Vacon NX6 Guide

vacon nx
ac drives
design guide
hybridization
®

vacon • 1
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TABLE OF CONTENTS
Document ID:DPD01887
Revision release date: 24.10.2016
1. BASICS ........................................................................................................................2
1.1 Power or energy storage....................................................................................................... 3
1.2 Battery current dimensioning............................................................................................... 5
2. BASIC TOPOLOGIES FOR CONNECTION....................................................................... 6
3. SPECIAL CHARACTERISTICS AFFECTING THE SELECTION ......................................... 8
3.1 Voltage window...................................................................................................................... 8
3.2 Galvanic isolation requirement........................................................................................... 11
3.3 Balance or maintenance charge......................................................................................... 14
3.4 System control principles ................................................................................................... 15
4. CHOOSING A CORRECT TOPOLOGY............................................................................ 17
4.1 Allowed topology configurations......................................................................................... 18
5. BASIC VARIANTS....................................................................................................... 19
5.1 Direct to DC ......................................................................................................................... 19
5.1.1 Control structure .................................................................................................. 20
5.2 DC to DC .............................................................................................................................. 22
5.2.1 Filter...................................................................................................................... 22
5.2.2 Control Structure.................................................................................................. 34
6. PRODUCT CONFIGURATION EXAMPLES.................................................................... 36
6.1 Scope of delivery ................................................................................................................. 36
6.1.1 Direct to DC........................................................................................................... 36
6.1.2 DC to DC ................................................................................................................ 37
6.2 Example configurations ...................................................................................................... 39
6.2.1 DC/DC for supply interruptions ............................................................................ 39
6.2.2 Direct DC for Grid Support.................................................................................... 40
7. SIZING OF THE SYSTEM AND PRODUCT .................................................................... 41
7.1 Direct to DC ......................................................................................................................... 41
7.2 DC/DC .................................................................................................................................. 42
8. INFORMATION TO ACQUIRE FROM CUSTOMERS ....................................................... 47
NOTE! You can download the English and French product manuals with applicable safety,
warning and caution information from
http://drives.danfoss.com/knowledge-center/technical-documentation/.
REMARQUE Vous pouvez télécharger les versions anglaise et française des manuels produit
contenant l’ensemble des informations de sécurité, avertissements et mises en garde
applicables sur le site http://drives.danfoss.com/knowledge-center/technical-documentation/
.

1
vacon • 2 BASICS
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1. BASICS
The basic idea is always to achieve energy and/or power management of Common Point of Coupling.
Typical use cases are
• time shift for production
• peak load shaving for distribution
• smoothen load for average energy
• backup power or black out start
• grid support
Figure 1. Power balancing
Energy Production
kW
Average Power
t
Charging
Discharging
Process Power
Grid Power
kW
Average Power
t
Charging
Discharging

BASICS vacon • 3
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1.1 Power or energy storage
It is important to distinguish the system’s "nature", that is, whether it is a power application or an
energy application. Another relevant thing to note is the dynamic requirements of the application.
Determining the application:
• Energy vs. power (kW/kWh ratio)
• Dynamic requirements:
o Grid support functions (Harmonics, FRT)
o Bulk energy time shift
Figure 2. Power vs. energy
Time [h]
Power: Energy
MW: MWh
4:1 3:1 2:1 1:1
1:1 1:4
1:2 1:3 1:4
Time [h] Time [h]
Power [MW] Power [MW] Power [MW]
Power Applications Energy Applications
4:1

1
vacon • 4 BASICS
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Figure 3. Comparision of battery systems
Table 1. Comparision of battery systems
#Reference #Reference
A Batteries E Li-ion
B Pb F Double layer capacitors
C NiCd G Electrolytic capacitors
DNiMH
Battery type Energy density
Wh/kg Power density W/kg Service life in cycles/years
Lead acid battery 30-50 150-300 300-1,000/3-5
Nickel-metal hybride
battery 60-80 200-300 >1,000/>5
Lithium-ion battery 90-150 500 -> 2,000 >2,000/5-10
Spercaps (double
layer capac.) 3-5 2,000-10,000 1,000,000/unlimited
BA C D E
F
G
100s
1,000s
1,000
100
10
1
0.1
0.01
10 100 1,000 10.000
10,000s
10s
1s
0.1s
Energy density in Wh/kg
Power density in W/kg

BASICS vacon • 5
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© Electricity storage association
Figure 4. System ratings
1.2 Battery current dimensioning
In a battery, the nominal current is denoted with C. For example, a 10Ah 1C current would be 10A.
In some cases, the below rated currents are marked as 0.5C = C5. In that case, for example a 10Ah
rated current used with a 1A current would mean 0.1C or C1. In the same example, 2C would mean
20A.
#Reference #Reference
A Energy management
Dicharge timeBBridgingpower
CPowerquality
CAES Compressed air Ni-Cd Nickel-cadmium
EDLC Dbl-layer capacitors Ni-MH Nickel-metal hybride
FW Flywheels PSH Pumped hydro
L/A Lead-acid VR Vanadium redox
Li-ion Lithium-ion Zn-Br Zinc-bromine
Na-S Sodium-sulfur
A
C
B
100
10
1
0.1
0.01
0.001
0.0001
0.001 0.01 0.1 1 10 100 1000 10,000
Ni-MH
VR
FW
Ni-CD
L/A
EDLC
Na-S
CAES
PHS
Discharge Time [hr]
Rated Power [MW]
Na-S
Li-ion
Zn-Br

2
vacon • 6 BASIC TOPOLOGIES FOR CONNECTION
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2. BASIC TOPOLOGIES FOR CONNECTION
The basic connections are divided into multible possibilities.
Table 2. Basic connections
Use case Topology Pros Cons
Common DC energy
storage connection
• No competitive
"technology" when
DC-grid connec-
tion needed
• Different storage
voltage/techno-
logy adaptations
Energy storage to AC-
grid with combination of
DC/DC converter + grid
converter
• Different storage
voltage/techno-
logy adaptations
•Expansioneasy
• Battery stack
replacing due to
ageing
•Largenumberof
components
• Lack of efficiency
•Size
Energy storage directly to
AC-grid with grid
converter
• Small number of
components
• Efficiency
•Size
• Power vs. energy
dimensioning is
independent from
each other
• Expansion difficult
• Battery stack
replacing due to
ageing
Energy storage close to
load and AC-grid with
DC/DC converter con-
nected between DC-link
and storage
•Loadpower/
energy support
close the con-
sumption
• Different storage
voltage/techno-
logy adaptations
•Expansioneasy
• Battery stack
replacing due to
ageing
•Largenumberof
components
•Size
Filter
Filter
Filter
Filter
Filter
Filter

BASIC TOPOLOGIES FOR CONNECTION vacon • 7
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Energy storage close to
load and AC-grid with
direct DC-link connection
•Loadpower/
energy support
close the
consumption
• Large number of
components
• Efficiency
•Size
• Power vs. energy
dimensioning is
independent from
each other
•Voltagewindow
limiting the scope
only in range of
400 Vac using DC
range 600-1100
Vdc
• System expansion
later with
additional
batteries difficult
Filter

3
vacon • 8 SPECIAL CHARACTERISTICS AFFECTING THE
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3. SPECIAL CHARACTERISTICS AFFECTING THE
SELECTION
Different chemistry causes different behavior in cell voltage as a function of charge/discharge and
SOC (State of Charge). This creates "voltage window" requirement similar to the solar inverter.
Galvanic isolation requirement is different from many industrial drive application. This is due to the
fact that the battery system should not be predisposed for common mode voltage.
For the Battery Management System (BMS) to be able to reset the SOC calculation, it is necessary
to charge the battery to 100% SOC. This ensures that BMS is able to calculate SOC accurately and
maintain the battery in safe operating area. For this, a balance charger or a maintenance charger is
needed in some cases.
3.1 Voltage window
For both the DC/DC converter and the GTC (Grid Tie Converter) the first dimensioning question
comes from energy storage (battery) voltage dimensioning. It is important to define the “voltage
window" for empty and full battery cell voltage. Depending on battery chemistry the ratio can be full/
empty = 1,2… 2… (meaning, for example, full being 1000 Vdc, and empty being from 800 Vdc to 500
Vdc) and for super capacitors even bigger. Especially for GTC this is a limiting factor. The limitations
come from minimum tolerable DC-link voltage to maintain controllable grid voltage and from
maximum allowed voltage to maintain within design criterion of the hardware.
The behavior of voltage stretch in a battery can be illustrated with a spring being pulled or pushed.
Figure 5. Spring analogy of the battery voltage change
120
100
80
020 40 60 80 100
UDC [%]
SOC [%]
Charging of batteryDischarging of battery
1C 2C 3C 6C 9C

SPECIAL CHARACTERISTICS AFFECTING THE SELECTION vacon • 9
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Figure 6. Battery voltage change as a function of State Of Charge (SOC)
The voltage window is important also from the process dynamics point of view. If we expect the
battery system to take energy (either discharge or charge), we create change in voltage of the
battery. The voltage controller needs to be capable to change the actual voltage of the battery in a
controlled way from full to empty value or from empty to full value. For example, if the battery is
wanted to be discharged in 30 s - 300V voltage window from 1000 Vdc - 700 Vdc it means roughly 10
V/s voltage change of rate. This is huge difference in comparison to for example case where
discharge time is longer, say 30 min resulting in 0,2 V/s. This way the SOC (State of Charge) behavior
is observed.
Below is a case where same sized of DC-power units are charged/discharged from the battery.
Figure 7. Battery string number effect on voltage change using the spring analogy
120
100
80
020 40 60 80 100
UDC [%]
SOC [%]
Charging of batteryDischarging of battery
1C 2C 3C 6C 9C

3
vacon • 10 SPECIAL CHARACTERISTICS AFFECTING THE
Tel. [phone] • Fax [phone]
The difference in the cases is that the battery size in energy is changed from 6 strings in parallel to
one string in parallel. This will lead in higher C-rates in the battery having smaller amount of strings
when the same amount of power is taken out of each battery setup (current going from 1C --> 6C).
The effect is visible in higher stretch of voltage levels needed in controlling the battery.
Figure 8. Number of batteries
Figure 9. Battery sizing effect on voltage change during equal power changes
The spring analogy works also when thinking of parallelizing of batteries (springs). The more you
have batteries (springs) in parallel, the less you need to use voltage stretch to gain the same
response.
123456 12345 12 1
120
100
80
120
100
80
8
6
4
2
0
-2
-4
-6
-8
0.2
0.25
0.2
0.35
0.4
0.6
0.65
0.7
0.75
0.8
0
0.1 0.2 0.7 0.5 0.4 0.3 0.8 0.9
1
0.6
tt t
increasing charge current
increasing load current
I [C-rating]UDC
[%] UDC [%]

SPECIAL CHARACTERISTICS AFFECTING THE SELECTION vacon • 11
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3.2 Galvanic isolation requirement
The pulse width modulation (PWM) produces common mode voltage. Because every phase (a, b and
c) can be connected only either to positive DC-bus (+Udc/2) or to negative DC-bus (-Udc/2), sum of
output voltages is always unequal to zero. The common mode voltage (CM-voltage) Ucm can be
calculated as average of output voltages:
Table 3 presents all possible common mode voltages produced by different switching states. Used
reference point is in the middle of the DC-link.
Table 3. Common mode voltage as function of modulation sequence
Switching vector a b c Ucm
U1+-- -Udc /6
U2++- Udc /6
U3-+- -Udc /6
U4-++ Udc /6
U5--+ -Udc /6
U6+-+ Udc /6
U7+++ Udc /2
U8--- -Udc /2

3
vacon • 12 SPECIAL CHARACTERISTICS AFFECTING THE
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Figure 10. Simulated CM-voltage, Udc=1025V, fsw=5kHz.
Because of the common mode DC-link starts to jump compared to ground. Main frequency for this
jumping is switching frequency but also higher frequencies will be present. As an example, a typical
measured DC+ to ground voltage can be seen in Figure 11. A rule of thumb is that with a typical DC-
link voltage 1025V, the voltage spikes will be about 1.5kV.
#Curve info max min rms
...... UDC/2 171 171 171
---- UDC/6 512 512 512
___ CM voltage 512 -512 264
600
400
40 40.10 40.20 40.30 40.40 40.50
Time [ms]
40.60 40.70 40.80 40.90 41
200
0
-200
-400
-600
UDC/6 UDC/2 CM voltage
CM voltageU [V] Common mode

SPECIAL CHARACTERISTICS AFFECTING THE SELECTION vacon • 13
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Figure 11. DC+ to ground voltage. On the left Udc = 1200 V, on the right 800 V.
The battery system does not withstand unfiltered common mode voltage. Because PWM modulation
is a CM voltage source, the DC side of the energy storage system must be stabilized. This means
that there must be a flexible element in electrical system that is able to take this common mode
voltage fluctuation. This element is now a transformer star point (instead of a motor stator star
point) that shall not be grounded.
Figure 12. Transformer must be isolated from ground.
In the grid side filter, if LCL is used, the grounded capacitors cannot be kept connected to ground. If
transformer inductance is bigger or at least the same as proposed grid side inductance, it is
possible to use only an LC filter (sine) to avoid additional voltage drop in the grid side choke.
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
-1000
-500
0
500
1000
1500
Sampled waveform
time [s]
voltage [V] voltage [V]
time [s]
-600
-400
-200
0
200
400
600
800
1000
1200
Sampled waveform
CM
Transformer
LCL-filter
AFE
(Active Front End)
DC-link

3
vacon • 14 SPECIAL CHARACTERISTICS AFFECTING THE
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Figure 13. LCL ground capacitor must be disconnected
3.3 Balance or maintenance charge
The maximum voltage of the battery is needed only when charging the battery at the fullest level.
Current in that voltage is small. However, the time during which this voltage prevails can be
theoretically infinite if the battery is continuously kept 100% full (which is not advisable because of
the aging of the battery). When the charging is finished and even only little load is given to the
battery, the voltage decreases rapidly.
It is necessary (after a certain time or a number of battery charge/discharge cycles) to "reset the
trip meter" of the Battery Management System. Otherwise the state of charge calculations can
become misleading and result in poor behavior or even in exceeding the safe operation limits. The
only good way to "reset the trip meter" is to charge the battery to the full state where the Battery
Management System can safely tune its SOC value back to 100%.
Every cell must be charged extremely slowly so that the current of each cell goes as low as possible
(the cell reaches its full voltage). For a big battery system that has many cells in parallel and in
serial this is done from the same DC+ and DC- connections with the same Udc control. Do not start
to dismantle batteries to charge them individually. Because of the differences in cell level (for
example SOC, impedance) this means that some of the cells fill up sooner than others.
To avoid overcharging, the natural passive balancing of the battery system is needed. However, this
is a slow process and that is why the balancing charge needs to be slow with an accurately
controlled small current. It is difficult to say how accurate and small the current needs to be, but
the rule of thumb is that 0.01C is needed. If the device is not able to provide accurately such a
current, it is necessary to add a balance charger to the system. The battery manufacturer can also
be consulted about balance chargers.
-L1
-L2.1
-L2.2
-L2.3
-C1
-C2
HF
HF
-C3
U2 U1
V2
W2
V1
W1
-R1
-C1.1 -C1.2 -C4.1 -C4.2
-C5.2
-R4
-R2
-C2.1 -C2.2 -C5.1
-R5
-C6.2
-R3
-C3.1 -C3.2 -C6.1
-R6
no HF

SPECIAL CHARACTERISTICS AFFECTING THE SELECTION vacon • 15
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Figure 14. The need of a balance charger
A balance charger is basically the same as a bulk power device (grid converter or DC/DC converter)
but with a smaller rating to be able to reach a control accuracy of storage current of 0.01C.
3.4 System control principles
The energy storage systems are often incorporated with different layers of controls having different
responsibilities.
The Energy Management System optimizes the energy efficiency of the system. This can include
choosing and prioritization the usage of different energy sources. Normal time scales are from tens
of seconds to hours.
The Power Management System includes controlling of power balance in a system that has multiple
energy/power sources. Normal time scales are from grid cycle (20ms - 50Hz) to seconds.
The Power Conversion System of this list is the system relevant to the product. The PCS includes
Power Conversion Control and Power Conversion Hardware, which is the VACON® hardware. It is
to control power conversion between the energy storage and the system. Normal time scales are
from micro seconds to grid cycles.
The Storage System includes Battery Management System and the battery. Battery Management
System monitors the storage system as well as the storage cell level phenomena.
#Reference #Reference
A
Not possible to reach 100%
SOC with big current =
Balance charger?
B
Not safe to go empty SOC
with big current. BMS to tell
when stop discharging.
A
B
120
100
80
020 40 60 80 100
UDC [%]
SOC [%]
Charging of batteryDischarging of battery
1C 2C 3C 6C 9C

3
vacon • 16 SPECIAL CHARACTERISTICS AFFECTING THE
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Figure 15. Typical system layers
Energy Management System (EMS)
Power Management System (PMS)
Power Conversion System
Power Conversion
Hardware
Power Conversion Control
(PCC)
Battery Management
System
Battery
Storage System

CHOOSING A CORRECT TOPOLOGY vacon • 17
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4. CHOOSING A CORRECT TOPOLOGY
Figure 16. Selection diagram
DC/DC
converter
DC/DC
converter
Connection to
AC or DC
Direct to
DC
Application
Control ref
P / Udc /Idc
Customer
primary
reference
Customer
system
tailoring
Control
modes
Island
AFE
uGrid
Voltage
window
AC
small large
Grid
Converter
needed in
all cases
Grid
Converter
needed in
all cases
DC
Filter
Filter
Filter
Filter
Filter
FilterFilter
For example
VACON®
Common
DC-buss

4
vacon • 18 CHOOSING A CORRECT TOPOLOGY
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4.1 Allowed topology configurations
In the following table, example of allowed and not allowed configurations are given.
These configurations are valid for both with DC/DC converter or with a direct battery connection into
the DC-link. Options shown below are DC/DC configurations A), B) and C) and Direct to DC
connection D). Note that the storage topology does not affect the allowed or not allowed topology of
the connection to the system. There might however be other limitations, for example voltage or
current ratings.
Figure 17. Options A, B, C, D
Table 4.
OK? Configuration Notes
No grounding
allowed in
transformer
No HF/EMC
capacitors in LCL
OK
OK, transformer has
enough inductance
to satisfy filtering
demand of grid
converter:
Ltransformer ~
Lgrid side choke
HF
HF
HF
HF
HF
HF
HF
HF
AB
CD
33
Options
A, B, C, D
33
HF
Options
A, B, C, D
33
Options
A, B, C, D
33
Options
A, B, C, D