Rohit Moghe

A scoping study of electric and magnetic field energy harvesting for wireless sensor networks in power system applications

This paper explores the existing energy harvesting technologies, their stage of maturity and their feasibility for powering sensor nodes. It contains a study of the energy requirements of the sensor nodes that are a part of the commercial domain. Further, it investigates methods and concepts for harvesting the energy from electric and magnetic fields present near utility assets through laboratory experimentation. The flux concentrator based approach that scavenges the magnetic field was considered to be the most promising solution providing nearly 250mW of power sufficient to power a sensor node.

Smart “Stick-on” Sensors for the Smart Grid

Rapid increase in electric power demand, introduction of RPS mandates, and a push towards electrification in the transportation sector is expected to increase power system stresses and disturbances. To tackle these power system issues and maintain high system reliability, it is essential to have information about the condition of assets present on the grid. Presently, due to the absence of low cost flexible grid wide monitoring solutions, complete information of the system is not achievable. This paper deals with the development of a new class of sensors called the smart “stick-on” sensors. These are low cost, self-powered, universal sensors that provide a flexible monitoring solution for grid assets. These sensors can be mass deployed due to low cost, need low maintenance as they are self-powered, and can be used for monitoring a variety of grid assets. This paper also presents the details on the network architecture, interoperability and integration, and different design aspects of the stick-on sensor, such as novel energy harvesting techniques, power management, wide operating range, and reliability. It is envisioned that the smart stick-on sensors shall be an enabling technology for monitoring a variety of grid assets and prove to be an essential element of the Smart Grid.

Power Electronics at the Grid Edge : The key to unlocking value from the smart grid

Utilities implementing diverse grid modernization initiatives are observing greater volatility at the grid edge that cannot be managed using traditional electromechanically switched centralized command and control solutions. The decentralized, distributed, and dynamic capabilities required can only be achieved with semiconductor-based power electronics solutions that are deployed appropriately along the grid edge. The key control objective is the fast and granular control of volts and vars at hundreds of points along the feeder, a functionality typically associated with static synchronous compensators (STATCOMs) and unified power flow controllers (UPFCs), albeit in a distributed manner and at lower voltage levels. Several companies are now offering grid-edge power-electronics solutions to solve this new set of challenges, with substantial data from the field validating the benefits that such solutions can provide. This article discusses the challenges, solutions, and some of the results that point to the benefits that power electronics at the grid edge can provide for utilities.

Field investigation and analysis of incipient faults leading to a catastrophic failure in an underground distribution feeder

This paper deals with the subject of incipient faults in underground distribution systems and their progression over time leading to an eventual permanent failure. Field data recorded from an underground distribution feeder were analyzed in both time and frequency domain to identify the symptom parameters and characterize the observed incipient behavior. This exploratory data analysis sheds additional light on the progressive characteristics and nature of these self-clearing faults and advances the fundamental knowledge in an effort to detect such pre-mature failures before developing into a full-blown fault.

A Low-Cost Wireless Voltage Sensor for Monitoring MV/HV Utility Assets

Voltage sensing of the utility network provide critical information for asset management, prioritizing asset replacements, increasing situational awareness and providing increased visibility of the grid. For ease of use, and to increase commercial appeal among utilities, these sensors should be designed to have a low cost, long life ( > 10 years), be self-powered, and require no maintenance. This paper deals with the development of a novel low-cost wireless voltage sensor for medium- and high-voltage (MV/HV) utility assets such as cables, transformers, switchgear, capacitor banks, and conductors. A review of existing techniques along with their drawbacks is outlined in this paper. Further, the challenges pertaining to the development a low-cost floating voltage sensor such as variability of voltage, self-calibration requirements, and distance-to-earth variations are presented. These challenges are circumvented by deriving a detailed mathematical model of the sensor. Further, using a set of valid assumptions, a new moving average voltage sensing (MAVS) algorithm is proposed, tested using simulations and validated using a high-voltage prototype. The wireless voltage sensor prototype is tested at up to 35 kV and is built to accommodate electric field energy harvesting in addition to voltage sensing. The prototype has a low-volume production cost of

A Low-Cost Electric Field Energy Harvester for an MV/HV Asset-Monitoring Smart Sensor

150 and shows promising results by providing self-calibrated measurements capable of tracking the voltage variation with less than 2.5% error.

Mitigating distribution transformer lifetime degradation caused by grid-enabled vehicle (GEV) charging

This paper investigates the powering of smart grid sensors with electric fields (E-fields) present in abundance near most medium-voltage to high-voltage (MV/HV) utility assets. A unique E-field energy harvester is proposed, which is integrated into a sensors enclosure, thereby ensuring low-cost and compact size. The proposed energy harvester can be used with multiple assets by virtue of its shape, which also allows installation without interruption of the MV/HV asset. Design methodology of the harvester through Maxwell simulations along with a new and efficient circuit design for obtaining a regulated dc supply is presented. A medium-voltage prototype of the proposed E-field energy harvester integrated with a wireless voltage sensor is built and tested on a 35-kV bus. The prototype provides 17 mW of continuous power at 35 kV with a high energy density. This power is enough to operate a low-duty-cycle sensor node stuck on to an MV/HV asset. The prototype shows promising results and demonstrates the efficacy of using E-fields for powering smart grid sensors for MV/HV assets.

Loss comparison between SiC, hybrid Si/SiC, and Si devices in direct AC/AC converters

Although 75% of the vehicle miles traveled in the US by 2040 could be electric, few studies have quantified their impact on the distribution network even at low GEV penetration levels. This paper presents a Monte Carlo simulation of transformer life degradation using a fundamental and harmonic transformer thermal model, historical distribution transformer load profiles, hourly temperature data, and surveyed vehicle data to determine transformer loss of life. A simple control strategy, based on transformer current, is proposed to mitigate lifetime degradation. Simulation results are presented for a fleet of distribution transformers in Phoenix, AZ and Seattle, WA under controlled and uncontrolled charging scenarios

Losses in Medium-Voltage Megawatt-Rated Direct AC/AC Power Electronics Converters

Direct AC/AC topologies for AC-to-AC power conversion benefit from the absence of DC-link capacitors and therefore high reliability as compared to traditional VSI-based topologies. Moreover, it is shown in this paper that the direct AC/AC converters also promise to provide higher efficiency than their voltage source inverter (VSI) based back-to-back (BTB) counterparts due to a dramatic reduction in switching losses. These factors allow the direct AC/AC converter to switch faster, and maintain much smaller size and lower cost relative to their competition. This paper compares the performance of three different device types (SiC, hybrid Si/SiC and Si) for use in a direct AC/AC converter. It is conjectured that traditional datasheets lack the level of detail needed for designing highly efficient direct AC/AC converters. Therefore, comprehensive loss models for all the devices are formed through a rigorous device characterization under varying (V, I, T) operating conditions. Finally, a loss comparison is performed to identify the most suitable device (among those characterized) for a specific 13 kV / 1 MW highly efficient direct AC/AC power flow controller.

Evaluating the application of energy storage and day-ahead solar forecasting to firm the output of a photovoltaic plant

Direct ac/ac topologies for ac-to-ac power conversion benefit from the absence of dc-link capacitors, and therefore, are highly reliable and have low cost as compared to the traditional voltage-source inverter (VSI)-based topologies. This paper deals with one of the more important tradeoffs considered in designing highly efficient converters: Losses. It is shown in this paper that the direct ac/ac converters have an inherently higher efficiency than their VSI-based back-to-back counterparts due to a dramatic reduction in switching losses (nearly 60%). Further, this paper compares the performance of three different device types (SiC MOSFETs, hybrid Si IGBT/SiC diode, and Si IGBTs) using wide-range device characterization that help to create detailed loss models. It is conjectured that traditional datasheets lack the level of detail needed for computing losses in direct ac/ac converters, and the availability of a multivalue voltage, current, and temperature-based loss profile is advocated. Using the obtained loss models, a comparison is drawn between the considered devices through simulations when operated in a 13-kV/1-MW direct ac/ac power flow controller, the controllable network transformer (CNT). The same loss-models are also used to compute losses in an experimental prototype of a 720-V, 10-kVA CNT and the results are compared with direct efficiency measurements. A similar computation is carried out for another experimental prototype at a 6.7-kV, 400-kVA, three-level, paralleled CNT. These experimental tests are used to confirm the validity of the analytical results presented in this paper.