Abstract:
A method is disclosed of controlling the supply of electrical power to an electrically propelled vehicle designed to operate in an external power supply mode or in an autonomous power supply mode. The vehicle includes an uninterrupted power supply bus connected both to an autonomous power supply system on board the vehicle and to an external power supply line which can be connected to an external power supply infrastructure by means of a connection member. Connection of the connection member to the external power supply infrastructure is detected by measuring the current flowing in the external power supply line. The presence of a non-zero current in the line indicates the presence of an external power supply infrastructure connected to the connection member.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a method of and to a system for controlling the supply of electrical power to an electrically propelled vehicle designed to operate in an external power supply mode or in an autonomous power supply mode as a function of the presence or the absence of an external power supply infrastructure along the route of the vehicle. The invention relates in particular to supplying electrical power to trams. 
   2. Description of the Prior Art 
   Patent application FR-A1-2 782 680 discloses a system of supplying power to electrically propelled vehicles enabling operation of public transport vehicles, such as high-capacity trams, without using an uninterrupted power supply via overhead contact lines. The system includes an autonomous power supply system on board the vehicle, consisting of an electric motor with a heavy flywheel, and stops provided with an overhead contact line for recharging the autonomous power supply system via a pantograph carried by the vehicle. 
   The above power supply system has the drawback of necessitating detection of the connection of the pantograph to the overhead contact line to optimize management of the changeover from one power supply mode to the other and the performance of the power supply system. To optimize the performance of the vehicle, it is further necessary for the vehicle to be always supplied with electrical power by the autonomous power supply system or by the overhead contact line, which leads to transition phases during which the vehicle is connected both to the autonomous power supply system and to the overhead contact line. During these transition phases the autonomous power supply system is active, i.e. used as a power generator, with an output voltage greater than the overhead contact line voltage, which causes a loss of power from the autonomous power supply system to the overhead contact line, accompanied by fast and costly discharging of the autonomous power supply system. Another drawback of the above power supply system is the possibility of electrical arcing when the pantograph separates from the overhead contact line, causing rapid wear of these components. 
   The invention therefore aims to remedy the above drawbacks by proposing a method of and a system for controlling the supply of electrical power to an electrically propelled vehicle operating in an autonomous power supply mode or in an external power supply mode, which method and system are adapted to detect connection of the vehicle to an external power supply infrastructure and to optimize management of transition phases between the two power supply modes and are simple and economic to put into practice. 
   SUMMARY OF THE INVENTION 
   The invention provides a method of controlling the supply of electrical power to an electrically propelled vehicle designed to operate in an external power supply mode or in an autonomous power supply mode as a function of the presence or the absence of an external power supply infrastructure ( 7 ) along the route of the vehicle, which includes an uninterrupted power supply bus ( 1 ) connected both to an autonomous power supply system ( 6 ) on board the vehicle and to an external power supply line ( 2 ) that can be connected to an external power supply infrastructure ( 7 ) by means of a connection member ( 5 ), in which method connection of the connection member ( 5 ) to the external power supply infrastructure ( 7 ) is detected by measuring the current flowing in the external power supply line ( 2 ), the presence of a non-zero current in the external power supply line ( 2 ) indicating the presence of an external power supply infrastructure ( 7 ) connected to the connection member ( 5 ). 
   According to one feature of the method according to the invention, when the vehicle is in a transient power supply phase during which the uninterrupted power supply bus ( 1 ) is simultaneously supplied with energy by the autonomous power supply system ( 6 ) and connected to the external power supply infrastructure ( 7 ), the output voltage of the autonomous power supply system ( 6 ) is controlled so that the current flowing in the external power supply line ( 2 ) is substantially zero. 
   According to another feature of the method according to the invention, when the vehicle is moving and supplied with power by the autonomous power supply system ( 6 ) only and reaches an area equipped with an external power supply infrastructure ( 7 ), the following steps are carried out:
         detecting connection of the connection member ( 5 ) to the external power supply infrastructure by the appearance of a non-zero current in the power supply line;   controlling the output voltage of the autonomous power supply system ( 6 ) so that the current flowing in the external power supply line ( 2 ) is substantially canceled; and   stopping the supply of power by the autonomous power supply system ( 6 ) to the uninterrupted power supply bus ( 1 ).       

   According to a further feature of the method according to the invention, when the vehicle is moving and is supplied with power only by the external power supply line ( 2 ) and reaches an area that is not equipped with an external power supply infrastructure ( 7 ), before disconnecting the connection member from the external power supply infrastructure, the following steps are carried out:
         starting the autonomous power supply system ( 6 ) so that it supplies power to the uninterrupted power supply bus ( 1 ); and   controlling the output voltage of the autonomous power supply system ( 6 ) so that the current in the external power supply line ( 2 ) is substantially canceled.       

   The invention also provides a system for controlling the supply of electrical power to an electrically propelled vehicle designed to operate in an autonomous power supply mode or in an external power supply mode as a function of the presence or absence of an external power supply infrastructure ( 7 ) along the route of the vehicle, which includes an uninterrupted power supply bus ( 1 ) connected both to an autonomous power supply system ( 6 ) on board the vehicle and to an external power supply line ( 2 ) that can be connected to an external power supply infrastructure ( 7 ) by means of a connection member ( 5 ), which system includes a current sensor ( 13 ) for measuring the current flowing in the external power supply line ( 2 ) in order to detect connection of the connection member ( 5 ) to the external power supply structure ( 7 ). 
   Particular embodiments of the system for controlling the supply of electrical power to a vehicle can include one or more of the following features, individually or in any technically feasible combination:
         the autonomous power supply system ( 6 ) includes a control module ( 12 ) for modifying the output voltage of the autonomous power supply system ( 6 );   the autonomous power supply system ( 6 ) is a system including a flywheel for accumulating kinetic energy; and   the connection member ( 5 ) is a pantograph carried by the vehicle and adapted to cooperate with an external power supply infrastructure consisting of an overhead contact line ( 7 ).       

   Objects, aspects and advantages of the present invention will be better understood from the following description of one embodiment of the invention, which description is given by way of example only and with reference to the accompanying drawing. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
       FIG. 1  is a diagram of the electrical power supply arrangements of a tram equipped with a control system according to the invention. 
       FIG. 2  is a diagram showing regulation of current in an external power supply line by a control method in accordance with the invention when the uninterrupted power supply bus of the tram is simultaneously supplied with power by the autonomous power supply system and by the overhead contact line. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1  is a diagram of the electrical power supply arrangements of a tram running on rails and equipped with electrical traction motors  4  that are reversible, i.e. which absorb electrical energy in traction and supply electrical energy during braking. 
   The traction motors are controlled by a traction module  3  connected to an uninterrupted power supply bus  1  supplied with power under conventional conditions via an external power supply line  2  and under autonomous conditions by an autonomous power supply system  6  on board the tram. The traction motors  4  are three-phase motors, for example, although this is not limiting on the invention, in which case the traction module  3  is an inverter. The traction module  3  is connected to a cable  10  providing the return path to ground for the current by conduction via the wheels of the tram and the rails of the track. 
   The external power supply line  2  terminates at a pantograph  5  on the roof of the tram and is designed to cooperate with an overhead contact line  7  when the tram is traveling on a portion of the track equipped with the above kind of infrastructure. The external power supply line  2  has a filter impedance  8  between the pantograph  5  and the uninterrupted power supply bus  1  and a capacitor  9  connected between the uninterrupted bus  1  and the ground return cable  10 . 
   The autonomous power supply system  6  is a system for accumulating kinetic energy including a synchronous permanent magnet electric motor whose rotor drives a flywheel, the motor being associated with a converter or an accumulator with a two-quadrant chopper for controlling the output voltage of the autonomous power supply system. During charging the flywheel is driven by the motor at a high speed and during discharging the motor functions as a generator and supplies power to the traction module  3 . 
   The output voltage of the autonomous power supply system  6  is controlled by a control module  12  which receives information from a current sensor  13  on the external power supply line  2 . The control module  12  regulates the output voltage within a range of voltages close to the range of voltages on the overhead contact line (typically 750 V), to enable identical operation of the traction module  3  whether it is supplied with power directly by the autonomous power supply system  6  or via the overhead contact line  7 . 
   The method of controlling the supply of power to the tram is described next. 
   When the tram is traveling on a portion of track that is not equipped with a overhead contact line  7 , the traction module of the tram is supplied with power exclusively by the autonomous power supply system  6 , which is then in an active mode, i.e. operating as a power generator, with the pantograph  5  lowered at the command of the driver, for example. During this phase, the pantograph  5  is not connected to an overhead contact line and no current flows in the external power supply line  2  of the tram. The control module  12  then receives from the sensor  13  the information that the current I ext  in the external line  2  is zero and regulates the output voltage to a nominal value of the order of 750 V. 
   When the tram reaches an area equipped with an overhead contact line  7 , the driver commands the deployment of the pantograph  5  so that the latter comes into contact with the overhead contact line  7 . During this phase the autonomous power supply system  6  is still in the active mode and the control module  12  of the autonomous power supply system  6 , which receives and analyzes continuously the value of the current flowing through the current sensor  13 , detects the moment at which the current I ext  becomes non-zero, substantially corresponding to the moment at which the pantograph  5  is connected to the overhead contact line  7 . 
   From this moment at which a non-zero current I ext  is detected by the sensor  13 , the autonomous power supply system  6  being still in the active mode, the control module  12  controls the output voltage of the autonomous power supply system  6  in such a manner as to regulate the current I ext  flowing in the external power supply line  2  to a value close to zero. This regulation of the current I ext  can be effected by a computer, for example, in accordance with the  FIG. 2  control diagram in which the value of the current I ext  from the sensor  13  is fed into first and second branches. The first branch includes a comparator  20  for calculating the difference between a reference current I ref  chosen to be zero and the measured value of the current I ext . The output of the comparator  20  is fed to a block  21  which calculates a set point voltage U bus/ref  close to the overhead contact line voltage in order substantially to cancel out the current I ext , the overhead contact line voltage being measured by means of a sensor in order to preset the voltage U bus/ref  to a value around the overhead contact line voltage; the sensor transmits the set point voltage U bus/ref  to a control unit  22 . As shown in  FIG. 2 , the second branch includes a block  23  for calculating the absolute value of the current I ext  and comparing that value to a threshold close to zero, for example chosen to be equal to 50 mA. The information that the absolute value of the current I ext  is above the threshold is then sent to an input of the control unit  22  which blocks sending of the new set point voltage U bus/ref  as long as the current I ext  is below the current threshold. 
   This regulation of the output voltage of the autonomous power supply system  6  when the uninterrupted power supply bus  1  is simultaneously supplied with power by the overhead contact line  7  and by the autonomous power supply system  6  in the active mode prevents the autonomous power supply system  6  from being discharged through the overhead contact line  7  if the overhead contact line voltage is less than the output voltage of the autonomous power supply system  6 . 
   Following detection of connection of the pantograph  5  to the overhead contact line  7 , the autonomous power supply system  6  is placed in a passive mode, either automatically by means of a time delay, or manually at the command of the driver. When the autonomous power supply system  6  is in the passive mode, i.e. is no longer supplying power to the uninterrupted power supply bus  1 , the traction module  3  is supplied with power exclusively by the overhead contact line  7  via the external power supply line  2 , and the autonomous power supply system  6  also receives current from the external power supply line  2  for topping up the kinetic energy of the flywheel, in particular when the tram is stationary at a stop, or during braking, when all of the power available via the overhead contact line can be used to charge the autonomous power supply system  6 . 
   When the tram is preparing to leave the area equipped with the overhead contact line  7  and enter an area that is not so equipped, the autonomous power supply system  6  is switched to the active mode again, either at the command of the driver or automatically, for example through interaction with a beacon disposed along the route, or by a computer estimating its position. During this phase the uninterrupted power supply bus  1  is supplied with power simultaneously by the autonomous power supply system  6  and the external power supply line  2  and the control module  12  then regulates the output voltage of the autonomous power supply system  6  so that the current I ext  flowing in the external power supply line is substantially canceled, thereby avoiding discharging of the autonomous power supply system  6  via the overhead contact line  7 . 
   The pantograph  5  can then be disconnected from the overhead contact line  7 , either naturally on reaching the end of the overhead contact line  7  or at the command of the driver, in which case disconnection is effected with no risk of electrical arcing because the current is substantially zero in the external power supply line  2  because of the regulation effected by the control module  12 . 
   The tram power supply control system and method according to the invention therefore provide a very simple way to detect the moment at which the pantograph is connected to the overhead contact line and therefore to optimize charging of the autonomous power supply system by preventing any fast discharging of the autonomous power supply system via the overhead contact line. What is more, the method according to the invention eliminates all risk of electrical arcing on disconnecting the pantograph, which considerably increases the service life of the components. 
   Of course, the invention is in no way limited to the embodiment described and shown, which is offered by way of example only and is open to modifications, in particular from the point of view of the composition of the various components or through substituting technical equivalents, without this departing from the scope of protection of the invention. 
   Thus, in an embodiment that is not shown, the connection member could be a shoe cooperating with an external power supply infrastructure in the form of a rail.