Page 284 - Power Electronics Handbook

274 D.C. to d.c. converters

boosting the voltage on capacitor C by an amount which is proportional to
this load current.

12.3 Output voltage control
The method of controlling the output voltage to the load, from a chopper,
has already been discussed, and the two methods of variable-frequency and
variable mark-space were illustrated in Figure 6.6. The mean output
voltage is given by equation (12.1), and the r.m.s. voltage by equation
(12.1 1).
(12.11)

The voltage waveforms are rich in harmonics and if constant k is defined
as the output duty cycle, given by equation (12.12) then the nth harmonic in
this voltage (V,) is given by equation (12.13).
k=- tC (12.12)
tc + to
v, = v, J(2) sin n krc (12.13)
nn

t& + to)
Figure 12.13 Variation of output voltage harmonics from a stepdown chopper