An isolated asymmetrical AC-DC converter based brushless direct current motor drive without bridge rectifier and low pass filter

• In the Negative cycle of the source voltage, the SEPIC converter's input inductance improves the source current profile; however, by functioning as a harmonic eliminator component with a capacitor CF, the same inductor also helps to increase the supply current profile in the PC of source voltage. • The null current switching control does away with the need for sensors and source voltage and current sensing. • The system's net order is lowered when four and second-order converters are combined in a bridgeless configuration. • To further enhance safety requirements, the system is further equipped with electrical/physical isolation between the source and the load. • By doing away with the need for a bridged rectifier, the bridgeless (BL) arrangement further enhances the system's compactness, cheap cost, and increased efficiency. The current article suggests the use of a sandwiched isolated AC-DC converter for a brushless direct current (BLDC) motor driver to improve power quality as per IEC/IEEE standards. Asymmetrical converter functions as an isolated buck-boost during positive cycle (PC) and works like an isolated SEPIC during negative cycle (NC) of the source voltage. The sandwiching of a fourth order converter with a second order converter lowers the system’s net order. The input inductor of the NC converter takes care of harmonics during NC, and the same inductor, along with an external capacitor, acts as a filter during PC and thus omits the need for a filter. In this work, the system is designed to function in null current switching (NCS) mode. NCS mode requires less rating/smaller components and senses DC link voltage only, unlike non null current switching (NNCS), which needs high rating/larger components along with additional sensors to sense source voltage and current. The use of this asymmetrical converter in NCS mode eliminates the bridge rectifier, a low pass filter, network completion diodes (generally used in bridgeless configuration), and extra sensors, resulting in system efficiency and compactness. Elaborated mathematics, state space models, and stability analysis of the converter are added in the article to check the stability of the presented converter, and outcomes of the system under different conditions are presented and studied to verify the working of the system.