A Level Enhanced Nearest Level Control for Modular Multilevel Converter Without Using Sensors

Modular Multilevel Converters (MMCs) have gained popularity in high and medium power applications. The nearest level control (NLC) is the suitable modulation technique as it offers low switching loss and easier implementation compared to the carrier-based pulse width modulation techniques. However, the harmonic performance is poor in case of MMC with low number of submodules (SMs). Apart from this, the SM capacitor voltage balance control is crucial, which demands expensive voltage and current measurement boards with conventional balancing approaches. This article presents a level enhanced NLC method for MMC. The proposed method derives the necessary switching patterns using simple logical operations based on the inherent property of NLC reference waveform. By which, equal insertion and bypass periods are ensured for the SM capacitors and eliminated the voltage and current sensors needed for the capacitor voltage balance control. Also, the output voltage level number increases to 2
N
+1 (where
N
is the number of SMs per arm) with reduced half step size. Hence, the quality of ac output waveform can be improved with low number of SMs. The proposed method is verified by simulations in MATLAB/SIMULINK software, and for the validation, experimental results are presented.