A Low-Power Photovoltaic Maximum Power Point Tracking Circuit for WSNs

Abstract:

Currently, most wireless sensor networks (WSNs) are powered by batteries. When energy stored in batteries is exhausted, the life of the WSNs goes to the end. The concept of energy harvesting provides a practical solution to the problem of the energy limitation. In this article, the feasibility and performance of a simple and low-cost analog solar energy harvesting circuit with the function of maximum power point tracking (MPPT) are investigated. The technique provided is based on the approximately linear relationship between the maximum power point (MPP) voltage and the open-circuit voltage of a solar panel under different irradiation levels. Several experiments have been carried out regarding the accuracy and efficiency of MPPT as well as the working process of the circuit. Results show that the maximum power point with different loads can be effectively tracked by the self-powered MPPT circuit, and in the meantime, a stable output voltage can be generated. The efficiency of energy conversion is guaranteed by a commercial off-the-shelf DC-DC chip. The detailed description of the circuit design and the comprehensive analysis of the circuit performance will provide a useful guide for the future applications.

• Periodical: Key Engineering Materials (Volumes 562-565)
• Pages: 1045-1051
• DOI: https://doi.org/10.4028/www.scientific.net/KEM.562-565.1045
• Online since: July 2013
• Authors: Gao Fei Zhang, Rui Ma, Zheng You, Zi Chen Zhang
• Keywords: Energy Harvesting, Low-Power, MPPT, Photovoltaic (PV)

References

[13] adopted the Hill Climbing MPPT method, while the work in [14] was based on the modeling of the desired optimal frequency of the charge pump to track MPP. The two systems were designed for applications with extremely low power (μW) and the efficiency needed to be improved. Although a noticeable number of related works have been reported, the contradiction among the size, the power overhead and the performance of the MPPT circuit still exists. In this paper, we focus on the development of a solar energy harvesting circuit with low power consumption for wireless sensor nodes and examine the performance from several different aspects. The structure of the paper is as follows. Firstly, the general architecture of energy harvesting systems is introduced. Secondly, several potential maximum power point tracking (MPPT) methods for low-power applications are discussed. Then, detailed design guidelines for the proposed MPPT circuit are described and corresponding experimental results are presented and analyzed. Working Principles for MPPT and Summary of Several MPPT Methods A photovoltaic (PV) cell is in nature a p-n junction with electrical contacts. The typical output characteristics of a PV cell are shown in Fig. 1 [9]. The dash dot line denotes the relationship between the current and the voltage, while the solid line denotes the relationship between the output power and the voltage. A Maximum Power Point (MPP) exists, which is corresponding to a specific VMPP and IMPP. The MPP varies with the incident light intensity and the ambient temperature [[] Villalva M.G., Gazoli J.R., Filho. E.R, Comprehensive Approach to Modeling and Simulation of Photovoltaic Arrays, IEEE Trans. on Power Electro., 24, 5 (2009) 1198-1208. ]. A MPPT circuit is needed to ensure that the maximum power is extracted at any given time. Essentially, MPPT is a process of impedance matching. The input impedance of the interface circuit is adjusted by the control unit to match the impedance of the energy harvester. The general architecture of MPPT is shown in Fig. 2. It also applies to other energy harvesting systems [[] Paul D. M., Tzern T. Toh, Power Management Electronics, in: Stephen Beeby, Neil White (Ed.), Energy Harvesting for Autonomous Systems, Artech House, MA, 2010, pp.159-162