Grid Interconnection of Solar and Battery System Using an Asymmetrical T-Type Multilevel Inverter to improve Conversion Efficiency with Reduced THD

A three-phase dual-port T-type asymmetrical multilevel inverter (ASMLI) using two sources, solar forming the high voltage level and the battery forming the low voltage level, is considered for grid interconnection. A vertical shifted SPWM is used for the ASMLI circuit. A transformerless system for grid interconnection is achieved for a 100-kW power range. A well-designed boost converter and a Buck/Boost converter is used on the front side of the inverter. Design of battery charge controller and its controlling logic are done and its SOC is found to be efficient during charging and discharging conditions. A closed-loop control using PQ theory is implemented for obtaining power balance at 0.7 modulation index. The THD of the current harmonics in the system is observed to be 0.01% and voltage harmonics is 0.029% which are well within the permissible limits of IEEE-519 standard. The power balance is found to be good between the inverter, load, and the grid during load disconnection for a period of 0.15s. A comparison of THD’s, voltage, current stresses on the switches, and conduction losses is also presented for a single-phase system with respect to a two-level inverter which shows improved efficiency and low THD. Hence this system can be proposed for use in grid interconnection with renewable energy sources.