In this paper, a novel three-phase parallel grid-connected multilevel inverter topology with a novel switching strategy is proposed. This inverter is intended to feed a microgrid from renewable energy sources (RES) to overcome the problem of the polluted sinusoidal output in classical inverters and to reduce component count, particularly for generating a multilevel waveform with a large number of levels. The proposed power converter consists of $n$ two-level $(n+1)$ phase inverters connected in parallel, where $n$ is the number of RES. The more the number of RES, the more the number of voltage levels, the more faithful is the output sinusoidal waveform. In the proposed topology, both voltage pulse width and height are modulated and precalculated by using a pulse width and height modulation so as to reduce the number of switching states (i.e., switching losses) and the total harmonic distortion. The topology is investigated through simulations and validated experimentally with a laboratory prototype. Compliance with the $\text{IEEE 519-1992}$ and $\text{IEC 61000-3-12}$ standards is presented and an exhaustive comparison of the proposed topology is made against the classical cascaded H-bridge topology.

https://hal.archives-ouvertes.fr/hal-01717607/document

Multilevel Inverter Topology for Renewable Energy Grid Integration

A capacitor voltage-balancing method for a nested neutral point clamped (NNPC) inverter is proposed in this paper. The NNPC inverter is a newly developed four-level voltage-source inverter for medium-voltage applications with properties such as operating over a wide range of voltages (2.4–7.2 kV) without the need for connecting power semiconductor in series and high-quality output voltage. The NNPC topology has two flying capacitors in each leg. In order to ensure that the inverter can operate normally and all switching devices share identical voltage stress, the voltage across each capacitor should be controlled and maintained at one-third of dc bus voltage. The proposed capacitor voltage-balancing method takes advantage of redundancy in phase switching states to control and balance flying capacitor voltages. Simple and effective logic tables are developed for the balancing control. The proposed method is easy to implement and needs very few computations. Moreover, the method is suitable for and easy to integrate with different pulse width modulation schemes. The effectiveness and feasibility of the proposed method is verified by simulation and experiment.

A Capacitor Voltage-Balancing Method for Nested Neutral Point Clamped (NNPC) Inverter

The purpose of this paper is to provide an analytical review of wind turbine-generator systems for stand-alone applications. The review focuses on variable-speed wind turbines, as the future trend in wind energy conversion, in contrast with the traditional fixed-speed wind turbines. Indirect-drive and direct-drive turbines are comparatively evaluated. The concerns about long-term availability of permanent magnet materials and its impact on the future of permanent magnet synchronous generator are addressed. Having cost and efficiency in mind, viability of indirect-drive squirrel cage induction generator for stand-alone wind energy conversion systems is discussed. As an efficient induction machine design, permanent magnet induction generator is also examined. Finally, the potential of using switched reluctance machine, as a generator, in a direct-drive wind turbine system is investigated.

An analytical literature review of stand-alone wind energy conversion systems from generator viewpoint

The Neutral Point Clamped (NPC) Multi-Level Inverters (MLI) have been ruling the power electronics industries for the past two decades. The Multi-Carrier Pulse Width Modulation (MCPWM) is common PWM techniques which are widely used in NPC-MLI applications. However, MCPWM is not having a good impact on the balancing of DC-link voltages, Common Mode Voltage (CMV) and limiting the Total Harmonics Distortion (THD). The Selective Harmonic Elimination (SHE) technique is introduced for reducing the THD, however all the switching angles should be maintained less than $\pi $ /2 to keep the eliminated harmonics at constant level which narrows down the modulation index range. Hence, in recent days Space Vector Modulation (SVM) technique is widely used in NPC-MLI, which gives better DC-link voltage balancing, self-neutral point balancing, near-zero CMV reduction, better-quality harmonics profile and switching loss minimization. Hence, it is a preferred solution for the majority of electrical conversion applications such as electric traction, high power industrial drives, renewable power generation, and grid-connected inverters, etc. The paper gives a comprehensive review of the SVM for NPC-MLI. First, this paper deliberates the state of art for two-level SVM and extends it to three-level (3L) SVM. Also compares the 3L SVM performance with other MCPWM techniques. Followed by the various modified MLI SVM techniques in terms of their implementations, DC-link capacitor balancing, and reduction of CMV. Further, the review of MLI SVM is widened to open-end winding Inverters and multiphase MLIs. The final part of this paper discussed the future trends and research directions on MLI SVM techniques and its applications.

/pdf/a-comprehensive-review-on-space-vector-modulation-techniques-4knkky1lpu.pdf

A Comprehensive Review on Space Vector Modulation Techniques for Neutral Point Clamped Multi-Level Inverters

A conventional grid-connected solar Photovoltaic (PV) inverter consists of Two-Level or Three-Level configuration is not suitable for very high power ratings and the size of AC side filter required is high to maintain the power quality as per the grid codes. It is inefficient in extracting maximum power as the tracking of Maximum power point is carried out for entire PV arrays connected together instead of independent MPPT of each PV array. With a conventional PV inverter, the utilization factor is also very less, since the system will be in idle state during night times or when the irradiation is weak. Hence a conventional solar inverter consists of Two-Level or Three-Level inverter suffers from the following drawbacks (a) Not suitable for very high Power Ratings (b) High filter size (c) Inefficient in harvesting maximum power (d) Less utilization factor. In this study, the need for the multilevel inverter (MLI) to minimize the drawbacks of the conventional inverter is discussed. Cascaded H-Bridge (CHB) configuration which is more preferred for solar power applications where isolated input DC sources are available and for STATCOM applications where there is no requirement of DC Sources is discussed in detail. The basic operation of CHB inverter, PWM techniques, and fault tolerant operations are explained through simulation results. The Independent MPPT control of each PV array using CHB inverter is reviewed. CHB inverter controls for PV applications and STATCOM applications are also reviewed. The concept of a PV-STATCOM which is required for improving the utilization factor of PV inverter is reviewed. The operation of PV-STATCOM is explained through simulation studies. Real and reactive power flow through a 11-Level, CHB MLI is verified through experimental results. Feasibility study for multilevel PV-STATCOM for High power applications using CHB configuration is carried out in this paper.

A comprehensive review on CHB MLI based PV inverter and feasibility study of CHB MLI based PV-STATCOM

Multilevel inverters have been attracting in favor of academia as well as industry in the recent decade for high-power and medium-voltage energy control. In addition, they can synthesize switched waveforms with lower levels of harmonic distortion than an equivalently rated two-level converter. The multilevel concept is used to decrease the harmonic distortion in the output waveform without decreasing the inverter power output. This paper presents the most important topologies like diode-clamped inverter (neutral- point clamped), capacitor-clamped (flying capacitor), and cascaded multilevel with separate dc sources. This paper also presents the most relevant modulation methods developed for this family of converters: multilevel sinusoidal pulse width modulation, multilevel selective harmonic elimination, and space-vector modulation. Authors strongly believe that this survey article will be very much useful to the researchers for finding out the relevant references in the field of topologies and modulation strategies of multilevel inverter.

/pdf/multilevel-inverters-a-literature-survey-on-topologies-and-3x54jdlrxm.pdf

Multilevel inverters: A literature survey on topologies and control strategies

This paper presents a literature survey on the stand alone power generation using three phase asynchronous generator Induction generators are increasingly being used in non-conventional energy systems such as wind, micro/mini hydro, etc The advantages of using an induction generator instead of a synchronous generator are well known Some of them are reduced unit cost and size, ruggedness, brushless (in squirrel cage construction), absence of separate dc source, ease of maintenance, self-protection against severe overloads and short circuits, etc In isolated systems, squirrel cage induction generators with capacitor excitation, known as Self-Excited Induction Generators (SEIGs), also presented the importance of renewable source of energy (solar energy, wind energy, geothermal energy, tidal energy) in energy crisis Auther strongly believe that the survey article will be very much useful to the research for finding out the relevant references in regarding with self excited induction generator network and it is also helpful for power generation in remote area

Nupur Mittal

Papers

Multilevel inverters: A literature survey on topologies and control strategies

Stand alone power generation by 3φ asynchronous generator: A comprehensive survey

Design and performance analysis of low power fully integrated tunable bandpass filter