Ansel Barchowsky

A comparative study of MPPT methods for distributed photovoltaic generation

Photovoltaic (PV) energy generation is becoming an increasingly prevalent means of producing clean, renewable power. PV is renewable, reliable, and domestically secure. One of the most important components of PV systems is the inverter technology that converts the direct current (DC) power output from the PV panel or array to alternating current (AC) used on both the individual end-user and centralized grid levels. The large variety of inverters share the same general goal: to allow for the most efficient and stable transfer of as much power as possible. One specific means of accomplishing this goal is the inclusion of a Maximum Power Point Tracking (MPPT) DC-DC converter. The purpose of MPPT is to ensure that the PV panel or array is always producing power as near to the knee of its I-V curve as possible. This extracts the maximum amount of power at any given time. In constantly sunny situations, there is little impact on overall performance of a particular MPPT design on the PV system, as only small voltage differences due to the particular construction of each panel effects the overall voltage outputs. However, cloud cover changes the output from a PV panel drastically with reduced solar irradiation causing the current of the solar panel to drop. It is postulated herein that the stability and quality problems created by central MPPT during periods of differing solar irradiation on various panels could be solved with a system of MPPT distributed on each panel. These would then feed collectively to a central inverter. To test these systems, a PSCAD model was developed for both centralized and distributed MPPT systems, and the solar irradiation was randomly varied. This allowed for observation of the stability and quality of the output voltage for each system.

Sample survey of smart grid approaches and technology gap analysis

Research and development in the field of “smart grids” is advancing at an ever expanding rate, with an increasing number of industry participants and other key constituents internationally, including government entities and educational institutions. It is vital to understand the approaches being taken by these various entities in order to determine the optimal method by which to proceed with defining the smart grid and associated future developments. This survey was undertaken with the intent of determining representative approaches from various participants, and combining them into an overarching view of the industry as a whole. As a result, the more practical and efficient methods of improving the electrical grid were revealed, as well as gaps within the existing technology and standards. The most apparent gaps were determined to be in the following main areas: common communications; improved transmission and distribution controls; real-time information and incentives for both the end-user and the utility; self-healing grids; energy storage and renewable integration; and improved standards for the industry. In particular, future work into the development of improved control software for renewable integration utilizing energy storage is discussed, which will contribute to further research within the field.

Design and Realization of an Innovative Workbench for Electric Power Systems Laboratories

With the increasingly high demand for well-trained power systems engineers, the University of Pittsburgh has partnered with Eaton in the creation of the new Electric Power Systems Laboratory at the Swanson School of Engineering. This laboratory demands the capability to perform a wide variety of experimental procedures while providing students and researchers with a seamless working environment. To accomplish that goal, a novel lab workbench was developed. This lab workbench integrates the load banks necessary for laboratory procedures with advanced metering, controls and safety features, and contains them within a work station ideally suited for the laboratory space. This paper details the development of those lab workbenches, from concept, to design, to prototype construction, to testing. Additionally, this work describes planned classroom experiments utilizing the developed bench. Ultimately the realized workbench demonstrates its capability to be reconfigured to suit the demands of both education as well as new research projects for undergraduate and graduate studies.

Analytical and experimental optimization of external gate resistance for safe rapid turn on of normally off GaN HFETs

This paper presents an analytical framework, supplemented with experimental validation, for optimizing the value of the external gate resistance employed in power conversion circuits using EPC enhancement-mode GaN transistors. A second order analytical model of the GaN device is utilized to determine a function that relates the external gate resistance to the peak gate voltage during turn-on. The results obtained from the analytical model were experimentally validated in a double pulse-test. The derived model allows for optimal selection of gate resistances such that GaN HFETs can be switched as rapidly as possible while keeping them in their safe operating region.

Fault Section Identification Protection Algorithm for Modular Multilevel Converter-Based High Voltage DC With a Hybrid Transmission Corridor

This paper addresses the protection of a high voltage direct current (HVDC) transmission system, utilizing the modular multilevel converter (MMC) topology in addition to incorporating a hybrid transmission corridor (transmission line including overhead line and cable sections). A solution is proposed for identifying the section within which a dc fault is located for the purpose of maintaining power delivery. A detailed model of the MMC-HVDC system is simulated using PSCAD and an in depth fault analysis is performed. A characteristic signal is discovered and then implemented into a novel solution. The end result is a fault section identification protection algorithm, implementing protective relay coordination to protect the system from false circuit breaker reclose as well as enabling fast system restart for nonpermanent faults. This restart protection algorithm is implemented without the use of a communications channel between converter stations, introducing novelty and quick restart response.

Electric power laboratory workbench for training the next generation of engineering professionals

With the increasingly high demand for well-trained power systems engineers, the University of Pittsburgh has partnered with Eaton in the creation of the new Electric Power Systems Laboratory at the Swanson School of Engineering. This laboratory demands the capability to perform a wide variety of experimental procedures while providing students and researchers with a seamless working environment. To accomplish that goal, a novel lab workbench was developed. This lab workbench integrates the load banks necessary for laboratory procedures with advanced metering, controls and safety features, and contains them within a work station ideally suited for the laboratory space. This paper details the development of those lab workbenches, from concept, to design, to prototype construction, to testing. Additionally, this work describes planned classroom experiments utilizing the developed bench. Ultimately the prototype bench demonstrates its capability to be reconfigured to suit the demands of both education as well as new research projects for undergraduate and graduate studies.

A GaN-based modular multilevel DC-DC converter for high-density anode discharge power modules

This paper proposes a DC-DC Modular Multilevel Converter (MMC) as an alternative to traditional isolated and non-isolated converter topologies for the purpose of achieving high voltage and power density in Anode Discharge Power Modules (ADPMs) for Solar Electric Propulsion (SEP) systems. The paper presents the background for the use of GaN HFETs in multilevel topologies at high frequency and makes the case for GaN HFETs in spacecraft power systems. It then presents an analytical model, simulation results, and initial hardware evaluation of the proposed topology. The result is a 2 kW converter system operating at 600 V output at a power density of 110 W/in3, achieving 83% full load efficiency at 1 MHz. The proposed topology is scalable to higher voltage and power ratings.

Improved designs of high power density inverters for 380 Vdc based microgrid architectures

This article describes a 380 Vdc based microgrid retrofitted within an existing, AC based, state-of-the-art trucking terminal in Pittsburgh, Pennsylvania. The DC microgrid is composed of renewable generation resources including 50 kW of solar photovoltaic generation, 5 kW of wind power, a 75 kWh energy storage system all coordinated to serve a 33.4 kW lighting load. A number of design constraints, including environmental conditions and renewable generation availability are considered in order to develop a design suited for the needs of the site. In such retrofit environments, however, there is often minimal space for the integration of new electric equipment indoors. To address this need, the second objective of this paper details the development of a high power density, GaN-based modular inverter capable of handling 2 kW at 400 Vdc within a 100W/in3 containment used to power motor loads in commercial settings.

Design and manufacturability of a high power density M2C inverter

The modular multilevel converter (M2C) circuit, a voltage source converter originally introduced to reduce the footprint of high voltage DC systems, is adapted here for a single-phase, low voltage, high power density inverter application (450 VDC, 2 kW, 100 W/in3). The adaptation is achieved by using small, high speed gallium nitride (GaN) transistors in the M2C half-bridge submodules that are stacked in series and parallel to achieve voltage and current requirements. Here the design and analysis of an individual half-bridge cell, and full arm of the M2C topology is presented. To achieve such high power density, factors including gate drive circuit design, submodule electrical performance and thermal management, and the manufacturability of the full arm were considered. This work presents the detailed process of designing and manufacturing the multiple printed circuit boards, as well as thermal and electrical experimental evaluation and analysis. The stringent size and operational requirements drove design iterations between circuit designers and manufacturers.