Abstract:
A portable power supply apparatus is provided having reduced impedance losses. The portable power supply apparatus is comprised of: a portable housing; a battery system residing in the housing; and an inverter circuit residing in the housing. The battery system generates a direct current (DC) voltage having a magnitude greater than or equal to a peak value of a desired alternating current (AC) voltage. The inverter circuit receives the DC voltage directly from the battery system, converts the DC voltage to an AC output voltage and outputs the AC output voltage to one or more outlets exposed on an exterior surface of the portable housing.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 14/673,356, filed Mar. 30, 2015, and a continuation of Ser. No. 12/917,128 filed on Nov. 1, 2010 now issued, which is a continuation-in-part of U.S. patent application Ser. No. 12/037,290 filed on Feb. 26, 2008 now issued. The disclosures of the above applications are incorporated herein by reference in their entirety. 
     
    
     FIELD 
       [0002]    The present disclosure relates to power supplies and more particularly to a portable alternating current (AC) inverter having reduced impedance losses. 
       BACKGROUND 
       [0003]    Portable power supplies such as internal combustion engine (ICE) generators may be used to power remote devices. For example, portable power supplies may be used at construction sites to power tools when no electrical power is available. Typical portable power supplies, however, may be too heavy and/or may generate an insufficient amount of power. For example, a single worker may be required to transport a portable power supply around a construction site and possibly between levels of a building (e.g., via a ladder). As the power generation of a portable power supply increases, however, the weight also increases. Specifically, larger generating devices (e.g., engines/alternators) may be required to provide adequate power to the point of use. 
         [0004]    The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure. 
       SUMMARY 
       [0005]    A portable power supply apparatus is provided having reduced impedance losses. The portable power supply apparatus is comprised of: a portable housing; a battery system residing in the housing; and an inverter circuit residing in the housing. The battery system generates a direct current (DC) voltage having a magnitude greater than or equal to a peak value of a desired alternating current (AC) voltage. The inverter circuit receives the DC voltage directly from the battery system, converts the DC voltage to an AC output voltage and outputs the AC output voltage to one or more outlets exposed on an exterior surface of the portable housing. 
         [0006]    According to other features, the portable power supply apparatus may have a weight and output electrical power at a power-to-weight ratio greater than 50 watts (W) per pound. In other features, the portable power supply apparatus may weigh between 20 and 50 pounds. In other features, the portable power supply apparatus may generate greater than or equal to 1500 W of continuous power and/or greater than or equal to 3000 W of peak power. 
         [0007]    Further areas of applicability of the present disclosure will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the disclosure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein: 
           [0009]      FIG. 1A  is a functional block diagram of a portable alternating current (AC) power supply according to the prior art; 
           [0010]      FIG. 1B  is a functional block diagram of a portable AC power supply according to one implementation of the present disclosure; 
           [0011]      FIG. 2A  is a view of a portable AC power supply system according to one implementation of the present disclosure; 
           [0012]      FIG. 2B  is a functional block diagram of the portable AC power supply system according to one implementation of the present disclosure; 
           [0013]      FIG. 3A  is a schematic of an AC power supply module according to one implementation of the present disclosure; 
           [0014]      FIG. 3B  is a schematic of an AC power supply module having a cluster control architecture according to one implementation of the present disclosure; 
           [0015]      FIG. 3C  is a schematic of an AC power supply module having inverter control architecture according to one implementation of the present disclosure; 
           [0016]      FIG. 4A  is a schematic of an inverter according to one implementation of the present disclosure; 
           [0017]      FIG. 4B  is a schematic of an inverter according to another implementation of the present disclosure; 
           [0018]      FIGS. 5A-5D  are graphs of various AC output power waveforms according to various implementations of the present disclosure; 
           [0019]      FIG. 6A  is view of the portable AC power supply system having a display according to one implementation of the present disclosure; 
           [0020]      FIG. 6B  is a view of the portable AC power supply system having various transport features according to one implementation of the present disclosure; 
           [0021]      FIG. 7A  is a view of the portable AC power supply system having an external internal combustion engine (ICE) generator according to one implementation of the present disclosure; 
           [0022]      FIG. 7B  is a view of the portable AC power supply system having an integrated ICE generator according to one implementation of the present disclosure; 
           [0023]      FIG. 8  is a functional block diagram of an ICE generator according to one implementation of the present disclosure; 
           [0024]      FIG. 9  is a functional block diagram of the portable AC power supply system having a direct feed-through of an external AC power source according to one implementation of the present disclosure; 
           [0025]      FIG. 10A  is a functional block diagram of the portable AC power supply system, the ICE generator, and a remote device, each having remote monitoring and/or remote control features via radio frequency (RF) communication according to one implementation of the present disclosure; 
           [0026]      FIG. 10B  is a flow diagram of a method for remote monitoring and control of the ICE generator according to one implementation of the present disclosure; 
           [0027]      FIG. 11A  is a functional block diagram of a plurality of portable AC power supply systems capable of charging via a single ICE generator according to one implementation of the present disclosure; and 
           [0028]      FIG. 11B  is a flow diagram of a method for monitoring and controlling charging of a plurality of portable AC power supply systems according to one implementation of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0029]      FIG. 1A  illustrates a portable alternating current (AC) power supply  10  according to the prior art. Specifically, portable AC power supply  10  includes an AC to direct current (DC) charger  12  that charges a low voltage battery bank  14  via a power source. The low voltage battery bank  14  supplies a low DC voltage to a low voltage DC to high voltage DC booster  16 . For example, the low voltage battery bank  14  may be a large lead-acid battery that supplies a low DC voltage of 12V or 24V. The low voltage DC to high voltage DC booster  16  boosts the low DC voltage to a high DC voltage. A high voltage DC to AC inverter  18  then converts the high DC voltage to a desired AC output voltage. For example, the desired AC output voltage may be 120V. 
         [0030]    A typical commercially available inverter  19  may include a combination of the low voltage DC to high voltage DC booster  16  connected before the high voltage DC to AC inverter  18 . In other words, the low voltage DC to high voltage DC booster  16  may operate continuously to boost the low DC voltage to the high DC voltage. The low voltage DC to high voltage DC booster  16  may require a large amount of current and will have large power losses (i.e., P=I 2 ×R). Therefore, larger/thicker components may be required to decrease losses due to high impedance, which in turn increases the weight of the portable AC power supply  10 . 
         [0031]      FIG. 1B  illustrates a portable AC power supply  20  according to one implementation of the present disclosure. Specifically, portable AC power supply  20  includes an AC to DC charger  22  that selectively charges a high voltage battery bank  26  via a power source. In some embodiments, the portable AC power supply  20  may also include a high voltage DC booster  24  between the power source and the high voltage battery bank  26  when a voltage greater than the voltage supplied by the power source is required. 
         [0032]    The high voltage battery bank  26  may include a plurality of batteries that collectively generate a high DC voltage. For example, the high DC voltage may be greater than 178V. The plurality of batteries may include, but is not limited to, lithium-based batteries, zinc-based batteries, and/or potassium-based batteries. In one implementation, for example only, the high voltage battery bank  26  may include two banks of batteries connected in parallel, each bank having 60 lithium phosphate batteries connected in series, the high voltage battery bank  26  generating approximately 200V DC (e.g., 3.3V per cell×60 cells=198V). A high voltage DC to AC inverter  28  then converts the high DC voltage to a desired AC output voltage. For example, the desired AC output voltage may be 120V. Alternatively, for example, the desired AC output voltage may be 240V. 
         [0033]    The portable AC power supply  20  requires much less current to operate compared to the continuously running low voltage DC to high voltage DC booster  16  of  FIG. 1A . Therefore, connectors and cables may be thinner/smaller, which in turn decreases the weight of the portable AC power supply  20 . For example, the portable AC power supply  20  may weigh between 20 and 50 pounds. In some implementations, the portable AC power supply  20  may weigh approximately 35 pounds. 
         [0034]    Furthermore, the high voltage DC to AC inverter  28  is not a typical inverter configuration as shown in  FIG. 1A  (i.e., booster→inverter). Rather, the high voltage battery bank  26  directly supplies the high DC voltage to the high voltage DC to AC inverter  28 . The portable AC power supply  20 , therefore, may generate more output power than typical portable AC power supplies while weighing less than typical AC power supplies. For example only, the portable AC power supply  20  may generate greater than or equal to 1500 watts (W) continuous power. Additionally, the portable AC power supply  20  may generate greater than or equal to 3000 W of peak power. Therefore, the portable AC power supply  20  may have a power-to-weigh ratio of approximately 50 W per pound, and in some implementations greater than 100 W per pound. 
         [0035]      FIG. 2A  illustrates an outer view of an example portable AC power supply system  40 . The portable AC power supply system  40  includes an enclosure  42  that houses an AC power supply module (not shown). The AC power supply module within the enclosure selectively charges a battery system via the AC source connector and an external AC power source. The battery system provides a high DC voltage which is converted to a desired AC voltage (e.g., 120V) by an inverter. Therefore, the AC power supply module is capable of providing AC power to remote devices while the battery system has sufficient charge. 
         [0036]    The enclosure  42  allows the system  40  to be portable. For example, the portable AC power supply system  40  may be transported around a construction site. The enclosure  42  further includes an AC source connector  44  and outlets  46 ,  48  on its surface that interface with the AC power supply module. The AC source connector  44  (e.g., a standard three prong plug) allows the portable AC power supply system  40  to connect to an external AC power source. For example, the external AC power source may be an internal combustion engine (ICE) generator capable of 1000 W output power and weighing approximately 35 pounds. The external AC power source, however, may also be a different size/type of generator, a standard wall outlet, a thermal diode, a fuel cell, a solar panel, a wind turbine, etc. The outlets  46 ,  48  allow devices (e.g., power tools) to receive AC power at remote locations. For example, the outlets  46 ,  48  may be standard three prong outlets. 
         [0037]    Referring now to  FIG. 2B , a functional block diagram of the example portable AC power supply  40  is shown. The portable AC power supply  40  includes the AC source connector  44 , outlets  46 ,  48 , and the AC power supply module  50 . The AC power supply module  50  includes a power supply module  52 , a control module  54 , a battery system  56 , and an inverter  58 . For example, the inverter  58  may be inverter  28  shown in and described with respect to  FIG. 1B . 
         [0038]    The power supply module  52  receives AC input (V IN ) from an external power source (e.g., ICE generator). The power supply module  52  converts the AC input into DC power to power the control module  54  and for recharging the battery system  56 . The control module  54  selectively controls recharging of the battery system  56 . More specifically, the control module  54  enables charging of the battery system  56  when a charge level is less than a threshold. Similarly, the control module  54  may disable charging of the battery system  56  when the charge level is greater than a threshold to prevent overcharging. The portable AC power supply  40 , however, may also generate output power independently of an external power source (i.e., when not connected to an external power source) using the battery system  56 . Additionally, the battery system  56  may include replaceable batteries. In other words, individual batteries, battery banks, or the entire battery system  56  may be removed and easily replaced with a fully-charged spare unit (i.e., “hot swappable”). For example, replaceable batteries may provide for extended operation without charging via an external AC source. 
         [0039]    The battery system  56  supplies a DC voltage to the inverter  58 . Specifically, the control module  54  controls discharging of the battery system  56  which supplies the DC voltage to the inverter  58 . The inverter  58  converts the DC voltage to a desired AC voltage to output via outlets  46 ,  48 . For example, the desired AC voltage may be 120V. The control module  54  may also control operation of the inverter  58 . For example, the control module  54  may control switching frequencies of the inverter  58  thereby controlling a shape of the output waveform. The control of the inverter  58  is described in more detail later. 
         [0040]    Referring now to  FIG. 3A , an example of the AC power supply module  50  is shown. The battery system  56  includes a plurality of battery banks B 1 -B N . Each of the battery banks B 1 -B N  includes a battery cell B C , a switch B SR , a resistor B R , and a battery control module B CC . For example, the switch B SR  may be a semiconductor-based transistor. The resistor B R  may also be referred to as a current sensor. The battery control module B CC  receives information from the current sensor B R  to control switching of the switch B SR . The battery control module B CC , however, may also receive other information, such as control signals from the control module  54  or information regarding other battery banks. 
         [0041]    The power supply module  52  receives AC input from an AC source via the AC source connector  44 . For example, the AC source may be a small ICE generator. Additionally, for example, the AC source connector  44  may be a standard three prong plug that connects to the AC source. The power supply module  52  converts the AC input to DC power for powering the control module  54  and for recharging the battery banks B 1 -B N . The control module  54  controls the charging of the battery banks B 1 -B N  via the DC power generated by the power supply module  52 . Specifically, the power supply module  52  may provide DC power to current sources I 1 -I N  which selectively supply current to the battery banks B 1 -B N , respectively, based on control from the control module  54 . 
         [0042]    The control module  54  also controls discharging of the battery banks B 1 -B N  to the inverter  58 . The series connection between the battery banks B 1 -B N  allows the control module  54  to supply a high DC voltage to the inverter  58 . Different numbers of battery banks may be implemented depending on the application. Similarly, different numbers of battery cells may be implemented in the battery banks depending on the application. The DC voltage supplied to the inverter  58 , however, should be greater than a peak voltage of a desired AC voltage output. In other words, for example, the DC voltage supplied to the inverter  58  should be approximately 178V for a desired 120V AC output. 
         [0043]    The inverter  58  converts the high DC voltage supplied via the battery cells B 1 -B N  to an AC voltage. For example, the inverter  58  may convert the high DC voltage to 120V AC at a frequency between 50 and 60 hertz (Hz). The inverter  58 , however, may also convert the high DC voltage to a different AC voltage having a different magnitude or frequency. When generating 120V AC, the power output of the inverter  58  may be greater than or equal to 1500 W continuous or 3000 W peak. The outlets  46 ,  48  may output the power generated by the inverter  58  to one or more remote devices (e.g., power tools). For example, the outlets  46 ,  48  may receive a standard three prong plug. 
         [0044]    The control module  54  may also communicate with the inverter  58 . Specifically, the control module  54  may monitor operation of the inverter. Based on the monitoring and/or other parameters (e.g., battery charge level, current flow, etc.), the control module  54  may control the inverter  58 . More specifically, the control module  54  may control switching in the inverter  58  to shape the AC sine wave approximation output by the inverter  58 . In other words, the AC sine wave output by the inverter  58  may be a square wave having a plurality of steps to achieve an approximate shape based on a desired amplitude and frequency. 
         [0045]    For example, as the battery charge level decreases the control module  54  may command the inverter  58  to increase the duty cycle of the inverter  58  effectively “stretching” the AC sine wave. The purpose of stretching the AC sine wave is to maintain a desired root-mean-squared (RMS) voltage output by the inverter  58  while having a lower DC voltage input to the inverter  58 . Specifically, the control module  54  may increase a duty cycle of the inverter  58  to adjust the output AC sine wave to maintain desired RMS accuracy. 
         [0046]      FIG. 3B  illustrates an example of the AC power supply module  50  having a cluster control architecture. Similar to  FIG. 3A , the power supply module  52  receives AC input power via the AC source connector  44 . For example, the AC source connector  44  may be a standard three prong plug that connects to an external AC source (e.g., an ICE generator). The power supply module  52  converts the AC input to DC power for powering a control module  54  and for recharging the battery system  56 . 
         [0047]    The battery system  56  is divided into a plurality of battery cells B C . Specifically, the battery cells B C  may be grouped in clusters C 1 -C N  each controlled by a cluster control module CCM 1 -CCM N , respectively. For example, cluster C 1  may include four pairs of discrete battery cells B C  connected in parallel and four transistors T S  connected across the terminals of each pair of battery cells B C . While four pairs of battery cells B C  are shown connected in parallel, other numbers of battery cells and other configurations may be implemented. The battery system  56  may also include diverting (i.e., bypass) circuitry used for charge balancing. For example, the control module  54  may control the diverting circuitry to bypass a battery cell/cluster when the corresponding charge level of a given cell/cluster exceeds a predetermined threshold. 
         [0048]    The transistors T S  are controlled by a respective cluster control module CCM 1 -CCM N , hereinafter referred to as CCM. The cluster control module CCM may control respective transistors T S  to prevent overcharging of respective battery cells B C . Specifically, the cluster control module CCM may switch transistor T S  to shunt current flow through transistor T S  effectively holding the voltage across corresponding battery cells B C . Additionally, the cluster control module CCM may communicate with the control module  54  to have the control module  54  reduce a current supply I Φ  to prevent overcharging of the battery cells B C . 
         [0049]    The inverter  58  converts the high DC voltage supplied via the battery cells B C  to an AC voltage. For example, the inverter  58  may convert the high DC voltage to 120V AC at a frequency between 50 and 60 hertz (Hz). The inverter  58 , however, may also convert the high DC voltage to a different AC voltage having a different frequency. When generating 120V AC, the power output of the inverter  58  may be greater than or equal to 1500 W continuous or 3000 W peak. The outlets  46 ,  48  may output the power generated by the inverter  58  to one or more remote devices (e.g., power tools). For example, the outlets  46 ,  48  may receive a standard three prong plug. 
         [0050]    The control module  54  may also receive temperature measurements of the battery cells B C . The temperature measurements may be generated by a battery temperature module  55 . For example, the battery temperature module  55  may include one or more temperature sensors that monitor temperature of one or more of the battery cells B C , respectively. The control module  54  may also communicate with the inverter  58  and send commands to control the inverter  58  as previously described with respect to  FIGS. 2B and 3A  and as further described later. 
         [0051]      FIG. 3C  illustrates an example of the AC power supply module  50  having an inverter control architecture and other additional features. A line filter  60  removes noise from AC input via the AC source connector  44 . A rectifier  62  converts the filtered AC to DC. A power factor correction (PFC) module  64  maintains an input power factor close to unity for the most efficient utilization of the AC input. The PFC stage may alternately be designed to directly produce/regulate the output DC current to the appropriate voltage/current level. This constant current/voltage output may be used to charge one or more of the battery banks B 1 -B N  and/or provide power to the inverter  58 . 
         [0052]    The PFC module  64  may interface with a solar panel via a solar connection module  65 . The solar panel may provide for solar charging of the battery system  56 . For example, the PFC module  64  may include an algorithm for maximum power point tracking (MPPT) for operating the solar panel. The MPPT algorithm, however, may be located and executed elsewhere such as in the solar connection module  65  or in an external solar panel control module (not shown). Specifically, the MPPT algorithm provides for control of electrical operating points of photovoltaic (PV) modules in the solar panel to maximize capturing of solar power. The PFC module  64  may also interface with a wind turbine via a wind connection module  67 . The wind turbine may provide for wind-based charging of the battery system  56 . The PFC module  64  may also include additional components that perform other features described in detail later such as adjusting the input load. 
         [0053]    The inverter  58  converts DC voltage received from the DC-DC converter  66  and/or the battery banks B 1 -B N  to an output AC voltage. For example, the inverter may generate a desired AC voltage having a magnitude of 120V. The inverter  58  is controlled by an inverter control module  68 . Specifically, the inverter control module  68  may monitor the peak of the AC voltage generated by the inverter  58  and control the inverter  58  accordingly. For example, when the peak of the AC voltage generated by the inverter  58  is less than the desired AC output voltage, the inverter control module  68  may increase a duty cycle of the inverter  58  to maintain a desired RMS voltage. The inverter  58  may output the AC voltage to a circuit breaker  72 . The circuit breaker  72  may interrupt the flow of current to prevent damage to components connected via outlets  46  or  48 . For example, the circuit breaker  72  may be a resettable circuit breaker. A diagnostic module  74  may include additional circuitry for providing current output information to the inverter control module  68  and/or a battery management module  70 . 
         [0054]    The battery management module  70  controls the battery system  56  which includes battery banks B 1 -B N . The battery banks B 1 -B N  may be connected in series. The battery management module  70  also communicates with the inverter control module  68 . For example, the inverter control module  68  may notify the battery management module whether the inverter  58  is on or off, whether a load is connected to the inverter  58  via outlets  46  and/or  48 , etc. Based on this information, the battery management module  70  may turn off the DC-DC converter  66 , request a low current output, or request a high current output. 
         [0055]    The battery management module  70  may be connected to a display  80 . The display  80  may provide information to a user. For example, the information may include, but is not limited to a charge level of the battery system  56 , a load connected to the system, an output voltage of the system, whether or not the system is connected to a charger, etc. The battery management module  70  may also be connected to an input/output (I/O) port  84 . For example, the I/O port may provide for connection to a computer or other suitable device for software programming and/or downloading of data for analysis. Lastly, the battery management module  70  may have security via a lock input  82 . For example, the lock input  82  may require a user to verify his or her identity (e.g., a fingerprint) before using the system. 
         [0056]    The system may also provide 12V DC power via an alternate outlet  90  using the battery system  56  or AC source power (i.e., when AC source power is connected). Specifically, a semiconductor switch  88  may be used to switch between powering a 12V DC converter  89  from AC power or the battery system  56 . For example, the alternate outlet  90  may be a cigarette lighter-type outlet. Another semiconductor switch  86  may be disposed between switch  88  and the battery system  56 . Switch  86  may be controlled by the battery management module  70 . For example, the battery management module  70  may open switch  86  to prevent over-discharge of the battery system  56 . 
         [0057]    A heat source  92  may be implemented for warming of the battery system  56 . For example, the heat source  92  may be heat tape or blankets. Warming the battery system  56  may allow operation during colder temperatures. Similarly, a cooling source  93  may be implemented for cooling of the battery system  56 . For example, the cooling source  93  may be a fan. Cooling the battery system  56  may prevent overheating. An auxiliary output  94  may provide for powering of audio/visual (A/V) devices such as a radio or a television. A charger module  96  may be used to charge additional battery packs. For example, removable/swappable battery packs from power tools may be charged via the charger module  96 . Lastly, a lamp  98  may be implemented. For example, the lamp may include a bulb and a reflector disposed within a housing. The lamp  98  may be used to illuminate a work area. 
         [0058]      FIG. 4A  illustrates an example of the inverter  58  that may generate a pure sine waveform as depicted in  FIG. 5A . Specifically, the inverter  58  may include a full H-bridge with a passive filtered output. A control module  100  may control switching of four transistors via pulse-width modulated (PWM) control signals. For example, the control module  100  may control the transistors such that a full positive battery voltage or a full negative battery voltage is applied to the output V OUT . The output V OUT , however, is also filtered to smooth voltage steps and thus can be a pure sine wave. Specifically, the filter includes a passive LC filter that includes an inductor and a capacitor connected in series with the output V OUT . 
         [0059]      FIG. 4B , on the other hand, illustrates another example of the inverter  58  that is capable of generating the square and modified square waveforms of  FIGS. 5B-5D . The inverter  58  may be generally described as an H-bridge with a polarity inverter (i.e., two H-bridges having opposing polarities). Specifically, the inverter  58  may include an isolated step-down converter module  120  having a voltage controlled output. The inverter  58  may also include a control module  110  which receives inputs from the inverter control module  68  and/or the battery management module  70 . 
         [0060]    The control module  110  may switch various transistors connected to the DC input and/or the output of the step-down converter module  120 . For example, the transistors may be insulated-gate bipolar transistors (IGBTs). Specifically, the control module  110  may switch the transistors in a specific order to create a desired output AC waveform. The inverter  58  may manipulate the shape of the output waveform as previously described herein to generate the waveforms depicted in FIGS.  5 B- 5 D. The modified sine wave of  FIG. 5D  represents an approximation of a desired AC voltage resembling the pure sine wave of  FIG. 5A . 
         [0061]    Referring now to  FIG. 6A , an example outer view of the portable AC power supply system  40  is shown. Specifically, the system  40  may include the AC power supply module  50  as shown in and described with respect to one of  FIGS. 3A-3C . The enclosure  42  may further include a display  200  for displaying information about the system  40 . In some embodiments, the display  200  may be the display  80  of  FIG. 3C . For example, the display  200  may display information that includes, but is not limited to, a charge level of the battery system  56 , a load connected to the system, an output voltage of the system, whether or not the system is connected to a charger, etc. 
         [0062]      FIG. 6B  illustrates a side view of the system  40  having various transport features. For example, the system  40  may include a handle  210  for carrying the system  40 . Additionally or alternatively, for example, the system  40  may include a strap  220  for carrying the system  40 . For example only, two straps  220  may be implemented to allow the system  40  to be carried on one&#39;s back in compliance with the Occupational Safety and Health Administration (OSHA) standards (e.g., transport up a ladder). The system  40  may also include other suitable features for carrying or transporting the enclosure, such as a cart, wheels, etc. 
         [0063]      FIG. 7A  illustrates an outer view of the system  40  connected to an internal combustion engine (ICE) generator  250  via the AC source connector  44 . While an ICE generator  250  is shown, the system  40  may also be connected to another power source such as a fuel cell, a thermal diode, a solar panel, a wind turbine, or a different type of engine/generator. For example only, the ICE generator  250  may generate approximately 1000 W of power and may weigh approximately 35 pounds. The ICE generator  250  may be also be carried or transported along with the enclosure  42  as shown in  FIG. 7B . Alternatively, the two may be carried separately. For example, one person may carry the system  40  in one hand and the ICE generator  250  in his or her other hand. The ICE generator  250  may supply the power supply module  52  with the input AC voltage for recharging the battery cells and/or powering the control module  54 . 
         [0064]      FIG. 8  illustrates an example of the ICE generator  250 . The ICE generator  250  may include a fuel supply  260 , a fuel level sensor  265 , an internal combustion engine (ICE)  270 , an electric generator  280 , and a control module  290 . The fuel supply  260  supplies the ICE  270  with fuel (e.g., gasoline). The fuel level sensor  265  measures a level of fuel contained in the fuel supply  260 . The ICE  270  combines the fuel with air and combusts the air/fuel mixture within cylinders to generate drive torque. For example, the ICE  270  may be started automatically using suitable systems such as a starter or an ignition module. The drive torque generated by the ICE  270  is converted to electrical energy by the generator  280 . The generator  280  may output the electrical energy as an AC voltage V OUT . The control module  290  controls operation of the ICE generator  250 . Specifically, the control module  290  controls start/stop operations of the ICE  270 . Additionally, the control module  290  may also monitor the fuel level using the fuel level sensor  265 . Furthermore, the control module  290  may transmit operational information to other components and/or receive commands from other components (described in more detail below). For example, the control module  290  may transmit a fuel level of the fuel supply  260  to other components such as the system  40  or a handheld monitoring device (described in more detail later). 
         [0065]    According to another feature, the system  40  may include a direct feed-through whereby the external AC power source is used as a main source of power.  FIG. 9  illustrates an example of the portable AC power supply system  40  having an AC power supply module  50  with a direct feed-through. Specifically, the external AC power source (e.g., a wall outlet or an ICE generator) provides power directly to the inverter  58  while the battery system  56  is selectively used when the external AC power source is insufficient or fails (e.g., a line dropout). For example, the control module  54  may monitor the external AC power source (e.g., via the power supply module  52 ) to determine when the external AC power source is insufficient or has failed. The control module  54  may then begin discharging the battery system  56  to power the inverter  58  and any components connected to outlets  46 ,  48 . Having the battery system  56  to power the inverter  58  during failure conditions provides for seamless transitions between power sources (i.e., no power outages). 
         [0066]    For example, the system  40  of  FIG. 9  may be implemented as immediate backup power in residential applications. The inverter  58  may also synchronize its output AC power with the external AC power. Specifically, the inverter  58  and the power supply module  52  may communicate to synchronize the output AC power to the external AC power. In other words, the output AC power of the inverter  58  may be in-phase with the external AC source. Having the inverter  58  in-phase with the external AC source may also provide for seamless transitions when the external AC source fails and the battery system  56  is then used. For example, the inverter  58  may send messages to the power supply module  52  requesting phase information of the external AC power, the power supply module may then send messages back to the inverter  58 , and the inverter  58  may then adjust a phase of the output AC waveform based on the received messages (including the requested phase information). 
         [0067]    Additionally, a plurality of systems  40  may be connected in parallel to provide increased power output. The outputs of each of the plurality of systems  40  may also be synchronized with each other to provide maximum power output. For example only, two systems  40  may be connected in parallel to generate greater than or equal to 6000 W of peak power (i.e., 3000 W×2 systems=6000 W). In some implementations, one of the plurality of systems  40  may act as a master with the remaining systems  40  acting as slaves (i.e., the master synchronizes the slaves to its output). For example, one of the plurality of systems  40  (“a slave system”) may send messages to another one of the plurality of systems  40  (“a master system”) requesting phase information of the output AC waveform of the master system. The master system may then send messages back to the slave system, and the slave system may then adjust a phase of its output AC waveform based on the received messages (including the requested phase information). Therefore, the slave system may synchronize its output to the output of the master system. 
         [0068]    According to another feature, the system  40  may automatically adjust the current drawn from the ICE generator  250 . In an exemplary embodiment, the control module  54  may variably control the current supplied by a charging circuit to the batteries and thereby control the current drawn from the ICE generator  250 . For example, the control module  54  may decrease a current drawn from the ICE generator  250  when the input AC waveform is sagging (i.e., drops below a threshold). In other words, the system  40  may decrease the current draw to prevent overloading of the external AC source (e.g., the ICE generator  250 ). For example only, if the ICE generator  250  is capable of generating 100 W and a standard current draw of the system is 1.5 amps (A), the charge range of the system  40  will be between 300 and 400 W (i.e., −180 V×1.5 A=360 W). Therefore, if not limited, the current draw of the system  40  could overload and damage the ICE generator  250 . These techniques for monitoring current draw and overload protection may be similarly applied to other external AC sources such as a solar panel or a wind turbine. 
         [0069]    Alternatively, the system  40  may transmit an inquiry to the ICE generator  250  as to how much power the ICE generator  250  can generate, and the system  40  may then adjust the current draw from the ICE generator based on the transmitted response from the ICE generator  250  (described in more detail later with respect to  FIGS. 10A-10B ). Additionally, a user may manually adjust the current draw of the system  40  from the ICE generator  250 . For example, the user may control a rotatable switch to select an input power to draw from the ICE generator (e.g., 250 W, 500 W, 750 W, 1000 W, etc.). The user may select an input power less than a maximum output power of the ICE generator  250  to allow the ICE generator  250  to power other components. 
         [0070]    According to another feature and as previously described, the system  40  may also have remote monitoring and/or control features. For example, a user may be working via an extension cord at a location far from the system  40  or on a different level of a building. Therefore, remote monitoring may allow the user to determine, for example, when the charge level of the battery system  56  is low. Additionally, remote control of the system  40  may also be beneficial. For example, when the charge level of the battery system  56  is low the user may remotely activate the ICE generator  250  to begin recharging the battery system  56 . Accordingly, remote monitoring and control of the system  40  may increase user efficiency which in turn may reduce costs. 
         [0071]      FIG. 10A  illustrates a functional block diagram of the system  40 , the ICE generator  250 , and the mobile device  300 . The system  40 , the ICE generator  250 , and the mobile device  300  are each capable of communicating via a radio frequency (RF) communication channel. For example, these components may communicate via the RF channel according to a suitable IEEE communication protocol (e.g., Bluetooth). The system, the ICE generator  250 , and the mobile device  300 , however, may also communicate using other suitable wireless communication methods and/or protocols. While each of the system  40 , the ICE generator  250 , and the mobile device  300  are shown to include two modules, each may further include additional modules or components such as those described herein. 
         [0072]    Specifically, the system  40  may include a communication module  305  that may transmit information (e.g., using a transceiver) to the mobile device  300  via the RF communication channel. For example, the information may include, but is not limited to, a charge level of the battery system  56 , a load connected to the system, an output voltage of the system, whether or not the system is connected to a charger, etc. Additionally, for example, the system may transmit fault conditions to the mobile device. The transmitted information may be received (e.g., using a transceiver) by a communication module  310  in the mobile device. The received information may be sent to a user interface module  320  which may then display the information to the user (e.g., via the display  275 ). In other words, the user may be located at a remote location with respect to the system  40  but may still monitor the system  40 . 
         [0073]    The user may also input commands (e.g., via a touchpad) to the user interface module  320 . The user interface module  320  may send the commands to the communication module  310  for transmission back to the system  40 . In other words, the user may command the ICE generator  250  via the mobile device  300 . For example, the user may start the ICE generator  250  when the charge level in the battery system is less than a first level (e.g., a critical threshold corresponding to the peak of the desired AC output). Similarly, for example, the user may stop the ICE generator  250  when the charge level of the battery system  56  is greater than or equal to a second level (e.g., full charge). 
         [0074]    The commands for the ICE generator  250  may be sent by the user (a “manual command”) using the mobile device  300  and relayed to the ICE generator  250  by system  40 . Additionally or alternatively, the system  40  may automatically send a command (an “automatic command”) to start/stop the ICE generator, such as when the system detects that the charge level of the battery system is less than a threshold. When the ICE generator  250  receives a command via communication module  330 , the communication module  330  may send the command to the control module  290 . The control module  290  may then start or stop the ICE generator  250  based on the received command. The control module  290  may also include sensors for measuring operating parameters. For example, the control module  290  may use the fuel level sensor  265  to measure an amount of fuel in the ICE generator  250  for transmission to the system  40  and/or the mobile device  300 . 
         [0075]      FIG. 10B  illustrates a method for remote control of the ICE generator  250 . While only remote control of the ICE generator  250  is described, other monitoring and control function may be implemented via communication across the RF communication channel. For example, the mobile device  300  may be used by a user for remote monitoring and/or control of the system  40  and/or the ICE generator  250 . For example, the method may be executed by the control module  54 . The method begins at  350 . At  350 , the control module  54  determines whether a command has been received to start/stop the ICE generator  250  (“a manual start/stop”). For example, the user may input the command to the user interface module  320  of mobile device  300  which may then transmit the command to the control module  54 . If true, the control module  54  may proceed to  358 . If false, the control module  54  may proceed to  354 . 
         [0076]    At  354 , the control module  54  may determine whether any fault conditions are present that require a start/stop operation of the ICE generator  250  (“an automatic start/stop”). For example, the control module  54  may determine whether a fuel level of the ICE generator  250  is less than a predetermined threshold. Alternatively, for example, the control module  54  may determine whether a charge level of the battery system  56  is less than a predetermined threshold. In some embodiments, the fuel level may be transmitted to the control module  54  by the ICE generator  250  (e.g., in response to a query). If true, the control module  54  may proceed to  358 . If false, the control module  54  may return to  350  (i.e., no manual or automatic start/stop operations). 
         [0077]    At  358 , the control module  54  transmits a command to communication module  330  to start/stop the ICE generator  250 . At  362 , the control module  290  determines whether the transmitted command was received (e.g., via communication module  330 ). If true, the control module  290  may proceed to  366 . If false, the control module  290  may return to  362 . At  366 , the control module  290  may start/stop the ICE generator  250  according to the received command. For example, the control module  290  may start/stop the ICE  270  via a starter or ignition module (previously described). The method may then return to  350 . 
         [0078]    According to another feature, the user may plug one or more portable AC power supply systems  40  into a single ICE generator  250  if more than one portable AC power supply system is needed at a jobsite. In a typical situation, an unequal amount of power may be drawn from these portable AC power supply systems. As an example, the user may plug two portable AC power supply systems  40  into the same ICE generator  250  for charging.  FIG. 11A  illustrates an example implementation of a system  400  having N portable AC power supply systems  40 - 1 ,  40 - 2 , . . . ,  40 -N (collectively referred to as “systems  40 ”) connected to a single ICE generator  250 . 
         [0079]    For example, portable AC power supply system  40 - 1  may have two power tools plugged into it that draw an average load of 2000 W. Since the ICE generator  250  can only supply a limited amount of charging power, the ICE generator  250  may not be able to charge all the systems  40  at full power. If each of the systems  40  monitors its own load and battery supply, the systems  40  can collectively determine which of the systems  40  should receive charge current and control their own charging accordingly. The following example shows how the inverters may decide how to control their individual charge. 
         [0080]    If system  40 - 2  is merely powering a light load (e.g., a light source) and has only ½ of its battery charge remaining, and system  40 - 1  (powering the large load power tools) still has ¾ of its charge remaining, the ICE generator  250  would ordinarily deliver more or an equal amount of power to the system  40 - 2 . However, since system  40 - 1  is supplying far more power, the battery in system  40 - 1  will run out of charge much sooner than system  40 - 2 . In the improved cooperative scenario, since system  40 - 2  can calculate its own remaining runtime and a remaining runtime of system  40 - 1 , system  40 - 2  will choose to forego charging so that system  40 - 1  can receive all of the power from the ICE generator  250 . This allows the systems  40  to optimize runtime of the entire system  400 . 
         [0081]      FIG. 11B  illustrates a method for monitoring and controlling charging of a plurality of systems  40 . For example, the method may be executed by one of the control modules  54  located in the various systems  40 . The method begins at  450 . At  450 , the control module  54  may determine whether a predetermined time has expired. For example, the control module  54  may determine whether a timer exceeds a predetermined time of 100 milliseconds. If true, the control module  54  may proceed to  454 . If false, the control module  54  may return to  450 . At  454 , the control module  54  may send its current draw (from the ICE generator  250 ) and its remaining capacity (in its battery system  56 ) to other the system(s)  40 . At  458 , the control module  54  may retrieve the current draw and remaining capacity from the other system(s)  40 . At  462 , the control module  54  may calculate an average current draw of the other system(s) during a period. For example, the period may be one minute. At  466 , the control module  54  may calculate a remaining runtime of the other system(s)  40  by dividing remaining capacity by average current draw. 
         [0082]    At  470 , the control module  54  may monitor its own current draw and remaining capacity. At  474 , the control module  54  may calculate its average current draw during a period (e.g., one minute). At  478 , the control module  54  may calculate its remaining runtime (e.g., remaining self capacity/average self current draw). At  482 , the control module  54  determines whether its remaining runtime is less than the remaining runtime(s) of the other system(s)  40 . If true, the control module  54  may proceed to  486 . If false, the control module  54  may proceed to  490 . At  486 , the control module  54  may draw all of the current from the ICE generator  250  to charge its battery system  56 . The method may then return to  400 . At  490 , the control module  54  may disable charging of its battery system  56 . All of the current from the ICE generator  250  may then be used to charge a battery system  56  of the system  40  having the shortest remaining runtime. The method may then return to  400 . 
         [0083]    In the previous examples, the systems  40  either chose to receive full charge or no charge. An alternative embodiment would allow the systems  40  to variably control the amount of current they each receive. Referring again to  FIG. 11A , system  40 - 2  may calculate that in order to allow itself and system  40 - 1  to run out of power at the same time (thus optimizing runtime of the system  400 ), that system  40 - 2  should receive 10% of the charging power to allow system  40 - 1  to receive 90% of the charging power. In some implementations, each of the systems  40  may vary an amount of charging power received from the ICE generator  250  by controlling respective internal charging circuits to vary charging of the respective battery systems  56 . Lastly, while examples power control distribution between two of the systems  40  were described herein, the same examples may be similarly applies to three or more of the systems  40 . 
         [0084]    The description herein is merely illustrative in nature and is in no way intended to limit the disclosure, its application, or uses. For purposes of clarity, the same reference numbers are used in the drawings to identify similar elements. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A or B or C), using a non-exclusive logical or. It should be understood that steps within a method may be executed in different order without altering the principles of the present disclosure. 
         [0085]    As used herein, the term module may refer to, be part of, or include an Application Specific Integrated Circuit (ASIC); an electronic circuit; a combinational logic circuit; a field programmable gate array (FPGA); a processor (shared, dedicated, or group) that executes code; other suitable components that provide the described functionality; or a combination of some or all of the above, such as in a system-on-chip. The term module may include memory (shared, dedicated, or group) that stores code executed by the processor. 
         [0086]    The term code, as used above, may include software, firmware, and/or microcode, and may refer to programs, routines, functions, classes, and/or objects. The term shared, as used above, means that some or all code from multiple modules may be executed using a single (shared) processor. In addition, some or all code from multiple modules may be stored by a single (shared) memory. The term group, as used above, means that some or all code from a single module may be executed using a group of processors. In addition, some or all code from a single module may be stored using a group of memories. 
         [0087]    The apparatuses and methods described herein may be implemented by one or more computer programs executed by one or more processors. The computer programs include processor-executable instructions that are stored on a non-transitory tangible computer readable medium. The computer programs may also include stored data. Non-limiting examples of the non-transitory tangible computer readable medium are nonvolatile memory, magnetic storage, and optical storage. 
         [0088]    The broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, the specification, and the following claims.