DC-DC Converter and Its Controlling Method

Abstract

A buck converter circuit and a boost converter circuit, which co-use a main inductor, are connected in series with each other between a DC power-supply and a DC load between output terminals a-b of a rectifier circuit. Moreover, utilizing energy accumulated into first and second auxiliary inductors which are loosely coupled to the main inductor magnetically, a current is flown through diodes during a short time-period including a point-in-time at which main switching elements of the buck and boost converter circuits are to be turned ON. Here, the diodes are connected in inversely parallel to the main switching elements.

1 . A unidirectional DC-DC converter, comprising: 
 a DC power-supply,    a buck converter circuit, said buck converter circuit including a first main switching element for intermittently intercepting and connecting a current flowing into a DC load via a main inductor from said DC power-supply,    a boost converter circuit, said boost converter circuit including a second main switching element for short-circuiting said DC load, and intermittently intercepting and connecting a current in a circuit for accumulating energy into said main inductor from said DC power-supply,    first and second snubber capacitors connected in parallel to said first and second main switching elements each,    first and second inversely-parallel diodes connected in inversely parallel to said first and second main switching elements each,    a control device for turning ON/OFF said first and second main switching elements, and controlling duties of said main switching elements, and    an output diode for releasing said energy onto said load side by said ON/OFF operation of said main switching elements, said energy being accumulated into said main inductor, wherein    said unidirectional DC-DC converter further comprises: 
 first and second auxiliary inductors which are magnetically coupled to said main inductor, and  
 first and second auxiliary switching elements for utilizing energy accumulated into said first and second auxiliary inductors, and flowing a forward-direction current through said corresponding first and second inversely-parallel diodes each during a short time-period including a point-in-time at which said main switching elements are to be turned ON.  
   
   
   
       2 . The unidirectional DC-DC converter according to  claim 1 , wherein 
 said first and second auxiliary inductors are loosely coupled to said main inductor magnetically.    
   
   
       3 . The unidirectional DC-DC converter according to  claim 1 , further comprising: 
 control means for turning ON said first and second auxiliary switching elements during said short time-period including said point-in-time at which said corresponding first and second main switching elements are to be turned ON, and flowing said forward-direction current through said corresponding first and second inversely-parallel diodes each.    
   
   
       4 . The unidirectional DC-DC converter according to  claim 1 , further comprising: 
 control means for turning ON said first and second auxiliary switching elements immediately before turning ON said corresponding first and second main switching elements each.    
   
   
       5 . The unidirectional DC-DC converter according to  claim 1 , further comprising: 
 identification means for making a comparison between voltage at said DC power-supply and output voltage to said DC load, and identifying a large-or-small relationship therebetween, and    control means for driving said first main switching element and said first auxiliary switching element if said identification means identifies that said voltage at said DC power-supply is higher, said control means, meanwhile, driving said second main switching element and said second auxiliary switching element if said identification means identifies that said voltage at said DC power-supply is lower.    
   
   
       6 . The unidirectional DC-DC converter according to  claim 5 , wherein 
 said control means comprises a DC circuit of said output diode and an output capacitor, said DC circuit being connected between both ends of said second main switching element,    said control means selectively driving either said boost converter circuit or said buck converter circuit by making a comparison between voltage occurring in said output capacitor and said voltage at said DC power-supply to identify a large-or-small relationship therebetween.    
   
   
       7 . The unidirectional DC-DC converter according to  claim 1 , further comprising: 
 driving means for turning ON said first main switching element when both-ends voltage of said main inductor lowers down to a predetermined voltage, and turning OFF said first main switching element when both-ends voltage of said main inductor rises up to a predetermined voltage.    
   
   
       8 . The unidirectional DC-DC converter according to  claim 7 , wherein 
 said driving means comprises    said first auxiliary inductor which is magnetically coupled to said main inductor, and    means for turning ON said first main switching element when terminal voltage of said first auxiliary inductor lowers down to a predetermined voltage, and turning OFF said first main switching element when said terminal voltage of said first auxiliary inductor rises up to a predetermined voltage.    
   
   
       9 . The unidirectional DC-DC converter according to  claim 1 , further comprising: 
 driving means for turning ON said first main switching element when both-ends voltage of said first main switching element lowers down to a predetermined voltage.    
   
   
       10 . The unidirectional DC-DC converter according to  claim 9 , wherein 
 said driving means comprises    means for connecting in-series-connected resistors to a point between both ends of said first main switching element, and turning ON said first main switching element when voltage at said connection point lowers down to a proximity to zero.    
   
   
       11 . A unidirectional DC-DC converter, comprising: 
 a DC power-supply,    a buck converter circuit, said buck converter circuit including a first main switching element for intermittently intercepting and connecting a current flowing into a DC load via a main inductor from said DC power-supply,    a boost converter circuit, said boost converter circuit including a second main switching element for short-circuiting said DC load, and intermittently intercepting and connecting a current in a circuit for accumulating energy into said main inductor from said DC power-supply,    first and second snubber capacitors connected in parallel to said first and second main switching elements each,    first and second inversely-parallel diodes connected in inversely parallel to said first and second main switching elements each,    a control device for turning ON/OFF said first and second main switching elements, and controlling duties of said main switching elements, and    an output diode for releasing said energy onto said load side by said ON/OFF operation of said main switching elements, said energy being accumulated into said main inductor, wherein    said unidirectional DC-DC converter further comprises:    a DC circuit of a first auxiliary switching element and a first auxiliary inductor, said first auxiliary inductor being magnetically coupled to said main inductor, said DC circuit being connected in parallel to said first main switching element, and    a DC circuit of a second auxiliary switching element and a second auxiliary inductor, said second auxiliary inductor being magnetically coupled to said main inductor, said DC circuit being connected in parallel to said second main switching element.    
   
   
       12 . The unidirectional DC-DC converter according to  claim 11 , wherein 
 said first and second auxiliary inductors are loosely coupled to said main inductor magnetically.    
   
   
       13 . The unidirectional DC-DC converter according to  claim 11 , further comprising: 
 control means for turning ON said first and second auxiliary switching elements during a short time-period including a point-in-time at which said corresponding first and second main switching elements are to be turned ON, and flowing a forward-direction current through said corresponding first and second inversely-parallel diodes each.    
   
   
       14 . The unidirectional DC-DC converter according to  claim 11 , further comprising: 
 DC diodes each of which is inserted into said DC circuits, and    inversely-parallel diodes connected in inversely parallel to said first and second auxiliary switching elements each.    
   
   
       15 . The unidirectional DC-DC converter according to  claim 11 , further comprising: 
 identification means for making a comparison between voltage at said DC power-supply and output voltage to said DC load, and identifying a large-or-small relationship therebetween,    buck driving means for driving said first main switching element and said first auxiliary switching element if said identification means identifies that said voltage at said DC power-supply is higher, and    boost driving means for driving said second main switching element and said second auxiliary switching element if said identification means identifies that said voltage at said DC power-supply is lower.    
   
   
       16 . The unidirectional DC-DC converter according to  claim 11 , further comprising: 
 driving means for turning ON said first main switching element when both-ends voltage of said main inductor lowers-down to a predetermined voltage, and turning OFF said first main switching element when both-ends voltage of said main inductor rises up to a predetermined voltage.    
   
   
       17 . The unidirectional DC-DC converter according to  claim 11 , further comprising: 
 driving means for turning ON said first main switching element when both-ends voltage of said first main switching element lowers down to a predetermined voltage.    
   
   
       18 . A method of controlling a unidirectional DC-DC converter, said unidirectional DC-DC converter, comprising: 
 a DC power-supply,    a buck converter circuit, said buck converter circuit including a first main switching element for intermittently intercepting and connecting a current flowing into a DC load via a main inductor from said DC power-supply,    a boost converter circuit, said boost converter circuit including a second main switching element for short-circuiting said DC load, and intermittently intercepting and connecting a current in a circuit for accumulating energy into said main inductor from said DC power-supply,    first and second snubber capacitors connected in parallel to said first and second main switching elements each,    first and second inversely-parallel diodes connected in inversely parallel to said first and second main switching elements each,    a control device for turning ON/OFF said first and second main switching elements, and    controlling duties of said main switching elements, and    an output diode for releasing said energy onto said load side by said ON/OFF operation of said main switching elements, said energy being accumulated into said main inductor,    said method, comprising a step of:    utilizing energy accumulated into first and second auxiliary inductors which are loosely coupled to said main inductor magnetically, and flowing a forward-direction current through said corresponding inversely-parallel diode immediately before turning ON said first or second main switching element.    
   
   
       19 . The method according to  claim 18 , further comprising a step of: 
 turning ON said first and second auxiliary switching elements during a short time-period including a point-in-time at which said corresponding first and second main switching elements are to be turned ON, and flowing said forward-direction current through said corresponding inversely-parallel diode.