Electronic device and method for controlling an electrical energy converter including piezoelectric element(s), and associated electronic system for converting electrical energy

Abstract

The present invention relates to an electronic device for controlling an electrical energy converter, which is configured, for a control cycle equal to s+1 resonance periods of the piezoelectric assemblies, s being an integer greater than or equal to zero, to control at least two phases at substantially constant voltage per control half-cycle, a first control half-cycle including a first phase (II) with a substantially constant voltage of a first voltage value and a first duration and a second phase (IV) with a substantially constant voltage of a second voltage value and a second duration, a second control half-cycle including a third phase (VI) with a substantially constant voltage of a value opposite to the first voltage value and a duration substantially equal to the first duration and a fourth phase (VIII) with a substantially constant voltage of a value opposite to the second voltage value and a duration substantially equal to the second duration.

Description

[0001] TITLE: Electronic device and method for controlling an electrical energy converter comprising piezoelectric element(s), associated electronic electrical energy conversion system

[0002] The present invention relates to an electronic device for controlling an electrical energy converter capable of converting an input voltage into at least one output voltage.

[0003] The invention also relates to a method for controlling an electrical energy converter capable of converting an input voltage into at least one output voltage and an associated electronic electrical energy conversion system.

[0004] The invention lies in the field of electronic electrical energy conversion systems, in particular those comprising a piezoelectric element, in particular systems for conversion into a direct electrical voltage, i.e. direct-direct conversion systems, also called DC-DC conversion systems (from the English Direct Current - Direct Current), and alternating-direct conversion systems, also called AC-DC conversion systems (from the English Alternating Current - Direct Current), direct-alternating (DC / AC) or alternating-alternating (AC / AC) conversion systems.

[0005] Documents FR 3 064 850 B1 and FR 3 086 471 B1 describe an electrical energy converter with piezoelectric element(s).

[0006] Document FR 3 130 096 discloses an electronic device for controlling a converter of an input voltage into at least one output voltage, comprising a first bridge comprising two first switching branches, each between two terminals of the input voltage and comprising two first switches connected at a first midpoint; at least one second bridge comprising two second switching branches, each between two terminals of the output voltage and comprising two second switches connected at a second midpoint; at least one pair of first and second piezoelectric assemblies, each connected between respective first and second midpoints, distinct from one piezoelectric assembly to the other.The control device is configured to control, during a respective resonance cycle of the piezoelectric assemblies, a switching of each of the switches to alternate phases at substantially constant voltage across the terminals of the piezoelectric assemblies and phases at substantially constant load across said piezoelectric assemblies. The electronic control device described in this document is configured to, during each phase at substantially constant load, control in the closed position at the same time at most one respective switch among the switches connected directly to the first piezoelectric assembly and at most one respective switch among the switches connected directly to the second piezoelectric assembly, and in the open position all the other switches of the first and second branches.This converter and associated driver device achieve better isolation between input and output, as well as transfer of power from input to output without injecting a common mode component.

[0007] The aim of the invention is then to propose an electronic device for controlling an electrical energy converter offering easier control of the converter and making it possible to obtain better electrical energy transfer performance, while retaining the advantage of the known control device.

[0008] To this end, the subject of the invention is an electronic device for controlling an electrical energy converter capable of converting an input voltage into at least one output voltage, the converter comprising a first switching bridge comprising two first switching branches, each first switching branch being connected to an input voltage source and comprising at least two first switches connected in series and connected together at a first midpoint; at least one second switching bridge comprising two second switching branches, each second switching branch being connected between two terminals for supplying an output voltage and comprising at least two second switches connected in series and connected together at a second midpoint;at least one pair of first and second piezoelectric assemblies, each piezoelectric assembly comprising at least one piezoelectric element and being connected between respective first and second midpoints, the midpoints between which the piezoelectric assemblies are connected being distinct from one piezoelectric assembly to the other, this electronic control device being configured to control, during a resonance period of the piezoelectric assemblies, a switching of each of the switches to alternate phases at substantially constant voltage across the terminals of the piezoelectric assemblies and phases at substantially constant charge across the terminals of said piezoelectric assemblies.;

[0009] This electronic control device is configured to, for a control cycle equal to s+1 resonance periods of the piezoelectric assemblies, s being an integer greater than or equal to zero, control at least two phases at substantially constant voltage per half-control cycle, a first half-control cycle comprising a first phase at substantially constant voltage of first voltage value and first duration and a second phase at substantially constant voltage of second voltage value and second duration, a second half-control cycle comprising a third phase at substantially constant voltage of value opposite to the first voltage value and of duration equal to the first duration at plus or minus 10%, preferably at plus or minus 5% and a fourth phase at substantially constant voltage of value opposite to the second voltage value and of duration equal to the second duration at plus or minus 10%, preferably at plus or minus 5%.

[0010] Advantageously, a balancing of the electrical energy transfers per half-cycle of control is obtained, which makes it possible to reduce the amplitude of energy oscillation within the piezoelectric assemblies, and consequently to improve the electrical energy transfer performance of the converter.

[0011] According to other advantageous aspects of the invention, the electronic device for controlling an electrical energy converter comprises one or more of the following characteristics, taken in isolation or in all technically possible combinations.

[0012] This device is configured to control in the closed position a pair of first switches comprising one of the first switches connected directly to the first piezoelectric assembly and one of the first switches connected directly to the second piezoelectric assembly during said first duration, and to control in the closed position another pair of first switches comprising another of the first switches connected directly to the first piezoelectric assembly and another of the first switches connected directly to the second piezoelectric assembly during said second duration.

[0013] This device is configured to control in the closed position a pair of second switches comprising one of the second switches connected directly to the first piezoelectric assembly and one of the second switches connected directly to the second piezoelectric assembly during said first duration, and to control in the closed position another pair of first switches comprising another of the second switches connected directly to the first piezoelectric assembly and another of the second switches connected directly to the second piezoelectric assembly during said second duration.When the number s+1 is an even positive number greater than or equal to 2, the electronic control device is configured to control in the closed position one pair of said pairs of first switches during (s+1) / 2 resonance periods of the first half-control cycle, and to control in the closed position the other pair of said pairs of first switches during (s+1) / 2 resonance periods of the second half-control cycle.

[0014] One of the voltage values ​​among the first voltage value and the second voltage value is equal to the difference (Vi n -V ou t) or opposite to the difference (-Vi n +V ou t) between the input voltage (Vj n ) and the output voltage (V ou t), and the other voltage value among the first voltage value and the second voltage value is equal to the sum (Vin+Vout) or the opposite of the sum (-Vi n -V out) of the input voltage (Vj n ) and the output voltage (V ou t).

[0015] This device is configured to control sequences of phases at substantially constant voltage and at substantially constant load per half-control cycle, the phases of the second half-control cycle being obtained by translation and sign inversion of the phases of the first half-control cycle.

[0016] This device is configured to regulate an output voltage, current or power of the converter by controlling a frequency of the converter control cycle.

[0017] This device is configured to regulate a dead time duration during which the first switches of each pair of first switches are open, so as to minimize the voltage across the first switches before closing.

[0018] This device is configured to control, in a voltage step-down configuration in which the input voltage is higher than the output voltage, a switching to the closed position of one of the pairs of switches at a determined switching angle with a tolerance margin.

[0019] The invention also relates to an electronic electrical energy conversion system comprising an electrical energy converter capable of converting an input voltage into at least one output voltage, the converter comprising a first switching bridge comprising two first switching branches, each first switching branch being connected to an input voltage source and comprising at least two first switches connected in series and connected together at a first midpoint; at least one second switching bridge comprising two second switching branches, each second switching branch being connected between two terminals for supplying an output voltage and comprising at least two second switches connected in series and connected together at a second midpoint;at least one pair of first and second piezoelectric assemblies, each piezoelectric assembly comprising at least one piezoelectric element and being connected between respective first and second midpoints, the midpoints between which the piezoelectric assemblies are connected being distinct from one piezoelectric assembly to the other, and an electronic device for controlling said electrical energy converter as described above.;

[0020] According to other advantageous aspects of the invention, the electronic electrical energy conversion system comprises one or more of the following characteristics, taken individually or in all technically possible combinations.

[0021] Each piezoelectric assembly is constituted according to one of the constitutions among the group consisting of: a single piezoelectric element; several piezoelectric elements connected in series; several piezoelectric elements connected in parallel; a piezoelectric element and an auxiliary capacitor connected in series; a piezoelectric element and an auxiliary capacitor connected in parallel; and an arrangement of several parallel piezoelectric branches, each branch comprising one or more piezoelectric elements connected in series or an auxiliary capacitor;the auxiliary capacitor preferably having a higher capacity, more preferably at least three times higher, than a reference capacity of the piezoelectric element(s), each piezoelectric element being modeled in the form of a capacitor and a resonant branch connected in parallel to the capacitor, the reference capacity being the capacity of said capacitor.;

[0022] Each of the first and second switches consists of a transistor, or a diode, or a transistor and a diode in antiparallel.

[0023] All first switches have the same operating characteristics, and all second switches have the same operating characteristics.

[0024] The electronic electrical energy conversion system is a system for converting direct current electrical energy, such as a direct current conversion system or an alternating current conversion system.

[0025] The invention also relates to a method for controlling an electrical energy converter capable of converting an input voltage into at least one output voltage, the converter comprising a first switching bridge comprising two first switching branches, each first switching branch being connected to an input voltage source and comprising at least two first switches connected in series and connected together at a first midpoint; at least one second switching bridge comprising two second switching branches, each second switching branch being connected between two terminals for supplying an output voltage and comprising at least two second switches connected in series and connected together at a second midpoint; at least one pair of first and second piezoelectric assemblies,each piezoelectric assembly comprising at least one piezoelectric element and being connected between respective first and second midpoints, the midpoints between which the piezoelectric assemblies are connected being distinct from one piezoelectric assembly to the other, the method being implemented by an electronic control device and comprising the control, during a resonance period of the piezoelectric assemblies, of a switching of each of the switches to alternate phases at substantially constant voltage at the terminals of the piezoelectric assemblies and phases at substantially constant charge at the terminals of said piezoelectric assemblies, comprising, for a control cycle equal to s+1 resonance periods of the piezoelectric assemblies, s being an integer greater than or equal to zero, the control of at least two phases at substantially constant voltage per half-control cycle,a first control half-cycle comprising a first phase at substantially constant voltage of first voltage value and first duration and a second phase at substantially constant voltage of second voltage value and second duration, a second control half-cycle comprising a third phase at substantially constant voltage of value opposite to the first voltage value and of duration equal to the first duration at plus or minus 10%, preferably at plus or minus 5% and a fourth phase at substantially constant voltage of value opposite to the second voltage value and of duration equal to the second duration at plus or minus 10%, preferably at plus or minus 5%.,

[0026] According to another advantageous aspect of the invention, the method for controlling an electrical energy converter comprises a determination, for each half-control cycle, of a switching angle in the closed position of the switches of a pair of first switches comprising one of the first switches connected directly to the first piezoelectric assembly and one of the first switches connected directly to the second piezoelectric assembly.

[0027] According to another advantageous aspect of the invention, when at least one output voltage is lower than the input voltage, the determination of a switching angle is carried out with a tolerance margin, following a dead time duration during which the first switches of each pair of first switches are open, the method comprises an estimation of said tolerance margin as a function of a frequency of the control cycle, of the input voltage and of the output voltage. The invention will appear more clearly on reading the description which follows, given solely by way of non-limiting example, and made with reference to the drawings in which:

[0028] - figure 1 is a schematic representation of an electronic electrical energy conversion system according to a first embodiment of the invention;

[0029] - Figure 2 is a schematic representation of an electrical energy converter of an electronic energy system according to a second embodiment;

[0030] - figure 3 is a representation of the curves of the evolution of the voltage at the terminals of the piezoelectric assemblies of the electrical energy converter in a voltage step-down type configuration and in a voltage step-up type configuration;

[0031] - Figure 4 is a representation of the voltage evolution curves and the control diagrams of pairs of switches in a voltage step-down type configuration;

[0032] - Figure 5 is a representation of the voltage evolution curves and the control diagrams of pairs of switches in a voltage booster type configuration;

[0033] - Figure 6 is a representation of the voltage evolution curves and the control diagrams of pairs of switches in a voltage step-down type configuration over a control cycle comprising several resonance periods of the piezoelectric assemblies;

[0034] - figure 7 is a representation of control diagrams of pairs of switches implemented by the control method;

[0035] - figure 8 is an example of a first variant of converter architecture with which the invention applies;

[0036] - figure 9 is an example of a second variant of converter architecture with which the invention applies;

[0037] - Figure 10 is a third example of converter architecture with which the invention applies.

[0038] The expression "substantially equal to" defines a relationship of equality to plus or minus 10%, preferably plus or minus 5%, unless otherwise indicated.

[0039] In Figure 1, an electronic electrical energy conversion system 5 comprises an electrical energy converter 10 comprising a pair of first 12A and second 12B piezoelectric assemblies, each piezoelectric assembly 12A, 12B comprising at least one piezoelectric element 15, the converter 10 comprising several switches Ki, K2, K3, K4, K5, Ke, K7, Ks capable of being controlled to alternate phases at substantially constant voltage across the piezoelectric assemblies 12A, 12B and phases at substantially constant charge across the piezoelectric assemblies 12A, 12B.

[0040] The electronic electrical energy conversion system 5 also comprises an electronic device 20 for controlling the electrical energy converter 10.

[0041] The electronic electrical energy conversion system 5 is typically a system for converting electrical energy under a first potential difference to electrical energy under a second potential difference, the first potential difference being, for example, direct or alternating and the second potential difference being, for example, direct or alternating.

[0042] The electronic electrical energy conversion system 5 is for example a system for converting into a direct voltage, a current or a direct electrical power, such as a direct-direct conversion system capable of converting a first direct electrical voltage received at the input into a second direct voltage / current / electric power delivered at the output, or even an alternating-direct conversion system capable of converting an alternating electrical voltage received at the input into a direct voltage / current / electric power delivered at the output of the conversion system 5.

[0043] As another example variant, the electronic electrical energy conversion system 5 is a system for converting into an alternating voltage, current or electrical power, such as a direct-to-alternating conversion system capable of converting a first direct electrical voltage received at the input into a second alternating voltage / current / electric power delivered at the output, or even an alternating-to-alternating conversion system capable of converting an alternating electrical voltage received at the input into an alternating voltage / current / electric power delivered at the output of the conversion system 5.

[0044] In the case of alternating or variable voltage at the input and / or output of the converter, the frequency of the control cycle of the converter must be at least 20 times greater, advantageously at least 100 times greater than the frequency of this alternating voltage or of the maximum frequency component of this variable voltage, so that over a control period the input / output voltages change little.

[0045] When the electrical energy conversion system 5 is an AC-DC conversion system, the electrical energy conversion system 5 preferably further comprises a voltage rectifier, not shown, connected to the input of the electrical energy converter 10 and capable of rectifying the AC electrical voltage received at the input of the conversion system 5 to deliver a rectified electrical voltage at the input of the converter 10, the electrical energy converter 10 preferably being a DC-DC converter capable of converting a DC electrical voltage into another DC electrical voltage. The voltage rectifier is for example a rectifier bridge, such as a diode bridge. Alternatively, the voltage rectifier is formed in whole or in part by switches of the converter 10.

[0046] Those skilled in the art will observe that these different examples for the conversion system 5, whether it is a DC-DC conversion system or an AC-DC, DC-AC, AC-AC conversion system, are also presented in the documents FR 3 086 471 A1 and FR 3 086 472 A1, in particular with regard to their figures 1 and 2.

[0047] The electrical energy converter 10 is preferably a DC-DC converter, and is also called a DC-DC converter. The DC-DC converter generally has the role of regulating a supply voltage of a load 22 to a stable value, by being supplied by an input voltage source 24 providing a voltage Vj n substantially continuous. The input voltage source 24 is for example a battery or a solar panel.

[0048] The electrical energy converter 10 is then configured to raise the value of the DC voltage between its input and its output, and is then also called a DC-DC step-up converter; or is configured to lower the value of the DC voltage between its input and its output, and is then called a DC-DC step-down converter.

[0049] The electrical energy converter 10 is configured to deliver N distinct output voltage(s), from E distinct input voltage(s), E and N each being an integer greater than or equal to 1.

[0050] In the example of Figure 1, the electrical energy converter 10 is configured to deliver an output voltage, denoted V ou t, from an input voltage, noted Vin, the number E of input voltage(s) and the number N of output voltage(s) then each being equal to 1.

[0051] In the example of Figure 2, the electrical energy converter 10 is configured to deliver several distinct output voltages, denoted V outj where j is an integer index between 1 and N, from the input voltage Vin, the number N of distinct output voltages then being greater than 1, N being equal to 2 in this example. According to this example, the converter 10 is typically connected to several loads 22.The electrical energy converter 10 comprises the piezoelectric assemblies 12A, 12B each formed of one or more piezoelectric elements 15, and the control device 20 is configured to operate the piezoelectric material of the piezoelectric elements 15 at their resonance in order to exploit charge transfer phases making it possible to dispense with the use of an inductive element, while regulating the output voltage by maintaining the resonance of the piezoelectric material, that is to say with control cycles repeated at a control cycle frequency depending on the resonance frequency of the piezoelectric elements 15, and by adjusting the durations of respective switching phases within the control cycle.

[0052] In steady state, the piezoelectric assemblies 12A, 12B exchange a charge and a power that is substantially zero over a control cycle, apart from losses.

[0053] In other words, each piezoelectric assembly 12A, 12B gives back, substantially as much as it receives, energy and charge over a control cycle. Two operating conditions then apply to the permanent / steady state, namely the charge balance and the energy balance over a control cycle. Even if during transients (start-up, variation of the values ​​of the voltage steps, change of the output current) this balance is not respected, it must nevertheless be possible to achieve it in steady state.

[0054] As known per se, the mechanical oscillation of the piezoelectric elements 15 is approximately sinusoidal over respective resonance cycles, also called resonance periods. The total mechanical deformation of the piezoelectric elements 15 is the sum of elementary mechanical deformations of each of the piezoelectric elements 15.

[0055] An increase or decrease in the energy stored over a control cycle leads to an increase or decrease in the oscillation amplitude, respectively.

[0056] Furthermore, during a phase with a substantially constant charge at the terminals of the piezoelectric assemblies 12A, 12B, that is to say when the piezoelectric elements 15 are placed in a substantially open electrical circuit, with a low exchange of electrical charges between the piezoelectric elements 15 and the exterior, an increase in the amplitude of the oscillations causes an increase in the speed of variation of the voltage V p at the terminals of the piezoelectric assemblies 12A, 12B, and during a phase at substantially constant voltage (or voltage level) at the terminals of the piezoelectric assemblies 12A, 12B, this increase in oscillation amplitude leads to an increase in a current l pexchanged between the piezoelectric elements 15 and the voltage levels. By substantially constant charge, we mean an exchange of a charge with the outside which is less than 30% of the charge which would have been exchanged with the outside if the voltage had been kept constant. In other words, by substantially constant charge, we mean a variation in charge less than 30% of the charge which would have been exchanged with the outside of the piezoelectric assemblies 12A, 12B if the voltage across the piezoelectric assemblies 12A, 12B had been kept constant over the time period considered.

[0057] By substantially open electrical circuit is meant a circuit in which a possible leakage current leads to a variation in charge of the piezoelectric assemblies 12A, 12B less than 30% of the charge which would have been exchanged with the exterior of the piezoelectric assemblies 12A, 12B if the voltage across the terminals of the piezoelectric assemblies 12A, 12B had been kept constant over the time period considered.

[0058] By substantially constant voltage is meant a voltage variation of less than 20%, preferably less than 10%, of the input or output voltage of the converter 10. For example, if the input voltage of the converter 10 is equal to 100V, then the voltage variation during each phase at substantially constant voltage, i.e. on each step at substantially constant voltage, is less than 20% of this voltage, i.e. less than 20V; preferably less than 10% of this voltage, i.e. less than 10V. Each phase at substantially constant voltage is also called a voltage step.

[0059] The converter 10 then comprises several switches Ki, K2, K3, K4, K5, Ke, K7, Ks visible in FIG. 1, capable of being controlled to alternate phases at substantially constant voltage and phases at substantially constant load at the terminals of the piezoelectric assemblies 12A, 12B, within periods of substantially constant duration corresponding to the frequency of the control cycle of the converter 10, depending on the resonance frequency, also called natural frequency, of the piezoelectric elements 15. The phases at substantially constant load make it possible, in steady state or permanent, to pass from one constant voltage to another and to close the switches which must be closed when the voltage at their terminals is preferably zero in order to have a so-called zero voltage switching, also called ZVS mode switching (from the English Zero Voltage Switching).

[0060] In particular, the converter 10 comprises a first switching bridge 30 comprising two first switching branches 32, each first switching branch 32 being connected between two terminals 34 for applying the input voltage n and comprising at least two first switches 36 connected in series and connected together at a first midpoint 38. Among the two application terminals 34, one has a lower potential, denoted Vj nn , to the other, noted Vj np The first switching bridge 30 preferably consists of the first two switching branches 32.

[0061] In the embodiment of Figure 1, each first switching branch 32 comprises two first switches 36 connected in series and connected at the first midpoint 38. Each first switching branch 32 is preferably made up of the two first switches 36.

[0062] The first two switches 36 are denoted Ks, Ks for one of the first two switching branches 32, and respectively K?, Ks for the other of the first two switching branches 32.

[0063] For the sake of distinguishing between the first switches 36 connected directly to the first piezoelectric assembly 12A and those connected directly to the second piezoelectric assembly 12B, the first switches 36 connected directly to the first piezoelectric assembly 12A are also denoted 36A, and the first switches 36 connected directly to the second piezoelectric assembly 12B are also denoted 36B.

[0064] In the example of Figure 1, the first switches 36A connected directly to the first piezoelectric assembly 12A are also denoted Ks, Ks, and the first switches 36B connected directly to the second piezoelectric assembly 12B are also denoted K?, Ks.

[0065] Similarly, the first midpoint 38 directly connected to the first piezoelectric assembly 12A is also denoted 38A, and the first midpoint 38 directly connected to the second piezoelectric assembly 12B is also denoted 38B.

[0066] The converter 10 comprises a second switching bridge 40 comprising two second switching branches 42, each second switching branch 42 being connected between two terminals 44 for supplying the output voltage V ou t and comprising at least two second switches 46 connected in series and linked together at a second midpoint 48. Among the two supply terminals 44, one has a lower potential, denoted V ou tn, to the other, noted V 0U t P The second switching bridge 40 preferably consists of the two second switching branches 42.

[0067] When the electrical energy converter 10 is configured to deliver several distinct output voltages V ou tj, as in the example of figure 2, it includes, for each output voltage V ou tj respective, a second respective switching bridge 40, each second switching branch 42 being connected between two terminals 44 for supplying the output voltage V ou tj respective. In the example of figure 1, each second switching branch 42 comprises two second switches 46 connected in series and connected at the second midpoint 48. Each second switching branch 42 is preferably made up of the two second switches 46. The two second switches 46 are denoted Ki, K2 for one of the two second switching branches 42, and respectively K3, K4 for the other of the two second switching branches 42.

[0068] For the sake of distinguishing between the second switches 46 connected directly to the first piezoelectric assembly 12A and those connected directly to the second piezoelectric assembly 12B, the second switches 46 connected directly to the first piezoelectric assembly 12A are also denoted 46A, and the second switches 46 connected directly to the second piezoelectric assembly 12B are also denoted 46B.

[0069] In the example of Figure 1, the second switches 46A connected directly to the first piezoelectric assembly 12A are also denoted Ki, K2, and the second switches 46B connected directly to the second piezoelectric assembly 12B are also denoted K3, K4.

[0070] Similarly, the second midpoint 48 directly connected to the first piezoelectric assembly 12A is also denoted 48A, and the second midpoint 48 directly connected to the second piezoelectric assembly 12B is also denoted 48B.

[0071] The converter 10 comprises one or more pairs of first 12A and second 12B piezoelectric assemblies, each piezoelectric assembly 12A.12B comprising at least one piezoelectric element 15 and being connected between respective first 38 and second 48 midpoints, the midpoints 38, 48 between which the piezoelectric assemblies 12A.12B are connected being distinct from one piezoelectric assembly 12A to the other 12B.

[0072] In the example of Figure 1, the converter 10 comprises a single pair of first 12A and second 12B piezoelectric assemblies.

[0073] When the electrical energy converter 10 is configured to deliver several distinct output voltages V ou tj, it includes, for each output voltage V ou tj respective, a respective pair of first 12A and second 12B piezoelectric assemblies.

[0074] In the example of Figure 2, the electrical energy converter 10 is configured to deliver two separate output voltages, and then comprises two pairs of first 12A and second 12B piezoelectric assemblies.

[0075] According to this example, the converter 10 then comprises two second switching bridges 40, the one associated with the first output voltage V ou t_i being noted 40_1 and that associated with the second output voltage V ou t_2 being noted 40_2. Each second switching branch 42 being connected between two terminals 44 supplying the output voltage V ou t_i, Vout_2 respectively. In this example, the lower potentials of the output voltages V ou t_i, V O ut_2 are respectively noted V ou tni, V ou tn2, and the higher potentials of the output voltages V ou t_i, Vout_2 are respectively denoted V 0U t P i, V O ut P2. In this example again, the second switches 46 are denoted Ku, K2,I, Ks,i, K4,I for the second switching bridge 40_1 associated with the first output voltage V ou t_i, and the second switches 46 are denoted KI,2, K22, Ka,2, K 41 2 for the second switching bridge 40_2 associated with the second output voltage V ou t_2.

[0076] Each switch of the converter 10, namely each of the first 36 and second 46 switches, is preferably a bidirectional current and unidirectional voltage switch. The switch 36, 46 comprises, for example, a transistor, or a diode, or a transistor and a diode in antiparallel, not shown. The switch 36, 46 is preferably made up of the transistor, or the diode, or the transistor and the diode in antiparallel or a transistor having the behavior of a diode in reverse current. Alternatively, the switch 36, 46 comprises a combination of several transistors, and is preferably made up of such a combination of several transistors. As a further variant, the switch 36, 46 comprises a mechanical switch, such as a MEMS (MicroElectroMechanical System) microswitch.

[0077] The transistor is, for example, an insulated gate field effect transistor, also called a MOSFET (from the English Metal Oxide Semiconductor Field Effect Transistor). Alternatively, the transistor is a bipolar transistor; an insulated gate bipolar transistor, also called an IGBT (from the English Insulated Gate Bipolar Transistor); a silicon (Si)-based transistor, a GaN (from the English Gallium Nitride)-based transistor; a silicon carbide (SiC)-based transistor, or a diamond-based transistor, or a thyristor.

[0078] Each piezoelectric assembly 12A, 12B is constituted according to one of the constitutions among the group consisting of: a single piezoelectric element 15; several piezoelectric elements 15 connected in series; several piezoelectric elements 15 connected in parallel; a piezoelectric element 15 and an auxiliary capacitor, not shown, connected in series; a piezoelectric element 15 and an auxiliary capacitor connected in parallel; and an arrangement of several parallel branches, each branch comprising one or more piezoelectric elements 15 connected in series or an auxiliary capacitor. The auxiliary capacitor is typically of greater capacity, preferably at least three times greater, than a reference capacity Co, described below, of the piezoelectric element(s) 15.

[0079] As an optional addition, the first 12A and second 12B piezoelectric assemblies share a common piezoelectric material, while having the electrodes of the first 12A assembly distinct from those of the second 12B assembly.

[0080] According to this optional addition, the electrode pairs of the first set 12A, and respectively those of the second set 12B, cover distinct material surfaces. Furthermore, the electrodes of the first set 12A cannot in this case directly induce a significant electric field in the part of the piezoelectric material belonging to the second set 12B.

[0081] According to this optional addition, the capacitance between any one of the electrodes of the first set 12A and any one of the electrodes of the second set 12B is negligible (at least 10 times lower) compared to a reference capacitance Co, described below, of each of the sets 12A, 12B, for example by not being directly opposite each other on either side of the material. This sharing of the same material makes it possible, for example, to facilitate the implementation of the first 12A and second 12B piezoelectric sets (limiting the number of part(s), sharing the fixing means); and also to synchronize the vibration of the two sets 12A, 12B, without however there being a significant transfer of energy from one set to the other (<1 / 10 ème of the output power).

[0082] A modeling of a piezoelectric element 15 in the form of an electrical circuit is illustrated in bubble 60 in Figure 1.

[0083] The piezoelectric element 15 is known per se, and is typically modeled, close to the resonance mode used, in the form of a capacitor 52 and a resonant branch 54 connected in parallel with the capacitor 52, the capacitor 52 and the resonant branch 54 being connected between a first electrode 56 and a second electrode 58 of the piezoelectric element 15. The resonant branch 54 is typically an RLC branch formed of a capacitor 62, a resistor 64 and an inductor 66 connected in series. The capacitance of the capacitor 52 connected in parallel with the resonant branch 54 is called parallel capacitance, or blocked capacitance, or reference capacitance, and denoted Co. The voltage across the terminals of the piezoelectric element 15 then typically corresponds to the voltage across the terminals of the capacitor 52. A current l, substantially sinusoidal, flows in the resonant branch of the equivalent model of the piezoelectric element.In the present description, a so-called total piezoelectric voltage V. p is by convention the sum of each of the voltages across the terminals of the first 12A, and respectively second 12B, piezoelectric assemblies. In particular, the voltage across the terminals of the first piezoelectric assembly 12A is denoted V p i, and that at the terminals of the second piezoelectric assembly 12B is noted V P 2. The total piezoelectric voltage V p is then equal to the sum of these voltages V pi and V P 2, or V p i+V P 2.

[0084] The two piezoelectric assemblies 12A, 12B, and the piezoelectric elements 15 constituting them, are preferably identical, and have substantially the same voltage at their terminals apart from a possible offset voltage Votrset, so that the voltages V pi and V P 2 are equal to V p / 2+ / -V O ff S and, according to the following equations:

[0085] [Math 1]

[0086] Vp pi H- Vp2

[0087] [Math 2]

[0088] The Votrset voltage is a substantially constant component over the scale of a resonance period and has little impact on the charge or energy balance over a resonance period.

[0089] This voltage Votfset evolves slowly with respect to the frequency of the control cycle, its ripple is typically at a frequency at least 10 times lower, advantageously at least 100 times lower than the frequency of the control cycle of the piezoelectric assemblies 12A, 12B. Furthermore, when the voltages V p i+V P 2, this offset voltage Votfset disappears, and we obtain the total piezoelectric voltage V p , as described in the different cycles. In practice, this offset voltage Votfset does not impact the control law, and allows potentials Vj nn and V outn completely independent at low frequency.

[0090] Furthermore, in the present description and as shown in Figure 1 the voltage between the first midpoints 38 is denoted V pa , and is by convention equal to the potential difference (V pai - V pa 2), where V pai is the potential of the first midpoint 38 connected to the first piezoelectric assembly 12A, and V pa 2 is the potential of the other first midpoint 38 connected to the second piezoelectric assembly 12B. The voltage between the second midpoints 48 is denoted V P b, and is by convention equal to the potential difference (V P b2 - V pb i), where V P bi is the potential of the second midpoint 48 connected to the first piezoelectric assembly 12A, and V Pb2 is the potential of the other second midpoint 48 connected to the second piezoelectric assembly 12B. By convention and as shown in Figure 1, the voltage across the first piezoelectric assembly V pi is equal to the potential difference (V pai - V P bi), and that at the terminals of the second piezoelectric assembly V P 2 is equal to the potential difference (V pb2 - V pa2 ).

[0091] The formulas shown above generalize to the example of Figure 2 in which the electrical energy converter 10 is configured to deliver the first V ou t_i and second V ou t_2 output voltages and then includes two pairs of first 12A and second 12B piezoelectric assemblies.

[0092] The resonance frequency is the frequency at which the piezoelectric element 15 oscillates and consequently its current l , visible in figure 1.

[0093] The conversion cycle is synchronized to a mechanical movement of the piezoelectric element 15, and the operating frequency is then set to the mechanical oscillation frequency. The period of the resulting control cycle then corresponds to a multiple of the operating period of the resonator. In practice, the operating / control frequencies depend on the operating point of the converter 10, the values ​​of the voltage steps and the output current. Depending on the operating point, the mechanical oscillation frequency of the resonator (i.e. operating) typically varies between the so-called series resonance frequency of the piezoelectric element 15 where L r etc r correspond to the inductance and capacitance of the resonant branch 54 and the so-called parallel resonance frequency of the piezoelectric element 15 (œ p =1A / (L r .C r.Co / (Cr+Co))), also respectively called resonance frequency and antiresonance frequency of the piezoelectric element 15. The operating frequency of the converter 10 is then between these two resonance and antiresonance frequencies of the piezoelectric element 15. The operating point varies slowly with respect to the oscillation frequency of the piezoelectric element 15. The operating point of the converter (i.e. the input voltage, the output voltage and the output power) typically changes at less than 10kHz, while the oscillation frequency of the piezoelectric element 15 is typically greater than or equal to 100kHz. As a result, the operating point changes little over a mechanical resonance period and the operating frequency of the converter 10 remains substantially constant.

[0094] Advantageously, in one embodiment, for the electrical energy converter 10 with the piezoelectric assemblies 12A, 12B and controlled by the electronic control device 20, the number of phases at substantially constant voltage is equal to four per resonance period, and more particularly the number of phases at substantially constant voltage is equal to two for each half-resonance period, with a particular arrangement, making it possible to obtain total piezoelectric voltage curves V p evolving symmetrically, with voltage values ​​of opposite signs over the respective resonance half-periods, as described in more detail below.

[0095] Each phase at substantially constant voltage can be obtained from a combination of the input and output voltages, in positive or negative value.

[0096] The input and output voltage values ​​are, as shown above, Vin and Vout respectively.

[0097] The four combinations of voltage values, which constitute the voltage values ​​of the voltage steps, are respectively:

[0098] [Math 3]

[0099] Go-Vjn-Vout

[0100] Vb — Vjn+ Vout

[0101] Vc — Vjn+Vout

[0102] Vd — Vjn-Vout

[0103] The voltage values ​​Vj n and V ou t are positive by definition.

[0104] As can easily be seen, V a and Vb have the same absolute value and opposite signs, and V c and V have the same absolute value and opposite signs.

[0105] For the rest of the description, we consider that the current l flowing in the piezoelectric assemblies has the direction indicated by the arrow shown in figure 1, and we associate by construction the voltage level of value V a to the positive alternation of current L and the voltage level of value Vb to the negative alternation of current II.

[0106] The electronic control device 20 is configured to control the electrical energy converter 10, in particular to control the control of the switches 36, 46 of the converter, in order to alternate phases at substantially constant voltage at the terminals of the piezoelectric assemblies 12A, 12B and phases at substantially constant charge, that is to say in substantially open circuit, at the terminals of said piezoelectric assemblies 12A, 12B.

[0107] The electronic control device 20 is for example produced in the form of an electronic circuit comprising one or more electronic components.

[0108] Alternatively, the electronic control device 20 is produced in the form of a programmable logic component, such as an FPGA (Field Programmable Gate Array), or in the form of an integrated circuit, such as an ASIC (Application Specific Integrated Circuit) or even in the form of a computer, such as a microcontroller, a processor.

[0109] According to the invention, the electronic control device 20 is configured to control the switches 36A, 46A connected directly to the first piezoelectric assembly and the switches 36B, 46B connected directly to the second piezoelectric assembly so that, for a control cycle of s+1 mechanical resonance periods (or operating periods) of the piezoelectric assemblies, s being an integer greater than or equal to zero, comprises:

[0110] - a first control half-cycle comprising a first phase at substantially constant voltage of first voltage value Vi and first duration d1 and a second phase at substantially constant voltage of second voltage value V2 and second duration d2;

[0111] - a second control half-cycle comprising a third phase at substantially constant voltage of value V3 opposite to the first voltage value (ie V3 = -14) and of duration d3 substantially equal to the first duration d1 and a fourth phase at substantially constant voltage of value V4 opposite to the second voltage value (ie 1 = -V2) et of duration d4 substantially equal to the second duration d2.

[0112] Substantially equal durations are understood to mean durations which have a duration difference of less than 5% of the period, advantageously 1% of the period.

[0113] The electronic control device 20 is configured in particular to control the closing and / or opening of at least one pair of switches comprising one of the first switches 36A connected directly to the first piezoelectric assembly and one of the first switches 36B connected directly to the second piezoelectric assembly.

[0114] Controlling a pair of switches to close or open means that the two switches forming the pair of switches are controlled to close substantially at the same time, or to open substantially at the same time.

[0115] More particularly, in the example of figure 1, closing the pair of switches Ks, K7, with switches K5 and Ks being open, makes it possible to obtain the voltage V P a=+Vin, and closing the pair of switches Ks, Ks, with switches Ks and K7 open, allows the voltage V to be obtained pa = -Vj n .

[0116] Closing the pair of switches Ki, K4, with switches K2 and K3 open, allows the voltage V to be obtained P b=+V O ut, and closing the pair of switches K2, K3, switches K1 and K4 being open, makes it possible to obtain the voltage V P b = -V out. As can be noted, the respective pairs of switches are such that each pair is formed of one of the switches 36A and one of the switches 36B, respectively of one of the switches 46A and one of the switches 46B.

[0117] Furthermore, preferably, during each phase at substantially constant load, at most one respective switch among the switches Ki, K2, K5, KG is in the closed position, and at most one respective switch among the switches K3, K4, K7, Ks is in the closed position, all the other switches of the first and second switching branches 32, 42 being in the open position. Advantageously, this allows better isolation without injecting common mode.

[0118] Figure 3 illustrates graphs of the evolution of the total piezoelectric voltage Vp in voltage step-down (GA graph) and voltage step-up (GE graph) configurations, over a control cycle equal to a resonance period of the piezoelectric assemblies.

[0119] In a first graph illustrating a normalized current (y-axis) as a function of the angle in radians, the current l flowing in the piezoelectric assemblies is represented, the amplitude of the current being normalized to 1. The current l is approximately sinusoidal, and represented over a period from 0 to 2TT, the current i being of a first given polarity, negative in the example, during the first half-period from 0 to TT and of a second given polarity, positive in the example of figure 3, during the second half-period from n to 2TT.

[0120] All other graphs in Figure 3, as well as Figures 4 to 7, include an angular variation expressed in radians on the abscissa.

[0121] The control method implements periodic angular control.

[0122] It should be noted that it is possible, equivalently, to express the mechanical resonance period as equal to a time period between 0 and T or an angular period between 0 and 2TT.

[0123] Thus, there is a mathematical correspondence between temporal duration and angular duration.

[0124] When two distinct phases are said to have the same duration, this means both the same temporal duration and the same angular duration.

[0125] The electronic control device 20 is configured to alternately control voltage levels or phases at substantially constant voltage and phases at substantially constant load, the controls preferably being carried out in angular values ​​t, according to an arrangement of the voltage levels illustrated in an example by the graphs of figure 3. The evolution of the total piezoelectric voltage V p over time in a step-down configuration, in which Vi n >V 0U t, is illustrated in the GA graph.

[0126] In this buck configuration, the control cycle, equal to the operating period (or resonance period) in this example, has two half-cycles.

[0127] The first half-cycle comprises two phases I, III at substantially constant charge and two phases II, IV at substantially constant voltage, defined between respective angles tj.

[0128] In detail, between to and ti, during phase I at substantially constant load, the total piezoelectric voltage V p goes from Vd to Vb.

[0129] During phase II at substantially constant voltage, between ti and t2, the total piezoelectric voltage V p is approximately equal to b=V 0U t- in.

[0130] During phase III at substantially constant load, between t2 and ta, the total piezoelectric voltage value V p evolves between Vb and V c =Wine+V O ut.

[0131] Finally, during phase IV at substantially constant voltage, between angles ta and t4=TT, the total piezoelectric voltage V p is substantially equal to V c .

[0132] The second half-cycle also includes two phases V, VII at substantially constant load and two phases VI, VIII at substantially constant voltage.

[0133] In detail, between t4 and ts, during phase V at substantially constant load, the total piezoelectric voltage V p V pass c to V a .

[0134] During phase VI at substantially constant voltage, between ts and te, the total piezoelectric voltage V p is substantially equal to V a =Vin-V O ut.

[0135] During phase VII at substantially constant load, between te and t?, the total piezoelectric voltage value V p evolves between V a and V = -Vin-V O ut.

[0136] Finally, during phase VIII at substantially constant voltage, between angles t? and t8=2ïT, the total piezoelectric voltage V p is substantially equal to V .

[0137] The respective substantially constant voltage phases II, VI are of substantially the same duration, or in other words t2- » t6- t5, and the respective voltage values ​​are substantially equal in absolute value and of opposite signs.

[0138] Similarly, the respective substantially constant voltage phases IV, VIII are of substantially the same duration, or in other words, t4- t3~ t8- t7 and the respective voltage values ​​are substantially equal in absolute value and of opposite signs.

[0139] Indeed, in view of the formulas [MATH 3], V a =-Vb and V c =-Vd. The evolution of the total piezoelectric voltage V p over time in a voltage-booster configuration, in which Vi n <V 0U t, is illustrated in the GE graph.

[0140] In this elevator-type configuration, the control cycle, equal to the resonance / operating period in this example, has two half-cycles.

[0141] The first half-cycle comprises two phases I', III' at substantially constant voltage and two phases II', IV' at substantially constant load.

[0142] In detail, between to and ti, during phase I' at substantially constant voltage, the total piezoelectric voltage V p is substantially equal to Vd.

[0143] During phase II' at substantially constant load, between ti and t2, the total piezoelectric voltage V p evolves between Vd and Vb=V 0U t-Wine.

[0144] During phase III' at substantially constant voltage, between t2 and ta, the total piezoelectric voltage value V p is approximately equal to Vb

[0145] Finally, during phase IV at substantially constant load, between angles ta and t4=TT, the total piezoelectric voltage V p evolves between Vb. and V c =Wine+V O ut.

[0146] The second half-cycle also includes two phases V', VII' at substantially constant voltage and two phases VI', VIII' at substantially constant load.

[0147] In detail, between t4 and ts, during the phase V' at substantially constant voltage, the total piezoelectric voltage V p is substantially equal to V c .

[0148] During phase VI' at substantially constant load, between ts and te, the total piezoelectric voltage V p evolves between V c and V a =Vin-V O ut.

[0149] During phase VII' at substantially constant voltage, between te and t?, the total piezoelectric voltage value V p is substantially equal to V a .

[0150] Finally, during phase VIII' at substantially constant load, between angles t? and t8=2ïT, the total piezoelectric voltage V p evolves between V a and Vd.

[0151] The respective substantially constant voltage phases I', V' are of substantially the same duration, or in other words, - t0~ t5- t4and the respective voltage values ​​are substantially equal and of opposite signs (respectively Vd and V c ).

[0152] Similarly, the respective substantially constant voltage phases III', VII' are of substantially the same duration, or in other words, t3- t2~ t7- t6 and the respective voltage values ​​are substantially equal and of opposite signs.

[0153] In each of the control configurations of the electrical energy converter 10, of the voltage step-down type or of the voltage step-up type, there is a symmetry in the evolution of the total piezoelectric voltage V pbetween the two half-cycles, the evolution in the second half-cycle being obtained by translation of the evolution in the first half-cycle, with an opposite voltage polarity. In addition, the voltage steps thus arranged per half-cycle of control, and more particularly in the example per half-period of resonance, are such that the respective voltage values ​​of the steps per half-cycle are of opposite polarities.

[0154] Generally, for both types of configurations, one of the voltage values ​​among the first voltage value and the second voltage value of the first half-control cycle is equal to the difference Vi n -V ou t or the opposite of the difference Vout-Vin between the input voltage Vj n and the output voltage V ou t, and the other voltage value among the first voltage value and the second voltage value is equal to the sum Vin+Vout or the opposite of the sum -Vi n -Vou t of the input voltage Vj n and the output voltage (V ou t).

[0155] Thus, the voltage levels thus arranged per half-cycle of control, and more particularly in the example per half-period of resonance, make it possible to achieve energy balancing per half-cycle of control.

[0156] Figure 4 illustrates a control cycle for a step-down configuration. More specifically, Figure 4 illustrates the evolution of the total piezoelectric voltage V p in this voltage-stepping configuration, in which Vi n >V 0U t, in the GA* graph which is of reverse polarity compared to the GA graph of figure 3, as well as the respective evolutions of the voltage V pa between the first midpoints 38 and the voltage V P b between the second midpoints 48 (graph GA*(V pa ,V Pb); and finally the closing or opening states of the respective switches Ks, K? and Ks, Ks.

[0157] By convention, in each control diagram, a high state is representative of the closing of the corresponding switches and a low state (e.g. 0) is representative of the opening of the corresponding switches.

[0158] The control diagram Ci illustrates the closing or opening states of the switches Ks, K? and the control diagram C2 illustrates the closing or opening states of the switches Ks, Ks to obtain the voltage V pa between the first midpoints 38.

[0159] Thus, the switches Ks, K? are controlled in the closed position between t? and ts=2TT, preferably at the angle t?, with a tolerance margin illustrated by a hatched portion in the diagram Ci, and following this closure, the voltage V pa between the first midpoints 38 takes the value +Vj n. The tolerance margin exists for switches Ks, K? having a reverse diode type behavior which conduct naturally in the presence of an opposite current, such as present between t? and ts. The switches Ks, K? are held in the closed position between to and t2, then controlled to open at the angle t2. The switches Ks, K? are held open between t2 and t?. The switches Ks, Ks are controlled substantially in phase opposition with respect to the switches Ks, K? , as illustrated in the control diagram C2. The switches K5, Ks are controlled in the closed position between ts and t4, with a tolerance margin illustrated by a hatched portion in the diagram C2, and following this closure, the voltage V pa between the first midpoints 38 takes the value -Vj n. As before, the tolerance margin exists for switches Ks, Ks having reverse diode type behavior. The switches Ks, Ks are held in the closed position between t4 and ts, then open at angle ts and held open between ts and ts, as well as between to and ts.

[0160] Advantageously, in the step-down configuration, in embodiments in which the switches K1, K2, K3, K4 have an intrinsic reverse diode or an additional diode placed in parallel, their conduction can be done naturally with regard to the sign of the current, and consequently the voltage levels making it possible to obtain the voltage values ​​of V P b between the second midpoints 48 are obtained without explicit control. In other words, in such an advantageous configuration, only the pairs of switches Ks, Ks and Ks, Ks are controlled by the electronic control device 20.

[0161] Alternatively, it is possible to control the switches Ki, K2, K3, K4 to reduce losses. In this case, in the GA* step-down configuration illustrated in Figure 4, it would be appropriate to control the switches K2, K3 in the closed position at angle ti, and held in the closed position between ti and t4, then open between t4 and ts, as well as between to and ti, and to control the switches Ki, K4 in the closed position at angle ts, and held in the closed position between ts and ts, the switches K1, K4 being open between to and ts.

[0162] Figure 5 illustrates a control cycle for a step-up configuration. More specifically, Figure 5 illustrates the evolution of the total piezoelectric voltage V p in this voltage-booster type configuration, in which V 0U t > Vin, in the GE graph, also represented in Figure 3, as well as the respective evolutions of the voltage V pabetween the first midpoints 38 and tension P b between the second midpoints 48 (graph GE( pa , P b); and finally the closing or opening states of the respective switches Ke, K? (diagram Ci), Ks, Ks (diagram C2), KI,K4 (diagram C3) and K2,K3 (diagram C4).

[0163] Diagram Ci illustrates the closing ("high state") or opening ("low state") states of the switches Ks, K? and diagram C2 illustrates the closing ("high state") or opening ("low state") states of the switches Ks, Ks to obtain the voltage V pa between the first midpoints 38. Thus, the switches KG, K? are controlled in the closed position at the angle t4, and maintained in the closed position between t4 and t?, and following this closure, the voltage V pa between the first midpoints 38 takes the value +Vj nThe switches Ke, K? are controlled to open at angle t?, and are kept open between t? and ts, as well as between to and t4.

[0164] The switches Ks, Ks are controlled, as shown in diagram C2, in the closed position at the angle to, then maintained in the closed position between to and ta, and following this closure, the voltage V pa between the first midpoints 38 takes the value -Vj n . Switches Ks, Ks are opened at angle ts, then held open between angle ts and angle ts.

[0165] Diagram C3 illustrates the closing ("high state") or opening ("low state") states of switches K1, K4 and diagram C4 illustrates the closing ("high state") or opening ("low state") states of switches K2, Ks to obtain the voltage V P b between the second midpoints 38.

[0166] Thus, the switches Ki, K4 are controlled in the closed position at the angle t2, and maintained in the closed position between t2 and ts, and following this closure, the voltage V P b between the second midpoints 48 takes the value +V 0U t. The switches Ki, K4 are controlled to open at angle ts, then kept open between ts and ts, as well as between to and t2.

[0167] The switches K2, Ks are controlled, as illustrated in diagram C4, in the closed position at the angle te, then maintained in the closed position between te and ts, and between to and ti, and following this closure, the voltage V P b between the second midpoints 48 takes the value -V ou t. Switches K2, K3 are controlled to open at angle ti, then kept open between angle ti and angle te.

[0168] Thus, in the described voltage booster type configuration, all the second switches 46 are controllable switches, and driven in the closed position as described by the electronic control device.

[0169] Advantageously, over a control cycle, the cumulative closing times on the one hand, and the cumulative opening times on the other hand, of all the second switches, are substantially equal and due to the symmetry (control in phase opposition) they support substantially the same average and effective current. Their dimensioning in terms of current / heating resistance naturally leads to the choice of identical or similar switches. This symmetry advantageously makes it possible to use switches with similar, and preferably identical, operating characteristics which will have substantially the same temperature rise, the same resistance in the on state, the same parallel capacitance, the same switching speed.In both configurations described, whether it is the voltage step-down type configuration described with reference to FIG. 4 or the voltage step-up type configuration described with reference to FIG. 5, the first switches 36 (i.e. the switches Ks, Ke, K?, Ks) are controllable switches, and driven in the closed position as described by the electronic control device.

[0170] Advantageously, over a control cycle, the cumulative closing times on the one hand, and the cumulative opening times on the other hand, of all the first switches 36, are substantially equal, which advantageously makes it possible to use switches with similar, and preferably identical, characteristics.

[0171] In particular, the choice of switches having substantially the same characteristics, for example identical, makes it possible to limit, or even avoid, the injection of a common mode component at the output of the converter compared to the input (differential common mode) during transitions.

[0172] In fact, the common input mode corresponds to:

[0173] [MATH 4]

[0174] The output common mode corresponding to:

[0175] [MATH 5]

[0176] The differential common mode is expressed by:

[0177] [MATH 6] mc-diff nc-out ^mc-in

[0178] In normal operation, for continuous conversion, the differential common mode may have a continuous or low-frequency component, typically less than 1 kHz, and typically at least 10 times lower than the control cycle frequency, advantageously 100 times lower. It is also appropriate to limit or avoid the occurrence of a high-frequency common mode component, due to the operation of the electrical energy converter itself. To do this, it is appropriate that V P ai, the potential of the first midpoint 38 connected to the first piezoelectric assembly 12A, and V pa 2, the potential of the other first midpoint 38 connected to the second piezoelectric assembly 12B, evolves in opposition, so that V mc-pa = (V pai + V pa2 ) / 2 is approximately equal to V mc-in over the entire resonance period. Similarly, it is appropriate that V Pbi, the potential of the second midpoint 48 connected to the first piezoelectric assembly 12A, and V P b2, the potential of the other second midpoint 48 connected to the second piezoelectric assembly 12B, evolves substantially in opposition, so that V mc-pb = (V pbl + V pb2 ) / 2 is approximately equal to V mc-out over the entire resonance period or control cycle. These conditions are met when all the first switches 36 have substantially the same characteristics, and all the second switches 46 have substantially the same characteristics.

[0179] Advantageously, the control of the electrical energy converter by applying a distribution of the voltage steps as described is naturally compatible with first switches 36 which have substantially the same characteristics, and second switches 46 which have substantially the same characteristics, insofar as the opening and closing times of the switches per control cycles are balanced. In addition, the fact that the switches are substantially identical in construction (same transistor technology, same dimensions) and pass substantially the same average and effective current, makes it possible to maintain substantially identical characteristics during operation (same temperature rise inducing the same drifts on the characteristics of the switches). This also makes it possible to limit, or even avoid, the presence of a high-frequency differential common mode component.

[0180] Figure 6 illustrates in parallel two examples of control cycles, respectively a Cycle-1, corresponding to the step-down type configuration described with reference to Figure 4, repeated over three resonance periods, between 0 and 6TT; and a Cycle-2, which is a spread control cycle.

[0181] Cycle-1 is formed respectively of a succession of a first half-period DPi and a second half-period DP2, which are repeated over the three resonance periods.

[0182] As already described above in relation to Figure 4, the first half-period DP1 includes, for the evolution of the total piezoelectric voltage V p , a phase with substantially constant load, followed by a first phase with substantially constant voltage (voltage plateau V p =Vb), followed by a phase at substantially constant load and a second phase at substantially constant voltage (voltage plateau V p=Vd). The second half-period DP2 includes, for the evolution of the total piezoelectric voltage V p , a phase at substantially constant load, followed by a third phase at substantially constant voltage (voltage plateau V p =V a =-Vb), of approximately the same duration as the first phase at approximately constant voltage, followed by a phase at approximately constant load and a fourth phase at approximately constant voltage (voltage plateau V p =V c =-Vd), of approximately the same duration as the second phase at approximately constant voltage.

[0183] The control Cycle-2 includes, during the first half-cycle (between 0 and 3TT), a phase during which the voltage V pa is frozen at + Vin, followed by the first half-period DPi; a second half-cycle (between 3TT and 6TT), comprising a phase during which the voltage V pa is frozen at -Vin, followed by the second half-period DP2.

[0184] The control diagram C'i illustrates the closing (high state) or opening ("low state") states of the switches Ke, K? and the control diagram C'2 illustrates the closing (high state) or opening ("low state") states of the switches K5, Ks to obtain the voltage V pa between the first midpoints 38, to carry out the Cycle-2 control cycle.

[0185] As can be observed, the command to switch the pair of switches Ke.Ky to closing is carried out once during the control cycle comprising P=1+s periods (here s=2), and the command to switch the pair of switches Ke.Ky to opening is carried out once during the control cycle.

[0186] Similarly, the command to switch the pair of switches Ks.Ks to close is carried out once during the control cycle comprising P=1+s periods (here s=2), and the command to switch the pair of switches Ks.Ks to open is carried out once during the control cycle.

[0187] This embodiment is particularly advantageous in a strongly step-down configuration, a configuration in which the gain, i.e. the ratio of the output voltage V ou t relative to Vj n is less than 1 HAS

[0188] Those skilled in the art will understand that the mechanism described above for a voltage step-down configuration applies analogously to a voltage step-up configuration, which is particularly advantageous in a high-step-up configuration, a configuration in which the gain, i.e. the ratio of the output voltage V out relative to Vj n is greater than 2.

[0189] Indeed, in strongly step-down or strongly step-up configurations, it is not efficient to perform numerous switching operations of the switches, because this induces a loss of energy.

[0190] In addition, this embodiment makes it possible to reduce the switching frequency of the first switches, and of the second switches where applicable, and makes it possible to reduce losses linked to the switching frequency. Furthermore, this embodiment limits the number of voltage excursions on V pa (very step-down mode) or on V P b (high boost mode) and thus reduces the proportion of time spent on constant load phases during the cycle in favor of constant voltage phases which allow power to be exchanged and contribute to the supply of output power.

[0191] The case of a control cycle of P=3 resonance periods has been described with reference to Figure 6.

[0192] This scenario can be generalized to the case of a control cycle P=s+1 resonance periods, s being a positive number greater than or equal to 0, in which s phases at voltage V are introduced pa between the first midpoints 38 fixed, inserted respectively between the half-periods DPi and DP2, the first half-period DP1 being part of the first half-cycle of control and the second half-period DP2 being part of the second half-cycle of control.

[0193] In the case where the number (s+1) is even and in step-down mode, it is advantageous to freeze V pa to a first polarity of the input voltage Vj n over the first (s+1) / 2 operating periods of the control cycle (forming a first half-control cycle), for example V pa =+Vj n , and to freeze V pato the second polarity, opposite to the first polarity, over the last (s+1) / 2 operating periods of the control cycle (forming a second half-control cycle), for example V pa =-Vj n .

[0194] Thus, in step-down mode, the electronic control device 20 is configured to control one of the pairs of first switches K5, Ks or Ke, K? in the closed position during (s+1) / 2 first resonance periods of the control cycle, and to control the other pair of said pairs of first switches Ks, Ks or Ks, K? in the closed position during the (s+1) / 2 last resonance periods of the control cycle, thus completing the s+1 periods of the cycle.

[0195] In the case where the number (s+1) is even and in elevator mode, it is advantageous to freeze V P b to a first polarity of the input voltage Vj n over the first (s+1) / 2 periods of the control cycle, for example V pa =+Vjn , and to freeze V P b to the second polarity, opposite to the first polarity, over the last (s+1) / 2 periods of the control cycle, for example V pa =-Vj n .

[0196] Thus, in elevator mode, the electronic control device 20 is configured to control one of the pairs of first switches Ki, K4 or K2, K3 in the closed position during the first (s+1) / 2 resonance periods of the control cycle, and to control the other pair of said pairs of first switches Ks, Ks or Ke, K? in the closed position during the last (s+1) / 2 resonance periods of the control cycle.

[0197] Figure 7 illustrates the control diagrams of the pairs of switches (Ke, K7) and (Ks.Ks) to realize a step-down type configuration described previously.

[0198] Advantageously, on each half-period, one of the pairs of switches (Ke, K7) or (Ks.Ks) is alternately commanded to close, over a duration D on , also called contact duration, and two phases of duration D on are separated by an intermediate phase, of duration Ddt during which the switches of the two respective pairs of switches (Ke, K7) and (Ks.Ks) are open, also called dead time duration.

[0199] The sum of the duration D on and the duration Ddt is equal to 2TT when the durations are angular durations, so it is sufficient to estimate one of the durations D on or Ddt to deduce the other by a simple arithmetic calculation.

[0200] For example, the dead time duration Ddt is estimated.

[0201] Furthermore, advantageously, when each of the switches Ke, K7, Ks, Ks comprises a transistor and an antiparallel diode, the respective antiparallel diodes being able to naturally allow the current to pass when it flows in the opposite direction, a tolerance margin is available for controlling the closing command.

[0202] In other words, the duration Ddt of dead time can be selected from a range of values ​​[Ddt-min, Ddt-max], forming the tolerance margin, between a minimum duration Ddt-min and a maximum duration Ddt-max.

[0203] Advantageously, the tolerance margin is estimated by the control device as a function only of the frequency Fcycle of the converter control cycle, of the input voltage Vj n and the output voltage V ou t.

[0204] Especially in the step-down configuration in which the output voltage V out is less than the input voltage Vj n the control process is particularly simplified, only the two parameters Ddt and the frequency F cy The control cycle time is controlled, these two parameters can be estimated from the input and output voltages of the converter, to control the converter.

[0205] For example, in one embodiment, the frequency of the converter control cycle is adjusted by a control loop that seeks to regulate the converter output voltage to a set voltage value.

[0206] Indeed, as the frequency of the control cycle is directly linked by the relation Ff O nc=F Cycie*(s+1) to the operating frequency of the converter, modulating the frequency of the control cycle modulates the operating frequency. In other words, the frequency of the control cycle of the converter dictates the frequency of the mechanical movement of the piezoelectric element(s) 15.

[0207] To achieve the desired effect, the piezoelectric element 15 is typically operated between its so-called series resonance frequency where L and C correspond to the inductance and capacitance of the resonant branch and the so-called parallel resonance frequency of the piezoelectric element 15 (œ p =1 / > / (LCCo / (C+Co))), also respectively called resonance frequency and antiresonance frequency of the piezoelectric element 15.

[0208] The frequency of the control cycle is therefore between these two frequencies or over a more restricted range to remain within a predefined impedance range, or to avoid parasitic resonance modes. In addition, the frequency of the control cycle is typically adjusted such that the frequency F C ycie*(1+s) is located between these frequency limits to adjust the amplitude of the current l and ultimately regulate the output voltage, current or power via a control loop.

[0209] The operating frequency impacts the output current and ultimately the output voltage that we are trying to regulate. Thus, lowering the operating frequency allows a decrease in the electrical impedance of the piezoelectric resonator and an increase in the output current and therefore allows an increase in the output voltage. Conversely, increasing the operating frequency allows an increase in the impedance of the piezoelectric resonator and a decrease in the output current and therefore allows a decrease in the output voltage. Ultimately, changing the frequency of the control cycle allows for modulating the power transfer at the converter output.

[0210] It is also possible to change the resonance mode on the piezoelectric assemblies during operation of the converter, for example to switch from a thickness resonance mode to a radial or elongation resonance mode, or to switch to a higher resonance mode to address different power ranges with improved efficiency. For this, the frequency F C ycie*(1+s) is advantageously chosen between the resonance frequency and the antiresonance frequency of the desired resonance mode.

[0211] For example, in one embodiment, dead time duration values ​​Ddt as a function of input voltage values ​​Vj nand values ​​of the frequency of the control cycle are previously calculated and stored, for example in a table or any other value storage structure adapted to the electronic control device. In another embodiment, the minimum dead time duration value Ddt-min is estimated in real time as a function of the input voltage Vin, the output voltage V ou t and frequency F cy cie of the converter control cycle, from a model of the piezoelectric resonator. As an optional addition, a maximum estimation error D e rr-max is also determined. For example, the maximum estimation error D err -max is determined in advance, depending on operating conditions, for example temperature, operating point (validity of the estimation model)....

[0212] In another more sophisticated embodiment, a control loop using an observer that estimates the conduction time of the antiparallel diodes of the first controlled switches is implemented, the dead time duration Ddt being adjusted to achieve a desired conduction time. For example, an observer as described in patent application FR 3 124042 is used.

[0213] In all embodiments, the dead time duration is calculated or advantageously regulated so as to minimize the voltage across the switches before closing, and therefore to ensure ZVS switching.

[0214] The invention has been described above with reference to the electrical energy converter described with reference to Figure 1, and to the two-level output electrical energy converter described with reference to Figure 2.

[0215] The electronic control device described also applies to electrical energy converter architecture variants such as those described below with reference to figures 8 and 9.

[0216] In the example of Figure 8, the electrical energy converter 10 has a similar architecture to that of the electrical energy converter 10 of Figure 1, but respective protection capacitors 80, 82 are added, the first protection capacitor 80 being connected in series between a first midpoint of a first branch of the first switching bridge and the input of the first piezoelectric assembly 12A, the second capacitor 82 being connected in series between another first midpoint of the first of a second branch of the switching bridge and the input of the second piezoelectric assembly 12B. These protection capacitors 80, 82 have a protective role in the case where one of the piezoelectric resonators is defective and generates a short circuit.

[0217] In the example of Figure 9, the electrical energy converter 10 has an architecture similar to that of the electrical energy converter 10 of Figure 1, but a transformer 84 of ratio m is connected between a first piezoelectric assembly 12A1, 12A1 and a second piezoelectric assembly 12B1, 12B2.

[0218] In this case, the total piezoelectric voltage is then expressed by:

[0219] Where m is the transformer ratio.

[0220] In such an architecture, only one of the piezoelectric assemblies 12A1, 12A2 is sufficient for operation in a voltage step-down configuration, the other piezoelectric assemblies being optional.

[0221] In such an architecture, only one of the piezoelectric assemblies 12B1, 12B2 is sufficient for operation in a voltage booster type configuration, the other piezoelectric assemblies being optional.

[0222] More generally, the control device and method described above apply to any electrical energy converter architecture 10 of the type with two switching bridges as described above.

[0223] The described electronic control device is also applicable in converter architectures in which the converter input is divided into several voltage levels, for example two voltage levels.

[0224] Such a converter architecture is described below with reference to Figure 10.

[0225] In this embodiment, the electrical energy converter 10' is powered by an input voltage Vj n-giobai, which is divided into two voltage levels, each voltage level being equal to half of the input voltage Vm-giobai, i.e. Vin= Vin- g iobai / 2.

[0226] In this architecture, each of the first switching branches 32i, 322 of the first switching bridge 30 is connected to an input voltage source Vj n .

[0227] The first switching branches 32i and 322 are connected in series, via an intermediate connection point 35, each being connected respectively between one of the terminals 34 for applying the input voltage Vin- g iobai and the intermediate connection point 35.

[0228] The electrical energy converter 10' of Figure 10 is controlled according to the principles described above.

[0229] Figure 10 depicts an electrical energy converter 10' which is powered by an input voltage Vm-giobai, which is divided into two voltage levels, but it is clear that an architecture with division into a larger number of input voltage levels is possible, for example into 4 input levels using two switching bridges, by multiplying the structure shown in Figure 10.

[0230] In the figures, we have represented at the output of the converter a voltage source, such as a battery. In practice any electrical load can be connected to the output, for example an electronic assembly, a motor, a resistive load, a DC BUS... In addition, to stabilize the output voltage, advantageously an electrical capacitor can be added in parallel of V ou t.

[0231] Similarly, at the input of the converter, we have represented a voltage source of the battery type, but any other source of electrical energy can be used, for example a photovoltaic panel, an AC or DC electrical network... In addition, to stabilize the input voltage, advantageously an electrical capacity can be added in parallel with Vj n .

[0232] In the case of an AC input voltage source having negative voltage transitions (for example an AC voltage centered on zero), it is possible to use bidirectional voltage switches K5, K6, K7, K8. Alternatively, a rectifier bridge can be arranged between the voltage source and the converter input, so that only unidirectional voltage transistors K5, K6, K7, K8 can be used. Similarly, in the case of an AC output voltage having negative voltage transitions, it is possible to use bidirectional voltage switches K1, K2, K3, K4.

Claims

CLAIMS 1. Electronic device (20) for controlling an electrical energy converter (10) capable of converting an input voltage ( j n ) in at least one output voltage (V ou t), the converter (10) comprising a first switching bridge (30) comprising two first switching branches (32), each first switching branch (32) being connected to an input voltage source ( j n ) and comprising at least two first switches (36) connected in series and connected to each other at a first midpoint (38); at least one second switching bridge (40) comprising two second switching branches (42), each second switching branch (42) being connected between two terminals (44) for supplying an output voltage (V out) and comprising at least two second switches (46) connected in series and connected to each other at a second midpoint (48); at least one pair of first (12A) and second (12B) piezoelectric assemblies, each piezoelectric assembly (12A.12B) comprising at least one piezoelectric element (15) and being connected between respective first (38) and second (48) midpoints, the midpoints (38, 48) between which the piezoelectric assemblies (12A.12B) are connected being distinct from one piezoelectric assembly (12A) to the other (12B); the electronic control device (20) is configured to control, during a resonance period of the piezoelectric assemblies (12A.12B), a switching of each of the switches (36, 46) to alternate phases at substantially constant voltage at the terminals of the piezoelectric assemblies (12A.12B) and phases at substantially constant charge at the terminals of said piezoelectric assemblies (12A.12B), characterized in that the electronic control device (20) is configured to, for a control cycle equal to s+1 resonance periods of the piezoelectric assemblies, s being an integer greater than or equal to zero, control at least two phases at substantially constant voltage per half-control cycle, a first half-control cycle comprising a first phase at substantially constant voltage of first voltage value and first duration and a second phase at substantially constant voltage of second voltage value and second duration, a second half-control cycle comprising a third phase at substantially constant voltage of value opposite to the first voltage value and of duration equal to the first duration at plus or minus 10%, preferably at plus or minus 5% and a fourth phase at substantially constant voltage of value opposite to the second value. of voltage and duration equal to the second duration plus or minus 10%, preferably plus or minus 5%.

2. Device according to claim 1, configured to control in the closed position a pair of first switches comprising one of the first switches (36A) connected directly to the first piezoelectric assembly and one of the first switches (36B) connected directly to the second piezoelectric assembly during said first duration, and to control in the closed position another pair of first switches comprising another of the first switches (36A) connected directly to the first piezoelectric assembly and another of the first switches (36B) connected directly to the second piezoelectric assembly during said second duration.

3. Device according to claim 1 or 2, configured to control in the closed position a pair of second switches comprising one of the second switches (46A) connected directly to the first piezoelectric assembly and one of the second switches (46B) connected directly to the second piezoelectric assembly during said first duration, and to control in the closed position another pair of first switches comprising another of the second switches (46A) connected directly to the first piezoelectric assembly and another of the second switches (46B) connected directly to the second piezoelectric assembly during said second duration.

4. Device according to any one of claims 2 or 3, wherein when the number s+1 is an even positive number greater than or equal to 2, the electronic control device (20) is configured to control in the closed position one pair of said pairs of first switches during (s+1) / 2 resonance periods of the first half-cycle of control, and to control in the closed position the other pair of said pairs of first switches during (s+1) / 2 resonance periods of the second half-cycle of control.

5. Device according to any one of claims 1 to 4, wherein one of the voltage values ​​among the first voltage value and the second voltage value is equal to the difference (Vi n -V ou t) or opposite to the difference (-Vi n +V ou t) between the input voltage (Vj n ) and the output voltage (V out), and the other voltage value among the first voltage value and the second voltage value is equal to the sum (Vi n +V ou t) or the opposite of the sum (-Vi n -V ou t) of the input voltage (Vj n ) and the output voltage (V ou t).

6. Device according to any one of claims 1 to 5, configured to control sequences of phases at substantially constant voltage and at substantially constant load per half-cycle of control, the phases of the second half-cycle control being obtained by translation and sign inversion of the phases of the first half-cycle of control.

7. Device according to any one of claims 2 to 6, configured to regulate an output voltage, current or power of the converter by controlling a frequency of the control cycle of the converter.

8. Device according to any one of claims 2 to 7, configured to regulate a dead time duration during which the first switches of each pair of first switches are open, so as to minimize the voltage across the terminals of the first switches before closing.

9. Device according to claim 8, configured to control, in a voltage step-down type configuration in which the input voltage is higher than the output voltage, a switching to the closed position of one of the pairs of switches at a determined switching angle with a tolerance margin.

10. Electronic electrical energy conversion system comprising an electrical energy converter (10) capable of converting an input voltage (Vj n ) in at least one output voltage (V out), the converter (10) comprising a first switching bridge (30) comprising two first switching branches (32), each first switching branch (32) being connected to an input voltage source (Vin) and comprising at least two first switches (36) connected in series and connected together at a first midpoint (38); at least one second switching bridge (40) comprising two second switching branches (42), each second switching branch (42) being connected between two terminals (44) for supplying an output voltage (V out) and comprising at least two second switches (46) connected in series and connected to each other at a second midpoint (48); at least one pair of first (12A) and second (12B) piezoelectric assemblies, each piezoelectric assembly (12A.12B) comprising at least one piezoelectric element (15) and being connected between respective first (38) and second (48) midpoints, the midpoints (38, 48) between which the piezoelectric assemblies (12A.12B) are connected being distinct from one piezoelectric assembly (12A) to the other (12B), and an electronic device (20) for controlling said electrical energy converter (10) according to claims 1 to 9.

11. System (5) according to claim 10, wherein each piezoelectric assembly (12A.12B) is constituted according to one of the constitutions among the group consisting of: a single piezoelectric element (15); several piezoelectric elements (15) connected in series; several piezoelectric elements (15) connected in parallel; a piezoelectric element (15) and an auxiliary capacitor connected in series; a piezoelectric element (15) and an auxiliary capacitor connected in parallel; and an arrangement of several parallel piezoelectric branches, each branch comprising one or more piezoelectric elements (15) connected in series or an auxiliary capacitor; the auxiliary capacitor preferably having a capacitance greater, more preferably at least three times greater, than a reference capacitance (Co) of the piezoelectric element(s) (15), each piezoelectric element (15) being modeled in the form of a capacitor (52) and a resonant branch (54) connected in parallel with the capacitor (52), the reference capacitance (Co) being the capacitance of said capacitor (52).

12. System (5) according to claim 10 or 11, in which each of the first (36) and second (46) switches is constituted by a transistor, or a diode, or even a transistor and a diode in antiparallel.

13. System (5) according to claim 12, wherein all the first switches have the same operating characteristics, and all the second switches have the same operating characteristics.

14. System (5) according to any one of claims 10 to 13, in which the electronic electrical energy conversion system (5) is a system for conversion into direct electrical energy, such as a direct-direct conversion system or an alternating-direct conversion system.

15. Method for controlling an electrical energy converter (10) capable of converting an input voltage (Vj n ) in at least one output voltage (V ou t), the converter (10) comprising a first switching bridge (30) comprising two first switching branches (32), each first switching branch (32) being connected to an input voltage source (Vj n) and comprising at least two first switches (36) connected in series and connected to each other at a first midpoint (38); at least one second switching bridge (40) comprising two second switching branches (42), each second switching branch (42) being connected between two terminals (44) for supplying an output voltage (V out) and comprising at least two second switches (46) connected in series and connected to each other at a second midpoint (48); at least one pair of first (12A) and second (12B) piezoelectric assemblies, each piezoelectric assembly (12A.12B) comprising at least one piezoelectric element (15) and being connected between respective first (38) and second (48) midpoints, the midpoints (38, 48) between which the piezoelectric assemblies (12A.12B) are connected being distinct from one piezoelectric assembly (12A) to the other (12B), the method being implemented by an electronic control device (20) and comprising the control, during a resonance period of the assemblies piezoelectrics (12A.12B), of a switching of each of the switches (36, 46) to alternate phases at substantially constant voltage at the terminals of the piezoelectric assemblies (12A.12B) and phases at substantially constant charge at the terminals of said piezoelectric assemblies (12A.12B), characterized in that it comprises, for a control cycle equal to s+1 resonance periods of the piezoelectric assemblies, s being an integer greater than or equal to zero, the control of at least two phases at substantially constant voltage per half-control cycle, a first half-control cycle comprising a first phase at substantially constant voltage of first voltage value and first duration and a second phase at substantially constant voltage of second voltage value and second duration, a second half-control cycle comprising a third phase at substantially constant voltage of value opposite to the first voltage value and of duration equal to the first duration at plus or minus 10%, preferably at plus or minus 5% and a fourth phase at substantially constant voltage of value opposite to the second voltage value and of duration equal to the second duration at plus or minus 10%, preferably at plus or minus 5%.

16. Method according to claim 15, comprising a determination, for each half-cycle of control, of a switching angle in closed position of the switches of a pair of first switches comprising one of the first switches (36A) connected directly to the first piezoelectric assembly and one of the first switches (36B) connected directly to the second piezoelectric assembly.

17. The method of claim 15 or 16, wherein, when at least one output voltage (V ou t) is lower than the input voltage (Vin), the determination of a switching angle is carried out with a tolerance margin, following a dead time duration during which the first switches of each pair of first switches are open, the method comprises an estimation of said tolerance margin as a function of a frequency of the control cycle, of the input voltage (Vj n ) and the output voltage (V ou t).

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