Control System Design for a STATCOM using Complex Transfer Function

This paper focuses on a new controller design for both AC output voltage and DC voltage sides of a 3-level voltage source converter (VSC) of STATCOM based on complex transfer function. With this approach, the current regulator control with two-input two-output for the AC side of VSC can be represented by a complex transfer function with single-input single-output. In addition, the complex pole-zero compensation by the complex proportional integral (PI) controller is proposed to eliminate the cross coupling effect between the real and reactive currents in the current regulator. As a result, the practical current regulator control loop can be implemented to control the AC output voltage of VSC. For the DC side, the DC voltage control loop is also established by a PI controller. Parameters of PI controllers in both AC and DC control loops are designed by modulus optimum and symmetrical optimum criteria. Simulation results by PSCAD/EMTDC show that the proposed controller provides superior stabilizing effects on the cross coupling over the decoupling control. Key-Words: STATCOM, complex transfer function, voltage source converter, decoupling control