Analysis and Design of Solar Power System Interface Utility Using ZVS Converter

The solar power generation system with minimal losses, high simplicity and easy control is attempted in this work, by developing a grid-tied zero-voltage switching (ZVS) inverter with a less number of power conversion stages and the least count of passive components, for single-phase applications that are suitable for conversion from low-voltage DC (40-60 V) to line voltage AC (230 VAC; RMS) at average power levels of 175 W and below. The ZVS full-bridge inverter fed from a PV panel is working on higher frequency with an asymmetric auxiliary circuit, which guarantees ZVS at the switching instants of the metal-oxide-semiconductor field-effect transistors (MOSFETs) by supplying the reactive current to these full-bridge semiconductor switches and reducing the switching losses. Checking of the constructional workability and analytical feasibility of the proposed topology with the highest efficiency and the simplest control was the target of this work, which was set on the basis of the results obtained in the MATLAB Simulink environment. The control strategies were planned for the optimum value of the reactive current injected by the auxiliary circuit to guarantee ZVS and use of phase shifted pulsewidth modulation (PWM) with varying frequencies for the full-bridge inverter and half-bridge cyclo-converter. The hybrid maximum power point tracking (MPPT) was part of this plan used to set the power at its maximum value against the environmental changes.Citation: Deshbhratar, R. G., and Renge, M. M. (2018). Analysis and Design of Solar Power System Interface Utility Using ZVS Converter. Trends in Renewable Energy, 4, 83-101. DOI: 10.17737/tre.2018.4.3.005

A multilevel energy buffer and voltage modulator for grid-interfaced micro-inverters

Micro-inverters operating into the single-phase grid from solar photovoltaic (PV) panels or other low-voltage sources must buffer the twice-line-frequency variations between the energy sourced by the PV panel and that required for the grid. Moreover, in addition to operating over wide average power ranges, they inherently operate over a wide range of voltage conversion ratios as the line voltage traverses a cycle. These factors make the design of micro-inverters challenging. This paper presents a multilevel energy buffer and voltage modulator (MEB) that significantly reduces the range of voltage conversion ratios that the dc-ac converter portion of the micro-inverter must operate over by stepping its effective input voltage in pace with the line voltage. The MEB also functions as an active energy buffer to reduce the twice-line-frequency voltage ripple at the output of the solar panel. The small additional loss of the MEB can be compensated by the improved efficiency of the dc-ac converter stage, leading to a higher overall system efficiency. A prototype micro-inverter incorporating a MEB, designed for 27 V to 38 V dc input voltage, 230 V rms ac output voltage, and rated for line cycle average power of 70 W, has been built and tested in grid-connected mode. It is shown that the MEB can successfully enhance the performance of a single-phase grid-interfaced micro-inverter by increasing its efficiency and reducing the total size of the twice-line-frequency energy buffering capacitance

A Single-Phase Photovoltaic Inverter Topology With a Series-Connected Energy Buffer

Module integrated converters (MICs) have been under rapid development for single-phase grid-tied photovoltaic applications. The capacitive energy storage implementation for the double-line-frequency power variation represents a differentiating factor among existing designs. This paper introduces a new topology that places the energy storage block in a series-connected path with the line interface block. This design provides independent control over the capacitor voltage, soft-switching for all semiconductor devices, and the full four-quadrant operation with the grid. The proposed approach is analyzed and experimentally demonstrated

Multilevel Converter Topologies for Utility Scale Solar Photovoltaic Power Systems

Renewable energy technologies have been growing in their installed capacity rapidly over the past few years. This growth in solar, wind and other technologies is fueled by state incentives, renewable energy mandates, increased fossil fuel prices and environmental consciousness. Utility scale systems form a substantial portion of electricity capacity addition in modern times. This sets the stage for research activity to explore new efficient, compact and alternative power electronic topologies to integrate sources like photovoltaics (PV) to the utility grid, some of which are multilevel topologies. Multilevel topologies allow for use of lower voltage semiconductor devices than two-level converters. They also produce lower distortion output voltage waveforms. This dissertation proposes a cascaded multilevel converter with medium frequency AC link which reduces the size of DC bus capacitor and also eliminates power imbalance between the three phases. A control strategy which modulates the output voltage magnitude and phase angle of the inverter cells is proposed. This improves differential power processing amongst cells while keeping the voltage and current ratings of the devices low. A battery energy storage system for the multilevel PV converter has also been proposed. Renewable technologies such as PV and wind suffer from varying degrees of intermittency, depending on the geographical location. With increased installation of these sources, management of intermittency is critical to the stability of the grid. The proposed battery system is rated at 10% of the plant it is designed to support. Energy is stored and extracted by means of a bidirectional DC-DC converter connected to the PV DC bus. Different battery chemistries available for this application are also discussed. In this dissertation, the analyses of common mode voltages and currents in various PV topologies are detailed. The grid integration of PV power employs a combination of pulse width modulation (PWM) DC-DC converters and inverters. Due to their fast switching nature a common mode voltage is generated with respect to the ground, inducing a circulating current through the ground capacitance. Common mode voltages lead to increased voltage stress, electromagnetic interference and malfunctioning of ground fault protection systems. Common mode voltages and currents present in high and low power PV systems are analyzed and mitigation strategies such as common mode filter and transformer shielding are proposed to minimize them

Designs for ultra-high efficiency grid-connected power conversion

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2011.Cataloged from PDF version of thesis.Includes bibliographical references (p. 213-215).Grid connected power conversion is an absolutely critical component of many established and developing industries, such as information technology, telecommunications, renewable power generation (e.g. photovoltaic and wind), even down to consumer electronics. There is an ever present demand to reduce the volume and cost, while increasing converter efficiency and performance. Reducing the losses associated with energy conversion to and from the grid can be accomplished through the use of new circuit topologies, enhanced control methods, and optimized energy storage. The thesis outlines the development of foundational methods and architectures for improving the efficiency of these converters, and allowing the improvements to be scaled with future advances in semiconductor and passive component technologies. The work is presented in application to module integrated converters (MICs), often called micro-inverters. These converters have been under rapid development for single-phase gridtied photovoltaic applications. The capacitive energy storage implementation for the double-line-frequency power variation represents a differentiating factor among existing designs, and this thesis introduces a new topology that places the energy storage block in a series-connected path with the line interface. This design provides independent control over the capacitor voltage, soft-switching for all semiconductor devices, and full four-quadrant operation with the grid.by Brandon J. Pierquet.Ph.D

Design Considerations of a Utility Interactive Fuel Cell Inverter

The concept of deregulated energy infrastructure is rapidly shaping the future of power generation and grid constitution. Control, communication and integration of various alternative energy resources within a Distributed Generation (DG) network have opened up areas of new challenges and opportunities. The power interface between a fuel cell system and the distribution grid is one such intriguing issue. With the advent of various grid-interactivity, safety, efficiency and power quality standards (such as, IEEE 1547), the design of a cost effective-high performance power electronic inverter for a fuel cell system is a challenge. In this paper, various design criteria, topologies and control aspects of a grid-tied fuel cell inverter are discussed. An overview of some fundamental design standards, and a systematic approach for topology selection is given. An outline of a possible DSP based hardware configuration, communication and control is also provided. Initial simulation of the proposed scheme along with considerations for practical implementations of fuel cell inverter are discussed

Development of a high-efficiency solar micro-inverter

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2009.Cataloged from PDF version of thesis.Includes bibliographical references (p. 77).In typical solar power installations, multiple modules are connected to the grid through a single high-power inverter. However, an alternative approach is to connect each solar module directly to the grid through a micro-inverter. This approach makes the system robust to single module failures and results in better power tracking. This project involves the development of a next generation micro-inverter architecture, including the design, assembly, and testing of a prototype converter. The topology involves a full bridge resonant inverter at the input, which supplies high-frequency current through a transformer to a cycloconverter at the output.by Alexander Khaled Hayman.M.Eng

Multilevel Converter Topologies for Utility Scale Solar Photovoltaic Power Systems

Renewable energy technologies have been growing in their installed capacity rapidly over the past few years. This growth in solar, wind and other technologies is fueled by state incentives, renewable energy mandates, increased fossil fuel prices and environmental consciousness. Utility scale systems form a substantial portion of electricity capacity addition in modern times. This sets the stage for research activity to explore new efficient, compact and alternative power electronic topologies to integrate sources like photovoltaics (PV) to the utility grid, some of which are multilevel topologies. Multilevel topologies allow for use of lower voltage semiconductor devices than two-level converters. They also produce lower distortion output voltage waveforms. This dissertation proposes a cascaded multilevel converter with medium frequency AC link which reduces the size of DC bus capacitor and also eliminates power imbalance between the three phases. A control strategy which modulates the output voltage magnitude and phase angle of the inverter cells is proposed. This improves differential power processing amongst cells while keeping the voltage and current ratings of the devices low. A battery energy storage system for the multilevel PV converter has also been proposed. Renewable technologies such as PV and wind suffer from varying degrees of intermittency, depending on the geographical location. With increased installation of these sources, management of intermittency is critical to the stability of the grid. The proposed battery system is rated at 10% of the plant it is designed to support. Energy is stored and extracted by means of a bidirectional DC-DC converter connected to the PV DC bus. Different battery chemistries available for this application are also discussed. In this dissertation, the analyses of common mode voltages and currents in various PV topologies are detailed. The grid integration of PV power employs a combination of pulse width modulation (PWM) DC-DC converters and inverters. Due to their fast switching nature a common mode voltage is generated with respect to the ground, inducing a circulating current through the ground capacitance. Common mode voltages lead to increased voltage stress, electromagnetic interference and malfunctioning of ground fault protection systems. Common mode voltages and currents present in high and low power PV systems are analyzed and mitigation strategies such as common mode filter and transformer shielding are proposed to minimize them

Feasibility of high frequency alternating current power distribution for the automobile auxiliary electrical system

This study investigates the feasibility and potential benefits of high frequency alternating current (HFAC) for vehicle auxiliary electrical systems. A 100Vrms, 50kHz sinusoidal AC bus is compared with 14V DC and 42V DC electrical systems in terms of mass and energy efficiency. The investigation is focused on the four main sub-systems of an on-board electrical network, namely: the power generation, power distribution, power conversion and the electrical loads. In addition, a systemlevel inquiry is conducted for the HFAC bus and a comparable 42V DC system. A combination of computer simulation, analytical analysis and experimental work has highlighted benefits for the HFAC power distribution sub-system and for low-torque motor actuators. Specifically, the HFAC conductor mass is potentially 70% and 30% lighter than comparable 14V DC and 42V DC cables, respectively. Also, the proposed cable is expected to be at least 80% more energy efficient than the current DC conductor technology. In addition, it was found that 400Hz AC machines can successfully replace DC motor actuators with a rated torque of up to 2Nm. The former are up to 100% more efficient and approximately 60% lighter and more compact than the existing DC motors in vehicles. However, it is argued that the HFAC supply is not feasible for high-torque motor actuators. This is because of the high energy losses and increased machine torque ripple associated with the use of HFAC power. The HFAC power conversion sub-system offers benefits in terms of simple power converter structure and efficient HFAC/DC converters. However, a significant limitation is the high power loss within HFAC/AC modules, which can be as high as 900W for a 2.4kW load with continuous operation. Similar restrictions are highlighted for the HFAC power generation sub-system, where up to 400W is lost in a 4kW DC/HFAC power module. The conclusion of the present work is that the HFAC system offers mass and energy efficiency benefits for the conventional vehicle by leveraging the use of compact lowtorque motor actuators and lightweight wiring technology