A unified N-SECE strategy for highly coupled piezoelectric energy scavengers

Abstract

This paper proposes a novel vibration energy harvesting strategy based on an extension of the Synchronous Electric Charge Extraction (SECE) approach, enabling both the maximization of the harvested power and a consequent bandwidth enlargement in the case of highly coupled/lightly damped piezoelectric energy harvesters. The proposed strategy relies on the tuning of the frequency of the energy extraction events, which is either times greater than the vibration frequency (Multiple SECE case, > 1) or 1/ times smaller (Regenerative SECE, < 1). We first prove analytically than increasing or decreasing both lead to a damping reduction. While has no impact on the system's resonance frequency in the Regenerative case ( < 1), we show that this resonant frequency becomes a function of in the Multiple SECE case ( > 1). Experimental results on a highly coupled/lowly damped piezoelectric harvester ( ( = 0.44, / = 20) demonstrates the potential of this strategy, leading to 257% harvested power improvement compared to SECE ( = 1). and the possibility to tune the resonant frequency on a range as large as 35% of the short-circuit resonant frequency of the harvester.Thanks to recent progresses in the mechanical design and the use of highly coupled piezoelectric materials, e.g. single crystal, piezoelectric harvesters may now exhibit much higher electromechanical coupling associated with low mechanical damping. For this particular kind of PEH, SECE strategy is not well adapted since it overdamps the mechanical resonator, leading to low displacements and harvested energy [7,8].Some research has been conducted to investigate new efficient strategies that could be used for highly coupled PEH, in order to optimize the damping induced by the electrical interface [8][9][10]. Indeed, in [8], we proposed to wait a certain number of semi-period before harvesting the accumulated energy in order to reduce the damping induced by the electrical interface. In [9] and [10], the damping is reduced thanks to the control of the number of electrical charges extracted from the piezoelectric material. Those two approaches, even though they allowed to reduce the damping, did not induce any frequency tuning effect which could although be used to enlarge the harvesting bandwidth.Electrically-based frequency tuning strategies have also been proposed in the literature [11][12][13][14][15]. In [11], a capacitive bank combined with a variable resistive load emulated thanks to a DC/DC converter allows to tune the phase of the piezoelectric voltage while optimizing the damping induced by the interface. However, this approach requires an important number of passive components. In order to overcome this issue, in [12], we proposed to replace the capacitive bank with a short-circuit control which emulates a tunable capacitive behavior.[13] and [14-15] proposed a new frequency tuning approach based on the combination of the tunable SECE explained in [9] and [10] with a phase tuning. This approach is theoretically very efficient, however it introduces two tuning para...

Maximum power point of piezoelectric energy harvesters: a review of optimality condition for electrical tuning

“…Examples of waveforms at the maximum power point are depicted in Figure 15. If > 1, one can simplify the expressions given in [50] into (37).…”

“…When required, their meaning is given in the following sections. [50] Synchronized Electric Charge Extraction with N extraction events by period PSSECE [25] Phase-shifted Synchronized Electric Charge Extraction SECPE [41] Synchronized Electric Charge Partial Extraction Tunable SECE [24] Tunable Synchronized Electric Charge Extraction Tunable USECE [51] Tunable Unipolar Synchronized Electric Charge Extraction USECE [38] Unipolar SECE In section 2, we start by an analysis to explain the hierarchy proposed in Figure 1. In section 3, we summarize the full mathematical background that is required to develop efficient MPPT strategies, following a similar approach as Halvorsen et al [8] or Hosseinloo et al [9].…”

Frequency tuning of piezoelectric energy harvesters thanks to a short-circuit synchronous electric charge extraction

“…The proposed SC-SECE strategy's aim is to overcome the standard SECE weaknesses thanks to the introduction of a tunable short-circuit phase. This short-circuit phase allows to limit the amount of energy converted from the mechanical resonator to the piezoelectric material, hence avoiding any overdamping effect when F W F > /4 [22]. First, let's define " ∈ [0, ] as the angle at which the short-circuit phase starts.…”

“…It has been proven in the last decade that such nonlinear harvester can drastically enhance the harvesting bandwidth compared to linear PEHs [10]. Recently, new electrically-based approaches have been investigated such as the FTSECE [17] and the N-SECE [22]. In this section, we compare the experimental results obtained with those different electrical and mechanical approaches with the proposed SC-SECE approach.…”

“…Thereafter, B. Zhao et al proposed to combine the idea of adding a tunable switching delay with the synchronized multiple bias-flip (SMBF) concept [20], which consists in optimizing the charges inversion processes thanks to multiple voltage-changing steps [21]. In 2017, our group developed a novel approach to electrically tune the resonant frequency of piezoelectric energy scavengers and enlarge their harvesting bandwidth: the N-SECE, which consists in harvesting the energy at a different frequency than the vibration's frequency [22]. Recently, we proposed another concept, the SC-SECE, which relies on a tunable short-circuit phase [23].…”