全桥型模块化多电平换流器损耗简化计算模型研究

Research on simplified loss model of full-bridge modular multilevel converters

半导体开关器件损耗特性的非线性以及全桥子模块开关状态的多样性,对全桥型模块化多电平换流器(MMC)损耗的精确计算提出了挑战。目前常用的基于仿真软件的查表法虽然能够较准确估算MMC损耗,但计算速度慢。对此,本文提出了一种基于桥臂电流有效值和绝对值的全桥型MMC简化损耗计算模型。该模型在考虑全桥子模块在调制时输出负电平的开关状态的基础上,分别推导出换流器的通态损耗和开关损耗的数学表达式。同时在忽略二倍频谐波环流分量的前提条件下,用直观的解析表达式描述了全桥型MMC的损耗特性,并能够快速计算多种工况下的损耗。最后,本文采用简化损耗模型和基于仿真软件的查表法,分别计算换流器的损耗,并对两种计算方法之间的损耗计算误差进行分析。PSCAD/EMTDC仿真结果验证了所提简化损耗模型的准确性。

The nonlinear loss characteristics of the semiconductor devices and the variety of the switching patterns impose great challenge on calculating the loss of full-bridge modular multilevel converters(MMC)accurately.The commonly used loss calculation methods are based on table-look-up of the IGBT module datasheet by using simulation software.These methods have high calculation accuracy,but the calculation speed is slow.This paper presents a simplified full-bridge MMC loss model based on the RMS and absolute value of the arm current.The negative levels during the modulation of the full-bridge MMC are considered in this model.And the analytical expressions of the conduction loss and the switching loss are derived.Then the loss characteristics of the MMC can be described explicitly and the loss can also be calculated fast under different operation conditions without the harmonic circulation current.At last the loss results are calculated by using the table-look-up method based on PSCAD/EMTDC and the presented loss model.Meanwhile the calculated errors between them are analyzed.Analysis simulation results verify the accuracy and correctness of the proposed loss model.