A Switched-Capacitor MLI with Modified Single-Carrier PWM for Transformerless PV Interfacing

Among different types of existing transformerless multilevel inverters (MLIs) employed for grid-tied PV applications, switched-capacitor (SC) MLIs are getting much popularity for having single source requirement, intrinsic self-voltage balancing of capacitors, and reduced electromagnetic interference (EMI). However, main operational issues of such converters are having several SC units for five level voltage output, large amount of semiconductor devices, high total harmonic distortion (THD). A reduced power semiconductor device count multilevel transformerless inverter (MLTI) is presented in this paper, which is structured on single SC, six switches, and one diode for five level voltage output. The proposed MLTI features self-voltage balancing of SCs, auto-boost capability, and reactive power transmission ability. Apart from this, a new single-carrier based pulse width modulation (PWM) scheme is also proposed in this paper which is known as single-carrier 3rd harmonic saturated PWM (SCTHSPWM). The proposed MLTI along with SCTHSPWM scheme offers low output voltage total harmonic distortion (THD), power loss, and improved thermal stability compared to several recently proposed MLTIs for PV applications. MATLAB/Simulink and PLECS simulations, along with a 1kW laboratory test, are conducted to validate the feasibility of the proposed MLTI.