A control apparatus for a power quality device comprises: a power quality analysis module, for sampling a power supply network to obtain a power quality information, and performing an analysis and computing on the sampling, so as to output an instruction information; N tracking control modules, for receiving respectively the instruction information and tracking the instruction information, so as to output N PWM control signals having a same frequency and constant phase shift therebetween, where N is a positive integer and N≧2, thereby to control the power quality device; wherein the power quality analysis module and the N tracking control modules are operated based on a synchronized signal.