Jinyeong Moon

Analysis Model for Magnetic Energy Harvesters

Energy harvesting offers an important design option for creating sensing and control elements without a requirement for custom wiring or batteries. An exciting possibility creates a “self-powered” sensor node with an integrated energy harvester that can extract power from the magnetic fields around a power line to a load, in the manner of a current transformer. However, this “current transformer” provides not just current sensing, but also power for a sensor package, all without ohmic contact. This paper provides a technique for design optimization for maximizing power harvest, revealing a critical result: For any given core in any particular application, power harvest is maximized when the core is permitted to saturate at an opportune time in the line cycle. Circuits for optimizing this power transfer window and experimental results supporting the analysis are presented in this paper.

VAMPIRE: A magnetically self-powered sensor node capable of wireless transmission

This paper presents a power electronic topology for providing a vibration monitor with in-situ magnetic energy harvesting. The energy harvesting circuit uses low voltage MOSFETs and a nano-crystalline magnetic core to extract energy from an operating electrical load like a motor. This topology can be used to power sensors and wireless circuitry for diagnostics with no need for battery or special power wiring. Harvesting energy from a 90 W-60 Hz load, a Vibration Assessment Monitoring Point with Integrated Recovery of Energy (VAMPIRE) produces 7.5mW with the core volume of 2.9 cm3, and powers up a 6.5mW electrical monitor that provides sampling, signal processing, and periodic wireless data transmission through an RF channel. The system samples the vibration data at 125 Hz, and enables wireless burst transfer every 160 ms.

Power Electronic Circuits for Magnetic Energy Harvesters

Compared to many other energy harvesting schemes, harvesting energy from magnetic fields offers potential advantages for energy extraction and sensing. A magnetic energy harvester provides great flexibility for sensors and monitoring applications for condition-based monitoring of electromagnetic actuators, including vibration and thermal monitoring. A core must be managed or operated with carefully timed saturation to ensure maximum power extraction, a complex problem given the nonlinear saturation characteristics of a magnetic core [1]. This paper presents a simulator-friendly “circuit model” for a magnetic core, and uses this model to design and demonstrate several power electronic circuit solutions for harvesting energy. The circuit model has an excellent accuracy to represent the core regardless of the level of saturation. The design techniques to enhance power harvest are proposed, and verified through simulation and experiments, substantially boosting the amount of power harvest.

Enhancement on energy extraction from magnetic energy harvesters

This paper presents a method for enhancing performance of a magnetic energy harvester. The harvester operates with a magnetically saturating core with high magnetic permeability. If the core saturates, the effective magnetizing inductance becomes small, and little power can be harvested from the core. Energy is harvested very efficiently during an operating cycle when the core is not saturated, a time period we call the “transfer window.” It can be shown that the location and the length of a transfer window are independent of each other. Based on this property, the transfer window alignment (TWA) method is introduced for maximizing power harvest. The TWA method manipulates the location of the time window, and harvests a greater amount of power compared to passive rectification. The principle of the TWA method reveals that deeper core saturation with higher voltage stress leads to a higher level of energy extraction. The analysis of the TWA method is presented, and verified with simulation and experiments. A detailed control sequence for actual implementation is presented. The TWA method poses little burden to hardware complexity.

Power flow control and regulation circuits for magnetic energy harvesters

This paper presents control schemes for power flow and voltage regulation for magnetic energy harvesters, using unique operating properties set by a current-driven harvester core. An active rectification circuit and a voltage regulation circuit are introduced based on assumptions of a supercapacitor and a MHz microcontroller that is already accompanied in the sensor node. Detailed analyses on circuits, control methods, and state transitions are provided from an implementational viewpoint. In the experiment, fine regulation of 48mV is achieved at the nominal voltage of 4.5 V with increased power dissipation in μW range, and the active rectification method boosts power harvest by more than 10% compared to a conventional full-bridge diode rectifier. An overall architecture of the power processing circuits are first introduced, and circuit and control analyses are proposed. Simulation and experimental verification subsequently follow to demonstrate effectiveness of the proposed circuits and control methods.

Retrofittable Machine Condition and Structural Excitation Monitoring From the Terminal Box

Retrofittable self-powered sensors for machine condition monitoring ease the burden of installation and decision-making for maintenance and acoustic performance assessment. Terminal box magnetic power harvesting sensors are nonintrusive. They require no special wiring and can simultaneously observe and correlate important variables for machine diagnostics, including vibration and speed. These correlated data can be used to detect and differentiate imbalances from failing structural mounts, among other possibilities. New hardware and algorithms are presented for enabling in situ vibration monitoring, with demonstrations on data sets from US Coast Guard vessels. A specific algorithmic focus of this paper is estimation of a machines contribution to structure-borne noise and vibration, an important consideration for ship acoustic signature.

“Stethoscopes” for nonintrusive monitoring

This paper provides a survey of example sensors that can be implemented with nonintrusive electromagnetic measurements. Stray electric and magnetic fields exist around many important components in commercial and industrial processes. For example, power cables operate surrounded by magnetic and electric fields. Flow meters operate with cyclically-varying magnetic fields. And stray electromagnetic fields can serve as an energy source for powering sensors wirelessly. These stray fields provide remarkable opportunities for nonintrusive sensing of industrial processes. Sensed information can be used to establish monitoring in new or retrofit systems, or can be used as a backup or redundant source to verify the operation of an installed sensor network. Three different example sensors are presented in this paper for power monitoring, fluid flow tracking, and electromechanical vibration monitoring. All three sensors make use of a common set of circuits for electric and magnetic field sensing. They illustrate approaches that could be applied for many other sensing applications.

A nonintrusive magnetically self-powered vibration sensor for automated condition monitoring of electromechanical machines

This paper presents a nonintrusive and electromagnetically self-powered embedded system with vibration sensor for condition monitoring of electromechanical machinery. This system can be installed inside the terminal block of a motor or generator and supports wireless communication for transferring data to a mobile device or computer for subsequent performance analysis. As an initial application, the sensor package is configured for automated condition monitoring of resiliently mounted machines. Upon detecting a spin-down event, e.g. a motor turnoff, the system collects and transmits vibration and residual backemf data as the rotor decreases in rotational speed. This data is then processed to generate an empirical vibrational transfer function (eVTF) rich in condition information for detecting and differentiating machinery and vibrational mount pathologies. The utility of this system is demonstrated via lab-based tests of a resiliently mounted 1.1 kW three-phase induction motor, with results showcasing the usefulness of the embedded system for condition monitoring.