Keywords: hybrid front-end converters, active front-end converters, power flow control, capacitors, voltage source converters, harmonic resistance
A power-flow control method for hybrid active front-end converters
The hybrid active front-end converter, which is composed of a capacitor and a voltage source converter in series connection, has been presented recently. Compared with grid-connected converter, the hybrid converter could be operated with reduced dc voltage as well as small-sized passive filters due to series-connected capacitor. This paper presents a power flow control method for a hybrid active front-end converter. Real power of the converter is controlled by the output voltage vector perpendicular to the grid voltage, whereas reactive power of the converter is determined by the output voltage vector parallel to the grid voltage. By dynamically adjusting voltage vector, power conversion between low-voltage dc side, such as PVs or batteries, and high-voltage grid side could be accomplished with no low-frequency transformer required. In addition, a harmonic resistance is emulated in the proposed method to avoid inrush current flowing into the converter due to unintentional voltage spike coming from the power system. Operation principles are explained in detail, followed by both computer simulations and experimental results validating effectiveness.