Standard Energy Harvesting Circuit Research Articles

A comparative analysis of parallel SSHI and SEH for bistable vibration energy harvesters

The present work focuses on ambient vibration energy harvesting. Specifically, this article deals with bistable piezoelectric energy harvesters (PEHs) which exhibits a wider bandwidth than linear oscillators. These complex systems require an energy extraction circuit (EEC) to rectify their voltage to supply power to autonomous sensors. This EEC needs to be optimized in order to increase the harvested power and even the bandwidth of PEHs. Because of the complex dynamics of bistable PEHs, there is a lack of simple and physically-insightful models in the literature that would allow the understanding and optimization of the extraction circuit. To address this issue, the present work derives closed-form models of a bistable PEH coupled to a passive and an active synchronous EEC: respectively the standard energy harvesting (SEH) circuit and the parallel synchronized switch harvesting on inductor (P-SSHI) circuit. Experimental measurements conducted on a custom bistable PEH demonstrate the validity of the proposed models with a relative error lower than 15% on the harvested power and the bandwidth. The proposed models allow to easily understand the influence of the P-SSHI circuit on the dynamics of a bistable PEH. Moreover, a comparison of the performance of the SEH and the P-SSHI circuits, valid for any bistable generator, is proposed. The latter shows that under low electromechanical coupling and low acceleration amplitude the P-SSHI circuit leads to multiply the maximum harvested power up to 4.3 compared to the SEH circuit, and the bandwidth by a factor of 2.3.

Mechanical Rectifier for Broadband Piezoelectric Vibration Energy Harvesting and Self-Adapting Synchronous Electric Charge Extraction

The synchronized switch interface circuit is believed to boost the piezoelectric power generation. The threshold voltage of electronic components causes rectification loss and delay of peak detection. This work reports a novel design of a mechanical rectification piezoelectric vibration energy harvester (MR-PVEH). Compact and low loss mechanical rectification is achieved by double switch with 5 electrodes contact at the cantilever tip. The switch as a mechanical stopper also contributes to broadband performance. The saturation voltage and response frequency range can be adjusted in modeling and simulation of nonlinear electromechanical coupling vibration. Self-adapting Mechanical rectification optimized synchronous electric charge extraction (M-OSECE) circuit is also proposed with less electronic components in this paper and shows an extra 60% increase in generated power than the traditional standard energy harvesting circuit (SEH) in test. This novel design gives a promising solution for self-adapting synchronous switching in broadband piezoelectric vibration energy harvesting.

An SSHC Interface Circuit for Energy Harvesting of Piezoelectric Flags

Piezoelectric flags have functions of both classic flags and energy harvesting, and are becoming a new research focus. Interface circuits that convert wind energy to electrical energy are the key component of piezoelectric flags. A new structure for piezoelectric flags was designed to generate vibration by wind induction. After theoretical analysis, only SEH (standard energy harvesting) and SSHC (synchronized switch-harvesting-on capacitors) interface circuits were found suitable for piezoelectric flags. Simulation in Multisim was performed to compare SEH and SSHC in different load resistance. Experiments were carried out using different wind speeds. The on-time and delay-time of each switch were controlled by the proposed control algorithm. Both simulation and experimental results indicate that the output voltage with SSHC is higher than the output voltage with SEH. When the resistance is 1700 kΩ and the wind speed is 24 m/s, the output power of SSHC can be increased by 45.63% compared with the SEH circuit.

A self-powered ultra-low-power intermittent-control SSHI circuit for piezoelectric energy harvesting

PurposeExisting control circuits for piezoelectric energy harvesting (PEH) suffers from long startup time or high power consumption. This paper aims to design an ultra-low power control circuit that can harvest weak ambient vibrational energy on the order of several microwatts to power heavy loads such as wireless sensors.Design/methodology/approachA self-powered control circuit is proposed, functioning for very brief periods at the maximum power point, resulting in a low duty cycle. The circuit can start to function at low input power thresholds and can promptly achieve optimal operating conditions when cold-starting. The circuit is designed to be able to operate without stable DC power supply and powered by the piezoelectric transducers.FindingsWhen using the series-synchronized switch harvesting on inductor circuit with a large 1 mF energy storage capacitor, the proposed circuit can perform 322% better than the standard energy harvesting circuit in terms of energy harvested. This control circuit can also achieve an ultra-low consumption of 0.3 µW, as well as capable of cold-starting with input power as low as 5.78 µW.Originality/valueThe intermittent control strategy proposed in this paper can drastically reduce power consumption of the control circuit. Without dedicated cold-start modules and DC auxiliary supply, the circuit can achieve optimal efficiency within one input cycle, if the input signal is larger than voltage threshold. The proposed control strategy is especially favorable for harvesting energy from natural vibrations and can be a promising solution for other PEH circuits as well.

An SECE array of piezoelectric energy harvesting

The paper studies the electrical response of an array of piezoelectric oscillators attached to the synchronized electric charge extraction (SECE) interface circuit. The analytic estimate of output power is derived and presented through the matrix formulation of generalized Ohm’s law (charging on capacitance) for the case of parallel (series) connection of energy harvesters. These formulations mainly depend on the proposed equivalent load impedances which are independent of external resistive loads. It therefore offers an advantage of enabling harvested power independent of DC output voltage and making the harvester array desirable for broadband energy scavenging. The proposed framework is subsequently validated both numerically and experimentally. The results show that the power output and bandwidth of an SECE-based array are superior to that based on the standard energy harvesting circuit. Further, it is found that the behavior of an SECE array electrically arranged in parallel connection is different from that connected in series. The former demonstrates the output power higher than the latter, while the latter exhibits roughly uniform peak power in frequency response. However, the experiment indicates the unexpected power drop deviated significantly from the prediction in the array of harvesters connected in series. Such a discrepancy is explained as a result of comparatively serious leakage current in the reverse-biased diodes.

Self-Powered Multi-Input Serial SSHI Interface Circuit With Arbitrary Phase Difference for Piezoelectric Energy Harvesting

A self-powered multi-input serial synchronized switch harvesting on inductor (MIS-SSHI) interface circuit with arbitrary phase difference for piezoelectric energy harvesting is proposed in this article. The proposed MIS-SSHI can extract energy from multiple PZTs based on S-SSHI technique and handle inductor access conflict to avoid mutual influence between the PZTs, without using extra inductor access controlling circuit. Four cases of different phases between PZTs are discussed to explain how to handle the inductor access conflict. Besides, the diodes in traditional S-SSHI circuit are removed to improve the conversion efficiency. An experimental platform is built for testing the power generation performance of the proposed circuit. The experimental results show that the proposed MIS-SSHI circuit can harvest energy from two PZTs with arbitrary phase difference (0-2π) based on single inductor. The maximum harvested power of the proposed MIS-SSHI circuit for single PZT can reach 3.7 times that of the standard energy harvesting circuit.

Self-made electromagnetic vibration energy harvester of different stroke length and number of coil turns

This paper presents the experimental work on a new tube-shape electromagnetic vibration energy harvester to obtain its optimum peak-to-peak voltage output based on different stroke length, number of coil turns and optimum frequency. The harvester is fabricated using Acrylonitrile Butadiene Styrene (ABS) material. It consists of housings with three different stroke lengths, top and bottom covers, Neodymium Iron Boron (NdFeB) magnets, spring and copper coil. The tested stroke lengths are 40 mm, 45 mm and 50 mm while the number of coil turns are 10, 20 and 30. A standard energy harvesting circuit which consists of full-wave bridge rectifier and a capacitor is designed and fabricated to conduct this experiment. The importance of this circuit is to convert alternating current (AC) to direct current (DC) as well as to enable harvesting and storing processes of electrical energy. The harvester is tested on external vertical vibrations generated by shaker with frequency ranged from 5 Hz to 50 Hz with interval of 5 Hz. The raw voltage readings have been extracted from Oscilloscope and are analysed using Microsoft Excel and Octave software. From the results obtained, the optimum peak-to-peak voltage harvested is 39.41 mV at resonant frequency of 5 Hz by 50 mm stroke length and 30 coil turns device. The higher the stroke length and number of coil turns, the higher the peak-to-peak voltage can be harvested.

New insight into piezoelectric energy harvesting with mechanical and electrical nonlinearities

This letter investigates the piezoelectric energy harvesting system with mechanical and electrical nonlinearities. Through impedance model, nonlinear interface circuits for energy harvesting purpose can be simplified as an electrical impedance with real and imaginary parts. Their effects on the mechanical structure can be regarded as circuit-induced damping and stiffness. The resulted equivalent mechanical vibratory system allows us to analytically obtain the system responses under different excitation and loading conditions by harmonic balance method. Furthermore, it becomes possible to achieve a comprehensive comparison among different nonlinear interface circuits, including the standard energy harvesting circuit, synchronized electric charge extraction circuit, series synchronized switching on inductor circuit, parallel synchronized switching on inductor circuit and parallel synchronized triple bias-flip circuit. The results from the theoretical model and experiments together reveal that the nonlinearities play a significant role in the energy harvester’s hysteresis region size, displacement amplitude, and piezoelectric voltage level. This investigation provides an insight into the design, optimization and implementation for the nonlinear energy harvester.

Modelling of a cantilevered energy harvester with partial piezoelectric coverage and shunted to practical interface circuits

This article presents a modelling methodology for a cantilevered energy harvester with partial piezoelectric coverage and shunted to practical power conditioning interface circuits. First, the distributed parameter model of the partially covered piezoelectric energy harvester is developed and the associated analytical solution is derived. Subsequently, the single-degree-of-freedom representation model is developed and the explicit expressions of equivalent lumped parameters are derived by taking the static deflection as the approximated fundamental vibration mode. Based on the comparison with the single-mode expression of the distributed parameter model, a correction factor is proposed to improve the accuracy of the single-degree-of-freedom model. The results of both the distributed parameter and the corrected single-degree-of-freedom models are compared. The accuracy of the corrected single-degree-of-freedom representation model is verified against the analytical and the finite element models. Finally, practical interface circuits including the standard energy harvesting circuit and the parallel synchronized switch harvesting on inductor circuit are considered. A modified equivalent impedance modelling method is proposed for the analysis of the standard energy harvesting and parallel synchronized switch harvesting on inductor circuits. The results of the modified equivalent impedance modelling method are verified against the existing method in the literature.

Boosting the efficiency of a footstep piezoelectric-stack energy harvester using the synchronized switch technology

In this article, the self-supported power conditioning circuits are studied for a footstep energy harvester, which consists of a monolithic multilayer piezoelectric stack with a force amplification frame to extract electricity from human walking locomotion. Based on the synchronized switch harvesting on inductance (SSHI) technology, the power conditioning circuits are designed to optimize the power flow from the piezoelectric stack to the energy storage device under real-time human walking excitation instead of a simple sine waveform input, as reported in most literatures. The unique properties of human walking locomotion and multilayer piezoelectric stack both impose complications for circuit design. Three common interface circuits, for example, standard energy harvesting circuit, series-SSHI, and parallel-SSHI, are compared in terms of their output power to find the best candidate for the real-time-footstep energy harvester. Experimental results show that the use of parallel-SSHI circuit interface produces 74% more power than the standard energy harvesting counterpart, while the use of series-SSHI circuit demonstrates a similar performance in comparison to the standard energy harvesting interface. The reasons for such a huge efficiency improvement using the parallel-SSHI interface are detailed in this article.

A Shock-Optimized SECE Integrated Circuit

This paper presents a fully integrated, self-starting shock-optimized Synchronous Electric Charge Extraction (SECE) interface for piezoelectric harvesters (PEHs). After introducing a model of the electromechanical system under shocks, we prove that the SECE is the most appropriate electrical interface to maximize the harvested energy from our PEH. The proposed interface is then presented, both at system-and transistor-levels. Thanks to a dedicated sequencing, its quiescent current is as low as 30nA. This makes the proposed interface efficient even under time-spaced shocks occurring at sporadic and unpredictable rates. The circuit is for instance able to maintain its self-powered operation while harvesting very small shocks of 8uJ happening every 100 seconds. Our chip was fabricated in CMOS 40nm technology, and occupies a 0.55mm^2 core area. The measured maximum electrical efficiency under shocks reaches 91%. Under shocks, the harvested energy by the proposed shock-optimized SECE interface is 4.2 times higher than using a standard energy harvesting circuit, leading to the best shock FoM among prior art.

Circuit nonlinearity effect on the performance of an electromagnetic energy harvester-structure system

Scavenging energy from structural vibration requires an efficient energy harvesting circuit which could introduce nonlinearity into the harvester-structure system. This study examines the performance of a linear structure equipped with an Electromagnetic (EM) energy harvester connected to a nonlinear standard energy harvesting circuit (SEHC) consisting of a full-wave bridge rectifier and a capacitor in parallel with a resistor. To facilitate the understanding of the nonlinear circuit effect on the behavior of the coupled harvester-structure system under sinusoidal excitation, a first-order harmonic balance approximation method is employed. Numerical simulation and experimental study are conducted to validate the accuracy of the proposed approximation method. Results suggest that the blockage effect of diodes in the bridge rectifier in the SEHC should be reduced by using diodes with small voltage drop value or by designing an EM energy harvester with large electromechanical coupling coefficient to improve the vibration mitigation performance and to enhance the optimal energy harvesting capability of the EM energy harvester. Results also show that circuit nonlinearity should be considered in order to estimate the response of the system accurately.

An Efficient Self-Powered Piezoelectric Energy Harvesting CMOS Interface Circuit Based on Synchronous Charge Extraction Technique

An efficient self-powered synchronous electric charge extraction CMOS interface circuit dedicated to piezoelectric harvesters is proposed in this paper. Self-powered peak detection (PKD) and switch circuits are used to reduce quiescent current so that the backup or pre-charged power can be saved. A new low phase lag (LPL) PKD circuit is designed to improve the synchronous extraction efficiency, which only requires one detection capacitor to perform positive and negative PKD. The circuit can be set at general mode (G-mode) or LPL mode (LPL-mode). Under LPL-mode, the phase lag can be reduced typically by 50%, the synchronous extraction efficiency can obtained up to 94%, while the output power can reach 659 μW when the piezoelectric transducer original opencircuit voltage Voc,org = 5 V, which is 3.56 times of that of full-bridge rectifier standard energy harvesting circuit at the maximum power point. The minimum harvesting startup voltage is 1.7 V and is independent of the energy storage capacitor voltage VDC. The harvesting efficiency can still reach 71.3% at Voc,org = 5 V. The size of the active area is 0.5 mm2 in a 0.18-μm CMOS technology. Circuit may be invoked as a functional block for energy autonomous wireless sensor network node of the Internet of Things.

Piezoelectric beam generator based on MFC as a self-powered vibration sensor

A piezoelectric generator is a device used to convert mechanical energy into electrical energy. The basic element of the generator is made from piezoelectric material in which electrical energy is created as a result of deformations caused by reactions of mechanical structure of the generator. The generators, in which the main element is a cantilever beam constructed from basic material and from piezoelectric material, are one of structures, which are used to the energy harvesting from the mechanical vibrations. The piezoelectric generator are used as a part of self-powered wireless sensor in many scientific research. Such self-powered sensor consists of a sensor measuring selected parameter, a radio transmitter, and aforementioned piezoelectric beam generator. However, the piezoelectric beam generator has a limited application in supply a sensor, because the amount of electric energy generated by such generator does not exceed a few mili Watts and is achieved only if the vibration frequency of mechanical energy source equals the resonant frequency of a cantilever beam of piezoelectric generator. This problem is mainly tried to solve by modifications of the generator beam structure or by introducing additional elements with geometry adapted to the source of mechanical vibration. In contrast to these approaches, the article presents the experimental investigation on the action of self-powered wireless sensor in which a decrease of consumed energy amount was achieved through an using of piezoelectric beam generator, which power the radio transmitter, as a vibration sensor. The piezoelectric beam generator should product an amount of electric energy which is enough to supply only the radio transmitter. Such self-powered wireless sensor is dedicated to a vibration monitoring, in which the basic purpose is a detection of an appearance of the dangerous for building structure vibration. The presented self-powered vibration sensor based on a piezoelectric beam generator equipped with a standard energy harvesting circuit, a radio transmitter and a system of energy transfer control enabling power of a radio transmitter for established level of stored energy in capacitor allows a detection of dangerous vibrations for building structure, monitored by this sensor. In laboratory stand vibration amplitudes of the free end of piezoelectric generator were obtained by changes of vibration frequency and vibration amplitudes of its fixed end. In laboratory experiments the time among radio signal was measured for selected values of capacitor capacity and for changed vibration amplitude of free end of piezoelectric generator beam. On the basis of this experiments it was found that full robustness of tested self-powered sensor was achieved for the capacitor capacity equal to 440μF. The sending of a full package of data by such sensor can be realized only above a minimum value of the capacity of applied capacitor equals 220μF. The capacity of capacitor in piezoelectric self-powered vibration sensor should be selected between minimum value for which full packages of data are sending, in tested sensor it equals 220μF, and maximum values for which full robustness to disturbances is achieved. It was found that an increase of the capacitor capacity caused an improvement of data sending robustness to disturbances in radio transmission. The full robustness manifested the sending of every package of data. On the other hand, an increase of capacitor capacity led to the decrease of detection sensitivity of appearance of short-lived vibrations with the big amplitudes due to longer time of capacitor charging. It was noted that the increase of capacitor capacity did not improve the acting of such sensor in case of appearance of long-lived vibrations.

Electromagnetic energy harvesting from structural vibrations during earthquakes

Energy harvesting is an emerging technique that extracts energy from surrounding environments to power low-power devices. For example, it can potentially provide sustainable energy for wireless sensing networks (WSNs) or structural control systems in civil engineering applications. This paper presents a comprehensive study on harvesting energy from earthquake-induced structural vibrations, which is typically of low frequency, to power WSNs. A macroscale pendulum-type electromagnetic harvester (MPEH) is proposed, analyzed and experimentally validated. The presented predictive model describes output power dependence with mass, efficiency and the power spectral density of base acceleration, providing a simple tool to estimate harvested energy. A series of shaking table tests in which a single-storey steel frame model equipped with a MPEH has been carried out under earthquake excitations. Three types of energy harvesting circuits, namely, a resistor circuit, a standard energy harvesting circuit (SEHC) and a voltage-mode controlled buck-boost converter were used for comparative study. In ideal cases, i.e., resistor circuit cases, the maximum electric energy of 8.72 J was harvested with the efficiency of 35.3%. In practical cases, the maximum electric energy of 4.67 J was extracted via the buck-boost converter under the same conditions. The predictive model on output power and harvested energy has been validated by the test data.

An efficient self-powered synchronous electric charge extraction interface circuit for piezoelectric energy harvesting systems

Harvesting ambient vibration energy using piezoelectric elements is a popular energy harvesting technique. Energy harvesting efficiency is the research focus. Using synchronous electric charge extraction technology in piezoelectric energy harvesting systems can greatly improve the energy harvesting efficiency. This article presents a self-powered efficient synchronous electric charge extraction circuit for piezoelectric energy harvesting systems, in which four self-powered switch circuits are used to optimize the time sequence of charge extraction so that the rectifier bridge circuit used in traditional synchronous electric charge extraction can be saved. The effect of phase lag on extraction efficiency, system energy, and loss of overall circuit is analyzed. A piezoelectric vibration experimental platform is built for testing the power generation performance of the self-powered efficient synchronous electric charge extraction and those published energy harvesting circuits. The experimental results accord with the theoretical analysis. Moreover, the harvesting energy of the proposed self-powered efficient synchronous electric charge extraction is about three times more than those of the standard energy harvesting circuit under its maximum power point and the self-powered synchronized switch harvesting on inductor in most cases. The energy harvesting efficiency of self-powered efficient synchronous electric charge extraction remains at a high level (>80%) in most cases, and the maximum energy harvesting efficiency is up to 85.1%.