Abstract
The Modular Multilevel Converter (MMC) is the best topology for medium and high voltage applications. The performance of MMC and the quality of the output waveform completely depends on the control applied. Nearest Level Modulation (NLM) is the conventional method used to control MMC that produces N+1 (N is the number of submodules per arm) AC output voltages. This article proposes a modified NLM control method for the MMC, which produces 2N+1 level which is twice the number of levels produced by conventional NLM. The proposed method is easy to implement and is extended in the article to produce a 4N+1 output voltage level which is never done in the literature. The THD of the output waveform is reduced to more than one-fourth compared to conventional NLM. The cost of switching devices, capacitors and size of circuit is also reduced to one-fourth for 4N+1 output waveform compared to conventional NLM. The method is verified through LabVIEW Multisim Co-simulation and real-time simulation using Field Programmable Gate Array (FPGA) based NI PXI.
Highlights
The concept of the Modular multilevel converter was introduced in 2003 [1], after that it has been adopted as the art of technology in the high-voltage and high-power applications, such as high-voltage direct current (HVDC) transmission, power derives, and STATCOM [2]–[5]
In Nearest Level Modulation (NLM), the arm voltages generated are taken as reference and are fed back to the modulator to generate the pulses for all the SMs present in the upper and lower arm of the Modular Multilevel Converter (MMC)
In [23] the circuit of the MMC is reduced and power quality is improved using binary, trinary, and modified MMCbased topology, but their algorithm involves complex calculation and Total Harmonic Distortion (THD) is higher compared to our proposed modified NLC
Summary
The concept of the Modular multilevel converter was introduced in 2003 [1], after that it has been adopted as the art of technology in the high-voltage and high-power applications, such as high-voltage direct current (HVDC) transmission, power derives, and STATCOM [2]–[5]. In [23] the circuit of the MMC is reduced and power quality is improved using binary, trinary, and modified MMCbased topology, but their algorithm involves complex calculation and THD is higher compared to our proposed modified NLC. The reference [24] proposes an improved NLC algorithm with a reduced number of SMs but their results are limited to offline simulation and involves complex calculation compared to our proposed method. The control is implemented in LabVIEW and the model is designed in Multisim to obtained offline simulation results using LabVIEW Multisim co-simulation platform and the results are taken using modified NLM and compared with conventional NLM technique with the different number of levels in the output waveform.
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