Reliability Of Inverter Research Articles

Reliability Analysis of Bifacial PV Panel-Based Inverters Considering the Effect of Geographical Location

Recent trends in the photovoltaic (PV) technology industry are moving towards utilizing bifacial PV panels. Unlike traditional PV panels, bifacial PV panels can yield energy from both sides of the panel. Manufacturers specify that bifacial PV panels can harness up to 30% more energy than traditional PV panels. Hence, bifacial PV panels are becoming a common approach at low solar irradiance conditions to yield more energy. However, a bifacial PV panel increases PV inverter loading. The PV inverter is the most unreliable component in the entire PV system. This results in a negative impact on PV system reliability and cost. Hence, it is necessary to anticipate the inverter’s reliability when used in bifacial PV panels. This paper analyzes the reliability, i.e., lifetime, of PV inverters, considering both monofacial and bifacial PV panels for the analysis. Results showed that the increase in bifacial energy yield could significantly affect PV inverter reliability performance, especially in locations where the average mission profile is relatively high.

Noninvasive Model-Based Open-Circuit Switch Fault Detection of AC-Bypass Leg Switches in Transformerless PV Inverter

Transformerless inverters are being used for integrating photovoltaic (PV) sources into the grid. Highly efficient and reliable inverter concept (HERIC) inverter is one such topology, which is derived from an H-bridge by adding a bypass leg on the ac side using two back-to-back insulated gate bipolar transistors (IGBTs). Open-circuit fault in the bypass leg would result in conduction of current through antiparallel diodes of the main switches of the inverter, effectively making the inverter operate in bipolar mode. As a result of the fault, there would not be an issue of leakage current, and the operation would continue at the expense of increased conduction losses and dc-offset in the grid current. This article proposes an online noninvasive model-based technique to detect switch faults in the bypass leg of the HERIC inverter. The grid current at the peak of the carrier signal is predicted based on the measured grid current at the start of the zero states. By comparing the estimated and measured grid currents at the peak of the carrier signal, the faulty switch in the bypass leg is localized. Once the fault is localized, the inverter’s modulation scheme is changed to conventional bipolar mode to improve the performance of the converter during the post-fault stage. A detailed simulation study is carried out to verify the effectiveness of the proposed approach. Experimental tests on the prototype converter show that the proposed algorithm can reliably detect the open-circuit fault in switches of the bypass leg, and once a fault is detected, the algorithm would change the modulation scheme to bipolar mode to minimize the inverter loss and dc-offset in the grid current.

On the Reliability of Transformerless Photovoltaic DC/AC Converters Based on Mission Profile

Photovoltaic systems are a technology for the generation of electrical energy that is constantly increasing thanks to current technological advances and that contributes to sustainable development. The main stages of photovoltaic systems are the conversion stage, using an inverter, and filtering. These systems may be considered as a mature and growing technology; however, regarding its reliability, there exists some uncertainties, and they are related to the operation, incidents, and its potential failures, due to the number of elements, the environment, and the operating nominal values. For this reason, this article presents a comparative analysis of the reliability of single-phase transformerless photovoltaic inverters used to inject active power into the grid. This evaluation is carried out under the same design specifications for all the inverters analyzed; the study is made using a mission profile considering the IEC TR 62380 standard, where the events and environmental operating conditions are defined, and numerical simulations. This work is aimed at providing suggestions to improve the quality of the photovoltaic system also considering reliability.

Reliability-based trade-off analysis of reactive power capability in PV inverters under different sizing ratio

Due to the intermittent characteristic of solar irradiance, photovoltaic (PV) inverters usually operate below rated power conditions. In this scenario, commercial PV inverters can be used to provide ancillary services, such as reactive power compensation. On the other hand, over-sizing PV inverters by increasing the number of installed PV panels can increase the generated energy during low irradiance conditions. Despite the advantages, both approaches can increase the PV inverter wear-out, leading to early failures. The trade-off between reactive power compensation and lifetime consumption under different inverter sizing ratios (ISR) was not previously addressed in the literature. Hence, this paper proposes to evaluate the system-level reliability of a single-phase two-stage PV inverter performing reactive power compensation. The analysis is carried out from three different mission profiles (Aalborg, Goiânia, and Izaña). The thermal loading on the inverter components is translated to lifetime prediction. The results from Goiânia show that the PV inverter lifetime is reduced from 22.6 to 6.2 years when compensating reactive power. In addition, this reduction is observed in all three regions, going from 40.8 to 12.4 years and 10 to 4.4 years, for Aalborg and Izaña, respectively. To improve the lifetime, a reactive power capability factor QR is applied to the maximum reactive power condition. The unreliability map is presented as a tool to match the inverter sizing ratio with reactive power capability in agreement with lifetime requirements. An economic analysis based on Levelized Cost of Electricity (LCOE) showed that the reactive power compensation increases the costs of the system installed in Goiânia with ISR = 100 % by 46.6 % in comparison with the conventional operation. These additional costs can be reduced if the reactive power is partially compensated.

Equivalent temperature estimation‐based FCS‐MPC for thermal stress balance of 3L‐NPC traction inverter

This paper proposes an equivalent temperature estimation-based finite control set model predictive control (ETE-FCS-MPC) method to balance the thermal stress among transistors in three level neutral point clamp (3L-NPC) traction inverters, which can be used to prolong the whole service life and improve the reliability of the traction inverter. Compared with other methods, the proposed ETE-FCS-MPC method requires lesser calculation without additional sensor. Firstly, an energy loss-based equivalent temperature estimation method is proposed to avoid the complexity of junction temperature prediction. Secondly, an energy variance-based thermal stress balance control objective is introduced. Then, a normalized evaluation function is established to select the optimal switching state. Finally, the effectiveness of this method is verified on hardware-in-the-loop tests.

Comparative Analysis Deferent Topologies for Photovoltaic Based Grid-Tied Transformerless Inverters

Transformerless inverters are widely used in grid-tied photovoltaic (PV) generation systems, due to the benefits of achieving high efficiency and low cost. Various transformer less inverter topologies have been proposed to meet the safety requirement of leakage currents. In this paper, a family of H6 transformer less inverter topologies with low leakage currents is proposed, and the intrinsic relationship between H5 topology, highly efficient and reliable inverter concept (HERIC) topology, and the proposed H6 topology has been discussed as well. One of the proposed H6 inverter topologies is taken as an example for detail analysis with operation modes and modulation strategy. The power losses and power device costs are compared among the H5, the HERIC, and the proposed H6 topologies. A universal prototype is built for these three topologies mentioned for evaluating their performances in terms of power efficiency and leakage currents characteristics. Experimental results show that the proposed H6 topology and the HERIC achieve similar performance in leakage currents, which is slightly worse than that of the H5 topology, but it features higher efficiency than that of H5 topology.

Review on Photovoltaic Based Grid-Tied System using H6 Transformer Less Full-Bridge Inverters

Transformer less inverters are widely used in grid-tied photovoltaic (PV) generation systems, due to the benefits of achieving high efficiency and low cost. Various transformer less inverter topologies have been proposed to meet the safety requirement of leakage currents, such as specified in the VDE-4105 standard. In this thesis, a family of H6 transformer less inverter topologies with low leakage currents is proposed, and the intrinsic relationship between H5 topology, highly efficient and reliable inverter concept (HERIC) topology, and the proposed H6 topology has been discussed as well. One of the proposed H6 inverter topologies is taken as an example for detail analysis with operation modes and modulation strategy. The power losses and power device costs are compared among the H5, the HERIC, and the proposed H6 topologies. A universal prototype is built for these three topologies mentioned for evaluating their performances in terms of power efficiency and leakage currents characteristics. Experimental results show that the proposed H6 topology and the HERIC achieve similar performance in leakage currents, which is slightly worse than that of the H5 topology, but it features higher efficiency than that of H5 topology.

Reliability Evaluation of Photovoltaic System Considering Inverter Thermal Characteristics

The reliable operation of photovoltaic (PV) power generation systems is related to the security and stability of the power grid and is the focus of current research. At present, the reliability evaluation of PV power generation systems is mostly calculated by applying the standard failure rate of each component, ignoring the impact of thermal environment changes on the failure rate. This paper will use the fault tree theory to establish the reliability assessment method of PV power plants, model the PV power plants working in the variable environment through the hardware-in-the-loop simulation system, and analyze the influence of the thermal characteristics of the inverter’s key components on the reliability of the PV power plant. Studies have shown that the overall reliability of bus capacitors, inverters, and PV power plants is reduced by 18.4%, 30%, and 18.7%, respectively, compared to when the thermal characteristics of bus capacitors are not considered. It can be seen that thermal attenuation has a great influence on the reliability of the PV power generation system.

PV Inverter Reliability-Constrained Volt/Var Control of Distribution Networks

The increasing penetration of photovoltaic (PV) systems promotes utilization of PV inverters for volt/var control (VVC) in distribution networks. However, PV inverters are vulnerable and their reliability is one of the most critical concerns for sustainable PV energy utilization. To enhance PV inverter reliability, this paper proposes a PV inverter reliability-constrained VVC method of distribution networks under uncertainties. Firstly, a full reliability analysis procedure for PV inverters is developed to estimate the lifetimes of core devices inside inverters. Secondly, considering the impacts of VVC on PV inverter reliability, reliability constraints are proposed based on regulation of inverter apparent power and application of a PV curtailment scheme. Thirdly, a multi-objective PV inverter reliability-constrained VVC optimization model is proposed, which aims to minimize network power loss and PV curtailed power, simultaneously. Accordingly, the nonconvex model is relaxed by a second-order cone programming method, and the uncertainties such as PV power generation and loads are addressed by a scenario-based stochastic optimization method. The proposed VVC method is tested on the 33-bus and 69-bus distribution networks, and the simulation results verify high efficiency of the proposed method in energy loss reduction and inverter reliability enhancement.

Development of a novel fault-tolerant reduced device count T-type multilevel inverter topology

Multilevel inverters (MLIs) are emerging topologies in medium and high power applications due to low total harmonic distortion (THD) and reduced voltage stress across switches. The reliability of semiconductor devices is a major concern for these multilevel inverter topologies to function properly. Therefore, a reliable single-phase fault-tolerant (SPFT) T-type 5-level multilevel inverter topology is presented in this paper. The proposed T-type topology can tolerate Open Circuit (OC)fault, either caused by a failure of anyone single switch or/and the failure of anyone leg of the H-bridge. The proposed configuration is not only fault-tolerant but also reliable due to the reduced number of switching devices as compared to the conventional T-type multilevel inverters. Moreover, the proposed T-type topology inherently achieves self-voltage balance in DC-Link capacitors. The proposed T-type topology is simulated in MATLAB/Simulink environment and results are discussed for normal (pre-fault), faulty and post-fault conditions. Experimental results validate the robustness and effectiveness of the proposed T-type topology to tolerate OC faults across the switch(es). Moreover, simulation and experimental results establish that proposed T-type topology significantly increase the reliability of the multilevel inverter. Furthermore, comprehensive analysis is presented to show the superiority of the proposed T-type topology over the recently proposed fault-tolerant topologies.

A single phase five-level inverter with single and multiple switch fault tolerance capabilities

The reliability of multilevel inverters (MLIs) is of great importance, when they are employed for applications such as aircrafts, electric vehicles, standalone, and grid connected photovoltaic (PV) system. To achieve required output voltage during post-fault scenarios, several fault tolerant topologies of multilevel inverter have been proposed. However, the primary constraints which add on a limitation to their implementation are increased device count and inability to tolerate single and multiple switch faults with the conduction of lesser or equal switches as in pre-fault case. The inability to tolerate various types of faults, such as open circuit or short circuit, cause severe impact on the system and further increase the cost. In this regard, a fault tolerant (FT) multilevel inverter topology which tolerates aforementioned faults is proposed. The proposed topology is able to withstand both single switch and multiple switch faults with equal or lesser blocking voltage. The proposed topology employs only unidirectional switches, thus increasing the reliability and reducing the cost of inverter. The proposed work is validated experimentally.

Impact of Solar Irradiance and Ambient Temperature on PV Inverter Reliability Considering Geographical Locations

Today inverter system is one of the enabling technologies for efficiently harnessing energy from renewable energy sources (Solar, Wind, etc.,) and also for high reliable grid interfacing systems. With the advancements in power electronics, inverter conversion efficiency pushed to 98%, also PV is becoming a major renewable energy source globally. Nevertheless, the reliability performance of PV inverter is of high concern. Different environmental factors like solar irradiance, ambient temperature (also called Mission Profile) affect the reliability performance of PV inverter. Environmental conditions vary from location to location. Hence to quantify the reliability performance of PV inverter all these factors need to be considered. In this paper reliability performance of PV inverter is evaluated considering environmental factors and geographical locations. For the reliability evaluation, a 1-ϕ, 3-kW grid connected PV system is developed in PLECS. Full bridge PV inverter with 600V/30A IGBT is employed as the interface between grid and PV source. Real time mission profile data of one-year logs at India (Relatively hot climate) and Denmark (Relatively cold climate) to account for environmental factors and geographical locations during the reliability performance evaluation of PV inverter. Monte Carlo simulation is used to generate a population of 20000 samples with 5% variation. Lifetime for 20000 samples is calculated and fitted in Two Parameter Weibull distribution. B10 lifetime is calculated at two locations. The results of this paper reveal that environmental factors and geographical locations have a significant impact on PV inverter reliability performance.

Reliability and Economic Efficiency Analysis of 4-Leg Inverter Compared with 3-Leg Inverters

The 4-leg inverter can adjust the load current or output voltage even under unbalanced load conditions, but it is known that the additional switch arm to the 3-leg inverter can increase the overall cost and the failure rate. This paper aims to analyze the failure rate and mean time between failures (MTBF) of 3-leg inverters and 4-leg inverters using part count failure analysis (PCA) and fault-tree analysis (FTA), and to compare the price of the inverters. The FTA can analyze the failure rate, including the type, number and connection status of the circuit components, and moreover the redundancy effect of the 4-leg inverter. For more accurate failure-rate prediction, the failure rate and MTBF of the 4-leg inverter according to the lifecycle of the controller are analyzed. Finally, by comparing the price of 3-leg inverters and 4-leg inverters using the cost model of major parts, the degree of reliability improvement against price increase is quantitatively analyzed.

Comparative Evaluation of Efficiency and Reliability of Single-Phase Five-Level NPC Inverters for Photovoltaic Systems

It is required to reduce the cost of PV energy to be competitive as an alternative energy source. The efficiency and reliability of PV inverters are important aspects to be enhanced to reduce the cost of PV energy since they contribute to the reduction of operational and maintenance costs and to the increase of annual energy production. Therefore, more comprehensive analysis on both efficiency and reliability together including the impacts of various factors is required. In this paper, single-phase five-level NPC inverter topologies for photovoltaic systems are comparatively evaluated in terms of efficiency and reliability by simulations and experiments, in which the impacts of pulse width modulation (PWM) methods and installation locations are considered. The results are expected to give an insight to determine the proper topology and PWM method depending on its installation location considering the reliability as well as the efficiency and total harmonic distortion (THD).

Capacitor Lifetime Extension in a Hybrid Active Neutral-Point-Clamped Inverter With Reduction of DC-Link Ripple Current and Common-Mode Voltage

This paper proposes a reduction method for DC-link ripple current and common-mode voltage (CMV) in a hybrid active neutral-point-clamped (ANPC) inverter. A Si and SiC hybrid ANPC inverter has been developed recently to overcome the extremely high cost of a full-SiC ANPC inverter. A hybrid ANPC requires much fewer SiC MOSFETs than a full-SiC ANPC inverter while providing a comparable power density. Voltage source inverters such as hybrid ANPC inverters utilize electrolytic capacitors, which have a large capacitance per volume, as a DC link. However, an electrolytic capacitor is one of the most vulnerable components in a power electronic converter due to its small allowable ripple current. A large ripple current flowing into the electrolytic capacitor generates a heat loss, which shortens the lifetime of the capacitor. Furthermore, the common-mode voltage (CMV) causes an undesirable leakage current and electromagnetic interference. The CMV depends on the pulse-width modulation of the voltage source inverters. The proposed method enhances the reliability of the hybrid ANPC inverter by reducing the DC-link ripple current and CMV simultaneously. The effectiveness and validity of the proposed method are verified through simulations and experimental results.

SSTPI-IM Reconfiguration and Diagnostic under OCF Appearance Used in PV System

In order to the increase of the conventional inverter reliability used in PV systems, many diagnostic methods have been investigated to these converters reliability. These diagnostic methods are applied in order to detect and identify the IGBT's OCF. In this paper, the proposed diagnostic method is based on the normalized currents and current's slope information's. Due to the continuity importance in PV systems after the appearance of IGBT's OCF, this paper presents a SSTPI-IM diagnostic method and reconfiguration strategy controlled by the direct RFOC used in PV system. The fault reconfiguration is based on the change of the SSTPI topology to the FSTPI topology using relays and a redundant leg. The redundant leg is only used in the cases of IGBT’s fault’s appearance in more than one SSTPI leg. The effectiveness and performance of the proposed SSTPI-IM diagnostic method and reconfiguration strategy in terms of systems continuity and fast detection and reconfiguration are validated by the simulation results.

Design and Implementation of a Transformer Less Single-Phase Symmetrical Z- Source Heric Inverter with Reduced Leakage Currents for PV Systems

A transformer less single-stage symmetric Z-source HERIC inverter including low spillage flows is proposed right now. It is an endeavor to use the Highly Efficient and Reliable Inverter Concept (HERIC) and an impedance source (Z-source) system to keep up a steady normal mode voltage and consequently low spillage flows in PV applications. The proposed inverter successfully eases the spillage current issue by expelling high-recurrence segments for the regular mode voltage. A lift DC/DC converter is ordinarily embraced in such frameworks, prompting a moderately low productivity, particularly when the PV voltage is low. Answers for this test are to adjust tweak techniques or exchanging designs and along these lines ease the variety of the regular mode voltage. The activity guideline of the proposed inverter is depicted together with its control system. The symmetric Z-source HERIC inverter requires dynamic switches. By and by, the activity recurrence of the switches is the line recurrence, prompting insignificant misfortunes.

Grid Voltage Estimation Based on Integral Resonant Current Controller for LCL-Filtered Grid-Connected Inverter without AC Voltage Sensors

A high reliability of a grid-connected inverter (GCI) system at reasonable cost is a critical requirement for maximizing renewable energy potential in the electrical energy market. Several grid voltage sensorless control approaches have been investigated not only to eliminate the vulnerability of faulty sensors but also to further reduce the GCI commercial price. In this paper, a frequency adaptive integral-resonant full-state feedback current control scheme with the facilitation of a full-state observer is adopted for a grid-connected inductive–capacitive–inductive (LCL) filtered inverter without sensing the grid voltages. The proposed scheme actively damps the filter resonance and ensures the robustness of the inverter system against unexpected severe grid conditions with low cost and simplified hardware construction. The synchronization of the inverter with the main grid is accomplished by the proposed current controller-based grid voltage estimator, in which the grid frequency and phase angle can be detected effectively. In addition, the actual grid voltages are precisely regenerated to ensure the stable performance of the full-state observer. A safe start-up procedure is also presented for the grid voltage sensorless control of the LCL-filtered inverter to avoid a critical overcurrent and long settling time during the start-up instant, offering a stable and reliable inverter system operation with low computational burden. The effectiveness and feasibility of the proposed voltage sensorless current control scheme are validated by the simulation and experimental results under non-ideal grid conditions such as the harmonic distortion, grid frequency variation, and sudden grid phase angle jump.

Open-circuit fault diagnosis of NPC inverter IGBT based on independent component analysis and neural network

Power switching devices are the core component of inverter, the fault diagnosis of power switching devices has very important significance for the reliability of inverter. The IGBT is usually used as power devices in the neutral-point-clamped (NPC) inverter, and it has 12 IGBTs totally. NPC inverter is the typical application scenario of the IGBT fault diagnosis. The premise of fault diagnosis method based on signal processing is fault feature extraction. A novel fault feature extraction method is proposed in this paper, which is based on the joint approximative diagonalization of eigenmatrix and independent component analysis (JADE–ICA). A neural network (NN) is used as the fault classification method. Through the JADE–ICA algorithm, the source signal and the separated signal can be effectively one-to-one correspondence, and the effects of nonlinearity and time difference can be overcome. The input of NN is reduce through the JADE–ICA algorithm effectively, which can reduce the time necessary to train an NN, and improve the classification accuracy. The proposed method is verified in the simulink simulation environment, and the fault diagnosis is more than 95.1%.

Loss study and reliability analysis of a new reconfigurable fault‐tolerant multilevel inverter topology

A high reliable inverter with photovoltaic systems improves the efficiency and longevity of the entire system. Recent research emphasises on developing new fault-tolerant multilevel inverter (FTMLI) topologies. However, these topologies are not able to maintain rated voltage and power with a minimum switch count under switch fault conditions. This study proposes a new multilevel inverter with a reduced device count, which can handle both single switch fault and multi-switch fault by preserving its rated voltage and power. Sine-carrier-based level-shifted pulse-width modulation is used to generate control signals. The carriers are reconfigured based on the type and location of the fault. The loss contribution of each switch is calculated in all modes of operation by considering variations in junction temperature using a Powersim (PSIM) thermal model tool. This study helps to choose an appropriate heat sink for the switches. The reliability density function is calculated using a Markov chain model. A comparative study is presented to assess the notable benefits of the proposed topology over other existing similar topologies. The experimental results from the laboratory prototype are provided to verify the efficacy and practicality of the proposed FTMLI configuration.