Method and system for operating an auxiliary power unit

Abstract

The invention relates to a method and system for operating an auxiliary power unit. A method and system for operating an auxiliary power unit (APU) of an aircraft are described. The method comprises: obtaining an external environmental parameter of the aircraft; determining an available output power for the APU in dependence on the external environmental parameter; and setting an overcurrent protection threshold of the APU to a level related to the available output power.

Description

Technical Field

[0001] This disclosure generally relates to auxiliary power units (APUs), and more specifically to dynamically controlling overcurrent protection thresholds in APUs. Background Technology

[0002] An auxiliary power unit (APU) is a device on a vehicle (such as an aircraft) that provides energy for functions other than propulsion. An aircraft APU can be used as additional energy to start one of the main engines. An APU (either separately from or integrated with a generator) can also function as a generator to power the aircraft's electrical loads, such as system controllers, high-current electrical equipment, cockpit avionics, and aircraft heating and cooling systems.

[0003] In many power systems, including APUs, overcurrent or overcurrent occurs when the system experiences a current greater than expected, leading to excessive heat generation and the risk of equipment fire or damage. Enhancing overcurrent protection prevents this from happening, thus preventing the power system from operating beyond current limits or thresholds.

[0004] APUs are typically designed to operate at predetermined points on their operating envelope, i.e., within parameter ranges where operation will result in safe and acceptable performance. Overcurrent protection is provided for the available power output at these predetermined points on the operating envelope. In this architecture, the full power of the APU is not used beyond its operating envelope.

[0005] Therefore, improvements are needed. Summary of the Invention

[0006] According to a broad perspective, a method for operating an auxiliary power unit (APU) of an aircraft is provided. The method includes: obtaining external environmental parameters of the aircraft; determining the available output power for the APU based on the external environmental parameters; and setting an overcurrent protection threshold for the APU to a level related to the available output power.

[0007] In some embodiments, external environmental parameters include the aircraft's altitude and the outside temperature.

[0008] In some embodiments, obtaining external environmental parameters includes measuring external environmental parameters.

[0009] In some embodiments, the method further includes comparing an overcurrent protection threshold with the actual current of the APU and reducing the electrical load when the actual current exceeds the overcurrent protection threshold.

[0010] In some embodiments, the method further includes: detecting changes in the external environment parameters by obtaining updated external environment parameters, determining updated available output power based on the updated external environment parameters, and setting an updated overcurrent protection threshold of the APU to a level related to the updated available output power.

[0011] In some embodiments, setting an updated overcurrent protection threshold includes applying a time delay to confirm updated external environmental parameters.

[0012] In some embodiments, the method further includes performing load management based on an updated overcurrent protection threshold.

[0013] In some embodiments, the APU operates as a generator in bleed or bleedless systems.

[0014] In some embodiments, setting an overcurrent protection threshold includes selecting an overcurrent protection threshold from a list of predetermined overcurrent protection thresholds having a corresponding output power range associated therewith.

[0015] In some embodiments, determining the available output power includes selecting the available output power from a lookup table.

[0016] According to another broad aspect, a system for operating an auxiliary power unit (APU) of an aircraft is provided. The system includes a processing unit and a non-transitory computer-readable medium thereon storing program instructions. The program instructions are executable by the processing unit to obtain external environmental parameters of the aircraft, determine the available output power for the APU based on the external environmental parameters, and set an overcurrent protection threshold for the APU to a level related to the available output power.

[0017] In some embodiments, external environmental parameters include the aircraft's altitude and the outside temperature.

[0018] In some embodiments, obtaining external environmental parameters includes measuring external environmental parameters.

[0019] In some embodiments, program instructions may also be executed to compare an overcurrent protection threshold with the actual current of the APU and reduce the electrical load when the actual current exceeds the overcurrent protection threshold.

[0020] In some embodiments, the program instructions may also perform actions to: detect changes in the external environment parameters by obtaining updated external environment parameters, determine updated available output power based on the updated external environment parameters, and set an updated overcurrent protection threshold of the APU to a level related to the updated available output power.

[0021] In some embodiments, setting an updated overcurrent protection threshold includes applying a time delay to confirm updated external environmental parameters.

[0022] In some embodiments, the program instructions may also execute to perform load management based on an updated overcurrent protection threshold.

[0023] In some embodiments, setting an overcurrent protection threshold includes selecting an overcurrent protection threshold from a list of predetermined overcurrent protection thresholds having a corresponding output power range associated with them.

[0024] In some embodiments, determining the available output power includes selecting the available output power from a lookup table.

[0025] According to yet another broad aspect, a non-transitory computer-readable medium is provided having program instructions stored thereon that are processor-executable for operating an auxiliary power unit. The program instructions are configured to: obtain external environmental parameters of the aircraft, determine the available output power for the APU based on the external environmental parameters, and set the APU's overcurrent protection threshold to a level related to the available output power.

[0026] The features of the systems, devices and methods described herein can be used in various combinations according to the embodiments described herein. Attached Figure Description

[0027] Now refer to the attached diagram, in which:

[0028] Figure 1 This is a block diagram of an example auxiliary power unit;

[0029] Figure 2 It is a graph showing the ambient temperature versus output power at multiple aircraft altitudes;

[0030] Figure 3 This is a flowchart of an example method for operating the auxiliary power unit;

[0031] Figure 4A It is a curve of ambient temperature relative to altitude;

[0032] Figure 4B An exemplary trip curve is shown; and

[0033] Figure 5 This is a block diagram of an example computing device.

[0034] It will be noted that in all the accompanying drawings, similar features are identified by similar reference numerals. Detailed Implementation

[0035] Figure 1An auxiliary power unit (APU) 100 that can be used, for example, in an aircraft is shown. The APU 100 can be used in general aviation, light helicopter and regional aircraft platforms, large helicopters, large business jets and / or commercial aircraft. The APU 100 includes a generator 102 and a generator control unit (GCU) 104 operatively coupled to the generator 102.

[0036] Generator 102 may be a synchronous generator with permanent magnet excitation (PMSG), which may operate as a single phase, or it may be a multiphase system for generating alternating current (AC) or direct current (DC). Generator 102 may be designed to operate on the principles of constant speed constant frequency (CSCF), constant speed variable frequency (CSVF), or variable speed variable frequency (VSVF). In some embodiments, generator 102 is a brushed generator with a rating ranging from 20 to 250 kVA. Alternatively, generator 102 may be a brushless generator with a rating ranging from 20 to 250 kVA. Generator 102 may be air-cooled, oil-cooled, or cooled using any other fluid.

[0037] The GCU 104 is configured to control, monitor, and / or protect the APU generation channel. It regulates the output voltage of the APU 100 to its nominal value at the set point (POR). Some functions of the GCU 104 can be implemented using software, firmware, logic circuitry, or a combination thereof. In some embodiments, the GCU 104 is part of an integrated control platform and interacts with control and protection devices such as solid-state power controllers.

[0038] In some embodiments, the APU 100 is part of a More Electric Aircraft (MEA), whereby the secondary energy source for the aircraft is electric. In some embodiments, the APU 100 is part of a no-exhaust system, whereby exhaust (i.e., compressed air) is replaced by additional power generation.

[0039] refer to Figure 2 Depending on one or more external environmental parameters of the aircraft, the APU 100 has an operating envelope spanning a wide range of output power values. In some embodiments, the external environmental parameters of the aircraft are ambient temperature and altitude. Other external environmental parameters, such as aircraft speed, may also be applicable. For the purposes of this disclosure, ambient temperature refers to the temperature of the air outside the aircraft. Output power is plotted along the y-axis of graph 200, and ambient temperature is plotted along the x-axis. Curves 2021–2029 represent the available output power for the APU 100 at different aircraft altitudes and varying ambient temperatures.

[0040] The available output power at higher aircraft altitudes is lower than that at lower aircraft altitudes. For example, curves 2021 through 2029 might represent altitudes of 45,000 feet (2021); 42,000 feet (2022); 39,000 feet (2023); 36,000 feet (2024); 33,000 feet (2025); 30,000 feet (2026); 27,000 feet (2027); 24,000 feet (2028); and 21,000 feet (2029). Output power could range from 20 kW to several hundred kW, and temperature ranges could be between -75°C and -5°C. In this example, the APU 100 is capable of supporting 500 kW of electrical power below 21,000 feet, but no more than 75 kW during cruise at 45,000 feet. These values ​​are merely illustrative.

[0041] To utilize the full power available to the APU 100, dynamic overcurrent protection is implemented in the GCU 104. Using this dynamic overcurrent protection, the generator 102 can operate at any output power within the APU 100's operating envelope. The available output power is determined based on external environmental parameters of the aircraft, such as aircraft altitude and ambient temperature, and the overcurrent protection threshold is set to a level related to the available output power.

[0042] refer to Figure 3 An example method 300 for operating an APU such as APU 100 is shown. In step 302, external environmental parameters of the aircraft are obtained. In some embodiments, the external environmental parameters are obtained by direct measurement using one or more sensors provided on the aircraft. For example, a temperature sensor on the outside of the aircraft can be used to measure the ambient temperature; a pressure sensor can be used to measure atmospheric pressure to determine altitude. In some embodiments, the external environmental parameters of the aircraft are obtained from one or more other devices on the aircraft, such as the engine computer and / or the aircraft computer. Obtaining the external environmental parameters according to step 302 can be passive, i.e., receiving parameters without prompting, or active, i.e., receiving parameters upon request.

[0043] At step 304, the available output power for the APU is determined based on external environmental parameters. In some embodiments, determining the available output power from the environmental parameters includes selecting the available output power from a lookup table, which may also be represented by an array, matrix, or graph. Figure 4AAn example is shown that uses altitude and ambient temperature as index variables to determine available output power. Graph 400 provides multiple power settings (i.e., from 50kW to 500kW) based on altitude and ambient temperature. An altitude of 15,000 feet and an ambient temperature of -15°C are shown as intersecting at point 402 corresponding to a 200kW power setting. These values ​​are merely exemplary.

[0044] To determine the trip point current, fault current and disconnection time were considered. For example, based on Figure 4B Curve 404 in the diagram indicates that a circuit breaker at Ipeak / I will interrupt 10 times the rated current I within 1.0 milliseconds.

[0045] In some embodiments, the corresponding current is retrieved from a trip curve lookup table to calculate the power-to-current conversion, and stored values ​​are set for multiple power levels.

[0046] Once the current I is determined, the overcurrent protection threshold can be set to the value of Ipeak / I, where Ipeak is the peak inrush current. In some embodiments, the overcurrent protection threshold is set to I + increment, where the increment is a buffer that allows the APU's current to exceed I with a small margin (e.g., 1%, 3%, 5%, or any other suitable margin). The value of the increment can be found through testing, simulation, and / or using historical data.

[0047] In some embodiments, the trip curve lookup table directly correlates the available output power to the overcurrent protection threshold.

[0048] Return to reference Figure 3 In step 306, the overcurrent protection threshold of the APU is set to a level related to the available output power. The overcurrent protection threshold corresponding to the level associated with the available output power is applied to the generator 102 via GCU 104. During operation, if the overcurrent protection threshold is exceeded, the APU 100 will trip or disconnect.

[0049] In optional step 308, following steps 302-306, after dynamically setting the overcurrent protection threshold, external environmental parameters are monitored. When a change is detected, a timer can be started at step 310. The available output power is updated based on the new value of the external environmental parameters, and the overcurrent protection threshold is set for the relevant power consumption.

[0050] In some embodiments, a change in an external environmental parameter is detected only when one or more parameters change to a minimum value, such as 1°C, 5°C, or 10°C for temperature, or 1000 feet, 3000 feet, or 5000 feet for altitude. The external environmental parameter may be associated with a predetermined band, thereby detecting a change when a change in the band's value is detected. An example is shown in Table 1 below.

[0051] high bring 0–15,000 feet 1 15,001–20,000 feet 2 20,000–25,000 feet 3 25,001 feet – 30,000 feet 4

[0052] Table 1

[0053] In some embodiments, a change is detected only when a band change occurs and the change in value includes a difference greater than a given threshold. For example, if the value threshold is set to 200 feet, a change in altitude from 14,900 feet to 15,025 feet will not result in a detected change. This prevents oscillations between bands unless the parameter change becomes more significant. Other embodiments may be applied depending on the actual implementation.

[0054] In some embodiments, when the overcurrent protection threshold is set to a new value, it is compared with the actual current of the APU. With reduced available output power, it may be necessary to release one or more loads to meet the new overcurrent protection threshold. A timer can be used to allow this load reduction without triggering a trip or disconnection of the APU. Alternatively, or in combination therewith, the comparison of the overcurrent protection threshold with the actual current of the APU is performed before setting the overcurrent protection threshold to a new level to allow load reduction before the new setting is applied. Depending on the actual implementation, the comparison can be performed before step 306, simultaneously with step 304, simultaneously with step 306, or after step 306.

[0055] Method 300 can be used to size generator 102 so that the entire power range of APU 100 is available. In some cases, this means allowing a larger generator to provide maximum power at low altitudes or on the ground. This may mean that if a single APU can provide power at different points in its operating envelope, and therefore can replace two or more APUs with limited available output power, fewer smaller-sized APUs need to be provided on the aircraft. For example, without dynamic overcurrent protection, an APU might provide 30kW of power at 30,000 feet and 30kW of power at 10,000 feet. With dynamic overcurrent protection, APU overcurrent protection thresholds can be set for 75kW at 10,000 feet and for 30kW at 30,000 feet.

[0056] Method 300 can be used to reduce load reduction by increasing the available output power of the generator at lower altitudes. In some embodiments, method 300 is used in conjunction with a smart load reduction system. In a smart load reduction system, various electrical loads of the aircraft are prioritized, and lower-priority loads are reduced before higher-priority loads. The smart load reduction system can be configured, for example, to determine whether more output power can be obtained from the APU by sampling external environmental parameters and comparing them with the APU's current settings when an increase in electrical load is needed. Where possible, overcurrent protection thresholds can be modified based on whether hysteresis is implemented as active or inactive, instead of performing load reduction. This provides additional electrical load management flexibility, increases the power budget, and reduces the risk of electrical overload.

[0057] Figure 5 This is an example embodiment of a computing device 500 for implementing some or all of the methods 300 described above. The computing device 500 includes a processing unit 502 and a memory 504 storing computer-executable instructions 506 therein. The processing unit 502 may include steps configured to perform a series of steps such that the instructions 506, when executed by the computing device 500 or other programmable means, cause the functions / actions / steps specified in the methods 300 described herein to be performed. The processing unit 502 may include, for example, any type of general-purpose microprocessor or microcontroller, digital signal processing (DSP) processor, CPU, integrated circuit, field-programmable gate array (FPGA), reconfigurable processor, other suitably programmed or programmable logic circuitry, or any combination thereof.

[0058] Memory 504 may include any suitable known or other machine-readable storage medium. Memory 504 may include non-transitory computer-readable storage media, such as, but not limited to, electrical, magnetic, optical, electromagnetic, infrared, or semiconductor systems, devices, or any suitable combination thereof. Memory 504 may include any suitable combination of computer memories, whether internal or external to a device, such as random access memory (RAM), read-only memory (ROM), electro-optical memory, magneto-optical memory, optical memory, erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), or ferroelectric RAM (FRAM), etc. Memory 504 may include any storage device (e.g., apparatus) suitable for retrievably storing machine-readable instructions 506 executable by processing unit 602.

[0059] It should be noted that computing device 500 can be implemented as part of a fully authorized digital engine control (FADEC) or other similar device, including electronic engine control (EEC), engine control unit (EUC), engine electronic electronics control system (EECS), and aircraft avionics systems. Furthermore, it should be noted that the techniques described herein can be executed substantially in real time by computing device 500.

[0060] For example, the methods and systems for operating an APU described herein may be implemented in a high-level procedural or object-oriented programming or scripting language, or a combination thereof, to communicate with or assist the operation of a computer system, such as computer device 500. Alternatively, the methods and systems for operating an APU may be implemented in assembly or machine language. This language may be compiled or interpreted. Program code for implementing the methods and systems for operating an APU may be stored on a storage medium or device, such as ROM, disk, optical disk, flash drive, or any other suitable storage medium or device. This program code may be read by a general-purpose or special-purpose programmable computer to configure and operate the computer when the computer reads the storage medium or device to perform the processes described herein. Embodiments of the methods and systems for operating an APU may also be considered to be implemented via a non-transitory computer-readable storage medium on which a computer program is stored. This computer program may include computer-readable instructions that cause the computer, or more specifically the processing unit 502 of computing device 500, to operate in a particular and predefined manner to perform the functions described herein.

[0061] Computer-executable instructions can take many forms, including program modules that are executed by one or more computers or other devices. Typically, program modules include routines, programs, objects, components, data structures, etc., that perform specific tasks or implement specific abstract data types. Generally, in various embodiments, the functionality of program modules can be combined or distributed as needed.

[0062] The above description is merely exemplary, and those skilled in the art will recognize that changes can be made to the described embodiments without departing from the scope of the disclosed invention. Other modifications falling within the scope of this invention will be apparent to those skilled in the art based on a review of this disclosure.

[0063] Various aspects of the methods and systems for operating the APU can be used individually, in combination, or in various arrangements not specifically discussed in the embodiments described above. Therefore, their application is not limited to the details and arrangements of the components set forth in the foregoing description or shown in the accompanying drawings. For example, an aspect described in one embodiment can be combined in any way with aspects described in other embodiments. The scope of the appended claims should not be limited by the embodiments set forth in the examples, but should be given the broadest reasonable interpretation consistent with the entire specification.

Claims

1. A method for operating an auxiliary power unit (APU) of an aircraft, the method comprising: Obtain the external environmental parameters of the aircraft at its current altitude; The available output power for the APU is determined based on the external environmental parameters. Set the overcurrent protection threshold of the APU to a level related to the available output power; Reduce the aircraft's current altitude; as well as After reducing the aircraft's current altitude, the overcurrent protection threshold of the APU is increased.

2. The method of claim 1, wherein, The external environmental parameters include the aircraft's current altitude and the outside temperature.

3. The method of claim 1, wherein, Obtaining the external environmental parameters includes measuring the external environmental parameters.

4. The method according to claim 1, further comprising: The overcurrent protection threshold is compared with the actual current of the APU, and the electrical load is reduced when the actual current exceeds the overcurrent protection threshold.

5. The method according to claim 1, further comprising: Changes in the external environment parameters are detected by obtaining updated external environment parameters; The updated available output power is determined based on the updated external environmental parameters; as well as Set the updated overcurrent protection threshold of the APU to a level related to the updated available output power.

6. The method according to claim 5, wherein, Setting the updated overcurrent protection threshold includes applying a time delay to confirm the updated external environmental parameters.

7. The method according to claim 5, further comprising: Load management is performed based on the updated overcurrent protection threshold.

8. The method according to claim 1, wherein, The APU operates as a generator in either a vented or non-vented system.

9. The method according to claim 1, wherein, Setting the overcurrent protection threshold includes selecting the overcurrent protection threshold from a list of predetermined overcurrent protection thresholds having a corresponding output power range associated with it.

10. The method according to claim 1, wherein, Determining the available output power includes selecting the available output power from a lookup table.

11. A system for operating an auxiliary power unit (APU) of an aircraft, the system comprising: Processing unit; as well as A non-transitory computer-readable medium having stored thereon program instructions executable by the processing unit, the program instructions being used to: Obtain the external environmental parameters of the aircraft at its current altitude; The available output power for the APU is determined based on the external environmental parameters. Set the overcurrent protection threshold of the APU to a level related to the available output power; Reduce the aircraft's current altitude; as well as After reducing the aircraft's current altitude, the overcurrent protection threshold of the APU is increased.

12. The system according to claim 11, wherein, The external environmental parameters include the aircraft's current altitude and the outside temperature.

13. The system according to claim 11, wherein, Obtaining the external environmental parameters includes measuring the external environmental parameters.

14. The system according to claim 11, wherein, The program instructions can also be executed to: compare the overcurrent protection threshold with the actual current of the APU, and reduce the electrical load when the actual current exceeds the overcurrent protection threshold.

15. The system according to claim 11, wherein, The program instructions can also be executed to: Changes in the external environment parameters are detected by obtaining updated external environment parameters; The updated available output power is determined based on the updated external environmental parameters; as well as Set the updated overcurrent protection threshold of the APU to a level related to the updated available output power.

16. The system according to claim 15, wherein, Setting the updated overcurrent protection threshold includes applying a time delay to confirm the updated external environmental parameters.

17. The system according to claim 15, wherein, The program instructions can also be executed to perform load management based on the updated overcurrent protection threshold.

18. The system according to claim 11, wherein, Setting the overcurrent protection threshold includes selecting the overcurrent protection threshold from a list of predetermined overcurrent protection thresholds having a corresponding output power range associated with it.

19. The system according to claim 11, wherein, Determining the available output power involves selecting the available output power from a lookup table.

20. A non-transitory computer-readable medium storing thereon program instructions executable by a processor to operate an auxiliary power unit (APU) of an aircraft, the program instructions being configured to: Obtain the external environmental parameters of the aircraft at its current altitude; The available output power for the APU is determined based on the external environmental parameters. Set the overcurrent protection threshold of the APU to a level related to the available output power; Reduce the aircraft's current altitude; as well as After reducing the aircraft's current altitude, the overcurrent protection threshold of the APU is increased.

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