The authors discuss high-voltage power conversion. Conventional series connection and three-level voltage source inverter techniques are reviewed and compared. A novel versatile multilevel commutation cell is introduced: it is shown that this topology is safer and more simple to control, and delivers purer output waveforms. The authors show how this technique can be applied to either choppers or voltage-source inverters and generalized to any number of switches.<<ETX>>

Multi-level conversion : high voltage choppers and voltage-source inverters

Multilevel inverters have created a new wave of interest in industry and research. While the classical topologies have proved to be a viable alternative in a wide range of high-power medium-voltage applications, there has been an active interest in the evolution of newer topologies. Reduction in overall part count as compared to the classical topologies has been an important objective in the recently introduced topologies. In this paper, some of the recently proposed multilevel inverter topologies with reduced power switch count are reviewed and analyzed. The paper will serve as an introduction and an update to these topologies, both in terms of the qualitative and quantitative parameters. Also, it takes into account the challenges which arise when an attempt is made to reduce the device count. Based on a detailed comparison of these topologies as presented in this paper, appropriate multilevel solution can be arrived at for a given application.

Multilevel Inverter Topologies With Reduced Device Count: A Review

This paper presents a single-phase five-level photovoltaic (PV) inverter topology for grid-connected PV systems with a novel pulsewidth-modulated (PWM) control scheme. Two reference signals identical to each other with an offset equivalent to the amplitude of the triangular carrier signal were used to generate PWM signals for the switches. A digital proportional-integral current control algorithm is implemented in DSP TMS320F2812 to keep the current injected into the grid sinusoidal and to have high dynamic performance with rapidly changing atmospheric conditions. The inverter offers much less total harmonic distortion and can operate at near-unity power factor. The proposed system is verified through simulation and is implemented in a prototype, and the experimental results are compared with that with the conventional single-phase three-level grid-connected PWM inverter.

Multilevel Inverter For Grid-Connected PV System Employing Digital PI Controller

Multilevel voltage source inverters offer several advantages compared to their conventional counterparts. By synthesising the AC output terminal voltage from several levels of voltages, staircase waveforms can be produced, which approach the sinusoidal waveform with low harmonic distortion, thus reducing filter requirements. The need of several sources on the DC side of the converter makes multilevel technology attractive for photovoltaic applications. This paper provides an overview an different multilevel topologies and investigates their suitability for single-phase grid connected photovoltaic systems. Several transformerless photovoltaic systems incorporating multilevel converters are compared regarding issues such as component count and stress, system power rating and the influence of the photovoltaic array earth capacitance.

Multilevel converters for single-phase grid connected photovoltaic systems-an overview

This paper proposes a single-phase seven-level inverter for grid-connected photovoltaic systems, with a novel pulsewidth-modulated (PWM) control scheme. Three reference signals that are identical to each other with an offset that is equivalent to the amplitude of the triangular carrier signal were used to generate the PWM signals. The inverter is capable of producing seven levels of output-voltage levels (Vdc, 2Vdc/3, Vdc/3, 0, -Vdc, -2Vdc/3, -Vdc/3) from the dc supply voltage. A digital proportional-integral current-control algorithm was implemented in a TMS320F2812 DSP to keep the current injected into the grid sinusoidal. The proposed system was verified through simulation and implemented in a prototype.

Single-Phase Seven-Level Grid-Connected Inverter for Photovoltaic System

A multilevel pulse-width modulated (PWM) single phase voltage-source inverter topology for photovoltaic applications is discussed in this paper. The use of the phase opposition (PO) carrier disposition multicarrier PWM switching technique for this topology is presented. Inverter switch control signals are derived. A 5-level and a 3-level PWM voltage waveform across the load is generated, for high and low modulation indexes respectively. Performance characteristics including total harmonic distortion for a range of operating conditions of the inverter are provided. Theoretical considerations discussed in this paper are supported with simulation and experimental results taken from a low power laboratory prototype.

A multilevel PWM inverter topology for photovoltaic applications

Electrical Engineering students at Curtin University are required to present a seminar based on their final year project. A simple model has been developed to enable critical thinking to be incorporated into students' seminar presentations. The method is presented to students at a presentation skills workshop which is described in the paper.

Improving the Quality of Engineering Students Seminar Presentations

In Electrical Engineering at Curtin University as in many universities world-wide, the trend recently has been towards larger classes, with a greater diversity in the student body. In this climate, it is especially important to try to make the curriculum, teaching and assessment methods more inclusive of this diversity. In this paper we describe the process undertaken to try to create an inclusive learning environment in a large first-year course in electrical engineering. First, the lecturer instigated in the first few lectures a number of unique and carefully thought through activities designed to facilitate this more personal approach. Second, the content of the course and the context of problems and examples were chosen to appeal to the diversity of students interests and backgrounds. Third, the lectures involved real-world applications and many illustrative graphics. In this paper, we describe the initial activities, the course content and delivery mode, and the students responses to the whole experience.

William B Lawrance

Papers

A multilevel PWM inverter topology for photovoltaic applications

Improving the Quality of Engineering Students Seminar Presentations

Creating an Inclusive Learning Environment in Electrical Engineering