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A NEW QUASI RESONANT DC-LINK FOR PHOTOVOLTAIC MICRO-INVERTERS

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Date Issued:
2012
Abstract/Description:
PV Inverters have the task of tracking the maximum power point (MPP), and regulating the solar energy generation to this optimal operation point. The second task is the conversion of direct current produced by the solar modules into alternating current compatible with the grid.A new inverter approach such as a single phase micro inverter is emerging aimed to overcome some of the challenges of centralized inverters. As a counterpart to the central inverter, a micro inverter is a small compact module attached directly to each solar panel.To provide for the constantly increasing demand for a small size, light weight and high efficiency micro inverter, soft switching power conversion technologies have been employed. The switching stress can be minimized by turning on/off each switch when the voltage across it or the current through it is zero at the switching transition. With the addition of auxiliary circuits such as auxiliary switches and LC resonant components the so called soft switching condition can be achieved for semiconductor devices.Four main purposes to investigate the soft switching technologies for single-phase micro-inverter are:(1) to improve overall efficiency by creating the favorable operating conditions for power devices using soft-switching techniques;(2) to shrink the reactive components by pushing the switching frequency to a higher range with decent efficiency.(3) to ensure soft switching does not exacerbate inverter performance, meaning all conventional PWM algorithms can be applied in order to meet IEEE standards.(4) to investigate which soft switching techniques offer the cheapest topology and control strategy as cost and simple control are crucial for low power inverter applications.An overview on the existing soft-switching inverter topologies for single phase inverter technology is summarized.A new quasi resonant DC link that allows for pulse- width- modulation (PWM) is presented in this thesis. The proposed quasi resonant DC link provides zero-voltage switching (ZVS) condition for the main devices by resonating the DC-link voltage to zero via three auxiliary switches and LC components. The operating principle and mode analysis are given. The simulation was carried out to verify the proposed soft switching technique. A 150W 120VAC single-phase prototype was built. The experimental results show that the soft switching for four main switches can be realized under different load conditions and the peak efficiency can reach 95.6%. The proposed quasi DC link can be applied to both single-phase and three-phase DC/AC micro inverter.In order to boost efficiency and increase power density it is important to evaluate the power loss mechanism in each stage of operation of the micro inverter. Using the datasheet parameters of the commercially available semiconductor switches, conduction and switching losses were estimated. This thesis presents a method to analyze power losses of the new resonant DC link inverter which alleviates topology optimization and MOSFET selection. An analytical, yet simple model for calculating the conduction and switching losses was developed. With this model a rough calculation of efficiency can be done, which helps to speed up the design process and to increase efficiency.
Title: A NEW QUASI RESONANT DC-LINK FOR PHOTOVOLTAIC MICRO-INVERTERS.
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Name(s): Grishina, Anna, Author
Batarseh, Issa, Committee Chair
Shen, Zheng, Committee Member
Kutkut, Nasser, Committee Member
, Committee Member
University of Central Florida, Degree Grantor
Type of Resource: text
Date Issued: 2012
Publisher: University of Central Florida
Language(s): English
Abstract/Description: PV Inverters have the task of tracking the maximum power point (MPP), and regulating the solar energy generation to this optimal operation point. The second task is the conversion of direct current produced by the solar modules into alternating current compatible with the grid.A new inverter approach such as a single phase micro inverter is emerging aimed to overcome some of the challenges of centralized inverters. As a counterpart to the central inverter, a micro inverter is a small compact module attached directly to each solar panel.To provide for the constantly increasing demand for a small size, light weight and high efficiency micro inverter, soft switching power conversion technologies have been employed. The switching stress can be minimized by turning on/off each switch when the voltage across it or the current through it is zero at the switching transition. With the addition of auxiliary circuits such as auxiliary switches and LC resonant components the so called soft switching condition can be achieved for semiconductor devices.Four main purposes to investigate the soft switching technologies for single-phase micro-inverter are:(1) to improve overall efficiency by creating the favorable operating conditions for power devices using soft-switching techniques;(2) to shrink the reactive components by pushing the switching frequency to a higher range with decent efficiency.(3) to ensure soft switching does not exacerbate inverter performance, meaning all conventional PWM algorithms can be applied in order to meet IEEE standards.(4) to investigate which soft switching techniques offer the cheapest topology and control strategy as cost and simple control are crucial for low power inverter applications.An overview on the existing soft-switching inverter topologies for single phase inverter technology is summarized.A new quasi resonant DC link that allows for pulse- width- modulation (PWM) is presented in this thesis. The proposed quasi resonant DC link provides zero-voltage switching (ZVS) condition for the main devices by resonating the DC-link voltage to zero via three auxiliary switches and LC components. The operating principle and mode analysis are given. The simulation was carried out to verify the proposed soft switching technique. A 150W 120VAC single-phase prototype was built. The experimental results show that the soft switching for four main switches can be realized under different load conditions and the peak efficiency can reach 95.6%. The proposed quasi DC link can be applied to both single-phase and three-phase DC/AC micro inverter.In order to boost efficiency and increase power density it is important to evaluate the power loss mechanism in each stage of operation of the micro inverter. Using the datasheet parameters of the commercially available semiconductor switches, conduction and switching losses were estimated. This thesis presents a method to analyze power losses of the new resonant DC link inverter which alleviates topology optimization and MOSFET selection. An analytical, yet simple model for calculating the conduction and switching losses was developed. With this model a rough calculation of efficiency can be done, which helps to speed up the design process and to increase efficiency.
Identifier: CFE0004379 (IID), ucf:49397 (fedora)
Note(s): 2012-08-01
M.S.E.E.
Engineering and Computer Science, Electrical Engineering and Computer Science
Masters
This record was generated from author submitted information.
Subject(s): micro inverters -- soft-switching -- quasi resonant DC link
Persistent Link to This Record: http://purl.flvc.org/ucf/fd/CFE0004379
Restrictions on Access: public 2012-08-15
Host Institution: UCF

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