The use of variable speed
generation to balance energy
loads in CHP applications
Professor Ron Bickerton
Industrial Professor of Mechanical Engineering
University of Lincoln
School of Engineering
©Professor R.A.Bickerton, University of Lincoln
1
Note this presentation is an amalgam of presentations on this subject by the
author, hence references are to differing prime movers and systems prepared
during the research and development and as such that charts and graphs are
from multiple sources
VARIABLE SPEED GENERATION
WHAT IF?
©Professor R.A.Bickerton, University of
Lincoln
2
Consideration of Advantages of
Variable speed Generation.
• If we had this technology what are the gains/
disadvantages?
• Gains
Balance of heat and electrical outputs for CHP
Loci of load rather than single point
• Issues
– Transient response
– Cost vs operational conditions
©Professor R.A.Bickerton, University of
Lincoln
3
GAINS IN CHP OPERATION WITH
VARIABLE SPEED GENERATION
©Professor R.A.Bickerton, University of
Lincoln
4
Use in Electrical Islands or with poor
feed in tarriffs
Full Load estimated heat balance
TCD2010 kW
Heat to
Full Power Kw
Exhaust heat kW
81.98
66.15
10.64
95.00
4.86
Heat to radiator est kW
5.78
Est EGR Cooler 10% to
200C
Intercooler Heat kW
Energy storage to offset “Time Shift” in energy balance
©Professor
R.A.Bickerton,
University
of
Or balance
the prime
mover
operational conditions? 5
Lincoln
Typical Heat Balance for a Diesel Engine
This Converts the energy
from the fuel into the
following categories of
useful energy.
Mechanical Power
High Grade Heat >100C
Low Grade Heat <100C
Direction of most
useful form of
energy
13/06/2013
Copyright R.A.Bickerton
It is relatively easy to convert a
higher energy state into a lower
version ie high grade heat into low
grade heat via heat exchangers
with higher flow rates.
To run the circle clockwise
however requires higher
technology and loss of some of the
higher engergy states ie immersion
heaters using electrical power to
move low grade heat to high grade
heat.
6
Engine Energy Balance also varies with
applied load
Balancing these differing energy loads with
time and engine variable output is one of the
big challenges for CHP .
Few processes achieve the “perfect balance”
for CHP. One example from RAB experience and
operation is a paper mill with:Power for crush rollers
High Grade steam heat for the drying drums
Low Grade hot water heat for the mash tubs
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7
Loci of operating points adds further
complexity when using conventional
fixed speed generating sets
Fixed operational speed limits the full
use of the engine operating map and
hence further restricts the ability to
balance heat loads on the CHP
system.
A variable speed generating system
provides a number of operating
points for a given electrical load thus
providing an advantage in both heat
balance as well as improved fuel
consumption and hence thermal
efficiency.
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Theoretical Considerations
16
NOX [g/k/Wh]
• Engine Operating Map
14
7
16
7
12
B.S.F.C [g/kWh]
Best Fuel Consumption
14
Minimum NOx Emissions
10
6
6
12
5
7
8
220
4
7
10
7
225
230
6
260
B.M.E.P. bar
8
240
4
8
3
3
12
2
2
4
280
0
320
400
2
500
800
2000
Engine speed rpm
3000
1000
2000
Engine speed rpm
1200
1000
6
3
4000
0
3000
4000
B.M.E.P. bar
215
6
Selected operational
point for 25% load
operational point
for 100% load
TRANSIENT RESPONSE ISSUES
©Professor R.A.Bickerton, University of
Lincoln
10
Variable speed generation has further Complexity
with load changes when compated to conventional
fixed speed generating sets
operational point
for 100% load
operational point
for 50% load
Selected operational
point for 25% load
Fixed operational speed limits the full
use of the engine operating map but
allows for simple load control
governing systems, ie only control of
fuel is required at fixed speed.
A variable speed generating system
provides a number of operating
points for a given electrical load thus
requiring a control system based on
both speed and torque.
Conventional and Transient response
between operating points uses the
full operating map of the engine.
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Theoretical Considerations
• Transient response
– ISO8528 gives current standard for transient
response
• Frequency dip
• Voltage drop
Theoretical Considerations
• Transient response for conventional
technology to minimise
• Frequency dip (linked to prime mover speed)
– Large Inertia's to provide energy reserve
• Voltage drop (Linked to speed and excitation)
– Fast acting AVRs with controlled under frequency roll off
settings
Theoretical Considerations
• Typical Transient response for convential
technology
ISO 8528 standard
G1 G2 G3
• Response to
• maximum
• load step
Transient frequency
response (%)
Frequency recovery
time (s)
Voltage deviation
(%)
Voltage recovery
time (s)
25 20 15
10 5
3
25 20 15
10 6
• Variable speed generation needs to better
these target responses (G2)
4
Theoretical Considerations for
Transient response
• Transient response has been the “Achilles
Heel” of previous Variable speed type
technologies.
• Dichotomy of needing high inertia for
“spinning energy reserve” vs low inertia for
rapid acceleration to accept load
Comparisons of typical transient
response requirements
• Torque curve and power curve with
conventional and variable speed/ torque
curves in time
• Study has considered this as “two halves” of
VSIG transient response
Transient response considerations
• Deceleration Phase
– High inertias needed
• Acceleration Phase
– Low inertias needed
• Overall transient response targets
– Volt drop & time
– Hz droop & time
– Effect on instantaneous power & acceleration
Transient response energy considerations
Energy input
Prime Mover Power
Output Energy
Generator Load
Stored Inertia Energy
Transient response energy considerations
Energy input
Prime Mover Power
Output Energy
Generator Load
Stored Inertia Energy
3500
1500
3000
1000
2500
500
2000
0
1500
-500
1000
500
-1000
0
-1500
0
2
4
Time sec
6
8
Engine acceleration rev/m in/sec
Engine speed (rpm)
VSIG Transient response
10
Engine speed
Engine acceleration
Transient response energy considerations
Energy input
Prime Mover Power
Output Energy
Generator Load
Stored Inertia Energy
3500
1500
3000
1000
2500
500
2000
0
1500
-500
1000
500
-1000
0
-1500
0
2
4
Time sec
6
8
Engine acceleration rev/m in/sec
Engine speed (rpm)
VSIG Transient response
10
Engine speed
Engine acceleration
Transient response Inertia
considerations
• Governor response time
– Typical 0.1 to 0.5 sec
– Need to minimise
– Control system integration
• Optimum Inertia to power ratio
– Balance between deceleration and acceleration
requirements
– Must meet or exceed ISO standard
Governor response and inertia matching are critical to transient operation
An increase in response time from 0.1 to 0.2 sec
will stall the set on a 10% load step
VSIG Transient response
VSIG Power & Torque curves
1000
0
800
-200
600
-400
400
-600
200
-800
0
-1000
0
-200
1
2
3
-1200
Engine speed
Time sec
Engine acceleration
40
180
35
160
140
30
120
100
25
80
20
60
40
15
20
0
500
Pow er kW
200
Torque Nm
1200
Engine acceleration rev/m in/sec
Engine speed (rpm)
200
Sales Nm
1000
1500
2000
Speed rpm
2500
10
Engine torque
3000
Load torque
Sales kW
Transient response Inertia Theoretical
Considerations
• Deceleration model
– Inertia and Governor response time
• Acceleration Model
– Engine Torque curve
– Output load torque
– “acceleration” torque
– Inertia and acceleration
Transient response Inertia Theoretical Considerations
• Deceleration model
•
•
•
(W1^2 –W2^2) = Prat * .G (volt% ) * td
-----------------------------Inertia (I) * 2
• Acceleration Model
•
t= voltage recovery time
•
•
•
•
t=0
•
•
Where f(engine torque) = a*W^3 + b*W^2 + c*W + k
f(load torque) = (Prat * G(volt)) / W
•
Method of integration
– Selection of fixed governor response times
– Integrate to find minimum Wmin to achieve ISO for a set inertia
_
| (f(engine torque) - f (load torque) }/ I
and
Transient response Inertia
Optimisations
• Iteration to find maximum speed range to
achieve ISO transient behaviour
• Iteration within mathematical model at
constant governor response time to assess
lowest Wmin meet ISO standards wrt inertia
Transient response Inertia Optimisations
W1 in % for G2 specification
G2 Prat/I Trade off for W1
%
100
Control System
Response
Time (sec)
95
90
0.1
0.2
85
0.3
80
0.4
0.5
75
0.75
1
70
100000
90000
80000
Prat/I (1/s^3)
70000
60000
50000
40000
30000
20000
10000
0
min line G2
1.5
2.5
5
COST VS OPERATIONAL
CONDITIONS
©Professor R.A.Bickerton, University of
Lincoln
27
Duty Cycle Considerations
• Low Load24 hours
Cycle
• Average Load 25%
Load %
Load %
Rated Power Condition
24 hours
High Load Cycle
Average load 60%
Steady State Operational Advantages
100kW Fuel consumption map
BSFC (G.kWhr)
540
500
460
420
380
340
300 Torque (Nm)
260
220
c 600 g/kW hr
140
Fuel Consumption
100
1800rpm
60
Speed (rpm)
2180
2020
1860
1700
1540
1380
1220
1060
900
20
740
25% Load point
180
875-900
850-875
825-850
800-825
775-800
750-775
725-750
700-725
675-700
650-675
625-650
600-625
575-600
550-575
525-550
500-525
475-500
450-475
425-450
400-425
375-400
350-375
325-350
300-325
275-300
250-275
225-250
200-225
175-200
150-175
125-150
100-125
75-100
50-75
25-50
0-25
Steady State Operational Advantages
100kW Fuel consumption map
5
4
5
Variable Speed
BSFC (G.kWhr)
0
540
0 0
4
6
0
4
2
0
3
8
0
3
4
0
500
460
Operation allows
Fuel consumptions
420
380
340
of c 250 g/kW hr
3
0 0
2
6
0
2
2
0
1
8
0
1
4
0
300 Torque (Nm)
260
220
180
100% load
9
5
0
1
1
5
0
1
3
5
0
1
5
5
0
Speed (rpm)
1
7
5
0
1
9
5
0
2180
0
2020
5
1860
7
1700
0
1540
2
60
1380
0
1220
25% load
50% load
75% load
6
740
10%l oad
100
0 0
1060
1
140
900
Load Torque curves
2
1
5
0
20
875-900
850-875
825-850
800-825
775-800
750-775
725-750
700-725
675-700
650-675
625-650
600-625
575-600
550-575
525-550
500-525
475-500
450-475
425-450
400-425
375-400
350-375
325-350
300-325
275-300
250-275
225-250
200-225
175-200
150-175
125-150
100-125
75-100
50-75
25-50
0-25
Steady State Fuel Consumption and
Emissions Gains
Engine
Load
Bsfc at
rated speed
Optimum
Engine
speed
Best bsfc
Reduction
in bsfc
Reduction
in speed
kW
g.(kWh)-1
rev.min-1
g.(kWh)-1
%
%
10
25
50
75
100
600
375
300
300
300
900
1100
1250
1350
2200
250
190
200
200
300
58.33
49.33
33.33
33.33
0
59.09
50.0
43.18
40.91
0
Fuel consumption gain
reductions in both
maintenance and noise
Operational Conclusions
• Released from the constraints of fixed speed
operation variable speed systems can
operate at optimum conditions to minimize
fuel consumption, emissions and noise
• Fuel consumption gains significantly reduce
through life costs
• Selection of the Prime Mover, PMM
Generator and Power Electronics coupled
with an integrated control system is vital to
achieving a successful design
DOES VARIABLE SPEED
GENERATION EXIST?
©Professor R.A.Bickerton, University of
Lincoln
33
VSIG ?
VSIG stands for
Variable Speed Integrated Generator
The technologies are similar to the new breed of
hybrid vehicles hence the title:VSIG A Hybrid Generator for the Future
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Copyright R.A.Bickerton
34
Concept
Permanent Magnet “Flywheel” engine mounted
alternator providing electrical power at 440V 135 to
400 Hz
Rectification to 420V dc
Inverter conversion with 1000Hz switching to give
sinusoidal AC
415V 3Ph 50 or 60HZ output
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35
Axial Gap Permanent Magnet Machine
(PMM)
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36
Prototype model
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Copyright R.A.Bickerton
37
Variable speed diesel engine powered generating system
Variable speed
engine (smaller)
Concept Diagram
Permanent Magnet
Generator (cheaper
and more efficient)
Battery charge
alternator
Generating set enclosure
Power Electronics Converter
rect
Start er
motor
boost
speed
demand
0-10v
Electronic
Governor
dc link
buck
battery
Generator output
460
2500
2000
1500
1000
500
0
2500
2000
1500
1000
500
0
Torque
VOLTS
Nm
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Constant volts
Constant Hz
Sinewave output
boost
batteries
Engine output
RPM
pwm
inv
Advantages
Smaller lower cost engine
Reduced engine exhaust emissions at light loads
Reduced engine noise at light loads
Reduced engine maintenance at light loads
Increased fuel economy at light loads
Increased engine life at light loads
Lower cost of ownership
Improved 3 phase unbalanced voltage regulation
Improved dynamic response time
Low output impedance
Regeneration ability
RPM
Copyright R.A.Bickerton
38
4
Prototypes Package
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Practical Advantages
•
•
•
•
•
•
•
•
Flexibility
Size
Weight
Power
BSFC
Performance
Durability
Noise
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VSIG 40 kVA Comparison