Aalborg Universitet

Review of Aircraft Electric Power Systems and Architectures

Zhao, Xin; Guerrero, Josep M.; Wu, Xiaohao

Published in:
Proceedings of the 2014 IEEE International Energy Conference (ENERGYCON)

DOI (link to publication from Publisher):

10.1109/ENERGYCON.2014.6850540

Publication date:
2014

Document Version
Early version, also known as pre-print

Link to publication from Aalborg University

Citation for published version (APA):

Zhao, X., Guerrero, J. M., & Wu, X. (2014). Review of Aircraft Electric Power Systems and Architectures. In
Proceedings of the 2014 IEEE International Energy Conference (ENERGYCON) (pp. 949-953). IEEE Press.
https://doi.org/10.1109/ENERGYCON.2014.6850540

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 This document is a preprint of the final paper:
X. Zhao, J. M. Guerrero, and X. Wu “Review of aircraft electric power systems and architectures,”
in Proc. IEEE International Energy Conference (EnergyCon’14), 2014.

Review of Aircraft Electric Power Systems

and Architectures
Xin Zhao #1, Josep M. Guerrero *2, Xiaohua Wu #3
#
Automation School Northwestern Polytechnical University
127 Youyixi Road, Xi'an Shaanxi, 710072, P. R. China
1
xzh@et.aau.dk
3
wxh@nwpu.edu.cn

*Microgrids Research Programme www.microgrids.et.aau.dk

Energy Technology Aalborg University
Pontoppidanstraede 101, 9220 Aalborg East. Denmark
2
joz@et.aau.dk

Abstract—In recent years, the electrical power capacity is ability and lower weight. Therefore, the aircraft EPS capacity
increasing rapidly in more electric aircraft (MEA), since the needs to sprint higher to meet the electrical equipment’s
conventional mechanical, hydraulic and pneumatic energy requirements. For example, the electrical capacity of Boeing
systems are partly replaced by electrical power system. As a 787 has increased to 1MW during a normal flight [8].
consequence, capacity and complexity of aircraft electric power
Apparently, compared with conventional EPS, more
systems (EPS) will increase dramatically and more advanced
aircraft EPSs need to be developed. This paper gives a brief advanced EPS is needed to achieve high availability, stability,
description of the constant frequency (CF) EPS, variable efficiency and low weight, volume in MEA. Besides, less
frequency (VF) EPS and advanced high voltage (HV) EPS. engine noise, emissions and fuel burn can be realized in
Power electronics in the three EPS is overviewed. MEA [9][10].
Keywords: Aircraft Power System, More Electric Aircraft, This paper introduces the structure of conventional and
Constant Frequency, Variable Frequency, High Voltage. modern aircraft EPS. The advantage of MEA is discussed.
Power electronic converters in aircraft EPS is also presented.

I. INTRODUCTION
In early stage of the aircraft history, aircraft is driven by II. CONSTANT FREQUENCY EPS
mechanical, electrical, hydraulic and pneumatic hybrid 2.1 Structure of Constant Frequency EPS
systems. An the end of 1970’s, the idea of using electricity as
In constant frequency aircraft EPS, aircraft generators are
dominant power source emerged and during this period the
three-stage Permanent Magnet (PM) excited wound field
concept of More Electric Aircraft was proposed [1][2][3].
synchronous machines. A Generator Control Unit (GCU),
The first commercial aircraft “Fly by Wire” (FBW) was
which is not depicted in Fig. 1, acts as exciter field controller,
introduced by Airbus with A320 series in 1980’s. The FBW
regulating the output voltage.
technology can reduce the weight and volume of aircraft by 115V 400Hz 28V
replacing part of the mechanical and hydro-mechanical AC Bus DC Bus
systems into electrical systems. In FBW system, power Auxiliary
electrical systems generally use 115V with fixed frequency Power
Unit 1 AC Loads DC Loads
at 400Hz AC for high power onboard equipment and 28V
DC for low power onboard equipment [4][5]. However, Engine
Constant
some onboard systems like flight control actuation, landing Shaft Gen 1
Speed
gear, de-icing device and engine starter/generator are still Device AC Battery
driven by hydraulic, pneumatic and mechanical hybrid DC
Engine DC Loads
systems which are inefficiency and heavy [6]. These defects Shaft
Constant
Speed Gen 2
foreshadow the wider implementation of electric power
Device
system in aircraft. TRU
In order to remedy these defects and make flights much Auxiliary
safer, reliable and environmental friendly, the “Power by Power
Unit 2 DC Battery
Wire” [7] technology emerges as the times require. In PBW DC
technology, most of the inefficient, heavy hydraulic systems AC Loads
were eliminated and replaced by electrical systems which
have relatively higher efficiency, stronger fault-tolerant Fig. 1 CF Aircraft EPS
 Fig. 1 shows the conventional CF aircraft EPS in which 115V 360-800Hz 115V 400Hz
bus voltage is 115V at 400Hz AC and 28V DC. This power AC Bus AC Bus

system employs constant speed device (CSD) [11] which is a Auxiliary

AC DC Loads
mechanical gearbox. It converts the speed of the engine shaft Power VF
Unit 1 AC Loads DC
from variable into constant. And the constant rotating speed
shaft connected with the generator will then generate a CF Engine
power at 400Hz. As we can see from the figure, AC loads are Shaft
Gen 1 CF
directly powered by AC bus while the Transformer Rectifier AC AC Loads
Units (TRU) is used to convert the AC power into 28V DC. AC
Engine
2.2 Power Electronics in Constant Frequency EPS Shaft 270V DC Bus
Gen 2
In CF aircraft EPS, AC/DC converter and TRU are the
main power converters. Generally, battery is used as an ATRU DC Loads
emergency power source. AC/DC inverter and Bi-directional Auxiliary
Power
DC/DC converter will connect the battery with the AC bus Unit 2
and DC bus respectively. DC Battery
VF
The DC power could be obtained conventionally from a AC Loads DC
DC generator. However, the space around the aircraft main
engine is extremely limited to install other AC or DC Fig. 3 VF Aircraft EPS
generators. In addition, DC cable, which is extremely heavy
and long, is also required to connect the generator with the 3.2 Power Electronics in Variable Frequency EPS
DC bus [12]. For these reasons, TRU [12][13][14] is Since the primary AC bus has a variable frequency,
introduced to convert AC voltage to DC voltage, since it can Back-to-Back converter [16] is needed to power CF loads.
be installed close to the DC bus, thus weight and volume of These converters must be designed carefully to meet the
EPS could be reduced to a relatively lower level. Besides, volume, weight and harmonic requirements in aviation
TRU could also reduce harmonic currents and achieve lower standard, such as DO-160 or MIL-704. Its topology is shown
THD. Topology of a typical 12-Pulse TRU is shown in Fig. in Fig. 4.
2.
Id/2 115Vrms 115Vrms
360-800Hz 400Hz
A
Id
a
Ld
c b
B Vd
R
Fig. 4 Back-to-Back Converter Structure
C
Two PWM converters are employed in Back-to-Back
converter. The first stage—high power factor rectifier, which
Fig. 2 Topology of 12-Pulse TRU adopt D-Q decouple strategy to control the active and
reactive current, can make the power factor approximate to 1.
Thus, current harmonic could meet higher standard [17]. The
III. VARIABLE FREQUENCY EPS second stage—SPWM inverter could stable the bus voltage
and frequency by utilizing voltage-current dual loop.
3.1 Structure of Variable Frequency EPS For DC bus, 270V DC voltage is chosen because it can be
In variable frequency aircraft EPS, shown in Fig. 3, the obtained directly by rectify 115V AC voltage. DC/DC
frequency of primary AC bus is 360Hz-800Hz at 115V since converter is used to obtain multi DC voltage levels.
the generator is connected with engine shaft directly. A As we all know that autotransformer has much smaller
variety kind of converter is employed to convert VF voltage size and weight than isolation transformer at same power
to multi voltage levels, such as 115V AC and 270V DC. level. So naturally, Autotransformer Rectifier Unit (ATRU)
It’s worth mentioning that the frequency of primary AC [14][18] replace the position of TRU. Fig. 5 shows the
bus, which varies between 360Hz and 800Hz, is proportional topology of the 24-Pulse ATRU. The ATRU utilizes
to the engine shaft speed [15]. By using VF power system, phase-shifting windings to generate 4 groups of AC voltage.
the bulky, heavy, inefficient CSD could be removed from the Each group has 15° phase difference [19], so that the output
aircraft. Thus, the aircraft EPS could achieve higher voltage can reach 270V.
performance.

2
 1 +
An example of HVAC EPS is depicted in Fig. 6. In this
L1 system, Auto transformer unit (ATU) is used to generate
-
115V variable frequency voltage. Buck Boost Converter Unit
K1
(BBCU), which consists of 2 DC-AC stages interfaced with a
4
A +
high frequency transformer, is used as the battery charger
L2
- [22]. Its topology is in the figure below.
K1
2 +
B
L3
S1 S3
K1
-
D1 Do1 Do2
C D2
3
Ro 28V
+
L4 270V Co
-

Fig. 5 Topology of 24-Pulse ATRU

Besides the converter aforementioned, Bi-directional S4 S2 Do3 Do4

DC/DC converter is used in VF aircraft EPS to D3 D4
charge/discharge batteries as the emergency power supply.

Fig. 7 BBCU Topology

IV. FUTURE AIRCRAFT EPS
In later design of aircraft EPS, as the consequence of 4.2 High Voltage DC (HVDC) Aircraft EPS
gradually substitute the hydraulic, pneumatic and mechanical Several possible architectures of HVDC aircraft EPS are
system, there is an obvious trend towards increasing demand analyzed in [23]:
of electrical power. However, the feeder cable current in • +/- 270V DC 2 phases with ground
conventional 115V or 28V EPS will increase proportionally • 270V DC 1 phase with ground
to power ratings. And this will definitely lead to higher • +/-135V DC two phases with ground
power loss and cable weight. • +/- 135V DC 2 phases without ground
As a consequence, increasing the voltage level in future The conclusion of [23] certifies that in most cases,
aircraft EPS is an obviously better choice than continuing HVDC EPS can save weight from 4% (270/0V architecture
apply the 115V AC and 28V DC low voltage EPS. By doing with 230V AC supply) up to 28% (270/0V architecture with
this, the feeder cable current could be reduced dramatically. 115V AC supply). Fig. 8 illustrates a typical 270V HVDC
Also, lower cable weight, higher efficiency and lower EPS.
consumption could be achieved [20][21].
270V DC Bus
4.1 High Voltage AC (HVAC) Aircraft EPS
270V
Some newer aircrafts have been adopted HVAC power DC Loads 28V DC Bus
system (230V at 360-800Hz), such as Boeing 787. Compared Engine
Shaft AC
with the conventional 115V EPS, power transmission loss Gen 28V
and converter weight can be reduced by 50.7% and 42.5% DC
Loads
DC
respectively [21].
DC
230V 360-800Hz 115V 360-800Hz AC
AC Bus
DC
AC Bus
Fuel Cell Battery DC
Auxiliary DC
AC DC Loads
Power VF
Unit 1 AC Loads DC DC
115V
Engine AC Loads
Shaft
Gen 1 115V
AC Loads 115V AC Bus
ATU

Engine Fig. 8 270V HVDC Aircraft EPS

Shaft 270V DC Bus
Gen 2
As we can see from Fig. 8, fuel cell system replaces the
ATRU DC Loads
position of conventional APU which is driven by turbines.
Auxiliary
Power This is because the efficiency of turbine powered APU is
Unit 2 typically less than 20% and also has undesirable noise and
DC Battery
VF gaseous emissions [24][25]. Some topology had been
AC Loads DC
proposed in [26] to integrate fuel cell system into aircraft
Fig. 6 HVAC Aircraft EPS

3
EPS. One of parallel architecture is depicted in Fig. 9. In this many effective way, such as SiC semiconductors and optimal
case, bi-directional DC/DC converter is employed. design at the system level.

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