Research On Additional Frequency Control Of Island HVDC System

The distribution of China’s energy resources and load center is extremely uneven, and the implementation of "power transmission from west to East, mutual supply between the South and the North, nationwide interconnection" power development strategy, has become our country’s inevitable choice to improve energy efficiency, optimize the allocation of resources, ensure energy supply security. With its obvious advantages in large capacity and long distance transmission,HVDC has become an important technical means to promote the development of China’s electric power.With the continuous expansion of China’s major energy power base is built and put into operation, the size of the national interconnected power grid, "strong tonic" AC/DC hybrid transmission pattern gradually formed.In the AC system fault or normal circumstances, a HVDC system with a delivery end of AC system island operation can be arranged, due to the operation at both ends of the system depends only on the DC line contact, grid structure is relatively weak and sending end lack the support of AC power grid, if the control strategy when not, will seriously affect the safe and stable operation of the system, and even the emergence of a large area blackout.Therefore, it is of great significance to study the operational stability of the isolated island operating system, especially the frequency stability of the system.In this paper, the general situation and research status of sending end islanded engineering at home and abroad, controllability of HVDC transmission system is analyzed in detail, and basic controller of HVDC system control part of the principle and operating characteristics, and describes the control principle and types of appendages in HVDC transmission system.Then,according to Tian-Guang HVDC project’s actual parameters, PSCAD/EMTDC electromagnetic transient simulation software is used to build a detailed model of the bipolar 12 pulse HVDC transmission project, and verifies the accuracy of the built model.Then, a brief overview of the development situation and research status on extension was made, detailing the by extension of discipline development and extension control theory and extension principle and structure of the controller. Based on HVDC control system’s research present situation and its own characteristics, using improved extension control method, to send the end of the AC system frequency deviation and differential as the characteristic quantity of the controlled system design a kind of extension of HVDC supplementary controller is used to adjust the control of DC transmission line DC power connection based on inhibition of island send HVDC systems because of the power imbalance caused by the oscillation of the system and improve the frequency stability of the system.To verify the designed controller is appended to the effectiveness of extension, on the basis of Tian-Guang HVDC project’s detailed model,building the extension additional controller and conventional supplementary controller model, and verifying the accuracy of the built model. Islanded operation, set the sending off the machine, the converter AC bus single-phase grounding short circuit and DC monopoles block three fault, simulated and analyzed the in conventional supplementary controller and an extension of the additional controller under send the frequency stability of the end system, the results show that based on extension control theory of the additional controller has more satisfactory control effect.