ASU Electronic Theses and Dissertations
This collection includes most of the ASU Theses and Dissertations from 2011 to present. ASU Theses and Dissertations are available in downloadable PDF format; however, a small percentage of items are under embargo. Information about the dissertations/theses includes degree information, committee members, an abstract, supporting data or media.
In addition to the electronic theses found in the ASU Digital Repository, ASU Theses and Dissertations can be found in the ASU Library Catalog.
Dissertations and Theses granted by Arizona State University are archived and made available through a joint effort of the ASU Graduate College and the ASU Libraries. For more information or questions about this collection contact or visit the Digital Repository ETD Library Guide or contact the ASU Graduate College at gradformat@asu.edu.
Displaying 21 - 30 of 42
Description
Underground transmission cables in power systems are less likely to experience electrical faults, however, resulting outage times are much greater in the event that a failure does occur. Unlike overhead lines, underground cables are not self-healing from flashover events. The faulted section must be located and repaired before the line can be put back into service. Since this will often require excavation of the underground duct bank, the procedure to repair the faulted section is both costly and time consuming. These added complications are the prime motivators for developing accurate and reliable ratings for underground cable circuits.
This work will review the methods by which power ratings, or ampacity, for underground cables are determined and then evaluate those ratings by making comparison with measured data taken from an underground 69 kV cable, which is part of the Salt River Project (SRP) power subtransmission system. The process of acquiring, installing, and commissioning the temperature monitoring system is covered in detail as well. The collected data are also used to evaluate typical assumptions made when determining underground cable ratings such as cable hot-spot location and ambient temperatures.
Analysis results show that the commonly made assumption that the deepest portion of an underground power cable installation will be the hot-spot location does not always hold true. It is shown that distributed cable temperature measurements can be used to locate the proper line segment to be used for cable ampacity calculations.
This work will review the methods by which power ratings, or ampacity, for underground cables are determined and then evaluate those ratings by making comparison with measured data taken from an underground 69 kV cable, which is part of the Salt River Project (SRP) power subtransmission system. The process of acquiring, installing, and commissioning the temperature monitoring system is covered in detail as well. The collected data are also used to evaluate typical assumptions made when determining underground cable ratings such as cable hot-spot location and ambient temperatures.
Analysis results show that the commonly made assumption that the deepest portion of an underground power cable installation will be the hot-spot location does not always hold true. It is shown that distributed cable temperature measurements can be used to locate the proper line segment to be used for cable ampacity calculations.
ContributorsStowers, Travis (Author) / Tylavsky, Daniel (Thesis advisor) / Karady, George G. (Committee member) / Holbert, Keith E. (Committee member) / Arizona State University (Publisher)
Created2015
Description
Shunt capacitors are often added in transmission networks at suitable locations to improve the voltage profile. In this thesis, the transmission system in Arizona is considered as a test bed. Many shunt capacitors already exist in the Arizona transmission system and more are planned to be added. Addition of these shunt capacitors may create resonance conditions in response to harmonic voltages and currents. Such resonance, if it occurs, may create problematic issues in the system. It is main objective of this thesis to identify potential problematic effects that could occur after placing new shunt capacitors at selected buses in the Arizona network. Part of the objective is to create a systematic plan for avoidance of resonance issues.
For this study, a method of capacitance scan is proposed. The bus admittance matrix is used as a model of the networked transmission system. The calculations on the admittance matrix were done using Matlab. The test bed is the actual transmission system in Arizona; however, for proprietary reasons, bus names are masked in the thesis copy in-tended for the public domain. The admittance matrix was obtained from data using the PowerWorld Simulator after equivalencing the 2016 summer peak load (planning case). The full Western Electricity Coordinating Council (WECC) system data were used. The equivalencing procedure retains only the Arizona portion of the WECC.
The capacitor scan results for single capacitor placement and multiple capacitor placement cases are presented. Problematic cases are identified in the form of ‘forbidden response. The harmonic voltage impact of known sources of harmonics, mainly large scale HVDC sources, is also presented.
Specific key results for the study indicated include:
• The forbidden zones obtained as per the IEEE 519 standard indicates the bus 10 to be the most problematic bus.
• The forbidden zones also indicate that switching values for the switched shunt capacitor (if used) at bus 3 should be should be considered carefully to avoid resonance condition from existing.
• The highest sensitivity of 0.0033 per unit for HVDC sources of harmonics was observed at bus 7 when all the HVDC sources were active at the same time.
For this study, a method of capacitance scan is proposed. The bus admittance matrix is used as a model of the networked transmission system. The calculations on the admittance matrix were done using Matlab. The test bed is the actual transmission system in Arizona; however, for proprietary reasons, bus names are masked in the thesis copy in-tended for the public domain. The admittance matrix was obtained from data using the PowerWorld Simulator after equivalencing the 2016 summer peak load (planning case). The full Western Electricity Coordinating Council (WECC) system data were used. The equivalencing procedure retains only the Arizona portion of the WECC.
The capacitor scan results for single capacitor placement and multiple capacitor placement cases are presented. Problematic cases are identified in the form of ‘forbidden response. The harmonic voltage impact of known sources of harmonics, mainly large scale HVDC sources, is also presented.
Specific key results for the study indicated include:
• The forbidden zones obtained as per the IEEE 519 standard indicates the bus 10 to be the most problematic bus.
• The forbidden zones also indicate that switching values for the switched shunt capacitor (if used) at bus 3 should be should be considered carefully to avoid resonance condition from existing.
• The highest sensitivity of 0.0033 per unit for HVDC sources of harmonics was observed at bus 7 when all the HVDC sources were active at the same time.
ContributorsPatil, Hardik U (Author) / Heydt, Gerald T (Thesis advisor) / Karady, George G. (Committee member) / Ayyanar, Raja (Committee member) / Arizona State University (Publisher)
Created2015
Description
The dissertation encompasses the transformer-less single phase PV inverters for both the string and microinverter applications. Two of the major challenge with such inverters include the presence of high-frequency common mode leakage current and double line frequency power decoupling with reliable capacitors without compromising converter power density. Two solutions are presented in this dissertation: half-bridge voltage swing (HBVS) and dynamic dc link (DDCL) inverters both of which completely eliminates the ground current through topological improvement. In addition, through active power decoupling technique, the capacitance requirement is reduced for both, thus achieving an all film-capacitor based solution with higher reliability. Also both the approaches are capable of supporting a wide range of power factor.
Moreover, wide band-gap devices (both SiC and GaN) are used for implementing their hardware prototypes. It enables the switching frequency to be high without compromising on the converter efficiency. Also it allows a reduced magnetic component size, further enabling a high power density solution, with power density far beyond the state-of-the art solutions.
Additionally, for the transformer-less microinverter application, another challenge is to achieve a very high gain DC-DC stage with a simultaneous high conversion efficiency. An extended duty ratio (EDR) boost converter which is a hybrid of switched capacitors and interleaved inductor technique, has been implemented for this purpose. It offers higher converter efficiency as most of the switches encounter lower voltage stress directly impacting switching loss; the input current being shared among all the interleaved converters (inherent sharing only in a limited duty ratio), the inductor conduction loss is reduced by a factor of the number of phases.
Further, the EDR boost converter has been studied for both discontinuous conduction mode (DCM) operations and operations with wide input/output voltage range in continuous conduction mode (CCM). A current sharing between its interleaved input phases is studied in detail to show that inherent sharing is possible for only in a limited duty ratio span, and modification of the duty ratio scheme is proposed to ensure equal current sharing over all the operating range for 3 phase EDR boost. All the analysis are validated with experimental results.
Moreover, wide band-gap devices (both SiC and GaN) are used for implementing their hardware prototypes. It enables the switching frequency to be high without compromising on the converter efficiency. Also it allows a reduced magnetic component size, further enabling a high power density solution, with power density far beyond the state-of-the art solutions.
Additionally, for the transformer-less microinverter application, another challenge is to achieve a very high gain DC-DC stage with a simultaneous high conversion efficiency. An extended duty ratio (EDR) boost converter which is a hybrid of switched capacitors and interleaved inductor technique, has been implemented for this purpose. It offers higher converter efficiency as most of the switches encounter lower voltage stress directly impacting switching loss; the input current being shared among all the interleaved converters (inherent sharing only in a limited duty ratio), the inductor conduction loss is reduced by a factor of the number of phases.
Further, the EDR boost converter has been studied for both discontinuous conduction mode (DCM) operations and operations with wide input/output voltage range in continuous conduction mode (CCM). A current sharing between its interleaved input phases is studied in detail to show that inherent sharing is possible for only in a limited duty ratio span, and modification of the duty ratio scheme is proposed to ensure equal current sharing over all the operating range for 3 phase EDR boost. All the analysis are validated with experimental results.
ContributorsRoy, Jinia (Author) / Ayyanar, Raja (Thesis advisor) / Karady, George G. (Committee member) / Qin, Jiangchao (Committee member) / Lei, Qin (Committee member) / Arizona State University (Publisher)
Created2017
Description
The growth of energy demands in recent years has been increasing faster than the expansion of transmission facility construction. This tendency cooperating with the continuous investing on the renewable energy resources drives the research, development, and construction of HVDC projects to create a more reliable, affordable, and environmentally friendly power grid.
Constructing the hybrid AC-HVDC grid is a significant move in the development of the HVDC techniques; the form of dc system is evolving from the point-to-point stand-alone dc links to the embedded HVDC system and the multi-terminal HVDC (MTDC) system. The MTDC is a solution for the renewable energy interconnections, and the MTDC grids can improve the power system reliability, flexibility in economic dispatches, and converter/cable utilizing efficiencies.
The dissertation reviews the HVDC technologies, discusses the stability issues regarding the ac and HVDC connections, proposes a novel power oscillation control strategy to improve system stability, and develops a nonlinear voltage droop control strategy for the MTDC grid.
To verify the effectiveness the proposed power oscillation control strategy, a long distance paralleled AC-HVDC transmission test system is employed. Based on the PSCAD/EMTDC platform simulation results, the proposed power oscillation control strategy can improve the system dynamic performance and attenuate the power oscillations effectively.
To validate the nonlinear voltage droop control strategy, three droop controls schemes are designed according to the proposed nonlinear voltage droop control design procedures. These control schemes are tested in a hybrid AC-MTDC system. The hybrid AC-MTDC system, which is first proposed in this dissertation, consists of two ac grids, two wind farms and a five-terminal HVDC grid connecting them. Simulation studies are performed in the PSCAD/EMTDC platform. According to the simulation results, all the three design schemes have their unique salient features.
Constructing the hybrid AC-HVDC grid is a significant move in the development of the HVDC techniques; the form of dc system is evolving from the point-to-point stand-alone dc links to the embedded HVDC system and the multi-terminal HVDC (MTDC) system. The MTDC is a solution for the renewable energy interconnections, and the MTDC grids can improve the power system reliability, flexibility in economic dispatches, and converter/cable utilizing efficiencies.
The dissertation reviews the HVDC technologies, discusses the stability issues regarding the ac and HVDC connections, proposes a novel power oscillation control strategy to improve system stability, and develops a nonlinear voltage droop control strategy for the MTDC grid.
To verify the effectiveness the proposed power oscillation control strategy, a long distance paralleled AC-HVDC transmission test system is employed. Based on the PSCAD/EMTDC platform simulation results, the proposed power oscillation control strategy can improve the system dynamic performance and attenuate the power oscillations effectively.
To validate the nonlinear voltage droop control strategy, three droop controls schemes are designed according to the proposed nonlinear voltage droop control design procedures. These control schemes are tested in a hybrid AC-MTDC system. The hybrid AC-MTDC system, which is first proposed in this dissertation, consists of two ac grids, two wind farms and a five-terminal HVDC grid connecting them. Simulation studies are performed in the PSCAD/EMTDC platform. According to the simulation results, all the three design schemes have their unique salient features.
ContributorsYu, Jicheng (Author) / Karady, George G. (Thesis advisor, Committee member) / Qin, Jiangchao (Thesis advisor, Committee member) / Ayyanar, Raja (Committee member) / Holbert, Keith E. (Committee member) / Lei, Qin (Committee member) / Arizona State University (Publisher)
Created2017
Description
Li-ion batteries are being used on a large scale varying from consumer electronics to electric vehicles. The key to efficient use of batteries is implementing a well-developed battery management system. Also, there is an opportunity for research for improving the battery performance in terms of size and capacity. For all this it is imperative to develop Li-ion cell model that replicate the performance of a physical cell unit. This report discusses a dual polarization cell model and a battery management system implemented to control the operation of the battery. The Li-ion cell is modelled, and the performance is observed in PLECS environment.
The main aspect of this report studies the viability of Li-ion battery application in Battery Energy Storage System (BESS) in Modular multilevel converter (MMC). MMC-based BESS is a promising solution for grid-level battery energy storage to accelerate utilization and integration of intermittent renewable energy resources, i.e., solar and wind energy. When the battery units are directly integrated in submodules (SMs) without dc-dc interfaced converters, this configuration provides highest system efficiency and lowest cost. However, the lifetime of battery will be affected by the low-frequency components contained in arm currents, which has not been thoroughly investigated. This paper investigates impact of various low-frequency arm-current ripples on lifetime of Li-ion battery cells and evaluate performance of battery charging and discharging in an MMC-BESS without dc-dc interfaced converters.
The main aspect of this report studies the viability of Li-ion battery application in Battery Energy Storage System (BESS) in Modular multilevel converter (MMC). MMC-based BESS is a promising solution for grid-level battery energy storage to accelerate utilization and integration of intermittent renewable energy resources, i.e., solar and wind energy. When the battery units are directly integrated in submodules (SMs) without dc-dc interfaced converters, this configuration provides highest system efficiency and lowest cost. However, the lifetime of battery will be affected by the low-frequency components contained in arm currents, which has not been thoroughly investigated. This paper investigates impact of various low-frequency arm-current ripples on lifetime of Li-ion battery cells and evaluate performance of battery charging and discharging in an MMC-BESS without dc-dc interfaced converters.
ContributorsPuranik, Ishaan (Author) / Qin, Jiangchao (Thesis advisor) / Karady, George G. (Committee member) / Yu, Hongbin (Committee member) / Arizona State University (Publisher)
Created2018
Description
In recent years, wide bandgap (WBG) devices enable power converters with higher power density and higher efficiency. On the other hand, smart grid technologies are getting mature due to new battery technology and computer technology. In the near future, the two technologies will form the next generation of smart grid enabled by WBG devices. This dissertation deals with two applications: silicon carbide (SiC) device used for medium voltage level interface (7.2 kV to 240 V) and gallium nitride (GaN) device used for low voltage level interface (240 V/120 V). A 20 kW solid state transformer (SST) is designed with 6 kHz switching frequency SiC rectifier. Then three robust control design methods are proposed for each of its smart grid operation modes. In grid connected mode, a new LCL filter design method is proposed considering grid voltage THD, grid current THD and current regulation loop robust stability with respect to the grid impedance change. In grid islanded mode, µ synthesis method combined with variable structure control is used to design a robust controller for grid voltage regulation. For grid emergency mode, multivariable controller designed using H infinity synthesis method is proposed for accurate power sharing. Controller-hardware-in-the-loop (CHIL) testbed considering 7-SST system is setup with Real Time Digital Simulator (RTDS). The real TMS320F28335 DSP and Spartan 6 FPGA control board is used to interface a switching model SST in RTDS. And the proposed control methods are tested. For low voltage level application, a 3.3 kW smart grid hardware is built with 3 GaN inverters. The inverters are designed with the GaN device characterized using the proposed multi-function double pulse tester. The inverter is controlled by onboard TMS320F28379D dual core DSP with 200 kHz sampling frequency. Each inverter is tested to process 2.2 kW power with overall efficiency of 96.5 % at room temperature. The smart grid monitor system and fault interrupt devices (FID) based on Arduino Mega2560 are built and tested. The smart grid cooperates with GaN inverters through CAN bus communication. At last, the three GaN inverters smart grid achieved the function of grid connected to islanded mode smooth transition
ContributorsYao, Tong (Author) / Ayyanar, Raja (Thesis advisor) / Karady, George G. (Committee member) / Qin, Jiangchao (Committee member) / Tsakalis, Konstantinos (Committee member) / Arizona State University (Publisher)
Created2017
Description
The utilization of power cables is increasing with the development of renewable energy and the maintenance replacement of old overhead power lines. Therefore, effective monitoring and accurate fault location for power cables are very important for the sake of a stable power supply.
The recent technologies for power cable diagnosis and temperature monitoring system are described including their intrinsic limitations for cable health assessment. Power cable fault location methods are reviewed with two main categories: off-line and on-line data based methods.
As a diagnostic and fault location approach, a new passive methodology is introduced. This methodology is based on analyzing the resonant frequencies of the transfer function between the input and output of the power cable system. The equivalent pi model is applied to the resonant frequency calculation for the selected underground power cable transmission system.
The characteristics of the resonant frequencies are studied by analytical derivations and PSCAD simulations. It is found that the variation of load magnitudes and change of positive power factors (i.e., inductive loads) do not affect resonant frequencies significantly, but there is considerable movement of resonant frequencies under change of negative power factors (i.e., capacitive loads).
Power cable fault conditions introduce new resonant frequencies in accordance with fault positions. Similar behaviors of the resonant frequencies are shown in a transformer (TR) connected power cable system with frequency shifts caused by the TR impedance.
The resonant frequencies can be extracted by frequency analysis of power signals and the inherent noise in these signals plays a key role to measure the resonant frequencies. Window functions provide an effective tool for improving resonant frequency discernment. The frequency analysis is implemented on noise laden PSCAD simulation signals and it reveals identical resonant frequency characteristics with theoretical studies.
Finally, the noise levels of real voltage and current signals, which are acquired from an operating power plant, are estimated and the resonant frequencies are extracted by applying window functions, and these results prove that the resonant frequency can be used as an assessment for the internal changes in power cable parameters such as defects and faults.
The recent technologies for power cable diagnosis and temperature monitoring system are described including their intrinsic limitations for cable health assessment. Power cable fault location methods are reviewed with two main categories: off-line and on-line data based methods.
As a diagnostic and fault location approach, a new passive methodology is introduced. This methodology is based on analyzing the resonant frequencies of the transfer function between the input and output of the power cable system. The equivalent pi model is applied to the resonant frequency calculation for the selected underground power cable transmission system.
The characteristics of the resonant frequencies are studied by analytical derivations and PSCAD simulations. It is found that the variation of load magnitudes and change of positive power factors (i.e., inductive loads) do not affect resonant frequencies significantly, but there is considerable movement of resonant frequencies under change of negative power factors (i.e., capacitive loads).
Power cable fault conditions introduce new resonant frequencies in accordance with fault positions. Similar behaviors of the resonant frequencies are shown in a transformer (TR) connected power cable system with frequency shifts caused by the TR impedance.
The resonant frequencies can be extracted by frequency analysis of power signals and the inherent noise in these signals plays a key role to measure the resonant frequencies. Window functions provide an effective tool for improving resonant frequency discernment. The frequency analysis is implemented on noise laden PSCAD simulation signals and it reveals identical resonant frequency characteristics with theoretical studies.
Finally, the noise levels of real voltage and current signals, which are acquired from an operating power plant, are estimated and the resonant frequencies are extracted by applying window functions, and these results prove that the resonant frequency can be used as an assessment for the internal changes in power cable parameters such as defects and faults.
ContributorsKim, Youngdeug (Author) / Holbert, Keith Edwin (Thesis advisor) / Papandreou-Suppappola, Antonia (Committee member) / Heydt, Gerald (Committee member) / Karady, George G. (Committee member) / Arizona State University (Publisher)
Created2015
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 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.
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.
ContributorsTang, Yingying (Author) / Ayyanar, Raja (Thesis advisor) / Karady, George G. (Committee member) / Heydt, Gerald (Committee member) / Vittal, Vijay (Committee member) / Arizona State University (Publisher)
Created2016
Description
With the growing importance of underground power systems and the need for greater reliability of the power supply, cable monitoring and accurate fault location detection has become an increasingly important issue. The presence of inherent random fluctuations in power system signals can be used to extract valuable information about the condition of system equipment. One such component is the power cable, which is the primary focus of this research.
This thesis investigates a unique methodology that allows online monitoring of an underground power cable. The methodology analyzes conventional power signals in the frequency domain to monitor the condition of a power cable.
First, the proposed approach is analyzed theoretically with the help of mathematical computations. Frequency domain analysis techniques are then used to compute the power spectral density (PSD) of the system signals. The importance of inherent noise in the system, a key requirement of this methodology, is also explained. The behavior of resonant frequencies, which are unique to every system, are then analyzed under different system conditions with the help of mathematical expressions.
Another important aspect of this methodology is its ability to accurately estimate cable fault location. The process is online and hence does not require the system to be disconnected from the grid. A single line to ground fault case is considered and the trend followed by the resonant frequencies for different fault positions is observed.
The approach is initially explained using theoretical calculations followed by simulations in MATLAB/Simulink. The validity of this technique is proved by comparing the results obtained from theory and simulation to actual measurement data.
This thesis investigates a unique methodology that allows online monitoring of an underground power cable. The methodology analyzes conventional power signals in the frequency domain to monitor the condition of a power cable.
First, the proposed approach is analyzed theoretically with the help of mathematical computations. Frequency domain analysis techniques are then used to compute the power spectral density (PSD) of the system signals. The importance of inherent noise in the system, a key requirement of this methodology, is also explained. The behavior of resonant frequencies, which are unique to every system, are then analyzed under different system conditions with the help of mathematical expressions.
Another important aspect of this methodology is its ability to accurately estimate cable fault location. The process is online and hence does not require the system to be disconnected from the grid. A single line to ground fault case is considered and the trend followed by the resonant frequencies for different fault positions is observed.
The approach is initially explained using theoretical calculations followed by simulations in MATLAB/Simulink. The validity of this technique is proved by comparing the results obtained from theory and simulation to actual measurement data.
ContributorsGovindarajan, Sudarshan (Author) / Holbert, Keith E. (Thesis advisor) / Heydt, Gerald (Committee member) / Karady, George G. (Committee member) / Arizona State University (Publisher)
Created2016
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) 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.
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.
ContributorsManchanahalli Ranganatha, Arkanatha Sastry (Author) / Ayyanar, Raja (Thesis advisor) / Karady, George G. (Committee member) / Qin, Jiangchao (Committee member) / Arizona State University (Publisher)
Created2015