Three-phase four-wire active front-end feeding a three-level voltage source inverter

A four-wire two-level active front-end (AFE) interlacing a three-level voltage source inverter (VSl) to the utility network is proposed. The AFE consists of a classical three-phase four-wire ac-dc boost rectifier with two split-capacitors. It absorbs almost sinusoidal currents with unity power factor. Moreover it is controlled in order to guarantee the dc-levels balancing. With reference to the control algorithm of the AFE a new robust synchronization mechanism to detect the phase angle of the positive sequence of the node voltages is proposed. Numerical simulations show the effectiveness of the proposed AFE applied to feed an induction motor based adjustable speed drive (ASD) controlled by means of a field oriented control (FOC) technique.