Three-phase buck active rectifier with power factor correction and low EMI

High-power DC applications often require power factor-controlled rectification from the three-phase grid, where the specifications of the IEC 1000-3-2 or IEC 1000-3-4 standards concerning low-frequency harmonics of the line current have to be met. Passive rectifiers with futed output voltage can be compensated by an active power filter that injects the reversed harmonic and reactive fundamental line currents drawn by the rectifier into the grid. The most common topology for power factor-controlled rectification is a boost converter with the disadvantage of a minimum DC voltage. The demand for a variable DC voltage in the range of 0-490V, with or without load and a power factor approaching unity, has led to the development of the proposed buck active rectifier. This rectifier is split into two buck converters, each one connected to the neutral line. This reduces radiated EM1 and allows compensation for unbalanced supply voltages. The switching frequency of > 30kHz eases filtering. Owing to the intrinsic safety of buck converters, misoperations by the controller will not destroy the power circuit. The one-step conversion yields excellent efficiency. The rectifier is controlled by a low-cost 8-bit microcontroller, without the need for line current feedback. A prototype for 12kW at 2301400 VAC has been developed and tested.