18-06-2014, 11:33 AM
Electric Springs—A New Smart Grid Technology
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INTRODUCTION
AMECHANICAL spring is an elastic device that can be
used to: i) provide mechanical support; ii) store mechanical
energy; and iii) dampmechanical oscillations [1]–[4].When
a mechanical spring is compressed or stretched, the force it exerts
is proportional to its change in displacement. Potential energy
is stored in the mechanical spring when the length of the
spring deviates from its natural length. The principle of the mechanical
springs has been described by Robert Hooke in 1678
[5]. The Hooke’s law states that the force of an ideal mechanical
spring is:
CONCLUSIONS
The Hooke’s law on mechanical springs has been developed
into an electric spring concept with new scientific applications
for modern society. The scientific principles, operating modes
and limits of the electric spring are explained. An electric spring
has been practically tested for both voltage support and suppression,
and for shaping load demand (of about 2.5 kW) to follow
the fluctuating wind power profile in a 10 kVA power system fed
by an ac power source and a wind power simulator. The electric
springs can be incorporated into many existing noncritical
electric loads such as water heaters and road lighting systems
[26] to form a new generation of smart loads that are adaptive
to the power grid. If many noncritical loads are equipped with
such electric springs and distributed over the power grid, these
electric springs (similar to the spring array in Fig. 1) will provide
a highly reliable and effective solution for distributed energy
storage, voltage regulation and damping functions for future
power systems. Such stability measures are also independent
of information and communication technology (ICT).
This discovery based on the three-century-old Hooke’s law
offers a practical solution to the new control paradigm that
the load demand should follow the power generation in future
power grid with substantial renewable energy sources. Unlike
traditional reactive power compensation methods, electric
springs offer both reactive power compensation and real power
variation in the noncritical loads. With many countries determined
to de-carbonize electric power generation for reducing
global warming by increasing renewable energy up to 20% of
the total electrical power output by 2020 [22]–[25], electric
spring is a novel concept that enables human society to use renewable
energy as nature provides. The Hooke’s law developed
in the 17th century has laid down the foundation for stability
control of renewable power systems in the 21st century.