An Overview of SMES Applications in Power and
Energy Systems
Mohd.Hasan Ali,Senior Member,IEEE,Bin Wu,Fellow,IEEE,and Roger A.Dougal,Senior Member,IEEE
Abstract—Superconducting magnetic energy storage(SMES) is known to be a very good energy storage device.This article provides an overview and potential applications of the SMES technology in electrical power and energy systems.SMES is categorized into three main groups depending on its power condi-tioning system,namely,the thyristor-bad SMES,voltage-source-converter-bad SMES,and current-source-converter-bad SMES.An extensive bibliography is prented on the applications of the three types of SMES.Also,a comparison is made among the three types of SMES.This study provides a basic guide-line to investigate further technological development and new applications of SMES,and thus benefits the readers,rearchers, engineers,and academicians who deal with the rearch works in the area of SMES.
Index Terms—Current source converter(CSC),electrical power and energy systems,superconducting magnetic energy storage (SMES),thyristor,voltage source converter(VSC).
I.I NTRODUCTION
A V ARIETY of storage technologies are in the market
but the most viable are battery energy storage systems (BESS),pumped storage hydroelectric systems,and supercon-ducting magnetic energy storage(SMES)systems.Some of the disadvantages of BESS include limited life cycle,voltage and current limitations,and potential environmental hazards. Again,some of the disadvantages of pumped hydro electric are large unit sizes,topographic and environmental limitations. SMES is a large superconducting coil capable of storing electric energy in the magneticfield generated by dc currentflowing through it[1].The real power as well as the reactive power can be absorbed by or relead from the SMES coil according to system power requirements.Although superconductivity was discovered in1911,SMES has been under study for electric utility energy storage application since the early1970s[2]. SMES systems have attracted the attention of both electric utilities and the military due to their fast respon and high efficiency(a charge–discharge efficiency over95%).Possible applications include load leveling,dynamic stability,transient stability,voltage stability,frequency regulation,transmission capability enhancement,power quality improvement,automatic
Manuscript received November30,2009;accepted February11,2010.Date of publication March18,2010;date of current version April19,2010.
M.H.Ali and R.A.Dougal are with the Electrical Engineering Department, University of South Carolina,Columbia,SC29208USA(e-mail:hasan@cec.sc. edu).
B.Wu is with the Department of Electrical and Computer Engineering,Ry-erson University,George Vari Engineering and Computing Center,Toronto,ON M5B1Z2,Canada.
Digital Object Identifier10.1109/TSTE.2010.2044901generation control,uninterruptible power supplies,etc.The one major advantage of the SMES coil is that it can discharge large amounts of power for a small period of time.Also,unlimited number of charging and discharging cycles can be carried out [3]–[8].
In SMES systems,it is the power conditioning system (PCS)that handles the power transfer between the super-conducting coil and the ac system.According to topology configuration,there are three kinds of PCSs for SMES,namely, the thyristor-bad PCS[9]–[18],voltage source converter (VSC)-bad PCS[19]–[28],and current source converter (CSC)-bad PCS[29]–[38].The thyristor-bad SMES can control mainly the active power,and has a little ability to con-trol the reactive power,also the controls of active and reactive powers are not independent[39]–[42].On the other hand,both the VSC-and CSC-bad SMES can control both active and reactive powers independently and simulta孟尝君的故事
neously.Therefore, the applications in which mainly the active power control is required,the thyristor-bad SMES is ud[43]–[52],while the applications in which reactive power or both active and reactive power controls are required,the VSC-[53]–[62]or CSC-bad SMES[63]–[70]is ud.
This paper attempts to prent an overview and a bibliography on the SMES technology.A comprehensive t of references mainly published in archival journals and international confer-ences starting from the early1970s to now on the above-men-tioned three types of SMES applications are prented.To the best of our knowledge,it is the most up-to-date information on the bibliography of the SMES applications in power and en-ergy systems.The potential applications and cost-effectiveness of SMES are discusd in this context.Moreover,a comparison is made among the three types of SMES.It is hoped this study would rve as a basic guideline to investigate further technolog-ical development and new applications of SMES,and thus ben-efit the readers,rearchers,engineers,and academicians who deal with the rearch works in the area of SMES.
The organization of this paper is as follows.Section II describes the overview of SMES technology.Section III de-scribes the applications of SMES in power and energy systems. In Section IV,the cost-effectiveness of SMES is discusd. Section V provides some conclusions regarding this
work.
II.O VERVIEW OF SMES T ECHNOLOGY AND C ONTROLS An SMES device is a dc current device that stores energy in the magneticfield.The dc currentflowing through a supercon-ducting wire in a large magnet creates the magneticfield.Since energy is stored as circulating current,energy can be drawn from an SMES unit with almost instantaneous respon with energy
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Fig.1.SMES unit with six-pul bridge ac/dc thyristor controlled converter.
stored or delivered over periods ranging from a fraction of a cond to veral hours.
An SMES unit consists of a large superconducting coil at the cryogenic temperature.This temperature is maintained by a cryostat or dewar that contains helium or nitrogen liquid ves-ls.A bypass switch is ud to reduce energy loss when the coil is on standby.And it also rves other purpos such as by-passing dc coil current if utility tie is lost,removing converter from rvice,or protecting the coil if cooling is lost [71].
Several factors are taken into account in the design of the coil to achieve the best possible performance of an SMES system at the least cost [5].The factors may include coil configura-tion,energy capability,structure,and operating temperature.A compromi is made between each factor considering the pa-rameters of energy/mass ratio,Lorentz forces,stray magnetic field,and minimizing the loss for a reliable,stable,and eco-nomic SMES system.The coil can be configured as a solenoid or a toroid.The solenoid type [56]has been ud widely due
to its simplicity and cost effectiveness.Coil
inductance
or PCS maximum
voltage
and
罗袜生尘
current ratings deter-mine the maximum energy/power that can be drawn or injected by an SMES coil.The ratings of the parameters depend on the application type of SMES.The operating temperature ud for a superconducting device is a compromi between cost and the operational requirements.Low-temperature superconductor (LTS)devices are available now,while high-temperature super-conductor devices are currently in the development stage.
Different types of SMES technologies and their control methodologies are described below.A.Thyristor-Bad SMES
Fig.1shows the basic configuration of a thyristor-bad SMES unit,which consists of a Wye-Delta transformer,an ac/dc thyristor controlled bridge converter,and a supercon-ducting coil or inductor.
The converter impress positive or negative voltage on the superconducting coil.Charge and discharge are easily controlled by simply changing the delay
angle that controls the quential firing of the thyristors [72]–[81].
If is less than 90,the converter operates in the rectifier mode (charging).
If is greater than 90,the converter operates in the inverter mode (discharging).As a result,power can be absorbed from or relead to the power system according to requirement.At the steady state,SMES should not consume any real or reactive power
[82]–[91].
Fig.2.Basic configuration of VSC-bad SMES system.
The
voltage of the dc side of the converter is expresd
by
(1)
where is the ideal no-load maximum dc voltage of the bridge.The current and voltage of superconducting inductor are related
as
(2)
where
is the initial current of the inductor.The real
power absorbed or delivered by the SMES can be given
by
(3)
Since the bridge
幼儿急疹症状current is not reversible,the bridge
output
power
is uniquely a function
of ,which can be positive or negative depending
on
.反脆弱读后感
If is positive,power is transferred from the power system to the SMES unit.
While
if
is negative,power is relead from the SMES unit [92]–[101].The energy stored in the superconducting inductor
is
(4)
where is the initial energy in the教授英语怎么说
inductor.
B.VSC-Bad SMES
Fig.2shows the basic configuration of the VSC-bad SMES unit [102]–[111],which consists of a Wye-Delta transformer,a six-pul pul width modulation (PWM)rectifier/inverter using insulated gate bipolar transistor (IGBT),a two-quadrant dc-dc chopper using IGBT,and a superconducting coil or inductor.The PWM converter and the dc-dc chopper are linked by a dc link capacitor.
The PWM VSC provides a power electronic interface be-tween the ac power system and the superconducting coil.The control system of the VSC is shown in Fig.3.The proportional-integral (PI)controllers determine the reference d-and q-axis
Fig.3.Control system of the VSC.
currents by using the difference between the dc link
voltage
清洁工鱼and reference
value,and the difference between
terminal
voltage and reference
value,respectively.
The reference signal for VSC is determined by converting d-and
q-axis voltages which are determined by the difference between
reference d-q axes currents and their detected values.The PWM
signal is generated for IGBT switching by comparing the refer-
ence signal which is converted to three-pha sinusoidal wave
with the triangular carrier signal.The dc voltage across the ca-
pacitor is kept constant throughout by the six-pul PWM con-
verter[112]–[121].
The superconducting coil is charged or discharged by a
two-quadrant dc-dc chopper.The dc-dc chopper is controlled
to supply positive(IGBT is turned ON)or negative(IGBT is
turned OFF)
voltage to SMES coil and then the stored
energy can be charged or discharged.Therefore,the supercon-
ducting coil is charged or discharged by adjusting the average
voltage across the coil which is determined by the duty
cycle of the two-quadrant dc-dc chopper.When the duty cycle
is larger than0.5or less than0.5,the stored energy of the coil
is either charging or discharging.In order to generate the PWM
gate signals for the IGBT of the chopper,the reference signal is
compared with the triangular signal[122].
C.CSC-Bad SMES
Fig.4shows the basic configuration of the CSC-bad SMES
unit.The dc side of CSC is directly connected with the super-
conducting coil,and its ac side is connected to the power line.A
bank of capacitors connected to a CSC input terminal is utilized
to buffer the energy stored in line inductances in the process
of commutating direction of ac line current.Furthermore,the
capacitors canfilter the high-order harmonics of the ac line
current.In CSC,through regulating the trigger signals of the
switching devices,the current in the superconducting coil can
be modulated to generate controllable three-pha PWM cur-
rent at the ac side.As the SMES system is inherently a current
system,the transfer of both active and reactive powers between
the CSC and power network is very fast
[36].
Fig.4.SMES system with a
CSC.
Fig.5.Block diagram of the dc current control algorithm.
In ca of12-pul CSC-bad SMES,to improve the total
harmonics distortion(THD)of the ac source currents,an op-
timal PWM switching strategy is ud to minimize the5th,7th,
11th,and13th harmonics.It has been proved that the5th,7th,
11th,and13th harmonics can be minimized to zero with the
modulation
index ranging from0.2to1[37].Compared to a
6-pul CSC,the12-pul CSC has smaller voltage ripples on
the dc side,which means a further reduction of the ac loss in
the SMES coil.
For the magnet training,a dc
current control algorithm is
applied[37].The block diagram is shown in Fig.5,
where
is the reference value
of,PI is a proportional-integral regu-
lator,is the inductance of the SMES
六年级下册英语单词
coil,is the resistance
in the dc circuit,
and is the dc voltage.With the pha
angle
beingfixed to zero,the dc voltage is proportional to the mod-
ulation
index,which determines the charging rate.
D.Comparison of Thyristor-Bad,VSC-Bad,and
CSC-Bad SMES
Table I shows a comparison of the thyristor-bad,
VSC-bad,and CSC-bad SMES.The comparison is done
in terms of real and reactive powers control ability,control
structure,THD,and SMES coil voltage ripple.
III.A PPLICATIONS OF SMES IN P OWER AND E NERGY S YSTEMS
It is the fast respon that makes SMES able to provide benefit
to many potential utility applications.The applications of SMES
are described in the following.
1)Energy storage—An SMES unit could provide the poten-
tial for energy storage of up to5000MWh with a high re-
turn efficiency(up to95%for a large unit)and a rapid re-
spon time for dynamic change of energyflow(millic-
onds)[123]–[131].This aspect makes it ideal for large vari-
ations in energy requirements between daytime peak de-
mand and off-peak back-down as well as large amounts of
energy available for replacement of major unit trips.This
TABLE I
C OMPARISON OF SMES T
ECHNOLOGIES
may provide for the potential reduction of spinning rerve requirements.
2)
Load following —An SMES unit has the ability to follow system load changes almost instantaneously which pro-vides for conventional generating units to operate at con-stant output [123],[126].
3)
System stability —An SMES unit has the capability to dampen out low frequency power oscillations and to stabi-lize system frequency as a result of system transients [42],[74],[96],[120],[123],[124].
4)
Automatic Generation Control —An SMES unit can be the controlling function in an AGC system to provide for a minimum of area control error (ACE)[123].
5)
Spinning rerve —In ca a major generating unit or major transmission line is forced out of rvice,
a certain amount of generation must be kept unloaded as “spinning rerve.”An SMES unit can reprent a tremendous amount of spinning rerve capacity when in the charged mode.This lowers the costs for spinning rerve require-ments over comparable values and methods of maintaining spinning rerve [123],[124],[126].
6)
Reactive volt-ampere (V AR)control and power factor correction —An SMES unit can increa the stability and power carrying capacity of a transmission system [123].7)
Black start capability —An SMES unit can provide power to start a generating unit without power from the grid.This provides for grid restoration when area failures have oc-curred [123].8)Bulk energy management —An SMES unit has the ability to store large quantities of energy,and thus can act as a storage and transfer point for bulk quantities of energy bad on the economics,potentially lowering the cost of electricity [123].
9)Transient voltage dip improvement —A transient voltage dip lasting for 10–20cycles can result when a major distur-bance on the power system occurs.SMES and associated converter equipment has been shown to be effective for providing voltage support which can result in increasing the powe
r transfer limitations on the transmission system [127].
10)Dynamic voltage stability —Dynamic voltage instability
can occur when there is a major loss of generation or heavily loaded transmission line and there is insuffi-cient dynamic reactive power to support voltages.SMES has been shown to be effective in mitigating dynamic voltage instability by supplying real and reactive power simultaneously supplanting loss of generation or a major transmission line [126],[127].
11)Tie line control —When power is scheduled between
utility control areas,it is important that the actual net power matches cloly with the scheduled power.Unfor-tunately,when generators are ramped up in one control area and down in the receiving control area to nd power,the system load can change causing an error in the actual power delivered.This ACE can result in inefficient u of generation.SMES can be designed with appropriate
controls to inject power to virtually eliminate this error and insure that generation is efficiently ud and power schedules are met[127].
12)Underfrequency load shedding reduction—When the
power system suffers the loss of a major resource such as a generating plant or major importing transmission lines the system frequency will drop and continue to decline until the generating resource—load balance is restored.Becau SMES can inject real power rapidly into the system,it is an effective method to offt,or reduce,underfrequency load shedding becau it reduces the mismatch between load and supply capability of the system disturbance[127].
13)Circuit breaker reclosing—Following clearance of a
fault,circuit breakers attempt to reclo and return the affected transmission line to rvice.This is accomplished routinely whenever the power angle difference across the circuit breaker is within acceptable limits.However, protective relays prevent the circuit breaker from reclosing if the angle difference is too large.By briefly supplying some fraction of the power normally transmitted by the transmission line,SMES can reduce the power angle difference across a circuit breaker and allow reclosure of the circuit breaker.This allows restoration of the system power transfers quickly following outages of major trans-mission lines[127].
14)Power quality improvement—SMES can provide ride
through capability and smooth out disturbances on power systems that would otherwi interrupt nsitive customer loads.When momentary disturbances such as transmis-sion lineflashovers or lightning strikes occur,power can be lost if the transmission line trips,or voltages can dip low.
SMES has very fast respon and can inject real power in less than one power cycle preventing important customers from losing power[127].
15)Backup power supply—The energy storage capacity of
SMES can be ud as a backup power supply for large in-dustrial customers in ca of loss of the utility main power supply.Studies have shown SMES can be sized with the appropriate energy storage and capacity to provide backup through most disturbances and be cost-effective[126], [127].
16)Subsynchronous resonance damping—Generators
which are connected to transmission lines which have high levels of ries compensation(ries capacitors) can be expod to a phenomenon called subsynchronous resonance(SSR)which can result in rious damage to the generator.SMES as an active device can be designed to provide mitigation of SSR and allow higher levels of ries compensation to be installed[12],[75],[76],[78], [111],[127].
17)Electromagnetic launcher—An electromagnetic
launcher requiring high power pul sources has been developed as a railgun for military applications.A railgun can launch projectiles at velocities higher than2000m/s, surpassing the conventional possibilities.Due to its high power density,SMES is a very interesting energy storage device for an electromagnetic launcher[132].18)Wind generator stabilization—Wind generators have
transient stability problems during network disturbances.
民主评议个人自评An SMES unit bad on a lf-commutated inverter using IGBT or gate-turn OFF(GTO)thyristor is capable of controlling both the active and reactive powers simultane-ously.Therefore,it can act as a good tool to stabilize the wind generator system considerably[112],[117].
19)Minimization of power and voltagefluctuations of
wind generator—Due to random variations of wind speed,output power and voltage of wind generatorfluc-tuate randomly.Thefluctuations po rious problems on the system,for example,lampflicker and inaccuracy in the timing devices.Since an SMES unit is capable of controlling both the active and reactive powers simulta-neously,it can act as a good tool to decrea voltage and powerfluctuations of the wind generator system consider-ably[102],[114],[118],[133].
In addition to direct applications and benefits from the SMES technology,the following are additional condary benefits that could be derived[123].
1)Lower u of oil and gas—An SMES unit can be charged
by the more efficient units in a system,thereby lesning the need for the lower efficiency units to operate during peak periods.
2)Incread efficiency and reduced maintenance of gener-
ating units—Becau an SMES unit can absorb thefluc-tuations in demand and ramp at extremely rapid rates,gen-erating units can be operated and maintained at their most efficient t points,thereby increasing efficiency,reducing maintenance,and extending operability.
3)Deferral of new conventional capacity—An SMES unit
has the ability to receive credit that would otherwi go to additional intermediate load and peak load generating units.It may also rve to reduce the calculated avoided cost.
4)Deferral of new transmission capacity—An SMES unit,
if strategically placed,can defer the need for new transmis-sion to high load centers by loading existing transmission systems during off-peak periods.
5)Incread availability of generating units—An SMES
unit provides for the back-up of additional generating units which were previously needed only during peak periods, thus increasing the overall capacity of the system.
6)Environmentally sound—The clean and efficient storage
of electricity by SMES from conventional units operating more efficiently at their t points will displace inefficient fossil-fueled units,conrve premium fuels,and reduce air pollutants.SMES may provide for some emissions credit.SMES has no emissions and its electromagnetic field is confined to an area comparable to generating technologies.
IV.C OST-E FFECTIVENESS OF SMES
The cost of an SMES system can be parated into two inde-pendent components where one is the cost of the energy storage capacity and the other one is the cost of the power handling capability[129],[134]–[143].Storage-related cost includes the
