Cascaded Multilevel Inverter Research Articles

An improved method of model predictive current control for multilevel cascaded H-bridge inverters

Abstract Finite control set ModelPredictive control (FCS-MPC) with the principle of considering all voltage vectors to find the optimal voltage vector for multilevel inverter in a very small sampling cycle is hardly feasible because there is no modulation part, the implementation of optimizing common-mode voltage and switching number for the multilevel inverter should be performed in the cost function. To solve the above problem, this paper proposes an improved method of model predictive current control selecting 19 adjacent voltage vectors and using weighting coefficients for common-mode voltage elimination and switching optimization. By using a discrete-time model of the system to predict the future value of the current for the voltage vector in the previous sampling cycle and its 18 adjacent voltage vectors, the one that minimizes a cost function will be selected. Thus, in a multilevel inverter with any number of levels, the cost function is performed only 19 times in a sampling cycle. The computation on FPGA allows 19 calculations of the cost function to be performed in parallel, so the executing time is very small. The feasibility of the proposed algorithm is verified by simulation model on MATLAB-simulink software and the experimental 11-level cascaded H-bridge multilevel inverter model.

Artificial neural network with modified rider optimization for design and control of PV-integrated quasi Z-source cascaded multilevel inverter system

The modeling of the controller for quasi Z-Source Cascaded Multilevel Inverter (qZS-CMI)-dependent 3-phase grid-tie Photovoltaic (PV) power system is considered in this paper. The state-of-the-art controller requires precise conceptual models and sophisticated optimization principles based on the derived models. However, such processes are limited to known system models, which are uncertain in future systems. Here, the controller for 3-phase qZS-CMI is modeled based on two phases, and the source PV voltage and output grid current are controlled. In Phase I, optimized Proportional Integral (PI) controller is used for finding out the total PV voltage, and Phase II utilizes the optimized Proportional Resonant (PR) controller enabled with the Artificial Neural Network (ANN) for controlling the grid current. For two phases, the modified optimization algorithm called Fitness Enabled-Rider Optimization Algorithm (FE-ROA) is used. Moreover, in Phase II, ANN is trained in an offline mode with the exact dataset arranged by the proposed FE-ROA, and it guarantees the control of grid current. The two phases plan to optimize the gain of both PI and PR controllers respectively using the same proposed algorithm. The main objective of phase I is to lessen the error among the reference PV voltage, and measured voltage, and phase II is to lessen the error among the reference and measured grid current. Hence, the grid-tie current injection is achieved by the developed module, and system-level control offers independent Maximum Power Point Tracking (MPPT). Lastly, the performance of the proposed controller for qZS-CMI is compared over the other controllers and substantiates the efficacy of the proposed one.

Computationally-Efficient Optimal Control of Cascaded Multilevel Inverters With Power Balance for Energy Storage Systems

This article proposes an optimal current control technique with switching event minimization for grid-interactive cascaded multilevel inverters (CMI) interfaced with battery energy storage sources. The proposed control scheme enables power-balancing functionality of battery cells, realizing optimal smart operation of CMI. Model predictive control (MPC) is known as a potential approach for multiobjective control schemes in single-loop manner for power electronics interfaces. However, MPC schemes are suffering from high computational burden that is magnified in topologies like the CMI, which have a substantial number of redundant control actions. The proposed control scheme utilizes a dynamic lookup matrix as an internal optimizer tool. The redundant switching sequences are cycled to equalize the power drawn from the independent battery energy storage sources while achieving a minimum energy control. The theoretical analysis and experimental case studies verify robustness and computational efficiency of the proposed multicriteria optimal controller with similar objective tracking when compared to finite-set MPC.

A Modular Multilevel Converter with an Advanced PWM Control Technique for Grid-Tied Photovoltaic System

Due to global warming and shortage of fossil fuels, the grid-connected solar photovoltaic (PV) system has gained significant popularity all over the world. The modular multilevel cascaded (MMC) inverter is the natural choice for step-up transformer and line filter less direct medium voltage grid integration of solar PV systems. However, power quality and loss are the important issues while connecting the PV system to the medium voltage grid through MMC inverter. Modulation technique is the key to maintain output power quality, e.g., total harmonic distortion (THD) and to ensure low switching and conduction losses. In this paper, an advanced modulation technique named “triangle saturated common mode pulse width modulation (TSCMPWM)” control is proposed for a 3-phase 5-level MMC inverter-based grid-tied PV system. Compared to traditional modulation techniques, the proposed TSCMPWM control offers the lowest voltage THD as well as lower inverter power losses. Performance of the proposed modulation technique is evaluated in MATLAB/Simulink environment and tested with a reduced scale prototype test platform. Both simulation and experimental results show the effectiveness of the proposed modulation technique.

Proposed topology of cascaded multilevel inverter used for reduced number of on state switches

This paper presents a novel topology for cascade multilevel inverter. Multilevel inverter is an alternative within the area of lot of power average voltage energy control. This proposed paper analyses a generalized cascaded inverter topology with minimized number of switching devices. In this proposed work of multilevel inverter, the aim is to reduce the number of dc voltage sources and switches to obtain number of voltage levels. The proposed circuit consists of series connected Switching units and it can generate DC voltage levels similar to other topologies. In this paper, six switches are used to generate 9 level inverter output. Topology of the proposed cascaded multilevel inverter considers some factors such as number of switching devices, number of output voltage levels and the standing voltage on the switches. The quality output voltage depends on the number of voltage level in the inverter. This new inverter shows superior capabilities when compared to other existing topologies. To verify the proposed topology, a 9-level inverter has been simulated. In this work the THD value is reduced to 7.58 % which is very low when compared to other existing topologies. The simulation results are carried out using MATLAB/SIMULINK.

Artificial Neural Network and Newton Raphson (ANN-NR) Algorithm Based Selective Harmonic Elimination in Cascaded Multilevel Inverter for PV Applications

In this article, a hybrid Artificial Neural Network - Newton Raphson (ANN-NR) is introduced to mitigate the undesired lower-order harmonic content in the cascaded H-Bridge multilevel inverter for solar photovoltaic (PV). Harmonics are extracted by the excellent choice of opting switching angles by exploiting the Selective Harmonic Elimination (SHE) PWM technique accompanying a unified algorithm in order to optimize and reduce the Total Harmonic Distortion (THD). ANN is trained with optimum switching angles, and the estimates generated by the ANN are the initial guess for NR. In this study, the CHB-MLI is combined with a traditional boost converter, it boosts the PV voltage to a superior dc-link voltage Perturb and Observe (P&O) based Maximum Power Point Tracking (MPPT) algorithm is used for getting a stable output and efficient operation of solar PV. The proposed system is proved over an eleven-level H-bridge inverter, the work is carried out in MATLAB/Simulink environment, and the respective results are confirmed that the proposed technique is efficient, and offers an actual firing angles with a few iterations results in a better capability of confronting local optima values. The suggested algorithm is justified by the experimental development of eleven-level cascaded H-bridge inverter.

Single stage Boost Cascaded Multilevel Inverter Based on Switched Inductor Structure

This paper presents the experimental investigations of Switched Inductor cell (SL-FLCHBqSBI) based Five-Level Cascaded H-Bridge quasi Switched Boost Inverter for Renewable Energy (RE) applications. The SL-FLCHBqSBI topology is based on the ripple input current Switched Inductor Boost Inverter (SLBI) structure which is available in the literature. In this work, a stiff DC voltage of 36 V is taken as input to deliver a power of 100 W across a resistive load is designed. The control signals for the active devices are generated using Phase-Shifted sinusoidal Pulse Width Modulation (PS-PWM) modulation technique. The SL-FLCHBqSBI topology provides a higher voltage gain of 2.83 compared to the conventional topologies for a low duty ratio. The simulation is performed in MATLAB/Simulink environment and the simulation results are presented. A hardware set up is implemented and experiments are carried out to check the consistency of the theoretical concepts with the working of the proposed topology in practical.

Hybrid PWM modulated cross switched asymmetrical multilevel inverter with reduced number of conducting devices

This paper brings out a new topology for a cascaded multilevel inverter (CMLI) with a view to reduce the number of power switching devices in the path of the current. The philosophy suggests the integration of a low voltage pulse width modulated (PWM) inverter along with a high voltage fundamental switching inverter to produce the specified number of output levels by switching the series connected DC sources of high voltage inverter in an additive and or subtractive combination with low voltage PWM inverter. It invites a hybrid PWM approach to the process of generating the pulses for synthesising the stepped nature in conjunction with the variable pulse width output. The use of a smaller number of switches to reach the output voltage show cases the ability of the modular architecture to expand the scope of CMLI. The artefacts of a field programmable gate array (FPGA) foster to realise its implementation in pulse generation for switching the devices and verify the simulated results for steady state and dynamic load conditions in order to attach a viability perspective for its use in the real world.

An enhanced 17-level hybridized multilevel inverter with stair case modulation

This paper proposes a Hybridized Symmetric Cascaded Multilevel Inverter for voltage levels ranging from 5 levels to 17 levels. The proposed Multi Level Inverter (MLI) topology is built using a modified H-bridge inverter that results in an increased output voltage levels with a smaller number of solid-state switches. This technique enhances the h-bridge configuration from three level to five level by means of a bi-directional switch at source. Gating pulses of hybridized symmetric MLI are generated through staircase modulation. The operation and performance of the proposed topology is tested for different output voltage levels, simulation results prove that the proposed technique results in less THD at all levels with lesser power consumption and are easily applicable for renewable energy applications.

A color harmony algorithm and extreme gradient boosting control topology to cascaded multilevel inverter for grid connected wind and photovoltaic generation subsystems

This paper introduces a hybrid control topology to cascaded multilevel inverter (CMLI) for grid connected hybrid system. The proposed control topology is joined implementation of color harmony algorithm (CHA) and extreme gradient boosting (XGBOOST). The modelling of CMLI is composed to gain the optimal control signal using the established controller. The proposed CMLI is composed with the decreased number of switches, diodes as well as sources. The aim of proposed control method is to meet the load power demand as well as to preserve the power regulation or maximal energy conversion of wind as well as solar subsystems. The proposed method strictly prohibits the difference present at output voltage of CMLI. Here, CHA is utilized for evaluating the optimal gain parameters in view of the variety of source currents from the normal value and it can be useful for building up optimal control signal dataset in offline way. In light of fulfilled dataset, the XGBOOST performs and predicts the most optimal control signals of the CMLI in the online way. The resultant control signals are utilized to control the insulated gate bi-polar switches (IGBT) of CMLI. Through, established model is implemented at MATLAB/Simulink working stage as well as implementation is considered by previous techniques. The efficiency for various sources using proposed and existing method is also analysed. The efficiency of PV and wind of the proposed technique are 99.3975% and 91.2138%.Overall, the outcomes of the comparison show the superiority of proposed method and confirm its potential to solve the issue.

Improved neutral shift method for fault tolerant operation of three phase MLCI

In a three-phase multilevel cascaded inverter (MLCI), when a failed module is bypassed, the number of modules in each phase becomes unbalanced. Under this condition, a method to obtain a balanced three-phase output is to move the neutral point of the MLCI. The neutral-point shift (NS) method has attracted a great deal of attention since the output of the inverter has a relatively low harmonic distortion when compared to other fault-tolerant operation methods. To move the neutral point, an offset voltage of the fundamental frequency component is injected. If the injected offset voltage exceeds the available range of the offset voltage, overmodulation occurs. Then, the output of the inverter is distorted. In this paper, the overmodulation regions of the NS method are analyzed for the fault-tolerant operation in the three-phase MLCI. In addition, a modified NS method is proposed to compensate for the overmodulation region. Both simulation and experimental results in a two-by-three MLCI demonstrate the performance of the proposed method.

Common-Ground-Type Single-Source High Step-Up Cascaded Multilevel Inverter for Transformerless PV Applications

The cascaded multilevel inverter (CMI) is one type of common inverter in industrial applications. This type of inverter can be synthesized either as a symmetric configuration with several identical H-bridge (HB) cells or as an asymmetric configuration with non-identical HB cells. In photovoltaic (PV) applications with the CMI, the PV modules can be used to replace the isolated dc sources; however, this brings inter-module leakage currents. To tackle the issue, the single-source CMI is preferred. Furthermore, in a grid-tied PV system, the main constraint is the capacitive leakage current. This problem can be addressed by providing a common ground, which is shared by PV modules and the ac grid. This paper thus proposes a topology that fulfills the mentioned requirements and thus, CMI is a promising inverter with wide-ranging industrial uses, such as PV applications. The proposed CMI topology also features high boosting capability, fault current limiting, and a transformerless configuration. To demonstrate the capabilities of this CMI, simulations and experimental results are provided.

Asymmetric cascade multilevel inverter with self‐balanced switched‐capacitor unit and single source

The technique of single-source cascaded H-bridge multilevel inverter (MLI) has been reported in previous works. In this study, a self-balanced series/parallel switched-capacitor (SC) is introduced to further develop this type of MLIs to generate more output levels. Each cascaded H-bridge is fed by an SC unit. All components in each SC unit withstand the same voltage stress, but different SC units address different voltages. With this asymmetric feature, different H-bridges are responsible for providing levels with different voltage intervals so that the cascaded MLI can generate numerous levels with a single dc source and fewer components. Compared with the conventional asymmetrical cascaded MLIs, just a single dc source is required, capacitors’ voltages are balanced automatically, high boosting ability and more output levels are achieved with SC technique in the proposed MLIs. To synthesise the output voltage as close as possible to sinusoidal shape but with less switching loss, comparative analysis of nearest level control and equal area criterion is provided to modulate the proposed MLI with 13-level output. Experimental results demonstrate that the proposed MLI has high efficiency and low harmonics.

Analysis of Cascaded Multilevel Inverter with a Reduced Number of Switches for Reduction of Total Harmonic Distortion

Multilevel inverters (MLI) are aligned with lower harmonics and less commutation losses, which offer high power capacity. MLI is one of the best widespread converters due to its ability to eliminate the harmonic distortion without dropping the converter power output. The cascaded MLI is utilized for a reduced number of switches. In this topology, the switching angles at fundamental frequency are attained by solving the selective harmonic eliminations using sine cosine algorithm. This attains the desired output voltage with the elimination of certain lower order harmonics. In this paper, the analysis of seven-level cascaded MLI is presented with the scheme of carrier-based modulation techniques i.e. Phase-Disposition (PD), Phase-Opposition Disposition (POD) and Alternative Phase-Opposition Disposition (APOD). The Artificial intelligence (AI) is carried out for PD technique. These techniques are capable of defining the required switching angles to eliminate the preferred values of harmonics. The harmonic contents of output voltage in carrier-based modulation are observed with the indices, such as the modulation index with frequency modulation index and amplitude modulation index. The simulation results are obtained for seven-level inverter using MATLAB/SIMULINK. The hardware implementation is carried out using Main Power Management IC TPS65217C Beagle Bone Black Board for seven-level open loop control to justify the achievement of the suggested topology.

Performance comparison between optimization algorithms for asymmetrical cascaded multilevel inverter control

This paper discusses the hardware and control system design of the asymmetric cascade multilevel inverter. The asymmetric cascaded multilevel inverter structure is adopted to minimize bridges, gate drive circuits and DC power source number. Therefore, the proposed structure is able to generate higher voltage at higher speed with low switching losses and high efficiency. Selective Harmonic Elimination (SHE) based on Newton-Raphson (N-R) algorithm is developed to calculate a switching angle for a range of modulation index to control asymmetric cascade multilevel inverter. Simulation results prove that Newton-Raphson technique is more effective than genetic algorithm (G-A) and equal calculated switching angles method (ECSA). A comparison between the algorithm performance for 9-level asymmetric cascade H-bridge inverter control was evaluated and experimentally tested on FPGA-based prototypes

Novel Level-Shifted PWM Technique for Equal Power Sharing Among Quasi-Z-Source Modules in Cascaded Multilevel Inverter

Phase-shifted pulsewidth modulation (PS-PWM) is a well-known switching technique for quasi-Z-source (qZS)-based cascaded multilevel inverters (qZS-CMI). PS-PWM ensures equal power distribution (among operating modules) and equal switchings in all the semiconductors of the every given module; however, this technique suffers from higher number of switchings. On the other hand, level-shifted pulsewidth modulation (LS-PWM) ensures optimal switching but suffers from uneven distribution of power among the all the operating modules and also all the semiconductors of the same module of qZSI. This article proposes a novel switching technique which combines the advantages of both PS-PWM and LS-PWM, such as equal power distribution (among operating modules) and optimal switching sequence along with equal switch utilization. The proposed method is phase opposed disposed PS-PWM. This article details the switching technique along with switching loss analysis and compares it with the PS-PWM technique to show its superiority. Simulation results are carried out to study the cascaded multilevel inverter (CMLI) performance. Experimental prototype is developed to validate the performance of the proposed modulation.

Hierarchical Model Predictive Control of Grid-Connected Cascaded Multilevel Inverter

This article presents a hierarchical finite-set model predictive control (MPC) scheme to enable autonomous operation and self-balancing cascaded multilevel inverter. The proposed approach is an alternative to MPC scheme based on a generic cost function, which in some applications is ill fit or challenging to design. The proposed controller has a hierarchical framework to eliminate the overall cost function optimization and associated weight factor design stage of the control objectives. The control formulation approach allows for multiobjective optimization with a cost-tolerance framework. The concept is well suited to simplify the control design stage of cascaded H-bridge inverters at the grid-edge with advanced functionality. The control scheme achieves active and reactive power control with switching event reduction while equalizing power draw from the independent voltage sources. The latter of these objectives is made possible by the proposed hierarchical approach to the control objective tracking. The control is modularized for each phase, making the system robust to unbalanced grid conditions. The concept is explained in depth in simulation, and then tested experimentally on hardware.

Selective Harmonic Elimination Pulse Width Modulation for Five-phase Cascaded Multilevel Inverter Using Non-notch and Notch Switching Technique

Selective Harmonic Elimination Pulse Width Modulation for Five-phase Cascaded Multilevel Inverter Using Non-notch and Notch Switching Technique

A Reduced Single-Phase Switched-Diode Cascaded Multilevel Inverter

The cascaded multilevel inverters (MLIs) are suitable topologies when a high number of voltage levels are needed. Nonetheless, cascaded topologies possess the main drawback of a high number of power switches and gate drivers that make sophisticated control, reducing efficiency, and increasing cost. This article proposes a new fundamental switched-diode topology that is capable of generating five positive-voltage levels with only three power switches, three power diodes, and three dc voltage sources. Based on a combination of the n number of new fundamental topology, two cascaded topologies are proposed, which increases the number of voltage levels and decreases the number of power switches and voltage stress. The proposed cascaded topologies can operate in asymmetric dc sources, so different dc voltage source magnitudes are submitted to minimize the number of components. The main advantages of the proposed cascaded topologies are reducing the number of power switches, and gate drivers with reasonable dc voltage sources count in comparison with other state-of-the-art cascaded topologies. Furthermore, the proposed topologies reduce the cost in comparison with other recent MLI topologies. The power loss analysis and the recommended application for the proposed topologies are discussed. The simulation and experimental works are presented to verify the operation correctness of the proposed topologies.

Analysis and Control of PV Cascaded H-Bridge Multilevel Inverter With Failed Cells and Changing Meteorological Conditions

This article proposes an approach to control a photovoltaic cascaded H-bridge multilevel inverter with failed cells and changing meteorological conditions for large-scale grid-connected applications. The controller development is based on an analysis of the interaction between the inverter common-mode and differential-mode quantities, which is done in the time domain, supported by a space vector representation analysis. The proposed approach is able to produce balanced three-phase line-to-line voltages and currents even if there is a failed cell or if the fluctuating meteorological conditions cause uneven power distribution among the bridges. This is achieved through the modification of the pulsewidth modulation reference phase voltage angles combined to the injection of a dynamic homopolar component. Such an approach avoids tripping the system due to the protective functions #25 and #87 for per grid applicable codes and standards. Numerical simulations and laboratory experiments performed on a seven-level converter with different abnormal conditions to confirm the effectiveness of the suggested control strategy.