Reliability Of Inverter Research Articles

Design and Implementation of a Ground Power Unit Based on the Fault-Tolerant Inverter

Due to the widespread use of static power converters in various industries and sensitive applications such as ground power units (GPUs), it is essential that the inverters have high reliability. A failure in the inverters can cause undesirable consequences such as; low performance, shutting down the system, and losing the stability of the entire system. On the other hand, in some critical industrial processes with high standstill cost and safety-aspect concerns, such as aircrafts, high reliability, and survivability of the system are very important. Therefore, the use of fault-tolerant (FT) inverters is inevitable in such applications. In this paper, using an FT inverter, the reliability of the GPUs is increased and it results in higher availability and continuous system performance. Furthermore, a simple automatic fault-detection (FD) algorithm is presented by taking the inverter pole voltage as a fault detection parameter. The inverter is analyzed for open-circuit (OC) fault in the switches and the reliability of the FT inverter is compared with the classic inverter. The simulation and experimental results of the 1 kVA converter prototype are presented to confirm the FT inverter performance and the proposed method.

Comparative Reliability Assessment of Hybrid Si/SiC and Conventional Si Power Module Based PV Inverter Considering Mission Profile of India and Denmark Locations

Energy harnessing from renewable energy sources has become more flexible with power electronic technologies. Recent advancements in power electronic technologies achieve converter efficiency higher than 98%. Today, reliable power electronic devices are needed to design a PV-based energy converter (inverter) to reduce the risk of failure and maintenance costs during operation. Wide-bandgap SiC devices are becoming more common in power electronic converters. These devices are designed to reduce switching loss and improve the efficiency of the system. Nevertheless, the cost of SiC devices is a major concern. Hence, to improve the reliability of the PV inverter while considering the economic aspects, this paper develops a highly reliable PV inverter with a hybrid Si/SiC power module that consists of a Si-IGBT with a SiC anti-parallel diode. A test case of a 3 kW PV inverter is considered for reliability analysis. The loading of the PV inverter is done under uncertain environmental conditions by considering the yearly Mission Profile (MP) data related to Ambient Temperature (AT) and Solar Irradiance (SI) at the India and Denmark locations. The effectiveness of the proposed hybrid Si/SiC power module is tested by comparing it with a conventional IGBT power module. The results showcase the marked improvement in PV inverter reliability with the proposed hybrid power module.

The LLCLC resonant converter based pseudo DC link inverter

Technological advancements in solar power systems necessitate highly reliable power inverters with high efficiency and small size. An LLC resonant converter-based pseudo-Direct Current (DC) link inverters offer these qualities to some extent. The resonant circuits of conventional pseudo-DC link inverters cannot attain a zero gain and cannot handle variable frequency control which in turn requires very large filters to produce pure sinusoidal output voltages for the grid. The usage of these filters consequences in the enhanced price and size of inverters; moreover, the reliability of inverters is also reduced. We propose a novel topology for a pseudo-DC link inverter based on an LLCLC resonant converter. The proposed inverter does not require large filters, because it generates rectified sinusoidal output voltages. An additional parallel LC component is added in series to the resonant circuit, which makes it able to attain a zero gain through an infinite circuit impedance. The 400 W pseudo-DC link inverter with a 40 V input and a 400 V output is designed and simulated on OrCAD PSpice software. The results showed that there is a significant improvement in achieving a zero gain. The possible lowest gain achieved is approximately 0.125. The proposed technique claimed to be more efficient than those formerly used, subsequently contributing to satisfying outcomes.

Open Circuit Fault Mitigation in a Nine-Level Modified Packed E-Cell Inverter

Reliability of the multilevel inverters (MLIs) is one of the most important concerns in industrial applications, mainly due to the semiconductor devices. Whenever a fault occurs in one of the switches of the inverter, it leads to abnormal conditions and can also cause serious damage to the equipment connected to the multilevel inverter. In this paper, a recently proposed nine-level Packed-E-Cell (PEC) multilevel inverter topology is investigated for its fault-tolerant capability and improved reliability. The analysis is carried out for a reduced device multilevel inverter topology that, due to a lack of redundant states, cannot tolerate switch failures. The fault-tolerant (FT) topology provides additional redundant states in the switching sequence of the existing topology. The work in this paper presents Packed-E-Cell MLI modified for fault tolerance against single-switch open-circuit faults. The modified FT topology inherently achieves self-voltage balance in the DC-link capacitors. Nearest Level Control(NLC) is used as the modulation strategy for generating the desired switching pulses. Simulation results are obtained in MATLAB/Simulink for the conditions prior to the fault, during the fault and post fault, and results are discussed. Experimental verification of the modified FT topology is also performed, in order to validate its effectiveness.

Lifetime evaluation method of PV inverter considering the influence of fundamental frequency and low frequency junction temperature

As an important part of photovoltaic (PV) system, the reliability of PV inverter is the key to ensure the safe and reliable operation of PV power generation system. The existing lifetime evaluation methods of PV inverter are restricted by the extraction accuracy of junction temperature profile, and it is impossible to accurately evaluate the service lifetime of PV inverter. This paper, thus, divides the junction temperature profile according to the time scales, defines the concepts of fundamental frequency junction temperature and low frequency junction temperature. Then, this paper reveals the influence mechanism of fundamental frequency and low frequency junction temperature on PV inverter lifetime evaluation, and proposes a PV inverter lifetime evaluation method considering the influence of fundamental frequency and low frequency junction temperature. Finally, based on this method, the lifetime damage of PV inverter under different mission profiles and different sampling periods is studied, and the influence of fundamental frequency and low frequency junction temperature on lifetime evaluation is analyzed, which improves the accuracy of lifetime evaluation of PV inverter. It is helpful to guide the regular maintenance of PV inverter and reduce economic losses.

A Review of Open-Circuit Switch Fault Diagnostic Methods for Neutral Point Clamped Inverter

Due to numerous advantages, a neutral point clamped (NPC) inverter is a preferred choice for high-power applications and renewable technology. The reliability of the NPC inverter is a major concerning factor during the assessment of system performance as power semiconductor switches are vulnerable to abnormal conditions. Open-circuit (OC) switch faults are not as dangerous as short circuit (SC) faults but eventually have enough potential to cause cascaded failure to other components in the system and thus need to be supervised carefully. The OC faults result in a distortion of voltage and current signals in the NPC converter. Based on these signals, over the past few years, many efforts have been made to identify and localize the OC switch fault to the switch level in the NPC topology. In this paper, a review of different OC switch fault diagnostic methods is provided. Starting from the NPC inverter operation under healthy and faulty conditions, the various possible and unavailable switching states along with the deviation in pole voltage under different switch fault conditions is discussed. Then, based on the approach used for system-based fault detection, the OC fault detection methods are classified. The various OC methods are further discussed on the basis of signal, i.e., current, voltage or a combination of both signals used as a signature for fault detection. Emphasis is given to the principle involved, diagnostic variables utilized, the implementation approach and the diagnostic time required. Finally, the approaches are tabulated so as to provide a quick reference for NPC fault diagnostics.

Single-Phase Five-Level IT-Type NPC Inverter With Improved Efficiency and Reliability in Photovoltaic Systems

The reduction in the cost of photovoltaic (PV) energy is still required 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 it is closely related not only to the annual energy production but also to the reduction in operational and maintenance costs of PV systems. In this article, a single-phase IT-type NPC inverter with one-leg clamping pulse width modulation (OLC-PWM) is proposed for efficiency and reliability improvements. The proposed IT-type NPC inverter with OLC-PWM can improve the efficiency by taking the advantages of I-type and T-type NPC inverters regarding the power loss. Furthermore, its reliability has been improved compared with the conventional I-type and T-type NPC inverters. The IT-type NPC inverter also has an ability to balance the neutral-point voltage. The superiorities of the proposed IT-type NPC inverter in terms of reliability and efficiency are validated through the simulations and experiments by comparing the reliability and efficiency of the conventional I-type and T-type, asymmetric I-type and T-type, and IT-type NPC inverters.

An FCS-MPC-based open-circuit and current sensor fault diagnosis method for traction inverters with two current sensors

Effective fault diagnosis methods can improve the reliability of the two-level inverter used in traction systems. Both the open-circuit (OC) fault and current sensor fault can affect the phase currents of the inverter, which makes it difficult to distinguish them. In this paper, a diagnosis method for OC faults and current sensor faults is proposed, which is based on finite control set-model predictive control (FCS-MPC). First, the cost function is constructed and the inverter is controlled by the FCS-MPC. Then, the actual and estimated values of the cost function are calculated. The difference between them is applied to fault detection. Next, Combine the command signals and current direction, the number of affected sampling points in a period is counted and normalized. Different faults correspond to different percentages and this feature is used to determine fault location. Finally, the hardware-in-the-loop (HIL) platform is built, the feasibility and effectiveness of the proposed fault diagnosis method are verified by the HIL tests.

Impact of Choice of Neutral Point Clamped and H-Bridge Multilevel Inverters for PV Systems

The exploitation of solar energy and the universal interest in photovoltaic systems have increased nowadays due to galloping energy consumption and current geopolitical and economic issues. This has led to high technical and economic requirements. The PV system still faces major obstacles such as high cost and low efficiency compared to other renewable technologies. In addition, the photovoltaic system suffers from the rate of undesirable harmonics of the generated power which could alter the quality of energy and the performance requested by users. In order to remedy this problem, the use of the multi-level inverter is in these cases one of the most promising solutions. Indeed, the multi-level technology seems to be well suited to photovoltaic applications to help fill the need for several sources on the DC side of the converter. The technical performance and reliability of the multi-level inverter used to connect the PV modules to the electrical power distribution networks can improve and make profitable the power produced. In this work, we compare two multi-level inverter topologies for PV systems: H-Bridge (HB) and Neutral Point Clamped (NPC). The comparison between these inverters is based on the criteria of spectral quality of the output voltage and the complexity of the power circuits.

IGBT Wirebonds Ageing: A New Test Bench Development for Dedicated Modules Assemblies

Wirebonds ageing in power modules used in electric vehicles is a main concern for the development of reliable inverters. The development of a specific test bench to study the evolution of their properties over time has allowed conclusions to be drawn on the possibility of accelerating or not accelerating ageing tests without distorting the mechanisms actually involved in ageing. Through the use of specifically developed test bench in terms of electrical and thermal properties the studied wirebonds samples are more easily thermally controllable, equipped with measuring devices and the energy consumption at a given cycle is divided by ten compared to a classical bench. The entire process of designing and producing the specific samples and the associated test bench and a description of the first results obtained to demonstrate the relevance of the approach is given.

Comparative Analysis Different Topologies of Grid-tied Transformer Less Inverters for Photovoltaic system.

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. 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.

Early detection of photovoltaic system inverter faults

Photovoltaic (PV) systems are increasingly adopted as a source of green energy. The reliability of PV systems mainly depends on the reliability of the power MOSFETs of their inverter(s). It has been shown that short and open faults are the most frequent power MOSFET faults. They may compromise the inverter reliability, with consequent significant impact on the PV system energy efficiency. It has been proven that the likelihood of such faults is related to the value of the MOSFET ON-state resistance, which may increase over time due to aging mechanisms. When the value of such a resistance reaches a critical value, the likelihood of the MOSFETs subsequently failing as open or short becomes very high. In this paper, we first evaluate the effects of the MOSFETs' ON-state resistance increase on the harmonic components of the inverter input and output currents. Then, based on the obtained results, we propose an innovative strategy for the early detection (also referred to as condition monitoring [1]) of inverter faults, which enables to generate an alarm message when the ON-state resistance of any inverter MOSFET reaches the critical value. Upon the generation of such an alarm message, proper recovery strategies can be activated, to enable the online replacement of the affected transistors before they actually become faulty. Our detection strategy does not require to interrupt the inverter normal operation in the field and can be implemented using the microcontroller typically embedded within the control circuitry of PV systems.

A Reconfigurable Fault-Tolerant PV Inverter via Integrating HERIC and H5 Topologies

Solar energy is prevalent in many applications, therefore, the reliability of solar energy systems has become an important topic for research communities and industry. High reliability and fault-tolerant capability are particularly vital for the solar energy systems that are mission-critical and/or inaccessible to affordable maintenance. In order to enhance the reliability of a grid-tied PV system, a fault-tolerant Photovoltaic (PV) inverter, termed Integrated Fault-Tolerant PV Inverter (IFTPVI), is proposed in this paper. The IFTPVI is based on the Highly Efficient and Reliable Inverter Concept (HERIC) and H5 inverters that are both popular and commercialized transformerless inverters in grid-tied PV applications. The IFTPVI can tolerate both open-circuit (OC) and short-circuit (SC) faults while maintaining the same voltage and current levels. The system description, reliability analysis, simulation in Matlab/Simulink 2018, and experimental results are provided to verify the feasibility and viability of the proposed inverter topology.

Lifetime Evaluation of a Three-Phase Photovoltaic Inverter During Harmonic Current Compensation

The Photovoltaic (PV) inverters operating with ancillary service capability have been discussed as a solution to improve the power quality of the electrical grid. In this context, the PV inverters can be used to provide services such as Harmonic Current Compensation (HCC). However, the analysis of how much this extra functionality can affect the reliability of the PV inverter is necessary.Thus, this work analyzes the lifetime of a three-phase PV inverter taking into account the degradation of the semiconductor devices (IGBTs and diodes) and the dc-link capacitors. The compensation of the 5th and 7th harmonic current components (and their combination) are considered.The lifetime evaluation is performed based on an mission profiles of solar irradiance, ambient temperature, harmonic current amplitude and phase-angle. Based on the results of the adopted case study, the HCC operation increases the lifetime consumption of the IGBTs, diodes and dc-link capacitors. Compared to traditional PV inverter operation, The results reveals a reduction in the predicted B10 lifetime of 3.4 and 4.1 years, when the PV inverter compensates 5th and 7th harmonic, respectively. The reduction is even more significant (5.6 years) when the 5th and 7th harmonic component are simultaneously compensated.

Analysis of power losses in multilevel pulse-width modulation inverters

The paper describes the types of multilevel pulse-width modulation, as well as methods for obtaining control signals for the inverter power switches for each of the types. The dependence of the harmonic composition of the output voltage of the inverter on the number of levels and the switching frequency of the keys of each level is analyzed. By modeling, the dependences of the transistor junction temperature on the number of voltage levels, switching frequency and load power are determined. The power switching system of an inverter with phase-shifted pulse-width modulation in high-frequency mode is analyzed, the dependence of switching losses on inductance is investigated. The ways of solving or improving the control systems of the conductivity losses of the converter flowing through the primary winding of a high-frequency transformer during the free-running period are formulated. The importance of this direction for the technological development of the economy, where efficiency improvements can lower individual utility bills, create jobs, and help stabilize electricity prices and volatility is shown. The most important stage of inverter design is called structural synthesis stage – the choice of topology and modulation algorithm that will ensure the greatest efficiency of the device. In addition, since the efficiency and reliability of inverters depend on the efficiency and reliability of secondary electricity consumers, the task of optimizing inverter circuits is a cornerstone for the effective development of technology and economy. The maximum dynamic power loss at a PWM frequency of 1 kHz reaches only 80 watts compared to the static power loss value of 800 watts

Third-Harmonic Current Injection for Wear-Out Reduction in Single-Phase PV Inverters

The expansion of grid-connected photovoltaic (PV) systems over the years has been followed by concerns about the PV inverter reliability. It is well known that single-phase grid-connected PV inverter has a double-line frequency ripple in the dc-link voltage, which increases the wear-out failure probability of the dc-link capacitor and affects the overall inverter reliability. This work uses a third-harmonic current injection to attenuate the double-line frequency ripple in the dc-link capacitor voltage and to improve the PV system reliability. An analytical model capable to describe the effects of the third-harmonic current injection method in the dc-link capacitor is derived. The proposed strategy is validated by simulation and experimental results. The lifetime evaluation is developed considering a 3 kVA PV inverter and one-year mission profiles. The PV inverter failure probability considering an operation period equal to 20 years decreased in 27.17% for the adopted case study. Moreover, this strategy provides a straightforward retrofit of the current inverter technology, requiring no hardwarechanges.

Five-phase induction motor drive for electric vehicle with high gain switched-inductor quasi impedance source inverter

Switched-inductor quasi-impedance source inverter (SL-qZSI) with high gain fed five-phase induction motor drive for electric vehicle (EV) applications is proposed in this paper. Multi-phase electric machines have been predicted for application where the entire system should have better reliability and demanded power per phase is low especially for autonomous applications like EVs. To supply variable voltage and frequency to multi-phase machines, multi-phase inverters are required. SL-qZSI offers enhanced boost capability with respect to traditional impedance source converters by inserting three diodes and only one inductor to the basic quasi-impedance source inverter (qZSI). Also, SL-qZSI offers withstanding capability during voltage dip results line harmonics are diminished; enhances reliability of inverter; and extended output voltage range. The key idea of this paper is to design and develop a high performance and highly reliable SL-qZSI fed five-phase Induction Motor drive and validate the proposed system depends on results of Simulation with the help of MATLAB; these findings were comparable to the similar type of existing converters. We can notice from the performance analysis of the proposed system that it can provide enhanced voltage boosting capability and proved that it has significant potential for the suggested multi-phase variable speed drive (VSD) system.

Impact of Mission Profile on Reliability of Grid-Connected Photovoltaic Inverter

In recent decades intense demand for energy increases the utilization of Photovoltaic (PV) energy as an alternative to fossil fuels. Today’s PV energy shares a significant electricity demand with the advancements in power electronic technologies. Nevertheless, reliability performance of PV system is a major concern. Environmental conditions like mission profile (Solar Irradiance; Ambient Temperature), installation location impacts the performance of PV system. Researchers reported PV inverter as the critical component of PV system. Furthermore, reliability assessment of PV inverter considering environmental conditions is needed for the reliable operation. Therefore, the aim of this paper is evaluating the impact of mission profile on reliability (lifetime) of PV. To accomplish this, a 3-kW single phase grid connected PV system with full bridge PV inverter is considered as test case and modelled in PLECS. A 600V/30A IGBT from leading manufacturer is considered as power electronic switch in PV inverter. Top ten countries of PV market are identified and selected as installation locations, real time mission profile for one year at each installation location is considered. With this mission profile reliability assessment of PV inverter is carried out on test case. The results reveal that mission profile have considerable impact on reliability performance of PV inverter.

An Open-Circuit Faults Diagnosis Approach for Three-Phase Inverters Based on an Improved Variational Mode Decomposition, Correlation Coefficients, and Statistical Indicators

To ensure the reliability and robustness of the three-phase inverter, it is important to accurately detect the faults of insulated gate bipolar transistor (IGBT) switches. Signal processing is widely used for monitoring and fault diagnosis of the three-phase inverters. The current signals are usually noisy, which can lead to a loss of fault information. This article proposes a new approach for identifying and detecting the IGBTs open-circuit faults of a three-phase inverter. This approach is based on an improved version of the variational mode decomposition (IVMD) technique associated with correlation coefficients and statistical indicators (variance and mean value). First, the IVMD is applied to the three-phase current signals to obtain an elementary function called the band-limited intrinsic mode functions (BLIMFs). Second, the correlation coefficients between the original signals and theirs BLIMFs are used to select the relevant modes. The variances of the modes that have the highest correlation coefficients among those selected are calculated to detect the faulty phase and, therefore, the faulty leg. Finally, the mean value of the mode that has the lowest correlation coefficients among those selected of the faulty phase is calculated to localize the fault position in either the upper or the lower IGBTs of the faulty leg. Different experimental data are used to test the effectiveness of the proposed approach. The results obtained show the merits of the proposed approach for the diagnosis and detection of open-circuit IGBTs compared to the conventional method.

Reliability Analysis and Fault-Tolerant Operation in a Multilevel Inverter for Industrial Application

The extensive employment of power semiconductor devices in multilevel inverters (MLIs) has the consequence of increased failure probabilities. With numerous applications demanding highly reliable inverters, several fault-tolerant schemes have been devised to address switch open-circuit faults. This paper analyzes a multilevel inverter topology for IGBT modules undergoing open-circuit faults, a major impediment to reliable operation within a power converter. Reconfiguration of modulation is performed post-fault. A modulation scheme is implemented across failure modes as a hybrid of nearest level control and selective harmonic elimination. Reliability assessment of the topology is performed, including a comparison with previous literature in terms of component requirements and reliability. Simulation results validate the proposed solutions.