Hybrid Multi Modular Converter for 25 Level Inverter

Abstract

Energy storage system plays an important role in electric vehicles. In these energy storage systems, a large number of battery cells are usually connected in series to enhance the output voltage for motor driving. The difference in electrochemical characters will cause state-of-charge (SOC) and terminal voltage imbalance between different cells. In the existing system, a hybrid cascaded multilevel converter which involves both battery energy management and motor drives. Each battery cell can be controlled to be connected into the circuit or to be bypassed by a half-bridge converter. All half bridges are cascaded to output a staircase shape dc voltage. Then, an H-bridge converter is used to change the direction of the dc bus voltages to make up ac voltages. The outputs of the converter are multilevel voltages with less harmonics and lower dv/dt, which is helpful to improve the performance of the motor drives. The imbalance of terminal voltage and SOC can also be avoided; Sso the life of the battery stack will be extended. In the proposed system, the level of the multi-level inverter can be increased to further reduce the total harmonic distortion without change in the circuit topology..
Keywords: Battery cell; charging and discharging; electric Vehicle (EV); hybrid cascaded multilevel converter; voltage balance