| Recent years, with the rapid development of China’s economy, the demand of electric power is rasing continuously. Flexible AC Transmission System(FACTS) has been paid more and more attention.Static synchronous series compensator,as a new generation of FACTS devices, has broad application propects and development space. SSSC is serried in the transmission line, and used to improve the route of transmission capacity effectively without changing the original grid structure.In order to make large capacity of SSSC for the transmissionline, especially for the high voltage situation, the most common way is to enlarge the capacity of the inverter’s main circuit. Cascade multilevel structure has the advantages of easy to implement modular and extensible, thus in this paper, the H bridge cascade multilevel inverter is used in SSSC. Through the comparison and analysis of commonly used multilevel modulation method, the carrier phase shift PWM modulation methods is selected as modulation strategy in this paper, when the SPWM modulation technique is applied to H-bridge cascaded multilevel inverter, it can reduce the harmonic content in inverter’s output voltage, thus improving the output waveform. The basic principle and topological structure of static synchronous series compensator is expounded in this paper, the mathematical model of SSSC is put forward to using in the transmissionline. Limit factors of transmission ability is discussed and the specific principle of SSSC to improve transmission line transmission capacity is further studied. Also the corresponding control strategy of SSSC is propsed in the paper. A transmission line model with SSSC is set up in the MATLAB/Simulink platform, simulation result shows that SSSC can change the equivalent parameters of transmission line,and it has the ability to compensate reactive power of transmission lines and improve the active power capacity of transmission line. |
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