PIEZOELECTIRC ENERGY HARVESTING SYSTEM WITH FREQUENCY MISMATCH TOLERANCE

• US 20160204717A1
• Filed: 02/16/2015
• Published: 07/14/2016
• Est. Priority Date: 01/09/2015
• Status: Active Grant

• Current Assignee: Analog Devices International Unlimited Company (Analog Devices, Inc.)
• Original Assignee: Analog Devices International Unlimited Company (Analog Devices, Inc.)
• Inventors: Li, Xing, Feng, Yong, Shao, Bin
• Granted Patent: US 10,056,849 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: H02N 2/181 Circuits; Control arrangements or methods

Abstract

An impedance matching circuit is provided for use with a piezotransducer that includes a parasitic capacitor comprising: an inductor coupled in parallel with the parasitic capacitor; a peak and valley detection circuit configured to detect output voltage waveform peaks and valleys; a first switch circuit configured to bias flip the output voltage waveform at a selectable first time relative to a detected peak and at a selectable first time relative to a detected valley; a second switch circuit configured to couple the inductor to the energy storage circuit at a selectable second time following each output voltage bias flip; an energy monitoring circuit to provide an indication of energy flow from the inductor to the energy storage circuit following each output voltage bias flip; and a maximum power point tracking (MPPT) circuit configured to select the first time and the second time based at least in part upon the indicated energy flow.

Claims

1. An impedance matching circuit, for use with a piezotransducer that can produce an output voltage waveform in response to a mechanical input stimulus and with an energy storage circuit that can harvest energy from the output voltage waveform, wherein the piezotransducer includes a parasitic capacitor, the impedance matching circuit comprising:

an inductor configured to be coupled in parallel with the parasitic capacitor;

a peak and valley detection circuit configured to detect output voltage waveform peaks and valleys;

a first switch circuit configured to bias flip the output voltage waveform at a selectable first time relative to a detected peak and at a selectable first time relative to a detected valley;

a second switch circuit configured to couple the inductor to the energy storage circuit at a selectable second time following each output voltage bias flip;

an energy monitoring circuit that includes a voltage detector configured to provide an indication of energy flow from the inductor to the energy storage circuit following each output voltage bias flip; and

a maximum power point tracking (MPPT) circuit configured to select the first time and the second time based at least in part upon the indicated energy flow.

2. The circuit of claim 1,

wherein the peak and valley detector includes a voltage peak and valley detector.

3. The circuit of claim 1,

wherein the peak and valley circuit includes a differentiator circuit.

4. The circuit of claim 1,

wherein the peak and valley circuit includes a differentiator circuit that includes a comparator and a capacitor coupled in series with resistor;

wherein the capacitor is coupled to the output voltage waveform; and

wherein the comparator is coupled to sense a voltage across the resistor.

5. The circuit of claim 1,

wherein the peak and valley circuit includes a differentiator circuit that includes a comparator and a capacitor coupled in series with resistor and third and fourth diodes;

wherein the capacitor is coupled to receive the output voltage waveform;

wherein the comparator is coupled to sense a voltage across the resistor; and

wherein the third and fourth diodes are coupled to provide opposite current paths parallel to the resistor.

6. The circuit of claim 1,

wherein the voltage detector includes a comparator circuit coupled to provide an indication of difference between voltage at the inductor and voltage at the energy storage device.

7. The circuit of claim 1,

wherein the energy monitoring circuit further includes a counter configured to produce a count value indicative of a duration of a monitored time interval during which current flows from the inductor to the energy storage circuit.

8. The circuit of claim 1,

wherein the voltage detector includes a comparator circuit coupled to provide an indication of whether current is flowing from the inductor to the energy storage circuit;

wherein the energy monitoring circuit further includes a counter responsive to the provided indication, that is configured to produce a count value indicative of duration of a monitored time interval during which the provided indication indicates that current is flowing from the inductor to the energy storage circuit.

9. The circuit of claim 1,

wherein the voltage detector is configured to provide an indication of whether current is flowing from the inductor to the energy storage circuit;

and

wherein the second switch is configured to decouple the inductor from the energy storage circuit in response to the provided indication indicating that current is not flowing from the inductor to the energy storage circuit.

10. The circuit of claim 1,

wherein the MPPT circuit is configured to use a hill climbing process to select the first time and the second time based at least in part upon the indicated energy flow.

11. The circuit of claim 1,

wherein the MPPT circuit is configured to search for a value for the first time and a value for the second time that maximize the indicated energy flow.

12. The circuit of claim 1,

wherein the energy monitoring circuit further includes a counter configured to produce a count value indicative of a duration of a monitored time interval during which current flows from the inductor to the energy storage circuit;

and

wherein the MPPT circuit is configured to search for a value for the first time and a value for the second time that maximizes duration of a monitored time interval.

13. The circuit of claim 1 further including:

a rectifier circuit coupled between the parasitic capacitance and the inductor and configured to rectify current provided to the inductor.

14. The circuit of claim 1,

wherein bias flipping includes, at the selectable first time relative to a detected peak and at the selectable first time relative to a detected valley, coupling the inductor from parallel coupling with the capacitor, and following each coupling, after a time interval at least long enough for an occurrence of an output voltage waveform bias flip in response to the coupling, decouple the inductor in parallel with the capacitor;

15. The circuit of claim 14 further including:

a first diode coupled in a first current path in parallel with the parasitic capacitance;

a second diode coupled in a second current path in parallel with the parasitic capacitance;

wherein the first diode coupled in the first current path and the second diode coupled in the second current path are coupled to have opposite current flow directions;

wherein the first switch circuit includes a first sub-switch circuit (S1, S4) configured to, at a selectable first time relative to a detected peak, couple the inductor from parallel coupling with the capacitor via the first current path, and following each coupling, after a time interval at least long enough for an occurrence of an output voltage waveform bias flip in response to the coupling, decouple the inductor in parallel with the capacitor via the first current path; and

wherein the first switch circuit includes a first sub-switch circuit (S2, S3) configured to, at a selectable first time relative to a detected valley, couple the inductor from parallel coupling with the capacitor via the second current path, and following each coupling, after a time interval at least long enough for an occurrence of an output voltage waveform bias flip in response to the coupling, decouple the inductor in parallel with the capacitor via the second current path.

16. An energy harvesting system comprising:

a piezotransducer configured to produce an output voltage waveform in response to a mechanical input stimulus, wherein the piezotransducer includes a parasitic capacitor;

an energy storage circuit that can harvest energy from the output voltage waveform;

an inductor configured to be coupled in parallel with the parasitic capacitor;

a peak and valley detection circuit configured to detect output voltage waveform peaks and valleys;

a first switch circuit configured to bias flip the output voltage waveform at a selectable first time relative to a detected peak and at a selectable first time relative to a detected valley;

a second switch circuit configured to, at a selectable second time following each output voltage bias flip, couple the inductor to the energy storage circuit;

an energy monitoring circuit that includes a voltage detector configured to provide an indication of energy flow from the inductor to the energy storage circuit following each output voltage bias flip; and

a maximum power point tracking (MPPT) circuit configured to select the first time and the second time based at least in part upon the indicated energy flow.

17. The system of claim 16,

wherein the energy storage circuit includes a battery.

18. A method to capture energy from a piezotransducer configured to produce an output voltage waveform in response to a mechanical input stimulus, wherein the piezotransducer includes a parasitic capacitor and wherein the parasitic capacitor is coupled in parallel with an inductor comprising:

bias flipping the output voltage waveform at times leading or lagging the output waveform peaks and at times leading or lagging the output waveform valleys;

coupling the inductor to an energy storage device following each bias flip;

determining an amount of energy captured by energy storage device during each coupling of the inductor to the energy storage device; and

determining the leading or lagging times based at least in part upon the amount of energy captured during each coupling of the inductor to the energy storage device.

19. The method of claim 18,

wherein determining the leading or lagging times includes using a maximum power point tracking (MPPT) process.

20. The method of claim 18,

wherein determining an amount of energy captured measuring duration of a time interval during which current flows during each coupling of the inductor to the energy storage device.