at the peaks of the line voltage waveform. These
currents and high harmonic content. The effect of
measured rms current and the rms line voltage 鈥?/div>
the "apparent power" being delivered by the line
鈥?will be significantly greater (typically 1.6X)
than the DC power delivered by the front end.
The "extra" rms current at the input is circulating
harmonic currents which deliver no power to the
load but which flow in the delivery system and
contribute to losses. Only the fundamental
component of the line current contributes to "real"
power flow. Power factor 鈥?the ratio of "real" to
"apparent" power 鈥?is a measure of the
effectiveness with which an AC load can extract
usable power from an AC source.
The VI-HAM
(see Fig. 2)
consists of a
full-wave rectifier, a proprietary high-frequency zero-
current switching (ZCS) boost regulator (patents
applied for), active inrush, short-circuit protection,
control and housekeeping circuitry. The incoming
AC line is rectified and fed to the ZCS boost
converter. The control circuitry varies the operating
frequency of the ZCS boost converter so as to
simultaneously maintain the output voltage of the
VI-HAM at a DC voltage value above the peak of
the incoming line, while forcing the input current
to the ZCS converter to follow the waveshape of
the rectified line. By this means, the AC input
current follows the AC voltage waveform and a
power factor better than 0.99 is achieved.
Operating efficiency of the ZCS boost converter is
optimized at any incoming line voltage by a
patented adaptive output voltage control scheme.
The VI-HAM also includes active circuitry which
controls inrush currents when power is applied
and active short circuit protection circuitry 鈥?/div>
features not normally found in conventional power
factor correctors.
Housekeeping circuitry provides two signals of
use to the system designer
(see Fig. 2):
Module
Enable and Power OK. Referencing the timing
diagram
(see Fig. 3),
the Module Enable signal,
which is connected to the Gate In inputs of the
Vicor DC-DC converters powered by the
VI-HAM, will come high and enable the DC-DC
converters when the VI-HAM output voltage
exceeds 240Vdc. The DC-DC converter voltage
outputs will be up approximately 10 ms after
Module Enable goes high. Typically, 20 ms after
Module Enable goes high the VI-HAM Power OK
signal, which can be used by the system designer
to enable circuitry powered by the DC-DC
converter modules, goes low. On loss of power or
brownout, the Power OK signal will go high when
the VI-HAM DC output voltage drops below
230V, signaling an impending loss of input power
to the converter modules. When the DC output
dips below 195V, the Module Enable signal will
toggle low, disabling the converter modules and
unloading the VI-HAM. The VI-HAM will
provide at least 16 ms of ride-through or holdup
time, and at least 5 ms of AC fail warning time
with a 1000 碌F output capacitor.
Figure 1a.
AC
Line
Recti-
fier
ZCS
Boost
Converter
Current
Sense
Inrush
& Short
Circuit
Protection
+
DC
Out
鈥?/div>
Note:
Non-Isolate
Output
Voltage
Waveform
High Frequency
Control
Output Voltage
Control
Module Enable
& House-
keeping
Power OK
Circuitry
Aux. Supply
Figure 1b.
Above: Oscilloscope photos showing input
voltage and current without power factor
correction (A) and with power factor correction
as provided by the VI-HAM (B).
Gate In
Gate Out
NOTE: No input to output isolation.
Figure 2 鈥?VI-HAM Block Diagram
Vicor Corp.
Tel: 800-735-6200, 978-470-2900 Fax: 978-475-6715
HAM, Harmonic Attenuator Module
Rev. 1.1
Page 1 of 6
Set your site on VICOR at www.vicorpower.com
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