High efficiency power management and charge boosting strategy for a triboelectric nanogenerator

Highlights

• A power management strategy for TENG is proposed and optimized.

• The proposed strategy exhibited universality for different modes TENG.

• Over 2600 times improvement in stored energy than standard circuit was achieved.

• More than 72% AC to DC power conversion efficiency was obtained.

Abstract

Triboelectric nanogenerator (TENG) has emerging as an important approach for energy harvesting. However, low charging efficiency as well as low power conversion efficiency have restricted its practical application for powering traditional electronics. Here we propose a power management (PM) strategy by extracting maximum energy from TENG and transferring the energy to storage unit employing optimized Inductor-Capacitor (LC) oscillating. PM module using this strategy designed shown universality and high-efficiency for different modes TENG. Over 2600 times improvement in stored energy than standard circuit was achieved, and more than 72% alternating current (AC) to direct current (DC) power transfer efficiency was obtained for different modes TENGs. The regulated and managed output shown the ability as a power source for the continuously working of commercial electronics, such as LED bulbs, calculators and pedometers. Our work provides an effective, universal and practical strategy for efficiently power management of TENG from theoretical derivation and experimental validation, which is promising to serve as a standard PM module for TENG as well as to guide its design.

Introduction

The tremendous development in wearable electronics [1], wireless sensor nodes [2] and implantable electronic devices [3] has raised urgent and challenging requirements for developing sustainable and stable power source. Though batteries or capacitors [4], [5], [6], as the traditional energy storage unit, are the mostly used power source for these devices, the limited capacity and large volume make them have to be frequently charged or replaced thus becoming more and more unpractical and unfavorable. One of the most promising methods to overcome such difficulties is the employment of energy-harvesting technologies from the ambient environment or human motion for sustainable operation [7], [8]. To date, the most commonly adopted mechanisms are electromagnetic induction [9], electrostatic induction [10] and piezoelectric effect [11], while different mechanisms show particular advantages to specific applications. Recently, the emerging energy conversion method, called triboelectric nanogenerator (TENG), is rising as a potential technology, which has the advantages of high output, simple design, and low cost [12], [13], [14], [15], [16]. Various mechanical energy sources from water wave [17], wind [18], human motions [19] and even heartbeat [20] have been successfully converted to electric energy by TENG.

However, working as a capacitive-behavior energy harvester, TENG has a high inherent impedance of typically in several Mega ohms’ level with high voltage of typically hundreds of volts and low output current (i.e. in ~μA level) [13], [21]. These characteristics lead to low energy transfer efficiency for either powering electronics [22] or charging a battery/capacitor directly, since usually they have relatively low impedance. A proper power management strategy is thereby required for TENG towards powering electronics and charging energy storage unit (i.e. battery or capacitor). From the features of output waveform, TENG includes two basic modes that are contact-separation mode (CS mode, including classical contact-separation mode [23] and single-electrode mode [24]) with low-frequency randomly-pulsed waveform and lateral-sliding mode (LS mode, including classical lateral sliding mode [25] and free-standing mode [26]) with uniform triangular waveform [27]. For the LS mode, a transformer with matched frequency has a satisfied performance [28], [29] Unfortunately, a huge power loss would occur once the working frequency changes, while the frequency of mechanical energy typically is very low and varies in a very wide range, which makes the transformer even incapable for the LS-mode TENG. As for the CS mode, the randomly-pulsed waveform is much harder to manage [30]. Consequently, there is an urgent requirement for a universal applicable power-management strategy for both modes TENG. Recently, as an alternative method, Niu et al. proposed a power management system for TENG using a matched capacitor as a bridge between TENG and management circuit, which shown good performance for CS-mode TENG [31]. But at least 25% energy loss would produce between energy transfer from TENG to the bridge capacitor, and this capacitor has to be optimized for TENGs with different parameters, making it inefficient and unpractical.

In this work, we aim at solving the mentioned challenge by designing and proposing an efficient, universal and practical power management strategy (PMS) for TENG. To achieve the goal, a two-steps strategy is adopted: (1) Maximizing the output energy of a TENG by using built-up voltage V-total transferred charges Q plot applicable to both-modes TENG; (2) Maximizing the transferred energy from TENG to energy storage unit by employing the LC oscillating model. Afterwards, a power management module (PMM) was designed and assembled under the guidance of this strategy to manage and regulate the electric outputs from CS-TENG and LS-TENG. Using this module, both huge improvements were achieved for the stored charges and energy in energy storage unit. Meanwhile, more than 70% power conversion efficiencies were obtained for both modes TENG. The regulated and managed direct current (DC) power can provide a continuously power source for driving conventional electronics, such as LED bulbs, calculators, pedometers. Our work proposed a strategy for designing universal and efficient PMM for TENG, which would set the foundation for the further applications and industrialization of the TENGs.