Transcutaneous power transmission system designed to power an implant.

Abstract

A transcutaneous power transmission system (1) for powering an implant (4) comprises: - a primary circuit (2a) including an inverter (7) capable of being powered by a DC voltage UpDC and a DC current IpDC, a primary capacitor Cp and a primary coil Lp capable of being powered by the inverter; - a secondary circuit (2b) including a secondary coil Ls for magnetic coupling with the primary coil, a secondary capacitor Cs, and a rectifier (8) capable of powering the implant (4) with a DC voltage UsDC; the secondary circuit further includes a switch IT for switching the rectifier on or off. The system further comprises: - a self-adaptive control circuit (3), connected to the primary circuit (2a) and configured to automatically control the DC voltage UpDC based solely on measurements of UpDC and IpDC, according to a constrained optimization algorithm. Figure for the abstract: Fig. 1

Description

Title of the invention: Transcutaneous energy transmission system intended to power an implant.

[0001] The present invention relates to a TETS (Transcutaneous Energy Transfer System) transcutaneous energy transmission system intended to power an implant.

[0002] This is a system for transferring energy without a percutaneous connection, by magnetic field.

[0003] The invention finds a particularly interesting application in the field of pulsatile cardiac implants, but it can be applied to any type of device requiring contactless energy transfer.

[0004] There are heart pumps that are pulsatile and synchronized to the native activity of the patient's heart, which is necessary to ensure certain vital physiological functions of the patient's cardiac system. For example, it is essential to reduce the rotation speed of the pump during diastole so as not to hinder the filling of the systemic ventricle. The typical duration of a cardiac cycle varies between 300ms and three seconds. The transition times between diastole and systole are of the order of a few 10ms.

[0005] It follows that the consumption is itself pulsatile with an instantaneous power of the mechanical part of the pump which varies in a ratio of 1 to 10 between the different cardiac phases, all on time scales of the order of 100ms.

[0006] This high intrinsic variability creates specific design constraints on the transcutaneous energy transmission device.

[0007] Documents US 6478820 and US 6458164 are known describing a conventional TET operating with minimalist implantable electronics and without requiring an external regulation loop in order to control the output voltage UsDC within a defined range.

[0008] The classic TET includes:

[0009] - a primary circuit comprising an inverter capable of being supplied by a voltage continuous UpDC and a direct current IpDC, a primary capacitor Cp and a primary coil Lp capable of being powered by the inverter, and

[0010] - a secondary circuit comprising a secondary coil Ls intended to be in magnetic coupling with the primary coil according to a magnetic coupling coefficient k, a secondary capacitor Cs, a rectifier capable of supplying the implant with a direct voltage UsDC; the secondary circuit further comprising an in IT switch to supply or not the rectifier and an IT switch control circuit controlled from the local voltage UsDC. By "local" we mean a voltage of the secondary circuit.

[0011] The advantage of the “classic TET” solution lies in its reliability: no need for an external radiofrequency feedback loop, very few implantable components, and perfect adaptation to implantable constraints: low temperature rise when the coupling and / or the transmitted power is optimal. On the other hand, its dimensioning imposes a certain number of compromises which ultimately make the solution difficult to use in practice. Indeed, the solution works very well for a reduced power range and / or for a reduced magnetic coupling range, but said ranges are ultimately too small. Furthermore, the operating ranges between output power and magnetic coupling are intertwined. In the case of the “classic TET”, as soon as one leaves the authorized PoutDC output power range, either heating becomes prohibitive, or the device no longer works at all beyond a certain coupling k.Conversely, as soon as we leave the authorized coupling range k, either heating becomes prohibitive, or the device no longer works at all because this has reduced its operating range in output power PoutDC.

[0012] Finally, it is the consideration of the combination of the high variability of k and PoutDC which leads to reducing the operating ranges of k and PoutDC and makes the device unsuitable outside a laboratory or a clinical trial in a controlled environment. This comes from the fact that the efficiency and the very operation of the "classic TET" depends in a non-linear way on both PoutDC and k. Thus, the optimal operating point of the system is different for each combination of PoutDC and k. It can be shown in particular that in the case of the "classic TET" this leads to systematically oversizing the value of UpDC. The counterpart is that the efficiency, heating and usability (kmaxi and kmini as well as PoutDCmaxi and PoutDCmini) of the classic TET are not optimal, outside these narrow ranges, which makes its use prohibitive for commercial use.

[0013] Documents US 9855376, US10149933, US11235141 and US 11534225 are also known, describing the “conventional TET” with the addition of an AC current sensor and a primary side switchover between two “all or nothing” modes depending on the estimation of the state of the secondary IT switch. This solution generates too much electromagnetic pollution and is not optimal from a performance point of view. This makes it unusable for a marketable product which must comply with the requirements of the standards to guarantee the safety of property and people.

[0014] The present invention aims to increase reliability by reducing the maximum the number of TETS components.

[0015] Another aim of the invention is to increase the safety of property and people by maintaining the voltage levels of the distributed power supplies below the so-called “very low voltage” thresholds and by allowing a fault-free operating mode despite a possible loss of telecommunication between the implant and the external power supply device.

[0016] Another object of the invention is to increase the usability of the TETS by widening the operating ranges of the coupling coefficient k and the output power PoutDC.

[0017] Another aim of the invention is to increase efficiency, reduce electromagnetic pollution, reduce the rise in temperature of living tissues, and reduce the dimensions and mass of the windings.

[0018] The invention also aims to increase the level of integration of implantable electronics, thus facilitating its implantation in the patient's body.

[0019] At least one of the objectives is achieved with a transcutaneous energy transmission system intended to power an implant, this system comprising:

[0020] - a primary circuit comprising an inverter capable of being supplied by a voltage continuous UpDC and a direct current IpDC, a primary capacitor Cp and a primary coil Lp capable of being powered by the inverter,

[0021] - a secondary circuit comprising a secondary coil Ls intended to be in magnetic coupling with the primary coil according to a magnetic coupling coefficient k, a secondary capacitor Cs, a rectifier capable of supplying the implant with a direct voltage UsDC; the secondary circuit further comprising a switch IT for supplying or not supplying the rectifier and a control circuit for the switch IT controlled locally from the voltage UsDC.

[0022] According to the invention, the system further comprises:

[0023] - a self-adaptive control circuit, connected to the primary circuit and configured to automatically control the direct voltage UpDC from only the measurements of UpDC and IpDC, and according to a constrained optimization algorithm.

[0024] Control consists of varying the UpDC voltage continuously or discretely. This variation is a function of at least one predetermined constraint.

[0025] The invention is particularly remarkable insofar as the only measurements carried out are those of UpDC and IpDC, they are local, within the optimized primary circuit (optimized by the presence of the self-adaptive control circuit). No measurement comes from the secondary circuit 2b, nor even from the primary circuit 2a, and even less from a wireless communication link as is done in the products of induction charging systems currently marketed.

[0026] Generally speaking, the primary circuit and the control circuit are intended to be arranged outside a patient, while the secondary circuit is intended to be arranged inside the patient in connection with the implant. The latter may be, for example, an electromechanical cardiac assistance device placed entirely or partially in the patient's heart.

[0027] With the invention, the performance and use of the transcutaneous energy transmission system are optimized by automatically adapting the direct voltage UpDC as a function of the variations in consumption PoutDC(t) and / or the coupling coefficient k. Indeed, the variations in consumption PoutDC(t) and the coupling coefficient k modify the performance quantities of the system, as well as the optimal operating point defined by the direct voltage UpDC and the direct current IpDC. By estimating these performance quantities of the system and by measuring the direct voltage UpDC and the direct current IpDC, a correction of the direct voltage UpDC can be applied or not so as to tend towards an optimum.

[0028] It is the self-adaptive control circuit which includes the algorithm necessary to control the primary circuit from data obtained via the sole measurement of the UpDC and IpDC quantities without the need to set up an ad hoc regulation circuit from the secondary circuit. There are several types of constrained optimization algorithms. The user can choose one according to one or more predetermined constraints.

[0029] The self-adaptive control circuit is powered by a battery or the mains.

[0030] The invention can in particular make it possible to automatically and to a minimum reduce the power absorbed by the transcutaneous energy transmission system as a function of its environment, by precisely adjusting the value of the direct voltage UpDC of the power supply line.

[0031] The present invention allows efficient operation without mandatory data communication between the implantable part and the external part. The only mandatory connection between the external part and the implantable part is the magnetic coupling between the two coils. No radio frequency or wired feedback connection, as in the prior art, is required.

[0032] The real-time self-adaptation of the direct voltage UpDC according to the invention makes it possible to optimize the performance of the transcutaneous energy transmission system, in particular by an increase in the transfer efficiency, a reduction in the heating of living tissues, a reduction in consumption, an increase in the range of k values, despite a high real-time variability of the coupling k and the power PoutDC.

[0033] The presence of the self-adaptive control circuit makes it possible to advantageously replace the feedback loop of the prior art by eliminating causes of faults.

[0034] The automatic control of UpDC according to the present invention allows a reduction in the amplitude of the voltage at the terminals of the coils Ls and Lp, thus improving the efficiency but also the reliability and safety of property and people. Preferably, the overvoltages can be kept below 70V peak (limit of very low voltage) in order to keep any leakage currents in the event of a fault in the insulators below a critical threshold for users.

[0035] According to an advantageous characteristic of the invention, the self-adaptive control circuit can be configured to estimate performance quantities of the system from the measurements of UpDC and IpDC. The constrained optimization algorithm can be parameterized with at least one predetermined constraint and associated with one of the performance quantities of the system.

[0036] Once again, an advantageous characteristic of the invention is that the performance quantities of the system such as for example the power consumed by the load, the efficiency, the magnetic coupling coefficient, the power dissipated at the secondary are obtained in real time without reporting measurements coming from the secondary circuit.

[0037] According to one embodiment of the invention, said system performance quantities may comprise at least one or more of the following instantaneous quantities: a duration Toff during which the switch IT is closed, a duration Ton during which the switch IT is open, a continuous instantaneous power PinDC supplying the inverter, a continuous power PoutDC at the output of the secondary circuit, an energy transfer efficiency RendTETS, a dissipated power Pdiss in the system.

[0038] Other quantities can be estimated, such as for example the magnetic coupling coefficient k.

[0039] The only measurements of the direct voltage UpDC and the direct current IpDC according to the invention are necessary to estimate real-time performance quantities such as k, PinDC, PoutDC and the efficiency of the energy transfer.

[0040] Toff is the duration during which the IT switch is closed (Off phase), the power is then not transferred from the source to the load of the implantable part.

[0041] Ton is the duration during which the switch IT is open, the power is then transferred from the external part to the load of the implantable part.

[0042] The invention makes it possible in particular to compensate for movements of the patient when these cause relative displacements between the coils and thus a variation in the magnetic coupling coefficient k, by modulating the direct voltage UpDC in order to maintain it at an optimal value (for example in order to maximize the efficiency of the power transfer). Furthermore, extreme values, an UpDCmax and an UpDCmin, can be defined, for example respectively at values ​​of 15V and IV. A nominal value UpDCnom, between UpDCmax and UpDCmin, can also be predefined by the user. The system can be started up by setting UpDC equal to UpDCnom, this voltage being chosen (by calculation or experience) by the user within a range of values ​​high enough to allow cyclic operation of the IT switch.

[0043] Power transmission is correct only under the necessary (but not sufficient) condition that the switch IT closes regularly, which means that the duration Toff must be non-zero, or in other words that the duration Ton must be less than a certain value TonMAX.

[0044] According to an advantageous characteristic of the invention, said constraints may comprise a minimum duration Toff during which the switch IT is closed, and / or a maximum duration Ton during which the switch IT is open, and / or a minimum instantaneous power PinDC, and / or a maximum efficiency RendTETS, and / or a minimum dissipated power Pdiss.

[0045] Thus the direct voltage UpDC is regularly adapted to each cycle in order to tend towards an optimum respecting the said constraints.

[0046] The constraint may therefore, for example, be the reduction to the maximum of the dissipated power Pdiss and in any event its maintenance below a maximum value deemed acceptable, so that the rise in temperature of living tissues does not exceed the limits imposed by physiology and / or international standards. Typically beyond 4K of temperature rise, the tissues necrotize and the standards impose a limit of 2K for internal tissues.

[0047] Advantageously, the measurements and the estimated quantities can be carried out cyclically.

[0048] A cycle can be defined by a pair of open and closed states of the IT switch. The measurements of UpDC and IpDC can be made during one cycle and the estimates during another cycle. The estimates can be based on averages of measurements made over several cycles.

[0049] The secondary coil is conventionally made with a Litz wire winding in order to reduce the equivalent resistance when the inverter frequency is high. This winding is connected to the electronics via a connector.

[0050] According to an advantageous characteristic of the invention, the secondary coil is produced from tracks of a printed circuit PCB, for example with multilayer conductors.

[0051] Indeed, the use of a secondary coil in a printed circuit (PCB for "Printed Circuit Board" in English) with in particular multilayer conductors makes it possible to reduce the value of the equivalent internal resistance of the system, which causes heating, while facilitating its industrial production.

[0052] Advantageously, the IT switch can be integrated into the PCB printed circuit of the secondary coil. The total equivalent resistance is thus reduced thanks in particular to the elimination of the connector between the coil and the electronics.

[0053] Indeed, the contribution of the series resistance of the IT switch circuit becomes very high if the switch is too far from the secondary coil. In order to limit this resistance, and at the same time the resistance of the primary circuit, and thus limit heating of the secondary circuit when the switch is closed, the invention provides for placing this switch in the immediate vicinity of the secondary coil, and ideally directly on the PCB. In this preferred configuration, all of the electronics of the secondary circuit can be placed on the PCB of the implantable coil. Thus, the connection between the transcutaneous energy transmission system and the rest of the implantable device can be made by a very low voltage DC connection, thus considerably improving patient safety in the event of accidental breakdown of the insulation.

[0054] According to one embodiment of the invention, a magnetic core can be placed preferentially in the secondary coil Ls or optionally in the primary coil Lp.

[0055] This improves the value of the secondary inductance Ls, which makes it possible to extend the range of values ​​k by reducing the minimum value kmini for a given voltage UpDCmaxi.

[0056] Preferably, the magnetic core may be a superparamagnetic composite core.

[0057] This is a non-conductive core and exhibits substantially no hysteresis losses.

[0058] The superparamagnetic charge can be directly placed in the core of the planar windings, or in the PCB, or in the overmolding and / or protection material of the secondary coil.

[0059] According to the invention, the primary coil Lp and the primary capacitor Cp can have values ​​so as to be in resonance when the coupling k between the primary coil and the secondary coil is below a predetermined coupling threshold. This coupling threshold can be equal to 1% or even 1 / 1000. In such a condition, it is considered to be in a decoupling situation.

[0060] Furthermore, the secondary coil Ls and the secondary capacitor Cs may have values ​​such that they are in resonance when the coupling k between the primary coil and the secondary coil is below a predetermined coupling threshold.

[0061] The primary and secondary circuits can thus be at resonance when the coupling is substantially zero, i.e. when k=0. Thus, this leads to having an overconsumption on the primary side in the event of decoupling, and thus to detecting the decoupling. This also allows for very low consumption (almost zero) on the primary side when the coils are coupled but the switch is closed.

[0062] The sole analysis of the PinDC(t) power can allow automatic control of the transcutaneous energy transmission system.

[0063] According to one embodiment of the invention, the transcutaneous energy transmission system may comprise a radio link capable of connecting the self-adaptive control circuit with the implant so as to recover real-time information from the implant.

[0064] This wireless radio link can be used for real-time exchange of information such as consumption in W, heart rate in Hz, QRS detection time, actual value of PoutDC(t), etc., between the implant and the external part of the transcutaneous energy transmission system.

[0065] This optional feedback loop further improves control but may not be available without limiting the overall operation of the transcutaneous energy transmission system.

[0066] This information can, for example, allow the evolutions of PoutDC(t) to be anticipated and thus the values ​​of UpDC to be optimized. Typically, the value of UpDC can be modified upwards or downwards with larger increments, depending on the estimate of the actual consumption. Thus, the convergence time of the system towards its optimum operating point is reduced. This option is all the more interesting for improving the dynamic properties of the system when the parameters k and PoutDC vary rapidly. In practice, the magnetic coupling variations are induced by the patient and are very slow, of the order of a second or even several seconds. The speed of variation of the magnitude PoutDC depends on the charge and the capacitance of the storage capacitor CStock placed in the rectifier.This speed of variation is therefore a design parameter which can be taken into account in optimizing the dynamics of convergence of the algorithm towards an optimum.

[0067] By way of example, the self-adaptive control circuit can be configured to adapt the operating frequency of the inverter to the resonant frequency of the secondary circuit based on information coming from the implant.

[0068] This adaptation can take place during a calibration and pairing step. The value of the frequency of the resonant circuit of the implant can be stored in a memory of the latter, so that the external system can be exchanged and automatically adapt to it.

[0069] According to one embodiment of the invention, the transcutaneous energy transmission system may comprise at least one pulse width modulator for driving the inverter at a frequency of less than 301kHz, less than 151kHz or less than 81kHz.

[0070] Such a low frequency allows both the implementation of quasi-sinusoidal control by pulse width modulation, thus controlling the quality of the network and limiting harmonics, to reduce electromagnetic pollution (improve electromagnetic compatibility EMC) and also allows the reduction of the skin effect in the windings, therefore losses due to heating.

[0071] The system according to the invention may comprise a precalculated pulse width modulator with one or more predefined harmonic contents of amplitude, frequency and phase.

[0072] These harmonic contents of the pulse width modulator can be precalculated to switch quickly from one to the other, in particular when decoupling has been detected, or during the OFF phase. The triggering of this total or partial deactivation is then controlled by the self-adaptive control circuit.

[0073] Advantageously, the system according to the invention may comprise a timer to trigger an action when an instantaneous power PinDC supplying the inverter does not vary in intensity beyond a predetermined power threshold for a predetermined duration. The threshold may be set at a value of 30% between max power and min power. And the duration may for example be 5 seconds. This absence of variation is synonymous with dropout, i.e. that the voltage UsDC is below the acceptable range.

[0074] In the event of a dropout, the UpDC voltage must be increased to allow reattachment. There are several strategies which depend on the nature of the implant:

[0075] - Slow increase in UpDC

[0076] - Instantaneous switch to UpDCMax

[0077] - Instantaneous switch to UpDCNominal

[0078] - Etc

[0079] According to one embodiment of the invention, the self-adaptive control circuit may comprise a DC voltage sensor, a DC current sensor and a processing unit.

[0080] The processing unit makes it possible to carry out the estimations in real time over an observation duration typically of 1 ms and to update periodically. This processing unit is also configured to execute the optimization algorithm under constraints.

[0081] According to another aspect of the invention, there is proposed a method for controlling a direct voltage UpDC in a transcutaneous energy transmission system as defined in any of the preceding systems, this method comprising, at each cycle defined by open and closed states of the switch IT, the following steps:

[0082] - measurement of the direct voltage UpDC and the direct current IpDC,

[0083] - estimation of system performance quantities, storage of these quantities, and comparison with values ​​of these quantities obtained during a previous cycle,

[0084] - control of the direct voltage UpDC from the measurements of UpDC alone and IpDC, and according to a constrained optimization algorithm.

[0085] Other advantages and characteristics of the invention will appear on examining the detailed description of a non-limiting embodiment, and the appended drawings, in which:

[0086] [Fig-1] [Fig.l] is an overall schematic view of the transmission system transcutaneous energy,

[0087] [Fig.2] [Fig.2] is a schematic view of the transcutaneous energy transmission system once installed on a patient,

[0088] [Fig.3] [Fig.3] is a more detailed schematic view of the transcutaneous energy transmission system,

[0089] [Fig.4] [Fig.4] is a schematic view of a graph of the instantaneous PinDC power supplied to the inverter of the transcutaneous power transmission system as a function of time,

[0090] [Fig.5] [Fig.5] is a schematic view of a graph of the UpDC voltage feeding the inverter of the transcutaneous power transmission system as a function of the coupling coefficient k.

[0091] The embodiments which will be described below are in no way limiting; it will be possible in particular to implement variants of the invention comprising only a selection of characteristics described below isolated from the other characteristics described, if this selection of characteristics is sufficient to confer a technical advantage or to differentiate the invention compared to the state of the prior art. This selection comprises at least one preferably functional characteristic without structural details, or with only a part of the structural details if this part alone is sufficient to confer a technical advantage or to differentiate the invention compared to the state of the prior art.

[0092] In particular, all the variants and all the embodiments described are intended to be combined with each other in all combinations where there is nothing technically opposed to this.

[0093] In the figures, the elements common to several figures retain the same reference.

[0094] Although the invention is not limited thereto, a transcutaneous energy transmission system will now be described for powering an implant which is an intraventricular heart pump.

[0095] In [Fig.l], we can generally distinguish the energy transmission system transcutaneous 1, TETS (for “Transcutaneous Energy Transfer System” in English) according to the invention. TETS 1 comprises a non-optimized transcutaneous energy transmission subsystem 2, in other words “classic TET”, intended to supply a resistance RL(t) representing the equivalent load of the implant and which can vary over time.

[0096] The transcutaneous energy transmission system TETS 1 according to the invention further comprises a control circuit 3 intended to supply the conventional TET 2 with direct voltage UpDC and direct current IpDC.

[0097] The control circuit 3 comprises inputs / outputs allowing data to be transmitted to the user via an output 5, and optionally receiving external data via an input 6.

[0098] The classic TET 2 consists of two circuits: a primary circuit 2a distinct from a secondary circuit 2b. The two primary circuits 2a and secondary 2b are magnetically coupled with a magnetic coupling coefficient k which can vary over time.

[0099] [Fig. 2] is a schematic view of the TETS 1 installed on a patient. The control circuit 3 and the primary circuit 2a are placed outside the patient's body. The secondary circuit 2b is installed inside the patient and is intended to supply direct voltage to the implant 4, which is, for example, a pulsatile heart pump.

[0100] The TETS 1 according to the invention has the function of self-adaptation in real time of the direct voltage UpDC in order to optimize the performance of the TETS 1 in particular by increasing the transfer efficiency, reducing the heating of living tissues, reducing consumption, increasing the maximum operating value of k (kmaxi), reducing the minimum operating value of k (kmini) despite a high real-time variability of the coupling k and the power PoutDC at the output of the secondary circuit 2b.

[0101] The TETS 1 also makes it possible to improve the accuracy of the system performance magnitude estimates as will be seen later. These performance magnitudes constitute in particular the data that the control circuit can transmit to the user to indicate the level of quality of the energy transmission.

[0102] Advantageously, the Classic TET 2 is a transcutaneous energy transmission system without a control loop between an implantable part and an external part as described in documents US6478820 and US6458164.

[0103] More precisely and with reference to [Fig.3], the classic TET 2 according to the invention is composed of: - an implantable secondary coil of self-inductance Ls, preferably planar, - an external primary coil of self-inductance Lp, preferably planar, magnetically coupled to the secondary coil Ls. The magnetic coupling k is defined by the value of the mutual inductance M between Ls and Lp, defined by m1 = k2Lp.Ls such that 0 < k < 1. The magnetic coupling can vary over time, over its entire possible range [0;1], - external power electronics of the inverter type 7 for converting the direct power PinDC into alternating power at a fundamental frequency Fex. The primary circuit 2a may include a resonance capacitor Cp, preferably placed in series (and / or in parallel) with the primary coil Lp and whose capacitance is chosen such that the circuit (Lp,Cp) resonates at the frequency Fex, i.e. Fex.2.pi=l / root(Lp.Cp), - a secondary capacitor Cs of series resonance whose capacitance is chosen so that the circuit (Ls,Cs) also resonates at the frequency Fex, i.e. Fex.2.pi=l / sqrt(Ls.Cs), - an IT switch placed in parallel with the circuit (Ls,Cs), controlled by the ON signal, - internal power electronics of the rectifier type 8 for converting alternating power into direct power PoutDC(t). Preferably, the rectifier 8 is a passive, single or double alternation rectifier based on one or more diodes, preferably low threshold Schottky, and an energy storage capacitor Cstock and - a control circuit 9 self-powered by the rectifier 8 and making it possible to generate the signal ON from a measurement of the direct voltage UsDC(t) such that ON<=' 1' if UsDC is increasing and / or passes above UsDCmax, then returns to ON<=' 0 if UsDC is decreasing and / or passes below UsDCmin (regulation by hysteresis). We denote by UsDC the average value of the voltage UsDC(t).

[0104] The classic TET 2 is connected to a load RL(t) whose characteristic can be variable over time, in particular pulsatile in the case of the heart pump for example.

[0105] The classic TET 2 allows to automatically transfer DC-DC energy with regulation of the output voltage UsDC between the values ​​UsDCmin and UsDCmax following a cycle of period Ton+Toff, automatic and clocked by the state of the switch IT. IT=1 (closed) during the time Toff and IT=0 (open) during the time Ton.

[0106] The conventional TET 2 used alone presents problems of heating and performance. The invention is particularly remarkable in that it introduces the control circuit 3 to adjust the value of the DC supply voltage of the circuit primary 2a without recourse, fundamentally, to a counter-reaction from the secondary circuit 2b.

[0107] In [Fig. 3], the control circuit performs self-adaptation based on a real-time analysis of the PinDC(t) power. For this, the control circuit 3 preferably comprises a means for measuring the PinDC(t) power, a DC voltage sensor 10 UpDC(t) and a DC current sensor 11 IpDC(t). It also comprises a processing unit 12 equipped with software and hardware means for executing functions and storing data. The data are evaluated in real time over an observation time Tobs (typically 1 ms) and periodically updated. The PinDC power is thus estimated according to the following formula:

[0108] PinDC\t} = ïTob UpDC(t) JpDC(t).dt (Ê4uation 7)

[0109] An integrated battery 13 is also distinguished for powering the control circuit 3. A power supply via the mains can also be envisaged, possibly in combination with the integrated battery.

[0110] We will now describe the dimensioning elements as well as the determination of the performance quantities of the TETS according to the invention.

[0111] The control circuit 3 is notably characterized by its capacity to automatically modulate the voltage UpDC(t).

[0112] It has an optional output 5, preferably digital, allowing data to be provided to the user.

[0113] It has an optional input 6, preferably digital, allowing the environment to provide it with data, in particular for its self-calibration.

[0114] The sizing elements of the TETS are as follows.

[0115] The yield of the complete TETS noted RendTETS is defined by:

[0116] RendTETS(h PoutDC, UpDC) = (Equation 2)

[0117] 0 < RendTETS < 1 (Equation 3)

[0118] The efficiency is a function of the losses, i.e. the dissipated power Pdiss in the TETS. This dissipated power in watts can be expressed as a function of the power PinDC and said efficiency.

[0119] Pdiss = PinDC (1 - RendTETS) (Equation 4)

[0120] The present invention has in particular as its object the reduction as much as possible of the dissipated power Pdiss and in any event of maintaining Pdiss below a maximum value deemed acceptable, so that the rise in the temperature of the living tissues does not exceed the limits imposed by physiology and / or international standards.

[0121] Toff is the duration during which the IT switch is closed (Off phase), the power is then not transferred from the source to the implant load. This in The IT switch closes when the voltage UsDC(t) has reached the value UsDCmax, and it remains closed until it reaches the value UsDCmin. During the Off phase, the load is powered by the rectifier's filter capacitor, whose capacity is noted CStock and will have been used to accumulate energy during the charging phase (IT open). During the Off phase PinDC(t) is substantially constant and is worth Poff. This power Poff is essentially dissipated as heat in the cables, the windings and the switch. This power Poff varies significantly according to the following formula in which Rsp represents the series resistive effects of the primary circuit and Rss represents the series resistive effects of the secondary circuit. The coefficient Coeffl depends on the design and is substantially constant whatever k and PoutDC.

[0122] / \ (Equation 5) PinDC(t)\ = POff\k,UpDC\ « coeffl..... \ / RP+ Ri '

[0123] The duration Toff of the Off phase is substantially defined by the following formula in which Coeff2 depends on the design and is substantially constant whatever k and PoutDC.

[0124] tO ff ~ (Equation 6) f J PoutDC

[0125] We see in the equation above that the measurement of Toff makes it possible to finely estimate the value of PoutDC by applying the following formula:

[0126] polltDC « (Equation 7)

[0127] Coeff2 is determined by the design and its value can be stored in a memory of the control circuit 3. Furthermore, its value can be updated / refined by data exchange between the implant and the control circuit 3, for example during an initialization phase and / or regularly.

[0128] It can be seen that POff depends on the coupling k and UpDC. It is understandable that it is useful to know the value of Toff in order to be able to possibly “deactivate” the inverter (UpDC=0 or a low value) for a duration substantially equal to Toff once this change of state has been detected. Knowledge of PoutDC in real time by data exchange between the implant and the control circuit 3 makes it possible to improve the estimation of Toff. This deactivation is not necessary, however, if the design has made it possible to sufficiently reduce the contribution of Poff to the total losses. In doing so, unacceptable electromagnetic pollution effects are eliminated in certain constrained environments, which is why the preferred embodiment does not implement such deactivation during the Off phase.

[0129] We see in the previous equation that in the absence of coupling (k=0 or less than kmini), the power at the PinDC input becomes very high. This power is then entirely dissipated in the external part. We can thus detect an absence of coupling and “deactivate” the inverter (UpDC=0 or a low value) for a predetermined duration, typically a 1s wait time, trigger an alert to the user and then reactivate it intermittently to detect coupling again when the user has realigned the primary and secondary coils.

[0130] Ton is the duration during which the switch IT is open, the power is then transferred from the external primary circuit to the implantable secondary circuit. During the On phase, when the TETS is in its correct operating range, the power absorbed by the TETS is noted POn and is substantially constant, it depends only on the coupling coefficient k nor on the direct voltage UpDC. It can be noted that this power POn does not depend substantially on the power absorbed by the load PoutDC either. [0i3i] PinDC( t ) | « POn(k, UpDC) (Equation 8)

[0132] The efficiency of the TETS can be expressed as a function of a maximum efficiency which depends on the coupling k, the power PoutDC and the direct voltage UpDC as well as the duration Ton and a design time constant denoted TEq. The following equation takes into consideration the highly non-linear behavior of the TETS. Thus, and according to the invention, the device will automatically modify the value of UpDC in such a way that both the maximum theoretical achievable efficiency is reached, but also that the duration Ton is as long as possible, in any case much longer than TEq.

[0133] VTETS « 77max( k, PoutDC, UpDC).-^^ (Equation 9)

[0134] This quantity TEq depends both on the design parameters (the width of the output hysteresis, the average voltage UsDC and the storage capacity Cstock), but also on the load resistance and an equivalent internal resistance RgEq(k), itself dependent on the coupling k. We understand the strong non-linearity of the TETS which makes its optimization delicate since both TEq, Ton, and the efficiency depend on UpDC, PoutDC and k.

[0135] ~ AUsPC 2JtgEq(k)J(l , (Equation 10) 1 ^l ~ UsDC • Rl+ZRgEq

[0136] The equivalent internal resistance RgEq depends significantly only on Ton, Toff, the coupling k and the design parameters. We define RdssOn as representing the series resistance of the switch circuit IT and we obtain:

[0137] RgEq ( Ton, Toff ) « Rss + .g (Equation 11 )

[0138] As already seen, Rss represents the series resistances of the secondary circuit and Rsp re shows the series resistances of the primary circuit.

[0139] We observe that this equivalent resistance RgEq must be minimized above all and that Ton must be maximized above all. In order to reduce Rss, we use as a priority a secondary winding with a very large copper section, and classically a wire of Litz in order not to suffer the skin effect when the frequency Fex is high. However, according to the present invention, this resistance Rss is minimized by using a frequency Fex not too high (typically < 300kHz) and by the use of a secondary coil in PCB ("Printed Circuit Board" in English) with multi-layer conductors.

[0140] The contribution of the resistance RdssOn becomes very high if the IT switch is too far from the secondary coil. According to the invention, provision is also made to place the IT switch in the immediate vicinity of the secondary coil, and ideally directly on the PCB. In this preferred configuration, all of the electronics of the control circuit 9 are placed on the PCB of the secondary coil. Thus the connection between the TETS and the implant can be made by a very low voltage DC connection, considerably improving patient safety in the event of accidental insulation breakdown.

[0141] The coupling coefficient k can be estimated according to the following law depending on Ton, Toff and UpDC, knowing that Coeff3 only depends on design parameters. We understand the interest in precisely identifying Ton and TOff as well as UpDC. [°1421 estimated « Coef / 3. UpDC.^—^ (Equation 12)

[0143] For a design of a conventional TET 2, the expression of the minimum coupling coefficient allowing the operation of the conventional TET 2 is given by the following equation in which coeff4 again depends only on design parameters. This value of kmini is that below which the conventional TET 2 can no longer operate, due to a "dropout". This value of kmini does not correspond in the conventional case with the minimum acceptable coupling value, taking into account in addition the fact that the loss power must not be too high. This value then also depends on the power PoutDC. This systematically leads in the conventional case to considerably reducing the operating range of the conventional TET 2 to include both the minimum coupling and the maximum power. Said losses depend on PoutDC and UpDC. For a given operating point (k and PoutDC fixed), the losses decrease when UpDC decreases.It is clear that there is every interest in reducing UpDC to reduce losses but that, in doing so, we reduce the operating range. We then understand the interest in automatically adapting the value of UpDC according to the real operating conditions k(t) and PoutDC(t). Starting from a reference UpDC, called UpDCNominal, and a nominal coefficient kNominal, and given a maximum value UpDCMax, and a minimum UpDCMin, we understand that as long as k > kmini, the optimal value of UpDC will be lower than UpDCMax. Starting from a situation for which UpDC=UpDCNominal, and k>kmini the control circuit will automatically . choose to increase or decrease UpDC in order to tend towards an optimal state for which the efficiency of the TETS according to the invention is improved compared to the conventional case. In doing so, the TETS according to the invention also has the possibility when the power PoutDC is not maximum, to operate at lower coupling and thus the invention also makes it possible to considerably increase the operating range of the TETS. [°1441 kmini « (Equation 13) UpDC

[0145] In the same way, the following expression describes the dropout coupling kmaxi beyond which the conventional TET 2 can no longer operate. This time we observe that the dropout depends on the voltage UpDC but also on the consumption of the load PoutDC. Again, and for other reasons, we observe that to increase the operating range (increase kmaxi), we must increase UpDC. For the same reasons as before, this systematically leads to oversizing UpDC in cases for which the coupling is not maximum and thus to overconsumption. In the same way as before, we understand the interest of adapting UpDC automatically. Starting from a reference UpDC, we understand that as long as k < kmaxi, the optimal UpDC value will be lower than UpDCMax.Starting from a situation where UpDC=UpDCNominal, and k <kmaxi le dispositif va automatiquement choisir d’augmenter ou de diminuer UpDC afin de tendre vers un état optimal pour lequel le rendement du TETS sera amélioré par rapport au cas classique. Cette situation peut évoluer dans le temps, même si k reste constant, en fonction de la valeur instantanée de PoutDC. .

[0146] kmaxi ~ coeff5----(Equation 14) ' J PoutDC.^LÎIJp :w

[0147] According to the invention, the operating range kmini can be increased by maximizing the value of the secondary inductance Ls. To do this, it is advantageous to add a magnetic core at the secondary coil. With regard to the formula giving the value of kmaxi, it is understood that increasing the value of Ls leads to reducing the operating range on the maximum coupling side. Thus, in the case of the Classic 2 TET, a compromise is made which does not optimize the solution. The present invention makes it possible to eliminate this compromise by automatically adapting the value of UpDC and thus it is preferred to increase the value of the secondary inductance Ls. Preferably, the magnetic core used is not conductive and has substantially no losses. One of the preferred solutions is the use of a superparamagnetic composite core placed at the secondary winding.The superparamagnetic filler can be directly placed in the core of the planar windings, or in the PCB, or in the overmolding and / or . secondary coil protection.

[0148] Preferably, the secondary and primary resonance capacitors are chosen so that the circuits are at resonance in the absence of coupling, i.e. when k=0. Thus, this leads to having an overconsumption on the primary side in the event of decoupling, and thus to detect the decoupling. This also makes it possible to have a very low consumption, almost zero on the primary side when the coils are coupled but the switch IT is closed. Thus, the sole analysis of the power PinDC(t) makes it possible to automatically control the TETS according to the invention.

[0149] It is possible to provide, optionally and without this interfering with the fundamental performance of the TETS according to the invention, to adapt the operating frequency of the inverter to the resonance frequency of the secondary circuit as a function of information provided by the implant during a calibration and pairing step.

[0150] According to the invention, it is planned to control the inverter preferably with a Pulse Width Modulation (PWM) control in order to optimize the current spectrum and therefore the electromagnetic pollution of the conventional TET 2. The choice of the frequency Fex is preferably relatively low, for example less than 301kHz, to reduce the electromagnetic pollution and the skin effect, and to allow the implementation of PWM. The frequency Fex can be chosen less than 151kHz, or even less than 81kHz, which corresponds to the limit frequencies of international standards.

[0151] Two precalculated PWM sequences can be provided to quickly switch from one to the other, in particular when decoupling has been detected, or during the OFF phase. The triggering of this total or partial deactivation is then controlled by the control circuit.

[0152] The automatic control of UpDC allows a reduction in the amplitude of the voltage at the terminals of the coils Ls and Lp, thus improving efficiency but also reliability and safety of property and people. Preferably, overvoltages are kept below 70V peak (limit of very low voltage) in order to keep any leakage currents in the event of insulation failure below a critical threshold for users.

[0153] In order to increase the efficiency of the rectifier, it is preferably "single-wave" and not double-wave, which would increase the diode dropout voltage. This precaution is not necessary if the UsDC voltage is sufficiently high compared to the diode dropouts (typically above 10V, or even 20V, or even 30V, or even 50V). In the case of single-wave rectification, it is planned to add a TVS ("transient-voltage-suppression" type) protection device to limit the reverse voltage across the diode.

[0154] In order to reduce losses in the entire TETS transfer line, it is planned to place the power electronics on the primary side, the inverter in particular, as close as possible to the primary coil, typically at a distance less than the diameter of the primary coil. This makes it possible to reduce the series resistances of the primary circuit Rsp and also electromagnetic pollution.

[0155] We will now describe a normal operating mode of the TETS according to the invention.

[0156] On the graph in [Fig.4], we can see a cycle of duration Ton+Toff. We observe that the power is systematically lower than a high threshold PinDCDec and that it falls below a low threshold PinDCOff, for example 1W.

[0157] The voltage UpDC(t) is set to a value at startup, for example the nominal value UpDC=UpDCNom.

[0158] This is not limiting of the invention, other tracking strategies are conceivable, in particular by starting with the minimum voltage UpDCMin or with a maximum voltage UpDCMax.

[0159] The estimated parameter Toff_est is characterized by the duration during which PinDC(t)< PinDCOff.

[0160] The Ton_est parameter is characterized by the duration during which PinDC(t)> PinDCOff.

[0161] The control circuit can then calculate the average value PinDC_est as follows

[0162] PinDC is = —J—— f PmDC(t)dt (Eciuation 15> — TOn_est+Tojf_estJion_est+Lojj_exr v '

[0163] The control circuit can calculate an estimate of the power delivered by the TETS to the load, PoutDC_Est according to the following formula:

[0164] PoutDC _is « (Equation 16)

[0165] The control circuit can therefore estimate the transfer efficiency RendTETS_est as well as the dissipated power Pdiss_est. [0i66] RendTETS is (Equation 17) — PinDC _esl

[0167] Pdiss_est - PinDC _est ( 1 -RendTETS_est) (Equation 18)

[0168] And finally the control circuit can estimate the coupling coefficient k_est [01691 kM - Coeffi UpDC19)

[0170] At the end of the cycle, the estimated quantities are delivered to the user and analyzed then placed in memory: Ton_Est, Toff_est, PinDC_est, PoutDC_est, RendTETS_Est, Pdiss_est, k_est. Depending on the threshold, certain alarms can be triggered, etc.

[0171] Particular attention can be paid to the value of Ton_Est. Indeed, if Ton_Est is too high, this means that the UpDC voltage is close to the dropout value. It should then no longer be reduced. It can be decided to keep it stable for one cycle or to increase it.

[0172] In all other cases, a priori, the value of the UpDC voltage is reduced by an increment DeltaUpDC.

[0173] At the end of the next cycle, the parameters are estimated again and the same logic is applied. In addition to the instantaneous quantities, the parameters are compared with their values ​​obtained in the previous cycle and which have been placed in memory. Thus, the control circuit is capable of identifying whether having reduced the UpDC voltage by the DeltaUpDC increment has made it possible to improve or degrade the instantaneous performance of the transfer, in particular the efficiency.

[0174] The decision to increase or decrease the value of UpDC is now based on the exploitation of real-time data, but also on their variation compared to those of the previous cycle. The cycle is thus repeated infinitely and we are assured of having a TETS whose operating point is automatically set to an optimum. It can be decided that the optimum performance is the minimum power PinDC, or the maximum efficiency, or the minimum loss Pdiss, or any other parameter estimated from the available quantities.

[0175] We will now describe a mode of operation in the event of decoupling.

[0176] At any time, even during a cycle or in the absence of a cycle, if PinDC(t) is If the voltage is too high, the TETS detects a loss of coupling and can be deactivated for a predefined time, for example a few seconds. Information is given to the user. After the waiting time, the TETS is reactivated from a start cycle.

[0177] We will now describe a mode of operation in the event of overconsumption or underconsumption.

[0178] At the end of a cycle, if the estimated consumption PoutDC is too high (overconsumption) or too low (underconsumption), it may be decided to inform the user and either continue to transfer energy or stop the transfer. There may obviously be several thresholds leading to different decisions depending on the nature of the implant. An exchange of data between the implant and the device may be useful in order to make the best possible decision.

[0179] We will now describe a mode of operation in the event of a stall.

[0180] It is possible that the TETS drops out, insofar as for example the power PoutDC and / or the coupling k varies suddenly, even while remaining within an acceptable operating range. In this specific case, there is no longer any cycle observation, that is to say that Ton or Toff are too long and no power switching is observed. This means that the switch IT is blocked, a priori in position open, and the TETS is not able to provide sufficient power to the implant. This case is detected by the use of a timer ("watchdog" in English), allowing an action to be triggered even if the value of PinDC(t) does not switch for a predetermined duration, for example 5s.

[0181] In this case, the UpDC voltage must be increased to allow re-attachment. There are several strategies that depend on the nature of the implant: - Slow increase of UpDC - Instant switch to UpDCMax - Instant switch to UpDCNom - Etc

[0182] We will now describe an operating mode specifically taking into account a heart pump type implant.

[0183] In the case of driving a pulsatile heart pump, the power PoutDC(t) is not constant but with high predictability. Indeed, in the case of a heart pump, the consumption follows the heart rate. In the case of a heart pump comprising a rechargeable battery, switching to recharge mode leads to an increase in consumption. This information can be provided by the implant in real time to the control circuit in order to further optimize the performance, for example via a measurement of T electrocardiogram, or via a measurement of cardiac output or any other means. Indeed, this information makes it possible to anticipate changes in PoutDC(t) and thus to optimize the values ​​of UpDC other than by a blind UpDC driving algorithm. Typically, the value of UpDC will be modified upwards or downwards with larger increments, depending on the estimate of the actual consumption.

[0184] Note, however, that this solution is optional, and that even in the event of loss of communication between the implant and the control circuit, the performance of the TETS is significantly improved compared to a conventional TET. Thus, the feedback link from the implant to the external part does not affect the reliability of the TETS function according to the invention.

[0185] When a storage capacitor is dimensioned as precisely as possible, which is of great interest from the point of view of size and reliability. And when the control circuit is working perfectly, then the optimal UpDC voltage will follow the instantaneous consumption of the load and present a pulsatile appearance.

[0186] There is a strong advantage in these conditions of having additional information which is the estimation of the instantaneous consumption in order to be able to anticipate it and accelerate the adjustment of the optimal value of UpDC. This synchronization can be achieved by exchanging real-time information such as consumption in watts, heart rate in Hz, the time of detection of the QRS, etc., between the implant and the external part of the TETS.

[0187] It follows that the control circuit takes this information into account to optimize the dynamic convergence towards the minimum power.

[0188] Ultimately, this makes it possible to extend the operating range of the TETS in extreme cases of PoutDC(t) and k(t), which improves the use of the TETS.

[0189] [Fig.5] illustrates the evolution of the operating curve of the TETS according to the invention. UpDC_Opt represents the value of UpDC allowing the efficiency of the power transfer to be maximized. The lower limits are characterized by a dropout or prohibitive heating.

[0190] We observe that the range of use according to the coupling k is increased because: - It is possible to have correct operation even with a maximum coupling of “1”, so the very notion of kmaxi no longer has any meaning with the invention - It is possible to adapt the value of kmini according to the power transferred to the load and thus extend the value of classic TET 2 when the actual power is lower than the maximum power. Knowing that the maximum power is systematically higher than the nominal power, this allows to greatly extend the usability of the TETS

[0191] It is observed that the UpDC value which leads to an optimization of the yield is largely dependent on the conditions of use and that the self-adaptive solution makes it possible to converge towards this optimum in a certain and reliable manner.

[0192] Of course, the invention is not limited to the examples which have just been described. Numerous modifications can be made to these examples without departing from the scope of the present invention as described.

Claims

Claims

1. Transcutaneous energy transmission system (1) intended to power an implant (4), this system comprising: - a primary circuit (2a) comprising an inverter (7) capable of being powered by a direct voltage UpDC and a direct current IpDC, and a primary coil Lp capable of being powered by the inverter, - a secondary circuit (2b) comprising a secondary coil Ls intended to be in magnetic coupling with the primary coil according to a magnetic coupling coefficient k, a secondary capacitor Cs, a rectifier (8) capable of powering the implant (4) with a direct voltage UsDC; the secondary circuit further comprising a switch IT for powering or not powering the rectifier and a control circuit for the switch IT controlled locally from the voltage UsDC, characterized in that: - it further comprises a self-adaptive control circuit (3), connected to the primary circuit (2a) and configured to automatically control the direct voltage UpDC from the measurements of UpDC and IpDC alone, and according to a constrained optimization algorithm; the self-adaptive control circuit (3) being further configured to estimate performance quantities of the system from the measurements of UpDC and IpDC; and the constrained optimization algorithm being parameterized with at least one predetermined constraint and associated with one of the performance quantities of the system, - said system performance quantities comprise at least one or more of the following instantaneous quantities: a duration Toff during which the switch IT is closed, a duration Ton during which the switch IT is open, a continuous instantaneous power PinDC supplying the inverter, a continuous power PoutDC at the output of the secondary circuit, an energy transfer efficiency RendTETS, a dissipated power Pdiss in the system, and - said constraints include a minimum duration Toff during which the switch IT is closed, and / or a maximum duration Ton during which the switch IT is open, and / or a minimum instantaneous power PinDC, and / or a maximum efficiency RendTETS, and / or a minimum dissipated power Pdiss.

2. System according to claim 1, characterized in that the measurements and the estimated quantities are carried out cyclically.

3. System according to any one of the preceding claims, characterized in that the secondary coil is made from tracks of a PCB printed circuit.

4. System according to claim 3, characterized in that the switch IT is integrated into the printed circuit PCB of the secondary coil Ls.

5. System according to any one of the preceding claims, characterized in that a magnetic core is placed in the secondary coil Ls or in the primary coil Lp.

6. System according to claim 5, characterized in that the magnetic core is a superparamagnetic composite core.

7. System according to any one of the preceding claims, characterized in that the primary circuit (2a) further comprises a primary capacitor Cp; the primary coil Lp and the primary capacitor Cp have values ​​so as to be in resonance when the coupling k between the primary coil and the secondary coil is below a predetermined coupling threshold.

8. System according to any one of the preceding claims, characterized in that the secondary coil Ls and the secondary capacitor Cs have values ​​so as to be in resonance when the coupling k between the primary coil and the secondary coil is below a predetermined coupling threshold.

9. System according to any one of the preceding claims, characterized in that it comprises a radio link capable of connecting the self-adaptive control circuit (3) with the implant (4) so ​​as to recover real-time information coming from the implant.

10. System according to claim 9, characterized in that the self-adaptive control circuit (3) is configured to adapt the operating frequency of the inverter to the resonant frequency of the secondary circuit from information coming from the implant (4).

11. System according to any one of the preceding claims, characterized in that it comprises at least one pulse width modulator for driving the inverter (7) at a frequency lower than 301kHz, lower than 151kHz or lower than 81kHz.

12. System according to any one of the preceding claims, characterized in that it comprises a precalculated pulse width modulator with one or more harmonic contents of predefined amplitude, frequency and phase.

13. System according to any one of the preceding claims, characterized in that it comprises a timer for triggering an action when the continuous instantaneous power PinDC supplying the inverter does not vary in intensity beyond a predetermined power threshold for a predetermined duration.

14. System according to any one of the preceding claims, characterized in that the self-adaptive control circuit (3) comprises a direct voltage sensor (10), a direct current sensor (11) and a processing unit (12).

15. Method for controlling a direct voltage UpDC in a transcutaneous energy transmission system as defined in any one of the preceding claims, this method comprising, at each cycle defined by open and closed states of the switch IT, the following steps: - measurement of the direct voltage UpDC and the direct current IpDC, - estimation of performance quantities of the system from the measurements of UpDC and IpDC, storage of these quantities, and comparison with values ​​of these quantities obtained during a previous cycle;said system performance quantities comprise at least one or more of the following instantaneous quantities: a duration Toff during which the switch IT is closed, a duration Ton during which the switch IT is open, a continuous instantaneous power PinDC supplying the inverter, a continuous power PoutDC at the output of the secondary circuit, an energy transfer efficiency RendTETS, a dissipated power Pdiss in the system, - control of the continuous voltage UpDC from the measurements of UpDC and IpDC alone, and according to a constrained optimization algorithm configured with at least one predetermined constraint and associated with one of the system performance quantities;said constraints include a minimum duration Toff during which the switch IT is closed, and / or a maximum duration Ton during which the switch IT is open, and / or a minimum instantaneous power PinDC, and / or a maximum efficiency RendTETS, and / or a minimum dissipated power Pdiss.;

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