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Owing to simplicity, lower total harmonic distortion, and higher power factor benefits, the 12-pulse uncontrolled rectifiers with a coupling interphase reactor are widely used as the power factor correction (PFC) converters, which are inserted between the power grid and the non-linear loads. However, the key parameters of the 12-pulse rectifier, such as transformer ratio, coupling coefficient and self-inductance of interphase reactor, and the capacitance of filter capacitor, are generally designed by trial and error, which is complicated and inefficient. In order to offer a useful reference for engineers to design the 12-pulse rectifier, a simply design program is proposed considering current ripple and output voltage ripple. Subsequently, optimized parameters of the 12-pulse rectifier are obtained after running the design program. Therefore, the rectifier can work in high performance with smaller size. Finally, the correctness of the theoretical analysis and the effectiveness of the proposed design program are validated by simulation results.

Thanks to sensor-less and simplicity benefits, the filter-based active damping, being directly plugged into the current regulator, is attractive for the $LCL$ -filtered grid-connected inverter. Typically, the notch filter (NF) is employed and yields a good damping effect when the notch frequency $f_{n}$ is placed higher than the $LCL$ resonance frequency $f_{r}$ . However, for the frequencies above $f_{n}$ , excessive phase lead is provided, worsening the damping effect and giving rise to limited robustness. To address this issue, a quasi-notch filter (QNF) is proposed in this paper, which provides suitable phase compensation to cover a wide range of $f_{r}$ up to the Nyquist frequency $(f_{s/2)}$ . As a result, the high robustness against the variations of $LCL$ parameters and grid impedance can be achieved. The effectiveness of the proposed method is validated by experimental results.

The single-loop weighted average current (WAC) control is attractive for the LCL-type grid-connected inverter owing to its inherent active damping. High robustness can be naturally harvested without any additional damping methods, but it requires two current sensors. Depending on the different weight values, a family of the splitting current single-loop control schemes with the associated filter configurations is developed in this paper, where only one current sensor is needed. As a result, high robustness, high-quality grid current and cost-efficiency can be concurrently achieved. Finally, experimental results from a 6-kW setup confirm the effectiveness and practicality of the splitting current single-loop control.