Abstract:
A method for supplying electrical power to a DC supply bus of a rotating electric motor of an electric vehicle is provided. The method includes the steps of selectively supplying electrical power to the bus via a first power supply at a first alternating voltage and selectively supplying electrical power to the bus via a second power supply at a second alternating voltage that is less than the first alternating voltage.

Description:
TECHNICAL FIELD 
   The invention relates to a method and a system for supplying electrical power to a supply bus of an electric vehicle, a recording medium, and a vehicle for this method. 
   The term DC supply bus is intended to refer to a bus which can be connected, successively by means of a controllable voltage rectifier/booster and a main transformer, to a first catenary which supplies a first alternating voltage. The main transformer is equipped at the secondary winding with a first connection terminal which corresponds to a first winding ratio of the transformer. 
   The winding ratio is defined in this instance as being the ratio of the number of turns used at the secondary winding over the number of turns used at the primary winding of the main transformer in order to carry out the transformation of alternating voltages. 
   In order to supply the bus with electrical power from the first catenary, known methods comprise:
         a step for controlling the closure of a precharge switch in order to connect the bus to the first terminal by way of a means for limiting current surge caused by at least one rechargeable temporary energy storage unit for the bus, then   when the direct voltage of the bus exceeds 70% of its nominal value, a step for controlling the closure of a first isolating switch in order to connect the bus to the first terminal without passing via the current surge limitation means.       

   In this instance “closing” is intended to refer to the action of placing the switch in the on state and “opening” the action of placing the switch in the off state. 
   BACKGROUND TO THE INVENTION 
   Nowadays, operators of these electric vehicles require the same bus to be able to be supplied with electrical power from the first catenary and, alternately, from a second catenary which supplies a second voltage which is lower than the first voltage. To this end, the main transformer is equipped at the secondary winding with a second connection terminal which corresponds to a second winding ratio of the main transformer greater than the first winding ratio. 
   In this context, the invention proposes a method which is capable of supplying the DC supply bus of the electric vehicle with electrical power from the first catenary and, alternately, from the second catenary. 
   SUMMARY OF THE INVENTION 
   The invention therefore relates to an electrical power supply method which comprises, when the bus is supplied with electrical power from the second catenary:
         a step for controlling the closure of the precharge switch in order to connect the bus to the first terminal via the same current limitation means, then   when the direct voltage of the bus has reached at least 70% of a maximum intermediate voltage defined by the following relationship:       

             V   mi     =         V   2       V   1       ×     V   n             
where:
 
   V mi  is the maximum intermediate voltage, 
   V 1  is the first voltage, 
   V 2  is the second voltage, and 
   V n  is the nominal voltage, 
   a step for controlling the rectifier/booster in order to rectify and increase the alternating voltage supplied by the first terminal and supply the bus with the voltage which has been rectified and increased in this manner, then
         when the direct voltage on the bus reaches at least 70% of the nominal voltage, a step for controlling the disconnection of the bus from the first terminal and a step for controlling the closure of a second isolating switch in order to connect the bus to the second terminal without passing via the precharge circuit.       

   The above method allows the bus to be supplied with electrical power from the second catenary by limiting the current surge. Furthermore, owing to the above method, the current surge limitation is brought about using the same current surge limitation means as that used to limit the current surge when electrical power is supplied from the first catenary. This method therefore requires very few physical modifications to existing electrical circuits in order to be implemented and in particular does not require the addition of a second current surge limitation means whose use would be limited to electrical power supplies from the second catenary. 
   The embodiments of this method may comprise one or more of the following features:
         when the precharge switch is closed, the rectifier/booster is not controlled and functions as a diode bridge;   the rectifier/booster is systematically controlled in order to function as a rectifier and a booster when the first or second isolating switch is closed.       

   The invention also relates to a data recording medium which comprises instructions for carrying out the electrical power supply method above, when these instructions are carried out by an electronic processor. 
   The invention also relates to a system for supplying electrical power to a DC supply bus of a rotating electric motor of an electric vehicle so that the direct voltage of the bus reaches a nominal value, this system comprising:
         a main transformer whose primary winding can be connected to a first catenary which supplies a first alternating voltage (V 1 ) and, alternately, to a second catenary which supplies a second lower alternating voltage (V 2 ), the main transformer being equipped at the secondary winding with a first and a second connection terminal corresponding to a first and a second winding ratio of the transformer, respectively, the second ratio of the transformer being greater than the first winding ratio,   a controllable electrical power supply circuit which is connected to the first and second terminals of the main transformer, this circuit comprising:   a means for limiting current surge caused by at least one rechargeable temporary energy storage unit of the bus,   a precharge switch which is capable of connecting the bus to the first terminal by way of the current surge limitation means,   a first isolating switch which is capable of connecting the bus to the first terminal without passing via the current surge limitation means, and   a second isolating switch which is capable of connecting the bus to the second terminal without passing via the current surge limitation means,   a controllable voltage rectifier/booster which is connected to the supply bus in order to supply it with rectified voltage produced from an alternating voltage which is supplied through the electrical power supply circuit via the first or second terminal, and   a unit for controlling the electrical power supply circuit and the rectifier/booster, in which the control unit is programmed to carry out the electrical power supply method above.       

   The embodiments of this electrical power supply system may comprise one or more of the following features:
         the electrical power supply circuit comprises a single current surge limitation means which is common to the electrical power supply from the first catenary and, alternately, from the second catenary;   the current surge limitation means is a resistor.       

   The embodiments of this power supply system further have the following advantage:
         the use of a single current limitation means and/or the fact that this current limitation means is a single resistor simplifies the system and therefore decreases the production costs thereof.       

   Finally, the invention also relates to an electric vehicle comprising the electrical power supply system described above. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be better understood from a reading of the following description, given purely by way of example and with reference to the drawings, in which: 
       FIG. 1  is a schematic illustration of an electric vehicle equipped with an electrical power supply system for a DC supply bus; 
       FIG. 2  is a flow chart of an electrical power supply method used in the system of  FIG. 1 ; and 
       FIG. 3  is a graph which illustrates the development of the direct voltage of the DC supply bus of the vehicle of  FIG. 1  as a function of time when the method of  FIG. 2  is carried out. 
   

   DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1  illustrates an electric vehicle  2  which is supplied with alternating voltage by means of a pantograph  4  which slides along a catenary  6 . 
   Catenary in this instance is intended to refer both to a supply wire which is suspended in the air and along which a pantograph slides, and a supply rail which is placed on the ground and along which a runner slides. In the railway industry, this rail which is placed on the ground is referred to as a “third rail”. 
   In this instance, the vehicle  2  is, for example, a locomotive. 
   The vehicle  2  is equipped with an asynchronous electric motor which is suitable for rotatably driving the driving wheels of the vehicle  2 . Typically, the vehicle  2  comprises as many asynchronous electric motors as axles for the vehicle  2 . 
   Each electric motor is supplied successively via a voltage converter, a DC supply voltage bus and an electrical power supply system for the bus. The DC supply voltage bus is known as a “DC bus”. 
   In this instance, in order to simplify the illustration, only an asynchronous electric motor  10  and the converter  12 , the bus  14  and the electrical power supply system  16  thereof are illustrated in order to simplify  FIG. 1 . 
   The converter  12  is suitable for converting the direct voltage V bus  present on the bus  14  into a three-phase alternating voltage used to supply the stator windings of the motor  10 . The control circuit of the converter  12  is not illustrated. 
   The bus  14  is formed by two electrical conductors  20  and  21  which are connected, on the one hand, to respective inputs of the converter  12  and, on the other hand, to the system  16 . 
   This bus  14  comprises rechargeable temporary energy storage units in order to temporarily maintain the voltage V bus  on this bus even in the event of an interruption to the power supply. In this instance, only one of these units  24  has been illustrated. 
   This unit  24  is formed by a capacitor  26  which is connected between the conductors  20  and  21  and a discharge resistor  28  which is connected in parallel with the terminals of this capacitor  26 . 
   After being supplied with electrical power, the bus  14  has, in the steady state, a nominal voltage V n  which is equal, for example, to 1800 Vdc. 
   The system  16  allows the bus  14  to be supplied with electrical power and this bus  14  to be supplied both from a catenary having an alternating voltage of 15 kV and a catenary having an alternating voltage of 25 kV. Catenaries having a voltage of 25 kV are found, for example, in countries such as France and Italy, whilst catenaries having a voltage of 15 kV are found, for example, in countries such as Germany. The system  16  thus allows the vehicle  2  to operate both on German and French rail networks. 
   The system  16  comprises a main voltage transformer  34  which is equipped with a primary winding  36  which is connected to the pantograph  4  by means of a circuit breaker  37 . The number of turns of the winding  36  is designated n 1 . 
   The transformer  34  also comprises a secondary winding  38  which is equipped with three connection terminals  39 ,  40  and  41 . The numbers of turns of the winding  38  between the terminals  39  and  40  and the terminals  39  and  41 , respectively, are designated n 25  and n 15 . 
   Inside the system  16 , a controllable rectifier/booster  44  is connected at the input, by means of a controllable electrical power supply circuit  46 , to the terminals  39  to  41 . 
   The rectifier/booster  44  is equipped with two output terminals which are connected to the conductors  20  and  21  of the bus  14 , respectively. 
   This rectifier/booster  44  is capable of functioning as a diode bridge when it is not controlled and as a voltage rectifier/booster when it is controlled. 
   Schematically, the rectifier/booster  44  comprises two parallel arms which are each formed by two switches which are connected in series by means of respective central points  50  and  51 . The ends of each of these arms are connected to the conductors  20  and  21  of the bus  14 . 
   In order to be able to function as a diode bridge when this rectifier/booster is not controlled, each switch is, for example, formed by a PNP transistor, to the terminals of which a free wheel diode is connected in parallel. Since rectifiers/boosters of this type are conventional, this will not be described in greater detail. 
   The electrical power supply circuit  46  connects the central point  51  to the terminal  39  of the winding  38 . The circuit  46  is also capable of connecting the central point  50  to the terminal  40  and, alternately, to the terminal  41 . To this end, the circuit  46  comprises:
         a conductor  56  which connects the terminal  39  directly to the central point  51 ,   a controllable isolating switch  58  which is capable of connecting the terminal  40  to the central point  50  when it is closed, and isolating the terminal  40  from the central point  50  when it is open, and   a controllable isolating switch  60  which is capable of connecting the terminal  41  to the central point  50  when it is closed, and isolating the terminal  41  from the central point  50  when it is open.       

   The circuit  46  also comprises a means  62  for limiting the current surge caused by the unit  24 . This limitation means  62  is connected in parallel with the terminals of the switch  58 . For example, in this instance, the limitation means  62  is formed only by a resistor whose value is between 25 and 150 Ω. 
   A controllable precharge switch  64  is also connected in series to the limitation means  62  and in parallel with the terminals of the switch  58 . 
   Finally, the system  16  comprises a control unit  70  which is capable of controlling the closure and opening of the switches  58 ,  60  and  64  and the rectifier/booster  44 . More precisely, the control unit  70  is capable of carrying out the electrical power supply method of  FIG. 2 . 
   This control unit  70  is, for example, produced from a conventional programmable electronic processor which is capable of carrying out instructions which are recorded on a data recording medium  72 . To this end, the medium  72  comprises instructions for carrying out the method of  FIG. 2  when these instructions are carried out by the unit  70 . 
   The operation of the system  16  will now be described with reference to the method of  FIG. 2 . 
   The method of  FIG. 2  substantially comprises two phases  80  and  82 . 
   During phase  80 , the bus  14  is supplied with electrical power from a catenary which has an alternating voltage of 15 kV. 
   Initially, as indicated in the graph of  FIG. 3 , the voltage V bus  of the bus  14  is zero and the switches  58 ,  60  and  64  are open. The transformer  34  is supplied with alternating voltage of 15 kV by means of the circuit breaker  37  and the pantograph  4 . 
   To begin with, the unit  70  controls the closure of the switch  64  during a step  84 . The rectifier/booster  44  is not controlled so that it functions as a diode bridge. Under these circumstances, the transformer  34  transforms the voltage of 15 kV into an alternating voltage V r  in the order of 570 Vac. This voltage V r  is rectified by the rectifier/booster  44  and supplies the bus  14 . The capacitor  26  is charged progressively with a time constant in accordance with the resistance value of the limitation means  62 . It should thus be understood that the limitation means  62  slows the charge of the capacitor  26  and therefore limits the current surge caused by the presence of the energy storage unit  24 . The step  84  lasts, for example, for a period of time equal to 3RC, where R is the resistance value of the limitation means  62  and C is the capacitance of the capacitor  26  in order to obtain a voltage V bus  on the bus greater than 70% of a maximum intermediate voltage V mi  defined by the following relationship: 
             V   mi     =         V   2       V   1       ×     V   n             
where:
 
   V 1  is the voltage of 25 kV, 
   V 2  is the voltage of 15 kV, and 
   V n  is the nominal voltage equal in this instance to 1800 Vdc. 
   This voltage V mi  corresponds to the maximum direct voltage which can be achieved on the bus  14  by supplying this bus from an alternating voltage taken between the terminals  39  and  40  of the winding  38 . 
   More precisely, in this instance, since the period of time is selected to be equal to 3RC, the voltage V bus  at the end of step  84  is equal to 90% of the voltage V mi , that is to say, in this instance, approximately equal to 972 Vdc. 
   On the graph of  FIG. 3 , the end of step  84  corresponds to the time t 1 . 
   At time t 1 , during a step  86 , the unit  70  controls the closure of the switch  58  then, during a step  88 , the opening of the switch  64 . When the switch  58  is closed, this short-circuits the limitation means  62  so that the voltage at the terminals of the capacitor  26  rapidly reaches the voltage V mi . 
   Then, during a step  90 , the unit  70  controls the rectifier/booster  44  in order to rectify and increase the voltage V r  so as to reach a voltage on the bus  14  greater than at least 70% of the nominal voltage V n . For example, in this instance, the rectifier/booster  44  is controlled in order to reach a voltage of 1700 Vdc on the bus  14 . The step  90  lasts until the voltage of 1700 Vdc is reached which occurs at a time t 2  in  FIG. 3 . 
   When the voltage of 1700 Vdc is reached on the bus  14 , the unit  70  controls the opening of the switch  58  during a step  92  and the closure of the switch  60  during a step  94 . From this time, the voltage V r  at the input of the rectifier/booster  44  corresponds to the voltage present between the terminals  39  and  41  of the winding  38 . Since the winding ratio of the transformer is greater under these conditions, the voltage V r  is therefore greater than that previously used. For example, in this instance, the voltage V r  is equal to 950 Vac. 
   As soon as the switch  60  is closed, the unit  70  controls the rectifier/booster  44  during a step  96  so that the voltage V bus  reaches the value of 1800 Vdc, that is to say, the nominal value at the time t 3 . 
   From the time t 3 , the steady state of the system  16  is reached. 
   When the vehicle changes rail network and travels on a railway whose catenary has a voltage of 25 kV, it is then necessary to carry out the phase  82  for supplying electrical power from a catenary under 25 kV. 
   Before beginning electrical power supply, the initial state is the same as the one preceding phase  80 . 
   At the beginning of phase  82 , the unit  70  controls the closure of the switch  64  during a step  100 . The rectifier/booster  44  is not controlled and functions as a diode bridge. Under these conditions, the voltage V r  is equal to 950 Vac since the voltage at the terminals of the primary winding  36  is equal to 25 kV. The step  100  lasts, for example, for a period of time selected to be equal to 3RC so that, at the end of step  100 , the capacitor  26  is charged to 90% of its capacitance and the voltage V bus  is equal to 1620 Vdc. 
   During a step  102 , the unit  70  subsequently controls the closure of the switch  58  then, during a step  104 , the unit  70  controls the opening of the switch  64 . 
   As soon as the switch  58  is closed, the unit  70  controls the rectifier/booster  44  during a step  106  in order to reach the nominal voltage V n  on the bus  14 . 
   Step  100  allows the current surge caused by the unit  24  to be limited. 
   A number of other embodiments of the system  16  and the method of  FIG. 2  are possible. For example, it is possible to simultaneously keep the switch  64  and the switch  58  or the switch  64  and switch  60  closed. The method of  FIG. 2  has been described for the specific case of an electrical power supply circuit which comprises a single common current surge limitation means and an electrical power supply from a catenary at 15 kV and from a catenary at 25 kV. In a variant, however, a second current surge limitation means is connected by means of a second precharge switch in parallel with the switch  60  and the second precharge switch is controlled when electrical power is supplied from a catenary at 15 kV in order to limit the current surge. In an embodiment of this type, the method of  FIG. 2  can be used if the second precharge switch or the second current surge limitation means malfunctions. 
   Finally, the transformer  34  has been described for the specific case in which the terminal  40  is an intermediate point of the winding  38 . The winding  38  in a variant is replaced by a first and a second secondary winding which are connected in parallel between the input terminals of the rectifier/booster  44 . The first and second secondary windings have winding ratios which are equal to those observed between the terminals  39  and  40  and between the terminals  39  and  41 , respectively.