This
paper discusses the causes of input current distortion
in ac-dc single-phase rectifier-capacitor filter circuits.
The paper also explains the mandatory low-frequency
harmonic limits of the European standard EN-61000-3-2
and the way in which these are applied to these circuits.
Different power-factor correction (PFC) techniques
and strategies useful for meeting this standard are
explored in this paper. Simulations and measurement
results are provided for some of the techniques.
After providing an understanding of the Class A/D
limits of the standard, the transition boundary
between them is defined. The practical differences
between the Class A/D limits and why it is easier
to meet the Class A limits, is clearly explained.
Three practical and popular power factor correction
strategies are discussed. The passive PFC approach
with its various advantages and disadvantages is
explained. A solution to the requirement of having
a variable inductance for rectifier circuits that
have a variable load, towards meeting the Class
A limits, is proposed. After this the low frequency
active PFC is described. Lastly the popular high
frequency active PFC scheme is discussed explaining
its clear advantages of being able to simulate a
unity power factor resistive load.
This paper will add to the discussion concerning
the harmonic limits by providing a number of feasible
methods for limiting the harmonic distortion and
complying with EN/IEC 61000-3-2 and other (future)
standards.
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