Operation of One-Cycle Controlled Three-Phase Active Power Filter With Unbalanced Source and Load

The power quality of the ac electric system has become a great concern due to the rapidly increasing numbers of electronic equipment being connected to the grid. In order to reduce harmonic contamination in power lines and to improve its transmission efficiency, the research on active power filters (APF) has become a hot topic. Many control methods for APF were proposed in recent years. Among them, one-cycle control (OCC) has shown great promise featuring excellent harmonic suppression, simple circuitry, robust performance, and low cost for the control of three-phase APFs. Theory and experiments in previous papers have demonstrated the validity of OCC-controlled APFs working with balanced line voltages and balanced nonlinear loads. However, in reality, neither three-phase grid voltages nor three-phase nonlinear loads are balanced at all times; therefore, it is vital for an APF to be able to handle unbalanced sources and/or loads. In this paper, the OCC-controlled three-phase APF working with unbalanced three-phase line voltages and unbalanced loads are studied, respectively. Theoretical analyses and experimental results indicate that with OCC control, sinusoidal input currents can be realized, whether the input voltages and/or the nonlinear loads are balanced or unbalanced