Abstract
Modular Multilevel Converters (MMC) are gaining importance because of their flexible structure, re-configurable property, and simplicity of operation. The operation of MMC at a low-switching frequency (LSF) helps in enhancing the performance of the converter. This paper proposes an improved harmonics mitigation scheme for a Multilevel DC-Link Inverter (MLDCLI), which is a variant of MMC. The proposed scheme is a modified version of the conventional Nearest Level Modulation (NLM) scheme, termed as modified Nearest Level Modulation (mNLM) Scheme. The proposed scheme is effective compared to NLM because of the choice of the switching angles obtained by the use of the algorithm proposed. The MLDCLI topology is operated for twelve different configurations, and mNLM is implemented on all the configurations. Using MATLAB software, the simulation results are validated, and the same is extended to a hardware prototype. The simulation and experimental results of NLM and mNLM schemes are compared. The effectiveness of the proposed scheme is evident by the reduced voltage THD, increased rms voltage, increased rms current, and increased output power.
Highlights
A multilevel inverter (MLI) is a combination of power semiconductor switches and dc voltage sources to generate ac output voltage in a stepped waveform
It can be observed that the THD generated using Nearest Level Modulation (NLM) scheme was 8.35% while it was 7.67% using modified Nearest Level Modulation (mNLM) scheme
The THD associated with NLM and mNLM schemes is less
Summary
A multilevel inverter (MLI) is a combination of power semiconductor switches and dc voltage sources to generate ac output voltage in a stepped waveform. The presence of multiple switches helps to reduce voltage sharing among the switches to generate high power output [1], [2]. The cascaded half-bridge cells operate to increase the levels at the output of the MMC, whereas the full-bridge plays the part of generating the negative polarity of the ac output. The new set of switching angles helps in improving the performance parameters of the inverters such as THD, rms voltage, rms current, and output power. The number of MLI levels at the output and the number of switches in MLDCLI circuit are related as equation (2).
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