变频器的切换分析与同步控制

Analysis and Synchronous Control of Switching of Variable Frequency Device

在变频调速控制系统中,变频器经常需要从变频到工频的切换,切换时机不当会产生很大的电流,该电流对变频器、电动机等设备产生严重的冲击甚至损坏,并对电网产生严重的电磁干扰。在分析切换所产生冲击电流的原因和同步切换原理基础上,提出用同步器实现同步切换,并用PSCAD/EMTDC电磁暂态仿真软件对同步切换进行了仿真。结果表明:用同步器实现的同步切换有效地避免了过大的电流冲击,保证了切换的平稳过渡。

In the variable frequency control system, the variable frequency device often needs to switch from the converting to fundamental frequency. If the switching time is improper, then great electric current will emerge. The current will make serious impact on or even cause damage to such equipment as variable frequency device, motor, etc. , and will make serious electromagnetic interference with the power grid. Using synchronizer to real- ize synchronous-switching as well as using the electro-magnetic transient simulation software named PSCAD/EMTDC to simulate synchronous-switching were suggested on the basis of analyzing the reasons for generating impulse current and the principle of synchronous-switching. The result shows that using synchronizer can avoid great electric current impact effectively and ensure the smooth transition of switching.