Abstract

In this paper, Modular Multilevel Converter MMC-Swiss rectifier for harmonic mitigation is presented and simulated by PLECS software package. The mathematical calculations and system simulation are performed for a converter with nominal power of 400 MW and 400KV DC. The characteristic of Swiss rectifier including the operation principle, modulation strategy and relevant equations are described in detail. The MMC is used as a combination with Swiss rectifier because of its simplicity to be integrated for applications that required different level of voltages and currents, such as offshore wind turbine. Where, there is a trend to generate the electricity and transmit it in DC form due to its economic reasons. Therefore, the usage of MMC-Swiss rectifier is viable for High Voltage Direct Current HVDC applications. The contribution of Swiss rectifier is to make the current drawn from the supply by a converter, pure sinusoidal and this achieved by injecting third harmonic current in the circulating current from the DC side. Thus, this would reduce the THD and improve the power quality of the AC side currents.

Highlights

  • The development of Power Electronic industry has increased the usage of non-linear loads

  • For three-phase Power Factor Correction (PFC) system, different topologies have been proposed for mitigating harmonics and some are based on third-harmonic current injection technique

  • The structure of Swiss rectifier consists of three-phase diode rectifier with active switches placed in the main path of the current to/from the load, which works as third-harmonic current injection circuit

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Summary

Introduction

The development of Power Electronic industry has increased the usage of non-linear loads. One of the converter topologies, which are based on third-harmonic current injection, is Swiss rectifier This rectifier would reduce the harmonics of input line current and under operating condition; it provides high efficiency [3]. The MMC-Swiss rectifier for offshore HVDC wind turbine applications would be implemented and controlled. The usage of MMC-Voltage Source Converter VSC in the HVDC transmission would add some advantage points, such as the possibility of obtaining independent control for the active and reactive power, and the AC voltage grid can be supported [8,9,10,11,12,13,14,15,16].

MMC voltage and current description
Swiss rectifier
PLECS modelling results
Current injection of upper leg
Circulating current
Results and discussion
Conclusions
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