Research On Control Strategy Of Fault Ride-through Of Integrating Wind Farm Based On D-PMSG Using MMC-HVDC

In the increasingly tense situation of energy, new energy development is particularly important. Wind energy has extensive attention and in-depth study as it’s a kind of clean and sustainable new energy. In the years of development of wind energy, direct-driven permanent magnet synchronous generator(D-PMSG) become the tend of the future of the wind energy development because it has many advantages such as it has no gearbox, no brushes and separates the generator and the grid. With the increasing scale of wind power,more demands are proposed by the grid for large-scale wind farm integrating, fault ride-through capability of wind farms is one of the demands.The integrating of wind farms based-on voltage source converter HVDC(VSC-HVDC), not only solves the problems of integrating wind farms with large scale and long distance,but also improves fault ride-through capability of wind farms. Modular multi-level converter(MMC), a new topology of VSC, receives many attentions because of its unique advantages and becomes a hotspot both in research work and actual project. Integrating with MMC, can not only improve the transmission capacity, but also improve the characteristics of integrating wind farms and fault ride-through capability.First, this paper analyzes the mathematical model and control theory of the direct-driven permanent magnet synchronous generator. An electromagnetic transient model of D-PMSG is built in PSACD/EMTDC, and then the wind farm is built. Second, the mathematical model of MMC-HVDC system and the control theory of the converter are studied. The converter controllers of the both terminal are improved because of the demands of the integrating wind farm. An electromagnetic transient model of the system of integrating wind farm based-on MMC-HVDC is built in PSACD/EMTDC, the result of the simulation verifies the correctness of this model. Then the fault characteristics of different faults of the integrating system is analyzed. For the fault in the wind farm side, the fault ride-through capacity is needed by the D-PMSG. The balance of active power is guaranteed by adding a DC chopper, to protect the security and stable operation of the converters and the system of S-PMSG. For the fault in the AC system, a DC chopper is added to guarantee the balance of active power firstly, then pitch angle of D-PMSG is controlled to avoid the danger by the DC chopper which is works for a while.The pitch angle is increased to reduce the active power of the generator, to achieve the fundamental balance of active power.Finally, simulations are provided for different faults in PSCAD/EMTDC. The results of the simulations verify feasibility and correctness of the control strategy of the fault ride-through by this paper,the fault ride-through capability of the integrating wind farm based-on MMC-HVDC is improved.