An advanced metering and monitoring system based on autonomous, ubiquitous and maintenance-free wireless sensor networks is of great significance to the smart grid. However, the power supply for sensor nodes (especially those installed on high-voltage side) remains one of the most challenging issues. To date, miniaturized, reliable, low-cost and flexible designs catering the massive application of self-powered sensor nodes in the smart grid are still limited. This paper presents a nonintrusive design of power supply to support the sensor network applied in the smart grid. Using a cantilever-structured magnetoelectric (ME) composite, the energy harvester is able to scavenge energy from the power-frequency (50 Hz) magnetic field distributed around the transmission line. Design considerations for this specific type of scavenger have been discussed, and optimized energy harvester prototypes have been fabricated, which are further tested on a power line platform. Experimental results show that the single-cell and double-cell energy harvesters are capable of producing 0.62 mW and 1.12 mW at 10 A, respectively, while corresponding power outputs are enhanced to 4.11 mW and 9.40 mW at 40 A. The good energy harvesting ability of this particular ME composite indicates its great potential to make a nonintrusive, miniaturized, flexible and cost-effective power supply, which possesses great application prospects in the smart grid.

A Nonintrusive Power Supply Design for Self-Powered Sensor Networks in the Smart Grid by Scavenging Energy From AC Power Line

Conventional AC power meters perform at least two distinct functions: power conversion, to supply the meter itself, and energy metering, to measure the load consumption. This paper presents Monjolo, a new energy-metering architecture that combines these two functions to yield a new design point in the metering space. The key insight underlying this work is that the output of a current transformer -- nominally used to measure a load current -- can be harvested and used to intermittently power a wireless sensor node. The hypothesis is that the node's activation frequency increases monotonically with the primary load's draw, making it possible to estimate load power from the interval between activations, assuming the node consumes a fixed energy quanta during each activation. This paper explores this thesis by designing, implementing, and evaluating the Monjolo metering architecture. The results demonstrate that it is possible to build a meter that draws zero-power under zero-load conditions, offers high accuracy for near-unity power factor loads, works with non-unity power factor loads in combination with a whole-house meter, wirelessly reports readings to a data aggregator, is resilient to communication failures, and is parsimonious with the radio channel, even under heavy loads. Monjolo eliminates the high-voltage AC-DC power supply and AC metering circuitry present in earlier designs, enabling a smaller, simpler, safer, and lower-cost design point that supports novel deployment scenarios like non-intrusive circuit-level metering.

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Monjolo: an energy-harvesting energy meter architecture

This paper presents a magnetic–piezoelectric smart material-structure using a novel magnetic-force-interaction approach to optimize the sensitivity of conventional piezoelectric current sensing technologies. The smart material-structure comprises a CuBe-alloy cantilever beam, a piezoelectric PZT sheet clamped to the fixed end of the beam, and an NdFeB permanent magnet mounted on the free end of the beam. When the smart material-structure is placed close to an AC conductor, the magnet on the beam of the smart structure experiences an alternating magnetic attractive and repulsive force produced by the conductor. Thus, the beam vibrates and subsequently generates a strain in the PZT sheet. The strain produces a voltage output because of the piezoelectric effect. The magnetic force interaction is specifically enhanced through the optimization approach (i.e., achieved by using SQUID and machining method to reorient the magnetization to different directions to maximize the magnetic force interaction). After optimizing, the beam’s vibration amplitude is significantly enlarged and, consequently, the voltage output is substantially increased. The experimental results indicated that the smart material-structure optimized by the proposed approach produced a voltage output of 4.01 Vrms with a sensitivity of 501 m Vrms/A when it was placed close to a conductor with a current of 8 A at 60 Hz. The optimized voltage output and sensitivity of the proposed smart structure were approximately 316 % higher than those (1.27 Vrms with 159 m Vrms/A) of representative piezoelectric-based current sensing technologies presented in other studies. These improvements can significantly enable the development of more self-powered wireless current sensing applications in the future.

A magnetic–piezoelectric smart material-structure utilizing magnetic force interaction to optimize the sensitivity of current sensing

This paper describes a novel method for scavenging energy for electric power systems sensing applications by the use of permanent magnets that couple to the magnetic field generated by an alternating current flowing through a nearby conductor. The resulting mechanical energy is converted to electrical energy using piezoelectric transduction. This electromechanical AC energy scavenging method is an attractive alternative to coil-based AC energy scavengers in cases where the scavengers cannot encircle the conductor. In such cases, the electromechanical AC energy scavenger has the potential to produce significantly more power than comparable coil-based methods. The components of an electromechanical AC energy scavenger are described in detail, and experimental data from prototypes that are fabricated and tested in our laboratory are shown. The 20 cm3 prototypes generated up to 2.7 mW of power each from 20 A of nearby current. Theoretical power densities of electromechanical AC energy scavengers are compared to the power densities of representative coil-based methods, showing that in some cases the electromechanical AC scavengers can generate an order-of-magnitude more power than coil-based AC scavengers. This paper demonstrates that electromechanical AC energy scavenging is a potential method for powering small size low cost stick-on wireless sensor networks.

Electromechanical Energy Scavenging From Current-Carrying Conductors

Spatial localization (colocation) of nodes in wireless sensor networks (WSNs) is an active area of research, with many applications in sensing from distributed systems, such as microaerial vehicles, smart dust sensors, and mobile robotics. This paper provides a comprehensive review and comparison of recent implementations (commercial and academic) of physical measurement techniques used in sensor localization, and of the localization algorithms that use these measurement techniques. Physical methods for measuring distances and angles between WSN nodes are reviewed, followed by a comprehensive comparison of localization accuracy, applicable ranges, node dimensions, and power consumption of the different implementations. A summary of advantages and disadvantages of each measurement technique is provided, along with a comparison of colocalization methods in WSNs across multiple algorithms and distance ranges. A discussion of possible improvements to accuracy, range, and power consumption of selected self-localization methods is included in the concluding discussion. Although the preferred implementation depends on the application, required accuracy, and range, passive optical triangulation is reported as the most energy efficient localization method for low-cost/low-power miniature sensor nodes. It is capable of providing micrometer-level resolution, however, the applicable range (internode distance) is limited to single centimeters.

Review and Comparison of Spatial Localization Methods for Low-Power Wireless Sensor Networks

We present a stick-on wireless electric current monitoring system that is designed to measure and report electricity usage from circuit breaker panels in residential and commercial settings. This monitoring system uses piezoelectromagnetic (PEM) AC current sensors to couple to the magnetic fields produced by the current-carrying conductors. The PEM sensors can be easily attached to the surfaces of common circuit breaker panels, facilitating the installation by non-technical individuals. This paper describes the sensing principles and provides an analytical model of the PEM AC sensors. It also presents the architecture for a wireless current monitoring system and describes its implementation for sub-metering a circuit breaker panel in a building at the University of California, Berkeley. The theory and experimental validation of a signal deconvolution and calibration method, essential for extracting signals from cross-coupled magnetic fields, are also included.

Stick-On Piezoelectromagnetic AC Current Monitoring of Circuit Breaker Panels

We describe an electric current monitoring system that can be used to non-intrusively measure individual loads on a circuit breaker panel in residential and commercial settings. The proximity-based piezoelectromagnetic (PEM) sensor uses permanent magnets to couple to the electric current in the circuit to be measured, and hence requires no galvanic connection to the circuits. This paper describes the theory for sensing current in a circuit breaker panel using PEM sensors, as well as the implementation of an integrated sensing system that stores the measured results in an on-line repository, which can be queried remotely using the world-wide web. We show the experimental results from implementing our sensors to measure loads on a circuit breaker panel in a campus building at UC Berkeley.

Integrated centralized electric current monitoring system using wirelessly enabled non-intrusive AC current sensors

Abstract A design methodology is proposed for electronic systems powered by energy harvesting. The methodology first considers the operating environment. It then evaluates the supply-side (the attributes of the harvester), the demand-side (the engineering application or load which receives and uses the converted power), and the power conditioning needed between supply and demand. A test case is presented in which the vibrations of an electromagnetic device are harvested, converted, and used to power a wireless sensor node. Such a node is being used for the condition based monitoring of manufacturing equipment.

Qiliang Xu

Papers

Electromechanical Energy Scavenging From Current-Carrying Conductors

Stick-On Piezoelectromagnetic AC Current Monitoring of Circuit Breaker Panels

Integrated centralized electric current monitoring system using wirelessly enabled non-intrusive AC current sensors

A Design Methodology for Energy Harvesting: With a Case Study on the Structured Development of a System to Power a Condition Monitoring Unit

Multi-objective optimization of a solar-driven trigeneration system considering power-to-heat storage and carbon tax