Patent Description:
Generators are often utilized in aircraft. A gas turbine engine on the aircraft provides a drive input into the generator shaft. The generator typically includes a disconnect shaft that can transmit mechanical power via a geared coupling. The geared coupling selectively drives a main generator to provide electric power for various uses on the aircraft.

It is desirable that the generated power be of a desired constant frequency. However, the speed from the input shaft will vary during operation of the gas turbine engine. This would result in variable frequency.

A constant speed drive (CSD) is a type of transmission that takes an input shaft rotating at a wide range of speeds, delivering this power to an output shaft that rotates at a constant speed, despite the varying input. They are used to drive mechanisms, typically electrical generators, that require a constant input speed. The CSD converts a variable speed input into a constant speed output, such that electric power of a desirable frequency is generated.

An aspect of the present invention is directed to a power supply system for a generator control circuit as defined by claim <NUM>.

Another aspect of the present invention is directed to a method as defined by claim <NUM>.

The diagrams depicted herein are illustrative. There can be many variations to the diagrams or the operations described therein without departing from the scope of the invention as defined by the claims. For instance, the actions can be performed in a differing order or actions can be added, deleted or modified. Also, the term "coupled" and variations thereof describes having a communications path between two elements and does not imply a direct connection between the elements with no intervening elements/connections between them. All of these variations are considered a part of the specification.

For the sake of brevity, conventional techniques related to making and using aspects of the invention may or may not be described in detail herein. In particular, various aspects of aircraft electric power systems to implement the various technical features described herein are well known. Accordingly, in the interest of brevity, many conventional implementation details are only mentioned briefly herein or are omitted entirely without providing the well-known system and/or process details.

Referring now to the figures, a perspective view of an aircraft <NUM> that may incorporate various components of the present disclosure. Aircraft <NUM> includes a fuselage <NUM> extending from a nose portion <NUM> to a tail portion <NUM> through a body portion <NUM>. Body portion <NUM> houses an aircraft cabin <NUM> that includes a crew compartment <NUM> and a passenger or cargo compartment <NUM>. Body portion <NUM> supports a first wing <NUM> and a second wing <NUM>. First wing <NUM> extends from a first root portion <NUM> to a first tip portion <NUM> through a first airfoil portion <NUM>. First airfoil portion <NUM> includes a leading edge <NUM> and a trailing edge <NUM>. Second wing <NUM> extends from a second root portion (not shown) to a second tip portion <NUM> through a second airfoil portion <NUM>. Second airfoil portion <NUM> includes a leading edge <NUM> and a trailing edge <NUM>. Tail portion <NUM> includes a stabilizer <NUM>. Aircraft <NUM> includes an engine <NUM> configured to provide propulsion to the aircraft <NUM>. Each engine <NUM> can have one or more generator and drive assemblies <NUM> having a generator <NUM> (described in greater detail in <FIG>).

Turning now to an overview of technologies that are more specifically relevant to aspects of the disclosure, aircraft electrical power generating systems use one or more three-phase AC synchronous generators to provide electrical power. The voltage produced from the main output terminals of such generators is induced in the machine's stator coils by way of the combination in shaft speed and magnetic flux offered by the rotating rotor. The frequency of a synchronous generator's electrical output is directly dependent on the generator's shaft speed. The electrical frequency output from the generator is thus maintained by controlling the shaft speed of the generator within precise rpm limits.

The main sources of primary mechanical power for a generator (i.e., the prime mover or primary mover, referred to interchangeably) can be one of either the main aircraft engines, a special purpose gas-turbine, or wind turbine. The latter two sources are used for either auxiliary or emergency power. Irrespective of the source used, the shaft speed is subject to considerable speed variation. For generators that are required to provide a fixed-frequency output, a method of mechanical speed control is required to regulate the frequency to precise limits. Within the industry, a hydraulic system is a widely used method of controlling shaft speed, with respect to the varying speed of the prime mover (e.g., the shaft of the main aircraft engines or a shaft indirectly connected to the main aircraft engine, for example).

<FIG> depicts a block diagram representation of an aircraft electrical power generation system <NUM> aircraft according to one or more embodiments. The system <NUM> includes generator control unit (GCU) <NUM>. The power generation system <NUM> can be utilized for providing power to aircraft loads. The system <NUM> also includes a constant speed drive (CSD) <NUM> and a generator <NUM>. The generator <NUM> is a combination of a permanent magnet generator (PMG) <NUM> and the main generator <NUM>. The CSD <NUM> receives mechanical input power from a shaft <NUM> attached to a prime mover <NUM> at varying speed and delivers mechanical power from the CSD's <NUM> output shaft <NUM> to the generator <NUM> at a constant speed. The generator <NUM> is driven by the shaft <NUM> and outputs electrical power through conversion of the mechanical energy of the generator shaft <NUM>. In one or more embodiments, the CSD <NUM> and the generator <NUM> are combined in a single unit referred to as the integrated drive generator (IDG) <NUM> (<FIG> and <FIG>).

With the CSD <NUM>, the generator shaft <NUM> speed is controlled using a method of variable fluid displacement. The CSD <NUM> provides a method to vary shaft speed by effectively changing the speed ratio at which the generator shaft <NUM> rotates with respect to the shaft <NUM> of the prime mover <NUM>. One method of speed control is by way of an electrical feedback circuit <NUM>. By sensing the frequency of any of the generator's <NUM> electrical outputs, or the shaft <NUM> speed directly, the output of the circuit drives the coil of a hydraulic servo-valve <NUM>. The action of the servo-valve <NUM> is to produce a variable fluid displacement in response to the magnitude of electrical current passed through its coil. When the system is active, current passed through the servo-valve coil causes the speed of the generator shaft <NUM> to increase to a higher ratio with respect to that of the prime mover <NUM> input. At low or zero coil current, the generator shaft defaults to the lowest speed ratio with respect to the input. Essentially the generator <NUM> has a gear shift that adjusts in response to the changing speed of the prime mover to keep the generator shaft <NUM> at essentially a constant speed.

A controller <NUM> is part of the generator control unit (GCU) <NUM>. The GCU <NUM> controls both the generator frequency (via the shaft speed) and the magnitude of the main ac output voltage (voltage regulation). The GCU <NUM> is powered from the separate, unregulated three-phase AC source, known as a permanent magnet generator (PMG) <NUM>. The PMG <NUM> voltage is induced in a separate set of stator coils by permanent magnets that are also mounted on the generator's rotor <NUM>. The voltage produced by the PMG <NUM> is unregulated. Both its voltage and frequency are directly proportional to the generator's shaft <NUM> speed. Hence the voltage produced by the PMG <NUM> varies from zero to a relatively high magnitude at maximum shaft speed.

The wide voltage range over which the GCU <NUM> is required to operate represents a challenge for a GCU's <NUM> internal power supply system. Adding to this challenge is the problem that until the GCU <NUM> is powered, the hydraulic system that controls the generator-to-input shaft speed ratio, defaults to the minimum. It is only after the GCU <NUM> has powered up, and the controller <NUM> is active, can the CSD <NUM> be actively controlled to increase the generator's shaft <NUM> speed higher by adjustment of the CSD's <NUM> shaft-speed ratio. Unfortunately given the limited input voltage range of most internal power supply circuits, by the time the GCU <NUM> is powered and able to pick up the speed of the generator shaft <NUM>, the prime mover <NUM> is already above the minimum input speed at which the generator <NUM> is required to provide regulated output voltage and frequency.

Most switched-mode power supply circuit topologies can comfortably operate over an input-voltage range of <NUM>:<NUM>. However, in order to provide power to the speed control circuit at a relatively low input voltage, and accommodate ample margin at the highest operating voltage, an operating range approaching <NUM>:<NUM> is desired.

<FIG> depicts a graph <NUM> illustrating the relationship between input shaft speed (related to the engine shaft) and generator shaft speed for a constant speed drive according to one or more embodiments. The shaded portion <NUM> indicates the limits of the minimum and maximum input-to-generator shaft-speed ratios. The generator shaft speed relates directly to a direct current (DC) input to the GCU's internal power supply system. The DC voltage is derived from the rectification of the three-phase AC PMG source which progressively rises from zero as the rotational speed of the generator shaft is increased. The solid line <NUM> of the graph <NUM> represents a desired start-up characteristic for the generator. In this example, the GCU and the speed-control circuit are powered at a generator shaft speed of <NUM>,<NUM> rev/min, equivalent to a DC input voltage to the GCU of <NUM> VDC. Once powered, the speed-control circuit can provide the necessary stimulus to the servo-valve coil to ensure the rapid adjustment of the CSD shaft-speed ratio from minimum to maximum. This allows the speed-control system to achieve the steady-state control of the generator shaft at the required speed of <NUM>,<NUM> rev/min, which is prior to the input shaft reaching the minimum governing speed of the CSD. The dashed line <NUM> of the graph <NUM> shows the effect of the GCU not being powered until a higher generator rpm of <NUM>,<NUM> rev/min is reached. This correlates to the GCU's internal power supply system not starting until the DC voltage (derived from the PMG three-phase AC source) has reached <NUM> VDC. As a result, the rapid adjustment in the speed of the generator shaft is not achieved early enough, requiring the input shaft to reach a rotational speed significantly higher than the minimum governing speed before the GCU can both raise and control the generator shaft speed at <NUM>,<NUM> rev/min. This requires that the input shaft speed be raised well above the minimum operating requirement before the generator's electrical output can be made available to the aircraft.

To address the issue described above, one or more embodiments introduce a low-power bias power supply to the GCU that is separate from the GCU's main internal power supply. The low-power bias supply is designed to provide power at a much lower PMG voltage and rpm as illustrated in <FIG>. In one or more embodiments, the amount of power can be limited to that required to provide current to a servo-valve coil and during the period before the main power supply becomes active. The stimulus can be made directly to the servo-valve coil or by powering a servo-valve drive circuit which can be configured to pass current to the servo-valve coil. Performing this operation of the servo-valve coil occurs when the GCU is unable to control the servo-valve coil due to the unavailability of power due to the delayed start-up of the main power supply.

As mentioned above, the low power bias supply can deliver power directly to the servo-valve coil or to the servo-valve drive circuit. The goal for each is to cause the hydraulic system to begin increasing the speed ratio of the CSD's generator shaft with respect to that of the prime mover. This has the effect of accelerating the generator shaft speed to a higher rpm which in turn further increases the PMG voltage. Any increase in the PMG voltage can further raise the magnitude of current passed to the servo-valve coil. This creates a condition of positive feedback that can result in a progressively more rapid acceleration of the generator input shaft. Any increase in generator shaft speed also increases the PMG voltage and correspondingly the DC voltage that supplies the GCU. At some point, the GCU's main internal power supply becomes active allowing the GCU to assume the normal control of both the generator shaft speed and voltage regulation. This is achieved before the input shaft speed reaches the minimum governing speed of the CSD. This enables a "boot-up" process that is initiated earlier and at a lower rpm so that the generator can be ready to supply the aircraft electrical system with the specified AC voltage and frequency at the minimum required operating shaft speed of the prime mover.

<FIG> depicts a block diagram of a GCU internal power system according to one or more embodiments. The GCU internal power system <NUM> includes a GCU main internal power supply <NUM> and a low-power bias supply <NUM>. The low-power bias supply <NUM> can provide enough voltage and current to the servo-valve <NUM> or to a servo-valve drive circuit <NUM> that drives the servo-valve <NUM> so it can deliver the magnitude of current needed to begin increasing the shaft-speed ratio of the CSD <NUM>. The low-power bias supply <NUM> can supply power for a short period of time prior to the GCU's main internal power supply <NUM> becoming active. Once active, the GCU's main internal power supply <NUM> can then supply power to the servo-valve <NUM> or drive circuit <NUM>. When the GCU's main internal power supply <NUM> is active, the lower-power bias supply <NUM> can be disabled or turned off.

Referring back to the example of <FIG>, the operating input speed range for the input shaft to operate the generators is between <NUM>,<NUM> rpm and <NUM>,<NUM> rpm shown as the "Operating Input Speed Range" on the graph <NUM>. However, without a low-power bias supply as described herein, the GCU can only start operation when receiving at least <NUM> VDC from the PMG which occurs between <NUM>,<NUM> and <NUM>,<NUM> rpm from the input shaft which is shown as the dotted-line <NUM> in graph <NUM>. However, with the low-power bias supply, the servo-valve coils or drive circuitry can be operated now at <NUM> VDC which can occur at <NUM> rpm for the input shaft. During start up, this allows for earlier stimulus of the CSD, such that the generator is able to reach its operating speed earlier and at a lower input speed as shown in graph <NUM> outlined by the solid line <NUM>. In one or more embodiments, the generator shaft speed, input shaft speed, and operational input range described herein in <FIG> are included for exemplary purposes. Depending on the aircraft and power generation system, the ranges of the input voltage, rpm and frequency, that the low power bias <NUM> and GCU main <NUM> power converters are active can be different. These values may also overlap such that the low-power bias converter <NUM> may continue to operate at input voltages above that in which the GCU main power converter <NUM> becomes active. This overlap can be designed to ensure the continued and uninterrupted stimulus of the servo-valve throughout the boot-up (IDG spin up) period. With a variety of system input voltage, rpm, and frequency ranges, the present system <NUM> ensures that the low-power bias converter <NUM> powers up at a lower voltage and rpm than the GCU main power converter <NUM>, and at a sufficiently low voltage to ensure the timely "boot up" of the system. The goal is for the GCU, as a whole to power up and gain control of the main generator by the time the prime mover (engine) has reached minimum idling speed. This is in terms of the main generator <NUM> providing power to the aircraft, at the specified output voltage and frequency.

In one or more embodiments, the internal power system <NUM> is driven by electrical power coming from the PMG <NUM> which is attached to the same generator shaft <NUM> (from <FIG>) as the main generator <NUM> (from <FIG>). As mentioned above, the PMG <NUM> is unregulated and the voltage and frequency are directly proportional to the generator's shaft <NUM> speed. The PMG <NUM> produces an AC voltage which is then rectified to DC by a rectifier circuit <NUM>. The two power sources (<NUM>, <NUM>) are power converters (DC-to-DC converters) and supply power to the servo-valve coil <NUM> or drive circuit <NUM>. The main internal power supply <NUM> supplies power to the GCU control circuits <NUM> as well. The two sources (<NUM>, <NUM>), in some embodiments, can be connected through current flow control devices <NUM> (e.g., a pair of semiconductor diodes, a pair of actively controlled solid-state switches, relay contact, or any other circuit topology) operated by the controller <NUM> that is receiving feedback from the generator through a feedback line/circuit <NUM>. The generator feedback <NUM> can include the output voltage or frequency of the PMG <NUM>, the generator <NUM> (from <FIG>) shaft speed, the generator <NUM> (from <FIG>) frequency, and/or any combination of these characteristics associated with the generator <NUM> (from <FIG>).

In one or more embodiments, the two power supplies (<NUM>, <NUM>) are power converters. The output voltage from the PMG source <NUM> is unregulated and varies significantly with the generator's shaft speed. During power up ("boot-up"), as the generator shaft begins moving responsive to movement by the primary mover, the PMG source <NUM> provides increasing voltage which is then rectified by the rectifier <NUM>. The low-power bias supply <NUM> can operate over a lower input voltage range of the PMG <NUM>; <NUM> - <NUM> V in this example. During this time, the low-power supply <NUM> can provide power to the servo-valve <NUM> or servo-valve drive circuit <NUM> through operation of the current flow control devices <NUM> which are operated by the controller <NUM>. Operation of the GCU main internal power supply <NUM> is over a higher input voltage range from the PMG <NUM>; <NUM> - <NUM> V in this example. During this time, the GCU main internal power supply <NUM> can provide power to the servo-valve <NUM> or servo-valve drive circuit <NUM> along with the GCU control circuits <NUM>. The operation of the servo-valve/drive circuit <NUM> by the main internal power supply <NUM> is similarly controlled by the controller <NUM> operating the current flow control devices <NUM>. The controller <NUM> can receive feedback from the generator <NUM> (from <FIG>) to determine when to switch from causing the low-power bias supply <NUM> to supply power to the servo-valve <NUM> or drive circuit <NUM> to the main internal power supply <NUM> supplying power to the servo-valve <NUM> or drive circuit <NUM> in the CSD <NUM> (from <FIG>). The low-power bias supply <NUM> can be disconnected by the current flow control devices <NUM> or simply turned off by the controller <NUM>. In one or more embodiments, the low-power bias supply <NUM> can be any type of power converter including, but not limited to, a flyback converter. In one or more embodiments, the use of the term "flyback" is to include any suitable power converter topology, regulated or unregulated, that can provide power at input voltages below the minimum operating input voltage of the main converter <NUM>. In one or more embodiments, as the input voltage ranges of the low power bias converter <NUM> and GCU main converter <NUM> may overlap, it is the control of the switches <NUM> that determines which converter (<NUM> or <NUM>) provides the stimulus to the servo-valve coil <NUM> or drive circuit <NUM>. In some embodiments, the two switches <NUM> may also operate differently. A first switch in the voltage control devices <NUM> that provides early stimulus during the spool-up period can be applied statically. This first switch has the purpose of initiating transition of the CSD speed ratio. There is no speed control associated with this first switch. The stimulus is essentially applied open loop. A second switch in the voltage control devices <NUM> incorporates (or allows for) pulse width modulation (PWM) control. This second switch has the ability to regulate the current to the servo-valve <NUM> in order to control the speed of the generator shaft <NUM>. The control to the servo-valve <NUM> is to adjust the speed ratio of the CSD up and down to precisely regulate the generator shaft speed to a fixed rpm, over the full operating speed range of the input shaft and prime mover.

In one or more embodiments, the controller <NUM> can perform functions such as monitoring voltage output from the PMG <NUM>, shaft speed of the generator <NUM> and/or prime mover <NUM>, bias power supply voltage output, GCU main internal power supply output, operate one or more current flow control devices <NUM> and/or other types of circuitry within the system <NUM>, and the like. In one or more embodiments, the controller <NUM> can monitor the shaft speed of the generator, the output voltage of the PMG <NUM>, or a combination of both to determine when to disconnect, using the current flow control devices <NUM>, the low-power bias supply <NUM> from the servo-valve or servo-valve drive circuit <NUM> and connect the GCU main internal power supply <NUM> to said servo-valve or servo-valve drive circuit <NUM>. This can be performed at a specified output frequency or voltage from the PMG and/or a specified shaft speed of the generator.

In one or more embodiments, the controller <NUM> or any of the hardware referenced in the system <NUM> can be implemented by executable instructions and/or hardware circuitry that could also include a processing circuit and memory. The processing circuit can be embodied in any type of central processing unit (CPU), including a microprocessor, a digital signal processor (DSP), a microcontroller, an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), or the like. Also, in embodiments, the memory may include random access memory (RAM), read only memory (ROM), or other electronic, optical, magnetic, or any other computer readable medium onto which is stored data and algorithms as executable instructions in a non-transitory form. In one or more embodiments, the controller <NUM> can be control circuitry implemented by a combination of logic gates and/or other components utilized to operate the current flow control device <NUM>. The combination of logic gates can include, but are not limited, to an overcharge comparator with a reference voltage that drives a configuration of logic gates that operate the current flow control device <NUM> and/or any other component, for example.

<FIG> depicts a flow diagram of a method for providing power to a generator control circuit according to one or more embodiments. The method <NUM> includes providing a generator as shown in block <NUM>. In some embodiments, the generator is a permanent magnet generator which is unregulated and the power supplied from this generator is based on the generator shaft speed associated with a prime mover such as an aircraft main engine or a shaft indirectly connected to the aircraft engine. In some embodiments, the prime mover can include, but is not limited to, a gas turbine often used in an auxiliary power unit and a wind turbine that is a source of emergency power. At block <NUM>, the method <NUM> includes providing a first power converter comprising a first input and a first output, the first input coupled to an output of the generator and the first output coupled to a valve circuit. In some embodiments, the first power converter is the low-power bias power supply <NUM> (from <FIG>) which is coupled to the servo-valve or servo-valve drive circuit <NUM>. At block <NUM>, the method <NUM> includes providing a second power converter comprising a second input and a second output, the second input coupled to the output of the generator and the second output coupled to the valve circuit. In some embodiments, the second power convertor is the GCU main internal power supply <NUM> (from <FIG>) which is coupled to both the GCU control circuits <NUM> and the servo valve or servo-valve drive circuit <NUM>. The method <NUM>, at block <NUM>, includes monitoring, by a controller <NUM> or control circuitry, a characteristic associated with the generator. Herein, the controller <NUM> can monitor the output voltage of the generator and/or the generator shaft speed. The method <NUM> then includes causing, by the controller, the first power converter to provide power to the valve circuit when the characteristic of the generator is within a first range of characteristic values, as shown at block <NUM>. And at block <NUM>, the method <NUM> includes causing, by the controller, the second power converter to provide power to the valve circuit responsive to the characteristic value of the generator being within a second range of characteristic values. The range of characteristic values can be tied to either the generator shaft speed and/or the output voltage, and frequency of the generator (e.g., PMG <NUM>). The low-power bias supply provides power to the servo-valves during the "boot-up" period where the generator shaft speed is low and thus the output voltage is low. The low-power bias supply is able to power the servo-valve or servo-valve drive circuit during this boot-up period before having the controller switch off or disconnect this low-power bias supply when the GCU main power supply has sufficient voltage to operate after this boot-up period.

Additional processes may also be included. It should be understood that the processes depicted in <FIG> represent illustrations.

Various embodiments of the invention are described herein with reference to the related drawings. Various connections and positional relationships (e.g., over, below, adjacent, etc.) are set forth between elements in the following description and in the drawings. These connections and/or positional relationships, unless specified otherwise, can be direct or indirect, and the present invention is not intended to be limiting in this respect. Accordingly, a coupling of entities can refer to either a direct or an indirect coupling, and a positional relationship between entities can be a direct or indirect positional relationship. Moreover, the various tasks and process steps described herein can be incorporated into a more comprehensive procedure or process having additional steps or functionality not described in detail herein.

Additionally, the term "exemplary" is used herein to mean "serving as an example, instance or illustration. " Any embodiment or design described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments or designs. The terms "at least one" and "one or more" may be understood to include any integer number greater than or equal to one, i.e. one, two, three, four, etc. The terms "a plurality" may be understood to include any integer number greater than or equal to two, i.e. two, three, four, five, etc. The term "connection" may include both an indirect "connection" and a direct "connection.

Claim 1:
A power supply for a generator control circuit (<NUM>) comprising:
a generator (<NUM>) that includes a permanent magnet generator (<NUM>) and a main generator (<NUM>);
a low-power bias supply (<NUM>) comprising a first input and a first output, the first input coupled to an output of the permanent magnet generator (<NUM>) and the first output coupled to a valve circuit (<NUM>), wherein the valve circuit controls a speed of the generator;
a generator control unit, GCU, main internal power supply (<NUM>) comprising a second input and a second output, the second input coupled to the output of the permanent magnet generator (<NUM>) and the second output coupled to the valve circuit; and
a controller (<NUM>) configured to:
monitor a characteristic associated with the generator, wherein the characteristic associated with the generator comprises an output voltage, or wherein the characteristic associated with the generator comprises a generator shaft speed, or wherein the characteristic associated with the generator comprises a frequency of the generator;
cause the low-power bias supply (<NUM>) to provide power to the valve circuit during a boot up period of the generator when the characteristic of the generator is within a first range of characteristic values until the GCU main internal power supply has sufficient voltage to operate after the boot up period; and
cause the GCU main internal power supply (<NUM>) to provide power to the valve circuit after the boot up period when the characteristic of the generator is within a second range of characteristic values.