Electric Motors and Drives, 2nd Edition

56 Electric Motors and Drives

connected to the mains by the pair of switches Tl and T4, or it

is connected the other way up by the pair of switches T2 and T3,

or it is disconnected. The load voltage therefore consists of

rectified chunks of the mains voltage. It is much smoother than

in the single-pulse circuit, though again it is far from pure d.c.

The waveform in Figure 2.8(a) corresponds to α = 30°, while

Figure 2.8(b) is for a= 120°. The mean value, V

dc

is shown in

each case. It is clear that the larger the delay angle, the lower the

output voltage. The maximum output voltage (V

do

) is obtained

with α = 0°, and is given by

where

V

rms

is