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Multilevel inverter (MLI) is gaining rapid popularity in high/medium power applications due to low THD and high quality output waveform. Recently, the MLI topologies with reduced part count has attracted the researchers by offering higher number of output voltage level with reduced part count as compared to classical topologies (CHB, NPC and FC). It is observed that these recently proposed topologies are aimed to increase the output level with less number of components but the discussion over their suitability for a particular application is not yet explored completely. The main purpose of this paper is to provide an instructive review and analysis of existing MLIs with reduced part count. An exhaustive comparison of MLIs are assessed based on the number of switches, standing/blocking voltage across the switches, conduction losses, switching losses and cost. With the outcome of comparison results, suitable structure of MLI can be judged with reduced number of components and losses for given applications. [ABSTRACT FROM AUTHOR]

Wind energy conversion system (WECS) is interfaced with the utility system through power electronic converters which plays an important role in the integration of wind power into the electric grid. The main power quality disturbances due to integration of WECS to grid are variation in power and harmonics. To maintain grid synchronization and to keep total harmonic distortion (THD) within operational limits, appropriate control schemes are required for the grid side converter. The main objective of grid side controller is to control the power delivered to the grid, grid synchronization, to supply high quality power to grid and to meet grid code compliance. In this paper control schemes used in grid interfaced wind energy conversion system for generator side and grid side converter control, are reviewed thoroughly. The paper presents a comparative study of rotor flux oriented control and direct torque control (DTC) techniques applied in generator side converter of permanent magnet synchronous generator (PMSG) drives for wind turbine application. For grid side converter, various control schemes are developed mainly based on voltage oriented control (VOC) or on direct power control (DPC). The performance of VOC based control system basically depends on method applied for current control. A comparative study is done among them and findings are tabulated. Integration requirements of wind turbine to grid, grid synchronization and requirement of monitoring unit are also discussed. [ABSTRACT FROM AUTHOR]

This paper presents a multilevel inverter that has been conceptualized to reduce component count, particularly for a large number of output levels. It comprises floating input dc sources alternately connected in opposite polarities with one another through power switches. Each input dc level appears in the stepped load voltage either individually or in additive combinations with other input levels. This approach results in reduced number of power switches as compared to classical topologies. The working principle of the proposed topology is demonstrated with the help of a single-phase five-level inverter. The topology is investigated through simulations and validated experimentally on a laboratory prototype. An exhaustive comparison of the proposed topology is made against the classical cascaded H-bridge topology. [ABSTRACT FROM PUBLISHER]

This paper presents the design and implementation of a simple neutral point potential (NPP) regulator for a three-level diode-clamped inverter employing a sine-triangle regulator in conjunction with a closed-loop controller with reduced switching losses. The regulator principle is based on adding a continuous variable offset voltage which regulates the midpoint potential of the dc bus. The novelty of the proposed NPP regulator is in the determination of the magnitude of variable offset voltage based upon the average value, peak-to-peak amplitude, total harmonic distortions, and third harmonic content in NPP. Aside from maintaining dc-bus voltage balance, the proposed regulator leads to a significant reduction in the voltage distortion at the NP, resulting in the reduction of the required dc-bus capacitance. It also reduces the switching losses of the inverter by inserting the “no-switching” zone within each half cycle of the fundamental voltage wave. Analytical, computer simulation, and experimental results verifying the approach are presented in this paper for various load power factor angles. [ABSTRACT FROM AUTHOR]

Abstract: Recently multilevel inverters are gaining popularity due to reduced voltage stress across power switches and low total harmonic distortion (THD) output voltage waveform. However, device count increases with increased voltage levels. This paper presents a novel multilevel topology which is capable of obtaining all additive and subtractive combinations of input DC levels in the output waveform. Though all such levels can be obtained using the proposed topology, the actual number of levels depends on the DC source arrangement. A comparison is made between proposed topology and the classical multilevel topologies on the basis of device count and number of levels in the output voltage waveform. A detailed study of the proposed topology is presented through the example of a nine-level inverter. Appropriate modulation scheme is also presented. The proposed concept is analyzed through simulation studies and verified experimentally. [Copyright &y& Elsevier]