Agenda
• Introduction
• AC Drive Overview
• AC Drives Topology Overview
• Comparison of MV drives
• Performance
• Component count
• Loss and efficiency
• Input/output waveforms
• Conclusion

Motor Starting Challenges
• High and Intermediate HP loads present certain
starting challenges:
• High current draw results in voltage drops
• Pump starts are usually associated with surges and water hammer
• High starting torques are challenges for MV motors
• High DOL torque characteristics subjects equipment to mechanical stresses
• Fans tend to be very high inertia loads (several times the NEMA standard) – motor thermal limitations
2

Induction motor torque, speed and current relationships
2.50
700
600
Breakdown Torque
2.00
Motor Currrent
1.50
500
400
1.00
0.50
Locked Rotor
Torque
Pull up Torque
Motor Torque
Breakaway
Torque
Constant Torque Load
Variable Torque Load
300
0.00
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
0
Synchronous Speed
200
100
3

How Drives Can Help
• IMPROVE process control by ‘infinite’ speed control
• IMPROVE process control by direct communication interface
(plug-and-play) with supervisory control system
• MINIMIZE equipment costs by increasing functionality of drive system through line synchronization and switching capability or multi-motor operation
• MAXIMIZE uptime by using the drives speed control and regeneration capability to reduce maintenance and stopping times and allow easy rebalancing (repetitive acceleration and deceleration cycles) after maintenance or cleaning
• Efficiency of most variable speed drives offer the best way to achieve energy savings.
4

Normal vs. Heavy Duty
• Definitions
• Evaluating required torques
• Accel/Decel, breakaway, overload conditions
• Evaluating duty cycle for continuous and overload operation
• Considering different motor base speeds (pole #) and base frequencies
120
110
100
90
80
70
60
50
40
30
20
10
0
0 6
Normal Duty Drive Torque Capability, 60 Hz base speed
12 18 24
170
160
150
140
130
120
110
100
90
80
70
Heavy Duty Drive Torque Capability, 60 Hz base speed
HD Drive momentary torque
HD Drive continuous torque
ND Drive 18P momentary torque
ND Drive PWM momentary torque
60
50
40
30
30 36
Speed - Hz
ND Drive continuous torque
42 48 54
20
10
(Confidential
– For Internal Use Only) Copyright © 2009
0 6 12 18 24 30 36 42
Speed - Hz
48 54 60 66
5
72

Drives and Soft Start Benefits
• REDUCE motor stress (lower heat, vibration, and transient torques)
• REDUCE system disruptions (by lowering current inrush from 600% to 100-150%)
• REDUCE maintenance costs
• INCREASE life of mechanical equipment (due to ‘soft start’ lower torques, lower speed operation)
• SAVE substantial energy costs (due to direct speed control of pumps at the optimum operating point)
6

Most Common MV VFD Topologies
• VFD manufacturers cover the market with a breadth of products
• Using 2-3 topologies
• The following are the main topologies
• CHB
• ANPC
• CNPC
• MMC
• NPC
• CSI
8

Most Common MV VFD Topologies
• VFD manufacturers cover the market with a breadth of products
• Using 2-3 topologies
• The following are the main topologies
• CHB = Cascaded H- Bridge
• ANPC = Active Neutral Point Clamped
• CNPC = Cascaded Neutral Point Clamped
• MMC = Modular Multilevel
• NPC = Neutral Point Clamped
• CSI = Current Source Inverter
9

Typical AC Drive Configuration
• Meeting harmonic requirements (IEEE-519)
• Meeting customer requirements
• High quality output waveforms
• Good performance with regards to controlling the customer process
• High PF, high efficiency
• High reliability and low cost

Topology Fundamentals: Multi Pulse DFE
Six pulse rectifiers
+
-
PST
Six pulse rectifiers
+
-
(a) 12-pulse rectifier d
=30 o
PST
(b) 18-pulse rectifier d
= 20 o
+
-
+
-
+
-
PST
(c) 24-pulse rectifier d
= 15 o
+
-
+
-
+
-
+
-
• harmonics cancel each other at primary:
Df
+
= (h-1) d
,
Df
-
= (h+1) d
• pulse #: p , secondary #: s , 1st harmonic at primary: h min
: s = p / 6, d
= 360 / p , h min
= p - 1
Line THD reduction!
11

Basic Concepts: Motor Side
• Achieve Good quality Waveforms
• Multi level inverters
• Series combination of LV converters
• Combination of the above
• Output filters
• Performance/Control
• Minimum V/Hz is offered
• Most often Vector Control used
• Higher performance with advanced control
• Space Vector Modulation
• Flux reduction for improved efficiency
• Direct Torque Control
.
12

Basic Concepts: Line Side
• Achieve harmonic mitigation
• Multi Pulse transformer
• With diodes
• With SCRs
• Active Front End Rectifiers
• Performance/Power flow control
• Diode rectifiers provide no control
• No regeneration
• SCR front end use phase shift control
• Offer regeneration
• Active Front End Rectifiers provide full switching control
• Phase shifting or Modulation index control: on line or offline switching pattern
• Regeneration
• Power Factor control, additional protection, etc
13

Medium Voltage Drive ac mains rectifier
MV drive dc link inverter
• Voltage Range ac motor
1 kV 2.3 kV
• Power Range
0.2 MW 0.5 MW
3.3 kV 4.16 kV 6.6 kV
1 MW 2 MW 4 MW 8 MW
11 kV 15 kV
35 MW
12 MW
14

Topology fundamentals: CSI vs VSI
M
Current Source Topology
Utility supply
~V ~  load
Voltage Source
Utility supply
~V ~V
• Differentiated by DC link components
Topology load
15
M

Low Voltage AC Drives
• Low voltage (up to 690V)
• All are Voltage Source Inverter (VSI) based
• Require a semiconductor switch with bi-directional current flow
• All use Low voltage IGBTs (mostly in module form)
• Mature topology and features

Control Strategy
• Control/Wave shape the output current by Pulse Width
Modulating the inverter switches:
• The inverter output voltage is chopped (PWMed)
• Note: this is true for all VFD types (2 level, 3level, multi-level)
• The output current is controlled and wave shaped to be close to sinusoidal
L i
Van
V phase
I
I

Medium Voltage AC Drives
• Medium Voltage Drives typically range from 1 kV to
7.2kV
• Two approaches in industry
• Series connection of low voltage ac drive modules (IGBT based)
• Series connection of MV semiconductors 3.3 kV to 6.5 kV
• for use in two and three level VSI and two level CSI
• The type and voltage/current rating of the semiconductors for MV applications depends on the type of topology used:
• IGBT, IGCT, SGCT (RB-IGCT), GTO

Thyristor Based Semiconductors
Diode (1955)
SCR (1955)
• Silicon
Controlled
Rectifier
• GateTurn Off thyristor
GTO (1980)
IGCT (1995)
• Integrated Gate
Commutated
Thyristor
• Symmetric
Gate
Commutated
Thyristor
SGCT (1998)
Trends
• Higher voltage
• Higher junction temperature
• Lower loss
• Improved switching speed
• Lower Gate drive requirement

Transistor Based Semiconductors
• Bipolar transistor
LV IGBT
(1990)
• Insulated Gate
Bipolar
Transistor
• High voltage
IGBT
New Gen
IGBT (2005)
• Trench gate, planar designs,
IEGT, etc
BPT (1975)
HV IGBT
(1998)
Trends
• Higher voltage
• Higher junction temperature
• Lower loss
• Higher insulation packaging, improved soldering and thermal management
• Reverse blocking IGBT
RB-IGBT
(2007)

IGCT Based Neutral Point Clamped
IGCT Based 3-Level NPC Voltage Source
Features:
• Each device sees only half DC voltage;
• Modular design;
• Share-DC-Link operation;
• Potentially transformerless.
21

3-Level VSI: Issues/Features
• Meeting IEEE-519
• May use 24pulse diode rectifier front end
• May use active front end
• Motor insulation/bearing current issue
• Use inverter output filter
• This makes it look like a sinusoidal output
• Good quality output waveforms
• Good performance, can do all applications

IGBT based NPC
IGBT Based 3-Level NPC Voltage Source m a
=0.8, f sw
=570Hz
Features:
• See IGCT based NPC
23

MMC Drive
4160 V
Grid
L s
L g
7-Level
MMC
( Rectifier )
Cell1
Cell2
Cell3
V d
Cell1
Cell2
Cell3
A
7-Level
MMC
( Inverter )
S
1
C1
S
2
S
3
C2
S
4
Cell
IM
4000V, 160 A
M

5-Level ANPC Drive
4160 V
L
 s
L g 1
Grid
L g 2 5-Level
ANPC
( Rectifier )
C g
C
C dc dc
5-Level
ANPC
( Inverter )
V d
E S a1
N
E
S a2
S
3
S
4
S
1
S
2
E
2
D
1
D
2
S
5
FC
D
5
S
6
D
6
D
3
D
4
A
IM
4000V, 160 A
M
27

5-Level ANPC Drive

5-Level CNPC IGBT

CNPC f sw
= 540 Hz, m a
= 0.9
Features:
• Low line THD;
• Low output harmonic and dV/dt;
• modular design;
30

Mechanical Layout

Cascaded H-Bridge m f
= 10, m a
= 1.0
Features:
• Low line THD;
• Low output harmonic and dV/dt;
• modular design;
• easy to achieve high voltage/power;
• Lots of manufactures:
Up to 13.8kV132MVA
32

Multi-level H Bridge VSI
4160 Volt Drive (750 V Power Cells)

CHB Fundamentals
# of cells versus voltage
Vcell
Vmot
2300
3300
4160
4800
6600
7200
10000
13800
14400
460 630 690 750 1375
3
4
5
6
2
3
4
4
6
7
9
6
6
2
3
3
4
5
6
4
6
3
3
6
2
• Highest voltage: 14.4kV.
• Highest power per drive: 35MVA.
• Bulky and complex xfmr.
• Large parts count
• Cannot take full advantage of HV semiconductors;
• Waveform at both line and motor side degrades for light load
• Extra pre-charge and braking circuits
N = V mot
/ V cell
/ 1.73; (# of cells)
P = 6 N ; (# of pulses)
V dc
~ V cell
*1.35;
V dev
~ 2* V dc or 2.7V
cell
;
34

Multi-level H Bridge VSI

Basic Topologies: CSR+CSI with DTD
SGCTs in series
Features:
• Xfmr-less design
• Intrinsic regen. and dynamic braking
• Near-sine output voltage waveform
• Low common mode voltage on both sides
36

CSR-CSI VFD
Features:
• Transformer less design
• 2.3-6.9. KV
• Standard Motors
• Regenerative AFE

A Symmetric Gate Commutated Thyristor (SGCT) rectifier dc link inverter
M
Cathode electrode Gate terminal Scroll spring
Ceramic seal
GCT chip
Anode electrode
Mo disks
Fig. 4. Cross-sectional structure of SGCT.
Gate ring
(electrode)

Basic Topologies: CSC Fundamentals
Fundamentals of CSC
Motor and device voltage ratings
V mot
V dc
(variable)
2300 3252
Device voltage rating
6500
3300 4666 2*6500
4160
6600
7200
5883
9334
101182
2*6500
3*6500
3*6500
• Highest voltage: 7.2kV.
• Single drive: up to 5MVA
• Flexibility:
• Input could be multi pulse TX,
• Could be AFE,
• Could be multi drives in parallel,
• Could run multi motors,
• Could do long cables,
• Could run with or without TX
39

Typical Waveforms for CSR+CSI or 18P SCR
Device current
Device voltage
Inverter current
Motor voltage
Motor current
Speed
40

Comparison of MV Drives: Performance
Typical Performance Criteria Values
Speed Regulation
Open Loop Close loop
CSIPWM-GTO 0.5%
CSIPWM-SGCT 0.5%
0.1%
<0.1%
3Level-IGCT
3Level-IGBT
0.5%
0.5%
0.01%
0.01%
Series H-Bridge 0.5% 0.1%
Speed Regulator
Bandwidth
< 10 rad/s
< 20 rad/s
Speed Range
0-75 Hz
0-75 Hz
Approx. 50 rad/s 0-66Hz
Approx. 50 rad/s 150Hz at 4 kV
66 Hz at 6.6 kV
Unknown 0-120 Hz
VFD
Efficiency
>97
>97
>97
>97
>97
Regeneration
Inherent
Inherent
With PWM rectifier
With PWM rectifier
Not available

Performance Requirement of Various Load Types
18% Constant Torque
Medium Performance
<10 rad/sec
Load Types
2% High Performance
<50 rad/sec
80% Variable Torque
Low Performance
< 5 rad/sec

Comparison of MV Drives:
Loss and Efficiency Estimation
• System efficiency greatly affected by :
• Semiconductor, control algorithms, fsw, selection of passive components
• Literature has numerous comparisons between the IGBT and
IGCT
• All manufactures indicate a drive efficiency of >97%
• Some do not include ancillary components
• fans, power supplies, etc..
• Which manufacturer is more correct ?
• difficult and challenging question for the end user to answer

Conclusions
• MV AC drive is a young industry and there is a diverse approach by industry
• Each of the topologies presented meet the performance requirements of a majority of the applications in industry
• Higher voltage semiconductors inherently reduce overall component count and system complexity
• Higher voltage semiconductor have a cost advantage over low voltage devices. The (S)(I)GCT technology is presently very cost effective
• IEEE519 can be met with 18P, 24P, and AFEs

Conclusions
High Voltage
CHB/ MMC
CNPC / CSI
NNPC / ANPC
NPC performance
ANPC/
CHB/ CNPC / CSI
MMC /
NPC
NNPC
Defining comparison criteria is key
CSI
ANPC / NNPC/ NPC
MMC
CHB/ MMC
CNPC/ NPC
ANPC / NNPC
CSI
45