, also called solid-state ballasts, are those power electronic converters used to supply
discharge lamps. The modern electronic ballasts with the development of low cost power
MOSFETs allow to supply ﬂuorescent lamps at
frequencies of several kilohertz
increasing lamp luminous ef±cacy
by operating at these high frequencies. The
main bene±ts of electronic ballasts are the increase in the lamp and ballast overall
ef±ciency, increase in lamp life, reduction of ballast size and weight, and improve-ment
in lighting quality.
Power distortions such as power interruptions, voltage sags and swells, voltage spikes,
and voltage harmonics can cause severe impacts on sensitive loads in the electrical
Uninterruptible power supply (UPS) systems are used to provide uninterrupted, reliable,
and high quality power for these sensitive loads.
Applications of UPS systems include medical facilities, life supporting systems, data
storage and computer systems, emergency equipment, telecommunications, industrial
processing, and on-line management systems .
The UPS systems are especially required in places where power outages and ﬂuctuations
occur frequently. A UPS provides a backup power circuitry to supply vital systems when
a power outage occurs. In situations where short time power ﬂuctuations or disturbed
voltage occur, a UPS provides constant power to keep the important loads running.
During extended power failures, a UPS provides backup power to keep the
systems running long enough so that they can be gracefully powered down.
Most of the UPS systems also suppress line transients and harmonic disturbances.
Generally, an ideal UPS should be able to simultaneously deliver uninterrupted power
and provide the necessary power conditioning for the particular power application.
Therefore, an ideal UPS should have the following features: regulated sinusoidal output
voltage with low total harmonic distortion (THD) independent from the changes in the
input voltage or in the load, on-line operation that mean zero transition time from normal
to back-up mode and vice versa, low THD sinusoidal input current and unity power
factor, high reliability, high ef±ciency, low EMI and acoustic noise, electric isolation,
low maintenance, low cost, weight, and size. Obviously, there is not a single
con±guration that can provide all of these features. Different con±gurations of UPS
systems emphasize on some of the features mentioned above. Classi±cations of UPS
systems are described in Section 24.2
Off-line UPS: Standby-UPS
This con±guration of UPS system is also known as “off-line UPS” or “line-preferred
It consists of an AC/DC converter, a battery bank, a DC/AC inverter, and a static
. A passive low pass ±lter may also be used at the output of the UPS or inverter to
remove the switching frequency from the output voltage.
The static switch is on