Patent Publication Number: US-2013250623-A1

Title: Resonant Conversion Circuit

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of International Application No. PCT/CN2012/076129, filed on May 26, 2012, which claims priority to Chinese Patent Application No. 201210079193.5, filed on Mar. 22, 2012, both of which are hereby incorporated by reference in their entireties. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     REFERENCE TO A MICROFICHE APPENDIX 
     Not applicable. 
     TECHNICAL FIELD 
     The present invention relates to the power supply field, and in particular, to a resonant conversion circuit. 
     BACKGROUND 
     A resonant conversion circuit has an advantage of high conversion efficiency, and therefore gains wider and wider application.  FIG. 1  shows a typical inductor-inductor-capacitor (LLC) symmetric half-bridge resonant conversion circuit unit, including switch devices Q 1  and Q 2 , a resonant inductor Lr, a magnetizing inductor Lm of a transformer Tr, resonant capacitors Cr 1  and Cr 2 , and rectifier devices D 1  and D 2 . The resonant conversion circuit is connected to a direct current power supply, and the energy of the power supply is transferred through a primary side of the transformer to a secondary side of the transformer, filtered by a filter capacitor C and then supplied to a load R. 
     Although the resonant conversion circuit is capable of achieving higher conversion efficiency, a ripple current passing the filter capacitor C tends to exceed a specified value easily during large power output. Therefore, in practical application, electricity is usually supplied to the load in a manner of interleaving two resonant conversion circuit units in parallel. For example, as shown in  FIG. 2 , two LLC resonant conversion circuit units having the same parameters are in parallel, their input ends are connected in parallel to the direct current power supply, and their output ends are connected in parallel to the filter capacitor C and the load R. Primary-side switch devices of the power supply of the two LLC resonant conversion circuits work at a same frequency, with a working phase difference of 90 degrees, and after rectification, a phase difference of the secondary side output current is 180 degrees. Ripple currents are offset mutually, and the ripple current flowing through the filter capacitor C is reduced. 
     However, in practical buck-manufactured products, because actual parameters of a resonant inductor, a resonant capacitor, and a transformer may inevitably have some deviations from standard values, gains of interleaved parallel resonant cavities may be different. Therefore, even though two resonant conversion circuit units work at a same switching frequency, the value of a current flowing through each resonant conversion unit is different from the other. In a case where the circuit is extremely not current balanced, a current in one phase of the circuit may be too great, thereby damaging a device. 
     SUMMARY 
     In view of this, embodiments of the present invention provide a resonant conversion circuit, for a purpose of solving a problem that current sharing is not achieved between existing interleaved and parallel-connected resonant conversion circuit units. 
     In order to achieve the foregoing purpose, the embodiments of the present invention provide the following solutions. 
     A resonant conversion circuit includes: resonant conversion circuit units having at least two phases interleaved in parallel, wherein magnetic devices in the resonant conversion circuit units are magnetically integrated in an inter-phase manner on a same magnetic core. 
     The resonant conversion circuit provided by the embodiments of the present invention is formed by interleaved and parallel-connected resonant conversion circuit units, where magnetic devices of different phases are integrated on the same magnetic core. A magnetic coupling action exists between the magnetic devices integrated on the same magnetic core, and therefore, automatic current sharing effect is produced between currents in circuit branches of different phases. In this way, current sharing of resonant conversion circuit units of various phases in the resonant conversion circuit is achieved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       To illustrate technical solutions in embodiments of the present invention or in the prior art more clearly, accompanying drawings required for describing the embodiments or the prior art are introduced in the following briefly. Apparently, the accompanying drawings in the following descriptions are only some of the embodiments of the present invention, and persons of ordinary skill in the art can obtain other drawings according to these accompanying drawings without creative efforts. 
         FIG. 1  is a schematic circuit diagram of an LLC symmetric half-bridge resonant conversion circuit unit; 
         FIG. 2  is a schematic circuit diagram of existing interleaved parallel LLC resonant conversion circuit units; 
         FIGS. 3A  and  FIG. 3B  are schematic circuit diagrams of a resonant conversion circuit according to an embodiment of the present invention; 
         FIG. 4  is a schematic structural diagram of a magnetically integrated resonant inductor Lr according to an embodiment of the present invention; 
         FIG. 5  is a schematic structural diagram of another magnetically integrated resonant inductor Lr according to an embodiment of the present invention; 
         FIGS. 6A  and  FIG. 6B  are schematic circuit diagrams of another resonant conversion circuit according to an embodiment of the present invention; 
         FIG. 7  is a schematic structural diagram of a magnetically integrated first-phase resonant inductor Lr 1  and a second-phase transformer Tr 2 , or of a magnetically integrated second-phase resonant inductor Lr 2  and a first-phase transformer Tr 1  according to an embodiment of the present invention; 
         FIGS. 8A  and  FIG. 8B  are schematic circuit diagrams of another resonant conversion circuit according to an embodiment of the present invention; and 
         FIG. 9  is a schematic structural diagram of a magnetically integrated transformer Tr according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present invention disclose a resonant conversion circuit. Magnetic devices in resonant conversion circuit units having two phases or multiple phases interleaved in parallel are integrated on a same magnetic core, and therefore, current sharing between resonant conversion circuit units of different phases is achieved by using a magnetic coupling action. In this way, a problem that current sharing is not achieved in resonant conversion circuit units of various phases in an existing resonant conversion circuit is solved. 
     Technical solutions in the embodiments of the present invention are described clearly and completely below with reference to accompanying drawings in the embodiments of the present invention. Apparently, the described embodiments are only part rather than all of the embodiments of the present invention. All other embodiments obtained by persons of ordinary skill in the art without creative efforts based on the embodiments of the present invention fall within the protection scope of the present invention. 
     An embodiment of the present invention discloses a resonant conversion circuit, including: resonant conversion circuit units having two phases or multiple phases interleaved and connected in parallel, where magnetic devices in the resonant conversion circuit units are inter-phase magnetically integrated on a same magnetic core. 
     Optionally, a resonant conversion circuit unit may be a symmetric half-bridge LLC resonant conversion circuit unit, and may also be an asymmetric half-bridge LLC resonant conversion circuit unit. 
     A resonant conversion circuit shown in  FIG. 3A  is a two-phase symmetric half-bridge LLC resonant conversion circuit formed by two interleaved and parallel-connected LLC resonant conversion circuit units shown in  FIG. 1 , including first-phase switch devices Q 1  and Q 2 , first-phase resonant capacitors Cr 1  and Cr 2 , a first-phase transformer Tr 1  and its magnetizing inductor Lm 1 , first-phase rectifier devices D 1  and D 2 , second-phase switch devices Q 3  and Q 4 , second-phase resonant capacitors Cr 3  and Cr 4 , a second-phase transformer Tr 2  and its magnetizing inductor Lm 2 , second-phase rectifier devices D 3  and D 4 , and a magnetically integrated inductor Lr. 
     A resonant conversion circuit shown in  FIG. 3B  is a two-phase asymmetric half-bridge LLC resonant conversion circuit, the difference of which from that in  FIG. 3   a  only lies in resonant capacitors, where in  FIG. 3B , a first-phase resonant capacitor is Cr 1  and a second-phase resonant capacitor is Cr 2 . 
     In  FIG. 3A  and  FIG. 3B , Lr is formed by magnetically integrating resonant inductors on the same magnetic core, where the resonant inductors are in the two resonant conversion circuit units. A specific magnetic integration manner may be shown in  FIG. 4 . 
     A first-phase resonant inductor  401  is disposed on a first E-type magnetic core  403 , and a second-phase resonant inductor  402  is disposed on a second E-type magnetic core  404 . A disposing manner may specifically be winding a coil of a resonant inductor around a central pillar of an E-type magnetic core, and integrating two E-type magnetic cores on one I-type magnetic core  405 . A coupling coefficient between the resonant inductors of two phases may be adjusted by adjusting an air gap between the E-type magnetic core and the I-type magnetic core. A value of the coupling coefficient may determine a current sharing effect between branches of the two phases. The larger the coupling coefficient is, the better the current sharing effect is. However, too large of a coupling coefficient may affect the performance of a resonant circuit. In practical application, coupling inductance between the resonant inductors of the two phases may be 0.5% to 5% of inductance of a single phase. 
     Alternatively, the E-type magnetic core in  FIG. 4  is replaced with a PQ-type magnetic core. A specific disposing manner of the magnetically integrated resonant inductor Lr may also be: disposing the first-phase resonant inductor on a first PQ-type magnetic core, and disposing the second-phase resonant inductor on a second PQ-type magnetic core. The disposing manner may specifically be winding the coil of the resonant inductor around a central pillar of a PQ-type magnetic core, and integrating two PQ-type magnetic cores on one I-type magnetic core. Similarly, the coupling coefficient between the resonant inductors of the two phases may also be adjusted by adjusting an air gap between the PQ-type magnetic core and the I-type magnetic core. 
     Alternatively, the specific disposing manner of the magnetically integrated resonant inductor Lr may also be shown in  FIG. 5 . 
     A first E-type magnetic core  503  and a second E-type magnetic core  504  are disposed oppositely, so that a central pillar of the first E-type magnetic core is opposite to a central pillar of the second E-type magnetic core, two side pillars of the first E-type magnetic core are opposite to two side pillars of the second E-type magnetic core. A first-phase resonant inductor  501  and a second-phase resonant inductor  502  are separately disposed on two opposite side pillars. A disposing manner may specifically be winding a coil of a resonant inductor around a side pillar of an E-type magnetic core. An air gap is disposed on the side pillar. A coupling coefficient may be adjusted by adjusting the length of an air gap between the central pillars of the two E-type magnetic cores. 
     In the resonant conversion circuits shown in  FIG. 3A  and  FIG. 3B , the resonant conversion circuit units of the two phases are connected in parallel to a direct current power supply, primary side switch devices of the two resonant conversion circuit units work at a same frequency, with a working phase difference of 90 degrees. Electric energy is transferred through primary sides of the first-phase transformer and second-phase transformer to secondary sides of the first-phase transformer and second-phase transformer. After rectification of rectifier devices, the phase difference of current waveforms of the two phases is 180 degrees. In this way, ripple currents are offset mutually, filtered by a filter capacitor C, and then supplied to a load R. When a current passes the magnetically integrated inductor Lr, a magnetic coupling action is produced so that current sharing is achieved for the currents in branches of the two phases. 
     To verify automatic current sharing effect of the resonant conversion circuit described in the embodiment of the present invention, this embodiment provides the following circuit emulation experiment: 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Emulation data table 
               
            
           
           
               
               
               
               
            
               
                 Variable 
                 Emulation 1 
                 Emulation 2 
                 Emulation 3 
               
               
                   
               
               
                 Lr1 (Resonant 
                 12 uH 
                 12 uH 
                 12 uH 
               
               
                 Inductor) 
               
               
                 Lr2 (Resonant 
                 12 uH 
                 12 uH 
                 12 uH 
               
               
                 Inductor) 
               
               
                 Lm1\Lm2 
                 72 uH 
                 72 uH 
                 72 uH 
               
               
                 (Magnetizing 
               
               
                 Inductor) 
               
               
                 Cr1\Cr2 
                 100 nF\100 nF 
                 97 nF\97 nF 
                 97 nF\97 nF 
               
               
                 (Resonant 
               
               
                 Capacitor) 
               
               
                 Cr3\Cr4 
                 100 nF\100 nF 
                 103 nF\103 nF 
                 103 nF\103 nF 
               
               
                 (Resonant 
               
               
                 Capacitor) 
               
               
                 K (Coupling 
                 0 
                 0 
                 0.01 
               
               
                 coefficient of an 
               
               
                 integrated 
               
               
                 inductor) 
               
               
                 Emulation of 
                 50%, 50% 
                 35.54%, 63.46% 
                 45.71%, 54.29% 
               
               
                 current sharing 
               
               
                 effect 
               
               
                   
               
            
           
         
       
     
     As shown in Table 1, emulation 1 simulates an ideal state where resonant element parameters are consistent, that is, a first-phase resonant inductor Lr 1  and a second-phase resonant inductor Lr 2  are 12 microhenries (uH) each, and first-phase resonant capacitors Cr 1  and Cr 2  are both 100 nanofarads (nF). Emulation 2 simulates a practical use state where a resonant element parameter in the interleaved parallel resonant conversion circuit shown in  FIG. 2  has a ±3% difference from a standard value, that is, the first-phase resonant inductor Lr 1  and the second-phase resonant inductor Lr 2  are  12  uH each, the first-phase resonant capacitors Cr 1  and Cr 2  are 97 nF each, and second-phase resonant capacitors Cr 3  and Cr 4  are 103 nF each. Emulation  3  simulates a practical use state where a resonant element parameter in the circuit shown in  FIG. 3A  of this embodiment also has a ±3% difference from a standard value, that is, a parameter of a resonant component in emulation 3 is the same as that in emulation 2. In a case where parameters of other components are the same, results of the three groups of emulation experiments show that in the ideal state where the resonant element parameters are consistent, currents of branches of two phases each accounts for 50% of the total current; in emulation 2 where resonant elements are not magnetically integrated, when the resonant element parameter has a ±3% difference from the standard value, the currents in the branches of the two phases accounts for 35.54% and 63.46% respectively, and it can be seen that, an obvious non-current sharing phenomenon occurs; in emulation  3  where the resonant devices are magnetically integrated in the circuit, when the resonant element parameter has a ±3% difference from the standard value, the current in the branches of the two phases accounts for 45.71% and 54.29% respectively, improving the non-current sharing effect in comparison with emulation 2. 
     In the resonant conversion circuit described in this embodiment, the resonant inductors of the two phases are integrated on the same magnetic core. Because magnetic coupling exists between the resonant inductors of the two phases, a problem which is non-current sharing of an input and output and is caused by inconsistency of resonant element parameters of the two phases, a precision requirement for the device parameters and the filtering cost during production is reduced, and the input and output currents between the two phases are balanced without any complicated control means, which increases the reliability of a power converter. In addition, a magnetic integration technology is used, and therefore the space that is occupied by a single integrated resonant inductor Lr in a power supply is smaller than a sum of volumes of two split resonant inductors. Therefore, the volume of the power supply is reduced and the power density of the power supply is further improved. 
     An embodiment of the present invention further discloses another resonant conversion circuit, as shown in  FIG. 6A  and  FIG. 6B .  FIG. 6A  shows a two-phase symmetric half-bridge LLC resonant conversion circuit formed by two interleaved and parallel-connected LLC resonant conversion circuit units shown in  FIG. 1 , including first-phase switch devices Q 1  and Q 2 , a first-phase resonant inductor Lr 1 , first-phase resonant capacitors Cr 1  and Cr 2 , a first-phase transformer Tr 1  and its magnetizing inductor Lm 1 , first-phase rectifier devices D 1  and D 2 , second-phase switch devices Q 3  and Q 4 , a second-phase resonant inductor Lr 2 , second-phase resonant capacitors Cr 3  and Cr 4 , a second-phase transformer Tr 2  and its magnetizing inductor Lm 2 , and second-phase rectifier devices D 3  and D 4 . The first-phase resonant inductor Lr 1  and the second-phase transformer Tr 2  are integrated on a same magnetic core, and the second-phase resonant inductor Lr 2  and the first-phase transformer Tr 1  are integrated on a same magnetic core.  FIG. 6B  shows a two-phase asymmetric half-bridge LLC resonant conversion circuit, the difference of which from that in  FIG. 6A  only lies in resonant capacitors, where in  FIG. 6B , a first-phase resonant capacitor is Cr 1  and a second-phase resonant capacitor is Cr 2 . 
     In  FIG. 6A  and  FIG. 6B , a specific disposing manner for magnetically integrating the first-phase resonant inductor Lr 1  and the second-phase transformer TR 2  or the second-phase resonant inductor Lr 2  and the first-phase transformer Tr 1  may be shown in  FIG. 7 . 
     A first-phase (or second-phase) resonant inductor  801  is disposed on a first E-type magnetic core  803 , and a second-phase (or first-phase) transformer  802  is disposed on a second E-type magnetic core  804 . A disposing manner may specifically be winding a coil of the resonant inductor or primary and secondary coils of the transformer around a central pillar of an E-type magnetic core, and integrating two E-type magnetic cores on one I-type magnetic core  805 . A coupling coefficient between the resonant inductor and the transformer may be adjusted by adjusting an air gap between the E-type magnetic core and the I-type magnetic core. 
     Alternatively, the E-type magnetic core is replaced with a PQ-type magnetic core. That is: 
     The first-phase (or second-phase) resonant inductor is disposed on a first PQ-type magnetic core, and the second-phase (or first-phase) transformer is disposed on a second PQ-type magnetic core. The disposing manner may specifically be winding the coil of the resonant inductor or primary and secondary coils of the transformer around a central pillar of a PQ-type magnetic core, and integrating two PQ-type magnetic cores on one I-type magnetic core. The coupling coefficient between the resonant inductor and the transformer may be adjusted by adjusting an air gap between the PQ-type magnetic core and the I-type magnetic core. 
     In the resonant conversion circuit described in this embodiment, the resonant inductor and the transformer are inter-phase magnetically integrated on the same magnetic core, solving a problem that current sharing is not achieved for currents in branches of two phases, and reducing the volume of the circuit. 
     An embodiment of the present invention further discloses another resonant conversion circuit, as shown in  FIG. 8A  and  FIG. 8B .  FIG. 8A  shows a two-phase symmetric half-bridge LLC resonant conversion circuit formed by two interleaved and parallel-connected LLC resonant conversion circuit units, including first-phase switch devices Q 1  and Q 2 , first-phase resonant capacitors Cr 1  and Cr 2 , first-phase rectifier devices D 1  and D 2 , second-phase switch devices Q 3  and Q 4 , second-phase resonant capacitors Cr 3  and Cr 4 , second-phase rectifier devices D 3  and D 4 , a magnetically integrated transformer Tr (the magnetically integrated Tr includes magnetizing inductors Lm 1  and Lm 2 ), and a magnetically integrated resonant inductor Lr. The magnetically integrated transformer is formed by integrating transformers of two resonant circuit units on a same magnetic core, and the magnetically integrated resonant inductor is formed by integrating resonant inductors of two resonant circuit units on a same magnetic core.  FIG. 8B  shows a two-phase asymmetric half-bridge LLC resonant conversion circuit, the difference of which from that in  FIG. 8A  only lies in resonant capacitors, where in  FIG. 8B , a first-phase resonant capacitor is Cr 1  and a second-phase resonant capacitor is Cr 2   
     In  FIG. 8A  and  FIG. 8B , a disposing manner of the magnetically integrated resonant inductor Lr may be shown in  FIG. 4  or  FIG. 5  of the foregoing embodiment. 
     A specific disposing manner of the magnetically integrated transformer Tr may be shown in  FIG. 9 . 
     A first transformer  1001  is disposed on a first E-type magnetic core  1003 , and a second transformer  1002  is disposed on a second E-type magnetic core  1004 . A disposing manner may specifically be winding coils on primary and secondary sides of a transformer around a central pillar of an E-type magnetic core, and integrating two E-type magnetic cores on one I-type magnetic core  1005 . 
     Alternatively, the E-type magnetic core is replaced with a PQ-type magnetic core. A specific disposing manner of the magnetically integrated transformer Tr may also be as follows: 
     The first transformer is disposed on a first PQ-type magnetic core, and the second transformer is disposed on a second PQ-type magnetic core. The disposing manner may specifically be winding the coils on the primary and secondary sides of the transformer around a central pillar of a PQ-type magnetic core, and integrating two PQ-type magnetic cores on one I-type magnetic core. 
     In the resonant conversion circuit described in this embodiment, resonant inductors in two resonant conversion circuit units are magnetically integrated on one magnetic core, and transformers in two resonant conversion circuit units are magnetically integrated on another magnetic core. In this way, not only automatic current sharing is achieved in the two-phase resonant conversion circuit, but also the volume of the circuit is reduced. 
     It should be noted that, the foregoing embodiments all use LLC resonant conversion units as examples for description. Those skilled in the art may easily find that in addition to the LLC resonant conversion units, the resonant conversion units may be series resonant conversion units, parallel resonant conversion units, series-parallel resonant conversion units and so on; and a connection type in the resonant conversion circuits is not limited to a symmetric half-bridge connection and a asymmetric half-bridge connection that are mentioned in the foregoing embodiments, but also includes a manner such as a full-bridge connection. 
     In the resonant conversion circuit described in the embodiments of the present invention, the magnetic devices are magnetically integrated in the inter-phase manner on the same magnetic core. Magnetic coupling exists between the magnetic devices of the two phases, thereby improving the problem which is non-current sharing of the input and output and is caused by the inconsistency of the resonant element parameters of the two phases, and reducing the precision requirement for the device parameters and the filtering cost during production, and balancing the input and output currents between the two phases without any complicated control means, which increases the reliability of power converters. In addition, the magnetic integration technology is used, and therefore, the volume of the power supply is reduced and the power density of the power supply is further improved. 
     All embodiments of the present invention are described in a progressive manner. Each embodiment emphasizes on illustration of the difference from other embodiments. For the same or similar parts among all embodiments, reference may be made to each other. 
     The foregoing illustration of the disclosed embodiments enables a person skilled in the art to implement or use the present invention. Multiple modifications to these embodiments are apparent for a person skilled in the art. The general principle defined in this document may be implemented in other embodiments without departing from the scope of the present invention. Therefore, the present invention will not be limited to the embodiments described in this document, but extends to the widest scope that complies with the principle and novelty disclosed in this document.