说明：  以LCL型三电平有源电力滤波器为研究对象，对其系统建模、并网锁相、控制系统设计、系统参数设计等关键问题进行了研究。
(Taking LCL type three level active power filter as the research object, the key problems of system modeling, grid connected phase locking, control system design and system parameter design are studied.)