1305

1 INTRODUCTION

The challenges associated with modern electric ship

propulsion, including a hybrid AC/DC systems and

pure DC systems, have gained significant attention.

These issues have become increasingly important due

to the pressing need for greater energy efficiency and

fuel savings, as well as the reduction of greenhouse gas

emissions, including CO₂, NOₓ, and SO₂. These

challenges represent some of the most intensively

studied topics in the maritime transport sector and

pose critical problems for shipbuilders, operators, and

regulatory bodies to address. Such challenges are

closely linked to issues as electrical stability, harmonic

distortion and power quality stand-alone microgrids,

like as those found in marine vessels. Furthermore, the

role of battery energy storage systems in enabling

emission-free operation within these microgrids is a

key area of interest.

Taking into account the historical context the

authors of the papers [1-3] have analyzed the impact of

new conversion technologies, such as power

electronics, battery energy storage and DC power

system on overall energy efficiency, power quality, and

emission level. These studies explore various

possibilities of using the batteries in different

configurations of ship power systems and present

cases where the BESS (Battery Energy Storage System)

is connected to the main bus (switchboard) in an

Integrated Power System Configuration or where BESS

is a part of a motor drive for propulsion. In the first

option an AFE power converter (Active Front End) is

installed alongside the BESS as a solution for

supervision and control purposes [3]. A few papers

have presented the main problems encountered by

designers of small, hybrid-powered ferries supplied by

lithium batteries, including energy balance issues and

the development of an energy management policy [4].

One of the most important solutions belonging to

the class of hybrid AC/DC systems is a modern ship

power system with batteries and diesel generators,

presented, among others, in the papers [5, 6]. In these

Power Quality Assessment of a Modern Ship Power

System With Batteries and Diesel Generators – Case

Study

J. Mindykowski

, M. Górniak

, A. Piłat

& Ł. Wierzbicki

Gdynia Maritime University, Gdynia, Poland

Gdansk Remontowa Ship-Repair Yard S.A., Gdańsk, Poland

ABSTRACT: In this study the authors firstly present a generic diagram of power quality assessment methodology

for a modern ship power system with batteries and diesel generators, and secondly, illustrate all methodology

procedures in the form of the case study results, obtained from sea trials. The proposed methodology is based on

analysis of the configuration and load of the system under consideration, taking into account the system’s

operation modes, while excluding the modes in which the ship is supplied via shore grid. The authors

experimentally examined and analysed the electric and hybrid modes using data collected from sea trials results

of the passenger-car ferry. Finally, an overall assessment of power quality in the considered power system is

presented.

http://www.transnav.eu

the International Journal

on Marine Navigation

and Safety of Sea Transportation

Volume 19

Number 4

December 2025

DOI: 10.12716/1001.19.04.XX

1306

papers, the authors considered and compared their

results with existing state-of-the-art methods in the

field of widely understood means to improve the

energy efficiency of ships, using a thruster supplied by

a hybrid power system [5] or by using an autonomous

hybrid system with a PMSG (Permanent Magnet

Synchronous Generator) [6]. It is worth noting that in

the first case [5], a ship power plant configuration is

equipped with two MSB (Main Switchboards): DC and

AC, respectively, but in the second case [6], the related

power plant configuration includes only AC MSB.

Another important property of the both

aforementioned ship power systems with batteries and

diesel generators is that their specific operational

characteristics must be analyzed in five basic modes, as

defined by the ship designers and operators [5, 6].

In this paper, the case study concerning the modern,

two-way hybrid electric ferry is presented and

thoroughly analyzed. The ferry was designed for

coastal shipping between Norwegian fjords with the

assumption that, during crossings between ports,

energy will be primarily sourced from battery banks,

which will be charged during stops at quay. However,

in unforeseen situations, it is possible to use diesel

generating set power units (part of a hybrid propulsion

system) in the electric power system of passenger-car

ferries.

Using the operational strategy adopted by the

Norwegian ferry operator, the project focuses on

minimising energy consumption, aligned with of the

policy of the reduction of greenhouse gases emission.

Achieving energy consumption reduction requires to

implement of several solutions, including innovative

hybrid power systems and selected electrical

installations such as: (I) powering the vessel from

battery banks combined with diesel generating sets, (II)

energy-efficient LED lighting, (III) flexible power

supply systems using power electronic frequency

converters [5].

The goal of this study is to examine the impact of

implementing conditions (I), (II) and (III) for

improving the energy efficiency of the ship in

accordance with philosophy and strategy of its

operation, while maintaining the appropriate values of

electrical energy quality parameters following the

standards of Det Norske Veritas (DNV) [7], which

surveys the construction process before classifying the

vessel. Notably, the DNV rules for DC battery-

powered systems are exclusively focused on the DC

busbar voltage as the main supply of the system. Other

switchboards supplying ship systems, such as AC 690

V / 50 Hz and AC 230 V / 50 Hz in complementary

configurations of electric power systems (without

energy storage systems), fulfil the function of the main

switchboards and should comply with full verification

conditions according to the requirements defined in

the appropriate regulations [7]. However, additional

checks of power quality standards related to currents

are justified by the fact that the systems described

under conditions (II) and (III) can significantly

minimise electrical energy consumption. Nevertheless,

strongly non-linear elements (LED lighting and power

electronic inverters) can negatively affect the power

quality in the considered electrical power system.

The first condition (using the power system with

batteries and DG generating sets) is an energy–saving

solution without negative consequences for power

quality. The second condition (applying energy-saving

LED lighting) may have a negative impact on selected

electricity quality parameters [8]. Results have shown

that LED lamps provide significant savings in

electricity, however they behave as nonlinear loads,

generating higher frequency harmonics, which may

degrade power quality in the distribution network [8,

9]. In our case, the problem concerns the large number

of devices equipped with rectifiers used to power

multiple of LED lamps in the AC system. The third

implemented solution involves flexible power supply

systems, using power electronic inverters. Some load

circuits consist of systems with motors controlled by

power converters, including propulsion, ventilation,

air conditioning and cooling systems. Powering motors

with variable frequency drives enables load

adjustment to actual operational needs. In such cases,

the total energy consumed by all electric motors on the

ship can be significantly reduced. However, using

multiple-power electronic converters may increase

total harmonic distortion (THD) in the current

waveforms. Therefore, although the primary concern

for the shipbuilders and operators is energy saving,

verifying power quality compliance with the

classifying institution standards remains essential. To

sum up, the main objective of this article is to draw

attention to the power quality on modern ships

equipped with different energy sources, operating

under various modes, and to emphasize the necessity

of its overall assessment.

The paper is organized as follows. In the second

section, we provide a short description of power

quality assessment methodology for a modern ship

power system with batteries and diesel generators,

based on the authors’ proposed flow-chart. In the next

section a recommended methodology is developed as

a case study using the test results obtained from sea

trials. This section covers various aspects, including a

brief characterization of the investigated object,

analysis of its configuration and load, measurements

and calculations of power quality parameters, and

overall power quality assessment for DC and AC

busbars as well as for selected PCC (Point of Common

Coupling) related to the thruster.

2 PROPOSED METHODOLOGY

Power quality assessment methodology for a modern

ship power system with batteries and diesel generators

is based on the authors’ concept presented in the form

of flow-chart in Fig.1.

The proposed methodology is based on analysis of

the configuration and load of the system under

consideration, taking into account its operational

modes, while excluding modes, when the ship is

supplied via shore grid such as shore supply (SS).

These modes, namely electric mode, hybrid mode and

diesel – electric mode are generally defined by

appropriate configurations of cooperating sources of

power, such as ESS (Energy Storage Systems) and DG

(Diesel Generator), together with the system’s load

conditions. Table 1 presents the five possible

operational modes of the ferry’s exploitation [5,6].

1307

Figure 1. Flow-chart of the performed investigation and

procedure for validation of the overall power quality

assessment.

Table 1. Five possible modes of operation of the ferry

Operating modes

Name

Source

power

Description of the system operation

M1*

(T1)

Electric

mode

ESS

Normal operating mode: AC 690 V / 50

Hz and AC 230 V / 50 Hz distribution

boards are powered by a converter from

DC 1000 V.

M2*

(T2/T3)

Hybrid

mode

ESS &

Mode used during extended voyages:

depending on current power demands,

generators provide propulsion power and

extra energy is transferred to the batteries

(battery charging). With higher power

demand, the batteries discharge power

into the grid, a process known as "peak

shaving".

Diesel–

electric

mode

Emergency operation mode: DG supplies

AC 690 V / 50 Hz, AC 230 V / 50 Hz

distribution boards, and thrusters

through DC 1000 V.

Shore

mode

Shore

grid

Supply via SS: allows for charging ESS at

low power; normal battery-charging

mode operates during night time.

Charging

mode

Shore

grid

High-power charging from shore:

provides the ability to charge the battery

banks quickly during short stop in port.

*under consideration in this study

The analysis of the results depends on three

operating cases of the electrical power system,

resulting from positions M1 and M2, as shown in Table

1. The selected cases - T1, T2 and T3, were subjected to

tests during sea trials and are explained in Table 2.

Table 2. Modes of operation of the electrical power system

verified during the sea trials

Mode of

work

Thruster 1

Thruster 2

DG1

DG2

Battery

Step load change

20...100%

Step load

change

20...100%

–

Load

Continuous load

change 0...100%

–

Load

Hybrid

Step load change

20...100%

Step load

change

20...100%

Load

Hybrid

Analysis of the load primarily focuses on the

essential load identified by the user, however, other

important loads were also taken into account from the

energy balance perspective. Next, the power quality

assessment procedure was developed with focus on

three aims of main objectives: DC busbars, AC busbars

and selected PCC (Point of Common Coupling) related

to the essential loads identified by operator of the

system (e.g. thrusters or important pumps). All

parameters were analyzed in appropriate operational

modes. The obtained results were compared with the

voltage and current limits established by the relevant

classifying institutions for DC battery-powered

systems, AC DG-battery-powered systems and for the

selected vital loads, respectively. Finally, a validation

of compliance with power quality standards

established by classifying institutions for the all

analyzed parts of the system under consideration, will

be conducted.

3 ANALYZED CASE STUDY

3.1 The object of the investigation

A simplified diagram of the considered modern ship

power system with batteries and diesel generators is

illustrated in Fig.2.

Figure 2. Simplified diagram of the modern passenger-car

ferry power system with batteries and diesel generators, the

elements shown in red colour indicate the selected loads of

the system.

The electrical power system of this ferry is divided

into two symmetrical sections: the bow (FWD –

Forward part of vessel) and the stern (AFT – After part

of vessel). Each section contains a power generation

Battery 1 Battery 2

Shore charging 1

Generator 1

AC 690 V/

50 Hz

DC 1000 V

AC 230 V/50 Hz

Loads

Generator 2

AC 690 V/

50 Hz

DC 1000 V

Shore charging 2

Loads

Transformer 1

Transformer 2

AC 230 V/50 Hz

Shore

supply

230 V

Shore

supply

400 V

DC Guard 1

Transformer 3

DC Guard 2

Thruster 1 Thruster 2

M M

1308

unit DG supplying an AC distribution board rated at

690 V / 50 Hz, a transformer with ratings of 500/99/500

kVA and 690/230/540 V / 50 Hz connecting the AC

distribution board at 230 V / 50 Hz and the DC at 1000

V, battery banks with a total capacity of 1,13 MWh and

a propulsion system with a motor rated at 960 kW, 600

V, and 68 Hz, which is powered by a DC/AC converter.

The propulsion unit from SCHOTTEL is supplied from

the 68 Hz DC 1000 V distribution board using a

VACON NXI power electronic converter, which

functions as an inverter. The inverter consists of IGBT

switches and generates a symmetrical, 3-phase PWM-

modulated AC voltage for the motor. The elements in

the configuration diagram are designated indexes as

follows: ‘1’ refers to the forward part of the electrical

power system and ‘2’ refers to the aft part of this

system. ‘DG’ indicates the generating sets and the

diesel generators. The ship's electrical power system is

equipped with shore charging and shore supply (SS),

connections for charging battery packs and supplying

the ship from the shore, and DC guard protection

modules [10], which enable fast disconnection and full

selectivity between forward and aft DC bus bars

sections.

3.2 Analysis of the system configuration and load

Analysis of the load primarily focused on the essential

load represented by thrusters (main ship propulsion).

However, other important loads were also considered

from the energy balance perspective. The energy

balance includes the specification of DC and AC energy

sources and their parameters, as well as specifications

and characteristics of the most important loads in the

analyzed system. Detailed specifications and in-depth

analysis concerning energy balance in the considered

case study can be found in [5]. It is important to note

that carried out analysis mainly covered loads active

during sea trials. Among them, certain devices were

supplied from AC 690 V, using power electronic

frequency converters, aspect particularly relevant from

the perspective of power quality standards. These

loads are shown in Table 3.

Table 3. The loads controlled by power electronic frequency

converters supplied from AC 690 V network

Name of device

Power

[kW]

Current

[A]

Switchboard

HP-1 Aers Central Heat/Cool

System

17,9 kW

16,6 A

FWD

Fire Bilge Pump 1

43,6 kW

40,5 A

FWD

Fire Pump 1

30 kW

27,9 A

FWD

Deluge Pump

160 kW

148,8 A

FWD

Steering Pump Fwd

22 kW

20,5 A

FWD

HP-2 Aers Central Heat/Cool

System

45 kW

41,8 A

AFT

Fire Bilge Pump 2

43,6 kW

40,5 A

AFT

Fire Pump 2

30 kW

27,9 A

AFT

Deluge Pump

160 kW

148,8 A

AFT

Steering Pump Aft

22 kW

20,5 A

AFT

* - In these control loops of the system a VLT®

HVAC Drive FC 102 unit was used as inverter

The analyses presented in [5] indicate that the total

sum of the energy loads from the thrusters supplied by

the 1000 V DC voltage (along with other loads powered

from the 690 V AC and 230 V AC voltages) reaches up

to 2619.7 kW (including 1920 kW for the thrusters) and

exceeds the sum of the energy sources corresponding

to 978 kVA (DGs, generating sets) plus 1130 kWh

(batteries). However, many of the loads shown in [5]

only operate during limited and different time

intervals, depending on ferry operation mode.

Thrusters typically consume power below their rated

values, governed by appropriately designed

simultaneity coefficient for the analyzed power system.

Some simultaneity load coefficient and degrees of

power source values shown in Table 2 [5] have been

determined on the basis of the shipyards’ ferry

documentation and the authors sea-going practice. It

was assumed that the sea trials loads and power

sources combinations corresponded to the routine,

regular conditions for scheduled ferry crossings

between two Norwegian fjords. Therefore, the

operating conditions were defined based on estimated

values for load coefficients, degrees of power sources

utilized, and a specific operational regime, i.e. a vessel

operating during a 15 minute crossing between

Norway fiords, 26 times in a normal day, where a

single crossing distance is 3 km. Therefore, achieving

energy balance in the analyzed electrical power system

is possible. This balance was maintained across all

possible operational modes of the ferry by

implementing energy management recommendations.

These recommendations focused on improving energy

efficiency, analyzing and implementing appropriate

battery maintenance strategies, and analyzing and

verifying all required functionalities across all

operational modes of the ferry.

3.3 Measurement and calculations of power quality

parameters

In order to obtain power quality parameters for the

power system of the considered ferry measurements of

instantaneous values of voltages and currents were

performed based on the diagram presented in Fig. 3a.

The voltage measurements were carried out via

transducers from LEM (Life Energy Motion) and the

current measurements were made using Rogowski’s

coils from PEM (Power Electronic Measurements). The

measurement system (Fig.3a) consisted of an industrial

computer from National Instruments, equipped with

PXIe-8135 controller and three PXIe-6358 data

acquisition cards. The registered samples of the

voltages and currents were used to determine the

power quality parameters. The parameters were

calculated using home-built software and a dedicated

spreadsheet. Technical realizations of the exemplary

voltage and current measurements are illustrated in

Fig.3b and 3c.

A main objective of the study was to determine and

analyse selected parameters of power quality related to

voltage and current, in both the DC and AC parts of the

system as well as to the frequency in the AC part. The

research scope not only included acceptable deviations

DC and AC voltages from their reference values, but

also the permissible levels of higher voltages and

current harmonics in the selected PCC of ship’s

electrical power system i.e. inverter supplying the

thruster (Fig.2). This was to assess the shape of the

voltage and current waveforms and to verify whether

these parameters were within the limits set by the DNV

classification guidelines. Maintaining these parameters

at appropriate levels is crucial for ensuring the safety

and reliability of maritime systems [11]. In the

presented case study three objectives were defined as

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follows: the 1000 V DC busbars as the main supply for

the ship, 690 V AC busbars as the complementary

supply and the PCC 600 V AC related to the inverter

supplying the thruster. The obtained measurement and

calculations results aimed to determine parameters

that characterize power quality at designated locations

in Fig.2, are: Udev, Uvar and Urip at the DC busbars,

Udev, fdev and THDU at the AC busbars and I, THDSI,

TWDSI an TIHDSI in the PCC corresponding to DC/AC

thruster converters. All parameters were analysed in

electric and hybrid modes (Table 1 and Table 2).

Examples of the cyclic voltage variations (Uvar) in DC

voltage, within the range of 0.2 s, are illustrated in

Fig.4. Authors also determined the highest observed

values of the Uvar (%) parameter obtained during full-

time recording for the T1, T2 and T3 modes of

operation.

Figure 3. Measurements of voltage and currents in the

passenger-car ferry power system: a) measurement system

diagram, b) voltage measurement on the DC busbars, c)

voltages and currents measurement on the AC terminals.

Figure 4. Voltage cyclic variation (Uvar) based on the

measurement in the DC main switchboard of 1000 V

(performed according to Fig.3a and 3b) for the different

modes of operation: a) T1, b) T3.

The configuration diagram of this power system

(Fig.2) shows that the 1000 V DC bus bars are the main

supply for this ship. Therefore, appropriate DNV limits

and measurement results from the tests were

compared. The results of this comparison are presented

in Table 4.

Table 4. Comparison of the DNV voltage limits and test

results for electric DC battery-powered systems

Indexes of power quality

DNV

voltage

limits

Ship tested

Measurement

results

Mode

of tests

Udev Voltage deviation in

equipment connected to battery

during charging

+30 to

−25%

−11.90%

−10.90%

Udev Voltage deviation in

equipment connected to the

battery not being charged

+20 to

−25%

−13.70%

Uvar Voltage cyclic variation

max 5%

4.07%

4.12%

4.07%

Urip Voltage ripple

max 10%

<<10.00%*

T1, T2

and T3

*did not observe considerable voltage ripples

The maximum value of Uvar was 4.12% (for T2

mode) and the obtained results of this index complied

with the DNV standards for all of regimes (T1, T2 and

T3). In addition to the research on the 1000 V DC

network, regarding voltage limits following DNV

standards, experiments for AC voltage limits at 690 V /

50 Hz were carried out. Exemplary waveforms are

illustrated in Fig.5 and the results of these experiments

are presented in Table 5.

Figure 5. The phase-to-phase voltage waveforms registered

on the AC main switchboard of 690 V (performed according

to Fig.3a), hybrid mode is T3, current load of DG is equal 367

A in all time of the test.

Table 5. Comparison of the DNV voltage limits and test

results for AC systems

Analysed parameters

DNV

limits

Measurement

results

Test

modes

Udev, Voltage deviation - Steady state

Deviation of nominal AC system

voltage for main power

distribution

±2.5%

<0.19%

T2 and

Deviation of nominal AC system

voltage for emergency power

distribution

±3.5%

T2 and

Udev, Voltage deviation - Transient state

Deviation of nominal AC voltage

from −15

to +20%

<0.35%

T2 and

fdev, Frequency deviation

Deviation of nominal frequency

of AC voltage:

- under steady state load

- under transient load

±5%

±10%

<0.24%

<0.6%

Voltage harmonic distortion

THDu

<4.5%

T2 and

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The THDu limit value specified in DNV standards

based on IEC 61000-2-4 class 2 norm is defined as the

ratio of root sum of squares of the RMS values of all the

harmonic components up to the 50th order to the RMS

value of the fundamental component. On the other

hand the acceptance of the THDS definition (Total

Harmonic Distortion Subgroup) applied in the IEC

61000-4-7 norm improves an evaluation of harmonic

distortion compared to the THDu criterion, especially

in ship systems, known as “soft systems” [3,11].

Therefore THDS factor is calculated as follows:

 

THDS 100 %

=



(1)

where: SG1 – RMS value of fundamental component

subgroup and harmonic subgroups SGh of h-order are

calculated as:

h h i

SG C

=−



(2)

where: SGh – RMS value of harmonic subgroup of h-

order, C10h – RMS value of respective frequency bin in

the Fourier Series, calculated by means of DFT, for 50

Hz system, index 10h refers to 10 periods (for 60 Hz

system, a designation C12h appears as referring to 12

periods).

An approach described by formulae (1) and (2) does

not cover distortions above 50

– order harmonics.

Even extension of the frequency band up to the 100th

harmonic does not provide a comprehensive solution

for many cases in ship networks, particularly where the

AFE PWM (Active Front End-Pulse Width

Modulation) drives are used [12]. In this kind of ship

power systems, only viable solution is the TWD (Total

Waveform Distortion) factor, defined as the ratio of the

RMS value of the voltage residue, after elimination of

the fundamental component, to the RMS value of the

fundamental component, expressed as a percentage.

Taking into account the above mentioned concept of

subgroups, this factor is calculated as follows [13, 14]:

 

TWDS 100 %

rms

U SG

−

=

(3)

where: Urms – is the voltage RMS value.

To complete a description of the waveform

distortions in ship power systems, a concept of TIHDS

(Total Interharmonic Distortion Subgroups) factor,

similarly to the formulae (1) and (3) may be described

as follows:

 

TIHDS 100 %

SGi

=



(4)

where interharmonic subgroups are expressed as:

h h i

SGi C



(5)

where: SGih is the RMS value of interharmonic

subgroups between harmonic h - order and h+1 order.

A relationship (4) covers interharmonic distortions up

to 50

– order.

In the analyzed case study the maximum registered

values of voltage distortion factors on the busbars AC

690 V, 50 Hz, (Fig.2), determined for the frequency

band up to 50

- harmonic order and up to 100

–

harmonic order were compared in Table 6.

Table 6. Comparison of maximal registered values of

voltage distortion factors on the busbars AC 690 V, 50 Hz

determined for both frequency bands, up to 50th and 100th

harmonic order

Analysed

parameters

Frequency band

Obtained values

[%]

TWDSU

Up to 50th – harmonic

order

3.72%

THDSU

3.66%

TIHDSU

0.55%

TWDSU

Up to 100th – harmonic

order

3.72%

THDSU

3.69%

TIHDSU

0.68%

All results presented in Table 5 complied with the

DNV classification requirements. Additionally, the

results shown in Table 6, although based on more

demanding criteria than those complied with the DNV

classification requirements [7].

Research on the variability of current distortion

factors in the PCC related to the thruster AC 600V, 68

Hz motor (Fig.2) has been performed using previously

presented factors: Total harmonic distortion subgroups

(THDS), Total waveform distortion subgroups (TWDS)

and Total interharmonic distortion subgroups (TIHDS)

[13,14], referred to the thruster current and named as

THDSI, TWDSI and TIHDSI respectively. In this case

there are more demanding criteria for waveform

distortion assessment than the traditional THD factor,

as included in [7]. Based on [14], these factors were

determined for frequency spectra up to the 100

harmonic. Figures 6 and 7 show current waveforms

changes in the three phases and current frequency

spectrum up to 50th harmonics in the first phase of

thruster’s motor (Thruster 1) for its load close to the

nominal working in T1 mode.

Figure 6. Current waveforms of Thruster 1 (according to

Fig.2) in three phases for its load close to nominal Irms=748 A,

TWDSI=2.96%, THDSI=1.85%, TIHDSI=1.67%.

1311

Figure 7. Current frequency spectrum of Thruster 1

determined up to 50

harmonic order for its load close to

nominal, for T1 operation mode (for better reliability the

fundamental component corresponding to 100% has been

removed).

In the presented spectrum of current (Fig. 7)

characteristic harmonic of 5

, 7

, 11

, 13

order are

visible, but also there are slightly increased values of

harmonic near end of the spectrum. The last ones are

related to the switching frequency of the drive inverter

transistors, which is 3 kHz (current fundamental

frequency is about 70 Hz).

It is worth adding that one of the leading

classification societies suggests analyzing the signal

spectrum up to the 100th harmonic in the case of AFE

systems [12]. However, in this case, such an approach

is not required for two reasons. Firstly, in a wider

frequency band (up to the 100

harmonic), no

increased level of harmonics is observed, and secondly,

the harmonic content values in the 50

range are

relatively small, which is generally reflected in the

TWDSI, THDSI, TIHDSI coefficients values.

Due to the lack of appropriate DNV standards

regarding the limitation of harmonic current emission

in thruster power supply systems, the power quality

criteria for THDSI and TWDSI for the I1 thruster

current were examined with reference to the PN/IEC

61000-3-4 standard [15]. This standard addresses the

“limitation of emission of harmonic current in low-

voltage power supply systems for equipment with

rated currents greater than 16 A”.

Although this standard could be helpful, due to its

scope, a rough analysis showed that, unfortunately, it

only applies to devices with a rated current limited to

75 A. Furthermore, for equipment exceeding 75 A as

the input current per phase, it states: “… the supply

authority may accept the connection of the equipment on the

basis of the agreed active power of the consumer’s

installation. The local requirements of the power supply

authority apply in this case”. Taking into account the fact

that the analysed passenger-car ferry, classified under

DNV rules, successfully began operation on February

2021 [16], this means that all technical conditions for

regular shipping, including power quality

requirements, were fulfilled and accepted by the ferry

operator.

Table 7. Comparison of the current limit requirements from

the classifying institutions and test results for the DC

battery power systems on the AC side of the inverter

installed in the Thruster 1 line

Indexes of

power quality

from [21]

DNV current

harmonic limits

I1 current

measurement

results for the

ship [%]

Mode of test

THDSI

Not applicable

1.90

TWDSI

2.96

TIHDSI

1.86

THDSI

Not applicable

2.07

TWDSI

2.89

TIHDSI

1.70

THDSI

Not applicable

1.96

TWDSI

2.99

TIHDSI

1.86

The THDSI, TWDSI and TIHDSI coefficient values

characterising the current supply of the thruster motor

(Thruster 1) are presented in Table 7. These data are

calculated in steady-state conditions for the maximum

thruster load, close to its nominal.

The measured I2 and I3 current results for Thruster

1 are approximately the same as the values for the I1

current, shown in Table 7.

4 CONCLUSIONS AND RECOMMENDATIONS

In the analysed system, energy consumption was

minimised by implementing solutions, such as an

appropriately controlled power supply i.e. battery

banks, in combination with generator sets. This was

partly achieved by selecting fixed and efficient

generator operation mode, using energy-efficient

lighting and power supply systems for selected

devices, such as propulsion, ventilation and air

conditioning systems controlled by power electronic

converters. Aforementioned technical solutions can

significantly reduce electrical energy consumption in

line with the strategy of shipbuilder and ferry operator,

but on the other hand they pose potential threats

regarding power quality deterioration in the system.

Thus, checking whether the power quality parameters

comply with the classifying institution standards is

justified and required.

The proposed methodology for power quality

assessment in a modern ship power system with

batteries and diesel generators is based on analysis of

the configuration and load of exemplary ferry system,

taking into account the modes of the system operation,

while excluding those modes, when the ship is

supplied via shore grid. These modes, namely the

electric mode, the hybrid mode i.e. diesel – electric

mode are generally defined by appropriate

configurations of cooperating sources of power, such

as ESS (Energy Storage Systems) and DG (Diesel

Generator), together with the system’s load conditions.

Starting from the aforementioned analysis

illustrated in flow-chart diagram, the power quality

assessment procedure was developed with focus on

three main objectives: 1000 V DC busbars as the main

power supply, 690 V AC busbars as the

complementary power supply and the PCC 600 V AC

related to the inverter supplying the thruster’s motor.

Although the primary issue for a shipbuilder and

operator is energy saving, checking whether the power

quality parameters are complying with the

classification standards is also important and

necessary. The checked power quality parameters for

1000 V DC network are: Udev  <–10.90%, –13.70%>,

Uvar  <4.07%, 4.12%>, Urip <<10%, and for 690 V AC

network: Udev < 0.19% (steady state), Udev < 0.35%

(transient state), fdev < 0.24% (steady state), fdev < 0.6%

(transient state), and THDu < 4.5%. Therefore it should

1312

be stated, that all of the analysed parameters

characterising power quality in the 1000 V DC and

690 V AC networks fully comply with the mandatory

requirements of the DNV classification standards.

Additionally the parameters describing voltage

waveform distortions on the AC 690 V busbars

determined according to more demanding criteria than

those defined above, indicate no significant threats

from the power quality point of view. Those

parameters were defined for the frequency band up to

50th harmonic order as: THDSU = 3.66%, TWDSU =

3.72%, and TIHDSU = 0.55% as well as for the frequency

band up to 100th harmonic order as: THDSU = 3.69%,

TWDSU = 3.73%, and TIHDSU = 0.68%.

Furthermore, some power quality parameters,

related to the thruster current on the AC side of the

inverter, were tested in this case study and the

following results were obtained: THDSI  < 1.90%,

2.07% >, TWDSI  < 2.89%, 2.99% > and TIHDSI  <

1.70%, 1.86% >. Taking into account the fact that the

presented data are steady-state values for the maximal

thruster load, these values are acceptable from a

practical operating point of view. However, this

analysis is outside the IEC standards.

In summary, the detailed conclusions and findings

regarding a power quality on modern ships equipped

with different energy sources such as ESS and DGS

with the application of a hybrid thruster power supply

system are:

− Electric hybrid systems, along with the operational

profile, increase the vessel’s operational safety, as

energy stored in battery banks can provide a stable

power source and immediate backup power in the

case of DG failures. This design approach for ship

power systems is essential and recommended for

future applications.

− The installed battery system ESS enables charging

via shore power, providing an alternative source of

power to DGs during port stops. This capability

reduces the ship’s local environment impact when

operating in battery mode.

− The advantages outlined above were achieved due

to the innovative application of the thruster

supplied by the hybrid power system without

negative impact on affecting the power quality in

the analysed system.

ACKNOWLEDGEMENTS

The authors are grateful to the authorities, designers and

shipbuilders from Remontowa Shipbuilding S.A. and

Remontowa Electrical Solutions for providing us with

company procedures to perform the sea trials and for the

related databases and raw measurements for this case study.

REFERENCES

[1] S.Kim, S.Choe, S.Ko, S.Sul, “A Naval Integrated Power

System with a Battery Energy Storage System: Fuel

efficiency, reliability, and quality of power”. IEEE

Electrification Magazine, Vol.3, No 2, pp. 22-33, June

2015.

[2] K.Divya, J.Stergaard, “Battery energy storage technology

for power systems—An overview”, Electric Power

Systems Research, Vol.79, No 4, pp. 511-520, April 2009.

[3] E. Skjong, R. Volden, E. Rødskar, M. Molinas, T.A.

Johansen, and J. Cunningham, “Past, Present, and Future

Challenges of the Marine Vessel’s Electrical Power

System”, IEEE Transactions on Transportation

Electrification. Vol. 2, No 4, pp. 522-537, 2016.

[4] M.Kunicka and W.Litwin, “Energy efficient small inland

passenger shuttle ferry with hybrid propulsion – concept

design, calculations and model tests”, Polish Maritime

Research, Vol. 26, No 2, pp. 85-92, 2019.

[5] J.Mindykowski, Ł.Wierzbicki, M.Górniak, A.Piłat,

“Analysis and Experimental Verification of Improving

the EEDI of a Ship using a Thruster Supplied by a Hybrid

Power System”, Polish Maritime Research, Vol. 31, No 1,

pp. 43-54, 2024.

[6] D.Tarnapowicz, S.German-Galkin, A. Nerc, M.Jaśkiewicz,

“Improving the Energy Efficiency of a Ship’s Power Plant

by Using an Autonomous Hybrid System with a PMSG”,

Energies, 2023, 16, 3158, pp. 1-19.

[7] DNV, Rules for the Classification of Ships, Part 4: Systems

and Components, Chapter 8, Electrical installation, July

2022 edition.

[8] A. Wantuch and M. Olesiak, “Effect of LED Lighting on

Selected Quality Parameters of Electricity”, Sensors.

23(3), 1582, 2023. https://doi.org/10.3390/s23031582.

[9] IEC 61000-3-2:2019-04-Electromagnetic Compatibility

(EMC). Part 3-2: Limits. Limits for Harmonic Current

Emissions (Equipment Input ≤ 16A per Phase), 2019.

[10] Information materials about VACON® NXP DCGuard.

Available online:

https://files.danfoss.com/download/Drives/DKDDPFP90

6A402_VACON%20NXP%20DCGuard_LR.pdf (accessed

on 13.12.2023).

[11] P. Gnaciński, T. Tarasiuk, J. Mindykowski, M. Pepliński,

M. Górniak, D. Hallmann, and A. Piłat, “Power Quality

and Energy – Efficient Operation of Marine Induction

Motors”, IEEE Access. Vol.8, pp.152193-152203, 2020.

doi:10.1109/ACCESS.2020.3017133.

[12] American Bureau of Shipping, Rules for Building and

Classing, Steel Vessels, ABS, Houston, TX, USA, 2008.

[13] J. Mindykowski and T. Tarasiuk, “Problems of power

quality in the wake of ship technology development”,

Ocean Engineering. Vol.107, pp.108-117, 2015.

doi:10.1016/j.oceaneng.2015.07.036.

[14] J. Mindykowski, T. Tarasiuk, and P. Gnaciński, “Review

of legal aspects of electrical power quality in ship systems

in the wake of the novelisation and implementation of

IACS rules and requirements”, Energies. 14(11), 3151,

2021. pp. 1-21, doi:10.3390/en14113151.

[15] IEC 61000-3-4 standard, “Limitation of emission of

harmonic current in low-voltage power supply systems

for equipment with rated current greater than 16A.”, First

edition 1998-10, Geneva, Switzerland.

[16] “Information materials about considered passenger-car

ferry”. Available online:

https://www.gospodarkamorska.pl/stocznia-

remontowa-shipbuilding-przekazala-norwegom-prom-

elektryczny-fodnes-57277#lg=1&slide=0 (accessed on

22.06.2023).