The invention relates to a device and method for coupling two parts of a dc network, particularly in an aircraft.
The following description is made using the example of a high voltage onboard dc network in an aircraft, for simplification reasons.
High Voltage Direct Current (HVDC) networks are more and more frequently used on future aircraft under development.
Capacitors are installed at various locations in the network, to give good network voltage quality (filtering, stability). The capacitances involved thus form distributed energy reserves.
Operation of aircraft leads to more or less frequent reconfigurations of the direct current network. Different parts are then automatically coupled or decoupled while the aircraft is in use.
Capacitors in an onboard dc network are thus present in all parts of this network. When different parts of the network are at different potentials (or voltages), it is preferable to take some precautions before connecting them together, because putting capacitors charged at different potentials in parallel causes strong overcurrents.
Coupling devices traditionally used are electromagnetic contactors. These contactors make on-off coupling, with the most robust part of the network violently applying its voltage to the weaker part. This technical problem remains exactly the same with an electronic coupling device (for example a thyristor).
Fast variations of electrical potentials generate fast variations of capacitor charges, and thus strong current peaks in the capacitors. Naturally, such overcurrents have an effect on coupling elements and on the equipment surrounding the capacitors. Excessive overcurrents can cause malfunctions and even some hardware damage.
The purpose of the invention is to reduce overcurrents that occur during such coupling operations by disclosing a device and method of coupling to connect two parts of a dc network together smoothly with no risks of hardware damage, by limiting the current intensity.
The invention relates to a coupling device between a first part and a second part of a high voltage onboard dc network, at least two capacitors being installed at various locations on this network to maintain good voltage quality of the network, first and second capacitors being present in these first and second parts respectively, characterised in that it comprises at least one static step-down voltage converter formed by at least one electronic power coupling device, comprising at least one transistor and one diode associated with an inductance, arranged between these first and second capacitors.
In one advantageous embodiment, the network is a high voltage network. The coupling device is an electronic power coupling device comprising at least one IGBT, MOSFET or bipolar type transistor and a diode. The control device comprises at least one transistor in series with a diode.
Advantageously, the control device comprises a first transistor in series with a first diode and a second transistor in series with a second diode, the first transistor and the second diode being connected to be anti-parallel, and the second transistor and the first diode being connected to be anti-parallel.
The invention also relates to a method for coupling a first and a second part of a high voltage onboard dc network together, at least two capacitors being installed at various locations on this network to maintain good quality of the network voltage, first and second capacitors being present in these first and second parts respectively, characterised in that it comprises the following steps:
Advantageously, said at least one capacitor is precharged by a slow charge of at least one capacitor in at least one of the two parts of the network. A load (for example a user terminal) or a set of loads connected to one of the two parts of the network can also be charged slowly, when they are switched on.
Advantageously, protection against overcurrents is provided by protecting electrical conductors and/or limiting the current absorbed by one of the two parts of the network or a user load or terminal.
Advantageously, protection against instabilities is provided by management of any instabilities that occur on the downstream part of the network.
Finally, the invention relates to an aircraft comprising at least one such device.
The device according to the invention has the following advantages:
The invention relates to a device enabling smooth coupling of two parts 10 and 11 of a dc network, for example a high voltage network, in which there are two capacitors C1 et C2, by progressively (slowly) precharging these two capacitors C1 and C2.
This coupling device 20, classically composed of a transistor T and a diode D, is associated with an inductance L and forms a static step-down voltage (“buck”) converter in the direction from the first part 10 of the network to the second part 11. In these figures, the transistor T is an IGBT transistor connected between the (+) power supply voltage and the 0 voltage in series with a diode D, its collector being connected to the (+) potential and the anode of the diode D being connected to the 0 potential, the inductance L being connected to the connection point of the emitter of transistor T and the cathode of the diode D.
If we assume that the second part 11 is initially switched off, coupling the first part 10 to the second part 11 will require that the capacitor C2 should be precharged. The convertor (electronic coupling device 20 and inductance L) is controlled by a control signal applied to the gate of the IGBT transistor T, in a manner that will be obvious to those skilled in the art (see example embodiment at the end of the description) to progressively increase the voltage at the terminals of the capacitor C2. Once this capacitor is charged, voltages between the two parts 10 and 11 of the network are balanced, switchings of this converter are stopped leaving the transistor T permanently in the conducting state.
This operating principle shown in
The precharge is done actively, in other words it does not require any passive dissipation elements such as resistors.
The device according to the invention has several advantages:
These last two advantages are made possible because the convertor control can be used, and the transistor T can be controlled classically so as to fix a precharge time and/or not allow a current higher than a determined value to pass.
In a first variant embodiment shown in
The structure of the convertor is thus standardised so that the same component 30, 30′ can be used for the positive (+) and negative (−) terminals as shown in
There are several advantages in this standardisation of the conversion device:
In a second variant embodiment shown in
The device according to the invention as shown in
Some electronic structures shown in
In
In
In
Control of this conversion device can avoid instabilities on the dc network on the output side of the device (second part). Therefore the device according to the invention can perform three functions:
The device according to the invention can thus control the voltage of the second part of the network or a load (user) or a set of loads, during the precharge of the capacitor(s) in this same part of the network or load (user) or set of loads. The device according to the invention can also control the line current in the second part of the network or in a load (user) or in a set of loads, while the capacitors are being precharged, and when overcurrents generated by this same part of the network or load (user) or set of loads occur.
As described above, in the case of a high voltage dc network, the device according to the invention is essentially composed of electronic power components, plus miniature control electronics. If the control electronics are digital and programmable, the entire device according to the invention then forms a generic whole and is programmable and reconfigurable to suit needs. An adapted control can then be installed to control the part of the network concerned.
Some precautions should then be taken when setting control parameters. Several parameters of the device according to the invention can thus be adjusted to control the user voltage and current:
The maximum operating frequency fmax and the maximum operating time Δtmax of the device according to the invention must be compatible with the temperature performances of the device to prevent temperature rise and premature aging of the device.
There are several possible operating strategies, and particularly the following three strategies that vary the above-mentioned parameters:
The final strategy illustrated on
Furthermore, the temperature rise of the device is also related to the operating duration of the device in active mode (Δtmax). This is why this duration is monitored. Thus, a fault is declared if the current has not returned to a nominal operating range within a determined time Δtmax, and the device is opened.
In one example embodiment shown in
Thus as shown in these figures, coupling of the user terminal 40 to the network (HVDC busbar 43) is ordered at time t=0. The coupling device 44 comes into action. The transistor T becomes conducting, increasing the current 54 circulating at the input to the user terminal. The voltage 51 at the terminals of the user terminal also increases by the charge of its internal capacitor C2. When the user current 54 reaches the predefined limiting value 53 (for example 75 A), the transistor T is blocked. The user current 54 decreases while the user voltage 51 is held constant by the capacitor C2. After a certain time that assures that a given switching frequency (for example 5 kHz) is not exceeded, the transistor T becomes conducting again, once again increasing the charge of the capacitor C2. The phenomenon is repeated until the capacitor C2 is almost completely charged, reaching almost 100% of the network voltage (for example 270 V).
The user terminal can start operation once this precharging phase of the user capacitor C2 is complete.
The strategy in this case is the priority ripple current (ΔI) strategy with limited frequency (fmax) shown in
As shown in
In this example embodiment, the first function of the device according to the invention is performed; the line current does not exceed the predefined maximum value, and the precharge of the user capacitor C2 is performed correctly.
Number | Date | Country | Kind |
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08 53511 | May 2008 | FR | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/FR2009/051006 | 5/28/2009 | WO | 00 | 4/11/2011 |
Publishing Document | Publishing Date | Country | Kind |
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WO2009/156654 | 12/30/2009 | WO | A |
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