Power amplification interface circuit for broadband piezoelectric energy harvester

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Abstract

Amplifying energy from a broadband energy harvester requires interfacing of energy harvester with energy harvesting circuitry. To interface the harvester, a mechanical and electrical equivalent model is developed. The resonance frequencies of these models differ with the finite element model by less than 5%. A developed electrical equivalent model is interfaced with basic and synchronous circuit methodologies providing a maximum power of 38.32 μW. A novel energy harvesting circuit consisting of the Schottky diode bridge rectifier and double voltage divider circuit is able to provide an output power of 27.87 mW.

Introduction

Energy harvesting is termed as conversion of ambient energy into useable energy. Energy harvesting can also be defined as “the collection and storage of ambient energy for on-demand, off-grid use”. Ambient energy is the energy all around us in the form of thermal, chemical, electrical and mechanical etc. Transducer convert these energies into useable off-grid energy at places where on-grid energy cannot be used. Another important aspect is on-demand supply which refers to the energy supplied when it is needed [1]. The research on energy harvesting has been mostly focused on the design and development of generator structures over the past several years. While designing the energy harvesting system, it is much essential to design the energy harvesting interface circuit as no application can directly use the extracted power from the harvester. A lot of research in the recent times has been undertaken on the design of efficient energy harvesting circuitry (EHC). Interface circuitry or EHC has two essential function, first is effective conversion of AC to DC and second is to provide adequate power to the output load circuitry to function throughout their lifetime. Most of the micro-scale devices require a direct current (DC) to operate efficiently. There are many techniques for converting the alternating current (AC) into useable DC [2]. These techniques involve around rectifier circuits for converting AC to DC. Secondary function for energy harvesting circuitry or the interface circuitry is to optimize the power extracted from the harvester by providing impedance matching with the input impedance. In other energy harvesting techniques i.e. thermoelectric and photovoltaic, DC power generated from the harvester is transferred to the load at an optimum output voltage. Maximum power point (MPP) is that optimal point and it depends on the input impedance of the harvester which effects the open circuit voltage that is function of input source i.e. temperature gradient for thermoelectric generator and sunlight for photovoltaic. Interface circuitry needs to perform maximum power point tracking (MPPT) for optimum performance [3,4]. Similar to these systems vibration systems also require MPP [5,6]. In addition to this the interface circuitry must handle electrical damping of the load circuit which also effects the output power. It is essential for interface circuitry to set the damping, so that maximum power from the harvester can be utilized. Another characteristic of the interface circuitry is to provide power on demand. Load circuit may not require power all the time, hence it is essential for interface circuitry to provide power on demand to the load circuit. To achieve this interface circuitry must charge the energy storage devices like capacitors or rechargeable batteries acting as buffers. This would enable the load circuit to take power from the buffer as per requirement independently. During intervals of no load activity, these buffers can be recharged. In general EHC, can be broadly classified under two categories. Firstly, being the basic circuit methodologies using impedance matching techniques after AC to DC conversion and the second being synchronous techniques to capture power using maximum power tracking scheme. It is essential for EHC to consume low power. Researchers have been focusing on decreasing the voltage drop of diodes used in rectifier circuits. The EHC developed can be used for all types of vibration based energy harvesting methods i.e. capacitive, inductive and piezoelectric. Hence, these methods are mostly based on load impedance matching which is independent of method of harvesting. The second category is concerned with the concept of extracting optimal power from the harvester either by using MPPT scheme or using non-linear techniques which utilize the capacitive characteristic of piezoelectric layer. Circuits in second category are much more complex and difficult to implement than those in first category. Some circuits developed as synchronous technique may require external power supply but most of these are based on custom designs capable of standalone operations.

The main objective is to have a low power circuitry that can transfer as much power as possible to the output. Le et al. [7] compared several half and full wave active and passive rectifiers. Active rectifiers have higher peak efficiency as compared to passive (0.86–0.66) but require quiescent current to operate. A power management system consisting of active full wave rectifier with power conditioning circuit having voltage buffer capacitor set at 1.2–1.5 V has been presented by Colmer et al. [8]. A low voltage active rectifier was also implemented by Peter et al. [9]. They utilized bulk input comparators, bringing input voltage down to 0.38 V. Maurth et al. [10] suggested a common-gate transistor implementation in combination with MPPT scheme using transistors working at voltages. MPPT technique have lower efficiency (0.48) due to high losses in integrated capacitance. Dallago et al. [11] used active voltage doubler having an efficiency of 0.82 and a current maintained at 500 nA. Cheng et al. [12] also utilized a voltage doubler and obtained positive and negative voltages. Active voltage doubler show high efficiency of 0.84 and have capability to tolerate low input voltages up-to 5 mV. They can also be implemented discretely. Voltage doubler have shown adequate applications with irregular input voltages but still require external voltage supply to power comparator. This limits their implementation in standalone energy harvesting system applications.

The synchronous circuit methodologies, mostly work on varying harvester open circuit generated voltages, by adjusting the duty cycle for DC-DC conversion to maintain maximum power. Although these harvesters are designed for piezoelectric energy harvesting but can be used for other vibration based energy harvesting. Non-linear energy extraction by actively actuating the piezoelectric harvester by switching the harvester at different time instants is another way of harvesting under synchronous circuit methodology. This switching can be achieved with or without inductors. The techniques implementing these methodologies are Synchronized Switch Harvesting on Inductor (SSHI) and Synchronous Electric Charge Extraction (SECE) [13]. Ottman et al.[6,14] used MPPT scheme on piezoelectric harvester by implementing DC-DC down conversion. A discrete implementation of harvester using 30 mW of extracted power was also implemented by them. This circuit has efficiency of 0.7 for voltage level higher than 50 V. The goal in SSHI and SECE is to tackle the timing for switching control signals from the piezoelectric voltage signals. The stand-alone implementation of SSHI is much more complex than SECE. Theoretical predicted power for self-powered SSHI is higher than practical implementation due to power consumed by control circuitry. It only over-rides first category techniques if excitation level are high [15]. Ramadass et al. [16] developed a practical self-powered SSHI technique having efficiency of 0.87 and generating 60 μW power. The drawback of the circuit is negative external voltage of 2 V. The time of switching was also not accurate, hence it was difficult to implement in real world applications. SECE technique has utilized a buffer capacitor pre-charged to certain voltage level [17]. The chip is self-powered having an efficiency of 0.7 and capable to capture a wide range of excitation. However, the generated piezoelectric voltage is at lower voltage level, hence, avoiding its usage in practical applications. Compared to discrete implementation of SSHI [15] a discrete implementation of SECE [18] requires a high power level (mW) to operate and provide acceptable efficiencies. Active rectifiers give more efficiency than passive rectifiers as demonstrated by Sun et al. [19] by modifying the circuit of Ramdass et al. [16], but the existing timing problem was not rectified. Kwon and Rincon [20,21] connected the harvester with DC-DC converter directly. Controlling switches helped in directing the energy to the buffer capacitor, similar to those used in SECE. As there were no rectifiers a voltage level of 0.35 V was achieved, which was only appropriate for low voltage and power level applications. But this process also required an external -2 V voltage signal, hence the system had practically limited applications. Buffer capacitors used in synchronous techniques have to be pre-charged for optimum power output. In real world applications, with no continuous excitation, the circuit would fail to provide the minimum required voltage level. An equivalent mechanical and electrical equivalent of a broadband seesaw energy harvester is described which helps in describing the behaviour of the energy harvester with basic and synchronous circuit methodologies [22].

Section snippets

Mechanical equivalent model

A broadband piezoelectric energy harvester based on a seesaw mechanism shown in Fig. 1a can be represented as a mass spring damper system connected on a pulley as shown in Fig. 1b [22,23]. The resonance frequency for a seesaw is similar to that for a cantilever system:K1δ1=mg=WK2δ2=mgWhere, δ1 and δ2 is the displacement due to mass. System is displaced y(t) from static equilibrium with a force F:F=2ma=2mÿApplying Newtons second law:2mÿ+K1(y+δ1)+K2(y+δ2)2mg=0Using eq. (1) and eq. (2), we get:2mÿ

Electrical equivalent model

Electrical analogy is used to determine the equivalent circuit of the energy harvester. Mechanical force is represented as voltage, while electric current acts as mechanical velocity [24,25]. Electrical circuit parameter can be determined in terms of energy harvester design parameters.

Energy harvesting circuit

Interface circuits or energy harvesting circuits (ECH) form a connecting link between the seesaw structure and the load circuit like WSN and IMD's. The main function of ECH is to convert extracted power of piezoelectric seesaw design to useable electrical power which can be both stored and utilized when required. A number of energy harvesting circuitry have been designed in literature starting with basic silicon based impedance matching to synchronous techniques using inductors. Seesaw

Conclusion

A mechanical and electrical equivalent model of a broadband energy harvester are developed. First two natural frequency from the model differ by 1.91% and 2.95% respectively. The damped natural frequency from equivalent model differs with the finite element model damped natural frequencies by 1.23% and 3.17% respectively. The electrical equivalent model is interfaced with different energy harvesting circuitry. Among the basic circuit methodologies, the schottky based diode rectifier generates a

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

References (30)

  • C. Peters et al.

    A sub-500 mv highly efficient active rectifier for energy harvesting applications

    IEEE Trans. Circuits Syst. I: Reg. Pap.

    (2011)
  • D. Maurath et al.

    Efficient energy harvesting with electromagnetic energy transducers using active low-voltage rectification and maximum power point tracking

    IEEE J. Solid State Circ.

    (2012)
  • E. Dallago et al.

    Self-supplied integrable active high-efficiency ac-dc converter for piezoelectric energy scavenging systems

  • S. Cheng et al.

    An active voltage doubling ac/dc converter for low-voltage energy harvesting applications

    IEEE Trans. Power Electron.

    (2010)
  • E. Lefeuvre et al.

    A comparison between several approaches of piezoelectric energy harvesting

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