Piezoelectric Energy Harvesting Interface Research Articles

Piezoelectric energy harvesting interface with fast open-circuit voltage sampling

This paper presents a piezoelectric energy harvesting interface with fast open-circuit voltage (VOC) sampling and a wide operating frequency range. The fractional open-circuit voltage (FOCV) method is the primary method for maximum power point tracking (MPPT) in energy harvesting systems, due to its easy implementation and relatively low cost. For this method to be efficient, it is necessary to shorten the time required for VOC sampling. To minimize power loss due to VOC sampling, a novel technique is proposed that is capable of sampling the VOC within a time shorter than half a cycle by using an adaptive tracking pulse instead of conventional fixed ones. We also present a peak detector design technique that can operate across a broad frequency spectrum and adapt to diverse vibration scenarios. The proposed technique reduces the duty cycle of the tracking pulse to 0.42%, which is 3.7 times smaller than the conventional 1.56%. The proposed circuit, designed using a 0.35μm complementary metal oxide semiconductor (CMOS) process, consumes just 94nA at 100Hz, 3V VOC, and a 1kΩ load. In a 2~4V VOC range and a 15~500Hz frequency range, the MPPT efficiency exceeds 95%, peaking at 99.9%, and the power efficiency remains over 93%, reaching a maximum of 97.7%.

Analysis and Optimization of Switched-Capacitor Piezoelectric Energy Harvesting Interface Circuits

Analysis and Optimization of Switched-Capacitor Piezoelectric Energy Harvesting Interface Circuits

A Fully Autonomous SSHIC Interface Circuit With Configurable Multi-Step Bias-Flip for Piezoelectric Energy Harvesting

This brief presents a piezoelectric energy harvesting interface circuit with a multi-step bias-flip strategy to boost the energy extraction capability. The optimized parallel synchronized switch on inductor and capacitor (SSHIC) technique is adopted. Except for the external inductor and capacitors, the proposed interface circuit is designed for fully integrated control without any external adjustment during the bias-flip process. Moreover, the steps for bias-flip can be configured flexibly, and the circuit can work even without an inductor. The interface circuit has been designed and implemented with 0.18- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\mu }\text{m}$ </tex-math></inline-formula> CMOS technology. With the 5-step bias-flip SSHIC topology and a 1-mH inductor, the simulated whole current dissipation is 106 nA, the measured maximum flipping efficiency is 90.3%, and the measured maximum power efficiency improvement is 642% compared to the ideal full bridge rectifier (FBR).

Piezoelectric Energy Harvesting Interface Using Self-Bias-Flip Rectifier and Switched-PEH DC–DC for MPPT

Piezoelectric Energy Harvesting Interface Using Self-Bias-Flip Rectifier and Switched-PEH DC–DC for MPPT

A Highly Adaptive and Flipping-Time Optimized Piezoelectric Energy Harvesting Interface IC With Synchronized Triple Bias-Flip

This article presents a piezoelectric energy harvesting interface circuit with high adaptability to external inductors, transducer types, and vibration frequencies. High output power can be obtained with the help of triple bias-flip and optimal flipping time control. The triple bias-flip enables both higher efficiency and the use of an inductor with lower volume compared to conventional bias-flip topologies. Besides, owing to the highly adaptive circuit design and reverse current reduction in the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> resonant loop, the proposed interface circuit not only automatically adjusts flipping time according to external inductance and piezoelectric transducer, but also reduces the reverse current of the inductor effectively. Also, an active rectifier that can reduce conduction loss of the diode-based rectifier has been implemented. The prototype integrated circuit has been fabricated in 180-nm CMOS technology and the chip area is 0.646 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The measurement results show that the proposed circuit achieves cold start-up without any external power supply, and can work with high efficiency when the external inductor is varying from 0 to 10 mH, transducer capacitance is changing from 20 to 90 nF, and vibration frequency is ranging from 35 to 200 Hz. The measured maximum output power of the proposed design can achieve as high as 473% enhancement to the full-bridge rectifier.

A review of nonlinear piezoelectric energy harvesting interface circuits in discrete components

Piezoelectric energy harvesting is considered as an ideal power resource for low-power consumption gadgets in vibrational environments. The energy extraction efficiency depends highly on the interface circuit, and should be highly improved to meet the power requirements. The nonlinear interface circuits in discrete components have been extensively explored and developed with the advantages of easy implementation, stable operation, high efficiency, and low cost. This paper reviews the state-of-the-art progress of nonlinear piezoelectric energy harvesting interface circuits in discrete components. First, the working principles and the advantages/disadvantages of four classical interface circuits are described. Then, the improved circuits based on the four typical circuits and other types of circuits are introduced in detail, and the advantages/disadvantages, output power, efficiency, energy consumption, and practicability of these circuits are analyzed. Finally, the future development trends of nonlinear piezoelectric energy harvesting circuits, e.g., self-powered extraction, low-power consumption, and broadband characteristic, are predicted.

Efficient self-powered piezoelectric energy harvesting interface circuit with wide rectified voltage

Synchronized Switching Harvesting on Inductor (SSHI) and Synchronous Electric Charge Extraction (SECE) are two classic interface circuit techniques for Piezoelectric energy harvesting. But the former has high peak output power with narrow rectified voltage range, while the latter has wide rectified voltage range with lower peak output power. This paper presents a self-powered interface circuit for piezoelectric energy harvesting to achieve a good balance between the two. The proposed interface circuit is based on the Series-SSHI (S–SSHI) and SECE. The circuit proposed can harvest energy through S–SSHI and SECE in positive and negative half cycles, respectively. Moreover, the figure of merit (FOM), optimal rectified voltage range (ORVR) and region of interest (SRoI) of simulation and experiment results are discussed. The maximum FOM of the proposed circuit is as high as 2.15, which is 1.68 times that of the SECE, and it can reach 6 times the ORVR of the S–SSHI. SRoI factor of the proposed circuit show that the proposed method has better performance. In addition, the circuit shows a simpler implementation compared with state-of-the-art designs.

Piezoelectric Energy-Harvesting Interface Using Split-Phase Flipping-Capacitor Rectifier With Capacitor Reuse for Input Power Adaptation

This article proposes a split-phase flipping-capacitor rectifier (SPFCR) to resolve the hard tradeoff between the number of capacitors and the energy-extraction efficiency for capacitive piezoelectric energy-harvesting (PEH) interfaces. By splitting the capacitor usage into multiple phases, this article can achieve the most number of flipping phases using the same number of capacitors when compared with the state of the art. We also relaxed the implementation complexity by removing insignificant SFPCR flipping phases without sacrificing the energy-harvesting efficiency. To improve further the input power adaptation, the flipping capacitors are reconfigured as a multiple-voltage-conversion-ratio (MVCR) switched-capacitor dc–dc converter during the non-flipping period without using extra passives. Maximum-power-point tracking (MPPT) is also accomplished using the full-bridge rectifier (FBR) fractional open-circuit voltage ( $V_{{\text {OC}, \text {FBR}}}$ ) to relax the voltage-tolerance requirements. Fabricated in 0.18- $\mu \text{m}$ CMOS, the proposed 21-phase SPFCR PEH interface demonstrates a measured maximum output power improving rate (MOPIR) of up to 9.3 $\times $ with $V_{D}= 0.12$ V (6.5 $\times $ with $V_{D}= 0$ V) when compared with the conventional FBR interface over an equivalent FBR input power range ( $P_{{\text {in, FBR}}}$ ) from 0.15 to 5.57 $\mu \text{W}$ .

A Piezoelectric Harvesting Interface with Capacitive Partial Electric Charge Extraction for Energy Harvesting from Irregular High-Voltage Input

A fully integrated piezoelectric energy harvesting interface is proposed for harvesting energy from irregular human motion. To handle irregular pulse inputs generated by the piezoelectric transducer (PZT), the proposed harvesting interface includes a wake-up controller that activates the harvesting interface only when human motion is detected and deformation is applied on the piezoelectric material, thereby keeping static power loss low. The PZT output voltage is increased to its peak voltage by removing any type of external load capacitance seen by the PZT during its deformation. Once the peak voltage is detected, a multi-voltage conversion-ratio-based switched-capacitor circuit is activated to transfer PZT-generated energy to the battery in multiple ratio steps to maximize the conversion efficiency, with the help of a carefully designed harvesting controller. To deal with open-circuit voltages (VOCS) higher than the maximum voltage tolerated (VMAX) by available technology, capacitive partial electric charge extraction is activated every time the PZT output voltage approaches the VMAX. The proposed harvesting interface extracts 3.37 times more energy than a conventional full-bridge rectifier-based harvesting scheme.

A dual-effect solution for broadband piezoelectric energy harvesting

Literature has shown that the bandwidth of a piezoelectric energy harvesting (PEH) system can be effectively broadened by introducing nonlinear mechanical dynamics. However, when connected to a practical PEH interface circuit for ac-to-dc conversion, the bandwidth improvement will be impaired because of the electrically induced damping effect. On the other hand, there is another bandwidth broadening solution, in which the resonant frequency is tunable to some extent by carrying out the phase-variable synchronized switch (PVSS) control in practical interface circuits. This Letter reports a synergistic design by combining these two mechanisms toward a dual-effect broadband PEH solution. The theoretical model of this nonlinear and electromechanically coupled system is derived. The experimental result shows that, by introducing the PVSS control to a PEH system, which is composed of a monostable piezoelectric cantilever beam and a practical synchronized switch interface circuit, its bandwidth can be broadened by 18.7%. This dual-effect solution incorporates two bandwidth broadening mechanisms toward practical broadband PEH systems.

Revisit of synchronized electric charge extraction (SECE) in piezoelectric energy harvesting by using impedance modeling

Piezoelectric energy harvesting (PEH) systems convert ambient vibration energy into useful electricity. An interface circuit intervenes the electromechanical energy conversion; it has a significant effect on the electromechanical joint dynamics and harvested power. Among the existing interface circuits, the synchronized electric charge extraction (SECE) solution was known for its unique feature of load independence. However, the actual harvested power was usually shown to be lower than the previous theoretical predictions. The reason is that the energy dissipation in power conditioning, e.g. the diode dissipation in the rectifier and the switching dissipation in each energy extraction, have not received sufficient consideration. This paper revisits the joint dynamics and harvested power of PEH systems with a SECE interface circuit by using the energy flow analysis and impedance modeling. By qualitatively scrutinizing the energy cycle of SECE, the electrically induced dynamic characteristics are broken down into three components: the equivalent capacitance, dissipative resistance, and harvesting resistance, which have the same effects but different values, like those in other PEH interface circuits. The three components are equivalent to an additional stiffness, a dissipative damper, and a regenerative damper in the mechanical domain. The theoretical harvested power, which is estimated based on the impedance modeling, shows good agreement with the experimental results under different loading conditions and operating frequencies. Owing to its modular way of thinking, the impedance modeling technique once again shows its effectiveness and efficiency towards the analyses of joint dynamics and harvested power in PEH systems using different power conditioning interface circuits.

A Self-Powered P-SSHI Interface Circuit with Adaptive On-Resistance Active Diode for PEH

This paper presents a two-stage synchronous rectifier interface circuit for piezoelectric energy harvesting (PEH) system. The proposed rectifier includes a first-stage negative voltage converter, a second-stage adaptive on-resistance active diode, and combines a precise switch-on-time controlled P-SSHI circuit. The traditional active two-stage synchronous rectifier has lower current detection accuracy and hardly achieves high efficiency rectification over a wide input current range. An adaptive on-resistance active diode (AOR active diode) is proposed to replace the traditional active diode to achieve higher current zero-crossing detection accuracy, improve the input current range and the output power of the rectifier. The proposed diode allows the rectifier to maintain high rectification efficiency over a wider input current range. Further, a parallel synchronized switch harvesting on inductor (P-SSHI) with precise switch-on-time controlled circuit is proposed to achieve higher voltage flipping efficiency and improve the power extraction capability of the rectifier. By using the AOR active diode and the P-SSHI with precise switch-on-time controlled circuit, a good performance improvement has been achieved for the proposed interface circuit. The design is fabricated in an SMIC 0.35[Formula: see text][Formula: see text]m standard CMOS technology with a die size of [Formula: see text][Formula: see text]mm2. The simulation results indicate that the proposed circuit achieves more than 80% power converting efficiency and its peak efficiency is 85%. The current zero-crossing detection accuracy of the proposed AOR active diode is less than 10[Formula: see text][Formula: see text]A. The proposed PEH interface circuit extracts up to 2.81 times more output power compared with a traditional rectifier. The voltage flipping efficiency of the P-SSHI circuit is up to 90%, which can effectively improve the power extraction capability of the rectifier. Moreover, the proposed circuit can be self-powered and cold started up.

A self-powered piezoelectric energy harvesting interface circuit with efficiency-enhanced P-SSHI rectifier * * Project supported by the National Natural Science Foundation of China (Nos. 61574103, U1709218) and the Key Research and Development Program of Shaanxi Province (No. 2017ZDXM-GY-006).

The key to self-powered technique is initiative to harvest energy from the surrounding environment. Harvesting energy from an ambient vibration source utilizing piezoelectrics emerged as a popular method. Efficient interface circuits become the main limitations of existing energy harvesting techniques. In this paper, an interface circuit for piezoelectric energy harvesting is presented. An active full bridge rectifier is adopted to improve the power efficiency by reducing the conduction loss on the rectifying path. A parallel synchronized switch harvesting on inductor (P-SSHI) technique is used to improve the power extraction capability from piezoelectric harvester, thereby trying to reach the theoretical maximum output power. An intermittent power management unit (IPMU) and an output capacitor-less low drop regulator (LDO) are also introduced. Active diodes (AD) instead of traditional passive ones are used to reduce the voltage loss over the rectifier, which results in a good power efficiency. The IPMU with hysteresis comparator ensures the interface circuit has a large transient output power by limiting the output voltage ranges from 2.2 to 2 V. The design is fabricated in a SMIC 0.18 μm CMOS technology. Simulation results show that the flipping efficiency of the P-SSHI circuit is over 80% with an off-chip inductor value of 820 μH. The output power the proposed rectifier can obtain is 44.4 μW, which is 6.7× improvement compared to the maximum output power of a traditional rectifier. Both the active diodes and the P-SSHI help to improve the output power of the proposed rectifier. LDO outputs a voltage of 1.8 V with the maximum 90% power efficiency. The proposed P-SSHI rectifier interface circuit can be self-powered without the need for additional power supply.

Fully Integrated Inductor-Less Flipping-Capacitor Rectifier for Piezoelectric Energy Harvesting

This paper presents a fully integrated piezoelectric energy harvesting interface without external components. Instead of relying on bulky external inductors with high quality factor as in the conventional parallel-synchronized-switch harvesting-on-inductor (P-SSHI) approach, we propose a flipping-capacitor rectifier (FCR) topology to achieve voltage inversion of the piezoelectric energy harvester through a reconfigurable capacitor array. This fundamentally preserves a fully integrated solution without inductors while achieving a high-energy extraction capability. Measurement results from FCR <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> using discrete components shows an output power enhancement of up to 3.4×, which is close to the theoretical prediction. We also fabricated a sevenphase FCR <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> with four MIM capacitors and 21 switches using a 0.18-μm 1.8/3.3/6 V CMOS process, occupying an active area of ~1.7 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Additionally, we implemented an active rectifier based on a common-gate comparator with phase alignment to ensure high-speed operation while minimizing the diode voltage drop. A phase generate-and-combine circuit eliminates redundant switching activities. Systematic optimization of the three main energy loss mechanisms during the finite flip time: 1) phase offset; 2) incomplete charge transfer; and 3) reduced conduction time, is also introduced. Measurement results show that the output power enhancement can reach up to 4.83× at an excitation frequency of 110 kHz.

A Self-Powered Piezoelectric Energy Harvesting Interface with Wide Input Range in 65 nm CMOS Process

ABSTRACTA self-powered piezoelectric energy harvesting interface circuit (PEHIC) with wide input range and good performance is presented in this paper. The proposed PEHIC consists of a two-stage active charge pump rectifier and an ultra-low power intermittent power management unit (IPMU). Active diodes based on unbalanced-biased comparators improve the reverse leakage current problem that conventional active diodes faced. By limiting the output voltage between 1.2 and 0.8 V, the IPMU working in intermittent mode can provide an expanded input range and ensure that the interface circuit has a large transient output power. Implemented in a 65 nm standard complementary metal oxide semiconductor (CMOS) technology, the PEHIC has been simulated and verified. Simulation results show that an AC signal with amplitude ranging from 0.32 to 1.5 V and frequencies of 20 Hz–3 kHz can be rectified. The maximum output current is as large as 5 mA. The peak power conversion efficiency is up to 81% when the input voltage is 0.8 V at 200 Hz. The PEHIC can be self-powered without the need for additional power supply.

Synchronized bias-flip interface circuits for piezoelectric energy harvesting enhancement: A general model and prospects

Piezoelectric energy harvesting (PEH) systems, as a kind of electromechanically coupled system, are composed of two essential parts: the piezoelectric structure and the power conditioning interface circuit. Previous studies have shown that the energy harvesting capability of a piezoelectric generator can be greatly enhanced by up to several hundred percent by using synchronized switch harvesting on inductor (SSHI) interface circuits, the most extensively investigated family of synchronized bias-flip interface circuits. After SSHI, some other bias-flip circuit topologies, which utilize active approaches for PEH enhancement, have been proposed sporadically. Yet, how active is active enough for harvesting as much energy as possible was not clear. This paper answers this question through the generalization and derivation of existing bias-flip solutions. The study starts by analyzing the energy flow in existing featured interface circuits, including the standard energy harvesting (bridge rectifier) circuit, parallel-SSHI, series-SSHI, pre-biasing/energy injection/energy investment scheme, etc. A synchronized multiple bias-flip (SMBF) model, which generalizes the bias-flip control and summarizes the energy details in these circuits, is then proposed. Based on the topological and mathematical abstraction, the optimal bias-flip (OBF) strategy towards maximum harvesting capability is derived. A case study on the series synchronized double bias-flip (S-S2BF) circuit shows that the potential of the PEH interface circuits can be fully released by using the OBF strategy. The proposed SMBF model and OBF strategy set the theoretical foundation and provide a new insight for future circuit innovations towards more powerful PEH systems.

Improving the Scavenged Power of Nonlinear Piezoelectric Energy Harvesting Interface at Off-Resonance by Introducing Switching Delay

This paper presents two interface circuit designs that improve the piezoelectric energy harvesting performance at offresonance. Complex impedance matching at different frequencies is achieved by introducing delay into the conventional switching methods. The proposed techniques can also be used in other applications, such as electromagnetic energy harvesting. The system is analyzed using equivalent impedance at fundamental of operating frequency. Design considerations such as two possible modes of operation, sensitivity to voltage and timing errors, loss due to nonlinear operations, and conduction loss of switches are detailed. As compared with the conventional methods, analytical results show that, with the electromechanical coupling coefficient k2e of 0.076 and the mechanical damping ratio ζm of 0.02, the proposed techniques can improve the 3-dB bandwidth by 76% with a flipping quality factor of 10. Experimental results with a commercially available piezoelectric device show a 23% improvement in 3-dB bandwidth and a 66% improvement in extracted power with 5% of frequency mismatch.

Best voltage bias-flipping strategy towards maximum piezoelectric power generation

In piezoelectric energy harvesting (PEH) systems, energy extracted from piezoelectric structure can be increased by making piezoelectric voltage in phase with vibration velocity and raising the voltage amplitude. Such voltage manipulations can be realized by synchronously flipping the piezoelectric voltage with respect to a bias dc source at every displacement extremum. Given that net harvested energy is obtained by deducting dissipated energy from total extracted energy, a sophisticated voltage bias-flipping scheme, which can maximize extracted energy at low dissipative cost, is required towards harvested energy optimization. This paper extends the state of the art by proposing the best bias-flip strategy, which is delivered on conceptual synchronized multiple bias-flip (SMBF) interface circuits. The proposed strategy coordinates both requirements on larger voltage change in synchronized instant for more extracted energy and smaller voltage change in each bias-flip action for less dissipated energy. It not only leads to further enhancement of harvesting capability beyond existing solutions, but also provides an unprecedented physical insight on maximum achievable harvesting capability of PEH interface circuit.