Improved NLM modulation method without measuring capacitor voltage applied to Modular Multilevel Converter

Abstract

The NLM modulation method is a very suitable method to apply to MMC multilevel converters with a large number of SMs. This method can produce a voltage on the ac side of the MMC with a number of levels up to 2N+1 (where N is the number of SMs on each branch). This article deals with improving the NLM modulation method for MMC converter through the use of an algorithm that does not need to use voltage information on capacitors. This algorithm uses simple logic operations are used to select which SMs will be turned on or off during a working duty cycle. This has great significance in reducing capacitors voltage and current sensors on branches as well as complex signal connections. As a result, the hardware design becomes more compact when MMC converter need to use a large number of SMs in medium and high voltage applications. The results of the study were performed on Matlab/simulink and compared with conventional NLM modulation method in which the measurement of capacitor voltages is required to evaluate the effectiveness of the proposed method.