Balancing of Capacitor Voltages with a Reduced Number of Voltage and Current Sensors in Alternate Arm Multilevel Converter (AAMC)

The alternate arm multilevel converter (AAMC) is a new type of voltage source converter topology introduced as an attractive option for medium voltage and high-power applications. In AAMC, many series full-bridge sub-modules (FB-SM) are used to achieve high-voltage applications. Despite this, a large number of voltage and current sensors are needed in this converter to balance the capacitor voltage of the SMs. This paper proposes a new method to estimate the SM capacitor voltage that needs only one voltage sensor in each arm and a current sensor in the converter’s output to balance capacitor voltages. By using a proposed method based on a Kirchhoff voltage law and circuit relations govern on AAMC, the capacitor voltages can be determined. Contrary to voltage balancing control schemes based on individual sensors, the number of voltage sensors in the proposed method has been substantially reduced, and arm current sensors are eliminated. In addition, there is low estimation error since the capacitor voltages are calculated with high accuracy and updated depending on the arm voltage sensor and switching signals. Analysis of the proposed method in MATLAB Simulink for different scenarios indicates its validity.