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Power Conversion Group
School of Electrical and Electronic Engineering
The University of Manchester
Multiphase machines offer a number of benefits toward the aerospace sector, particularly when considering DC power distribution systems. The high number of phases allows for the possibility for a reduction in DC voltage ripple magnitude. This offers the potential to remove the filter capacitance necessary when rectifying AC to DC for a three-phase system. These capacitors are an expensive, sizeable and hazardous component in aerospace applications.
Multiphase Synchronous Generators for DC Aircraft Power Systems
For details contact: Steven Jordan; Tel.: +44 (0)161 306 2843;
E-Mail: [email protected]
Supervisor: Dr Judith Apsley; Tel.: +44 (0)161 306 4732;
E-Mail: [email protected]
Acknowledgements: Rolls-Royce PLC, the EPSRC and
Cummins Generator Technologies UK
Mathematical modelling can accurately simulate machine dynamics, however, when considering electric machine design, it is important to understand the internal performance of the generator.
Finite element modelling gives a mathematical solution of internal distribution of magnetic quantities such as flux density. These can be analysed to allow the machine to be designed so that, when moving toward a multiphase machine, harmonic loss components are not introduced into the generator air-gap.
The compromise between generator performance and DC power quality is of significant interest. Star (Y) connected machines offer greater fault tolerance but draw higher peak currents as phase number increases. Delta (Δ) connected machines draw a more uniform current but offer a severely reduced fault tolerance. DC ripple voltage reduction remains consistent.
Electric Machine Design
Electric Machine Performance Overview
System Application
The current power distribution system found on the Boeing 787 Dreamliner, which utilises the Rolls-Royce Trent 1000 gas turbine engine, is a variable frequency AC network. The variation in frequency over the flight cycle poses problems with loads that are directly connected to the distribution network.
Stator Windings
Rotor
Damper Windings
Generator Output Housing and Control Unit
Field Winding
Future Work
Future work to be carried out:
• Design and construction of a IGBT rectifier
• Characterisation of multiphase machine upon receipt
• Integration of a full system multiphase test rig
Figure 9: Test Rig Multiphase Synchronous Generator
Density Plot: |B|, Tesla
1.236e+000 : >1.301e+000
1.171e+000 : 1.236e+000
1.106e+000 : 1.171e+000
1.041e+000 : 1.106e+000
9.761e-001 : 1.041e+000
9.110e-001 : 9.761e-001
8.459e-001 : 9.110e-001
7.809e-001 : 8.459e-001
7.158e-001 : 7.809e-001
6.507e-001 : 7.158e-001
5.856e-001 : 6.507e-001
5.206e-001 : 5.856e-001
4.555e-001 : 5.206e-001
3.904e-001 : 4.555e-001
3.254e-001 : 3.904e-001
2.603e-001 : 3.254e-001
1.952e-001 : 2.603e-001
1.302e-001 : 1.952e-001
6.508e-002 : 1.302e-001
<1.303e-005 : 6.508e-002
Figure 3: Uncontrolled Rectifier System
http://news.medill.northwestern.edu/chicago/news.aspx?id=158445
Figure 8: IGBT Controlled Rectifier System
Figure 1: Boeing 787 Dreamliner Figure 2: Rolls-Royce Trent 1000
Flight control surfaces such as ailerons, found on the Boeing 787 Dreamliner, require power electronic conversion at present. This could be eliminated by using a DC power network. Uncontrolled rectification provides DC output with less complexity and at low cost. However, the currents drawn from the generator can induce saturation and increase stator losses. Introducing control of switching will allow for an increase in generator performance.
Variable Frequency Synchronous Generator
Figure 4: Generator Star Current Figure 5: Generator Delta Current
Figure 10: Finite Element Flux Density Solution
0
2
4
6
8
10
12
14
16
0 5 10 15 20
% A
vera
ge D
C V
olt
age
Number of Phases
star delta
0
50
100
150
200
250
300
350
400
450
3 5 7 9 11
Stat
or L
oss
(W)
Number of Phases
Star Delta
Figure 6: DC Output Ripple Voltage Figure 7: Stator Losses
AC SynchronousGenerator
Gas Turbine Prime Mover
MultiphaseAC Output
Uncontrolled Rectifier
DC Bus
Filter Capacitance
AC SynchronousGenerator
Gas Turbine Prime Mover
MultiphaseAC Output
IGBT Rectifier
DC Bus
Filter Capacitance
Switching Control Input
-60
-40
-20
0
20
40
60
0.00 0.01 0.02 0.03 0.04C
urr
ent (
A)
Time (s)
ia3 ia5 ia7 ia9 ia11
-20
-15
-10
-5
0
5
10
15
20
0.00 0.01 0.02 0.03 0.04
Cu
rren
t (A
)
Time (s)
ia3 ia5 ia7 ia9 ia11
ab
cnth phase
a bc
nth phase
