| The ±800kV UHV DC transmission project is the world’s highest voltage-level DC transmission project currently.Its high voltage level,large transmission capacity and long-distance transmission economy are more and more suitable for China’s domestic power grid technical requirements,regional power grids and delivery requirements.One of the core technologies of UHV DC transmission technology is the DC control protection logic and strategy.This article is based on the analysis of the basic principles and control and protection configuration of Yunguang UHV,Puqiao UHV DC control,focuses on the important role of forced phase shifting technology in the control and protection of UHV DC transmission systems.The so-called forced phase shift is that during the failure of the HVDC transmission system,the control system increases the firing angle α of the rectifier to 120°~160°rapidly,The rectifier operates as an inverter,allowing the energy in the HVDC system to be sent back to the AC system in a short time.Forced phase shifting is a common protection strategy for DC transmission projects.Traditional DC transmission systems use forced phase shifting strategies in pole-lock,pole ESOF,and DC line fault restarts the same as throw bypass,lock trigger pulse,jump open AC switch.The ±800kV UHV DC transmission system also needs coordinated control of the two valve groups through forced phase shifting when the dual valve group operation valve group protection is for the single valve group ESOF.The logic principle and strategy of UHV DC control protection is the core key technology of UHV DC.Before focusing on the analysis of forced phase shifting technology.This paper summarizes the basic principles and control strategies of UHV DC control systematically before focus on analysis of forced phase shifting technology,especially for the actual operation of the light-triggered converter valve structure and the trigger angle control principle.Then the paper introduces the configuration and functions of the main control stages of UHV DC.On the basis of these,combined with the actual operation experience,debugging conclusion and recorded data of two ±800kV UHV DCs of Yunguang DC and Puqiao DC,the in-depth study of forced phase shifting function is under control,the important role in the protection strategy;combined with the design of the forced phase shifting function in the cloud-wide double-circuit DC control logic,the improvement measures are proposed at the same time.Main works in the paper mainly include:1)Carding UHV DC basic control functions and principles,especially the basic principles of fixed firing angle control and constant current control.It is theoretically derived how the forced phase shift changes the direction of the power flow and the variation of DC voltage and current.The basic structure of the converter valve of the DC system and the control mechanism of the firing angle are summarized,and the functions and functions of the control stages of the two clouds and DCs are summarized.2)Analyze the difference of forced phase shift phase shift between ±800kV UHV DC project ±500kV UHV DC project.List four cases of ±800kV Yunguang UHV DC project adopting forced phase shifting strategy,especially the forced phase shift adopted by DC fault restart function;study the control protection logic under various conditions between rectifier station and inverter station The combination of conditions,system voltage and current changes,listed several special protection functions that lead to forced phase shift.3)Discuss the important role of forced shifting relative to the coordinated control of the valve group,and analyze under which conditions the double valve group has the same operating characteristics in which case one valve group is isolated and stopped,and the other valve group is forced to phase shift;The ESOF signal of the valve group causes the forced phase shift function of the same-pole unlocking valve group to malfunction,find the source of the problem and propose related improvement measures. |
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