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investigation of dual-stage high efficiency (&)density micro inverter for solar application
Title
investigation of dual-stage high efficiency (&)density micro inverter for solar application.
Creator
Chen, Lin, Batarseh, Issa, Mikhael, Wasfy, Wu, Xinzhang, Behal, Aman, Kutkut, Nasser, University of Central Florida
Abstract / Description
Module integrated converters (MIC), also called micro inverter, in single phase have witnessed recent market success due to unique features (1) improved energy harvest, (2) improved system efficiency, (3) lower installation costs, (4) plug-N-play operation, (5) and enhanced flexibility and modularity. The MIC sector has grown from a niche market to mainstream, especially in the United States. Due to the fact that two-stage architecture is commonly used for single phase MIC application. A DC...
Show moreModule integrated converters (MIC), also called micro inverter, in single phase have witnessed recent market success due to unique features (1) improved energy harvest, (2) improved system efficiency, (3) lower installation costs, (4) plug-N-play operation, (5) and enhanced flexibility and modularity. The MIC sector has grown from a niche market to mainstream, especially in the United States. Due to the fact that two-stage architecture is commonly used for single phase MIC application. A DC-DC stage with maximum power point tracking to boost the output voltage of the Photovoltaic (PV) panel is employed in the first stage, DC-AC stage is used for use to connect the grid or the residential application. As well known, the cost of MIC is key issue compared to convention PV system, such as the architecture: string inverter or central inverter. A high efficiency and density DC-DC converter is proposed and dedicated for MIC application. Assuming further expansion of the MIC market, this dissertation presents the micro-inverter concept incorporated in large size PV installations such as MW-class solar farms where a three phase AC connection is employed. A high efficiency three phase MIC with two-stage ZVS operation for grid tied photovoltaic system is proposed which will reduce cost per watt, improve reliability, and increase scalability of MW-class solar farms through the development of new solar farm system architectures. This dissertation presents modeling and triple-loop control for a high efficiency three-phase four-wire inverter for use in grid-connected two-stage micro inverter applications. An average signal model based on a synchronous rotation frame for a three-phase four-wire inverter has been developed. The inner current loop consists of a variable frequency bidirectional current mode (VFBCM) controller which regulates output filter inductor current thereby achieving ZVS, improved system response, and reduced grid current THD. Active damping of the LCL output filter using filter inductor current feedback is discussed along with small signal modeling of the proposed control method. Since the DC-link capacitor plays a critical role in two-stage micro inverter applications, a DC-link controller is implemented outside of the two current control loops to keep the bus voltage constant. In the end, simulation and experimental results from a 400 watt prototype are presented to verify the validity of the theoretical analysis.
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Date Issued
2014
Identifier
CFE0005148, ucf:50699
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0005148
THREE-PORT MICRO-INVERTER WITH POWER DECOUPLING CAPABILITY FOR PHOTOVOLTAIC (PV) SYSTEMS APPLICATIONS
Title
THREE-PORT MICRO-INVERTER WITH POWER DECOUPLING CAPABILITY FOR PHOTOVOLTAIC (PV) SYSTEMS APPLICATIONS.
Creator
Harb, Souhib, Batarseh, Issa, University of Central Florida
Abstract / Description
The Photovoltaic (PV) systems have been realized using different architectures, starting with the string and centralized PV system to the modular PV system. Presently, decentralized inverters are being developed at the PV panel power level (known as AC – PV Modules). Such new PV systems are becoming more attractive and many expect this will be the trend of the future. The AC-Module PV system consists of an inverter attached to one PV panel. This integration requires...
Show moreThe Photovoltaic (PV) systems have been realized using different architectures, starting with the string and centralized PV system to the modular PV system. Presently, decentralized inverters are being developed at the PV panel power level (known as AC – PV Modules). Such new PV systems are becoming more attractive and many expect this will be the trend of the future. The AC-Module PV system consists of an inverter attached to one PV panel. This integration requires that both devices have the same life-span. Although, the available commercial inverters have a relatively short life-span (10 years) compared to the 25 –year PV. It has been stated in literature that the energy storage capacitor (electrolytic type) in the single-phase inverter is the most vulnerable electronic component. Hence, many techniques such as (power decoupling techniques) have been proposed to solve this problem by replacing the large electrolytic capacitor with a small film capacitor. This thesis will present a quick review of these power decoupling techniques, and proposes a new three-port micro-inverter with power decoupling capability for AC-Module PV system applications.
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Date Issued
2010
Identifier
CFE0003357, ucf:48474
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0003357
A NEW QUASI RESONANT DC-LINK FOR PHOTOVOLTAIC MICRO-INVERTERS
Title
A NEW QUASI RESONANT DC-LINK FOR PHOTOVOLTAIC MICRO-INVERTERS.
Creator
Grishina, Anna, Batarseh, Issa, Shen, Zheng, Kutkut, Nasser, University of Central Florida
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...
Show morePV 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.
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Date Issued
2012
Identifier
CFE0004379, ucf:49397
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0004379
Optimization and design of photovoltaic micro-inverter
Title
Optimization and design of photovoltaic micro-inverter.
Creator
Zhang, Qian, Batarseh, Issa, Shen, Zheng, Wu, Xinzhang, Lotfifard, Saeed, Kutkut, Nasser, University of Central Florida
Abstract / Description
To relieve energy shortage and environmental pollution issues, renewable energy, especially PV energy has developed rapidly in the last decade. The micro-inverter systems, with advantages in dedicated PV power harvest, flexible system size, simple installation, and enhanced safety characteristics are the future development trend of the PV power generation systems. The double-stage structure which can realize high efficiency with nice regulated sinusoidal waveforms is the mainstream for the...
Show moreTo relieve energy shortage and environmental pollution issues, renewable energy, especially PV energy has developed rapidly in the last decade. The micro-inverter systems, with advantages in dedicated PV power harvest, flexible system size, simple installation, and enhanced safety characteristics are the future development trend of the PV power generation systems. The double-stage structure which can realize high efficiency with nice regulated sinusoidal waveforms is the mainstream for the micro-inverter.This thesis studied a double stage micro-inverter system. Considering the intermittent nature of PV power, a PFC was analyzed to provide additional electrical power to the system. When the solar power is less than the load required, PFC can drag power from the utility grid.In the double stage micro-inverter, the DC/DC stage was realized by a LLC converter, which could realize soft switching automatically under frequency modulation. However it has a complicated relationship between voltage gain and load. Thus conventional variable step P(&)O MPPT techniques for PWM converter were no longer suitable for the LLC converter. To solve this problem, a novel MPPT was proposed to track MPP efficiently. Simulation and experimental results verified the effectiveness of the proposed MPPT.The DC/AC stage of the micro-inverter was realized by a BCM inverter. With duty cycle and frequency modulation, ZVS was achieved through controlling the inductor current bi-directional in every switching cycle. This technique required no additional resonant components and could be employed for low power applications on conventional full-bridge and half-bridge inverter topologies. Three different current mode control schemes were derived from the basic theory of the proposed technique. They were referred to as Boundary Current Mode (BCM), Variable Hysteresis Current Mode (VHCM), and Constant Hysteresis Current Mode (CHCM) individually in this paper with their advantages and disadvantages analyzed in detail. Simulation and experimental results demonstrated the feasibilities of the proposed soft-switching technique with the digital control schemes.The PFC converter was applied by a single stage biflyback topology, which combined the advantages of single stage PFC and flyback topology together, with further advantages in low intermediate bus voltage and current stresses. A digital controller without current sampling requirement was proposed based on the specific topology. To reduce the voltage spike caused by the leakage inductor, a novel snubber cell combining soft switching technique with snubber technique together was proposed. Simulation and experimental waveforms illustrated the same as characteristics as the theoretical analysis.In summary, the dissertation analyzed each power stage of photovoltaic micro-inverter system from efficiency and effectiveness optimization perspectives. Moreover their advantages were compared carefully with existed topologies and control techniques. Simulation and experiment results were provided to support the theoretical analysis.
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Date Issued
2013
Identifier
CFE0005286, ucf:50540
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0005286
Control Based Soft Switching Three-phase Micro-inverter: Efficiency and Power Density Optimization
Title
Control Based Soft Switching Three-phase Micro-inverter: Efficiency and Power Density Optimization.
Creator
Amirahmadi, Ahmadreza, Batarseh, Issa, Lotfifard, Saeed, Mikhael, Wasfy, Wu, Xinzhang, Kutkut, Nasser, University of Central Florida
Abstract / Description
In the field of renewable energy, solar photovoltaic is growing exponentially. Grid-tied PV micro-inverters have become the trend for future PV system development because of their remarkable advantages such as enhanced energy production due to MPPT implementation for each PV panel, high reliability due to redundant and distributed system architecture, and simple design, installation, and management due to its plug-and-play feature. Conventional approaches for the PV micro-inverters are mainly...
Show moreIn the field of renewable energy, solar photovoltaic is growing exponentially. Grid-tied PV micro-inverters have become the trend for future PV system development because of their remarkable advantages such as enhanced energy production due to MPPT implementation for each PV panel, high reliability due to redundant and distributed system architecture, and simple design, installation, and management due to its plug-and-play feature. Conventional approaches for the PV micro-inverters are mainly in the form of single-phase grid connected and they aim at the residential and commercial rooftop applications. It would be advantageous to extend the micro-inverter concept to large size PV installations such as MW-class solar farms where three-phase AC connections are used.The relatively high cost of the three-phase micro-inverter is the biggest barrier to its large scale deployment. Increasing the switching frequency may be the best way to reduce cost by shrinking the size of reactive components and heat-sink. However, this approach could cause conversion efficiency to drop dramatically without employing soft switching techniques or using costly new devices.This dissertation presents a new zero voltage switching control method that is suitable for low power applications such as three-phase micro-inverters. The proposed hybrid boundary conduction mode (BCM) current control method increases the efficiency and power density of the micro-inverters and features both reduced number of components and easy digital implementation. Zero voltage switching is achieved by controlling the inductor current bi-directional in every switching cycle and results in lower switching losses, higher operating frequency, and reduced size and cost of passive components, especially magnetic cores. Some practical aspects of hybrid control implementation such as dead-time insertion can degrade the performance of the micro-inverter. A dead-time compensation method that improves the performance of hybrid BCM current control by decreasing the output current THD and reducing the zero crossing distortion is presented.Different BCM ZVS current control modulation schemes are compared based on power losses breakdown, switching frequency range, and current quality. Compared to continuous conduction mode (CCM) current control, BCM ZVS control decreases MOSFET switching losses and filter inductor conduction losses but increases MOSFET conduction losses and inductor core losses. Based on the loss analysis, a dual-mode current modulation method combining ZVS and zero current switching (ZCS) schemes is proposed to improve the efficiency of the micro-inverter.Finally, a method of maintaining high power conversion efficiency across the entire load range of the three-phase micro-inverter is proposed. The proposed control method substantially increases the conversion efficiency at light loads by minimizing switching losses of semiconductor devices as well as core losses of magnetic components. This is accomplished by entering a phase skipping operating mode wherein two phases of an inverter are disabled and three inverters are combined to form a new three-phase system with minimal grid imbalance. A 400W prototype of a three-phase micro-inverter and its hybrid control system have been designed and tested under different conditions to verify the effectiveness of the proposed controller, current modulation scheme, and light load efficiency enhancement method.
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Date Issued
2014
Identifier
CFE0005125, ucf:50703
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0005125
Design Optimization of LLC Topology and Phase Skipping Control of Three Phase Inverter for PV Applications
Title
Design Optimization of LLC Topology and Phase Skipping Control of Three Phase Inverter for PV Applications.
Creator
Somani, Utsav, Batarseh, Issa, Wu, Xinzhang, Seyedi-Esfahani, Seyed-alireza, University of Central Florida
Abstract / Description
The world is heading towards an energy crisis and desperate efforts are being made to find an alternative, reliable and clean source of energy. Solar Energy is one of the most clean and reliable source of renewable energy on earth. Conventionally, extraction of solar power for electricity generation was limited to PV farms, however lately Distributed Generation form of Solar Power has emerged in the form of residential and commercial Grid Tied Micro-Inverters. Grid Tied Micro-Inverters are...
Show moreThe world is heading towards an energy crisis and desperate efforts are being made to find an alternative, reliable and clean source of energy. Solar Energy is one of the most clean and reliable source of renewable energy on earth. Conventionally, extraction of solar power for electricity generation was limited to PV farms, however lately Distributed Generation form of Solar Power has emerged in the form of residential and commercial Grid Tied Micro-Inverters. Grid Tied Micro-Inverters are costly when compared to their string type counterparts because one inverter module is required for every single or every two PV panels whereas a string type micro-inverter utilizes a single inverter module over a string of PV panels. Since in micro-inverter every panel has a dedicated inverter module, more power per panel can be extracted by performing optimal maximum power tracking over single panel rather than over an entire string of panels. Power per panel extracted by string inverters may be lower than its maximum value as few of the panels in the string may or may not be shaded and thereby forming the weaker links of the system.In order to justify the higher costs of Micro-Inverters, it is of utmost importance to convert the available power with maximum possible efficiency. Typically, a micro-inverter consists of two important blocks; a Front End DC-DC Converter and Output DC-AC Inverter. This thesis proposes efficiency optimization techniques for both the blocks of the micro-inverter. Efficiency Optimization of Front End DC-DC Converter-This thesis aims to optimize the efficiency of the front end stage by proposing optimal design procedure for resonant parameters of LLC Topology as a Front End DC-DC Converter for PV Applications. It exploits the I-V characteristics of a solar panel to design the resonant parameters such that resonant LLC topology operates near its resonant frequency operating point which is the highest efficiency operating point of LLC Converter.Efficiency Optimization of Output DC-AC Inverter-Due to continuously variable irradiance levels of solar energy, available power for extraction is constantly varying which causes the PV Inverter operates at its peak load capacity for less than 15% of the day time. Every typical power converter suffers through poor light load efficiency performance because of the load independent losses present in a power converter. In order to improve the light load efficiency performance of Three Phase Inverters, this thesis proposes Phase Skipping Control technique for Three Phase Grid Tied Micro-Inverters. The proposed technique is a generic control technique and can be applied to any inverter topology, however, in order to establish the proof of concept this control technique has been implemented on Three Phase Half Bridge PWM Inverter and its analysis is provided. Improving light load efficiency helps to improve the CEC efficiency of the inverter.
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Date Issued
2013
Identifier
CFE0005265, ucf:50573
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0005265