2011 International Conference on Alternative Energy in Developing Countries and Emerging Economies
- 251 -
Sizing and Control of a Flywheel Energy Storage
System for Ramea Hybrid Power System
K. Islam, M.T. Iqbal and R. Ahshan
Faculty of Engineering & Applied Science
Memorial University of Newfoundland,
(Canada)
1
Email:
Abstract
--
In this paper sizing and control of flywheel energy
storage for Ramea wind-hydrogen-diesel hybrid power system is
presented. At present the hybrid power system in Ramea consists
of diesel generators, wind turbines, hydrogen generator and
Electrolyzer. Main purpose of this proposed flywheel energy
storage system is to minimize the sudden variation of grid voltage
due to variable wind speed and variable load. HOMER is used
for sizing and steady-state simulations. A DC machine based
flywheel energy storage is designed, tested and verified in the
energy systems lab of Memorial University. A 2 kW DC
machine is used as a motor/generator unit coupled with a cast
steel flywheel rotor, a programmable data acquisition card, two
controllable power supply units, two electromechanical relays
and relay driving circuits are used for the experimental
observations. Simulation results show that, an addition of
flywheel energy storage will be very effective to maintain a
regulated grid voltage and frequency. Steady state analysis
indicates flywheel storage will reduce the fuel consumption and
number of switching of the generator and increase the life span
of the generators.
Index Terms
--Flywheel energy storage, FESS
I. I
NTRODUCTION
Many years ago, pure mechanical flywheels were used solely
to keep machines running smoothly from cycle to cycle. Apart
from the traditional use, now a days, flywheels are becoming
more popular for energy back up in power system. In recent
years, flywheel energy storage systems (FESS) have been
rediscovered by industry due to their advantages in
comparison with other short-term energy storage systems [1],
[2], [3], [4]. Flywheels are simple and characterized by high
power and energy density, longer-life, low-maintenance,
highly cyclic (charge-discharge) capability, and zero fuel
consumption or CO2 or other emissions that makes them
environment friendly. On the other hand, wind-hydrogen-
diesel hybrid system offers an appropriate solution for some
isolated power system and the numbers of such systems are
increasing in the world at a rapid pace. Purpose of wind
turbine and hydrogen generator operating in parallel with the
diesel generator is to reduce the fuel consumption or allows
that to shut down when the wind power exceeds the load.
Although wind power is popular and well known celebrity of
renewable energy but it generates energy intermittently
because wind speed varies every hour, every minute. So
frequent switching of the generator may be necessary in order
to maintain a stable grid with regulated voltage and constant
frequency that reduces the life span of the generator and
increases the fuel consumption. Short-term energy storage like
FESS can be a good choice in this situation to reduce the
number of switching and to make the system more stable.
From the literature review it was found that the flywheel
energy storage system (FESS) can have many applications
including uninterruptible power supplies (UPS), dynamic
voltage compensators, overload compensators, and start-up of
standby diesels. In the overload compensation the FESS
supports the main grid by supplying power to part of the load
in case of overload [5], [6]. This occurs when there is a
voltage or frequency dip in the main grid and thus it is not
capable, for a few seconds, to supply all the power needed by
the load. In such situations, the grid gets the help from the
FESS that has stored kinetic energy. Therefore, the main
purpose of the flywheel is to accumulate rotational kinetic
energy which can be injected into the electric system
whenever it is required.
A lot of projects based on the FESS have been implemented in
several countries especially USA and several European
countries. However, with the advancements in power
electronics, machines, materials and magnetic bearings of
machines, new ideas are being researched and new projects
are implemented. High-speed flywheel [7], [8] systems (more
than 30,000 rpm) are now in the prototype stage and it is
expected that these systems will be in market within 5 to 10
years. From our literature survey, we noticed that the
maximum speed that has been reached in experiments is
around 60000 rpm [9] but it still has issues due to the resulting
speed oscillations.
II. F
LYWHEEL
E
NERGY
S
TORAGE
S
YSTEM
After a major improvement in technology and power
electronics, flywheel energy storage system (FESS) has come
around again and has been a promising alternative to
traditional battery [6]. FESS or also called electromechanical
batteries are typically comprised of the rotor, motor/generator,
power electronics, controllers, bearings. FESS is a kinetic
energy storage device storing energy in a rotating rotor. The
