Search Results (71)

Monitoring the peak junction hotspot temperature in IGBT modules is critical for ensuring the reliability of high-power industrial multilevel inverters, particularly when operating under extreme thermal conditions, such as in traction applications. This study presents a comprehensive chip-level analytical loss and thermal model for estimation of the peak junction hotspot temperature in a three-level T-type neutral-point-clamped (TNPC) IGBT module. The developed model includes a detailed analytical assessment of conduction and switching losses, along with transient thermal network modeling, based on the actual electrical and thermal characteristics of the IGBT module. Additionally, a hybrid thermal–electrical stress experimental setup, designed to replicate real operating conditions, was implemented for a balanced three-phase inverter circuit utilizing a Semikron three-level IGBT module, with testing currents reaching 100 A and a critical case temperature of 125 °C. The analytically estimated module losses and peak junction hotspot temperatures were validated through direct experimental measurements. Furthermore, thermal simulations were conducted with Semikron’s SemiSel benchmark tool to cross-validate the accuracy of the thermo-electrical model. The outcomes show a relative estimation error of less than 1% when compared to experimental data and approximately 1.15% for the analytical model. These findings confirm the model’s accuracy and enhance the reliability evaluation of TNPC-IGBT modules in extreme thermal environments. Full article

Fast open-circuit (OC) fault diagnosis is essential to ensure that a multilevel inverter operates under stable conditions. Conventional diagnosis methods either require additional hardware sensors or complex calculations. However, these conditions are difficult to realize in some low-cost application scenarios. For this reason, a two-step process-based OC fault diagnosis method is proposed according to available data that can be acquired using the existing sensors in the application. At the same time, the proposed method does not involve complex and precise calculation. By analyzing the effects of an OC fault on the AC-side three-phase current, the faulty bridge arm can be quickly located via the average current. Furthermore, through establishing the calculation model of the neutral point potential, an accurate diagnosis of faulty switching devices can be achieved quickly and easily based on the residuals. The proposed OC fault diagnosis method is also proved to be correct and effective based on simulation and experience. Full article

With increasing interest in integrating solar power into the utility grid, multilevel inverters are gaining much more attention for medium- and high-power applications due to their high-quality waveform, low voltage stress across active components, and low total harmonic distortion in output voltage. However, to achieve these benefits, a large number of active and passive components are required. A transformer is also required to provide galvanic isolation, which increases its size and weight and reduces its power density and efficiency. In order to overcome the disadvantages posed by transformer-based inverters, research is being conducted on the transformerless topology of multilevel inverters. The first aim of this review article is to summarize traditional transformerless multilevel inverters (TMLIs) considering both single- and three-phase topologies. Secondly, the main aim of this article is to provide a detailed overview of the hybrid topologies of TMLIs that employ fewer components for photovoltaic applications. In addition, this study compares traditional and hybrid single-/three-phase topologies in terms of component count and performance factors, which will be useful to researchers. Full article

Multi-level inverters have characteristics suitable for high-voltage and high-power applications through various topology configurations. These reduce harmonic distortion and improve the quality of the output waveform by generating a multi-level output voltage waveform. In particular, an active neutral-point-clamped topology is one of the multi-level inverters advantageous for high-power and medium-voltage applications. It has the advantage of controlling the output waveform more precisely by actively clamping the neutral point using an active switch and diode. However, it has a problem, which is that an unwanted zero-crossing current may occur if an inaccurate switching signal is applied at the time when the polarity of the output voltage changes. In this paper, a control strategy to suppress the zero-crossing current of a single-phase half-bridge three-level active neutral-point-clamped inverter is proposed. The operating principle of a single-phase half-bridge three-level active neutral-point-clamped inverter is identified through an operation mode analysis. In addition, how the switching signal is reflected in an actual digital signal processor is analyzed to determine the situation in which the zero-crossing current occurs. Through this, a control strategy capable of suppressing zero-crossing current is designed. The proposed method prevents a zero-crossing current by appropriately modifying the update timing of reference voltages at the point where the polarity of the output changes. The validity of the proposed method is verified through simulation and experiments. Based on the proposed method, the total harmonic distortion of the output current is significantly reduced from 12.15% to 4.59% in a full-load situation. Full article

Multilevel inverters with improved voltage quality are widely used in applications such as motor control and electric vehicles. The four-level active neutral point clamped (4L-ANPC) inverter effectively meets the demands for high power density and low device voltage stress. However, balancing the capacitor voltage and reducing its low-frequency voltage fluctuation are critical challenges that need to be addressed. To address these challenges, this paper proposes a “variable reference + zero-sequence injection” method that requires only three reference voltage signals to determine the injected zero-sequence components. Particularly, the expression of the midpoint current, regarding the modulation index and phase current amplitude, is theoretically derived. This reveals the fundamental connection between the zero-sequence voltage signal and the midpoint current, providing a theoretical foundation for the zero-sequence injection method in four-level inverters. Subsequently, a simulation model and an experimental platform of the 4L-ANPC inverter were developed to compare and analyze the waveforms of the upper and lower capacitor voltages, phase currents, and line voltages under different modulation methods. Additionally, the upper and lower capacitor voltage waveforms were examined for various modulation indices. The results indicate that as the modulation index increases, the low-frequency voltage fluctuation in the upper and lower capacitor voltages also rises. At a modulation index of 0.95, the “variable reference + zero-sequence injection” method effectively suppresses the fluctuation in the upper and lower capacitor voltages to be no more than 1 V. These experimental findings validate the effectiveness of the proposed method. Full article

This paper presents a high-performance, multilevel inverter with symmetry and simplification. This inverter is a single-phase, seven-level symmetric switched-capacitor inverter based on the concept of the double voltage clamping circuit connected to the half-bridge circuit. Above all, only a single DC power supply is used to achieve a single-phase inverter with seven levels and a voltage gain of three. In addition to analyzing the operating principle of the proposed switched-capacitor multilevel inverter in detail, the stability analysis and controller design are carried out by the state-space averaging method. The feasibility and effectiveness of the proposed structure are validated by some simulated results based on the PSIM simulation tool and by some experiments using FPGA as a control kernel, respectively. However, in this study, the switches were implemented by MOSFETs to meet a high switching frequency. These MOSFETs can be replaced by IGBTs in the motor drive applications so that the used switching frequency can be reduced. Full article

A three-phase multilevel inverter (MLI), synthesized with 31 levels in regard to its output voltage, is used to provide the AC supply to a three-phase, squirrel cage induction motor. The gating angles required for the 30 power switches on the MLI are optimized using both the genetic algorithm (GA) and the grey wolf optimizer (GWO), in which the optimal angles are determined through solving the trigonometric equations taken from Fourier analysis to target the minimum total harmonic distortion (THD) at the MLI output. A simulation model and an experimental prototype are developed for performance analysis and validation. The results demonstrate that the MLI is effectively able to produce 31 levels of three-phase AC output voltage, with the THD not exceeding 5% when loaded with a resistive load and a three-phase induction motor. The voltage and current are measured and recorded for different loads and operating conditions, including the amount of energy consumed by the load. The results of the frequency analysis demonstrate that most of the triple harmonics, which can harm the efficiency of the inverter, are cancelled. Full article

Stratospheric drones operating in extreme environments are very important for predicting reliability and are high-efficiency, high-performance, and lightweight power units. Multilevel inverters are suitable for application as power conversion units for stratospheric drones. A guideline is needed to evaluate whether it is suitable for practical application from a reliability perspective among various multilevel topologies. Existing reliability prediction models cannot reflect the operating characteristics of multilevel inverters. In this paper, we analyze the driving characteristics of each topology from the perspective of half-bride, which is the basic configuration of multilevel inverters, and we propose a fault tree analysis (FTA) design with three operating modes. The proposed method has the advantage of being able to easily analyze the failure rate by expanding to single-phase and three-phase and to analyze the failure rate according to changes in modulation index (MI) and power factor (PF). The failure rates of the proposed method and the part count method are analyzed using MIL-HDBK-217F. We also analyze the impact of different various operating characteristics on the failure rate. From a reliability perspective, we provide a variety of guidelines for selecting a multilevel topology that fits the operation conditions. Full article

In this study, a wind energy conversion system is designed using a three-phase permanent magnet synchronous generator, a six-diode bridge rectifier, a DC–DC boost converter, an inverter, and a load. The proposed inverter is a Packed U-Cell-based multilevel inverter having five or seven voltage levels at the output. It is also a topology that is not widely used in wind energy applications. Furthermore, a dual-mode PI-PI control technique is proposed to regulate the auxiliary capacitor voltage in the PUC MLI. The inverter is designed and simulated for a permanent magnet synchronous generator-based variable speed wind energy conversion system. Additionally, the design and experimental application of the proposed system is carried out in a laboratory environment. In the experimental application, the rated voltage of the Packed U-Cell multilevel inverter is chosen as 45 V. The switching frequency of the multilevel inverter is set to 4 kHz, and a generator with rated power of 700 W is selected. The output voltage of the generator is varied between 25 V and 35 V through an induction motor. This varying voltage is increased to 45 V using a DC–DC boost converter. Finally, it is observed that the power generated by the permanent magnet synchronous generator is successfully transferred to the load and the designed system operates with low harmonic content. Full article

This paper presents a passive concentrator for single-phase inverters with a three-phase output, which uses magnetically coupled reactors. Due to the development of renewable energy systems, the proposed systems may enable the easier integration of converters in the form of inverters with the power system. Two variants of cooperation of the concentrator with single-phase voltage inverters were considered. The first variant proposed a system topology in which three single-phase full-bridge inverters were connected to the concentrator, while the other variant proposed six half-bridge inverters. A control system of the inverters that does not use PWM was developed. A common star point was created for the supply voltages in the form of a capacitive divider covering all the inverters. An analysis of the concentrator system was presented, taking into account the cooperation with inverters. The overall power of the TDSλ system was defined and the relationship for its determination was given. Simulation studies were described, presenting the obtained voltage and current waveforms. The impact of changing the supply voltage of the inverters on the operation of the concentrator and the shape of the output voltages was assessed. The proposed systems allow you to connect 3 or 6 single-phase inverters. The use of magnetically coupled reactors enables the use of a magnetic system of lower power and size. The described concentrators enable the generation of multi-level three-phase output voltage with a low THD content. Full article

An improved segment reduction-based space vector pulse width modulation (SVPWM) for an F-type three-level inverter (FT²LI) is presented in this article. The proposed SVPWM algorithm decreases the additional switching state transition of each triangle with the application of an improved nine- and three-segment reduction switching strategy. The main feature of the segment reduction technique is that it eliminates second-order harmonics in the inverter output side with good total harmonic distortion (THD), low switching losses, and minimum filter requirements when compared with carrier-based PWM (CBPWM) techniques such as multi-carrier sine PWM (MC-SPWM), sixty-degree PWM (60° PWM), and switching frequency optimal PWM (SFO PWM). The proposed modulation algorithm for FT²LI is implemented on the MATLAB/Simulink platform. The performance of the proposed segment reduction-based SVPWM algorithm is tested experimentally on an FT²LI at various amplitude and frequency modulation indices, and the experimental results are verified with the simulation results. Additionally, a comparative analysis carried out to study the relationship between the segment reduction-based SVPWM and CBPWM techniques inferred that the suggested segment reduction-based SVPWM algorithms can optimize high-order harmonic distributions and have a minimum computational burden. Full article

With the increasing number of new energy sources connected to the grid, the unbalanced output of three-phase grid-connected inverters and the lack of no inertia and damping characteristics in the traditional microgrid control system will seriously affect the stability of voltage, frequency, and power angle for microgrids. This paper proposes a novel cascaded three-phase bridge inverter topology for the battery system used for the electric vehicle. Compared with traditional cascaded H-bridge inverters, the proposed multilevel inverter can achieve self-adaptive balance for three phases. The mathematical model of a cascaded three-phase bridge inverter is established in this paper. Based on the voltage and current equations of a multilevel inverter, a new modulation strategy named carrier phase-shifted-distributed pulse width modulation (CPSD-PWM) was developed, which is more suitable for cascaded three-phase bridge inverters. The harmonic analytic equations of carrier phase-shifted pulse width modulation (CPS-PWM) and CPSD-PWM are constructed by the double Fourier analysis method. Compared with the traditional PWM modulation strategy, the CPSD-PWM can reduce the output harmonics and improve the balance of the three-phase output, which can realize the three-phase adaptive balance in the cascaded three-phase bridge inverter. This paper develops a cascaded three-phase bridge multilevel power converter system based on the virtual synchronous generator (VSG) control strategy. The voltage and frequency of inverter output can be accurately controlled in both island mode and grid-connected mode through active power-frequency regulation and reactive power–voltage regulation, and the stability of primary frequency regulation for the multilevel microgrid inverter can be improved by collaborative optimization of virtual inertia and virtual damping. The CPSD-PWM modulation strategy and VSG control strategy are verified by the simulation results and experimental data for the cascaded three-phase bridge inverter. Full article

The key goal of this effort is to develop an efficient control system for a three-phase cascaded H-bridge multilevel inverter powered by the photovoltaic (PV) system. The power for the system is generated through the use of PV modules, which serve as DC inputs for the cascaded H-bridge multilevel inverter. The authors aim to achieve a nearly sinusoidal signal at the voltage level and are specifically focused on minimizing the total harmonic distortion (THD) to the smallest possible value. Hence, an advanced N-level space vector modulation (SVM) is developed to ensure an appropriate control for the cascaded inverter. The aim is to design an effective control strategy to increase inverter efficacy and, thus, supply the best output quality. In addition, a robust approach to the maximum power point (MPP) tracking (MPPT) technique is developed based on an adaptive perturb and observe (P&O) algorithm to ensure superior tracking of the MPP. The developed algorithm eliminates 90% of the power curve area in the search space process and only maintains 10% of the area that includes the MPP. Each PV system employs its own improved MPPT control. The numerical results confirm that the enhanced P&O algorithm attains a precise response with superior efficiency and a fast response under the fast alteration of environmental conditions. Hence, the energy loss is reduced. The simulation results validate the effectiveness of this study, highlighting the high efficiency of the control strategy and the enhanced performance of the proposed scheme with lesser THD values. Full article

Boost converters and multilevel inverters (MLI) are frequently included in low-voltage solar photovoltaic (PV) systems for grid integration. However, the use of an inductor-based boost converter makes the system bulky and increases control complexity. Therefore, the switched-capacitor-based MLI emerges as an efficient DC/AC voltage convertor with boosting capability. To make classical topologies more efficient and cost-effective for sustainable power generation, newer topologies and control techniques are continually evolving. This paper proposes a reduced-component-count five-level inverter design for generating stable AC voltages for sustainable grid-integrated solar photovoltaic applications. The proposed topology uses seven switching devices of lower total standing voltage (TSV), three diodes, and two DC-link capacitors to generate five-level outputs. By charging and discharging cycles, the DC capacitor voltages are automatically balanced. Thus, no additional sensors or control circuitry is required. It has inherent voltage-boosting capability without any input boost converter. A low-frequency-based half-height (HH) modulation technique is employed in the standalone system for better voltage quality. Extensive simulations are performed in a MATLAB/Simulink environment to estimate the performance of the proposed topology, and 17.58% THDs are obtained in the phase voltages. Using a small inductor in series or an inductive load, the current THD reduces to 8.23%. Better dynamic performance is also observed with different loading conditions. A miniature five-level single-phase laboratory prototype is developed to verify the accuracy of the simulation results and the viability of the proposed topology. Full article

This paper deals with the real-time simulation of power electronic converters. It discusses a new approach for designing embedded real-time simulators (eRTSs) that approximate the static and dynamic behavior of a power converter at the switching scale. The main concept is to approximate the voltage/current experimental characteristics of each switch using dedicated transfer functions obtained after a system identification process. The adaptive feature of such eRTS consists of developing varying and online reconfigurable coefficients transfer functions. The main potential of doing so is the possibility of reconfiguring the model according to the actual electrical/thermal environment where the power converter is used. Then, the latter is subdivided into independent switching cells, represented by dedicated RT models that are fully parallelized. Furthermore, using FPGA devices makes it possible to achieve very low latencies and, consequently, a short simulation time step. Previous work was published in this context, where this approach was deeply described and tested with half-bridge DC–DC, full-bridge DC–AC, and multi-level cascaded H-bridge (five-level and nine-level) power converters. This paper recalls the main basics and, more importantly, discusses additional case studies, namely a three-phase voltage source inverter, a half-bridge NPC (neutral-point clamped) inverter, and a three-phase NPC inverter. Full article