A Compact Generalized Switched-Capacitor MLI with a Modified Single-Carrier PWM Scheme for Transformerless PV Interfacing

Among the various transformerless multilevel inverters (MLIs) used in grid-tied PV systems, single-phase switched-capacitor (SC) based MLIs have gained significant attention in recent decades because they require only a single power source, offer intrinsic self-voltage balancing of capacitors, and have reduced electromagnetic interference (EMI). Nonetheless, these converters face challenges such as utilizing multiple SCs to achieve only a five-level output voltage, a large number of semiconductor components, and high total harmonic distortion (THD). This paper proposes a more efficient multilevel transformerless inverter (MLTI) design for a single-phase application, featuring a single SC, six switches, and one diode to deliver a five-level voltage output. The proposed MLTI showcases self-voltage balancing, auto-boost functionality, and the capability to handle reactive power transmission. Moreover, the circuit architecture is generalized to produce n-level voltage output. Additionally, an advanced pulse width modulation (PWM) method, referred to as single-carrier third harmonic saturated PWM (SCTHSPWM), is introduced. This new MLTI design, combined with the SCTHSPWM method, achieves lower total harmonic distortion (THD) in the output voltage, minimizes power loss, and enhances thermal stability compared to some recent MLTI designs for PV applications. Simulations using MATLAB/Simulink and PLECS, along with a 1 kW laboratory test, are performed to demonstrate the effectiveness of the proposed MLTI.