Patent Publication Number: US-8987938-B2

Title: Hybrid inverter generator

Description:
RELATED APPLICATIONS 
     The present application claims priority to U.S. Provisional Patent Application Ser. No. 61/436,848, filed Jan. 27, 2011, the entire contents of which are hereby incorporated by reference. 
    
    
     BACKGROUND 
     The invention relates to inverter generators. 
     SUMMARY 
     In one embodiment, the invention provides a hybrid engine and battery generator and a method of operating the same. The generator is controlled to operate in at least three modes: a battery-only mode, a battery charging mode, and a boost mode. In the battery-only mode, the engine is off and an internal battery of the generator is used by an inverter to generate AC output. In the battery charging mode, the engine generates DC power, via an alternator and rectifier, which is used to charge the battery and to supply power to the inverter to generate AC output. In the boost mode, the battery and the engine generate DC power that is used by the inverter to generate an AC output with increased wattage, relative to the battery-only mode and battery charging mode. The generator automatically switches between the modes based on battery level and load demand. 
     In another embodiment, the invention provides a method of operating a hybrid engine and battery generator. The method includes operating the generator in the at least three modes described above. The method further includes automatically switching between the modes based on battery level and load demand. 
     Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts a hybrid inverter generator with an engine generator according to embodiments of the invention. 
         FIG. 2  depicts a battery used in the hybrid inverter generator. 
         FIGS. 3-4  depict state diagrams illustrating modes of operation of the hybrid inverter generator. 
         FIG. 5  illustrates a method of operating a hybrid inverter generator according to embodiments of the invention. 
         FIG. 6  depicts a plot of battery charge over time for a varying load demand. 
         FIGS. 7A-C  depict hybrid inverter generators according to embodiments of the invention. 
         FIG. 8  depicts a hybrid inverter generator with fuel cells according to embodiments of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. 
       FIG. 1  depicts a hybrid inverter generator  100  coupled to an AC load  105 . The generator  100  includes an engine  110 , an alternator  115 , a rectifier  120 , a battery  125 , an inverter  130 , and a controller  135 . The engine  110  is, for instance, a gas-powered combustion engine that rotates an output shaft  140  when enabled. The output shaft  140  rotates a rotor of the alternator  115 . The rotating rotor induces an AC output from a stator of the alternator  115 . The AC output by the alternator  115  is received by the rectifier  120 . 
     The rectifier  120  converts the AC power received from the alternator  115  to DC power. The DC power is output from the rectifier  120  to the inverter  130 . The battery  125  is coupled in parallel between the rectifier  120  and inverter  130 . That is, a positive terminal of the battery  125  is coupled to a positive output of the rectifier  120  and to a positive input of the inverter  130 , and a negative terminal of the battery  125  is coupled to a negative output of the rectifier  120  and to a negative input of the inverter  130 . The inverter  130  inverts the DC power received from one or both of the rectifier  120  and battery  125  to AC power using, for instance, high-speed switching elements controlled by the controller  135  via inverter control signals. 
     The AC power output by the inverter  130  is received by an AC load  105 . The AC load  105  includes one or more AC-powered devices. The AC load  105  is coupled to the generator  100  via, for instance, a two or three-prong AC outlet on an outer casing of the generator  100 . In some instances, the generator  100  includes multiple AC outlets for separately coupling multiple AC loads  105  to the generator  100 . 
     The controller  135  monitors the battery  125  and load demand of the AC load  105 . The controller monitors the voltage level of the battery  125 . In some embodiments, the battery  125  has internal circuitry for monitoring its own voltage level and outputs a signal representative of its voltage level to the controller  135 . In other embodiments, the controller  135  directly measures the voltage and/or current level being output by the battery  125  to determine the battery level. The load demand of the AC load  105  is determined by, for example, the controller  135  monitoring the amount of current being drawn by the AC load  105 . The controller  135  also monitors the voltage level and frequency of the AC power output by the inverter  130 . 
     The controller  135  controls and is coupled to the engine  110  and alternator  115 . The controller  135  is operable to adjust a throttle of the engine  110  to control the speed thereof. For instance, the throttle is controlled by sending control signals to a stepper motor or other device that receives electrical control signals and provides mechanical control of a throttle. Additionally, the controller  135  controls the alternator  115  to function as a starter motor for the engine  110  to optionally start the engine without the use of a recoil. For instance, a starting circuit (not shown) coupling the battery  125  and the alternator  115  may be selectively enabled by the controller  135  to provide power from the battery  125  to the stator of the alternator  115 . The power received by the stator causes rotation of the rotor of the alternator  115 , which is coupled to the output shaft  140  of the engine  110 . Rotation of the output shaft  140  along with opening the throttle to provide fuel to the engine  110  enables starting of the engine  110 . In some embodiments, a pull or recoil starter or separate electric motor starter (not combined with the alternator) is provided in place of or in addition to the aforementioned electronic starting system. 
     In addition, in some embodiments, the controller  135  induces a wireless receiver  145  for receiving control signals from a remote transceiver  150 . The remote transceiver  150  is operable to send control signals to the controller  135 . Example control signals include an on/off signal to selectively turn the inverter generator on and off and a sleep timer to turn off the inverter generator after a predetermined amount of time. 
     The controller  135  includes or is connected to a memory such as RAM and ROM and executes software that can be stored in the RAM (particularly during execution), the ROM (on a generally permanent basis), or another non-transitory computer readable medium such as other memory or disc. If necessary, the controller can be connected to such memory or a disc drive to read such software. In some embodiments, the controller is a microcontroller, microprocessor, field programmable gate array (FPGA), application specific integrated circuit (ASIC), or other programmable device with suitable memory and I/O devices. 
     In some embodiments, a DC load (not shown) is coupled to the DC output of the rectifier  120  and battery  125 . In some instances, a DC-to-DC converter is coupled between the DC load and the DC output of the rectifier  120  and battery  125  to condition the DC power to an appropriate level. 
       FIG. 2  depicts the battery  125  in greater detail. The battery  125  includes one or more battery cells  155 , battery charging, discharging, and protection circuitry (battery circuitry)  160 , and terminals  165 . In some instances, the battery circuitry  160  is external to the battery  125  and, in some cases, integrated with the controller  135 . The battery cells  155  include 45-60 lithium-ion cells generally outputting 180-300 V DC , which may be removable in some embodiments. Since the battery  125  has a relatively high DC output, the battery  125  is coupled to the inverter  130  without a boost circuit to boost the DC output of the battery  125 , such as a DC/DC or DC/AC/DC power converter. Lithium-ion cells have a faster charging capability, a smaller size, and a better power-to-weight ratio relative to lead acid or Ni-Cad batteries. In other embodiments, however, the battery  125  includes a different number of battery cells, a different type of battery cell, and a different voltage output. For instance, in some embodiments, lead acid, Ni-Cad, and other battery types are used to reduce costs. In some embodiments, if the battery  125  outputs a lower DC output, a boost circuit may be used to increase the DC input to the inverter  130 . The battery circuitry  160  includes charging circuitry for receiving DC power at the terminals  165  and providing charging power to the battery cells  155 . The battery circuitry  160  also includes discharging circuitry for providing DC power from the battery cells  155  to the terminals  165 . The discharging circuitry may include filtering circuitry to condition the output power to meet particular voltage, current, and noise specifications. The protection circuitry detects when the battery cells  155  are at or below a minimum threshold (“battery protection threshold”) and prevents further discharge of the battery cells  155 . Preventing further discharge prevents damage to the battery cells  155 . 
     The battery  125  also stabilizes DC output from the rectifier  120 . In some embodiments, the generator  100  includes a voltage regulator circuit (not shown) to provide additional regulation and stabilization of the DC output from the rectifier  120 . The voltage regulator circuit may be within the battery circuitry  160  or outside the battery  125 . 
     The battery  125 , which may include one or more batteries coupled in series and/or in parallel, is coupled to the hybrid inverter generator  100  using various techniques. For instance, in some embodiments, the battery  125  is built into the generator such that it is non-modular and not removable by the user. For instance, the battery  125  may be hard-wired to electrical terminals of the generator to prevent a user from removing the battery  125  during general use (e.g., without cutting wires or breaking soldered connections). In some embodiments, the hybrid inverter generator  100  includes one or more battery receptacles for selectively inserting one or more batteries  125  into the generator circuit shown in  FIG. 1 . In such embodiments, the receptacles and batteries have electrical contacts (i.e., electrical terminals) that are coupled when the battery is inserted into the receptacle. In some embodiments, a combination of one or more built-in batteries  125  and selectively inserted batteries  125 . The option to selectively insert batteries  125  enables a user to adjust the length of time that the hybrid inverter generator  100  is able to run by battery power alone and enables a user to charge one or more batteries  125  for other use (e.g., to provide power to battery-operated power tools). In instances with multiple batteries  125 , the batteries  125  may be referred to as a battery bank. 
     In some instances, multiple receptacles are used that receive the same battery type and size, that receive a unique battery type or size, that receive multiple battery types or sizes, or a combination thereof. In some embodiments, one or more battery receptacles are exposed on the outside of a housing of the generator to, for example, enable quick insertion and removal by a user. In some embodiments, one or more battery receptacles are placed within a housing of the generator  100 , for example, to protect the batteries  125  from the weather or other potential sources of damage. Additionally, in some embodiments, one or more external batteries  125  are coupled to the hybrid inverter generator  100  via cables attached to terminals (not shown) on the generator  100 . The external battery may be used in combination with the built-in batteries and selectively inserted batteries described above. In embodiments with multiple batteries  125 , the battery charging, discharging, and protection circuitry  160  may be shared by the multiple batteries  125 . However, in other embodiments, one or more of the batteries  125  each include separate battery charging, discharging, and protection circuitry  160 . 
     The hybrid inverter generator  100  uses the battery  125 , the engine  110 , and a combination thereof to generate and provide output power to the AC load  105 .  FIG. 3  includes a state diagram illustrating three modes of operation of the generator  100 . In a battery-only mode  200 , the engine  110  is disabled and the battery  125  provides the DC output to the inverter  130 . The battery-only mode  200  is used for low load demands and is generally the starting operational mode for the generator  100 . The generator  100  leaves the battery only mode  200  when 1) the battery  125  drops below a predetermined low battery threshold, or 2) the load demand of the AC load  105  increases above a medium or high level. If the battery  125  drops below a low battery threshold (e.g., below 10% of total battery capacity) or the load demand of the AC load  105  increases to a medium level, the generator  100  enters a battery charging mode  205 . In the battery charging mode  205 , the controller  135  detects the low battery situation and sends a start engine signal to the alternator  115 . The controller  135  also controls the throttle to maintain the engine  110  1) at a low or idling speed if the load demand of the AC load  105  is at a low level and 2) at a medium speed if the load demand of the AC load  105  is at a medium level. The generator  200  remains in the battery charging mode until either 1) the load demand changes to a high load or 2) the load demand changes to a low load and the battery  125  is charged above a charged battery threshold, which is generally above the low battery threshold (see, e.g.,  FIG. 6 ). In some embodiments, even after the battery has been charged above the charged battery threshold, the engine may continue to operate at a low or medium speed for a predetermined amount of time while the battery charging, discharging, and protection circuitry  160  prevents overcharging of the battery. 
     Regardless of whether the generator  100  is in the battery-only mode  200  or the battery charging mode  205 , the generator proceeds to the boost mode  210  if the load demand increases to a high load level (e.g., at start-up of a power tool or appliance). In the boost mode  210 , the engine  110  is turned on (if necessary) and controlled to operate at a high speed. Additionally, the battery  125  is controlled to discharge DC power. Thus, the DC power output by the rectifier  120 , which is generated by the engine  110  and alternator  115 , is boosted by the battery  125  to provide a boosted DC power level to the inverter  130 . The inverter  130  is, in turn, able to output more power to meet a higher load demand than otherwise possible with the engine  110  or battery  125  alone. 
     The generator  100  leaves the boost mode  210  upon a load decrease and returns to the battery charging mode  205 , as the battery  125  will likely need charging after being in the boost mode  210 . In some instances, however, after the load demand decreases to a low load level from the high load level, the generator  100  proceeds to the battery-only mode  200  if the battery  125  is above the low battery threshold. If, while in the boost mode  210 , the battery  125  is drained below the battery protection threshold and the protection circuitry of the battery circuitry  160  is activated, the engine  110  operates at a high speed and the battery  125  neither charges nor discharges. Rather, the battery  125  maintains its present level of charge until the generator  100  leaves the boost mode  210  and returns to the battery charging mode  205 . 
     When the load demand of the AC load  105  increases, the battery  125  is first used to meet the increase in load demand until the engine  110  can either be started (e.g., going from mode  200  to  205  or  210 ) or until the speed of the engine  110  is sufficiently increased (e.g., going from mode  205  to  210 ). Thus, the battery  125  enables the generator  100  to quickly react to and satisfy changes in load demand. As such, although the battery  125  is primarily charging in battery charging mode  205 , the battery  125  is also used to output power in certain instances while the generator  100  is in battery charging mode  205 . 
       FIG. 4  provides another state diagram illustrating four modes of operation of the generator  100 . In  FIG. 4 , the battery-only mode  200  and boost mode  210  operate as in  FIG. 3 , but the battery charging mode  205  is separated into two modes: battery charging, low load mode  205   a  and battery charging, medium load mode  205   b . In battery charging, low load mode  205   a , the engine is operating at a low or idling speed to charge the battery  125  and supply power to the low load demand of the AC load  105 . In battery charging, medium load mode  205   b , the engine is operating at a medium speed to charge the battery  125  and supply power to meet the medium load demand of the AC load  105 . In  FIG. 4 , the generator  100  switches between modes as a result of either the battery  125  being below a low battery threshold, above a charged battery threshold, or an increase or decrease in the load demand of AC load  105 . In contrast to the state diagram of  FIG. 3 , the generator  100  only switches to the boost mode  210  through the battery charging, medium load mode  205   b . In some embodiments, however, the generator  100  switches directly to the boost mode  210  upon detecting a high load demand of the AC load  105 , rather than first passing through battery charging, medium load mode  205   b . In some embodiments, even after the battery has been charged above the charged battery threshold while in low load mode  205   a , the engine may continue to operate at a low or medium speed for a predetermined amount of time while the battery charging, discharging, and protection circuitry  160  prevents overcharging of the battery. Additionally, in the modes of both  FIGS. 3 and 4 , when the load decreases below a load threshold that would necessitate switching modes, the hybrid inverter generator  100  uses a time delay before stepping down the power output in some embodiments. With this delay, the hybrid inverter generator  100  avoids switching between modes and adjusting engine speed unnecessarily when the load demand fluctuates above and below a load demand threshold. 
       FIG. 5  illustrates a method  300  of controlling a hybrid generator, such as generator  100 , according to some embodiments of the invention. In step  305 , the generator  100  is enabled, for example, by depressing a power-on button, toggling an on/off switch, or through remote activation. Thereafter, the controller  135  determines the load demand of the AC load  105  (step  310 ). If the load demand is high, the controller  135  controls the generator  100  to operate in the boost mode  210  (step  315 ). If the controller  135  determines that the load demand is medium in step  310 , the controller  135  controls the engine  110  to operate at a medium speed (step  320 ) and the generator  100  to operate in the battery charging mode  205  (step  325 ), which is also referred to as the battery charging, medium load mode  205   b . If the controller  135  determines that the load demand is low in step  310 , the controller  135  determines the charge level of the battery  125  (step  330 ). If the charge level is below a low battery threshold, the controller  135  proceeds to step  335  and controls the engine  110  to operate at a low speed. Thereafter, the controller  135  controls the generator  100  to operate in the battery charging mode  205  (step  325 ), which is also referred to as the battery charging, low load mode  205   a . If the charge level is above a low battery threshold, the controller  135  proceeds to step  340  and controls the generator  100  to operate in the battery-only mode  200  (step  340 ). In some embodiments, the steps of method  300  are performed in a different order to achieve a similar functionality (e.g., to achieve the state diagrams of  FIG. 3  or  4 . 
       FIG. 6  illustrates a plot  400  of the state of charge of the battery  125  over time with an exemplary changing load demand of AC load  105 . At t=0, the battery  125  has a full charge and the AC load  105  has a low load demand. Thus, the generator  100  operates in a battery-only mode  200  and the battery discharges until t=A. At t=A, the charge of the battery  125  has dropped to the low battery threshold  405  and the generator  100  enters the battery charging, low load mode  205   a . Thus, the charge of the battery  125  increase as the engine  110  operates at a low speed. At t=B, the load demand increases to a medium load demand. The generator  100  then enters the battery charging, medium load mode  205   b , which continues to charge the battery  125  as the engine  110  operates at a medium speed. At t=C, the load demand increases to a high load demand. The generator  100  enters the boost mode  210 , which discharges the battery  125  and operates the engine  110  at a high speed. At t=D, the charge of the battery  125  has reached a battery protection threshold and the battery circuitry  160  prevents further discharge of the battery  125 . Although not depicted in  FIG. 6 , if after t=A, the charge of the battery  125  reached the charged battery threshold while the load demand was low, the generator  100  would return to the battery-only mode  200  and the engine  110  would be turned off. 
       FIGS. 7A-C  depict exemplary hybrid inverter generators  100   a ,  100   b , and  100   c , respectively, each with different power ratings (e.g., 1000 Watts, 2000 Watts, and 3000 Watts). The generator  100   a  is lighter than the generators  100   b  and  100   c  and includes a carrying handle  500   a . The generators  100 B and  100 C include push handles  505   b  and  505   c  and wheels  510   b  and  510   c , respectively. The generators  100   a ,  100   b , and  100   c , also include a control panel with outlet(s)  515   a ,  515   b , and  515   c , respectively; a recoil starter  520   a ,  520   b , and  520   c , respectively; and fuel caps  525   a ,  525   b , and  525   c , respectively, for covering access to internal fuel tanks. The generators  100   a ,  100   b , and  100   c  also use internal cooling techniques, such as fans, heat sinks, cooling air flow paths, etc., to maintain the generators  100   a ,  100   b , and  100   c  within proper operational temperatures. 
     In the case of a DC output and DC load coupled to the generator  100 , the controller  135  considers the total load demand (load demand of AC load and DC load) of the generator  100  for the state diagrams of  FIGS. 3 and 4  and the method of  FIG. 5 . In some embodiments, the generator  100  includes an AC or DC power-in cable or outlet to receive power to charge the battery  125 . This enables charging of the battery  125  without starting the engine  110 . 
     In some embodiments, the generator  100  includes a physical switch to prevent the use of engine  110 . This switch enables the generator  100  to rely solely on the battery  125  to produce power, which may be desirable in indoor areas or areas where very low noise operation is desired. In some embodiments, one or more additional physical switches or other inputs enable a user to particularly select one of the generator  100  operation modes  200 ,  205 , and  210 , overriding the automatic mode selection by the controller  135 . 
     Although the modes of the generator  100  were described above as having three discrete engine speeds and load demand levels and three or four discrete operation modes, additional discrete modes, engine speeds, and load demand levels are used in other embodiments. For example, instead of low, medium, and high engine speeds, the controller  135  is operable to adjust the engine  110  to additional speeds to more precisely meet various load demands (e.g., in modes  205  and  210 ). 
       FIG. 8  depicts a hybrid inverter generator  550  that is similar to the hybrid inverter generator  100 , but replaces the engine  110 , alternator  115 , and rectifier  120  with fuel cells  555 . Unless otherwise specified herein, components of the hybrid inverter generator  550  with the same element numbers as the hybrid inverter generator  100  generally operate in the same manner. The fuel cells  555  output DC power to the battery  125 , similar to how the rectifier  120  outputs DC power to the battery  125 . The controller  135  communicates with the fuel cells  555  to monitor and control the generation of DC power, rate of fuel consumption, etc., similar to how the controller  135  controls the generation of AC power and engine speed of engine  110  in the hybrid inverter generator  100  of  FIG. 1 . For instance, as the controller  135  adjusts the engine rate of speed in the various modes to meet changing load demands (see, e.g.,  FIGS. 3-6 ), the controller  135  also controls the fuel cells  555  to adjust their power output level according to the various modes. 
     The fuel cells  555  include one or more electrochemical cells that generate DC power from a chemical reaction between a fuel and an oxidant. In some embodiments, the fuel cells  555  are hydrogen fuel cells that use hydrogen as a fuel and oxygen as an oxidant. In some embodiments, other fuel types (e.g., hydrocarbons or alcohols) and oxidant types (e.g., chlorine or chlorine dioxide) are used. 
     Thus, the invention provides, among other things, a hybrid engine and battery generator and a method of operating the same. The various modes of operation offer flexibility in power output and noise levels of the generator. Various features and advantages of the invention are set forth in the following exemplary claims. These claims describe various embodiments of the invention, but the invention may include additional embodiments not claimed herein.