Electronic device and method for controlling an electrical energy converter, associated electronic electrical energy conversion system

Abstract

Electronic device and method for controlling an electrical energy converter, associated electronic electrical energy conversion system This electronic control device, suitable for controlling an electrical energy converter comprising at least one piezoelectric assembly, comprises: a measurement module (50) configured to measure a value of the output voltage of the converter; a control unit (61) configured to control several successive phases during a conversion cycle, having an associated cycle frequency (fcycle), controlled by switching angles; a first regulation module (56) configured to correct a measured output voltage or current value with respect to a setpoint value, and providing a corrected estimate of output current;a calculation module (60) using a mathematical model for calculating the switching angles based on the corrected current estimate, the measured output voltage value, an input voltage value, and an estimator (72) of the conversion cycle frequency. Figure for abstract: Figure 4;

Description

Title of the invention: Electronic device and method for controlling an electrical energy converter, associated electronic electrical energy conversion system

[0001] 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.

[0002] 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.

[0003] The invention lies in the field of electronic electrical energy conversion systems, in particular those with piezoelectric resonators, in particular voltage conversion systems, 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.

[0004] Various topologies of electrical energy converters with piezoelectric elements are known.

[0005] For example, electrical energy converters with piezoelectric element(s) are described in documents FR 3 064 850 B1, FR 3 086 471 B1 and FR 3 130 096 AL

[0006] In known systems, 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 piezoelectric assembly or assemblies and phases at substantially constant charge across the piezoelectric assembly or assemblies. The control is configured to produce a given number of phases at substantially constant voltage (or voltage steps), while respecting operating constraints of the piezoelectric converter depending on its topology, for example the switching of the switches at zero voltage (or switching in ZVS mode from the English "Zero Voltage Switching"), and the optimization of the power transfer between the input and the output.

[0007] In particular, control methods with three voltage levels are known, requiring the implementation of several regulation loops to comply with the constraints of desired operation. To implement such known control methods, it is necessary to observe the evolution of the current flowing in the piezoelectric resonator(s) of the converter, and to determine precise switching times synchronized with the current evolution. For control with three voltage levels, to respect the load and energy balance over a conversion cycle, it is necessary to control at least the opening and closing times of two switches, i.e. at least four switching times, or even six switching times if all the switches must be controlled. Estimating each switching time requires the detection of an event and / or an error measurement and / or the use of a control loop.

[0008] The invention aims to present a less complex, and therefore less expensive, device and method for controlling the converter, while retaining the performance of the electrical energy converter.

[0009] For this purpose, the invention relates to an electronic device for controlling an electrical energy converter capable of converting an input voltage into an output voltage, the converter comprising two input terminals for receiving the input voltage, two output terminals for delivering the output voltage, a piezoelectric assembly comprising at least one piezoelectric resonator, the piezoelectric assembly being connected between an input point and an output point, the piezoelectric assembly resonating according to successive resonance periods, the converter comprising several switches connected between said input terminals, output terminals and input and output points of the piezoelectric assembly, the electronic control device comprising:

[0010] - a measurement module configured to measure a value of the output voltage of said converter;

[0011] - a control unit configured to control a switching of at least one switch, following several successive phases during a conversion cycle, equal to one or more resonance periods and having an associated cycle frequency, the conversion cycle comprising at least three phases at substantially constant voltage at the terminals of the piezoelectric assembly, separated by phases at substantially constant charge at the terminals of the piezoelectric assembly.

[0012] This electronic control device comprises:

[0013] -a first regulation module, implemented in a first regulation loop, configured to correct a measured output voltage or current value with respect to a set voltage or current value, the first regulation module providing as output a corrected estimate of output current,

[0014] - a module for calculating a conversion cycle frequency and a plurality of switching angles, the calculation module receiving said estimate as input current corrected, the measured output voltage value, an input voltage value, the calculation module implementing a mathematical model for calculating said switching angles and an estimator of the conversion cycle frequency, said conversion cycle frequency and said plurality of switching angles being provided as input to the control unit.

[0015] Advantageously, the proposed electronic control device allows simplified control, in particular thanks to the implementation of a mathematical model for calculating the switching angles. In particular, the number of physical quantities representative of the operation of the electrical energy converter to be controlled is limited. Advantageously, the proposed electronic control device does not require observation of the evolution of the current in the piezoelectric assembly and synchronization of a switching command with an event observed in the evolution of the current, because the implementation of the mathematical model implicitly ensures synchronization between the calculated switching angles and the evolution of the current.

[0016] 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.

[0017] It further comprises a module for estimating a voltage excursion at the terminals of the piezoelectric assembly, and a second regulation module, implemented in a second regulation loop, the second regulation module providing as output an estimated energy loss, as a function of a difference between the voltage excursion estimated by the estimation module and a setpoint voltage excursion, said estimated energy loss also being provided as input to the calculation module and used for calculating said switching angles.

[0018] The module for estimating a voltage excursion at the terminals of the piezoelectric assembly is a passive module, produced by a set of analog filters comprising a high-pass filter configured to isolate a high-frequency signal generated by an abrupt voltage front.

[0019] The module for estimating a voltage excursion at the terminals of the piezoelectric assembly is an active module comprising an active control unit, comprising a switch controlled by a control signal, the control signal being configured to authorize a measurement of the voltage excursion over a range centered on a chosen measurement angle.

[0020] The module for estimating a voltage excursion across the terminals of the piezoelectric assembly further comprises at least one envelope detector and at least one low-pass filter.

[0021] The first control loop is adjusted for a first response time, the second control loop is adjusted for a second response time, the first and second response times being distinct.

[0022] Each of said first and second control loops comprises corrector modules adjusted so that the first response time of the first control loop is faster than the second response time of the second control loop.

[0023] The first regulation module receives as input a current difference between the measured output current value and the setpoint current value, and comprises a proportional-integral correction module which provides a corrected estimate of the output current from said current difference.

[0024] The first regulation module receives as input a voltage difference between the measured output voltage value and the set voltage value, and comprises a unit for applying a gain making it possible to transform the voltage difference into a current difference, the current difference then being supplied as input to a proportional-integral correction module which provides a corrected estimate of the output current from said current difference.

[0025] The calculation module comprises an estimator of the conversion cycle frequency, the estimator implementing a numerical resolution method for iteratively solving a system of equations representative of a balance of charges and energy over the conversion cycle.

[0026] The invention also relates to an electronic electrical energy conversion system capable of converting an input voltage into an output voltage, the converter comprising two input terminals for receiving the input voltage, two output terminals for delivering the output voltage, a piezoelectric assembly comprising at least one piezoelectric resonator, the piezoelectric assembly being connected between an input point and an output point, the piezoelectric assembly resonating according to successive resonance periods, the converter comprising several switches connected between said input terminals, output terminals and input and output points of the piezoelectric assembly, and an electronic control device configured to control said electrical energy converter, in which said electronic control device is of the type briefly described above.

[0027] The invention also relates to a method for controlling an electrical energy converter capable of converting an input voltage into an output voltage, the converter comprising two input terminals for receiving the input voltage, two output terminals for delivering the output voltage, a piezoelectric assembly comprising at least one piezoelectric resonator, the piezoelectric assembly being connected between an input point and an output point, the piezoelectric assembly resonant following successive resonance periods, the converter comprising several switches connected between said input terminals, output terminals and input and output points of the piezoelectric assembly. The method is implemented by an electronic device for controlling said converter and comprises steps of:

[0028] -measuring a value of the output voltage of said converter;

[0029] -control, by a control unit, of a switching of at least one switch, following several successive phases during a conversion cycle, equal to one or more resonance periods and having an associated cycle frequency, the conversion cycle comprising at least three phases at substantially constant voltage at the terminals of the piezoelectric assembly, separated by phases at substantially constant charge at the terminals of the piezoelectric assembly.

[0030] The method further comprises:

[0031] -a first regulation step, implemented in a first regulation loop, comprising a correction of a measured output voltage or current value relative to a set voltage or current value, the first regulation providing as output a corrected estimate of output current,

[0032] -a step of calculating a conversion cycle frequency and a plurality of switching angles, as a function of said corrected current estimate, the value of the measured output voltage, an input voltage value, the calculation step implementing a mathematical model for calculating said switching angles and an estimate of the conversion cycle frequency, said conversion cycle frequency and said plurality of switching angles being provided as input to the control unit.

[0033] According to an optional characteristic, the control method further comprises an estimation of a voltage excursion at the terminals of the piezoelectric assembly, and a second regulation, implemented in a second regulation loop, the second regulation providing as output an estimated energy loss, as a function of a difference between the voltage excursion estimated by the estimation module and a setpoint voltage excursion, said estimated energy loss also being provided as input to the calculation step and used for the calculation of said switching angles.

[0034] 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:

[0035] [Fig-1] [Fig.l] is a schematic representation of an electronic system of electrical conversion;

[0036] [Fig.2] [Fig.2] is a schematic representation of a piezoelectric resonator and a corresponding equivalent electrical circuit;

[0037] [Fig.3] [Fig.3] is a representation of the curves of evolution of the current and the voltage across a piezoelectric assembly over a 3-step voltage conversion cycle;

[0038] [Fig.4] [Fig.4] schematically represents an electronic conversion system and an electronic control device in one embodiment;

[0039] [Fig.5] [Fig.5] is a graph of the evolution of the current and the voltages at the terminals of a piezoelectric assembly on a conversion cycle in the absence of zero voltage switching;

[0040] [Fig.6] [Fig.6] represents a first embodiment of the estimation module of a voltage excursion across the terminals of the piezoelectric assembly;

[0041] [Fig.7] [Fig.7] represents a second embodiment of the module estimation of a voltage excursion across the terminals of the piezoelectric assembly;

[0042] [Fig.8] [Fig.8] is a graph of the evolution of the current and the voltages at the terminals of a piezoelectric assembly on a conversion cycle in the absence of zero voltage switching, comprising the representation of a control signal emitted by the module for estimating a voltage excursion in the embodiment of [Fig.7].

[0043] In the remainder of the description, the expression “substantially equal to” defines a relationship of equality to plus or minus 10%, preferably to plus or minus 5%, unless otherwise specified.

[0044] [Fig.l] schematically illustrates an electronic electrical energy conversion system 2, configured to supply electrical energy to a load 6 from a source 4.

[0045] The electronic electrical energy conversion system 2 comprises an electrical energy converter 10 and an electronic control device 20 for the electrical energy converter 10.

[0046] The electrical energy converter 10 is configured to convert an input voltage Vin into an output voltage Vout.

[0047] The electrical energy converter 10 comprises a first input terminal 12 and a second input terminal 14, a first output terminal 16 and a second output terminal 18.

[0048] By convention, the potential Vinn applied to the first input terminal 12 is lower than the potential Vinp applied to the second input terminal 14. The potential Voutn supplied to the first output terminal 16 is lower than the potential Voutp applied to the second output terminal 18.

[0049] To simplify the description, in the presence of an input voltage which changes sign, Vinn and Vinp are then redefined at each instant so that Vinn is always in lower than Vinp. Similarly, if an output voltage is supplied that changes sign, Voutn and Voutp are then redefined at each instant so that Voutn is always lower than Voutp.

[0050] The electrical energy converter 10 comprises a piezoelectric assembly 30, comprising one or more piezoelectric elements or resonators, connected to each other, but of which a modeling in the form of an electrical circuit similar to the modeling of an elementary piezoelectric resonator can be obtained. A modeling 40 in the form of an electrical circuit of a piezoelectric resonator operated around a resonance mode is described with reference to [Fig.2].

[0051] The electronic electrical energy conversion system 2 is, for example, a DC-DC conversion system capable of converting a first DC electrical energy or voltage received at the input into a second DC electrical energy or voltage delivered at the output, or an AC-DC conversion system capable of converting an AC electrical energy or voltage received at the input into a DC electrical energy or voltage delivered at the output of the electrical energy conversion system. For example, the electrical energy source 4 is a battery, a solar panel, a voltage from a rectified AC electrical network or a DC power supply bus.

[0052] When the electrical energy conversion system is an AC-DC conversion system, with for example an AC input voltage centered on 0V, the electrical energy conversion system 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 to deliver a rectified electrical voltage at the input of the converter 10. The voltage rectifier is for example a rectifier bridge, such as a diode bridge.

[0053] Alternatively, in the presence of an input voltage which changes sign, the use of bidirectional voltage switches, allowing an input voltage which changes sign, makes it possible to dispense with a rectifier bridge.

[0054] The electronic control device 20 is configured to operate the piezoelectric material of the piezoelectric assembly 30 in its inductive zone, i.e. between its so-called series resonance frequency (cos=l / 'V(Lm.Cm) where Lm and Cm correspond to the inductance and capacitance of the resonant branch and the so-called parallel resonance frequency of the piezoelectric assembly 30 (œp=l / ^(Lm.Cm.Cp / (Cm+Cp))), also respectively called resonance frequency and antiresonance frequency of the piezoelectric assembly 30. At a given operating point, which depends on the input voltage, the output voltage, the output current and the topology, there corresponds a current resonance frequency located between these two frequencies. This resonance makes it possible 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, i.e. with repeated conversion cycles at a conversion cycle frequency (or operating frequency), denoted fcyde, depending on the resonance frequency fres of the piezoelectric assembly 30, and by adjusting the respective switching phase durations within a conversion cycle. A conversion cycle comprises one or more resonance periods of the piezoelectric assembly, the conversion cycle frequency being linked to the resonance frequency by:

[0055] [Math.l] f = cycle 1+À'

[0056] k being an integer greater than or equal to 0.

[0057] The electrical energy converter 10 further comprises respective switches K2, K3, K4, the switches K, K2 being connected in series, at a first midpoint 32, which is an input point of the piezoelectric assembly 30, the switches K3 K4 being connected in series, at a second midpoint 34, which is an output point of the piezoelectric assembly 30.

[0058] It should be noted that the topology of the converter 10 of [Fig.l] is simplified, various additional elements, in particular additional switches, for example an additional switch between the first midpoint 32 and the second output point 18, being present according to various possible piezoelectric converter topologies.

[0059] Each switch of the converter 2, namely each of the switches K2, K3, K4 is preferably a unidirectional voltage switch, and comprises for example a transistor, or a diode, or even a transistor and a diode in antiparallel, not shown.

[0060] The switch Kb K2, K3, K4 is preferably made up of the transistor, or the diode, or the transistor and the diode in antiparallel.

[0061] Alternatively, the switch Kb K2, K3, K4 comprises an association of several transistors, and is preferably made up of such an association of several transistors.

[0062] As a further variant, the switch Kb K2, K3, K4 comprises a mechanical switch, such as a MEMS (MicroElectroMechanical System) microswitch.

[0063] 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; a bipolar transistor insulated gate, also called 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.

[0064] The electronic control device 20 is configured to control the switching of at least some of the switches Kb K2, K3, K4 to alternate phases at substantially constant voltage and phases at substantially constant load.

[0065] By substantially constant charge is meant 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 is meant a variation in charge less than 30% of the charge which would have been exchanged with the outside of the piezoelectric assembly 30 if the voltage across the terminals of the piezoelectric assembly 30 had been kept constant over the time period considered.

[0066] By substantially open electrical circuit, we mean a circuit in which a possible leakage current leads to a variation in charge of the piezoelectric assembly 30 of less than 30% of the charge which would have been exchanged with the exterior of the piezoelectric assembly 30 if the voltage across the terminals of the piezoelectric assembly 30 had been kept constant over the time period considered.

[0067] 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.

[0068] [Fig.2] illustrates a modeling of a piezoelectric assembly 30, or piezoelectric resonator, in the form of an equivalent electrical circuit 40 around a resonance mode.

[0069] The piezoelectric resonator 30 is known per se, and is typically modeled, close to the resonance mode used, in the form of a capacitor 42 and a resonant branch 44 connected in parallel with the capacitor 42, the capacitor 42 and the resonant branch 44 being connected between the input point 32 and the output point 34 of the piezoelectric resonator 30.

[0070] The resonant branch 44 is typically an RLC branch formed of a resistor Rm, a capacitor of capacitance Cm, and an inductance Lm connected in series. The capacitance Cp of the capacitor 42 connected in parallel with the resonant branch 44 is called parallel capacitance, or blocked capacitance, or reference capacitance. The voltage Vp across the terminals of the piezoelectric resonator 30 then typically corresponds to the voltage across the capacitor 42. In steady state, a current iL, substantially sinusoidal, flows in the RLC branch of the equivalent model of the piezoelectric resonator 30.

[0071] By convention, the voltage Vp across the terminals of the piezoelectric resonator is equal to a difference between two potentials, denoted respectively Vp+ and Vp.

[0072] The respective values ​​of the resistance Rm, the capacitance Cm and the inductance Lm, as well as the reference capacitance Cp define the dimensioning of the piezoelectric assembly 30.

[0073] As known per se, the mechanical oscillation of the piezoelectric resonator 30 is approximately sinusoidal. An increase or decrease in the energy stored over a resonance period leads respectively to an increase or decrease in the oscillation amplitude and therefore in its internal mechanical energy.

[0074] Furthermore, during a phase with a substantially constant charge across the terminals of the piezoelectric resonator 30, i.e. when the piezoelectric resonator 30 is placed in a substantially open electrical circuit, with a low exchange of electrical charges between the piezoelectric resonator 30 and the outside, an increase in the amplitude of the mechanical oscillations causes an increase in the amplitude of oscillation of the voltage Vp across the terminals of the piezoelectric resonator 30. During a phase with a substantially constant voltage across the terminals of the piezoelectric resonator 30, an increase in the amplitude of the mechanical oscillation leads to an increase in the amplitude of the current iL flowing in the mechanical branch Rm-Lm-Cm of the piezoelectric element 30.

[0075] [Fig. 3] illustrates a graph Gi of the evolution of the current iL, circulating in the piezoelectric assembly 30, multiplied by a variable [3, equal to 1 or to -1, as explained below, over a resonance period and a graph G2 of the piezoelectric voltage Vp at the terminals of the piezoelectric assembly 30 of an electrical energy converter 10, also multiplied by the variable [3, the converter 10 being controlled with a conversion cycle equal to a mechanical resonance period of 2ir of the piezoelectric assembly, according to a control mode known as three voltage steps, or in other words comprising 3 phases at substantially constant voltage.

[0076] It should be noted that the invention applies generally to control with N voltage levels, with N being an integer greater than or equal to 3.

[0077] The graphs Gi, G2 include on the abscissa angular values ​​(or angles) varying between 0 and 2ir.

[0078] It should be noted that it is possible, in an equivalent manner, to express the mechanical resonance period of the piezoelectric assembly as equal to a period temporal period between 0 and T or an angular period between 0 and 2ir.

[0079] Thus, there is a mathematical correspondence between temporal duration and angular duration.

[0080] When two distinct phases are indicated to have the same duration, this means both the same temporal duration and the same angular duration.

[0081] The command is carried out at angle a evolving over a period between 0 and 2ir radians, each angle corresponding to an instant of the period considered.

[0082] By convention, we designate by { y9î y3} the voltage values ​​of the three voltage levels over a conversion cycle, and by the median voltage value among the three voltage values, [3 being a variable designating the sign of the current iL for the voltage level

[0083] Thus, fi = 1 if the current iL is positive for the voltage level, and fi = - 1 if the current iL is negative for the voltage level

[0084] In other words, fi = 1 when a positive current is supplied to the piezoelectric assembly during the substantially constant voltage phase of voltage value Vy?, and fi = - 1 when a positive current is supplied to the voltage step Vp from the piezoelectric assembly, during the substantially constant voltage phase of voltage value

[0085] The use of the variable [3 makes it possible to obtain a general modeling of the six-phase conversion cycle, comprising an alternation of phases at substantially constant load and phases at substantially constant voltage, whether an electrical power is supplied to the piezoelectric assembly during the phase at substantially constant voltage corresponding to the highest voltage during the cycle, or whether a power is delivered from the piezoelectric assembly during the phase at substantially constant voltage corresponding to the highest voltage during the cycle.

[0086] The general modeling presented below applies both to control in voltage step-down mode and to control in voltage step-up mode.

[0087] Using the variable [3, we obtain the voltage values ​​associated with the voltage levels:

[0088] [Math.21] fiVc^^{fiVYfiV2,fiV3}

[0089] [Math.22] fiVh = median {fiV^ fiV2, fiV3}

[0090] [Math.23] fiVc = min{fiVl,fiV2>fiV3]

[0091] Furthermore, over a conversion cycle, fiVtnax denotes the maximum value of the voltage fiVP, and fiVmin the minimum value of the voltage fi Vp.

[0092] By definition, the relation: &Vc < pV h < PVa is verified.

[0093] Furthermore, each of the voltage values ​​Va, Vb, Vc (respectively the values ​​Vb V2, V3) is a combination of the values ​​of the input voltage Vin and the output voltage Vout of the converters according to the formula:

[0094] [Math.3] V^Ô^ + y^ , with [Math.3] rxE {-ioio, i) And [Math.3] x = {a, b, fl)

[0095] The effective values ​​of the parameters yx and ôx depend on the topology of the electrical energy converter 10 and the chosen conversion cycle.

[0096] The control configuration illustrated by graph G2 comprises phases I, III, V at substantially constant load and phases II, IV and VI at substantially constant voltage, with respective voltage values ​​PVb, PVa, PV^

[0097] The illustrated configuration corresponds to control in voltage step-down mode when [3=1.

[0098] In the phases with substantially constant load, at most only one of the switches Ki, K2, K3, K4 is closed, the other switches being open. In the phases with substantially constant voltage, one of the switches Kb K2 is controlled in the closed position, the other being open, and also one of the switches K3, K4 is in the closed position, the other being open.

[0099] Switching one of the switches from the open position to the closed position is done:

[0100] - either on command at a closing switching angle (or closing control angle), the switching angles being calculated by the electronic control device by implementing a mathematical model as explained in more detail below,

[0101] - either by natural switching of the switches when the switches are made in the form of diodes or have an intrinsic reverse diode or an additional diode placed in parallel.

[0102] In the first phase (phase I) at substantially constant load, the piezoelectric voltage [3Vpp passes from [3Vmin to [3Vb, between a0=0 and ap

[0103] Then, in phase II at substantially constant voltage, the piezoelectric voltage [3Vp is maintained at PV b between ai and a2.

[0104] Phase II is followed by a phase III at substantially constant charge, during which the piezoelectric voltage [3V] drops from [3Vb to [3Va between a2 and a3b

[0105] Phase III comprises a first excursion of the piezoelectric voltage [3VP up to the maximum voltage value PVmax in «bl» then a second excursion of the voltage from the maximum voltage value PVmax to the value PVa between a3a and a3b, which advantageously makes it possible to carry out a switching of the switches in closing at zero voltage (or switching in ZVS mode).

[0106] Phase III is followed by a phase IV at substantially constant voltage, the piezoelectric voltage [3V] being maintained at pVa between a3b and a4.

[0107] The conversion cycle then includes a phase V at substantially constant charge, during which the piezoelectric voltage [3Vp] rises from [3Va to [3Vc between a4 and a5

[0108] Phase V is followed by a phase VI at substantially constant voltage, the piezoelectric voltage [3V] being maintained at PVC between a5 and a6.

[0109] Finally, the cycle includes a phase VII at substantially constant charge, which joins phase I when the cycle is repeated, this phase VII including an excursion of the piezoelectric voltage [3VP from the value [3VC up to the minimum voltage value between a6 and a7=2ir so as to then allow a closing of the ZVS switches at the angle a7=2ir. Indeed, in view of the cyclic repetition, the periods are expressed at modulus 2ir, in other words a7=0= a0.

[0110] In other words, it can be considered that phases I and VII form a phase with substantially constant load comprising a first excursion of the piezoelectric voltage [3VP between [3Vcet PVmin, then a second excursion of the piezoelectric voltage [3VP between PVmin and [3Vb, allowing switching of the ZVS switches, as in phase III.

[0111] Note that in some cases, PVmax can be equal to [3Va, and consequently the angles a3a and a3b are the same. Similarly, in some cases, P^min can be equal to [3VC, in this case a6 and a7 are the same.

[0112] Depending on the application cases, for example in step-down mode, only the switches Ki and K2 need to be controlled in closing to carry out the conversion cycle illustrated in [Fig.3], K3 and K4 then operating as simple diodes with natural conduction without a control signal.

[0113] The cycle in [Fig.3] illustrates a case of conversion with 6 operating phases on a conversion cycle whose conversion period is carried out on the mechanical resonance period, i.e. fres=fCycie- In order to operate optimally, the charge of the piezoelectric resonator and its energy must be balanced over a conversion cycle. Thus, 3 phases at constant voltage are at least mandatory during the conversion cycle corresponding to fcycie. Nevertheless, it may be advantageous to spread these three phases of exchanges at constant voltage over several mechanical periods fres and / or to add other phases at constant voltage Vx during a conversion cycle. For the rest of the description, the explanation is based on the simplified case where fres= f CyCie and using only 6 conversion phases as illustrated in [Fig.3]. Nevertheless, the invention also applies to the case where the cycle extends over several mechanical resonance periods and / or comprises more than 6 phases.

[0114] We denote by Qa, Qb, Qc the charges exchanged during the respective voltage levels, in other words Qa is the integral of the current iL from a3b to a4 Qb is the integral of the current iL from oq to a2 and Qc is the integral of the current iL from a5 to a6.

[0115] In the general case, we note Qx the charge corresponding to the integral of the current iL exchanged by the resonator with its external environment during the constant voltage phase Vx. x taking its value among the number of constant voltage stages considered during the cycle.

[0116] The electrical energy converter 10 respects a condition of equilibrium between the charge supplied and the charge restored during a conversion cycle, which corresponds to a resonance period in the example presented, the condition of equilibrium being translated by the following equations:

[0117] [Math.41] Qa + Qh + QC = Q

[0118] In the general case we then have: [Qu'l Ea=o

[0120] The above equation expresses the charge balancing condition over a conversion cycle.

[0121] Furthermore, in steady state, the energy of the piezoelectric assembly cannot diverge as the conversion cycles progress, which requires compliance with an energy balance condition such that:

[0122] [Math.42] pVaQa + UVhQb + PVCQC = Eloss

[0123] In the general case:

[0124] y Q = El r lOSS

[0125] Where Eims is the energy lost in practice over a conversion cycle of the converter compared to a perfect theoretical model, the energy loss being for example due to losses in the piezoelectric assembly at the level of the series resistance, or at the level of the switches. In certain cases, it can be considered that £w=0, which amounts to considering an operating model approaching in practice the theoretical model.

[0126] In a more optimized case described in more detail below, a term of re-

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[0144] regulation relating to an estimated energy loss is added. Finally, the average output current lout can be expressed as a function of the charges exchanged by the resonator with its environment during the constant voltage phases: [Math.43] In the general case: E J'A = - 7“ Where T'a' ^bXc are defined in [MATH 3], fcycie is the frequency of the conversion cycle. The operating conditions of the electrical energy converter 10, comprising the piezoelectric assembly 30, lead to the following formulas for the switching angles of the switches making it possible to carry out the phases of the conversion cycle at three levels of substantially constant voltage: [Math.5] a{) = 0 — ciCOS L'Vo A) J ~ / J / / v 07' 1 a-, = amq cos( a. ) + -4-\ ' 1 / pi I a3a ~ 77 \ 7( inax ) cw \ a,h = 2tt- acos cav a3--y---— y \ -'ct ylj a4 = 2æ - acos co s (a3b) - 777 j a5-2n- acosi cos( a4)--.....) a6 = 2æ - acos I cos ( a5 j - 777 j “7 = 2tt In the general case, the transition from a level Vx to the next level Vx+i during a constant load phase is written: [Math.6] has \ / / \ \ = H TT+a / / 2np27r - signhr - ab%27Tj acos [cos (ah) - j With % which corresponds to the modulo operation and / / allowing to obtain the quotient of the Euclidean division of the number on the left by the number on the right. Also the operator sign(r) allows to determine the sign of the result r in parentheses and is worth -1 for sign(0).

[0145] Furthermore, IL is the amplitude of the current iL flowing in the piezoelectric assembly, cos() is the cosine function, acos() the reciprocal arc cosine function, and w = Inj is the pulsation associated with the frequency / which is the mechanical resonance frequency of the piezoelectric element 30, controlled by the electronic control device 20.

[0146] In the general case, the exchange of Qx charges during a phase at constant voltage Vx induces the following relation:

[0147] [Math.7] aM - ((Æ + ai^ 11 2æ- sign^TT - ab%2n^acos ( cos ( ab ) - sigï^jr - aho / c2jr^^ j

[0148] The set of instants where the current passes through zero imposes the following relations:

[0149] [Math.8] ^+1 = ((^ + ^) / / ^)^

[0150] .

[0151] In addition, the capacitances Ci, C3b and C5 represent the parallel capacitance Cp of the piezoelectric assembly, increased by the parasitic capacitances relating to each of the phases I, III, V at substantially constant load. More generally, the capacitance Cx represents the parallel capacitance Cp of the piezoelectric assembly, increased by the parasitic capacitances relating to each of the phases x.

[0152] Several implementations of mathematical modeling are possible.

[0153] According to a simplified implementation mode, it is possible to consider that each of the capacities Ci, C3b and C5 is equal to Cp.

[0154] According to an intermediate implementation mode, it is possible to consider that each of the capacities Ci, C3b and C5 is equal to Cp increased by the same estimated parasitic capacitance value, Cpar.

[0155] According to a more complex mode of implementation, it is possible, for each phase at substantially constant load, to estimate the parasitic capacitance, in particular as a function of the open / closed switches, and also, optionally, of the value of the piezoelectric voltage Vp.

[0156] Furthermore, the amplitude IL of the current in the piezoelectric assembly depends on the average output current Iout according to the formula:

[0157] [Math.9] h = Kl„,+D(V„œ-V„.„)

[0158] Where K and D are factors depending on the piezoelectric assembly and the conversion cycle controlled by the electronic control device. For a 3-step cycle at substantially constant voltage whose frequency is equal to the resonant frequency of the resonator, K and D can be expressed as follows:

[0159] [Math. 10] _

[0160] And:

[0161] [Math. 11] D = ^Cpw

[0162] For a more general case with a cycle having more than 3 constant voltage steps and / or a cycle spread over several mechanical resonance periods, then the K factor must be reformulated accordingly.

[0163] The formulas [MATH 5], and more generally the formulas [MATH 6] to [MATH 8], are advantageously applied by the electronic control device to calculate the switching angles of the switches to carry out the various phases.

[0164] In addition, the frequency / } of the conversion cycle is estimated by numerical calculation, by solving the system of equations formed by the equations [MATH 4.1] to [MATH 4.3] introduced above.

[0165] In the following part, an example is presented for determining the operating frequency of the piezoelectric cycle in the case with six operating phases where fcycie=fres.

[0166] Considering the charge and energy balance equations, the charges Qa, Qh and Qc are found in this way:

[0167] [Math. 12]

[0168] And:

[0169] [Math. 13] P — 'Loss 2

[0170] The inductance Lm in the mechanical branch imposes the current iL to be without discontinuity. In addition, the capacitances Cs and Cp impose the derivative of the current iL to also be without discontinuity. Thus, at each phase transition (between the phases k and k+F) the following equations must be respected:

[0171] [Math. 14] kA) “ 'Lik+Fb)

[0172] Then, due to the high quality factor of the piezoelectric resonator, it is possible to consider the current in the mechanical branch of the resonator as almost sinusoidal. It follows that for each of the phases (both open and closed), the current iL in the mechanical branch of the resonator can be written as follows:

[0173] [Math. 15]

[0174] with ILk the associated amplitude, <bk, la phase associée et cok, la pulsation de fonctionnement associée. Il est à noter que la pulsation de fonctionnement dépend des capacités placées en parallèle du résonateur (capacités parasites) mais aussi de la phase de fonctionnement (tension constante ou non).

[0175] In other words, the continuities of the current and its first derivative within the mechanical branch of the resonator are considered. Indeed, the inductance Lm and the capacitors Cp and Cm require iL to be of class C1, that is to say that the current iL cannot suddenly change in value due to the inductive behavior of Lm and the derivative of iL linked to the voltage across Lm cannot change suddenly either due to a ZVS mode control which does not generate sudden voltage variations across the piezoelectric.

[0176] Also, for the resolution, we consider that at the instant (t=0), the phase ¢1 is zero. Then by combining the current continuity equations with the expression of the current, we determine the following relations:

[0177] [Math. 16] ^+1 = arcos (co^tk + - œk+ïtk #

[0178] Then by integrating the current iL on each phase, the following relationships are determined:

[0179] [Math. 17] ak. = œktk+6k a0 = 0 # a^acos^tao) -(Vb-Vmin)C^ilhî) $ a2 = cos(a})+ Qbw2[lL2 # a3a = 71 # «3b = 2tt - acos (cos () - (Va - V / k3b) # «4 = 2tt - acos (cos (a3h) - Qw4 / l^)# a5 = 2rr- acos(cos(a4) -(Vc- V4)C5a>5 / / L5) # a6 = 2 / r - acos ( cos ( a5 ) - / IL6 ) # aj = 2tt#

[0180] Thus, knowing IL] and the operating frequency fres of the resonator, it is first possible to determine the exchanged charges (Qa, Qb, Qc). This then makes it possible to determine the set of angles ak. Finally, we find that the initial system which depended on a set of operating angles and an operating frequency now only depends on a frequency and an initial current. Also, in order to be complete, the system loops back over a period, that is to say that the last switching angle corresponding to the end of the period is t7=l / fres.

[0181] In the same way, the resonator is required to perform a voltage excursion for the closure of the switches to zero voltage at time a3a.

[0182] We then set two new constraints:

[0183] [Math. 18] y2 - JL2(cos(a3a) - cos(à2)) / œ2C2 = Vmax t7=T#

[0184] Finally, assuming a certain current amplitude and an operating frequency, it is possible to calculate the two constraints above which mean on the one hand, that the cycle is carried out in one period and on the other hand, that the voltage excursion reached is indeed the desired one.

[0185] We can then use a non-linear equation solving tool which takes as input the two constraint functions and determines the torque which minimizes the error on these constraints. It is thus possible to determine the operating frequency numerically.

[0186] We then have:

[0187] [Math. 19] fre) = f ^constraint,

[0188] with fsolve representing a numerical resolution method, for example using the Levenberg-Marquardt or Gauss Newton algorithm. Initial values ​​iLheg of current amplitude and / 0 of frequency are used to give a starting point for the resolution.

[0189] It then remains to provide good starting conditions. For the initial frequency / 0, ​​we choose it in the operating band and for the current lLheg, we use the approximation of 1L seen in [MATH 6].

[0190] Finally, by taking up the construction approach of this model, it is possible to extend it to cycles with more than 6 operating phases but also to cycles spread over several resonance periods of the resonator.

[0191] Alternatively, to determine the operating frequency fres of the resonator, other mathematical resolutions are possible, such as that presented in the article: L. d. A. Pereira, A. Morel, M. Touhami, T. Lamorelle, G. Despesse and G. Pillonnet, “Operating Frequency Prediction of Piezoelectric DC-DC Converters,” in IEEE Transactions on Power Electronics, vol. 37, no. 3, pp. 2508-2512, March 2022, doi: 10.1109 / TPEL.2021.3115182.

[0192] Thus, the formulas [MATH 4.1] to [MATH 4.3], [MATH 5], [MATH 6] form a mathematical model, used to calculate a theoretical estimate of the converter control parameters which are the switching angles and the frequency of the conversion cycle.

[0193] As can be seen, the equations [MATH 5], and more generally [MATH 6] to [MATH 8], express the switching angles as a function of the characteristics of the piezoelectric assembly (i.e. the capacities Cb C3b, C5), the parameters of the converter and the frequency of the conversion cycle.

[0194] [Fig.4] schematically represents the main functional blocks of the electronic control device 20 in one embodiment, for controlling the electrical energy converter.

[0195] The electronic control device 20 is configured to control the electrical energy converter 10, in particular to control the switching of the switches Kb K2, K3, K4 of the converter 10 to carry out a conversion cycle as described with reference to [Fig. 3], comprising at least 3 phases at substantially constant voltage at the terminals of the piezoelectric assembly 30.

[0196] The control device 20 can also control an electrical energy converter that can include more than 4 switches around the piezoelectric assembly, for example the following converter that includes 5 switches around the piezoelectric assembly but expresses a three-phase operating cycle: M. TOUHAMI, G. DESPESSE and F. COSTA, "A New Topology of DC-DC Converter Based On Piezoelectric Resonator," 2020 IEEE 21st Workshop on Control and Modeling for Power Electronics (COMPEL), Aalborg, Denmark, 2020, pp. 1-7, doi: 10.1109 / COMPEL49091.2020.9265767.

[0197] The electronic control device 20 is for example produced in the form of an electronic circuit comprising one or more electronic components.

[0198] 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.

[0199] The electronic control device 20 comprises a measurement module 50 configured to measure a value Vout of the output voltage of the converter 10. In the case where it is sought to regulate an electrical output parameter (or electrical parameter to be regulated) other than the voltage, it is then necessary to have a complementary measurement additional, such as a measurement of the output current if one wants to regulate the output current or power.

[0200] For example, the output voltage measurement module 50 is produced in the form of a divider bridge and a low-pass filter.

[0201] Optionally, a module 52 for measuring a value Vin of the input voltage is also implemented. This module 52 is optional, because in certain applications, the input voltage is substantially constant and known in advance.

[0202] The electronic control device 20 further comprises, advantageously, a calculation module 60, which implements the mathematical model for calculating the switching angles and an estimator of the conversion cycle frequency, by implementing the mathematical model described above (see in particular formula [MATH 19]). The switching angles and the frequency of the conversion cycle are parameters of the conversion cycle.

[0203] The calculation module 60 is configured to implement calculations to determine the parameters of the conversion cycle, as a function of the input voltage value Vin, the output voltage value Vout, of a corrected estimate of the output current, îest, provided by a first regulation module 56 implemented in a first regulation loop 58.

[0204] The first regulation module 56 performs a first step of regulation of the method of controlling an electrical energy converter, comprising a correction of a measured output voltage or current value with respect to a set voltage or current value, the first regulation module 56 providing as output a corrected estimate of output current.

[0205] The calculation module 60 performs a step of calculating a conversion cycle frequency and a plurality of switching angles of the method of controlling an electrical energy converter.

[0206] Optionally, the calculation module 60 also receives as input an estimated energy loss, taking into account this estimated energy loss making it possible to regulate the energy transfer during a conversion cycle, the estimated energy loss being provided by a second regulation module 62 implemented in a second regulation loop 64. This estimated energy loss results from the measurement of the voltage excursion naturally reached by the resonator or from an observation of the sign of the error of this excursion compared to what it should be to ensure the closing of at least one of the switches at zero voltage.

[0207] In one embodiment, the execution frequency of the control loops may be similar or identical, but the correctors of each of the loops are adjusted so that the first response time of the first control loop is faster than the second response time of the second control loop. preferably, the first response time is faster than the second response time by at least a factor of 4, advantageously by at least a factor of 8.

[0208] Alternatively, the correctors of the first control loop are adjusted so that the first response time of the first control loop is slower than the second response time of the second control loop.

[0209] The outputs of the calculation module 60 are provided as input to a control unit 61 (or generator 61), configured to generate periodic switching control signals to the switches KP. .KM of the electrical energy converter 10, at the conversion cycle frequency provided by the calculation module 60, for example to the switches Ki to K4 in the example described with reference to [Fig.l].

[0210] For example, the control unit 61 is a pulse width modulation or PWM unit (for “Pulse Width Modulation” in English) capable of generating several control signals of different durations and phases. For example, the control unit 61 implements high-resolution clocks (in English “timers”), present in certain types of microcontrollers.

[0211] Alternatively, the control unit 61 uses controllable frequency ramps, and comparators which detect a voltage level to send a command to open or close a switch.

[0212] The first regulation loop 58 makes it possible to adjust the transfer of the electrical power and regulate the output voltage or current, as a function of a setpoint voltage Vcons or a setpoint current Icons. Indeed, when the voltage excursion between Vmax and Vmin is carried out over a conversion cycle, the amplitude IL of the current flowing in the piezoelectric assembly depends, according to the equation [MATH 9], on the term and the amplitude of the output current is linked to the frequency f le of the conversion cycle.

[0213] The first control loop 58 implements a subtraction unit 55 which provides a difference between the measured output voltage or current value and the corresponding voltage or current setpoint value.

[0214] Two embodiments of the first regulation loop 58 are envisaged, depending on whether the regulation carried out is a current regulation or a voltage regulation.

[0215] According to a first embodiment, current regulation is implemented.

[0216] In this first embodiment, the first regulation module 56, implemented in the first regulation loop, comprises a corrector module 66, which is a first corrector module, which has the objective of canceling the difference between the output current value and the setpoint current value while maintaining a stable system. For example, the corrector module 66 is a proportional integral corrector, PI. Alternatively, other types of corrector modules can be used.

[0217] At the output of this module, a corrected estimate of the output current, îest, is obtained, which is supplied to the calculation module 60.

[0218] In a second embodiment, voltage regulation is implemented. In this second embodiment, the first regulation module 56, implemented in the first regulation loop, further comprises a unit 63 for applying a gain making it possible to transform the voltage difference into an estimated current difference, the estimated current difference then being provided as input to the corrector module 66 previously described. Alternatively, the gain 63 is directly integrated into the corrector 66.

[0219] The second regulation loop 64 makes it possible to regulate the voltage excursion at the terminals of the piezoelectric assembly, directly or indirectly, so as to ensure the criterion to be respected to carry out switching in ZVS mode.

[0220] Indeed, the first regulation loop 58 carries out a regulation of the output voltage or current as a function of a corresponding setpoint voltage or current value, under the assumption that the second term of [MATH 9], DiVmax" is kept constant.

[0221] In a more optimized embodiment, the losses in the electrical energy converter 10, in particular losses due to the non-linearities of the piezoelectric assembly, or losses generated at the switches, are taken into consideration thanks to the implementation of the second regulation loop.

[0222] The second regulation loop 64 has the function of correcting the energy supplied to the piezoelectric assembly to enable the piezoelectric voltage excursion to be achieved as precisely as possible between Vtnin and Vmax.

[0223] In fact, the energy input to the piezoelectric assembly is compensated by introducing into the formula [MATH 4.2] the system of equations representing the charge balance conditions:

[0224] [Math.42a] PVaQa + PVbQb + [iVcQc — Eloss + A Eloss

[0225] Or in the general case:

[0226] liL,yxQ=Elm+

[0227] Where the term A Efoss represents the energy loss estimated by the second regulation module 62.

[0228] For this purpose, the electronic control device 20 also comprises a module 68 for estimating the voltage excursion at the terminals of the piezoelectric assembly.

[0229] In one embodiment, the excursion estimation module 68 provides an estimated voltage excursion value per period, AV, and a subtraction unit 65 that provides a voltage excursion deviation, £av> between the estimated value voltage excursion per period, A VPR and a voltage excursion setpoint.

[0230] The voltage excursion setpoint value is for example a theoretical reference value, for example Vmax-Vmin.

[0231] In another embodiment, the excursion estimation module 68 provides an image of a lack or excess of voltage excursion per period.

[0232] Embodiments of the module 68 for estimating the voltage excursion at the terminals of the piezoelectric assembly will be described below.

[0233] The second regulation module 62 implements a unit 67 which implements a function for transforming the voltage excursion deviation into an energy deviation (a^SS) representative of a lack of energy supplied to the piezoelectric assembly over a conversion cycle.

[0234] The energy difference is provided as input to a second correction module 70, which provides as output the estimated energy loss A Eloss to be compensated.

[0235] Preferably, the second corrector module 70 has an integral compensation term, for example is a proportional integral corrector, PL. Alternatively, other types of corrector modules can be used. Alternatively, the transformation carried out by the module transforming the excursion deviation into energy deviation can be integrated into the corrector module 70.

[0236] In this second embodiment, the calculation module 60 also receives as input the estimated energy loss A Eloss, which is used in the formula [MATH 4.2a],

[0237] The calculation module 60 is for example produced in the form of program code executable by a processor or a microcontroller, an FPGA or an ASIC.

[0238] The calculation module 60 implements an estimator 72 of the conversion cycle frequency and a module 74 for calculating the switching angles according to the mathematical model of the equations [MATH 5].

[0239] In one embodiment, the estimator 72 implements the method for determining the operating frequency of the piezoelectric cycle described above, with reference to formulas [MATH 12] to [MATH 19] in the case with six operating phases.

[0240] Thus, by using the numerical resolution method to solve [MATH 19], the estimator 72 determines the operating frequency fres of the driving cycle by taking as input the input voltage Vin, output voltage Vout and the estimated output current Lst and the estimated energy shortage AE(l.,ss.

[0241] According to another embodiment, the frequency fcycie of the conversion cycle is calculated by simulation for the operating point defined by output = est}

[0242] For example, a calculation carried out upstream makes it possible to calculate the frequency fcyde of the conversion cycle for a set of operating points (Vhp Vmi(Iaut), the results being memorized, in an appropriate memorization structure, and stored in an electronic memory unit of the electronic control device 20.

[0243] More generally, the numerical resolution of the equations upstream makes it possible to subsequently accelerate real-time operation.

[0244] From such a stored structure, the conversion cycle frequency estimator 72 can access a previously calculated frequency value fcyde.

[0245] Module 74 uses the mathematical model provided by the formulas [MATH 5] to calculate the switching angles oqà aNN being equal to 7 in the example corresponding to the conversion cycle of Figure 3, by applying the frequency value f cyde of the conversion cycle for the operating point (y, yt ï

[0246] Embodiments of the module 68 for estimating the voltage excursion at the terminals of the piezoelectric assembly are described below with reference to FIGS. 5 to 8.

[0247] In the case of application of a three-step conversion cycle at substantially constant voltage, as described with reference to [Fig. 3], a constraint on the voltage excursion at the terminals of the piezoelectric assembly is observable at a 3a or at a7: when the amplitude of the voltage excursion of the piezoelectric assembly is not sufficient, an abrupt voltage front is observed at a3a and at a7 on each of the terminals Vp+ and Vp- of the piezoelectric assembly, representative of a closing of a switch without respecting the ZVS condition or closing at non-ZVS, as shown schematically in [Fig. 5]. This abrupt voltage front generates a high-frequency signal on the two terminals of the resonator which is difficult to observe.

[0248] In a first embodiment, described with reference to [Fig. 6], the module 68 for estimating the voltage excursion at the terminals of the piezoelectric assembly is a passive module, produced by a set of analog filters, which provides an image of the non-compliance with the ZVS (i.e. lack or excess of voltage excursion) by observing the derivative of one of the terminals of the piezoelectric. This module 68 implements a high-pass filter 76, to isolate the high-frequency signal generated by the abrupt voltage front, then envelope detectors 78 and low-pass filters 80 make it possible to obtain information on non-ZVS closure at low frequency, making it possible to obtain an image of the positive derivative of the high-frequency signal Vdev+ and one of the negative derivative of the high-frequency signal Vdev-

[0249] Thus, in this embodiment, the switching mode of the zero voltage switches (ZVS mode) is ensured by means of a zero or close to zero derivative setpoint.

[0250] The cut-off frequency Fc of the high-pass filter is higher than the frequency fcyde of the conversion cycle, for example approximately 100 times higher than the frequency of the conversion cycle.

[0251] Advantageously, the module 68 for estimating the voltage excursion at the terminals of the piezoelectric assembly produced in this way is a passive module, inexpensive and simple to implement because no specific control is necessary. However, this module 68 thus produced is disturbed by parasitic oscillations when it is connected to the piezoelectric assembly over the entire conversion cycle.

[0252] In a second embodiment, described with reference to [Fig.7], the module 68 for estimating the voltage excursion at the terminals of the piezoelectric assembly differs from its first embodiment by replacing the high-pass filter 76 with a connecting capacitor 84, of connecting capacitance Cdec, connected to an active control unit 82, which makes it possible to activate the estimation of the voltage excursion only in chosen angular or temporal measurement ranges, for example around the mid-period angles a3a and end of period angles a7=2ir, in the case of the three-step conversion cycle at substantially constant voltage.

[0253] A measurement range centered on a given angle a is defined by [ a - Ô, a + Ô ] with 5 preferably chosen to be less than 1 / 20th of the mechanical resonance period, advantageously less than 2 / 100th of the mechanical resonance period. The angle(s) to be monitored is / are advantageously the angle(s) where Vp reaches its maximum theoretical value before the application of a voltage step and / or the angle where Vp reaches its minimum theoretical value before the application of a constant voltage step. Thus, in the 6-phase case described in [Fig.3], we will seek to monitor the angle a3a=iret / or a7=2ir.

[0254] The estimation of the voltage excursion is inhibited outside the chosen ranges. For example, the inhibition is done by means of an active switch of the active control unit 82, for example a transistor T1 which is, according to variants, a bipolar transistor or a MOSFET transistor, a mechanical relay, controlled by a control signal Vcom, such a control signal being illustrated in [Fig.8].

[0255] Indeed, when the control signal Vcom is in the high state, point 86 is at the potential Vmid=Vpol / 2, therefore does not change. The voltage Vmid is the input voltage of the envelope detectors 78.

[0256] Thus, advantageously, thanks to the active control unit 82, during the inhibition ranges, the input voltage of the envelope detectors 78 remains constant, in other words the envelope detectors 78 are immune to voltage variations at the terminals of the piezoelectric assembly, and therefore are no longer disturbed by parasitic oscillations.

[0257] The sizing of the components of the module 68 for estimating the voltage excursion at the terminals of the piezoelectric assembly is chosen to obtain a compromise between speed and measurement precision.

[0258] The active control unit 82 is dimensioned so that the sum of the parasitic capacitances CDL, CDH of the diodes DL and DH and the parasitic capacitance Cn of the switch Tl is less than the connection capacitance Cdec, and preferably at least 10 times less than the connection capacitance Cdec, and the capacitance Cdec is at least 10 times, advantageously at least 20 times less than the capacitance Cp of the piezoelectric assembly.

[0259] The voltage difference across the piezoelectric assembly around the angle a3a is considered:

[0260] [Math.20] A y (“3”) = y (“3“-) - v ()

[0261] In the absence of ZVS closure, the voltage variation in the piezoelectric assembly induces a voltage variation in the module 68, which will be captured by the envelope detectors 78.

[0262] An induced charge Qind, supplied to the envelope detector, as a function of the voltage difference AV(a^) and the respective capacitances is calculated.

[0263] The envelope detector is sized to have a cutoff frequency at least 10 times lower than the frequency fcycie of the conversion cycle.

[0264] The resistance Rc can be calculated as a function of the induced charge Qind, the maximum observed voltage difference, A the frequency fcycie, and a predetermined target voltage Umax that we would like to obtain at the output of the low-pass filter for the desired A.

[0265] [Math.21] TT1 Ti ma.x

[0266] Advantageously, the observation duration during which the control signal V com is at zero (i.e. duration of the non-inhibition range), is typically less than 2% of the total duration of a conversion cycle (as presented in [Fig.8]), which makes the module 68 for estimating the voltage excursion at the terminals of the piezoelectric assembly not very sensitive to noise.

[0267] The invention has been described in the case of application of a three-stage conversion cycle at substantially constant voltage.

[0268] It is clear that the electronic control device and the associated method are applicable for a conversion cycle with N steps at substantially constant voltage, with N greater than or equal to 3. Indeed, the mathematical model [MATH 5] allowing the calculation of the switching angles is then reformulated for the conversion cycle chosen, with the number of stages chosen, as well as the equations [MATH 4] relating to the balance of charges on a conversion cycle, and, where appropriate, the equations [MATH 12] to [MATH 19] to determine the operating frequency of the piezoelectric cycle.

[0269] The invention has been described in detail in a case in which a conversion cycle is equal to a resonance period of the piezoelectric assembly. The invention is generalized for any conversion cycle with (k+1) resonance periods (see equation [MATH 1]), the balancing of charges and energy being ensured per conversion cycle.

[0270] As is clear from the description, the invention applies to numerous topologies of electrical energy converter comprising one or more piezoelectric resonators.

[0271] The invention also applies to a double switching bridge converter topology as described for example in patent application EP 4 191 854A1.

[0272] Furthermore, it also appears clearly that the invention also applies to converter topologies comprising several elementary piezoelectric converters connected to each other by one of the branches of the switching bridge, by adapting the voltage step values ​​to be controlled as a function of the converter topology.

Claims

1. Claims Electronic control device (20) for an electrical energy converter (10) capable of converting an input voltage (Vin) into an output voltage (Vout), the converter comprising two input terminals (12; 14) for receiving the input voltage (Vin), two output terminals (16, 18) for delivering the output voltage (Vout), a piezoelectric assembly (30) comprising at least one piezoelectric resonator, the piezoelectric assembly (30) being connected between an input point and an output point, the piezoelectric assembly resonating according to successive resonance periods, the converter (10) comprising several switches (Kb K2, K3, KJ connected between said input terminals, output terminals and input and output points of the piezoelectric assembly, the electronic control device (20) comprising: - a measurement module (50) configured to measure a value of the output voltage of said converter; - a control unit (61) configured to control a switching of at least one switch, following several successive phases during a conversion cycle, equal to one or more resonance periods and having an associated cycle frequency (fcycie), the conversion cycle comprising at least three phases at substantially constant voltage at the terminals of the piezoelectric assembly, separated by phases at substantially constant charge at the terminals of the piezoelectric assembly, the electronic control device (20) being characterized in that it comprises: -a first regulation module (56), implemented in a first regulation loop (58), configured to correct a measured output voltage or current value with respect to a setpoint voltage or current value, the first regulation module (56) providing as output a corrected estimate of output current, -a calculation module (60) of a conversion cycle frequency and a plurality of switching angles, the calculation module (60) receiving as input said corrected estimate of current, the value of the measured output voltage, an input voltage value, the calculation module implementing a mathematical model for calculating said switching angles and an estimator (72) of the conversion cycle frequency conversion, said conversion cycle frequency and said plurality of switching angles being provided as input to the control unit (61).

2. Electronic control device according to claim 1, further comprising a module (68) for estimating a voltage excursion at the terminals of the piezoelectric assembly (30), and a second regulation module (62), implemented in a second regulation loop (64), the second regulation module (62) providing as output an estimated energy loss, as a function of a difference between the voltage excursion estimated by the estimation module and a set voltage excursion, said estimated energy loss also being provided as input to the calculation module (60) and used for calculating said switching angles.

3. Electronic control device according to claim 2, in which the module (68) for estimating a voltage excursion at the terminals of the piezoelectric assembly (30) is a passive module, produced by a set of analog filters comprising a high-pass filter (76) configured to isolate a high-frequency signal generated by an abrupt voltage front.

4. Electronic control device according to claim 2, in which the module (68) for estimating a voltage excursion at the terminals of the piezoelectric assembly (30) is an active module comprising an active control unit (82), comprising a switch controlled by a control signal (Vcom), the control signal being configured to authorize a measurement of the voltage excursion over a range centered on a chosen measurement angle (a3).

5. Electronic control device according to one of claims 3 or 4, in which the module (68) for estimating a voltage excursion at the terminals of the piezoelectric assembly further comprises at least one envelope detector (78) and at least one low-pass filter (80).

6. Electronic control device according to any one of claims 2 to 5, in which the first control loop (58) is set for a first response time, the second control loop (64) is set for a second response time, the first and second response times being distinct.

7. Electronic control device according to claim 6, in which each of said first and second regulation loops (58, 64) comprises correction modules (66, 70) adjusted so that the first response time of the first control loop (58) is faster than the second response time of the second control loop (64).

8. Electronic control device according to any one of claims 1 to 7, in which the first regulation module (56) receives as input a current difference between the measured output current value and the setpoint current value, and comprises a proportional-integral correction module (66) which provides a corrected estimate of the output current from said current difference.

9. Electronic control device according to any one of claims 1 to 7, in which the first regulation module (56) receives as input a voltage difference between the measured output voltage value and the set voltage value, and comprises a unit (63) for applying a gain making it possible to transform the voltage difference into a current difference, the current difference then being supplied as input to a proportional-integral correction module (66) which provides a corrected estimate of the output current from said current difference.

10. Electronic control device according to any one of claims 1 to 9, in which the calculation module (60) comprises an estimator (72) of the conversion cycle frequency (fcyde), the estimator (72) implementing a numerical resolution method for iteratively solving a system of equations representative of a balance of charges and energy over the conversion cycle.

11. Electronic electrical energy conversion system (2) comprising an electrical energy converter (10), capable of converting an input voltage (Vin) into an output voltage (Vout), the converter comprising two input terminals (12, 14) for receiving the input voltage (Vin), two output terminals (16, 18) for delivering the output voltage (Vout), a piezoelectric assembly comprising at least one piezoelectric resonator, the piezoelectric assembly being connected between an input point and an output point, the piezoelectric assembly (30) resonating according to successive resonance periods, the converter comprising several switches connected between said input terminals, output terminals and input and output points of the piezoelectric assembly, and an electronic control device (20) configured to control said electrical energy converter (10),wherein said electronic control device (20) is in accordance with claims 1 to 10.,

12. Method for controlling an electrical energy converter (10) capable of converting an input voltage (Vin) into an output voltage (Vout), the converter (10) comprising two input terminals for receiving the input voltage (Vin), two output terminals for delivering the output voltage (Vout), a piezoelectric assembly (30) comprising at least one piezoelectric resonator, the piezoelectric assembly being connected between an input point and an output point, the piezoelectric assembly resonating according to successive resonance periods, the converter comprising several switches connected between said input terminals, output terminals and input and output points of the piezoelectric assembly, the method being implemented by an electronic device for controlling said converter and comprising steps of - measuring a value of the output voltage of said converter;-control, by a control unit, of a switching of at least one switch, following several successive phases during a conversion cycle, equal to one or more resonance periods and having an associated cycle frequency, the conversion cycle comprising at least three phases at substantially constant voltage at the terminals of the piezoelectric assembly, separated by phases at substantially constant charge at the terminals of the piezoelectric assembly, the method being characterized in that it comprises:; - a first regulation step, implemented in a first regulation loop, comprising a correction of a measured output voltage or current value relative to a set voltage or current value, the first regulation providing as output a corrected estimate of output current, -a step of calculating a conversion cycle frequency and a plurality of switching angles, as a function of said corrected current estimate, the value of the measured output voltage, an input voltage value, the calculation step implementing a mathematical model for calculating said switching angles and an estimate of the conversion cycle frequency, said conversion cycle frequency and said plurality of switching angles being provided as input to the control unit.

13. Method for controlling an electrical energy converter according to claim 12, further comprising an estimation of a voltage excursion at the terminals of the piezoelectric assembly, and a second re regulation, implemented in a second regulation loop, the second regulation providing as output an estimated energy loss, as a function of a difference between the voltage excursion estimated by the estimation module and a set voltage excursion, said estimated energy loss also being provided as input to the calculation step and used for the calculation of said switching angles.

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