Abstract:
The present invention features a voltage-limiting regulator for use with an AC generator having DC-excited fields. The AC output voltage from the generator is sensed and compared to a fixed reference voltage. An algebraic difference voltage representative of the sensed difference is amplified and applied to the DC field excitation input of the AC generator. As the DC voltage supplied to the field varies, the AC output voltage from the generator may be held constant under varying load conditions. The voltage-limiting regulator is particularly useful for vehicle-mounted, high power, single phase AC generators.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a voltage limiting regulator. More particularly, the invention comprises a voltage limiting regulator for use cooperatively with an alternator having split, DC-excited fields and wherein the voltage output from the alternator may be controlled by varying the DC-excitation voltage provided to the field windings.  
           [0003]    The need for portable, compact, high-power AC electric power generators is widely felt. Not only are such devices useful for powering the tools in the field away from normal AC supply mains, they are particularly useful for providing emergency power during time that AC power is unavailable from the power grid. Vehicle-mounted AC generators have proven to be particularly useful because of the ease with which they may be transported to a job site or other location in need of locally-generated, AC power.  
           [0004]    2. Description of the Prior Art  
           [0005]    U.S. Pat. No. 3,982,173 for AC-DC VOLTAGE REGULATOR, issued Sep. 21, 1976 to Clyde Raymond Berry, et al. teaches an AC-to-DC convertor employing a rectifier and a crowbar type voltage regulator. A control voltage is developed and fed back to a current-controlled switch which functions to maintain a constant output voltage from the converter under varying loads.  
           [0006]    In contradistinction, the inventive regulator is designed for use with an alternator producing a single-phase AC output voltage and using DC excitation of its field windings. The applied DC excitation voltage may be varied thereby varying the AC output voltage from the alternator. The voltage limiting regulator circuit senses a changing AC output voltage and responds by changing the DC excitation voltage thereby maintaining a substantially constant AC output voltage under a varying load.  
           [0007]    U.S. Pat. No. 4,800,291 for ELECTRONIC CIRCUIT FOR CONTROL OF A VOLTAGE REGULATOR OF AN ELECTRICAL GENERATOR, issued Jan. 24, 1989 to Jack K. Bowers discloses an apparatus for synchronizing the voltage and phase of an AC generator to an existing power grid. Unlike the voltage-limiting regulator of the instant invention, BOWERS uses sophisticated electronic circuitry to accomplish the synchronization function. The inventive regulator, on the other hand, is intended for application with stand-alone AC generators, each driving a varying load. The phase of each individual generator is essentially constant. Consequently, there is no need to match its phase to that of any other generator. The output voltage of a generator using the inventive regulator is controlled as the load applied to the generator changes.  
           [0008]    U.S. Pat. No. 5,617,011 for METHOD AND SYSTEM FOR LIMITING GENERATOR FIELD VOLTAGE IN THE EVENT OF REGULATOR FAILURE, issued Apr. 1, 1997 to Kathleen M. Hammer, et al. teaches a circuit for limiting the field voltage provided a generator in the event of a field coil short circuit or regulator failure. Nothing in HAMMER, et al. teaches the regulation of an AC generator&#39;s output voltage using a rectified feedback signal, a comparitor and an output stage to directly provide a varying DC field energization voltage to the generator.  
           [0009]    U.S. Pat. No. 5,656,922 for VEHICLE BASED AC POWER SYSTEM, issued Aug. 12, 1997 to William J. LaVelle, et al. teaches a hybrid AC generator utilizing both permanent magnets and DC-driven coils for field generation. The field coils may be arranged in switchable buck or boost modes to control the alternator output, thereby preventing an overvoltage output. The LaVELLE, et al. apparatus allows designing a vehicle-mounted alternator capable of full output at any range of engine speeds, from idle to full throttle.  
           [0010]    The inventive regulator, on the other hand, is designed to provide a continuously varying DC voltage for excitation of the field windings of a conventional (i.e., not a hybrid) alternator whereby the AC output voltage is maintained substantially constant under varying load conditions.  
           [0011]    U.S. Pat. No. 5,675,237 for OUTPUT CONTROL DEVICE FOR VEHICLE AC GENERATOR, issued Oct. 7, 1997 to Shiro Iwatani discloses a switching arrangement which allows utilization of a single alternator for selectively charging a vehicle&#39;s battery and providing a high-voltage AC output for powering an external load. Unlike the inventive regulator, there is no teaching of a voltage regulation function based upon changing the DC voltage applied to the alternator for field excitation.  
           [0012]    U.S. Pat. No. 5,686,819 for CONTROL APPARATUS FOR AC GENERATOR OF MOTOR VEHICLES, issued Nov. 11, 1997 to Shiro Iwatani, et al. also teaches a switching arrangement for directing alternator output to a vehicle battery or, in a second mode of operation, to an external AC load. There is still no teaching of a voltage regulation function based upon changing the DC voltage applied to the alternator for field excitation.  
           [0013]    None of the above inventions and patents, taken either singly or in combination, is, however, seen to anticipate or suggest the instant invention as claimed.  
         SUMMARY OF THE INVENTION  
         [0014]    The present invention relates to a voltage-limiting regulator for use with an AC generator having DC-excited fields. The AC output voltage from the generator is sensed and compared to a fixed reference voltage. An algebraic difference voltage, representative of the sensed difference, is amplified and applied to the DC field excitation input of the AC generator. As load changes, the AC output voltage from the generator varies. By sampling the generator&#39;s AC output voltage, a feedback voltage is developed which is supplied to the generator&#39;s field windings. In this way the AC output voltage is held constant under varying load conditions. The voltage-limiting regulator is particularly useful for vehicle-mounted, high power, single phase AC generators.  
           [0015]    Accordingly, it is a principal object of the invention to provide a voltage-limiting regulator for use with an AC generator having DC-excited fields.  
           [0016]    It is another object of the invention to provide a voltage-limiting regulator for use with an AC generator having DC-excited fields which provides a substantially constant generator output under varying load conditions.  
           [0017]    It is a further object of the invention to provide a voltage-limiting regulator for use with an AC generator having DC-excited fields which provides a substantially constant generator output under varying load conditions by changing a DC excitation voltage supplied to the field-generating mechanism.  
           [0018]    Still another object of the invention is to provide a voltage-limiting regulator for use with an AC generator having DC-excited fields which uses a comparitor to provide a feedback voltage which is derived from the algebraic comparison of the instantaneous AC output voltage from the AC generator and a fixed, predetermined reference voltage.  
           [0019]    An additional object of the invention is to provide a voltage-limiting regulator for use with an AC generator having DC-excited fields which allows the construction of high-power, single phase AC generators which are capable of maintaining essentially constant output voltage under varying load conditions.  
           [0020]    It is again an object of the invention to provide a voltage-limiting regulator for use with an AC generator having DC-excited fields which allows the construction of high-power, single phase AC generators which are suitable for mounting on a motor vehicles.  
           [0021]    These and other objects of the present invention will become readily apparent upon further review of the following specification and drawings.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]    Various other objects, features, and attendant advantages of the present invention will become more fully appreciated as the same becomes better understood when considered in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the several views, and wherein:  
         [0023]    [0023]FIG. 1 is schematic, cross-sectional view of an AC generator suitable for use with the voltage-limiting regulator of the invention;  
         [0024]    [0024]FIG. 2 is a system block diagram of the regulator of the invention connected to a suitable AC generator;  
         [0025]    [0025]FIG. 3 is a more detailed system block diagram of the inventive regulator;  
         [0026]    [0026]FIG. 4 a  is an overview schematic diagram showing the relationship of schematic diagram portions  4   b  and  4   c;    
         [0027]    [0027]FIG. 4 b  is a first section of a schematic diagram of the preferred embodiment of the inventive regulator; and  
         [0028]    [0028]FIG. 4 c  is a second section of a schematic diagram of the preferred embodiment of the inventive regulator.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0029]    The present invention relates to a voltage limiting regulator for use in conjunction with an AC alternator having DC-excited field. The terms alternator and generator have been used interchangeably herein.  
         [0030]    Referring first to FIG. 1, there is shown a schematic cross-sectional view of an alternator suited for use with the voltage limiting regulator of the invention, generally at reference number  100 . An armature  102  is located between at least two independent field producing elements  104  on either side of armature  102 . Each field-producing element  104  is shown having a coil  106  which is connected to an external voltage source  107   a ,  107   b . Both field producing elements  104  may be powered either independently or in parallel as operating circumstances dictate. A shaft  108  extends beyond both distal ends of armature  102 . A pulley  110  on a first distal end of shaft  108  allows for the connection of alternator  100  to an external prime mover (not shown), A set of slip rings  112  at a second distal end of shaft  108  allows for the transfer of the generated AC voltage from armature  102  to an external AC bus  114 . Any alternator configuration, many of which are well known to those of skill in the art, may be used with the regulator of the present invention. This assumes, of course, that the alternator&#39;s field is produced from an externally-applied DC voltage  107   a ,  107   b  (FIG. 1).  
         [0031]    Referring next to FIG. 2, there is shown a schematic block diagram of a system including the inventive voltage limiting regulator and an alternator  100  (FIG. 1). An external AC load  122  is connected to AC bus  114 . An AC pickup  124  monitors the voltage and/or current of AC bus  114 . The function of AC pickup  124  may be performed by a number of devices well known to those of skill in the art. These devices may be either directly connectable to AC bus  114  or, in alternate embodiments, may be inductively coupled devices such as current probe, hall effect devices, or the like. The invention is not considered limited by the device chosen for implementing AC pickup  124 . AC pickup  124  is connected to an input of regulator  120 . An external battery  126  is also connected to regulator  120 . At least one output from regulator  120  is connected to alternator  100  and DC voltages  107   a  and, optionally,  107   b  are thereby supplied.  
         [0032]    Referring next to FIG. 3, there is shown a slightly more detailed schematic diagram on the regulator of the present invention in it operating environment. An AC sense voltage  114  related to the actual output of the alternator is clamped by a varistor  115  or other similar spike-suppressing device well know to those skilled in the art. A bridge rectifier  204  provides a time-varying DC voltage related to AC input voltage  114 . A DC set-point control potentiometer  218 , connected to a first input of a voltage comparitor circuit  221 , is used to adjust the desired AC output voltage from the alternator being controlled. A negative DC balance control  225 , feed from the negative DC output of bridge rectifier  204  is connected to a second input of comparitor circuit  221 , in effect providing a stable reference voltage to the comparitor  221 . The output of comparitor  221  is coupled through and optical isolator  224  to an output controller  225 . Output controller  225  accepts a DC input voltage from a battery  126  (FIG. 1) or similar DC voltage source. Output controller  225  then provides a time-varying DC output voltage responsive to the output of comparitor circuit  221  whereby the output of the controlled alternator is held substantially constant at a voltage determined by set point control  218 . A detailed description of one embodiment of the inventive regulator is provided hereinbelow.  
         [0033]    Referring now to FIGS. 4 b  and  4   c , there are shown two portions of an electrical schematic diagram of voltage-limiting regulator  120  (FIG. 2), generally at reference number  200 . AC bus  114  is bridged by a surge suppressor  202  such as a varistor or similar device, and then connected to a bridge rectifier arrangement  204 . A smoothing capacitor  206  is connected at the output of bridge rectifier  204  and a DC voltage bus  208  is established. The DC voltage on DC voltage bus  208  is typically in the range of 350 VDC. A zenar diode  210 , is connected to DC voltage bus  208  through voltage divider resistors  214 , to the base of a regulator transistor  212 . The regulated output voltage is typically in the range of 24 volts DC.  
         [0034]    A second voltage divider network is formed by resistors  216 , potentiometer  218  and resistor  220  is also connected to DC voltage bus  208 . The output from the second voltage divider network is typically in the range of 5 volts DC.  
         [0035]    A comparitor  222  has a first input connected to regulator transistor  212  and a second input connected to the pick-off point of the voltage divider  216 ,  218 ,  220 . In the embodiment chosen for purposes of disclosure, resistive element  218  is a potentiometer which allows adjustment of a voltage feed to comparitor  222 . This adjustable voltage ultimately controls the output voltage of the AC generator which is in the approximate range of 110-130 Volts AC in the preferred embodiment. The output of comparitor  222  is connected to an isolator  224 , typically an optical isolator. A variety of devices suitable for use as an isolator are well known to those skilled in the circuit design art.  
         [0036]    A pair of output power devices  226 ,  228  are connected to the output of isolator  224 . Typically, devices  226 ,  228  are MOSFETs. Flyback diode  230  is connected to devices  226 ,  228 . A second surge suppressor  232  is connected across DC output buses  234   a ,  234   b  which are connected to the field excitation inputs of alternator  100  (FIG. 2).  
         [0037]    In operation, an AC voltage in the range of either 120-130 or 220-240 volts, depending upon the specific configuration, is applied to the input of regulator circuit  200  from AC bus  114 . The AC voltage is dependant upon the alternator configuration selected. This applied AC voltage supplies an input sensing voltage, the exact voltage depending upon the configuration. Surge suppressor  202  is designed to clamp down the input sensing voltage thereby removing spikes which may be present thereupon. The DC output from bridge rectifier  204 , appearing on DC voltage bus  208 , will typically be in the range of 180 volts DC for a 120 volt AC input and 350 volts DC when 220 volts AC is applied.  
         [0038]    The combination of resistors  214 , zenar diode  210  and regulator transistor  212  from a voltage regulator providing a fixed, stable DC voltage for use as a supply voltage for comparitor  220 . In the embodiment chosen for purposes of disclosure, approximately 24 volts DC has been chosen as the supply voltage. It should be obvious to those of skill in the art that other supply voltages could be chosen and obtained by varying component values.  
         [0039]    The second voltage divide network (i.e., resistors  216 , potentiometer  218 , etc.) are used to develop a reference voltage for comparitor  222 . The embodiment chosen for purposes of disclosure, the reference voltage is approximately 5 volts DC. Potentiometer  218  may be used to adjust the ultimate nominal AC output voltage of alternator  100 . In the embodiment chosen for purposes of disclosure, potentiometer  218  can vary the nominal output voltage in a range of approximately 110-130 volts AC, assuming that the 120 volt configuration has been selected. A similar range of output voltage adjustment is also available in the 220 volt configuration. It will also be obvious to those of skill in the circuit design art that other reference voltage values could be chosen to meet a particular operating requirement.  
         [0040]    Comparitor  222  is supplied a fixed, reference voltage at a first input and a portion of the rectified DC sense voltage at a second input. When the sense input drops below the reference voltage (e.g., 5 volts DC), the output of comparitor  222  shifts from its nominal “high” signal level to a “low” signal level. This causes a “high” signal to be applied to output transistors  226 ,  228 . The output of comparitor  222  is isolated from the remainder of the output circuitry by isolator  224 . This prevents the relatively high output voltages from reaching the low-voltage portions of the regulator circuitry in the event of circuit failure. In addition, isolator  224  minimizes the possibility of electrical shock to the user.  
         [0041]    In the embodiment chosen for purposes of disclosure, the DC output voltage may assume a range of approximately 4 VDC to 14.4 VDC thereby allowing the output voltage of alternator  100  be held constant under a wide range of loads.  
         [0042]    It is to be understood that the present invention is not limited to the embodiments described above, but encompasses any and all embodiments within the scope of the following claims.