Secondary resonant circuit

Abstract

The invention relates to a secondary resonant circuit (5) for contactlessly transmitting power in a recharging mode through resonant inductive coupling, with a primary resonant circuit (3) comprising at least a first capacitor (Cp) and a first inductor (Lp), this transmission of power being directed to the resistive load (2) coupled to the secondary resonant circuit (5), this resistive load having an equivalent impedance, this secondary resonant circuit (2) comprising: - a second capacitor (Cs) of capacitance Cs and a second inductor (Ls) of inductance Ls, which are coupled magnetically and partially to the first capacitor (Cp) and the first inductor (Lp), - a controlled variable inductor Le(t) designed to be controlled so as to activate a parameteric amplification effect for the current in the secondary circuit, - a decoupling assembly (10).

Description

Description Title of the invention: Secondary resonant circuit [1] The present invention relates to a secondary resonant circuit. [2] The present invention relates to a secondary resonant circuit and to a contactless power transmission device by resonant inductive coupling, in particular for charging or recharging a battery of a motor vehicle or any type of vehicle, land, air, or sea, propelled by means of electrical energy. [3] It is technically possible to power a motor vehicle or any other object equipped with an electrical energy storage device by contactless transmission at a power level between 3 and 50 kW, whether the object is stationary (this is referred to as a static load) or moving (this is referred to as a dynamic load). This contactless power supply is achieved using magnetically coupled, frequency-tuned, remote electrical circuits. Each magnetically coupled circuit contains at least one resonant LC element, where L and C represent inductance and capacitance, respectively. [4] One problem with this type of solution is that to transmit a satisfactory power level, particularly several kW, it is necessary to operate at high frequencies, specifically on the order of 85 kHz or higher, for both the operating frequency and the natural frequency of each resonant circuit. Furthermore, this type of solution requires operating at a short distance between the resonant elements located at the source and the load. [5] The frequency and power levels mentioned above, for implementation in kilowatts, may also constitute a danger to the health of people exposed nearby, or to the environment in general. [6] The present invention proposes in particular to achieve a charging of electric vehicle, or other on-board electrical storage system, at very low transfer frequency, optionally with a reversible power flow. [7] The invention thus relates to a secondary resonant circuit for achieving, in a charging mode, contactless power transmission by coupling inductive resonant circuit, with a primary resonant circuit comprising at least a first capacitance and a first inductance, this power transmission being directed towards the resistive load coupled to the secondary resonant circuit, this resistive load having an equivalent impedance, this secondary resonant circuit comprising: - a second capacitance and a second inductance, magnetically and partially coupled to the first capacitance and the first inductance, - a controlled variable inductor Le(t) arranged to be controlled in such a way as to activate a parametric amplification effect of the current in the secondary circuit, - a decoupling assembly arranged to decouple the equivalent impedance of the resistive load, in particular a vehicle battery, from the charging power, this decoupling assembly comprising a rectifier arranged to provide a DC voltage to supply charging power to the resistive load, and an impedance matching assembly which is arranged to, at a given charging power, vary the equivalent impedance of the resistive load. [8] [9] According to one aspect of the invention, the controlled variable inductance Le(t) is arranged to be controlled such that the total inductance L(t) in the secondary circuit follows the following law: L(t) = Ls + Le(t) = L0.(1 / (1 + h.cos(2πθ.t))), where h is a parameter used to activate a parametric current amplification effect in the secondary resonant circuit, t is time, L0 is a fixed inductance value preferably less than the value Ls of the inductance (Ls), h is a parametric amplification parameter strictly less than 1, and co0 is the natural frequency of the circuits Lp,Cp and Ls,Cs with Lp.Cp.co0 2 =1 and LO.Cs. coO 2 = 1.

[0010] According to a variant of the invention, the controlled variable inductance Le(t) is arranged to be controlled such that the total inductance L(t) in the secondary circuit follows the following law: L(t) = Ls + Le(t) = L0.(1 + h.cos(2πωt + cφ), where t is time, L0 is a fixed inductance value preferably greater than or equal to the value of Ls, h is a parametric amplification parameter, and cφ is the natural frequency. circuits Lp,Cp and Ls,Cs with Lp.Cp. coO 2 =1 and LO.Cs. coO 2 = 1 and cp the phase which can be chosen to be zero or non-zero.

[0011] The equivalent impedance of the resistive load is represented by the ratio V / l where V is the voltage across the impedance matching circuit and I is the current flowing through it.

[0012] The invention thus makes it possible to decouple the equivalent impedance of the resistive load (in particular of the battery) from the charging power (Vxl) and to make it possible to reach a value of the parameter h ensuring the parametric amplification effect.

[0013] Preferably, the resonant pulsation coO of the primary and secondary circuits is equal to 2.TT.F0 with FO the pulsation frequency of a source to the primary circuit that provides the charging power.

[0014] The aforementioned expression for L(t) includes the parameter h, a real-time adjustable variable between 0 and 1, whose role is to activate a parametric current amplification effect in the circuit. The minimum value of h, denoted hc for critical h, necessary for the implementation of the parametric current amplification phenomenon in unstable conditions, can be established by the following relation: hc = 2R / (L0 co0), where R is the sum of the resistances of the secondary circuit 5, including the equivalent load impedance, and L0 is a fixed inductance value less than the value Ls of the inductance Ls. The parametric current amplification phenomenon in unstable conditions results in an exponential growth of the current amplitude, whereas if h < hc, the envelope of the current peak levels is indeed enlarged (all peak levels are higher in absolute value) but is convex rather than concave as in exponential growth.

[0015] For a given operating point, adjusting the parameter h will modulate the amplitude of the currents in the primary and secondary circuits.

[0016] The mathematical expression of hc is proportional to Ls and coO, two so-called fixed quantities of the circuit, and R the sum of the resistances including the equivalent load impedance.

[0017] In other words, it is not possible to achieve the parametric current amplification effect required for the proper functioning of the circuit for any load impedance value.

[0018] Some operating points would be impossible to achieve since they would imply a value hc which would be hc > 1.

[0019] In other words, for a fixed-voltage load like a battery, varying the charging power is equivalent to modulating its impedance. Using the relationship between power, voltage, and current (P=Vlx), we vary I, so the V / l ratio changes with the power. We see here that for a V / l ratio above a certain value, the critical value hc becomes hc>1 and therefore impossible to achieve in practice.

[0020] The instability, which is sought to achieve the parametric amplification of the current, is ensured if the parameter h is chosen between 0 and 1 and greater than hc. We can thus see that h and hc cannot exceed 1.

[0021] The invention ensures that, regardless of the charging power, the load impedance seen by the secondary circuit is always sufficiently low to allow the parametric amplification effect made possible by an appropriate value of h, less than 1.

[0022] To this end, as already explained, the invention proposes decoupling the equivalent load impedance (which could be a vehicle battery) from the charging power. In other words, the invention ensures that, regardless of the charging power, the load impedance seen by the circuit is always sufficiently low to allow the parametric amplification effect.

[0023] The rectification functions by the rectifier and the impedance matching functions by the impedance matching circuit can be performed by two separate electronic stages or within a single electronic structure.

[0024] According to one aspect of the invention, the source to the primary circuit presents an alternating voltage, of sinusoidal or square form, and at a frequency of pulsation FO.

[0025] According to one aspect of the invention, this voltage attacks a resonant Lp / Cp circuit, magnetically and partially coupled to a second resonant Ls / Cs circuit, the coupling of which is denoted k.

[0026] The coupling coefficient k is in the range 0 <k<1 . On note que le coefficient k est lié à l’inductance mutuelle par la relation M 2 = k 2 .Lp.Ls which translates the inductive coupling between two self-inductances.

[0027] According to one aspect of the invention, the power transfer frequency between the primary and secondary circuits is less than 3 kHz, or even less than 2 kHz or 1 kHz, and in particular substantially equal to 400 Hz or 50 Hz. The frequency range can be 50–2000 Hz. Alternatively, the power transfer frequency between the primary and secondary circuits can be between 3 kHz and 5 kHz.

[0028] The invention allows for the transfer of electrical power from the source to the load in charging mode.

[0029] According to one aspect of the invention, the controlled variable inductance Le(t) is realized by a voltage source (Vind(t)) whose voltage value Vind(t) follows the equation Vind(t)=L(t) dlin(t) / dt, this voltage source containing a time-varying part.

[0030] According to one aspect of the invention, this source is achieved by an inverter with an isolated rectifier.

[0031] The low-frequency voltage can be generated by a DC / AC converter, isolated or not, which comes after the rectifier / impedance matching stage that interfaces.

[0032] The invention also relates to a contactless power transmission device using resonant inductive coupling, particularly for charging or recharging a resistive load such as a vehicle battery, comprising: - a primary resonant circuit comprising a first capacitance and a first inductance (L1), the primary resonant circuit being powered by a low-frequency energy source, - a secondary resonant circuit as above, which receives, in charging mode, electrical power from the primary circuit, with a transfer frequency between the primary and secondary circuits that is less than 5 kHz, or even 3 kHz, or even less than 2 kHz or 1 kHz, in particular still substantially equal to 400 Hz or 50 Hz.

[0033] In typical electric vehicle chargers, it is common to find a power reversibility function to participate in the so-called function Intelligent electrical network, or "smart grid" in English, of an urban electrical network.

[0034] According to one aspect of the invention, the device is arranged to be reversible in power, allowing the secondary circuit to send power to the primary circuit, this power received in the primary circuit being able, for example, to be injected into an urban electrical network.

[0035] In this case, the primary circuit includes a controlled inductance similar to the secondary circuit, to activate a parametric amplification effect.

[0036] According to one aspect of the invention, the device includes, on the side of the secondary circuit, an onboard charger stage, in particular of the "Single-Phase Single-Stage Bidirectional Onboard Charger" type, arranged to exchange electrical power without contact with the secondary circuit to allow an additional onboard wired charging function.

[0037] In all of the above, the primary circuit can be integrated into an electric or hybrid vehicle charging station. This station then receives electrical power from the electrical grid via a cable, which can be either single-phase or three-phase. In this case, the primary and secondary circuits are not integrated into the same physical component.

[0038] Alternatively, the primary and secondary circuits can be integrated into a single physical component. Such a component, which is for example called a "charger," can be installed in a vehicle.

[0039] Other features, details and advantages of the invention will become clearer upon reading the detailed description given below, and the illustrative and non-limiting examples of embodiments given with reference to the attached schematic drawings, in which:

[0040] [Fig.1] is a schematic representation of a contactless power transmission device using resonant inductive coupling according to an example of an implementation of the invention,

[0041] [Fig.2] is a schematic representation of the implementation of a controlled inductance in the secondary circuit of the transmission device in Figure 1.

[0042] [Fig.3] schematically represents the decoupling setup of the secondary circuit of the device in Figure 1,

[0043] [Fig.4] schematically represents an on-board charger stage connected to the device in Figure 1.

[0044] Figure 1 shows a contactless power transmission device 1 using resonant inductive coupling, for charging or recharging a resistive load 2, here a vehicle battery, with electrical energy.

[0045] Device 1 comprises: - a primary resonant circuit 3 comprising a first capacitance Cp and a first inductance Lp, the primary resonant circuit 3 being powered by an energy source 4, here a domestic electrical network, - a secondary resonant circuit 5 which receives, in charging mode, electrical power from the primary circuit 3.

[0046] The primary circuit 3 further includes, after the source 4, a rectifier stage with power factor corrector 7, or PFC rectifier 7 (PFC stands for "Power Factor Correction"), followed by a DC / AC converter 8 (DC-AC converter) which provides a Vaci voltage.

[0047] The source to the primary circuit presents an alternating voltage Vaci, of sinusoidal or square shape, and at a frequency of pulsation FO.

[0048] The frequency is 50 Hz in the example described.

[0049] The PFC 7 rectifier stage serves, firstly, to convert alternating current (AC) to direct current (DC), and secondly, to ensure that the current drawn from the AC network 4 is as close as possible to a perfect sine wave at the network frequency. One of the goals is to reduce reactive current and subharmonics, which increase energy losses during conduction.

[0050] The secondary resonant circuit 5 is used to achieve, in a charging mode, a contactless power transmission by resonant inductive coupling with the primary resonant circuit 3, this power transmission being directed towards the resistive load 2 coupled to the secondary resonant circuit 5, this resistive load 2 having an equivalent impedance.

[0051] The secondary resonant circuit 5 comprises: - a second capacitance Cs of value Cs and a second inductance Ls of value Ls, magnetically and partially coupled to the first capacitance Cp and the first inductance Lp, - a controlled variable inductor Le(t) arranged to be controlled in such a way as to activate a parametric amplification effect of the current in the secondary circuit, - a decoupling assembly 10 arranged to decouple the equivalent impedance of the resistive load 2 from the charging power.

[0052] As can be seen in Figure 3, this decoupling assembly 10 includes a rectifier 11 arranged to provide a DC voltage to supply charging power to the resistive load 2, and an impedance matching circuit 12 which is arranged to vary the equivalent impedance of the resistive load at a given charging power.

[0053] Rectifier 11 includes, in a conventional manner, four diodes D1 to D4.

[0054] The impedance matching circuit 12, or PFC, includes two capacitors C1, C2 and a switch Q, all in respective parallel branches, and an inductor L and a diode D5.

[0055] This circuit 12 sees a voltage Vin as input and delivers a voltage Vout as output.

[0056] The decoupling assembly 10 thus performs two functions. The first function is to rectify the alternating current to provide a direct current to the battery 2. The second function is to ensure that the ratio of the voltage present at the input of assembly 10 divided by the input current is equal to a reference impedance R. In other words, this assembly 10 transforms the rectified signal coupled to the battery into an equivalent resistance as seen by the resonant mesh on the vehicle side. The goal of this equivalent load impedance regulation is to position the resonant mesh in a way that promotes current flow to maximize power transfer to the battery. The reference value for this load is a compromise. It must be high enough to avoid requiring excessive current to transfer power, yet low enough to ensure that the input voltage is strictly lower than the battery voltage; otherwise, the system would become uncontrollable and regulation impossible.

[0057] The variable controlled inductance Le(t) is arranged to be controlled such that the total inductance L(t) in the secondary circuit 5 follows the following law: L(t) = Ls + Le(t) = L0.(1 / (1 + h.cos(2πωt))), where h is a parameter used to activate a parametric current amplification effect in the secondary resonant circuit, t is time, L0 is a fixed inductance value preferably less than the value Ls of the inductance (Ls), h is a parametric amplification parameter strictly less than 1, and co0 is the natural frequency of the circuits Lp,Cp and Ls,Cs with Lp.Cp.co0 2 =1 and LO.Cs. coO 2 = 1.

[0058] The equivalent impedance of the resistive load 2 is represented by the ratio V / l where V is the voltage across the terminals of the impedance matching circuit 12 and I is the current intensity through it.

[0059] The invention thus makes it possible to decouple the equivalent impedance of the resistive load 2 from the charging power Vxl and to achieve a value of the parametric amplification parameter h ensuring the parametric amplification effect.

[0060] The resonant pulsation coO of the primary 3 and secondary 5 circuits is equal to 2.TT.F0 with FO the pulsation frequency of the source to the primary 3 circuit which provides the charging power.

[0061] The aforementioned expression for L(t) includes the parameter h, a real-time adjustable variable between 0 and 1, whose role is to activate a parametric current amplification effect in the circuit. The minimum value of h, denoted hc for critical h, necessary for the implementation of the parametric current amplification phenomenon in unstable conditions, can be established by the following relation: hc = 2R / (L0 co0), where R is the sum of the resistances of the secondary circuit 5, including the equivalent load impedance, and L0 is a fixed inductance value less than the value Ls of the inductance Ls. The parametric current amplification phenomenon in unstable conditions results in an exponential growth of the current amplitude, whereas if h < hc, the envelope of the current peak levels is indeed enlarged (all peak levels are higher in absolute value) but is convex rather than concave as in exponential growth.

[0062] For a given operating point, adjusting the parameter h will modulate the amplitude of the currents in the primary 3 and secondary 5 circuits.

[0063] The mathematical expression of he is proportional to Ls and coO, two so-called fixed quantities of the circuit, and R the sum of the resistances including the equivalent load impedance.

[0064] Instability, which is preferred to achieve parametric current amplification, is ensured if the parameter h is chosen between 0 and 1 and greater than hc.

[0065] In the case where we have a state of stability with h < hc (instead of h > hc which is the preferred case), we can still be satisfied with it, given the useful energy contribution from the pumping towards the evolution of the current, which will have higher peak levels in absolute value, because of the phenomenon of negative resistance induction related to the controlled variation of inductance.

[0066] The invention ensures that, regardless of the charging power, the load impedance seen by the secondary circuit 5 is always sufficiently low to allow the parametric amplification effect made possible by an appropriate value of h, less than 1. Impedance matching is useful to make pumping as efficient as possible, with h > hc.

[0067] For the case h < hc, impedance matching gives access to the production of an effect similar to the introduction of a negative partial resistance by pumping at h < hc.

[0068] The rectification functions by the rectifier 11 and the impedance matching functions by the impedance matching circuit 12 can be achieved by two separate electronic stages, as illustrated in Figure 3, or within a single electronic structure.

[0069] Assembly 10 can be an electronic assembly of the type "Totem POLE dual Boost PFC rectifier" known in the electronic literature.

[0070] The voltage Vaci, called source voltage, at the output of converter 8 drives a resonant Lp / Cp circuit, magnetically and partially coupled to the second resonant circuit Ls / Cs, coupling whose magnetic coupling coefficient is noted k.

[0071] The coupling coefficient k is in the range 0 <k<1 .

[0072] The power transfer frequency between the primary and secondary circuits is less than 5 kHz, or even less than 3 kHz, or even less than 2 kHz or 1 kHz, and in particular, approximately equal to 400 Hz or 50 Hz. This The transfer frequency is notably that applied to the resonant LC element of the primary circuit.

[0073] The invention allows for the transfer of electrical power from the Vaci source to the load 2 in charging mode.

[0074] As illustrated in Figure 2, the controlled variable inductance Le(t) is achieved by a voltage Vind(t) across the terminals of the variable inductance whose voltage value Vind(t) follows the equation Vind(t)=L(t) dlin(t) / dt, where lin(t) is the current across the terminals of the variable inductance, this voltage containing a time-varying part.

[0075] As can be seen in Figure 2, the voltage Vbatt across the terminals of battery 2 is coupled to the voltage Vind(t) across the terminals of the variable inductance via an inverter 15 and an inductance 17, on one side, and an isolated rectifier 16 and an inductance 18 on the other side.

[0076] Inductors 17, 18 allow for contactless energy transfer.

[0077] In common electric vehicle chargers, it is common to find a power reversibility function to participate in the so-called Smart Grid function of an urban electrical network.

[0078] It is possible to have a contactless power transmission device by resonant inductive coupling arranged to be reversible in power, allowing the secondary circuit to send power to the primary circuit, this power received in the primary circuit being able for example to be injected into an urban electrical network.

[0079] In this case, the primary circuit includes a controlled inductance similar to the secondary circuit, to activate a parametric amplification effect.

[0080] According to one aspect of the invention, the device includes, on the side of the secondary circuit, an onboard charger stage 30, in particular of the "Single-Phase Single-Stage Bidirectional Onboard Charger" type, arranged to exchange electrical power without contact with the secondary circuit to allow an additional onboard wired charging function.

[0081] This on-board charger stage 30, known in itself, is represented by dotted lines in Figure 1.

[0082] This on-board charger stage 30 is an isolated AC / DC converter type which integrates rectifier functions, including at 50Hz, High Frequency inverter and PFC with a single MOSFET input stage.

[0083] As illustrated in Figure 4, this on-board charger stage 30 is connected to a rectifier bridge 29 of the decoupling assembly 10 which includes the impedance matching assembly 12, present in parallel with the battery.

[0084] This stage 30 serves an embedded network 31 which enables wired charging.

Claims

Demands

1. A secondary resonant circuit (5) for achieving, in a charging mode, contactless power transmission by resonant inductive coupling, with a primary resonant circuit (3) comprising at least a first capacitance (Cp) and a first inductance (Lp), this power transmission being directed towards the resistive load (2) coupled to the secondary resonant circuit (5), this resistive load having an equivalent impedance, this secondary resonant circuit (2) comprising: - a second capacitance (Cs) of value Cs and a second inductance (Ls) of value Ls, magnetically and partially coupled to the first capacitance (Cp) and the first inductance (Lp), - a controlled variable inductor Le(t) arranged to be controlled in such a way as to activate a parametric amplification effect of the current in the secondary circuit, - a decoupling assembly (10) arranged to decouple the equivalent impedance of the resistive load, in particular a vehicle battery, from the charging power, this decoupling assembly comprising a rectifier (11) arranged to make available a DC voltage to supply charging power to the resistive load, and an impedance matching assembly (12) which is arranged to, at a given charging power, vary the equivalent impedance of the resistive load.

2. A circuit according to the preceding claim, wherein the controlled variable inductance Le(t) is arranged to be controlled such that the total inductance L(t) in the secondary circuit follows the following law: L(t) = Ls + Le(t) = L0.(1 / (1 + h.cos(2πθt))), where h is a parameter used to activate a parametric current amplification effect in the secondary resonant circuit, t is time, L0 is a fixed inductance value preferably less than the value Ls of the inductance (Ls), h is a parametric amplification parameter strictly less than 1, and co0 is the natural frequency of the circuits Lp,Cp and Ls,Cs with Lp.Cp.co0 2 = 1 and LO.Cs. coO 2 = 1.

3. A circuit according to claim 1, wherein the controlled variable inductance Le(t) is arranged to be controlled such that the total inductance L(t) in the secondary circuit follows the following law: L(t) = Ls + Le(t) = L0.(1 + h.cos(2πωt + cp)) with t the time, L0 a fixed inductance value preferably greater than or equal to the value Ls, h a parametric amplification parameter, and c0 the natural frequency of the circuits Lp,Cp and Ls,Cs with Lp.Cp.co0 2 =1 and LO.Cs. coO 2 = 1 and cp the phase which can be chosen to be zero or non-zero.

4. Circuit according to any one of the preceding claims, wherein the resonant pulsation coO of the primary (3) and secondary (5) circuits is equal to 2.TT.F0 with FO the pulsation frequency of a source to the primary circuit which provides the charging power, in particular with an alternating voltage (Vaci), sinusoidal or square wave, and at the pulsation frequency FO.

5. Circuit according to the preceding claim, wherein the power transfer frequency between the primary circuit and the secondary circuit is less than 5 kHz, or even less than 3 kHz, or even less than 2 kHz or 1 kHz, in particular still substantially equal to 400 Hz or 50 Hz.

6. Circuit according to any one of claims 4 and 5, wherein the low frequency voltage (Vaci) is generated by a DC / AC converter, isolated or not, which comes after the rectifier / impedance matching stage.

7. Circuit according to any one of claims 4 to 6, wherein this source (Vaci) is realized by an inverter with an isolated rectifier.

8. Circuit according to any one of the preceding claims, wherein the rectification functions by the rectifier (11) and the impedance matching functions by the impedance matching circuit (12) are performed by two separate electronic stages.

9. Circuit according to any one of claims 1 to 7, wherein the rectification functions by the rectifier (11) and impedance matching by the impedance matching circuit (12) are performed by a single electronic structure.

10. Circuit according to the preceding claim, wherein the controlled variable inductance Le(t) is realized by a voltage source (Vind(t)) whose voltage value Vind(t) follows the equation Vind(t)=L(t) d lin (t) / dt, this voltage source containing a time-varying part.

11. A contactless power transmission device by resonant inductive coupling, in particular for charging or recharging a resistive load such as a vehicle battery, comprising: - a primary resonant circuit (3) comprising a first capacitance and a first inductance (Lp), the primary resonant circuit being powered by a low-frequency energy source, - a secondary resonant circuit (5) according to any one of the preceding claims, which receives, in charging mode, electrical power from the primary circuit, with a transfer frequency between the primary and secondary circuits which is less than 3kHz, or even less than 2kHz or 1 kHz, in particular still substantially equal to 400 Hz or 50 Hz.

12. Device according to the preceding claim, arranged to be reversible in power allowing the secondary circuit to send power to the primary circuit, this power received in the primary circuit being able for example to be injected into an urban electrical network.

13. Device according to any one of claims 11 and 12, wherein the resonant pulsation coO of the primary (3) and secondary (5) circuits is equal to 2.TT.F0 with FO the pulsation frequency of a source to the primary circuit which provides the charging power, in particular with an alternating voltage (Vaci), sinusoidal or square wave, and at the pulsation frequency FO.

14. Device according to the preceding claim, wherein the low frequency voltage (Vaci) is generated by a DC / AC converter, isolated or not, which comes after the rectifier / impedance matching stage.

15. Device according to any one of claims 13 and 14, wherein this source (Vaci) is realized by an inverter with an isolated rectifier.

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