(19)
(11)EP 3 506 487 B1

(12)EUROPEAN PATENT SPECIFICATION

(45)Mention of the grant of the patent:
06.01.2021 Bulletin 2021/01

(21)Application number: 18214947.6

(22)Date of filing:  20.12.2018
(51)Int. Cl.: 
H02N 2/18  (2006.01)

(54)

CIRCUIT AND METHOD FOR ENERGY RECUPERATION

VORRICHTUNG UND VERFAHREN ZUR ENERGIERÜCKGEWINNUNG

CIRCUIT ET PROCÉDÉ DE RÉCUPÉRATION D'ÉNERGIE


(84)Designated Contracting States:
AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR

(30)Priority: 28.12.2017 FR 1763295

(43)Date of publication of application:
03.07.2019 Bulletin 2019/27

(73)Proprietor: Commissariat à l'Energie Atomique et aux Energies Alternatives
75015 Paris (FR)

(72)Inventors:
  • MOREL, Adrien
    38000 GRENOBLE (FR)
  • PILLONNET, Gaël
    38120 PROVEYSIEUX (FR)
  • WANDEROILD, Yohan
    38240 MEYLAN (FR)

(74)Representative: Cabinet Beaumont 
4, Place Robert Schuman B.P. 1529
38025 Grenoble Cedex 1
38025 Grenoble Cedex 1 (FR)


(56)References cited: : 
EP-A1- 2 579 445
WO-A1-2019/121860
WO-A1-2017/149289
  
      
    Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).


    Description

    FIELD



    [0001] The present disclosure relates to the field of energy recuperation, and in particular to the recuperation of electrical energy from a mechanical resonator.

    BACKGROUND



    [0002] Materials having piezo-electrical properties permit electrical energy to be recuperated from the oscillations of a mechanical resonator, which is for example excited by a mechanical vibration. Such energy harvesters may be employed in a broad range of environments, and permit for example a battery to be charged from the movement of the resonator.

    [0003] A difficulty for the implementation of a circuit for energy recuperation from such an alternating electrical signal is to harvest a high amount of energy. Indeed, while a diode bridge can be used to recuperate electrical energy at the positive and negative peaks of the electrical signal, such a solution is relatively inefficient given that the energy is extracted only during a limited portion of each cycle, and thus the power that can be recuperated by such a solution is limited.

    [0004] While some systems have been proposed providing alternatives to a simple diode bridge that permit the amount of energy that is harvested to be increased, there is a difficulty in reducing energy loss in such systems.

    [0005] The International patent application published as WO2017/149289 relates to energy harvesting systems and methods.

    [0006] The European patent application published as EP2579445 relates to a peak detector for a switched AC/DC converter. The International patent application refers an electrical energy harvesting system including variable capacitors.

    SUMMARY



    [0007] It is an aim of embodiments of the present description to at least partially address one or more problems in the prior art.

    [0008] According to one aspect, there is provided a circuit for recuperating electrical energy from a mechanical resonator according to the independent device claim 1.

    [0009] According to one embodiment, the inductance of the charge transfer circuit is used in a boost converter configuration during the discharging of the voltage of the first polarity to the capacitance of the mechanical resonator, and in a buck converter configuration during the charging of the voltage of opposite polarity to the capacitance of the mechanical resonator.

    [0010] According to one embodiment, the circuit further comprises a control circuit configured to control the at least one switch to conduct a current from a first node of the capacitance, through said inductance and back to a second node of the capacitance during a first portion of the first period and to conduct a current from the first node of said capacitance, through said inductance and to said capacitor during a second portion of the first period.

    [0011] According to one embodiment, the control circuit is configured to control said at least one switch such that there is a plurality of the first and second portions during the first period.

    [0012] According to one embodiment, the at least one switch is controlled by a clock signal generated by said control circuit.

    [0013] According to one embodiment, the at least one switch is controlled by the control signal to conduct the current to the capacitor when a measured current in said inductance reaches a threshold limit.

    [0014] According to one embodiment, the charge transfer circuit comprises an H-bridge and a voltage converter, the H-bridge coupling first and second terminals of the mechanical resonator to first and second inputs of the voltage converter.

    [0015] According to one embodiment, the voltage converter comprises: the series connection of an inductor and a first switch of the at least one switch coupled between the first input of the voltage converter and a first node of the capacitor; and a second switch of the at least one switch coupled between an intermediate node and the second input of the voltage converter, the intermediate node being between the inductor and the first switch.

    [0016] According to one embodiment, the charge transfer circuit comprises a transformer having a primary winding coupled between first and second terminals of the mechanical resonator and a secondary winding coupled between first and second nodes of the capacitor.

    [0017] According to one embodiment, the transformer further comprises a further primary winding coupled to a further mechanical resonator.

    [0018] According to one embodiment, the charge transfer circuit is further configured: to discharge a voltage of an opposite polarity to the first polarity held by the capacitance of the mechanical resonator to said capacitor during a third period; and to charge a voltage of the first polarity to the capacitance of the mechanical resonator during a fourth period using the voltage potential stored by said capacitor during the third period.

    [0019] According to a further aspect, there is provided a method of recuperating electrical energy from a mechanical resonator according to the independent method claim 12.

    BRIEF DESCRIPTION OF THE DRAWINGS



    [0020] The foregoing and other features and advantages will become apparent from the following detailed description of embodiments, given by way of illustration and not limitation with reference to the accompanying drawings, in which:

    Figure 1 schematically illustrates an energy harvesting system according to an example embodiment;

    Figure 2A schematically illustrates a circuit for energy recuperation according to an example embodiment that has been proposed;

    Figure 2B is a graph representing signals in the circuit of Figure 2A according to an example embodiment;

    Figure 3A schematically illustrates a circuit for energy recuperation according to a further example embodiment that has been proposed;

    Figure 3B is a graph representing signals in the circuit of Figure 3A according to an example embodiment;

    Figure 3C schematically represents a model of the electrical behaviour of a mechanical resonator;

    Figure 4 schematically illustrates an energy harvesting system according to an embodiment of the present disclosure;

    Figure 5 schematically illustrates a voltage inversion circuit of the system of Figure 4 in more detail according to an example embodiment;

    Figure 6 is a timing diagram representing an example of signals in the circuit of Figure 5 during one type of voltage inversion according to an embodiment of the present disclosure;

    Figure 7 is a state diagram representing the operation of the circuit of Figure 5 during one type of voltage inversion according to an example embodiment;

    Figures 8A to 8D schematically illustrate the circuit of Figure 5 during various operating states according to an example embodiment;

    Figure 9 is a flow diagram representing the operation of the circuit of Figure 5 in more detail according to an example embodiment;

    Figure 10 is a graph representing a comparison of current flow in a standard voltage inversion circuit and in the circuit of Figure 5;

    Figure 11A is a graph representing a comparison of the voltage across a mechanical resonator in the circuit of Figure 3A and in the circuit of Figure 5;

    Figure 11B is a graph representing a period of Figure 11A in more detail according to example embodiment;

    Figure 12 schematically illustrates a voltage inversion circuit of the system of Figure 4 in more detail according to a further example embodiment;

    Figure 13 is a state diagram representing operating states of a voltage inversion circuit during one type of voltage inversion according to a further example embodiment;

    Figure 14 schematically illustrates a voltage inversion circuit according to yet a further example embodiment of the present disclosure; and

    Figure 15 is a state diagram representing operating states of the voltage inversion circuit of Figure 14.


    DETAILED DESCRIPTION



    [0021] Throughout the present disclosure, the term "connected" is used to designate a direct electrical connection between circuit elements, whereas the term "coupled" is used to designate an electrical connection between circuit elements that may be direct, or may be via one or more further elements such as resistors, diodes, capacitors or transistors. Unless specified otherwise, when elements are described as being coupled, they may also be connected directly. The term "approximately" is used to designate a tolerance of plus or minus 10% of the value in question.

    [0022] Figure 1 schematically illustrates an energy harvesting system 100 comprising a mechanical resonator 102 and an energy recuperation circuit (ENERGY RECUPERATION) 104.

    [0023] The mechanical resonator 102 for example comprises a beam 106 adapted to resonate mechanically. In the example of Figure 1, the beam 106 has one end attached to a support surface 108, although in alternative embodiments other arrangements would be possible. The resonator 102 further comprises a layer 110 of piezoelectric material coupled to the energy recuperation circuit 104. A ground plane of the beam 106 is also for example coupled to the energy recuperation circuit 104.

    [0024] Figure 2A schematically illustrates the mechanical resonator 102 and the energy recuperation circuit 104 according to example embodiment that has been proposed. In the example of Figure 2A, the energy recuperation circuit 104 comprises a diode bridge 202 coupling the output terminals of the mechanical resonator 102 to the parallel connection of a capacitor Cr and a load R representing the consumption of the harvested energy.

    [0025] Figure 2B is a graph representing an example of the displacement u of the mechanical resonator 102, and of the voltage Vcc across the capacitor Cr and the load R of Figure 2A. The diode bridge 202 of Figure 2A permits energy to be recuperated from the mechanical resonator each time the output voltage exceeds the voltage Vcc.

    [0026] A drawback of the arrangement of Figure 2A is that power is only recuperated during the peaks of the each cycle, and therefore the amount of power that can be recuperated is limited.

    [0027] Figure 3A schematically illustrates the mechanical resonator 102 and energy recuperation circuit 104 of Figure 1 in more detail according to further example embodiment.

    [0028] The energy recuperation circuit 104 of Figure 3A is similar to that of Figure 2A, except that a voltage inversion circuit formed by the series connection of a switch 302 and an inductor 304 is coupled between the output terminals of a mechanical resonator 102. The switch 302 for example permits a rapid inversion of the voltage across the mechanical resonator 102 as will now be described with reference to Figure 3B.

    [0029] Figure 3B illustrates the mechanical displacement u of the mechanical resonator 102, and the voltage V the across mechanical resonator of Figure 3A. As illustrated, in the example of Figure 3B, once the voltage V reaches the level Vcc, energy recuperation can be performed during a period tH, and then the voltage V across the mechanical resonator is inverted by activating the switch 302. Thus the voltage across the resonator 102 rapidly falls to the level close but not equal to -Vcc due to energy loss in the inductor, and a new energy recuperation period tH can commence. The voltage Vcc in Figure 3B is higher than the voltage Vcc of Figure 2B.

    [0030] Figure 3C schematically illustrates an electrical model of the mechanical resonator 102, which can for example be considered to comprise an alternating current source ip, coupled in parallel with a capacitor Cp and a resistor Rp. The resistance Rp represents the dielectric losses of the material, which are generally relatively low and will be considered to be negligible in the following description.

    [0031] While the arrangement of Figure 3A permits improved energy recuperation with respect to that of Figure 2A, it has been found that the amount of extracted energy can be further increased. In particular, the maximum power that can be harvested can be expressed as follows:

    where Vopen represents the open circuit voltage amplitude of the piezo-electric material, f represents the frequency of oscillation of the mechanical resonator, and Q represents the quality factor of the charge inversion mechanism, which is for example directly related to the inductor that is used. For example, the quality factor Q can be expressed as:

    where Rl is the series resistance of the inductor and L is the inductance of the inductor.

    [0032] Thus it can be seen that the higher the Q factor, the lower the energy loss and the higher the harvested energy.

    [0033] Figure 4 schematically illustrates an energy harvesting system 400 according to example embodiment of the present disclosure. For example, the energy harvesting system 400 forms part of a medical device such as a pace maker, or may be used to recuperate energy from the vibrations of industrial machines, vehicle engines, sports shoes, etc.

    [0034] The system 400 for example comprises a mechanical resonator 402, which is for example similar to the mechanical resonator 100 of Figure 1. The resonator 402 is coupled to an energy recuperation circuit 404, which for example extracts electrical energy from the mechanical resonator and stores it to a capacitor 406. Furthermore, the harvesting system 400 for example comprises a voltage inversion circuit 408, which performs the role of inverting the voltage across the mechanical resonator 402 at precise moments during each cycle in order to amplify the resonance of the system.

    [0035] The circuit 408 is for example controlled by a control circuit (CTRL) 410, which for example receives as inputs the voltage Vp across the mechanical resonator 402, and further voltages V'p and Vint described in more detail below. The circuit 410 may also receive a clock signal CLK. The circuit 410 for example generates control signals for controlling switches of the circuit 408, as will be described in more detail below.

    [0036] Figure 5 schematically illustrates the mechanical resonator 402 and the voltage inversion circuit 408 of Figure 4 in more detail according to an example embodiment.

    [0037] The mechanical resonator 402 is for example modelled in the example of Figure 5 by a current source conducting an alternating current ip, and a capacitor Cp coupled in parallel between output terminals 502 and 504 of the mechanical resonator 402.

    [0038] The voltage inversion circuit 408 for example comprises an H-bridge 506 and a voltage converter 507.

    [0039] The H-bridge 506 for example has output nodes 508 and 510, and comprises four switches, a switch 512 coupling the input node 502 to the output node 508, a switch 514 coupling the input node 502 to the output node 510, a switch 516 coupling the input node 504 to the output node 508, and a switch 518 coupling the input node 504 to the output node 510. The switches 512 to 518 are respectively controlled by control signals S1 to S4 generated by the control circuit 410 of Figure 4.

    [0040] The output nodes 508 and 510 of the H-bridge 506 are coupled to the voltage converter 507, which has output nodes 522 and 524 coupled to respective terminals of a capacitor Cint. The capacitor Cint for example has a capacitance significantly smaller than the capacitance Cp, for example equal to 50% or less of the capacitance Cp.

    [0041] The voltage converter 507 for example comprises an inductor 526 coupled between the node 508 and an intermediate node 528. The node 528 is in turn coupled to the node 510 via a switch 530 and to the output node 522 of the voltage converter 507 via a switch 532. The switch 530 is controlled by a signal T1, and the switch 532 is controlled by a signal T2.

    [0042] In operation, the voltage inversion circuit 408 is configured to invert the voltage across the capacitance Cp of the mechanical resonator 402. For this, the H-bridge 506 and voltage converter 507 form a charge transfer circuit, which is configured to discharge a voltage of a first polarity held by the capacitance Cp to the capacitor Cint during a first period, and to charge a voltage, of opposite polarity to the first polarity, to the capacitance Cp during a second period using the voltage potential stored by the capacitor Cint. As will be explained in more detail below, the discharging and/or charging operations involve passing a current through an inductance, such as through the inductor 526, in a switched manner such that the current is limited. An advantage of limiting the current in this manner is that the energy losses in the inductor will be reduced.

    [0043] Operation of the circuit of Figure 5 will now be described in more detail with reference to Figures 6, 7 and 8A to 8D.

    [0044] Figure 6 is a timing diagram representing, for states of the voltage inversion circuit 408, an example of the timing of the control signals S1, S2, S3, S4, T1 and T3.

    [0045] Figure 7 is a state diagram representing the operation of the circuit of Figure 5.

    [0046] Figures 8A to 8D schematically illustrate the circuit of Figure 5 during various operating phases.

    [0047] As illustrated in Figures 6 and 7, the circuit 408 is for example initially in a standby state (STANDBY) in which the signals S1 to S4 and T1 and T2 are all for example low. A signal START provided to the control circuit 410 of Figure 4 for example indicates when energy harvesting is to begin, which is for example when the current ip=0, in other words when |Vp| starts to decrease, and thus ∂|Vp|/∂t < 0.

    [0048] In the example of Figure 6, energy harvesting begins at a time t0. The example of Figure 6 assumes the case in which Vp>0. The circuit then enters a state Φ11 in which the signals S1, S4 and T1 are for example asserted, while the other control signals remain low. As illustrated in Figure 8A, this for example causes a current to flow from the capacitance Cp of the mechanical resonator 402, through the switch 512 of the H-bridge 506, through the inductor 526 and the switch 530 of the voltage converter 507, thereby bypassing the capacitor Cint, and then back through the switch 518 of the H-bridge 506.

    [0049] After a certain time period, for example determined by the clock signal CLK or by a measured current level through the inductor, the state Φ12 is for example entered, in which the signal T1 is brought low to block the current flow through the switch 530. For example, the transition from the state Φ11 to the state Φ12 is implemented by the control circuit 410 when it detects that the current level through the inductor 526 has reached an upper limit I_high measured by the control circuit 410. As represented in Figure 8B, the inductor 526 causes a continuation of current flow, which then passes through a diode parallel to the switch 532, and charges the capacitor Cint. This diode is for example the intrinsic diode of a MOS transistor in the case that the switch 532 is implemented by one or more MOS devices. Alternatively, a diode may be coupled in parallel with the switch 532.

    [0050] After a certain time period, for example determined by the clock signal CLK or by a measured current level through the inductor, the circuit returns to the state Φ11. For example, the transition from the state Φ12 to the state Φ11 is implemented by the control circuit 410 when it detects that the current level through the inductor 526 has fallen to a lower limit I low.

    [0051] The circuit 408 then for example continues to alternate between the states Φ11 and Φ12, during which the capacitance of the mechanical resonator 402 is discharged, until the voltage Vp across the terminals of the mechanical resonator 402 has fallen to 0 V or to another low level. In the example of Figure 6, this occurs at a time t1.

    [0052] The circuit 408 then enters a state Φ21 in which the signals S1 and S4 are brought low, and the signals T2, S2 and S3 are asserted. Thus, as represented in Figure 8C, the capacitor Cp is charged by a current flowing from the capacitor Cint, through the switch 532 and the inductor 526 of the voltage converter 507, through the switch 516 of the H-bridge to the terminal 504 of the mechanical resonator 402, and then back through the switch 514 of the H-bridge to the capacitor Cint.

    [0053] After a certain time period, for example determined by the clock signal CLK or by a measured current level through the inductor, the state Φ22 is for example entered, in which the signal T2 is brought low to block the current flow through the switch 532. For example, the transition from the state Φ21 to the state Φ22 is implemented by the control circuit 410 when it detects that the current level through the inductor 526 has reached an upper limit I_high. As represented in Figure 8D, the inductor 526 causes a continuation of current flow, which then passes through a diode parallel to the switch 530, and continues to charge the capacitance Cp. This diode is for example the intrinsic diode of a MOS transistor in the case that the switch 530 is implemented by one or more MOS devices. Alternatively, a diode may be coupled in parallel with the switch 530.

    [0054] After a certain time period, for example determined by the clock signal CLK or by a measured current level through the inductor, the circuit returns to the state Φ21. For example, the transition from the state Φ22 to the state Φ21 is implemented by the control circuit 410 when it detects that the current level through the inductor 526 has fallen to the lower limit I_low.

    [0055] The circuit 408 then for example continues to alternate between the states Φ21 and Φ22, during which the capacitance of the mechanical resonator 402 is charged, until the voltage Vint across the capacitor Cint has fallen to V'p. In the example of Figure 6, this occurs at a time t2.

    [0056] The H-bridge 506 is for example controlled such that V'p is always positive. Thus, in the case of an inversion from a negative level of Vp to a positive level of Vp, during the states Φ11 and Φ12, the signals S2 and S3 are for example asserted, and during the states Φ21 and Φ22, the signals S1 and S4 are for example asserted.

    [0057] Figure 9 is a flow diagram representing the state transitions of the circuit 408 of Figure 4 in more detail according to an example embodiment. The operations represented by this flow diagram are for example implemented by the control circuit 410 of Figure 4.

    [0058] Two parallel flows 901 and 902 are represented in Figure 9. The flow 901 comprises a loop 904 implementing the transitions between the states Φ11 and Φ12, and a loop 906 implementing the transitions between the states Φ21 and Φ22. The flow 902 controls the transition between the loops 904 and 906 and the value of a parameter SENS.

    [0059] The standby state is represented by boxes with states "0" and "10" in the flows 901 and 902 of Figure 9. Once the start condition (START) is met, the flow 901 enters the state Φ11 as described above in which the signal T1 is asserted, and the flow 902 enters a state "X1" in which the sign of the voltage Vp across the capacitance Cp is for example monitored. A parameter SENS is for example set equal to the sign of the voltage Vp across the capacitance Cp of the mechanical resonator. The parameter SENS is used to control the operation of the H-bridge 506 to ensure that the voltage Vp' is always positive, as described above.

    [0060] While in the state "X1", the flow 901 remains in the loop 904. In particular, from the state Φ11, when the current I through the inductor 526 reaches the higher limit I high, or a clock signal CLK is asserted, the state Φ12 is entered. From the state Φ12, when the current falls to 0 or to a lower limit I_low, or when the clock signal CLK falls low, the state Φ11 is returned to.

    [0061] In the flow 902, when it is determined that the voltage V'p has fallen below a threshold TH and the flow 901 is in the state Φ12, a state "X2" is entered, and the parameter SENS is inverted. The flow 901 thus transitions to the loop 906, and to the state Φ21, in which the signal T2 is asserted. While in the state "X2", the flow 901 remains in the loop 906. In particular, from the state Φ21, when the current I through the inductor 526 reaches the upper limit I_high, or a clock signal CLK is asserted, the state Φ22 is entered. From the state Φ22, if the voltage Vint across the capacitor Cint has fallen below the voltage V'p, the loop 906 is exited, and the standby states "0" and "10" are returned to. Alternatively, when the current falls to 0 or to a lower limit I_low, or when the clock signal CLK falls low, the state Φ21 is returned to.

    [0062] Figure 10 is a graph representing a comparison of current flow in a standard voltage inversion circuit, such as through the inductor 304 of Figure 3A, and the current flow through the inductor 526 in the circuit of Figure 5.

    [0063] A curve 1002 represents the current in the circuit 104 of Figure 3A during a discharge of the capacitance Cp of the mechanical resonator, and it can be seen that in the example of Figure 10 this current rises to a peak of around 80 mA.

    [0064] A curve 1004 represents the current in the circuit of Figure 5, in which the current limit I_high is for example set at 20 mA, and it can be seen that in this case the current for example remains below a level 1006 only slightly higher than this current limit.

    [0065] While in the example of Figure 10 the current falls to zero between each charge transfer, in alternative embodiments the current limit I_low could be regulated to always remain between two positive current levels, such that the average current remains at a desired relatively low level, and the charge transfer can be performed relatively quickly.

    [0066] Figure 11A is a graph representing a comparison of the voltage across a piezoelectric material based on a standard energy recuperation circuit such as that of Figure 3A and on the circuit of Figure 5.

    [0067] A curve 1102 represents the case for the circuit of Figure 3A, and it can be seen that the voltage is inverted rapidly from around 10 V to around -6 V.

    [0068] A curve 1104 represents the case for the circuit of Figure 5, in which a period 1106 corresponds to the switching between the states Φ11 and Φ12, and a period 1108 corresponds to the switching between the states Φ21 and Φ22. While a relatively long time interval between the periods 1106 and 1108 is shown in Figure 11A, in practise these periods can be separated by less than a millisecond. It can be seen that the voltage falls from the initial level of around 10 V to a level of around -9 V, which is considerably lower than the curve 1102 due to the reduced energy loss in the circuit of Figure 5.

    [0069] Figure 11B is a graph representing the period 1106 of Figure 11A in more detail. A curve 1110 represents the case for the circuit of Figure 3A. A curve 1112 represents the case for the circuit of Figure 5, and it can be seen than transition occurs over many discrete steps in which small amounts of energy are transferred.

    [0070] While in the example of Figure 4 the energy is harvested directly by the energy recuperation circuit 404 from the voltage Vp at the output of the mechanical resonator, in alternative embodiments the energy can additionally or alternatively be harvested from the capacitor Cint of the voltage inversion circuit 408, as will now be described in more detail with reference to Figure 12.

    [0071] Figure 12 schematically illustrates the voltage inversion circuit 408 of the system of Figure 4 in more detail according to an alternative to that of Figure 5.

    [0072] With respect to the circuit of Figure 5, the circuit of Figure 12 comprises an energy recuperation circuit comprising a switch 1202 and capacitor Cout coupled in series between the input 508 of the voltage converter 507 and the output 524 of the voltage converter. In some embodiments, a diode 1204 is also coupled between the node 508 and the switch 1202, the anode of the diode 1204 being coupled to the node 508. The switch 1202 is for example controlled by a control signal S5 in order to extract energy from the capacitor Cint during peaks of the voltage Vp', as will be apparent to those skilled in the art. In some cases, the diode 1204 can be omitted if the timing of the switch 1202 can be controlled in a relatively precise manner. The inductor 526 between the capacitors Cint and Cout for example allows a reduction in energy loss when the voltages across the capacitors are not equal.

    [0073] While in the example of Figure 5 the current is limited by a switching operation during both the discharging and recharging of the capacitance Cp, in alternative embodiments a gain can be obtained by limiting the current in this way only during one of the discharging and charging operations, as will now be described with reference to Figure 13.

    [0074] Figure 13 is a state diagram representing operating states of a voltage inversion circuit according to a further example embodiment similar to that of Figure 7. As illustrated, the states Φ21 and Φ22 are replaced by a single state Φ2 in which the capacitance Cp is charged during a continuous operation, until the voltage Vint has fallen to 0 V. In the case of Figure 13, the capacitance of Cint is for example approximately equal to that of the capacitance Cp.

    [0075] Figure 14 schematically illustrates the voltage inversion circuit 408 of Figure 4 in more detail according to yet a further alternative embodiment to that of Figure 5.

    [0076] In the example of Figure 14 there is a plurality of mechanical resonators 1402_1 to 1402_n. Each mechanical resonator 1402_1 to 1402_n is coupled to a corresponding inductive circuit 1404_1 to 1404_n, and these circuits are coupled by a transformer 1405 to a common inductive circuit 1406 comprising the capacitor Cint.

    [0077] The inductive element of each of the circuits 1404 1 to 1404 n is for example a corresponding primary winding 1408 of the transformer 1405. The primary winding 1408 of each circuit is coupled between nodes 1409 and 1410, the node 1409 being coupled to one terminal of the corresponding mechanical resonator. The other terminal of each mechanical resonator is coupled to a node 1412. The nodes 1410 and 1412 of each circuit are coupled together by the series connection of a switch 1414 and a diode 1416 having its anode coupled to the node 1412, and by the series connection of a switch 1418 and a diode 1420 having its anode coupled to the switch 1418. The switches 1414 and 1418 of the circuit 1404_1 are controlled by control signals S11 and S12 respectively, the switches 1414 and 1418 of the circuit 1404_2 are controlled by control signals S21 and S22 respectively and the switches 1414 and 1418 of the circuit 1404_n are controlled by control signals Sn1 and Sn2 respectively.

    [0078] The transformer 1405 for example comprises a single secondary winding 1422, which is for example coupled, via an H-bridge (H-BRIDGE) 1424, to nodes 1426 and 1428. The nodes 1426 and 1428 are for example coupled together via the series connection of a diode 1430 and the capacitor Cint, the diode 1430 for example having its anode coupled to the node 1426. A switch 1432 controlled by a control signal S3 is for example coupled in parallel with the diode 1430 between the node 1426 and the capacitor Cint.

    [0079] In operation, the inversion of the voltage across the terminals of the resonators 1402_1 to 1402_n may be performed in parallel, or in sequence. An example of the inversion of the voltage across the resonator 1402_1 will now be described with reference to Figure 15.

    [0080] Figure 15 is a state diagram representing operating states of the circuits 1404_1 and 1406 of the voltage inversion circuit of Figure 14.

    [0081] During the standby state (STANDBY) the control signals S11, S12 and S3 are for example low. The transition (START) to the state Φ11 for example occurs when the current ip1 generated within the mechanical resonator 1402 1 is equal to zero.

    [0082] In the case that VP1>0 (SENS=1), in the state Φ11 the signal S11 is for example asserted, and the signals S21...Sn1 may also be asserted in the case that the resonators 1402_2 to 1402_n are inverted in parallel with the resonator 1402_1. The transition to the state Φ12 for example occurs when the current in the winding 1408 reaches a limit Ihigh, and in the state Φ12, the signal S11 is brought low (and also the signals S21...Sn1 if asserted). The transition back to the state Φ11 occurs when the current falls to a limit I_low, and a transition from the state Φ12 to the state Φ21 for example occurs when the voltage Vp1 across the resonator 1401_n is at or close to zero. In the state Φ21, the signal S3 is asserted. A transition to the state Φ22 for example occurs when the current reaches the limit I high, and in the state Φ22, the signal S3 is for example brought low, the signal S12 is for example asserted, and the signals S12...Sn2 may also be asserted in the case that the resonators 1402_1 to 1402_n are inverted in parallel.

    [0083] In the case that VP1<0 (SENS=0), in the state Φ11 the signal S12 is for example asserted, and the signals S22...Sn2 may also be asserted in the case that the resonators 1402_2 to 1402_n are inverted in parallel with the resonator 1402_1. The transition to the state Φ12 for example occurs when the current in the winding 1408 reaches a limit I_high, and in the state Φ12, the signal S12 is brought low (and also the signals S22...Sn2 if asserted) . The transition back to the state Φ11 occurs when the current falls to a limit I_low, and a transition from the state Φ12 to the state Φ21 for example occurs when the voltage Vp1 across the resonator 1401_n is at or close to zero. In the state Φ21, the signal S3 is asserted. A transition to the state Φ22 for example occurs when the current reaches the limit I high, and in the state Φ22, the signal S3 is for example brought low, the signal S11 is for example asserted, and the signals S21...Sn1 may also be asserted in the case that the resonators 1402_1 to 1402_n are inverted in parallel.

    [0084] An advantage of the embodiments described herein is that energy loss can be reduced by limiting the current in an inductor of a voltage inversion circuit. This for example permits an improvement in the energy efficiency of an energy harvesting system, and/or a reduction in the Q factor of the inductor, allowing for example the cost and/or the size of the inductor to be reduced.

    [0085] Having thus described at least one illustrative embodiment, various alterations, modifications and improvements will readily occur to those skilled in the art. For example, it will be apparent to those skilled in the art that while switches have been described in relation with the various embodiments that are activated by high voltage levels, some or all of the switches could instead be activated by low voltage levels. Furthermore, the various features described in relation with the various embodiments could be combined, in alternative embodiments, in any combination.


    Claims

    1. A circuit for recuperating electrical energy from a mechanical resonator (402) comprising:

    a control circuit (410); and

    a voltage inversion circuit (408) configured to invert the voltage across a capacitance (Cp) of the mechanical resonator, the voltage inversion circuit comprising:

    a capacitor (Cint); and

    a charge transfer circuit (506, 507) configured:

    - to discharge a voltage of a first polarity held by the capacitance of the mechanical resonator to said capacitor during a first period; and

    - to charge a voltage, of opposite polarity to the first polarity, to the capacitance of the mechanical resonator during a second period using the voltage potential stored by said capacitor during the first period;

    characterized in that the charge transfer circuit comprises an inductance and at least one switch (530, 532), the control circuit (410) being configured to switch the at least one switch during the first and/or second period to limit the current passing through the inductance.


     
    2. The circuit of claim 1, wherein the inductance of the charge transfer circuit is configured to be used in a boost converter configuration during the discharging of the voltage of the first polarity to the capacitance of the mechanical resonator, and in a buck converter configuration during the charging of the voltage of opposite polarity to the capacitance of the mechanical resonator.
     
    3. The circuit of claim 2, wherein the control circuit (410) is configured to control said at least one switch to conduct a current from a first node of said capacitance, through said inductance and back to a second node of said capacitance during a first portion of the first period and to conduct a current from the first node of said capacitance, through said inductance and to said capacitor during a second portion of the first period.
     
    4. The circuit of claim 3, wherein the control circuit is configured to control said at least one switch such that there is a plurality of said first and second portions during the first period.
     
    5. The circuit of claim 3 or 4, wherein said at least one switch is configured to be controlled by a clock signal generated by said control circuit (410).
     
    6. The circuit of claim 3 or 4, wherein said at least one switch is configured to be controlled by said control signal to conduct the current to said capacitor when a measured current in said inductance reaches a threshold limit.
     
    7. The circuit of any of claims 3 to 6, wherein said charge transfer circuit comprises an H-bridge (506) and a voltage converter (507), the H-bridge (506) coupling first and second terminals (502, 504) of the mechanical resonator (402) to first and second inputs (508, 510) of the voltage converter.
     
    8. The circuit of claim 7, wherein said voltage converter (507) comprises:

    the series connection of an inductor (526) and a first switch (532) of said at least one switch coupled between said first input (508) of the voltage converter and a first node of said capacitor; and

    a second switch (530) of said at least one switch coupled between an intermediate node (508) and the second input (510) of the voltage converter, the intermediate node being between the inductor (526) and the first switch (532).


     
    9. The circuit of any of claims 3 to 6, wherein said charge transfer circuit comprises a transformer having a primary winding coupled between first and second terminals of the mechanical resonator and a secondary winding coupled between first and second nodes of said capacitor (Cint).
     
    10. The circuit of claim 9, wherein the transformer further comprises a further primary winding coupled to a further mechanical resonator.
     
    11. The circuit of any of claims 1 to 10, wherein the charge transfer circuit (506, 507) is further configured:

    - to discharge a voltage of an opposite polarity to the first polarity held by the capacitance of the mechanical resonator to said capacitor during a third period; and

    - to charge a voltage of the first polarity to the capacitance of the mechanical resonator during a fourth period using the voltage potential stored by said capacitor during the third period.


     
    12. A method of recuperating electrical energy from a mechanical resonator (402), the method comprising:

    inverting the voltage across a capacitance (Cp) of the mechanical resonator by:

    - discharging a voltage of a first polarity held by the capacitance of the mechanical resonator to a capacitor (Cint) during a first period; and

    - charging a voltage, of opposite polarity to the first polarity, to the capacitance of the mechanical resonator during a second period using the voltage potential stored by said capacitor during the first period;

    characterized in that said discharging and/or charging operation comprises switching, by a control circuit (410), at least one switch (530, 532) during the first and/or second period to limit the current passing through an inductance.


     


    Ansprüche

    1. Eine Schaltung zur Rückgewinnung elektrischer Energie aus einem mechanischen Resonator (402), wobei die Schaltung Folgendes aufweist:

    eine Steuerschaltung (410); und

    eine Spannungsinversionsschaltung (408), die konfiguriert ist, zum Invertieren der Spannung über einer Kapazität (Cp) des mechanischen Resonators, wobei die Spannungsinversionsschaltung Folgendes aufweist:

    einen Kondensator (Cint); und

    eine Ladungstransferschaltung (506, 507), die konfiguriert ist:

    - zum Entladen einer Spannung einer ersten Polarität, die durch die Kapazität des mechanischen Resonators gehalten wird, zu dem Kondensator während einer ersten Periode; und

    - zum Laden einer Spannung, die eine entgegengesetzte Polarität zur ersten Polarität besitz, zur Kapazität des mechanischen Resonators während einer zweiten Periode unter Verwendung des Spannungspotentials, das von dem Kondensator während der ersten Periode gespeichert wurde;

    dadurch gekennzeichnet, dass die Ladungstransferschaltung eine Induktivität und wenigstens einen Schalter (530, 532) aufweist, wobei die Steuerschaltung (410) konfiguriert ist zum Schalten des wenigstens einen Schalters während der ersten und/oder zweiten Periode, um den durch die Induktivität fließenden Strom zu begrenzen.


     
    2. Schaltung nach Anspruch 1, wobei die Induktivität der Ladungstransferschaltung konfiguriert ist zur Verwendung in einer Aufwärtswandlerkonfiguration während des Entladens der Spannung der ersten Polarität der Kapazität des mechanischen Resonators und in einer Abwärtswandlerkonfiguration während des Ladens der Spannung entgegengesetzter Polarität zur Kapazität des mechanischen Resonators.
     
    3. Schaltung nach Anspruch 2, wobei die Steuerschaltung (410) konfiguriert ist zum Steuern des wenigstens einen Schalter zum Leiten eines Stroms, von einem ersten Knoten der Kapazität durch die Induktivität und zurück zu einem zweiten Knoten der Kapazität, während eines ersten Abschnitts der ersten Periode, und zum Leiten eines Stroms, von dem ersten Knoten der Kapazität durch die Induktivität und zu dem Kondensator, während eines zweiten Abschnitts der ersten Periode.
     
    4. Schaltung nach Anspruch 3, wobei die Steuerschaltung konfiguriert ist zum Steuern des wenigstens einen Schalters so, dass es während der ersten Periode eine Vielzahl der ersten und zweiten Abschnitte gibt.
     
    5. Schaltung nach Anspruch 3 oder 4, wobei der wenigstens eine Schalter konfiguriert ist, um durch ein von der Steuerschaltung (410) erzeugtes Taktsignal gesteuert zu werden.
     
    6. Schaltung nach Anspruch 3 oder 4, wobei der wenigstens eine Schalter konfiguriert ist, um durch das Steuersignal gesteuert zu werden, um den Strom zu dem Kondensator zu leiten, wenn ein gemessener Strom in der Induktivität einen Schwellenwert erreicht.
     
    7. Schaltung nach einem der Ansprüche 3 bis 6, wobei die Ladungstransferschaltung eine H-Brücke (506) und einen Spannungswandler (507) aufweist, wobei die H-Brücke (506) einen ersten und einen zweiten Anschluss (502, 504) des mechanischen Resonators (402) mit einem ersten und einem zweiten Eingang (508, 510) des Spannungswandlers verbindet.
     
    8. Schaltung nach Anspruch 7, wobei der Spannungswandler (507) Folgendes aufweist:

    die Reihenschaltung eines Induktors (526) und eines ersten Schalters (532) des wenigstens einen Schalters, die zwischen dem ersten Eingang (508) des Spannungswandlers und einem ersten Knotenpunkt des Kondensators gekoppelt ist; und

    einen zweiten Schalter (530) des wenigstens einen Schalters, der zwischen einem Zwischenknoten (508) und dem zweiten Eingang (510) des Spannungswandlers gekoppelt ist, wobei der Zwischenknoten zwischen der Induktivität (526) und dem ersten Schalter (532) liegt.


     
    9. Schaltung nach einem der Ansprüche 3 bis 6, wobei die Ladungstransferschaltung einen Transformator aufweist, mit einer Primärwicklung, die zwischen einem ersten und einem zweiten Anschluss des mechanischen Resonators gekoppelt ist, und mit einer Sekundärwicklung, die zwischen einem ersten und einem zweiten Knoten des Kondensators (Cint) gekoppelt ist.
     
    10. Schaltung nach Anspruch 9, wobei der Transformator ferner eine weitere Primärwicklung aufweist, die mit einem weiteren mechanischen Resonator gekoppelt ist.
     
    11. Schaltung nach einem der Ansprüche 1 bis 10, wobei die Ladungstransferschaltung (506, 507) weiter konfiguriert ist:

    - zum Entladen einer Spannung entgegengesetzter Polarität zur ersten Polarität, die von der Kapazität des mechanischen Resonators gehalten wird, an den Kondensator während einer dritten Periode; und

    - zum Laden einer Spannung der ersten Polarität zur Kapazität des mechanischen Resonators während einer vierten Periode, unter Verwendung des Spannungspotentials, das von dem Kondensator während der dritten Periode gespeichert wurde.


     
    12. Verfahren zur Rückgewinnung von elektrischer Energie aus einem mechanischen Resonator (402), wobei das Verfahren Folgendes aufweist:

    Invertieren der Spannung an einer Kapazität (Cp) des mechanischen Resonators durch:

    - Entladen einer Spannung mit einer ersten Polarität, die durch die Kapazität des mechanischen Resonators gehalten wird, zu einem Kondensator (Cint) während einer ersten Periode; und

    - Laden einer Spannung entgegengesetzter Polarität zur ersten Polarität zur Kapazität des mechanischen Resonators während einer zweiten Periode unter Verwendung des Spannungspotentials, das von dem Kondensator während der ersten Periode gespeichert wurde;

    dadurch gekennzeichnet, dass der Entlade- und/oder Ladevorgang das Schalten wenigstens eines Schalters (530, 532) durch eine Steuerschaltung (410) während der ersten und/oder zweiten Periode aufweist, um den durch eine Induktivität fließenden Strom zu begrenzen.


     


    Revendications

    1. Circuit de récupération d'énergie électrique à partir d'un résonateur mécanique (402) comprenant :

    un circuit de commande (410) ; et

    un circuit d'inversion de tension (408) agencé pour inverser la tension aux bornes d'une capacité (Cp) du résonateur mécanique, le circuit d'inversion de tension comprenant :

    un condensateur (Cint) ; et

    un circuit de transfert de charge (506, 507) agencé :

    - pour décharger une tension d'une première polarité maintenue par la capacité du résonateur mécanique dans le condensateur pendant une première période ; et

    - pour charger une tension, de polarité opposée à la première polarité, dans la capacité du résonateur mécanique pendant une deuxième période en utilisant le potentiel de tension stocké par le condensateur pendant la première période ;

    caractérisé en ce que le circuit de transfert de charge comprend une inductance et au moins un commutateur (530, 532), le circuit de commande (410) étant configuré pour commuter l'au moins un commutateur pendant la première et/ou deuxième période pour limiter le courant passant dans l'inductance.


     
    2. Circuit selon la revendication 1, dans lequel l'inductance du circuit de transfert de charge est configurée pour être utilisée dans une configuration de convertisseur élévateur pendant la décharge de la tension de la première polarité dans la capacité du résonateur mécanique, et dans une configuration de convertisseur abaisseur pendant la charge de la tension de polarité opposée dans la capacité du résonateur mécanique.
     
    3. Circuit selon la revendication 2, dans lequel le circuit de commande (410) est agencé pour contrôler ledit au moins un commutateur pour conduire un courant à partir d'un premier nœud de la capacité, à travers l'inductance, et le ramener vers un deuxième nœud de la capacité pendant une première portion de la première période, et pour conduire un courant à partir du premier nœud de ladite capacité, à travers l'inductance et vers le condensateur pendant une deuxième portion de la première période.
     
    4. Circuit selon la revendication 3, dans lequel le circuit de commande est agencé pour contrôler ledit au moins un commutateur de telle sorte qu'il y a une pluralité des premières et deuxième portions pendant la première période.
     
    5. Circuit selon la revendication 3 ou 4, dans lequel ledit au moins un commutateur est configuré pour être contrôlé par un signal d'horloge généré par le circuit de commande (410).
     
    6. Circuit selon la revendication 3 ou 4, dans lequel ledit au moins un commutateur est configuré pour être contrôlé par le signal de commande pour conduire le courant vers le condensateur lorsqu'un courant mesuré dans l'inductance atteint une limite de seuil.
     
    7. Circuit selon l'une quelconque des revendications 3 à 6, dans lequel le circuit de transfert de charge comprend un pont en H (506) et un convertisseur de tension (507), le pont en H (506) couplant des première et deuxième bornes (502, 504) du résonateur mécanique (402) à des première et deuxième entrées (508, 510) du convertisseur de tension.
     
    8. Circuit selon la revendication 7, dans lequel le convertisseur de tension (507) comprend :

    la connexion en série d'une inductance (526) et d'un premier commutateur (532) desdits au moins un commutateur, couplé entre la première entrée (508) du convertisseur de tension et un premier nœud du condensateur ; et

    un deuxième commutateur (530) desdits au moins un commutateur couplé entre un nœud intermédiaire (508) et la deuxième entrée (510) du convertisseur de tension, le nœud intermédiaire étant entre l'inductance (526) et le premier commutateur (532).


     
    9. Circuit selon l'une quelconque des revendications 3 à 6, dans lequel le circuit de transfert de charge comprend un transformateur ayant un enroulement primaire couplé entre des première et deuxième bornes du résonateur mécanique et un enroulement secondaire couplé entre des premier et deuxième nœuds du condensateur (Cint).
     
    10. Circuit selon la revendication 9, dans lequel le transformateur comprend en outre un autre enroulement primaire couplé à un autre résonateur mécanique.
     
    11. Circuit selon l'une quelconque des revendications 1 à 10, dans lequel le circuit de transfert de charge (506, 507) est en outre agencé :

    - pour décharger une tension de polarité opposée à la première polarité maintenue par la capacité du résonateur mécanique dans le condensateur pendant une troisième période ; et

    - pour charger une tension de la première polarité dans la capacité du résonateur mécanique pendant une quatrième période en utilisant le potentiel de tension stocké par le condensateur pendant la troisième période.


     
    12. Procédé de récupération d'énergie électrique à partir d'un résonateur mécanique (402), le procédé comprenant :

    inverser la tension aux bornes d'une capacité (Cp) du résonateur mécanique :

    - en déchargeant une tension d'une première polarité maintenue par la capacité du résonateur mécanique dans un condensateur (Cint) pendant une première période ; et

    - en chargeant une tension, de polarité opposée à la première polarité, dans la capacité du résonateur mécanique pendant une deuxième période en utilisant le potentiel de tension stocké par le condensateur pendant la première période ;

    caractérisé en ce que l'opération de décharge et/ou de charge comprend la commutation, par un circuit de commande (410), d'au moins un commutateur (530, 532) pendant la première et/ou la deuxième période pour limiter le courant passant dans l'inductance.


     




    Drawing





















    REFERENCES CITED IN THE DESCRIPTION



    This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.

    Patent documents cited in the description