A new hybrid power flow controller topology and control based on three-level NPC inverter

With the large-scale integration of new energy into the power grid, the problem of uneven distribution of power flow is prominent, seriously affecting the reliability and flexibility of the power grid. Therefore, there is an urgent need for means to improve the power grid dynamic control capability of power flow. Firstly, a new hybrid power flow controller (HPFC) based on a three-level neutral point clamp (NPC) inverter is proposed in this paper, combined with a phase-shifting transformer (PST) large discrete adjustment and three-level NPC small-range flexible adjustment to achieve precise control of large-scale power flow. Secondly, the working principles of PST and three-level NPC are theoretically analyzed, a control strategy for synergy between the two is proposed, and the overall operation mode and working scope of HPFC are determined. Finally, taking the 220 kV double-circuit line as the application scenario, the effectiveness of the proposed new HPFC control strategy and its ability to control the power flow were verified through simulation on the PSCAD/EMTDC platform. The results show that the proposed new HPFC effectively optimizes the shortcomings of the traditional two-level voltage source converter (VSC) output with high harmonic content, it can achieve large-scale flexible control of power flow, and can also quickly and accurately respond to dynamic scenarios where the target power flow changes frequently.