Capacitor voltage balancing with Reduction of Arm current and THD control of MMC: A modified triangular injection approach.
AbstractFor high power applications, in recent time, multilevel converter has become popular because of the composition of a number of DC sources. In both variable and controllable frequency system, stair voltage output waveform of this type of converter is controllable. Different types of DC sources like as batteries, fuel cells, solar cell, wind and micro turbines are used in Modular Multilevel Converter (MMC) topology has been popular in the distributed energy resources area. Harmonic profile of a converter with a modulation scheme much depends on the carrier frequency used in it. On the other hand, with the control of Total Harmonic Distortion (THD), the arm current control is also the necessity to drive an MMC in smooth operation. Imbalance of the SM capacitor voltage affect the arm current as well as the life time of the capacitor. In this way the overall performance of the converter could be affected. As a result, several efforts of research in this area focuses on to minimize THD, to 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 maintains minimum harmonic profile as well as to achieve lower arm current and capacitor voltage balancing of SM within a single algorithm structure. Some well-known modulation methods are compared with proposed method so that percentage of THD and arm current can be identified as minimum and quality of the output voltage is better.
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