Patent Description:
The shipping industry and navies around the world are interested in upgrading their watercrafts (i.e. ships and/or submarines) using advanced technologies to provide, for example, improved fuel efficiency, greater electric capacity, and more sophisticated onboard systems. The terms watercraft, ship, and/or submarine may be used interchangeably throughout this document and each shall be interpreted to encompass any waterborne vessels, including, for example, boats, ships, hovercraft and submarines. Size and weight reductions in propulsion and power generation systems will provide additional room for more equipment, cargo, and/or crew, improved fuel economy, and enhanced survivability and flexibility. For naval ships and submarines, new varieties of electric weapons, advanced sensors, and integrated support systems may be of interest to navies around the world. Such systems may include electromagnetic guns and high-powered laser or microwave directed-energy weapons, which present especially rigorous electrical power demands. For example, they require large amounts of electrical power over very short time periods of time.

Typical propulsion and energy generation systems utilize single function marine gas turbine and diesel engine technologies to drive propeller shafts through a main reduction gear for mobility and separate dedicated electric power generated by prime movers are used to drive electrical generators to power electrical grids which feed the onboard electrical systems. There are physical limits in size and weight reductions that can be achieved with gas turbine technologies and significant advancements are not likely. In addition, marine gas turbine and diesel engine generator technologies, which are used to produce electrical power are typically designed to operate efficiently and reliably at constant loading. Therefore, they are unable to support the above described dynamic loads associated with advanced electrical systems, such as electric weapons, without significant and costly electrical system upgrades which may not even fit on the ship. For example, with a conventional gas turbine generator system an additional energy storage system, such as batteries or a fly wheel, may be needed to isolate the pulse effects of the primary energy storage powering the electric weapons.

The concept of an all-electric watercraft has been deployed in the form of a ship, which may include the use of electrical means for all power needs, including propulsion, in lieu of other means such as mechanical, pneumatic, and hydraulic, is gaining momentum. Such all-electric ships, having an integrated power system (IPS), in particular those utilizing high temperature superconductor motors and generators, will result in size and weight reductions, which will provide additional room and weight capacity for more equipment, cargo, weapons, and/or crew, as well as improved efficiency and fuel economy. These systems are envisioned to share electric power seamlessly across a common electric bus allowing for universally shared power for all electric functions of the watercraft from powering the propellers, to energizing the combat systems, to feeding the lighting and other hotel loads.

Such all-electric ships conventionally include one or more electric drive motors which are each for driving a propelling unit and are each fed by way of a respective electric power converter by an electrical power network on the ship (i.e. the ship's drive). The electrical power network is in turn fed by one or more diesel, gas or steam turbine generators. In this arrangement, the voltage of the electrical power network is of a fixed predetermined amplitude and frequency, for example having a medium voltage with a nominal voltage of <NUM> kV at a nominal frequency of <NUM>. Where appropriate, a transformer is additionally connected between the converter and the power network. The converters convert the power network voltage (stepped down where necessary) to a voltage required to operate the electric motors driving the propellers, which electric motors have a different amplitude and frequency from the power network voltage.

The power converter system or drive is a very large, complex and expensive system. A known electric drive solution is described in <CIT> (the '<NUM> patent), which manages without using the ship's drive and instead it operates by coupling the generators and the electric propulsion motors to one another with no converters connected in between. The electric propulsion motors are driven by using one or more electric generators of variable speed and the electric motors are controlled and/or regulated indirectly, by control and/or regulation of the internal combustion engines for driving the generators. In this case the electric motors are connected to the generators in a fixed electrical coupling, that is to say that a change in rotational speed of the generators brings about a corresponding proportional frequency change which in turn changes the rotational speed of the electric propulsion motors. Thus, the function of a mechanical shaft is imitated using electrical machines. A drive solution of this kind is also called an "electric shaft".

The '<NUM> patent utilizes the electrical energy from the electric shaft and converts the voltage having variable amplitude and frequency using a power converter and a power network synchronizing device to a voltage of constant amplitude and constant frequency for an onboard power network. While the power converter and power network synchronizing device described in the '<NUM> patent are not as large and complex as the ship's drive described above with conventional the all-electric ships, it is still a large and complex system.

Therefore, there exists a need for a more compact and less complicated power system for providing power to all of the ship's electrical loads, including its electric propulsion motors, electrical weapons systems, and various onboard electrical equipment such as lighting and other hotel loads.

<CIT> discloses a ship drive system includes a first and one second drive shaft for driving a respective propulsion unit, wherein each of the electric drive shafts includes at least one speed-variable generator driven by an internal combustion engine for generating a motor voltage having a variable amplitude and variable frequency, and at least one speed-variable drive motor that is supplied with the voltage and coupled to the propulsion unit. The first and second drive shafts can be switched from a first operating state, in which they are electrically disconnected from each other, to a second operating state, in which they are electrically coupled to each other such energy can be transmitted from the at least one generator of the one drive shaft to the at least one drive motor of the other drive shaft. To this end, the at least one generator includes a superconductor winding.

The invention is defined by the features of the independent claim <NUM>. Preferred embodiments are defined in the dependent claims <NUM> to <NUM>.

In one aspect, the disclosure features an electrical power system for a watercraft, including a first electrical power plant configured to selectively operate either in one of a variable frequency mode to output variable frequency power to a first electrical network or a fixed frequency mode to output fixed frequency power to a second electrical network wherein the first electrical power plant includes a prime mover and a generator. There is a first electrical load including a first high temperature superconductor (HTS) motor connected to the first electrical network to provide propulsion for the watercraft and a second electrical load connected to the second electrical network. There is a controller configured to selectively connect the generator of the first electrical power plant to the first electrical network and to operate the first electrical power plant in the variable frequency mode to output variable frequency power from the generator to power the first HTS motor or to selectively connect the generator of the first electrical power plant to the second electrical network and to operate the first electrical power plant in a fixed frequency mode to output fixed frequency power from the generator to power the second electrical load.

In other aspects of the disclosure, one or more of the following features may be included. The second electrical load includes at least one of an electric weapons system and a ship service system. There may further be included a third electrical network interconnected to a third load which includes at least one of an electric weapons system and a ship service system. The controller may be configured to selectively connect the first electrical power plant to one of the first electrical network, the second electrical network, and the third electrical network. The first electrical power plant may include at least one high inertia HTS generator. The first electrical power plant may include at least one gas turbine, steam turbine, or diesel engine prime mover interconnected to the at least one high inertia HTS generator. There may further be included a second electrical power plant configured to selectively power the first electrical network, the second electrical network, and the third electrical network. The second electrical power plant may include at least one high inertia HTS generator and at least one gas turbine, steam turbine, or diesel engine prime mover may be interconnected to the at least one high inertia HTS generator. The controller may connect the first electrical power plant to the first electrical network and operate the first electrical power plant in a variable frequency mode and the controller may connect the second electrical power plant to one or both of the second and third electrical networks and operates the second electrical power plant in a fixed frequency mode. There may further be included a fourth electrical load connected to the first electrical power network and the fourth electrical load may include a second high temperature superconductor (HTS) motor to provide propulsion for the watercraft. The watercraft may be one of a ship or a submarine.

Embodiments of the present disclosure will now be described, by way of example only, with reference to the attached Figures, wherein:.

The disclosure and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments and examples that are described and/or illustrated in the accompanying drawings and detailed in the following description. It should be noted that the features illustrated in the drawings are not necessarily drawn to scale, and features of one embodiment may be employed with other embodiments as the skilled artisan would recognize, even if not explicitly stated herein. Descriptions of well-known components and processing techniques may be omitted so as to not unnecessarily obscure the embodiments of the disclosure.

The examples used herein are intended merely to facilitate an understanding of ways in which the system may be practiced and to further enable those of skill in the art to practice the embodiments of the disclosure. Accordingly, the examples and embodiments herein should not be construed as limiting the scope of the disclosure. Moreover, it is noted that like reference numerals represent similar parts throughout the several views of the drawings.

While the preferred embodiment described herein as being incorporated into a ship, this is merely an exemplary application, as the multi-function integrated power systems according to this disclosure may be incorporated into any type of waterborne vessels, including, for example, boats, ships, hovercraft, submarines, or other type of watercraft, including unmanned water craft.

Referring to <FIG>, there is shown ship <NUM>, which may be a naval ship, e.g. a destroyer. While the inventive aspects of this disclosure are particularly applicable to naval ships, the disclosure is not limited to naval ships and could be applied to other types of ships with significant/rigorous noise and power requirements and need for size and weight reductions, such as oceanographic research ships and cruise ships. Ship <NUM> may include a first all-electric drive <NUM> and a second all-electric drive <NUM>, which together form part of an all-electric propulsion and energy system. Alternatively ship <NUM> could be outfitted with a hybrid electrical and mechanical propulsion and energy system, as described and claimed in <CIT>. Moreover, the disclosure is not limited to a ship with two drives and could be applied to a greater number of drives, provided there is at least one all electric propulsion system.

The propulsion and energy system according to this disclosure may be installed in a newly built ship according to a new ship design or it may be installed as a retrofit to an older/existing ship/design. The retrofit may be of an already built ship wherein a mechanical drive is replaced with an all-electric drive or it may be a retrofit of an existing ship design wherein the ship will be newly built with an all-electrical (or hybrid) propulsion and energy system.

Ship <NUM> may also include certain electric weapons <NUM> and <NUM>, which may be, for example, electromagnetic guns and high-powered laser or microwave directed-energy weapons that require large amounts of power over very short time periods of time. Typical ships outfitted with existing, marine gas/steam turbine and diesel engine generator technologies, may not be able to support such advanced electrical weapons, since marine gas turbine, steam turbine, and diesel engine generators were originally designed to operate efficiently and reliably at constant loading. While an all-electric ship will support electric weapons systems, the power quality requirements for the onboard ship systems are stringent (so-called Type <NUM> power) and require expensive additional power quality components not fully developed yet, such as series inductance or other energy storage means. This results in many more large system components which are difficult and maybe impossible to find space for in the ship and are high in cost.

One of the advantages to the electric power system described herein is that it is capable of powering advanced electric weapon systems and other electric ship systems requiring Type <NUM> power (Mil Std. <NUM>), as well as providing ship propulsion with one common multi-function power source, at an affordable cost while reducing size, weight and technical complexity. In one aspect of the disclosure, ship power may be produced using one or more turbo-generators <NUM>, <FIG>, having gas turbine <NUM>, which may drive a high inertia HTS generator <NUM> via shaft <NUM>. In this example, high inertia HTS generator <NUM> may be a 29MW <NUM> rpm <NUM> pole generator. However, the disclosure is not limited to any particular prime mover generator or gas-turbine power level, pole count or configuration and is applicable to various gas turbine systems. Moreover, this disclosure is not limited to gas turbine systems, as steam turbines could be used as the prime mover in place of gas turbines.

In one aspect of the disclosure, the turbo-generators <NUM> may be configured to operate in dual modes, i.e. in a fixed frequency (e.g. <NUM>)/fixed voltage (e.g. <NUM> VAC) mode and a variable frequency/variable voltage mode. The turbo-generators <NUM> may comprise gas turbine <NUM> and high inertia HTS generator <NUM>. Alternatively the high inertia HTS generator may be replaced with a more typical HTS generator, designed to minimize size and weight and having a lower rotational inertia. In a fixed frequency mode the power output of the one or more turbo-generators may be used for electric weapons systems and hotel loads. The operation of the multi-function turbo-generators in this mode is described below with regard to <FIG>. In a variable frequency mode of operation, the one or more turbo-generators may be directly connected to one or more electric motors in a dedicated manner (i.e. they are not also connected to other electric loads). With the variable frequency mode, the generator kinetics are coupled directly to the electric motor kinetics without the large power electronic electric motor drive typically required for an electric ship propulsion motor. In other words, the rotational speed of the turbo-generator directly affects the rotational speed of the electric motor/propeller and hence the speed of the ship. This may be referred to herein as a synchronous propulsion drive.

The dual modes operation of the turbo-generators <NUM> may be engaged under the control of a master controller typically operated from the ship's bridge. In addition, and as will be described further below, the disclosure may utilize separate grids to power the ship's electric propulsion, electric ship systems (hotel loads), and electric weapon systems. The grids may be used in a dedicated fashion or they may be interconnected also under the control of the master controller. Various functional configurations may be implemented that allow one or more of the turbo-generators to be operated in fixed or variable frequency mode, as desired, and to connect the one or more turbo-generators to the various loads in a dedicated or a combined way.

Before describing the integrated power system topology utilizing a dual mode of turbo-generator operation, a prior art all-electric ship configuration utilizing HTS generators and motors and capable of operating ships electric propulsion, electric ship systems, and electric weapon systems is shown in <FIG>. However, with this prior art topology, a large and complex power electronic drive system is required and is depicted in ship power grid configuration <NUM> of <FIG>.

In <FIG>, only one electric motor (starboard side) and two turbo generators are depicted for ease of description; however, one skilled in the art will understand that the port side of the ship would include an additional electric motor and two additional turbo generators, as well as associated electric components and electric drive. Ship power grid configuration <NUM> includes two turbo generators <NUM> and <NUM>, which may be of the type shown in <FIG>. Each generator in this example may output 29MW of three phase power at <NUM> V AC at <NUM>. In this example, turbo-generator <NUM> is connected to the power grid through three phase switchgear <NUM> while turbo-generator <NUM> is connected to the power grid through three phase switchgear <NUM>.

Switchgear <NUM> is connected to switchgear <NUM> by port/starboard cable <NUM> so that in the event of a failure of one of the turbo-generators its respective switchgear can be back fed and powered by the operational turbo-generator. Cables <NUM> and <NUM> from switchgear <NUM> and <NUM>, respectively, supply power to electric propulsion motor <NUM>, which may be a conventional electric motor or a HTS motor. In this example, the variable speed electric motor <NUM> is a HTS motor and the input voltage is nine phase AC at <NUM> V (approximately 37MW); therefore, the power from switchgear <NUM> and <NUM> must be converted and conditioned by a suitable power converter system.

The output from switchgear <NUM> may be connected to a motor drive comprising a rectifier <NUM> and inverter <NUM>. Power from switchgear <NUM> may be converted to DC power by rectifier <NUM> and then the DC may be converted to nine phase AC by inverter <NUM>. Rectifier <NUM> and inverter <NUM> form a motor drive for controlling the current input to/rotational speed of motor <NUM> when they are connected to the motor <NUM> by disconnect cabinet <NUM>. The maximum output power of motor drive in this example is <NUM> MW. The output from switchgear <NUM> may be converted to DC by rectifier <NUM> and then the DC may be converted to nine phase AC by inverter <NUM>. Rectifier <NUM> and inverter <NUM> form a motor drive for controlling the current input to/rotational speed of motor <NUM> when they are connected to the motor <NUM> by disconnect cabinet <NUM>. The maximum output power of motor drive in this example is also <NUM> MW. When full power (<NUM> MW) is needed for electric motor <NUM>, both motor drives are connected via disconnect cabinet <NUM> to motor <NUM>.

Continuing to refer to <FIG>, ship power grid configuration <NUM> is also configured to supply power to pulsed power loads (not shown) through energy storage switchgear <NUM> powered by cables <NUM> and <NUM> connected to switchgear <NUM> and <NUM>, respectively. In addition, transformer <NUM> connected to switchgear <NUM> converts <NUM> V AC to <NUM> V AC and feeds that to distribution switchgear (not shown) to deliver lower voltage power to various systems on the ship. Thus, all loads (propulsion, electric weapons, and hotel loads) may be interconnected and powered by a common electric grid energized by one or more turbo-generators.

Pulsed power loads may consist of several seconds (e.g. <NUM> seconds) of very high power draw (e.g. 10MW or greater) through the energy storage switchgear <NUM> followed by a pause (e.g. <NUM> second) with no energy draw. The system design assumes that this cycle will be repeated indefinitely. As noted above, such pulsed loads can severely impact the proper operation of grid <NUM>. A drop in rotational speed results in a proportionate drop in frequency, voltage and power from the turbo-generator. In <FIG>, the impact on the rotational speed of such a pulsed load on turbo-generator <NUM>/<NUM> with a HTS generator is depicted over multiple pulse periods (assuming only one of the turbo-generators is operational).

As shown by waveform <NUM>, turbo-generator rpm dips from <NUM> to approximately <NUM> over the course of a few seconds with the initial pulsed load of 18MW. The rotational speed of the turbo-generator recovers somewhat over time as the cyclic 18MW pulses continue, but it still remains substantially below its initial <NUM> rpm rotational speed. In this cases, the estimated rotational inertia of the generator is approximately <NUM>-m2, which is based on the use of a HTS generator optimized for cost for a <NUM> MVA turbo-generator. In this example, the EM shield may be formed of steel and copper with an approximate thickness of <NUM> (4in). In a weight optimized design, which may use aluminum in the EM shield, the rotational inertia may be significantly lower than in the cost optimized design. This means that the negative impact of the pulsed loads would be even greater.

With relatively low inertia in the turbo-generator, the torque imposed during the pulsed load on the turbo-generator has a more significant impact in reducing the rotational speed. In the example of waveform <NUM>, this translates into a nearly <NUM>% drop in rotational speed and a commensurate drop in voltage, frequency, and power on power grid <NUM>. Moreover, with this level of cyclic loading on the turbo-generator it is certain to shorten turbine life and it may even cause the engine to shut down.

According to one aspect of this disclosure, it was realized that with greater rotational inertia in the HTS generator, the impact of the torque on the turbo-generator may be reduced and thus pulsed power loads, like electric weapons systems, powered by a common grid powering type I loads and electric ship propulsion motors without requiring expensive additional power quality/storage components, such as series inductance or other energy storage means.

Waveform <NUM> shows the impact on the rotational speed (approximately a <NUM>% initial drop) of the turbo-generator, with a cyclic pulsed load of 18MW. In this case, the HTS generator used has an increased rotational inertia resulting in an overall turbo-generator rotational inertia of approximately <NUM>-m<NUM>. The EM shield may be formed of steel with an approximate thickness of <NUM> (7in). As is evident from waveform <NUM>, as compared to waveform <NUM>, increasing the rotational inertia of the turbo-generator to <NUM>-m<NUM> reduces substantially the impact of the initial and the subsequent cyclic pulsed loads on the rotational speed of the turbo-generator as well as the impact on voltage, frequency, and power on power grid <NUM>. Adding a tungsten alloy to the EM shield would further increase the rotational inertia to approximately <NUM>-m<NUM>.

Referring to <FIG>, there is shown a prior art HTS generator <NUM> which has been designed to be optimized for minimum size and weight. As with the lower rotational inertia generator that produced the waveform <NUM> in <FIG>, this example may have a rotational inertia such that the overall rotational inertia of the turbo-generator will also be approximately <NUM>-m<NUM>. HTS generator <NUM> includes a stator assembly <NUM> having stator coil assemblies <NUM><NUM>-n. As is well known in the art, the specific number of stator coil assemblies <NUM><NUM>-n included within stator assembly <NUM> varies depending on various design criteria, such as whether the machine is a single phase or a poly-phase machine. For example, in one <NUM> MVA, <NUM>-phase HTS generator described herein outputting 4500V AC at <NUM>, stator assembly <NUM> may include seventy-two (<NUM>) stator coil assemblies <NUM><NUM>-n.

A rotor assembly <NUM> rotates within stator assembly <NUM>. As with stator assembly <NUM>, rotor assembly <NUM> includes rotor winding assemblies <NUM><NUM>-n. In the same <NUM> MVA, <NUM>-phase HTS generator, rotor assembly <NUM> may include two rotor winding assemblies (forming <NUM> poles), which may be in a saddle coil configuration, as they are well suited to high rpm generator applications. These rotor winding assemblies, during operation, generate a magnetic flux that links rotor assembly <NUM> and stator assembly <NUM>. While this generator is designed as a two-pole machine, it will be understood by those skilled in the art that various pole count machines could be used and the particular design will be dependent upon the application. During operation of generator <NUM>, a three-phase voltage <NUM> is generated in stator coil assemblies <NUM><NUM>-n which, in turn, is output to the power grid of the ship as shown, for example, in <FIG>. The three-phase voltage in the stator coil assemblies <NUM><NUM>-n, is produced by the rotor winding magnetic flux generated by the rotor coil assemblies <NUM><NUM>-n that links rotor assembly <NUM> and stator assembly <NUM>, as the rotor rotates when driven by turbo-generator shaft <NUM>.

The rotor winding assemblies <NUM><NUM>-n may be mounted on an outside surface of support structure <NUM>, which is connected to a first flange <NUM> that transfers the torque from torque tube <NUM>. It should be noted that the rotor winding assemblies <NUM><NUM>-n may, alternatively, be mounted on an inside surface support structure <NUM>. Torque tube <NUM> is connected to a second flange <NUM>, which is connected to turbo-generator shaft <NUM>. Flanges <NUM> and <NUM> may be incorporated into torque tube <NUM> or may be separate assemblies. Of course, other torque tube designs may be used to transfer the torque from the shaft <NUM> to the rotor assembly in the cold space.

During operation of superconducting rotating machine <NUM>, field energy <NUM>, for example, from a DC current source (not shown) may be applied to rotor winding assembly <NUM><NUM>-n through a slip ring/rotating disk assembly <NUM>. Rotor winding assemblies <NUM> <NUM>-n, require DC current to generate the magnetic field (and the magnetic flux) required to link the rotor assembly <NUM> and stator assembly <NUM>. Stator coil assemblies <NUM><NUM>-n are formed of non-superconducting copper coil assemblies, for example, while rotor winding assemblies <NUM><NUM>-n are superconducting assemblies incorporating HTS windings. Examples of HTS conductors include: thallium-barium-calcium-copper-oxide; bismuth-strontium-calcium-copper-oxide; mercury-barium-calcium-copper-oxide; and yttrium-barium-copper-oxide.

As these superconducting conductors only achieve their superconducting characteristics when operating at low temperatures, HTS generator <NUM> includes a refrigeration system <NUM>. Refrigeration system <NUM> is typically in the form of a cryogenic cooler that maintains the operating temperature of rotor winding assemblies <NUM><NUM>-n at an operating temperature sufficiently low to enable the conductors to exhibit their superconducting characteristics. Since rotor winding assemblies <NUM><NUM>-n must be kept cool by refrigeration system <NUM>, torque tube <NUM> may be constructed from a high strength, low thermal conductivity metallic material (such as Inconel™) or composite material (such as G-<NUM> phenolic or woven-glass epoxy).

Rotor assembly <NUM> includes an electromagnetic shield <NUM> positioned between stator assembly <NUM> and rotor assembly <NUM> to shield or filter asynchronous fields from harmonics produced in the stator assembly <NUM>. As rotor assembly <NUM> is typically cylindrical in shape, electromagnetic shield <NUM> is also typically cylindrical in shape. It is desirable to shield the rotor winding assemblies <NUM><NUM>-n of rotor assembly <NUM> from these asynchronous fields. Accordingly, electromagnetic shield <NUM>, which is fitted to rotor assembly <NUM>, covers (or shields) rotor winding assemblies <NUM><NUM>-n from the asynchronous fields and is constructed of a non-magnetic material (e.g., copper, aluminum, etc.). The electromagnetic shield <NUM> should be of a length sufficient to fully cover and shield rotor winding assemblies <NUM><NUM>-n. Typically, the shield may be formed of aluminum with a thin overcoat of copper and having a thicknesses selected to shield ac fields and withstand fault loads. Aluminum is lightest solution but steel could be selected if weight is of less interest than cost. The shield also provides vacuum containment and steel presents a simpler sealing solution with welding.

The electromagnetic shield <NUM> may be rigidly connected to shaft <NUM> via a pair of end plates <NUM>, <NUM>. This rigid connection can be in the form of a weld or a mechanical fastener system (e.g., bolts, rivets, splines, keyways, etc.). For shielding, the thickness of electromagnetic shield <NUM> varies inversely with respect to the frequency of the three-phase AC power <NUM>, which in this example is <NUM> Hertz. For low pole count designs the thickness may be selected to withstand transient forces during fault. For this frequency, typically, the thickness of electromagnetic shield <NUM> would be no more than <NUM> (4in) of steel and copper. In order to reduce the size and weight of the generator, prior art systems such as this one, minimized the thickness of the electromagnetic shield <NUM> to the point where it was of a sufficient thickness to filter the asynchronous fields and to support fault ovalizing forces on the shield, but no thicker, so as to minimize generator weight and size.

Although not shown in generator <NUM> of <FIG>, an inner ferromagnetic core (e.g. an iron core) may be used to increase the magnetic permeance of the rotor and hence may allow for a reduced amount of HTS material needed to generate a given magnetic field. It also adds to the rotational inertia of the generator in a significant way. In <FIG> there is shown a schematic cross-sectional view of HTS generator <NUM>, which is similar to the type of HTS generator shown in <FIG>. The cross-sectional view is taken across the width of the generator, to depict the dimensions of the generator including electromagnetic shield thickness and the electromagnetic gap. In this example, HTS generator <NUM> includes a rotor assembly <NUM> having an inner iron core <NUM> depicted as a two pole generator. Rotor windings 306a and 306b are in the form of saddle coil windings and are each shown with two arc sections, which are joined at the ends to form the saddle coil.

In designing HTS generator <NUM>, the limit on tip speed for HTS saddle coils 306a/b must be considered. Centrifugal loading on the HTS coils results in strain in the superconductor material. This strain is proportional to the square of the tip speed of the coils. Experience and analysis indicates that <NUM>/sec tip speed is an acceptable limit for such coils. Generators for naval use may require over-speed testing up to <NUM>% of rated speed. For a design speed of <NUM> rpm, this corresponds to an over-speed test at <NUM>,<NUM> rpm requiring a field winding with a ~<NUM> radius from the longitudinal axis of the generator to the mid-plane of coils 306a/b, which is depicted as R1 in <FIG>. The saddle coils are supported on their outside by a coil support cylinder <NUM>.

The nonrotating part of generator <NUM> begins at radius R2, which extends from the generator longitudinal axis to the inside radius of the stator <NUM>, and consists of stator <NUM> and back iron <NUM>. Outside of the coil support cylinder <NUM> is the EM shield <NUM>, which is the outermost rotating member of rotor assembly <NUM>. As described above, it shields the rotor assembly <NUM> from electromagnetic fields that are asynchronous with respect to the rotation to reduce AC losses in the HTS coil. The field strength produced by saddle coils 306a/b is proportional to the ampere-turns in each coil, but is inversely proportional to the electromagnetic ("EM") gap (R2-R1) between the saddle coils and stator. Thus, increasing the EM gap increases the number of ampere-turns and hence the amount of HTS wire needed to generate a given electromagnetic field.

The majority of the EM gap (R2-R1) consists of the EM shield <NUM> and in a weight or cost optimized design, the EM shield is only made thick enough to perform its shielding function and its weight/mass is minimized by selecting a low density material with shielding capabilities. The EM shield <NUM> thickness, t, is generally < <NUM>% of R1/p, where p is the number of pole pairs in the design (p=<NUM> for a two pole generator). For this design the thickness, t, may be <NUM> (<NUM> in) and the material used for the EM shield may be a moderate-density material such as steel.

To determine the rotational inertia for EM shield <NUM>, the inner radius Ri and outer radius Ro and a mass M would be calculated as follows: <MAT> which, in this case, is approximately <NUM>-m<NUM>. The EM shield rotational inertia relative to the rotational inertia of the other system components in the turbo-generator would be as follows:.

For this example, the rotational inertia of the EM shield relative to the rotational inertia of the total generator is approximately seventy percent (<NUM>%). For typical cost/weight optimized designs, the rotational inertia in the EM shield is generally ≤ <NUM>% of the overall HTS generator rotational inertia (referred to herein as "low inertia" HTS generators).

An HTS generator with increased rotational inertia is shown in <FIG> as HTS generator <NUM>'. All components are essentially the same as HTS generator <NUM> of <FIG>, however, by constructing a thicker EM shield <NUM>' the rotational inertia of the generator can be increased at the expense of additional ampere-turns in saddle coils 306a'/b'. In other words, a greater amount of HTS material will be required to produce the same electromagnetic field in HTS generator <NUM>' as in HTS generator <NUM>, since the EM gap (R2'-R1') of HTS generator <NUM>' is greater than the EM gap (R2-R1), due to the increased thickness of the EM shield <NUM>'.

For the increased rotational inertia design of HTS generator <NUM>', the EM shield <NUM>' thickness, t', may be ≥ <NUM>% of R1/p. For this design, the thickness, t', may be approximately <NUM> (<NUM> in). In addition to increasing the thickness of the EM shield to increase its rotational inertia, higher density materials could be used. Examples of such materials may include copper (<NUM>/cm3), steel (<NUM>/cm<NUM>), lead (<NUM>/cm<NUM>), gold (<NUM>/cm<NUM>), tungsten (<NUM>/cm<NUM>), and spent uranium (<NUM>/cm<NUM>). One or more of these materials may be used to construct the EM shield.

By selecting the appropriate thickness and material composition of the EM shield <NUM>', the amount of additional rotational inertia of the EM shield can be tailored to obtain desired operational characteristics for the particular turbo-generator and expected level and frequency of pulsed power loads.

To determine the rotational inertia for EM shield <NUM>', the inner radius Ri' and outer radius Ro' and a mass M' (using a combination of steel and tungsten alloy, for example) would be calculated as follows: <MAT> which, in this case, is approximately <NUM>,<NUM>-m<NUM>. The EM shield rotational inertia relative to the rotational inertia of the other system components in the turbo-generator would be as follows:.

For this rotational inertia optimized example, the rotational inertia of the EM shield relative to the rotational inertia of the total generator is approximately eighty-five percent (<NUM>%). For typical rotational inertia optimized designs, the rotational inertia in the EM shield may be generally ≥ <NUM>% of the overall HTS generator rotational inertia (referred to herein as "high inertia" HTS generators).

If this design with a thick EM shield were constructed with just stainless steel in the EM shield the generator rotational inertia would still be <NUM>-m<NUM> which is still nearly <NUM>% of the rotational inertia of the cost and weight optimized design. The design of the HTS generator according to this disclosure has a number of important advantages; namely, it fits within a short axial length, has low reactance that avoids pole slipping in a highly pulsed application, and has high rotational inertia.

As noted above, an aspect of the disclosure utilizes HTS generators (preferably high inertia HTS generators) which may be configured to operate in two modes (i.e. fixed frequency mode and variable frequency mode) for the ships main turbine generators (MTG) turbo-generators. Each of the MTGs may be configured and operated in either mode and used to selectively power the ship's electric propulsion systems (variable frequency mode), electric ship systems (fixed frequency mode), and electric weapon systems (fixed frequency mode), creating a multi-functional integrated power system (MF-IPS) with significant flexibility powering the various ships systems.

A simplified schematic diagram of a multi-function main turbine generator (MF-MTG) <NUM> according to an aspect of this disclosure is depicted in <FIG>. MF-MTG <NUM> may be used to selectively power shipboard electric grids connected to three primary ship systems. The ship systems include a synchronous propulsion drive system <NUM>, which may include a <NUM> MW HTS electric motor, connected via electrical power network <NUM>. MF-MTG <NUM>, when connected to electrical power network <NUM> may be configured to operate in variable frequency power mode (variable frequency and variable voltage) to drive the HTS electric motor. Type <NUM> ship service power system, <NUM> may be connected to MF-MTG <NUM> by electrical power network <NUM>. In this configuration, electrical power network <NUM> would be powered by MF-MTG <NUM> operating at a fixed frequency power mode (fixed voltage, e.g. fixed voltage <NUM> VAC, and fixed frequency, e.g. <NUM>). And, in another configuration, electric weapons systems <NUM>, connected to electrical power network <NUM>, may be powered by MF-MTG <NUM> operating at a fixed frequency (e.g. <NUM>) and voltage. In this simple example, a single MF-MTG is used; however, in a typical application, multiple MF-MTG's operating in either mode depending on the system load may be used to power the various onboard systems. In the examples described below with regard to <FIG>, four MF-MTGs are used; however, any suitable number may be used.

Unlike prior art IPS systems, which incorporate all electric power on a single bus operating at a fixed voltage (e.g. <NUM> VAC) and fixed frequency (e.g. <NUM>) for the distribution to all demanded loads, the multi-functional integrated power system of the disclosure, uses multiple separate buses. The separate busses may be used in a dedicated or interconnected manner to power specific demanded load types. This minimizes the complication, risk and attendant significant volume of power electronics and computing power required to maintain stability and near type <NUM> quality power required for single bus operation. It eliminates the large and complex power electronics motor drive typically needed for electric propulsion motors and it utilizes high inertia HTS generators to directly connect to the electric weapons, rather than connecting through large and expensive intermediary energy storage devices and filter.

In a fixed frequency mode the power output of the turbo-generators may be used for electric weapons systems, and/or type <NUM> ship service loads. In a variable frequency mode of operation, the turbo-generators may be directly connected to one or more electric motors in a dedicated manner (i.e. they are not also connected to other electric loads). With the variable frequency mode, the generator kinetics are coupled directly to the electric motor kinetics without the large power electronic electric motor drive typically required for an electric ship propulsion motor. In other words, the rotational speed of the turbo-generator directly affects the rotational speed of the electric motor/propeller and hence the speed of the ship. This may be referred to herein as a synchronous propulsion drive.

In <FIG>, the topology of multi-functional integrated power system <NUM>, according to an aspect of this disclosure, is shown. Also in <FIG>, three functional configurations of the MF-IPS <NUM> are depicted only as exemplary configurations. It should be noted that other configurations are possible and are within the scope of the disclosure. As will be described, in certain configurations, the turbo-generators will be operated in a fixed frequency/fixed voltage mode and in others it will be operated in a variable frequency mode/variable voltage mode to power different ship systems. In the figures, cables that are depicted with thicker lines are energized with cables depicted as thinner lines are de-energized. The turbo-generators that are depicted with solid colors are online and operational while the turbo-generators which are not depicted with solid colors are off-line and not operational.

Referring to <FIG>, in the ship described in this example, there are two main engine rooms, ER1 <NUM> and ER2 <NUM>. In ER1 <NUM> there is included turbo-generator <NUM> connected to three phase switchgear <NUM> via cable <NUM>. Also in ER1 <NUM> is turbo-generator <NUM> connected to three phase switchgear <NUM>. The turbo-generators may be 29MW <NUM> rpm <NUM> pole generators as shown in <FIG> and may include a high inertia HTS generator, as described above with regard to <FIG>. <FIG> depicts the standard configuration for the MF-IPS system described herein. In <FIG> and <FIG> two alternative operating configurations are depicted.

First, ER1 <NUM> will be described. In this configuration, turbo-generator <NUM> is connected to and powers electric propulsion motor <NUM>, which in this case may be a <NUM> MW HTS motor, via disconnect switch <NUM> which is fed by switchgear <NUM> interconnected to cable <NUM>. Turbo-generator <NUM> is operated in a variable frequency/voltage mode with the speed of the motors/ship varied by adjusting the frequency and hence rotation of the turbo-generator and in turn the HTS motors. Electric propulsion motor <NUM> is connected to the starboard shaft (not shown) to drive starboard propeller <NUM>. Starboard propeller <NUM> uses controllable pitch controller <NUM> to operate as a controllable pitch propeller to provide finer control over the ship's movement when needed for maneuvering and docking, for example.

Switchgear <NUM> is also connected to switchgear <NUM> by cross-connect cable <NUM> in order to power switchgear <NUM>, as needed. Switchgear <NUM> is also connected to ER2 <NUM> via cross-connect cable <NUM> in the event that supplemental power from ER1 <NUM> is needed by ER2 <NUM> and vice-versa. Switchgear <NUM> is normally connected to and powered by turbo-generator <NUM> via switchgear <NUM>. In alternate configurations, switchgear <NUM> may be used to power electric propulsion motor <NUM>, via cable <NUM> (with the turbo-generator <NUM> operating in a variable frequency/variable voltage mode), or it may be used to provide supplemental power to ER2 <NUM> via cross-connect cable <NUM>. In the current configuration depicted, turbo-generator <NUM> is connected through switchgear <NUM> to electric weapons switchgear units 430a and 430b via cables 432a and 432b, respectively. Electric weapons switch gear units 430a and 430b are connected to electric weapons 434a and 434b, respectively. Turbo-generator <NUM> is operated in a fixed voltage/fixed frequency mode (e.g. <NUM> VAC and <NUM>).

Operation of the various components in ER1 <NUM> are under the control of ER1 machine controller <NUM> which is in communication with a master controller (not shown) which receives control signals from the ship's bridge. Through the master controller and the ER1 machine controller <NUM> and ER2 machine controller (discussed below), various functional configurations of the multi-functional integrated power system <NUM> may be implemented as described with regard to <FIG>.

In ER2 <NUM> there is included turbo-generator <NUM> connected to three phase switchgear <NUM> and turbo-generator <NUM> connected to three phase switchgear <NUM>. These turbo-generators may also be configured as shown in <FIG> and may include a high inertia HTS generator as described above with regard to <FIG>. In this configuration, electric propulsion motor <NUM>, which in this case is a <NUM> MW HTS motor, is powered by turbo-generator <NUM>. Turbo-generator <NUM> is connected to and powers electric propulsion motor <NUM>, via disconnect switch <NUM> which is fed by switchgear <NUM> interconnected to cable <NUM>. Turbo-generator <NUM> is operated in a variable frequency/voltage mode, as described above.

HTS motor <NUM> is connected to port shaft which drives port propeller <NUM>. Port propeller <NUM> uses controllable pitch controller <NUM> to operate as a controllable pitch propeller to provide finer control over the ship's movement when needed for maneuvering and docking, for example.

Turbo-generator <NUM> connected to three phase switchgear <NUM> is, in this configuration, primarily used to power electric weapons switchgear units 430a and 430b (in conjunction with or alternative to turbo-generator <NUM>, as described above) via cables 447a and 447b, respectively. Turbo-generator <NUM> is operated in a fixed voltage/fixed frequency mode (e.g. <NUM> VAC and <NUM>). Electric weapons switch gear units 430a and 430b are connected to electric weapons 434a and 434b, respectively. Switchgear <NUM> is also connected to switchgear <NUM> by cross-connect cable <NUM> in order to back-feed switchgear <NUM>, as needed. Switchgear <NUM> is connected to switchgear <NUM> and additionally it is connected to switchgear <NUM> in ER1 <NUM> via cross-connect cable <NUM> in the event that supplemental power from ER2 <NUM> is needed by ER1 <NUM> and vice-versa. Switchgear <NUM> is also connected to electric propulsion motor <NUM>, via disconnect switch <NUM> which is fed by cable <NUM>. In an alternate configuration, turbo-generator <NUM> may be used to power electric propulsion motor <NUM> by changing its mode of operation to variable frequency/voltage mode.

Operation of the various components in ER2 <NUM> are under the control of ER2 machine controller <NUM> which is in communication with a master controller (not shown) which receives control signals from the ship's bridge. Through the master controller, the ER1 machine controller <NUM> and ER2 machine controller <NUM>, various functional configurations of the multi-functional integrated power system <NUM> may be implemented.

In addition to the four primary turbo-generators <NUM>, <NUM>, <NUM>, and <NUM>, there may be included one or more small turbo-generators (on a naval ship referred to as ship service gas turbine generators or "SSGTGs"), each outputting approximately <NUM>. 9MW, such as SSTG's <NUM> and <NUM> located, respectively, in auxiliary machinery room (AMR <NUM>) <NUM> and generator room <NUM>. These SSGTG's may provide power to ship service network. SSGTGNo. <NUM> may be connected to ship service transformer A <NUM> via ship service switchgear <NUM>. Similarly, SSGTG No. <NUM><NUM> may be directly connected to ship service transformer B <NUM> via ship service switchgear <NUM>.

Ship service switchgear <NUM> may also be interconnected to ship service switchgear <NUM> in generator room <NUM> via cable <NUM>. It may also be connected to a third ship service switchgear <NUM> in ER <NUM><NUM> via cable <NUM> and switchgear <NUM> via cable <NUM>. Cable <NUM> may connect ship service switchgear <NUM> to sensor system. Ship service switchgear <NUM> may also be interconnected to service switchgear <NUM> in ER <NUM><NUM> via cable <NUM> and to switchgear <NUM> in ER <NUM><NUM> via cable <NUM>. Switchgear <NUM> may further be connected to the sensor system via cable <NUM>.

With respect to <FIG>, a standard mode of operation of the MF-IPS <NUM> are described above. In the standard mode of operation turbo-generators <NUM> and <NUM> are operated in a variable frequency/variable voltage mode operation in order to drive electric propulsion motors <NUM> and <NUM>, respectively. The weapons systems 434a and 434b are powered by either turbo-generator <NUM> or turbo-generator <NUM> individually or in combination, with both turbo-generators operating in a fixed frequency/fixed voltage mode.

A second mode of operation is depicted in <FIG>, which enables fuel efficient transit at slower speeds (e.g. <NUM> knots) without the electric weapons systems energized. In this configuration, turbo-generator <NUM> in ER <NUM><NUM> is on-line and is powering both HTS motors <NUM> and <NUM> in a variable frequency mode. Turbo-generators <NUM>, <NUM>, and <NUM> are off-line. SSTG's <NUM> and <NUM> are online and are energizing to ship service transformer A <NUM> and ship service transformer B <NUM> to supply all of the power to the ship service network.

In a third mode of operation (full combat) depicted in <FIG>, turbo-generator <NUM>, <NUM>, and <NUM> are online and operating in a variable frequency/variable voltage mode to power HTS motors <NUM> and <NUM> which allows the ship to travel at <NUM> knots. Turbo-generator <NUM> is online and operating in a fixed frequency/fixed voltage mode to power electric weapons systems 434a and 434b. In addition, both SSTG's <NUM> and <NUM> are online and are energizing to ship service transformer A <NUM> and ship service transformer B <NUM> to supply all of the power to the ship service network.

Claim 1:
An electrical power system for a watercraft, comprising:
a first electrical power plant (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) configured to selectively operate in either a variable frequency mode to output variable frequency power to a first electrical network (<NUM>) or a fixed frequency mode to output fixed frequency power to a second electrical network (<NUM>, <NUM>);
wherein the first electrical power plant includes a primer mover and a generator;
a first electrical load (<NUM>) including a first high temperature superconductor, HTS, motor (<NUM>, <NUM>) connected to the first electrical network (<NUM>) to provide propulsion for the watercraft;
a second electrical load (<NUM>, <NUM>) connected to the second electrical network (<NUM>, <NUM>); and characterized by
a controller configured to selectively connect the generator of the first electrical power plant (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) to the first electrical network (<NUM>) and to operate the first electrical power plant in the variable frequency mode to output variable frequency power from the generator to power the first HTS motor (<NUM>, <NUM>) or to selectively connect the generator of the first electrical power plant (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) to the second electrical network (<NUM>, <NUM>) and to operate the first electrical power plant in the fixed frequency mode to output fixed frequency power from the generator to power the second electrical load (<NUM>, <NUM>).