Quasi-resonant DC-link control of three-level active power filter

This paper presents a three-level three-phase four-wire active power filter with a quasi-resonant dc-link (QRDCL) soft-switching auxiliary circuit. The three-level quasi-resonant dc-link circuit is constructed by two symmetrical two-level quasi-resonant dc-link snubbers and each snubber can be operated independently. Its operating principle is presented in this paper. Additionally, a direct pulse width modulation (PWM) is employed which can simplify the calculation and can be easily implemented in a digital signal processor (DSP). Simulation of the three-level soft-switched active power filter is provided. Switching losses between the hard switching and soft switching of active power filter is also illustrated.