A Novel Asymmetrical Single-Phase Multilevel Inverter Suitable for Hybrid Renewable Energy Sources

This paper introduces a novel single-phase asymmetrical multilevel inverter suitable for hybrid renewable energy sources. The proposed inverter consists of two isolated DC sources and six power semiconductor controlled switches. The suggested inverter is capable of generating seven-level output when the input DC voltage is taken in the ratio of 1:2. The higher magnitude DC source is fed from Photo Voltaic (PV) panels, whereas the lower magnitude DC source is fed from Wind Turbine (WT) driven Permanent Magnet DC (PMDC) generator. Both the renewable energy sources are connected to the inverter via two DC-DC boost converters connected in cascade (i.e. one for maximum power point tracking and another for DC-link voltage control). The proposed hybrid renewable energy source inverter is connected to single-phase grid via proper control systems. The complete system is simulated using MATLAB/SIMULINK and the results are presented in detail.

An improved SVPWM control algorithm for three-level inverter

In the traditional three-level space vector pulse width modulation(SVPWM)algorithm,the sector judgment is computationallycomplex since the sector is divided into triangles and hexagons.In addition,the switching frequency is high becausethe seven-segment switching sequence is adopted.For this reason,a new SVPWM control algorithm for three-level inverteris proposed,in which the sector judgment is simplified by dividing the sector into quasi hexagons?and the new four-segmentswitching sequence is adopted to reduce the switching frequency.Simulation results show that the total harmonic distortiongrows down with the switching frequency decreasing,moreover,the algorithm runtime is also decreased.

Model predictive flux control of permanent magnet synchronous motor driven by three-level inverter based on fine-division strategy

Aiming at the difficulty of setting the weight coefficient in the value function of model predictive torque control(MPTC)for permanent magnet synchronous motor(PMSM)driven by three-level inverter,a fine-division model predictive flux control(MPFC)method is proposed.First,establish a mathematical model between the motor torque and the stator flux linkage according to the mathematical equations of PMSM.Thus,the control of the motor torque and stator flux linkage in the MPTC is transformed into the control of a single stator flux linkage vector,omitting the cumbersome weight setting process in the traditional MPTC.The midpoint potential control strategy is proposed,which uses the characteristics of redundant small vectors to balance the midpoint potential.After that,a fine-division strategy is proposed,which effectively reduces the number of candidate vectors and the computational burden of the system.Finally,the proposed MPFC is compared with MPTC by simulation.The results show that the proposed fine-division MPFC effectively reduces the system calculation,and has the advantages of simple principle and better dynamic and steady-state control performance.The feasibility of the control strategy is verified.

Model predictive current control for PMSM driven by three-level inverter based on fractional sliding mode speed observer

Based on the fractional order theory and sliding mode control theory,a model prediction current control(MPCC)strategy based on fractional observer is proposed for the permanent magnet synchronous motor(PMSM)driven by three-level inverter.Compared with the traditional sliding mode speed observer,the observer is very simple and eases to implement.Moreover,the observer reduces the ripple of the motor speed in high frequency range in an efficient way.To reduce the stator current ripple and improve the control performance of the torque and speed,the MPCC strategy is put forward,which can make PMSM MPCC system have better control performance,stronger robustness and good dynamic performance.The simulation results validate the feasibility and effectiveness of the proposed scheme.

A Modified Neutral-point Voltage Control Strategy for Three-level Inverters Based on Decomposition of Space Vector Diagram

Capacitor voltage imbalance is a significant problem for three-level inverters.Due to the mid-point modulation of these inverter topologies,the neutral point potential moves up or down depending on the neutral point current direction creating imbalanced voltages among the two capacitors.This imbalanced capacitor voltage causes imbalanced voltage stress among the semiconductor devices and causes increase output voltage and current harmonics.This paper introduces a modified voltage balancing strategy using two-level space vector modulation.By decomposing the three-level space vector diagram into two-level space vector diagram and redistributing the dwell times of the two-level zero space vectors,the modified voltage balancing method ensures minimal NP voltage ripple.Compared to the commonly used NP voltage control method(using 3L SVM[9]),the proposed modified NP voltage control method offers a slightly higher neutral-point voltage ripple and output voltage harmonics but,it has much lower switching loss,code size and execution time.

An asymmetrical multilevel inverter with minimum voltage stress and fewer components for photovoltaic renewable-energy system

The enhanced power quality provided by multilevel inverters(MLIs)has made them more appropriate for medium-and high-power applications,including photovoltaic systems.Nevertheless,a prevalent limitation involves the necessity for numerous switches and increased voltage stress across these switches,consequently increasing the overall system cost.To address these challenges,a new 17-level asymmetrical MLI with fewer components and low voltage stress is proposed for the photovoltaic system.This innovative MLI configuration has four direct current(DC)sources and 10 switches.Based on the trinary sequence,the proposed topology uses photovoltaics with boost converters and fuzzy logic controllers as its DC sources.Mathematical equations are used to calculate cru-cial parameters for this proposed design,including total standing voltage per unit(TSVPU),cost function per level(CF/L),component count per level(CC/L)and voltage stress across the switches.The comparison is conducted by considering switches,DC sources,TSVPU,CF/L,gate driver circuits and CC/L with other existing MLI topologies.The analysis is carried out under various conditions,encompassing different levels of irradiance,variable loads and modulation indices.To reduce the total harmonic distortion of the suggested topology,the phase opposition disposition approach has been incorporated.The suggested framework is simulated in MATLAB®/Simulink®.The results indicate that the proposed topology achieves a well-distributed stress profile across the switches and has CC/L of 1.23,TSVPU of 5 and CF/L of 4.58 and 5.76 with weight coefficients of 0.5 and 1.5,respectively.These values are not-ably superior to those of existing MLI topologies.Simulation results demonstrate that the proposed topology maintains a consistent output at varying irradiance levels with FLCs and exhibits robust performance under variable loads and diverse modulation indices.Furthermore,the total harmonic distortion achieved with phase opposition disposition is 7.78%,outperforming alternative pulse width modulation techniques.In summary,it provides enhanced performance.Considering this,it is suitable for the photovoltaic system.

Research of Wavelet Modulation for Single-Phase Three-Level Inverter

The single-phase three-level voltage source inverter based on wavelet modulation(WM) is proposed.The WM technique is based on constructing a nondyadic-type multi-resolution analysis(MRA),which supports sampling continuous-time sinusoidal signals in a nonuniform recurrent manner,and then reconstructing it by using inverter switching actions. In order to further improve the output voltage waveform and reduce harmonic distortion,the wavelet modulation is used to three-level inverter. The high magnitude of fundamental component and significantly reduced harmonic contents of the inverter output voltage can be achieved by using WM in the single-phase three-level voltage source inverter. Furthermore,the WM algorithm is implemented by using only one element government(EV) in DSP. The simulated and experimental results prove the accuracy and feasibility of the WM scheme for single-phase three-level voltage source inverter.

A neutral point potential drift control method for NPC three-level inverter

The output current harmonic distortion of a three-level inverter is less than the traditional twolevel inverter.The voltage stress of the semiconductor switch is low.A neutral point potential drift control method is proposed to solve the problem of the neutral point potential drift of the three-level inverter.The interaction mechanism between the neutral point potential and the space voltage vector is presented.The small vector output by the inverter is found to be the root cause of the midpoint potential drift.It is found that the fluctuation of the midpoint potential could be suppressed by increasing the capacitance value of the inverter bus voltage stabilizing capacitor.Furthermore,it inhibits the fluctuation of the midpoint potential.The experimental results verify the efficiency and precision of the proposed method.

A neutral-point potential balance control strategy for three-level inverter based on VSVPWM

The topology of diode neutral-point-clamped(NPC)three-level inverter is prone to neutral-point potential offset.When the sum of three-phase current is zero,the virtual space vector pulse width modulation(VSVPWM)scheme does not cause the neutral-point voltage offset,but it lacks the ability to balance the deviation.For this reason,a neutral-point potential control strategy combining virtual space vector modulation and loop width control is proposed.The neutral-point potential is balanced by introducing the distribution factor for the regions with redundant vectors.For other regions,the potential is controlled by selecting a suitable switching sequence.Meanwhile,the effect on the virtual vector modulation is reduced within the loop width by setting an appropriate loop width,thereby improving the balance effect.The simulation results show that the proposed method has a strong ability to control the offset and has excellent potential balance performance under the conditions of balanced load,unbalanced load and asymmetric capacitance parameters.

Ride through Strategy for a Three-Level Dual Z-Source Inverter Using TRIAC

A new ride through strategy is introduced in a three-level dual Z-source inverter, for isolation under semiconductor switching failure condition. Here the output will have no significant decrease in the amplitude and quality. Instead of diodes, the triacs are added to the inverter source ends, as it can perform a bidirectional power transfer also it can operate well in both low and high voltage operating conditions. The faulted part can be isolated by simply altering the firing pulses for turning on/off the triacs using the carrier based SPWM technique and resulting in a boosting output with zero common mode voltage. Consequently, it forms a common floating point or null point with a zero common mode voltage. It is experimentally verified by using MATLAB, and digital oscilloscope.

A Study of DTC-Power Electronic Cascade Fed by Photovoltaic Cell-Three-Level NPC Inverter

This paper proposes a high performance three-level inverter Neutral Point Clamped (NPC) structure for photovoltaic system. The proposed configuration which can boost the low voltage of photovoltaic (PV) array, can also convert the photovoltaic DC power into high quality AC power. Attention has been paid to the problem of neutral point potential variation. In this way, a Direct Torque Control (DTC) technique has been applied and the estimated value of the Neutral Point Potential (NPP) is used, which is calculated by motor currents. This control strategy uses the redundancy presented by the inverter for selecting appropriate switching state through a switching table to achieve the control of NPP. This study shows the effect of the stability problem of the DC voltages and good static and dynamic performances were obtained in simulation of the proposed cascade “photovoltaic cell-three-level NPC VSI-induction motor”.

Three-level inverter configuration with common mode voltage elimination for induction motor drive (To continue)

The multiplicity of vector combinations for vectors of combined three-level inverters plays an important role, when deciding on the modulation scheme, to obtain minimum switching per inverter vector change, as described in the next Section. This is not possible with reduced common-mode three-level inverter structure, obtained with a five-level cascaded H-bridge configuration, as the space vectors locations do not exhibit multiplicity. Moreover, the proposed configuration requires only two power supplies, whereas the scheme with the five-level H-bridge configuration requires six isolated power supplies.

Three-level inverter configuration with common mode voltage elimination for induction motor drive

The multiplicity of vector combinations for vectors of combined three-level inverters plays an important role, when deciding on the modulation scheme, to obtain minimum switching per inverter vector change, as described in the next Section. This is not possible with reduced common-mode three-level inverter structure, obtained with a five-level cascaded H-bridge configuration, as the space vectors locations do not exhibit multiplicity. Moreover, the proposed configuration requires only two power supplies, whereas the scheme with the five-level H-bridge configuration requires six isolated power supplies.

Modeling and Analysis of Novel Multilevel Inverter Topology with Minimum Number of Switching Components

This paper proposes a novel single phase symmetrical and asymmetrical type extendable multilevel inverter topology with minimum number of switches.The basic circuit of the proposed inverter topology consist of four dc voltage sources and 10 main switches which synthesize 9-level output voltage during symmetrical operation and 17-level output voltage during asymmetrical operation.The comparison between the proposed topology with conventional and other existing inverter topologies is presented in this paper.The advantages of the proposed inverter topology include minimum switches,less harmonic distortion and minimum switching losses.The performance of the proposed multilevel inverter topology has been analyzed in both symmetrical and asymmetrical conditions.The simulation model is developed using MATLAB/SIMULINK software to verify the performance of the proposed inverter.

A new multilevel voltage source inverter configuration with minimum number of circuit elements

An advanced configuration for multilevel voltage source converters is proposed. The proposed converter is able to apply asymmetrical DC sources. The configuration of the proposed inverter is well designed in order to provide the maximum number of voltage levels in output terminals using lower number of circuit devices. The authority of the proposed inverter versus the conventional H-bridge cascaded inverter and the most recently introduced ones, is verified with a provided comparison study. The proposed inverter is able to generate the desired voltage levels using a lower number of circuit devices including power semi-conductor switches, IGBTs, diodes, related gate driver circuits of switches and DC voltage sources. As a result, the total cost and installation area are considerably reduced and the control scheme gets simpler. To confirm the feasibility of the proposed multilevel structure, both the simulation and experimental results are provided and compared which shows good agreements.

A New Topology for a Single Phase Multilevel Voltage Source Inverter with Reduced Number of Components

Multilevel inverters have gained much attention for its operation involving applications ranging values of high power rating. This paper proposes a switching topology for asymmetric multilevel inverter utilizing less number of power electronics components. When the number of the output level increases, it requires more switching states and eventually the number of switching components. The increased number of switches results in higher switching losses which may lead to power loss, and reduction of efficiency of the overall conversion system. The salient feature of this proposed topology is that the module can be used as a sub multiple level structure and can be extended for any number of level with minimal increase in the switching components.

Hybrid Control Strategy for BCD Topology Based Modular Multilevel Inverter

In this paper, a Binary Coded Decimal (BCD) topology of modular multilevel inverter with reduced component count is proposed. For the control of this inverter, hybrid control strategy is used. The proposed modular multilevel inverter uses asymmetrical dc sources and reduced number of switches topology. This hybrid modulation technique uses the multicarrier based Pulse Width Modulation (PWM) and the fundamental frequency modulation strategy. The hybrid modulation algorithm is implemented with “NUC140” micro-controller. In comparison with the conventional and some of the recently reported inverter topologies, the proposed inverter topology is able to generate high number of voltage levels in the output by using minimum number of components such as dc sources, power switches and driver circuits. This inverter offers significant performance with less number of components. The feasibility of the proposed topology is confirmed by simulation and experimental results.

Reduction of THD in Thirteen-Level Hybrid PV Inverter with Less Number of Switches

Multilevel inverter (MLI) is one of the most efficient power converters which are especially suited for high power applications with reduced harmonics. MLI not only achieves high output power and is also used in renewable energy sources such as photovoltaic, wind and fuel cells. Among various topologies of MLI, this paper mainly focuses on cascaded MLI with three unequal DC sources called asymmetric cascaded MLI which reduces the number of power switches. Various modulation techniques are also reviewed in literature [1]. In this paper we focus on sinusoidal (or) multicarrier pulse width modulation (SPWM) which improves the output voltage at lower modulation index for obtaining lower Total Harmonic Distortion (THD) level. The gating signal for the 13-level hybrid inverter using SPWM technique is generated using Field Programmable Gate Array (FPGA) processor. The proposed modulation technique results in reduced percentage of THD, but lower order harmonics are not eliminated. So a new technique called Selective Harmonic Elimination (SHE) is also implemented in order to reduce the lower order harmonics. The optimum switching angles are determined for obtaining minimum THD. The performance evaluation of the proposed PWM inverter is verified using an experimental model of 13-level cascaded hybrid MLI and compared with MATLAB/SIMULINK model.

基于非对称U型卷积神经网络的脑肿瘤图像分割

在计算机视觉分割任务中,基于Transformer的图像分割模型需要大量的图像数据才能达到最好的性能,医学图像相对于自然图像,数据量非常稀少,而卷积本身具有更高的感应偏差,使得它更适合医学图像方面的应用.为了将Transformer的远程表征学习与CNN的感应偏差相结合,本文设计了残差ConvNeXt模块来模拟Transformer的设计结构,采用深度卷积和逐点卷积组成的残差ConvNeXt模块来提取特征信息,极大地降低了参数量.并对感受野和特征通道进行了有效的缩放和扩展,丰富了特征信息.此外,本文提出了一个非对称3D U型网络ASUNet用于脑肿瘤图像的分割.在非对称U型结构中,采用残差连接,将最后两个编码器的输出特征进行连接来扩大通道数.最后,在上采样的过程中采用深度监督,促进了上采样过程中语义信息的恢复.在BraTS 2020和FeTS 2021数据集上的实验结果表明,ET、WT和TC的骰子分数分别达到了77.08%、90.83%、83.41%和75.63%、90.45%、84.21%.并且通过对比实验,ASUNet在准确性方面完全可以与Transformer构建的模型竞争,同时保持了标准卷积神经网络的简单性和高效性.

不对称级联九电平逆变器线性功率均衡控制策略

三单元不对称级联逆变器通常采用传统混合调制策略控制,但该策略下逆变器存在单元间输出功率不均衡以及低压单元开关损耗分配不均的问题,同时由于高低压单元之间输出电压极性不同时会出现电流倒灌,导致逆变器直流侧电压难以维持稳定,影响输出电压波形质量。针对上述问题,该文提出基于功率元重组的混合功率均衡调制策略,该策略对逆变器高压单元采用低频方波调制,在控制单元输出功率大小的同时可以降低开关损耗,而对于低压单元,所提策略结合载波移幅调制和载波移相调制策略对其功率元进行分析重组,使逆变器在输出高质量电压波形的同时实现单元间输出功率的线性均衡和低压单元间开关损耗的均匀分配。最后进行仿真和实验验证。