Asymmetric Cascaded H-bridge Multilevel Inverter Research Articles

A Comparative Study of 9-Level Inverter and 15-Level Multi Inverter for a Grid Connected System

Abstract: Recently, the emergence of single phase multilevel inverter has been increased due to its advantages over traditional one. Multilevel Inverters [MLI] are the ones which can give out a stepwise output waveform with the use of power electronic switches, power diodes and some DC voltage source which might be a series/parallel connected PV cells, a renewable source or a battery. Multilevel inverters not only produce low harmonic distortion but also decrease the dv/dt stresses on the equipment Multilevel inverters is a good option as the output voltage of a Multilevel inverter is a stepped waveform which approaches a sinusoid providing lesser harmonic distortion. As the number of levels are increased the harmonic distortion reduces but at the same time the number of switching devices and the DC voltage sources required increases, thus increasing the complexity of the system design and control. Multilevel inverter proposed in this paper uses only 7 switches to provide 9 levels and 15 levels of output voltage. A symmetrical Cascaded H bridge Multi level inverter (SCHBMLI) and Asymmetrical Cascaded H bridge Multilevel Inverter (ASCHBMLI) using PD-PWM technique have been analysed in this paper for grid connection. The Asymmetric Cascade H Bridge [ASCHMLI] implemented in real time system using PIC16F877A microcontroller with RL load. This type of proposed system is used for high power applications in photovoltaic and it’s reduce overall cost as well as size of the system.

THD Minimization and Reliability Analysis of Cascaded Multilevel Inverter

Inverters are DC to AC power converters that are widely used in AC motor drives and distributed energy generation systems. Multi-Level Inverters (MLIs) have emerged as the preferred inverter technology because of their advantages of reduced switching losses and better harmonic profile. This paper deals with the Minimization of Total Harmonic Distortion (MTHD) of Symmetric Cascaded H-bridge Multi-Level Inverter (SCMLI) and Asymmetric Cascaded H-bridge Multi-Level Inverter (ACMLI). A hybrid memetic algorithm composed of heuristic PSO (Particle Swarm Optimization) algorithm and traditional MAS (Mesh Adaptive direct Search) is proposed to optimize the switching angles. In Photo Voltaic (PV) system, the input DC voltage generally varies from its nominal value due to the change in temperature and irradiance. Thus, the sensitivity analysis of THD and harmonics is also carried out considering the variations with non-integer magnitudes of input DC sources. The experimental prototype of SCMLI and ACMLI topology is developed and validated with simulation results. The reliability and Mean Time to Failure (MTTF) of SCMLI and ACMLI are investigated based on power losses of the MOSFET and thermal parameters.

Selected Harmonic Mitigation PWM Power Matching Control Strategy for Asymmetric Cascaded H-Bridge Multilevel Inverter

In order to suppress high-order harmonics to meet the requirements of power quality standards and solve the power mismatching problem of asymmetric multilevel inverter, an improved power matching control strategy of asymmetric selected harmonic mitigation pulse width modulation (ASHM-PWM) is proposed in this article. This strategy is based on asymmetric dc-link voltage applied asymmetric cascaded H-bridge (ACHB) multilevel inverter. First, a new harmonic mitigation model based on the power matching control is proposed and the output active power of each H-bridge cell is analyzed theoretically. Second, switching angles are obtained by transforming multiobjective inequality problems of ASHM-PWM into single objective equation groups combined with improved particle swarm optimization (IPSO), which can simplify the solving process. Finally, the simulation model and experimental platform of ACHB multilevel inverter have been implemented to verify the ASHM-PWM power matching control strategy proposed in this article. The result shows that each H-bridge cell of ACHB can have power matching performance by meeting the power match of 1: <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$k1$ </tex-math></inline-formula> : <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$k2$ </tex-math></inline-formula> in one cycle. Meanwhile, the total harmonic distortion (THD) of the output line–line voltage is reduced and the performance of harmonic mitigation is better.

A Generalized Scheme With Linear Power Balance and Uniform Switching Loss for Asymmetric Cascaded H-Bridge Multilevel Inverters

Under the traditional hybrid modulation strategy, the output voltage of 2:1:1 asymmetric cascaded H-bridge multilevel inverter is proved to be of high quality. However, the cascaded cells operate in unbalanced power regime and the switching loss of low-voltage cells is extremely uneven. To resolve the mentioned problems, the average power of cascaded cells is analyzed and the internal mechanism of power imbalance is revealed. Based on this, a power balance modulation strategy is proposed in this article. The modulation strategy effectively equalizes the switching loss of cells H2, H3 by modifying the triangular carriers, and then controls the conducting angle of cell H1 achieving a balanced power distribution among cascaded cells under the full modulation indexes. Compared with the existed modulation strategies, the proposed method has the merits of easy implementation, good dynamic performance, balancing low-voltage cells switching loss, and linearizing output power of cascaded cells. In addition, the modulation strategy also offers a generalized scheme, which can achieve a balanced power distribution among cascaded cells with an asymmetric ratio of i:1:1:1…. Finally, the simulation and experiment results confirm the feasibility of the modulation strategy under changes in modulation index and load.

A 129-level Asymmetrical Cascaded H-Bridge Multilevel Inverter with Reduced Switches and Low THD

Abstract: The multilevel inverter is a power conversion device which is uses multiple dc sources to provide required alternating current level. It is can be used for medium to high power applications. This paper presents a 129 level asymmetrical cascaded Hbridge multilevel inverter with reduced switching components and higher THD. The proposed inverter uses multiple dc sources with voltage ratio 1:1:2:4:8:16:32. The proposed inverter uses voltage reference technique to control the switching components of the topology. The comparative analysis of 129 level ASCHBMLI and conventional inverter topologies have been presented. The main advantages of the proposed topology is lower switching components, lower losses, and lower THD without the need of filter. MATLAB/SIMULINK software is used to perform simulation and analyse the performance of the proposed topology. Keywords: Multilevel Inverter (MLI), Asymmetrical Cascaded H Bridge Multilevel Inverter (ASCHBMLI), Cascaded H Bridge (CHB), MATLAB, Total Harmonic Distortion (THD).

Five-phase multilevel inverter with output voltage waveform optimized using soft-computing methods

In this paper, genetic algorithm (GA) and particle swarm optimization (PSO) are employed to optimize the switching angles for 5-phase 15-level asymmetrical cascaded H-bridge multilevel inverter (ACHBMLI). Both optimization algorithms are applied in selective harmonic minimization pulse width modulation (SHMPWM) based switching-angle calculation technique that aims to maintain the desired fundamental harmonic while minimize the undesired harmonics. The performance of GA- and PSO-SHMPWM are compared in term of switching angles, objective function, and cumulative distribution function. For fair comparison, both GA- and PSO-SHMPWM are implemented and analyzed in MATLAB with the same population size and total number of iterations. Furthermore, a PSIM simulation model of 5-phase 15-level ACHBMLI has also been developed to validate the effectiveness of GA- and PSO-SHMPWM.

Design and Analsyis of 31-Level Asymmetric Cascaded H-Bridge Multilevel Inverter with Reduced Number of Switches

A new multilevel inverter with less no of power switches is proposed. This is based on cascaded H-bridge topology. The design and analysis of 31-level reduced switch inverter with different modes of operation are presented in this paper. The proposed inverter is asymmetric in nature and it uses unequal DC voltage sources. PD-PWM modulation technique has been used here to get proper switching. The proposed idea has been validated through simulation and the received results provides better efficiency, less low order harmonics and less switching losses.

Improved performance with fractional order control for asymmetrical cascaded H-bridge multilevel inverter

This paper proposes a control scheme for seven level asymmetrical cascaded H-bridge multi level inverter (ACHBMLI) based on fractional order calculus. The seven level ACHBMLI consists of two H-bridges that are connected in series and are excited by different dc voltage sources. A simplified model is developed by assuming the small signal variation component is equal in both the H-bridges. A fractional order PID (FO-PID) controller is designed for the ACHBMLI using the simplified model. Simulation study shows the adequacy of FO-PID controller in giving an output voltage with minimum distortions. A conventional PID controller is also designed for ACHBMLI using the same simplified model. The performance of the ACHBMLI with FO-PID controller is compared with the performance of ACHBMLI with conventional PID controller. The simulation results prove the superiority of FO-PID controller in maintaining the output voltage of the ACHBMLI close to the reference voltage and in reducing the harmonic distortion of output voltage of the inverter. The simulation was done using MATLAB and the parameters of FO-PID controller was designed using FOMCON tool box.

Harmonic Analysis of Symmetrical and Asymmetrical Cascaded H-Bridge Multilevel Inverter

This paper proposes harmonic comparison between Symmetrical and Asymmetrical CHB MLI using multiple carrier based phase disposition PWM technique (PDPWM). Topologies of different multilevel inverter are reported in the literature, but mainly this work focuses on the harmonic comparison of Symmetrical and Asymmetrical cascaded MLI with same count of sources and switches. In this paper, PWM switching technique for harmonic comparison of both symmetrical and asymmetrical cascaded MLI is PD. Total harmonic distortion is analyzed in FFT window. Results are observed in SIMULINK/MATLAB software. In these comparative results we can see that an asymmetrical configuration is producing higher voltage levels in voltage output with equal quantity of component compared with the 5-level symmetric inverter and this could lead towards the reduction in harmonic content of output voltage. The benefits of this method of control are applicability and simplicity for n-levels MLI, with no any considerable change in the control circuitry. The experimental measurement results validate proper operation of the discussed MLI

Harmonic Analysis of Symmetrical and Asymmetrical Cascaded H-Bridge Multilevel Inverter

This paper proposes harmonic comparison between symmetrical and asymmetrical CHB MLI using multiple carrier based phase disposition PWM technique (PDPWM). Topologies of different multilevel inverter are reported in the literature, but mainly this work focuses on the harmonic comparison of symmetrical and asymmetrical cascaded MLI with same count of sources and switches. In this paper, PWM switching technique for harmonic comparison of both symmetrical and asymmetrical cascaded MLI is PD. Total harmonic distortion is analyzed in FFT window. Results are observed in SIMULINK/MATLAB software. In these comparative results we can see that an asymmetrical configuration is producing higher voltage levels in voltage output with equal quantity of component compared with the 5-level symmetric inverter and this could lead towards the reduction in harmonic content of output voltage. The benefits of this method of control are applicability and simplicity for n-levels MLI, with no any considerable change in the control circuitry. The experimental measurement results validate proper operation of the discussed MLI.

Harmonic Analysis of Symmetrical and Asymmetrical Cascaded H-Bridge Multilevel Inverter

This paper proposes harmonic comparison between Symmetrical and Asymmetrical CHB MLI using multiple carrier based phase disposition PWM technique (PDPWM). Topologies of different multilevel inverter are reported in the literature, but mainly this work focuses on the harmonic comparison of Symmetrical and Asymmetrical cascaded MLI with same count of sources and switches. In this paper, PWM switching technique for harmonic comparison of both symmetrical and asymmetrical cascaded MLI is PD. Total harmonic distortion is analyzed in FFT window. Results are observed in SIMULINK/MATLAB software. In these comparative results we can see that an asymmetrical configuration is producing higher voltage levels in voltage output with equal quantity of component compared with the 5-level symmetric inverter and this could lead towards the reduction in harmonic content of output voltage. The benefits of this method of control are applicability and simplicity for n-levels MLI, with no any considerable change in the control circuitry. The experimental measurement results validate proper operation of the discussed MLI

Understanding the Staircase Modulation Strategy and Its Application in Both Isolated and Grid-Connected Asymmetric Cascaded H-Bridge Multilevel Inverters

The staircase modulation strategy is the best choice for asymmetric cascaded H-bridge multilevel inverter (ACMI) because it makes the output voltage to present a high number of levels and makes one of the ACMI modules to operate at low frequency. However, the staircase modulation is usually employed without giving its deserved attention. This paper presents a clear understanding of the staircase modulation strategy and its applications in both isolated and grid-connected ACMI. The main novelty of this paper is the obtaining of the switching function for each module. The principle of operation is carefully described, also indicating how to command the ACMI transistors. The output voltage of the two superior modules is evaluated for different values of iterations. Special attention is given to the power distribution among the ACMI modules when the staircase modulation is applied. It is demonstrated on how the power is processed in each module considering an ACMI with three modules. The analysis is presented showing the staircase modulation within a closed-loop control strategy for isolated and grid-connected modes of operation, showing that the content of this paper is valid for both modes. Experimental results clarify and show the efficacy of the content presented in this paper.

Asymmetric Cascaded H-Bridge Multilevel Inverter With Single DC Source per Phase

This article proposes a self-balanced cascaded H-bridge multilevel inverter with a binary asymmetric ratio. The inverter uses only one dc source per phase that will feed the H-bridge with the highest dc-link voltage (called main bridge). The dc links of all other H-bridges (called auxiliary bridges) are formed by floating capacitors. Floating capacitors converge to the corresponding steady-state voltages by the principle of a level-doubling network without using any closed-loop control technique. In a steady state, the dc-link voltage of each auxiliary bridge will be equal to half of the dc-link voltage of its preceding H-bridge. This will result in an inherent binary asymmetric ratio among all the dc-link voltages. Operation of the proposed topology is validated by MATLAB simulations and experimentation on the hardware prototype. Experimental results match well with simulation results.

An Improved Model Predictive Controller for 27-Level Asymmetric Cascaded Inverter Applicable in High-Power PV Grid-Connected Systems

The asymmetric cascaded H-bridge multilevel inverter (MLI) topology is more suitable for high-power/high-voltage applications compared with other topologies if the highest voltage H-bridge (the main cell) is modulated with the grid frequency (50/60 Hz). With specific modulation indexes, the power that passes through the main cell is more than 80% of the total power. This improves the efficiency and limits leakage current to the grid. However, achieving such a task is challenging using linear controllers and it was not proposed before in the literature using nonlinear controllers. This article presents a novel finite control set model predictive control (FCS-MPC) algorithm suitable for high-voltage/high-power single-stage central inverter connecting photovoltaic (PV) system to the grid. In addition to tracking the reference, multiple constraints are proposed; the first constraint is to modulate the main cell with the grid frequency, and the second constraint is to achieve nonregenerative operation in the lower voltage (the auxiliary) H-bridge cells to ensure the unidirectional power flow for the prerectifier. It should be noted that such constraints using weight factors added to the cost function in conventional FCS-MPC are not applicable to the implementation because the application requires separate independent control signals to individual H-bridge cells. Therefore, the proposed FCS-MPC controller implements the constraints using individual algorithms added to the respective H-bridge cell control signals. The proposed algorithm results in better mymargin THDs in the output current waveform compared with previous schemes. Furthermore, a duty-cycle optimization algorithm is implemented in addition to the conventional algorithms to achieve reduced errors at a relatively lower sampling frequency. The controller is verified and implemented using 2kW hardware prototype for grid-connected operation.

Floquet-Theory-Based Small-Signal Stability Analysis of Single-Phase Asymmetric Multilevel Inverters With SRF Voltage Control

This paper proposes a small-signal model and Floquet-theory-based method for analyzing small-signal stability of a single-phase asymmetric cascaded H-bridge multilevel inverter (ACHMI) operating in the stand-alone mode. The studied ACHMI system consists of the power stage and cascaded control loops, which includes the voltage loop in the synchronous reference frame (SRF), capacitor current feedback control, and hybrid modulation scheme. Due to the SRF voltage control, the derived small-signal model under linear and nonlinear load conditions are inherently periodically time-variant. Therefore, the Floquet theory is employed to analyze the stability regions of the dual-loop control parameters of the ACHMI. Furthermore, the loci and moduli of Floquet multipliers are calculated to accurately evaluate the respective effects of control parameters on the stability of the system. With the stability analysis based on the small-signal model and Floquet-theory-based method, an effective selection range of control parameters of the multilevel inverter can be obtained. Finally, the experimental results from a reduced-scale laboratory prototype ACHMI are presented to validate the theoretical analysis, and the effectiveness of proposed analysis method in high-power applications is verified by the simulation results from a 10-kV medium-voltage ACHMI.

Stability Analysis for the Grid-Connected Single-Phase Asymmetrical Cascaded Multilevel Inverter With SRF-PI Current Control Under Weak Grid Conditions

This paper analyzes the influence of phase-locked loop (PLL) on the stability of LCL -type single-phase grid-connected asymmetrical cascaded H-bridge multilevel inverter (ACHMI) with synchronous reference frame proportional-integral (SRF-PI) grid current control under weak grid scenarios. The ACHMI system is composed of power stage circuit and control system, where the control system contains the dual-loop current control strategy established in the hybrid reference frame, the SRF-PLL, and the hybrid modulation method employed to synthesize the multilevel output voltage. The small-signal model of the whole ACHMI system is first established by using a simple step-by-step derivation method, and then, the small-signal analysis method is adopted to linearize the ACHMI, which is then utilized to derive the impedance model of the ACHMI system. Furthermore, an improved impedance stability criterion is derived, which is then employed to analyze the system stability. By using this criterion, the stability of the ACHMI can be evaluated with the variation of the bandwidth of PLL, the output power factor angle of the ACHMI, and the amplitude of the grid current reference signal under weak grid conditions. In this paper, a systematic design procedure for the optimal selection of the PI controller of the PLL is presented, which guarantees the steady-state performance and dynamic response of the ACHMI system. With this design method, the dual-loop current control and PLL can be taken into account simultaneously when analyzing the stability margin of the ACHMI. Finally, the simulation and experimental results from a down-scaled grid-connected ACHMI prototype system are provided to confirm the validity of theoretical analysis.

Selective harmonics elimination in multilevel inverter by a derivative-free iterative method under varying voltage condition

Selective Harmonics Elimination Pulse width modulation (SHE PWM) presents an alternative modulation technique to operate medium voltage medium and high power converters as it reduces the switching losses. SHE PWM generates high-quality output waveform at the low switching frequency. Its application to multilevel converters furthers leads to improvement in output waveforms with lower switching losses, lesser dv/dt and lowers switching devices ratings. In this Paper SHE PWM for an asymmetrical cascaded H-bridge multilevel inverter under unequal DC voltage condition for fundamental and multiple switching cases are investigated. More harmonics can be eliminated by considering multiple switching’s. The Solution of the Nonlinear transcendental SHE equation is obtained using an advanced derivative free numerical technique which. The method is simple in implementation with fast calculations per iteration as it avoids the evaluation of Jacobian and its matrix. Also the need for precise initial guess in the proximity of actual solution is not needed as an identity matrix of the size of designed variable serves the purpose. Different inequality in the dc voltages is taken to eliminate the lower order harmonics from the output. Only exact solutions for the switching angles which ensure the complete elimination of targeted harmonics are reported. Simulation and Hardware results are presented to confirm the validity of the proposed technique.

SBO-based selective harmonic elimination for nine levels asymmetrical cascaded H-bridge multilevel inverter

ABSTRACTThe number of bridges, gate drive circuits and dc sources decrease by using asymmetrical is used to solve SHE equations to get the optimal switching angles. Genetic algorithm (GA) is also used to solve these equations to make comparison between Satin bowerbird optimisation (SBO) and GA algorithms. Matlab/Simulink software tool is used to carry out the simulation construction multilevel inverter. The selective harmonic elimination pulse width modulation (SHE-PWM) and sinusoidal pulse width modulation (SPWM) are carried out for a nine levels cascaded H-bridge (CHB) inverter with asymmetrical construction. Comparison between SHE and SPWM is done to get the benefit of SHE over SPWM. The elimination of some lower order harmonics and satisfy fundamental component in output voltage are the major purpose of SHE-PWM. The solving of the non-linear transcendental equations of SHE is the challenge to find out the switching angles, SBO technique.

Simplified Small-Signal Model for Output Voltage Control of Asymmetric Cascaded H-Bridge Multilevel Inverter

This paper proposes a simplified small-signal model for output voltage control of a single-phase asymmetrical cascaded H-bridge multilevel inverter (ACHMI). The ACHMI is an n -series connected H-bridge converter, each one with a unique value at the dc link and usually scaled at {1:2:6:…} or {1:3:9:…}. By assuming that the small-signal variation component is equal in all n converter terminal ports, a simplified small-signal model is obtained. This assumption is carefully described and justified. To verify the veracity of the proposed model, two distinct control strategies are applied. One is a single-loop control scheme based on a modified proportional-integral (PI) controller. The other one is a double-loop control scheme based on a PI controller with feedforward action of the load current. Both controllers are tuned based on the dynamic behavior of the proposed model. Since the designed controllers based on the simplified model make the ACHMI output voltage to follow the reference without steady-state error, the proposed simplified model truly represents the inverter. Experimental results show the efficacy of the simplified model of the ACHMI through the two mentioned control strategies as well as the ACHMI installed in a microgrid.

A PV Power Conditioning System Using Nonregenerative Single-Sourced Trinary Asymmetric Multilevel Inverter With Hybrid Control Scheme and Reduced Leakage Current

A power conditioning system (PCS) using multiple module-integrated converters and a single sourced 27-level asymmetric cascaded H-bridge multilevel inverter (MLI) without regeneration for photovoltaic (PV) applications is proposed. A newly suggested hybrid-switching closed-loop strategy is proposed to enable the use of a 27-level inverter in PV systems. The suggested hybrid-switching strategy implements fundamental line-frequency switching in the main H-bridge to ensure a high efficiency and low leakage current operation. Furthermore, high-frequency switching is used in the auxiliary H-bridge cells to achieve a higher bandwidth control loop. A cost-effective unidirectional single-ended 1-kW dc–dc module based on a boost coupled inductor and charge-pump circuits is proposed to achieve a single PV source per module for a multistring configuration. To couple the unidirectional converters with the central inverter, a jumping element in the hybrid switching strategy is introduced to enable an optimal nonregenerative operation. The proposed PCS with the control scheme is analyzed and verified using hardware results in a grid connected mode of operation.