To reduce the size and weight of the magnetic energy harvester (MEH), the magnetic core should be designed to work in the maximum power region, i.e., in the saturated region. However, the conventional analysis model of the MEH, which ignores the phase difference between the primary and secondary currents, is only suitable for the unsaturated region. When the core is in the saturated region, the results of the numerical calculation severely deviate from the experimental observations due to the non-negligible phase difference. To address this vital problem, this article establishes an excitation current model (ECM) to calculate the phase difference caused by the magnetizing inductance. An accurate model of the MEH is presented based on the ECM in this article, which can calculate the harvesting power of the MEH in the saturated region. Besides, a strategy for finding the maximum power point is proposed, which can be used for the designing of the MEH. Finally, an experimental prototype is constructed to verify the effectiveness of the proposed analysis model and the design method of the MEH. The experimental results show that the proposed analysis model can maintain high accuracy when the magnetic core enters the saturated region, and the MEH designed by the proposed model can reach the expected power with a compact size. Compared with the theoretical value, the output voltage deviation of the MEH is only 0.4%, and the output power deviation is only 0.8%. 

An Accurate Model of Magnetic Energy Harvester in the Saturated Region for Harvesting Maximum Power: Analysis, Design, and Experimental Verification

Electromagnetic energy harvesting extracts energy from magnetic fields and can provide power to sensors, monitoring nodes, cyber-physical systems and control elements without additional battery and external power source and wiring. This article presents a novel ac-driven electromagnetic energy harvester based on periodically saturating, cascaded magnetics, consisting of a clampable magnetic core and an ungapped high permeability core. The high permeability core guarantees the maximum energy extraction, whereas the clampable core enables the nonintrusive installation of the energy harvester for more pervasive applications. This article first builds a comprehensive mathematical model based on this saturating cascaded magnetic structure, considering the reachability of an individual saturation flux density of the two magnetic cores. This model resolves the new challenges introduced by the cascaded magnetics with respect to a traditional single-core case, providing the accurate calculation of the lengths of the relevant time windows for harvesting and the amount of the harvested power. Our mathematical model is verified against simulation and experiment, showing excellent agreement among them with the maximum discrepancy of less than 6%. This article also reveals that the maximum power extraction occurs when the ungapped core operates in its slightly saturated state and that the harvested power increases with a higher primary current as well as a higher line frequency. 

Mathematical Modeling and Validation of Saturating and Clampable Cascaded Magnetics for Magnetic Energy Harvesting

Recently, maintenance applications around power lines have been actively studied. These applications usually supply power through magnetic energy harvesting(MEH) to devices around the power line. A major challenge for practical MEH is to overcome magnetic saturation, which can cause degradation of power density under a wide current range in the power line. In this paper, we propose a design methodology to harvest maximized output power by considering the saturation effect. To consider magnetic saturation, the output power model and the saturable magnetizing inductance model based on magnetizing current were comprehensively analyzed. Additionally, the critical point of saturation for the maximum harvested power was analyzed by considering different primary side current conditions. With the proposed design methodology, the accuracy and efficiency of the output model were verified with experimental results compared to the conventional model. To consider the real environment, a 150 kW class of AC resistor load bank was implemented to control the primary current from 0 to 100 A with power frequency of 60 Hz. Experimental results show that the proposed method can harvest an average power of 14.32 W on 70 A power line, which is an increase of 39.8 % compared with the conventional design method.

/pdf/the-magnetic-energy-harvester-with-improved-power-density-4uan96aku3.pdf

The Magnetic Energy Harvester With Improved Power Density Using Saturable Magnetizing Inductance Model for Maintenance Applications Near High Voltage Power Line

Magnetic field energy harvesters (MFEHs) from current-carrying structures/conductors are usually modelled as decoupled electromagnetic and electrical systems. The current-carrying structures may affect the performance of MFEH through the generation of the eddy current and the alteration of the magnetic reluctance. Moreover, the load circuit affects the current generated in the coil and therefore the flux density and eddy current generated. The effects of the current-carrying structure and the load circuit cannot be fully described by the decoupled models. This work develops a finite element model (FEM) that fully couples the electromagnetic and electrical systems by simulating both the magnetic field and eddy current distribution of an MFEH connected to an electrical circuit. The FEM first simulates the coil inductance and resistance of a magnetic field energy harvester (MFEH) placed close to a current-carrying structure exemplified by a rail track. The FEM then simulates the outputs of the MFEH connected to an electrical circuit consisting of a compensating capacitor and optimal load resistor determined by the first step. An MFEH was fabricated and tested under a section of current-carrying rail track. Both experiment and simulation show an increase of both coil resistance and inductance when the MFEH is placed close to the rail track. The good agreement between experimental and simulation results validates that the FEM can predict the full-matrix performances of the MFEH, including the coil parameters, power output and magnetic flux density under the influence of the current-carrying structure and the load circuit. Simulation results reveal that in addition to the permeability of the magnetic core, the electrical conductivity and magnetic permeability of the current-carrying structure considerably affect the performance of the MFEH, which cannot be predicted by decoupled models.

/pdf/magnetic-field-energy-harvesting-from-current-carrying-za31vkeudm.pdf

Magnetic Field Energy Harvesting From Current-Carrying Structures: Electromagnetic-Circuit Coupled Model, Validation and Application

Electromagnetic energy harvesting extracts energy from magnetic fields and can provide power to sensors, monitoring nodes, cyber-physical systems and control elements without additional battery and external power source and wiring. This article presents a novel ac-driven electromagnetic energy harvester based on periodically saturating, cascaded magnetics, consisting of a clampable magnetic core and an ungapped high permeability core. The high permeability core guarantees the maximum energy extraction, whereas the clampable core enables the nonintrusive installation of the energy harvester for more pervasive applications. This article first builds a comprehensive mathematical model based on this saturating cascaded magnetic structure, considering the reachability of an individual saturation flux density of the two magnetic cores. This model resolves the new challenges introduced by the cascaded magnetics with respect to a traditional single-core case, providing the accurate calculation of the lengths of the relevant time windows for harvesting and the amount of the harvested power. Our mathematical model is verified against simulation and experiment, showing excellent agreement among them with the maximum discrepancy of less than 6%. This article also reveals that the maximum power extraction occurs when the ungapped core operates in its slightly saturated state and that the harvested power increases with a higher primary current as well as a higher line frequency.

This article presents a novel method to improve energy scavenging from ac power lines under magnetic saturation conditions. The extracted power level of a conventional magnetic energy harvester is limited by the maximum flux density of the magnetic core. When a magnetic core is clamped on ac power lines, the flux density in the core is proportional to the magnetic field strength around the power line. Choosing a high-permeability core has the advantage of harvesting more energy for a given primary current. The flux density in such a core could reach its maximum value when the magnetic field increases. In this scenario, very little energy can be harvested since flux density variation in the core is small. Here we introduce an artificial magnetic field by adding an additional control coil to manipulate the magnetic field of power lines. A power management circuit is employed to store the energy harvested by the control coil and feed it back to the harvester to generate a counter magnetic field. As a result, the core will not be easily driven into the saturation region; hence, more energy can be harvested. Experimental results show that the proposed energy harvester can harvest an average power of 283 mW on a 50 Hz 10 Arms power line (2.34 mW/cm3/Arms), which is increased by 45% compared with the device without the control coil. This new method could provide a promising solution for smart grid monitoring and other industrial sensing applications.

Improving Current Transformer-Based Energy Extraction From AC Power Lines by Manipulating Magnetic Field

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Improving Current Transformer-Based Energy Extraction From AC Power Lines by Manipulating Magnetic Field