The rotation of the compressor shaft <NUM> drives rotation of the first stage compressor <NUM>. The rotation of the coupling assembly <NUM> drives rotation of the second stage compressor <NUM>. The third stage compressor <NUM> is operably connected to the second stage compressor <NUM> and the turbine shaft <NUM>, and thus rotation of the second stage compressor <NUM> and the turbine shaft <NUM> drives rotation of the third stage compressor <NUM>.

It is understood that while the compressor shaft <NUM>, the turbine shaft <NUM>, and the coupling assembly <NUM> are described as three different shafts, the embodiments disclosed herein may be applicable to micro-turbine alternator system <NUM> having one or more shafts. In an embodiment, the electric generator <NUM> is disposed along the one or more shafts between the first stage compressor <NUM> and the second stage compressor <NUM>. In another embodiment, the electric generator <NUM> is disposed along the compressor shaft <NUM> between the first stage compressor <NUM> and the second stage compressor <NUM>. The electric generator <NUM> is located aft of the first stage compressor <NUM> and forward of the second stage compressor <NUM>. In another embodiment, at least one of the one or more drive shafts passes through the electric generator <NUM>. In another embodiment, the compressor shaft <NUM> passes through the electric generator <NUM>.

The compressor shaft <NUM>, the turbine shaft <NUM>, and the coupling assembly <NUM> are coaxial and rotate via the bearing systems about the engine centerline longitudinal axis A, which is co-linear with their longitudinal axes. The bearing system includes a first journal bearing <NUM> located between the compressor transfer tube <NUM> and the frame <NUM> of the micro-turbine alternator system <NUM>. The bearing system includes a second journal bearing <NUM> located between the coupling assembly <NUM> and the frame <NUM> of the micro-turbine alternator system <NUM>. The bearing system includes a third journal bearing <NUM> located between the turbine shaft <NUM> and the frame <NUM> of the micro-turbine alternator system <NUM>.

Advantageously, locating the electric generator <NUM> between the first stage compressor <NUM> and the second stage compressor <NUM> provides for very effective bearing placement around the compressor shaft <NUM>, which increases the stiffness of the compressor shaft <NUM>. The increased stiffness of the compressor shaft <NUM> allows for an increase in the critical speed of the compressor shaft <NUM>.

Also, advantageously, by locating the electric generator <NUM> between the first stage compressor <NUM> and the second stage compressor <NUM>, the alternator stator cooling heat exchanger <NUM> helps reduce the operating temperature of the electric generator <NUM>, while the airflow through the alternator stator cooling heat exchanger <NUM> also experiences a pressure drop. This pressure drop through the alternator stator cooling heat exchanger <NUM> forces some of the airflow from the first stage compressor <NUM> through the rotor element <NUM> and to a stator gap between the rotor element <NUM> and the stator element <NUM>, which provides cooling air to the rotor element <NUM>, the first journal bearing <NUM>, and the second journal bearing <NUM>.

The compressor transfer tube <NUM> extends from the first stage compressor <NUM> to the second stage compressor <NUM> through the electric generator <NUM>. The compressor transfer tube <NUM> is co-axial with the electric generator <NUM>. The rotor element <NUM> with the annular base member <NUM> and the annular array of permanent magnets <NUM> are located radially inward of the compressor transfer tube <NUM> measured relative to the central longitudinal axis A. The stator element <NUM> with the hub <NUM>, the conductive elements <NUM>, and the spokes <NUM> are located radially outward of the compressor transfer tube <NUM> measured relative to the central longitudinal axis A.

The first stage compressor <NUM>, the second stage compressor <NUM>, and the third stage compressor <NUM> drive air along a core flow path C for compression and communication in the combustion chamber <NUM>. The airflow in the core flow path C is compressed by the first stage compressor <NUM>, the second stage compressor <NUM>, and the third stage compressor <NUM>, is mixed with fuel and burned in the combustion chamber <NUM>, and is then expanded over the first stage turbine <NUM> and the second stage turbine <NUM>. The first stage turbine <NUM> and the second stage turbine <NUM> rotationally drive the turbine shaft <NUM> in response to the expansion. The combustion products are exhausted from the second stage turbine <NUM> through a turbine exit <NUM>.

Each of the first stage compressor <NUM>, the second stage compressor <NUM>, the third stage compressor <NUM>, the first stage turbine <NUM>, and the second stage turbine <NUM> may include rows of rotor assemblies (shown schematically) that carry airfoils that extend into the core flow path C. For example, the rotor assemblies can carry a plurality of rotating blades <NUM>. The blades <NUM> of the rotor assemblies create or extract energy (in the form of pressure) from the core airflow that is communicated through the micro-turbine alternator system <NUM> along the core flow path C.

The micro-turbine alternator system <NUM> may include an auxiliary turbo charger <NUM> to pre-compress the airflow <NUM> prior to entering the core flow path C. The auxiliary turbo charger <NUM> includes a compressor <NUM> and a turbine <NUM> operably connected to the compressor <NUM> through a turbo compressor drive shaft <NUM>. The compressor <NUM> is configured to rotate when the turbine <NUM> rotates.

The compressor <NUM> is configured to pull external airflow <NUM> through one or more air inlets <NUM> in the frame <NUM> into a compressor flow path C1. The compressor <NUM> is configured to compress the external airflow <NUM> in the compressor flow path C1 and deliver the airflow <NUM> to the first stage compressor <NUM> in the core airflow path C.

Each of the turbine <NUM> and the compressor <NUM> may include rows of rotor assemblies (shown schematically) that carry airfoils that extend into the compressor flow path C1. For example, the rotor assemblies can carry a plurality of rotating blades <NUM>. The blades <NUM> of the rotor assemblies for the turbine <NUM> extract energy (in the form of pressure and temperature) from the exhaust <NUM> that is communicated through the micro-turbine alternator system <NUM> along the core flow path C. The blades <NUM> of the rotor assemblies for the compressor <NUM> create energy (in the form of pressure and temperature) from the airflow <NUM> that is communicated through the micro-turbine alternator system <NUM> along the compressor flow path C1.

Combustor exhaust <NUM> exiting the turbine exit <NUM> is directed to the turbine <NUM> of the auxiliary turbo charger <NUM>. The exhaust <NUM> is then expanded over the turbine <NUM> of the auxiliary turbo charger <NUM>. The turbine <NUM> rotationally drives the turbo compressor drive shaft <NUM> in response to the expansion. Rotation of the turbo compressor drive shaft <NUM> causes the compressor <NUM> to rotate and compress the airflow <NUM> within the compressor flow path C1.

Some embodiments further include a thermal electric energy recovery system <NUM>, configured to recover additional energy from exhaust <NUM> of the micro-turbine alternator system <NUM> before the exhaust <NUM> has flowed through the turbine <NUM> of the auxiliary turbo charger <NUM>.

Technical effects and benefits of the features described herein include an electric generator located between two stages of a compressor to reduce the inlet diameter of the compressor hub as close to zero as possible so that the micro-turbine alternator could provide more power and operate with a lower inlet pressure.

Claim 1:
An electrical power generation system, comprising:
a micro-turbine alternator (<NUM>), comprising:
a combustion chamber (<NUM>);
at least one turbine (<NUM>, <NUM>) driven by combustion gases from the combustion chamber;
a first stage compressor (<NUM>);
a second stage compressor (<NUM>) located aft of the first stage compressor, the first stage compressor and the second stage compressor being operably connected to the combustion chamber to provide a compressed airflow thereto;
one or more shafts (<NUM>, <NUM>) connecting the at least one turbine to the first stage compressor and the second stage compressor such that rotation of the at least one turbine drives rotation of the first stage compressor and the second stage compressor; and
an electric generator (<NUM>) disposed along the one or more shafts such that electrical power is generated via rotation of the one or more shafts, wherein the electric generator is disposed along the one or more shafts between the first stage compressor and the second stage compressor;
wherein the electric generator (<NUM>) further comprises:
a stator element (<NUM>), the stator element comprising:
a hub (<NUM>);
a plurality of spokes (<NUM>) extending radially inward from the hub; and
one or more conductive elements (<NUM>) that are wound around the spokes to form windings; and
a rotor element (<NUM>) operable connected to and configured to rotate with the one or more shafts, the rotor element further comprising:
an annular base member (<NUM>); and
an annular array of permanent magnets (<NUM>) coupled to the annular base member; and characterised in that:
the first stage compressor has an inlet hub diameter that is smaller than the diameter of the rotor element (<NUM>).