Prafullachandra M. Meshram

A Simplified Nearest Level Control (NLC) Voltage Balancing Method for Modular Multilevel Converter (MMC)

In this paper, a simplified nearest level control balancing method for modular multilevel converter is presented. The proposed method neither requires individual sorting of the submodule voltages nor the redundancy of the switching states. Once the sorting of the submodules is done on the basis of the number of the submodules to be switched on, the identifications of the submodules can be carried out throughout the stages of the implementation of the this method. The proposed method also does not require the individual submodule status in the gate pulse generation stage. The gate logic in the presented method can be implemented with the help of the switching states of the voltage levels. Those simplifications and removing of the some of the stages by the proposed balancing method may ease and lead to the less processor time at the implementation level. The pictorial presentation further helps in consolidating the understanding of the different stages of the method. Rigorous simulations are carried out for open and one of the prominent closed-loop applications, i.e., modular multilevel converter-based high-voltage direct current to demonstrate the validity and effectiveness of the proposed simplified balancing method under normal and emergency conditions.

A Three-Phase Hybrid Cascaded Modular Multilevel Inverter for Renewable Energy Environment

This paper presents a three-phase hybrid cascaded modular multilevel inverter topology which is derived from the proposed modified H-bridge module. This topology results in the reduction of number of power switches, losses, installation area, voltage stress and converter cost. For renewable energy environment such as photovoltaic (PV) connected to the microgrid system, it enables the tranformerless operation and enhances the power quality. This multilevel inverter is an effective and efficient power electronic interface strategy for renewable energy systems. The basic operation of single module and the proposed cascaded hybrid topology is explained. The ability to operate in both symmetrical and asymmetrical modes is analyzed. The comparative analysis is done with classical cascaded H-bridge and flying capacitor multilevel inverters. The nearest level control method is employed to generate the gating signals for the power semiconductor switches. To verify the applicability and performance of the proposed structure in PV renewable energy environment, simulation results are carried out by MATLAB/Simulink under both steady-state and dynamic conditions. Experimental results are presented to validate the simulation results.

Simplified Space Vector Modulation Techniques for Multilevel Inverters

This paper presents simplified techniques for the space vector modulation (SVM) of any n-level multilevel inverter. Three techniques have been presented to simplify the identification of the nearest three vectors to the reference vector. The first two techniques are based on resolving the multilevel inverter space vector diagram into appropriate two-level hexagons. This results in simplification of the multilevel SVM problem into a two-level SVM problem. The third technique is an algorithm-based technique which makes use of a 60°-spaced gh coordinate system to perform the SVM of a multilevel inverter. Switching sequence design for all the three techniques is presented with the aim of minimization of the device switching frequency. Simulation and experimental results have been provided to verify the feasibility of the proposed techniques. Simulation results are provided for up to 21-level cascaded H-bridge (CHB) inverters, while the experimental verification is done on a five-level laboratory prototype. Although only the CHB inverter is considered in this study, the proposed techniques are perfectly general and can be applied to all types of multilevel inverters, and are extendable to any number of levels.

A Modified Switched-Diode Topology for Cascaded Multilevel Inverters

In this paper, a single phase modified switched-diode topology for both symmetrical and asymmetrical cascaded multilevel inverters is presented. It consists of a Modified Switched-Diode Unit (MSDU) and a Twin Source Two Switch Unit (TSTSU) to produce distinct positive voltage levels according to the operating modes. An additional H-bridge synthesizes a voltage waveform, where the voltage levels of either polarity have less Total Harmonic Distortion (THD). Higher-level inverters can be built by cascading MSDUs. A comparative analysis is done with other topologies. The proposed topology results in reductions in the number of power switches, losses, installation area, voltage stress and converter cost. The Nearest Level Control (NLC) technique is employed to generate the gating signals for the power switches. To verify the performance of the proposed structure, simulation results are carried out by a PSIM under both steady state and dynamic conditions. Experimental results are presented to validate the simulation results.

A novel voltage balancing method of Modular Multilevel Converter (MMC)

The main problem in the new potential Modular Multilevel converter (MMC) topology for high and medium level is the voltage balancing of the capacitors of their sub modules. The novel balancing technique which is introduced in this paper based on sorting of the capacitor voltages. After sorting and detection of the arm current direction, neither require individual switch to get on nor require redundancy of the voltage levels to achieve voltage balance which is reported in the earlier publications. Rigorous MATLAB — Simulink simulation has been carried out for three level and seven levels with different parameters variations to validate the proposed technique.

An asymmetrical multilevel inverter topology with reduced source count

In this paper, an asymmetrical topology for cascaded multilevel inverter based on basic converter unit, series unit and full-bridge is proposed. It offers lower total harmonic distortion, switching losses and voltage stress on switches than conventional inverters. An algorithm to determine dc voltage sources magnitudes is proposed. The gating signals for the power switches are generated by employing Nearest Level Control (NLC) method. This structure allows a reduction of the system cost and size. Effectiveness of the proposed topology has been demonstrated by analysis and simulation.

GA based hybrid selective harmonic elimination (SHE) technique applied to five-level Nested Neutral Point Clamped (NNPC) Converter

This paper presents, genetic algorithm based hybrid selective harmonic elimination scheme for recently introduced Nested Neutral Point Clamped (NNPC) Converter. The Selective harmonic elimination (SHE) modulation scheme reduces device stress, switching losses and filter size in high power and high voltage applications. SHE technique aims to solve non-linear and transcendental equations while keeping the objective, to maintain the fundamental harmonic component at its reference value and to eliminate lower order odd harmonics. To solve these nonlinear equations Hybrid algorithm has been adopted in this paper. This algorithm has two stages, during first stage GA has been run for four iterations and in second stage obtained solution from GA is used to initialize newton algorithm, which finally gives the exact converged solution. Thus, proposed algorithm overcomes the drawback of newton algorithm to have strong initial guess. This work also investigates the performance of five-level NNPC inverter by doing spectral analysis of phase and line voltages. The MATLAB/SIMULINK software is used for comprehensive simulation of five-level NNPC inverter.

Cascaded Multi-level Inverter Topology Developed from a Modified H-bridge

Abstract In this paper, a single-phase cascaded multi-level inverter topology is proposed. It is basically developed from a modified H-bridge module. This topology reduces the switch count, the gate drive requirement, and voltage stress. The significant advantages of the proposed inverter are modular structure, simpler control, and lower number of switches. The Nearest Level Control algorithm is employed to generate the gating signals for the power switches. To verify the performance of the proposed structure, simulation results are carried out by MATLAB (The MathWorks, Natick, Massachusetts, USA)/SIMULINK. Experimental results are presented to validate the simulation results.

Genetic algorithm (GA) based SHE technique applied to seven-level Nested Neutral Point Clamped (NNPC) Converter

This paper presents, selective harmonic elimination technique based on genetic algorithm applied to recently introduced seven-level Nested Neutral Point Clamped (NNPC) Converter. The Selective harmonic elimination (SHE) technique aims to eliminate lower order harmonic and maintain reference value of fundamental component. This demands the solution of nonlinear and transcendental equations. Thus, optimization problem has been formulated by defining proper objective function which covers all the constraints. GA is a matured and well known optimization algorithm, hence it is preferred to solve the concerned optimization problem. Solution gives the switching angles to switch the inverter. In this work, switching angles are determined offline for seven-level inverter, which are tuned for eliminating fifth and seventh harmonics. The MATLAB/SIMULINK software is used for comprehensive simulation of seven-level NNPC converter.

SHE technique for MMC based on modified flying capacitor multicell converter

Modular multilevel converter (MMC) based on modified flying capacitor multicell converter has been discussed. It is a recently introduced topology which is an extension of flying capacitor multicell (FCMC) converter topology. This paper uses selective harmonic elimination(SHE) technique to eliminate the lower order harmonics from the inverter output and maintain the fundamental voltage. The nonlinear and transcendental equations are needed to be solved to obtain the switching angles at which the inverter must be fired. This paper presents the Newton-Raphson method to solve these nonlinear equations. There are numbers of method such as homotopy algorithm, resultant theory method, particle swarm optimization, genetic algorithm, ant colony optimization etc. to solve these non-linear equations however Newton-Raphson method is easiest of all to understand and compute. The simulations of 7-level MMC with selective harmonic elimination (SHE) technique have been carried in MATLAB/SIMULINK software.