A broad active filter (BAF) is formed from a PWM voltage style inverter which is specially used to eliminate harmonics under 35/sup th/. It can compel the output voltage to be a positive sequence voltage source. It has the functions of an efficient active filter and an efficient negative-sequence filter. In addition, it can regulate reactive power continuously, quickly and flexible to stabilize voltage and improve load power factor. In this paper, the authors relate the theory of BAF, prove the correctness of the theoretical analysis and present the broad future applications of the device by means of computer simulation.<<ETX>>