Research On Reliability Evaluation Method Of HVDC Grid

With the global warming and the traditional fossil energy depleting,countries around the world are facing great challenges in the adjustment of the energy system,for the reason that the new energy resources revolution has emerged.However,the large-scale clean energy resources grid-connection brings difficulties to the operation of the AC power grid.Therefore,the development of next-generation power grid technology has become the main task of China's power system.With its flexible controllability,flexible DC technology promotes the flexible transmission and decentralization of clean energy in a wider area,becoming the key technology of the future development of power systems.At present,the DC power grid is still at the theoretical stage,and there are many forward-looking technical studies urgently to be researched before it is put into practice.In particular,the establishment of the reliability evaluation model of the DC power grid needs to be prioritized over the development and construction of the power grid.In view of the above background,this paper will carry out systematic research from the device-level,equipment-level and system-level to put forward a high voltage DC grid reliability assessment method.1)In order to perform device-level reliability evaluation,this paper starts with the physical failure process of IGBT devices,and establishes an MMC thermal model by analyzing the internal heat dissipation path of the press-pack IGBT sub-module.Extract multi-time scale junction temperature cycle information and estimate the life of the press-pack IGBT based on the fatigue cumulative damage theory and life model,and then predict the life of the sub-module.Identify the factors that limit the life of the device and propose a series of measures to increase the life of the sub-module.2)In order to perform equipment-level reliability assessment,this paper samples equipment life model parameters based on non-sequential Monte Carlo method to obtain equipment life exponential distribution.Using Copula function to construct the joint probability distribution of bridge arm reliability function obtains the sub-module life distribution function after correlation decoupling.Analyze the influence of redundancy,correlation coefficient and other factors on MMC reliability.3)In order to perform system-level reliability assessment,this paper extends the DC power flow model on the basis of AC power flow,considers the control strategy of the converter station,and establishes a DC power grid embedded AC power grid load reduction model.Use the second-order truncated state enumeration method to sample the system state and introduce state variables.Through reliability assessment and sensitivity analysis,quantitatively study the influence of control strategies and component reliability parameters on the reliability of DC grid embedded AC systems.