Matching Items (43)

152216-Thumbnail Image.png

A single-phase current source solar inverter with constant instantaneous power, improved reliability, and reduced-size DC-link filter

Description

This dissertation presents a novel current source converter topology that is primarily intended for single-phase photovoltaic (PV) applications. In comparison with the existing PV inverter technology, the salient features of the proposed topology are: a) the low frequency (double of

This dissertation presents a novel current source converter topology that is primarily intended for single-phase photovoltaic (PV) applications. In comparison with the existing PV inverter technology, the salient features of the proposed topology are: a) the low frequency (double of line frequency) ripple that is common to single-phase inverters is greatly reduced; b) the absence of low frequency ripple enables significantly reduced size pass components to achieve necessary DC-link stiffness and c) improved maximum power point tracking (MPPT) performance is readily achieved due to the tightened current ripple even with reduced-size passive components. The proposed topology does not utilize any electrolytic capacitors. Instead an inductor is used as the DC-link filter and reliable AC film capacitors are utilized for the filter and auxiliary capacitor. The proposed topology has a life expectancy on par with PV panels. The proposed modulation technique can be used for any current source inverter where an unbalanced three-phase operation is desires such as active filters and power controllers. The proposed topology is ready for the next phase of microgrid and power system controllers in that it accepts reactive power commands. This work presents the proposed topology and its working principle supported by with numerical verifications and hardware results. Conclusions and future work are also presented.

Contributors

Agent

Created

Date Created
2013

154051-Thumbnail Image.png

Solar micro inverter modeling and reliability

Description

The demand for cleaner energy technology is increasing very rapidly. Hence it is

important to increase the eciency and reliability of this emerging clean energy technologies.

This thesis focuses on modeling and reliability of solar micro inverters. In

order to make photovoltaics (PV)

The demand for cleaner energy technology is increasing very rapidly. Hence it is

important to increase the eciency and reliability of this emerging clean energy technologies.

This thesis focuses on modeling and reliability of solar micro inverters. In

order to make photovoltaics (PV) cost competitive with traditional energy sources,

the economies of scale have been guiding inverter design in two directions: large,

centralized, utility-scale (500 kW) inverters vs. small, modular, module level (300

W) power electronics (MLPE). MLPE, such as microinverters and DC power optimizers,

oer advantages in safety, system operations and maintenance, energy yield,

and component lifetime due to their smaller size, lower power handling requirements,

and module-level power point tracking and monitoring capability [1]. However, they

suer from two main disadvantages: rst, depending on array topology (especially

the proximity to the PV module), they can be subjected to more extreme environments

(i.e. temperature cycling) during the day, resulting in a negative impact to

reliability; second, since solar installations can have tens of thousands to millions of

modules (and as many MLPE units), it may be dicult or impossible to track and

repair units as they go out of service. Therefore identifying the weak links in this

system is of critical importance to develop more reliable micro inverters.

While an overwhelming majority of time and research has focused on PV module

eciency and reliability, these issues have been largely ignored for the balance

of system components. As a relatively nascent industry, the PV power electronics

industry does not have the extensive, standardized reliability design and testing procedures

that exist in the module industry or other more mature power electronics

industries (e.g. automotive). To do so, the critical components which are at risk and

their impact on the system performance has to be studied. This thesis identies and

addresses some of the issues related to reliability of solar micro inverters.

This thesis presents detailed discussions on various components of solar micro inverter

and their design. A micro inverter with very similar electrical specications in

comparison with commercial micro inverter is modeled in detail and veried. Components

in various stages of micro inverter are listed and their typical failure mechanisms

are reviewed. A detailed FMEA is conducted for a typical micro inverter to identify

the weak links of the system. Based on the S, O and D metrics, risk priority number

(RPN) is calculated to list the critical at-risk components. Degradation of DC bus

capacitor is identied as one the failure mechanism and the degradation model is built

to study its eect on the system performance. The system is tested for surge immunity

using standard ring and combinational surge waveforms as per IEEE 62.41 and

IEC 61000-4-5 standards. All the simulation presented in this thesis is performed

using PLECS simulation software.

Contributors

Agent

Created

Date Created
2015

154495-Thumbnail Image.png

Distribution system modeling, analysis and design with high penetration of photovoltaic generation

Description

Present distribution infrastructure is designed mainly for uni-directional power flow with well-controlled generation. An increase in the inverter-interfaced photovoltaic (PV) systems requires a thorough re-examination of the design, operation, protection and control of distribution systems. In order to understand the

Present distribution infrastructure is designed mainly for uni-directional power flow with well-controlled generation. An increase in the inverter-interfaced photovoltaic (PV) systems requires a thorough re-examination of the design, operation, protection and control of distribution systems. In order to understand the impact of high penetration of PV generation, this work conducts an automated and detailed modeling of a power distribution system. The simulation results of the modeled distribution feeder have been verified with the field measurements.

Based on the feeder model, this work studies the impact of the PV systems on voltage profiles under various scenarios, including reallocation of the PV systems, reactive power support from the PV inverters, and settings of the load-tap changing transformers in coordination with the PV penetration. Design recommendations have been made based on the simulation results to improve the voltage profiles in the feeder studied.

To carry out dynamic studies related to high penetration of PV systems, this work proposes a differential algebraic equation (DAE) based dynamic modeling and analysis method. Different controllers including inverter current controllers, anti-islanding controllers and droop controllers, are designed and tested in large systems. The method extends the capability of the distribution system analysis tools, to help conduct dynamic analyses in large unbalanced distribution systems.

Another main contribution of this work is related to the investigation of the PV impacts on the feeder protection coordination. Various protection coordination types, including fuse-fuse, recloser-fuse, relay-fuse and relay-recloser have been studied. The analyses provide a better understanding of the relay and recloser settings under different configurations of the PV interconnection transformers, PV penetration levels, and fault types.

A decision tree and fuzzy logic based fault location identification process has also been proposed in this work. The process is composed of the off-line training of the decision tree, and the on-line analysis of the fault events. Fault current contribution from the PV systems, as well as the variation of the fault resistance have been taken into consideration. Two actual fault cases with the event data recorded were used to examine the effectiveness of the fault identification process.

Contributors

Agent

Created

Date Created
2016

151100-Thumbnail Image.png

Experimental demonstration of photovoltaic powered solar cooling with ice storage

Description

The ability to shift the photovoltaic (PV) power curve and make the energy accessible during peak hours can be accomplished through pairing solar PV with energy storage technologies. A prototype hybrid air conditioning system (HACS), built under supervision of project

The ability to shift the photovoltaic (PV) power curve and make the energy accessible during peak hours can be accomplished through pairing solar PV with energy storage technologies. A prototype hybrid air conditioning system (HACS), built under supervision of project head Patrick Phelan, consists of PV modules running a DC compressor that operates a conventional HVAC system paired with a second evaporator submerged within a thermal storage tank. The thermal storage is a 0.284m3 or 75 gallon freezer filled with Cryogel balls, submerged in a weak glycol solution. It is paired with its own separate air handler, circulating the glycol solution. The refrigerant flow is controlled by solenoid valves that are electrically connected to a high and low temperature thermostat. During daylight hours, the PV modules run the DC compressor. The refrigerant flow is directed to the conventional HVAC air handler when cooling is needed. Once the desired room temperature is met, refrigerant flow is diverted to the thermal storage, storing excess PV power. During peak energy demand hours, the system uses only small amounts of grid power to pump the glycol solution through the air handler (note the compressor is off), allowing for money and energy savings. The conventional HVAC unit can be scaled down, since during times of large cooling demands the glycol air handler can be operated in parallel with the conventional HVAC unit. Four major test scenarios were drawn up in order to fully comprehend the performance characteristics of the HACS. Upon initial running of the system, ice was produced and the thermal storage was charged. A simple test run consisting of discharging the thermal storage, initially ~¼ frozen, was performed. The glycol air handler ran for 6 hours and the initial cooling power was 4.5 kW. This initial test was significant, since greater than 3.5 kW of cooling power was produced for 3 hours, thus demonstrating the concept of energy storage and recovery.

Contributors

Agent

Created

Date Created
2012

152025-Thumbnail Image.png

Mitigating the detrimental impacts of solar PV penetration on electric power transmission systems

Description

At present, almost 70% of the electric energy in the United States is produced utilizing fossil fuels. Combustion of fossil fuels contributes CO2 to the atmosphere, potentially exacerbating the impact on global warming. To make the electric power system (EPS)

At present, almost 70% of the electric energy in the United States is produced utilizing fossil fuels. Combustion of fossil fuels contributes CO2 to the atmosphere, potentially exacerbating the impact on global warming. To make the electric power system (EPS) more sustainable for the future, there has been an emphasis on scaling up generation of electric energy from wind and solar resources. These resources are renewable in nature and have pollution free operation. Various states in the US have set up different goals for achieving certain amount of electrical energy to be produced from renewable resources. The Southwestern region of the United States receives significant solar radiation throughout the year. High solar radiation makes concentrated solar power and solar PV the most suitable means of renewable energy production in this region. However, the majority of the projects that are presently being developed are either residential or utility owned solar PV plants. This research explores the impact of significant PV penetration on the steady state voltage profile of the electric power transmission system. This study also identifies the impact of PV penetration on the dynamic response of the transmission system such as rotor angle stability, frequency response and voltage response after a contingency. The light load case of spring 2010 and the peak load case of summer 2018 have been considered for analyzing the impact of PV. If the impact is found to be detrimental to the normal operation of the EPS, mitigation measures have been devised and presented in the thesis. Commercially available software tools/packages such as PSLF, PSS/E, DSA Tools have been used to analyze the power network and validate the results.

Contributors

Agent

Created

Date Created
2013

150050-Thumbnail Image.png

A DC-DC multiport converter based solid state transformer integrating distributed generation and storage

Description

The development of a Solid State Transformer (SST) that incorporates a DC-DC multiport converter to integrate both photovoltaic (PV) power generation and battery energy storage is presented in this dissertation. The DC-DC stage is based on a quad-active-bridge (QAB) converter

The development of a Solid State Transformer (SST) that incorporates a DC-DC multiport converter to integrate both photovoltaic (PV) power generation and battery energy storage is presented in this dissertation. The DC-DC stage is based on a quad-active-bridge (QAB) converter which not only provides isolation for the load, but also for the PV and storage. The AC-DC stage is implemented with a pulse-width-modulated (PWM) single phase rectifier. A unified gyrator-based average model is developed for a general multi-active-bridge (MAB) converter controlled through phase-shift modulation (PSM). Expressions to determine the power rating of the MAB ports are also derived. The developed gyrator-based average model is applied to the QAB converter for faster simulations of the proposed SST during the control design process as well for deriving the state-space representation of the plant. Both linear quadratic regulator (LQR) and single-input-single-output (SISO) types of controllers are designed for the DC-DC stage. A novel technique that complements the SISO controller by taking into account the cross-coupling characteristics of the QAB converter is also presented herein. Cascaded SISO controllers are designed for the AC-DC stage. The QAB demanded power is calculated at the QAB controls and then fed into the rectifier controls in order to minimize the effect of the interaction between the two SST stages. The dynamic performance of the designed control loops based on the proposed control strategies are verified through extensive simulation of the SST average and switching models. The experimental results presented herein show that the transient responses for each control strategy match those from the simulations results thus validating them.

Contributors

Agent

Created

Date Created
2011

150154-Thumbnail Image.png

Advanced nanostructured concepts in solar cells using III-V and silicon-based materials

Description

As existing solar cell technologies come closer to their theoretical efficiency, new concepts that overcome the Shockley-Queisser limit and exceed 50% efficiency need to be explored. New materials systems are often investigated to achieve this, but the use of existing

As existing solar cell technologies come closer to their theoretical efficiency, new concepts that overcome the Shockley-Queisser limit and exceed 50% efficiency need to be explored. New materials systems are often investigated to achieve this, but the use of existing solar cell materials in advanced concept approaches is compelling for multiple theoretical and practical reasons. In order to include advanced concept approaches into existing materials, nanostructures are used as they alter the physical properties of these materials. To explore advanced nanostructured concepts with existing materials such as III-V alloys, silicon and/or silicon/germanium and associated alloys, fundamental aspects of using these materials in advanced concept nanostructured solar cells must be understood. Chief among these is the determination and predication of optimum electronic band structures, including effects such as strain on the band structure, and the material's opto-electronic properties. Nanostructures have a large impact on band structure and electronic properties through quantum confinement. An additional large effect is the change in band structure due to elastic strain caused by lattice mismatch between the barrier and nanostructured (usually self-assembled QDs) materials. To develop a material model for advanced concept solar cells, the band structure is calculated for single as well as vertical array of quantum dots with the realistic effects such as strain, associated with the epitaxial growth of these materials. The results show significant effect of strain in band structure. More importantly, the band diagram of a vertical array of QDs with different spacer layer thickness show significant change in band offsets, especially for heavy and light hole valence bands when the spacer layer thickness is reduced. These results, ultimately, have significance to develop a material model for advance concept solar cells that use the QD nanostructures as absorbing medium. The band structure calculations serve as the basis for multiple other calculations. Chief among these is that the model allows the design of a practical QD advanced concept solar cell, which meets key design criteria such as a negligible valence band offset between the QD/barrier materials and close to optimum band gaps, resulting in the predication of optimum material combinations.

Contributors

Agent

Created

Date Created
2011

151039-Thumbnail Image.png

Photovoltaic sub-module integrated converter analysis

Description

With the rapid expansion of the photovoltaic industry over the last decade, there has been a huge demand in the PV installations in the residential sector. This thesis focuses on the analysis and implementation of a dc-dc boost converter at

With the rapid expansion of the photovoltaic industry over the last decade, there has been a huge demand in the PV installations in the residential sector. This thesis focuses on the analysis and implementation of a dc-dc boost converter at photovoltaic sub-module level. The thesis also analyses the various topologies like switched capacitors and extended duty ratio which can be practically implemented in the photovoltaic panels. The results obtained in this work have concentrated on the use of novel strategies to substitute the use of central dc-dc converter used in PV module string connection. The implementation of distributed MPPT at the PV sub-module level is also an integral part of this thesis. Using extensive PLECS simulations, this thesis came to the conclusion that with the design of a proper compensation at the dc interconnection of a series or parallel PV Module Integrated Converter string, the central dc-dc converter can be substituted. The dc-ac interconnection voltage remains regulated at all irradiance level even without a dc-dc central converter at the string end. The foundation work for the hardware implementation has also been carried out. Design of parameters for future hardware implementation has also been presented in detail in this thesis.

Contributors

Agent

Created

Date Created
2012

149523-Thumbnail Image.png

Environmental, policy and social analysis of photovoltaic technologies

Description

Many expect renewable energy technologies to play a leading role in a sustainable energy supply system and to aid the shift away from an over-reliance on traditional hydrocarbon resources in the next few decades. This dissertation develops environmental, policy and

Many expect renewable energy technologies to play a leading role in a sustainable energy supply system and to aid the shift away from an over-reliance on traditional hydrocarbon resources in the next few decades. This dissertation develops environmental, policy and social models to help understand various aspects of photovoltaic (PV) technologies. The first part of this dissertation advances the life cycle assessment (LCA) of PV systems by expanding the boundary of included processes using hybrid LCA and accounting for the technology-driven dynamics of environmental impacts. Hybrid LCA extends the traditional method combining bottom-up process-sum and top-down economic input-output (EIO) approaches. The embodied energy and carbon of multi-crystalline silicon photovoltaic systems are assessed using hybrid LCA. From 2001 to 2010, the embodied energy and carbon fell substantially, indicating that technological progress is realizing reductions in environmental impacts in addition to lower module price. A variety of policies support renewable energy adoption, and it is critical to make them function cooperatively. To reveal the interrelationships among these policies, the second part of this dissertation proposes three tiers of policy architecture. This study develops a model to determine the specific subsidies required to support a Renewable Portfolio Standard (RPS) goal. The financial requirements are calculated (in two scenarios) and compared with predictable funds from public sources. A main result is that the expected investments to achieve the RPS goal far exceed the economic allocation for subsidy of distributed PV. Even with subsidies there are often challenges with social acceptance. The third part of this dissertation originally develops a fuzzy logic inference model to relate consumers' attitudes about the technology such as perceived cost, maintenance, and environmental concern to their adoption intention. Fuzzy logic inference model is a type of soft computing models. It has the advantage of dealing with imprecise and insufficient information and mimicking reasoning processes of human brains. This model is implemented in a case study of residential PV adoption using data through a survey of homeowners in Arizona. The output of this model is the purchasing probability of PV.

Contributors

Agent

Created

Date Created
2010

149383-Thumbnail Image.png

Power rating of photovoltaic modules: repeatability of measurements and validation of translation procedures

Description

Power rating photovoltaic modules at six irradiance and four temperature matrix levels of IEC 61853-1 draft standard is one of the most important requirements to accurately predict energy production of photovoltaic modules at different climatic conditions. Two studies were carried

Power rating photovoltaic modules at six irradiance and four temperature matrix levels of IEC 61853-1 draft standard is one of the most important requirements to accurately predict energy production of photovoltaic modules at different climatic conditions. Two studies were carried out in this investigation: a measurement repeatability study and a translation procedure validation study. The repeatability study was carried out to define a testing methodology that allows generating repeatable power rating results under outdoor conditions. The validation study was carried out to validate the accuracy of the four translation procedures: the first three procedures are from the IEC 60891 standard and the fourth procedure is reported by NREL. These translation procedures are needed to translate the measured data from the actual test conditions to the reporting rating conditions required by the IEC 61853-1 draft standard. All the measurements were carried out outdoors on clear days using a manual, 2-axis tracker, located in Mesa/Tempe, Arizona. Four module technologies were investigated: crystalline silicon, amorphous silicon, cadmium telluride, and copper indium gallium selenide. The modules were cooled and then allowed to naturally warm up to obtain current-voltage data at different temperatures. Several black mesh screens with a wide range of transmittance were used for varying irradiance levels. From the measurements repeatability study, it was determined that: (i) a certain minimum distance (2 inches) should be maintained between module surface and the screen surface; (ii) the reference cell should be kept outside the screen (calibrated screen) as opposed to inside the screen (uncalibrated screen); and (iii) the air mass should not exceed 2.5. From the translation procedure validation study, it was determined that the accuracy of the translation procedure depends on the irradiance and temperature range of translation. The difference between measured and translatet power at maximum power point (Pmax) is determined to be less than 3% for all the technologies, all the irradiance/ temperature ranges investigated and all the procedures except Procedure 2 of IEC 60891 standard. For the Procedure 2, the difference was found to fall between 3% and 17% depending on the irradiance range used for the translation. The difference of 17% is very large and unacceptable. This work recommends reinvestigating the cause for this large difference for Procedure 2. Finally, a complete power rating matrix for each of the four module technologies has been successfully generated as per IEC 61853-1 draft standard.

Contributors

Agent

Created

Date Created
2010