WO2024112582A1

WO2024112582A1 - Regulating power of heater devices in electrically powered aircraft using pulse width modulation (pwm)

Info

Publication number: WO2024112582A1
Application number: PCT/US2023/080260
Authority: WO
Inventors: Hoai Xuan LE; David Brian Welch
Original assignee: Itt Manufacturing Enterprises Inc.
Priority date: 2022-11-21
Filing date: 2023-11-17
Publication date: 2024-05-30

Abstract

A method and related system for regulating power to a heating device that is coupled to a discharging high voltage DC battery bank in which a voltage level of the discharging DC power source is continuously measured. Based on the measured voltage level, a variable duty cycle is determined for switching on and off the voltage, creating a pulse width modulation (PWM) waveform that controls and maintain power levels to the heating device in spite of the discharge of the DC power source.

Description

REGULATING POWER OF HEATER DEVICES IN ELECTRICALLY POWERED AIRCRAFT USING PULSE WIDTH MODULATION (PWM)

Cross Reference to Related Application

[0001] This application claims priority to US Provisional Patent Application Serial No. 63/426,954, filed November 21, 2022, and entitled: REGULATING POWER OF HEATER DEVICES IN ELECTRICALLY POWERED AIRCRAFT USING PULSE WIDTH MODULATION (PWM), under relevant portions of 35 U.S. C. §119 and 35 U.S.C. §120, the entire contents of which are herein incorporated by reference.

Technical Field

[0002] This application is generally directed to the field of aircraft and more specifically to a system and related method for regulating power of heater devices in electrically powered aircraft.

Background

[0003] Traditionally, conventional internal combustion engine powered aircraft (i.e., jet, turbo-prop, etc.) utilize 115 VAC generated voltage available for the power source for each of the various resistance type heating devices provided throughout the aircraft, as found in the cockpit, galley, cabin, etc. Today, however, there is a push for both hybrid and all-electric powered aircraft, which will utilize an electric motor having high voltage DC power battery banks as their power source in lieu of the internal combustion engine as powered by fossil fuels. That is, the electric motor can be the sole source of propulsion in an all-electric aircraft or the electric motor can be used in combination with a conventional engine in hybrid versions; for example, in order to provide a burst of power to the propulsion system during portions of flight.

[0004] As is known, various heater and heater control systems are used for heating various portions of a commercial aircraft, such as but not limited to the cabin, cockpit, air ducts, feet, galley. An exemplary heater device 10 is shown in FIGS. 1 and 2, which operates with at least one heater element, typically resistive, disposed in a housing and coupled to a power source through a control or operating system on the aircraft. In these new, all-electrically powered aircraft, the voltage level coming from the high voltage DC battery bank will vary significantly, from when the batteries are fully charged, to when the batteries have been nearly or completely discharged. As an example, high voltage battery voltage, when fully charged, may begin at perhaps 1000 VDC, and when nearing the end of the flight, become discharged to perhaps 500 VDC. In traditional internal combustion powered aircraft, the 115 VAC power systems aboard the aircraft maintain their 115 VAC voltage throughout the flight (from beginning to end) without deviations, which is a preferred condition or state.

[0005] Accordingly, it is a desire to be able to provide substantially constant heater output power levels maintained in all electric, high voltage DC powered aircraft, which was not a problem with traditional conventional, constant voltage systems. However and with the noted wide ranging (depleting) battery voltage of electric aircraft, being able to successfully maintain power levels as in traditional aircraft heating and heating control systems will require additional techniques not current employed in connection with these systems.

Summary

[0006] Therefore and to address this issue, there is herein described a method and related system in which power levels for a heating device in an electric aircraft can be regulated/maintained in spite of the variable (discharging) voltage level of the battery voltage over time.

[0007] More specifically and according to an aspect of the invention, there is provided a method for regulating power to a heating device that is coupled to a discharging high voltage DC battery pack in an aircraft. The method comprises continuously measuring the voltage level of the discharging DC power source coupled to the heating device, and based on the measured voltage level, switching the voltage on and off in accordance with a variable duty cycle.

[0008] The amount of switching on and off is based on pulse width modulation (PWM) in which the root mean square of the battery voltage (Vrms) is made constant based on the measured battery voltage and the duty cycle in accordance with a waveform for controlling the voltage and power levels to the heater. [0009] The herein described method and control system provides or enables an effective constant voltage level over the duration of a flight or other effective use period of the heating device with resulting stable power levels from the heating device.

[0010] An advantage of the herein described invention is that the heater elements of the heating device can be maintained in spite of having a discharging variable DC power source.

[0011] Yet another advantage is that the analog look up table approach described herein allows error correction due to small changes in heater resistance at different battery voltage levels and different on and off times of the heater driver.

[0012] Additionally, heater power levels can be advantageously maintained without user intervention.

[0013] Furthermore, heaters can be developed or purposed for a specific power output capability (e.g., 1500 W). Using the herein described control technique and by way of example, a generic 1500 W capable heater can be used in application(s) in which the maximum heater output is desired to be a lesser value, e.g., 1000 W. As a result, design specific heaters or heater components would not be necessary in order to suit a given application.

[0014] Other features and advantages will be readily apparent from the following Detailed Description, which should be read in conjunction with the accompanying drawings.

Brief Description of the Drawings

[0015] The accompanying drawings, which are incorporated herein and constitute part of this specification, illustrate presently preferred embodiments of the invention, and together with the general description given above and the Detailed Description given below, serve to explain features of the invention (in which like numerals represent like elements), of which:

[0016] FIG. 1 depicts a side elevational view of an exemplary heating device for an aircraft; [0017] FIG.2 is an end view of the aircraft heating device of FIG. 1;

[0018] FIG. 3 is a schematic block diagram of a heater control system in accordance with aspects of the invention; and

[0019] FIG. 4 is an exemplary pulse width modulation waveform used in the heater control system of FIG. 3.

Detailed Description

[0020] The following Detailed Description should be read in reference to the accompanying drawings, in which like elements in different drawings are identically numbered. The drawings, which are not necessarily to scale, depict selected embodiments and are not limited to the scope of the invention. The detailed description illustrates, by way of example, not by way of limitation, the principles of the invention. This description will clearly enable one skilled in the art to make and use the invention, and describes several embodiments, adaptations, variations, alternatives and uses of the invention, including what is believed to be the best mode of carrying out the invention.

[0021] The invention relates to describes an exemplary embodiment for a control system and related methodology for a heating device for an electric aircraft powered by a variable (discharging) power supply and more specifically a high voltage DC battery bank. As discussed herein, the control system utilizes pulse width modulation (PWM) in order to rapidly switch the input voltage on and off, as needed to maintain the effective voltage (Vrms) being applied to the heating element(s) of a heating device, which, in turn will result in controlling/regulating the output power of the heating device to a substantially constant level.

[0022] As used herein, the terms “about” or “approximately” for any numerical values or ranges indicate a suitable dimensional tolerance that allows the part or collection of components to function for the intended purpose as described herein. More specifically, “about” or “approximately” may refer to the range of values + 10 percent of the recited value, e g., “about 90%” may refer to the range of values from 81 % to 99%. As used here, the term “electrical signal” or “signal” is intended to include direct current signal, alternating signal or any signal within the electromagnetic spectrum. The terms “processor”, “controller”, “microprocessor” or “microcontroller” are intended to have the same meaning and are intended to be used interchangeably.

[0023] With reference to the figures, an exemplary embodiment for a control system and related methodology for a heating device for an electric aircraft powered by a variable (discharging) power supply and more specifically a high voltage DC battery bank is described. As discussed herein, the control system utilizes pulse width modulation (PWM) in order to rapidly switch the input voltage on and off, as needed to maintain the effective voltage (Vrms) being applied to the heating element(s) of a heating device, which, in turn will result in controlling/regulating the output power of the heating device to a substantially constant level.

[0024] An embodiment of a control system is illustrated in FIG. 3 in which an input control for a variable power source and more specifically, a high voltage DC battery bank 20 is measured in conjunction with a heating device, the latter being shown schematically by reference number 60. For purposes of best describing an example of the methodology, specific voltage levels for the battery bank 20 are utilized. It will be understood that these levels can be suitably varied. More specifically, the voltage levels from the battery bank 20 according to this embodiment vary between a highest or maximum level of 1000 VDC when the batteries in the battery bank 20 are fully charged, to a minimum or lowest depleted level of 500 VDC.

[0025] As shown at block 30, the input voltage is measured (Vbattery). Based on a measured variable voltage level (Vbattery), the herein described system is then configured to switch the input voltage on and off in accordance with a duty cycle (determined herein as voltage On time (ti)/voltage Off time (T- ti) and expressed as a percentage) as determined by a controller at block 40, in order to create a pulse width modulation (PWM) waveform 80, best shown in FIG. 4. The substantially constant heater voltage is based on the root mean square of the voltage, Vrms. By knowing the measured voltage level of the battery pack (Vbattery) and the Vrms, the duty cycle of the PWM waveform can be suitably determined in order to provide the constant voltage level over time.

[0026] For example and at the highest level (Vbatteiy = 1000 VDC) and desiring a constant heater value Vims of 500 VDC, a duty cycle (on time/off time) of 25 percent is required to produce a Vrms of 500 VDC. More specifically and in this example, the input voltage is switched on for 25 percent and then off for 75 percent of the duty cycle. That is and for the pulse waveform shown in FIG. 4, Vrms = Vbattery * SQRT(Duty Cycle) = 1000 VDC * SQRT(0.25) = 500 VDC.

[0027] As the battery voltage (Vbatteiy) is depleted over time and use, for example, from 1000 VDC to 612.37 VDC, the same effective heater voltage of 500 VDC can be maintained by switching the voltage on and then off 1/3 of the time (that is, the voltage being on 2/3 of the time). Using the same relation for the pulse waveform, Vrms = Vbattery * SQRT(Duty Cycle) = 612.37 VDC * SQRT(0.33) = 500 VDC.

[0028] When the measured voltage level has depleted to its lowest level according to this example, which is 500 VDC, there is no switching off of the voltage required (that is, the input voltage remains 100% “ON”), the average heater voltage again remains 500 VDC, and the stepped waveform is no longer required.

[0029] Consequently, power that is applied to the heater 70 is determined by the relation: P = Vrms² / R (1) in which:

P represents the heater output power (which is targeted for 1000 Watts in this specific example/discussion);

Vrms = Applied Voltage (effective) as measured in VDC; and

R refers to the resistance of the heater element of the heating device (R remains a fixed value, which according to this specific example is assumed to be 250 ohms). Since the Vrms and R values are fixed, the power levels are also maintained in accordance with this invention based on the applied PWM waveform.

[0030] The determination of the appropriate duty cycle in accordance with the PWM technique described herein for maintaining a constant voltage level to the heating device essentially equates to an analog look-up table approach so that preferably any small resistance changes due to changes to battery voltage level and different on and off times of the heater driver can also be compensated by changing its corresponding duty cycle.

[0031] While the invention has been described in terms of particular variations and illustrative figures, those of ordinary skill in the art will recognize that the invention is not limited to the variations or figures described. In addition, where methods and steps described above indicate certain events occurring in certain order, those of ordinary skill in the art will recognize that the ordering of certain steps may be modified and that such modifications are in accordance with the variations of the invention. Additionally, certain of the steps may be performed concurrently in a parallel process when possible, as well as performed sequentially as described above. Therefore, to the extent there are variations of the invention, which are within the spirit of the disclosure or equivalent to the inventions found in the claims, it is the intent that this patent will cover those variations as well.

[0032] To the extent that the claims recite the phrase “at least one of’ in reference to a plurality of elements, this is intended to mean at least one or more of the listed elements, and is not limited to at least one of each element. For example, “at least one of an element A, element B, and element C,” is intended to indicate element A alone, or element B alone, or element C alone, or any combination thereof. “At least one of element A, element B, and element C” is not intended to be limited to at least one of an element A, at least one of an element B, and at least one of an element C.

[0033] This detailed description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.

[0034] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprise” (and any form of comprise, such as “comprises” and “comprising”), “have” (and any form of have, such as “has” and “having”), “include” (and any form of include, such as “includes” and “including”), and “contain” (and any form of contain, such as “contains” and “containing”) are open-ended linking verbs. As a result, a method or device that “comprises,” “has,” “includes,” or “contains” one or more steps or elements possesses those one or more steps or elements, but is not limited to possessing only those one or more steps or elements. Likewise, a step of a method or an element of a device that “comprises,” “has,” “includes,” or “contains” one or more features possesses those one or more features, but is not limited to possessing only those one or more features. Furthermore, a device or structure that is configured in a certain way is configured in at least that way, but may also be configured in ways that are not listed.

[0035] The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below, if any, are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description set forth herein has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the disclosure. The embodiment was chosen and described in order to best explain the principles of one or more aspects set forth herein and the practical application, and to enable others of ordinary skill in the art to understand one or more aspects as described herein for various embodiments with various modifications as are suited to the particular use contemplated and in accordance with the following appended claims. Additional embodiments include any one of the embodiments described above and described in any and all exhibits and other materials submitted herewith, where one or more of its components, functionalities or structures is interchanged with, replaced by or augmented by one or more of the components, functionalities or structures of a different embodiment described above.

[0036] It will be understood that other variations and modifications can be included in accordance with this description and the following appended claims. For example, the herein described methodology can be applied to other devices and other applications and fields in addition to those that have been described here and in accordance with the following claims.

Claims

1. A method for regulating power to a heating device that is coupled to a discharging high voltage DC battery pack, the method comprising: continuously measuring the voltage level of the discharging DC power source coupled to the heating device; based on the measured voltage level, applying a pulse width modulation (PWM) waveform whereby the voltage is switched on and off in accordance with a variable duty cycle to control a voltage level applied to the heating device.

2. The method in accordance with claim 1, wherein a regulated heater voltage Vrms is determined for use with the PWM waveform by the relation = Vbattery x SQRT (Duty Cycle) in which Vrms is the regulated voltage level to which the heater device is to be maintained, Vbattery is the measured voltage, and the Duty Cycle is the ratio of on time to off time for switching the voltage of the heater device.

3. The method in accordance with claim 1, wherein the method is employed in electric aircraft.

4. The method in accordance with claim 1, wherein the discharging DC power source is a battery bank.

5. A system for regulating power levels to a heating device from a discharging DC battery high voltage power source coupled to the heating device, the system comprising: a detector for measuring the voltage level of the discharging DC battery high voltage power source over time; and a controller configured to: determine a variable duty cycle based on the measured voltage level to switch the voltage on and off order to yield a constant Vrms; and applying a pulse width modulation waveform having the determined duty cycle.

6. The system in accordance with claim 5, in which the discharging DC power source is a battery bank.

7. The system in accordance with claim 5, in which the system is used in conjunction with a heating device of an electric aircraft.

8. The system in accordance with claim 5, in which the controller is configured to determine the pulse width modulation waveform based on the relationship Vrms = Vbatteiy x SQRT (Duty Cycle) in which Vrms is the regulated voltage level, Vbatteiy is the measured voltage, and the Duty Cycle is the ratio of on time to off time for switching the voltage of the heater device.

9. The invention as disclosed herein.