FR2910850A1 - Public transport vehicle e.g. bus, has step-down transformer transforming electric energy extracted from bus to capacitor under step down voltage, which is lower than maximum load voltage and higher than nominal continuous voltage - Google Patents

Abstract

The vehicle (2) has an ultra capacitor (30) storing electric energy provided by an electric energy source, and connected to a direct current (DC) bus. Electric loads (10, 12) operating under a nominal continuous voltage are connected between conductors (6, 8) of the bus. A DC-DC step-down transformer (40) is coupled to the capacitor and the bus at two sides. The transformer transforms the energy extracted from the bus to terminals of the capacitor under a step down voltage, which is lower than a maximum load voltage of the capacitor, and is higher than the continuous voltage. An independent claim is also included for a method for utilizing a public transport vehicle.

Description

The present invention relates to a public transport vehicle equipped

  a supercapacitor and a method of using the vehicle. There are public transport vehicles 5 comprising: a DC bus formed of two conductors between which are connected, in parallel, various electrical charges on board this vehicle, these electric charges being designed to operate under a nominal DC voltage VDCnom, a fluctuating source of energy which, when connected to the DC bus, is capable of supplying the DC bus with electrical power fluctuating between 10 kW and 150 kW, this power source being able to vary the electrical power provided with more than 20 kW in less than 20 seconds, and - a supercapacitor connected to the DC bus for storing the electrical energy supplied by the energy source, this supercapacitor having a maximum voltage Vcmax of load beyond which the supercapacitor may be damaged and a capacity strictly greater than 1F, this supercapacitor being also able to deliver on or store from the DC bus an electric power of 20 kW in less than 20 s. By supercapacitor, is meant in this description capacitors whose capacity is at least greater than 1 Farad and typically greater than 1000 Farads. In practice, supercapacitors whose capacity is high, that is to say greater than 1000 Farads, are put in series to produce a supercapacitor high voltage, that is to say a supercapacitor at the terminals of which the voltage is greater than 125 Vdc, the capacity of which is lower. Thus, in this description, the term supercapacitor means both a supercapacitor and a set of supercapacitors connected to each other in series, so as to form a supercapacitor of lower capacity but higher voltage.

  In existing vehicles, the supercapacitor is chosen so that its voltage VCmax is strictly greater than the voltage VDCnom • Thus, the risks of deterioration of the supercapacitor are reduced. In existing vehicles, when releasing the electrical energy stored in the supercapacitor, a DC-DC converter must be used to lower the voltage at the terminals of the supercapacitor to a value close to the voltage VDCnom • At the Conversely, when storing electrical energy in the supercapacitor, this DC-DC converter is used to raise the voltage present on the DC bus to a value close to the voltage Vcmax. The electrical energy stored in the supercapacitor is, for example, produced by an alternator when braking the vehicle.

  Existing vehicles are working properly. However, it is desirable to further increase the transfer of electrical energy between the rectifier and the supercapacitor during the storage of electrical energy in the latter.

  The invention aims to satisfy this desire by proposing a public transport vehicle in which the energy transfer during the charging of the supercapacitor is faster. The subject of the invention is therefore a public transport vehicle in which: the voltage V cmax is less than or equal to the voltage VDCnom, and the vehicle comprises a step-down (40) of DC-DC voltage connected on one side to the DC bus and on the other side to the supercapacitor, this step-down being capable of delivering, at the terminals of the supercapacitor, electrical energy, extracted from the DC bus, at a lowering voltage lower than or equal to the voltage Vcmax while the voltage on the DC bus is greater than or equal to the voltage VDCnom • In the above vehicle, since the voltage Vcmax is lower than the voltage VDCnom / during the braking of the vehicle by the alternator, the voltage on the DC bus can be maintained beyond above the voltage Vcmax without damaging any of the electrical loads connected to the DC bus. Under these conditions, only the voltage step-down is used to transfer the electrical energy generated by the rectifier to the supercapacitor for storage. However, a voltage step-down can transfer more electrical energy than a voltage booster with equal complexity and size. Thus, the power transfer capacity of the DC bus to the supercapacitor is increased. The embodiments of the above vehicle may comprise one or more of the following features: at least one of the electrical charges is capable of creating a large current draw when it is powered up, and the vehicle comprises a voltage booster 25 DC-DC connected between the supercapacitor and the DC bus, this voltage booster being able to deliver, on the DC bus, a voltage close to the voltage VDCnom while the voltage across the supercapacitor is less than or equal to this voltage VDCname ; The voltage step-down is able to cut off the current flowing from the rectifier to the supercapacitor and the vehicle also comprises a circuit-breaker able to cut the current flowing from the rectifier to the supercapacitor and in the opposite direction to electrically isolate the supercapacitor from the rectifier and the electrical loads connected to the DC bus, and the vehicle also comprises a control unit adapted to control the voltage step down to cut the current flowing from the rectifier to the supercapacitor and to maintain the current cut for a predetermined time, and to control the opening the circuit breaker according to the down switch control to ensure that the breaker opening occurs when the current is zero; the vehicle comprises: a cut-off device capable of electrically isolating the supercapacitor from the electrical charges connected to the DC bus; a voltage limiter connected to the DC bus between the supercapacitor and the cut-off device, this clipper being able to clip, by dissipation; of electrical energy, the voltage on the DC bus when it exceeds a voltage VDCmax beyond which the electrical charges may be damaged, the voltage VDCmax being greater than or equal to the voltage VDCnom,. a voltage booster connected to the DC bus between the supercapacitor and the breaking device, and. a control unit capable of controlling the voltage booster when the switching device isolates the supercapacitor from the electrical charges, to generate from the electrical energy stored in the supercapacitor a voltage across the limiter which is strictly greater than the voltage VDCmax; - The voltage step is able to maintain the intensity of the current flowing from the rectifier to the supercapacitor less than or equal to a predetermined maximum charge intensity of the supercapacitor; the voltage step-down is a chopper / step-down capable of lowering the voltage at the terminals of the supercapacitor by mincing the charge current of the supercapacitor; The elevator is a chopper / voltage booster comprising an energy storage inductor having a first end connected to a first terminal of the supercapacitor and a second end connected to the rectifier, the energy stored in this inductor being used for generating the higher voltage, and the step-down is a chopper / step-down having an inductance to limit the current draw during the charge of the supercapacitor, this inductance being the same as that used by the chopper / elevator to store energy ; the vehicle comprises a voltage limiter connected to the DC bus, this limiter being capable of systematically maintaining the voltage on the DC bus less than or equal to a voltage VDCmax beyond which the electrical charges connected to the DC bus may be damaged; , the voltage VDCmax being strictly greater than the voltage VDCnom; the energy source comprises an alternator mechanically coupled to at least one driving wheel of the vehicle for generating an alternating voltage when the shaft is rotated by the driving wheel, and a voltage rectifier connected on one side to the alternator and, on the other hand, the DC bus to deliver on the DC bus rectified current and voltage.

  These embodiments of the vehicle also have the following advantages: - the fact that the voltage VCmax is strictly less than the voltage VDCnom ensures that only the voltage booster is used to restore the DC bus of 6 the energy stored in the supercapacitor. However, a voltage booster naturally has a limited capacity to transfer electrical energy, so that the voltage booster naturally limits the intensity of the current consumed by the electrical charges, which makes it unnecessary to provide another circuit specifically dedicated to this task or simplifies the implementation of a current limiter, - the presence of a control unit able to control the voltage step down to cut the current flowing from the rectifier to the supercapacitor and then to control the opening of the circuit breaker simplifies the design of this circuit breaker because the breaking capacity of the latter will be used in case of failure, - a control unit adapted to control the voltage booster to generate a voltage across the clipper greater than the voltage VDCmax makes it possible to use the voltage booster to discharge the supercapacitor, which avoids providing a specific circuit dedicated to this task or simplifies the design of such a specific circuit, - using the voltage step-down device to maintain the supercapacitor charging current intensity below a predetermined maximum intensity makes it possible to avoid resorting to to a precharging circuit of the supercapacitor, that is to say a first power circuit, or simplifies the design of such a precharge circuit, - use as a voltage drop a chopper / step-down allows at equal performance, to reduce the bulk, - using a common inductance to the voltage booster and the voltage step-down also reduces the size of the elevator and the voltage step-down, and The voltage limiter connected to the DC bus ensures that the different electrical loads connected to this bus 5 will not be damaged by an overvoltage. The invention also relates to a method of using the public transport vehicle above. This method comprises a phase of storing electrical energy in the supercapacitor, during the entire duration of which, systematically, only the voltage step-down is used. The embodiments of this method may comprise the following characteristic: the method comprises a phase of release of the energy stored in the supercapacitor on the DC bus, and systematically for the duration of the release phase only voltage booster is used. The invention will be better understood on reading the description which follows, given solely by way of nonlimiting example and with reference to the drawings, in which: FIG. 1 is a schematic illustration of the architecture of FIG. a public transport vehicle; and FIG. 2 is a flowchart of a method of using the vehicle of FIG. 1. In the rest of this description, the features and functions well known to those skilled in the art will not be described in detail. Figure 1 shows a common transport vehicle 2 such as, for example, a bus, a trolleybus, a tram, or the like. The vehicle 2 comprises a DC bus formed of two electrical conductors 6, 8 between which are connected different electrical charges to supply DC voltage 8. To simplify the figure, only two charges 10 and 12 have been represented. The electrical charges can be air conditioners, auxiliary electrical loads such as hydraulic pumps, or a transformer adapted to supply another on-board electrical network of lower voltage. Each of the electrical charges is designed to operate at a nominal operating voltage VDCnom. For example, in the vehicle 2, this voltage VDCnom is greater than 300 volts DC and preferably greater than or equal to 350 volts DC. The electrical charges also have a voltage VDCmax beyond which it may be damaged. For example, here, the voltage VDCmax is greater than or equal to 400 volts DC. In the embodiment of FIG. 1, an inverter / rectifier 14 is connected on one side, between the conductors 6 and 8 and on the other side to a traction motor 16 of the vehicle 2. For example, the motor 16 is a three-phase motor / alternator equipped with a shaft 18 adapted to drive in rotation at least one drive wheel 20 of the vehicle 2. The motor 16 is also able to operate as an alternator to produce an alternating voltage. The inverter / rectifier 14 is also connected to a main source of electric power 24. Thus, when the inverter / rectifier 14 operates as an inverter, the latter is able to supply the motor 16 from the source 24 and / or DC bus. Conversely, when the inverter / rectifier 14 operates as a rectifier, the AC voltage generated by the motor 16 rotated by the wheel 20, is converted into DC voltage delivered on the DC bus. A switch 26 makes it possible to disconnect the source 24 of the inverter / rectifier 14 when the latter operates as a rectifier.

  Here, when the inverter / rectifier 14 operates as an inverter connected to the DC bus, it is considered as an electrical load connected to this DC bus. Conversely, when the inverter / rectifier 14 operates as an alternator, the assembly formed by the motor 16 operating as an alternator and the inverter / rectifier 14 operating as a rectifier constitute a source of fluctuating electrical energy. By source of fluctuating electrical energy, is meant here a source of electrical power capable of providing on the DC bus electrical power fluctuating between 10 kW and 150 kW. When this source of electrical energy consists of an engine and an alternator of a public transport vehicle, the electric power supplied to the DC bus can fluctuate by more than 20 kW in less than 20 s.

  Typically, for applications in the field of public transport vehicles, the electric power supplied by the energy source can fluctuate by more than 50 kW in less than 20 s. Generally, these variations in the electrical power supplied to the DC bus still occur in more than 1 s. A supercapacitor 30 is also connected between the conductors 6 and 8 via a DC-DC converter 32. The supercapacitor 30 is chosen to be able to deliver on the DC bus, and store from the DC bus, a electrical power of x kW in less than 20 s. The value of x is chosen equal to or greater than the maximum variation in less than 20 s of the electric power supplied on the DC bus by the fluctuating energy source. For example, here, the value of x is chosen greater than or equal to 50. Thus, such a supercapacitor is able to compensate for variations in the electric power supplied or consumed by the fluctuating energy source. A filter capacitor 34 is connected between the conductors 6 and 8 immediately at the output of the DC-DC converter. A circuit breaker 36, forming a cut-off device, is arranged between the outputs of the converter 32 and all the electrical loads connected to the DC bus so as to be able to isolate all of the charges 10, 12 and 14 of the supercapacitor 30. all the charges fed from the DC bus are connected to the conductors 6 and 8 downstream of the circuit breaker 36. Conversely, the supercapacitor 30, the converter 32 and the capacitor 34 are connected upstream of the circuit breaker 36. Finally, a voltage clipper 38 is connected to the conductors 6 and 8 upstream of the circuit breaker 36. This clipper 38 is able to clog the voltage present on the DC bus when it exceeds the voltage VDCmax • For this purpose, typically, the clipper dissipates the excess electrical energy present on the DC bus in, for example, a rheostat.

  The converter 32 comprises a voltage chopper / step-down 40 and a voltage chopper / booster 42. Here, the chopper 40 is able to generate a voltage across the supercapacitor 30 lower than the voltage VCmax from a voltage strictly greater than the voltage VCmax and lower than the voltage VDCmax present between the conductors 6 and 8. This chopper / step-down is also able to cut a charge current of the supercapacitor 30 whose intensity is greater than 100 amperes and preferably greater than 300 amperes.

  Here, the chopper / buckener 40 is made using an inductor L connected in series with a controllable switch I2. Specifically, one end of the inductor L is directly connected to a connection terminal of the supercapacitor 30 while its other end 44 is connected to a first side of the switch I2. The other side of the switch I2 is connected to the conductor 6 of the DC bus. For example, the switch I2 comprises a diode D2 whose anode is connected to the end 44 of the inductor L, and a transistor Q2, connected in parallel across the diode D2. The emitter of the transistor Q2 is connected to the end 44 of the inductor L. The chopper / elevator 42 is able to generate, between the conductors 6 and 8, a voltage close to the voltage VDCnom from a voltage VC Strictly lower present at the terminals of the supercapacitor 30. For this purpose, the chopper / elevator 42 is formed of the inductor L and a controllable switch I1 connected on one side to the end 44 and on the other side to the driver 8. For example, the structure of the switch I. is identical to that of the switch I2 except that the diode and the transistor respectively bear the references D1 and Q.

  An ammeter 46 and a voltmeter 48 are also provided for measuring, respectively, the charging or discharging current of the supercapacitor 30 and the voltage at the terminals of the supercapacitor 30. Finally, the vehicle 2 comprises a drive unit 50 for controlling the converter 32 and the circuit breaker 36. Other characteristics of the unit 50 will appear on reading the description of the method of FIG. 2. The operation of the vehicle 2 will now be described with reference to the method of FIG. 2.

  Initially, in a step 60, the control unit 50 receives an instruction indicating whether it must proceed to a phase 62 of release of the energy stored in the supercapacitor 30, or a phase 64 of storage of electrical energy in the supercapacitor 30 or a phase 66 of neutralization of the supercapacitor 30. During phases 62 and 64, the circuit breaker 36 is permanently closed and the limiter 38 is permanently activated.

  More specifically, during step 62, during a step 70, the inverter / rectifier 14 is controlled so that the motor 16 rotates the shaft 18. In parallel, during a step 72, the chopper / step down 40 is disabled. More specifically, during this step, the transistor Q2 is kept non-conducting so that only a discharge current of the supercapacitor 30 can pass through the switch I2. Then, during a step 74, the chopper / elevator 42 is activated so that the voltage delivered on the DC bus is close to the voltage VDCnom • For this purpose, the switching frequency of the transistor Q1 is adjusted according to the voltage at the terminals of the supercapacitor 30 and the value of the voltage VDCnom • Under these conditions, in parallel, during a step 76, the supercapacitor 30 discharges and the electric charges, such as the charges 10, 12 and 14 consume the power electric delivered by the supercapacitor. Thus, in particular, the energy stored in the supercapacitor 30 is used to drive the shaft 18 in rotation. This energy extracted from the supercapacitor 30 can complement or replace the electrical energy supplied by the source 24. When phase 64 of energy storage in the supercapacitor 30, during a step 80, the shaft 18 of the motor is rotated by the drive wheels. Under these conditions, the motor 16 operates as an alternator and generates a three-phase alternating current that is rectified by the inverter / rectifier 14 before being transmitted in the form of DC current and DC voltage rectified on the DC bus. In parallel, during a step 82, the chopper / elevator 42 is deactivated. More specifically, the transistor Q1 is kept non-conducting, during the phase 64. Then, during a step 84, the unit 50 activates the chopper / step-down 40 so as to generate from the voltage present on the bus DC a voltage across the supercapacitor 30 less than the value Vcmax. For this purpose, during step 84, the unit 50 sets the switching frequency of the transistor Q2 as a function of the current and / or voltage measured by the ammeter 46 and the voltmeter 48. step 84, during a step 86, the supercapacitor 30 charges and stores the energy related to the braking of the vehicle 2 by the engine 16. During the phase 66 of neutralization of the supercapacitor 30, the unit 50 deactivates the For example, the transistor Q1 is held non-conducting during the entire phase 66. Then, in a step 92, the unit 50 controls the chopper / step down 40 to cut the load current. In step 92, transistor Q2 is off. In this state, the diode D2 prevents the flow of the charging current since the voltage on the DC bus is greater than the voltage across the terminals of the supercapacitor 30. Once the current flowing between the supercapacitor 30 and the DC bus has been interrupted, during a step 94, the unit 50 triggers the opening of the circuit breaker 36. Thus, the supercapacitor 30 is now isolated from the DC bus. Once the circuit breaker 36 is open, the unit 50 activates the chopper / elevator 42 so that it generates across the limiter 38 a voltage greater than the voltage VDCmax from the voltage present at the terminals of the supercapacitor 30, when of a step 96.

  Under these conditions, during a step 98, the clipper dissipates the electrical energy stored in the supercapacitor. Thus, the clipper 38 is here used to discharge the supercapacitor 30. The phase 66 is, for example, performed during a prolonged stop of the vehicle 2 or during maintenance operations on the vehicle 2. Many other modes of realization are possible. For example, the inverter / rectifier 14 is replaced, alternatively, only by a rectifier. In this variant, the motor 16 only functions as an alternator (generator). The source of fluctuating electrical energy has here been described in the particular case where it is formed from an alternator and a rectifier. In another embodiment, it is formed of a fuel cell connected to the DC bus. This latter embodiment can be combined with the embodiment described with respect to FIG. 1 to obtain a third embodiment in which the fuel cell and the alternator / rectifier are both connected to the same DC bus. The vehicle 2 has been described in the particular case where it is a towed vehicle. Alternatively, the teaching given above obviously applies to powered vehicles, that is to say, for example, whose driving wheels are located at the rear of the vehicle.

Claims (11)

  1. Public transport vehicle comprising: - a DC bus formed of two conductors (6, 8) between which are connected, in parallel, different electrical charges (10, 12) embedded in the vehicle, these electric charges being designed to operate at a nominal DC voltage VDCnom, - a fluctuating source of energy which, when connected to the DC bus, is able to supply the DC bus with electrical power fluctuating between 10 kW and 150 kW, this energy source being suitable to fluctuate the electric power supplied by more than 20 kW in less than 20 seconds, and - a supercapacitor (30) connected to the DC bus to store the electrical energy supplied by the energy source, this supercapacitor having a maximum voltage VC max charge beyond which the supercapacitor may be damaged and a capacity strictly greater than 1F, this supercapacitor being also able to deliver on or store from the DC bus an electrical power of 20 kW in less than 20 seconds, characterized in that: - the voltage Vcmax is less than or equal to the voltage VDCnom, and -the vehicle has a step down (40) voltage DC-DC connected on one side to the DC bus and on the other side to the supercapacitor, this step-down being capable of delivering, at the terminals of the supercapacitor, electrical energy, extracted from the DC bus, under a lowering voltage lower than or equal to the voltage VCmax then that the voltage on the DC bus is greater than or equal to the voltage VDCnom.   2. Vehicle according to claim 1, wherein at least one of the electrical charges (10, 12) is able to create a large current draw when it is turned on, and wherein the vehicle comprises a voltage elevator (42). DC-DC connected between the supercapacitor (30) and the DC bus, this voltage booster being able to deliver, on the DC bus, a voltage close to the voltage VDCnom while the voltage across the supercapacitor is below this voltage VDCname •   3. Vehicle according to any one of the preceding claims, wherein the step-down (40) voltage is adapted to cut the current flowing from the rectifier to the supercapacitor and wherein the vehicle also comprises a circuit breaker (36) adapted to cut the current flowing from the rectifier to the supercapacitor and in reverse direction, for electrically isolating the supercapacitor from the power source (14) and the electrical loads (10, 12) connected to the DC bus, and wherein the vehicle also comprises a unit ( 50) capable of: - controlling the step-down switch to cut the current flowing from the rectifier to the supercapacitor and to keep the current cut for a predetermined time, and - to control the opening of the circuit-breaker according to the control of the step down so as to ensure that the opening of the circuit breaker occurs when the intensity of the current is zero.   4. Vehicle according to any one of the preceding claims, wherein the vehicle comprises: a cut-off member adapted to electrically isolate the supercapacitor from the electrical charges connected to the DC bus; a connected voltage limiter (38). to the DC bus between the supercapacitor and the cut-off device, this clipper being able to clip, by dissipation of electrical energy, the voltage on the DC bus when it exceeds a voltage VDCmax beyond which the electric charges ( 10, 12) may be damaged, the voltage VDCmax being greater than or equal to the voltage VDCnom, - a voltage booster connected to the DC bus between the supercapacitor and the breaking device, and - a control unit (50). adapted to control the voltage booster when the switching device isolates the supercapacitor electrical charges, to generate from the electrical energy stored in the supercapacitor a tensi the limits of the clipper are strictly greater than the voltage VDCmax-   5. Vehicle according to any one of the preceding claims, wherein the step-down (40) voltage is adapted to maintain the intensity of the current flowing from the rectifier to the supercapacitor less than or equal to a predetermined maximum charge intensity of the supercapacitor.   A vehicle according to any one of the preceding claims, wherein the voltage step-down (40) is a chopper / step-down capable of lowering the voltage across the supercapacitor by chopping the charge current of the supercapacitor.   The vehicle according to claim 2 or 4, wherein the elevator (42) is a voltage chopper / booster having an energy storage inductor (L) having a first end connected to a first terminal of the supercapacitor and a second end (44) connected to the rectifier (14), the energy stored in this inductor being used to generate the higher voltage, and wherein the step-down (40) is a chopper / step-down having an inductance (L) to limit the current draw when charging the supercapacitor, this inductance being the same as that used by the chopper / elevator to store energy.   8. Vehicle according to any one of the preceding claims, wherein the vehicle comprises a voltage limiter (38) connected to the DC bus, this limiter being adapted to systematically maintain the voltage on the DC bus less than or equal to a voltage VDCmax at beyond which the electric loads (10, 12) connected to the DC bus may be damaged, the voltage VDCmax being strictly greater than the voltage VDCnom   9. Vehicle according to any one of the preceding claims, wherein the energy source comprises: - an alternator (16) mechanically coupled to at least one drive wheel of the vehicle for generating an alternating voltage when the shaft is rotated by the driving wheel, and - a voltage rectifier (14) connected, on one side, to the alternator and, on the other hand, to the DC bus for delivering on the DC bus a rectified current and voltage.   10. A method of using a public transport vehicle according to any one of the preceding claims, this method comprising a phase (64) for storing electrical energy in the supercapacitor, characterized in that, systematically, during the entire duration of the energy storage phase only the voltage step-down is used.   11. The method of claim 10, wherein the method comprises a phase (62) for releasing the energy stored in the supercapacitor on the DC bus, and wherein, systematically, throughout the duration of the release phase alone. voltage booster is used.