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.