Reliability Of Power Converters Research Articles

Enhancing power conversion efficiency in five-level multilevel inverters using reduced switch topology

This paper presents extensive research on improving the power conversion efficiency of five-level multilevel inverters (MLIs) by utilizing a reduced switch topology. MLIs have received an abundance of focus because of their ability to generate high-quality output waveforms and have better harmonic outcomes than traditional two-level inverters. The high number of switches in MLIs, on the other hand, can result in increased power losses and lower overall efficiency. In this paper, a novel reduced switch topology for five-level MLIs, which is having five switches is proposed with the aim of minimizing power losses while preserving superior performance due to lesser number of switches. To achieve efficient power conversion, the proposed topology employs advanced pulse width modulation control strategies and optimized switching patterns. The simulation results show that the minimized switch topology improves the power conversion efficiency of the five-level MLI, resulting in lower losses and better overall system performance. The total harmonic distortion (THD) value of the output current has been reduced to 7.12% and the efficiency has been achieved to 96.92%. The findings of this investigation help to advance MLI technology, allowing for more efficient and reliable power conversion in a variety of applications such as renewable energy systems, electric vehicles, and industrial drives.

A Lambert importance model‐based reliability design method for power converters in switched reluctance motor systems

SummaryThe reliability of power converters is crucial for achieving high‐performance operation in switched reluctance motor (SRM) systems. However, there is a notable deficiency in reliability‐oriented design of power converters that can effectively integrate both static and dynamic reliability indicators. To address this issue, this paper proposes a reliability design methodology for power converters based on the Lambert importance model, aimed at enhancing reliability of SRM systems. Firstly, the modeling principles of Lambert importance model are presented. Subsequently, a reliability design method is proposed to maximize reliability within a unit economic cost framework. Especially, the proposed design scheme is designed to maximize reliability enhancement potential through a two‐pronged approach: strategic topology selection informed by potential reliability assessments and component selection guided by importance calculations. Meanwhile, dynamic reliability evaluation is carried out to form a double‐loop reliability feedback and increase the credibility of design scheme. Finally, an example is developed to verify the validity of proposed reliability design scheme.

Design and Implementation of GaN-Based Two Switch Flyback With Synchronous Rectification for New Space Applications

This article presents a comprehensive investigation and implementation of a continuous conduction mode pulse width modulated two-switch DC/DC flyback converter utilizing Gallium Nitride Field Effect Transistors (GaNFETs) for New Space applications. The New Space concept advocates for the integration of Commercial Off-The-Shelf (COTS) materials in the space industry. The approach offers cost-effective solutions and reduces lead time for space designs. The study provides steady-state analysis and design considerations for two switch flyback converters, highlighting the transformative capabilities of GaNFETs, especially in high-frequency operations. The rationale behind the preference for GaNFETs over MOSFETs in satellite power supply applications and the strategic benefits of COTS materials are explained in detail. In addition, the synchronous rectification method is implemented to obtain better efficiency, particularly for high-output current operations. The converter achieves an efficiency of over 87% when the load exceeds 50%, with varying input voltages from 20 V to 40 V and a switching frequency of 300 kHz. The experimental findings show that the designed converter can serve as a high efficiency and reliable satellite power converter.

Cosmic Radiation Reliability Analysis for Aircraft Power Electronics

Cosmic Ray induced failures are a major concern for the electronic system reliability of airborne and space systems. Power system voltages on aerospace platforms are on a steady upward trend. High voltage power converters suffer from Single Event Burnout failures caused by cosmic rays. The established standards propose a scaling factor based on measured background galactic cosmic rays intensity at operating altitude to apply de-rating factors. The radiation environment in the atmosphere can be increased due to the cascading of primary solar energetic particles during solar eruptions. In this work, the altitude profile of the radiation environment is simulated using a GEANT4 Monte-Carlo code. The failure rates due to both background Galactic Cosmic Rays and Solar Energetic Particles are quantitatively evaluated. Further to the known influence of geomagnetic shielding of cosmic rays, the geographical distribution of cosmic rays at flight altitudes of 10 km are also presented. The estimated cosmic ray intensity can then be combined with experimentally measured failure rate data to predict the impact on the reliability of power converters, giving a new level of accuracy in the modeling of such failure mode in more electric aircraft applications. It is shown for the first time in the scientific literature by using experimental data and state-of-the-art models, that the solar energetic particles storms fluxes vastly exceed the recommended standard and constitute a risk for the power electronics reliability.

Understanding wind turbine power converter reliability under realistic wind conditions

AbstractThe reliability of wind turbine power converters is crucial for analyzing wind energy project costs, and for estimating maintenance and downtime. The published literature in this field relies on evaluating the reliability effect of wind speed to estimate the converter lifetime. However, this paper demonstrates that wind turbulence intensity, which has not been widely considered in similar reliability analyses, shows a significant impact on converter lifetime. This paper uses 821 10‐min wind speed time series sampled at 1 Hz on the two most commonly deployed wind turbine converter topologies: the two‐level voltage source and the three‐level neutral point clamped. Electromechanical and thermal modelling, combined with statistical analysis shows that mean wind speed and turbulence intensity both impact the lifetime of both converter topologies. However, the paper estimates that the three‐level converter can operate 2.4 to 4.0 times longer than the two‐level converter depending on the operating wind speed and turbulence intensity.

Thermo-sensitive electrical parameters of high-power IGBTs based on gate-emitter voltage measurement during switching delay intervals

High-power insulated gate bipolar transistors (IGBTs) are widely used for wind power conversion and electric traction. Accurate estimation of IGBT junction temperature and active thermal control improve the reliability of power converters in such applications. Among the various available methods for junction temperature estimation, thermo-sensitive electrical parameter (TSEP) based estimation is simple, fast and amenable to real-time implementation. Evaluation of many TSEPs (e.g. forward voltage, threshold voltage, peak dv/dt, peak di/dt etc.) require measurement of multiple electrical quantities in the power circuit and/or in the gate-drive circuit. The measurement systems need to have high precision and/or high bandwidth as well. Moreover, the quantities in the power circuit require isolated measurement systems. This paper explores possible new TSEPs, that could be obtained through a single measurement of low-voltage quantity, namely, the gate-emitter voltage. Since the gate-emitter voltage varies primarily during turn-on and turn-off delay intervals, these switching intervals and their parameters are studied over a wide range of operating conditions. Since many practical converters are expected to operate at an ambient temperature as low as −35 °C, the experimental study is carried out over a wide temperature range from −35 °C to 125 °C. Further, to ensure wider applicability of the findings of the study, four IGBTs of different makes are considered for the experimental investigations. The experimental results bring out four different parameters pertaining to turn-on delay and another four parameters pertaining to turn-off delay, which are potential TSEPs. Of these eight TSEPs, five of them can be evaluated based on measurement of gate-emitter voltage only, and four of these have not been reported in the literature previously. In addition, the experimental data are useful for development of temperature-sensitive device models for simulation, performance assessment and design of gate-drive circuit for different temperatures, and for temperature-sensitive compensation of inverter dead-time effect.

An Eigendecomposition-based dynamic characteristics design method of three-phase grid-connected inverters with considering reliability

Power converters often suffer the disturbance from input source or load during operation. The disturbance could cause large overshoot and harmful oscillation and even make the power converter break down. In order to ensure the reliability of the converter, it is necessary to accurate design the dynamic characteristics of a power converter, namely, the settling time and the overshoot. However, there is no quantitative dynamic characteristics design method of power converters so far. In this paper, an eigendecomposition-based (ED) dynamic characteristics design method is firstly proposed for the quantitative dynamic characteristics design of power converters and is employed into a three-phase grid-connected inverter. Then, the control-parameter regions of the three-phase inverter that satisfy the indexes of the settling time and the overshoot are obtained by using the proposed ED dynamic characteristic design method. Finally, the effectiveness and correctness of the proposed ED dynamic characteristics design method is verified by circuit simulation. Therefore, this paper provides an accurate and quantitative dynamic characteristic design method for power converters, which is helpful to improve the reliability of power converters.

Performance analysis of digitally controlled nonlinear systems considering time delay issues

In this paper, a comprehensive investigation into discretization, effective sample time selection considering delays in the system, and time and frequency domain analysis of a DC-DC buck converter, which plays a vital role in photovoltaic (PV) systems, is conducted to enhance the understanding of their dynamic behavior, optimize control algorithms, improve system efficiency, and ensure reliable power conversion in photovoltaic applications. To effectively address the non-linear behavior and enhance digital control of a buck converter by selecting the best sample time, several approaches can be employed. These include accurate modeling and identification of non-linear elements, development of advanced control algorithms that account for non-linearities, implementation of adaptive control techniques, and utilization of feedback mechanisms to compensate for deviations from linearity. By considering and mitigating the non-linear behavior, digital control systems can achieve improved accuracy, stability, and transient behavior in regulating the buck converter's output waveforms (voltage or current). The results of the study demonstrated that the trapezoidal integration method which is also known as bilinear approximation, or Tustin's approach outperformed other commonly used discretization methods, such as first-order hold (FOH), zero-order hold (ZOH), impulse response matching (impulse invariant), and matched pole-zero (MPZ) technique, in dual-domain (both time and frequency) analysis. The key finding highlighting the superiority of the bilinear approximation was its ability to achieve the closest match in the frequency domain bridging the continuous-time and discrete systems. This finding emphasizes the significance of the bilinear approach in preserving the frequency characteristics of the original continuous-time system during discretization. By employing this method, the discrete system closely approximated the behavior of its continuous-time counterpart, ensuring accurate frequency-domain representation.

Active Thermal Control in Neutral-Point-Clamped Multilevel Converters Based on Switching-Cell Arrays

Neutral-point-clamped multilevel converters are a suitable solution to the implementation of low–medium voltage and power applications at present, thanks to their intrinsic superior voltage and current quality. The conventional configurations of these converters present uneven power loss distribution, causing thermal stress in some power semiconductors, which weakens the power converter reliability. To overcome this, an implementation of the neutral-point-clamped multilevel converter based on a switching-cell array is introduced, adding redundant conduction paths on one side and more options to distribute the switching losses on the other side. An active thermal control is proposed to balance the temperature distribution in the converter. A four-level converter has been implemented to evaluate the proposed solution. The experimental results show that the proposed implementation and active thermal control presents an enhanced temperature distribution in the converter and, therefore, reduced thermal stress and better reliability.

An Online Condition Monitoring Method for IGBT Gate Oxide Degradation Based on the Gate Current in Miller Plateau

The reliability of power converters is one of the important issues due to the widespread applications of power electronics in many industrial fields. Accordingly, condition monitoring (CM) methods for the assessment of the converter components health are considered as a practical topic for researchers and experts of the field. This paper aims to propose a CM method for insulated gate bipolar transistors (IGBTs) gate-oxide degradation. The proposed CM is based on the gate-emitter current during the turning-on process. It is shown that in the degradation process, the gate current peak value majorly increases. The proposed CM method captures this peak value and uses it as a degradation indicator. The proposed method is simple and analogous that can be served easily for online health assessment of the IGBTs under operation. It can be integrated into the driver module to assess the gate oxide degradation of the device. The functionality of the proposed method is evaluated using experimental prototyping. The target devices are a 1200 V, and 40 A trench-gate field-stop and a 600 V and 60 A planner gate punch-through (PT) discrete IGBTs. The achieved results show the validity and acceptable performance of the proposed CM for detecting the gate-oxide degradation of the device.

A Reliability-Optimized Maximum Power Point Tracking Algorithm Utilizing Neural Networks for Long-Term Lifetime Prediction for Photovoltaic Power Converters

The reliability of power converters in photovoltaic systems is critical to the overall system reliability. This paper proposes a novel active thermal-controlled algorithm that aims to reduce the rate of junction temperature increase, therefore, increasing the reliability of the device. The algorithm works alongside a normal perturb and observe maximum power point tracking algorithm, taking control when certain temperature criteria are met. In conjunction with a neural network, the algorithm is applied to long-term real mission profile data. This would grant a better understanding of the real-world trade-offs between energy generated and lifetime improvement when using the proposed algorithm, as well as shortening study cycle times. The neural network, when applied to 365 days of data, was 28 times faster than using standard electrothermal modeling, and the lifetime consumption was predicted with greater than 96.5% accuracy. Energy generated was predicted with greater than 99.5% accuracy. The proposed algorithm resulted in a 3.3% reduction in lifetime consumption with a 1.0% reduction in the total energy generated. There is a demonstrated trade-off between lifetime consumption reduction and energy-generated reduction. The results are also split by environmental conditions. Under very variable conditions, the algorithm resulted in a 4.4% reduction in lifetime consumption with a 1.4% reduction in the total energy generated.

Comprehensive reliability evaluation of three types of connection of DC–DC converters: single‐phase, two‐phase, and parallel input‐series output

AbstractWith the increasing use of power electronic converters, the reliability studies of these converters are essential. The most important factor in increasing the reliability of power converters is their structures. In this paper the reliability evaluation of a DC–DC converter with various connections including single‐phase, interleaved, and parallel‐input and series‐output (PISO) topologies is presented. In the first view, it seems that the interleave topology has high reliability, but considering the more presented detailed indexes, it is identified that the PISO structure has a higher reliability than the interleave structure. In this paper for better evaluation, the various topologies are considered which operate at full rated power and half power. To calculate the reliability of the converters the important parameters such as the thermal and electrical stresses of elements are considered. The Markov model is used to evaluate the reliability. In order to verify the presented studies and analysis, the DC–DC converters with single‐phase, interleaved, and PISO have been implemented. The experimental results show that the PISO topology has higher reliability.

Investigation of Off-State Stress Induced Degradation of SiC MOSFETs Under Short-Circuit Condition

Investigation of SiC MOSFETs short-circuit (SC) degradation mechanism is critical to improve the overall reliability of power converters. At present, research on the SiC MOSFETs degradation mechanism mainly focuses on the on-state phase of the SC period. While, ruggedness of SiC MOSFETs in the off-state phase of short-circuit tests (SCTs) were neglected. In this paper, SiC MOSFETs degradation mechanism in the off-state phase of SCTs are investigated comprehensively. Specifically, distribution and magnitude of electrothermal stress of devices under test (DUTs) in the off-state phase of SCTs are analyzed by TCAD simulation. Which reveals two important phenomena: i) the device will suffer from long-term high temperature and high electric field stress in the off-state phase when negative turn-off gate voltage (Vgs-off) is applied; ii) high hole current in the channel region will last for several microseconds after the device is turned off. The observed SiC MOSFETs degradation in the off-state phase of SCTs is then proved by experiments, through which, the excessively low Vgs-off can reduce the SC capability of SiC MOSFETs is concluded. Moreover, the degradation results of static parameters of SiC MOSFETs are presented and the degradation mechanism is analyzed in detail.

Charging Infrastructure and Grid Integration for Electromobility

Electric vehicle (EV) charging infrastructure will play a critical role in decarbonization during the next decades, energizing a large share of the transportation sector. This will further increase the enabling role of power electronics converters as an energy transition technology in the widespread adoption of clean energy sources and their efficient use. However, this deep transformation comes with challenges, some of which are already unfolding, such as the slow deployment of charging infrastructure and competing charging standards, and others that will have a long-term impact if not addressed timely, such as the reliability of power converters and power system stability due to loss of system inertia, just to name a few. Nevertheless, the inherent transition toward power systems with higher penetration of power electronics and batteries, together with a layer of communications and information technologies, will also bring opportunities for more flexible and intelligent grid integration and services, which could increase the share of renewable energy in the power grid. This work provides an overview of the existing charging infrastructure ecosystem, covering the different charging technologies for different EV classes, their structure, and configurations, including how they can impact the grid in the future.

Power Electronics Technology for Large-Scale Renewable Energy Generation

Grid integration of renewable energy (REN) requires efficient and reliable power conversion stages, particularly with an increasing demand for high controllability and flexibility seen from the grid side. Underpinned by advanced control and information technologies, power electronics converters play an essential role in large-scale REN generation. However, the use of power converters has also exposed several challenges in conventional power grids, e.g., reducing the system inertia. In this article, grid integration using power electronics is presented for large-scale REN generation. Technical issues and requirements are discussed with a special focus on grid-connected wind, solar photovoltaic, and energy storage systems. In addition, the core of the energy generation and conversion—control for individual power converters (e.g., general current control) and for the system level (e.g., coordinated operation of large-scale energy systems)—is briefly discussed. Future research perspectives are then presented, which further advance large-scale REN generation technologies by incorporating more power electronics systems.

A Unified Open-Circuit-Fault Diagnosis Method for Three-Level Neutral-Point-Clamped Power Converters

Fast and accurate fault diagnosis is important to enhance the reliability of power converters. Since both open-circuit faults in insulated gate bipolar translator (IGBTs) and diodes deteriorate power quality, diagnosis methods only focusing on IGBT failures are easily disturbed by diode failures. In this work, we propose a unified effective residual-based open-circuit fault diagnosis method for <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">all</i> semiconductor devices including IGBTs, clamping diodes, and freewheeling diodes in three-level neutral-point-clamped power converters. The voltage and current residuals are calculated from the mismatches between the actual current path and the estimated one, requiring <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">solely</i> the already existing current measurement of the system. By analyzing the variation of the voltage and current residuals in all open-circuit failure cases, the proposed diagnosis method can locate the faulty switch within several sampling periods, i.e., less than 1 ms. Finally, the proposed diagnosis method is incorporated in the model predictive current control framework. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Both</i> experimental <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">and</i> hardware-in-the-loop results confirm the effectiveness and robustness of the proposed diagnosis method at various operation scenarios.

A Center-Tapped Transformer Based Multifunctional Single-Phase Converter with Wide DC-Bus Control.

Alongside the rapid increase in distributed power generation and load, the demand for highly efficient and reliable power converters is increasing. This has resulted in the rise of grid interfaced renewable energy sources (RES), rapid deployment of battery energy storage systems (BESS) coupled with energy managment systems (EMS), and DC based grid. This paper presents a center-tapped transformer-based single-stage single-phase full-bridge (FB) bidirectional AC-DC converter and its control strategy to improve controllability and reliability in applications such as DC distribution, PV/BESS grid interfacing, vehicle to grid (V2G), and so on. In contrast to conventional galvanically isolated topologies, a single-phase center-tapped transformer is introduced. It links and galvanically isolates the converters and the grid and provides its leakage inductance as the needed inductor required for current control (depending on the design). Furthermore, it reduces the number of conventionally required power conversion stages by employing a wide DC-bus voltage control strategy, resulting in a single converter that undergoes a single power conversion. Additionally, the voltage level can be increased to further enhance the output quality by cascading multiple converters (Multi-Level). The structure, operation, and basic control scheme are discussed in detail. Verification through a 220 Vrms, 1.8 kVA, and 45∼100 VDC simulation and small-scale experimental prototype (60∼100 VDC voltage) for practical validation of the topology is also presented.

Guest editorial: Highly efficient and reliable power converters for microgrid applications

Guest editorial: Highly efficient and reliable power converters for microgrid applications

Two-Switch Boost Converter With Improved Voltage Gain and Degree of Freedom of Control

The use of renewable resources for low power generation has led to extensive research on power converters for reliable and efficient power conversion. Though conventional boost converter (CBC) remains the widely used topology, its operating range is limited due to constraints on voltage gain and degree of freedom of control (DoFoC). This paper presents a two-switch boost converter (TSBC) which improves the voltage gain and DoFoC by cascading an additional switch-diode pair to the CBC circuit. The additional switch enhances the range of voltage gain without operating CBC at high duty ratios. Additionally, TSBC offers more choices to adjust voltage gain, which enhances DoFoC. The switching interval selection is detailed considering the voltage gain and constraints on circuit variables. The design formulations of TSBC are examined to facilitate optimal choice of components. The features of TSBC are theoretically established with mathematical derivations and are validated by simulations and experiments. The experimental results indicate that for a duty ratio of 0.7 for the existing switch of CBC, an increase in voltage gain from 3.2 to 4.3 is achieved when the duty ratio of the additional switch in TSBC is varied from 0 to 0.1. Similarly, improved DoFoC is demonstrated with inductor current control as well as with constant ripple ratios while maintaining the required output voltage. The proposed converter can easily replace the commonly CBC to improve the gain and DoFoC by simply cascading a switch-diode pair at the input-side of CBC.

An Enhanced Fault-Tolerant and Autoreconfigurable BLDC Motor Drive for Electric Vehicle Applications

Semiconductor switching devices are susceptible to open-circuit (OC) and short-circuit (SC) faults, adversely affecting the reliability of power converters. This article proposes a multiple-switch fault-tolerant and autoreconfigurable brushless direct current (BLDC) motor drive configuration, suitable for electric vehicle applications, owing to its enhanced reliability. The proposed power circuit configuration, along with its fault diagnostic algorithm, is capable of achieving fault tolerance against multiple OC and SC faults. The proposed drive configuration is capable of delivering rated power to the BLDC motor even after the development of several faults in the power semiconductor switching devices. In this power converter, additional switching resources, provided to achieve fault tolerance, get connected only after the occurrence of faults. This feature avoids their unnecessary exposure before the occurrence of faults. Furthermore, the proposed topology requires fewer sensors to implement the fault diagnostic algorithm resulting in reduced cost and increased reliability. This article also presents an analysis that assesses the cost-effectiveness of the proposed drive configuration, which reveals that the additional cost to implement the proposed topology is not more than 6% of the total raw material cost of the conventional BLDC motor drive. Simulation and experimental studies validate the concept of the proposed drive configuration.