KR20170135042A - Auto-switching energy harvesting circuit using vibration and thermoelectric energy - Google Patents

Abstract

According to an embodiment of the present invention, an automatic switching energy harvesting circuit using vibration and thermal energy comprises: a piezoelectric conversion unit for converting vibration into electricity; a thermoelectric conversion unit for converting heat into electricity; a power switching unit for outputting a higher voltage among a voltage outputted from the piezoelectric conversion unit and a voltage outputted from the thermoelectric conversion unit; and a maximum power point tracking (MPPT) control unit for outputting a voltage of a maximum power point (MPP) from the piezoelectric conversion unit and the thermoelectric conversion unit. The present invention is less sensitive to the environmental change, and an MPPT circuit of each energy source can be merged into one. The size and costs of an overall system are reduced, and thus can be easily applied to a micro sensor node. The maximum available power can be harvested from an energy source having greater output power by applying an automatic switching function.

Description

{AUTO-SWITCHING ENERGY HARVESTING CIRCUIT USING VIBRATION AND THERMOELECTRIC ENERGY}

The present invention relates to an energy harvesting circuit, and more particularly to an automatic switching energy harvesting circuit using vibration and thermal energy.

Today, the development of integrated circuits enables the application of ultra-small, ultra-low power sensors in various fields such as implant devices, environmental monitoring, and wearable sensors. Depending on the development of the sensor, the battery that supplies the power to the sensor must also be developed, but the development of the battery is slow due to technical limitations. Conventional batteries are large, heavy, and have a finite lifespan, making them difficult to apply to ultra-small sensors, and battery replacement can be difficult depending on the location of the sensor. Energy harvesting technology is one of the ways that these ultra-small, ultra-low power sensors can be used as a self-charging or battery replacement.

The energy conversion elements required for energy harvest have a maximum power point (MPP) that outputs the maximum available power. Since the MPP varies in real time due to the surrounding environment, the maximum power point tracking (MPPT : Maximum Power Point Tracking). Among the various MPPT methods, a hill-climbing method and a fractional open-circuit (FOC) method are mainly used. The hill-climbing method continuously changes the switching frequency or the duty cycle of the power converter until the MPP is reached. The FOC method is a method of continuously changing the MPC of the photovoltaic (PV) cell, And a linear relationship between the voltage and the open-circuit voltage is utilized.

Because energy harvesting changes the amount of energy harvested as a result of environmental changes, harvesting energy using multiple energy sources is less sensitive to environmental changes than using one energy source. In the conventional multi-input energy harvesting method, the energy harvested from each energy source is stored in a storage capacitor, and then the storage capacitors are connected in series (non-patent document [2]) or instantaneously output maximum power And a method of selecting and harvesting an energy source (Non-Patent Document [3]). DC-DC converter structure of switching type is widely used as a method of harvesting multiple energies at the same time, and a method of using several inductors and a method of sharing one inductor are proposed. However, these methods require bulky external inductors and may not be suitable for ultra-small, ultra-low power sensors because separate MPPT circuits are required for each energy source to implement the MPPT function.

Non-Patent Document [5] proposes a system for harvesting light, vibration and thermal energy by applying MPPT using one inductor, but vibration and heat energy are known as MPP Under the assumption, the input impedance of the DC-DC converter is fixed, and the hill-climbing type MPPT is applied only to the light energy. Non-patent document [4] applies a heel-climbing type MPPT to each energy source, but since it is implemented using a microcontroller, there is a problem that a lot of cost and power are required.

[1] J. Colomer-Farrarons, P. Miribel-Catala, A. Saiz-Vela, M. Puig-Vidal, and J. Samitier, "Power-Conditioning Circuitry for a Self-Powered System Based on Micro PZT Generators in Low-Voltage Low-Power Technology, "IEEE Trans. on Industrial Electronics, vol. 55, no. 9, pp. 3249-3257, September 2008. [2] N. J. Guilar, R. Amritharajah, P. J. Hurst, and S.H. Lewis, "An energy-aware multiple-input power supply with charge recovery for energy harvesting applications," Dig. Tech. Papers in IEEE ISSCC, pp. 298-299, 2009. [3] H. Lhermet, C. Condemine, M. Plissonnier, R. Salot, P. Audebert, and M. Rosset, "Efficient power management circuit: From thermal energy harvesting to above-IC microbattery energy storage", IEEE J. Solid-State Circuits, vol. 43, no. 1, pp. 246-255, Jan. 2008. [4] Y. C. Kuoa, Y. M. Huang, L. J. Liub, "Integrated Circuit and System Design for Renewable Energy Inverters," International Journal of Electrical Power & Energy Systems, Volume 64, pp. 50-57, 2014. [5] S. Bandyopadhyay and A.P. Chandrakasan, " Platform Architecture for Solar, Thermal, and Vibration Energy Combining with MPPT and Single Inductor " IEEE Journal of Solid-State Circuits, pp. 2199-2215, 2012. [6] Y. S. Yuk, et al., "An energy pile-up resonance circuit extracting maximum 422% energy from piezoelectric material in a dual-source energy-harvesting interface," 2014 Dig. Tech. Papers in IEEE ISSCC, pp. 402-403, 2014. [7] C. Lu, V. Raghunathan, and K. Roy, "Maximum Power Point Considerations in Micro-Scale Solar Energy Harvesting Systems," ISCAS, pp. 273-276, 2010. [8] K. Kadirvel, Y. Ramadass, U. Lyles, J. Carpenter, VI vanov, V. McNeil, A. Chandrakasan, B. Lum-Shue-Chan, "A 330nA energy- and thermoelectric energy harvesting, " 2012 IEEE International Solid-State Circuits Conference Digest of Technical Papers, pp. 106-108, 2012. [9] E. Mendez-Delgado, G. Serranoy and E. Ortiz-Rivera, "Monolithic integrated solar energy harvesting system," 35th IEEE PVSC, pp. 2833-2838, 2010. [10] V. Leonov, P. Fiorini, S. Sedky, T. Torfs, and C. Van Hoof, "Thermoelectric MEMS generators as a power supply for a body area network," Proc. Int. Conf. Solid-State Sensors, Actuators and Microsystems, pp. 291-294, 2005. [11] D. H. Lee, J. H. Jeon, J. T. Park and C. G. Yu, "Design of a High-Efficiency Rectifier for Vibration Energy Harvesting," The Institute of Electronics and Information Engineers, 2010 SoC Conference, pp.197-200, 2010. [12] E. J. Yoon, I. H. Hwang, J. T. Park and C. G. Yu, "Design of an Energy Harvesting Circuit Using Solar and Vibration Energy with MPPT Control," Institute of Electrical and Electronics Engineers, Vol. 16, No. 3, pp.224-234, 2012. [13] M. Ghovanloo and K. Najafi, "Fully integrated wideband high-current rectifiers for inductively powered devices," IEEE J. Solid-State Circuits, vol. 39, 2004, pp. 1976-1984. [14] T. Y. Man, P. K. T. Mok, and M. J. Chan, "A 0.9V Input Discontinuous Conduction Mode Boost Converter with CMOS Control Rectifier" IEEE Journal of Solid-State Circuits, vol. 43, pp. 2036-2046, Sep. 2008.

The problem to be solved by the present invention is that the MPPT circuit of each energy source can be merged into one, which is less susceptible to environmental changes, thereby reducing the size and cost of the entire system and thus being easily applied to a small-sized sensor node. And to provide an automatic switching energy harvesting circuit using vibration and heat energy capable of harvesting the maximum available power from a power source having a larger power.

According to an aspect of the present invention, there is provided an automatic switching energy harvesting circuit using vibration and thermal energy,

A piezoelectric conversion unit for converting the vibration into electricity;

A thermoelectric conversion unit for converting heat into electricity;

A power switching unit for outputting a higher voltage among a voltage output from the piezoelectric transducer and a voltage output from the thermoelectric transducer; And

And a maximum power point tracking (MPPT) controller for causing the piezoelectric transducer and the thermoelectric converter to output a voltage of a maximum power point (MPP).

In the automatic switching energy harvesting circuit using vibration and thermal energy according to an embodiment of the present invention,

A first power switching unit for interrupting supply of a voltage output from the piezoelectric transducing unit;

A second power switching unit for interrupting the supply of the voltage output from the thermoelectric conversion unit; And

And an automatic switching control unit for controlling operations of the first power switching unit and the second power switching unit such that a higher voltage is output among an output voltage of the piezoelectric transducer unit and an output voltage of the thermoelectric conversion unit.

In the automatic switching energy harvesting circuit using vibration and thermal energy according to an embodiment of the present invention,

Wherein the first power switching unit comprises:

A first power switch connected to an output of the piezoelectric conversion unit; And

And a first power switching circuit for turning on or off the first power switch in accordance with the control signal of the automatic switching controller,

Wherein the second power switching unit comprises:

A second power switch connected to an output of the thermoelectric conversion unit; And

And a second power switching circuit for turning on / off the second power switch in accordance with the control signal of the automatic switching controller.

In the automatic switching energy harvesting circuit using vibration and thermal energy according to an embodiment of the present invention,

Wherein the automatic switching control unit comprises:

Wherein the control unit compares the open circuit voltage of the piezoelectric conversion unit with the open circuit voltage of the thermoelectric conversion unit and turns on the first power switch when the open circuit voltage of the piezoelectric conversion unit is higher than the open circuit voltage of the thermoelectric conversion unit, Outputs a signal for turning off the second power switch,

And to output a signal for turning off the first power switch and turning on the second power switch when the open circuit voltage of the thermoelectric conversion unit is higher than the open circuit voltage of the piezoelectric conversion unit.

Also, an automatic switching energy harvesting circuit using vibration and thermal energy according to an embodiment of the present invention,

A first bulk regulation circuit coupled to the body terminal of the first power switch; And

And a second bulk regulation circuit connected to the body terminal of the second power switch.

According to an embodiment of the present invention, an automatic switching energy harvesting circuit using vibrations and thermal energy can be configured such that a voltage output from the piezoelectric conversion unit or a voltage output from the thermoelectric conversion unit is converted into a load Further comprising a load power supply intermittence switch that does not supply or supply power to the load,

The maximum power point tracking (MPPT)

By controlling the operation of the load power supply intermittent switch based on the obtained open circuit voltages to intermittently supply power to the load, thereby obtaining the open circuit voltage of the piezoelectric transducer and the open circuit voltage of the thermoelectric transducer, And the voltage of the maximum power point (MPP) may be outputted from the converter and the thermoelectric conversion unit.

Further, the automatic switching energy harvesting circuit using vibration and thermal energy according to an embodiment of the present invention further includes a storage capacitor for storing the output of the piezoelectric conversion unit or the output of the thermoelectric conversion unit,

The maximum power point tracking (MPPT)

A pulse generator for generating a predetermined operation pulse;

A sampler for obtaining an open circuit voltage of the piezoelectric transducer and an open circuit voltage of the thermoelectric transducer; And

And an enable generator for controlling the operation of the load power supply intermittent switch based on the output of the pulse generator and the voltage of the storage capacitor.

In the automatic switching energy harvesting circuit using vibration and thermal energy according to an embodiment of the present invention,

The first power switching circuit compares the output voltage of the piezoelectric transducer with the voltage of the storage capacitor to output a higher voltage at logic level '1'

The second power switching circuit may compare the output voltage of the thermoelectric conversion unit with the voltage of the storage capacitor to output a higher voltage at a logic level '1'.

In the automatic switching energy harvesting circuit using vibration and thermal energy according to an embodiment of the present invention,

Wherein the thermoelectric conversion unit includes a thermoelectric element,

The piezoelectric transducer includes:

A piezoelectric element for converting vibration into electricity; And

And an AC-DC converter for converting the AC voltage output from the piezoelectric element to a DC voltage.

In the automatic switching energy harvesting circuit using vibration and thermal energy according to an embodiment of the present invention,

The AC-DC converter includes:

An active AC-DC converter including two active diodes and two MOS switches,

Each of the active diodes may include a PMOS switch and a comparator.

According to the automatic switching energy harvesting circuit using vibration and thermal energy according to an embodiment of the present invention, the MPPT circuit of each energy source can be merged into one by being less sensitive to the environmental change, thereby reducing the size and cost of the entire system, It is easy to apply to the sensor node, and it can apply the automatic switching function to harvest the maximum available power from the energy source with higher output power.

1 is a block diagram illustrating an automatic switching energy harvesting circuit using vibration and thermal energy according to an embodiment of the present invention;
2A and 2B are diagrams showing an equivalent circuit of an energy conversion element.
3 is a graph showing current-voltage characteristics and power-voltage characteristics of a piezoelectric element and a thermoelectric element.
4 is a detailed circuit diagram of an AC-DC converter;
5 is a detailed block diagram of the MPPT control unit.
6 shows an output waveform of a pulse generator;
7 is a detailed block diagram of the automatic switching control section.
8 is a diagram showing an operation waveform of the automatic switching control section;
9 is a detailed circuit diagram of the first and second power switching circuits;
10 illustrates simulation results of automatic switching and power switching;
11 shows waveforms of V _TEG , V _Sto, and V _Load .
12 is a diagram showing a simulation result of the MPPT control unit.
13 illustrates power efficiency of an automatic switching energy harvesting circuit using vibration and thermal energy according to an embodiment of the present invention.
FIG. 14 illustrates a layout of an automatic switching energy harvesting circuit using vibration and thermal energy according to an embodiment of the present invention; FIG.

BRIEF DESCRIPTION OF THE DRAWINGS The objectives, specific advantages and novel features of the present invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which: FIG.

Prior to that, terms and words used in the present specification and claims should not be construed in a conventional and dictionary sense, and the inventor may properly define the concept of the term in order to best explain its invention Should be construed in accordance with the principles and the meanings and concepts consistent with the technical idea of the present invention.

It should be noted that, in the present specification, the reference numerals are added to the constituent elements of the drawings, and the same constituent elements are assigned the same number as much as possible even if they are displayed on different drawings.

Also, the terms "first", "second", "one side", "other side", etc. are used to distinguish one element from another, It is not.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the following description of the present invention, a detailed description of known arts which may unnecessarily obscure the gist of the present invention will be omitted.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

An embodiment of the present invention proposes an automatic switching energy harvesting circuit using vibration and thermal energy. The energy output from the thermoelectric element and the oscillation element can use the same maximum power point tracking (MPPT) control circuit because the maximum available power point is equal to 1/2 of the open-circuit voltage. The proposed circuit uses one MPPT control circuit and monitors the output of the thermoelectric device and the output of the oscillator by applying the automatic switching function to harvest the maximum available power from the device with higher voltage.

In applications such as ultra-small, ultra-low-power sensor nodes, it may not be necessary to harvest energy from multiple energy sources simultaneously, since it must be implemented to operate with very low power. Rather, reducing the size and weight of the system and reducing costs by reducing the number of discrete components required can be a priority.

Therefore, in one embodiment of the present invention, a system capable of selecting the vibration and thermal energy that can use the same MPPT control circuit as an energy source and harvesting the maximum available power from an energy source having a larger output power by applying an automatic switching function The Since the proposed circuit uses one MPPT control circuit, it is suitable to reduce the size of the whole system and to reduce the cost.

1 is a block diagram illustrating an automatic switching energy harvesting circuit using vibration and thermal energy according to an embodiment of the present invention.

The automatic switching energy harvesting circuit using vibration and thermal energy according to an embodiment of the present invention shown in FIG. 1 includes a piezoelectric conversion unit 100 for converting vibration into electricity, a thermoelectric conversion A power switching unit 111 for outputting a higher voltage of a voltage V _VB output from the piezoelectric transducer unit 100 and a voltage V _TEG output from the thermoelectric conversion unit 112, And a maximum power point tracking (MPPT) controller 118 for outputting a voltage of a maximum power point (MPP) from the piezoelectric transducer 100 and the thermoelectric converter 112, .

The power switching unit 111 includes first power switching units SW1, _VB , and 110 for interrupting the supply of the voltage V _VB output from the piezoelectric transducer unit 100, the thermoelectric conversion unit 112, A second power switching unit SW1, _TRG 114 for interrupting the supply of the voltage V _TEG output from the piezoelectric transducer unit 100 and an output voltage V _VB of the piezoelectric transducer unit 100, the one, more so that high voltage is output from the output voltage (V _TEG) a first power switching unit (SW1, _VB, 110) and said second power switching unit automatically switches to control the operation of (SW1, _TRG, 114) And a control unit 116.

The first power switches SW1, _VB and 110 are connected to the first power switches SW1 and _VB connected to the output of the piezoelectric transducer 100 and the control signals VMC of the automatic switching controller 116, And a first power switching circuit 110 for _turning on and off the first power switches SW1 and _VB according to the first power switch SW1 and the second power switch SW2.

The second power switching units SW1, _TRG and 114 are connected to the second power switches SW1 and _TRG connected to the output of the thermoelectric conversion unit 112 and the control signal TMC of the automatic switching control unit 116, And a second power switching circuit 114 for _turning on / off the second power switches SW1, _TRG according to the second power switch SW1, _TRG .

The automatic switching control unit 116 compares the open circuit voltages V _{VB and OC} of the piezoelectric conversion unit 100 with the open circuit voltages V _{TEG and OC} of the thermoelectric conversion unit 112, The first power switches SW1 and _VB are turned on when the open circuit voltages V _{VB and OC} of the converting unit 100 are higher than the open circuit voltages V _{TEG and OC} of the thermoelectric conversion unit 112 on) and the second power switch (SW1, _TRG) for outputting a signal to off (off), the thermoelectric conversion unit 112, an open circuit voltage (V _{TEG, OC),} a piezoelectric conversion portion (100) in the case of an open circuit is higher than the voltage (V _{VB, OC),} the first power switch (SW1, _VB) to off (off) and the second power switch (SW1, _TRG) the on (on) and outputs a signal for do.

In addition, an automatic switching energy harvesting circuit using the vibration and thermal energy according to an embodiment of the invention shown in Figure 1, the first power switch, a first connected to the body terminal (not shown) of (SW1, _VB) A bulk regulation circuit 106 and a second bulk regulation circuit 108 connected to the body terminals (not shown) of the second power switches SW1, _TRG .

In addition, the automatic switching energy harvesting circuit using vibration and thermal energy according to an embodiment of the present invention shown in FIG. 1 may include a voltage (V _VB ) output from the piezoelectric transducer (100) And a load power supply intermittence switch SW2 that does not supply or supply the voltage (V _TEG ) output from the load power supply control signal (EN) 112 to the load (not shown) in accordance with the load power supply control signal EN.

The maximum power point tracking (MPPT) controller 118 is for efficiently harvesting energy using a linear relationship between a maximum power point (MPP) voltage and an open circuit voltage, and the piezoelectric transformer 100 (V _{VB, OC} ) of the thermoelectric conversion unit 112 and the open circuit voltage (V _{TEG, OC} ) of the thermoelectric conversion unit 112, and based on the obtained open circuit voltages, SW2 to intermittently supply power to the load so that the output of the piezoelectric transducer 100 and the output of the thermoelectric converter 112 operate at the maximum power point MPP .

In addition, the automatic switching energy harvesting circuit using vibration and thermal energy according to an embodiment of the present invention shown in FIG. 1 may store the output of the piezoelectric transducer 100 or the output of the thermoelectric transducer 112 And a storage capacitor C _Sto for storing the data.

The thermoelectric conversion unit 112 includes a thermoelectric conversion element and the piezoelectric conversion unit 100 includes a piezoelectric element 102 for converting vibration into electricity and an alternating current AC DC converter 104 for converting a voltage to a direct current (DC) voltage. In an embodiment of the present invention, a piezoelectric element is used as an element for converting vibration into electricity. However, the present invention is not limited to this, and any type of vibration-electric conversion element for converting vibration into electricity may convert As shown in Fig.

1, the piezoelectric transducer 100, which is an oscillation energy unit, and the thermoelectric transducer 112, which is a heat energy unit, are connected in parallel, and energy harvested through the MPPT is stored in a storage capacitor C _Sto , (Not shown) through the switch SW2.

The energy conversion element converts the harvested energy into electrical energy. The vibrational energy is generated by a piezoelectric element (PEG) 102 included in the piezoelectric conversion unit 100, a thermal energy is converted into a thermal energy by the thermoelectric conversion unit 112 And is converted into electric energy by a thermoelectric element (TEG: Thermoelectric Generator).

The automatic switching control unit 116 outputs control signals VMC and TMC for selecting an energy source that outputs a higher voltage in the two energy sources.

The first power switching circuit 110 and the second power switching circuit 114 are connected to the first power switches SW1 and SW2, which are pMOS power switches at respective stages, based on the signals VMC and TMC output from the automatic switching controller 116. [ OFF signals VPSW and TPSW to the first and second power switches SW1 and _VB and the second power switches SW1 and _TEG , respectively.

The first power switching circuit 110 and the second power switching circuit 114 are connected to the output of the energy conversion element to cut off the leakage current in the first power switches SW1 and _VB and the second power switches SW1 and _TEG . The voltage V _VB or V _TEG is compared with the magnitude of V _Sto so that the signal with the higher voltage is applied to the gates of the first power switches SW1 and _VB or the second power switches SW1 and _TEG , .

Bulk regulation circuits 106 and 108 are added to the body terminals (not shown) of the first power switches SW1 and _VB or the second power switches SW1 and _TEG , And latch-up, and increased power transfer efficiency.

The MPPT control unit 118 is a circuit for harvesting the maximum usable power from the selected energy conversion element. The MPPT control unit 118 uses an FOC scheme that uses the relationship between the open circuit voltage V _OC of the energy conversion element and the voltage V _{MPP at MPP} Respectively.

The piezoelectric element 100 converts the vibration energy into electrical energy, and the output signal is in the form of an alternating current. Therefore, an AC-DC converter 104 that converts an AC signal into a DC signal is required. 2A is an equivalent circuit of a piezoelectric element. The amplitude of the alternating current source (I _PEG ) varies with the frequency and magnitude of the oscillation, and C _PEG is a unique capacitor present in the piezoelectric element.

In the case of the piezoelectric element (QP20W) used in the embodiment of the present invention, the value of C _PEG is 200 mV. At a frequency of 80 Hz and a vibration size of 7 m / s ² , the open circuit voltage is 3 V or less, to be.

The thermoelectric element 112 for converting heat energy into electric energy uses a Seebeck effect in which an electromotive force is generated by a temperature difference between two different metal joints. 2B is modeled as a voltage source (V _TE ) and a series parasitic resistance (R _TEG ) of a thermoelectric element as an equivalent circuit of a thermoelectric element. The thermoelectric element 112 used in one embodiment of the present invention was designed by using an equivalent circuit having an open circuit voltage of 3 V and an internal resistance of 20 k? Referring to a thermoelectric element manufactured by a MEMS process.

3 is a current-voltage (IV) characteristic and a power-voltage (PV) characteristic of the piezoelectric element 100 (including the AC-DC converter 104) and the thermoelectric element 112. FIG. In the case of piezoelectric elements and thermoelectric elements, ½V _OC The maximum available power is output at the point, which is called the maximum power point (MPP) and the voltage at _{MPP is} called V _MPP . In one embodiment of the present invention, the MPPT is implemented by using the relationship between the open circuit voltage (V _OC ) of the energy conversion element and the voltage (V _MPP ) at the _MPP .

FIG. 4 shows the structure of the designed AC-DC converter 104 and functions to full-wave rectify the AC voltage generated by the piezoelectric element 102 to a DC voltage. A conventional full-wave rectifier composed of four diodes is disadvantageous in that the power conversion efficiency is deteriorated due to the voltage drop of the diode. A rectifier consisting of four MOSFETs reduces the voltage drop across the switch but fails to block reverse current flow, resulting in poor power conversion efficiency.

In one embodiment of the present invention, the AC-DC converter 104 is comprised of an active AC-DC converter including two active diodes 400 and 402 and two MOS switches M2 and M4, The switching device 400 includes a PMOS switch M1 and a comparator CP1 and the active diode 402 includes a PMOS switch M3 and a comparator CP2.

In an embodiment of the present invention, the AC-DC converter 104 can minimize the loss due to the threshold voltage of the transistor and effectively reverse the reverse current to increase the efficiency.

The active diodes 400 and 402 constituted by the PMOS switches M1 and M3 and the comparators CP1 and CP2 are turned on when the output voltage V _VB is greater than the input voltage V _PEG and the outputs of the comparators CP1 and CP2 are ' The PMOS switches M1 and M3 are turned off to shut off the reverse current and when the output voltage V _VB becomes smaller than the input voltage V _PEG , the PMOS switches M 1 and M 3 are turned on, To the output.

That is, in an embodiment of the present invention, an active diode having the comparators CP1 and CP2 added to the MOSFET switches M1 and M3 is used to solve the problem caused in the rectifier of the previous structure. Simulation results show that the maximum efficiency is 95.6% at 20kΩ load resistance.

5, the MPPT controller 118 includes a pulse generator 500 for generating a predetermined operation pulse, an open circuit voltage of the piezoelectric transducer 100 and an open circuit voltage of the thermoelectric conversion unit 112, For controlling the operation of the load power supply intermittence switch (SW2) based on a sampler (508) for obtaining a voltage of the storage capacitor (C _Sto ) and a voltage of the storage capacitor And an enable generator 510 for outputting a signal.

The MC signal MC output from the pulse generator 500 is used to generate on / off signals of the first power switches SW1 _{and VB} and the second power switches SW1 _{and TEG} , / Hold signal.

The MC signal MC is output in a 128-cycle period of the CLK signal, as shown in Fig. When the MC signal MC is '1', the first power switches SW1 _{and VB} and the second power switches SW1 _{and TEG} are turned off, and the piezoelectric transducer 102 and the thermoelectric transducer 112, When the MC signal MC is '0', the first power switches SW1 _{and VB} and the second power switches SW1 _{and TEG} are turned on so that the piezoelectric transformer 102 and the thermoelectric converter So that the maximum power of the converter 112 is supplied to the load.

The sampler 508 periodically samples the open circuit voltages of the piezoelectric transducer 102 and the thermoelectric converter 112 by the MC signal MC and outputs MPPT reference voltages V _{MPP, MAX} and V _{MPP , MIN} , and supplies it to the enable generator 510.

The enable generation unit 510 based on the MPPT reference voltage V _Sto / 4 is V _{MPP, MAX} / 4 is greater than the supply power to the load and V _Sto / 4 that is smaller than V _{MPP, MIN} / 4 power to the load Supply is cut off so that the outputs of the piezoelectric transducer 102 and the thermoelectric transducer 112 always operate near the MPP.

Thermal energy harvester with a series circuit of the voltage supply (V _{TEG, OC)} and the resistance (R _TEG), as shown in Figure 2b as can be expressed equivalently, vibration energy harvester (including the AC-DC converter), the voltage supply (V _{VB, OC} ) and a resistor (R _VB ).

In the case of the piezoelectric element and the thermoelectric element used in the embodiment of the present invention, the internal resistance is equal to 20 k ?. Therefore, since the maximum usable power of each device is proportional to the square of the open circuit voltage, a device with a large open circuit voltage has a higher usable power.

Even if the internal resistance of the two devices is not the same, there is no big problem even if the energy source is selected by simply comparing the open circuit voltage with a power comparison that requires more cost. Since the probability of the two energy sources to harvest energy at the same time is not so great, and in the case of harvesting at the same time, an embodiment of the present invention aims at an application field which can be driven by only one of the two energy sources. It is more important.

The automatic switching control section 116 compares the open circuit voltages V _{VB and OC} of the piezoelectric transducer section 100 with the open circuit voltages V _{TEG and OC} of the thermoelectric conversion section 112 and outputs a higher voltage The power switch of the energy stage is turned on and the signals VMC and TMC for turning off the power switch of the energy stage outputting a low voltage are outputted.

The configuration is made up of a comparator 700 and digital blocks 702, 704, 706, 708, 710 and 712 as shown in FIG. The comparator 700 compares V _{VB, OC} and V _{TEG, OC} output when the MC signal MC is '1', and the compared result is stored in the D-latch 702.

The digital blocks 702, 704, 706, 708, 710 and 712 are operated by a power on reset (POR) signal and an MC signal MC of the MPPT control section 118. As a result, VMC is transmitted to the first power switching circuit 110 of the piezoelectric transducer 100, which is a vibration energy unit, and TMC is transmitted to the second power switching circuit 114 of the thermoelectric conversion unit 112, which is a heat energy unit. VMC and TMC have the same waveform as the on / off signals VPSW and TPSW of the power switches 110 and 114 at the respective stages, but the magnitude of '1' is equal to V _Sto as a signal before power switching.

Figure 8 shows that V _{VB, OC up} to t2, V _{TEG, OC} And after t2, V _{VB, OC} is higher than V _{TEG, OC} The operation of the automatic switching control unit 116 is summarized. Since V _Sto is 0V at the beginning of system operation, the output of POR becomes '0', and VMC and TMC are also '0'. Therefore, the two power switches SW1, _VB , SW1, and _TEG can be kept ON at the same time. When energy is taken from two energy sources or one energy source and V _{Sto boosts} to the voltage necessary for circuit operation, POR outputs '1'. At the same time, MC signal is outputted and VMC and TMC are operated by MC signal.

The comparator 700 of the automatic switching control unit 116 compares the V _OC of each energy source output while MC is '1', so that the power switch signal of the energy stage that outputs a higher voltage follows the MC signal, '1' is applied to the power switch of the energy stage outputting the voltage to turn off the switch. As a result, VMC follows MC from t1 to t2, and TMC maintains '1' to turn off the second power switches SW1 _{and TEG} . After t2, V _{TEG, OC} is higher than V _{VB, OC} , so TMC follows MC signal and VMC maintains '1'. To reduce the current consumption of the circuit, the comparator 700 is operated while the MC signal is only '1' and is off for the rest, and during the off time, the output of the comparator 700 is applied to the D- Voltage was stored.

9 is a detailed circuit diagram of the first power switching circuit 110 and the second power switching circuit 114. As shown in FIG. The first power switching circuit 110 and the second power switching circuit 114 each include a plurality of transistors 900, 902, 908, 910, 916 and 918, a plurality of inverters 904, 906, 912, 914, 922, 924, 926, 928, a plurality of current sources 930, 932, 934, 936, and a resistor 920. The first power switching circuit 110 and the second power switching circuit 114 of each energy stage receive the VMC and TMC signals output from the automatic switching control unit 116 as respective inputs and output the first power switches SW1 _{and VB} , Off signals VPSW and TPSW to the first and second power switches SW1 _{and TEG} .

First and first power switch circuit 110 the second power switching circuit 114, the voltage at the output and the storage capacitor (C _Sto) of the energy conversion element of the piezoelectric converter 100 and the thermoelectric converting unit (112), (V _Sto And outputs a higher voltage as '1' to effectively turn off the first power switches SW1 _{and VB} and the second power switches SW1 _{and TEG, which are pMOSs} .

For example, V _VB, if the _OC is 3V and V _{TEG, OC} is 2.8V, when MPPT operation V _Sto is be about _{1.5V (1 / 2V VB, OC} ), a second power switch _{(SW1, TEG)} is It should be off. 1 'is applied to the gate to turn off the second power switches SW1 _{and TEG} which are the pMOS switches. If the power switching circuits 110 and 114 are not used, the voltage corresponding to the' 1 'level is V _Sto , that is, about 1.5V. However, at the source terminal of the second power switches SW1 _{and TEG} , 2.8 V higher than the gate voltage is applied, and the second power switches SW1 _{and TEG} are not turned off properly.

The automatic switching energy harvesting circuit using vibration and thermal energy according to one embodiment of the present invention is designed by a 0.35 탆 CMOS process and its operation is verified by simulation. The chip area of the designed circuit is 1.4 mm x 1.2 mm including the pad (PAD).

The performance of a circuit according to an embodiment of the present invention designed using a piezoelectric element that outputs an open circuit voltage of 3 V and a frequency of 80 Hz, a thermoelectric element having an open circuit voltage of 3 V, and an internal resistance characteristic of 20 kΩ has been simulated. C _VB is set to 300nF, C _TEG is set to 100nF, C _Sto is set to 47uF, and 5kΩ resistance is connected to the load.

10 shows the result of simulating automatic switching and power switching operation characteristics. V V _{, OC} , V _{TEG and OC} are 2.8V and 0V respectively for the output of the energy conversion element from 0 second to 2 seconds. After 2 seconds, V _{TEG and OC} are changed from 0V to 3.3V If it changes, you can see the changes in the output signals by automatic switching and power switching.

VPSW and TPSW which are on / off signals of the first power switches SW1 _{and VB} of the oscillation energy stage and the second power switches SW1 _{and TEG} of the heat energy stage output the initial POR of '0''0', the two switches are on, and V _Sto gradually increases as power is supplied from the vibration energy stage. When V _Sto becomes 1.1 V, the POR outputs '1' and at the same time, the MC signal is outputted, and the automatic switching controller 116 compares V _{VB, OC} , V _{TEG, and OC} .

As a result, during zero-second 2 seconds V _TEG, because _OC a 0V VPSW is following the MC signal, TPSW is the signal to output a '1' follows the voltage of V _Sto is greater than the V _Sto V _TEG. After 2 seconds, V _VB.OC is maintained at 2.8V but V _{TEG, OC} voltage increases to 3.3V, and VPSW is '1' and TPSW follows MC signal. However, between 2 seconds and 3 seconds, since the automatic switching control unit 116 is before the comparison operation due to the MC signal, the VPSW maintains the MC signal and the TPSW remains '1'. The signal amplitude of the TPSW maintains the voltage magnitude of V _Sto 2 seconds before and after 2 seconds the V _TEG is greater than V _{Sto so} that TPSW follows the voltage magnitude of V _TEG . Also, the size of '1' of VPSW is larger than V _Sto because V _VB is larger, so it follows the voltage of V _VB .

Figs. 11 and 12 show simulation results when V _{VB, OC} are 0 V, V _{TEG, OC} are 3 V _, and the load resistance is 5 k OMEGA. 11 shows the resultant waveforms of V _TEG , V _Sto , and V _Load . In order to sample the open circuit voltage of the thermoelectric element 112, V _TEG periodically becomes 3 V, which is the open circuit voltage by the MC signal, and V _TEG and V _Sto are the MPP voltage of the thermoelectric element 112 It can be seen that the maximum power is output by maintaining the half value (1.5 V) of the open circuit voltage as a reference. Therefore, C _TEG and C _Sto are repeatedly charged and discharged by MPPT control, and the voltage at the time of discharging is supplied to the load.

12 is a simulation result of the MPPT control unit 118. FIG. The MPPT reference voltages V _{MPP, Max} / 4 generated by the sampler 508 are 420 mV, V _{MPP, Min} / 4 is 396.7 mV, and V _Sto / 4 is maintained at this interim value. The actual V _Sto is controlled to be between 1.4V and 1.57V, and the MPPT controller 118 controls the output of the thermoelectric converter 112 near the actual MPP voltage of 1.5V. When the load voltage V _Sto / 4 reaches V _{MPP, Max} / 4, the EN signal becomes '0', so that the load power supply intermittence switch SW2, which is a pMOS switch, is turned on and the thermoelectric conversion unit 112 Energy is supplied to the load. When V _Sto / 4 becomes V _{MPP, Min} / 4, the load power supply intermittent switch (SW2) is turned off and the supply of energy to the load is cut off.

13 shows the power efficiency of the vibration energy harvesting circuit when V _{OC and VB} are 3 V and V _{OC and TEG} is 0 V and the power efficiency of the thermal energy harvesting circuit when V _{OC and VB} are 0 V and V _{OC and TEG} are 3 V And the load resistance was measured between 200Ω and 30kΩ. As a result, the maximum efficiency for vibration energy harvesting is 91.5% at 10kΩ, and the maximum efficiency is 95.9% at 15kΩ for thermal energy harvesting. Vibrational energy is slightly lower than that of thermal energy harvesting because the power is supplied to the load through an AC-DC converter with a power efficiency of up to 95.6% (@ 20kΩ).

14 is a layout of a designed circuit. The chip area is 1.4 mm x 1.2 mm including the pad.

Table 1 compares the performance of the conventional multiple input energy harvesting circuits with the performance of the automatic switching energy harvesting circuit using vibration and thermal energy according to one embodiment of the present invention. Non-patent document [3] applies a method of harvesting the energy source that outputs the maximum power to RF and thermal energy as priority, but the thermal energy harvesting circuit uses the 0.35 탆 process and the RF energy process uses 0.18 탆 process It is disadvantageous in terms of cost and area. Non-patent document [5] uses MPPT, but it uses a method of fixing the input impedance of a DC-DC converter under the assumption that vibration and heat energy know MPP, and hill-climbing only for light energy. The MPPT method is applied, and there is a limitation in actual application. In addition, existing researches are using external devices in addition to capacitors and inductors, which is disadvantageous for application to ultra-small sensor nodes and the overall efficiency is less than 90%.

An automatic switching energy harvesting circuit using vibration and thermal energy according to an embodiment of the present invention is a structure for harvesting energy by selecting an energy source outputting a higher voltage and applying the FOC method for MPPT. The total current consumption was 2.48 μA, and the maximum power efficiency was 91.5% at 10 kΩ and 95.9% at 15 kΩ when the vibration energy was harvested.

In an embodiment of the present invention, an energy harvesting circuit using a vibration and thermal energy having an automatic switching function and an MPPT function using a 0.35 탆 CMOS process is proposed. The designed circuit has the advantage that it is less sensitive to environmental change than the single input harvesting circuit because it harvests energy harvestable by sensing each energy source in real time through automatic switching control block. The MPPT circuit of each energy source is merged into one by utilizing the fact that the relationship between the open circuit voltage of vibration and thermal energy and the voltage at MPP is the same, so that it is easy to apply to a small sensor node by reducing the size and cost of the whole system. Designed circuits can be applied to monitoring of structures such as roads and bridges, which are relatively low in duty rate required and easy to obtain vibration and heat energy, and environmental monitoring of forests and the like.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. It is clear that the present invention can be modified or improved.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

100: piezoelectric conversion unit 102: piezoelectric element
104: AC-DC converter 106, 108: Bulk regulation circuit
110: first power switching circuit 112: thermoelectric conversion unit
114: second power switching circuit 116: automatic switching control section
118: MPPT control unit 400, 402: active diode
500: Pulse generator 502: Clock generator
504: Counter 506: MC Generator
508: Sampler 510: Enable generator

Claims (10)

A piezoelectric conversion unit for converting the vibration into electricity;
A thermoelectric conversion unit for converting heat into electricity;
A power switching unit for outputting a higher voltage among a voltage output from the piezoelectric transducer and a voltage output from the thermoelectric transducer; And
And a maximum power point tracking (MPPT) controller for causing the piezoelectric transducer and the thermoelectric converter to output a voltage of a maximum power point (MPP) Energy harvesting circuit. The method according to claim 1,
Wherein the power switching unit comprises:
A first power switching unit for interrupting supply of a voltage output from the piezoelectric transducing unit;
A second power switching unit for interrupting the supply of the voltage output from the thermoelectric conversion unit; And
And an automatic switching control unit for controlling operations of the first power switching unit and the second power switching unit such that a higher voltage is output among an output voltage of the piezoelectric conversion unit and an output voltage of the thermoelectric conversion unit, Automatic switching energy harvesting circuit. The method of claim 2,
Wherein the first power switching unit comprises:
A first power switch connected to an output of the piezoelectric conversion unit; And
And a first power switching circuit for turning on or off the first power switch in accordance with the control signal of the automatic switching controller,
Wherein the second power switching unit comprises:
A second power switch connected to an output of the thermoelectric conversion unit; And
And a second power switching circuit for turning on or off the second power switch in accordance with a control signal of the automatic switching control unit. The method of claim 3,
Wherein the automatic switching control unit comprises:
Wherein the control unit compares the open circuit voltage of the piezoelectric conversion unit with the open circuit voltage of the thermoelectric conversion unit and turns on the first power switch when the open circuit voltage of the piezoelectric conversion unit is higher than the open circuit voltage of the thermoelectric conversion unit, Outputs a signal for turning off the second power switch,
And outputting a signal for turning on the first power switch and turning on the second power switch when the open circuit voltage of the thermoelectric conversion unit is higher than the open circuit voltage of the piezoelectric conversion unit, Automatic switching energy harvesting circuit using. The method of claim 3,
A first bulk regulation circuit coupled to the body terminal of the first power switch; And
Further comprising a second bulk regulation circuit coupled to the body terminal of the second power switch. The method of claim 3,
Further comprising a load power supply intermittence switch that does not supply or supply the voltage output from the piezoelectric conversion unit or the voltage output from the thermoelectric conversion unit to the load in accordance with the load power supply control signal,
The maximum power point tracking (MPPT)
By controlling the operation of the load power supply intermittent switch based on the obtained open circuit voltages to intermittently supply power to the load, thereby obtaining the open circuit voltage of the piezoelectric transducer and the open circuit voltage of the thermoelectric transducer, And an automatic switching energy harvesting circuit using vibration and thermal energy to output a voltage of a maximum power point (MPP) in the converting unit and the thermoelectric converting unit. The method of claim 6,
Further comprising a storage capacitor for storing an output of the piezoelectric conversion unit or an output of the thermoelectric conversion unit,
The maximum power point tracking (MPPT)
A pulse generator for generating a predetermined operation pulse;
A sampler for obtaining an open circuit voltage of the piezoelectric transducer and an open circuit voltage of the thermoelectric transducer; And
And an enable generator for controlling operation of the load power supply intermittent switch based on the output of the pulse generator and the voltage of the storage capacitor. The method of claim 7,
The first power switching circuit compares the output voltage of the piezoelectric transducer with the voltage of the storage capacitor to output a higher voltage at logic level '1'
And the second power switching circuit compares an output voltage of the thermoelectric conversion unit with a voltage of the storage capacitor to output a higher voltage at a logic level '1'. The method according to claim 1,
Wherein the thermoelectric conversion unit includes a thermoelectric element,
The piezoelectric transducer includes:
A piezoelectric element for converting vibration into electricity; And
And an AC-DC converter for converting an AC voltage output from the piezoelectric element into a DC voltage. 2. The automatic switching energy harvesting circuit according to claim 1, The method of claim 9,
The AC-DC converter includes:
An active AC-DC converter including two active diodes and two MOS switches,
Each of said active diodes comprising a PMOS switch and a comparator, said automatic switching energy harvesting circuit using vibration and thermal energy.

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