Junction Temperature Analysis And Modulation Strategy Research Of IGBT Module In Three-level Converter Used In Doubly-fed Pumped Storage Unit

Adjustable speed pumped storage unit used double-fed machine not only improve operation efficiency of pump-turbine,operating conditions and capacity of independent frequency modulation,but also enhance system stability by fast adjusting active power and reactive power.Neutral Point Clamped topology of three-level converter is usually chosen in double-fed pumped storage unit.Complexly flow current during switching process cause unequal loss and junction temperature distribution of three-level converter,influencing operating reliability and lifetime of converter.Thus,to further improve the reliability of three-level converter used in doubly fed pumped storage unit focusing on unequal junction temperature distribution of IGBT modules,the IGBT thermoelectric coupling model,the change rules of junction temperature and improved modulation strategy are studied in this paper.The main contents of this thesis are followings:(1)Base on the topology of three-level converter used in doubly-fed pumped storage unit and combining control strategy of double-fed machine,system control strategy of doubly-fed pumped storage unit is built and performance simulation is carried out.First,model of three-level converter and control strategy of double-fed machine are built.Then,based on control methods of stator voltage oriented and grid voltage oriented,system control strategy of pumped storage unit is established.Finally,operating performance of generating,motoring and phase modulation is analyzed by simulation.(2)Regarding with the issue of unequal loss distribution in three-level converter caused by complexly flow current,equivalent thermal network and calculation model of junction temperature of power device are built to analysis loss and junction temperature distribution in three-level converter under different operating conditions.First,based on operation feature of pumped storage system,power module of single-phase bridge arm in rotor converter is taken as an example to study power device switch and current path under different operation conditions and analysis unequal loss distribution of power device in theory.Then,based on the calculation model of conduction loss and switching loss of power device and combined the equivalent thermal network with calculation model of junction temperature,electric and thermal coupled model of NPC three-level converter is established on PLECS platform with control strategy of pumped storage system.Finally,simulation analysis on loss and thermal distribution of three-level converter under generating,motoring and phase modulation is researched.(3)Regarding with the issue of unequal loss distribution in three-level converter used in doubly fed pumped storage unit,an improved modulation strategy is proposed to depress loss of power device in three-level converter.First,based on three-level space vector diagram,implementation process of space vector modulation is analyzed.Then,by reducing working time of device of largest loss device in different region and considering impact on neutral point,short vectors are used to form improved strategy.Finally,based on improved strategy in rotor converter,simulation analysis of thermal performance in rotor converter are carried out under generating and motoring.(4)Based on DSP control technology,three-level space vector modulation strategy is designed and experiment platform of inverter circuit used three-level converter is set up to analyze and verify the distribution of three-level converter.The combined junction temperature simulation model of three-level converter used in double-fed pumped storage unit established in this paper can provide support for the accurate calculation and analysis of the junction temperature,the proposed loss depression strategies can provide technical support for the improvement of the control strategy of converter.