Abstract:
Embodiments are directed towards hybrid power supply that provides electric power to a multirotor rotorcraft to extend range or flying time. In one embodiment, an internal combustion engine and fuel tank are provided that interoperate with a battery provided by a commercial multirotor rotorcraft to substantially extend flying time or flying distance.

Description:
BACKGROUND 
       [0001]    The current generation of multirotor rotorcraft is typically small and is severely constrained in terms of flying time. The state-of-the-art is in the range of 10-15 minutes of flying time for small size, commercial class quad copters and hex copters. Thus, a flying-time or range extending power solution is desirable; especially one that significantly increase the flying time of relatively, small, inexpensive commercial craft, referred to generically herein as multirotor rotorcraft. 
         [0002]    Currently, batteries are exclusively used to power multirotor rotorcraft. However, compared to other energy storage and supply materials, typical batteries have relative low energy densities. For example, the energy density of a lithium-ion battery is in the range of 0.9 to 2.63 Mega Joules (MJ). By contrast, gasoline has an energy density of 32.4 MJ and ethanol has an energy density of 15.6 MJ. 
         [0003]    Hybrid electric vehicles (HEVs) have been developed that combine a conventional internal combustion engine (ICE) propulsion system with an electric propulsion system that derives its power from a rechargeable battery combining the efficiency of one with the energy density advantage of the other. However, an equivalent type of hybrid power solution to that used in hybrid vehicles has not been employed for multirotor rotorcraft. Thus, it would be desirable to provide a hybrid power supply that is both small enough and yet powerful enough to work with commercial multirotor rotorcraft. 
         [0004]    A key goal of a hybrid power supply for a multirotor rotorcraft is to achieve a sufficient power output, for an allowed vehicle weight. One way to achieve this is to reduce the component count. 
         [0005]    Thus, it is with respect to these considerations and others that the present invention has been made. 
       SUMMARY OF THE DESCRIPTION 
       [0006]    Various embodiments are directed towards a hybrid power supply that provides electric power to a multirotor rotorcraft to extend range and flying time. In one embodiment, an internal combustion engine, induction motor, electronic speed control, computer control system and fuel tank are provided that interoperate with the battery used by a commercial multirotor rotorcraft to substantially extend flying time and flying distance. 
         [0007]    To achieve the desired power output density, the component count of the hybrid power supply is reduced by using a single component for dual roles. Instead of having 2 one-way current flow circuits the subject invention innovation has a single multi-direction implementation. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    Non-limiting and non-exhaustive embodiments of the present invention are described with reference to the following drawings. In the drawings, like reference numerals refer to like parts throughout the various figures unless otherwise specified. 
           [0009]    For a better understanding of the present invention, reference will be made to the following Detailed Description of the Preferred Embodiment, which is to be read in association with the accompanying drawings, wherein: 
           [0010]      FIG. 1  is a generalized block diagram that illustrates the flow of energy between input or charging elements, a battery and output or load elements in a hybrid power supply for a multirotor rotorcraft; 
           [0011]      FIG. 2  is a generalized block diagram that illustrates the operation of a hybrid power supply for a multirotor rotorcraft from the perspective of a control unit; 
           [0012]      FIG. 3  illustrates the flow of current during a starting sequence and a charging sequence as performed by an electronic speed control (ESC) as managed by control unit, according to one embodiment of the subject invention; 
           [0013]      FIG. 4  is an illustration of an embodiment of a hybrid power supply for a multirotor rotorcraft; 
           [0014]      FIG. 5  is a flow diagram that provides an exemplary overall method used by the control unit of a hybrid power supply for a multirotor rotorcraft; 
           [0015]      FIG. 6  illustrates an embodiment of a hybrid power supply for a multirotor rotorcraft (HPSM) that includes multiple gensets that connect to output/load elements, such as batteries, via a power bus; 
           [0016]      FIG. 7  illustrates one example layout of an integrated circuit board that implements the control unit of a hybrid power supply for a multirotor rotorcraft; and 
           [0017]      FIG. 8  illustrates one example of the electronic circuits that implement the control unit of a hybrid power supply for a multirotor rotorcraft. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    The invention now will be described more fully hereinafter with reference to the accompanying drawings, which form a part hereof, and which show, by way of illustration, specific exemplary embodiments by which the invention may be practiced. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Among other things, the invention may be embodied as methods, processes, systems, business methods or devices. Accordingly, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. The following detailed description is, therefore, not to be taken in a limiting sense. 
         [0019]    As used herein the following terms have the meanings given below: 
         [0020]    Multirotor rotorcraft—a relatively small copter with more than a single rotor. A multirotor rotorcraft may be remote controlled by an operator or, as used herein, may refer to a UAV or drone that is capable of autonomous flight. 
       Generalized Operation 
       [0021]    The operation of certain aspects of the invention is described below with respect to  FIGS. 1-8 . 
         [0022]      FIG. 1  is a generalized block diagram that illustrates the flow of energy between input or charging elements, a battery and output or load elements in a hybrid power supply for a multirotor rotorcraft  100  (henceforth referred to as HPSM  100 ). Generally, HPSM  100  is a hybrid energy supply for a multirotor rotorcraft, a drone, a robot, or other moving electronic device. In some cases, HPSM  100  is a complete solution and includes a battery  110  and in other cases HPSM  100  acts to provide a recharging solution for a battery  110  provided by the multirotor rotorcraft, drone, robot or other moving electronic device. Thus, in certain embodiments, battery  110  is part of the subject invention and in other embodiments, battery  110  is external to and interfaces with the subject invention. 
         [0023]    HPSM  100  includes one or more input or charge elements that generate electricity. The input elements illustrated in  FIG. 1  are an internal combustion (IC) engine genset  120 , a fuel cell  122 , a thermoelectric generator  124 , and an external power source  126 . Additional input or charging elements may be included and different input elements from those depicted in  FIG. 1  may be included without departing from the scope and spirit of the subject invention. In general, the input elements generate or supply a DC electric current into a DC bus  140  that is controlled by a control unit, described in further detail with reference to  FIG. 2 . The current may be used to charge a battery  110  or may be supplied directly to one or more output or load elements, depicted along the right side of  FIG. 1 . 
         [0024]    The output or load elements identified in  FIG. 1  are one or more direct load propulsion motors  130 , henceforth referred to as motor  130 , a 5 volt DC auxiliary load  132 , a 12 volt regulated DC load  134  and a 120 volt alternating current (AC) load  136 . Typically, the principal output element is motor  130 , which is a motor provided by a commercial multirotor rotorcraft that HPSM  100  is supplying electric power to. As with the input elements, more or less different output elements may be implemented without departing from the scope and spirit of the subject invention. Further, in certain embodiments output or load elements such as motor  130  may be included in the subject invention, while in other embodiments output or load elements are outside the subject invention. 
         [0025]    Further, the voltage of the various output elements does not need to correspond to the voltage of battery  110 . 
         [0026]    In certain embodiments, battery  110  refers to a battery provided by a multirotor rotorcraft, in which case battery  110  is outside the subject invention, i.e. it is external to HPSM  100 . In other embodiments, battery  110  is included in HPSM  100 . Each of these various embodiments is within the scope and spirit of the subject invention. 
         [0027]    Battery  110  may use any battery chemistry, eg. LIPO, LIFE and may operate at any voltage. Generally, battery  110  is illustrated at the center of  FIG. 1  to illustrate its central role. In most operating scenarios, input elements  120 - 126  charge battery  110  and battery  110  supplies power to output elements  130 - 136 . Further, battery  110  may be implemented as one or more physical batteries. 
         [0028]    It may be appreciated by one skilled in the art, that the architecture depicted in  FIG. 1  is substantially different than prior art power solutions for multirotor rotorcraft. Generally, the subject invention enables output elements  130 - 136 , to operate independently from power generation, represented by input/charge elements  120 - 126 . In fact, energy production can be entirely halted, or disconnected via a quiet mode, described in further detail with reference to  FIG. 3  herein below. Further, typical power supplies for multirotor rotorcraft exclusively use batteries, whereas HPSM  100  offers a hybrid solution that also incorporates obtain input power from IC engine genset  120 , fuel cell  122 , thermoelectric generator  124  or another external power source  126 . For example, use of an internal combustion engine such as that provided by IC engine genset  120  uses a fuel such as gasoline or ethanol that has a much higher energy power density than typical batteries. 
         [0029]      FIG. 2  is a generalized block diagram that illustrates the operation of HPSM  100  from the perspective of a control unit  200 . Generally, control unit  200  manages an arbitrary number of different types of input/charge elements, as previously described with reference to  FIG. 1 .  FIG. 2  illustrates an embodiment in which there are N input elements, represented as genset  1   202  and genset N  202 , i.e. each genset is referred to as genset  202 . Genset  202  can be considered as one or more instances of IC engine genset  120 ; alternatively, IC engine genset  120  can be considered as representing one or more instances of an IC engine genset. For purposes of  FIG. 2 , genset  202  refers to an internal combustion engine, referred to as IC engine  204 , together with a transmission  206  that provides the mechanical connection to a 3 phase motor  208 , and a 3-phase electronic speed control (ESC) unit, referred to herein as ESC  209 , which is capable of serving as a starter for the engine and a generator that provides DC current. Generally, IC engine  204  burns fuel to rotate an axle and transmission  206  provides gearing to change the torque and rotational speed delivered to motor  208 . 
         [0030]    One unique aspect of genset  202 , as further illustrated in  FIG. 4 , is that a single element, ESC  209 , both starts the engine and generates DC power. In contrast, prior art systems typically employ two different elements or subsystems to accomplish these two functions: one system for starting the motor and a separate system for generating electricity by capturing the rotational power of the engine. For example, prior art motor control systems for both vehicles and generators typically employ two separate systems: (1) a starter motor to start the engine, and (2) an alternator to generate electric power needed by the vehicle or other load. The subject invention, is the first to use an ESC  209  in a bi-directional mode, thus eliminating the need for separate motors and their respective circuitry. This results in a smaller and lighter device. Unique control logic performed by control unit  200  manages ESC  209  to always be in the correct mode and ensures the proper flow of current to the motor (for starting) and from the motor (to charge the battery or supply the loads as necessary) during the operation of HPSM  100 . 
         [0031]    ESC  209  is managed by control unit  200  in such a way as to manage the back EMF in a way that allows current to flow through the ESC negative to the original design direction. This is accomplished through the synchronization of the frequency of the induction motor output wave and the ESC output wave. The induction motor output frequency is directly proportional to the shaft RPM which is adjusted by controlling the IC engine&#39;s throttle position. The output frequency of ESC  209  is controlled by adjusting the PWM input signal. The RPM of the engine is increased to induce current flow out of the induction motor through ESC  209 , which converts it to DC to charge the battery or power loads. The engine RPM, AC frequency and DC current flow is continuously monitored to ensure that frequency sync is maintained and back EMF exceeds ESC  209  voltage to ensure current flow out of ESC  209  to battery  216  and/or other loads. 
         [0032]      FIG. 2  illustrates a single output/load element, namely battery  216 , labeled drone/robot battery  216 . More generally, control unit  200  is capable of managing an arbitrary number of batteries  216 . As previously discussed, battery  216  may be a part of HPSM  100  or may be external to HPSM  100 . 
         [0033]    More generally, control unit  200  manages current flow to one or more output/load elements  130 - 136 . 
         [0034]    Control unit  200  supervises the delivery of power from battery  216 , gensets  202  and any other input/charge elements to output/load elements. To accomplish this, control unit  200  interacts with a cooling and heating element  218 , a fuel management element  220  and a wireless communication module  212  to ensure the safe, reliable and efficient operation of all systems. 
         [0035]    Control unit  200  includes a computer processor, nontransitory memory for storing data and program code. It further includes sensors, and heating and cooling control logic as required. 
         [0036]    One example of an integrated circuit board layout of control unit  200  is given in  FIG. 7 . Further, one example of an electronic circuit design that implements control unit  200  is given in  FIG. 8 . 
         [0037]    Cooling and heating elements  218  provide heating elements and cooling elements such as fans that maintain the necessary temperature levels required of the various hardware components in HPSM  100 . Control unit  200  actively controls heating and cooling elements  218 . Heating elements may include resistance wire, or other resistance elements that are controlled electronically by control unit  200 . Cooling elements may include fans of various sizes that are likewise controlled by control unit  200 . 
         [0038]    Fuel management element  220  refers to the various mechanisms that dynamically adjust the fuel mixture and flow of air and fuel to the engine, also referred to as throttle. In one embodiment, fuel management element  220  uses servos to perform these adjustments. Fuel management element  220  regulates mixture and flow of any fuel required by any of input/charge elements  120 - 126 , such as genset  120  and thermoelectric generator  124 . For example, if genset  120  is under a relatively light load then a leaner fuel to air mixture may be used to reduce fuel consumption. Generally, fuel management element  220  adjusts fuel to air mixture to minimize fuel usage given the output power requirements. 
         [0039]    Fuel management element  220  also senses the fuel level and provides the information to control unit  200 . This is critical to avoid letting the engine run out of fuel; typically the fuel mixture is gradually reduced, or throttled back, prior to stopping the engine. 
         [0040]    It may be appreciated by one skilled in the art, that control unit  200  working in coordination with fuel management element  220  and cooling and heating element  218  provides an active, intelligent approach to managing the generation and consumption of power in a hybrid power supply. 
         [0041]    Wireless communication module  212  enables control unit  200  to communicate with an external controller, such as a remote control unit, or a mobile device or other control device. Wireless communication module  212  may support a variety of communication methods such as BLUETOOTH, WIFI, and GSM. 
         [0042]    Wireless communication module  212  enables control unit  200  to receive commands from an external controller and to send status information to an external controller. Status information that may be provided includes charge level of battery  206 , the load drawn by output/load elements, and level of the fuel tank(s). Commands received from wireless communication module  212  and processed by control unit  200  include setting operation to quiet mode. 
         [0043]      FIG. 3  illustrates the flow of current during a starting sequence and a charging sequence as performed by an electronic speed control (ESC) as managed by control unit  200 , according to one embodiment of the subject invention. To start IC engine  204 , ESC  209  draws DC current from battery  216 , converts the DC current to 3-phase AC current that flows to induction motor  208 , which converts the AC electrical current to mechanical energy, typically in the form of rotation of an axle. Induction motor  208  is coupled to IC engine  204  and thus the mechanical energy is used to start IC engine  204 . 
         [0044]    In a charging sequence, ESC  209  draws AC current from IC engine  204  via the induction motor  208  and converts the current to DC and supplies the DC current to battery  216  for purposes of charging. 
         [0045]      FIG. 4  is a simplified illustration of one embodiment of the physical layout of HPSM  100 . As illustrated, HPSM  100  includes an internal combustion engine  402 , a mechanical linkage or connection  404  to an electric motor  408 , a control unit  406 , a fuel tank  410 , a 3 phase electronic speed control (ESC)  412 , and a fuel intake valve  414 . 
         [0046]    Fuel intake valve  414  receives fuel from fuel tank  410  via a fuel line (not depicted). In certain embodiments a fuel pump or fuel injection system regulates the flow of fuel from fuel tank  410  to fuel intake valve  414 . 
         [0047]    While transmission  206  is depicted in  FIG. 4  as a mechanical linkage without gears, in other embodiments transmission  206  may include gears or the like. 
         [0048]    HPSM  100  may include a housing (not depicted) that encloses the various components described with reference to  FIGS. 1-2 . The housing may be made of carbon fiber, plastic or another material. In certain embodiments there is a user settable switch that enables a user to set HPSM  100  to quiet mode which prevents control unit  200  from turning on genset  202  to generate power to battery  216 . In other embodiments, when HPSM  100  is set to quiet mode then no input charge elements  120 - 126  are allowed to supply power to battery  110 . In certain embodiments, there is a second switch that enables the user to turn HPSM  100  on and off. When HPSM  100  is set to off then the device halts and input charge elements  120 - 126  are blocked from supplying or generating power to battery  110  and battery  110  is blocked from supplying power to output/load elements  130 - 136 . 
         [0049]    While  FIG. 4  illustrates one shape and design for HPSM  100 , in fact the invention is not so limited and other shapes can be used without departing from the scope and spirit of the subject invention. In a product form, there are likely to be different product sizes that offer varying amounts of power. For example, there may be a version that offers 1000 watt of power and another that offers 2000 watt of power. Generally, an output power in the range of 500-3000 watts is desirable. To accomplish this a fuel tank size in the range of 1000 to 4000 cubic centimeters (cc) is desirable. 
         [0050]    The objective is for HPSM  100  fit in the size and weight envelope of a standard multirotor rotorcraft. Thus, in a preferred embodiment a weight range of substantially 0.5 to 3 kilograms is desirable. Further, dimensions of HPSM  100  should be relatively small. Thus, in a preferred embodiment width, height and depth dimension sizes in the range of 6″ to 18″ are desirable and sizes in the range of 6″ to 12″ per side are preferred. 
         [0051]      FIG. 5  is a flow diagram that provides an exemplary overall method used by control unit  200  of HPSM  100 . After HPSM  100  is switched on or started, at step  502  control unit  200  checks monitors power consumption and at step  504  monitors or checks the state of battery  216 . If may be appreciated, that battery  216  may in fact be implemented as one or more physical batteries. At step  506  a determination is made as to whether battery  216  needs to be charged, i.e. whether the remaining power level is above a threshold level. If battery  216  doesn&#39;t need to be charged then control returns to the start state and steps  502  and  504  are repeated. Note that steps  502  and  504  are depicted as being performed in parallel, whereas they can also be performed sequentially and can be performed in the reverse order. 
         [0052]    If at step  506  it is determined that battery  216  needs to be charged then processing flows to step  510 . If at step  506  it is determined that battery  216  is not too low then control returns to the initial state and steps  502  and  504  are performed. 
         [0053]    At step  508  if an external control source, e.g. a multirotor rotorcraft or robot or an incoming command received via wireless communication module  212 , wants to charge battery  216  then processing flows to step  510 . If at step  508  no external control source has issued a command to charge battery  216  then processing returns to the initial state and steps  502  and  504  are performed. 
         [0054]    At step  510 , control unit  200  determines the number of engines, and which engines to use to recharge batteries  216 . For example, if there are four batteries  216  in HPSM  100  then control unit  200  may determine to start batteries #2 and #4 based on various criteria. 
         [0055]    At step  512  control unit  200  issues signals to the engines determined at step  510  to start. 
         [0056]    At step  514  control unit  200  monitors the engines and adjusts the throttle opening (controls power production) and fuel/air mixture (controls lubrication and combustion temperature) to optimize fuel consumption and engine life for the current power output requirement and number of engines active. 
         [0057]    At step  515 , control unit  200  monitors RPM and adjusts ESC  209  to properly manage current flow out of motor  208  through ESC  209  to battery  216 , or as is discussed with reference to  FIG. 6 , hereinbelow, to a power bus that supplies DC power to one or more output/load elements. 
         [0058]    At step  516  control unit  200  monitors the temperature of the engines that it has started and adjusts the fans for optimal performance. Furthermore, throttle opening and fuel/air mixture are again adjusted to protect engines. When operating limits are approached, power output is reduced to protect engines and extend component life. 
         [0059]    At step  518  control unit  200  monitors the power consumption and at step  520  control unit  200  monitors the state of battery  216 . Then, at step  522 , this information is used to determine if the batteries are sufficiently charged. If not, control returns to step  510  to determine if the new current conditions require adjustments to the number of engines needed to operate. Temperature and fuel are also readjusted. This loop continues until the batteries reach a full state. If at step  522  a determination is made that battery  216  has been sufficiently charged then at step  524  the engines that were started at step  512  are turned off and control returns to the initial state. 
         [0060]      FIG. 6  illustrates an embodiment of a hybrid power supply for a multirotor rotorcraft (HPSM)  600  that includes multiple gensets  202  connected in parallel to a DC power bus  602  to supply power to output/load elements such as batteries. Use of a power bus  602  enables each individual genset  202  to be hot swappable, i.e. capable of being individually inserted or removed from HPSM  600  while a multirotor rotorcraft is running, without causing damage or affecting performance. This innovation allows for multiple gensets to be managed by the control unit  200  to best meet the power demands of the loads. Individual gensets can be turned on and off during operation to handle loads, to rotate operation, to enhance durability and reliability, to optimize fuel economy and to facilitate maintenance. 
         [0061]    It will be understood that each step of a flow description need not be limited in the ordering shown in the illustrations or described above, and might be performed in any ordering, or even performed concurrently, without departing from the spirit of the invention. It will also be understood that each step, and combinations of steps can be implemented by computer program instructions. These program instructions might be provided to a processor to produce a machine, such that the instructions, which execute on the processor, create means for implementing the actions specified in the steps. The computer program instructions might be executed by a processor to cause a series of operational steps to be performed by the processor to produce a computer implemented process such that the instructions, which execute on the processor to provide steps for implementing the actions specified in the illustrated or described step or steps. 
         [0062]    Accordingly, steps of the flow illustration support combinations of means for performing the specified actions, combinations of steps for performing the specified actions and program instruction means for performing the specified actions. It will also be understood that each step of the flow illustration, and combinations of steps in the flow illustration, can be implemented by special purpose hardware-based systems which perform the specified actions or steps, or combinations of special purpose hardware and computer instructions. 
         [0063]    The above specification, examples, and data provide a complete description of the manufacture and use of the composition of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter.