| Today,bundling wind and solar energy with traditional energy sources and using UHVDC transmission is a major form of large-scale new energy delivery.When the wind,solar and thermal bundling system is sent out by UHVDC,there is still a risk of transient overvoltage,which may cause the new energy station in the near area to go off the grid.It is of great significance to study the transient overvoltage characteristics caused by DC faults under the new situation of wind,solar and fire bundling delivery.Firstly,this paper uses PSCAD(Power System Computer Aided Design)simulation software to build the basic simulation model of the wind-solar thermal bundling UHVDC transmission system,and builds the doubly-fed wind turbine model,photovoltaic aggregation multiplication model and thermal power unit model respectively,and finally completes the construction of the wind-solar thermal bundling UHVDC transmission model according to the actual UHVDC transmission system in Northwest China.Then,taking the UHVDC transmission system in a certain area as an example,the effects of different wind and solar permeability,different new energy units from the converter bus and different DC transmission power on the transient overvoltage of the sending end system were simulated respectively.The simulation results show that with the increase of wind and solar permeability,the transient overvoltage peak does not have a specific change trend: under the lower permeability,the transient overvoltage fluctuation will be aggravated to a certain extent,and the overvoltage peak will be increased.When the permeability is higher than 15%,the transient overvoltage level is controlled as the proportion of wind and solar output increases.With the increase of the electrical distance between the new energy station and the rectifier side busbar,the transient overvoltage level also increases simultaneously.Similarly,with the increase of DC transmission power,after DC failure,the commutation bus voltage and the overvoltage level of the wind power grid connection point increase.Therefore,effective measures must be taken to reduce the impact of DC disturbances to ensure the stability and safe operation of the power system.Finally,by connecting dynamic reactive power compensation equipment to alleviate transient overvoltage at the sending end,the difference between different reactive power compensation devices for transient overvoltage suppression in the system is analyzed,and the capacity of the condenser is optimized by improving the DC control strategy.The above conclusion has certain reference value for the planning and construction of China’s multi-form energy bundling DC transmission project. |
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