JPS57137864A - Reactive power detecting device - Google Patents

Abstract

PURPOSE:To detect a reactive power with a quick response and a high precision, by using a phase detector, which detects a phase and an amplitude continuously, to constitute a circuit. CONSTITUTION:A three-phase AC voltage is inputted from an AC bus 22 through a transformer 23 to an E detecting circuit 25 consisting of a phase detector to obtain voltage phase signals sinalpha and cosalpha and a voltage amplitude ¦E¦. Similarly, a three-phase AC current is inputted from the AC bus 22 through a current transformer 24 to an I detecting circuit 26 consisting of a phase detector to obtain current phase signals sinbeta and cosbeta and a current amplitude ¦I¦. The product between the voltage amplitude ¦E¦ and the current amplitude ¦I¦ is obtained in a multiplying circuit 27, and sin(beta-alpha) is obtained through multiplying circuits 28 and 29 and a subtracting circuit 30, and the product between an apparent power and sin(beta-alpha) is obtained in a multiplying circuit 31, thereby obtaining a reactive power signal Q. Thus, the reactive power of an AC system is detected easily with a quick response and a high precision.