POWER SUPPLY CIRCUIT OF A VEHICLE, CORRESPONDING TRAIN CHAIN ​​AND CORRESPONDING VEHICLE

Description

[0001] The present invention relates to an electrical power supply circuit for a vehicle, particularly a railway vehicle. The present invention also relates to an associated traction system and an associated vehicle.

[0002] In railway vehicles, there is a need to protect and disconnect vehicle equipment (power converters, traction inverters) from the catenary during short circuits.

[0003] For this purpose, it is known to use a protection device comprising a high-speed current mechanical circuit breaker (HSBC) associated with a pre-charge circuit.

[0004] However, such a mechanical circuit breaker is expensive and bulky. Furthermore, its reaction time is limited. This limitation means that the current interrupted during a short circuit or overvoltage is very high in peak value, leading to oversizing the input filter of a traction inverter or auxiliary converter. Moreover, given the components of the protection device, it is preferable for the input filter inductor to be an air-core inductor rather than a core-core inductor to allow for interrupting the short-circuit current at the inverter input. However, an air-core inductor is considerably larger than its core-core equivalent.

[0005] A known protection device comprises an ultra-fast mechanical switch and IGBT transistors to block short-circuit current. The principle of this solution is to pass the main current through a first branch containing a low-voltage IGBT (thus low conduction losses). In the event of a fault, the IGBT is isolated by the ultra-fast mechanical switch, and then the current is interrupted via a second branch in parallel with the first branch, which includes IGBTs and varistors. Such a solution allows for rapid interruption of the short-circuit current. However, it is complex and expensive to implement due to the use of an ultra-fast mechanical switch and two branches.

[0006] Documents EP 2 768 102 A and US 2009 / 213513 A describe examples of protective devices.

[0007] There is therefore a need for a protection device for the converters of a traction chain that is simple to implement and occupies a small volume.

[0008] For this purpose, the present description relates to an electrical power supply circuit for a vehicle, in particular a railway vehicle, according to claim 1, from an electrical power source, the power supply circuit comprising: a connector intended to be connected to the power supply to receive a DC power signal, a filter suitable for filtering the DC power signal received by the connector to obtain a filtered DC power signal, an inverter suitable for converting the filtered DC power signal into an AC power signal to power at least one traction motor, characterized in that the power supply circuit includes a power supply circuit protection device connected between the connector and the filter, the protection device comprising a junction field-effect transistor made of a material having a band gap energy strictly greater than two electronvolts, preferably three electronvolts, the junction field-effect transistor being the only transistor in the protection device, and the junction field-effect transistor includes a drain connected to the connector, a source connected to the filter and a gate connected to the source;

[0009] According to other advantageous aspects of the invention, the power supply circuit comprises one or more of the following features, taken individually or in any technically possible combination: The material of the junction field-effect transistor is chosen from silicon carbide and gallium nitride; the junction field-effect transistor is of the normally closed type; the protection device includes a diode connected in antiparallel to the field-effect transistor; the protection device includes a diode connected between the field-effect transistor and the filter and in parallel with the filter; the power supply circuit includes an input contactor connected between the connector and the protection device; the connector is a pantograph.

[0010] This description also relates to a traction chain of a vehicle, in particular a railway, comprising at least one traction motor and a power supply circuit as described above.

[0011] This description also relates to a vehicle, in particular a railway vehicle, comprising at least one traction chain as described above.

[0012] Other features and advantages of the invention will become apparent from the following description of embodiments of the invention, given by way of example only, and with reference to the drawings which are: [ Fig 1] figure 1 , a schematic representation of an example of a vehicle traction system, in particular a railway system, comprising a power supply circuit according to the invention equipped with a device for protecting said power supply circuit, and [ Fig 2] figure 2 , a graphical representation of an example of the evolution of the current intensity in the coil of a filter in the power supply circuit of the figure 1 and the evolution of the voltage across a transistor in the power supply circuit protection device.

[0013] A traction chain 10 for a railway vehicle is illustrated by the figure 1 . A railway vehicle is, for example, a train, a tram or a tram-train.

[0014] The traction chain includes one or more traction motors 12 and a supply circuit 14 for the traction motors 12 from a power source 16.

[0015] Two traction motors 12 are illustrated by the figure 1 . Traction motors 12 are, for example, alternating current (AC) motors.

[0016] In the example illustrated by the figure 1 The power source 16 is a catenary providing a direct current (DC) power signal. Alternatively, the power source 16 is a fuel-powered engine, such as a diesel engine, or any other power source. When the power source 16 is an engine, the engine is mounted on the vehicle.

[0017] The power supply circuit 14 includes a connector 20, a filter 22, an inverter 24 and a protection device 26. Advantageously, the power supply circuit 14 further includes an input contactor 28.

[0018] Connector 20 is intended to be connected to the power supply 16 to receive a continuous power signal. In the example illustrated by the figure 1 , connector 20 is a pantograph.

[0019] The filter 22 is connected between the protection device 26 and the inverter 24.

[0020] Filter 22 is designed to filter the power supply signal received via connector 20 and arriving at inverter 24, resulting in a continuous, filtered power supply signal. This reduces, or even eliminates, harmonics in the received power supply signal.

[0021] In the example illustrated by the figure 1 The filter 22 comprises a capacitor 30 and an inductor 32. The capacitor 30 filters the voltage supply signal. The inductor 32 filters the current supply signal.

[0022] In this example, capacitor 30 is connected in parallel with inverter 24. One terminal of capacitor 30 is thus connected between one terminal of coil 32 and one terminal of inverter 24. The other terminal of capacitor 30 is connected to the other terminal of inverter 24 and to ground. One terminal of coil 32 is connected to a terminal of the protection device 26, and the other terminal of coil 32 is connected to capacitor 30 (via the terminal not connected to ground).

[0023] The inverter 24 is connected to the output of the filter 22. The inverter 24 is designed to convert the filtered direct current supply signal at the output of the filter 22 into an alternating current signal to power the traction motors 12.

[0024] The inverter 24 includes, for example, at least one insulated-gate bipolar transistor (IGBT), advantageously several IGBTs in a four-quadrant configuration.

[0025] The protection device 26 is connected between the connector 20 and the filter 22.

[0026] The protection device 26 includes a junction field-effect transistor 40. The term "junction field-effect transistor" (abbreviated as JFET, i.e., in English "Junction Field Effect Transistor") is understood to be a field-effect transistor whose gate is in direct contact with the channel.

[0027] In the example illustrated by the figure 1 , the protection device 26 also includes a first diode 42 and a second diode 44.

[0028] Apart from diodes 42 and 44, the protection device 26 contains no other semiconductor elements, specifically no IGBTs and no mechanical switches. Thus, the junction field-effect transistor 40 is the only transistor in the protection device 26.

[0029] In the example illustrated by the figure 1 , the junction field-effect transistor 40 includes a drain D connected to connector 20 (optionally via contactor 28), a source S connected to filter 22 (specifically to coil 32) and a gate G connected to source S.

[0030] Advantageously, the field-effect transistor 40 is made of a wide-bandgap material. Such a material typically has a bandgap energy strictly greater than two electron volts, preferably three electron volts. Such a material exhibits low on-state resistance and is capable of withstanding high voltages, typically exceeding a few kilovolts.

[0031] Advantageously, the material of the field-effect transistor 40 is chosen from silicon carbide and gallium nitride or other large energy gap material.

[0032] Advantageously, the 40 field-effect transistor is of the normally closed (NC) type. A junction field-effect transistor is said to be normally closed when the gate-source voltage is close to zero. This means that the drain-source path is conducting in the absence of a gate-source voltage. Conversely, a junction field-effect transistor is said to be normally open (NC) when the drain-source path is not conducting in the absence of a gate-source voltage. A normally closed JFET is faster to switch on, generates less conduction loss in the on-state (low on-state resistance), has better temperature resistance, and is smaller in size than other transistors, such as MOSFETs or IGBTs.

[0033] The first diode 42 is connected in antiparallel to the field-effect transistor 40, that is, the cathode of the first diode 42 is connected to the drain D of the transistor 40 and the anode of the first diode 42 is connected to the source S of the transistor 40.

[0034] The first diode 42 is designed to protect the JFET transistor 40. Indeed, in the event of a short circuit on the input side, the JFET transistor 40 will see a negative voltage between its terminals which could damage it in the absence of the first diode 42.

[0035] The second diode 44 is optional. It is connected between the field-effect transistor 40 and the filter 22, and is in parallel with the filter 22. Specifically, the cathode of the second diode 44 is connected to the source of the JFET transistor 40 and the anode of the second diode 44 is connected to ground.

[0036] The second diode 44 is designed to reduce the overvoltage when the JFET transistor 40 is opened. Indeed, when the JFET transistor 40 is opened, the input inductance of the JFET is decoupled with the second diode 44 which acts as a freewheeling diode.

[0037] The input contactor 28 is connected between the connector 20 and the protection device 26. The input contactor 28 is an electromagnetic component designed to establish or interrupt the flow of current, from an electrical or pneumatic control.

[0038] The operation of the traction chain is illustrated in figure 1 will now be described. For this, reference will be made to the figure 2 which represents the intensity IL of the current in the coil 42 of the filter 22 (and therefore in the JFET transistor 40) and the voltage V JFET across the terminals of the JFET transistor 40.

[0039] In operation and in the absence of a short circuit (phase A on the figure 2 The JFET transistor 40 of the protection device 26 is in a conducting state, and the input contactor 28 (when present) is also in a conducting state. Thus, the DC power supply signal received by connector 20 is sent to filter 22 for filtering, and then to inverter 24, which converts it into an AC power supply signal to power the traction motors 12. The current IL in coil 42 is constant, as is the JFET voltage V across JFET transistor 40.

[0040] When a short circuit occurs, for example at the inverter 24 or the capacitor 30 of the filter 22, this will impact the behavior of the JFET transistor 40.

[0041] In particular, in a first phase (phase B on the figure 2 During this phase, the current IL in coil 32 increases sharply (the rate of rise being determined by the inductance of coil 32). Consequently, the JFET voltage V across JFET transistor 40 also increases. The increase in current IL during this phase is made possible by the low resistance of JFET transistor 40 in the on-state. However, this increase in current IL also raises the junction temperature TJ of JFET transistor 40.

[0042] When the junction temperature TJ of JFET 40 exceeds a threshold value, the resistance of JFET 40 increases rapidly. Consequently, the current IL decreases and the JFET voltage V across JFET 40 increases until it reaches the input voltage E of the power supply circuit 14 (phase C on the figure 2 ).

[0043] After a certain time (a few hundred milliseconds), the limited current IL is eventually cut off either by the JFET transistor 40 itself, or by the input contactor 28 (phase D on the figure 2 ). Such a cut may cause a very small overvoltage compared to a normal cut because the current is already very limited.

[0044] The protection device 26 also limits the current due to an input overvoltage. Thus, the use of a JFET transistor 40 in the protection device 26 allows the input current (Iin) to be automatically reduced during a catenary overvoltage. Therefore, the influence of the catenary overvoltage (Vin) on the inverter bus voltage is less pronounced with the JFET transistor 40.

[0045] Thus, the use of a JFET transistor 40 in the protection device 26 enables very rapid current interruption, allowing for very quick and efficient isolation of the traction system converters from the catenary. This protection device 26 also protects the converters from catenary overvoltages.

[0046] Furthermore, the protection device 26 eliminates the need for a current sensor. Indeed, it is possible to determine the current in real time by measuring the voltage drop across the terminals of the JFET transistor 40.

[0047] Furthermore, the current limiting performed by JFET transistor 40 is automatic; that is, no command is sent to transistor 40. It is the temperature rising above a certain threshold that triggers this current limiting by JFET transistor 40. It should be noted that a JFET transistor can withstand very high junction temperatures, notably above 600°C, which is the melting point of aluminum connections. This means that in the event of a failure, the JFET transistor will break in an open circuit, and the inverter will be automatically and galvanically isolated from the catenary. This is a significant safety advantage.

[0048] The use of a JFET 40 transistor eliminates the need for a mechanical circuit breaker and a pre-charge circuit, and avoids oversizing the components of filter 22 to absorb catenary overvoltages. It also allows the use of a core inductor instead of an air-core inductor.

[0049] Compared to a traditional mechanical circuit breaker, it has been calculated that for a 1500V railway application, the JFET 26 protection device allows a saving of at least 20% to 30% on cost and volume.

[0050] The use of a silicon carbide JFET transistor and gallium nitride allows for a current limiting component capable of withstanding a high voltage, also called desaturation voltage, across its terminals.

[0051] Thus, the protection device 26 as described in this application makes it possible to protect the converters of a traction chain efficiently and quickly while being simple to implement and occupying a small volume.

Claims

1. A power supply circuit (14) for a vehicle, especially railway vehicle, from a power supply source (16), the supply circuit (14) comprising: - a connector (20) to be connected to the power supply source (16) to receive a DC supply signal, - a filter (22) capable of filtering the DC supply signal received by the connector (20) to obtain a DC supply signal filtered, - an inverter (24) capable of converting the DC supply signal filtered into an AC supply signal to supply to at least one traction motor (12), characterised in that the supply circuit (14) comprises a protection device (26) for the supply circuit (14) connected between the connector (20) and the filter (22), the protection device (26) comprising a junction field effect transistor (40) made of a material having a band gap energy strictly greater than two electronvolts, preferably three electronvolts, the junction field effect transistor (40) being the only transistor of the protection device (26), and the junction field effect transistor (40) comprises a drain (D) connected to the connector (20), a source (C) connected to the filter (22), and a gate (G) connected to the source (S).

2. The supply circuit (14) according to claim 1, wherein the material of the junction field effect transistor (40) is selected from silicon carbide and gallium nitride.

3. The supply circuit (14) according to any one of claims 1 or 2, wherein the junction field effect transistor (40) is of the normally closed type.

4. The supply circuit (14) according to any one of claims 1 to 3, wherein the protection device (26) comprises a diode (42) connected anti-parallel to the field-effect transistor (40).

5. The supply circuit (14) according to any one of claims 1 to 4, wherein the protection device (26) comprises a diode (44) connected between the field effect transistor (40) and the filter (22) and parallel to the filter (22).

6. The supply circuit (14) according to any one of claims 1 to 5, wherein the supply circuit (14) comprises an input contactor (28) connected between the connector (20) and the protection device (26).

7. The supply circuit (14) according to any one of claims 1 to 6, wherein the connector (20) is a pantograph.

8. A traction chain (10) for a vehicle, in particular railway vehicle, comprising at least one traction motor (12) and a supply circuit (14) according to any one of claims 1 to 7.

9. A vehicle, in particular railway vehicle, comprising at least one traction chain (10) according to claim 8.