Research On Control Strategy Of SSSC Device For Power Flow Control In Power Supply Network

Static synchronous series compensation (SSSC) as a important device of power flow control in flexible AC transmission technology, it can control the polarity and size of output active power. According to the real-time parameter compensation system and operation demand, SSSC realized to adjust the power flow flexibly, improved the transmission capacity and the system dynamic stability.The capacity of SSSC conventional topology was smaller, which output lower voltage level and had more harmonics. In order to solve the problems, the topology of inverter cascade combined with independent three-phase coupling transformer for main circuit was proposed in this paper. Applying the topology based on the modulation techniques of unipolar octave CPS-SPWM can improve the frequency of equivalent switching and reduct device loss as well as output harmonics.Combined with topology structure for the device, a new control strategy was put forward. A mathematical model for cascaded SSSC with LC filter was builded, obtained relationships between input and output from the model, then formed the overall control strategy, which can divided into three parts. The first one is software phase-locked loop (SPLL) for detection method based on separation of space vector; The second is double-close-loop control for inverter output side with current loop and voltage outer loop; The third is capacitor voltage balance and stable control strategy for DC side. Finally output amplitude and phase for the sinusoidal modulation signal, which guided to drive cascade inverter input the right signal, that making SSSC output compensation voltage as the given value.Finally, the SSSC system model based on cascaded topology was established in MATLAB. The unipolar frequency multiplication CPS-SPWM modulation and control strategy were applied in this model. Simulated the open-loop control system in detail to test and looked for the principles and rules of active control or impedance regulation. Then, simulated the closed loop system, got the expected effect, verified the validity of the control strategy.