Study On Operation Characteristics Of Hybrid HVDC Transmission System With New Energy

Due to the characteristics of the distribution of energy in China,the demand for electric energy in South China and East China is large,while the “Three North” and the West Inner Mongolia have a large amount of electricity.There are constraints such as grid constraints and self-volatility.The number and capacity of the original transmission systems can no longer meet the needs of modern economic development.Many HVDC transmission lines are simultaneously located at the same load center.A large number of applications in densely populated areas have formed a hybrid multi-infeed HVDC transmission system that not only ensures grid stability,but also improves new energy consumption.The advantages and disadvantages of a large number of complex DC grid structures in new energy consumption and system stability issues need to be verified.The development and utilization of large-scale new energy has formed many regional energy bases.Energy bases can be integrated into the confluence station for grid connection in various ways,and then sent to the receiving channel through the current source type direct current(LCC)delivery channel.End grid.Hybrid multi-infeed HVDC(H-MIDC)consisting of a Voltage Source Converter HVDC(VSC-HVDC)system and an LCC-HVDC system for improving new energy consumption is discussed.The feasibility of grid-connected,the topology of the grid-connected mode and the traditional AC grid-connected method are constructed.The simulation model is built in PSCAD software.The hybrid multi-feed and traditional multi-feed transient characteristics are based on wind farm fault perturbation method.An analysis was made to explore the fault recovery capabilities of the two systems.The conclusion is: when the three-phase short-circuit fault occurs in the wind farm,the hybrid grid is more connected to the traditional AC,and the voltage and current are less affected.The recovery rate is fast,the power fluctuation is small,and the transient power quality is improved.In view of the problems of large reactive loss,high risk of commutation failure and poor transient stability of traditional double-induction HVDC transmission system,consider combining STATCOM and MMC to form mixed double-feed high voltage based on traditional dual-induction HVDC transmission system.HVDC transmission system to improve the transient operation characteristics of LCC-HVDC.Firstly,the topological structure of different hybrid dual-infeed systems is analyzed comprehensively and the effectiveness of its related control strategies is described.Then,the electromagnetic transient simulation model of hybrid HVDC transmission system is built,and CFII and CFPI indicators are introduced to quantitatively evaluate different hybrid DC transmission systems.The influence of the immune characteristics of the LCC-HVDC subsystem commutation failed,and the indicators were compared and analyzed.Finally,the improvement effects of different subsystems on the transient operation characteristics of the LCC-HVDC system were studied.The results show that compared with the traditional HVDC transmission system,the reactive power compensation link in the hybrid double-fed DC transmission system can effectively adjust the common AC bus voltage,so that the equivalent strength of the receiving AC system is enhanced,thus suppressing the change.The phase fails to improve the transient operation stability of the HVDC transmission system.