PFC Circuits - Active
In addition to lowering power usages to the consumers, improved power factor also
contributes towards the conservation of energy and helps in reducing air pollution, by virtue of
less fossil fuel required for generating same amount of electrical power. Other resultant effects are lower I2R losses, steadier terminal Voltages, released system capacity and
reduced cable & switchgear sizes. Active PFC front ends also help meet the IEEE 519-
92, IEC-555 and European EN 61000-3-2 standards for allowable harmonic contents of
Although there are some passive and active 3-Phase PFC solutions, Vienna Rectifier is unique by virtue of its embodiment of several advantages:
1. It is a 3-Phase, three level PWM rectifier, utilizing three MOSFETS, with controlled
output Voltage; three wire input, not requiring any connection to Neutral.
2. It is a dual boost type PFC with continuous sinusoidal input current and
unidirectional power flow
3. It needs only three active switches, i.e. MOSFETS
4. It is Operational even in presence of unbalanced mains or only two phases.
5. Total switching losses are reduced by a factor of six, assuming switching
frequency below 50 KHz.
6. Any malfunction in control circuit does not manifest itself in short circuit of output or
PFC front end.
7. Sinusoidal input currents with Power Factor = 0.997, THD<5% and overall
efficiency > 97% are obtainable with current designs.
As can be seen, Vienna Rectifier is the 3-Phase PFC solution that needs to be fully
exploited. Ready-made Vienna Power Semiconductor modules, embodying MOSFETS+
FREDS to make a stand alone Direct Copper Bonded Power Circuit, make it quite convenient and user-friendly. Powerful, yet inexpensive, microcomputers and DSPs make it attractive to design compact controllers for the Vienna Rectifiers.
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