Environmental Engineering Reference
In-Depth Information
Table 4.2
Comparison between synchronous and asynchronous generators
Synchronous generator
Induction generator
Features
E f fi cient
Moderately effi cient
Expensive
Less expensive
Requires maintenance
Rugged and robust, little maintenance
Reactive power fl ow can be controlled through
fi eld current
Sink of reactive power
Fixed speed hence very stiff
Small change in speed with torque, hence
more compliant
Responds in an oscillatory manner to sudden
changes in torque
Responds to sudden torque inputs in a
nonoscillatory way
Can be built with permanent magnets for a large
number of pole pairs and low rotational speed
( ' ring ' form)
Cannot be built economically for low
rotational speeds
Suitable for variable speed operation through a
power electronic interface
Suitable for variable speed in its rotor wound
form in conjunction with a power electronic
converter
Suitable for connection to weak networks. Used
in autonomous systems
Suitable for week networks only in
conjunction with power electronics
Requires special synchronization equipment to
connect to mains
Can be simply synchronized to the mains
Use in RE generation
Used in wind power mainly in its ' ring ' form
for gearless coupling to a wind turbine
Used extensively with a gear box in wind
power
Variable speed provided through a DC link
power electronic interface
Variable speed provided with power
electronics in the rotor wound form
Used in water power when reactive power
control is required
Used in water power with gearbox
4.4.6 Comparison between Synchronous and Asynchronous Generators
Table 4.2 provides an overall comparison of the characteristics of induction and synchronous
generators with particular reference to renewable energy applications.
4.5 Power Electronics
4.5.1 Introduction
Power electronics is concerned with the application of electronic devices to control and con-
dition electrical power. Power control involves the regulation of the power transfer from the
renewable energy generator to the mains either to maximize this transfer continuously as the
available resource changes or to limit the transfer for operational reasons. Power conditioning
involves the transformation of power from one voltage/current/frequency/waveform to a dif-
ferent voltage/current/frequency/waveform.
