A Modified Droop Control Method for Parallel-Connected Three-Phase Inverter in Railway Auxiliary Power Supply

In this paper, a modified droop control method is proposed to minimize variation of common bus voltage. The proposed control method models line impedance between load and auxiliary power supply to compensate for voltage drop of power line. The expected voltage drop of the modelled line impedance is mathematically analyzed and applied to the traditional droop curve to design the modified drop equation. The controller has a cascaded structure with inner current and voltage control loops and outer power control loop. A droop curve for power control is applied a modified droop equation to reduce the load voltage drop due to the line impedance. The validity of a modified droop control is verified using two 85kVA auxiliary power supply units connected in parallel.