A PWM Rectifier Control Technique for
Three-Phase Double Conversion UPS under Unbalanced Load
Min Dai, Mohammad N. Marwali,
Jin-Woo Jung, Ali Keyhani
Ohio State Univ., Columbus, OH, USA
Twentieth Annual IEEE Applied Power Electronics Conference
and Exposition, APEC'05, Vol. 1, pp.548-552, March 2005
Date: March 6-10, 2005
Location: Austin, TX
Abstract:
PWM rectifiers are widely used in three-phase ac-dc- ac systems due to its
capability in dc voltage boost and regulation, input power factor correction,
and input current harmonic control. However, with the conventional rectifier
control technique, the input current tends to be unbalanced under unbalanced
inverter load, which contaminates input power source and is therefore
undesirable. In this paper, the cause of the unbalancing is disclosed by
evaluating the spectra of the switching functions of the full bridge three-phase
inverter analytically using Bessel function under standard space vector PWM
switching scheme, which relates the dc link current and voltage ripples to the
inverter load balancing. The analysis shows that the dc link voltage contains
significant second order harmonic component which affects the voltage loop of
the rectifier controller, especially when the control gain is high. A notch
filter based voltage control loop is proposed to eliminate the second harmonic
component in the dc-link voltage feedback signal and achieve balanced three
phase input currents. Simulation and experimental results are presented to
demonstrate the effectiveness of the proposed control technique in decoupling
the rectifier and the inverter under unbalanced load.