A Control Strategy for a Series APF With Critical-Load-Bus Voltage Feedback That Avoids Injection Transformer Saturation

Series active power filters (APF) are an important solution to deal with power quality issues in weak grids under the presence of non-linear loads. The use of voltage feedback from the critical-load-bus (cload-bus) in the series APF allows for a control strategy that has performance and processing power advantages, when compared to other strategies in literature, but can cause saturation of injection transformers. This paper presents a control strategy that uses cload-bus voltage feedback with an additional control loop of the dc current in the output of the series APF voltage source converter (VSC), to avoid injection transformer saturation. The controlled dc current is additionally used for balancing the split dc-bus capacitors voltage in the VSC. The series APF and the proposed control strategy are modeled using small signal analysis for allowing controller design. Experimental results from a 3 kVA prototype are presented, with cload-bus voltage total harmonic distortion improving from 9% to 3% in each phase, while achieving the objectives of improved cload voltage waveform, controlled transformer dc current, and balanced dc-bus capacitors voltage.