Multilevel VSC-HVDC Applied in Wind Power Integration

Higher transmission technology is needed to meet requirements of the development of large-scale wind power and its concentrated integration.Therefore,on the basis of the d-q vector orientated direct current control,we proposed an active power control strategy for voltage-source-converter high-voltage direct-current(VSC-HVDC) transmission that made the VSC-HVDC to adjust the transmission power real-timely and to keep the wind farm stable.Taking wind fluctuation and grid faults into consideration,we compared and analyzed AC transmission and VSC-HVDC schemes,and simulated the control strategy and both connection schemes by the software PSCAD/EMTDC.The simulative results show that the voltages of point of common coupling(PCC) and the DC voltage of receiving end can be both controlled as their reference values,and that the transmission power is consistent with wind power,meanwhile,the DC voltage of sending end changes according to power fluctuates.Compared with AC transmission,VSC-HVDC schemes appear to be more effective in controlling the voltage of wind farms at the reference value and stabilizing the voltage and frequency of wind farms during instant faults.