FIELD

[0001] The present disclosure relates to management of energy harvesting, such as harvesting of triboelectric or other capacitive energy sources with high output voltage.

BACKGROUND

[0002] The triboelectric effect is a phenomenon where materials obtain electrical charge once they are separated from materials with which they were in contact. For example, if a piece of rubber is placed in contact with glass, the rubber surface will become negatively charged and the glass positively charged, overall charge remaining zero. When the materials are then separated, each will maintain its charge for a period of time depending on several environmental factors. The voltage difference of the surfaces due to the separated charges may be fairly high, for example, it may be in the range of hundreds of volts to even tens of kilovolts.

[0003] Triboelectricity presents itself as a potential way to power certain kinds of devices, such as sensors and portable devices, which do not require a large amount of power. Triboelectric nanogenerators, TENG, convert mechanical energy to electrical energy as mechanical work is done against the electrostatic force of the induced triboelectric charges. As the triboelectric effect may be observed in a broad range of materials, TENGs have a large number of potential use cases.

[0004] Materials used in TENGs may be selected and engineered such that the triboelectric charge density is increased, which increases also the available energy. . Examples of triboelectric materials used in different applications include metals, such as aluminium, copper and gold, organic materials such as paper, silk and cotton, rubber and polymers such as PTFE, PP and PE, which can be treated with nanomaterials to enhance the charge density. SUMMARY

[0005] According to some aspects, there is provided the subject-matter of the independent claims. Some embodiments are defined in the dependent claims.. [0006] According to a first aspect of the present disclosure, there is provided an electronic converter comprising first terminals to connect the electronic converter to an electric generator and second terminals to provide an output of the electric converter, and a trigger voltage detector configured with electronic components to provide a first trigger signal to a voltage downconverter responsive to a voltage at the first terminals exceeding a threshold voltage, the electronic converter comprising the voltage downconverter.

[0007] According to a second aspect of the present disclosure, there is provided a method comprising using an electronic converter with an electric generator, the electronic converter comprising first terminals to connect the electronic converter to the electric generator and second terminals to provide an output of the electric converter, and a trigger voltage detector configured with electronic components to provide a first trigger signal to a voltage downconverter responsive to a voltage at the first terminals exceeding a threshold voltage, the electronic converter comprising the voltage downconverter.

BRIEF DESCRIPTION OF THE DRAWINGS [0008] FIGURE 1A illustrates an example system in accordance with at least some embodiments of the present invention;

[0009] FIGURE IB illustrates an example system in accordance with at least some embodiments of the present invention;

[0010] FIGURE 2 illustrates an example discharge pattern in accordance with at least some embodiments of the present invention;

[0011] FIGURE 3 illustrates an example electronic converter capable of supporting at least some embodiments of the present invention; [0012] FIGURE 4 illustrates an example electronic converter capable of supporting at least some embodiments of the present invention, and

[0013] FIGURE 5 illustrates an example electronic converter capable of supporting at least some embodiments of the present invention.

EMBODIMENTS

[0014] An electronic converter is described herein to facilitate harvesting of electrical energy from an electric generator which generates a high voltage, such as a voltage in the kilovolt range, for example. The electronic converter is configured, using electrical components, to discharge the generator voltage in parts such that voltage ratings of conventional electronics components are not exceeded and energy is harvested efficiently from a high impedance generator such as a TENG. This provides the benefit that standard electronic components may be used, in other words, voltage rating requirements of the used components may be relaxed and specialized components are not needed. The electronic converter uses at least one of: a trigger voltage detector configured to trigger discharging of the voltage responsive to the voltage reaching a predefined threshold voltage, and a peak detector configured to trigger discharging of the voltage responsive to the voltage reaching a plateau and no longer increasing as a function of time. Thus during one mechanical cycle of the electric generator, such as, for example, a triboelectric or piezoelectric generator, the voltage is discharged more than once, to prevent the voltage from rising to a very high level and to keep the voltage on a level which is easier to manage using standard electronics components.

[0015] FIGURE 1A illustrates an example system in accordance with at least some embodiments of the present invention. The system comprises a mechanical system which is schematically illustrated as system 101. Surfaces of triboelectric materials 102, 103 are disposed opposite to each other, such that system 101, during operation, repeatedly and altematingly presses surfaces 102, 103 against each other and separates surfaces 102, 103 from each other. This repeating, alternating motion forms mechanical cycles of the electric generator which comprises system 101 and surfaces 102, 103. System 101 may comprise, for example, a sole of a shoe which is repeatedly compressed as the user walks. Such a compression may press surfaces 102, 103 repeatedly against each other, once per each step. Another example of a system 101 is a type of an automobile, which experiences compression and decompression as the tyre rotates. The triboelectric generator thus converts mechanical energy into electrical energy.

[0016] Surfaces 102, 103 may comprise suitably selected triboelectric materials, such as aluminium, paper, rubber and/or polymer, for example. The selection of materials may depend on the application that it is the intention to power using the triboelectric generator. Surfaces 102, 103 are connected, via electrical leads 104, with first terminals 112 of electronic converter 110. Electronic converter 110 is configured to discharge the triboelectric generator plural times during a mechanical cycle of the triboelectric generator, for example, plural times during a phase of a mechanical cycle where the voltage across surfaces 102, 103 increases. As this phase may be relatively short, less than a second, this means that electronic converter 110 may be configured to discharge the triboelectric generator plural times during a single second. A down-converted voltage is provided from electronic converter 110 to application 120 via second terminals 114. Application 120 may comprise a sensor or light, for example. Application 120 may have a fairly limited requirement for electrical power, such that it may be successfully powered using the triboelectric generator, which may typically produce a fairly limited quantity of electrical energy. Application 120 may comprise a sensor, such as, for example, an Internet of Things, IoT, sensor or another kind of electronic device

[0017] Electronic converter 110 may be powered using electrical energy from the electric generator such that, advantageously, no further source of electrical energy is needed. Provided a sufficient energy is input by the generator, this enables single-cycle operation, such as generation of electrical energy from impacts, as no initial energy need be used with e.g. the structure illustrated in FIGURE 4.

[0018] FIGURE IB illustrates an example system in accordance with at least some embodiments of the present invention. The system of FIGURE IB is the same one as in FIGURE 1A, in a phase of the mechanical cycle where surfaces 102, 103 are pressed against each other, causing an electrical charge to accumulate in each one of the surfaces 102, 103 owing to the triboelectric effect.

[0019] Triboelectric generators, which may be referred to as triboelectric harvesters, may present challenges when put to use in practical implementations, to power applications such as application 120, since the output voltage may be impracticably high in the kilovolt, kV, or tens of kilovolt, range. Managing this voltage using simple interface circuits, such as a rectifier and a filter capacitor or a converter employing standard electronic components is challenging and easily leads to losses which consume a significant portion of the generated electrical power. For example, rectification and direct connection to a capacitor or a battery is very inefficient due to impedance mismatch, by which it is meant a high source impedance used with a low load impedance. .

[0020] The challenges posed by the inherent high voltage generated using high impedance triboelectric generators may be alleviated by using an electronic converter as described herein. In detail, electronic converter 110 is configured to discharge the electric generator plural times during the time the voltage in the generator is increasing, thus preventing the voltages in the converter circuit from exceeding the component voltage ratings. . As the energy is simultaneously harvested from the electric generator, there is less energy loss compared to direct charging of a capacitor via rectifier or when utilising a converter employing peak detector triggered control circuit only . As a simple conceptual example, in case the triboelectric generator would produce a open circuit voltage of 5 kV, electronic converter 110 may be configured with a trigger voltage detector with a threshold voltage of 1 kV, such that the triboelectric generator is discharged up to five times during each voltage-accumulating phase of the mechanical cycle. This will be explained in more detail on connection with FIGURE 2. In general, the voltage-accumulating phase is the phase of the mechanical cycle when the voltage between surfaces 102, 103 rises.

[0021] Using plural discharges per voltage-accumulating phase of the mechanical cycle provides the benefit that the voltage is kept in a range which does not exceed the component voltage ratings utilised in the electronic converter 110. On the other hand, using very many discharges, such as setting the threshold voltage to 0,1 kV in the example where the triboelectric generator would produce an open circuit voltage of 5 kV, incurs losses from the large number of switching events. Thus an optimum area may be seen in plural discharges, but not too many discharges. For example, between two and seven discharges, or between two and four discharges.

[0022] In addition to discharging the electric generator responsive to the threshold voltage, electronic converter 110 may be configured to discharge the electric generator responsive to a peak being reached in the voltage between surfaces 102, 103. This is useful, as the voltage will continue to increase after the last time the voltage reaches the threshold voltage. As the voltage ceases increasing before the threshold voltage is again reached, discharging the electric generator responsive to detecting the voltage has ceased increasing provides the benefit that substantially all of the triboelectricity generated may be harvested. Merely limiting the generated voltage using Zener diodes, for example, causes a loss of a major part of the generated energy compared to repeatedly discharging the voltage, as described herein. In other words, the threshold voltage may be used together with the peak detector, such that discharging is triggered by either one.

[0023] Both the trigger voltage detector and the peak detector in electronic converter 110 may be configured to operate using suitable electronic components. In other words, the trigger voltage detector comprises electronic components configured to provide a first trigger signal to a voltage downconverter of electronic converter 110 responsive to a voltage at surfaces 102, 103 exceeding a threshold voltage. Likewise, the peak detector may comprise electronic components configured to provide a second trigger signal to the voltage downconverter responsive to the voltage at surfaces 102, 103 ceasing increasing. Electronic converter 110 may experience the voltage between surfaces 102, 103 between first terminals 112, since the surfaces are electrically coupled to the first terminals 112. A further reason the peak detector may be useful is in the event a mechanical cycle of the electric generator happens to be so weak, that the threshold voltage is not reached even once.

[0024] While discussed herein primarily with reference to triboelectric generators, the described electronic converter may also be used with piezoelectric generators or other capacitive generators, for example, which present similar challenges in terms of high voltage and low power as do triboelectric generators.

[0025] In general, the electronic converter 110 may be a synchronous power converter. By this it is meant a synchronous switching type converter, wherein the conversion process comprises time intervals where energy is accumulated into a generator capacitor and the electric generator load is open, switch OFF, and time intervals where the charge accumulated in the capacitor is discharged to output 114, switch ON. The switch may be a bistable switch, for example. The capacitor may be connected in parallel with the first terminals, for example. In capacitive and triboelectric generators, mechanical energy may be converted to electric energy by variable capacitance that has an initial charge/voltage. When each discharge is complete, for example responsive to a determination the voltage drops to zero or another preconfigured threshold, the switch may be moved back to the OFF position.

[0026] FIGURE 2 illustrates an example discharge pattern in accordance with at least some embodiments of the present invention. The figure should be rotated 90 degrees clockwise before use. On the longer, horizontal, axis time advances from the left to the right, and on the shorter, vertical, axis voltage between surfaces 102, 103 increases from the bottom toward the top. In this example, the time axis may extend from zero to 300 milliseconds and the voltage axis from zero to 550 volts. In this example the threshold voltage is set to 500V. One mechanical cycle of the electric generator are illustrated with the plates initially being separated, and then being pressed together once more. The axes are linear and the graph is drawn to scale.

[0027] In a first half of the mechanical cycle, the trigger voltage detector detects the threshold voltage four times during the voltage-accumulating phase of the first mechanical cycle. These detections are identified in FIGURE 2 by black arrows 201. As the electric generator is discharged responsive to detecting the threshold voltage, the voltage drops to zero, or close to zero, promptly after each detection of the threshold voltage.

[0028] In the first half of the mechanical cycle, after being discharged four times the voltage no longer rises to the threshold level, rather, the voltage plateaus. Alternatively, the peak detector may be configured to respond to a derivative of the voltage turning negative. A peak detector may detect this and discharge the electric generator responsive to detecting the peak. This is denoted in FIGURE 2 by a black circle 202.

[0029] In a second half of the mechanical cycle of the electric generator, as the distance between the plates is declining, the threshold voltage is reached twice, these detections again being denoted by black arrows 201 in FIGURE 2. The second mechanical cycle occurs after the first mechanical cycle. Following the latter one of these threshold voltage detections, the voltage rises to a level which does not reach the threshold voltage, however a peak detector of electronic converter 110 detects the ceasing of the rise of the voltage, and responsively triggers discharging of the electric generator. This is, again, denoted by a black circle 202 in FIGURE 2. The second mechanical cycle, generating less energy than the first one, may be associated with a less pronounced mechanical motion. A final weak voltage peak is visible in the figure. The final weak voltage peak did not trigger the peak detector in this example.

[0030] FIGURE 3 illustrates an example electronic converter capable of supporting at least some embodiments of the present invention. The electronic converter 110 comprises first terminals 112, corresponding to first terminals 112 in FIGURES 1 A and IB. These terminals may be interfaced with the electric generator, such as, for example, a triboelectric generator as described in connection with FIGURES 1A and IB. First terminals 112 are connected with rectifier 310, which may comprise a full- wave rectifier or a voltage doubler, for example. A full-wave rectifier converts the whole of an input waveform to one of constant polarity, positive or negative, at its output. Mathematically, this corresponds to the absolute value function. Full-wave rectification converts both polarities of the input waveform to pulsating direct current, and yields a higher average output voltage. On the other hand, a voltage doubler is an electronic circuit configured to charge capacitors from an input voltage and switch these charges so that twice the input voltage is produced as the output. In a TENG application with already high voltages, using a voltage doubler might be beneficial for efficiency or achieving faster charging of the parasitic or intentional capacitances following the rectifier. Other rectifier types may also be used.

[0031] Rectifier 310 is connected with voltage downconverter 340, as illustrated in FIGURE 3. Voltage downconverter 340, in turn, has second terminals 114 which may be used to provide electric power to an application, such as application 120 in FIGURES 1A and IB. Voltage downconverter 340 may comprise a buck converter, for example.

[0032] Connected in parallel between rectifier 310 and voltage downconverter 340 are peak detector 320 and trigger voltage detector 330. Peak detector 320 is configured to provide trigger 321 to the voltage downconverter 340 responsive to detecting that the voltage at first terminals 112 ceases increasing, as described herein above. Trigger voltage detector 330 is configured to provide trigger 331 to voltage downconverter 340 responsive to detecting that the voltage at first terminals 112 reaches a preconfigured threshold voltage. The threshold voltage may be configured in trigger voltage detector 330 by physical, electronic components.

[0033] Voltage downconverter 340 is configured to respond to trigger 321 and trigger 331 by discharging the electric generator. Further, not illustrated in FIGURE 3, a capacitor may be connected in parallel with peak detector 230 and trigger voltage detector 330. This capacitor may be used to store charge as the voltage at first terminals 112 builds up.

[0034] Trigger voltage detector 330 may be configured with the threshold voltage by electronic components internal to trigger voltage detector 330. Likewise, peak detector 230 may be configured with electronic components to provide the peak detecting functionality. This provides the advantage that losses incurred in the system are lower than in case the threshold voltage was set using, for example, an air gap, or when the voltage is limited with a Zener diode or other voltage limiting circuit which dissipates the excess charge as opposed to collecting the energy.

[0035] FIGURE 4 illustrates an example electronic converter capable of supporting at least some embodiments of the present invention. FIGURE 4 provides a more detailed example than FIGURE 3. In the electronic converter of FIGURE 4, rectifier 310 is a full- wave rectifier comprising four diodes connected as illustrated in the figure.

[0036] Peak detector 320 comprises, in the embodiment of FIGURE 4, a capacitor, a transistor, two diodes and two resistors connected as illustrated in the figure. Box 320 of FIGURE 4 thus forms an example of how to implement a peak detector in electronic converter 110 using electronic components.

[0037] Trigger voltage detector 330 comprises, in the embodiment of FIGURE 4, two diodes and a resistor connected in series. In detail, these diodes may comprise one ordinary diode and one Zener diode, or one ordinary diode and plural Zener diodes, the Zener diodes connected in series, depending on the desired threshold voltage. Box 330 of FIGURE 4 thus forms an example of how to implement a trigger voltage detector in electronic converter 110 using electronic components. The threshold voltage may be configured in trigger voltage detector 330 by selecting the diodes appropriately.

[0038] It is the intention of FIGURE 4 to disclose the example structures of peak detector 320 and trigger voltage detector 330 both together and separately.

[0039] Voltage downconverter 340 comprises, in the embodiment of FIGURE 4, two diodes, two resistors, three transistors forming a thyristor circuit, an inductor and a capacitor, connected to each other as illustrated in the figure. Voltage downconverter 340 is configured to receive the triggers 321 and 331 described in connection with FIGURE 3, to trigger discharging of the electric generator. An advantage of the thyristor arrangement is that the duration of the conductive state is determined automatically, such that further power-consuming components are not needed. The thyristor arrangement ceases discharging the generator as the voltage declines to zero or near-zero. Ordinary thyristors may be poorly suitable for this purpose, since they are components designed for power electronics.

[0040] FIGURE 5 illustrates an example electronic converter capable of supporting at least some embodiments of the present invention. In the electronic converter of FIGURE 5, separate peak detectors and trigger voltage detectors are provided for positive and negative phases of the cycle of the mechanical system. In the positive phase, distance between the plates increases and in the negative phase the distance between the plated declines.

[0041] Positive-phase triggering rectifier 510, negative-phase triggering rectifier 540 and power rectifier 570 are each connected with the first terminals 112, as illustrated.

[0042] Positive-phase triggering rectifier 510 is connected with its dedicated voltage peak detector 520 and trigger voltage detector 530, which are configured to provide respective triggers to voltage downconverter 580, as illustrated in FIGURE 5 by arrows.

[0043] Negative-phase triggering rectifier 540 is connected with its dedicated voltage peak detector 550 and trigger voltage detector 560, which are configured to provide respective triggers to voltage downconverter 580, as illustrated in FIGURE 5 by arrows. Second terminals 114 provide the output to the application, such as application 120 of FIGURES 1A and IB.

[0044] Peak detectors 520 and 550 may have internal structure as illustrated in FIGURE 4, for example. Likewise, trigger voltage detectors 520 and 560 may have internal structure as illustrated in FIGURE 4, for example. When in the positive phase, peak detector 520 alone, trigger voltage detector 530 alone, or both peak detector 520 and trigger voltage detector 530 may be used. When in the negative phase, peak detector 550 alone, trigger voltage detector 560 alone, or both peak detector 550 and trigger voltage detector 560 may be used. An advantage of the embodiments of FIGURE 5 is that separate threshold voltages may be configured for the positive and negative phases, enhancing efficiency as the threshold voltages may be set to discharge the electric generator a few times in each phase.

[0045] In general, in FIGURE 5, the electronic converter comprises a first rectifier configured to trigger in a positive phase of the electric generator and a second rectifier configured to trigger in a negative phase of the electric generator, the first rectifier being connected with a first peak detector and a first trigger voltage detector and the second rectifier being connected with a second peak detector and a second trigger voltage detector, the second trigger voltage detector having a second threshold voltage, different from a first threshold voltage of the first trigger voltage detector. Outputs of rectifiers 510 and 540 form inputs to trigger voltage detectors 530 and 560, and peak detectors 520 and 550.

[0046] It is to be understood that the embodiments of the invention disclosed are not limited to the particular structures, process steps, or materials disclosed herein, but are extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting.

[0047] Reference throughout this specification to one embodiment or an embodiment means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Where reference is made to a numerical value using a term such as, for example, about or substantially, the exact numerical value is also disclosed.

[0048] As used herein, a plurality of items, structural elements, compositional elements, and/or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary. In addition, various embodiments and example of the present invention may be referred to herein along with alternatives for the various components thereof. It is understood that such embodiments, examples, and alternatives are not to be construed as de facto equivalents of one another, but are to be considered as separate and autonomous representations of the present invention.

[0049] Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the preceding description, numerous specific details are provided, such as examples of lengths, widths, shapes, etc., to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention. [0050] While the forgoing examples are illustrative of the principles of the present invention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.

[0051] The verbs “to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of also un-recited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of "a" or "an", that is, a singular form, throughout this document does not exclude a plurality.

INDUSTRIAL APPLICABILITY

[0052] At least some embodiments of the present invention find industrial application in harvesting of electrical energy.

ACRONYMS LIST kV kilovolt

IoT Internet of Things

TENG triboelectric nanogenerator

REFERENCE SIGNS LIST