| China Southern Power Grid Corporation plans to complete the multi-terminal HVDC transmission project of Wudongde Power Station in 2020(the starting point is Yunnan,and it will be located in Guangdong and Guangxi).The initial delivery scale is 5 million kilowatts,and the long-term is 8 million to 10 million kilowatts to ensure the consumption of Wudongde Power and improve the flexibility of power delivery.As the first hybrid multi-terminal UHVDC project in Yunnan Power Grid,it is bound to put forward new requirements for the grid structure and power grid security of the Yunnan province.Relying on the scientific and technological project of "Yunnan Power Grid's Adaptability to Wudongde Multi-terminal HVDC and Related Measures",this thesis researches on the operation characteristics and control strategy of Wudongde hybrid multi-terminal HVDC and the coordination of Wudongde hybrid multi-terminal DC and Yunnan power grid.Firstly,this thesis builds the electromechanical transient model and electromagnetic transient model of Wudongde hybrid multi-terminal HVDC.The self-defined modeling mechanism of hybrid multi-terminal HVDC based on PSS/E is studied.The electromechanical transient modeling of multi-terminal hybrid HVDC system is completed on PSS/E electromechanical transient platform.The modeling mechanism of the hybrid MMC converter electromagnetic transient model based on full-bridge sub-module and half-bridge sub-module is studied.The electromagnetic transient modeling of hybrid multi-terminal HVDC system is completed in PSCAD/EMTDC electromagnetic transient platform.The accuracy of the constructed model is verified by the comparison of steady-state power flow and dynamic simulation in PSS/E and PSCAD/EMTDC.Secondly,this paper studies the operating characteristics and control strategy of Wudongde hybrid multi-terminal HVDC.The operation characteristics of Wudongde hybrid multi-terminal HVDC during power down operation and voltage reduction operation are analyzed.Wudongde hybrid multi-terminal HVDC can operate stably under these two conditions.The HVDC fault control strategy is proposed.When the HVDC line fault of Wudongde hybrid multi-terminal HVDC is happened,the LCC converter station in Yunnan side is inverted,and the hybrid MMC converter station on the Guangxi side and the Guangdong side is locked,so that the fault current can be quickly cleared.The operation characteristics of the U-dode hybrid multi-terminal HVDC in the DC line fault under the DC fault control strategy are analyzed.The coordination strategy between hybrid multi-terminal HVDC converter stations is proposed.When the Guangdong side converter station that controls the HVDC voltage exits for some reason,it immediately informs the Guangxi side converter station that the fixed power control is converted to the constant HVDC voltage control,so that the DC voltage can be effectively control.The effectiveness of the coordination strategy is verified by simulation.Finally,this paper studies the influence under the Wudongde hybrid multi-terminal on frequency stability of Yunnan power grid.Based on the analysis of the single HVDC control method,a multi-circuit HVDC coordinated control strategy is proposed for the high cycle cutting machine caused by the system frequency crossing caused by the bipolar blocking of the Wudongde hybrid multi-terminal HVDC Yunnan and the Guangdong side.The active power that Wudongde multi-terminal HVDC can't send due to the blocking fault is sent out through other HVDCs of Yunnan Power Grid,thus ensuring the frequency stability of Yunnan Power Grid.The simulation analysis of PSS/E is used to verify the effectiveness of the proposed multi-circuit HVDC coordinated control strategy. |
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