Nonlinear PID controller of H-bridge cascade SSSC top level control

As a series FACTS device based on Voltage Source Converter (VSC), Static Series Synchronous Compensators (SSSC) can optimize power flow and improve power system stability by controlling the line impedance rapidly. According to the three levels control structure of SSSC proposed in this paper, when SSSC middle level control operates at constant impedance mode, it has characteristic of controllable impedance as viewed from the top level. In this paper, the output of SSSC is equivalent to controllable impedance and then affine nonlinear equation of the single machine infinite bus (SMIB) power system including a SSSC can be obtained without the compound coordinate transformation approach which is proposed by other documentation and the feedback exact linearization method can be used directly to obtain the SSSC top level nonlinear controller. For avoiding solving the partial differential equation, the direct method is used to realize the exact linearization simply and conveniently. For overcome the shortcoming of low robustness of exact feedback linearization approach due to uncertainty of parameters and model of controlled system, the nonlinear PID control is used to design the SSSC top level controller. Finally the paper applies Real Time Digital Simulator (RTDS) to validate the feasibility of the proposed modeling and control approach in damping out power system oscillations.