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

This paper gives an overview of medium-voltage (MV) multilevel converters with a focus on achieving minimum harmonic distortion and high efficiency at low switching frequency operation. Increasing the power rating by minimizing switching frequency while still maintaining reasonable power quality is an important requirement and a persistent challenge for the industry. Existing solutions are discussed and analyzed based on their topologies, limitations, and control techniques. As a preferred option for future research and application, an inverter configuration based on three-level building blocks to generate five-level voltage waveforms is suggested. This paper shows that such an inverter may be operated at a very low switching frequency to achieve minimum on-state and dynamic device losses for highly efficient MV drive applications while maintaining low harmonic distortion.

Medium-Voltage Multilevel Converters—State of the Art, Challenges, and Requirements in Industrial Applications

Multilevel inverters have been widely accepted for high-power high-voltage applications. Their performance is highly superior to that of conventional two-level inverters due to reduced harmonic distortion, lower electromagnetic interference, and higher dc link voltages. However, it has some disadvantages such as increased number of components, complex pulsewidth modulation control method, and voltage-balancing problem. In this paper, a new topology with a reversing-voltage component is proposed to improve the multilevel performance by compensating the disadvantages mentioned. This topology requires fewer components compared to existing inverters (particularly in higher levels) and requires fewer carrier signals and gate drives. Therefore, the overall cost and complexity are greatly reduced particularly for higher output voltage levels. Finally, a prototype of the seven-level proposed topology is built and tested to show the performance of the inverter by experimental results.

Design and Implementation of a New Multilevel Inverter Topology

In this paper, authors propose a new power multilevel converter topology that is very competitive compared to the existing ones. It consists of packed U cells (PUC). Each U cell consists of an arrangement of two power switches and one capacitor. It offers high-energy conversion quality using a small number of capacitors and power devices and consequently, has a very low production cost. An averaged model of the topology is detailed. The operating principle of the transformerless seven-level inverter is analyzed and detailed. The multilevel sinusoidal modulation has been adapted for use with the PUC-based structure. The control strategy has been designed to reduce the harmonic contents of the load voltage. With such converters, filters' rating is considerably reduced. A comparative study is performed to highlight the advantages of the new packed U cells topology. The operation of the proposed converter topology has been verified through simulation. Experimental validation was performed using DS1103 DSP of dSpace.

Packed U Cells Multilevel Converter Topology: Theoretical Study and Experimental Validation

Multilevel inverters are in state-of-the-art power conversion systems due to their improved voltage and current waveforms. Cascaded H-bridge (CHB) multilevel inverters have been considered as an alternative in the medium-voltage converter market and experimental electric vehicles. Their variant, the asymmetrical CHB (ACHB) inverter, optimizes the number of voltage levels by using dc supplies with different voltages. However, the CHB and ACHB inverters require a large number of bidirectional and isolated dc supplies that must be balanced, and as any multilevel inverter, they reduce the power quality with the voltage amplitude. This paper presents a solution to improve the already mentioned drawbacks of ACHB inverters by using a high-frequency link using only one dc power source. This single power source can be selected according to the application (regenerative, nonregenerative, and with variable or permanent voltage amplitude). This paper shows the experimental results of a 27-level ACHB inverter with a variable and single dc source, but the strategy can be applied to any ACHB inverter with any single dc source. As a result, the reduction of active semiconductors, transformers, and total harmonic distortion was achieved using only one dc power source.

High-Frequency Link: A Solution for Using Only One DC Source in Asymmetric Cascaded Multilevel Inverters

This paper proposes an isolated cascaded multilevel inverter employing low-frequency three-phase transformers and a single DC input power source. The proposed circuit configuration can reduce a number of transformers compared with traditional three-phase multilevel inverters using single-phase transformers. It controls switching phase angles to obtain an optimal switching pattern identified with the fundamental frequency of the output voltage. Owing to this control strategy, harmonic components of the output voltage and switching losses can be diminished considerably. To verify the performance of the proposed approach, we implemented computer-aided simulations and experiments using a prototype.

Cascaded Multilevel Inverter Employing Three-Phase Transformers and Single DC Input

In this study, the solution plasma sputtering method was used in the synthesis of silver nanoparticles, instead of the chemical and physical synthesis method. Synthesis of the silver nanoparticles was conducted for 1 hour in 360 ml distilled water, and the effects of changing the input DC voltage and input frequency of the synthesized silver nanoparticles using power supply and the solution plasma sputtering method were analyzed via FESEM (field emission scanning electron microscopy) and EDS (energy-dispersive X-ray spectroscopy). The 8 kV input DC voltage in the solution plasma reactor was changed to 10 kV, and the 20 kHz input frequency was changed to 30 kHz, with the advanced device, which can control the input DC voltage and input frequency. It was confirmed that the average size of the silver nanoparticles became larger when the input DC voltage and frequency were changed.

Feel Soon Kang

Papers

Cascaded Multilevel Inverter Employing Three-Phase Transformers and Single DC Input

Synthesis of Silver Nano-Particles for the Application to Transparent Conductive Electrodes