Abstract:
A universal power converter for generating a regulated voltage, current or power with a large input voltage range. The power converter has a voltage boost function configured to boost the rectified input voltage and provide power factor correction. The power converter also includes a voltage chop function to chop the boosted voltage to form an AC voltage. The power converter further includes at least one relay in electrical communication with the AC voltage and a transformer. The primary winding has at least two inputs operative to selectively vary the voltage generated on a secondary winding thereof selected by the relay. Accordingly, the power converter can generate different voltages at the output based upon the position of the relay and the boosted voltage. The power converter provides maximum power operation at a wide output voltage range, maximizing the charging energy.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of Invention  
           [0002]    The present invention relates generally to AC/DC power converters and more particularly to a high efficiency AC/DC power converter operative to produce regulated DC output power with utility AC power as the input source.  
           [0003]    2. Status of The Prior Art  
           [0004]    In a conventional AC/DC converter, power is usually delivered to a DC load or multiple DC loads at a constant rate. Due to the fundamental nature of a single-phase AC source, power drawn from such a source has a pulsating nature with an average value equal to the output power plus losses incurred by the converter. Accordingly, the AC/DC converter must provide means for storing and retrieving energy during each half-cycle of the AC line.  
           [0005]    In the conventional AC/DC converter, large value capacitors are used for energy storage. The voltage present on these capacitors determines the output voltage of the AC/DC converter and is regulated. In other words, the regulated output voltage of the AC/DC converter is a linear function of the capacitor voltage. When the conventional converter is used in universal input applications where the input line voltage can vary from 108Vac to 264Vac it is not feasible to maintain a regulated capacitor voltage. In order to mitigate the need for an AC/DC converter with a regulated output voltage and a wide range of input voltages, multiple AC/DC power converter designs have been developed. These are generally multiple designs of a dual power processing stage AC/DC converter. The first power processing stage is generally the voltage boost stage consisting of an AC rectified input followed by a choke-boosted converter. The choke-boosted converter has a capacitor output to provide for the energy storage described earlier.  
           [0006]    The capacitor output presents an equivalent DC voltage source to the second power processing stage. The capacitor output, used for storing and retrieving energy, is generally a high capacitance capacitor or capacitors that are expensive and large in volume. The transformer turns ratio and the regulated output voltage of the first power processing stage defines the regulated output voltage of the AC/DC converter. The second power processing stage is a DC/DC converter with a transformer-rectified output.  
           [0007]    In addition to providing regulated DC output voltage, the first power processing stage may provide for power factor correction (PFC). The second power processing stage accepts the regulated DC voltage from the first power processing stage and provides for input to output voltage amplification (via the transformer turns ratio) and galvanic isolation. Because of the large variations in utility voltages that exist in the global market place (i.e., 108Vac to 264Vac), a single conventional AC/DC converter design cannot process the full input voltage range and provide for the desired regulated output voltages. Accordingly, different converter designs are used to satisfy different portions of the input voltage range. As such, the AC/DC converter design for 120Vac input will be different than that for 240Vac input. Specifically, due to large variations in worldwide household and commercial AC power sources, multiple designs for the AC/DC converter are available. Furthermore, the desire for unity power factor by utility companies, the requirement for galvanic isolation for safety, and the large differences in application usage of power converter creates application specific designs. For example, conventional AC/DC power converters for battery chargers are designed for the specific application. The input voltage, as well as the output voltage requirements, are taken into considerations in the design process. Accordingly, the design of a conventional AC/DC converter for a given battery pack will change according to different AC input voltage sources.  
           [0008]    The present invention addresses the above-mentioned deficiencies in AC/DC power converter designs by providing a single power converter design which can accept universal input voltages (i.e., 108Vac to 264Vac) and provide regulated DC output with a large voltage range. The invention is primarily an AC/DC power converter utilizing universal utility power to charge a battery pack. A battery pack is a group of batteries connected in series or series-parallel. The present invention operates using a single power processing stage, and provides power factor correction (PFC), input to output isolation (galvanic), and sine square output power. With the aid of relay(s) and a tapped transformer, the single stage AC/DC power converter of the present invention accepts input voltages of a global range (i.e., 108Vac to 264Vac) and provides regulated DC power with a large output voltage and power range capability, (i.e., 0 to 6 kW). The proposed invention provides constant power operation at large battery voltage range. For higher output power requirements, the multiple AC/DC power converters of the present invention can be operated in parallel or multiphase configuration without more effort than connecting the inputs and outputs accordingly. The AC/DC power converter of the present invention maintains a single design with higher efficiency, lower cost, and smaller volume than the conventional AC/DC power converters serving the same function.  
         SUMMARY OF THE INVENTION  
         [0009]    In accordance with the present invention, there is provided a universal AC/DC power converter for generating regulated DC output power with large voltage range from a varying AC input voltage source of a global range (i.e., 108Vac to 264Vac). The AC/DC power converter has a single power processing stage, at least one relay in electrical communication with the output of the single power processing stage, a transformer in electrical communication with the relay, an output rectifier network in electrical communication with the output of the transformer, and a processor that contains the control for logic of the AC/DC power converter. The single power processing stage includes an input rectifier network to rectify the AC input voltage to a DC input voltage, and a voltage boost function to increase the DC input voltage to a higher regulated voltage defined herein as the boosted voltage. The boosted voltage is the regulated output voltage of the voltage boost function. The voltage boost function entails at least one inductor, at least one diode, at least four switching devices, an input current transducer, and the function of the processor. The four switching devices may be transistors such as power MOSFET&#39;s or IGBT&#39;s, and the input current transducer may be a sense resistor. In addition to the voltage boost function, the single power processing stage includes a voltage chop function that chops the boost voltage to form AC voltage. This AC voltage is in electrical communication with the transformer via the relays. The electrical components that make up the voltage chop function are some of the same components that make up the voltage boost function. For this reason the voltage boost function and the voltage chop function are defined as a single integrated power processing stage.  
           [0010]    The relay (or relays) in electrical communication with the output of the single power processor stage is configured with at least two switching positions operated by the processor. The transformer (in electrical communication with the relays) has a primary winding and at least one secondary winding. The primary winding has at least two inputs operative to selectively vary the voltage generated on the secondary winding from the position of the relays. Alternatively, the relays can also be located on the secondary winding of the transformer without altering the intended function of the invention. Finally, an output rectifier network (in electrical communication with the transformer secondary winding) converts the AC voltage to DC voltage. The relays can selectively change the output DC voltage range of the AC/DC power converter by choosing the inputs of the transformer.  
           [0011]    In accordance with the present invention, the AC/DC power converter includes a processor. The processor contains the control logic for the AC/DC power converter and may include a microprocessor and a power factor pre-regulator circuit. The processor is in electrical communication with the DC input voltage and the DC output voltage. The processor is operative to selectively position the relay or relays in response to the DC input voltage and the DC output voltage. In this sense, the processor directs the relays into a position that sets the AC/DC power converter into the proper output voltage range to charge a battery pack connected to its output. In addition to the DC input voltage and the DC output voltage, the processor may be in electrical communication with the input current transducer to perform the power factor correction function. The input current transducer may be a sense resistor or isolated current sensor. In addition to the processor, the sense resistor is in electrical communication with the switching devices and the input rectifier network. The processor also contains a logic circuit to perform the voltage boost function and the voltage chop function. In addition to the DC input voltage, the DC output voltage, and the input current transducer, the processor is in electrical communication with the output current transducer, and at least one external charge command to increase and regulate the DC input voltage to produce the boosted voltage. The output current transducer is also in electrical communication with the output rectifier network.  
           [0012]    The processor is in electrical communication with the four switching devices. The four switching devices are modulated on and off by the processor in accordance with the external charge command for level charging, and for voltage, or current, or power modes of regulation. The processor may be preprogrammed to accept the DC input voltage data, input current data, output voltage data, output current data, and modulate the on and off time of the four switching devices to boost and regulate the DC input voltage as dictated by the external charge command for output voltage regulation, or output current regulation, or output power regulation.  
           [0013]    The voltage chop function of the single power processing stage entails the four switching devices. The four switching devices are connected in an “H” bridge configuration and switched at a fixed frequency. During the voltage boost function the processor commands all four switching devices on for a portion of the period followed by turning off two of the switching devices for the remaining period. The two switching devices are two diagonal devices of the H-bridge. The processor determines the switching device operating duty for the voltage boost function. The duty is defined as the switching device on time divided by the on time plus the off time of the given period. The processor (in electrical communication with the external charge command, the DC input voltage, and DC output voltage) computes the duty for the four switching devices. As for the voltage chop function, the processor alternately sequences the diagonal switching devices of the “H” bridge on and off at a time when all four switches are not on. This complex switching sequence of the four switching devices will be described in more detail. The voltage boost function in conjunction with the voltage chop function boost the DC input voltage to a higher regulated voltage, herein defined as the boosted voltage and electrically chop it to form the AC voltage. The output of the single power processing stage is a regulated AC voltage with its amplitude consistent with the external charge command. This AC voltage is in electrical communication with the primary winding of a transformer via the relays. The inputs of the transformer may have primary inputs, tap inputs, or primary and tap inputs.  
           [0014]    In the preferred embodiment, the AC/DC power converter is configured to produce regulated DC output power that is operative to charge at least one battery pack. In the preferred embodiment, the processor may be in electrical communication with the DC input voltage and the DC output voltage in order to determine the output voltage. The processor determines whether the inputs to the transformer should be the primary inputs, or tap inputs, or primary and tap inputs. As will be recognized by those of ordinary skill in the art, the transformer may include multiple taps for generating different secondary AC voltages therefrom and corresponding output DC voltages. The output rectifier network is in electrical communication with the secondary winding of the transformer. The transformer secondary AC voltage is rectified to form the DC output voltage.  
           [0015]    In accordance with the present invention, there is provided a method of converting an unregulated AC input voltage into a regulated DC output with large voltage range, with an AC/DC power converter having a single power processing stage, at least one relay, a transformer with multiple inputs, an output rectifier network, and an output current transducer. The method comprises applying an unregulated AC input voltage to the input rectifier network of the single power processing stage to produce an unregulated DC input voltage. The unregulated DC input voltage is applied to a voltage boost function of the single power processing stage. The voltage boost function boosts the unregulated DC input voltage to form a regulated boosted voltage defined as the boosted voltage. A voltage chop function of the single power processing stage applies the boosted voltage to the input of the transformer via the relay(s) in an alternating sequence accomplished by sequentially switching the four switching devices. The result is the single power processing stage generates a regulated AC voltage output via the relays to the input of the transformer. The relay(s) select the transformer inputs for the application of the regulated AC voltage. The four switching devices are in electrical communication with the relay(s) and are operative by the processor. The processor modulates the on and off time of the four switching devices. With the four switching devices being modulated, the voltage to the input of the transformer is a regulated AC voltage. This regulated AC voltage is induced into the secondary winding of the same transformer. The output rectifier network is in electrical communication with the secondary winding of the transformer. The regulated AC voltage induced onto the transformer secondary is rectified by the output rectifier network to form a regulated DC voltage that is the AC/DC power converter output. Depending on the external charge command (in electrical communication with the processor), the AC/DC power converter output may be voltage regulated, current regulated, or power regulated.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    These, as well as other features of the present invention, will become more apparent upon reference to the drawings wherein:  
         [0017]    [0017]FIG. 1 is a circuit diagram for a Prior Art AC/DC Power Converter; and  
         [0018]    [0018]FIG. 2 is a circuit diagram for an AC/DC Power Converter constructed in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0019]    Referring now to the drawings wherein the showing are for the purposes of illustrating a preferred embodiment of the present invention only, and not for purposes of limiting the same, FIG. 1 is a circuit diagram of a prior art AC/DC power converter  10 . The prior art AC/DC power converter  10  is a two-stage power processor with a first power processor stage as a boost converter and a second power processor stage as a DC-DC converter. The prior art AC/DC power converter  10  has a bridge rectifier network input consisting of diodes  14 ,  16 ,  18 , and  20  operative to rectify an AC input voltage  12  from a utility line. The bridge rectifier network is in electrical communication with an inductor  36 . The term inductor and choke may be used interchangeably herein. The boost converter consists of an inductor  36  in electrical communication with switching device  40  and the anode of diode  42 . The cathode of diode  42  is in electrical communication with a capacitor  44 . The positive terminal of a current transducer  32  is in electrical communication with the switching device  40 , the capacitor  44 , and a power factor pre-regulator controller  34 . A negative terminal of the current transducer  32  is in electrical communication with the diodes  18  and  20 , and the power factor controller  32 .  
         [0020]    Energy from the AC input voltage  12 , and the inductor  36  are stored in the capacitor  44  via the diode  42  during the boost period, when switching device  40  is off. The increase in energy in the capacitor  44  boosts the voltage of capacitor  44 . The DC-DC converter, (i.e., the second power processing stage) retrieves energy from capacitor  44  when switching device  40  is on. During this period, the current from AC input voltage  12  increases. The increasing current flows from the AC input voltage  12  through diode  14 , through inductor  36 , switching device  40 , input current transducer  32 , and diode  20 . Increasing current through inductor  36  results in increasing energy stored in inductor  36 .  
         [0021]    Voltage boosting with power factor correction is operative by power factor pre-regulator controller  34 . The power factor pre-regulator controller  34  is in electrical communication with the voltage of capacitor  44  via line  46 , a rectified AC input voltage  22  via line  26 , and the input current transducer  32  via lines  28  and  30 , as shown in FIG. 1.  
         [0022]    The prior art AC/DC power converter  10  may include an external charge command  24  in electrical communication with the power factor pre-regulator controller  34  in order to dictate the level of charging. The power factor preregulator controller  34  senses the capacitor  44  voltage via line  46  and the rectified AC input voltage  22  via line  26 , and the input current via lines  28  and  30 . Upon receiving the external charge command  24 , the power factor pre-regulator controller  34  modulates the on and off time of switching device  40  via line  38  to achieve a regulated boosted voltage across capacitor  44 . The on and off modulation of switching device  40  determines the energy stored in the inductor  36  and the energy released to the capacitor  44  via diode  42 , respectively. The energy from the inductor  36  released to the capacitor  44  determines the boosted voltage on capacitor  44 . The voltage across capacitor  44  is regulated by the power factor pre-regulator  34  to the level defined by the external charge command  34 .  
         [0023]    Switching devices  48 ,  50 ,  52 , and  54 , transformer  58 , and the diodes  62 ,  64 ,  66 , and  68  form the second power processing stage, (i.e., the DC-DC converter). Switching devices  48 ,  50 ,  52 , and  54  are connected in an H-bridge configuration as shown in FIG. 1 and are in electrical communication with capacitor  44  and a primary winding  56  of transformer  58 . Switching devices  48 ,  50 ,  52 , and  54  may be transistors, such as MOSFET&#39;s that are switched on and off at a 50% duty cycle at a fixed frequency. Herein, the duty is defined as the switching device on time divided by the switching device on time plus the off time. The four switching devices  48 ,  50 ,  52 , and  54  are switched on and off in such a sequence to form an AC voltage. This AC voltage is in communication with the primary winding of transformer  58 . The presence of the AC voltage on the primary winding  56  of transformer  58  induces a voltage of the same kind onto the secondary winding  60  of the same transformer  58 , but of a different amplitude. The difference in amplitude is a function of the turns ratio of transformer  58 . Herein, the transformer turns ratio is defined as the transformer primary turns divided by the transformer secondary turns.  
         [0024]    In electrical communication with the secondary winding  60  of transformer  58  is a bridge rectifier network having diodes  62 ,  64 ,  66 , and  68  that rectify the AC voltage from the secondary winding  60  to produce a DC voltage. The DC voltage is the AC/DC power converter  10  output voltage  70 . In this respect, the power converter output voltage  70  of the prior art AC/DC power converter  10  is the secondary winding  60  voltage rectified by the diodes  62 ,  64 ,  66 , and  68 . The power converter output voltage  70  is defined by the regulated voltage across capacitor  44 , which is controlled by the power factor pre-regulator controller  34 , as previously explained. The power converter output voltage  70  of the prior art AC/DC power converter  10  is the regulated voltage across capacitor  44  amplified by the transformer  58  turns ratio.  
         [0025]    The prior art AC/DC power converter  10  may provide power factor correction, regulated DC output voltage, and input to output isolation. However, as previously discussed, the prior art AC/DC power converter  10  cannot adequately provide for wide range of regulated DC output voltage for the total range of global AC input voltages  12  (i.e., 108Vac to 264Vac). To cover this wide range of AC input voltages and output DC voltages different prior art AC/DC power converter designs are required. Primarily, the turns ratio of transformer  58  must be changed to accommodate the wide range of AC input voltage. Meaning, transformer  58  would require a different transformer turns ratio if its AC input voltage to the AC/DC power converter  10  is 120Vac verses 240Vac.  
         [0026]    Referring to FIG. 2, an AC/DC power converter  100  constructed in accordance with the present invention is shown. The AC/DC power converter  100  has a single power processing stage  102 , two relays  164  and  166  in electrical communication with the output of the single power processing stage, a transformer  178  in electrical communication with the relays  164 , and  166 , an output rectifier network consisting of rectifiers  186 ,  190 ,  192 , and  194  in electrical communication with the output of the transformer  178 , an output transducer  202  in electrical communication with rectifiers  190  and  194 , and a processor  136  that contains the control and logic for the AC/DC power converter  100 . The single power processing stage  102  contains an input rectifier network consisting of rectifiers  112 ,  114 ,  116 , and  118 , a voltage boost function, a voltage chop function, and an input current transducer  130 , such as a sense resistor. The input rectifier network consisting of rectifiers  112 ,  114 ,  116 , and  118  rectifies an unregulated AC input voltage  110  to an unregulated DC input voltage  120 . The voltage boost function consists of a choke  122 , a diode  124 , four switching devices  142 ,  144 ,  152 , and  154 , and the function of the processor  136 . The electrical components that make up the voltage chop function are the four switching devices  142 ,  144 ,  152 , and  154 , and the processor  136 . These are the same components required by the voltage boost function, and for that reason both the voltage boost function and the voltage chop function constitute a single power processing stage.  
         [0027]    Rectifiers  112  and  116  are in electrical communication with the inductor  122  that is in electrical communication with the anode of diode  124 . The cathode of diode  124  is in electrical communication with the drain of switching devices  142  and  152 . The source of switching devices  142  and  152  are in electrical communication with the drain of switching devices  144  and  154 , respectively. The terms drain, source, and gate are consistence with MOSFET switching devices. The source of switching devices  144  and  154  are in electrical communication with the positive terminal of the input current transducer  130 . The negative terminal of the input current transducer  130  is in electrical communication with the anode of rectifiers  114  and  118 . The voltage developed across the drain of switching device  142  and the source of switching device  144  can be identified as boosted voltage  148 .  
         [0028]    The processor  136  may contain a power factor pre-regulator and/or a microprocessor. The processor  136  is in electrical communication with the DC input voltage  120  via line  126 , input current transducer  130  via lines  128  and  132 , and a DC output voltage  196  via line  182 . The processor  136  controls the operation of relays  164  and  166  via lines  160  and  162 , respectively, as will be further explained. In addition, the processor  136  is in electrical communication with an external charge command  134  and the processor  136  controls the on and off operation of switching device  142  via line  138 , switching device  144  via line  140 , switching device  152  via line  146 , and switching device  154  via line  156 . The switching devices  142 ,  144 ,  152 , and  154  along with inductor  122 , diode  124 , sense resistor  130 , and processor  136  perform multiple functions such as:  
         [0029]    1. The processor  136  modulates the on and off time of the four switching devices  142 ,  144 ,  152 , and  154  to boost the DC input voltage  120  to a higher regulated voltage identified as the boosted voltage  148  per the charge command  134 ;  
         [0030]    2. The processor  136  modulates the on and off time of the four switching devices  142 ,  144 ,  152 , and  154  to provide for input power factor correction; and  
         [0031]    3. The processor  136  modulates the on and off time of the four switching devices  142 ,  144 ,  152 , and  154  to electrically chop the boosted voltage  148  to generate an AC voltage for transformer application.  
         [0032]    The operating frequency of the four switching devices  142 ,  144 ,  152 , and  154  is fixed and synchronized. The detailed operation of the four switching devices  142 ,  144 ,  152 , and  154  can best be described by illustrating the operation in four separate quadrants. The first and third quadrants are of equal time duration; the second and fourth quadrants are of equal time duration. The first and third quadrants perform the boost function that determine the voltage level of the boosted voltage  148 ; the second and fourth quadrants perform the chop function. The boosted voltage  148  is electrically chopped to form AC voltage for transformer application.  
         [0033]    First Quadrant:  
         [0034]    All four switching devices  142 ,  144 ,  152 , and  154  are switched on and are saturated. The on time duration of the switching devices  142 ,  144 ,  152 , and  154  is a function of the required energy stored in choke  122 , and is determined by the processor  136  and the external charge command  134 . During this period, increasing current flows from the AC input voltage  110  through the rectifier  112 , through the choke  122 , through the diode  124 , through the four switching devices  142 ,  144 ,  152 , and  154 , through the input current transducer  130 , and rectifier  118 . Stored energy builds up in the choke  122  as the current increases. The on condition of the four switches  142 ,  144 ,  152 , and  154  thereby shorts the primary winding  176  of transformer  178  via relays  164  and  166 . No voltage is present across the primary winding  176  of transformer  178  and thus no voltage is induced across the secondary winding  180  of transformer  178 . Accordingly, during this quadrant no power is transferred from the AC input voltage  110  to a load  204  connected to an output  220  of the AC/DC power converter  100 . The load  204  may be a battery pack.  
         [0035]    Second Quadrant:  
         [0036]    Two switching devices  152  and  144  are turned off. The other two switching devices  142  and  154  remain on and saturated. Primary winding  176  of transformer  178  is no longer shorted. Due to the load  204  reflected back onto the primary winding  176  of transformer  178 , decreasing current now flows from the AC input voltage  110  through rectifier  112  through choke  122 , diode  124 , switching device  142 , relay  164 , primary input  168 , through winding  176  of transformer  178 , tap  174 , relay  166 , switching device  154 , input current transducer  130 , and rectifier  118 . Choke  122  releases energy due to the decreasing current and boost the voltage, defined as boosted voltage  148 . The boosted voltage  148  is applied across the primary winding  176  of transformer  178  via switching devices  142  and  154 , and relays  164  and  166 . The boosted voltage  148  is transformed to the secondary winding  180  via the transformer action. Current flows from the secondary winding  180  of transformer  178  through diode  186  to the load  204  and returns through the output current transducer  202  and diode  194 . The output current transducer  202  may be a sense resistor. During this quadrant, power is transferred from the AC input voltage  110  and the choke  122  to the AC/DC power converter load  204 .  
         [0037]    Third Quadrant:  
         [0038]    All four switching devices  142 ,  144 ,  152 , and  154  are switched on and are saturated. The on time duration of the switching devices  142 ,  144 ,  152 , and  154  is the same duration as that in the first quadrant. During this period the primary winding  176  is shorted via the on condition of the four switching devices  142 ,  144 ,  152 , and  154 , and the relays  164  and  166 . Increasing current now flows from the AC input voltage  110  through rectifier  112 , choke  122 , diode  124 , and through the four switching devices  142 ,  144 ,  152 , and  154 , the input current transducer  130 , and rectifier  118 . Stored energy builds up in choke  122  as the current increases. The four switches  142 ,  144 ,  152 , and  154  short the primary winding  176  of transformer  178 , and no voltage is induced across the secondary winding  180  of transformer  178 . Accordingly, during this quadrant no power is transferred from the AC input voltage  110  to the load  204 .  
         [0039]    Fourth Quadrant:  
         [0040]    The two switching devices  142 , and  154  are turned off. The other two switching devices  152  and  144  remain on and saturated. Primary winding  176  of transformer  178  is no longer shorted. Due to the load  204  reflected back onto the primary winding  176  of transformer  178 , decreasing current now flows. The decreasing current flows from the AC input voltage  110  through the rectifier  112 , through choke  122 , diode  124 , switching device  152 , relay  166 , tap  174 , through primary winding  176  of transformer  178 , primary input  168 , relay  164 , switching device  144 , input current transducer  130 , and rectifier  118 . Note that during the second quadrant, current flows into the primary winding  176  of transformer  178  via primary input  168  and exits through tap  174 . In this fourth quadrant, current flows into the primary winding  176  of transformer  178  via tap  174  and exits through primary input  168 . This reversal of current flow between the second and fourth quadrants presents an alternating voltage (AC voltage) across the primary winding  176  of transformer  178 , and resets the transformer core. Resetting the transformer core is a necessary action for transformer operation. Choke  122  releases energy due to the decreasing current and boosts the voltage (boosted voltage  148 ) to a higher level as is commonly known in choke operation. This higher voltage (boosted voltage  148 ) is applied across the primary winding  176  of transformer  178  via switching devices  152  and  144 , and relays  166  and  164 , as described earlier. The boosted voltage  148  is transformed to the secondary winding  180  of transformer  178  via transformer action. Current flows from the secondary winding  180  of transformer  178  through diode  192  to the load  204  and returns through output current transducer  202  and diode  190 . During this quadrant, power is transferred from the AC input voltage  110  and the choke  122  to the AC/DC power converter load  204 .  
         [0041]    The operation of the four switching devices described in the four quadrants performs the following functions:  
         [0042]    1. Conditions the AC input current for power factor correction;  
         [0043]    2. Boosts the DC input voltage  120  to a regulated voltage identified as boosted voltage  148 ; and  
         [0044]    3. Electrically chops the boosted voltage  148  for transformer  178  application.  
         [0045]    The above three (3) functions just described are accomplished by modulating the on and off time of switching devices  142 ,  144 ,  152 , and  154  via the processor  136  at some fixed frequency and sequence. The modulation is determined by the processor  136  and is a function of the external charge command  134 , DC input voltage  120 , the input current sensed via lines  128  and  132 , the DC output voltage  196 , and the output current sensed via lines  198  and  200 .  
         [0046]    As previously mentioned, the AC/DC power converter  100  includes a transformer  178  having a primary winding  176  and a secondary winding  180 . An AC voltage applied across the primary winding  176  will induce an AC voltage across the secondary winding  180  of the same kind, but may be of different amplitude depending on the turns ratio of transformer  178 , as is commonly known in the electrical operation of transformers. The primary winding  176  of transformer  178  has primary connections  168  and  172  wherein the entire primary winding  176  will be used. Additionally, the primary winding  176  has taps  170  and  174  which are used for isolating sections of the primary winding  176 , as is commonly known in the art of transformer design. Accordingly, by applying an AC voltage across different pairs of the primary and tap connections  168 ,  172 ,  170 , and  174 , it is possible to change the voltage induced in the secondary winding  180  of transformer  178 .  
         [0047]    Referring to FIG. 2, the source of switching device  142  is electrically connected to the drain of switching device  144 . The terms source, drain, and gate of the switching devices are consistence with MOSFET switching devices, however it will be recognized that other types of switching devices may be used interchangeably. Connected between the switching devices  142  and  144  (i.e., between the source of switching device  142  and drain of switching device  144 ) is a first lead  150  that is connected to the first relay  164 . The first relay  164  is operative to switch the first lead  150  between the primary connection  168  and the tap connection  170  of the primary winding  176 . The switching operation of the first relay  164  is controlled by the processor  136  via line  160 . As such, the processor  136  can switch the first lead  150  from the primary connection  168  to the tap connection  170 , as will be further explained below.  
         [0048]    Similarly, a second lead  158  is connected between the source of switching device  152  and the drain of switching device  154 . The second lead  158  is connected to a second relay  166  that is operable to switch between the tap connection  174  and the primary connection  172  of the primary winding  176 . The second relay  166  is controlled via control line  162  from processor  136 . In this respect, the processor  136  can switch the second lead  158  from the tap connection  174  to the primary connection  172 .  
         [0049]    In order to determine the proper switching operation of the first relay  164  and second relay  166 , the processor  136  contains a preprogrammed algorithm. The processor  136  in electrical communication with the DC input voltage  120  and the DC output voltage  196  operates relays  164  and  166  via lines  160  and  162 , respectively, per the preprogrammed algorithm. In other words, the processor  136  controls the operating range of the AC/DC power converter  100  by monitoring the DC input voltage  120 , and the DC output voltage  196 , and applying the monitored voltages to a preprogrammed algorithm in the processor  136  to position relays  164  and  166 .  
         [0050]    Additionally, the processor  136  is in electrical communication with the gates of switching devices  142 ,  144 ,  152 , and  154  via lines  138   140 ,  146 , and  156 , respectively, in order to control the operation thereof. Specifically, the processor  136  controls the operation of the switching devices  142 ,  144 ,  152 , and  154  to charge the load  204  to levels dictated by charge command  134 . The charge command  134  is an external command that may be issued by the user or another control unit to command the AC/DC power converter  100  to charge the load  204  (battery pack) to a specific current level, voltage level or power level. The processor  136  accepts the charge command  134  and adjusts the on and off time of switching devices  142 ,  144 ,  152 , and  154  to achieve the charge level dictated by the charge command  134  while maintaining input power factor correction by virtue of the power factor pre-regulator in the processor  136 .  
         [0051]    Referring to FIG. 2, the secondary winding  180  of the transformer  176  has a first output  184  and a second output  188 . The first output  184  is in electrical communication with the anode of diode  186  and the cathode of diode  190 . Similarly, the second output  188  is in electrical communication with the anode of diode  192  and cathode of diode  194 . The cathode of diodes  186  and  192  are in electrical communication with the load  204  via lead  206 . The positive terminal of the output current transducer  202  is in electrical communication with load  204  via lead  208 . The negative terminal of output current transducer  202  is in electrical communication with the cathode of diodes  190  and  194 . In this respect, the diodes  186 ,  190 ,  192 , and  194  form a bridge rectifier network operative to rectify the AC voltage from secondary winding  180  of transformer  178  to a DC output voltage  196 .  
         [0052]    In accordance with the present invention, the preferred method of operating the AC/DC power converter  100  includes charging a battery pack with an AC input voltage  110  and an external charge command  134 . The battery pack being the load  204  and in electrical communication with the output  220  of the AC/DC power converter  100 . Alternatively, the load  204  can be any electrical device that needs regulated DC power. The AC input voltage  110  is rectified by the rectifier network consisting of diodes  112 ,  114 ,  116 , and  118  to form DC input voltage  120  as shown in FIG. 2. As previously mentioned, the AC input voltage  110  can vary from location to location. Specifically, the AC input voltage  110  varies from country to country. The processor  136  senses the DC input voltage  120  via line  126  and DC output voltage  196  via line  182  and selects the positions of relays  164  and  166  via lines  160 , and  162 , respectively. A preprogrammed algorithm in the processor  136  determines the selections of the different relay positions to determine the operating range of the AC/DC power converter  100 . The preprogrammed algorithm takes into account the voltages, DC input voltage  120 , and DC output voltage  196  in making the selections. After positioning relays  164  and  166 , the processor  136  in electrical communication with the charge command  134 , the input current transducer  130  via lines  128  and  132 , and the output current transducer  202  via lines  198  and  200 , modulates the on and off times of switching devices  142 ,  144 ,  152 , and  154  via lines  138 ,  140 ,  146 , and  156 , respectively, to a duty that is consistent with the charge command  134 . The DC input voltage  120  is thus boosted by the modulation of switching devices  142 ,  144 ,  152 , and  154  to a voltage defined as the boosted voltage  148 . This boost function is defined as the voltage boost function and its circuit consists of inductor  122 , diode  124 , four switching devices  142 ,  144 ,  152 , and  154 , input transducer  130 , and the function of processor  136 . The output of the voltage boost function circuit is a regulated output voltage identified as the boosted voltage  148 . The switching devices  142 ,  144 ,  152 , and  154 , and the function of the processor  136 , also perform the voltage chop function, which converts the regulated DC boosted voltage  148  to an AC voltage. This AC voltage is in electrical communication with the primary winding  176  of transformer  178  via relays  164  and  166 . The voltage across the primary winding  176  of transformer  178  is induced into the secondary winding  180 . The boosted voltage  148  is regulated at a level such that the DC output voltage  196  developed by the secondary winding  180  of transformer  178 , and rectified by diodes  186 ,  190 ,  192 , and  194 , is adequate to supply the current level to the load  204  that is consistent with the charge command  134 . The voltage chop function electronically chops the boosted voltage  148  for transformer application. This operation was described earlier in the four-quadrant section.  
         [0053]    The relays  164  and  166  are in electrical communication with primary winding  176  of transformer  178  through primary connections  168  and  172 , and taps connections  174  and  172 . The processor  136 , as previously described, selects the positions of the relays  164  and  166 . The processor  136  is in electrical communication with the DC input voltage  120  via line  126  and the power converter DC output voltage  196  via line  182  and activates relays  164  and  166  via lines  160  and  162 , respectively, to a preprogrammed algorithm in the processor  136 . The processor  136  monitors AC/DC power converter  100  input voltage, DC input voltage  120 , and DC output voltage  196 , and positions the relays  164 , and  166  as required to set the AC/DC power converter  100  to proper operating range to charge the load  204 . This feature enables the AC/DC power converter  100  to charge a battery pack load  204  with universal input voltage (108Vac to 264Vac).  
         [0054]    More particularly, with the AC/DC Power Converter  100  output in communication with a battery pack as the load  204 , and its input in communication with an utility AC input voltage  110  as the source, and a prescribed charge command  134  at the processor  136 , the processor  136  senses the DC input voltage  120  via line  126 , and the DC output voltage  196  (battery pack voltage) via line  182  and positions relays  164  and  166  via lines  160 , and  162 , for proper transformer tap positions determined by a preprogrammed algorithm in the processor  136 . Then the processor  136  acknowledges the charge command  134  and modulates the on and off time of switching devices  142 ,  144 ,  152 , and  154  to boost the DC input voltage  126  to a regulated boosted voltage  148 , consistent with the charge command  134 . In addition, the modulation of switching devices  142 ,  144 ,  152 , and  154  electronically chop the boosted voltage  148  as previously described and apply it to the primary winding  176  of transformer  178  via relays  164  and  166  as previously described. The transformed voltage at secondary winding  180  of transformer  178  is rectified by diodes  186 ,  190 ,  192 , and  194 . The DC output voltage  196  generated from diodes  186 ,  190 ,  192 , and  194  is the regulated DC output voltage  196  of the AC/DC power converter  100 . The regulated DC output voltage  196  is at a level that is consistent with the charge command  134 .  
         [0055]    Additional modifications and improvements of the present invention may be apparent to those of ordinary skill in the art such as providing different configurations for the single power processing stage. Thus, the particular combination of parts described and illustrated herein is intended to represent only certain embodiments of the present invention, and is not intended to serve as limitations of alternative devices within the spirit and scope of the invention.