Superconducting Magnetic Energy Storage
Concepts and applications
Antonio Morandi
DEI − Guglielmo Marconi
Dep. of Electrical, Electronic and
Information Engineering
University of Bologna, Italy
ESAS Summer School on
High Temperature Superconductors Technology for
Sustainable Energy and Transport Systems
Outline
• SMES technology
SC material and Conductor
Coil
Power conditioning system
A case study - 1 MW / 5 s SMES
• Applications
Energy storage
SMES applications
Grid
Customer / Industry
• SMES actvities at the University of Bologna
2
SMES – Superconducting Magnetic Energy Storage
PCS
grid
Current leads
vacuum
vessel
Control and
protection
system
Superconducting
coil
Cooling
system
2
2
B
B
1 2
E=∫
dτ ≈ ∫
dτ = L I
2
τ ∞ 2µ0
τ coil 2 µ 0
3
Advantages
• High deliverable power
• Infinite number of charge discharge cycles
• High efficiency of the charge and discharge phase
(round trip)
• Fast response time from stand-by to full power
• No safety hazard
Critical aspects
• Low storage capacity
• Need for high auxiliary power (cooling)
• Idling losses
4
Conductor and cable
YBCO
16 K
20 K
24 K
YBCO, B perpendicular
16 K
MgB2
20 K
24 K
MgB2
Main characteristics of a typical MgB2 Conductor
Manufacturer
Columbus
Nominal radius
1.13 mm
Number of filaments
36
Filling factor
0.14
Matrix
Ni 70%, Copper 20 %
Critical tensile strength
300 MPa
Critical current, 22 K, self field 550 A
Main charact. of a typical YBCO Coated Conductor
Manufacturer
Superpower
Nominal Width
12 mm
Nominal thickness
0.1 mm
YBCO
1 µm
Stabilizer, copper
2×20 µm
Substrate, Hastelloy
100 µm
Critical tensile strength
550 MPa
Critical current, 77 K, self field
330 A
5
• Typical current for the SMES operating in the MW range is in the order of several kA
• Several conductors have to be put in parallel for reaching the required transport
current
High current conductor made of 2G HTS tapes
Continuously transposed (Roebel) cable
•
•
Scraps are produced
Je cable = 0.8 – 0.9 Je tape
Slotted cable made of Roebels
•
Je cable << Je tape
6
Twisted stacked-tapes
Cable made of twisted stacks
•
Je cable << Je tape
Conductor on Round Core (CORC) cable
Institute of Electrical Engineering
Slovak Academy of Science
7
CCRP Cable
Centre de Recherches
en Physique des Plasmas
ENEA Cable
10 kA – class cable:
150 2G-wires (5 stacks x 30 wires)
8
High current conductor made of MgB2 wires
Flat Rutherford cable
example
2 × 6 wires
Stranded MgB2/Cu rope
Copper
MgB2
Example of Base Cable Unit:
12 MgB2 strands
+ 7 copper strands
1×
3×
7×
9
Layout of the winding – Arrangement of multiple pancake
5 MJ coil - 4T
Solenoid
• Simpler and more cost effective
• Easier handling of the
electromagnetic stress
• Smaller foot-print
Torus
• Low stray field
• Reduced component of magnetic
field perpendicular to the conductor
10
Length of conductor versus the perpendicular field
at the maximum current
5 MJ coil - 4T
A large portion of conductor experiences a large perpendicular
field in the toroid as well
11
Coil design – electromagnetic
R′1 = p R1
L′= p L
∆ R′1 = ∆ R1
R′1
R1
L′
L
∆R
H = Je ∆ R1
H = Je ∆ R′1
∆R′
H2
E' =
π R'12 L' = p 3 E
2µ0
(
)
VSC ' = π ( R'1 + ∆R ' ) 2 − R'12 L' ≈ p 2VSC
The volume of the superconductor scales less than linearly with
the energy of the coil
VSC = k E
2
3
12
Coil design – mechanic
V ≥k
1
σ
E
Virial’s theorem limit
V, volume of structural material [m3]
E, total energy of the coil [J]
σ, allowable stress [N/m2]
k, numerical coefficient ( ≥ 1 )
At high energy the structural
constraint is stricter than the
electromagnetic one
Additional structural (and stabilizing )
material is required
volume
For solenoid k ranges from 1 if D/L tends to zero to
3 if D/L tends to infinite.
∝E
∝ E2/3
energy
13
Field dependence of the total conductor’s length
• The required stored energy E is assigned
• The operating field B of a the SC coil is a design choice
By increasing the field
• A reduced overall size of the coil is obtained which
requires less conductor
• More ampere-turns at reduced Jc are needed which
require more conductor
Which of the two effects is dominant?
14
E
B
p
Stape
Je
k
• slim solenoid
• given aspect ratio
• Isotropic conductor
Volume of the solenoid
Stored Energy
Nominal Field
aspect ratio ( L / D ) of the solenoid
cross section of the tape
Eng. current dens. of the tape at field B
I / Ic ratio
Vsolenoid ≈ 2µ 0 E / B 2
1
3
 8µ 0  − 23
D
=π
L ⇒ D = 
E  B
π
4
p


2
Diameter of the solenoid
Vsolenoid
Height of the solenoid
 8µ0 p  − 23
L = p D = 
E  B
π


Superconducting cross
section
2
1
3
k J e ( B ) S SC = H L ⇒ S SC
Total length of tape
N tape
1
3
8p
 13
S SC
1

=
=
E B
Stape Stape k J e ( B )  π µ 20 
2
Number of turns
1
3
 13
1 8p

=
E B
k J e ( B )  π µ 20 
2
LSC
π
1
3
−
1
3
 64 p 2  B
 2
= π N tape D =
E 
Stape k  π µ 0
 J e ( B)
15
LSC ( B ) ≤ LSC ( B' ) ⇔
 B' 
J e ( B) ≥ J e ( B' )  
B
1
3
YBCO, 16 K,
B perpendicular
J e (4) * (4 B )
13
MgB2 ,
16 K
J e (2) * (2 B )
13
For practical superconductors (YBCO and MgB2) the required length of
conductor needed for a solenoid with given Energy E increases with the
operating field
16
Outline
• SMES technology
SC material and Conductor
Coil
Power conditioning system
• Applications
Energy storage
SMES applications
Grid
Customer / Industry
17
PCS – the magic box
P
I
0
AC
Grid
PCS
SMES
I0, current of SMES at
time t0
I1, current of SMES at
time t1
1
1 2
2
L I − LI 0 = − P (t − t0 )
2
2
I = I 02 −
2
P (t − t0 )
L
1 2 1 2
L I − L I1 = P (t − t1 )
2
2
I = I12 +
2
P (t − t1 )
L
During discharge
During charge
I0
I1
t0
t1
18
PCS - Power Conditioning System
Voltage source converter (VSC)
Vdc
L
C
ISMES
• A controlled power is transferred from the DC bus to the grid by
means of the inverter
• The voltage of the DC bus is kept constant by the SMES by means of
the two quadrant chopper
19
Idc
P = V I cosϕ
Vdc
C
The inverter regulates the
power transfer between the
grid and the capacitor
An average positive current is established on
the DC bus during power transfer to grid
P ≈ Vdc < Idc >
Vdc
The voltage of DC bus decreases if the
capacitor is not recharged
time
20
The chopper controls the voltage of the DC bus
Idc
Discharge
P = V I cosϕ
I′dc
Vdc
L
C
i′dc
ISMES
ISMES
< I ′dc > = < Idc >
⇓
Vdc ≈ constant
The current of the SMES decreases during the ON phase
TON
< I ′dc >
TOFF
Tcycle
time
If the power P is delivered to the grid during the
interval ∆t final current of the SMES is
1 2 1 2
L I 2 − L I1 = P ∆t
2
2
I2, current of he SMES at the end of the delivery
I1, current of he SMES at the start of the delivery
21
Charge
Idc
P = V I cosϕ
I′dc
Vdc
L
C
i′dc
TOFF
− ISMES
time
< I ′dc >
TON
Tcycle
ISMES
< I ′dc > = < Idc >
⇓
Vdc ≈ constant
The current of the SMES increase during the ON phase
If the power P is absorbed from the grid during the
interval ∆t final current of the SMES is
1 2 1 2
L I 2 − L I1 = P ∆t
2
2
I2, current of he SMES at the end of the delivery
I1, current of he SMES at the start of the delivery
22
Implementation - control algorithm
Grid
Load
SW
vg
Ls
iL
is
inverter
PWM
vs*
vg
is
R2
Vdc*
+
−
Vdc
ic*
R3
PWM
chopper
−
is*
iL
ig* +
R1
vg
Qg* ( = 0)
Pg*
• The inverter is controlled in order to provide the required service
to the grid
• The SMES is controlled independently in order to stabilize the
23
voltage of the DC bus
Idling Loss
If no power is delivered/absorbed the SMES current of the free-wheels
P=0
Vdc
L
C
Losses are produced
during the idling phase
ISMES
Von IGBT = 0.5 − 1 V
Von DIODE = 0.5 − 1 V
PIGBT = ISMES Von IGBT
PDIODE = ISMES Von DIODE
Pidling = 1 − 10 kW / kA
• Time constants of RL circuit of typical SMES (1-5 MJ) during the standby
phases are in the order of hundreds of seconds at most
24
SMES
• The whole energy of the SMES is lost in the power electronics
within a few minutes
• Continuous recharge/compensation is needed
The use of a thermal actuated SC switch for avoiding the losses during the standby is
possible in principle but it is unfeasible in practice since it lowers the response time of
the SMES
P=0
Vdc
C
ISMES
L
26
Outline
• SMES technology
SC material and Conductor
Coil
Power conditioning system
A case study - 1 MW / 5 s SMES
• Applications
Energy storage
SMES applications
Grid
Customer / Industry
• SMES actvities at the University of Bologna
27
Main characteristics of the 1 MW - 5s SMES Systems
28
Grid performance of the 1 MW - 5s SMES System
29
Estimated AC losses of the 1 MW - 5s SMES System during
one discharge/charge cycle.
Round trip efficiency of the 1 MW - 5 s SMES System
during one discharge/charge cycle.
30
Outline
• SMES technology
SC material and Conductor
Coil
Power conditioning system
• Applications
Energy storage
SMES applications
Grid
Customer / Industry
31
National electric balance - Italy
Production (grid immission)
Thermal
Rinnovabili
Importazioni
Loss
310 TWh, 2014
47.5%
37.9%
14.0%
19.5 TWh (6 %)
Average power demand
• Night average (2011)
• Day average(2011)
• Absolute minimum (2009)
• Absolute maximum ( 2015)
39.1 GW
22.0 GW
52.0 GW
21.5 GW
53.3 GW, 21 July
Installed power (2012 )
Installed power (2010 )
Average available power (2012)
124.0 GW
106.0 GW
69.3 GW
Usage rate
57.3 %
32
Electric power system
ICT
storage
storage
Non progr.
power.
Non progr.
power
Non progr.
power
Active load
Active load
33
Grid energy management
• Generation / load imbalance is inherent in the power grid due to
random fluctuation of loads induced by customers
variation of generation from renewables
• Sudden and Large generation / load imbalance can also occur due to contingency
• Continuous and fast regulation of the generated power and/or loads is
required for controlling the frequency and stability of the grid.
Technology for grid energy management
• Improved controllability of conventional
generation
• Responsive load
• Supergrid (multi-terminal DC links )
• Energy storage
34
Energy storage
T&D system only allows to move energy in space
Total power produced must instantaneously balance the total load
(including the losses).
Energy storage system allows to shift electric energy in time
so as to decouple production and consumption
35
Energy intensive storage
Performance of Storage Technologies
Power intensive storage
1 MWh = 3600 MJ
1 MW × 6h NAS module
1 MW × 10 s SMES
38
6 MWh
NAS system
6 MWh SMES
system
Efficiency of an Energy Storage System
P, deliverable power
∆t , duration of delivery
∆ tcycle , duration of the cycle
∆ tidle, duration of idling phase
ηs , intrinsic efficiency of the storage device
ηc , efficiency of the converters
Paux , power required for auxiliary services
Pidle , power loss (if any) during idling
energy
idle
power
cycle
PPP∆∆∆ttt
η= η= η=
P ∆t P ∆t P ∆t
+ Pidle ∆+tP
+ Pidle ∆tcycle
idle
idle ∆ taux
η s ηc η s ηc η η
s c
40
By summarizing …
• Energy capacity of SMES is ridiculous compared to batteries
• Idling losses in power converters do not allow long term storage
• Cooling losses further complicate losses
Is the SMES
useless and hopeless?
41
Parameters of the energy storage
• Power that can be absorbed or supplied, P
• Duration of the power delivery, ∆t
• Number of cycles, N
• Response time, tr
42
Grid and Customer Applications of Energy Storage
Bulk energy management
market / less need for inefficient (low load) operation of power plants
∼ 10 - 100 MW × 1 h , 1 cycle per day
grid
Transient Stability
Increased transmission limit
∼ 10 - 100 MW × 1-10 s, occasional
Frequency regulation
less need inefficient (low load) operation of power plant
∼ 1 - 50 MW × 1-15 min, 10-1000 cycles per day
Other applications with more limited cost/benefit trade-off
• damping of sub-synchronous resonance
• black start
• deferral of new transmission and distribution
43
Customer
Power quality and UPS
compensation of voltage sag + Power Quality services to the customer
∼ 1 - 10 MW × 0.1-100 s, occasional deep cycle
+ continuous minor cycles
Leveling of impulsive power
constant power absorption from grid
1 - 10 MW × 0.1-1 s, continuous cycles
44
Parmeters of Storage for Grid and CustomerApplications
• lev. imp. power
• Voltage quality
• UPS
• Trans. stability
• lev. imp. power
• Voltage quality
• UPS
• Trans. stability
• Freq. regulation
• Freq. regulation
• Bulk en. man.
• Bulk en. man.
• lev. imp. power
• Freq. regulation
• Voltage quality
• Bulk en. man.
• UPS
• Trans. stability
1. Power intensive systems
Cost of battery scales with power and is roughly independent
on the energy
Example: battery system
made of 1 MW × 1 h
module, 1M€ cost each
Case 1
Rated power
Duration of delivery
Rated energy
Num. of modules
Total Cost
Specific cost
30 MW
1h
30 MWh
30
30 M€
1 M€ / MWh
Case 2
Rated power
Duration of delivery
Rated energy
Total Cost
Specific cost
30 MW
6 min
3 MWh
30 M€
10 M€ / MWh
46
Cost of SMES scales with energy and is roughly independent
on the power
For example SMES is
competitive in case 2 if the
cost of 3 MWh storage is
lower than 10 M€
Case 1
Rated power
Duration of delivery
Rated energy
Num. of modules
Total Cost
Specific cost
30 MW
1h
30 MWh
30
30 M€
1 M€ / MWh
Case 2
Rated power
Duration of delivery
Rated energy
Total Cost
Specific cost
30 MW
6 min
3 MWh
30 M€
10 M€ / MWh
If a large power is required for a more limited time SMES can
represent a cost effective storage technology
47
2. Hybrid SMES - Battery systems
load
battery
Low pass
control
PCS
High pass
control
SMES
SMES can be conveniently used in combination with battery due to the
complementary characteristics
•
•
Battery provides long term base power – hence energy
SMES provides peak power and fast cycling
48
• Reduced power rating of batteries
• Reduced wear and tear of batteries
(no minor cycling)
• Reduced energy rating of SMES
SMES
Advantages:
battery
total
Power vs time
49
3. Increasy peak power of industry scale batteries
1 MW × 6h NaS battery system with double peak power capacity
• The power rating of the system is to be doubled for short times ( < 10 s )
due to power quality requirement
• No impact is obtained on the total storage requirement due to the
increased peak power capacity
Solution 1
the battery pack is doubled
• Cost is doubled
• Energy capacity is also doubled but
the system is greatly underexploited
50
Solution 2
SMES is added to the battery to provide short term peak power
To scale
(roughly)
1 MW – 6 h
+
1 MW – 10 s
Size and cost of the system can be greatly reduced !!
51
4. Protection of sensitive equipment
Sensitive customer
Voltage sags may occur in
power grid due to faults
Sensitive customers can
only tolerate a voltage
reduction f 30 &% for 200
ms
1 MW – 5 s SMES system
The Kameyama SMES
10 MW – 1 s SMES system
54
5. Leveling of impulsive loads by SMES
Pgrid
Pload
Ismes
Pload
Pload
•
•
Pgrid
Iload
Igrid
No battery can be used for this application due to the prohibitive number
of cycles
Advantages brought by SMES can be significant also for moderate size
systems
55
Auxiliary network services by SMES
Iload
Igrid
Ifilter
ISMES
•
•
Harmonic compensation
Power factor correction
56
6. Hybrid SMES - Liquid Hydrogen system
• Liquid Hydrogen is used as energy intensive storage
• Free cooling power is available for SMES due to the
presence of LH2 at 20 K
• SMES is used as power intensive storage
57
Shintomi et al.
58
Outline
• SMES technology
SC material and Conductor
Coil
Power conditioning system
A case study - 1 MW / 5 s SMES
• Applications
Energy storage
SMES applications
Grid
Customer / Industry
• SMES actvities at the University of Bologna
59
1. A 200 kJ Nb-Ti µSMES ( 2004 – 2007 )
Cold test in 2014 (and 2013)
60
2. Conduction cooled MgB2 SMES demonstrator (2014 – 2016)
• 3 kJ MgB2 Magnet
• 40 KW Mosfet Based PCS
Cold test in porgress
Full test at 1-10 kW to come shortly
61
3. Conduction cooled MgB2 SMES Prototype (2016 – 2019)
MISE - Italian Ministry of Economic Development
Competitive call: research project for electric power grid
Project funded
Budget: 2.7 M€
Duration: 2016-2019
300 kJ – 100 kW prototype
full system
To resume on SMES …..
• SMES is feasible, but AC loss need to be investigated
SMES is an option if
• Continuous deep charge/discharge cycling is
required (leveling of impulsive loads)
• Short term increase of peak power of energy
intensive systems is required
• Fast delivery of large power is required for short
time
63
Thank you for your
kind attention …
… antonio.morandi@unibo.it