Abstract:
There are apparatus and methods for generating a plurality of voltage levels. There is a rotor that includes a first and a second portion of rotor windings. The first portion of rotor windings is constructed and arranged to establish a first magnetic field of a first number of poles. The second portion of rotor windings is constructed and arranged to establish a second magnetic field of a second number of poles. A stator is disposed adjacent the rotor. The stator includes a first and a second portion of stator windings. The first portion of stator windings is related to the first number of poles and has a first output port configured for furnishing an electrical output at a first voltage level. The second portion of stator windings is related to the second number of poles and has a second output port configured for furnishing an electrical output at a second voltage level.

Description:
[0001]     This invention relates to generators, and more particularly to generating multiple voltages.  
       BACKGROUND OF THE INVENTION  
       [0002]     To supply an automobile with power once the engine is running, an automobile includes a generator. A typical generator contains a moving rotor and a stationary stator. A voltage regulator circuit supplies current to the moving rotor to generate a magnetic field in the rotor. The magnetic field from the moving rotor induces a voltage in the stator as the rotating rotor moves past the stationary stator. Typically a regulator regulates the voltage by controlling current to the rotor, thus regulating the voltage induced in the stator to produce a constant voltage for the electrical load.  
         [0003]     Generators for automobiles typically generate a voltage of 14 volts after rectification. With electrical loads for automobiles increasing, the automobile industry is considering higher voltages, such as 42 volts.  
       SUMMARY OF THE INVENTION  
       [0004]     It is an important object of the invention to provide multiple voltages from a generator, such as for a vehicle.  
         [0005]     In one aspect there is an apparatus for generating an electrical output of a plurality of voltage levels. The apparatus includes a rotor and a stator disposed adjacent the rotor. The rotor includes a first portion of rotor windings corresponding to a first magnetic field of a first number of poles, and a second portion of rotor windings corresponding to a second magnetic field of a second number of poles. The stator includes a first portion of stator windings corresponding to the first number of poles and having a first output port configured for an electrical output at a first voltage level. The stator also includes a second portion of stator windings corresponding to the second number of poles and having a second output port configured for an electrical output at a second voltage level.  
         [0006]     In other examples, the apparatus can include the following features. The first magnetic field can be orthogonal to the second magnetic field. The first portion of stator windings and the second portion of stator windings can be electrically independent. The apparatus can include a first excitation port electrically connected to the first portion of rotor windings and a second excitation port electrically connected to the second portion of rotor windings. The apparatus can include a first voltage regulator electrically connected to the first excitation port and the first output port, and a second voltage regulator electrically connected to the second excitation port and the second output port.  
         [0007]     The apparatus can include a first AC to DC circuit electrically connected to the first output port, and a second AC to DC circuit electrically connected to the second output port. The apparatus can include a first full-bridge diode rectifier included in the first AC to DC circuit, and a second full-bridge diode rectifier included in the second AC to DC circuit. The rotor can include a salient pole rotor. The apparatus can include a shaft on which the rotor is disposed. The first number of poles can correspond to two poles and the second number of poles can correspond to six poles. The first voltage level can be substantially 14 volts and the second voltage level can be substantially 42 volts. The apparatus can include a first commutator electrically connected to the first portion of stator windings and a second commutator electrically connected to the second portion of stator windings.  
         [0008]     In another aspect, there is a method for generating a plurality of voltage levels using a single generator. The method includes generating a first voltage including, controlling current into a first portion of rotor windings corresponding to a first magnetic field of a first number of poles, and moving the first portion of rotor windings past a first portion of stator windings corresponding to the first number of poles to thereby induce the first voltage in the first portion of stator windings. The method also includes generating a second voltage including, controlling current into a second portion of rotor windings corresponding to a second magnetic field of a second number of poles, and moving the second portion of rotor windings past a second portion of stator windings corresponding to the second number of poles to thereby induce the second voltage in the second portion of stator windings.  
         [0009]     In other examples, the method can include the following features. The method can include rectifying the first voltage to generate a first DC voltage, and rectifying the second voltage to generate a second DC voltage. The method can include orienting the first magnetic field orthogonal to the second magnetic field. The method can include arranging the first portion of stator windings and the second portion of stator windings to be electrically independent. The rotor can reside on a shaft and the method can include moving the first portion of rotor windings by rotating the shaft, and moving the second portion of rotor windings by rotating the shaft. The first number of poles can correspond to two poles and the second number of poles can correspond to six poles.  
         [0010]     In another aspect, there is a method for making a single generator that generates a plurality of voltage levels. The method includes winding a first portion of rotor windings corresponding to a first magnetic field of a first number of poles, and winding a second portion of rotor windings corresponding to a second magnetic field of a second number of poles. The method also includes winding a first portion of stator windings corresponding to the first number of poles, and connecting a first output port configured for an electrical output at a first voltage level to the first portion of stator windings. The method also includes winding a second portion of stator windings corresponding to the second number of poles, and connecting a second output port configured for an electrical output at a second voltage level to the second portion of stator windings. In other examples, the method can include any of the features described above.  
         [0011]     The details of one or more examples are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawing, in which: 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
       [0012]      FIG. 1  is a block diagram of a dual voltage electrical system;  
         [0013]      FIG. 2  is a diagram of stator windings of different pole numbers and corresponding graphs of current effects on radial magnetic fields;  
         [0014]      FIG. 3  is a perspective view of stator windings of different pole numbers;  
         [0015]      FIG. 4  is a diagram of rotor windings of different pole numbers and corresponding graphs of generated fields;  
         [0016]      FIG. 5  is a diagram of single 3-phase stator windings of different pole numbers;  
         [0017]      FIG. 6  is a diagram of stator windings of different pole numbers and corresponding graphs of current effects on radial magnetic fields;— 
         [0018]      FIG. 7  is a diagram of generated voltage of a stator winding;  
         [0019]      FIG. 8  is a cross-sectional view of an armature for a direct current generator; and  
         [0020]      FIG. 9  is a side view of an armature for a direct current generator. 
     
    
       [0021]     Like reference symbols in the various drawings indicate like elements.  
       DETAILED DESCRIPTION  
       [0022]      FIG. 1  illustrates a dual-voltage electrical system  100 . System  100  includes a dual voltage alternator  105  that has a first output port  110  corresponding to a first voltage level and a second output port  115  corresponding to a second output voltage. Generator  105  provides independent control of the two output ports in a single-frame generator. Generally, in a generator the radial air-gap magnetic field is a space sinusoid produced by a rotating field structure of a designated number of poles. This radial magnetic field induces voltage in a stator winding of the same pole number. As described in more detail below, to produce the two voltages, generator  105  generates a magnetic field of a first pole number and a magnetic field of a second pole number and has corresponding stator windings corresponding to these two fields, allowing independent control of each. In other words, generator  105  includes a first radial air-gap magnetic field of a first pole number, produced by a suitable winding on the rotating field structure to induce a first voltage in a first stator winding of the first pole number. Generator  105  also includes a second radial air-gap magnetic field of a second pole number, produced by a suitable winding on the rotating field structure to induce a second voltage in a second stator winding of the second pole number. In one example, the two radial air-gap magnetic fields are selected to be orthogonal so that the fundamental components do not interfere with each other in the stator windings. The radial air-gap magnetic fields are orthogonal when, for example, the integral of the product of the space sinusoidal functions describing the radial magnetic fields over the periphery of the stator is zero.  
         [0023]     To use the dual voltage output of generator  105 , system  100  may include a first alternating current (AC) to direct current (DC) circuit  120  that is electrically connected to the first output terminal  110  of alternator  105  and a second AC to DC circuit  125  that is electrically connected to the second output terminal  115  of generator  105 . The first and second AC to DC circuits  120  and  125  include, for example, a full-bridge diode rectifier to perform the conversion. The first AC to DC circuit  120  is electrically connected to a 14-volt conductor  130  and the second AC to DC circuit  125  is electrically connected to 42-volt conductor  135 . Conductors  130  and  135  are electrically connected to batteries  140  and  145 , respectively. Batteries  140  and  145  can supply electricity to their respective conductors when generator  105  is not running and become loads to the generator when the generator is running. In an automobile system, generator  105  includes a shaft on which the rotor is located. The shaft is connected to the engine, for example by a pulley and belt. When the engine is running, the engine causes rotation of the rotor via the belt and shaft, which, as described in more detail below, causes a generated voltage in the stator windings. The two voltage levels (i.e., 14 and 42) are chosen in this illustrative example because they represent a suitable dual-voltage system for automobiles. Other voltage level combinations are applicable for the techniques described herein.  
         [0024]     As described above, generator  105  uses fields corresponding to different pole numbers to independently generate and control different voltage levels.  FIGS. 2-4  illustrate exemplary stator windings and rotor windings of generator  105  that correspond to two pole numbers. The examples use a 2-pole field and a 6-pole field to illustrate the concept, but other pole numbers can be used. As described above, some examples choose pole numbers that advantageously provide two orthogonal fields that do not interact in the air-gap or in the windings.  
         [0025]      FIG. 2  illustrates a portion  200  of a stator, with one phase of a 6-pole winding, referenced as a-a, and a 2-pole winding, referenced as a′-a′. Portion  200  illustrates 19 slots, to show that 18 slots are used for the 2-pole and 6-pole windings, and then the winding pattern is repeated. The first winding a-a is a 6-pole winding with a span of 3 slots. The second winding a′-a′ is a 2-pole winding with a span of 9 slots. The position of the coil sides is shown in portion  200 , using the convention of a dot representing the winding coming out of the page and an x representing the winding going into the page. The radial magnetic air-gap fields produced by unit current in each winding are shown in graphs  205  and  210 . Graph  205  corresponds to the 6-pole winding a-a and graph  210  corresponds to the 2-pole winding a′-a′. For single conductors in the slots, the radial field is a square wave in space. The sinusoidal waveforms shown in graphs  205  and  210  can be regarded as the fundamental component of the magnetic field, or the effect of a distributed winding in generator  105 .  
         [0026]      FIG. 3  illustrates a perspective view of a stator core  305  and windings a′-a′, corresponding to a 2-pole winding, and a-a, corresponding to a 6-pole winding. For simplicity, stator core  305  is illustrated as a “flattened” section of the cylindrical core of alternator  105 . The positions of the two windings a-a and a′-a′ are shown in shared or independent slots. In this example, the windings are electrically independent.  
         [0027]      FIG. 4  illustrates a portion  400  of a rotor with a 6-pole winding and a 2-pole winding. Portion  400  depicts the two windings on a salient-pole rotor to produce 6-pole and 2-pole radial air-gap magnetic fields. Other winding patterns, for example, a non-salient pole (wound rotor) can also be used. Portion  400  includes 6 salient poles  405   a - f . Each pole  405  has one coil for the 6-pole winding pattern and one coil for the 2-pole winding pattern. The direction of the winding for each pole  405  depends on the pole number to which the rotor winding corresponds. The two windings can be excited independently from the batteries through slip rings or other means and be controlled by independent voltage regulators. Generally, the voltage regulators are electrically connected to excitation terminals of the rotor coils. The voltage regulator controls the average current through the rotor coils, thus controlling the magnetic fields generated by the coils to maintain the voltage substantially constant. Because each rotor coil has its own excitation terminals and voltage regulator, the voltage outputs of generator  105  can be independently regulated.  
         [0028]      FIG. 4  also includes graph  410 . Graph  410  illustrates the radial air-gap magnetic fields produced by the salient poles of portion  400 . For the 2-pole field, three sequential poles,  405   a - c  and  405   d - f , produce elements  415   a  and  415   b  of the 2-pole field. For the 6-pole field, each independent pole  405   a - f  produces each element of the field  420   a - f.    
         [0029]      FIGS. 2-4  illustrate single phase, electrically independent windings to describe the concept of rotor and stator windings corresponding to two different poles numbers. In other examples, alternator  105  can have 3-phase windings. Further, including two different pole number windings can be implemented using windings that are not electrically independent. For example,  FIG. 5  illustrates a 3-phase stator winding  500  where the coils for two different pole numbers are not electrically independent. Winding  500  includes 18 coils  501 - 518 . Using stator winding  500  with, for example, the rotor windings illustrated in  FIG. 4 , the A, B, C terminals correspond to the 6-pole field and the a, b, c terminals correspond to the 2-pole field. This combination can produce two sets of 3-phase voltages under the control of the two rotor field currents, again advantageously allowing independent control of the two voltage levels. Winding  500  can be used, for example, in a 42/14V DC automotive system if the 42V and 14V loads do not use a common ground, e.g., the frame.  
         [0030]      FIG. 6  illustrates a single-phase stator winding portion  600  of winding  500 , where the coils for two different pole numbers are not electrically independent. Winding portion  600  includes six coils of winding  500 , namely coils  501 - 506  shown in their spatial order in the periphery of the stator. Using stator winding portion  600 , for example, and the rotor windings illustrated in  FIG. 4 , the A terminal corresponds to the 6-pole field and the a, b, c terminals correspond to the 2-pole field.  FIG. 6  also includes graphs  620  and  625  to illustrate how the single winding portion  600  produces radial air-gap magnetic fields with 6- and 2-pole numbers. The six coils  501 - 506  of winding portion  600  each span 60 degrees, electrical, to cover 360 degrees. The arrows show the directions of the radial air-gap field for current into the dotted end of each coil. The 2-pole field produced by the currents in terminals a, b, and c, is shown in graph  620 . The graphed 2-pole field corresponds to a time when the current in terminal a is at, e.g., 1.0 per unit (p.u.), which refers to the base value, and the currents in terminals b and c are at −0.5 p.u. The winding is wye-connected, because the ends of the windings opposite terminals a, b, and c, terminate at the same point, terminal A. The 6-pole field produced by the currents into terminal A is shown in graph  625 . The graphed 6-pole field corresponds to a time when the current in terminal A is at, e.g., 1.0 p.u.  
         [0031]     As described above, graphs  620  and  625  illustrate the fields produced by currents through the winding. These fields react with fields produced by the rotor windings to generate a voltage across the stator windings.  FIG. 7  illustrates how voltages are generated across a stator winding, using winding  505  as an example. The “armature reaction” arrow represents the radial air-gap magnetic field produced by current in the winding (e.g., graphs  620  and  625 ). The windings of a rotor (e.g.,  400  of  FIG. 4 ) produce the “rotor field” arrow. The resultant radial magnetic field generates the voltage v that appears at the output terminals of alternator  105 .  FIG. 7  illustrates a case where the direction of the radial magnetic field applied by the rotor is in the opposite direction to the armature reaction field. In this case, the polarity of the generated voltage v in coil  505  coincides with the direction of the current at that instant of time.  
         [0032]      FIG. 8  illustrates a cross-sectional view of a direct current (DC) generator that produces two voltage levels using a 2-pole field and a 4-pole field. The DC generator includes an armature  805 , which includes a 4-pole winding  810  and a 2-pole winding  815 . Armature  805  is attached to a shaft  820 , which rotates armature  805  in operation. To induce current in armature  805  during rotation, the DC generator also includes 4-pole field coils  825   a - d  and 2-pole field coils  830   a - b . As described above, the field coils of each pole number can be controlled independent of each other, so that each of the output voltage levels associated with each pole number can be regulated independent of each other.  
         [0033]      FIG. 9  illustrates a side view of armature  805 . A DC generator includes commutators  905  and  910 , both of which are attached to shaft  820  and electrically connected to armature  805 . Commutator  905  is electrically connected to the 4-pole winding  810  and commutator  910  is electrically connected to the 2-pole winding  815 . A commutator is basically a slip ring that is split into two or more elements that are insulated from each other and from the shaft  820 . For example, commutator  905  has two elements  905   a  and  905   b . Each element  905   a  and  905   b  is connected to a different end of the 4-pole winding  810 . In the illustrated position of shaft  820 , brush  915   a  is in electrical contact with commutator element  905   b  and brush  915   b  is in electrical contact with commutator element  905   a . As the shaft rotates one-half a turn (180 degrees), then the brushes  915   a  and  915   b  are now in contact with element  905   a  and  905   b , respectively, the opposite of what is illustrated. The same thing happens with brushes  915   c - d  and the elements of commutator  910 . Commutators  905  and  910  eliminate the need for an additional rectifying circuit, as the commutators perform this function.  
         [0034]     Implementations can realize one or more of the following advantages. There is a simple self-contained unit, compared to two generators, or an generator plus one or more dc/dc converters. The generator can be built of standard laminations and utilize standard voltage regulators. The generator is not limited in size. There is relatively low internal impedance of the windings, which reduces rectifier commutation effects and internal voltage drop. For example, use of a salient-pole or round rotor over the Lundell rotor, commonly used in automobile generators, reduces the internal impedance of the generator. The consequence can be a reduction in rectifier commutation overlap angle and a reduction in ac internal voltage and generator size to achieve prescribed rectified dc voltage. In addition, the peak-to-peak ripple in the rectified voltage is reduced.  
         [0035]     A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, the generator can produce three or more levels of voltage by using three or more pole numbers for the radial air-gap magnetic fields. For certain pole combinations, a single rotor winding with two excitation ports can produce radial magnetic fields of two pole numbers. The generator can utilize a rotor with permanent magnets for the poles corresponding to a first one of the pole numbers and windings for a second one of the pole numbers. In such embodiments, the voltages produced by the by the wound field are regulated. The functions of the rotor and the stator can be interchanged by using slip rings and brushes to make connections to the winding ports. Accordingly, other embodiments are within the scope of the following claims.