Energy Efficient Ships, 23-24 November 2016, London, UK
© 2016: The Royal Institution of Naval Architects
MODELLING OF DIESEL ELECTRIC PROPULSION
I Karakitsos, Mott MacDonald, UK
G Theotokatos, Department of Naval Architecture, Ocean and Marine Engineering, University of Strathclyde, UK
SUMMARY
Diesel Electric Propulsion (DEP), in which the ship propeller is driven by electric motors and diesel-generator sets that
provide the energy necessary to cover the demand in mechanical and electrical loads of a ship, is gaining ground in
marine applications. This paper deals with alternative ways of modelling of DEP electrical and mechanical components
in MATLAB/Simulink® and simulations that are carried out for an offshore supply vessel. Firstly, a comprehensive
model for the diesel-generator set of the DEP, which includes the diesel engines and synchronous generators, is
developed. Different types of short-circuits are imposed at the terminals of the generator in order to assess the transient
response of the diesel engine-generator set, and to identify if any dangerous operations conditions arise. Furthermore, the
development of a detailed model for the overall DEP that includes variable speed drives and propulsion motors has been
implemented. Scenarios that correspond to realistic ship operating conditions have been simulated.
NOMENCLATURE
C: DC link capacitance (F)
effcomb: Combustion efficiency
0
f
E
Initial field voltage of
generator (pu)
q d
i
,
:
Current of synchronous
generator of d, q axis
respectively (A)
qs ds
i
,
:
Stator current of induction
motor for d, q axis
respectively (A)
J :
Moment of inertia of
propulsion motor (kg m
2
).
T
J :
Moment of inertia of generator
engine system (kg m
2
).
K : Revolutions per cycle
fi
k :
Friction model constant
D I p
K
, ,
:
Proportional, integral and
derivative constant of speed
governor
'
lr
L :
Rotor inductance of
propulsion motor (H)
m
L :
Mutual inductance for
propulsion motor (H)
N :
Filter constant of speed
governor
cyl
n :
Number of cylinders
de
N :
Engine generator shaft speed
(rpm)
P : Number of pole pairs
bme
p :
Break mean effective pressure
(N m
-2
)
fme
p :
Friction mean effective
pressure (N m
-2
)
ime
p :
Indicated mean effective
pressure (N m
-2
)
a
R :
Armature resistance of
synchronous generator (pu)
s
R
Stator resistance of propulsion
motor (Ω)
r R
'
Rotor resistance of propulsion
motor (Ω)
pos
r :
Fuel rack position of diesel
engine
rr: Reduction ratio of propulsion
system
n
S : Apparent power (VA)
act
T : Actuator time constant (s)
D
T : Engine time delay constant (s)
de
T : Diesel engine torque (Nm)
e
T : Electromagnetic torque (Nm)
L
T : Propeller torque (Nm)
d
v :
Displacement volume of one
cylinder (m
3
)
LL
V : Line voltage (V)
0
t
V :
Initial terminal voltage of
generator (pu)
q d
X
,
:
Direct and quadrate axis
reactance respectively (pu)
q d ,
:
Magnetic flux of synchronous
generator of d, q axis
respectively (Wb)
dr
:
Rotor magnetic flux of
induction motor for d axis
(Wb)
m r ,
:
Angular speed of engine
generator shaft and propeller
respectively (rad s
-1
)
1. INTRODUCTION
The DEP systems consist of the diesel engine that drives
a synchronous generator, with its frequency and power
output being controlled by the speed governor. The
alternating current (AC) output of the generator is used to
supply the ship auxiliary loads (e.g. hotel loads, lighting,
ventilation, bow thruster motors) and to supply the power
demand into the ship’s electric motors which drive the
ship’s propeller(s). The supply of the ship induction AC
motors is achieved by using the following configurations