双馈抽水蓄能机组用中点箝位式三电平变流器损耗与结温分布

Loss and junction temperature distribution of NPC three-level converter in doubly-fed pumped storage unit

针对双馈抽水蓄能机组(DFPSU)运行工况转换频繁,分析不同运行工况下中点箝位式(NPC)三电平变流器功率器件损耗及结温分布。基于DFPSU运行特点,以机侧变流器单相桥臂功率模块为例,研究了不同运行工况下各个功率器件开关动作和电流通路,理论上分析了器件损耗分布不均现象;基于功率器件导通损耗和开关损耗计算模型,建立其热网络等效电路和结温计算模型,考虑DFPSU控制策略,并基于PLECS平台建立了NPC三电平变流器功率器件电热耦合仿真模型;对机组在发电、电动和调相运行工况下的器件损耗和结温分布进行仿真。理论分析与仿真结果表明,不同运行工况下器件损耗不同,变流器中间位置的主开关和箝位二极管的损耗和平均结温最大,且机组在同步转速点附近器件结温波动最大。

In view of the frequent conversion of DFPSU（Doubly-Fed Pumped Storage Unit） operating condition,the loss and junction temperature distribution of NPC （Neutral Point Clamped ） three-level converter under different operating conditions are analyzed. Based on operating characteristics of DFPSU, power module of single-phase bridge arm in rotor converter is taken as an example, where the switch motion and current path of power device under different operating conditions are illustrated, and the unequal loss distribution phenomenon of power device is analyzed theoretically. Then, the equivalent circuit of thermal network and the calculation model of junction temperature are proposed according to the calculation model of conduction and switching loss. The electrothermal coupling model of NPC three-level converter is established on PLECS platform, in which the loss and junction temperature of power device are simulated under the operating conditions of generation, motor and phase modulation. The theoretical analysis and simulative results indicate that the device loss varies with operating conditions of pumped storage system, and the most dangerous devices in NPC three-level converter are the middle switch and clamp diode. In addition, the biggest junction temperature fluctuation of power device occurs near the synchronous speed.