Abstract:
A system for converting a first voltage into a second voltage includes input terminals and output terminals, switching members disposed between the terminals which can convert voltage, and a device for controlling the switching members. The device includes a cell for controlling a switching member, and a member for managing and supplying the control cell. The member is connected to the control cell by a link allowing the simultaneous transmission of a control signal and electrical energy. The member includes a device for generating a pulse, and which includes at least two different control intervals.

Description:
FIELD OF THE INVENTION 
     Embodiments of the present invention relate to a system for the conversion of a first electrical voltage into a second electrical voltage and, in particular, to the conversion system with high electrical power, such as power in excess of 1 MW. 
     BACKGROUND OF THE INVENTION 
     A voltage converter of the aforementioned type is known. The converter is a three-phase voltage inverter comprising two input DC voltage terminals and one output terminal for each phase of the three-phase output voltage. The three-phase inverter includes two switching branches for each phase. Each switching branch is connected between the corresponding output terminal and a respective input terminal and includes a switching element. The switching elements are controlled by a control device and are suitable for converting the DC input voltage and the alternating output voltage. The switching elements include, for example, controllable electronic switches. The control device includes a cell controlling a switching element, and a control and supply unit for respective control cells. The control and supply unit is connected to the control cell by means of a connection for the simultaneous transmission of the corresponding control signal and the associated electrical energy. In this way, the energy is transferred at the same time as the control signals, which makes it possible to have a single connection between the control and supply unit and the respective control cells. 
     However, the time taken to establish a current between the control unit and the control cells is relatively long, and this is an increasing function of the number of control cells connected to the control and supply unit. The switching of the switches of a voltage converter of this kind is therefore relatively slow, which limits the frequency of the switching of the switches in the converter. 
     BRIEF SUMMARY OF THE INVENTION 
     Embodiments of the present invention propose a conversion system that makes it possible to accelerate the switching of the switching elements in order to increase the switching frequency of said switching elements and also to reduce possible timing discrepancies between the switchings of the switching elements. 
     A system for the conversion of a first electrical voltage into a second electric voltage, the system comprising: at least two input and two output terminals, switching elements positioned between the input terminals and the output terminals that are suitable for converting the first voltage into the second voltage, and a control device for the switching elements, the switching device including a cell controlling a respective switching element and a control and supply unit for the control cell, the control and supply unit being connected to the control cell by means of a link for the simultaneous transmission of a control signal and electrical energy. 
     For this purpose, an embodiment of the present invention is a conversion system of the aforementioned type, characterised in that the control and supply unit includes means of generating a pulse comprising at least two distinct control slots, the pulse having a substantially constant value during the second control slot distinct from a reference value corresponding to the absence of control, the value of the pulse being distinct from one control slot to the other and the pulse having a value during the first control slot that is strictly greater than that during the second control slot. 
     Embodiments of the present invention includes one or more of the following features, taken in isolation or in accordance with all the technically possible combinations: the control slots for the same pulse follow each other in succession, the system comprises at least one group of switching elements connected in series, the group or each group being connected between corresponding output and input terminals, a respective control cell being associated with each switching element, and the control and supply unit is unique for the control cells of the switching elements in the same group, and is suitable for controlling the plurality of control cells in the switching elements in the group, the control device also includes means of electrical insulation arranged between each control cell and the control and supply unit, the electrical insulation means include, for each group of switching elements, a plurality of secondary windings, a plurality of magnetic circuits and a single primary winding, each secondary winding being electrically connected to the input of a respective control cell and wound around a respective magnetic circuit, the single primary winding being wound around each of the circuits and electrically connected to the output of the single control and supply unit, the single primary winding comprises a single turn passing through each of the corresponding magnetic circuits, the pulse comprises a first control slot and a second control slot, the value of the pulse during the first slot being at least twice as great as that during the second slot, the duration of the first control slot is between 50 ns and 200 ns, more particularly equal to 100 ns, the value U2 of the pulse during the second slot satisfies the following equation:
 
 U 2=( N×Uc )/ M   (1)
 
     where N represents the number of switching elements of the corresponding group, N being an integer equal to or greater than 2, Uc is the input voltage of the corresponding control cell, and M represents the number of turns on the corresponding secondary winding, each control cell includes a first branch and a second branch connected in parallel, each branch comprising a transistor and a diode connected in series, the transistor of the second branch being complementary to that of the first branch, and the diode of the second branch being connected in an opposite direction compared with that of the first branch, and the means of generation of a pulse comprise an output terminal for the delivery of the pulse, and a first branch and a second branch connected to the output terminal, each branch comprising a transistor connected between a reference point and the output terminal, a resistor connected between the reference point and a first potential, a diode connected between the reference point and a second potential, and a capacitor connected between the reference point and an electrical earth, the transistor of the second branch being complementary to that of the first branch, and the diode of the second branch being connected in the opposite direction compared with that of the first branch. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These features and advantages of the present invention will become apparent when reading the description which will follow, which is given solely as example, and refers to the attached drawings, of which: 
         FIG. 1  is a schematic representation of a conversion system in accordance with an embodiment of the present invention, comprising six switching elements suited to converting the input voltage into an output voltage, 
         FIG. 2  is an electrical diagram of a group of switching elements and of a control device for the switching elements, the control device comprising a control cell for each respective switching element, and a control and supply unit for the control cells, 
         FIG. 3  is an electrical diagram of the control cell of  FIG. 2 , 
         FIG. 4  is an electrical diagram of the control and supply unit of  FIG. 2 , and 
         FIG. 5  is a set of curves representing on the one hand the voltage pulse generated by the control and supply unit intended for the control cells, and on the other hand, the current circulating in the connection between the control cells. 
     
    
    
     DETAILED DESCRIPTION 
     An embodiment of the present invention relates to a system  10  for conversion of a first electrical voltage into a second electrical voltage comprising at least two input terminals  12  and at least two output terminals  14 . The conversion system  10  comprises switching elements  16  positioned between the input terminals  12  and the output terminals  14 , which are suitable for the conversion of the first voltage into the second voltage. 
     The conversion system is suitable for allowing the circulation of a high electrical power, for example higher than 1 MW. 
     In the execution example in  FIG. 1 , the conversion system  10  is a voltage inverter suitable for converting a DC input voltage received between the two input terminals  12  into an alternating output voltage delivered at each output terminal  14 . 
     The voltage inverter  10  comprises two switching branches  18  for each phase of the alternating output voltage, each switching branch  18  being connected between the corresponding output terminal  14  and a respective input terminal  12 , and including a switching element  16 . 
     The voltage inverter comprises a diode  22  connected in antiparallel with each switching element  16  and means  24  of controlling the switching elements. 
     In the example embodiment in  FIG. 1 , the voltage inverter  10  is a three-phase inverter  10  and includes three output terminals  14  and six switching branches  18 , namely an output terminal and two switching branches for each phase of the three-phase output voltage. 
     The switching element  16 , visible on  FIG. 2 , comprises at least two arms  26  connected in parallel, a common control terminal  28 , a first common conduction terminal  30  and a second common conduction terminal  32 . 
     In the example embodiment in  FIG. 2 , the switching element  16  comprises three arms  26  connected in parallel. 
     In the example embodiment in  FIGS. 1 and 2 , each switching element  16  comprises at least two arms  26  connected in parallel, more particularly three arms  26  connected in parallel. 
     In addition, each switching element  16  comprises an additional arm  27  connected in parallel with the arms  26 . 
     The control device  24 , visible in  FIG. 2 , comprises a control cell  34  for each respective switching element  16  and a control and supply unit  36  for the control cells  34 , the control and supply unit  36  being connected to the or each control cell  34  by a connection  38  for the simultaneous transmission of a control signal and electrical energy. 
     In addition, the control device  24  includes electrical insulation means  40  arranged between each control cell  34  and the control and supply unit  36 . 
     In the example embodiment in  FIG. 2 , a group  42  of switching elements  16  connected in series comprises three switching elements  16 , the group  42  being connected between an output terminal and a corresponding input terminal. A respective control cell  34  is associated with each switching element  16 , and there is a single control and supply unit  36  for the three control cells  34  of the switching elements in the group  42 . 
     Each arm  26  is connected between the first and second common conduction terminals  30 ,  32  and includes an electronic switch  44  controllable between an on and off state, the switch  44  comprising a control electrode  46 , a first conduction electrode  48  and a second conduction electrode  50 . 
     Each arm  26  also comprises an inductor  52  connected between the same electrode of the two electrodes of conduction  48 ,  50  and the corresponding common conduction terminal  30 ,  32 . 
     In addition, each arm  26  comprises a resistor  54  connected between the control electrode  46  and the common control terminal  28 . 
     The additional arm  27  comprises a resistor  56  and a capacitor  58  connected in series. 
     The common control terminal  28  is connected, for example, by means of the resistor  54 , to the control electrode  46  of the switch of each of the arms  26  connected in parallel. 
     The first common conduction terminal  30  is connected to the first conduction electrode  48  of the switch of each of the arms  26  connected in parallel. 
     The second common conduction terminal  32  is connected by means of the inductor  52  to the second conduction electrode  50  of the switch of each arm  26  connected in parallel. 
     Each control cell  34 , visible in  FIG. 3 , comprises two input terminals  60  connected to the insulation means  40  and two output terminals  62  respectively connected to the common control terminal  28  and to the second common conduction terminal  32 . 
     Each control cell  34  includes a first branch  64  and a second branch  66  connected in parallel, each branch  64 ,  66  comprising one transistor  68  and one diode  70  connected in series. 
     Each control cell  34  also comprises a resistor  72  connected between the branches  64 ,  66  and the output terminal  62 , which is intended to be connected to the common control terminal  28 . Each control cell  34  comprises two Zener diodes  74  connected in series and head to tail between the terminal of the resistor  72 , which is not connected to the output terminal  62  and the other output terminal  62 . 
     The control and supply unit  36  comprises means  78 , visible in  FIG. 4 , of generating a pulse  80 , visible in  FIG. 5 , the pulse  80  comprising a first  82  and a second  84  distinct control slot and one transition slot  86 , the pulse  80  having during the second control slot  84  a substantially constant value U2 distinct from a reference value U0 corresponding to the absence of control, the value of the pulse being distinct from one control slot to the other. During the first control slot  82 , the pulse  80  has a value U1 that is strictly greater than the value U2 of the pulse during the second control slot  84 . 
     The control and supply unit  36  is suitable for controlling the plurality of control cells  34  of the switching elements  16  in the group  42 . 
     The transmission connection  38  is a wired connection. 
     The electrical insulation means  40  include, for each group of switching units  42 , a plurality of secondary windings  87 , a plurality of magnetic circuits  88 , and a single primary winding  89 , each secondary winding  87  being electrically connected to the input of a respective control cell  34  and wound around a respective magnetic circuit  88 . The single primary winding  89  is wound around each of the circuits  88  and electrically connected to the output of the single control and supply unit  36 . 
     The electronic switch  44  comprises at least one transistor from the group consisting of: a field-effect transistor, an IGBT transistor (insulated gate bipolar transistor) and an IEGT transistor (injection enhanced gate transistor). In the example embodiment in  FIG. 2 , each electronic switch  44  consists of an IGBT transistor. 
     The or each transistor in the switch  44  is, for example, suitable for allowing the circulation of a current with a voltage equal to 1.2 kV or 600 V and an intensity equal to 30 or 40 A. 
     The switches in the same switching element  16  comprise transistors of the same type, namely field-effect transistors, IGBT transistors, or IEGT transistors. The transistors of the same switching element  16 , although of the same type, are likely to display electrical characteristics that are substantially different from one transistor to another. 
     The control electrode  46  is also called the gate electrode when the switch  44  includes a field-effect transistor, an IGBT transistor or an IEGT transistor. 
     The first conduction electrode  48  and the second conduction electrode  50  are also referred to as collector electrode and emitter electrode respectively when the switch  44  includes an IGBT transistor or IEGT transistor. 
     In a variant, the first conduction electrode  48  and the second conduction electrode  50  are also referred to as the drain electrode and source electrode respectively, when the switch  44  comprises a field-effect transistor. 
     In the example embodiment in  FIG. 2 , said electrode among the two conduction electrodes  48 ,  50  which is connected to the inductor  52  is the second conduction electrode  50 . In other words, said electrode among the two conduction electrodes which is connected to the inductor  52  is the emitter electrode when the transistor is an IGBT transistor or an IEGT transistor. In a variant, said electrode among the two conduction electrodes which is connected to the inductor  52  is the source electrode when the transistor is a field-effect transistor. 
     The inductor  52  has an L value greater than 10 nH and is substantially identical for each of the arms  26  connected in parallel. The inductor  52 , for example, has an L value of between 10 nH and 100 nH. 
     The resistor  54  is a dedicated passive component and has value of approximately a few ohms. 
     The resistor  56  of the additional arm  27  is a damping resistor for the parasitic voltages liable to appear at high frequency, for example for frequencies greater than 1 MHz. The resistor  56  has an impedance of approximately a few ohms. The capacitor  58  is suited to absorbing a major portion of the current and to limiting the drift in the voltage over time. The capacitor  58  has a capacitance with a value of for example between P and 10×P nF, more particularly equal to 5×P nF, where P represents the number of arms  26  connected in parallel. Each capacitor  58  is able to charge when the switches  44  of each switching element are off, and to discharge when the switches  44  are on. The transistor  68  of the second branch  66 , also denoted  68 B, is complementary to that of the first branch  64 , also denoted  68 A. The diode  70  of the second branch  66  is connected in the opposite direction to that of the first branch  64 . 
     The transistor  68 A of the first branch is a p-type MOSFET transistor, and the transistor  68 B of the second branch is an n-type MOSFET transistor. In a variant, the transistor  68 A of the first branch is an npn-type bipolar transistor, and the transistor  68 B of the second branch is a pnp-type bipolar transistor. 
     The generation means  78 , visible in  FIG. 4 , comprise two output terminals  90  connected to the two ends of the transmission connection  38  for the delivery of the pulse  80 , and input terminals  92  connected to potentials of predetermined values. 
     The generation means  78  comprise a first branch  94  and a second branch  96  connected to the same output terminal  90 , the other output terminal  90  being connected to the electrical earth  98 . The generation means  78  also comprise a resistor  100  connected between the output terminal connected to the first and second branches  94 ,  96  and the electrical earth  98 . The pulse  80 , visible in  FIG. 5 , generated by the generation means  78  comprises the first control slot  82 , the second control slot  84  and the transition slot  86 . In the example embodiment in  FIG. 5 , the pulse  80  is a voltage pulse and the current circulating in the wired transmission connection  38  corresponding to this pulse  80  is represented by the curve  120  visible in  FIG. 5 . The current in the wired transmission connection  38  therefore comprises a rising edge  122  corresponding to the first control slot  82 , a plateau  124  where the current has a substantially constant value that corresponds to the second control slot  84 . The current in the wired connection  38  finally has a falling edge  126  corresponding to the transition slot  86  of the pulse. 
     The value U2 of the pulse  80  during the second control slot  84  satisfies the following equation: U2=(N×Uc)/M, where N represents the number of switching elements  16  of the corresponding group  42 , N being an integer equal to or higher than 2, Uc is the voltage at the input of the corresponding control cell  34 , and M represents the corresponding number of secondary winding turns  87 . The duration of first slot  82  is between 50 ns and 200 ns, more particularly substantially equal to 100 ns. The duration of second slot  84  is between 0.2 ns and 3 ns, more particularly substantially equal to 1 ns. 
     The transition slot  86  begins with the opening of the branch  94 , the current imposed by the secondary windings  87  then circulating in the resistor  100  connected between the output terminal  90  and the electrical earth  98 . During the transition slot  86 , the voltage of the pulse  80  falls to a minimum voltage with a value greater than or equal to a value −U′1, and then gradually decays. The magnetic circuit  88 , for example, is toroidal. 
     In the example embodiment in  FIG. 2 , the single primary winding  89  comprises a single turn passing through each of the corresponding rings  88 . In other words, the wired transmission connection  38  forms the single primary winding  89 . 
     Each branch  94  or  96  comprises a transistor  102  connected between a reference point  104  and the corresponding output terminal  90 , a resistor  106  connected between the reference point  104  and an input terminal  92  connected to a first potential with a value of U1 or U′1 respectively, a diode  108  connected between the reference point  104  and another input terminal  92  connected to a second potential with a value of U2 or U′2 respectively, and a capacitor  110  connected between the reference point  104  and the electrical earth  98 . 
     The value U1, −U′1 of the first potential is higher in absolute value than that U2, −U′2 of the second potential. The values U1, U2 corresponding to the first branch are positive, and those corresponding to the second branch  96  are negative. Otherwise, the value U1 is higher than U2, which itself is higher than −U′2, which is itself higher than −U′1. 
     The transistor  102  of the first branch  94 , also denoted  102 A, is complementary to that of the second branch  96 , also denoted  102 B. The diode  108  of the second branch  96  is connected in the opposite direction to that of the first branch  94 . 
     The transistor  102 A of the first branch is a p-type MOSFET transistor, and the transistor  102 B of the second branch is an n-type MOSFET transistor. In a variant, the transistor  102 A of the first branch is an npn-type bipolar transistor, and the transistor  102 B of the second branch is a pnp-type bipolar transistor. 
     During the operation of the conversion system, the control pulse  80  is generated by the control and supply unit  36  on the wired transmission connection  38 , which has an inductance which is added to the parasitic inductance of the toroid  88 . In other words, the primary winding  89  formed by the wired connection  38  and comprising a single turn has a high leakage inductance liable to result in an increase in the time taken to establish the current. 
     The pulse  80  generated by the control and supply unit  36  comprises the first high voltage control slot  82  to allow the establishment of current for a short duration (rising edge  122 ), the second slot  84  of relatively long duration corresponding to the maintenance of the current (plateau  124 ) and finally the parasitic slot  86  corresponding to the return of the current to a zero value (falling edge  126 ). 
     The two successive first slots  82 ,  84  make it possible to control the switching element  16 , for example, in switched-on mode in the example embodiment in  FIG. 5 . 
     In addition, the pulse  80  also includes three slots, not shown, with voltages with a sign opposite to those previously described for the control of the switching element  16  in off mode. In other words, the pulse  80  for the control of the switching element  16  in off mode has the value −U′1 during the first control slot, then the value −U′2 during the second control slot. During the transition slot, the voltage of the pulse  80  increases up to a maximum voltage with a value lower than or equal to U1, then gradually decays. 
     When the pulse  80  has positive control slots  82 ,  84 , the p-type transistor  68 A of the first branch of the control cell  34  is on, while the n-type transistor  68 B of the second branch of the control cell is off. The current then passes through the first branch  64  of the control cell to the control electrodes  46  of the switches  44 , which turns on the switches  44 . At the end of pulse  80 , the n-type transistor  68 B remains off, which makes it possible to keep the control electrode  46  in a charged state. 
     The operation is reversed for the control of the switching element  16  in its off mode. More precisely, the control slots, not shown, of the pulse  80  have successive negative voltages, and the n-type transistor  68 B of the control cell  34  is on, while the p-type transistor  68 A of the same control cell is off. The current circulates from the output  62  of the control cell to the corresponding input terminal  60 . In other words, the control electrode  46  of the switches  44  does not receive any further control current, and the switches  44  are then in off mode. 
     A person skilled in the art will also understand that several positive pulses  80  can be successively generated in order to maintain the control signal on the control electrodes  46  of the switches for a relatively long duration. 
     The connection in series of the switching elements to form a group of elements  42  makes it possible to obtain an output voltage of a higher value, while limiting imbalances in voltage between the switching elements connected in series, the drift over time of the voltage at the terminal of each switching element  16  being controlled via the value of the capacitance of each capacitor  58 . 
     It will thus be understood that the conversion system  10  according to embodiments of the present invention makes it possible to accelerate the switching of the switch elements in order to increase the switching frequency of these switching elements and also to reduce possible timing discrepancies between the switching of the switching elements. 
     This written description uses examples to disclose the various embodiments, including the best mode, and also to enable any person skilled in the art to practice the embodiments, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the embodiments is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.