Converter and method for extracting maximum power from piezo vibration harvester
First Claim
1. A power converter for recieving energy from a piezo energy harvesting system coupled to a vibration source, comprising:
- (a) an active rectifier receiving an output voltage and output current representing energy harvested from the vibration source including first and second switches coupled in series between a harvester output conductor and a first reference voltage, third and fourth switches coupled in series between the harvester output conductor and the first reference voltage, a first comparator for controlling the third and fourth switches, and a second comparator for controlling the first and second switches, a first terminal of the piezo harvester being coupled to a junction between the first and second switches and a first input of the first comparator, and a second terminal of the piezo harvester being coupled to a junction between the third and fourth switches and a first input of the second comparator, wherein the first and second comparators control the rectifying of the harvester output current to charge a capacitance coupled between the harvester output conductor and the first reference voltage, and wherein the first and second comparators also generate output signals indicative of direction reversals of the output current of the piezo harvester;
(b) a DC-DC converter having a first input coupled to the harvester output conductor, a second input coupled to the first reference voltage, and an output for supplying current to a battery, the DC-DC converter including an inductor coupled to the harvester output conductor, a fifth switch coupled to the inductor, and a rectifying device coupled to the inductor;
(c) a third comparator for comparing a voltage on the harvester output conductor with a second reference voltage to determine when to stop discharge of the capacitance into the inductor; and
(d) enable circuitry coupled to the outputs of the first and second comparators, respectively, for both starting the discharge of the capacitance into the inductor and causing switching operation of the fifth switch to steer current in the inductor into the battery in response to each direction reversal to substantially eliminate waste of power for recharging the capacitance of the piezo harvester, wherein the enable circuitry operates as a state machine having a first state in which an enable signal generated by the enable circuitry is at a logical “
1”
level to enable the DC-DC converter and a second state wherein the enable signal is at a logical “
0”
level to disable the DC-DC converter, wherein the enable logic circuit switches from the first state to the second state in response to an output of the third comparator going from a “
1”
level to a “
0”
level, and wherein the enable logic circuit switches from the second state to the first state in response to either the output of the first comparator going from a “
1”
level to a “
0”
level or the output of the second comparator going from a “
1”
level to a “
0”
level.
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Accused Products
Abstract
A system (1-2) for efficiently transferring harvested vibration energy to a battery (6) includes a piezo harvester (2) generating an AC output voltage (VP(t)) and current (IPZ(t)) and an active rectifier (3) to produce a harvested DC voltage (Vhrv) and current (Ihrv) which charge a capacitance (C0). An enable circuit (17) causes a DC-DC converter (4) to be enabled, thereby discharging the capacitance into the converter, when a comparator (A0,A1) of the rectifier which controls switches (S1-S4) thereof detects a direction reversal of the AC output current (IPZ(t)). Another comparator (13) causes the enable circuit (17) to disable the converter (4) when the DC voltage exceeds a threshold (VREF), thereby causing the capacitance be recharged.
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Citations
12 Claims
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1. A power converter for recieving energy from a piezo energy harvesting system coupled to a vibration source, comprising:
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(a) an active rectifier receiving an output voltage and output current representing energy harvested from the vibration source including first and second switches coupled in series between a harvester output conductor and a first reference voltage, third and fourth switches coupled in series between the harvester output conductor and the first reference voltage, a first comparator for controlling the third and fourth switches, and a second comparator for controlling the first and second switches, a first terminal of the piezo harvester being coupled to a junction between the first and second switches and a first input of the first comparator, and a second terminal of the piezo harvester being coupled to a junction between the third and fourth switches and a first input of the second comparator, wherein the first and second comparators control the rectifying of the harvester output current to charge a capacitance coupled between the harvester output conductor and the first reference voltage, and wherein the first and second comparators also generate output signals indicative of direction reversals of the output current of the piezo harvester; (b) a DC-DC converter having a first input coupled to the harvester output conductor, a second input coupled to the first reference voltage, and an output for supplying current to a battery, the DC-DC converter including an inductor coupled to the harvester output conductor, a fifth switch coupled to the inductor, and a rectifying device coupled to the inductor; (c) a third comparator for comparing a voltage on the harvester output conductor with a second reference voltage to determine when to stop discharge of the capacitance into the inductor; and (d) enable circuitry coupled to the outputs of the first and second comparators, respectively, for both starting the discharge of the capacitance into the inductor and causing switching operation of the fifth switch to steer current in the inductor into the battery in response to each direction reversal to substantially eliminate waste of power for recharging the capacitance of the piezo harvester, wherein the enable circuitry operates as a state machine having a first state in which an enable signal generated by the enable circuitry is at a logical “
1”
level to enable the DC-DC converter and a second state wherein the enable signal is at a logical “
0”
level to disable the DC-DC converter, wherein the enable logic circuit switches from the first state to the second state in response to an output of the third comparator going from a “
1”
level to a “
0”
level, and wherein the enable logic circuit switches from the second state to the first state in response to either the output of the first comparator going from a “
1”
level to a “
0”
level or the output of the second comparator going from a “
1”
level to a “
0”
level. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A power converter for efficiently transferring harvested vibration energy to an energy storage device including:
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(a) an active rectifier couplable to an AC output voltage and AC output current for rectifying the AC output voltage and AC output current to produce a harvested DC output voltage and a harvested DC output current; (b) a DC-DC converter for conducting the harvested DC output current into a capacitance to charge the capacitance until the harvested DC output voltage reaches a level at which a direction of the AC output current reverses; (c) a comparator for detecting the direction reversal; (d) an enable circuit for enabling the DC-DC converter in response to the detecting to cause discharging of the capacitance into an inductor of the DC-DC converter in response to the direction reversal; and (e) a disable circuit for disabling the DC-DC converter in response to a comparison of the harvested DC output voltage with a reference voltage wherein the harvested DC output voltage is less than the reference voltage, wherein the comparator for detecting reversal comprises a comparator for comparing a voltage generated by a harvester with a reference voltage to determine when to stop discharge of the capacitance into an inductor.
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Specification