Variable frequency drives (VFDs) are electrical systems that control the frequency and voltage supplied to an electric motor to vary its speed. The document describes VFD components including an input transformer, variable frequency converter, and AC motor. It also discusses VFD applications, design compliance with standards, and Nidec ASI's product families of VFDs including the Silcovert TN, GN, TH/NH, and S models.

1. Variable Frequency Drives
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2. Index – Part 1
VARIABLE FREQUENCY DRIVE
• definition
• main components
• applications
• design compliance
VARIABLE FREQUENCY CONVERTER
OUR PRODUCT FAMILIES
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3. Variable Frequency Drive
Definition
Variable frequency drives (VFDs) belong to a group of equipment called
“adjustable speed drive systems” (ASDSs) or “variable speed drive systems”
(VSDSs)
Variable speed drives can be electrical or mechanical, VFDs are electrical only
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4. Variable Frequency Drive
Definition
A possible definition of VFD is given by the IEC EN 61800 reference standard
that rules the “adjustable speed electrical power drive system (PDS)” with
voltage above 1 kV a.c.
input transformer
variable frequency converter
induction or
synchronous motor
main
power
supply
driven machine
a.c. adjustable speed power drive system (PDS)
as defined by CEI EN 61800-4
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5. Variable Frequency Drive
Main Components
Input transformer: adaptation of voltage levels, insulation
Variable frequency converter (VFC): change of fixed frequency power source
into variable frequency voltage and current
A.C. motor: conversion of electrical power into mechanical rotating power
input transformer
variable frequency converter
induction or
synchronous motor
main
power
supply
driven machine
a.c. adjustable speed power drive system (PDS)
as defined by CEI EN 61800-4
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6. Variable Frequency Drive
Main Components
An integrated engineering approach
Understanding the overall system issues allows us to design products and
solutions which fit your needs better.
NIDEC ASI is able supply the whole variable frequency drive system
Subsystem Design
• Substation
• Power Conversion
• Control System
• Auxiliaries
• Power Quality
Electric Grid interface
•Current & Voltage distortion
• Power factor Improvement
• Flicker Control
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Automation
• Process Design
• Algorithm Development
• Greenfield turn-key plants,
revampings, expansions
• System Integration
Motor side connection
• Torque distortion
• Motor thermal stresses
• Train dynamics
• Train operability
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7. Integrated Engineering
NIDEC ASI designs and supplies electric motors, generators
and VFDs to fulfill the application requirements optimizing
the overall efficiency and performance.
Concept
Basic & detailed design engineering
•
Process engineering
•
Engineering and Systems Integration
•
Complete project and procurement management
•
Design
•
Hardware manufacturing
Construction •
Software development and testing
•
•
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Commissioning and tuning
•
Upgrades
•
Support
Installation tests
After sales service, support and training
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8. Integrated Engineering
Our R&D Department conducts advanced research in power devices and is able to work with
customers on innovative products and prototypes.
Our Engineering team in Milan works in close collaboration with both R&D Department and our
Motors & Generators Engineers in Monfalcone to optimize package configuration.
Through our Lean Manufacturing Teams, Engineering & Manufacturing meet on a regular
basis to optimize product configuration and manufacturing processes.
Our field technicians provide constant feedback to our Engineering Dept. and upgrades are
designed to guarantee a full life cycle to your components.
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9. Variable Frequency Drive
Applications
The VFD is used to
• continuously drive a load

(speed / torque control, ..)

• soft start large motors


(weak network, more than one)

• control the output frequency and voltage
(wind generator, tidal turbine, ..)
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

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10. Variable Frequency Drive
Design Compliance
The design of the system complies with the IEC EN applicable standards
Variable frequency converters for the North-American market UL marked by
Field Evaluation (FE) Services or CSA marked by Special Site Acceptance.
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11. Index – Part 2
VARIABLE FREQUENCY DRIVE
VARIABLE FREQUENCY CONVERTER
• main assemblies
• design criteria
• converter & inverter
• d.c. link
• air cooling
• water cooling
• controller
OUR PRODUCT FAMILIES
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12. Variable Frequency Drive
VCF Main Assemblies
The variable frequency converter consists of several standard assemblies:
converter, inverter, d.c. link, cooling system, controller
cooling system
from input transformer 
~
d.c. link
=
 to a.c. motor
=
~
converter
inverter
controller
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13. Variable Frequency Drive
VCF Main Assemblies
Converter: change of a.c. power with fixed frequency into d.c. power
Inverter: change of d.c. power into a.c. power with variable voltage and frequency
D.C. link: energy storage
Cooling system: removal of the heat
Controller: control of the motor, monitor and protection of the system
cooling system
from input transformer 
~
d.c. link
=
=
 to a.c. motor
~
converter
inverter
controller
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14. Variable Frequency Drive
VCF Design Criteria
NIDEC ASI manufactures with the same design criteria different
product lines
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15. Variable Frequency Drive
Converter & Inverter
Proven design
• VSI and LCI solutions
• multi-phase diode and active front-end configurations
+
State-of-the-art technology

0
• Thyristor/SCR: Current controlled device, Semi-controlled
(turn-on only), Highest V-I rating @ lowest cost, Mature
technology
• IGBT: Voltage controlled device, Fully controlled, Faster
switching, Module (mature) or press-pack (emerging), proven
technology.
• IGCT: Current controlled device, Fully controlled, Lower
conduction loss, Press-pack packaging, Proven technology
Reliability of operation:
• device selection
• sizing (application, load cycle)
• full load current test
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16. Variable Frequency Drive
Inverter Topology
LCI
• High distortion
• More subsystems to
get high performances
• Use SCR
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VSI (3-Level NPC)
VSI (Multi Level H-bridge)
• Extensively adopted in
Steel industry
• Complexity @ high
power
• Easy & flexible to
control
• Complex failure
modes
• Use IGBT, IGCT
• Use IGBT and IGCT
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17. Variable Frequency Drive
Converter & Inverter
Modularity
• stack (diode and thyristor), phase module (IGBT and IGCT)
• compactness and robustness
• fast change
Switching
• insulation HV/LV by optical fibres
• monitoring
Safety
• HV and LV circuits separation
• key interlock
• IP20 with open doors
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18. d.c. link
Variable Frequency Converter
Integrated in the phase assembly together with the
capacitors (VSI)
Integrated in the cabinet together with the iron-core
reactance (LCI)
Insulation monitor
Earth switch (safety)
+
0

-
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19. Variable Frequency Converter
Air Cooling
Air cooling system
• forced, in open loop (T environment ≤ 45°C, size)
• draft fan on top
• low pressure inside the cabinet
• suction from the front
• fan redundancy
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20. Variable Frequency Converter
Water Cooling
Water cooling system
• deionized, in closed loop (T raw water ≤
35°C)
• water pump, redundancy
• filter cartridges
• monitoring (pressure, temperature, flow,
conductivity)
• piping (PVC, stainless steel)
• water cooling unit integrated in the cabinet
• fast connections to easily remove the power assemblies
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21. Variable Frequency Converter
Water Cooling
Water-to-water heat exchanger
• integrated in the cooling unit (VFC cabinet)
Water-to-air heat exchanger (fin fans)
• raw water not available, T external air < 50°C
• external to the cabinet
• deionized water loop only
Water chiller unit
• raw water not available, T external air up to 52°C
(higher T on request)
water
chiller
• special machines
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22. Variable Frequency Converter
Controller
Drive controller
• full digital
• motor control (V/Hz, sensorless, FOC algorithms)
• monitoring and protecting functions (transformer, VFC, motor)
• auxiliary circuits management
• hardwired and serial interface
• remote monitoring and diagnostic capability
HMI
• graphic display
• indication in full language (user friendly)
• local control of the system
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23. Index – part 3
VARIABLE FREQUENCY DRIVE
VARIABLE FREQUENCY CONVERTER
OUR PRODUCT FAMILIES
• SILCOVERT TN
• SILCOVERT GN
• SILCOVERT TH / NH
• SILCOVERT S
• customized solutions
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24. Our Product Families
SILCOVERT TNTM
cooling system

~
=
=
front end

~
control
unit
induction motor
A single converter with maximum adaptability.
A NPC type, Voltage Source, IGBT inverter
with both Diode Front End and Active Front End
configurations and easy integration into
automation solutions with serial communication
capabilities.
input transformer
SILCOVERT TN 3300V are medium voltage IGBT based voltage source inverters for variable
frequency supply of induction motors. These modular units are built using standard
assemblies that can be customized to the most demanding applications.
inverter
Applications
Extruders, pumps, fans, mixers, compressors, metals applications, propellers and
thrusters for marine applications and wind generators
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25. Our Product Families
SILCOVERT TNTM
Technical Characteristics
Main Supply 3-phase:
DFE(12P) 2 x 1800 V±10%;
DFE(24P) 4 x 1800 V±10%; and
AFE: 3000 V +/- 10%
Efficiency: ≥ 0.98 (50 Hz, rated load)
+
Output Frequency: 5 – 70Hz (extended to 140Hz)
Output Voltage: 0 – 3300V (3 phase); PWM
Output power range: Air Cooling 1300-10400 KVA
0

Water Cooling 3600-21600 KVA
Diode front-end, 12 or 24 pulse (power factor  0,96)
-
Active front end (regenerative operations)
Induction motor control
Strongly standardized (15 sizes)
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26. Our Product Families
SILCOVERT GNTM
cooling system

~
=
=
front end

~
control
unit
inverter
induction motor
It provides ultra high efficiency, very high power
factor (> 0,96), minimum torque ripple and low
input and output harmonic content and easy
integration into automation solutions.
input transformer
SILCOVERT GN 3300V are medium voltage IGCT based voltage source inverters.
Modular units using standard assemblies: a front end, inverter section, cooling system and
control unit.
Applications
ship propulsion, high torque / overload / dynamic requirements (metals), large centrifugal
loads (pumps, compressors, fans) …
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27. Our Product Families
SILCOVERT GNTM
Technical Characteristics
Mains Supply Voltage (3-phase): DFE(12p) 2 x 1850V ± 10%
DFE(24p) 4 x 1850V ± 10%
AFE 2850V ± 10%
Efficiency: ≥ 0,98
Output Frequency: 10 – 65Hz normal / 10 – 110Hz extended
Output Voltage: DFE 0 – 3000V / AFE 0 – 3300V
Output power range: water cooling 9000 to 24.000kVA (higher power on request)
Diode front-end, 12 or 24 pulse (power factor  0,96)
+
Active front end (regenerative operations)
Induction or synchronous motor control
Standardized (6 sizes)
0

-
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28. Our Product Families
SILCOVERT THTM / NHTM
Silcovert H Series are Multi Level Converters with IGBT power devices and a more
efficient and precise control for induction and synchronous motors.
Silcovert TH – Multi-Level, LV IGBT based, PWM controlled. Available configurations with
air cooling systems and water cooling system (power range 500/18700 KVA).
Silcovert NH - The PWM technique with high switching frequency allows an almost
sinusoidal motor current with low total losses and ripple-free torque. Its water cooling
method permits to achieve high output power ranges.
This Series are compatible with your existing motor systems, regardless of brand or age.
With our customized retrofit you can achieve increased levels of safety, reliability and
efficiency.
Applications
ship propulsion, large centrifugal loads (pumps, compressors, fans) …
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29. Our Product Families
SILCOVERT THTM / NHTM
Technical Characteristics
+
VSI type
IGBT based
PWM controlled
4,16 up to 7,2 kV
250 Hz, extended range up to 330 Hz

+
NH Power range: water cooling 2900/14400 KVA
air Cooling 1500/3700 KVA
0
TH Power range: air cooling up to 8100 KVA
water cooling up to 18700 KVA
Higher power on request for water cooling (NH)
Diode front-end, multipulse (power factor  0,96)
Input transformer integrated or close to the electric cabinet
Induction or synchronous motor control
Centrifugal loads (pumps, compressors, fans), revamping of
Existing motor, high speed applications, …
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-
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30. Our Product Families
VSI Diagram
iU1
iU2
iU3
iV1
iV2
iV3
=
~
12 pulse diode front end configuration
=
iU1
iU2
iU3
~
oU
iV1
iV2
iV3
iW1
iW2
iW3
=
=
~
active front end configuration
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oW
iW1
iW2
iW3
24 pulse diode front end configuration
~
oV
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multipulse diode front end configuration
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31. Our Product Families
SILCOVERT STM
SILCOVERT S is a medium voltage load-commutated current source inverter (LCI) for
synchronous motors and provides speed regularity, monitoring and braking torque regulation,
V/Hz low shaping, Easy integration into automation solutions due to Ethernet communication
capabilities with digital and analogue interface.
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=


~ =
~
rectifier
inverter
induction motor
Applications
soft starter or drive for large centrifugal loads
(pumps, compressors, fans), ship propulsion, gas
and hydro turbine starter, …
input transformer
cooling system
DC line reactor
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32. Our Product Families
SILCOVERT STM
Technical Characteristics
Mains Supply(3-phase)
Efficiency: >0,99
+
Output Frequency: 5 - 95Hz
Output Voltage: Air Cooling up to 4500 V

Water Cooling up to 72000 V
6/6 , 12/6, 12/12, 24/12 pulse configurations
4 quadrants operations
Synchronous motor control
Design on project, based on standard stack frames
-
High reliability (mature technology)
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33. Our Product Families
LCI diagrams
~
6 pulse / 6 pulse configuration
~
12 pulse / 6 pulse configuration
~
12 pulse / 12 pulse configuration
~
24 pulse / 12 pulse configuration
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34. Our Product Families
Customized Solutions
NIDEC ASI is able to design solutions ad hoc
• auxiliaries (disconnector, switchgear, harmonic
filters, ..)
• ratings
• electric cabinet (overall dimensions, cable i/o, IP,
..)
• containerization
• system automation
• serial communication
• ..
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