| At present,China’s wind energy resources and load centers are inversely distributed,and the supply and consumption of energy are extremely unbalanced.Therefore,China has implemented the strategy of transmitting electricity from west to east,achieving maximum wind power consumption and long-distance transmission through high-voltage direct current transmission lines.When a DC fault occurs in a large-scale wind power transmission system,severe transient overvoltage(TOV)phenomena will occur at the transmission end,and may even cause wind turbine disconnection or system collapse.Therefore,starting from the mechanism analysis,this paper proposes an overvoltage suppression strategy that comprehensively considers the control system performance and reactive compensation,and achieves a better suppression effect.The main work is as follows:Analyzed the mechanism of transient overvoltage.Based on the equivalent two machine model with wind field,the transient change process of the bus voltage at the sending end was discussed in stages.The reactive power conversion and the response of various control links were comprehensively considered,and the causes of overvoltage after commutation failure and bipolar locking fault were explored.Then,based on the power supply system model,an estimation method for transient voltage rise was proposed,and the mechanism of wind turbine overvoltage generation and the mechanism of wind turbine disconnection from the power grid were analyzed.Finally,the suppression law of overvoltage levels was studied based on wind power output,electrical distance between wind farm and converter station,wind turbine control mode,and DC transmission power,and simulation verification was conducted.Studied the overvoltage suppression effect of DC and fan control parameters.Screen the control links closely related to overvoltage from the mechanism analysis,and derive the suppression law of overvoltage levels by control parameters such as proportional integration coefficient and time constant.Subsequently,through simulation and verification of the two machine model,the key control parameters with the greatest impact on overvoltage were selected based on the Ttrack Violation Indicator and the Transient overvoltage Suppression Index,taking into account the impact of parameters on the dynamic performance of the system.Studied the overvoltage suppression effect of dynamic reactive power compensation equipment.Exploring the mechanism of static var compensator(SVC),static synchronous compensator(STATCOM),and synchronous condenser(SC),and establishing a controller model,comparing the key performance of each device.The condenser has certain advantages in reactive power response ability,response speed,and other aspects,and is more practical in most cases.By comparing the economic costs and suppression capabilities of different devices with different capacities in a two machine system,the theoretical analysis of performance was validated,and a certain basis was provided for the initial selection of devices in different scenarios.A transient overvoltage suppression strategy based on improved imperial competition algorithm combined with time-domain simulation,which combines control parameters and dynamic reactive power compensation optimization configuration,has been proposed.On the premise of ensuring stable system operation,data transfer and interactive iteration of PSCAD-PYTHON-MATLAB were achieved,and real-time joint calls of time-domain simulation and optimization algorithms were completed,resulting in the optimal configuration scheme for suppressing overvoltage.Finally,the effectiveness and universality of the strategy were verified based on the two machine model and the improved 39 node model.This suppression strategy is of great significance in improving the planning and construction of large-scale wind power DC transmission systems,increasing line transmission capacity,promoting efficient wind power consumption,maintaining equipment safety,and grid stability. |
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