Optimized control of the operation of one or more traction systems of a train for entering and exiting from a coasting condition

Abstract

A railway vehicle comprises a traction system including an asynchronous electric motor or a synchronous electric DC motor operable by an inverter electronic drive system. The vehicle further comprises an electronic control unit coupled to the traction system and configured to receive signals/data/commands indicative of operating conditions of the vehicle and of the traction system and to determine, based on the received signals/data/commands, the occurrence of a coasting condition of the vehicle and the occurrence of an exit condition from the coasting condition of the vehicle. If a coasting condition of the vehicle occurs, the electronic drive system is controlled to cause the electric motor to undergo magnetic flux changes. If an exit condition from the coasting condition occurs, and depending whether the electronic drive system is on or off, the electronic drive system is controlled to increase torque of the electric motor or to reduce magnetic flux reduction.

Claims

1. A train comprising a plurality of railway vehicles, each of which comprises: a respective traction system, which includes a respective electric motor operable by a respective electronic drive system; wherein the respective electric motor of each traction system is an asynchronous motor and the respective electronic drive system is an inverter system, or the respective electric motor of each traction system is a synchronous DC motor and the respective electronic drive system is a chopper-type system; a respective electronic control unit coupled to the respective traction system; wherein the train comprises a central control unit connected to the electronic control units of the railway vehicles, and being configured to: receive quantities indicative of a strain request for the train and of an available strain for each traction system; select one or more traction system on the basis of the received quantities; send traction commands to the respective electronic control units of the selected traction systems; and send coasting commands to the respective electronic control units of the non-selected traction systems; wherein, for each railway vehicle, the respective electronic control unit is configured to: determine an occurrence of a coasting condition when the electronic control unit receives a coasting command from the central control unit; when the electronic control unit determines the occurrence of the coasting condition, control an operation of the respective electronic drive system so as to cause the respective electric motor to undergo a magnetic flux reduction and, during the magnetic flux reduction of the respective electric motor, said controlling the operation comprises: monitoring the magnetic flux of the respective electric motor, determining whether the magnetic flux of the respective electric motor decreases under a magnetic flux threshold, and when the electronic control unit detects that the magnetic flux of the respective electric motor has decreased under the magnetic flux threshold, switch off the respective electronic drive system, and determine an occurrence of an exit condition from the coasting condition when the electric control unit receives a traction command from the central control unit; when the electronic control unit determines the occurrence of the exit condition, determine whether the respective electronic drive system is on or off, wherein the electronic control unit is configured to determine that the respective electronic drive system is; on when the magnetic flux of the respective electric motor exceeds the magnetic flux threshold, or off when the magnetic flux of the respective electric motor is lower than the magnetic flux threshold; when the electronic control unit determines the occurrence of the exit condition and the electronic control unit also determines the respective electronic drive system is on, cause a torque of the respective electric motor to start increasing; when the electronic control unit determines the occurrence of the exit condition and the electronic control unit also determines the respective electronic drive system is off, switch on the respective electronic drive system, control the operation of the respective electronic drive system so that the respective electric motor undergoes a magnetic flux increase, and, during said magnetic flux increase of the respective electric motor; monitor the magnetic flux of the respective electric motor, determine whether the magnetic flux of the respective electric motor exceeds said magnetic flux threshold, and when the electronic control unit determines that the magnetic flux of the respective electric motor has exceeded the magnetic flux threshold, cause the torque of the respective electric motor to start increasing.

2. The train of claim 1, wherein, for each railway vehicle, the respective electronic control unit is further configured to: calculate a square wave magnetic flux value (Fdoq) on a basis of magnitudes indicative of a supply voltage (vFIL) of the traction system and of a supply frequency (freal) of the electric motor; calculate a magnetic flux reference target value (FdRif) on a basis of a square wave magnetic flux value (Fdoq) and of a predetermined magnetic flux nominal value (FdNom); and calculate the magnetic flux threshold on the basis of the magnetic flux reference target value (FdRif).

3. The train of claim 1, wherein: each respective electronic control unit of each railway vehicle is a first electronic control unit that includes software code portions configured to be executed thereby; wherein the train includes a second electronic control unit connected to the first electronic control units; wherein said software code portions comprise: first portions, which are designed to be executed by each of the first electronic control units and are such that to cause, when executed, each first electronic control unit to become configured as the electronic control units of the railway vehicles of the train; and second software portions, which are designed to be executed by the second electronic control unit and are such that to cause, when executed, said second electronic control unit to become configured as the central control unit of the train.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For a better understanding of the present invention, some preferred embodiments thereof will be illustrated only by way of non-limitative example, and with reference to the accompanying drawings (not in scale), in which:

(2) FIG. 1 diagrammatically shows a typical architecture of a unit for controlling the operation of an inverter which drives an asynchronous electric motor used for traction of a train;

(3) FIG. 2 diagrammatically shows a first control logic for controlling the operation of an inverter used for operating an asynchronous electric motor used for traction of a train according to the prior art;

(4) FIG. 3 shows a time chart of characteristic magnitudes of an asynchronous electric motor of a train operated by means of an inverter controlled with the logic in FIG. 2;

(5) FIG. 4 diagrammatically shows a second control logic for controlling the operation of an inverter used for operating an asynchronous electric motor used for traction of a train according to the prior art;

(6) FIG. 5 shows a time chart of characteristic magnitudes of an asynchronous electric motor of a train operated by means of an inverter controlled with the logic in FIG. 4;

(7) FIG. 6 diagrammatically shows a control logic for controlling the operation of an inverter used for operating an asynchronous electric motor used for traction of a train according to a preferred embodiment of the present invention;

(8) FIG. 7 shows a time chart of characteristic magnitudes of an asynchronous electric motor of a train operated by means of an inverter controlled with the logic in FIG. 6;

(9) FIG. 8 shows the trend of an index of reduction of the performances as a function of the train speed.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

(10) The following description is provided to allow a person skilled in the art to implement and use the invention. Various changes to the illustrated embodiments will be immediately apparent to the person skilled in the art and the generic principles may be applied to other embodiments and applications without because of this departing from the scope of protection of the present invention.

(11) Thus, the present invention shall not be limited to the described and illustrated embodiments only, but shall be given the broadest scope of protection coherently with the principles and features presented and defined in the appended claims. With this regard, explicit reference will be made in the following description to the control and management of the operation of an inverter-type drive system used to operate an asynchronous electric motor for traction of a railway vehicle, without because of this loosing in generality, it being understood that the present invention may be used for controlling and managing the operation of a chopper-type drive system used for operating a synchronous electric DC motor (i.e., not of the permanent magnet type) used for the traction of a railway vehicle, or, more in general, for the control and management of the operation of one or more traction systems based on electric motors of any type of railway vehicle or train not of the permanent magnet type.

(12) Furthermore, it is worth noting that a specific aspect of the present invention may be advantageously exploited to control and manage the operation of a plurality of traction systems of any type of train, which traction systems may also be based on permanent magnet electric motors.

(13) The present invention, by virtue of an appropriate modification made to the control software for controlling an electronic drive system of an electric motor used for the traction of a railway vehicle, allows to switch off the electronic drive system when a coasting (or freewheeling) condition of the railway vehicle occurs and to switch it back on very rapidly when a traction or braking command is received.

(14) More in particular, a first aspect of the present invention concerns a control logic for controlling the operation of an electronic drive system of an electric motor not of the permanent magnet type used for the traction of a railway vehicle, which control logic includes:

(15) controlling the magnetic flux reduction of the motor when a coasting condition of the railway vehicle occurs to take the magnetic flux to under 20% of its nominal value; and then

(16) switching off the electronic drive system of the motor.

(17) Such a control logic, in addition to saving energy, also allows to re-apply torque to the motor in any instant, also during flux reduction, and when the electronic drive system is off, minimizing delays in this manner.

(18) With this regard, FIG. 6 is a flow chart showing a software control logic (indicated by reference numeral 60 as a whole) for controlling the operation of an inverter used for operating an asynchronous electric motor for the traction of a train according to a preferred embodiment of the first aspect of the present invention.

(19) In particular, according to said preferred embodiment of the first aspect of the present invention, the control logic 60 is implemented by a control unit programmed by means of an appropriate software and/or firmware code. The functional architecture of such a control unit conveniently corresponds to that of the control unit 10 shown in FIG. 1 and described above, in which, however, the operation software logic of the reference flow calculating module 13 was appropriately modified.

(20) As shown in FIG. 6, by implementing the control logic 60, the control unit in use executes all the operations of the logic 20 shown in FIG. 2 as described above (with this regard, it is worth noting that blocks 61, 62, 63, 64 and 65 of the logic 60 shown in FIG. 6 correspond to blocks 21-25 of the logic 20 shown in FIG. 2), which, therefore, will not be described again because the description provided above with this regard still applies.

(21) Furthermore, by implementing the control logic 60, the control unit, in use, also performs the following further operations:

(22) checking, on the basis of the received signals/data/commands indicative of a current running condition of the train, whether the train is in a coasting condition (or freewheeling) (block 66);

(23) if it is determined that the train is not in a coasting condition, controlling the operation of the inverter so that the electric motor undergoes magnetic flux increase (i.e. so that the intensity of the magnetic flux of the electric motor increases) and at the same time calculating a current value Fd of the magnetic flux of the electric motor (block 63);

(24) if, instead, it is determined that the train is in a coasting condition, controlling the operation of the inverter so that the electric motor undergoes magnetic flux reduction (i.e. so that the intensity of the magnetic flux of the electric motor decreases) and calculating a current value Fd of the magnetic flux of the electric motor at the same time (block 67);

(25) checking whether the current magnetic flux value Fd is lower than 20% of the reference target value FdRif (block 68);

(26) if it is determined that the current value Fd of the magnetic flux is lower than 20% of the reference target value FdRif, generating an inverter switching off command (block 69); and,

(27) if, instead, it is determined that the current value Fd of the magnetic flux is not lower than 20% of the reference target value FdRif, continuing to control the operation of the inverter so that that the electric motor continues to undergo magnetic flux reduction and continuing to calculate the current value Fd of the magnetic flux of the electric motor at the same time (block 67).

(28) In other words, the control logic 60 includes setting the reference current to zero in the instant in which strain is zero. During this step, named flux reduction, the reference current follows an exponential-type law and when the value reaches 20% of the nominal value is set to zero. The inverter is switched off completely from this moment.

(29) Once the inverter is off, the control unit switches the inverter back on when it receives a traction or braking command and the motor flux increase step starts. The strain ramp starts to nominal value when the flux reaches 20% of the nominal flux (i.e. after approximately 100 ms).

(30) The strain ramp will start immediately without any delay if the command is received from the control unit before the inverter is completely off.

(31) In other words, the control logic 60 includes controlling the motor current during flux reduction to 20% of the nominal flux so that torque can be reapplied instantly if requested. Without using the control logic 60 it would not be possible to apply torque instantaneously because the position of the rotor flux is not known, and this condition could cause an overcurrent with corresponding inverter switch-off until the protection is reset by the train driver and/or the train logic.

(32) Therefore, the changes made according to the first aspect of the present invention to the reference flux calculating module allow, during the phase of coasting, to hook the inverter current immediately after switch-off.

(33) According to the description above, the control logic 60, in addition to saving energy, allows also to reapply motor torque in any instant, both during flux reduction and with the inverter off, minimizing in this manner the delays which in the past did not allow to apply the coasting technique with the inverter off to tram and underground train vehicles. Therefore, the control logic 60 allows to apply the coasting technique with the inverter off also to tram and underground train vehicles.

(34) The applicant has estimated that, by virtue of the use of the control logic 60 which allows to switch the inverter off during coasting, it is possible to obtain a reduction of the global energy drawn at the pantograph equal to 5% for a regional transport service.

(35) FIG. 7 shows a chart which was obtained by the Applicant by means of experimental tests and which shows the time trend of the characteristic magnitudes of an asynchronous electric motor of a train operated by means of an inverter controlled with the logic 60 as a coasting condition of the train occurs.

(36) In particular, FIG. 7 shows the time trend:

(37) of the current drawn from the line iLin;

(38) of the filter voltage vFIL;

(39) of the motor current Imot;

(40) of the train speed speed;

(41) of the train acceleration accel;

(42) of the motor torque Torque;

(43) of the reference current IRif;

(44) of the strain reference rifman, which indicates the maximum strain percentage which can be achieved by the inverter; and

(45) of the strain DelivEff calculated on the basis of the weight of the train and of the strain reference rifman.

(46) Two regions of the chart shown in FIG. 7 are highlighted by means of two ellipsis.

(47) In detail, with reference to the area highlighted on the left, it is worth noting that in a first instant of time t.sub.1 in which a coasting signal/command is received, the motor torque Torque goes to zero and the reference current IRif start decreasing for motor flux reduction. Furthermore, when at a second time instant t.sub.2 the control unit receives a traction signal/command, the reference current IRif and the motor torque Torque starts increasing immediately. In this case, the inverter is not switched off completely because the control unit receives the traction signal/command before the complete inverter switch-off.

(48) Furthermore, with reference to the area highlighted on the right, it is worth noting that when a coasting signal/command is received, the control unit starts motor flux reduction until the magnetizing current is zero; at this point, because coasting condition persists, the inverter is switched off completely. When a traction signal/command is received, the inverter is switched on instantaneously; the motor flux increase step thus starts. When the flux reaches 20% of the nominal value, the motor torque Torque starts increasing to the reference value.

(49) The innovative railway coasting management logic described above may be advantageously extended also to railway train level considering the onboard limit speed management. Indeed, in a distributed traction train, each control unit of the operation of an electronic drive system of an electronic traction motor generally receives the traction and braking commands, the strain reference and the speed limit from the railway vehicle running control system. Thus, each control unit of the operation of an electronic drive system which operates for traction adjusts the strain applied in traction also as a function of the speed limit. Typically, when the train speed is higher than the limit speed minus 3 km/h, the control unit reduces the strain in percentage steps to zero at the limit speed and for higher speeds, as shown in the chart in FIG. 8 in which veLim indicates the speed limit and the performance reduction index represents the strain percentage applied with respect to the requested.

(50) Currently, in order to maintain the limit speed, all the electronic drive systems are left on even if the total required strain of the vehicle is lower than that available for a single electronic drive system.

(51) Therefore, a second aspect of the present invention stems from the Applicant's idea to exploit the innovative quick switch-on logic of the electronic drive system described above also to manage the strain request of the vehicle during train cruising to keep on only the electronic drive systems which are really needed. With this regard, it is worth noting that the algorithm is applicable for traction, while it cannot be used for braking in order not to impact on the combined pneumatic or hydraulic brake management systems.

(52) In particular, said second aspect of the present invention concerns a control system for controlling the operation of electronic drive systems of electric motors used for train traction, which system comprises:

(53) for each electronic drive system, a corresponding control unit designed to operate as described above in relation to the management of a coasting condition according to the first aspect of the present invention; and

(54) a central control unit for controlling the operation of the train which is connected to all the aforesaid control units of the electronic drive systems and is configured to: select one or more drive systems to be operated according to the quantities indicative of a strain request calculated as the product of the current weight of the train with respect to the maximum weight by the strain percentage reference by the maximum strain of the train and an available strain of each drive system, which considers the maximum torque and maximum power limitations set by the electronic drive system in order to guarantee respect of the thermal performance without making protections trip, send coasting commands to the control units of the non-selected drive systems, and send traction commands to the electronic control units of the selected drive systems.

(55) In order words, in use the control unit calculates the number of electronic drive systems to be switched on according to the strain request and the available strain for each of the electronic drive systems. For example, on a train with four electronic drive systems, if a strain lower than 25% is required, the central control unit requires the switching on of only one electronic drive system, from 25% to 50% of two electronic drive systems and so on to four electronic drive systems on when the required strain is from 75% to 100%.

(56) Furthermore, according to said second aspect of the present invention, the control unit of each electronic drive system is also configured to:

(57) determine the occurrence of a coasting condition if it receives a coasting command from the central control unit; and

(58) determine the occurrence of an exit condition from the coasting condition if it receives a traction command from the central control unit.

(59) Therefore, in this manner, the control unit of each electronic drive system causes a flux reduction of the respective electronic motor when it receives a coasting command of the central control unit and switches off the respective electronic drive system when the magnetic flux decreases under the 20% of the flux reference value.

(60) Furthermore, the control unit of each electronic drive system performs one of the following operations (previously described above) when a traction command is received from the central control unit:

(61) if the respective electronic drive system is on, generating a command to increase the drive torque of the respective electric motor;

(62) if the respective electronic drive system is off, causing a flux increase of the respective electric motor and, when the magnetic flux value exceeds 20% of the flux reference value, generating a command to increase the drive torque of the respective electric motor.

(63) This solution, currently not implemented on any railway vehicle, allows to reduce the power drawn at the pantograph by 3% (data obtained by the Applicant by means of simulations carried out on an underground-type vehicle).

(64) Such an energy saving is obtained by virtue of the massive switch-off of non-required electronic drive systems, switch-off which allows to reduce drastically traction converter losses.

(65) The central control unit may further control the cyclic switch-on of the electronic drive systems, reducing in this manner the line thermal current drawn by each electronic drive system thus obtaining:

(66) a reduction of the required cooling power, which additionally allows to use smaller cooling systems; and

(67) an increase of the average mean time between failures (MTBF) of the electronic drive systems by virtue of a reduction of the hours of operation (the hours of service of the railway vehicle being equal).

(68) It is worth noting here that the control system according to said second aspect of the present invention may be advantageously exploited to control and manage the operation of a plurality of traction systems of any type of train, which traction systems may also be based on permanent magnet electric motors.

(69) The advantages of the invention can be readily understood from the description above.

(70) In particular, it is worth noting once again that the fact that this invention allows to reduce the energy consumption of railway vehicles provided with electric traction systems by eliminating magnetizing current losses in the electronic drive systems of the electric motors and in the motors themselves during the phases of coasting of such vehicles.

(71) In detail, the present invention allows to obtain the following technical advantages:

(72) an increase of the operative efficiency of the electric traction system of the railway vehicles;

(73) a reduction of energy consumptions, for example, a reduction of energy drawn at the pantograph by the railway vehicles (e.g. trains, underground trains, trams etc.);

(74) a reduction of acoustic pollution.

(75) Furthermore, the present invention, by implementing an optimized management of the devices already existing on vehicle and the energy fluxes between them by means of the use of innovative control software techniques as described above, allows to obtain better performances without requiring changes to the vehicles, and thus without additional costs or developing times deriving from the introduction of new hardware technologies.

(76) It is worth emphasizing once again the fact that the first aspect of the present invention may be advantageously exploited to control and manage the operation of:

(77) inverter-type drive systems used for operating asynchronous electric motors; and

(78) chopper-type drive systems used for operating synchronous electric DC motors.

(79) With this regard, it is worth mentioning that the use of the first aspect of the present invention is not particularly advantageous in case of permanent magnet synchronous motors because such electric motors already intrinsically implement an automatic magnetic flux control.

(80) On the contrary, the use of the second aspect of the present invention is particularly advantageous also in the case of permanent magnet electric motors.

(81) Furthermore, the present invention may be advantageously exploited to control and manage the operation of electronic drive systems of the electric motors used for the traction of railway vehicles of any type, such as mass-transit trains, electric multiple unit (EMU) trains, heavy traction trains, high speed trains, long distance trains, underground trains, regional trains, trams with or without driver, etc.

(82) Finally, it is apparent that many changes can be made to the present invention all included within the scope of protection defined by the appended claims.