Capacitor Voltage Balancing with Reduction of Arm Current and THD Control of MMC: A Modified Triangular Injection Approach
For high power applications, in recent time, Modular Multilevel Converter (MMC) has become popular because it consists of number of DC sources. Stair voltage output waveform of this type of converter can be controlled by different modulation techniques. Harmonic profile of a converter with a modulation scheme much depends on the carrier frequency used in it. On the other hand, with the importance of lower Total Harmonic Distortion (THD), the arm current control is also the necessity to drive an MMC in smooth operation. Moreover, imbalance of the Sub-Module (SM) capacitor voltages affects the arm current as well as the life time of the capacitors. In this way the overall performance of the converter could be affected. As a result, several efforts of research in this area focused on to minimize the THD, balance the capacitor voltage of Sub-module (SM) and to control the arm current of the converter. This paper proposed a modified triangular injection modulation structure for MMC converters to maintain minimum harmonic profile as well as to achieve lower arm current and capacitor voltage balancing of SM within a single algorithm structure. Several well-known modulation methods have been compared with the proposed method so that percentage of THD and the arm current can be identified as minimum and SM’s capacitor voltages could be compared.
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