Environmental Engineering Reference
In-Depth Information
A power electronic interface that controls and/or conditions power is referred to as a
con-
verter
. Converters are interposed between the RE generator and the mains and often carry
the total power transfer. They should be designed so that as little power as possible is lost in
this transfer and that their capital cost is as slow as possible per watt transferred. Transform-
ers can be viewed as power conditioning devices. Converters, not unlike transformers, are
rated in volt-amps (VA).
The devices (transistors, etc.) used in power electronic converters are made from semicon-
ductor silicon, like those in a computer processor, but physically they are much larger, and
usually they are discrete - one device per piece of silicon. A converter will typically contain
between one and a hundred power semiconductor devices.
Power electronic converters are found in an enormous range of applications and sizes, from
the 2 GW UK-France Channel DC Link down to the 40 W energy-saving light bulbs in homes.
In renewable energy, power electronic converters are already used in most PV systems and
many wind turbines. It is also expected that they will be used in the future in practically all
the emerging wave and tidal power technologies.
Despite the enormous range of converter sizes and applications, they are mostly based on
just a handful of device types and basic circuit confi gurations. This section will discuss the
most common of these. The aim is not that the reader will be able to design converters, but
that he or she will understand their specifi cations, potential uses and limitations. The follow-
ing section will deal with the application of these converters in the conditioning of power
from renewable energy sources.
More details on solid state switching devices and converters can be found in many topics
on power electronics (see, for example, Reference. [3]). Some of the most common devices
are reviewed below.
4.5.2 Power Semiconductor Devices
Diodes
The
diode
in Figure 4.19 conducts current from anode to cathode, (in the direction of
the arrow) whenever the anode is made positive with respect to the cathode, i.e., posi-
tive
bias voltage
is applied across the device, and blocks current in the reverse direction
when the device is negatively biased. The diode has no capability to control the current
after it has been established. Diodes are readily available with ratings up to thousands
of volts and thousands of amps. They are very reliable and very cheap (per VA) and
very useful.
Anode
I
V
Cathode
Figure 4.19
Diode
