Sensorless operation of active damping methods for three-phase PWM converters

The three-phase PWM (active) rectifiers with bi-directional power flow and regulation of power factor to unity become to be more popular. These converters are connected to the supply network through inductance or LCL filter, what ensures attenuation of switching harmonics. LCL filter is more effective and reduce harmonic distortion at lower switching frequency, however such solution brings stability problems. In order to assure stable operation either a damping resistor or active damping algorithm has to be used. However, extra resistor causes additional losses and active damping algorithm usually needs extra sensors. This paper shows possibility to eliminate AC voltage sensors in two active damping methods making them more reliable and inexpensive.