A Simplified Logical Method (SLM) Based Capacitor Balancing Technique for Modular Multilevel Converter

Abstract

The modular and voltage scalable features of modular structure based power converter has attracted for wide power range applications. However, balancing the capacitor voltage becomes complex when the number of sub modules is increased. In a conventional system, for balancing a capacitor voltage, separate monitoring and control are required for each sub module, which further increases the cost and burden to the converter. This paper proposes a simplified logical method (SLM) for balancing the capacitor voltage of each sub module without any additional sensors and controllers. The capacitor voltage of N sub modules is balanced based on the simple logical function, which eventually balances the capacitor voltage and thus reduces the voltage ripple of each capacitor. In addition, this method suppresses the circulating current and common mode voltage, which increases the efficiency and cost effective of the converter. The level shifted carrier technique is used for providing desired pulse signals for the switching devices in the converter. The effective performances of the proposed method are validated using simulation and experimental setup.

Keywords

• Simplified logical method (SLM)
• capacitor voltage balancing
• HVDC applications
• modular multilevel converter (MMC)
• phase logic method