Control of variable speed electric generators :

1
Control of variable speed electric generators
present status and perspective
Prof. Ion BOLDEA Department of Electrical
Machines and Drives, University Politehnica of
Timisoara, V.Parvan 2, RO - 1900 Timisoara,
Romania, Tel.[phone], E-mail
boldea_at_lselinux.utt.ro,
2
Contents

• Introduction
• Variable speed wind-generator systems
• Variable speed hydro-generator systems
• Stand-alone variable speed generators
• Superhigh speed gas turbine PM generator systems
• Automotive starter (torque-assist)/alternator
  systems
• Home and space electric generator systems
• Conclusion

3
Variable speed wind-generator systems

• 13,932 MW by the end of 1999
• 2 2.5 MW units

Wind turbine induction generator system with
blade angle control and soft-starter 1
CR-IG
4
Connection circuit for fixed speed wind turbine
using external resistors
CR-IG
5
Measured (gray) and calculated (black) current
magnitude as the 15- kW machine is connected
using external resistance 26
Measured (gray) and calculated (black) rotor
speed magnitude as the 15- kW machine is
connected using external resistance 26
Measured (gray) and calculated (black) machine
voltage as 15- kW machine is connected using
external resistance 26
CR-IG
6
Variable speed generator connected to the grid
through bidirectional converter
CR-IG
7
Grid side converter control
CR-IG
8
Machine side converter control
CR-IG
9
CR-IG
? Unity power factor
Phase current and voltage.Speed 1500 rpm,
generator, torque 100
Phase current and voltage per phase.Speed 1500
rpm, generator, torque 100, reactive power 50
Results with inverter control at power grid
10
Stand alone SCIG control systems 3
CR-IG
11
Full load application over 50 load application
3
CR-IG
12
Doubly-fed IG (DFIG) wind turbine system
DFIG
13
a)
b)
Vector control of DFIG a) and step active power
response b), without and with decoupled control
4
14
Sensorless DFIG with operating modes I, II, III
8
15
Rotor and stator current and their
harmonics content at s -0.27with controlled
rectifier - current source inverter in the rotor
DFIG
16
DFIG connected to the power grid
17
Implemented wind turbine characteristics
aerodynamics characteristics
DFIG
18
DFIG
The block diagram of the supply side converter
control 8
19
The block diagram of the machine-side converter
control in a doubly-fed wind turbine 8
DFIG
20
a) The active and b) reactive stator power
control 8
DFIG
21

• Three-phase short-circuit on the power grid
• Stator voltage
• Stator currents
• Rotor currents
• Speed
• Turbine torque
• Electromagnetic torque
• Active power
• Reactive power
• 8

DFIG
22
Modified vector controller for unbalanced
voltages in the power grid 6
DFIG
23
Stator currents in individual phases for 10
negative-sequence voltage applied -
conventional controller 6
Stator currents in individual phases for 10
negative-sequence voltage applied - modified
controller 6
DFIG
24
Stator currents in individual phases for two-
phase operation-modified controller
6
DFIG
25
Sensorless control of DFIG
DFIG
26
Sensorless control of DFIG
DFIG
27
DFIG
Sensorless control of DFIG
a) Before filtering 2
b) After filtering
Experimental waveforms showing estimated and
actual ? at starting
28
Variable speed hydrogenerator systems
Pump storage necessities prompted by nuclear
power usage led to the design and application of
two rather large (310MW) power DFIGs one with a
cycloconverter and the other with a GTO
inverter-converter in the rotor circuit 10
29
Ramp power response for motoring mode (Ohkawachi
unit 4) 10
DFIG
30
Ramp power response for generating mode
(Ohkawachi unit 4) 10
DFIG
31
Goldishtal pump-storage station 300 MW 27
DFIG
32
Power flow at constant torque in turbine and pump
operation 27
DFIG
33
Stand-alone variable speed generators
Stand-alone MG generator converter with battery
quick back up
PMSG
34
PMSG
PM generator advanced mobile genset 28
PMSG
35
PM generator advanced mobile genset 28
Peak torque, power and fuel consumption
PMSG
36
PM alternator genset with Diesel engine 28
PMSG
37
Dual stator winding IG with reduced count
inverter battery system
CRIG
38
Starter generators for vehicular technologies

• Induction type
• IPM brushless type
• Transverse flux PM brushless type
• Switched reluctance type
• Claw pole rotor synchronous type

• Characteristics
• High starting torque
• Large power speed range
• Low volume and system costs
• Low total system losses at 42 Vdc battery
  mild hybrids, 200 400 Vdc battery full
  hybrids and electric vehicles

ISG
39
Starter-alternators (continued)
So there is the low voltage (42 V d.c.)
starter-alternator and the high voltage (150-400
V d.c.) motor-generator for mild and respective
heavy hybrids electric vehicles. Typical peak
torque and voltage versus speed for a PM-RSM mild
hybrid starting and, respectively, torque-assist
mode are shown in next slide, with corresponding
efficiency.
ISG
40
Starter-alternators (continued)
42V battery voltage versus d.c. current load
ISG
41
Starter-alternators PM-RSM cross-section 12
ISG
42
Rotor position
in relation to
and
ISG
43
Starter-alternators (continued)
a)
b)
Peak torque, voltage a) and corresponding machine
efficiency versus speed b) 12
ISG
44
a)
b)
Potential 42V d.c. automotive starter/alternator
system with winding switch (a.c. machines) and
passive (capacitor) voltage a) and with
boost/buck converter b)
ISG
45
H-bridge dc dc boost bidirectional converter
with transformer and inductance (T L) 11
ISG
46
IGBT losses for the induction motor drive base
and max speed, with and without boost converter
11
Total power loss at 30 kW max. delivered power
motor design of Table 2 with boost converter,
Vb 180 V 11
Total power loss at 30 kW max. delivered power
motor design of Table 1 with boost converter,
Vb 180 V 11
47
Fundamental rotor position and speed tracking
observer 14
ISG
48
Estimated initial electrical rotor position 14
ISG
49
Superhigh speed gas turbine PM generator systems

• Typical power speed ranges
• to 150 kW at 70 80 000 rpm
• to 1.4 5 MW at 18 000 15 000 rpm

Applications Stand alone, standby or
cogeneration in distributed power systems.
PMSG
50
The superhigh PM generator rotors
a) cylindrical
b) disk shape
PMSG
51
Variable speed PMSG system with constant output
voltage and frequency
PMSG
52
3 5 MW medium voltage superhigh speed PMSG (
) With dc voltage booster
and three level PWM inverter
53
Home and space electric generator systems
Stirling engine linear PM generator 25
54
Various PM linear alternators 25
55
Conclusion
The present paper leads to conclusions such
as   variable-speed generator technologies for
power systems are already available up to 400 MW
with doubly-fed induction generator motors. They
bring more flexibility and better efficiency to
power production and transportation for
distributed/power systems wind and hydro electric
generators are prime candidates for variable
speed    better system design optimisation and
sensorless control methodologies are still desired
56

•  automotive starter-alternator system for mild
  (42V d.c.) and heavy (150-600V d.c.) hybrid
  vehicles have been proposed in various
  configurations. The IM solution has been brought
  to markets by Toyota and Honda. Up to 35 fuel
  consumption reduction in town driving has been
  reported for Toyota Prius but the additional
  electrical equipment has been rated at 3000 USD.
  PM-RSM or transverse flux PM rotor configurations
  are currently proposed as they are credited with
  slightly less initial system costs for lower
  total system losses.

57

•    PM or induction generators with full
  (respectively fractionary) power electronics
  rating are proposed for dedicated stand alone or
  mobile gensets in the tens or hundreds of kW.
  Faster availability, lower volume and better
  energy conversion ratio with faster response for
  load transients are expected for such solutions.
• Superhigh speed PM generators with powers up to
  150kW and 75 krpm and for higher powers (up to 5
  MW and 15 krpm ) are proposed for distributed
  power systems, aircraft and small vessel.

58
     Home combined electricity and heat
production through burning natural gas has been
demonstrated with quiet, free piston Stirling
engines and linear PM generators for efficiency
above 85, and at the power electric grid for
tens of thousands of hours in the kW range. More
compact configurations with still high efficiency
and lower initial costs are required to make home
electricity generation truly practical with all
implicit advantages.
59
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