Classifications

• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
  • H02M7/00—Conversion of AC power input into DC power output; Conversion of DC power input into AC power output
  • H02M7/02—Conversion of AC power input into DC power output without possibility of reversal
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
  • H02M7/00—Conversion of AC power input into DC power output; Conversion of DC power input into AC power output
  • H02M7/02—Conversion of AC power input into DC power output without possibility of reversal
  • H02M7/04—Conversion of AC power input into DC power output without possibility of reversal by static converters
  • H02M7/12—Conversion of AC power input into DC power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
  • H02M7/21—Conversion of AC power input into DC power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
  • H02M7/217—Conversion of AC power input into DC power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
  • H02M7/219—Conversion of AC power input into DC power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only in a bridge configuration
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
  • H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
  • H02J7/02—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries for charging batteries from AC mains by converters
  • H02J7/04—Regulation of charging current or voltage
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
  • H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
  • H02J7/32—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries for charging batteries from a charging set comprising a non-electric prime mover rotating at constant speed
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
  • H02M7/00—Conversion of AC power input into DC power output; Conversion of DC power input into AC power output
  • H02M7/02—Conversion of AC power input into DC power output without possibility of reversal
  • H02M7/04—Conversion of AC power input into DC power output without possibility of reversal by static converters
  • H02M7/12—Conversion of AC power input into DC power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
  • H02M7/21—Conversion of AC power input into DC power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
  • H02M7/217—Conversion of AC power input into DC power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
  • H02M7/219—Conversion of AC power input into DC power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only in a bridge configuration
  • H02M7/2195—Conversion of AC power input into DC power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only in a bridge configuration the switches being synchronously commutated at the same frequency of the AC input voltage
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02N—ELECTRIC MACHINES NOT OTHERWISE PROVIDED FOR
  • H02N2/00—Electric machines in general using piezoelectric effect, electrostriction or magnetostriction
  • H02N2/18—Electric machines in general using piezoelectric effect, electrostriction or magnetostriction producing electrical output from mechanical input, e.g. generators
  • H02N2/181—Circuits; Control arrangements or methods
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
  • H02M1/00—Details of apparatus for conversion
  • H02M1/0067—Converter structures employing plural converter units, other than for parallel operation of the units on a single load
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
  • H02M1/00—Details of apparatus for conversion
  • H02M1/0067—Converter structures employing plural converter units, other than for parallel operation of the units on a single load
  • H02M1/007—Plural converter units in cascade
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
  • Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
  • Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Definitions

• the invention relates generally to efficient transfer of power from a piezo vibration harvester to a DC-DC converter, and more particularly to an improved DC-DC converter circuit for efficiently receiving a maximum amount of power from a piezo harvester.
• nano-power integrated circuits that require extremely low amounts of operating current
• various very low power integrated circuits that require extremely low amounts of operating current (often referred to as “nano-power” integrated circuits)
• nano-power integrated circuits which can be powered by very small amounts of power scavenged or harvested from ambient solar, vibrational, thermal, and/or biological energy sources by means of micro-energy harvesting devices. The harvested power then usually is stored in batteries or super capacitors.
• nano-power as used herein is intended to encompass circuits and/or circuit components which draw DC current of less than roughly 1 microampere.
• FIG. 1A shows an energy harvesting system 1-1 that includes a conventional piezo-electric harvester 2, an active rectifier circuit 3, and a DC-DC converter 4 for charging a battery or supercapacitor 6 and/or a load (not shown) which includes a switch control and PWM (pulse width modulation) circuit 9.
• Rectifier circuit 3 includes four switches S1-S4, two comparators AO and Al, and two inverters 22 and 23.
• Active rectifier circuit 3 generates a harvested voltage Vhrv on conductor 18 which is applied to an input of switch control and PWM circuit 9 of DC-DC converter 4.
• DC-DC converter 4 generates an output voltage and output current which are supplied by conductor 5 to the battery 6.
• harvester 2 can be modeled as a parallel connection of a sinusoidal current source, an internal capacitance C PIEZO , and an internal resistance RpiEzo-
• An optional filtering capacitor CO may be connected between conductor 18 and ground.
• Piezo energy harvesters always have an output capacitance C PIEZO , which is not necessarily smaller than CO, depending on the brand or kind of harvester being used.
• DC-DC converter 4 in FIG. 1A is 80-90% efficient in transferring energy from conductor 18 to battery 6.
• the waveform represents the actual voltage Vp(t) across piezo harvester 2.
• +Vhrv and -Vh rv are threshold voltages of the DC-DC converter, which may be determined by a maximum power point tracking (MPPT) circuit (not shown).
• MPPT maximum power point tracking
• DC-DC converter 4 is in its "off condition in which it does not convert Vhrv, and vibration energy is being wasted for recharging of the harvester output capacitance C PIEZO - [0006]
• energy generated by piezo harvester 2 is wasted by the charging and discharging of the capacitance C PIEZO - (Note that capacitor CO is connected to the output of rectifier 3 and therefore is not charged and recharged by piezo harvester 2.) That energy is lost during the time interval between time tO and t2 of transition B of the Vp(t) waveform shown in FIG.
• Piezo harvesters with the structure shown in FIG. 1A are able to actually collect less than 1/3 of the energy available from piezo harvester 2. See the article "A Comparison Between Several Vibration-Powered Piezo Electric Generators for Stand- Alone Systems" by E. Lefeuvere, A. Badel, C. Richard, L. Petit, and D. Guyomar, 2005, Science Direct, Sensors and Actuators A 126 (d006) 405-416, available online at www.sciencedirect.com; especially see FIGS. 6 and 7.
• the voltage Vp(t) across piezo harvester 2 should reach the input threshold +Vh rv of DC-DC converter 4.
• the total harvester output capacitance including C PIEZO , must be recharged to -Vhrv
• This recharging energy i.e., the subsequently mentioned CV energy
• the mechanical vibration source and the piezo harvester 2 receiving that vibration but the recharging energy is wasted every vibration cycle.
• V hrv because the amount of wasted energy CV 12 is proportional to the square of the voltage across the capacitance.
• a known technique can be used to increase the amount of energy collected from the piezo harvester. That technique is to connect a switch across piezo harvester 2 and briefly short-circuit it at time tO in FIG. 2 until the voltage Vp(t) goes through zero.
• This counterintuitive technique of dissipating collectible energy can improve the amount of charging of battery 6 because the amount of wasted power from piezo harvester 2 is reduced by a factor of 2. This avoids the need to waste the CV energy to recharge CPIEZO-
• use of a large inductor in series with the foregoing switch can further enhance the efficiency of power transfer from the piezo harvester to the battery.
• the invention provides a system (1-2) for efficiently transferring harvested vibration energy to a battery (6).
• the system 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 (V hrv ) and current (3 ⁇ 4 nom) which charge a capacitance (CO).
• An enable circuit (17) causes a DC-DC converter (4) to be enabled, thereby discharging the capacitance into the converter, when a comparator ( ⁇ , ⁇ ) of the rectifier which controls switches (S1-S4) of the rectifier 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 (V REF ), thereby causing the capacitance be recharged.
• the invention provides a piezo energy harvesting system (1-2) coupled to a vibration source.
• the piezo energy harvesting system (1-2) includes a piezo harvester (2) for generating an output voltage (Vp(t)) and an output current (Ipz(t)) representing energy harvested from the vibration source.
• An active rectifier (3) includes first (SI) and second
• a first comparator (AO) controls the third (S3) and fourth (S4) switches
• a second comparator (Al) controls the first (SI) and second (S2) switches.
• a first terminal (7 A) of the piezo harvester (2) is coupled to a junction between the first (SI) and second (S2) switches and a first input (+) of the first (AO) comparator
• a second terminal (7B) of the piezo harvester (2) is coupled to a junction between the third
• the first (AO) and second (Al) comparators control rectifying of the harvester output current (Ipz(t)) to charge a capacitance (CO) coupled between the harvester output conductor (18) and the first reference voltage (GND).
• the first (AO) and second (Al) comparators also generate output signals (20-4, 20-2) which indicate direction reversals of the output current (Ipz(t)) of the piezo harvester (2).
• a DC-DC converter (4) has a first input coupled to the harvester output conductor (18), a second input coupled to the first reference voltage (GND), and an output (5) for supplying current to a battery (6).
• the DC-DC converter (4) includes an inductor (L0) coupled to the harvester output conductor (18), a fifth switch (SO) coupled to the inductor (L0), and a rectifying device (D) coupled to the inductor (L0).
• a third comparator (13) compares a voltage (V hrv ) on the harvester output conductor (18) with a second reference voltage (V REF ) to determine when to stop discharge of the capacitance (CO) into the inductor (L0).
• Enable circuitry (17) is coupled to the outputs (20-4,20-2) of the first (AO) and second (Al) comparators, respectively, for both starting discharge of the capacitance (CO) into the inductor (L0) and causing switching operation of the fifth switch (SO) to steer current in the inductor (L0) into the battery (6) in response to each direction reversal, so as to substantially eliminate waste of CV power for recharging the capacitance (CPIEZO) of the piezo harvester (2).
• the enable circuitry (17) operates as a state machine (FIG.
• the enable logic circuit (17) switches from the first state (A) to the second state (B) in response to an output (V 16 ) of the third comparator (13) going from a "1" level to a "0" level.
• the enable logic circuit (17) switches from the second state (B) to the first state (A) in response to either the output (V20-4) of the first comparator (AO) going from a "1" level to a "0" level or the output (V20-2) of the second comparator (Al) going from a "1" level to a "0" level.
• the rectifying device (D) is a synchronous rectifier.
• the DC-DC converter (4) can be a boost converter, a buck converter, or a buck-boost converter.
• PWM (pulse width modulation) circuitry (14) is coupled between the output (EN) of the enable circuitry (17) and a control terminal of the fifth switch (SO).
• each of the first (AO) and second (Al) comparators has a second input (-) coupled to the first reference voltage (GND).
• PWM circuitry (14) causes the fifth switch (SO) to switch at a frequency of several megahertz when the output (EN) of the enable circuitry (17) is at a "1" level, and the PWM circuitry (14) also keeps the fifth switch (SO) open when the output (EN) of the enable circuitry (17) is at a "0" level.
• the DC-DC converter (4) is enabled for intervals (tl-tO or t3-t2) which are less than approximately 100 microseconds.
• the first comparator (AO) switches from a "1" state to a "0" state in response to a magnitude of the output current (Ipz(t)) falling below a predetermined low value when the output current (Ipz(t)) flows in a first direction
• the second comparator (Al) switches from a "1" state to a "0” state in response to a magnitude of the output current (Ipz(t)) falling below the predetermined low value when the output current (Ipz(t)) flows in a second direction.
• the invention provides a method for efficiently transferring harvested vibration energy to a battery (6), including coupling the vibration energy to a piezo harvester (2) thereby causing the piezo harvester (2) to generate an AC output voltage (Vp(t)) and an AC output current (Ipz(t)) that together constitute the harvested vibration energy; coupling the AC output voltage (Vp(t)) and AC output current (Ipz(t)) to an active rectifier (3) and rectifying the AC output voltage (Vp(t)) and AC output current (Ipz(t)) to produce a harvested DC output voltage (V hrv ) and a harvested DC output current (I hrv ); conducting the harvested DC output current (3 ⁇ 4 token) into a capacitance (CO) to charge the capacitance (CO) until the harvested DC output voltage (V hrv ) reaches a level at which a direction of the AC output current (Ipz(t)) reverses; detecting the direction reversals by means
• the enabling includes operating PWM (pulse width modulation) circuitry (14) to cause a switch (SO) connected to the inductor (L0) in the DC-DC converter (4) to switch at a frequency of several megahertz when the enable signal (EN) is at a "1" level, and wherein the PWM circuitry (14) keeps the switch (SO) open when the enable signal (EN) is at a "0" level.
• PWM pulse width modulation
• the method provides a system (1-2) for efficiently transferring harvested vibration energy to a battery (6), including piezo harvester means (2) for receiving the vibration energy and a generating an AC output voltage (Vp(t)) and an AC output current (Ipz(t)) that together constitute the harvested vibration energy; means (18) for coupling the AC output voltage (Vp(t)) and AC output current (Ipz(t)) to active rectifier means (3) for rectifying the AC output voltage (Vp(t)) and AC output current (Ipz(t)) to produce a harvested DC output voltage (Vhrv) and a harvested DC output current (Ihrv); means (18) for conducting the harvested DC output current (Ihr V ) into a capacitance (CO) to charge the capacitance (CO) until the harvested DC output voltage (V hrv ) reaches a level at which a direction of the AC output current (Ipz(t)) reverses; means ( ⁇ , ⁇ ) for detecting the direction
• FIG. 1A is a schematic diagram of a prior art energy harvesting system including a piezo harvester and a DC-DC converter arranged to charge a battery.
• FIG. IB shows a model of the piezo harvester 2 in FIG. 1A.
• FIG. 2 is a graph useful in explaining the wasted energy in the energy harvesting system of FIG. 1A.
• FIG. 3A is a schematic diagram of a piezo energy harvester system of the invention.
• FIG. 3B is a schematic diagram of one basic implementation of DC-DC converter
• FIG. 3C is a schematic diagram of another basic implementation of DC-DC converter 4 in FIG. 3A.
• FIG. 4 is a graph useful in explaining the operation of the piezo energy harvester system of FIG. 3.
• FIG. 5 is a state diagram for the enable logic in block 17 of FIG. 3A.
• FIG. 3A shows an energy harvesting system 1-2 that includes conventional piezo-electric harvester 2, active rectifier circuit 3, a comparator 13, an enable logic circuit 17, a switch control and PWM (pulse width modulation) circuit 14, and a DC-DC converter 4 for charging a battery or supercapacitor 6 and/or a load (not shown).
• piezo harvester 2 can be modeled as a parallel connection of a sinusoidal current source, internal capacitance C PIEZO , and internal resistance R PIEZO - Rectifier circuit 3 includes four switches S1-S4, two comparators AO and Al, and two inverters 22 and 23.
• Piezo harvester 2 receives mechanical vibration energy or the like and converts it into a harvested AC voltage Vp(t) across piezo harvester 2 and a harvested AC current Ipz(t) in its terminals 7 A and 7B.
• Filtering capacitor CO can be connected between conductor 18 and ground (i.e., Vss)- [0033]
• a first terminal of switch SI is connected to conductor 18 on which the output V hrv of active rectifier is generated.
• a second terminal of switch S 1 is connected by (+) terminal 7A of piezo harvester 2 to a first terminal of switch S2, the second terminal of which is connected to ground.
• a first terminal of switch S3 is connected to conductor 18.
• a second terminal of switch S3 is connected by (-) terminal 7B of piezo harvester 2 to a first terminal of switch S4, the second terminal of which is connected to ground.
• Inverter 22 has its output 20- 1 connected to the control terminal of switch S 1.
• the input of inverter 22 is connected by conductor 20-2 to the control terminal of switch S2 and the output of comparator Al, which has its inverting input connected to ground.
• the non-inverting input of comparator Al is connected to piezo harvester terminal 7B.
• Inverter 23 has its output connected by conductor 20-3 to the control terminal of switch S3.
• the input of inverter 23 is connected by conductor 20-4 to the control terminal of switch S4 and the output of comparator AO.
• the inverting input of comparator AO is connected to ground, and its non-inverting input is connected to piezo harvester terminal 7A.
• the switch control circuitry of active rectifier 3 includes
• comparators AO and Al comparators AO and Al and inverters 22 and 23.
• the output conductor 18 of active rectifier 3 is connected to the high-side voltage input terminal of DC-DC converter 4, the output 5 of which is connected to battery 6.
• the low- side voltage input of DC-DC converter 4 is connected to ground.
• Conductor 18 also is connected to the (+) input of a comparator circuit 13.
• Active rectifier 3 generates a harvested DC output current I hrv in conductor 18 and a harvested DC output voltage V hrv on conductor 18.
• the (-) input of comparator circuit 13 is connected to a reference voltage V REF , which can be zero or some other voltage.
• DC-DC converter 4 can be a boost converter as shown in FIG. 3B, a buck converter as shown in FIG. 3C, or a buck/boost converter (not shown).
• the presently preferred embodiment of DC-DC converter 4 is a boost converter, but it is expected that a future implementation will include a buck-boost converter.
• FIG. 3B shows a simplified schematic diagram of a boost converter 4-1, wherein conductor 18 is connected to one terminal of inductor LO, the other terminal of which is connected by conductor 12 to one terminal of switch SO and to the anode of a synchronous rectifier circuit represented by diode D.
• Inductor LO typically has an inductance of 10 to 40 micro-henrys.
• the anode of diode D is connected by conductor 5 to the battery 6.
• the other terminal of switch SO is connected to ground.
• the control terminal of switch SO is connected to the output 15 of control and PWM circuit 14 in FIG. 3A.
• DC-DC converter 4 may be implemented by means of a buck converter 4-2, a simplified schematic diagram of which is shown in FIG. 3C, wherein conductor 18 is connected to one terminal of switch SO.
• the other terminal of switch SO is connected by conductor 12 to one terminal of inductor L0 and to the cathode of a synchronous rectifier circuit represented by diode D.
• the other terminal of diode D is connected to ground.
• the other terminal of inductor L0 is connected by conductor 5 to the battery 6.
• the other terminal of diode D is connected to ground.
• the control terminal of switch SO is connected to the output 15 of control and PWM circuit 14 in FIG. 3A. (Note that a buck-boost converter should be used if Vhrv can be above the battery voltage.)
• the output 16 of comparator circuit 13 is connected to one input of an enable logic circuit 17.
• a state diagram of the circuitry of enable logic circuit 17 is shown in FIG. 5, described below.
• Two other inputs of enable logic circuit 17 are connected to the output 20-2 of comparator Al and to the output 20-4 of comparator AO, respectively.
• Enable logic circuit 17 performs several functions, including removing/diminishing glitches which are associated with the signals V 16 , V20-2, and V20-4 on conductors 16, 20-2, and 20-4, respectively, and generating the enable signal EN on conductor 19 in accordance with the state diagram shown in FIG. 5.
• the state diagram of enable logic circuit 17 in FIG. 3A includes a first state “A” in which the enable signal EN generated on conductor 19 is at a logical “1” level to enable DC-DC converter 4.
• Enable logic circuit 17 also has second state “B” wherein enable signal EN is at a logical "0" level.
• enable logic circuit 17 When enable logic circuit 17 is in state “B” and condition “D” is met, i.e., if either the output V 20 - 2 of comparator Al goes from a “1" level to a “0” level or the output V 20 -4 of comparator AO goes from a “1” level to a “0” level, enable logic circuit 17 switches from state “B” to state “A", causing DC-DC converter 4 to be enabled.
• Enable logic circuit 17 can be readily provided by implementing the simple state diagram of FIG. 5 as a simple state machine.
• the state machine can be implemented using an edge-triggered flip-flop and a bit of associated logic circuitry.
• enable logic circuit 17 generates converter enable signal EN on conductor 19, which is connected to an input of control and PWM circuit 14.
• Control and PWM circuit 14 performs the functions of controlling DC-DC converter switches in order to determine and limit the current in inductor L0.
• the output 15 of control and PWM circuit 14 is coupled to the gate of the switch SO (shown in FIG. 3B or FIG. 3C) that controls the flow of current in inductor L0 of DC-DC converter 4.
• the logic level on the (+) input of comparator Al in FIG. 3 A controls the control terminals of switches SI and S2, and the logic level on the (+) input of comparator AO controls the control terminals of switches S3 and S4.
• Comparators AO and Al switch states when the magnitude of piezo harvester current Ipz(t) reaches a maximum or minimum value, and segment A of the Vp(t) waveform in FIG. 4 shows how Vp(t) decreases as Ipz(t) flows through switch S 1 and charges capacitor CO relatively slowly while switches S 1 and S4 are closed and the other two switches S2 and S3 are open.
• segment B of the Vp(t) waveform shows how capacitor CO is relatively very rapidly discharged into inductor L0 (e.g., as shown in FIG. 3B or 3C).
• DC-DC converter 4 is enabled at time tO and steers the inductor current into an output conductor 5 to charge battery 6.
• DC-DC converter 4 is disabled while CO is discharged to 0 volts.
• segment D of the Vp(t) waveform shows how capacitor CO is relatively very rapidly discharged into inductor L0.
• DC-DC converter 4 is enabled at time t2 and steers the inductor current into output conductor 5 to charge battery 6.
• DC-DC converter 4 is disabled while CO is discharged to 0 volts.
• the switch control circuitry including comparators AO and Al in active rectifier 3 of FIG. 3 A determines the operation of switches S1-S4 so as to control the synchronous rectifying of the harvested AC signal Ipz(t) each time the magnitude of piezo harvester current Ipz(t) falls to zero while charging CO and CPIEZO during the positive and negative phases of the present vibration cycle.
• Comparator AO turns switch S4 off and turns switch S3 on (or comparator Al turns switch S2 off and turns switch SI on), and vibration energy imparted to piezo harvester 2, along with whatever amount of current I hrv piezo harvester 2 and active rectifier 3 continue to generate, are conducted to and stored in inductor LO (e.g., as in FIG.
• Enabling DC-DC converter 4 is a matter of allowing SO to operate as required for normal DC-DC conversion operation. Disabling DC-DC converter 4 is simply a matter of keeping the switch SO connected to inductor L0 in its OFF condition.
• DC-DC converter 4 in FIG. 3A is controlled by sensing the direction of the current Ipz(t) in piezo harvester 2, which involves determining when either one of the outputs V20-2 or V20-4 goes to a "0" level.
• the piezo harvester current Ipz(t) reverses direction.
• the energy stored in inductor L0 of DC-DC converter 4 is steered into battery 6 while DC-DC converter 4 remains enabled.
• the vibration frequency typically is below about 2 kHz, and the switching frequency of DC-DC converter 4, established by control and PWM circuit 14, typically is several megahertz.
• DC-DC converter 4 is effectively enabled by the enable signal EN generated by enable logic circuit 17, starting at time tO and continuing until the time tl at which Vp(t) is equal to VREF, which may be zero, which occurs when CO and CPIEZO are completely discharged into inductor L0, if the vibration displacement is sufficient to cause V hrv to exceed VREF- AS the charged-up capacitances CO and CPIEZO are being discharged into the inductor L0, the resulting current stored in inductor L0 is transferred into battery 6 according to the ordinary switching procedure of control and PWM circuit 14.
• Ipz(t) current direction reversal of Ipz(t) is detected as a reversal in the output of one of comparators AO and Al .
• DC-DC converter 4 is immediately enabled in response to that Ipz(t) direction reversal.
• V hrv across CO is CO/CPIEZO times smaller than voltage Vp(t) across the piezo harvester 2 while DC-DC converter 4 is disabled, i.e., effectively disconnected from piezo harvester 2, during the same vibration half cycle.
• DC-DC converter 4 is implemented by means of boost converter 4-1 in FIG. 3B, V hrv is limited by the 3 to 4 volt voltage of battery 6, which is effectively short-circuited to conductor 18 through inductor LO.
• DC-DC converter 4 When DC-DC converter 4 is enabled, DC-DC converter 4 starts conducting a maximum allowed current (indicated by current pulses E and F in FIG. 4) into inductor LO until CO and C PIEZO are fully discharged, and at the same time the resulting current in inductor LO is steered into battery 6 in accordance with the output of control and PWM circuit 14. Then DC-DC converter 4 is immediately disabled or effectively disconnected from Vhrv, until the end of the next vibration half cycle during which CO and C PIEZO are being recharged by piezo harvester 2.
• the discharge time of CO and C PIEZO is less than approximately 100 microseconds and therefore is negligible compared to the duration of the vibration cycle, which typically is less than roughly a few milliseconds. (The discharge time of CO and C PIEZO typically is at least 100 times less than the vibration cycle (which is relatively much shorter than illustrated in FIG. 4).
• the above described piezo energy harvesting system avoids the large amount of wasted power characteristic of the prior art shown in FIG. 1A by providing a new DC-DC converter structure including associated circuitry for extracting maximum power from piezo harvesters. This is accomplished by using an active rectifier which detects reversals in the direction of the current through the piezo harvester and utilizes that information to enable the DC-DC converter only as long as required to transfer all of the charge and current produced by the piezo harvester earlier in the present vibration half cycle. This is accomplished without use of additional switches.

Landscapes

• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Dc-Dc Converters (AREA)
• Rectifiers (AREA)

Priority Applications (2)

Applications Claiming Priority (2)

Publications (1)

Family

ID=44646691

Family Applications (1)

Country Status (4)

Cited By (2)

Families Citing this family (39)

Citations (4)

Family Cites Families (31)

• 2010
  • 2010-03-19 US US12/661,578 patent/US8674663B2/en active Active
  • 2010-12-21 WO PCT/US2010/061423 patent/WO2011115652A1/en not_active Ceased
  • 2010-12-21 CN CN201610835716.2A patent/CN107026576B/zh active Active
  • 2010-12-21 CN CN201080065534.2A patent/CN102804586B/zh active Active
  • 2010-12-21 JP JP2013501239A patent/JP5990158B2/ja active Active
• 2014
  • 2014-01-24 US US14/163,861 patent/US9112374B2/en active Active
• 2015
  • 2015-08-17 US US14/828,332 patent/US9941722B2/en active Active

Patent Citations (4)

Also Published As

Similar Documents

Legal Events