Single-Phase Transformer-less Dynamic Power Flow Control of Transmission Network using Cascaded Converter based SSSC

Three-phase static Synchronous Series Compensators (SSSC) are being used to resolve the non-uniform loading of transmission lines in an existing interconnected system by controlling the flow of power. Implementation of a three-phase SSSC is complex owing to its intricate control structure, complex PWM techniques and its requirement of a coupling transformer to be connected to the grid. This paper presents a complete implementation of a single-phase cascaded converter topology for the SSSC. The proposed system is implemented by IGBTs based Voltage Source Converters (VSC) which consists of 5 H-bridge modules per phase connected directly in series with the line without a coupling transformer. A simplified direct voltage control system employing a PID regulator is implemented using Pulse Width Modulation (PWM) technique to control the magnitude of the injected voltage. The dynamic performance of the SSSC is investigated on PSCAD/EMTDC simulation tool in inductive operation mode and the effect of the variation of the injected voltage level on power flow is observed. For the synchronization of SSSC with the grid, SOGI-PLL is implemented which provides a better steady-state and dynamic performance. It is seen that SOGI-PLL provides accurate tracking of the grid parameters even in the presence of harmonics and distortion.