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In this study, some issues of voltage sags in the AC mains are discussed. The characteristics of voltage sags and the SEMI F47 requirements are outlined. Existing solutions to solve the voltage sag problems are compared. The design methodologies of AC voltage sag compensators are introduced. The detailed design and the flow chart of the control programme of a new parallel-type AC voltage sag compensator are described. The main advantage of the parallel-type compensator is that it can disconnect the load from the AC mains to eliminate the effects of interruptions or faults that occur in the AC mains during the compensation period. A practical 1-kVA parallel-type voltage sag compensator has been designed and constructed for evaluation. Measurements have been carried out to verify the performance of the compensator under different voltage sag conditions.