Page 66 - Power Quality in Electrical Systems

Harmonics and Interharmonics 49

v(t)
+170

t

Figure 4.7 A pure sine wave.
−170

DC current
A DC current (Figure 4.6) has an rms value equal to the steady-state
current, or:
I rms 5 I

Pure sine wave
A pure sine wave (Figure 4.7) has an rms value equal to the peak value
divided by the square root of two. In the case of a sine wave with peaks
at 170 V, the rms value is

V pk 170
V rms 5 5 5 120 V
!2 !2

Square wave
A 50 percent square wave (Figure 4.8) can be generated by full-bridge
and half-bridge power converters. The rms value of this waveform is

I rms 5 I pk

i(t)

I pk

t

Figure 4.8 A50 percent duty-cycle
square wave.
−I pk