Voltage Balancing of Capacitors Using Kalman Filter in Modular Multilevel Converters without Current Sensors

Modular multilevel converters (MMCs) play an essential role in power conversion for medium and high voltage industrial applications. These types of converters use many sensors for the process of measuring and sorting the voltage of their capacitors, but this increases cost and hardware complexity, as well as decreases reliability. One of the most widely used methods for voltage sorting of capacitors in MMCs is based on current measuring and detecting the current sign of each arm. This paper uses the capacitor voltages estimation scheme by the Kalman filter (KF) algorithm at each sampling time. Moreover, with the difference between the total voltage of the capacitors in each arm during two consecutive processes, their sorting is done without the current sensor. Therefore, by the proposed scheme, current sensors are entirely removed from the arms, and the MMC control process is implemented by only two voltage sensors in a phase branch. The simulation results in the MATLAB Simulink environment confirm the accuracy of the proposed method.