Abstract:
A photovoltaic power source for an electric automobile includes at least one window including a transparent photovoltaic cell; a DC-DC converter in electrical communication with the at least one window transparent photovoltaic cell; and a battery in electrical communications with the DC-DC converter.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of priority based on U.S. Provisional Patent Application No. 62/212,736 filed on Sep. 1, 2015, the entire disclosure of which is incorporated by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present disclosure relates generally to photovoltaic cell power systems and, more specifically, to photovoltaic cell power systems incorporated into automobile windows. 
         [0003]    Total electric automobiles are distance-limited both by the amount of charge the automobile can hold in its batteries beforeit needs to recharge and how fast the automobile draws on that charge. The amount of storage is limited by the size and capacity of the batteries. Larger capacity batteries carry more charge, but typically increase the weight of the automobile and this in turn requires the automobile motors to use more energy to move the automobile because of the extra mass. Therefore, rather than increasing the battery capacity, continuous charging of the batteries using photovoltaic cells has been considered to supplement the range of the electric automobile and to help avoid over-discharging the batteries. 
         [0004]    Experimental models of long distance, solar powered electric automobiles are generally single person vehicles having substantially the automobile&#39;s entire available surface covered with solar cells. In order to travel the furthest distance on a single charge, most experimental long distance, solar powered automobiles are designed for a single passenger to conserve weight and have an extreme aerodynamic profile configured to reduce drag on the automobile as it moves. These automobiles, although interesting technologically, would not be acceptable for everyday use. 
         [0005]    Present day electric automobiles charge batteries at charging stations that draw power from the electric grid. Because recharging the batteries takes a non-negligible amount of time, whatever can be done to conserve the charge in the battery should be considered. 
         [0006]    The disclosed solar windows for electric automobiles are directed to mitigating or overcoming one or more of the problems set forth above and/or other problems in the prior art. 
       SUMMARY 
       [0007]    One aspect of the present disclosure is directed to a photovoltaic power source for an electric automobile. The power source may include at least one window including a transparent photovoltaic cell; a DC-DC converter in electrical communication with the at least one window transparent photovoltaic cell; and a battery, in electrical communications with the DC-DC converter. 
         [0008]    Another aspect of the present disclosure is directed to an electric automobile. The electric automobile may include: a body; at least one window in the body, the at least one window comprising a transparent photovoltaic cell; a DC-DC converter, mounted in the body and in electrical communication with the at least one window transparent photovoltaic cell; and a battery, mounted in the body and in electrical communication with the DC-DC converter. 
         [0009]    Yet another aspect of the present disclosure is directed to a method for charging a battery in an electric automobile. The method may include steps of: generating power from a transparent photovoltaic cell included in at least one window of the electric automobile; controlling the generated power with a DC-DC converter in electrical communication with the at least one window transparent photovoltaic cell; and charging a battery mounted in the vehicle and in electrical communication with the DC-DC converter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0010]    The structure and function of the disclosed embodiments can be best understood from the description herein in conjunction with the accompanying figures. The figures are not necessarily to scale, emphasis instead generally being placed upon illustrative principles. The figures are to be considered illustrative in all aspects and are not intended to limit the disclosed embodiments, the scope of which is defined only by the claims. 
           [0011]      FIG. 1  is a perspective diagram of an embodiment of an electric automobile with photovoltaic transparent windows as the sunroof and rear windows; 
           [0012]      FIG. 2  is a schematic diagram of an embodiment of a DC-DC converter for use with the photovoltaic transparent windows of  FIG. 1 ; and 
           [0013]      FIG. 3  is a table showing the states of the transistors and diodes in the embodiment of the converter shown in  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    Referring to  FIG. 1 , an embodiment of an electric automobile  10  includes transparent photovoltaic cells (throughout this application the term “photovoltaic cells” is used interchangeably with the term “solar cells”) connected together to form one or more photovoltaic or solar panels  14 , voltage-conditioning electronics  18  (also referred to as a “DC-DC power converter  18 ”) and a plurality of battery strings  23 ,  23 ′ (generally  23 ) (also referred to as “battery pack strings”) that make up a vehicle battery  24  mounted within the body of the automobile  10 . 
         [0015]    The solar panels  14  replacing the sunroof window and rear window of the automobile will generate a maximum of about 200 watts of power at 50 volts. The sunroof and rear window were chosen because of their position in the automobile. These windows are exposed to significant sunlight and yet the reduction in light passing through the panels will not affect the safety of the vehicle as would be the case, for example, in placing the transparent solar panels in the position of the windshield. However, depending on the level of transparency, transparent photovoltaics may be used for all windows. It is noted that as the transparency of photovoltaic cells increases, the amount of power generated decreases. For example with a transparency of 10% the power produced is about 47 W/m 2 . As the transparency increases to 30%, the power generated decreases to 35 W/m 2 . 
         [0016]    Referring to  FIG. 2 , the photovoltaic cells of the solar panels  14  are connected to the battery  24  through the DC-DC power converter  18 . In one embodiment, converter  18  is provided as a Maximum Power Point Tracker (MPPT) DC-DC converter and power from the solar panels  14  at 50 VDC and 200 W maximum power is passed through the MPPT DC-DC converter. The MPPT DC-DC converter utilizes a MPPT Power Converter controller  28  to control the power being supplied to the battery  24 . In effect, the MPPT  28  matches the power supplied by the photovoltaic cells of the solar panels  14  to the requirements of the battery  24  to reduce power loss. The DC-DC power converter is mounted within the body of the automobile  10 . 
         [0017]    The MPPT Power Converter controller  28  is programmed to monitor a current  32  and a voltage  36  supplied to the battery strings  23 ,  23 ′, an input voltage  44 , and an input current  48  from the solar panels  14 . Because the power output by the solar panels  14  varies with temperature, the solar panels  14  include a temperature sensor  52 . The panel temperature sensor  52  provides an input signal to a temperature input  56  of the MPPT Power Converter controller  28 . 
         [0018]    Power from the solar panels  14  is input to a first side  57  of a primary coil  58  of a transformer  60  through a FET Q 1   64 . A second FET Q 2   68  is connected between a second side  62  of the primary coil  58  and ground. A diode D 1  is connected between the second side  62  of the primary coil  58  and the output of the photovoltaic panels  14 . A second diode D 2  is connected between first side  57  of the primary coil  58  and ground. 
         [0019]    A first side  75  of a secondary coil  76  of the transformer  60  is connected to a first side  78  of battery  24  through a FET Q 3   80 . A second side  77  of the secondary coil  76  of transformer  60  is connected to the second side  82  of the battery  24 . A FET Q 4   84  is connected between the first and second sides  75 ,  77  of the secondary coil  76 . A filter  95  constructed from an inductor  96  and a capacitor  100  is positioned between the FET Q 4   84  and the battery  24 . The inductor  96  is connected between FET Q 3   80  and the first side  78  of the battery  24 , and the capacitor is connected between the first side  78  and second side  82  of the battery  24 . 
         [0020]    The gate of FET Q 1   64  is controlled by an output port  72 , and the gate of FET Q 2   68  is controlled by an output port  73  of the MPPT Power Converter controller  28 . Similarly, the gate of FET Q 3   80  and the gate of FET Q 4   84  are controlled by an isolated high side driver  88  and an isolated low side driver  92 , respectively, under control of two output ports of the MPPT Power Converter controller  28 . An isolated current feedback monitor  102 , in one embodiment a Hall effect current sensor, and an isolated voltage feedback monitor  104  provide information about the current and voltage provided to the battery  24  to the input ports  32  and  36 , respectively, of the MPPT Power Converter controller  28 . 
         [0021]    Each of the battery strings  23 ,  23 ′ is connected to the first and second sides of the battery  24  through respective individual switches  110 ,  110 ′. The switches  110 ,  110 ′ are controlled by an external vehicle electronic control unit (ECU)  120 . 
         [0022]    The MPPT Power Converter controller  28  communicates with the vehicle Electronic Control Unit  120  through a CAN (Controller Area Network) bus interface  124  to exchange data such as maximum voltage, maximum charge current, temperature, system status, system faults and estimated available power, among others. 
         [0023]    Referring to  FIG. 3 , in operation, the MPPT Converter controller  28  first turns on FET Q 1   64 , FET Q 2   68 , and FET Q 3   80  and turns off FET Q 4   84 . In this state, diodes D 1  and D 2  are reverse-biased, and are off. This allows current to flow through the primary coil  58  of the transformer  60  and induce a current in the secondary coil  76 . This current is allowed to pass through FET Q 3   80  to the filter  95 . 
         [0024]    The MPPT Power Converter controller  28  next turns off FET Q 1   64 , FET Q 2   68 , and FET Q 3   80  and turns on FET Q 4   84 . This stops the current from flowing through the primary coil  58 , collapsing the field of the transformer  60  and reducing the current in the secondary coil  76  to zero. The turning on and off FET Q 1   64  effectively changes the DC voltage from the photovoltaic panel into square wave DC, causing an oscillating magnetic field to be generated by the primary coil  58 . 
         [0025]    The MPPT Power Converter controller also turns on FET Q 4   84 , allowing the secondary winding to redistribute charge and reset. In this state, diodes D 1  and D 2  are forward-biased and are on. Once the transformer  60  is reset, the diodes D 1  and D 2  are again reverse-biased and are off, and only FET Q 4   84  is on to permit current from FET Q 1   64  to flow to the battery  24 . 
         [0026]    The MPPT Power Converter controller  28  controls other functions of the charging system. For example, if the temperature of the photovoltaic cell array  14  exceeds a certain value, the MPPT Power Converter controller monitors the temperature, current, and voltage of the solar panels  14  so that it may take proper action depending upon the values of the parameters. If any of the values are out of range, the converter will shut off. The converter uses the monitored input values to estimate the available output power and to maintain maximum power output from the converter despite changing incident light and without collapsing the photovoltaic cell voltage, so as to maintain the highest efficiency. 
         [0027]    In another embodiment, the vehicle turns off or reduces power to any non-essential vehicle electronics to reduce current draw, which leads to a more effective transfer of energy from sunlight to the battery. 
         [0028]    Unless otherwise indicated, all numbers expressing lengths, widths, depths, or other dimensions, and so forth used in the specification and claims are to be understood in all instances as indicating both the exact values as shown and as being modified by the term “about,” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the specification and appended claims are approximations that nay vary depending upon the desired properties sought to be obtained. At the very least, and not as an attempt, to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Any specific value may vary by 20%. 
         [0029]    The terms “a,” “an,” “the,” and similar referents used in the context of describing the disclosed embodiments (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein is intended merely to better illuminate the disclosure and does not pose a limitation on the scope of any claim. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the disclosed embodiments. 
         [0030]    Groupings of alternative elements or embodiments disclosed herein are not to be construed as limitations. Each group member may be referred to and claimed individually or in any combination with other members of the group or other elements found herein. It is anticipated that one or more members of a group may be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is deemed to contain the group as modified, thus fulfilling the written description of all Markush groups used in the appended claims. 
         [0031]    Certain embodiments are described herein, including the best mode known to the inventor for trying out the spirit of the present disclosure. Of course, variations on these described embodiments will become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventor expects skilled artisans to employ such variations as appropriate, and the inventor intends for the disclosed embodiments to be practiced otherwise than specifically described herein. Accordingly, the claims include all modifications and equivalents of the subject matter recited in the claims as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is contemplated unless otherwise indicated herein or otherwise clearly contradicted by context. 
         [0032]    It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed remote control system and related methods. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed remote control system and related methods. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.