WO2013190248A2

WO2013190248A2 - Method for controlling a reversible dc-dc voltage converter

Info

Publication number: WO2013190248A2
Application number: PCT/FR2013/051453
Authority: WO
Inventors: Maxime MOREAU; Luis De Sousa
Original assignee: Valeo Systèmes de Contrôle Moteur
Priority date: 2012-06-22
Filing date: 2013-06-21
Publication date: 2013-12-27
Also published as: FR2992499A1; FR2992499B1; WO2013190248A3

Abstract

The invention relates to a method for controlling a reversible DC-DC voltage converter (1) operating in a cyclically in order to transfer power from a low-voltage source (101) to a high-voltage source (100), the converter including a high-voltage circuit, including in addition to the high-voltage source: a first and second arm, each arm including two controllable two-way switches separated by a midpoint, each controllable two-way switch being connected in parallel to a capacitor; and a primary transformer winding having a first current passing therethrough, connected by one end to the midpoint of the first arm and by the other end to the midpoint of the second arm; and a low-voltage circuit, including in addition to the low-voltage source (Vs): an arm including two controllable two-way switches; and a secondary transformer winding connected in parallel to said arm and having a second current passing therethrough.

Description

Method of controlling a reversible DC / DC converter

The present invention relates to the control of a voltage converter

reversible DC / DC for transferring electrical energy from a low voltage source to a high voltage source using the converter.

The invention applies in particular, but not exclusively, to a DC / DC voltage converter forming part of an electrical circuit on a vehicle. In such a case, the transfer of energy from the low voltage source, which is, for example, the battery supplying the vehicle's on-board network to the high voltage source, which is for example the battery supplying the vehicle's electric motor, enables to the latter to start, even in case of failure of the battery or even in very cold conditions in which this battery can be frozen.

There is a need to be able to use a DC / DC voltage converter, initially designed to transfer electrical energy from the high voltage source to the low voltage source, in the case where it is desired to transfer electrical energy from the low voltage source to the high voltage source, without modifying the structure of the converter and obtaining satisfactory performance.

The invention aims to meet this need and it achieves this, according to one of its aspects, using a method of controlling a reversible DC / DC voltage converter, operating cyclically to transfer power. the electrical energy from a low voltage source to a high voltage source, the converter comprising:

a high voltage circuit, comprising in addition to the high voltage source:

a first and a second arm, each arm comprising two controllable bidirectional switches separated by a mid-point, each bidirectional controllable switch being connected in parallel with a capacitor, and a primary transformer winding traversed by a first current, connected by a end at the midpoint of the first arm and at the other end at the midpoint of the second arm,

a low voltage circuit, comprising in addition to the low voltage source:

an arm comprising two controllable bidirectional switches, and

a secondary transformer winding connected in parallel with said arm and traversed by a second current, a first inductance mounted between one end of the secondary transformer winding and the positive terminal of the low voltage source and a second inductance mounted between the other end of the secondary transformer winding and the positive terminal of the low voltage source; the maximum absolute value taken by the current passing through the first inductance over the entire operating cycle being in particular equal to the maximum absolute value taken by the current flowing through the second inductance over the entire operating cycle,

the operating cycle comprising at least one succession of the following two steps: a first step in which the first current flows in a bidirectional switch controllable from the first arm, the high voltage source and a bidirectional switch controllable from the second arm,

a second step during which the bidirectional controllable switches of the low voltage circuit arm are both in the on state to short-circuit the transformer secondary winding,

the first sign-changing current in the second step and the controllable bidirectional electronic switch of the first arm traversed by the first current during the first step being controlled in the on state during the second step for a first duration fraction of the duration of the second step and sufficient so that after this first duration, the second current is greater in absolute value than the maximum absolute value of the current flowing through the first or the second inductance.

In a variant, another aspect of the invention is a method for controlling a reversible DC / DC voltage converter operating cyclically to transfer electrical energy from a low voltage source. at a high voltage source, the converter comprising:

a high voltage circuit, comprising in addition to the high voltage source:

a first and a second arm, each arm comprising two controllable bidirectional switches separated by a mid-point, each bidirectional controllable switch being connected in parallel with a capacitor, and a primary transformer winding traversed by a first current, connected by a end at the midpoint of the first arm and at the other end at the midpoint of the second arm, a low voltage circuit, comprising in addition to the low voltage source:

an arm comprising two controllable bidirectional switches, and

a secondary transformer winding connected in parallel with said arm and traversed by a second current,

the operating cycle comprising at least one succession of the following two steps:

a first step in which the first current flows in a controllable bidirectional switch of the first arm, the high voltage source and a controllable bidirectional switch of the second arm;

the first current changing sign in the second stage and the switch

bidirectional control of the first arm traversed by the first current during the first step being controlled in the on state during the second step for a first fractional duration of the duration of the second step, the first current having at the end of this first step; duration an absolute value allowing that at the end of the second step, the bidirectional switch controllable arm of the low voltage circuit which is then no longer controlled in the on state remains traversed by current.

At the end of the second step, one of the bidirectional controllable switches of the low voltage circuit arm can remain controlled in the on state while the other bidirectional controllable switch of said arm is no longer controlled in the on state. but there is still a current.

The choice of the first duration avoids, unlike what would happen in the case where at least one bidirectional switch controllable low voltage circuit would no longer be traversed by current at the end of the second step, that a Sudden variation of current does not occur in the secondary transformer winding, this sudden variation being associated with a large overvoltage appearing across the bidirectional switch controllable low voltage circuit when no longer flows through current. This overvoltage can degrade or even destroy controllable bidirectional switches of the low voltage circuit.

With the above method, the current continues to flow in a bidirectional switch controllable low voltage circuit at the end of the second step, even when no longer controlled in the on state. It is thus possible to switch this bidirectional switch controllable zero Volt, according to a soft switch (also called "Zero Voltage Switching" or "ZVS" in English).

The method can overcome the incompatibility that exists when two current sources having different initial current values are put in series.

The first duration may correspond to the total duration on the first and the second step during which the controllable bidirectional switch of the first arm which is traversed by the first current during the first step is controlled in the on state. In other words, said controllable bidirectional switch may not be controlled in the on state during the first step but only in the second step.

As a variant, said bidirectional controllable switch can already be controlled in the on state for a certain fractional duration of the first step, or even during the entire first step, and then during the first fractional duration of the second step.

A switching inductance (1 _R ) can be connected in series with the primary transformer winding and the first duration (Î ₀ N) can verify the relation ''ON> ml- where Is is the average value of the current flowing through the source low voltage, m is the ratio of the transformer and E is the average value of voltage that one seeks to obtain at the terminals of the high voltage source during its charging by the low voltage source.

When the first duration is higher one ensures:

that after this first duration, the second current will be greater in absolute value than the maximum absolute value over the entire operating cycle of the current flowing through one of the inductances connected to the positive terminal of the low voltage source and,

that at the end of the second step, each bidirectional switch controllable from the arm of the low-voltage circuit is still carrying current, even when one of these switches is no longer controlled in the on state.

The advantages mentioned above can thus be obtained.

Each cycle of operation of the converter for charging the high voltage source by the low voltage source may include: (i) the first step in which the first current flows in the bidirectional switch controllable at the top of the first arm, the high voltage source and the bidirectional switch controllable at the bottom of the second arm, and the second step during which the first current becomes negative and controllable bidirectional switch at the top of the first arm is controlled passing during the first duration, and

(ii) the first step in which the first current flows in the bidirectional switch controllable at the bottom of the first arm, the high voltage source and the bidirectional switch controllable at the top of the second arm, and the second step during which the first current becomes positive and the bidirectional switch controllable at the bottom of the first arm is controlled passing during the first duration.

The first and second steps according to (i) can respectively correspond to:

a transfer of electrical energy from the low voltage source to the high voltage source through the transformer with a first positive current, and

reversing the first current followed by freewheeling operation through the controllable bidirectional switches at the bottom of each arm of the high voltage circuit.

The first and second steps according to (ii) can respectively correspond to:

a transfer of electrical energy from the low voltage source to the high voltage source through the transformer with a first negative current, and

- A reversal of the first current followed by freewheel operation through the controllable electronic switches from the top of each arm of the high voltage circuit.

The low voltage circuit can include:

a first inductor connected on the one hand to the positive terminal of the low voltage source and on the other hand to one end of the secondary transformer winding, and

a second inductor connected on the one hand to said positive terminal of the low-voltage source and on the other hand to the other end of the secondary transformer winding. The maximum absolute value taken by the current passing through the first inductance over the entire operating cycle may or may not be equal to the maximum absolute value taken by the current flowing through the second inductance over the entire cycle of operation.

operation and the first duration may be such that at the end of this first duration, the second current is greater in absolute value than greater of said maximum absolute values. No bidirectional switch controllable high voltage circuit is for example controlled during the first step. Circulation of the electric current through the bidirectional controllable switches of the high voltage circuit to ensure the transfer of energy from the low voltage source to the high voltage source can be via diodes, parasites or not, these bidirectional switches controllable during the first step, whether it is the first step according to (i) or according to (ii).

The second step can be constituted by the following successive phases:

a phase during which the first current varies abruptly, this phase corresponding to the on-state control during the first duration of the controllable bidirectional switch of the first arm traversed by the first current during the first immediately preceding step,

a phase during which the first current varies attenuated and in the same direction of variation as in the immediately preceding phase, and

a phase during which the first current is substantially constant.

These phases respectively correspond to the inversion of the first current in the high voltage circuit, to a resonance transition to coasting operation and freewheeling proper.

In the second step, the controllable bidirectional switch of the second arm traversed by the first current during the immediately preceding first step can be controlled in the on state.

One of the bidirectional controllable switches of the low voltage circuit arm may not be current flowed in the first step. Thus, the secondary winding of the transformer is not short-circuited in the first step, so that a transfer of energy from the low voltage source to the high voltage source is possible.

Each operating cycle may comprise, immediately after each second step:

a third step in which the first current varies attenuated with a direction of variation opposite to that which it has during the second step, and

a fourth step in which the first current varies suddenly maintaining the same direction of variation as in the third step and without changing the sign, the current in the bidirectional switch controllable low voltage circuit traversed by current during the first step and then no longer controlled in the state passing decreasing in absolute value and canceling at the end of this fourth step. The third and fourth steps may correspond to a resonant transition to the next energy transfer between the low voltage source and the high voltage source.

A complete cycle of operation of the method according to the invention may comprise:

the first step in which the first current flows in the bidirectional switch controllable at the top of the first arm, the high voltage source and the bidirectional switch controllable at the bottom of the second arm while the controllable bidirectional switch at the bottom of the low voltage circuit; is traversed by current,

the second step in which the first current becomes negative and the bidirectional switch controllable at the top of the first arm of the high voltage circuit is controlled during the first duration,

the third step in which the first current increases attenuated while remaining negative,

the fourth step in which the first current increases abruptly while remaining negative, the current in the bidirectional switch controllable at the bottom of the low voltage circuit decreasing in absolute value and canceling at the end of this fourth step,

the first step in which the first current flows in the bidirectional switch controllable at the bottom of the first arm, the high voltage source and the bidirectional switch controllable at the top of the second arm while the switch

bidirectional commandable at the top of the low voltage circuit is traversed by current, - the second step in which the first current becomes positive and the bidirectional switch controllable at the bottom of the first arm of the high voltage circuit is controlled during the first duration,

the third step in which the first current decreases attenuated while remaining positive, and

the fourth step in which the first current decreases abruptly while remaining positive, the current in the bidirectional switch controllable at the top of the low voltage circuit decreasing in absolute value and canceling at the end of this fourth step.

In all the foregoing, the attenuated variation of the first current may correspond to the passage of current in the capacitor in parallel with each controllable bidirectional switch of the same arm of the high voltage circuit. This produces a soft switching or ZVS.

According to the above method, the controllable bidirectional switch of the first arm traversed by the first current during a first step is controlled in the on state when of the second consecutive step during a first fraction of the duration of said second stage and sufficient period that, at the end of this first duration, the second current is greater in absolute value than the maximum absolute value, over all the two successions of the four steps above, the current flowing through one or the other of the inductances connected to the positive terminal of the low voltage source.

The invention further relates, in another of its aspects, to a voltage conversion assembly, comprising:

a reversible DC / DC voltage converter between a high voltage source and a low voltage source, the converter comprising:

a high voltage circuit, comprising in addition to the high voltage source, a first and a second arm, each arm comprising two controllable bidirectional switches separated by a midpoint, each bidirectional controllable switch being connected in parallel with a capacitor, and a primary winding of transformer traversed by a first current, connected at one end to the midpoint of the first arm and at its other end to the midpoint of the second arm,

a low voltage circuit comprising, in addition to the low voltage source, an arm comprising two controllable bidirectional switches and a transformer secondary winding connected in parallel with said arm and traversed by a second current,

a device for controlling the electronic switches of the voltage converter, said device being configured to implement the method as defined above.

The low voltage source has for example a nominal voltage of between 12 and 16 V. The high voltage source has for example a nominal voltage of between 220 V and 450 V.

The voltage converter can be part of an electrical circuit embedded on a vehicle, for example a hybrid or electric propulsion vehicle.

In all of the above, the bidirectional controllable switches may comprise a transistor. When it is a bipolar transistor or IGBT type, a diode can be mounted in antiparallel of the transistor to ensure the reversibility of the switch. When it comes to a field effect transistor, the reversibility can be ensured by the parasitic diode intrinsic to this transistor.

A capacitor may be connected in parallel with the high voltage source and an auxiliary power source may be provided for charging the capacitor prior to implementing the method for charging the high voltage source from the low voltage source using of the converter. All bidirectional controllable switches of the high voltage circuit may be identical.

All bidirectional controllable switches of the low voltage circuit can be identical.

Preferably, no capacitor is connected in parallel with each controllable bidirectional switch of the low voltage circuit.

The invention will be better understood on reading the following description of a nonlimiting example of implementation thereof and on examining the appended drawing in which:

FIG. 1 schematically represents an example of a DC / DC voltage converter according to the invention,

FIGS. 2 and 3 show a similar model to the converter of FIG. 1 and FIG. 4 represents various curves associated with the model of FIGS. 2 and 3, FIG. 5 schematically represents an example of a control device of the bidirectional controllable switches of the converter. of Figure 1, Figure 6 shows the state of the controls applied to the switches

two-way controllable converter,

FIGS. 7 to 13 represent several successive states of the converter of FIG. 1 during an operating cycle for transferring electrical energy from the low voltage source to the high voltage source,

FIG. 14 represents the evolution of electrical quantities of the converter during the operating cycle described with reference to FIGS. 7 to 13, and

FIG. 15 shows the evolution of the current in the two switches

bidirectional low voltage circuit during the operating cycle described with reference to Figures 7 to 13.

FIG. 1 shows a reversible DC / DC converter 1. The converter 1 is for example part of an electrical circuit embedded on a vehicle with hybrid or electric propulsion.

This voltage converter 1 allows either to transfer electrical energy from a high voltage source 100 to a low voltage source 101 or vice versa. In what follows, we will describe a method of controlling this converter 1 in order to transfer electrical energy from the low voltage source 101 to the high voltage source 100. The source high voltage 100 is in the example described the source of electrical energy supplying the electric motor of the vehicle and the low voltage source 101 is in the example described the source of electrical energy supplying the on-board network of the vehicle.

As shown in FIG. 1, the voltage converter 1 comprises a high voltage circuit 2 and a low voltage circuit 3.

The high voltage source 100 is here represented by a capacitor with its load resistor in parallel.

The high voltage circuit 2 comprises, in addition to the high voltage source 100, a first arm 5 and a second arm 6. Each arm comprises two bidirectional switches

controllable 10 and 11 separated by a midpoint 12. Each controllable bidirectional switch 10 or 11 comprises in this example in parallel transistor 14, a diode 15 in antiparallel. A capacitor 16 is connected in parallel with each transistor 14. Depending on the nature of the transistor 14, the diode 15 is a component as such or the parasitic diode intrinsic to the transistor. The bidirectional controllable switch 10 is connected to the positive terminal of the high voltage source 100 and will be called hereinafter "bidirectional switch controllable at the top" for the high voltage circuit while the bidirectional controllable switch 11 is connected to the negative terminal of the high voltage source 100 and will be called thereafter "bidirectional switch controllable at the bottom" for the high voltage circuit. The transistors 14 of the high voltage circuit 2 are numbered K1 to K4, as can be seen in FIG.

According to this numbering:

Kl denotes the transistor 14 of the cell 10 at the top of the first arm 5,

K2 denotes the transistor 14 of the cell 11 at the bottom of the first arm 5,

K3 denotes the transistor 14 of the cell 10 at the top of the second arm 6,

K4 denotes the transistor 14 of the cell 11 at the bottom of the second arm 6.

The high voltage circuit 2 further comprises a primary winding of transformer 18 traversed by a first current 11, connected at one end to the midpoint 12 of the first arm 5 via a switching inductance 19 of value 1 _R and at its other end to the midpoint. 12 of the second arm 6.

The low voltage circuit 3 comprises, in the example under consideration, in addition to the low voltage source 101: an arm 20 comprising two controllable bidirectional switches 21 and 22 between which is disposed a midpoint 23, each switch 21 or 22 comprising a transistor 24 in antiparallel of which is mounted a diode 25, parasite or not, and

a secondary transformer winding 27 connected in parallel with said arm 20 and traversed by a second current i2.

In the example considered, the controllable bidirectional switch 21 is connected indirectly to the positive terminal of the low voltage source 101 and directly to the negative terminal of the low voltage source 101 and will be called thereafter "bidirectional switch controllable at the top For the low voltage circuit while the controllable bidirectional switch 22 will be called "bidirectional switch controllable bottom" for the low voltage circuit. In this example, the low voltage circuit 3 further comprises two inductors 30 and 31, of common value L. The first inductor 30 is connected on the one hand to the positive terminal of the low voltage source 101 and on the other hand to one end the bidirectional controllable switch 21 opposite the midpoint 23 and at one end of the secondary transformer winding 27. The second inductor 31 is connected on the one hand to the positive terminal of the low voltage source 101 and secondly at one end of the controllable bidirectional switch 22 opposite the midpoint 23 and at the other end of the transformer secondary winding 27.

Still in the example described, the negative terminal of the low voltage source 101 is connected to the midpoint 23 of the arm 20.

The transistors 24 of the low voltage circuit 3 are numbered K5 and K6, as shown in FIG. 1, K5 being the transistor of the cell 21 while K6 is the transistor of the cell 22.

In the example described, all the transistors K1 to K6 are field effect transistors, so that the diodes shown in the figures are parasitic diodes intrinsic to these transistors.

In what follows, it will be considered that the transistors 14 and 24, the diodes 15 and 25, the transformer formed by the windings 18 and 27, the inductors 30 and 31 and the capacitors 16 are ideal.

A problem which the invention seeks to solve will be described with reference to FIGS. 2 to 4. Figures 2 and 3 show a similar circuit to the converter 1 of Figure 1 and brought back to the secondary of the transformer. The inductance L _f corresponds to the equivalent series inductance of the transformer, the switch K represents one of the transistor K5 and the transistor K6 of the low voltage circuit 3 and the inductance L represents one of the inductor 30 and inductance 31.

During a time interval between 0 and aT, the switch K is on and the high-voltage circuit and the low-voltage circuit operate in freewheel mode. The current λ Lf in the inductance Lf takes a value I ₀ imposed by the high voltage circuit and such that the current i _K in the electronic switch K is positive. During this time interval, energy is accumulated in the inductance L across which the voltage Vs of the low voltage source is applied.

At the instant aT, the switch K is no longer on and a voltage mE is imposed by the high voltage circuit. The current i _K in the electronic switch K will then cancel, so that the current i _Lf increases abruptly from I ₀ to its maximum value I _Lm ax as shown in FIG. 4. A significant surge then appears terminals of the switch K, as can also be seen in Figure 4.

The invention is based on the observation that, if between 0 and aT the current flowing through the inductance L _f is large enough for the current i _{K to} be negative, at the instant when the switch K is no longer conducting, the current i _K can continue to flow through the diode anti-parallel of the switch K. The current i _K can then decrease, passing through this diode, to cancel, allowing a smooth switching . The method according to the invention consists in controlling the transistors K1 to K6 of the different bidirectional controllable switches of the voltage converter 1 so as to ensure smooth switching in the bidirectional controllable switches of the low voltage circuit.

A functional example of a control circuit 40 making it possible to control the converter 1 to transfer electrical energy from the low voltage source 101 to the high voltage source 100 is shown schematically in FIG. 5 and the control applied to the transistors K1. to K6 of the converter 1 is shown in FIG. 6. Conventionally, the commands are shown schematically in the form of rectangles whose high (or non-zero) state corresponds to an on-state control of a transistor 14 and whose low (or zero) state corresponds to a blocked state control of this transistor 14. The control circuit 40 implements a comparator 41, a component 42 inducing a shift of one half control period, flip-flops 43 and 44 as well as pulse generators 45 and 46. The controls applied to the transistors K1 to K6 are represented in FIG. 5 by the name of the transistor in question disposed at the output of one of the components 41 to 46.

An example of a method of controlling transistors K1 to K6 of voltage converter 1 of FIG. 1 will be described with reference to FIGS. 6 to 14 to avoid the problem described with reference to FIGS. 2 to 4.

The converter 1 transfers electrical energy from the low voltage source 101 to the high voltage source 100 in a cyclic manner and each operating cycle comprises in the example described four successive steps, designated respectively by 200, 201, 202 and 203 on Figure 14, followed by a repetition of four successive steps and similar to the previous four steps, as explained below.

At time t = 0, the converter 1 is as shown in FIG. 7. The flow of current through the controllable bidirectional switch 21 at the top of the arm 20 of the low voltage circuit 3 has just been interrupted.

On the whole of the voltage converter 1, only the transistor K6 of the controllable bidirectional switch 22 at the bottom of the arm 20 of the low voltage circuit 3 is controlled in the on state during this first step which is between the instants 0 and tl. A transfer of energy from the low voltage source 101 to the high voltage source 100 takes place during this first step in which the current i _s in the low voltage source 101 is divided between a current flowing in the inductor 30 and a current circulating in the inductor 31. The bidirectional controllable switch 21 is not traversed by current, the current in the inductor 30 corresponds to the second current i2 in the secondary winding 27 of the transformer.

The first current flowing in the transformer primary winding 18 is during this first positive step and it flows through the bidirectional switch.

controllable 10 at the top of the first arm 5 through the diode 15 to charge the high voltage source 100 before looping back to the primary transformer winding 18 via the diode 15 of the controllable bidirectional switch 11 at the bottom of the second arm 6. As mentioned above, during this first step, none of the transistors K1 to K4 of the high-voltage circuit is on and the transistor K5 of the low-voltage circuit 3 is also not on.

At the end of this first step, that is to say at time tl, the first current remains positive, although having decreased linearly and the voltage vl across the primary winding 18 of transformer is equal to the average value E of the voltage across the high voltage source.

The second step will now be described with reference to FIGS. 8 to 11. This second step comprises several successive phases, as will be seen. The second step is initiated by the on-state control of the transistor K5 of the controllable bidirectional switch 21 at the top of the low-voltage circuit 3. In the example considered, the transistors K1 and K4 are controlled in the on state as soon as possible. the beginning of the second stage.

During the entire duration of the second step, the transistors K5 and K6 of the low-voltage circuit 3 are controlled bypassers, as can be seen in FIG. 6, so that the secondary transformer winding 27 is short-circuited during this second step.

During a first phase shown in FIG. 8 and between times t1 and t2, the path of the current in the high voltage circuit 2 is not modified, the latter always flowing in the bidirectional controllable switch 10 at the top of the first arm 5, in the high voltage source 100, and in the bidirectional controllable switch 11 at the bottom of the second arm 6.In the low voltage circuit 3, the current flowing through the inductor 30 is no longer equal to the second current i2 in the second transformer winding 27, since part of the current flowing in the inductor 30 loops back into the low voltage source 101 through the transistor K5 which is now in the on state.

As can be seen in Figure 14, the first current decreases sharply during this phase and changes sign, becoming negative. At the end of this phase, which corresponds to the expiration of the duration ION, calculated from t1 and then called "first duration", during which the transistor K1 is maintained in the on state, the absolute value of the first current it is greater than mid _Lmax , which is highlighted in Figure 14 using the hatched area. The value λLmax corresponds to the maximum current value in the inductor 30 or in the inductor 31. In other words, at the end of the first duration t ₀ N, the second current i2 in the transformer secondary winding 27 is greater in absolute value than the maximum current value in either of these inductors 30 or 31.

In the example considered, the first duration ÎON corresponds exactly to the duration during which the transistor K1 is controlled in the on state over the whole of the first and second stages. In a variant not shown, the transistor K1 can be controlled in the on state while the first step is still in progress and the first duration t ₀ N then corresponds to the duration during which the second step occurs and during which the transistor Kl is controlled in the on state.

At the expiration of the duration ÎON, that is to say in the example described at time t2, the converter 1 is in the configuration shown in Figure 9. In this new phase, which extends between at times t2 and t3, the transformer secondary winding 27 is always short-circuited by the bidirectional switches

controllable 21 and 22 of the low voltage circuit 3 in which current flows. Still during this phase, the two bidirectional controllable switches 10 and 11 of the first arm are traversed by current via the capacitor 16. The capacitor 16 in parallel with the bidirectional controllable switch 10 at the top of the first arm 5 carries a current flowing thereafter. in the high voltage source 100 before looping back into the primary transformer winding 18 through the transistor K4. The capacitor 16 in parallel with the controllable bidirectional switch 11 at the bottom of the first arm 5 conveys a looping current in the primary transformer winding 18 through the transistor K4.

As can be seen in Figure 14, during this phase, the first current it decreases again but significantly less than in the previous phase. This phase corresponds to a resonant transition to coasting operation occurring during the next phase and which will be described with reference to FIG.

At the end of the phase described with reference to FIG. 9, a zero-volt switching of the controllable bidirectional switch 10 at the top of the first arm 5 is performed.

The last phase of the second step will now be described with reference to FIG. During this last phase, which extends between the instants t3 and t4, the secondary transformer winding 27 is always short-circuited, since current flows through each controllable bidirectional switch 21 and 22 of the low voltage circuit 3. The current flows in the low voltage circuit 3 in the same manner as described with reference to FIG. 9.

The high voltage circuit 2 operates freewheeling, that is to say that no transfer of electrical energy takes place to the high voltage source 100. In the high voltage circuit 2, the bidirectional switch 10 controllable the top of the first arm 5 is not traversed by current, as the bidirectional switch controllable 10 at the top of the second arm 6. The first current it flows in the bidirectional controllable switches 11 at the bottom of each arm 5 and 6. In the case of the controllable bidirectional switch 11 at the bottom of the first arm 5, the first current it flows in the diode 15 and in the case of the bidirectional controllable switch 11 at the bottom of the second arm 6, the first current flows in the transistor K4 which is controlled in the on state.

As shown in FIG. 14, during this last phase of the second step, the first current remains constant and is minimal. The voltage across the high voltage source 100 is zero.

The second step ends at the instant t4 at which the transistor K6 is no longer controlled in the on state. At the end of this second step, the transistor K4 is no longer controlled in the on state.

The third step, which extends between the instants t4 and t5, will now be described with reference to FIG. 11. During this third step, the transistor K6 of the controllable bidirectional switch 22 of the low voltage circuit 3 is more controlled in the on state but current still flows through the controllable bidirectional switch 22 through the diode 25 of this switch 22. This flow of current in the switch 22 while the transistor K6 is no longer controlled at the passing state is due to the value taken by the first current it at the end of the first duration, that is to say at t2. In the high-voltage circuit 2, only the controllable bidirectional switch 11 at the bottom of the first arm 5 is traversed by current in this first arm 5. In the second arm 6, each bidirectional controllable switch 10 or 11 carries current only through the intermediate capacitor 16 in parallel with the latter. In this third step, the high voltage source is traversed by current.

As can be seen in FIG. 14, during this third step, the first current it increases attenuated, in a form of curve similar to that described with reference to FIG. Figure 9, while remaining negative. Also during this step, the voltage across the high voltage source 100 decreases until the average value -E.

The fourth step, which extends between the instants t5 and T / 2, will now be described with reference to FIG. 12. In this fourth step, the configuration of the low voltage circuit 3 is the same as that described with reference to FIG. Figure 11.

In the high-voltage circuit 2, the configuration is inverted with respect to that described with reference to FIG. 7, that is to say that the first current 11, which is negative, flows from the primary transformer winding 18 to the high-voltage source 100 through the diode 15 of the controllable bidirectional switch 10 at the top of the second arm 6 and loops back to the primary transformer winding 18 via the diode 15 of the controllable bidirectional switch 11 at the bottom of the first arm 5.

As can be seen in FIG. 14, during this fourth step, the first current increases while remaining negative and the voltage across the high voltage source 100 is equal to -E. Still during this fourth step, the current flowing through the controllable bidirectional switch 22 through the diode 25 decreases in absolute value until it cancels out. The bidirectional controllable switch 22 can thus switch smoothly, without an overvoltage is generated at its terminals, contrary to what has been described with reference to Figures 2 to 4. This soft switching is allowed by the value taken by the first current II at time t2, ie at the end of the phase described with reference to FIG. 8. The fourth step ends at the instant T / 2 at which the current has been canceled in the bidirectional controllable switch 22 of the low voltage circuit 3, as can be seen in Figure 15.

During the next operating cycle of the converter 1, a succession of first, second, third and fourth steps similar to those just described occur.

The first step, between the instants T / 2 and tl + T / 2, will be described with reference to FIG. 13. At the instant t = T / 2, only the transistor K5 of the controllable bidirectional switch 21 upper arm of the low voltage circuit 3 is controlled in the on state. In this first step, an electric power transfer from the low voltage source 101 to the high voltage source 100 takes place. During this first step, the current i _s in the low voltage source is divided between a current flowing in the inductor 30 and a current circulating in the inductor 31. The controllable bidirectional switch 22 is not traversed by current, the current in the inductor 31 corresponds to the second current i2 in the secondary winding 27 of the transformer.

The first current flowing in the transformer primary winding 18 is during this first negative step and it flows through the bidirectional switch.

controllable 11 at the bottom of the first arm 5 through the diode 15 to charge the high voltage source 100 before looping back to the primary winding 18 via the diode 15 of

the controllable bidirectional switch 10 at the top of the second arm 6.

It is noted that during this first step, none of the transistors K1 to K4 of the high voltage circuit is conducting and that the transistor K6 of the low voltage circuit 3 is not passing either.

At the end of this first step, that is to say at time tl + T / 2, the first current remains negative, even though it has grown linearly and the voltage v1 at the terminals of the Transformer primary winding 18 is equal to the voltage -E across the high voltage source 100.

The second, third and fourth steps succeeding this first step will not be described because they are easily deduced from the description made with reference to FIGS. 8 to 14 of the second, third and fourth steps of the preceding succession of steps. It will be simply indicated that during this third step, the transistor K5 of the controllable bidirectional switch 21 of the low voltage circuit 3 is no longer controlled in the on state but current is still flowing through the bidirectional controllable switch 21. current flow in the switch 21, while the transistor K5 is no longer controlled in the on state, is due to the value taken by the first current it at the end of the first duration, that is to say say at t2 + t / 2.

By way of example, with as a parameter of the control device 40 of FIG. 6 a voltage V _ref of 0.695 V, a triangular voltage V _tr i varying between 0 and 1 V at a frequency of 100 kHz, with a voltage of a low voltage source of 14 V, with a load resistance of 35 Ω for the high voltage source 100, it is possible to reach 332.5 V as the average voltage value E at the terminals of the high voltage source 100 when the first duration ÎON is for value 0.6 μ $. It is thus possible to transfer to the high voltage source 100 a power of the order of 3 160 W thanks to the voltage converter 1 controlled as explained above.

The invention is not limited to the examples which have just been described.

The expression "comprising a" shall be understood as synonymous with the expression "including at least one" unless the contrary is specified.

Claims

1. Method for controlling a reversible DC/DC voltage converter (1), operating cyclically to transfer electrical energy from a low voltage source (101) to a high voltage source (100), the converter (1) including:

a high voltage circuit (2), comprising in addition to the high voltage source (100):

- a first (5) and a second (6) arm, each arm (5, 6) comprising two controllable bidirectional switches (10, 11) separated by a midpoint (12), each controllable bidirectional switch (10, 11) being mounted in parallel with a capacitor (16), and

- a primary transformer winding (18) carried by a first current (il), connected by one end to the midpoint (12) of the first arm (5) and by its other end to the midpoint (12) of the second arm (6 ),

a low voltage circuit (3), comprising in addition to the low voltage source (101):

- an arm (20) comprising two controllable bidirectional switches (21, 22), and

- a secondary transformer winding (27) mounted in parallel with said arm (20) and carried by a second current (i2),

the operating cycle comprising at least a succession of the following two stages: - a first stage (200) during which the first current (it) circulates in a controllable bidirectional switch (10, 11) of the first arm (5), the source high voltage (100) and a controllable bidirectional switch (10, 11) of the second arm (6),

- a second step (201) during which the controllable bidirectional switches (21, 22) of the arm (20) of the low voltage circuit (3) are both controlled in the on state to short-circuit the transformer secondary winding ( 27),

the first current (il) changing sign during the second step (201) and the controllable bidirectional switch (10, 11) of the first arm (5) traversed by the first current during the first step (200) being controlled to the on state during the second step (201) for a first duration (Î ₀ N) fraction of the duration of the second step (201), the first current (il) having at the end of this first duration (ÎON ) an absolute value allowing that at the end of the second step (201), one of the controllable bidirectional switches (21, 22) of the arm (20) of the low voltage circuit (3), which is then no longer controlled in the on state, remains current flowing through it.

2. Method according to claim 1, in which a switching inductance (1 _R ) is connected in series with the primary transformer winding (18) and in which the first duration (ION) verifies the relation ''ON> mL— where I _s is the average value of the current across the low voltage source (101), m is the ratio of the transformer formed by the primary (18) and secondary (27) windings and where E is the average value of the voltage that which we seek to obtain at the terminals of the high voltage source (100).

3. Method according to claim 1 or 2, in which each operating cycle of the converter (1) for charging the high voltage source (100) by the low voltage source (101) comprises:

- the first step (200) during which the first current (it) flows in P controllable bidirectional switch (10) at the top of the first arm (5), the high voltage source (100) and the controllable bidirectional switch (11) at the bottom of the second arm (6), and the second stage (201) during which the first current (it) becomes negative and the controllable bidirectional switch (10) at the top of the first arm (5) is controlled in the on state during the first duration (Î ₀ N), and

- the first step during which the first current (it) flows in P controllable bidirectional switch (11) at the bottom of the first arm (5), the high voltage source (100) and the controllable bidirectional switch (10) at the top of the second arm (6), and the second stage during which the first current (it) becomes positive and the controllable bidirectional switch (11) at the bottom of the first arm (5) is controlled in the on state during the first duration (ION ).

4. Method according to any one of the preceding claims, the low voltage circuit (3) comprising:

- a first inductor (30) connected on the one hand to the positive terminal of the low voltage source (101) and on the other hand to one end of the secondary transformer winding (27), and

- a second inductance (31) connected on the one hand to said positive terminal of the low voltage source (101) and on the other hand to the other end of the secondary winding of

transformer (27).

5. Method according to any one of the preceding claims, wherein no controllable bidirectional switch (10, 11) of the high voltage circuit (2) is controlled in the on state during the first step (200).

6. Method according to any one of the preceding claims, in which the second step (201) comprises, in particular is constituted by, the following successive phases:

- a phase during which the first current (it) varies suddenly, this phase corresponding to the control in the on state during the first duration (ÎON) of

the controllable bidirectional switch (10) of the first arm (5) carried by the first current (il) during the first immediately preceding step,

- a phase during which the first current (it) varies in an attenuated manner and in the same direction of variation as during the immediately preceding phase, and

- a phase during which the first current (it) is substantially constant.

7. Method according to any one of the preceding claims, in which during the second step (201), the controllable bidirectional switch (10, 11) of the second arm (6) carried by the first current (il) during the first step (200) immediately preceding is controlled in the on state.

8. Method according to any one of the preceding claims, in which one of the controllable electronic switches (21, 22) of the arm (20) of the low voltage circuit (3) does not carry current during the first step ( 200)

9. Method according to claim 8, in which each cycle comprises immediately after each second step (201):

- a third step (202) during which the first current (it) varies in an attenuated manner with a direction of variation opposite to that which it has during the second step (201), and

- a fourth step (203) during which the first current (it) varies suddenly while maintaining the same direction of variation as during the third step (202) and without changing sign, the current in the controllable bidirectional switch (21 , 22) of the low voltage circuit (3) carried by current during the first step (200) and then no longer being controlled in the on state decreasing in absolute value and canceling out at the end of this fourth step ( 203).

10. Method according to claim 6 or 9, in which the attenuated variation of the first current (it) corresponds to the passage of current in the capacitor (16) in parallel with each controllable bidirectional switch (10, 11) of the same arm (5, 6) of the high voltage circuit (2).

11. Voltage conversion assembly, including:

- a reversible DC/DC voltage converter (1) between a high voltage source (100) and a low voltage source (101), the converter (1) comprising:

- a high voltage circuit (2), comprising in addition to the high voltage source (100), a first (5) and a second (6) arm, each arm (5, 6) comprising two separate controllable bidirectional switches (10, 11) by a midpoint (12), a

capacitor (16) being connected in parallel to each controllable bidirectional switch (10, 11), and a primary transformer winding (18) carried by a first current (il), connected by one end to the midpoint (12) of the first arm (5) and by its other end at the midpoint (12) of the second arm (6),

- a low voltage circuit (3), comprising in addition to the low voltage source (101) an arm (20) comprising two controllable bidirectional switches (21, 22), and a secondary transformer winding (27) mounted in parallel with said arm (20) ) and traversed by a second current (i2),

- a control device (40) of the controllable bidirectional switches (10, 11, 21, 22) of the voltage converter (1), said device (40) being configured to implement the method according to any one of the preceding claims .