Parallel of Two Unidirectional AC–DC–AC Three-Leg Converters to Improve Power Quality

A unidirectional single-phase ac-dc-ac converter is proposed and analyzed in this paper. It is composed of paralleled rectifiers and inverters sharing two legs with two dc-link capacitor voltages. Models and a control strategy of the systems including circulating currents are developed. Compared to the conventional four-leg and three-leg (4L and 3L) single-phase ac-dc-ac converters, the proposed topology allows the decreasing of the current and power ratings of the power switches, the harmonic distortion, and semiconductors power losses. And compared to the unidirectional three-leg ac-dc-ac converter, it allows us to decrease the current and power ratings of the power switches and the harmonic distortion. In addition, a modified interleaved pulse width modulation (PWM) strategy using four-carrier PWM is presented, ensuring five-level voltage at the input and output sides of the converter. Simulation and experimental results are also presented to demonstrate the viability of the proposed circuit.