9 research outputs found
Open-circuit fault resilient ability multi level inverter with reduced switch count for off grid applications
In a multi-level inverter (MLI), the switching component number effect on volume and reliability is a major concern in on-grid and off-grid applications. The recent trend in MLI, reduced component number of power switches, and capacitors in multi-level inverter topologies have been driven for power conversion. The concept of fault tolerance is not considered in many such configurations; due to this the reliability of the MLI is very low. So now it is a major research concern, to develop a strong fault resilient ability power electronic converter. In this work, a novel configuration of a multilevel inverter with a lower switch count is proposed and analyzed with fault tolerance operation for improvement of reliability. Generally, the fault-tolerant operation is analyzed in only any one of the switches in MLI. But the proposed topology is concerned with multiple switch fault tolerance. Further, the phase disposition pulse width modulation (PDPWM) control scheme is utilized for the operation of the proposed inverter topology. The proposed inverter topology is simulated in MATLAB/Simulink environment under normal and faulty condition; the results are obtained and validated
Modified impedance-source inverter with continuous input currents and fault-tolerant operations
Impedance-source (Z-source) inverters are increasingly adopted in practice, where a high voltage gain is required. However, issues like drawing a non-continuous current from the DC source and ceasing the energy supply under DC source faults are also observed. In this paper, an embedded enhanced-boost Z-source inverter (EEB-ZSI) is thus proposed to tackle the issues. The proposed EEB-ZSI employs two DC sources, which enable the continuous input current and fault-tolerant operations (e.g., open-circuit and short-circuit faults in the DC sources). The operational principles are presented in detail with an in-depth circuit analysis. Moreover, the proposed EEB-ZSI is benchmarked with prior-art Z-source inverters. Experimental tests further demonstrate the effectiveness of EEB-ZSI regarding the continuous input current and flexible fault tolerance.</jats:p
Model predictive control applied to an improved five-level bidirectional converter
This paper presents an improved five level bidirectional converter (iFBC) controlled by finite control set model predictive control (FCS-MPC). This control strategy consists in using the discrete time nature of the iFBC to define its state in each sampling interval. Using FCS-MPC the switching frequency is not constant; however, it is suitable to follow the current reference with low total harmonic distortion (THD). The iFBC prototype that was specially developed for obtaining experimental results is described in detail along the paper, as well as its principle of operation, power theory, and current control strategy. The iFBC was experimentally validated connected to the power grid through a second order LfCf passive filter, operating as an active rectifier and as a grid tie inverter. For both operation modes, the experimental results confirm the good performance (in terms of efficiency, low current THD and controlled output voltage) of the iFBC controlled by FCS-MPC.FC
A Fault-Tolerant Single-Phase Five-Level Inverter for Grid-Independent PV Systems
In this paper, a fault-tolerant single-phase five-level inverter configuration is proposed for photovoltaic (PV) generation systems. Conventional two-level inverters are popularly used in PV applications, but these inverters provide the output voltage with considerable harmonic content. One of the efficient ways to improve the power quality of PV generation systems is to replace a two-level inverter with a multilevel inverter. Conventional multilevel inverters reduce total harmonic distortion and filter requirements effectively, but it has limitations in terms of reliability due to increased device count and capacitor voltage balancing issues. Therefore, a fault-tolerant single-phase five-level inverter is presented, which is constructed by using a half-bridge two-level inverter, a three-level diode clamp inverter, and a bidirectional switch. The proposed inverter topology can tolerate the system faults due to failure of the source and/or switching devices with least modification in the switching combinations. It has less number of switching devices compared to conventional five-level inverters. The topology also has the energy-balancing capability between sources which helps in reducing uneven charge of batteries in case of partial shading or hotspots on one side of the PV panels. The proposed system under normal and faulty condition is simulated in MATLAB/Simulink environment, and results are verified with a laboratory prototype
Investigations of New Fault-Tolerant Methods for Multilevel Inverters
The demands of power electronics with high power capability have increased in the last decades. These needs have driven the expansion of existing power electronics topologies and developing new power electronics generations. Multilevel inverters (MLI) are one of the most promising power electronics circuits that have been implemented and commercialized in high-voltage direct current (HVDC), motor drives, and battery energy storage systems (BESS). The expanding uses of the MLI have lead to creation of new topologies for different applications. However, one of the disadvantages of using MLIs is their complexity. MLIs consist of a large number of switching devices, which can result in a reduction of system reliability. There are significant challenges to the design of a reliable system that has the MLI’s capability with integrated fault-tolerance. In other words, design a system that can handle the fault, totally or partially, while maintaining high power capabilities and efficiency.
This aim of this dissertation is to investigate the fault-tolerance of MLIs from two different points of view:
1- Develop new solutions for existing MLI topologies. In other words, add some features to existing MLIs to improve their reliability when a fault occurs.
2- Design new MLIs that have a fault-tolerant capability.
A new open-circuit fault detection is proposed in this dissertation. The new fault detection method is based on monitoring the output voltage of each cell and leg voltage polarity along with each switch state. By monitoring each cell output voltage and leg voltage, the faulty cell can be detected and isolated.
A novel circuit to maintain system operation under the condition of one (or more) components suffering from a faulted condition is also proposed in this dissertation. This results in a topology that continues to operate at full capability.
Additionally, a new topology is proposed that offers reducing the number of batteries by 50%. Also, it has the ability to operate under non-unity power factor, which enables it to be suitable for battery energy storage systems, and static compensator (STATCOM) applications.
Another novel hybrid cascaded H-bridge (CHB), known as the X-CHB, for a fault-tolerant operation is proposed in this dissertation. It ensures seamless operation of the system under an open/short circuit switching fault or dc supply fault
Fault Tolerant Multilevel Inverter Topologies with Energy Balancing Capability: Photovoltaic Application
The continuous increase in energy demand and depletion of conventional
resources motivates the research towards the environment friendly renewable energy
sources like solar and wind energy. These sources are best suitable for rural, urban
and offshore locations, because of easy installation, less running cost and ample
resources (sun light and wind). The remote locations are mostly islanded in nature
and far away from technical expertise in case of troubleshooting. This motivates the
research on development of fault tolerant converters. These fault tolerant converters
increases the reliability, which provides the continuous power supply to critical
loads. From the last few decades, the integration of multilevel inverters with
renewable energy systems is also increasing because of advantages like, improved
power quality, total harmonic distortion (THD) and reduced output filter size
requirement. Employing conventional multilevel inverters for increasing the number
of voltage levels increases the device count and isolated DC sources. As a result
probability of semiconductor switch failure is more and energy balancing issue
between sources, which in-turn degrades the reliability and performance of the
inverter. The majority of conventional multilevel inverter topologies cannot address
energy balancing issues between multiple photovoltaic (PV) sources, which may
need because of partial shading, hotspots, uneven charging and discharging of
associated batteries etc. If energy sharing not addressed effectively, the batteries
which are connected to the shaded or faulty PV system will discharge faster which
may cause total system shutdown and leads to under-utilization of healthier part of
the system. To address these issues, fault tolerant multilevel inverter topologies with
energy balancing capability are presented in this thesis.
The major contributions of the proposed work are
Single phase and three phase fault tolerant multilevel inverter
topologies.
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Energy balancing between sources and dc off set minimization (or
batteries) due to uneven charging and discharging of batteries for
five-level inverter.
Extending the fault tolerance and energy balancing for higher number
of voltage levels.
The first work of this thesis is focused to develop fault tolerant single phase
and three phase multilevel inverter topologies for grid independent photovoltaic
systems. The topologies are formed by using three-level and two-level half bridge
inverters. The topology fed with multiple voltage sources formed by separate PV
strings with MPPT charge controllers and associated batteries. Here the topologies
are analyzed for different switch open circuit and/or source failures. The switching
redundancy of the proposed inverters is utilized during fault condition for supplying
power with lower voltage level so that critical loads are not affected.
In general, the power generation in the individual PV systems may not be
same at all the times, because of partial shading, local hotspots, wrong maximum
power point tracking, dirt accumulation, aging etc. To address this issue energy
balancing between individual sources is taken care with the help of redundant
switching combinations of proposed five-level inverter carried out in second work.
Because of partial shading the associated batteries with these panels will charge and
discharge unevenly, which results voltage difference between terminal voltages of
sources because of SOC difference. The energy balance between batteries is
achieved for all operating conditions by selecting appropriate switching
combination. For example during partial shading the associated battery with low
SOC is discharged at slower rate than the battery with more SOC until both SOC’s
are equal. This also helps in minimization of DC offset into the ac side output
voltage. The mathematical analysis is presented for possible percentage of energy
shared to load by both the sources during each voltage level.
The third work provides single phase multilevel inverter with improved fault
tolerance in terms of switch open circuit failures and energy balancing between
sources. Generally multilevel inverters for photovoltaic (PV) applications are fed
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with multiple voltage sources. For majority of the multilevel inverters the load
shared to individual voltage sources is not equal due to inverter structure and
switching combination. This leads to under-utilization of the voltage sources. To
address this issue optimal PV module distribution for multilevel inverters is
proposed. Mathematical analysis is carried out for optimal sharing of PV resources
for each voltage source. The proposed source distribution strategy ensures better
utilization of each voltage source, as well as minimizes the control complexity for
energy balancing issues. This topology requires four isolated DC-sources with a
voltage magnitude of Vdc/4 (where Vdc is the voltage requirement for the
conventional NPC multilevel inverter). These isolated DC voltage sources are
realized with multiple PV strings. The operation of proposed multilevel single phase
inverter is analyzed for different switch open-circuit failures.
All the presented topologies are simulated using MATLAB/Simulink and the
results are verified with laboratory prototyp
Análise e simulação de pontos quentes em painéis fotovoltaicos
Dissertação para obtenção do grau de Mestre em Engenharia Electrotécnica, ramo de EnergiaEsta dissertação aborda a análise e simulação de pontos quentes em painéis fotovoltaicos. Os pontos quentes são um fenómeno de falha que causa perdas de eficiência energética e degradação física dos painéis fotovoltaicos. Esta falha resulta da dissipação da energia que ocorre quando células ou módulos fotovoltaicos que constituem o sistema ficam inversamente polarizados. A polarização inversa surge na maioria das vezes como consequência do sombreamento que ocorre devido à deposição de poeiras, dejetos de pássaros, folhas, neve ou efeito de sombra provocado por edificações ou arvoredos próximos. O sombreamento pode ser parcial ou total relativamente a uma célula ou a um módulo fotovoltaico. Quando uma célula ou módulo sombreado fica inversamente polarizado passa a assumir um comportamento de carga, começando a dissipar energia elétrica e a aumentar de temperatura. O objetivo desta dissertação consiste em analisar e simular em MATLAB/Simulink o comportamento dos pontos quentes utilizando um modelo elétrico e um modelo térmico. O modelo elétrico é utilizado para analisar as perdas de energia elétrica que ocorrem quando um módulo fotovoltaico sombreado está em condições de ponto quente, usando as curvas características I-V e P-V do sistema fotovoltaico. O modelo térmico é utilizado para simular a evolução da temperatura do ponto quente ao longo do tempo utilizando os resultados provenientes do modelo elétrico. Ambos os modelos são utilizados em diferentes configurações do sistema fotovoltaico por forma a conhecer os aspetos característicos dos módulos fotovoltaicos que mais favorecem a formação de pontos quentes.Abstract: This dissertation addresses the analysis and simulation of hot-spots in photovoltaic (PV)panels. Hot-spots are a failure that causes losses of energy efficiency and physical degradation of PV panels. This failure results of power dissipation that occurs when PV cells or PV modules operate in reverse bias. The reverse bias appears most often as a result of shading that occurs due to the dust, bird droppings, leaves, snow or shadowing caused by near buildings or trees. The shading can be partial or full with respect to a PV cell or a PV module. When a shaded cell or a shaded module becomes reverse biased takes a load behavior and then beginning to dissipate electric power and increasingtemperature. The aim of this dissertation is to analyze and simulate the behavior of thehot-spots using an electrical model and a thermal model in MATLAB/Simulink. The electrical model is used to analyze the electric power losses that occur when a shaded PV module is under hot-spot condition, using the I-V and P-V characteristic curves of the PVsystem. The thermal model is used to simulate the evolution of the hot-spot temperature over time using the results from the electrical model. Both models are used in different system configurations in order to know the characteristic aspects of PV modules more prone to the formation of hot-spots.N/