Stability investigation of control system for power electronic converter acting as load interface in AC distribution system

This paper presents the tuning techniques for the control system of the regulated loads in AC distribution system. A mathematical model of a voltage source converter based power electronic load in synchronous reference frame is considered with the implementation of vector control. The transfer function for the voltage and current control loops are derived. A frequency domain analysis based on the derived analytical expressions is performed with the decreasing values of the grid voltage. The analysis confirms the decrease in phase margins with the decrease in grid voltage. A time domain simulation analysis is carried out to validate the results from frequency domain analysis. The control system shows a very stiff control up to 0.6 pu decrease in grid voltage. A similar simulation study proves that the converter control system is more robust and stable in generation mode.