Patent ID: 6985821

Claim:
An apparatus for calculating an effective voltage comprising: a voltage reducer for stepping down instantaneous output voltages of a generator at a predetermined rate; an analogue to digital converter for converting each analogue signal of the instantaneous output voltages, which are stepped down by the voltage reducer, into a digital signal; a first detector for detecting a first signal of instantaneous output voltage which is digitized by the analogue to digital converter; a second detector for detecting a second signal of instantaneous output voltage which is digitized by the analogue to digital converter and differs in terms of phase by 120 deg. from the first signal; and a calculator for calculating an effective voltage of the generator according to the first and second signals which are detected by the first and second detectors respectively, by executing a calculation with an expression (1): E= {2( V a 2 +V a V b +V b 2 )/3} 1/2 (1) where E represents the effective voltage, V a the first signal of instantaneous output voltage and V b the second signal of instantaneous output voltage, respectively.