Abstract:
The invention relates to a voltage converter ( 100 ), including: a plurality of two-way conversion cells ( 303 ), each cell comprising a primary circuit ( 307,  Wp), and a secondary circuit ( 308,  Ws) that is insulated from the primary circuit, wherein each circuit can be separately activated in order to supply an output voltage from the converter; and at least one control circuit ( 306 ) configured to, in a first operating mode, control the activated cells in order to transfer electrical energy from the primary circuit to the secondary circuit, and control the inactivated cells in order to transfer electrical energy from the secondary circuit to the primary circuit.

Description:
BACKGROUND  
       [0001]    The present disclosure relates to D.C.-to-D.C. voltage converters, and more particularly aims at a configurable converter comprising a plurality of elementary conversion cells capable of being individually activated to take part in the provision of an output voltage. Converters where the operation of the elementary conversion cells is based on the carrying out of cycles of power transfer between the primary and secondary windings of an insulating transformer are here more particularly considered. 
       DISCUSSION OF THE RELATED ART  
       [0002]    A configurable voltage converter comprising a plurality of elementary conversion cells having identical or different transformation ratios, the cells being capable of being individually activated to take part in the conversion of a D.C. input voltage into a A.C. output voltage, has already been provided, for example, in patent application US2007/0159862. The total transformation ratio of the converter depends on the selection of the activated cells. This type of converter has the advantage of being able of accept a wide variety of input voltage ranges and/or of being able to provide a wide variety of output voltage ranges. 
         [0003]    In practice, dynamically reactivating a cell which has previously been disconnected without stopping the converter operation appears to be likely to raise a number of issues. Indeed, in a configurable multiple-cell converter, each elementary cell generally comprises an input capacitive element between its input terminals. When the cell is disconnected, the input capacitive element of this cell tends to discharge, for example, due to leakages inevitably present in its dielectric space, which may result in unwanted voltage or current peaks when the cell is reactivated. Further, if the input capacitive element of the cell is totally discharged, for example, when the cell has remained disconnected for a long period, it may be impossible to reactivate the cell without inputting power from an external source (cell restarting). 
         [0004]    As a result, configurable converters generally comprise at least one secondary power supply, specifically dedicated to maintaining an appropriate charge level in the capacitive input elements of the non-activated cells. More generally, configurable converters comprise at least one secondary power supply to reactivate disconnected cells. This increases the complexity, the bulk, and the cost of converters. 
       SUMMARY  
       [0005]    Thus, an object of an embodiment of the present invention is to provide a configurable converter comprising a plurality of elementary conversion cells capable of being individually activated to take part in the provision of an output voltage, such a converter overcoming at least partly some of the disadvantages of known converters. 
         [0006]    An object of an embodiment of the present invention is to provide a converter which does not require using an external power supply source to reactivate cells which have been deactivated. 
         [0007]    An object of an embodiment of the present invention is to provide a converter which does not require using an external power source to solve reconfiguration problems due to the discharge of the input capacitive elements of the elementary conversion cells which do not take part in the provision of the output voltage. 
         [0008]    An object of an embodiment of the present invention is to provide a converter having a structure enabling to satisfactorily optimize the conversion performance, and particularly the quality factor and the power efficiency, whatever the configuration of the converter. 
         [0009]    Thus, an embodiment of the present invention provides a voltage converter, comprising: a plurality of bidirectional conversion cells, each cell comprising a primary circuit and a secondary circuit isolated from the primary circuit, and being capable of being individually activated to take part in the provision of an output voltage of the converter; and at least one control circuit configured to, in a first operating mode, simultaneously control activated cells to transfer electric power from the primary circuit to the secondary circuit, and non-activated cells to transfer electric power from the secondary circuit to the primary circuit. 
         [0010]    According to an embodiment of the present invention, the primary circuits are series-connected between first and second terminals of the converter and the secondary circuits are connected in parallel between third and fourth terminals of the converter. 
         [0011]    According to an embodiment of the present invention, the control circuit is further configured to, in a second operating mode, control the activated cells and the non-activated cells to transfer electric power from the secondary circuit to the primary circuit. 
         [0012]    According to an embodiment of the present invention, each cell further comprises an input capacitive element between first and second input terminals of the cell, on the primary circuit side. 
         [0013]    According to an embodiment of the present invention, each cell comprises activation switches, and a circuit for driving the activation switches powered with the voltage across said input capacitive element. 
         [0014]    According to an embodiment of the present invention, each cell further comprises an output capacitive element between first and second output terminals of the cell, on the secondary circuit side. 
         [0015]    According to an embodiment of the present invention, the primary and secondary circuits of each cell respectively comprise a primary winding and a secondary winding coupled to each other. 
         [0016]    According to an embodiment of the present invention, the primary circuit of each cell comprises four chopper switches assembled as a full bridge, the primary winding connecting the midpoints of the two arms of the bridge. 
         [0017]    According to an embodiment of the present invention, each cell further comprises a circuit for driving the chopper switches of the primary circuit, powered with the voltage across said input capacitive element. 
         [0018]    According to an embodiment of the present invention, the secondary circuit of each cell comprises four chopper switches assembled as a full bridge, the secondary winding connecting the midpoints of the two arms of the bridge. 
         [0019]    Another embodiment of the present invention provides a component comprising a plurality of converters of the above-mentioned type, the component having at least four connection elements per converter, respectively connected to first, second, third, and fourth terminals of the converter. 
         [0020]    Another embodiment of the present invention provides a method of controlling a voltage converter comprising a plurality of bidirectional conversion cells, each cell comprising a primary circuit and a secondary circuit isolated from the primary circuit, and being capable of being individually activated to take part in the provision of an output voltage of the converter, the method comprising the step of: simultaneously controlling activated cells to transfer electric power from the primary circuit to the secondary circuit, and non-activated cells to transfer electric power from the secondary circuit to the primary circuit. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0021]    The foregoing and other features and advantages will be discussed in detail in the following non-limiting description of specific embodiments in connection with the accompanying drawings, among which: 
           [0022]      FIG. 1  is a simplified electric diagram of an example of a configurable converter; 
           [0023]      FIG. 2  is an electric diagram of another example of a configurable converter; 
           [0024]      FIG. 3  is a simplified electric diagram of an embodiment of a configurable converter; and 
           [0025]      FIG. 4  is a more detailed electric diagram of an embodiment of a configurable converter of the type described in relation with  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION  
       [0026]    For clarity, the same elements have been designated with the same reference numerals in the different drawings. Further, only those elements which are useful to the understanding of the present invention have been shown and described. In particular, the various uses that can be made of the described configurable converters have not been mentioned, such converters being compatible with all known uses of D.C.-to-D.C. voltage converters. 
         [0027]      FIG. 1  is a simplified diagram of an example of a converter  100  of the type described in above-mentioned patent application US2007/0159862, comprising a plurality of elementary D.C.-to-D.C. conversion cells  103 . The operation of elementary cells  103  is based on the carrying out of cycles of power transfer between the primary and secondary windings of an isolation transformer. Each cell is capable of being individually activated to take part in the conversion of an input voltage v IN  applied between input terminals E 1  and E 2  of the converter into an output voltage v OUT  delivered between output terminals S 1  and S 2  of the converter. 
         [0028]    Each cell  103  comprises two input terminals e 1  and e 2 , and two output terminals s 1  and s 2 . The inputs of cells  103  are series-connected between input terminals E 1  and E 2  of the converter. More particularly, input terminal e 1  of each cell  103  in the series is connected to input terminal e 2  of the previous cell  103 , input terminal e 1  of first cell  103  in the series being connected to input terminal E 1  of the converter, and input terminal e 2  of last cell  103  in the series being connected to input terminal E 2  of the converter. The outputs of cells  103  are connected in parallel between output terminals S 1  and S 2  of the converter. More particularly, output terminals s 1  of the elementary cells are connected to output terminal S 1  of the converter, and output terminals s 2  of the elementary cells are connected to output terminal S 2  of the converter. 
         [0029]    Each cell  103  has two associated configuration switches SW 1  and SW 2  arranged as shown in  FIG. 1 . Switch SW 1  is series-connected with input terminal e 1  of the cell, and more particularly between input terminal e 1  of the cell and input terminal E 1  of the converter for the first cell in the series, and between input terminal e 1  of the cell and input terminal e 2  of the cell of previous rank in the series for the other cells. Switch SW 2  is in parallel with the cell input, and more particularly between terminal e 2  and the terminal of switch SW 1  which is not connected to terminal e 1 . A cell  103  is activated, and takes part in the provision of output voltage v OUT , when switches SW 1  and SW 2  associated with this cell are respectively on and off. A cell  103  is disconnected (or deactivated), and does not take part in the provision of output voltage v OUT , when switches SW 1  and SW 2  associated with this cell are respectively off and on. 
         [0030]    A circuit  105  for controlling the configuration switches (LADDER SWITCH CONTROLLER) is provided to control the activation or the disconnection (deactivation) of cells  103 . Circuit  105  may receive as an input one and/or the other of the images of input and output voltages v IN  and v OUT  of the converter, and activate or dynamically disconnect (in real time) cells to adjust the total converter transformation ratio to regulate output voltage v OUT . In other words, the converter configuration may be controlled by the levels of v IN  and/or v OUT  to always respect a given voltage set point. 
         [0031]    In such a converter, each elementary cell generally comprises an input capacitive element between its input terminals e 1  and e 2 . To be able to reactivate disconnected (non-activated) cells, and more particularly to avoid problems of reconfiguration due to the discharge of the input capacitive elements of the disconnected cells, it is necessary to provide at least one secondary power supply (not shown) to maintain the capacitive elements at an appropriate charge level. 
         [0032]      FIG. 2  is a diagram illustrating another example of a converter  200  of the type described in the above-mentioned patent application. Converter  200  comprises a plurality of input cells  201  coupled to a single output cell  202 . 
         [0033]    Each input cell  201  comprises a primary circuit, this circuit comprising a primary winding Wp and four cut-off switches, respectively SW 3 , SW 4 , SW 5 , and SW 6  assembled as a full bridge between input terminals e 1  and e 2  of the cell. Primary winding Wp connects the midpoints of the two arms of the bridge. Capacitive and inductive resonance elements (not shown) may be series-connected with winding Wp between the arms of the bridge to set the resonance frequency of the primary winding. Each cell  201  further comprises a capacitive element c in  between its input terminals e 1  and e 2  to set the input voltage of the primary circuit. 
         [0034]    Output cell  202  comprises a secondary circuit, this circuit comprising a secondary winding Ws and a rectifying circuit having its input connected to terminals of secondary winding Ws and having its output connected to output terminals s 1  and s 2  of cell  202 . Secondary winding Ws is magnetically coupled to primary windings Wp of all converter input cells  201 . The rectifying circuit is a circuit with two diodes D 1  and D 2 . Output cell  202  further comprises a capacitive element c out  between its output terminals s 1  and s 2 . 
         [0035]    Input cells  201  are series-connected between input terminals E 1  and E 2  of the converter (terminals of application of input voltage v IN ). Output terminals s 1  and s 2  of output cell  202  are respectively connected to output terminals S 1  and S 2  of the converter (terminals delivering output voltage v OUT ). Each input cell  201  has two associated configuration switches SW 1  and SW 2  arranged as in the example of  FIG. 1 . As in the example of  FIG. 1 , an input cell  201  is activated and takes part in the provision of output voltage v OUT  when the switches SW 1  and SW 2  associated with this cell are respectively on and off, and an input cell  201  is disconnected and does not take part in the provision of output voltage v OUT  when switches SW 1  and SW 2  associated with this cell are respectively off and on. 
         [0036]    A circuit  205  for controlling configuration switches SW 1 , SW 2  (LADDER SWITCH CONTROLLER) is provided to control the activation or the disconnection of input cells  201 . A circuit  206  for controlling chopper switches SW 3 , SW 4 , SW 5 , SW 6  (RESONANT SWITCH CONTROLLER) is provided to control the power transfer from the primary circuit of each activated input cell  201  to the common secondary circuit of output cell  202 . 
         [0037]    When an input cell  201  of converter  200  is disconnected, or non-activated, it is provided to keep on controlling chopper switches SW 3 , SW 4 , SW 5 , and SW 6  of this cell to maintain input capacitance c in  of the cell at an appropriate charge level, to suppress inrush current problems on reconfiguration of the converter. 
         [0038]    However, a disadvantage of converter  200  is due to the fact that this converter comprises a plurality of primary circuits capable of being individually activated, coupled to a single secondary circuit. This inevitably results in significantly altering the conversion performance, and particularly the quality factor and the power efficiency, in certain converter configurations. 
         [0039]      FIG. 3  is a simplified electric diagram of an embodiment of a configurable converter  300  comprising a plurality of D.C.-to-D.C. elementary conversion cells  303 , that is, at least two cells  303 , each cell  303  being capable of being individually activated to take part in the conversion of an input voltage v IN  applied between input terminals E 1  and E 2  of the converter into an output terminal v OUT  delivered between output terminals S 1  and S 2  of the converter. 
         [0040]    Each conversion cell  303  comprises an input cell  301  comprising two input terminals e 1  and e 2 , and one output cell  302 , coupled to input cell  301 , comprising two output terminals s 1  and s 2 . Input cell  301  comprises a primary circuit, this circuit comprising a primary winding Wp of a transformer and a circuit  307  capable of converting a D.C. voltage (DC) received between input terminals e 1  and e 2  of the cell into a variable voltage (AC) provided across primary winding Wp. Input cell  301  further comprises an input capacitive element c in  between its terminals e 1  and e 2  to set the voltage applied to the input of the primary circuit. Output cell  302  comprises a secondary circuit, this circuit comprising a secondary winding Ws, coupled to primary winding Wp of input cell  301 , and a circuit  308  capable of rectifying a variable voltage (AC) received across secondary winding Ws into a D.C. voltage (DC) provided across an output capacitive element c out  connected between output terminals s 1  and s 2  of cell  302 . 
         [0041]    Thus, unlike converter  200  of  FIG. 2  which comprises a plurality of primary circuits coupled to a single secondary circuit, converter  300  comprises a plurality of primary circuits and a plurality of secondary circuits coupled two by two. 
         [0042]    Input cells  301  are series-connected between input terminals E 1  and E 2  of the converter (terminals of application of voltage v IN ) and output cells  302  are connected in parallel between output terminals S 1  and S 2  of the converter (terminals of provision of output voltage v OUT ), for example, as described in the example of  FIG. 1 . In this example, each conversion cell  303  has two associated configuration switches SW 1  and SW 2  arranged as in the example of  FIG. 1 . Thus, a conversion cell  303  is activated to take part in the provision of output voltage v OUT  when switches SW 1  and SW 2  associated with this cell are respectively on and off, and a conversion cell  303  is disconnected or deactivated, and does not take part in the provision of output voltage v OUT , when switches SW 1  and SW 2  associated with this cell are respectively off and on. It should be noted that in the shown example, switches SW 1  are connected to input terminals e 1  of the corresponding cells. As a variation, it may be provided to connect series switches SW 1  to input terminals e 2  of the cells (that is, on the bottom input branch of the cells in the diagram of  FIG. 3 , rather than on the top input branch). 
         [0043]    A circuit  305  for controlling the configuration switches (CONFIG SWITCH CONTROLLER) is provided to control the activation or the disconnection of elementary conversion cells  303 . A circuit  306  for controlling the elementary cells (CONVERTING CELL CONTROLLER) is provided to control the power transfer from the primary circuit to the secondary circuit of the activated cells, to take part in the provision of output voltage v OUT . 
         [0044]    According to an aspect of an embodiment, elementary conversion cells  303  are bidirectional, that is, each cell  303  can be controlled either to transfer power from the primary circuit to the secondary circuit when a D.C. voltage source is applied between its terminals e 1  and e 2 , or to transfer power from the secondary circuit to the primary circuit when a D.C. voltage source is applied between its terminals s 1  and s 2 . In other words, circuit  308  of an elementary conversion cell is not only capable of rectifying a variable voltage (AC) received across secondary winding Ws into a D.C. voltage (DC) provided between output terminals s 1  and s 2  of the cell, but may further be controlled to convert a D.C. voltage (DC) applied between terminals s 1  and s 2  of the cell into a variable voltage (AC) provided across secondary winding Ws. Further, circuit  307  of an elementary conversion cell is not only capable of converting a D.C. voltage (DC) received between its terminals e 1  and e 2  into a variable voltage (AC) provided across primary winding Wp, but may further be controlled to rectify a variable voltage (AC) received across primary winding Wp into a D.C. voltage (DC) provided between input terminals e 1  and e 2  of the cell. 
         [0045]    According to another aspect of an embodiment, it is provided to control the cells  303  which do not take part in the provision of output voltage v OUT  (disconnected cells) to transfer electric power from their secondary circuit to their primary circuit in order to maintain an appropriate charge level between input capacitive elements c in  of the deactivated cells  303 . In this example, circuit  306  is configured not only to control the activated cells to transfer power from their primary circuit to their secondary circuit, but also to control the disconnected cells to transfer power from their secondary circuit to their primary circuit. In other words, control circuit  306  is configured to, in a same operating mode, simultaneously control activated cells to transfer electric power from the primary circuit to the secondary circuit, and non-activated cells to transfer electric power from the secondary circuit to the primary circuit. 
         [0046]    An advantage of converter  300  is that it enables to maintain at an appropriate charge (or voltage) level input capacitive elements c in  of the elementary cells which do not take part in the provision of the output voltage, which avoids problems of converter reconfiguration, without for all this providing an external power supply specifically dedicated to this function. 
         [0047]    Another advantage of converter  300  is that each elementary conversion cell  303  comprises its own primary circuit and its own secondary circuit coupled to each other. The conversion performance, and particularly the quality factor and the power efficiency, can thus be optimized cell by cell. This provides, at least in certain configurations of the converter, a much better performance than in a converter of the type described in relation with  FIG. 2 , comprising a single secondary circuit coupled to a plurality of primary circuits. 
         [0048]    Another advantage of converter  300  is that it is fully bidirectional. In particular, a usage mode of converter  300  may be provided where all conversion cells  303 , be they activated or not, are controlled to transfer power from their secondary circuit to their primary circuit, to convert a D.C. input voltage applied between terminals S 1  and S 2  of the converter into a D.C. output voltage provided between terminals E 1  and E 2  of the converter. In this case, as in the previously-described usage mode, the activated cells take part in the provision of the output voltage and transfer an amount of power which particularly depends on the load (not shown) powered by the converter, and the disconnected cells do not take part in the provision of the output voltage and only transfer the amount of power necessary to maintain the charge of input capacitive element c in . 
         [0049]    In a preferred embodiment, configuration switches SW 1  and SW 2  of each cell are integrated on an integrated circuit chip together with other elements of the cell, for example, together with chopper elements of the cell. This chip may further comprise amplification circuits to guarantee a sharp switching and with the least possible losses of switches SW 1  to SW 6 . The chip may also comprise control circuits implementing functions of control of the cell transformation coefficient, of control of the current level in the cell, and/or of control of the flow direction of the current in the cell, for example, by varying the phase-shift of the cell chopper switches. This chip, and particularly the amplification and control circuits associated with switches SW 1  to SW 6  (also called circuits for closely controlling switches SW 1  to SW 6 ), may be powered with the power stored in capacitor c in  of the cell (that is, with the voltage between terminals e 1  and e 2 ). In this case, the circuits external to the cell, that is, circuits  305  and  306  in the shown example, only provide the cell with control signals (activation or not of the cell, cell operating direction, value of the transformation coefficient or of the current level in the cell, etc.). In other words, all or part of circuit  306  (CONVERTING CELL CONTROLLER) can be locally transferred into cells  303 , and powered with the power stored in capacitors c in . In an embodiment, the transformation coefficient of the disconnected converter cells (cells transferring power from their secondary circuit to their primary circuit) may be selected to maintain the voltage between terminals e 1  and e 2  of the cell deactivated at an optimal value enabling to efficiently reactive the cell (particularly to maintain an optimal biasing of configuration switch SW 2  which short-circuits the primary stage of the cell). 
         [0050]      FIG. 4  is an electric diagram showing in more detailed fashion an embodiment of a configurable converter  400  of the type described in relation with  FIG. 3 . In particular, as compared with  FIG. 3 , control circuits  307  and  308  of the primary and secondary stages of the elementary conversion cells have been detailed. The elements already described in relation with  FIG. 3  will not be detailed again hereafter. 
         [0051]    In each elementary conversion cell  303 , primary stage control circuit  307  comprises four chopper switches SW 3 , SW 4 , SW 5 , and SW 6 , assembled as a full bridge between input terminals e 1  and e 2  of the cell. Primary winding Wp connects the midpoints of the two arms of the bridge. Capacitive and inductive resonance elements (not shown) may be series-connected with winding Wp to set the resonance frequency of the primary circuit. Further, in each cell  303 , secondary stage control circuit  308  comprises four chopper switches SW 7 , SW 8 , SW 9 , and SW 10 , assembled as a full bridge between output terminals s 1  and s 2  of the cell. Secondary winding Ws connects the midpoints of the two arms of the bridge. Capacitive and inductive resonance elements (not shown) may be series-connected with winding Ws to set the resonance frequency of the secondary circuit. 
         [0052]    Switches SW 1  to SW 10  are two-way current switches, for example, MOS transistors. Switches SW 3  to SW 6  of circuit  307  may be controlled either to convert a D.C. input voltage applied between terminals e 1  and e 2  of cell  303  into a variable voltage provided across primary winding Wp (power transfer from the primary to the secondary), or to rectify a variable voltage received across primary winding Wp into a D.C. voltage provided between terminals e 1  and e 2  of cell  303  (power transfer from the secondary to the primary). Further, switches SW 7  to SW 10  of circuit  308  may be controlled either to rectify a variable voltage received across secondary winding Ws into a D.C. voltage provided between terminals s 1  and s 2  of cell  303  (power transfer from the primary to the secondary), or to convert a D.C. voltage applied between terminals s 1  and s 2  of cell  303  into a variable voltage provided across secondary winding Ws (power transfer from the secondary to the primary). It should be noted that in the absence of a sufficient power to properly control the switching of switches SW 1  to SW 6  or SW 7  to SW 10 , for example, in a converter power-on phase, the rectifications and power transfers are performed via the diodes intrinsic to the MOS transistors. 
         [0053]    As an example, to reverse the power transfer direction in an elementary cell  303 , control circuit  306  may be configured to vary the phase-shift between the switchings of the switches of the primary and the switchings of the switches of the secondary. Control circuit  306  may also be configured to vary the switching frequency and/or the switching duty cycle of chopper switches SW 3  to SW 10 . It should be noted that by varying one or a plurality of the above-mentioned parameters (phase shift, frequency, and duty cycle), it is possible to adjust the transformation ratio of an elementary cell around a nominal transformation ratio. This provides an additional possibility of setting the converter. In other words, the transformation coefficient or the current ratio of each cell is individually settable. As an example, a phase reference may be defined for each cell by the secondary circuit of the cell, and the cell may be set by varying the phase shift of the switches of the primary with respect to the switches of the secondary. In this case, it may be provided for the secondary circuits of the converter to all operate in phase or, as a variation to operate with a phase shift (which eases possible control signal filtering operations). 
         [0054]    Specific embodiments of the present invention have been described. Various alterations, modifications, and improvements will readily occur to those skilled in the art. 
         [0055]    In particular, the invention is not limited to the example of elementary cell  303  described in relation with  FIG. 4 . More generally, it will be within the abilities of those skilled in the art to form a converter of the type described hereabove whatever the structure of the elementary cell, provided that each elementary cell comprises a primary circuit and a secondary circuit coupled to each other and forming a transformer isolating the input terminals of the cell from its output terminal, and that each cell is bidirectional in terms of current. 
         [0056]    Further, to increase the conversion possibilities offered by a single component, it will be within the abilities of those skilled in the art to form a component comprising a plurality of configurable converters of the type described in relation with  FIGS. 3 and 4 , this component comprising two input terminals and two output terminals for each converter, and at least one control circuit for controlling the configuration and chopper switches of the converters. It should be noted that the component may comprise one control circuit per converter, or a control circuit common to all converters. As a variation, the control circuit may be external to the component and control converters of one or a plurality of components. The choice of associating or not the converters and the way to associate them (series or parallel at the input, series or parallel at the output) may be left to the user, and the associations may for example be made by soldering contact elements of the component (a contact element may be a connection pad, a contact bump, or any other known connection element).