Three-level Inverter Research Articles

Open-Circuit Fault Analysis and Recognition in Three-Level Inverters Based on Recurrence Plot and Convolution Neural Network

Power electronics is vital to modern infrastructure, but it is susceptible to open-circuit faults that can cause serious damage. Three-level inverters are commonly used in such equipment, but their high sensitivity and probability of failure make them particularly challenging to diagnose. In this groundbreaking study, we present a new method for accurately detecting and locating open-circuit faults in three-level, neutral-clamped inverters. Using advanced simulation tools and nonlinear dynamic methods, we develop a new diagnostic model that outperforms existing fault classification algorithms. By converting the current signal into an unthreshold recurrence plot (URP) and mapping its nonlinear features to a two-dimensional plane, it is possible to extract key spatial information and train a residual neural network model for fault diagnosis. The method represents a major advance in power electronics and has the potential to save equipment from costly damage. By accurately detecting and locating open-circuit faults in three-level inverters, the reliability and safety of power electronics can be guaranteed for years to come.

Fault diagnosis of three-level inverter based on convolutional neural network and support vector machine

ABSTRACT Due to the strong nonlinearity and high complexity of NPC three-level inverter system, the model-based method is difficult to be used for open-circuit fault diagnosis of power switches. A fault diagnosis method (CNN-SVM) based on the combination of convolutional neural network (CNN) and support vector machine (SVM) is proposed. The data fusion method is used to integrate the output voltage characteristics of the inverter. The connection between data before and after is increased by it into a grayscale map. CNN is used to obtain the integrated voltage-related features, and SVM is used to classify the obtained features and then judge whether the fault occurs and the location of the fault. The experimental results show that the accuracy of the CNN-SVM model for inverter fault diagnosis is more than 96%, and it has high processing speed and strong generalization ability.

A Novel Modulation Scheme for Simultaneous Common-Mode Voltage Reduction and Neutral-Point Voltage Balance in the Reduced Switch Count Quasi-Z-Source Three-Level Inverter

The reduced switch count quasi-Z-source three-level inverter (RSC-QZS-TLI) not only maintains the advantages of continuous input current in the conventional quasi-Z-source three-level inverter (C-QZS-TLI), but also reduces the number of power switches and system cost. However, it inevitably faces the challenges of high common-mode voltage (CMV) and neutral-point voltage (NPV) imbalance, which threaten system safety and reliability. Moreover, due to the inherent features of this topology, the medium vectors cannot be generated, which means that the traditional modulation method is not applicable any more. To address the above challenges, a novel modulation method is proposed. The pre-selected basic vectors are optimized primarily, which restrict the CMV magnitude within one-sixth of dc-link voltage. Then, for the particularity of RSC-QZS-TLI, the distribution factor of small vector and its limitation range are introduced for the first time, and an indirect calculating approach is developed to obtain the duty cycles of the pre-selected four vectors, which maintains the correct ac output voltage and dc voltage boosting ability. Meanwhile, according to sector number and output of NPV controller, the distribution factor is modified to control the NPV balance. Compared with the traditional modulation method, the CMV magnitude of the proposed method is reduced by 50 %, and the balanced NPV is controlled actively. Simulated and experimental results verify the feasibility of the proposed scheme.

Weighting-Factor-Less Model Predictive Control With Multiobjectives for Three-Level Hybrid ANPC Inverter Drives

Weighting-Factor-Less Model Predictive Control With Multiobjectives for Three-Level Hybrid ANPC Inverter Drives

An Online Multiple Open-Switch Fault Diagnosis Method for T-Type Three-Level Inverters Based on Multimodal Deep Residual Filter Network

With the development of the processing capacity of the embedded chip, it is possible to implement a machine learning algorithm in the embedded system. To achieve the fault status without poor portability, tricky threshold selection and complex rulemaking, this paper proposes a multi-modal deep residual filter network for online multiple open-switch fault diagnosis of T-type three-level inverter. It contains low-rank matrix fusion (LMF), deep residual filter network (DRFN), and cross transformer mechanism. The LMF fuses the voltage signal and the current signal for obtaining the unified representation. And then, the DRFN filters noise adaptively and extracts information effectively. Finally, the cross-transformer mechanism output the fault state of the T-type three-level inverter. The data sets consist of the dc-link voltage and load side current of the inverter control system. The data time window is selected as 20 ms. Through the real-time calculation of online monitored data, the experimental results show the effectiveness of the proposed fault diagnosis approach. Moreover, the accuracy of fault diagnosis obtains 99.18% and the average open-circuit fault diagnosis time is 21 ms.

A Resonant Switched-Capacitor Converter for Neutral-Point Voltage Balancing of Three-Level Inverters

A Resonant Switched-Capacitor Converter for Neutral-Point Voltage Balancing of Three-Level Inverters

Influence of switching sequences on the neutral point voltage balance in a three-level voltage source invertor

BACKGROUND:Ensuring the voltage balance of the neutral point of the DC link within acceptable limits is one of the mandatory requirements during the operation of a three-level autonomous neutral point clamped voltage source inverter. It is known that neutral point voltage imbalance can adversely affect the operation of the inverter and the load at all, lead to the failure of both power switches and capacitors in the DC link. Neutral point voltage imbalance mostly often occurs due to the asymmetry of the nominal values of DC capacitors, inconsistent properties of switching devices, asymmetric three-phase load, and also due to the imperfection of the converter control algorithm.
 AIMS:Selection of the optimal switching sequence that ensures the smallest deviation of the neutral point voltage and the number of switching of power switches in a three-level voltage source inverter.
 METHODS:For an objective comparison of the considered switching sequences and their influence on the neutral point voltage balance, a simulation model of a three-level neutral point clamped voltage source inverter was developed in theMATLAB/Simulinksoftware. To control this inverter, a space vector modulation method was used with three different switching sequences: five-segment, seven-segment and standard.
 RESULTS:The topology of a three-level neutral point clamped voltage source inverter is presented. The experimental dependencies of the neutral point voltage deviation error was taken with a change in the modulation coefficient, the frequency of the fundamental harmonic at the inverter output, and load characteristics for three different switching sequences.
 CONCLUSIONS:In this paper, the influence of the basic vectors and the influence of switching sequences on the neutral point voltage balance are studied. Combinations of states of large and zero basic vectors do not affect the neutral point voltage. For the medium basic vectors, the neutral point voltage can increase or decrease depending on the operating conditions of the inverter. The small basic vectors significantly affect the neutral point voltage. Considering the abovementioned, the seven-segment sequence that ensures both the optimal balance of the neutral point voltage and the level of switching losses should be considered as the best switching sequence for a three-level inverter.

A unified duty-cycle modulation algorithm for a three-level NPC inverter

In this paper, it is a kind of challenge to simplify the conventional pulse width modulation (PWM) algorithms for a three-level neutral-point-clamped inverter. Thus, the unified duty-cycle modulation (UDM) algorithm is presented. It is more attractive than the carrier-based PWM (CBPWM), space-vector PWM (SVPWM), and unified PWM algorithms with a simpler calculation by utilizing the usefulness of the SVPWM algorithm to synthesize the duty cycles in time-domain and the CBPWM algorithm to synthesize the duty cycles in frequency-domain with the lesser conditions and the blankness of the lookup tables, switching sequence design, and zero-sequence component finding. Besides, it is outstanding with three outcomes: (1) comprehensive mathematical models of the dwell times, (2) permanent mathematical models of the duty cycles in time-domain, and (3) simplified PWM algorithm, which has a better workflow with the reduction of the computation burden. As it is very easy to implement as the sinusoidal PWM technique while its performance is equivalent to the SVPWM algorithm, this makes the proposed UDM algorithm a good candidate to optimize between the performance and the cost. Both the simulation and experimental results can confirm the feasible practicability and performance. The comparison with the conventional algorithms can evidently emphasize the superiority.

Segment Reduction-Based Space Vector Pulse Width Modulation for a Three-Phase F-Type Multilevel Inverter with Reduced Harmonics and Switching States

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.

Review, Comprehensive Analysis and Derivation of Analytical Power Loss Calculation Equations for Two- to Three-Level Midpoint Clamped Inverter Topologies with Hybrid Switch Configurations

Increased performance requirements in new power electronics areas of application, such as electric aircraft, make innovations on different design levels necessary. In order to quickly compare different topologies, analytical loss equations provide a fast and straightforward way to narrow down the possible solution space. The approach widely used in the literature results in long and complex terms, which can only be compared between different literature sources with great effort. Moreover, the literature lacks a detailed summarizing description of these analytical equations and their derivation, starting from the standard two-level VSI up to three-level midpoint clamped inverter topologies, such as the ANPC topology in its different modulation schemes. The application of such higher-level inverter topologies allows hybrid device configurations to become performant solutions. This work aims to give a closed-form description of the analytical loss modeling and the theoretical background and provide an implementation approach for a wide span of inverter topologies and for different modulation methods.

Improving Power Quality in Grid-Connected Photovoltaic Systems: A Comparative Analysis of Model Predictive Control in Three-Level and Two-Level Inverters.

The Single-Stage Grid-Connected Solar Photovoltaic (SSGC-SPV) topology has recently gained significant attention, as it offers promising advantages in terms of reducing overall losses and installation costs. We provide a comprehensive overview of the system components, which include the photovoltaic generator, the inverter, the Incremental Conductance Maximum Power Point Tracking (IC-MPPT) algorithm, and the PI regulator for DC bus voltage control. Moreover, this study presents detailed system configurations and control schemes for two types of inverters: 2L-3PVSI and 3L-3PNPC. In order to perform a comparative study between the two structures, we subjected them to the same irradiation profile using the same grid configuration. The Photovoltaic Array (PVA) irradiance is increased instantaneously, in 0.2 s, from 400 W/m2 to 800 W/m2, is kept at 800 W/m2 for 0.2 s, is then gradually decreased from 800 W/m2 to 200 W/m2 in 0.2 s, is then kept at 200 W/m2 for 0.2 s, and is then finally increased to 1000 W/m2 for 0.2 s. We explain the operational principles of these inverters and describe the various switching states involved in generating output voltages. To achieve effective control, we adopt the Finite Set-Model Predictive Control (FS-MPC) algorithm, due to the benefits of excellent dynamic responsiveness and precise current tracking abilities. This algorithm aims to minimise the cost function, while taking into account the dynamic behaviour of both the PV system and the inverter, including any associated delays. To evaluate the performance of the FS-MPC controller, we compare its application in the three-level inverter configuration with the two-level inverter setup. The DC bus voltage is maintained at 615 V using the PI controller. The objective is to achieve a Total Harmonic Distortion (THD) below 5%, with reference to the IEEE standards. The 2L-3PVSI inverter is above the threshold at an irradiance of 200 W/m2. The 3L-3PNPC inverter offers a great THD percentage, meaning improved quality of the power returned to the grid.

Hybrid Modulation Strategy for Common-mode Voltage Suppression in Three-level Inverters

A hybrid modulation strategy is proposed to suppress the common-mode voltage (V com) of the three-level PWM inverter on the strength of the SVPWM modulation algorithm (space vector pulse width modulation) for V com generated during the run of the three-level inverter. The three-level space vector is classified as two different modulation areas by modulation ratios. In the low modulation ratio region, according to the nearest three vectors principle, the spatial voltage vector is obtained by combining the small vector with the medium vector, which suppresses V com and ensures that only one bridge arm is switched for any voltage vector. In the high modulation ratio region, the vector with large common-mode voltage is discarded, and the zero-vector, medium-vector, and large-vector are selected to synthesize the space voltage vector, which suppresses V com and ensures the good output current waveform of the PWM inverter. From the simulation results, we can see the hybrid modulation strategy of dividing the region by modulation ratio reduces the magnitude of V com to 1/6 of the dc bus voltage, and at the same time, a good current waveform is obtained at the output of the three-level inverter.

Passivity-Based Control Method for Three-Level Photovoltaic Inverter to Mitigate Common-Mode Resonant Current

In transformerless three-level photovoltaic inverter systems, the modified LC filter, which directly connects the dc-side neutral point to the common point of filter capacitors, is considered to be an ideal scheme to suppress the troublesome leakage current. However, a new common-mode (CM) resonant current is emerged, which leads to inverter-side current distortion and even system instability. Therefore, a second-order passivity-based controller in time domain featuring with excellent system stability is proposed for the CM resonant current mitigation. First, the reason of CM resonant current generation with the modified LC filter is analysed in detail. Then, the CM current model is derived, which reveals that it is a second-order system. The passivity of this second-order model is strictly proved. Moreover, based on the passive control theory, zero state detectable theory and Lyapunov stability theorem, a second-order passivity-based controller is designed step by step to suppress the CM resonant current, and the system global asymptotic stability is also proved. The proposed controller is based on time domain, which is more intuitive and avoids the error amplification in the conversion from frequency domain to time domain. Finally, the effectiveness and the correctness of theoretical derivation of the passivity-based control method are validated by experiments. Compared with passive damping resistor method, the proposed method not only has better performance, but also avoids the use of real resistor and reduces the cost by using software instead of hardware.

Reduction of Spurious Switching in Direct Vector Quantized Space Vector Pulse Density Modulation Scheme for Multilevel Inverters

A generalized online switching scheme for multi-level inverter based on Direct Vector Quantized Space Vector Pulse Density Modulation (DVQSVPDM) suitable for adjustable speed drive is proposed in this article. The existing DVQSVPDM schemes have spurious switching as the voronoi region is determined from integrated error vector of Sigma Delta Modulator (SDM). This results in high Total Harmonic Distortion (THD) of Common Mode Voltage (CMV) at lower modulation index. In the proposed DVQSVPDM the nearest three space vectors to the reference vector forms the triangular voronoi region. The integrated error vector of SDM is quantized to its nearest space vector in the voronoi region to generate the switching vectors. This reduces spurious switching associated with DVQSVPDM schemes and improves the performance at lower modulation index by reducing THD of CMV. The proposed scheme works for all n-level inverter topologies and the computations required remain same irrespective of level of inverter. Redundant states of switching vectors are not considered for switching which results in the discontinuous nature of proposed scheme. The performance of proposed DVQSVPDM is compared with space vector based modulation schemes and third harmonic injected sine PWM scheme and the results are presented. The proposed scheme is experimentally validated for a 3hp open end winding induction motor fed with three-level inverters on both sides.

An Improved Model Predictive Control to Enhance Voltage Performance for $LC$ Filtered Three-Level Inverters With Voltage Feedback Only

This article proposes a double vector model predictive control (MPC) method for the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$LC$</tex-math></inline-formula> filtered three-level T-type inverter (3LT <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{2}$</tex-math></inline-formula> I) to gain superior voltage performance, which is current sensorless and computationally efficient. In the proposed scheme, inverter voltage increment is induced in the multi-objectives cost function, and the desired voltage is derived based on the simplified discrete model, which optimizes the output voltage control performance. The prepositive prediction calculation is shifted out from the evaluation circle, and the computation is lessened simultaneously. Then, aiming to estimate the capacitor current of the simplified discrete model with voltage feedback only, the strong-tracking Kalman filter (STKF)-based observer is designed, which gets rid of the dependence on current sensors and lowers hardware cost. Furthermore, to improve the control accuracy of tracking the desired voltage, a two-layer decision algorithm based on the search tree is developed to find the optimal double vector easily, which obtains a low-complexity selection process using the univariate cost function. Finally, the simulation and experimental results are given to demonstrate the effectiveness of the theoretical analyses and the proposed method.

F-Type Single Phase Five Level Inverter

In modern industrial and power electronics applications, high-voltage and high-current integrated modular power transistors (IGBTs) are increasingly being utilized. The F-type inverter, which is a modified version of the T-type inverter, has emerged as a promising option. This configuration separates the common point of the bidirectional power switch, reducing voltage stress and resulting in lower inverter costs and losses. The F-type inverter has a simplified design and lower conduction losses, making it a viable choice for medium-voltage applications compared to the clamp diode NPC inverter configuration. Detailed analysis of losses and efficiency has been conducted, and a simulation and experimental prototype have been built to validate the theoretical basis. In addition, the voltage rating of the power switches in the T-type three-level inverter is a limiting factor, as it is only 50% of the input DC voltage for each inverter phase leg.

A Low Switching Frequency Model Predictive Control Method for an Induction Motor Fed by a 3-Level Inverter

Traditional model predictive control (MPC) for the induction motor fed by a three-level inverter needs to explore 27 voltage vectors to obtain the optimal one, which leads to high switching frequency and requires too much computation. To solve this issue, a low switching frequency model predictive control with partition optimization is proposed. First, the reference voltage vector can be gained from the prediction model at the next time, and the space voltage vector plane is divided into 12 sectors for further vector choice. Furthermore, considering inverter constraints, the candidate voltage vectors are determined according to the sector location of the reference voltage vector. In this way, the candidate vectors can be reduced to 3 at most. Then, a boundary circle limit is designed to avoid unnecessary switch changes. If the reference voltage vector is within the boundary limit, the switches do not act, which can reduce the system switching frequency without introducing the extra weight coefficient into the cost function. These selected voltage vectors are substituted into the cost function to determine the optimal one. Finally, the neutral point voltage deviation is controlled by the positive and negative redundant small vectors to realize the multi-objective constraint without weighting coefficients. The simulation results show that the proposed control method can significantly reduce the switching frequency; at the same time, both the dynamic and steady performances can be maintained well, and the cost function has no weight coefficients.

Modelling and Performance Analysis of a Tidal Current Turbine Connected to the Grid Using an Inductance (LCL) Filter

Nowadays, integrating renewable energy sources, such as tidal power, into the existing power grids of turbines is crucial for sustainable energy generation. However, tidal turbine energy transforms the potential energy of moving water into electrical energy. When both nonlinear load and dynamic load harmonics are present, the tide speed variance causes serious power quality issues such as low power factor, unstable voltage, harmonic distortions, frequency fluctuations, and voltage sags. The integration of an LCL-filter-based connection scheme can address these challenges by improving power quality and the overall performance of the tidal current turbine grid system. This study shifts LCL filter research from its conventional wind energy emphasis to the emerging field of tidal stream generation systems. The LCL filter analysed in this paper is modelled to exhibit adequate mechanical, electrical, and hydrodynamic characteristics. This model accounts for tidal current variations, turbine speed control, and power extraction dynamics. The LCL filter is evaluated for its effectiveness in reducing harmonic distortions, voltage fluctuations, and reactive power fluctuations. This system is composed of a 1.5 MW/C, a 1.2 MW three-level inverter with a nominal voltage of 600 V, and an inductance (LCL) filter. The results show that the inverter produces a harmonic distortion of less than 0.5%, which demonstrates the effectiveness of the filter in improving total harmonic distortion, reactive power consumption, and voltage control.

Research on DC Component Disturbance Suppression Strategy of Islanded T-Type Three-Level Inverter Based on Improved Backstepping Control Theory

Research on DC Component Disturbance Suppression Strategy of Islanded T-Type Three-Level Inverter Based on Improved Backstepping Control Theory

Multivector Model Predictive Current Control for Paralleled Three-Level T-Type Inverters With Circulating Current Elimination

Paralleled three-level T-type inverters face the unavoidable pitfall of the zero-sequence circulating current (ZSCC). Although the conventional model predictive control (MPC) could eliminate the ZSCC, the control error occurs inevitably since only one vector is adopted in each sampling period, which decreases the current control performance. Thus, simultaneous ZSCC elimination and accurate current tracking become imperative to the inverter using MPC. This article proposed a multi-vector MPC to eliminate the ZSCC and reduce the current distortion without the weighting factor. As the common-mode voltage (CMV) and neutral point (NP) voltage are the main factors that induce the ZSCC, the virtual vector with zero-average CMV is constructed to eliminate the ZSCC. Meanwhile, the small vector is introduced to improve the NP voltage control capability. Additionally, to enhance the current accuracy and reduce the ZSCC ripple, three optimal vectors are adopted to synthesize desired voltage. Moreover, the multi-vector preselection algorithm is proposed to reduce the computational complexity of implementation process. Finally, the effectiveness of the proposed method is verified with comprehensive simulation and experimental results.