Analysis and experimentation of modular differential inverter utilizing SEPIC modules and sic devices for grid connected applications

Abstract

This paper presents a three-phase Modular Differential Inverter (MDI) utilizing DC-DC modules that provide AC power to the utility grid with step-up voltage capability. The construction of the MDI has many advantages such as flexibility and reliability, and can be designed, optimized and scaled to any power level. Moreover, Single-Ended Primary-Inductor Converter (SEPIC) modules have been proposed to incorporate in the MDI because it has many merits that enhance the overall performance of the differential inverter. SiC devices are also integrated into the SEPIC modules for efficient operation at a high switching frequency. An in-depth mathematical model discussing the practical issues of differential inverter such as variable duty cycle, low order harmonics and circulating power is also presented. The design steps of the proposed SEPIC modules are presented in detail considering the standard grid side requirements of total harmonic distortion (THD). The MDI, which implements three parallel modules in each phase, is investigated using PSIM simulation software. A mismatch of ±20% in the SEPIC module parameters of each phase is investigated to confirm the system performance. Moreover, a laboratory prototype of the system, considering only one SEPIC module in each phase with 200 V grid-side voltage, 1.6 kW, and 50 kHz switching frequency, is carried out to verify the validity of the system.