Amrit Iyer

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.

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

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.

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.

Dynamic Grid Power Routing Using Controllable Network Transformers (CNTs) With Decoupled Closed-Loop Controller

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.

Power flow controller for meshed systems with a fractionally rated BTB converter

Increases in system loads and in levels of penetration of renewable energy, together with limited investment in transmission infrastructure, are fostering the need for a smarter and more dynamically controllable grid. Flexible ac transmission systems devices can be used to dynamically control the grid and more efficiently route power and thus mitigate these stresses, but such devices are either too complicated and expensive for implementation or incapable of independently controlling active and reactive powers. A controllable network transformer (CNT) has a fractionally rated direct ac/ac converter and was introduced as a simpler and more cost-effective solution to realize dynamic power control between two areas. The CNT utilizes the dual virtual quadrature source (DVQS) technique to change both the line voltage amplitude and phase angle, thus enabling a dynamic power control; however, the control variables defined in this technique have a cross-coupling effect between active and reactive powers. In this paper, the CNT operating ranges with and without considering line resistance are analyzed; then, a decoupled closed-loop controller is designed to achieve independent active and reactive power control based on a reference power control command. To address the possibility of power overshoot in a CNT with DVQS, a hybrid open-loop/closed-loop proportional-integral controller is also proposed. Simulations and experimental results are given to verify the controller design.

Plug-and-play AC/AC power electronics building blocks (AC-PEBBs) for grid control

The increasing load demand, increasing level of penetration of renewable energy and limited transmission infrastructure investments have significantly increased the need for a smart dynamically controllable grid. Existing solutions based on FACTS devices, are complex and expensive to implement at transmission level or even sub-transmission level voltages. This paper proposes a novel power flow controller for dynamic control of active/reactive power in a meshed network. The proposed controller is realized by augmenting a transformer with a fractionally rated bi-directional Back to Back (BTB) converter. The main advantages of the proposed converter are the fractional converter rating, reliability and scalability.

Experimental validation of active snubber circuit for direct AC/AC converters

As ac-to-ac power conversion becomes increasingly importantly in applications such as grid power flow control and motor control, the demand for a plug-and-play converter is increased. Traditional VSI-based ac-to-ac power converters such as the back-to-back converter require bulky dc-link capacitors that limit their reliability. Therefore, approaches that offer direct ac-to-ac power conversion are gaining popularity. This paper proposes a plug-and-play concept for achieving ac-to-ac power conversion via the ac/ac power electronic building block (AC-PEBB). The AC-PEBB is a compact, self-contained cell requiring no energy storage. It can be used in a variety of direct ac/ac converters including matrix converters, controllable network transformers (CNT), etc. This paper details the construction of a prototype AC-PEBB to be used in a 13 kV, 1 MVA application. The effectiveness of the AC-PEBB is demonstrated experimentally in an example application of controlling grid power flows via a 10 kVA CNT prototype built by augmenting a standard transformer with a single AC-PEBB cell. Series and parallel connection of multiple AC-PEBBs to increase maximum voltage and current handling capability is also demonstrated.

A low-cost electric-field energy harvester for an MV/HV asset-monitoring smart-sensor

Although direct ac/ac converters such as the Matrix converter have been in existence for a long time, scaling of these converters to higher voltage levels has not been addressed widely in the literature. Tremendous challenges in terms of device voltage sharing, safe commutation, and fault protection inhibit the application of these converters to high voltage applications such as dynamic grid control. The novel active snubber concept remedies this problem by placing a half-wave rectified envelope around every device, absorbing excess energy and ensuring proper voltage sharing. This paper examines a high frequency active snubber design for direct ac/ac converters. The performance of the snubber is analyzed at 13 kV / 1 MVA via simulations, and a proof-of-concept is implemented in a 10 kVA lab prototype.

Scaling the controllable network transformer (CNT) to utility-level voltages with direct AC/AC power electronic building blocks (PEBBs)

This paper investigates the powering of smart-grid-sensors with electric fields (E-fields) present in abundance near most medium-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.