Secondary resonant circuit

Abstract

The invention relates to a secondary resonant circuit (5) for wireless power transmission in a recharging mode by way of resonant inductive coupling, with a primary resonant circuit (3) comprising at least a first capacitor (Cp) and a first inductance (Lp), said power transmission being directed to the resistive load (2) coupled to the secondary resonant circuit (5), the resistive load having an equivalent impedance, and the secondary resonant circuit (2) comprising: - a second capacitor (Cs) of value Cs and a second inductance (Ls) of value Ls, magnetically and partially coupled to the first capacitor (Cp) and the first inductance (Lp), and - 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 device for contactless power transmission by inductive resonance 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] In a manner known per se, it is technically possible to supply by contactless transmission a motor vehicle or any other object equipped with an electrical energy storage device with a power of between 3 and 50 kW, when this object is stationary (in this case we speak of a static load), or when it is moving (we then speak of a dynamic load). This supply by contactless transmission is then carried out by means of distant electrical circuits coupled magnetically and tuned to the same frequency. The magnetically coupled circuits each comprise at least one resonant LC element, L and C designating inductors and capacitors respectively. [4] A problem with this type of solution is that to transmit a satisfactory power level, especially several kW, it is necessary to operate at high frequencies, especially of the order of 85 kHz or more, for the resonant frequency of each resonant sub-circuit. In addition, this type of solution requires operating at a short distance between the resonant elements located at the source and at the load. [5] The frequency and power levels mentioned above, for implementation in kWatts, may also constitute a danger to the health of people exposed nearby, or to the environment in general. [6] It is known from application US2011 / 0204845 to carry out contactless charging of an electric vehicle by inductive resonance coupling at a frequency between 60Hz and 1200Hz. This application does not, however, specify the nature of the electrical components allowing contactless charging by inductive coupling in this frequency range. [7] The present invention proposes in particular to carry out recharging of an electric vehicle, or other on-board electrical storage system, at very low transfer frequency, optionally with a reversible power flow. [8] The invention thus relates to a secondary resonant circuit for carrying out, in a recharging mode, a contactless power transmission by inductive resonance coupling, with a primary resonant circuit comprising at least a first capacitor and a first inductance, this power transmission being directed towards the resistive load coupled to the secondary resonant circuit, this secondary resonant circuit comprising: - a second capacitor and a second inductor, capable of being magnetically and partially coupled to the first capacitor and to the first inductor, - a decoupling assembly comprising a rectifier arranged to provide a direct voltage to supply recharging power to the resistive load, and an impedance matching assembly which is arranged to vary the equivalent impedance on the input of this impedance matching assembly, independently of the impedance of the resistive load at the output of this impedance matching assembly. [9] The equivalent impedance at the input of the impedance matching assembly is represented by the ratio V / l where V is the voltage across the impedance matching assembly and I the intensity of the current flowing through it.

[0010] The invention thus makes it possible to achieve contactless power transmission by low-frequency resonant inductive coupling, unlike the prior art, thus overcoming the aforementioned drawbacks. The use of an impedance matching assembly makes it possible to increase the transmitted power, which is all the more favorable in contactless transfer by low-frequency resonant inductive coupling. This provides a simple and effective solution for increasing the transmitted power.

[0011] Preferably, the resonant pulsation of the primary and secondary circuits is equal to 2.TT.FO with Fo the pulsation frequency of a source to the primary circuit which provides the recharging power.

[0012] The functions of rectification by the rectifier and impedance matching by the impedance matching assembly can be performed by two separate electronic stages or by a single electronic stage.

[0013] According to one aspect of the invention, the source in the primary circuit has an alternating voltage, of sinusoidal or square shape, and at a pulse frequency Fo.

[0014] According to one aspect of the invention, this voltage drives a resonant Lp / Cp circuit, magnetically and partially coupled to a second resonant Ls / Cs circuit, coupling whose magnetic coupling coefficient is noted k.

[0015] 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 natural inductances.

[0016] According to one aspect of the invention, the power transfer frequency between the primary circuit and the secondary circuit is less than 3 kHz, or even less than 2 kHz or 1 kHz, in particular still substantially equal to 400 Hz or 50 Hz. The frequency range may be 50-2000 Hz. The power transfer frequency between the primary circuit and the secondary circuit may alternatively be between 3 kHz and 5 kHz. Alternatively, the power transfer frequency between the primary circuit and the secondary circuit may be greater than 5 kHz, being for example of the order of 85 kHz.

[0017] The second capacitor and the second inductor can be connected in series, i.e. arranged between two nodes of the secondary circuit. Such an arrangement allows the value of the capacitance of the second capacitor to be independent of the aforementioned coupling coefficient k and to further increase the power transfer.

[0018] The secondary circuit may be devoid of a controlled variable inductance, this variable inductance being arranged to be controlled so as to activate a parametric amplification effect of the current in the secondary circuit. When the second capacitor and the second inductance are connected in series, this series connection may be directly received on the alternating input of the decoupling assembly of the secondary circuit.

[0019] The invention allows a transfer of electrical power from the source to the load in recharging mode.

[0020] The invention also relates to a device for contactless power transmission by inductive resonance coupling, in particular for charging or recharging with electrical energy a resistive load such as a vehicle battery, comprising: - a primary resonant circuit comprising a first capacitor and a first inductance, the primary resonant circuit being powered by a voltage source, - a secondary resonant circuit as mentioned above, which receives, in recharging mode, electrical power from the primary circuit, with a transfer frequency between the primary circuit and the secondary circuit which 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, or alternatively which is greater than 5 kHz, being in particular equal to 85 kHz.

[0021] The first capacitor and the first inductor are, for example, connected in series.

[0022] The decoupling assembly may comprise two arms mounted in parallel, each arm comprising two switches controllable in series, which are for example MOS transistors, and one of the arms may switch at the frequency of the power transmitted from the primary circuit and with a duty cycle of 50%, and the other arm may switch at a frequency higher than that of the power transmitted from the primary circuit, for example at a frequency equal to or greater than 5 times or 10 times the frequency of the power transmitted from the primary circuit, and with a duty cycle modulated according to the measured alternating current and the voltage on the alternating input of the decoupling assembly.

[0023] In standard electric vehicle chargers, it is common to find a power reversibility function to participate in the so-called smart grid function of an urban electricity network.

[0024] 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 electricity network.

[0025] According to one aspect of the invention, the device comprises, on the secondary circuit side, 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 enable an additional onboard wired charging function.

[0026] In all of the above, the primary circuit can be integrated into an electric or hybrid vehicle charging station. This station then receives electrical energy from an electrical network via a cable that can be a single-phase cable or a three-phase cable. In this case, the primary circuit and the secondary circuit are not integrated into the same physical component.

[0027] Alternatively, the primary circuit and the secondary circuit can be integrated into a single physical component. Such a component, which is for example called “charger”, can be loaded into a vehicle.

[0028] In all of the above, the resistive load may be a battery, the latter then having a nominal voltage of 12V, 48V, 60V or more, for example greater than 300V, for example 400V, 800V or 1000V.

[0029] In all of the above, the first and / or second inductance may be made of metal wire, such as copper. Such metal wire is solid, as opposed to Litz wire. A solid metal wire does not have its cross-section hollowed out. Alternatively, at least one of these inductances, or even each of these inductances, is made of Litz wire.

[0030] Other characteristics, details and advantages of the invention will emerge more clearly on reading the detailed description given below, and examples of embodiment given for informational and non-limiting purposes with reference to the appended schematic drawings, in which:

[0031] [Fig.1] is a schematic representation of a contactless power transmission device by inductive resonance coupling according to an exemplary implementation of the invention,

[0032] [Fig.2] schematically represents the decoupling assembly of the secondary circuit of the device of figure 1,

[0033] [Fig.3] schematically represents a variant of the decoupling assembly of the secondary circuit of the device of figure 1,

[0034] [Fig.4] schematically represents an on-board charger stage connected to the device of Figure 1.

[0035] Figure 1 shows a device 1 for contactless power transmission by inductive resonance coupling, for charging or recharging a resistive load 2, here a vehicle battery, with electrical energy.

[0036] Device 1 includes: - a primary resonant circuit 3 comprising a first capacitor Cp and a first inductance Lp, the primary resonant circuit 3 being supplied by a voltage source 4 here a domestic electrical network, - a secondary resonant circuit 5 which receives, in recharge mode, electrical power from the primary circuit 3.

[0037] The primary circuit 3 further comprises, after the source 4, a rectifier stage with power factor corrector 7, or PFC rectifier 7 (PFC designating in English “Power Factor Correction”), followed by a DC / AC converter 8 (direct alternating current converter) which provides a voltage VACL

[0038] The source in the primary circuit has an alternating VAO voltage, sinusoidal or square in shape, and at a pulse frequency Fo.

[0039] The frequency is 50 Hz in the example described.

[0040] The PFC rectifier stage 7 serves, on the one hand, to transform alternating current (AC) into direct current (DC), and, on the other hand, to allow the current taken from the alternating network 4 to be as close as possible to a perfect sine wave at the network pulse. One of the goals is to reduce the reactive current and sub-harmonics which increase energy losses in conduction.

[0041] The secondary resonant circuit 5 is used to carry out, in a recharging mode, a contactless power transmission by inductive resonance 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 active impedance.

[0042] The secondary resonant circuit 5 comprises: - a second capacitor Cs of value Cs and a second inductance Ls of value Ls, magnetically and partially coupled to the first capacitor Cp and the first inductance Lp, - a decoupling assembly 10 arranged to decouple the equivalent impedance of the resistive load 2 from the recharging power.

[0043] As can be seen in Figure 2, this decoupling assembly 10 may in one example comprise a rectifier 11 arranged to provide a direct voltage to supply recharging power to the resistive load 2, and an impedance matching assembly 12 which is arranged to vary the equivalent impedance on the input of this impedance matching assembly, independently of the equivalent active impedance of the resistive load at the output of this impedance matching assembly.

[0044] The rectifier 11 conventionally comprises four diodes D1 to D4.

[0045] The impedance matching circuit 12, or PFC, comprises two capacitors C1, C2 and a switch Q, all in respective parallel branches, and an inductor L and a diode D5.

[0046] This assembly 12 sees at the input a rectified voltage from the voltage Vin and delivers at the output a voltage Vout. being in the example described equal to the voltage Vbatt at the terminals of the resistive load.

[0047] The decoupling assembly 10 thus performs two functions. The first function is to rectify the alternating current to bring a direct current to the battery 2. The second function is to ensure that the ratio of the voltage present at the input of the assembly 10 divided by the input current is equal to a reference impedance R. In other words, this assembly 10 transforms the rectification coupled to the battery into an equivalent resistance seen from the on-board resonant mesh on the vehicle side. The purpose of this equivalent load impedance regulation is to place the resonant mesh in a favorable arrangement for establishing a current to maximize the power transfer to the battery. The reference value of this load is a compromise. It must be high enough to not require a lot of current to transfer power. It must be low enough to ensure that at the input of this assembly, the voltage is strictly lower than the battery voltage, otherwise the system would be out of control and regulation becomes impossible.

[0048] The resonant pulsation of the primary 3 and secondary 5 circuits is equal to 2.TT.FO with Fo the pulsation frequency of the source to the primary circuit 3 which provides the recharging power.

[0049] The functions of rectification by the rectifier 11 and of impedance adaptation by the impedance adaptation assembly 12 can be carried out by two separate electronic stages, as illustrated in FIG. 2, or within a single electronic stage, as illustrated in FIG. 3.

[0050] The assembly 10 may be an electronic assembly of the “Totem POLE PFC rectifier” or “dual Boost PPC rectifier” type, these assemblies being known in the electronic literature for their structure.

[0051] In the example of Figure 3, the assembly 10 constitutes a single electronic stage performing both voltage rectification and impedance matching by means of two arms 20 connected in parallel. Each arm comprises two series-controllable switches which are, for example, MOS transistors. One of the two arms switches at the frequency of the power transmitted from the primary circuit and with a duty cycle of 50%, and the other arm switches at a frequency higher than that of the power transmitted from the primary circuit, for example at a frequency equal to or greater than 5 times or 10 times the frequency of the power transmitted from the primary circuit, and with a duty cycle modulated according to the measured alternating current and the voltage on the alternating input of the assembly 10.

[0052] The impedance matching assembly 10 of figure 3 is arranged to vary the equivalent impedance RRef at the terminals of the alternating input, defined between the two midpoints of the arms, independently of the impedance of the resistive load at the output of this assembly 10.

[0053] The equivalent impedance RRef is represented by the ratio V / l where V is the voltage across the AC input, and I the current intensity on this AC input.

[0054] RRef has for example a value between 5'Q and 15'Q. For a given recharge configuration, this configuration being notably determined by at least one of: the position of the secondary resonant circuit 5 with respect to the primary resonant circuit 3 and / or the power level to be transmitted and / or the voltage at the terminals of the battery, RRef may have a fixed value and this value is for example in the aforementioned range. From one recharging configuration to another, for example in the event of a greater distance between the primary resonant circuit 3 and the secondary resonant circuit 5 and / or to take into account the aging of the system, the value of RRef may be modified, remaining in particular in the aforementioned range.

[0055] One of the controllable switches of the arm which switches at a frequency higher than that of the power transmitted from the primary resonant circuit 3 is for example controlled according to a duty cycle a while the other controllable switch of this arm is controlled according to a duty cycle 1 - a, and a is for example determined according to the equation below oc= Rfie / X| / | beats

[0056] The VACI voltage, called source voltage, at the output of converter 8 drives a resonant Lp / Cp cell, magnetically and partially coupled to a resonant Ls / Cs cell of the secondary resonant circuit, coupling whose magnetic coupling coefficient is noted k.

[0057] The coupling coefficient k is in the range 0 <k<1 .

[0058] 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. This transfer frequency is in particular that applied to the resonant LC cell of the primary circuit.

[0059] The invention allows a transfer of electrical power from the VAO source to the load 2 in recharging mode.

[0060] According to one aspect of the invention, the device comprises, on the secondary circuit side, 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 enable an additional onboard wired charging function.

[0061] This on-board charger stage 30, known per se, is shown in dotted lines in FIG. 1.

[0062] This on-board charger stage 30 is an isolated AC / DC converter type which integrates the functions of rectifier, notably at 50Hz, High Frequency inverter and PFC with a single MOSFET input stage.

[0063] 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.

[0064] This floor 30 serves an on-board network 31 which allows wired charging.

Claims

Claims

1. Secondary resonant circuit (5) for carrying out, in a recharging mode, a contactless power transmission by inductive resonance coupling, with a primary resonant circuit (3) comprising at least a first capacitor (Cp) and a first inductance (Lp), this power transmission being directed towards the resistive load (2) coupled to the secondary resonant circuit (5), this secondary resonant circuit (5) comprising: - a second capacitor (Cs) of value Cs and a second inductance (Ls) of value Ls, capable of being magnetically and partially coupled to the first capacitor (Cp) and to the first inductance (Lp), and - a decoupling assembly (10), this decoupling assembly comprising a rectifier (11) arranged to provide a direct voltage to supply recharging power to the resistive load, and an impedance matching assembly (12) which is arranged to vary the equivalent impedance on the input of this impedance matching assembly, independently of the impedance of the resistive load at the output of this impedance matching assembly.

2. Circuit according to the preceding claim, in which 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.

3. Circuit according to one of the preceding claims, in which the functions of rectification by the rectifier (11) and of impedance adaptation by the impedance adaptation assembly (12) are carried out by two separate electronic stages.

4. Circuit according to one of the preceding claims, in which the rectification and impedance adaptation functions are performed by a single electronic stage.

5. Circuit according to any one of the preceding claims, the second capacitor (Cs) and the second inductor (Ls) being connected in series.

6. Circuit according to any one of the preceding claims, the second inductance (Ls) being made of metal wire other than Litz wire.

7. Device (1) for contactless power transmission by inductive resonance coupling, in particular for charging or recharging with electrical energy a resistive load such as a vehicle battery, comprising: - a primary resonant circuit (3) comprising a first capacitor 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 recharging mode, electrical power from the primary circuit, with a transfer frequency between the primary circuit and the secondary circuit which 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, or which is greater than 5 kHz, being in particular substantially equal to 85 kHz.

8. Device according to the preceding claim, the first capacitor (Cp) and the first inductance (Lp) being connected in series.

9. Device according to claim 7 or 8, the first inductance (Lp) being made of metal wire other than Litz wire.

10. Device according to any one of claims 7 to 9, the decoupling assembly (10) comprising two arms mounted in parallel, each arm comprising two switches controllable in series, and one of the arms switching at the frequency of the power transmitted from the primary circuit and with a duty cycle of 50%, and the other arm switching at a frequency higher than that of the power transmitted from the primary circuit, in particular at a frequency equal to or greater than 5 times or 10 times the frequency of the power transmitted from the primary circuit, and with a duty cycle modulated according to the measured alternating current and the voltage on the alternating input of this decoupling assembly (10).

11. Device according to any one of claims 7 to 9, 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 electricity network.

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