Cascaded Multilevel Inverter Research Articles

A Comprehensive Approach for Control of Grid-Connected Quasi-Z-Source Cascaded Multilevel Inverters

In this paper, a new control method for quasi-Z-source cascaded multilevel inverter (CMI) based grid-connected photovoltaic (PV) system using evolutionary algorithm and artificial neural network (ANN) is proposed. The proposed method is capable of boosting the PV array voltage to a higher level and solves the imbalance problem of DC-link voltage in traditional cascaded H-bridge inverters using ANN. The proposed control system adjusts the grid injected current in phase with the grid voltage and achieves independent maximum power point tracking (MPPT) for the separate PV arrays by proportional-integral (PI) controllers. For achieving the best performance, this paper presents an optimum approach to design the controller parameters using particle swarm optimization (PSO). The primary design goal is obtaining good response by minimizing the integral absolute error. Also, the transient response is guaranteed by minimizing the overshoot, settling time and rise time of the system response. The effectiveness of the new proposed control method has been verified through simulation studies in a seven level quasi-Z-source cascaded multilevel inverter.

A PWM method for single-phase cascade multilevel inverters to reduce leakage ground current in transformerless PV systems

SUMMARY A single-phase cascade multilevel inverter is able to synthesize AC output voltages with considerably reduced harmonic distortion, which results in reduced size output filters. In addition, the amplitude of the output voltage in the cascade multilevel inverter topology is usually higher than in a single H-Bridge inverter, which makes possible the power injection into the grid without a voltage boost stage. These benefits make cascade multilevel inverter a suitable topology for PV applications. However, cascade multilevel inverters may exhibit large leakage ground current in a grid-connected PV transformerless system, which is caused by a variable voltage across the stray capacitances formed between the PV panel and ground. In this paper, a modulation strategy for the cascade multilevel inverter is proposed to deal with leakage ground currents arising in transformerless PV applications. Numerical and experimental results are performed to assess the effectiveness of the proposed modulation strategy in the reduction of leakage ground currents and improving the topology efficiency. Copyright © 2016 John Wiley & Sons, Ltd.

An Improved SPWM Strategy to Reduce Switching in Cascaded Multilevel Inverters

The analysis of the switch status of each unit module of a cascaded multi-level inverter reveals that the working condition of the switch of a chopper arm causes unnecessary switching under the conventional unipolar sinusoidal pulse width modulation (SPWM). With an increase in the number of cascaded multilevel inverters, the superposition of unnecessary switching gradually occurs. In this work, we propose an improved SPWM strategy to reduce switching in cascaded multilevel inverters. Specifically, we analyze the switch state of the switch tube of a chopper arm of an H-bridge unit. The redundant switch is then removed, thereby reducing the switching frequency. Unlike the conventional unipolar SPWM technique, the improved SPWM method greatly reduces switching without altering the output quality of inverters. The conventional unipolar SPWM technique and the proposed method are applied to a five-level inverter. Simulation results show the superiority of the proposed strategy. Finally, a prototype is built in the laboratory. Experimental results verify the correctness of the proposed modulation strategy.

Selective Harmonic Elimination Technique Based Cascaded Multilevel Inverter with Reduced Number of Switches

Selective Harmonic Elimination Technique Based Cascaded Multilevel Inverter with Reduced Number of Switches

Theoretical Comparison in Energy-Balancing Capability Between Star- and Delta-Configured Modular Multilevel Cascade Inverters for Utility-Scale Photovoltaic Systems

This paper provides a theoretical discussion and comparison in energy balancing between a modular multilevel cascade inverter based on single-star bridge cells (SSBC) and that on single-delta bridge cells (SDBC). Attention is paid to applications involving asymmetric active-power generation in utility-scale grid-tied photovoltaic systems. Both qualitative and quantitative evaluation metrics to assess the energy-balancing capability are introduced and applied to both SSBC and SDBC inverters. As for the SSBC inverter, six zero-sequence voltage waveforms with different harmonic content enabling enhanced energy-balancing capability are analyzed and compared regarding their effectiveness. This paper also emphasizes on the SDBC as an alternative to the SSBC and highlights its superior operating characteristics under asymmetric active-power generation.

A computationally efficient finite state model predictive control for cascaded multilevel inverter

Abstract This paper investigates a new scheme for Finite State Model Predictive Control fed five level Cascaded Multilevel Inverter. This proposed method uses 19 voltage vectors out of totally 125 voltage vectors of the Cascaded Multilevel inverter. Since this inverter has many switches, reducing the average switching frequency is the matter of great importance for high voltage applications, as they contribute to significant switching losses. Two schemes of Finite State Model Predictive Control (FSMPC) are proposed i.e. FSMPC1 employing the current control of the Cascaded Multilevel inverter with less (19) voltage vectors and FSMPC2 aiming the control of inverter load current as well as reducing the average switching frequency using 19 vectors. The performance of the proposed schemes is compared with conventional 61 voltage vector scheme of the Cascaded multilevel Inverter. The results show that both the proposed schemes perform well for steady state and dynamic operating conditions.

Modulation and Control of Transformerless UPFC

In this paper, a modulation and control method for the new transformerless unified power flow controller (UPFC) is presented. As is well known, the conventional UPFC that consists of two back-to-back inverters requires bulky and often complicated zigzag transformers for isolation and reaching high power rating with desired voltage waveforms. To overcome this problem, a completely transformerless UPFC based on an innovative configuration of two cascade multilevel inverters has been proposed. The new UPFC offers several advantages over the traditional technology, such as transformerless, light weight, high efficiency, low cost and fast dynamic response. This paper focuses on the modulation and control for this new transformerless UPFC, including optimized fundamental frequency modulation for low total harmonic distortion and high efficiency, independent active and reactive power control over the transmission line, dc-link voltage balance control, etc. The new UPFC with proposed control method is verified by experiments based on 4160-V test setup. Both the steady-state and dynamic-response results will be shown in this paper.

A Real-Time Selective Harmonic Elimination Based on a Transient-Free Inner Closed-Loop Control for Cascaded Multilevel Inverters

Applying the selective harmonic elimination (SHE) technique to grid-connected-cascaded modular multilevel inverters has been widely discussed in the literature. However, due to the difficulties of solving high-order nonlinear transcendental equations, the SHE technique cannot be implemented in real time so its applications are limited. This paper presents a technique to convert the nonlinear equations to a specific control system and use a look-up table, integral controllers and a decoupling controller to help the system converge to a zero-error steady state. An inner instantaneous observer is introduced to directly extract the harmonic spectrum of the output voltages without applying FFT algorithm to output step voltage waveforms. It can not only simplify software design but also eliminate the phase delay generated by conventional spectrum extracting algorithm. The proposed technique can achieve an accurate switching angle control and a fast response. Simulation and experimental results verified that the system can achieve zero-error steady state within one line period.

Opal-RT based Analysis and Implementation of Single Phase Cascaded Multilevel Inverter with Minimum Number of Switches

Objective: In this paper, the detailed analysis and performance of a single phase multilevel inverter topology is dicussed in order to produce a high quality of output voltage. Method: A seven level cascaded inverter topology having six switches is utilized to reduce the total harmonic distortion and the switching losses. This in turn reduces the overall cost of the system. The comparison between the proposed architecture and the existing architectures is done based on the power switches, DC voltage at the inputs, the number of clamping diodes and capacitors used. It is observed that the switch count is halved. Findings: Evaluation is done using phase disposition multicarrier pulse width modulation technique where all the carriers are in phase. Thus this technique is found to be capable of achieving minimum harmonic voltage distortion, thereby resulting in a nearly sinusoidal waveform. Improvements: The performance of the suggested topology is validated in real time environment using Opal-RT Lab simulator and adequate results were taken. The results obtained proved that by using lesser number of switches there is reduction in harmonic voltage distortion in comparison with the traditional multilevel inverter topologies. Keywords: Cascaded Multilevel Inverter, Multicarrier Pulse Width Modulation, Opal-RT, Sinusoidal Waveform, Total Harmonic Distortion

Investigation on stacked cascade multilevel inverter by employing single-phase transformers

In the present paper a new version of multilevel inverter is investigated. This new version is based on hybrid association of commutation cells with H-bridge cells. The association allows a significant reduction of the volume of the capacitors. In fact, presented topology allows us to work on higher input voltage levels with the same power switches. This new version is generally called as SCMI (stacked cascade multilevel inverter). The proposed inverter has potential to generate high quality waveforms, reduction in switching frequency, capable to operate at higher voltage levels and finally utilizes minimum number of switching components. The presented version of SCMI is simulated in Matlab-simulink and further, experimental validation is carried out in the laboratory with prototype setup.

Modeling and Analysis of Variable Frequency Inverted Sine PWM Technique for a Hybrid Cascaded Multilevel Inverter

In cascaded H-bridge multilevel inverter, a variable frequency inverted sine PWM technique is modeled for hybrid electric vehicles. It has a particular advantage of increasing power which is achieved using series connection of H-bridge and also this topology is capable to produce superior spectral quality with considerable improvement of fundamental voltage. The variable frequency inverted sine PWM technique produces lesser torque ripple and enhances the fundamental output voltage mainly at lower modulation index ranges. The topologies of multilevel inverter are flying capacitor, diode clamped and cascaded inverter. In the paper, we will discuss about the cascaded multilevel inverter based on inverted sine PWM technique. The two switching strategies widely used to control multilevel inverters are constant frequency inverted sine PWM (CF-ISPWM) and variable frequency inverted sine PWM (VF-ISPWM). This implies that switch utilization substantially reduces 32.35% of the constant frequency inverted sine PWM switching technique. The performance of the technique is validated in terms of Total Harmonic Distortion (THD) and Torque ripple which significantly reduces when compared to constant frequency ISPWM. The analysis of conventional triangular PWM inverter and inverted sine PWM inverter using constant and variable switching scheme is done in MATLAB Simulink and verified experimentally by FPGA Spartan 3E processor.

Efficiency Improvement of Three-Phase Cascaded H-Bridge Multilevel Inverters for Photovoltaic Systems

Medium-scale photovoltaic (PV) systems using cascaded H-bridge multilevel inverters have a capability to perform individual maximum power point tracking (MPPT) for each PV panel or each small group of panels, resulting in minimization of both power losses from panel mismatch and effect of partial shading. They also provide high power quality, modularity, and possibility of eliminating dc-dc boost stage and line-frequency transformer. However, each PV panel in the system is subjected to a double-line-frequency voltage ripple at the dc-link which reduces the MPPT efficiency. This paper proposes a dc-link voltage ripple reduction by third-harmonic zero-sequence voltage injection for improving the MPPT efficiency. Moreover, a control method to achieve individual MPPT control of each inverter cell is also presented. The validity and effectiveness of the proposed methods were verified by computer simulation.

Harmonic Minimization in Seven-Level Cascaded Multilevel Inverter Using Evolutionary Algorithm

Inverters are power electronic devices that change over DC to sinusoidal AC quantity. Be that as it may, in down to earth, these devices produce non-sinusoidal yield which contains harmonics, so as to blend a close sinusoidal component and to lessen the harmonic distortion multilevel inverters developed. Mathematical methods, which were developed, are derivative based and need initial considerations. To overcome this, evolutionary algorithms, which are derivative free and accurate, were developed for obtaining multi levels of output voltage. The proposed work uses two evolutionary algorithms, namely, Genetic Algorithm (GA) and Particle Swarm Optimization (PSO) algorithm. These algorithms are used to generate the switching angles by satisfying the non linear transcendental equations that govern the low order harmonic components. A seven level cascaded full bridge inverter is designed using MATLAB/Simulink and the results validate the results for switching angles. The Total Harmonic Distortion (THD) value obtained for GA and PSO is 11.81% and 10.84% respectively. The solution obtained from GA algorithm was implemented in hardware using dsPIC controller to validate the simulation results. The THD value obtained for cascaded seven-level multilevel inverter in the hardware prototype is 25.9%.

Performance Analysis of a 15 Level Cascaded Multilevel Inverter with Reduced Switches

Multi-level inverters are widely used in high and medium voltage applications as it affords high voltage output without transformer. Apart from this, it also reduces switching losses and voltage stress on switches. When the number of levels are increased, there will be a reduction in Total Harmonic Distortion (THD) but the usage of more number of semiconductor switches is increased. This in turn increases the size and cost of the inverter. Hence in order to overcome this problem, this work proposes a novel 15 level multilevel inverter topology with the reduced number of switches. Space Vector Pulse Generation Circuit is implemented to generate switching pulses for voltage source inverter. This proposed topology was simulated using the MATLAB and experimental results are furnished to validate the efficiency of this method.

A Five-Level Cascaded Multilevel Inverter Suitable for the Use of Non-Conventional Energy Sources

A Five-Level Cascaded Multilevel Inverter Suitable for the Use of Non-Conventional Energy Sources

Cascaded Multilevel Inverters for Reduce Harmonic Distortions in Solar PV Applications

The paper presents, a reverse system for sustainable energy function developed using the Cascaded H-bridge Multilevel Inverter (CHMI) that is able to produce a desired voltage by changing levels of DC voltages. A CHMI using Photovoltaic (PV) as source cells model was developed by means of the MATLAB Simulink. It was used to explore and validate the quality of the AC output voltage, harmonic traces of the output voltage and effects of varying switching schemes. The paper examine Sinusoidal Pulse Width Modulation (SPWM) technique applied to the CHMI in order to make sure a proficient voltage utilization and good harmonic band. The system simulation results using simulink program are shown and discussed together with a distinguish study for the various control techniques of the CHMI. A FPGA based controller is utilized to produce the PWM pulses for triggering the switches. By using this control method THD value less than 5% in hardware set up was obtained.

Performance Metric of Z Source CHB Multilevel Inverter FED IM for Selective Harmonic Elimination and THD Reduction

This paper focuses on a Z source cascaded multilevel inverter which is designed to minimize harmonics in the output voltage. A balanced dc-link peak voltage can be achieved. The power generation module is built by PV panels which are connected to Z-Source Cascade H-bridge inverter. Cascaded multilevel inverter can achieve the distributed maximum power point tracking to increase the system efficiency and achieve high voltage/high power grid tie without a transformer. This paper analyzes the different PWM switching scheme and the operating states of a ZSI module and comparison is made with different PWM and total harmonic distortion of various PWM schemes.

Modified Cascaded Multilevel Grid-Connected Inverter to Enhance European Efficiency and Several Extended Topologies

This paper proposes a modified cascaded multilevel grid-connected inverter (MCM-GCI) suitable for photovoltaic grid-connected generation system, which considers wide operation range, low grid current total harmonics distortion (THD), and high European efficiency. In the proposed topology, a bidirectional power switch is added to the standard single-phase cascaded multilevel inverter (CMI) to implement the transformation between CMI mode and H-bridge inverter (HBI) mode. An online topology transformation approach of the MCM-GCI is proposed to guarantee the topology modes transformed safely and smoothly. The proposed MCM-GCI operates in CMI mode when the PV arrays’ output voltage and power are low, and transforms into HBI mode when the PV arrays’ output voltage and power are high. Experimental results of five-level MCM-GCI are represented to validate the feasibility of the proposed topology and it is also compared with other three classic grid-connected inverters to highlight its advantages. Furthermore, more structures based on hybrid CMI, which possess the topology transformation ability, are shown to further improve the generation range and obtain a higher efficiency of the system.

Technique to Determine the Optimized Harmonic Switching Angles of a Cascaded Multilevel Inverter for Minimum Harmonic Distortion

ABSTRACTMultilevel inverters have received considerable attention from industries and researchers for its high power and voltage applications. Various switching techniques have been suggested for improving the quality and performance of inverters. One of the conventional techniques for implementing the switching algorithm in these inverters is optimized harmonic-stepped waveform. However, this technique involves the major problem of solving non-linear and complex equations, which indicates a possibility of multiple solutions. This paper describes a novel technique that uses the simple arithmetic sequence of natural numbers to determine the optimized switching angles of a single-phase cascaded multilevel inverter of any number of levels and fed by equal dc sources. The basic objective was to avoid the laborious process of solving the non-linear equations using complex switching algorithm for finding the optimal solution of the switching angles. This technique is implemented to calculate the optimized switching angles of a nine-level cascaded inverter that reduces the total harmonic distortion to below 9%.

Optimum Structures of Proposed New Cascaded Multilevel Inverter With Reduced Number of Components

In this paper, a new cascaded multilevel inverter is proposed. For the proposed inverter, two different algorithms to determine the magnitude of the dc voltage sources are proposed. Then, in order to generate maximum numbers of output voltage levels by using a constant number of power switches and/or dc voltage sources, several optimum structures of the proposed inverter are obtained. In comparison with the conventional cascaded multilevel inverters, the proposed inverter is able to generate a high number of output voltage levels by using a lower number of power electronic devices such as power switches, driver circuits, power diodes, and dc voltage sources. In addition, the low amount of blocked voltage by switches is another advantage of the proposed inverter. The accuracy performance of the proposed inverter in generating the positive and negative voltage levels is verified through the experimental results on a 61-level inverter.