PATENT DOCUMENT

Publication Number: US-12021401-B2
Application Number: US-202318153744-A
Country: US
Kind Code: B2

Title: Single stage charger for high voltage batteries

Abstract:
A charger for a battery power system can include first and second switching bridges with inputs couplable to an AC source, at least one transformer having two or more primary windings (connected in series and coupled to the switching bridges) and at least two secondary windings, and second rectifier/chargers, each coupled to at least one of the secondary windings and couplable to at least one battery. The switching bridges may be respectively operable during positive and negative half cycles of the AC source to deliver an AC voltage to the transformer. The rectifier/chargers may be operable in a first mode to receive an AC voltage from the transformer and deliver a DC voltage for charging the respective battery. In some multi-battery embodiments, the rectifier/chargers may also be operable in a second mode to deliver an AC voltage from a respective battery to the transformer to balance charge between the batteries.

Claims:
The invention claimed is: 
     
       1. A charger for a battery power system, the charger comprising:
 at least first and second switching bridges each having an input terminal configured to be coupled to an AC input power source and commonly coupled neutral terminals; 
 at least one transformer having two or more primary windings connected in series and coupled to the at least first and second switching bridges, the at least one transformer further comprising at least two secondary windings; and 
 at least first and second rectifier and chargers each coupled to at least one of the secondary windings and configured to be coupled to a battery; 
 wherein:
 the first switching bridge is operable during a positive half cycle of the AC input power source to deliver an AC voltage to the at least one transformer, and the second switching bridge is operable during a negative half cycle of the input power source to deliver an AC voltage to the at least one transformer; and 
 the first and second rectifier and chargers are operable in a first mode to receive an AC voltage from the at least one transformer and deliver a DC voltage for charging the battery. 
 
 
     
     
       2. The charger of  claim 1  wherein the charger is a charger and balancer for a multi battery system and wherein the first and second rectifier and chargers are operable in a second mode to convert a DC voltage from a respective battery to an AC voltage delivered to the at least one transformer to balance charge between a first and a second batteries. 
     
     
       3. The charger of  claim 1  wherein the first and second switching bridges are each full bridges comprising four switching devices. 
     
     
       4. The charger of  claim 3  wherein the at least one transformer comprises four transformers each having a primary winding and a secondary winding, and:
 a first series connected primary winding comprises the primary winding of a first transformer coupled in series with the primary winding of a third transformer; 
 a second series connected primary winding comprises the primary winding of a second transformer coupled in series with the primary winding of a fourth transformer; and 
 the at least two secondary windings include a first series connected secondary winding comprising the secondary winding of the first transformer coupled in series with the secondary winding of the second transformer and a second series connected secondary winding comprising the secondary winding of the third transformer coupled in series with the secondary winding of the fourth transformer. 
 
     
     
       5. The charger of  claim 4  wherein the first rectifier and charger is coupled to the first series connected secondary winding and the second rectifier and charger is coupled to the second series connected secondary winding. 
     
     
       6. The charger of  claim 4  wherein the at least one transformer comprises a single transformer having four primary windings and four corresponding secondary windings, and:
 a first series connected primary winding comprises a first primary winding coupled in series with a third primary winding; 
 a second series connected primary winding comprises a second primary winding coupled in series with a fourth primary winding; and 
 the at least two secondary windings include a first series connected secondary winding comprising a first secondary winding coupled in series with a second secondary winding and a second series connected secondary winding comprising a third secondary winding coupled in series with a fourth secondary winding. 
 
     
     
       7. The charger of  claim 4  wherein the first rectifier and charger is coupled to the first series connected secondary winding and the second rectifier and charger is coupled to the second series connected secondary winding. 
     
     
       8. The charger of  claim 1  wherein the first and second rectifier and chargers are full bridges comprising four switching devices. 
     
     
       9. A charger for a battery power system, the charger comprising:
 first and second switching bridges coupled to an AC input power source; 
 at least one transformer having at least one pair of series connected primary windings coupled to the first and second switching bridges, the at least one transformer further having at least two secondary windings; 
 first and second rectifier and chargers each coupled to at least one of the secondary windings and configured to be coupled respectively to a first and second battery; and 
 a controller configured to:
 operate the first switching bridge during a positive half cycle of the input power source to deliver AC voltage to the at least one transformer; 
 operate the second switching bridge during a negative half cycle of the input power source to deliver AC voltage to the at least one transformer; and 
 operate the first and second rectifier and chargers in a first mode to convert AC voltage from the at least one transformer to DC voltage for charging the battery. 
 
 
     
     
       10. The charger of  claim 9  wherein the charger is a charger and balancer for a multi battery system and wherein the controller is further configured to operate the first and second rectifier and chargers in a second mode to convert DC voltage from a respective battery to an AC voltage delivered to the at least one transformer to balance charge between the first and second batteries. 
     
     
       11. The charger of  claim 9 , wherein the controller is further configured to:
 operate the first switching bridge during a positive half cycle of the input power source to deliver AC voltage to the at least one transformer by closing all switches of the second switching bridge and operating the switches of the first switching bridge to deliver a pulse width modulated AC voltage to the at least one transformer; 
 operate the second switching bridge during a negative half cycle of the input power source to deliver AC voltage to the at least one transformer by closing all switches of the second switching bridge and operating the switches of the second switching bridge to deliver a pulse width modulated AC voltage to the at least one transformer. 
 
     
     
       12. A method of providing charging to a battery system, the method comprising:
 operating a first switching bridge during a positive half cycle of an input power source to deliver AC voltage to at least one transformer having at least two primary windings connected in series; 
 operating a second switching bridge during a negative half cycle of the input power source to deliver AC voltage to the at least one transformer; and 
 operating first and second rectifier and chargers in a first mode to convert AC voltage from the at least one transformer to DC voltage for charging a battery. 
 
     
     
       13. The method of  claim 12 , wherein:
 operating the first switching bridge during a positive half cycle of the input power source to deliver AC voltage to the at least one transformer comprises closing all switches of the second switching bridge and operating the switches of first switching bridge to deliver a pulse width modulated AC voltage to the at least one transformer; and 
 operating the second switching bridge during a negative half cycle of the input power source to deliver AC voltage to the at least one transformer comprises closing all switches of the second switching bridge and operating the switches of the second switching bridge to deliver a pulse width modulated AC voltage to the at least one transformer. 
 
     
     
       14. The method of  claim 12  wherein method further comprises providing balancing to a dual battery system by operating the first and second rectifier and chargers in a second mode to convert DC voltage from a respective battery to an AC voltage delivered to the at least one transformer to balance charge between first and second batteries. 
     
     
       15. The method of  claim 12 , wherein operating the first and second rectifier and chargers in a second mode to convert DC voltage from a respective battery to an AC voltage delivered to the at least one transformer to balance charge between first and second batteries comprises closing all switches of the first and second switching bridges and operating one of the first and second rectifier and chargers as an inverter to deliver a pulse width modulated AC voltage to the at least one transformer while operating the other of the first and second rectifier and chargers in the first mode.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. patent application Ser. No. 17/032,721, filed Sep. 25, 2020, entitled “SINGLE STAGE CHARGER FOR HIGH VOLTAGE BATTERIES,” the disclosure of which is incorporated by reference in its entirety for all purposes. 
     BACKGROUND 
     There have been many recent developments in AC-DC systems that include batteries for energy storage. Some such system may include relatively high voltages and/or relatively high power levels. Applications of such systems include, but are not limited to, electric vehicles, grid battery systems, battery systems for solar systems, and the like. Additionally, in some arrangements, such AC-DC systems may include multiple batteries (each comprising multiple cells), each having their own charging system as well as a system for balancing charge between the multiple batteries. Depending on the implementation of such arrangements a relatively high number of power converters, and thus a relatively high number of switching devices may be provided. This increased number of converters and switching devices can lead to increases in complexity and cost as well as decreases in reliability and efficiency. 
     SUMMARY 
     Thus, for at least some applications, it may therefore be desirable to provide switching power converters that integrate multiple converters into a single converter that reduces the number of switching devices required. For example, it may be desirable to provide single-stage chargers as described in greater detail below. Additionally, in multi-battery embodiments, it may be desirable to provide includes integrated charger/balancer circuitry, thereby reducing the number of converters and switching devices required to achieve the functional objectives of the system. 
     A charger/balancer for a multi-battery power system can include at least first and second switching bridges each having an input terminal configured to be coupled to an AC input power source and commonly coupled neutral terminals, at least one transformer having two or more primary windings connected in series and coupled to the at least first and second switching bridges, the transformer further comprising at least two secondary windings, and at least first and second rectifier/chargers each coupled to at least one of the secondary windings and configured to be coupled to a respective battery. The first switching bridge may be operable during a positive half cycle of the AC input power source to deliver an AC voltage to the at least one transformer, and the second switching bridge may be operable during a negative half cycle of the input power source to deliver an AC voltage to the at least one transformer. The first and second rectifier/chargers may be operable in a first mode to receive an AC voltage from the at least one transformer and deliver a DC voltage for charging the respective battery, and the first and second rectifier/chargers may be operable in a second mode to convert a DC voltage from the respective battery to an AC voltage delivered to the at least one transformer to balance charge between the first and second batteries. The first and second switching bridges may each be full bridges comprising four switching devices. 
     The at least one transformer can include four transformers each having a primary winding and a secondary winding, with: a first series connected primary winding including the primary winding of a first transformer coupled in series with the primary winding of a third transformer; a second series connected primary winding including the primary winding of a second transformer coupled in series with the primary winding of a fourth; and the at least two secondary windings including a first series connected secondary winding comprising the secondary winding of the first transformer coupled in series with the secondary winding of the second transformer and a second series connected secondary winding comprising the secondary winding of the third transformer coupled in series with the secondary winding of the fourth transformer. The first rectifier/charger may be coupled to the first series connected secondary winding and the second rectifier/charger may be coupled to the second series connected secondary winding. 
     The at least one transformer can alternatively include a single transformer having four primary windings and four corresponding secondary windings, and: a first series connected primary winding including a first primary winding coupled in series with a third primary winding; a second series connected primary winding including a second primary winding coupled in series with a fourth primary winding; and the at least two secondary windings including a first series connected secondary winding comprising the first secondary winding coupled in series with the second secondary winding and a second series connected secondary winding comprising the third secondary winding coupled in series with the fourth secondary winding. The first rectifier/charger may be coupled to the first series connected secondary winding, and the second rectifier/charger may be coupled to the second series connected secondary winding. 
     The first and second rectifier/chargers can all each or all be full bridges comprising four switching devices. The first and second switching bridges can also each or all be each half bridges. The first and second switching bridges can each or all be dual half bridges comprising four switching devices. The first and second half bridges may be coupled to the at least one transformer by blocking capacitors. 
     A charger/balancer for a multi-battery power system can include: first and second switching bridges coupled to an AC input power source; at least one transformer having at least one pair of series connected primary windings coupled to the first and second switching bridges, the transformer further having at least two secondary windings; first and second rectifier/chargers each coupled to at least one of the secondary windings and configured to be coupled to respective first and second batteries; and a controller. The controller may be configured to: operate the first switching bridge during a positive half cycle of the input power source to deliver AC voltage to the at least one transformer; operate the second switching bridge during a negative half cycle of the input power source to deliver AC voltage to the at least one transformer; operate the first and second rectifier/chargers in a first mode to convert AC voltage from the at least one transformer to DC voltage for charging the first and second batteries; and operate the first and second rectifier/chargers in a second mode to convert DC voltage from a respective battery to an AC voltage delivered to the at least one transformer to balance charge between the first and second batteries. The controller may be further configured to operate the first switching bridge during a positive half cycle of the input power source to deliver AC voltage to the at least one transformer by closing all switches of the second switching bridge and operating the switches of the first switching bridge to deliver a pulse width modulated AC voltage to the at least one transformer; and operate the second switching bridge during a negative half cycle of the input power source to deliver AC voltage to the at least one transformer by closing all switches of the second switching bridge and operating the switches of the second switching bridge to deliver a pulse width modulated AC voltage to the at least one transformer. The controller may be still further configured to operate the first and second rectifier/chargers in a second mode to convert DC voltage from a respective battery to an AC voltage delivered to the at least one transformer to balance charge between the first and second batteries by closing all switches of the first and second switching bridges and operating one of the first and second rectifier/chargers as an inverter to deliver a pulse width modulated AC voltage to the at least one transformer while operating the other of the first and second rectifier/chargers in the first mode. The controller may be further configured to operate the first and second rectifier/chargers in a second mode to convert DC voltage from a respective battery to an AC voltage delivered to the at least one transformer to balance charge between the first and second batteries by closing all switches of the first and second switching bridges and operating one of the first and second rectifier/chargers as an inverter to deliver a pulse width modulated AC voltage to the at least one transformer while operating the other of the first and second rectifier/chargers in the first mode. 
     A charger for a battery power system can include at least first and second switching bridges each having an input terminal configured to be coupled to an AC input power source and commonly coupled neutral terminals; at least one transformer having two or more primary windings connected in series and coupled to the at least first and second switching bridges, the transformer further comprising at least two secondary windings; and at least first and second rectifier/chargers each coupled to at least one of the secondary windings and configured to be coupled to a battery. The first switching bridge may be operable during a positive half cycle of the AC input power source to deliver an AC voltage to the at least one transformer, and the second switching bridge may be operable during a negative half cycle of the input power source to deliver an AC voltage to the at least one transformer. The first and second rectifier/chargers may be operable in a first mode to receive an AC voltage from the at least one transformer and deliver a DC voltage for charging the battery. The charger may be a charger/balancer for a multi battery system, and the first and second rectifier/chargers may be operable in a second mode to convert a DC voltage from a respective battery to an AC voltage delivered to the at least one transformer to balance charge between a first and a second batteries. The first and second switching bridges are each full bridges comprising four switching devices. 
     The at least one transformer can include four transformers each having a primary winding and a secondary winding, with: a first series connected primary winding including the primary winding of a first transformer coupled in series with the primary winding of a third transformer; a second series connected primary winding including the primary winding of a second transformer coupled in series with the primary winding of a fourth; and the at least two secondary windings including a first series connected secondary winding comprising the secondary winding of the first transformer coupled in series with the secondary winding of the second transformer and a second series connected secondary winding comprising the secondary winding of the third transformer coupled in series with the secondary winding of the fourth transformer. The first rectifier/charger may be coupled to the first series connected secondary winding and the second rectifier/charger is coupled to the second series connected secondary winding. 
     Alternatively, the at least one transformer comprises a single transformer having four primary windings and four corresponding secondary windings, with: a first series connected primary winding including a first primary winding coupled in series with a third primary winding; a second series connected primary winding including a second primary winding coupled in series with a fourth primary winding; and the at least two secondary windings including a first series connected secondary winding comprising the first secondary winding coupled in series with the second secondary winding and a second series connected secondary winding comprising the third secondary winding coupled in series with the fourth secondary winding. The first rectifier/charger may be coupled to the first series connected secondary winding and the second rectifier/charger may be coupled to the second series connected secondary winding. The first and second rectifier/chargers may be full bridges comprising four switching devices. 
     A charger for a battery power system can include first and second switching bridges coupled to an AC input power source; at least one transformer having at least one pair of series connected primary windings coupled to the first and second switching bridges, the transformer further having at least two secondary windings; first and second rectifier/chargers each coupled to at least one of the secondary windings and configured to be coupled to a battery; and a controller. The controller may be configured to operate the first switching bridge during a positive half cycle of the input power source to deliver AC voltage to the at least one transformer; operate the second switching bridge during a negative half cycle of the input power source to deliver AC voltage to the at least one transformer; and operate the first and second rectifier/chargers in a first mode to convert AC voltage from the at least one transformer to DC voltage for charging the battery. The controller may be further configured to operate the first and second rectifier/chargers in a second mode to convert DC voltage from a respective battery to an AC voltage delivered to the at least one transformer to balance charge between the first and second batteries. The controller may be further configured to operate the first switching bridge during a positive half cycle of the input power source to deliver AC voltage to the at least one transformer by closing all switches of the second switching bridge and operating the switches of the first switching bridge to deliver a pulse width modulated AC voltage to the at least one transformer; and operate the second switching bridge during a negative half cycle of the input power source to deliver AC voltage to the at least one transformer by closing all switches of the second switching bridge and operating the switches of the second switching bridge to deliver a pulse width modulated AC voltage to the at least one transformer. 
     A method of providing charging to a battery system can include operating a first switching bridge during a positive half cycle of an input power source to deliver AC voltage to at least one transformer; operating a second switching bridge during a negative half cycle of the input power source to deliver AC voltage to the at least one transformer; and operating first and second rectifier/chargers in a first mode to convert AC voltage from the at least one transformer to DC voltage for charging a battery. The method can further include operating the first switching bridge during a positive half cycle of the input power source to deliver AC voltage to the at least one transformer comprises closing all switches of the second switching bridge and operating the switches of first switching bridge to deliver a pulse width modulated AC voltage to the at least one transformer; and operating the second switching bridge during a negative half cycle of the input power source to deliver AC voltage to the at least one transformer comprises closing all switches of the second switching bridge and operating the switches of the second switching bridge to deliver a pulse width modulated AC voltage to the at least one transformer. The method further can further include providing balancing to a dual battery system by operating the first and second rectifier/chargers in a second mode to convert DC voltage from a respective battery to an AC voltage delivered to the at least one transformer to balance charge between the first and second batteries. Operating the first and second rectifier/chargers in a second mode to convert DC voltage from a respective battery to an AC voltage delivered to the at least one transformer to balance charge between the first and second batteries can include closing all switches of the first and second switching bridges and operating one of the first and second rectifier/chargers as an inverter to deliver a pulse width modulated AC voltage to the at least one transformer while operating the other of the first and second rectifier/chargers in the first mode. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    illustrates a charger-balancer system for dual batteries. 
         FIGS.  2 A- 2 B  illustrate the switching scheme for a charger of a single battery system. 
         FIG.  3    illustrates a full bridge single stage charger-balancer for a dual battery system. 
         FIG.  4    illustrates a half bridge single stage charger-balancer for a dual battery system. 
         FIGS.  5 A- 5 C  illustrate a switching scheme for a full bridge single stage charger-balancer for a dual battery system. 
         FIGS.  6 A- 6 C  illustrate a switching scheme for a half bridge single stage charger-balancer for a dual battery system. 
         FIG.  7    illustrates a high level block diagram of a controller for a single stage charger-balancer for a dual battery system. 
         FIG.  8    illustrates a full bridge single stage charger for a single battery system. 
         FIGS.  9 A- 9 B  illustrate a switching scheme for a full bridge single stage charger for a single battery system. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, for purposes of explanation, numerous specific details are set forth to provide a thorough understanding of the disclosed concepts. As part of this description, some of this disclosure&#39;s drawings represent structures and devices in block diagram form for sake of simplicity. In the interest of clarity, not all features of an actual implementation are described in this disclosure. Moreover, the language used in this disclosure has been selected for readability and instructional purposes, has not been selected to delineate or circumscribe the disclosed subject matter. Rather the appended claims are intended for such purpose. 
     Various embodiments of the disclosed concepts are illustrated by way of example and not by way of limitation in the accompanying drawings in which like references indicate similar elements. For simplicity and clarity of illustration, where appropriate, reference numerals have been repeated among the different figures to indicate corresponding or analogous elements. In addition, numerous specific details are set forth in order to provide a thorough understanding of the implementations described herein. In other instances, methods, procedures and components have not been described in detail so as not to obscure the related relevant function being described. References to “an,” “one,” or “another” embodiment in this disclosure are not necessarily to the same or different embodiment, and they mean at least one. A given figure may be used to illustrate the features of more than one embodiment, or more than one species of the disclosure, and not all elements in the figure may be required for a given embodiment or species. A reference number, when provided in a given drawing, refers to the same element throughout the several drawings, though it may not be repeated in every drawing. The drawings are not to scale unless otherwise indicated, and the proportions of certain parts may be exaggerated to better illustrate details and features of the present disclosure. 
       FIG.  1    illustrates a block diagram of a multi-battery AC-DC system  100  with separately implemented chargers and balancers. More specifically, multi-battery AC-DC system  100  can include a first battery  101   a  and a second battery  101   b . In some applications these batteries may be relatively high voltage batteries, e.g., having a nominal voltage on the order of a few to several hundred volts. First battery  101   a  may be provided with a first charger  103   a  that can charge the first battery from an AC power grid  105 . (In some embodiments, AC power grid  105  may alternatively be a DC power source, such as a photovoltaic system. This will change the construction of charger  103   a  slightly, as discussed in greater detail below.) Similarly, second battery  101   b  may be provided with a second charger  103   b  that can charge the second battery from the AC power grid  105  (or, in some applications, a DC source). Additionally, balancer circuitry  106  may be provided to equalize charge between first battery  101   a  and  101   b . Each of chargers  103   a  and  103   b  and balancer circuitry  106  are discussed in greater detail below. 
     First charger  103   a  and second charger  103   b  can each include a plurality of converter blocks that perform a power conversion function necessary to convert the received AC input voltage from AC power grid  105  to DC power suitable for charging first and second batteries  101   a  and  101   b . More specifically, chargers  103   a / 103   b  can include rectifiers  131   a / 131   b  that convert the received sinusoidal AC input voltage to a DC voltage. Rectifiers  131   a / 131   b  may be constructed of switching components such as diodes, silicon controlled rectifiers (SCRs/thyristors), or transistors, such as MOSFETs or IGBTs. These semiconductor components may be made from various semiconductor technologies including silicon, silicon carbide (SiC), or gallium nitride (GaN), as appropriate for a given application. Depending on the nature of AC input grid, rectifiers  131   a / 131   b  may be single phase, split phase, or polyphase (e.g., three-phase), with the particular rectifier topologies selected appropriately. Alternatively, in embodiments in which the grid is a DC source, rectifiers  131   a / 131   b  may be omitted, and the input DC voltage may be provided directly to bus capacitors  132   a / 132   b  and inverters  133   a / 133   b , discussed in greater detail below. 
     In either case, a DC voltage may be provided to inverters  133   a / 133   b  via a DC bus supported by capacitors  132   a / 132   b . Inverters  133   a / 133   b  can convert the DC voltage to a pulse width modulated (PWM) AC voltage that may be supplied to transformers  134   a / 134   b . Like rectifiers  131   a / 131   b , the inverters may be made from suitable semiconductor switching devices made using a suitable semiconductor material/technology and may have any suitable topology and phase configuration. Transformers  134   a / 134   b  can provide galvanic isolation between the battery system and the input power source Transformers  134   a / 134   b  may also change the voltage level of the PWM AC voltage produced by inverters  133   a / 133   b , or, alternatively, can be 1:1 transformers that do not change the voltage level. In some embodiments, the AC voltage received by chargers  103   a / 103   b  may be provided directly to the transformers  134   a / 134   b , omitting the rectifiers  131   a / 131   b  and inverters  133   a / 133   b . In this case, a sinusoidal voltage will be provided rectifier/chargers  135   a / 135   b . In still other embodiments, rectifiers  131   a / 131   b  and inverters  133   a / 133   b  may be integrated into a single stage charger, discussed in greater detail below with respect to  FIGS.  2 A and  2 B . 
     Chargers  103   a / 103   b  may also include rectifier/chargers  135   a / 135   b  that rectify the transformed PWM AC voltage to a variable/controllable DC voltage that may be provided to the battery via a battery bus supported by capacitors  136   a  and  136   b . Rectifier/chargers  135   a / 135   b  may be constructed in any suitable topology, using switching devices of any suitable type/material, such as those listed above. Rectifier/chargers  135   a / 135   b  may be controlled to produce a variable DC output voltage corresponding to a desired charging program/configuration for batteries  101   a / 101   b.    
     To summarize, chargers  103   a / 103   b  may operate to convert power received from an input grid  105  to a DC level suitable for charging batteries  101   a  and  101   b , respectively. In at least some embodiments, chargers  103   a  and  103   b  operate independently. As a result, and depending further on the nature of the loads presented to batteries  101   a / 101   b , there may arise significant differences in the amount of energy stored in batteries  101   a / 101   b . Thus, in some cases, it may be desirable to equalize or balance the charge as between batteries  101   a / 101   b . Balancer circuitry  106  may be provided to achieve this objective. 
     A variety of configurations for balancer circuitry  106  may be provided. In the illustrated embodiment, balancer  106  includes a first bidirectional rectifier/inverter  161   a  and a second bidirectional rectifier/inverter  161   b , which have their DC sides coupled respectively to batteries  101   a  and  101   b  and their AC sides coupled to balancer transformer  162 . To equalize charge as between the batteries, the rectifier/inverter coupled to the battery having excess charge may be operated as an inverter to deliver AC power, via balancer transformer  162  to the rectifier/inverter coupled to the battery having an energy deficit. The rectifier/inverter coupled to the battery having an energy deficit may be operated as a rectifier/charger to deliver energy to the coupled battery. It will be appreciated that the bidirectional nature of each converter means that excess charge may be delivered from either battery to its counterpart. It will be appreciated that balancer transformer  162  provides galvanic isolation between the two battery systems. However, in some embodiments, balancer  106  may be constructed using a single bi-directional DC-DC converter omitting balancer transformer  162 . 
       FIGS.  2 A and  2 B  illustrate operation of a single stage charger  203  during an positive half cycle ( FIG.  2 A ) and negative half cycle ( FIG.  2 B ) of an AC input waveform. Single stage charger  203  integrates the input rectifier  131   a / 131   b  and inverter  133   a / 133   b  into a single switching stage  232  made up of a ladder of switching devices SaP, SaN, SbN, and SbQ, which may be operated as described in greater detail below. It will be further appreciated that the illustrated arrangement corresponds to a single phase AC input and that other configurations may be used with split phase or polyphase (e.g., three phase) AC input arrangements. 
     During the positive half cycle of the AC input waveform, switches SbN and SbQ may be closed, effectively short circuiting input capacitor  102   a , and providing a return current path from transformer  134   a . Switch SaP may be operated using a suitable pulse width modulation scheme to provide a positive half cycle AC voltage at the input of transformer  134   a  (via blocking capacitor  140   a ) that may have a peak voltage equal to approximately one-half the AC input voltage. Similarly, during the negative half cycle of the AC input waveform, switches SaP and SaN may be closed, effectively short circuiting input capacitor  102   a , and providing a return current path from transformer  134   a . Switch SbQ may be operated using a suitable pulse width modulation scheme to provide a negative half cycle AC voltage at the input of transformer  134   a  (via blocking capacitor  140   a ) that may have a peak voltage equal to approximately one-half the AC input voltage. 
     As a result of the foregoing switching operations, transformer  134   a  is driven with a pulse-modulated sinusoidal voltage that is suitable scaled by the turns ratio of the transformer to produce an AC voltage on the secondary side of the transformer. During the positive half cycle, switches S 1  of rectifier  135   a  may be closed (with switches S 2  open), allowing energy to be delivered to battery  101   a . During the negative half cycle, switches S 2  of rectifier  135   a  may be closed (with switches S 1  open), also allowing energy to be delivered to battery  101   a.    
       FIG.  3    illustrates a dual-battery AC-DC system  300  including an improved single stage charger with integrated balancer functionality. As discussed above with respect to  FIG.  1   , system  300  includes first and second batteries  301   a  and  301   b . In at least some embodiments these batteries may be high voltage batteries, e.g., batteries having voltage on the order of a few hundred to several hundred volts, though other voltage are also possible. System  300  may be configured to receive AC input power from an AC grid  305  via an input filter  307 . Construction of such input filters is known to those skilled in the art and is therefore not repeated here. System  300  further includes an integrated charger/balancer configuration including full bridge input circuitry  337 , transformer  334 , and rectifier/chargers  335   a / 335   b , operation of which is discussed below with respect to  FIGS.  5 A and  5 B . 
       FIG.  4    illustrates a dual-battery AC-DC system  400  including an improved single stage charger with integrated balancer functionality. As discussed above with respect to  FIGS.  1  and  3   , system  400  includes first and second batteries  401   a  and  401   b . In at least some embodiments these batteries may be high voltage batteries, e.g., batteries having voltage on the order of a few hundred to several hundred volts, though other voltage are also possible. System  400  may be configured to receive AC input power from an AC grid  405  via an input filter  407 . Construction of such input filters is known to those skilled in the art and is therefore not repeated here. System  400  further includes an integrated charger/balancer configuration including half bridge input circuitry  437 , transformer  434 , and rectifier/chargers  435   a / 435   b , operation of which is discussed below with respect to  FIGS.  6 A and  6 B . 
     For purposes of the following description, there are at least three distinctions between full-bridge single stage charger with integrated balancer circuitry of  FIGS.  3 ,  5 A, and  5 B  and half-bridge single stage charger with integrated balancer circuitry of  FIGS.  4 ,  6 A, and  6     b . First, as implied by the names of the circuits, the full-bridge arrangement includes a full bridge of switches on the AC input side, while the half-bridge arrangement includes dual half bridges of switches on the AC input side. Although this results in the same number of switching devices, operation of such circuits is different as described in greater detail below. Additionally, the full-bridge configuration includes four transformers  334   a - 334   d  (or a quad transformer), while the half-bridge configuration includes two transformers  434   a - 434   b  (or a dual transformer). Finally, the half-bridge embodiment includes blocking capacitors  440   a - 440   b , which are not required in the full bridge embodiment. 
     With reference to  FIG.  3   , full bridge input circuitry  337  may be constructed from two full bridge circuits. A first/upper full bridge circuit may include switches SaP, SbP, SaN, SbN. First/upper full bridge circuit has an input terminal P coupled to one side of the AC input source and a neutral terminal N that is coupled in common to a second/lower full bridge circuit. This second/lower full bridge circuit may include switches Sa′Q, Sb′Q, Sa′N, and Sb′N. The second/lower full bridge circuit has an input terminal Q coupled to the other side of the AC input source and a neutral terminal N that is coupled in common to the first/upper full bridge circuit. 
     The first/upper full bridge circuit has two output terminals, output terminal “a” corresponding to the junction of switches SaP and SaN, and output terminal “b” corresponding to the junction of switches SbP and SbN. First output terminal “a” may be coupled to a first terminal of transformer primary winding  334   a . Second output terminal “b” may be coupled to a second terminal of transformer primary winding  334   c . Additionally, a second terminal of transformer primary winding  334   a  may be coupled to a first terminal of transformer primary winding  334   c . This allows for a series connection of transformer windings  334   a  and  334   c  described in greater detail below with respect to  FIG.  5 A . 
     The second/lower full bridge circuit has two output terminals, output terminal “a′” corresponding to the junction of switches Sa′Q and Sa′N, and output terminal “b′” corresponding to the junction of switches Sb′Q and Sb′N. First output terminal “a′” may be coupled to a second terminal of transformer primary winding  334   d . Second output terminal “b′” may be coupled to a first terminal of transformer primary winding  334   b . Additionally, a first terminal of transformer primary winding  334   d  may be coupled to a second terminal of transformer primary winding  334   b . This allows for a series connection of transformer windings  334   b  and  334   d  described in greater detail below with respect to  FIG.  5 B . 
     Turning to the secondary side of transformer  334 , transformer secondary winding  334   a  may be coupled in series with transformer secondary winding  334   b . Thus, a first terminal of transformer secondary winding  334   a  may be coupled to an input terminal “u” of first/upper output rectifier/charger  335   a , which may be a full bridge rectifier made up of first switch pair S 1  and second switch pair S 2 . A second terminal of transformer secondary winding  334   a  may be coupled to a first terminal of transformer secondary winding  334   b . A second terminal of transformer secondary winding  334   b  may be coupled to an input terminal “v” of first/upper output rectifier charger  335   a . First/upper rectifier charger  335   a  may be operated as described below with reference to  FIGS.  5 A and  5 B  provide a DC voltage for charging battery  301   a  and may further be operated as described below with reference to  FIG.  5 C  to provide a balancing function as between batteries  301   a  and  301   b.    
     Additionally, transformer secondary winding  334   c  may be coupled in series with transformer secondary winding  334   d . Thus, a first terminal of transformer secondary winding  334   c  may be coupled to an input terminal “u” of second/lower output rectifier/charger  335   b , which may be a full bridge rectifier made up of first switch pair S 1  and second switch pair S 2 . A second terminal of transformer secondary winding  334   c  may be coupled to a first terminal of transformer secondary winding  334   d . A second terminal of transformer secondary winding  334   d  may be coupled to an input terminal “v” of second/lower output rectifier charger  335   b . Second/lower rectifier charger  335   b  may be operated as described below with reference to  FIGS.  5 A and  5 B  provide a DC voltage for charging battery  301   a  and may further be operated as described below with reference to  FIG.  5 C  to provide a balancing function as between batteries  301   a  and  301   b.    
     Finally, transformer  334  may be constructed in a variety of configurations. In one configuration, transformer  334  may include four separate transformers  334 ( a ),  334 ( b ),  334 ( c ), and  334 ( d ), with each transformer having an individual primary winding, secondary winding, and magnetic core, with the windings interconnected as described above. In another configuration, transformer  334  may be constructed as a single transformer having four primary windings (a)-(d), four secondary windings (a)-(d) and a common magnetic core, with the windings interconnected as described above. It will be appreciated by those skilled in the art that a variety of physical construction arrangements are possible for the single integrated transformer, with different numbers of core legs and different arrangements of the eight windings on those core legs. The particular arrangements depend upon the particular voltage, current, and power requirements of a given application as well as physical constraints such as packaging and thermal requirements. Thus, detailed transformer design information is not included here. 
       FIGS.  5 A- 5 C  illustrate operation of the full bridge single stage charger with integrated balancer described above with respect to  FIG.  3   .  FIG.  5 A  illustrates the positive half cycle charging operation.  FIG.  5 B  illustrates the negative half cycle charging operation.  FIG.  5 C  illustrates the charge balancing operation. 
       FIG.  5 A  shows circuit configuration  500   a  for a positive half cycle charging operation for the full bridge single stage charger. During the positive half cycle of the input voltage from AC grid  305 , all four switches of the second/lower full bridge are turned on/closed, providing a return current path from the transformer. In the upper full bridge, switches SaP and SbN may be switched together using a suitable pulse width modulation (PWM) algorithm to cause positive current flow from the AC grid  305 , through switch SaP, through series connected transformer primary windings  334   a  and  334   c , through upper full bridge switch SbN, returning to the AC grid  305  through the shorted second/lower bridge. This will provide a controllable AC voltage across transformer windings  334   a  and  334   c , which will induce corresponding AC voltages in the series combination of transformer secondary windings  334   a  and  334   b  and in the series combination of transformer secondary windings  334   c  and  334   d.    
     The voltage induced in the series combination of transformer secondary windings  334   a  and  334   b  may be used by rectifier/charger  335   a  to charge battery  301   a  in a manner similar to that described above with respect to  FIG.  2 A . Likewise, the voltage induced in the series combination of transformer secondary windings  334   c  and  334   d  may be used by rectifier/charger  335   b  to charge battery  301   b  in a manner similar to that described above with respect to  FIG.  2 A . More specifically, in rectifier/charger  335   a , switch pair S 1  may be closed while switch pair S 2  remains open, providing a current path from the first terminal of transformer secondary winding  334   a , through upper switch S 1 , through battery  301   a , through lower switch S 1 , returning to the second terminal of transformer secondary winding  334   b . Similarly, in rectifier/charger  335   b , switch pair S 2  may be closed while switch pair S 1  remains open, providing a current path from the first terminal of transformer secondary winding  334   c , through upper switch S 2 , through battery  301   b , through lower switch S 2 , returning to the second terminal of transformer secondary winding  334   d.    
       FIG.  5 B  shows circuit configuration  500   b  for a negative half cycle charging operation for the full bridge single stage charger. During the negative half cycle of the input voltage from AC grid  305 , all four switches of the first/upper full bridge are turned on/closed, providing a return current path from the transformer. In the lower full bridge, switches Sa′Q and Sb′N may be switched together using a suitable pulse width modulation (PWM) algorithm to cause positive current flow from the AC grid  305 , through switch Sa′Q, through series connected transformer primary windings  334   b  and  334   d , through upper full bridge switch Sb′N, returning to the AC grid  305  through the shorted first/upper bridge. This will provide a controllable AC voltage across transformer windings  334   b  and  334   d , which will induce corresponding AC voltages in the series combination of transformer secondary windings  334   a  and  334   b  and in the series combination of transformer secondary windings  334   c  and  334   d.    
     The voltage induced in the series combination of transformer secondary windings  334   a  and  334   b  may be used by rectifier/charger  335   a  to charge battery  301   a  in a manner similar to that described above with respect to  FIG.  2 B  and immediately above with respect  FIG.  5 A . Likewise, the voltage induced in the series combination of transformer secondary windings  334   c  and  334   d  may be used by rectifier/charger  335   b  to charge battery  301   b  in a manner similar to that described above with respect to  FIG.  2 B  and immediately above with respect to  FIG.  5 A . More specifically, in rectifier/charger  335   a , switch pair S 1  may be closed while switch pair S 2  remains open, providing a current path from the first terminal of transformer secondary winding  334   a , through upper switch S 1 , through battery  301   a , through lower switch S 1 , returning to the second terminal of transformer secondary winding  334   b . Similarly, in rectifier/charger  335   b , switch pair S 2  may be closed while switch pair S 1  remains open, providing a current path from the first terminal of transformer secondary winding  334   c , through upper switch S 2 , through battery  301   b , through lower switch S 2 , returning to the second terminal of transformer secondary winding  334   d.    
       FIG.  5 C  shows circuit configuration  500   c  for a charge balancing operation for the full bridge single stage charger. In the charge balancing mode, the lower switches of each full bridge on the AC input side of the circuit (i.e., switches SaN, SbN, Sa′N and Sb′N) may be closed, while the upper switches of each full bridge (i.e., switches SaP, SbP, Sa′Q and Sb′Q) remain open. This effectively short circuits the series combination of transformer primary windings  334   a  and  334   c , effectively short circuits the series combination of transformer primary windings  334   b  and  334   d , and also effectively disconnects AC input source  305 . As a result, transformer  334  is effectively reconfigured to couple the battery-side circuit corresponding to battery  301   a  to the battery-side circuit corresponding to battery  301   b.    
     One of rectifier/charger bridges  335   a  or  335   b  may then be operated as an inverter to drive transformer  334  with energy from the battery having excess charge, with the other rectifier/charger bridge being operated as a rectifier to allow energy from transformer  334  to be delivered to the battery having a charge deficit. For example, the switches of rectifier/charger  335   a  may be operated using a pulse width modulation algorithm to generate a desired voltage across the series combination of transformer secondary windings  334   a  and  334   b , which may act as the primary winding for a charge balancing transfer from battery  301   a  to battery  301   b . Then, the series combination of transformer secondary windings  334   c  and  334   d  will act as the secondary windings for a charge balancing transfer from battery  301   a  to battery  301   b . In the positive half cycle of such an operation, switches S 1  of charger  335   a  may be used to generate the positive half cycle of the AC charge balancing voltage with switches S 2  of charger  335   a  being used to generate the negative half cycle of the AC charge balancing voltage. On the rectifier side (i.e., the battery circuit corresponding to battery  301   b ), switches S 2  may be closed to rectify the positive voltage appearing across the series combination of secondary windings  334   c  and  334   d  to deliver charging current to battery  301   b , with switches S 1  of charger  335   b  being used to rectify the negative half cycle of the AC charge balancing voltage. 
     With reference to  FIG.  4   , dual half bridge input circuitry  437  may be constructed from two half bridge circuit pairs, each including two half bridges connected in parallel. A first/upper dual half bridge circuit may include switch pairs SaP and SaN. First/upper dual half bridge circuit has an input terminal P coupled to one side of the AC input source and a neutral terminal N that is coupled in common to a second/lower full bridge circuit. This second/lower dual half bridge circuit may include switch pairs SbQ and SbN. The second/lower dual half bridge circuit has an input terminal Q coupled to the other side of the AC input source and a neutral terminal N that is coupled in common to the first/upper dual half bridge circuit. 
     The first/upper dual half bridge circuit has two output terminals, output terminal “a” corresponding to the junction of left switch pair SaP and SaN, and output terminal “a′” corresponding to the junction of right switch pair SaP and SaN. First output terminal “a” may be coupled to a first terminal of transformer primary winding  434   a  via a blocking capacitor  440   a . Second output terminal “a′” may be coupled to the same first terminal of transformer primary winding  434   a , also via blocking capacitor  440   a.    
     The second/lower dual half bridge circuit has two output terminals, output terminal “b” corresponding to the junction of left switch pair SbQ and SbN, and output terminal “b” corresponding to the junction of right switch pair SbQ and SbN. First output terminal “b” may be coupled to a second terminal of transformer primary winding  434   b  via a blocking capacitor  440   b . Second output terminal “b′” may be coupled to the same second terminal of transformer primary winding  434   b , also via blocking capacitor  440   b . Additionally, a first terminal of transformer primary winding  434   b  may be coupled to a second terminal of transformer primary winding  434   a . This allows for a series connection of transformer windings  434   a  and  434   b  described in greater detail below with respect to  FIGS.  6 A and  6 B . 
     Turning to the secondary side of transformer  434 , transformer secondary winding  434   a  may be coupled to rectifier/charger circuit  435   a  corresponding to first battery  401   a . Thus, a first terminal of transformer secondary winding  434   a  may be coupled to an input terminal “u” of first/upper output rectifier/charger  435   a , which may be a full bridge rectifier made up of first switch pair S 1  and second switch pair S 2 . A second terminal of transformer secondary winding  434   a  may be coupled to an input terminal “v” of first/upper output rectifier/charger  435   a . First/upper rectifier charger  435   a  may be operated as described below with reference to  FIGS.  6 A and  6 B  provide a DC voltage for charging battery  301   a  and may further be operated as described below with reference to  FIG.  6 C  to provide a balancing function as between batteries  401   a  and  401   b.    
     Additionally, transformer secondary winding  334   b  may be coupled to rectifier/charger circuit  435   b  corresponding to second battery  401   b . Thus, a first terminal of transformer secondary winding  434   b  may be coupled to an input terminal “u” of second/lower output rectifier/charger  435   b , which may be a full bridge rectifier made up of first switch pair S 1  and second switch pair S 2 . A second terminal of transformer secondary winding  434   b  may be coupled to an input terminal “v” of second/lower output rectifier charger  435   b . Second/lower rectifier charger  435   b  may be operated as described below with reference to  FIGS.  6 A and  6 B  provide a DC voltage for charging battery  401   a  and may further be operated as described below with reference to  FIG.  6 C  to provide a balancing function as between batteries  401   a  and  401   b.    
     Finally, transformer  434  may be constructed in a variety of configurations. In one configuration, transformer  434  may include two separate transformers  434 ( a ), and  434 ( b ), with each transformer having an individual primary winding, secondary winding, and magnetic core, with the windings interconnected as described above. In another configuration, transformer  434  may be constructed as a single transformer having two primary windings (a)-(b), two secondary windings (a)-(b) and a common magnetic core, with the windings interconnected as described above. It will be appreciated by those skilled in the art that a variety of physical construction arrangements are possible for the single integrated transformer, with different numbers of core legs and different arrangements of the four windings on those core legs. The particular arrangements depend upon the particular voltage, current, and power requirements of a given application as well as physical constraints such as packaging and thermal requirements. Thus, detailed transformer design information is not included here. 
       FIGS.  6 A- 6 C  illustrate operation of the dual-half bridge single stage charger with integrated balancer described above with respect to  FIG.  4   .  FIG.  6 A  illustrates the positive half cycle charging operation.  FIG.  6 B  illustrates the negative half cycle charging operation.  FIG.  6 C  illustrates the charge balancing operation. 
       FIG.  6 A  shows circuit configuration  600   a  for a positive half cycle charging operation for the dual half bridge single stage charger. During the positive half cycle of the input voltage from AC grid  405 , all four switches of the second/lower dual half bridge are turned on/closed, providing a return current path from the transformer. In the upper dual half bridge, switches SaP may be switched together using a suitable pulse width modulation (PWM) algorithm to cause positive current flow from the AC grid  405 , through switches SaP, through blocking capacitor  440   a , through series connected transformer primary windings  434   a  and  434   b , through blocking capacitor  440   b , returning to the AC grid  405  through the shorted second/lower dual half bridges. This will provide a controllable AC voltage across transformer windings  434   a  and  434   b , which will induce corresponding AC voltages in the transformer secondary windings  334   a  and  334   b.    
     The voltage induced in transformer secondary winding  434   a  may be used by rectifier/charger  435   a  to charge battery  401   a  in a manner similar to that described above with respect to  FIG.  2 A . Likewise, the voltage induced in transformer secondary winding  434   b  may be used by rectifier/charger  435   b  to charge battery  401   b  in a manner similar to that described above with respect to  FIG.  2 A . More specifically, in rectifier/charger  435   a , switch pair S 1  may be closed while switch pair S 2  remains open, providing a current path from the first terminal of transformer secondary winding  434   a , through upper switch S 1 , through battery  301   a , through lower switch S 1 , returning to the second terminal of transformer secondary winding  434   a . Similarly, in rectifier/charger  435   b , switch pair S 2  may be closed while switch pair S 1  remains open, providing a current path from the first terminal of transformer secondary winding  434   b , through upper switch S 2 , through battery  401   b , through lower switch S 2 , returning to the second terminal of transformer secondary winding  434   b.    
       FIG.  6 B  shows circuit configuration  600   b  for a negative half cycle charging operation for the dual half bridge single stage charger. During the negative half cycle of the input voltage from AC grid  405 , all four switches of the first/upper dual half bridge are turned on/closed, providing a return current path from the transformer. In the lower full bridge, switches SbQ may be switched together using a suitable pulse width modulation (PWM) algorithm to cause positive current flow from the AC grid  405 , through switches SbQ, through blocking capacitor  440   b , through series connected transformer primary windings  434   a  and  434   b , through blocking capacitor  440   a , returning to the AC grid  405  through the shorted first/upper dual half bridges. This will provide a controllable AC voltage across transformer windings  434   a  and  434   b , which will induce corresponding AC voltages in transformer secondary windings  434   a  and  434   b.    
     Similarly to the description above with respect to  FIG.  6 A , the voltage induced in transformer secondary winding  434   a  may be used by rectifier/charger  435   a  to charge battery  401   a  in a manner similar to that described above with respect to  FIG.  2 B  and immediately above with respect  FIG.  6 A . Likewise, the voltage induced in transformer secondary winding  434   b  may be used by rectifier/charger  435   b  to charge battery  401   b  in a manner similar to that described above with respect to  FIG.  2 B  and immediately above with respect to  FIG.  6 A . More specifically, in rectifier/charger  435   a , switch pair S 1  may be closed while switch pair S 2  remains open, providing a current path from the first terminal of transformer secondary winding  434   a , through upper switch S 1 , through battery  401   a , through lower switch S 1 , returning to the second terminal of transformer secondary winding  434   a . Similarly, in rectifier/charger  435   b , switch pair S 2  may be closed while switch pair S 1  remains open, providing a current path from the first terminal of transformer secondary winding  434   b , through upper switch S 2 , through battery  401   b , through lower switch S 2 , returning to the second terminal of transformer secondary winding  434   b.    
       FIG.  6 C  shows circuit configuration  600   c  for a charge balancing operation for the dual half bridge single stage charger. In the charge balancing mode, the lower switches of each half bridge on the AC input side of the circuit (i.e., switches SaN and SbN) may be closed, while the upper switches of each half bridge (i.e., switches SaP and SbP) remain open. This effectively short circuits the series combination of transformer primary windings  434   a  and  434   b  and blocking capacitors  440   a  and  440   b , and also effectively disconnects AC input source  405 . As a result, transformer  434  is effectively reconfigured to couple the battery-side circuit corresponding to battery  401   a  to the battery-side circuit corresponding to battery  401   b.    
     One of rectifier/charger bridges  435   a  or  435   b  may then be operated as an inverter to drive transformer  434  with energy from the battery having excess charge, with the other rectifier/charger bridge being operated as a rectifier to allow energy from transformer  434  to be delivered to the battery having a charge deficit. For example, the switches of rectifier/charger  435   a  may be operated using a pulse width modulation algorithm to generate a desired voltage across transformer secondary winding  434   a , which may act as the primary winding for a charge balancing transfer from battery  401   a  to battery  401   b . Then, transformer secondary windings  434   b  will act as the secondary windings for a charge balancing transfer from battery  401   a  to battery  4301   b . In the positive half cycle of such an operation, switches S 1  of charger  435   a  may be used to generate the positive half cycle of the AC charge balancing voltage with switches S 2  of charger  435   a  being used to generate the negative half cycle of the AC charge balancing voltage. On the rectifier side (i.e., the battery circuit corresponding to battery  401   b ), switches S 2  may be closed to rectify the positive voltage appearing across secondary winding  434   b  to deliver charging current to battery  401   b , with switches S 1  of charger  435   b  being used to rectify the negative half cycle of the AC charge balancing voltage. 
     The foregoing embodiments relate to multi-battery systems and therefore include the balancer circuitry/modes of operation described above. However, the single stage chargers described above may also be used in systems incorporating only a single battery. In those cases, the balancer functionality may be omitted while still achieving some of the aforementioned advantages. One such single stage charger for a single battery system is illustrated in  FIG.  8   , with its switching operations depicted in  FIGS.  9 A and  9 B . At a high level, the system of  FIGS.  8 ,  9 A and  9 B  may be understood as generally similar to the system described above with respect to  FIGS.  3 ,  5 A, and  5 B , except that the two batteries  301   a  and  301   b  have been connected in series and the lower rail of rectifier/charger  335   a  has been connected to the upper rail of rectifier charger  335   b , as described in greater detail below. 
       FIG.  8    illustrates a single-battery AC-DC system  800  including an improved single stage charger. System  800  includes a single battery  801 . In at least some embodiments this battery may be a high voltage battery, e.g., a battery having voltage on the order of a few hundred to several hundred volts, though other voltage are also possible. System  800  may be configured to receive AC input power from an AC grid  805  via an input filter  807 . Construction of such input filters is known to those skilled in the art and is therefore not repeated here. System  800  further includes an integrated charger configuration including full bridge input circuitry  837 , transformer  834 , and rectifier/chargers  835   a / 835   b , operation of which is discussed below with respect to  FIGS.  9 A and  9 B . 
     Full bridge input circuitry  837  may be constructed from two full bridge circuits. A first/upper full bridge circuit may include switches Sa, Sb, Sa′, Sb′. First/upper full bridge circuit has an input terminal AC_P coupled to one side of the AC input source and a central terminal AC_0 that is coupled in common to a second/lower full bridge circuit. This second/lower full bridge circuit may include switches Sc, Sd, Sc′, and Sd′. The second/lower full bridge circuit has an input/neutral terminal AC_N coupled to the other side of the AC input source and a central terminal AC_0 that is coupled in common to the first/upper full bridge circuit. The illustrated embodiment corresponds to a single phase AC input. Other configurations may be used if another AC input configuration is provided, such as a split phase AC input or a polyphase (e.g., three-phase) AC input. 
     The first/upper full bridge circuit has two output terminals, output terminal “a” corresponding to the junction of switches Sa and Sa′, and output terminal “b” corresponding to the junction of switches Sb and Sb′. First output terminal “a” may be coupled to a first terminal of transformer primary winding  834   a . Second output terminal “b” may be coupled to a second terminal of transformer primary winding  834   c . Additionally, a second terminal of transformer primary winding  834   a  may be coupled to a first terminal of transformer primary winding  834   c . This allows for a series connection of transformer windings  834   a  and  834   c  described in greater detail below with respect to  FIG.  9 A . 
     The second/lower full bridge circuit has two output terminals, output terminal “c” corresponding to the junction of switches Sc and Sc′, and output terminal “d′” corresponding to the junction of switches Sd and Sd′. First output terminal “c” may be coupled to a second terminal of transformer primary winding  834   d . Second output terminal “d′” may be coupled to a first terminal of transformer primary winding  834   b . Additionally, a first terminal of transformer primary winding  834   d  may be coupled to a second terminal of transformer primary winding  834   b . This allows for a series connection of transformer windings  834   b  and  834   d  described in greater detail below with respect to  FIG.  9 B . This configuration is also similar to that discussed above with respect to  FIG.  3   . 
     Turning to the secondary side of transformer  834 , transformer secondary winding  834   a  may be coupled in series with transformer secondary winding  834   b . Thus, a first terminal of transformer secondary winding  834   a  may be coupled to an input terminal “1” of first/upper output rectifier/charger  835   a , made up of first switch pair S 1 /S 1 ′ and second switch pair S 2 /S 2 ′. (Input terminal 1 is the junction of switches S 1 /S 1 ′.) A second terminal of transformer secondary winding  834   a  may be coupled to a first terminal of transformer secondary winding  834   b . A second terminal of transformer secondary winding  834   b  may be coupled to an input terminal “2” of first/upper output rectifier charger  835   a . (Input terminal 2 is the junction of switches S 2 /S 2 ′.) First/upper rectifier charger  835   a  may be operated as described below with reference to  FIGS.  9 A and  9 B  to provide a DC voltage for charging battery  801 . 
     Additionally, transformer secondary winding  834   c  may be coupled in series with transformer secondary winding  834   d . Thus, a first terminal of transformer secondary winding  834   c  may be coupled to an input terminal “3” of second/lower output rectifier/charger  835   b , which may include first switch pair S 3 /S 3 ′ and second switch pair S 4 /S 4 ′. (Input terminal 3 is the junction of switches S 3 /S 3 ′.) A second terminal of transformer secondary winding  334   c  may be coupled to a first terminal of transformer secondary winding  334   d . A second terminal of transformer secondary winding  334   d  may be coupled to an input terminal “4” of second/lower output rectifier charger  835   b . Second/lower rectifier charger  835   b  may be operated as described below with reference to  FIGS.  9 A and  9 B  provide a DC voltage for charging battery  801 . 
     Finally, transformer  834  may be constructed in a variety of configurations. In one configuration, transformer  834  may include four separate transformers  834 ( a ),  834 ( b ),  834 ( c ), and  834 ( d ), with each transformer having an individual primary winding, secondary winding, and magnetic core, with the windings interconnected as described above. In another configuration, transformer  834  may be constructed as a single transformer having four primary windings (a)-(d), four secondary windings (a)-(d), and a common magnetic core, with the windings interconnected as described above. A variety of physical construction arrangements are possible for the single integrated transformer, with different numbers of core legs and different arrangements of the eight windings on those core legs. The particular arrangements depend upon the particular voltage, current, and power requirements of a given application as well as physical constraints such as packaging and thermal requirements. Thus, detailed transformer design information is not included here. 
       FIGS.  9 A- 9 B  illustrate operation of the full bridge single stage charger described above with respect to  FIG.  8   .  FIG.  9 A  illustrates the positive half cycle charging operation.  FIG.  9 B  illustrates the negative half cycle charging operation. 
       FIG.  9 A  shows circuit configuration  900   a  for a positive half cycle charging operation for the full bridge single stage charger. During the positive half cycle of the input voltage from AC grid  805 , all four switches of the second/lower full bridge are turned on/closed, providing a return current path from the transformer. In the upper full bridge, switches Sa and Sb′ may be switched together using a suitable pulse width modulation (PWM) algorithm to cause positive current flow from the AC grid  805 , through switch Sa, through series connected transformer primary windings  834   a  and  834   c , through upper full bridge switch Sb′, returning to the AC grid  805  through the shorted second/lower bridge. This will provide a controllable AC voltage across transformer windings  834   a  and  834   c , which will induce corresponding AC voltages in the series combination of transformer secondary windings  834   a  and  834   b  and in the series combination of transformer secondary windings  834   c  and  834   d.    
     The voltage induced in the series combination of transformer secondary windings  834   a - 834   d  may be used by rectifier/chargers  835   a  and  835   b  to charge battery  801  in a manner similar to that described above. More specifically, in rectifier/charger  835   a , switches S 1  and S 2 ′ may be closed while switches S 1 ′ and S 2  remain open. Similarly, in rectifier/charger  835   b , switches S 3 ′ and S 4  may be closed while switches S 3  and S 4 ′ remain open. This provides a current path from the first terminal of transformer secondary winding  834   a , through upper switch S 1 , through battery  801 , through lower switch S 4 , returning to the second terminal of transformer secondary winding  834   d . Additionally, switches S 2 ′ and S 3  provide for a series combination of the series combination of secondary windings  834   a  and  834   b  with the series combination of secondary windings  834   c  and  834   d . In other words, all of secondary windings  834   a - 834   b  are connected in series, allowing the sum of the voltages across all four windings to be applied to battery  801  (and series capacitors  836   a / 836   b ). 
       FIG.  9 B  shows circuit configuration  900   b  for a negative half cycle charging operation for the full bridge single stage charger. During the negative half cycle of the input voltage from AC grid  805 , all four switches of the first/upper full bridge are turned on/closed, providing a return current path from the transformer. In the lower full bridge, switches Sc and Sd′ may be switched together using a suitable pulse width modulation (PWM) algorithm to cause positive current flow from the AC grid  805 , through switch Sc, through series connected transformer primary windings  834   b  and  834   d , through upper full bridge switch Sd′, returning to the AC grid  805  through the shorted second/lower bridge. This will provide a controllable AC voltage across transformer windings  834   b  and  834   d , which will induce corresponding AC voltages in the series combination of transformer secondary windings  834   b  and  834   d  and in the series combination of transformer secondary windings  834   a  and  834   b.    
     The voltage induced in the series combination of transformer secondary windings  834   a - 834   d  may be used by rectifier/chargers  835   a  and  835   b  to charge battery  801  in a manner similar to that described above. More specifically, in rectifier/charger  835   a , switches S 1  and S 2 ′ may be closed while switches S 1 ′ and S 2  remain open. Similarly, in rectifier/charger  835   b , switches S 3 ′ and S 4  may be closed while switches S 3  and S 4 ′ remain open. This provides a current path from the first terminal of transformer secondary winding  834   a , through upper switch S 1 , through battery  801 , through lower switch S 4 , returning to the second terminal of transformer secondary winding  834   d . Additionally, switches S 2 ′ and S 3  provide for a series combination of the series combination of secondary windings  834   a  and  834   b  with the series combination of secondary windings  834   c  and  834   d . In other words, all of secondary windings  834   a - 834   b  are connected in series, allowing the sum of the voltages across all four windings to be applied to battery  801  (and series capacitors  836   a / 836   b ). 
       FIG.  7    illustrates a high level block diagram of a controller  701  that may be used in conjunction with the various embodiments described above. Controller  701  may be implemented using any combination of analog control circuitry, digital/discrete control circuitry, programmable processors and/or controllers, etc. Controller  701  may be configured with a plurality of inputs  702 ,  704 ,  706 ,  708  that correspond to various measured circuit parameters. Although four inputs are shown, any number of inputs may be provided as appropriate for a given embodiment. For example, inputs may include, input (grid) voltage and current, battery voltage and current, battery temperature, etc. Controller  701  may use these inputs together with its internal circuitry and/or programming to generate output control signals  712 ,  714 ,  716 , and  718  that may be used to operate the switches in the manner described above. Although four outputs are shown, any number of outputs may be provided as appropriate for a given embodiment. For example, outputs might include drive signals for the switches of an upper input bridge, drive signals for the switches of a lower input bridge, drive signals for a first rectifier/charger, drive signals for the switches of a second rectifier/charger, etc. as described above. Numerous variations are possible depending on the particular objectives and requirements of a given embodiment, and are thus not repeated here. 
     The foregoing embodiments of systems with single stage chargers for use in single battery systems and for single stage chargers having integrated balancer functionality for use in multi battery systems provide a variety of benefits over the prior art and provide for various tradeoffs among themselves. For example, the full bridge embodiments of  FIGS.  3  and  5 A- 5 C  require a more complex transformer configuration and an arguably more complex switching operation on the primary side, while eliminating the blocking capacitors. Alternatively, the dual-half bridge embodiments of  FIGS.  4  and  6 A- 6 C  provide for simpler transformer configuration and simplified switching control on the primary side, but requires the additional blocking capacitors. As another example, the single battery embodiment described with reference to  FIGS.  8 ,  9 A, and  9 B  can eliminate blocking capacitors, operate at higher voltages (for a given switching device rating) and operate with a variable AC duty cycle resulting in a wider range of operating voltages as compared to a conventional stacked half bridge converter. Each embodiment may have further advantages and disadvantages rendering it more suitable or less suitable for a given application. Additionally, although the foregoing embodiments have been described with respect to dual battery systems, it will be appreciated that the teachings herein may be extended to multi-battery systems including more than two batteries. Additionally, the switching topologies disclosed herein are exemplary, and other topologies of rectifiers, inverters, and other converters may be used as appropriate. Finally, as noted above, various switch types (diodes, thyristors, IGBTs, MOSFETs, etc.) implemented in various semiconductor technologies (Si, SiC, GaN, etc.) may be used as appropriate for a given application. 
     The foregoing describes exemplary embodiments of single stage chargers, some for use in single battery systems and some for use in multi battery systems, with the latter having integrated charge balancing functionality. Such systems may be used in a variety of applications but may be particularly advantageous when used in conjunction with relatively high voltage and/or high power systems, such as may be used in electric vehicles, grid storage batteries, photovoltaic systems, and the like Although numerous specific features and various embodiments have been described, it is to be understood that, unless otherwise noted as being mutually exclusive, the various features and embodiments may be combined various permutations in a particular implementation. Thus, the various embodiments described above are provided by way of illustration only and should not be constructed to limit the scope of the disclosure. Various modifications and changes can be made to the principles and embodiments herein without departing from the scope of the disclosure and without departing from the scope of the claims.

Metadata:
Filing Date: 20230112
Publication Date: 20240625
Grant Date: 20240625
Priority Date: 20200925
Inventors: Sahoo, Ashish K.
PIERQUET, BRANDON
Assignee: APPLE INC
CPC Classifications: [{"code": "H02J7/04", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J3/38", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02M7/219", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02M7/217", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02M5/293", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02M3/33584", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02M3/01", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02M3/33571", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02M3/33573", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02M3/33561", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02M1/007", "inventive": true, "first": false, "tree": "[]"}, {"code": "Y02T10/70", "inventive": false, "first": false, "tree": "[]"}, {"code": "H02J2207/20", "inventive": false, "first": false, "tree": "[]"}, {"code": "H02J7/04", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J7/0014", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02J7/0014", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02M7/219", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J7/04", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J3/38", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J7/0014", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 80821560