Search

Fuzzy logic control (FLC) systems have found wide utilization in several industrial applications. This paper proposes a fuzzy logic-based fault detection and identification method for open-circuit switch fault in grid-tied photovoltaic (PV) inverters. Large installations and ambitious plans have been recently achieved for PV systems as clean and renewable power generation sources due to their improved environmental impacts and availability everywhere. Power converters represent the main parts for the grid integration of PV systems. However, PV power converters contain several power switches that construct their circuits. The power switches in PV systems are highly subjected to high stresses due to the continuously varying operating conditions. Moreover, the grid-tied systems represent nonlinear systems and the system model parameters are changing continuously. Consequently, the grid-tied PV systems have a nonlinear factor and the fault detection and identification (FDI) methods based on using mathematical models become more complex. The proposed fuzzy logic-based FDI (FL-FDI)method is based on employing the fuzzy logic concept for detecting and identifying the location of various switch faults. The proposed FL-FDI method is designed and extracted from the analysis and comparison of the various measured voltage/current components for the control purposes. Therefore, the proposed FL-FDI method does not require additional components or measurement circuits. Additionally, the proposed method can detect the faulty condition and also identify the location of the faulty switch for replacement and maintenance purposes. The proposed method can detect the faulty condition within only a single fundamental line period without the need for additional sensors and/or performing complex calculations or precise models. The proposed FL-FDI method is tested on the widely used T-type PV inverter system, wherein there are twelve different switches and the FDI process represents a challenging task. The results shows the superior and accurate performance of the proposed FL-FDI method. [ABSTRACT FROM AUTHOR]

• A new distributed MPPT for three-phase grid-connected cascaded MLIs is presented. • The proposed distributed MPPT method is depending on the phase-shift PWM. • A compensation method is proposed to solve the unbalance problems due shading. The modularity and decreased filter size properties have made cascaded multilevel inverters (MLIs) more applicable than conventional two-level inverters, especially in high and medium power photovoltaic (PV) applications. However, partial shading of PV modules will affect negatively the output power of the unshaded modules. There are several existing solutions in the literature to address this challenge, however almost all of them suffer from complex implementations, low efficiency, and high cost. This paper presents a new simplified feedforward distributed maximum power point tracking (MPPT) method for three-phase grid-connected cascaded MLIs. The cascaded MLI provides a modular, and highly efficient single stage power conversion for PV systems. The proposed distributed MPPT method is depending on the phase-shift pulse width modulation (PS-PWM) method with a simplified implementation. The proposed method is developing a feedforward signal that is proportional to the maximum power of the individual module. Then, the current controller, and the modulating signal are multiplied with the proportionality factor of the module maximum power. Furthermore, a modified modulation compensation method without using proportional-integral (PI) controllers is introduced to solve the problem of the unbalanced three-phase PV output currents that results from PV power mismatches and shading. A case study is implemented for 15 kW PV system to investigate the performance of the proposed method. In addition, comprehensive comparisons with the previous attempts in the literature are provided to verify the superior performance of the new proposed control method. [ABSTRACT FROM AUTHOR]

Reliability of power inverters is of dominant importance in various applications, including industrial, military, aerospace, and commercial applications. Therefore, developing fault tolerant (FT) power inverters is extremely needed from the viewpoints of system availability and avoiding harmful consequences. Tolerating various types of faults, preserving full output ratings after the fault, and being cost-effective represent the main challenges for most of existing FT solutions. In this paper, a new FT single-phase five-level inverter topology is proposed. The proposed topology can effectively tolerate both of single or multiple switches faults whether they are of open- or short-circuit fault types. Moreover, the proposed topology does not deteriorate system efficiency in postfault operation compared to the previously developed FT solutions. Evaluation of the effectiveness and robustness of the proposed topology is verified in both of simulation and experimental environments. Different case studies are investigated in order to cover various types and locations of switches’ faults. Moreover, comprehensive comparisons are provided to validate the superiority of the proposed topology over the previously addressed techniques. [ABSTRACT FROM AUTHOR]

Enhancing power cycling capability of power semiconductor devices is highly demanded in order to increase the long-term reliability of multilevel inverters. Ageing of power switches and their cooling systems leads to their accelerated damage due to excess power losses and junction temperatures. Therefore, thermal stresses relief (TSR) is the most effective solution for lifetime extension of power semiconductor devices. This paper presents a new TSR carrier-based pulse width modulation (TSRPWM) strategy for extending the lifetime of semiconductor switches in single-phase multilevel inverters. The proposed strategy benefits the inherent redundancy among switching states in multilevel inverters to optimally relieve the thermally stressed device. The proposed algorithm maintains the inverter operation without increased stresses on healthy switches and without reduction of the output power ratings. In addition, the proposed algorithm preserves voltage balance of the dc-link capacitors. The proposed strategy is validated on a single-phase five-level T-type inverter system with considering different locations of thermal stresses detection. Experimental prototype of the selected case study is built to verify the results. Moreover, comparisons with the most featured strategies in literature are given in detail. [ABSTRACT FROM PUBLISHER]

Research concerns have grown towards precede diagnosis and prognosis of faults in power converters that result from thermal overheating problems of semiconductor devices. These problems directly affect the overall system availability and reliability as well. Many papers in the literature have addressed these problems. However, almost all of them suffer from major challenges such as increased components count, reduced output current ratings, reduced output voltage levels, and unbalanced voltages over the DC-link capacitors. These challenges impede the maximum energy harvesting, especially in renewable energy systems. A novel space vector modulation (SVM) algorithm has been proposed for lifetime prolongation of thermally aged power semiconductor devices in multilevel inverters. The proposed SVM algorithm functions to alleviate the affected device and to prevent the harmful consequences such as short-open circuit faults. The feasibility of the proposed method has been verified by simulation and experimental results on the three-phase three-level T-type inverter and compared with the previously addressed approaches. It can be concluded that the proposed algorithm provides a significant reduction of thermal stresses on the thermally aged power devices in addition to maintaining the same components count, the same output ratings, the same output levels, and balanced capacitors' voltages as well. [ABSTRACT FROM AUTHOR]

As promising and suitable candidates for high-power applications, multilevel inverters have become one of the most promising solutions in various applications. However, power switching devices are highly subjected to thermal overheating, which leads to shortened lifetime and reduced reliability. Thermal overheating may result from the degradation of power switching devices due to continuous overloading and power cycling. In addition, degradation and faults in the cooling system of power switching devices may cause thermal stresses as well. A new overheating-tolerant space vector modulation algorithm is proposed in this paper to alleviate thermal stresses from overheated power switching device. The proposed algorithm relies on using the redundancy property between switching states in multilevel inverters to continuously evaluate a cost function of the junction temperature of the overheated device for all possible switching sequence sets and then selects the optimal switching sequence. In addition, the proposed algorithm preserves the DC-link capacitor voltage without reduction in the output current of the inverter. The proposed algorithm is general, which can be applied to n-level inverters. Both simulation and experimental results reveal the efficient performance of the proposed algorithm using a three-level T-type inverter as a case study. Accordingly, the lifetime and reliability of the inverter are enhanced considerably using the proposed algorithm. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

The integration of photovoltaic (PV) systems with three-phase four-wire (3P4W) distribution networks has imposed several challenges related to existing unbalanced loads, reactive power generation and harmonics content. In this paper, a multifunctional distributed maximum power point (MPPT) controller for grid integration of PV systems is proposed. The proposed distributed MPPT controller is developed based on employing a four-leg three-level T-type multilevel inverter. The proposed inverter performs multifunctionalities, including distributed MPPT, neutral current compensation for the unbalanced loads, supplying reactive power into the grid and the grid integration. Moreover, the proposed inverter overcomes the stochastic behavior of both the PV generation with partial shading problems and its operation with unbalanced loads as well. Furthermore, the new proposed controller injects sinusoidal output currents with decreased levels of total harmonic distortion (THD) into the grid. The tested case study is investigated for the various operating scenarios of PV generation and load demands. The results and tabulated performance comparisons have proven the superior performance of the proposed multifunctional PV generation system. The results show the ability of the proposed controller to efficiently extract distributed MPPT for all PV modules at all the tested scenarios. Additional improvement of the energy efficiency is achieved through the elimination of the neutral current due to existing unbalanced loads. [ABSTRACT FROM AUTHOR]