Multi-time Scale Reliability Evaluation And Customized Design Of The Power Electronics Devices Of MMC In Wind Power System

Modular Multilevel Converter(MMC)has been widely used in wind power systems due to its advantages of high waveform quality,low switch loss,convenient expansion and maintenance.In wind power system,MMC works in complex conditions.The outputs of MMC fluctuate severely and frequently for a long time.Its core components,power electronics devices IGBTs,are subjected to thermal loads for a long time,so IGBTs are also the most vulnerable components of the converter.It is of great significance to the design,long-term safety and reliability of the operation and maintenance of wind power system to disscuss the reliability,design and selection methods of IGBTs.In this paper,multi-time scale reliability evaluation and customized design of IGBT modules of MMC in wind power system are carried out.The main contents of the research are as follows:First of all,according to the multi-time scale characteristics of various influencing factors in wind power system,the factors is divided into short time scale,long time scale and full lifetime scale to evaluate the reliability of power devices in the wind power system.In the short time scale,the chip failure mode of the device is concerned to avoid the junction temperature exceeding the upper limit.The long time scale and the full lifetime scale focus on the package failure mode of the device.It extracts the junction temperature curve in a long term by means of numerical iteration,considering the influence on the device lifetime of the fundamental and low frequency junction temperature fluctuation.In full lifetime scale,it considers the influence of the power device aging on the device lifetime at the same time.Secondly,according to the current stress disequilibrium characteristic of IGBT module of MMC in wind power system,the chip area of IGBT module is reasonably customized by means of multi-objective optimization,so as to improve the device utilization rate and reduce the design margin.As a results,it can achieve the comprehensive optimization of chip cost and full lifetime scale average loss of IGBT under the premise of ensuring reliability.Last but not least,before the project is under operation,the reliability and feasibility of the design need to be tested first.Therefore,a test platform is designed to reproduce the stress of power devices under the actual working conditions of MMC.In the test circuit,the H-bridge current source works in high frequency to produce a smooth test current to ensure the equivalence of current stress.The switching signal of low frequency is applied to the module under test to reproduce the switching stress of the MMC.Capacitance voltage controller is designed for the tested module and auxiliary module to ensure the normal operation of the test circuit.Based on it,the experimental prototype of the test circuit is built.The selection of hardware parameter of the main power circuit of the test circuit is deduced.The software design method is given in this paper as well.The experimental results show that the test platform can reproduce the stress information of MMC power device.