Power supply units (PSUs) are essential parts of contemporary electronic systems because they convert and distribute electrical power to different areas of the system. Power Factor Correction (PFC), a crucial idea that has drawn more attention recently, maximises the effectiveness and performance of power supply. To ensure that the power taken from the grid is as close to the ideal sinusoidal waveform as feasible, PFC in power supplies is specifically made to increase the electrical input's power factor. This lowers losses, harmonics, and inefficiencies.
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The ratio of perceived power (the total power given by the source) to real
power (the power needed to do productive work) is known as the power factor
(PF).
The Significance of Power Factor
Understanding the importance of power factor, particularly in alternating
current (AC)-powered electrical systems, is crucial before delving into PFC.
The voltage and current waveforms should ideally be sinusoidal and precisely
aligned (in phase), indicating that all of the power supplied to the load is
put to good use. A power factor of 1.0 is the outcome of this.
However, because non-linear loads, such switching power supplies, are used in
real-world power supplies, the current waveform is frequently distorted. A
portion of the power taken from the grid is not put to good use when the
current waveform and the voltage waveform are out of sync; instead, it moves
back and forth between the source and the load.
A low power factor, usually less than 0.9, can cause a
number of problems, such as:
increased losses in the distribution system and power supply.
Inadequate control of voltage results in supply instability.
electrical system overload because more current is needed to provide the same
amount of actual power.
increased electricity costs, as utilities frequently impose additional fees on
consumers with low power factors to offset the cost of supplying reactive
power.
Power Factor Correction's (PFC) Function in Power Supplies
Power supplies are the main application for power factor correction, which
optimises the relationship between the voltage and current waveforms. In order
to ensure that the input current waveform is sinusoidal and in phase with the input
voltage, PFC circuits allow the power supply to draw current in a manner that
closely resembles the properties of an ideal load. As a result, the power
factor approaches unity (1.0), which lessens the overall load on the electrical
grid and boosts system effectiveness.
Power Factor Correction comes in two primary varieties:
Passive Power Factor Correction (Passive PFC): This technique raises the power
factor by using passive parts like resistors, capacitors, and inductors.
Passive PFC is less efficient than active PFC and does not offer the degree of
correction needed for contemporary power supplies, although being easier to use
and less expensive.
Active components including diodes, transistors, and control circuitry are used
in the Active Power Factor Correction (Active PFC) technique. Since active PFC
is better at reaching a high power factor (around 1.0), it is frequently found
in contemporary power supply, particularly in devices that require high
efficiency, such consumer electronics, computers, and industrial machinery.
Circuit Types for Power Factor Correction
1. PFC circuits that are passive
Simpler passive PFC circuits are mostly made up of passive parts like
resistors, capacitors, and inductors. These elements smooth the input current
waveform and remove high-frequency noise. Usually, low-power devices or
applications where efficiency is not a top concern employ passive PFC.
An inductor and a capacitor are connected in series or parallel in the most
basic type of passive PFC. Passive circuits usually cannot reach a power factor
above 0.7-0.8, but this combination aids in filtering out harmonics from the
input current. Additionally, they are heavy and can produce more heat,
particularly when working with higher currents.
2. PFC Circuits That Are Active
Power electronics like transistors and diodes are used in active power factor
correction to actively modify the current waveform. Although active PFC
circuits can produce substantially higher power factor correction—often nearing
unity (1.0)—they are more complicated than passive circuits.
There are two primary types of active PFC circuits:
The most popular active PFC topology is called "Boost Converter PFC,"
in which the input current is shaped and the voltage is raised by means of a
boost converter, a kind of DC-DC converter. It ensures that the input current
follows the voltage waveform by storing energy in an inductor and releasing it
to the load in a controlled manner.
Key elements of an active PFC system usually include the
following:
Power switches, such as MOSFETs or IGBTs, are parts that regulate power flow
and mould the waveform of current.
Inductors: Inductors smooth out current variations and store energy.
Diodes: Diodes are used to steer the current in the proper direction and stop
reverse current flow.
The active PFC circuit's brain, or control circuitry, keeps an eye on the input
voltage and current, modifies the power switches, and makes sure the input
current is following the intended waveform.
Benefits and Drawbacks of PFC Power Supplies Benefits:
Enhanced Energy Efficiency: PFC power supplies make sure that the electrical
system runs more effectively by optimising the power factor, which lowers
energy waste and enhances system performance in general.
Decreased Transmission Losses: A high power factor lowers transmission and
distribution network losses, which benefits the utility company and the user by
lowering energy costs.
Regulation Compliance: A number of nations have laws requiring certain power
supply to fulfil predetermined power factor standards. Manufacturers can abide
by these rules and stay out of trouble by using PFC.
Drawbacks:
Increased Cost: Because active PFC circuits require more components and are
more sophisticated, they are more costly to design and produce.
Enhanced Complexity: The power supply design becomes more complex when PFC is
implemented, necessitating additional parts such control circuits and
complicating troubleshooting.
Heat Generation: Although active PFC increases efficiency, high-power
applications need stronger cooling solutions because of the potential for heat
generation from the additional components.
Potential Electromagnetic Interference (EMI): In order to avoid interfering
with other electrical devices, active PFC circuits may produce more EMI,
necessitating further filtering.