Full Simulation Modeling of All-Electric Ship with Medium Voltage DC Power System

: This paper proposes the full simulation model for the electrical analysis of all-electric ship (AES) based on a medium voltage DC power system. The AES has become popular both in the commercial and the military areas due to a low emission, a high fuel consumption efﬁciency, and a wide applicability. In spite of many advantages, it is complex and difﬁcult to construct the whole system with many mechanical and electrical components onboard. Full electrical analysis is essentially required to simplify the design of the AES, a control and optimization of a ship electric system. The proposed full simulation model of the AES includes the mechanical and the electrical elements by using the MATLAB/Simulink. The mechanical elements are comprised of a steam turbine and a hydrodynamic model of a ship which is adopted by an average value model that is based on the characteristic equation of the mechanical system. The electrical elements are developed by full detailed models which consist of generators, a propulsion motor, a battery, and a power electronics system. In order to design the distribution of the ship, the presented simulation model combined the mechanical and the electrical systems. The consistency of the developed individual models and the integrated AES was veriﬁed through the results of the presence or absence of the energy storage system for the speed acceleration and deceleration, loss of prime mover, and full propulsion load rejection.


Introduction
The all-electrical ship (AES) is becoming an advanced technology that will dominate the future shipbuilding industry.The conventional ship directly generates a rotating force by a prime mover with a propeller that is connected to a high-speed reduction gear.Hence in the past, the efficiency of the propeller system was a critical factor.However, nowadays, as ships become faster and larger, vibration and noise have become the main problems [1][2][3][4][5].Unlike conventional propulsion system, the AES is directly applied from a power supply to the high-output propulsion motor.Adopting an electric ship system offers many advantages: space utilization, a reduction of vibration and noise, and reduced fuel consumption of the ship.Furthermore, automation and reliability are increased, which makes the electric propulsion system suitable to reduce labor and the installation of equipment.
Moreover, a medium voltage DC system offers higher energy efficiency by reducing the number of energy conversion steps to feed a large percent of DC loads, higher power density, lower losses, and greater space flexibility.In addition, it is easier to integrate energy storage systems in a DC power system than an AC power system [6,7].
Despite the benefits that are offered by the AES, the electric ship network is infinite, and different from a land electric system.Since the AES operates in various conditions, the Energies 2022, 15, 4184 2 of 16 electric load and the fluctuation of power consumption change within wide ranges.As such, understanding the interaction between the mechanical and the complex electrical components of the AES is challenging.Also, experimental verification is complicated since the capacity of the ship components is large and complex.A large number of simulation studies have been conducted on the electrical analysis of the AES with a variety of conditions [8][9][10][11][12][13][14].The papers in [8][9][10][11] have studied transient responses according to the generator output and load regulation of AES.The paper in [12] deals with the effect of variation of AES parameters.The paper in [13] suggests the general design method for AES.The paper in [14] improves the stability of AES using SMES/battery.The paper in [15] proposes the optimal operation strategy under fault conditions.Therefore, this paper proposes a full simulation model for the electrical characteristic analysis of the AES with medium voltage DC system according to the operating conditions and the insertion of the energy storage system.

System Configuration and Modeling
Figure 1 shows the full simulation block diagram of the AES.The full simulation model is made with the mechanical and the electrical components that include the power generation system, propulsion system, power electronics system, energy storage system, and power management system, listed in Table 1.The detailed simulation model of the mechanical components and the electrical model are referred to [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33]: the system turbine, the three-phase synchronous generator, the exciter and the governor [16][17][18], the threephase diode rectifier, the three-phase PM motor, the DC/AC inverter, the DC/DC buck converter, DC/AC inverter and bi-directional DC/DC converter [19][20][21], the hydrodynamic model of the ship [22][23][24], the li-ion battery [25][26][27][28], the ship service load [28,29], the distribution system, and the power management system [30][31][32].The main DC bus feeds the propulsion motor through a DC/AC PWM inverter.The rated power of the propulsion motor is approximately 90% of the total generation power.Other ship service loads are connected to the secondary low voltage bus through DC/DC converters and a DC/AC inverter.The detailed parameters are referred in the Appendix A.
The three-phase synchronous generator is used by adopting the modified preset model in MATLAB/Simulink.The three-phase diode rectifier is chosen to provide a constant DC voltage.It cannot control the generator output voltage.The voltage is regulated by the excitation system.The excitation system ensures the quality of the generator voltages and the reactive power.The applied excitation system is IEEE standard type of DC1A [17,18].The governor regulates the fuel injection to control the turbine speed.This is integrated into the power generation system.
Figure 2 shows the waveforms of the simulation results of the power generation system.Figure 2a shows the output power of the propulsion motor which was driven by the ramped reference.According to the demand of the load power, Figure 2b-d shows the

Power Generation System
The power generation system serves as an electrical power supply for the AES.It is composed of two steam turbines, two three-phase synchronous generators, two excitergovernors, and two three-phase diode rectifiers.
The steam turbine extracts thermal energy from the pressurized steam.And this steam causes mechanism work on a rotating shaft.[16].
MATLAB/Simulink provides the preset model of the steam turbine which embodies the transfer function of the heat and the flow [16,22,29].The output torque of the steam turbine T m can be expressed as Equation (1), where k is the coefficient of the turbine torque and Q is the flow rate.
The three-phase synchronous generator is used by adopting the modified preset model in MATLAB/Simulink.The three-phase diode rectifier is chosen to provide a constant DC voltage.It cannot control the generator output voltage.The voltage is regulated by the excitation system.The excitation system ensures the quality of the generator voltages and the reactive power.The applied excitation system is IEEE standard type of DC1A [17,18].
The governor regulates the fuel injection to control the turbine speed.This is integrated into the power generation system.
Figure 2 shows the waveforms of the simulation results of the power generation system.Figure 2a shows the output power of the propulsion motor which was driven by the ramped reference.According to the demand of the load power, Figure 2b-d shows the output power of the steam turbine, DC bus voltage, and the frequency of the generator, respectively.

Propulsion System
The propulsion system generates the driving force for all-electric ships.It consists of two controllable DC/AC PWM inverters, two propulsion motors, and a ship hydrodynamics model [19][20][21]23].Various types of propulsion motor have been researched.The propulsion motor adopted the permanent magnet synchronous motor for the simple analysis in this paper.The motor parameters have been modified for the simulation of the MATLAB/Simulink model.The d-q voltages and the torque equations of the propulsion motor are shown in Equation (2), where   ,   ,   ,   ,   ,   ,   ,   , and   denote the stator resistance, the stator inductance, the flux density, the rotational angular speed, the mechanical speed, the electric torque, the load torque, the coefficient inertia, and the friction, respectively.

{
The DC/AC PWM inverter produces the variable output voltage and the frequency for the control of the propulsion motor.Modeling of the propeller can be acquired from the relationships with thrust, torque, and speed.It can be expressed by Equation (3), where   is the propeller thrust [N],   is the propeller shaft speed [rpm], and   is the propeller torque [Nm].The parameters ρ,   ,   , and   are the water density, the propel-

Propulsion System
The propulsion system generates the driving force for all-electric ships.It consists of two controllable DC/AC PWM inverters, two propulsion motors, and a ship hydrodynamics model [19][20][21]23].Various types of propulsion motor have been researched.The propulsion motor adopted the permanent magnet synchronous motor for the simple analysis in this paper.The motor parameters have been modified for the simulation of the MATLAB/Simulink model.The d-q voltages and the torque equations of the propulsion motor are shown in Equation ( 2), where R s , L s , λ m , ω r , ω m , T e , T L , J m , and B m denote the stator resistance, the stator inductance, the flux density, the rotational angular speed, the mechanical speed, the electric torque, the load torque, the coefficient inertia, and the friction, respectively.
The DC/AC PWM inverter produces the variable output voltage and the frequency for the control of the propulsion motor.Modeling of the propeller can be acquired from the relationships with thrust, torque, and speed.It can be expressed by Equation (3), where T p is the propeller thrust [N], n m is the propeller shaft speed [rpm], and Q p is the propeller torque [Nm].The parameters ρ, D p , K T , and K Q are the water density, the propeller diameter, the thrust coefficient, and the torque coefficient, respectively.V A is the advanced Energies 2022, 15, 4184 5 of 16 velocity of the propeller which is normally less than the ship speed V s due to the wake of the ocean.
In order to calculate the ship speed from the hydrodynamic model, the ship hydrodynamics model is usually obtained through the experimental results.However, it is impossible to get those data directly.The applied variables of the simulation model that are related to the ship model were acquired indirectly and employed by MATLAB/Simulink Marine system toolbox [22].Figure 3 shows the simulation results of the propulsion system.Figure 3a-d show the output torque, the motor speed, the output phase currents, and output power of the propulsion, respectively.ler diameter, the thrust coefficient, and the torque coefficient, respectively vanced velocity of the propeller which is normally less than the ship speed wake of the ocean.
In order to calculate the ship speed from the hydrodynamic model, th dynamics model is usually obtained through the experimental results.How possible to get those data directly.The applied variables of the simulation related to the ship model were acquired indirectly and employed by MAT Marine system toolbox [22].Figure 3 shows the simulation results of the p tem. Figure 3a-d show the output torque, the motor speed, the output phas output power of the propulsion, respectively.

Power Electronics System
The power electronics system consists of three DC/DC converters an inverters for supplying power to the electric loads except the main power sion motor [19][20][21].There were two types of DC/DC converters that were the ship service load and the energy storage system, respectively.Figure 4 s ulation results of the DC/DC buck converter for the ship service load.Alth power is changed, the output voltages of the DC/DC converter and the D are maintained by the constant power control of the DC/DC converter.

Power Electronics System
The power electronics system consists of three DC/DC converters and two DC/AC inverters for supplying power to the electric loads except the main power of the propulsion motor [19][20][21].There were two types of DC/DC converters that were simulated for the ship service load and the energy storage system, respectively.Figure 4 shows the simulation results of the DC/DC buck converter for the ship service load.Although the load power is changed, the output voltages of the DC/DC converter and the DC/AC inverter are maintained by the constant power control of the DC/DC converter.

Energy Storage System
The energy storage system is used for the purpose of improving the which is especially affected by a start/stop of the propulsion motor, an abru and some fault conditions [25][26][27][28]30].This system is composed of the buck/boost DC/DC converter and the Li-ion battery.The capacity of the Li decided from the difference between the output power of the generation ca load power.To verify the operation performance of the modeled energy s the constant charging and discharging currents were both regulated.Figu simulation results of the energy storage system.The charge and discharge c battery SOC are shown according to the current reference.

Energy Storage System
The energy storage system is used for the purpose of improving the power quality which is especially affected by a start/stop of the propulsion motor, an abrupt load change and some fault conditions [25][26][27][28]30].This system is composed of the bidirectional buck/boost DC/DC converter and the Li-ion battery.The capacity of the Li-ion battery is decided from the difference between the output power of the generation capacity and the load power.To verify the operation performance of the modeled energy storage system, the constant charging and discharging currents were both regulated.Figure 5 shows the simulation results of the energy storage system.The charge and discharge current and the battery SOC are shown according to the current reference.

Power Management System
Figure 6 shows the configuration of the power management system performs a variety of roles: total ship system control, monitoring, and chec ability of the electrical power depending on the electrical network status [31 makes it possible to determine the operating status, limit the output power sion motor, shed the load in accordance with the priorities, control the e system, and detect the system operating mode.Figure 6 suggests a general without designing and reflecting the actual PMS and is modeled to be the the simulation results.

Power Management System
Figure 6 shows the configuration of the power management system (PMS), which performs a variety of roles: total ship system control, monitoring, and checking the availability of the electrical power depending on the electrical network status [31][32][33][34][35][36].The PMS makes it possible to determine the operating status, limit the output power of the propulsion motor, shed the load in accordance with the priorities, control the energy storage system, and detect the system operating mode.Figure 6 suggests a general configuration without designing and reflecting the actual PMS and is modeled to be the background of the simulation results.

Modeling of Integrated Power System
The full simulation model of the AES was combined to obtain the electrical characteristics of the various ship operating conditions.Both voltage and frequency stability are important issues in the power system of the all-electric ship.As such, strict rules need to be established to guarantee secure operation under various operating conditions, such as STANAG 1008, IEC 60092/101, IEEE Std 1709-2010, and MIL Std 1339 [37][38][39][40].IEEE Std 1709−2010 and STANAG 1008 were used to evaluate the resulting simulation performance.As per IEEE Std 1709−2010, the limitations of the steady state DC voltage tolerances should be within ±10%.Transient state DC voltage can be allowed to have a tolerance of 200% from 0.1 to 10 ms.Frequency stability is referenced with regard to STANAG 1008.This defines the frequency limits for the steady state to be ±3%, and momentary deviations could be allowed to be about ±4%, respectively.A total of three different operating conditions were simulated for the purpose of evaluating the performance of the proposed simulation model.Figure 7 shows three operation conditions of the propulsion motor.

•
Acceleration and deceleration (ACC&DEC): Figure 7a shows that the two turbine generators set are initially operating to supply the service load of 10% rated power.Then after 10 s, a 7 %/s acceleration of the propulsion motor is introduced to the system until it reaches to 80% rate power, where it stays for 10 s.Starting from this point, a 7 %/s deceleration is applied to the system, until it finally settles to 10% rated power.

•
Loss of prime mover trip (LPMT): 80% of the propulsion power demand is presented in Figure 7b.The circuit breaker for one of the two turbine generators is tripped.The propulsion motors operate at a reduced load, then immediately restored to a power

Modeling of Integrated Power System
The full simulation model of the AES was combined to obtain the electrical characteristics of the various ship operating conditions.Both voltage and frequency stability are important issues in the power system of the all-electric ship.As such, strict rules need to be established to guarantee secure operation under various operating conditions, such as STANAG 1008, IEC 60092/101, IEEE Std 1709-2010, and MIL Std 1339 [37][38][39][40].IEEE Std 1709−2010 and STANAG 1008 were used to evaluate the resulting simulation performance.As per IEEE Std 1709−2010, the limitations of the steady state DC voltage tolerances should be within ±10%.Transient state DC voltage can be allowed to have a tolerance of 200% from 0.1 to 10 ms.Frequency stability is referenced with regard to STANAG 1008.This defines the frequency limits for the steady state to be ±3%, and momentary deviations could be allowed to be about ±4%, respectively.A total of three different operating conditions were simulated for the purpose of evaluating the performance of the proposed simulation model.Figure 7 shows three operation conditions of the propulsion motor.
Energies 2022, 15, 4184 9 of 16 dure, the turbine generator shall adjust its output power according to the reduced load demand.

•
Full propulsion load rejection (FPLR): As shown in Figure 7c, this condition denotes the loss of the full propulsion load.Load rejection is initiated at 30 s with 80% of the propulsion power load.The supply frequency varies directly with the steam turbine speed and frequency because the shaft of the generator is directly coupled to the steam turbine.

Simulation Results
Figure 8 shows the simulation results of the acceleration and the deceleration operations.The power of the propulsion motor is initially increasing at a rate of 7%/s.After a steady state at 80%, it starts the decreasing of the rate of 7%/s until the resuming power is at 10% power.Note that the transient DC bus voltage agrees with the IEEE std 1709-2010 voltage tolerance from Figure 8b. Figure 8a,c shows the output power of the propulsion motor and steam turbine, respectively.And Figure 8d shows the pulsation of the frequency which is above the transient state tolerance limit of STANAG 1008.

•
Acceleration and deceleration (ACC&DEC): Figure 7a shows that the two turbine generators set are initially operating to supply the service load of 10% rated power.Then after 10 s, a 7 %/s acceleration of the propulsion motor is introduced to the system until it reaches to 80% rate power, where it stays for 10 s.Starting from this point, a 7 %/s deceleration is applied to the system, until it finally settles to 10% rated power.

•
Loss of prime mover trip (LPMT): 80% of the propulsion power demand is presented in Figure 7b.The circuit breaker for one of the two turbine generators is tripped.The propulsion motors operate at a reduced load, then immediately restored to a power level that is sustainable by the remaining one turbine generator.During this procedure, the turbine generator shall adjust its output power according to the reduced load demand.

•
Full propulsion load rejection (FPLR): As shown in Figure 7c, this condition denotes the loss of the full propulsion load.Load rejection is initiated at 30 s with 80% of the propulsion power load.The supply frequency varies directly with the steam turbine speed and frequency because the shaft of the generator is directly coupled to the steam turbine.

Simulation Results
Figure 8 shows the simulation results of the acceleration and the deceleration operations.The power of the propulsion motor is initially increasing at a rate of 7%/s.After a steady state at 80%, it starts the decreasing of the rate of 7%/s until the resuming power is at 10% power.Note that the transient DC bus voltage agrees with the IEEE std 1709-2010 voltage tolerance from Figure 8b. Figure 8a,c shows the output power of the propulsion Energies 2022, 15, 4184 10 of 16 motor and steam turbine, respectively.And Figure 8d shows the pulsation of the frequency which is above the transient state tolerance limit of STANAG 1008.In the case of the trip of one prime mover, Figure 9 shows the simulation results in accordance with IEEE Std 1709-2010 and STANAG 1008.The output power of the propulsion motor is reduced to half due to the control of the power management system to protect the ship electric system.As shown in Figure 9b,d, although the stability of the main DC bus voltage is satisfied, the frequency pulsation during the transient state is increased to about 10%. Figure 10 shows the simulation results of the full propulsion load rejection.The turbine generator set supplies the propulsion motor at 80% power, then the circuit breaker of the propulsion motor is open for the purpose of the trip operation.As shown in Figure 10, after the full propulsion load is removed from the electrical distribution system of the ship, the DC bus voltage rises to 1.1 times higher than the rated voltage but it is tolerable by the IEEE Std 1709-2010.However, as shown in Figure 10d, the generator frequency In the case of the trip of one prime mover, Figure 9 shows the simulation results in accordance with IEEE Std 1709-2010 and STANAG 1008.The output power of the propulsion motor is reduced to half due to the control of the power management system to protect the ship electric system.As shown in Figure 9b,d, although the stability of the main DC bus voltage is satisfied, the frequency pulsation during the transient state is increased to about 10%.In the case of the trip of one prime mover, Figure 9 shows the simulation results in accordance with IEEE Std 1709-2010 and STANAG 1008.The output power of the propulsion motor is reduced to half due to the control of the power management system to protect the ship electric system.As shown in Figure 9b,d, although the stability of the main DC bus voltage is satisfied, the frequency pulsation during the transient state is increased to about 10%. Figure 10 shows the simulation results of the full propulsion load rejection.The turbine generator set supplies the propulsion motor at 80% power, then the circuit breaker of the propulsion motor is open for the purpose of the trip operation.As shown in Figure 10, after the full propulsion load is removed from the electrical distribution system of the ship, the DC bus voltage rises to 1.1 times higher than the rated voltage but it is tolerable by the IEEE Std 1709-2010.However, as shown in Figure 10d, the generator frequency Figure 10 shows the simulation results of the full propulsion load rejection.The turbine generator set supplies the propulsion motor at 80% power, then the circuit breaker of the propulsion motor is open for the purpose of the trip operation.As shown in Figure 10, after the full propulsion load is removed from the electrical distribution system of the ship, the DC bus voltage rises to 1.1 times higher than the rated voltage but it is tolerable by the IEEE Std 1709-2010.However, as shown in Figure 10d, the generator frequency exceeds over approximately 35% and remains around there for about 25   As shown in Figures 8-10, the transient and the steady state voltages satisfy the IEEE Std 1709-2010 limits.However, note that the energy storage system is required to reduce the fluctuation of the generator frequency and the transient times.
Figure 11 shows the simulation results that focused on the stability of the generator frequency after inserting the energy storage system to reduce the transient time.When the energy storage system is connected, the frequency excursion is reduced in all operating conditions.For two operating conditions (acceleration and deceleration, loss of prime mover trip), the transient of the frequency appears to be slightly higher than the limits of STANAG 1008.Despite the insertion of the energy storage system, the transient of the frequency excess and the transient time of full propulsion load rejection and does not satisfy the STANAG limits.In this case, from the operation of the power management system, the output power of the generator is reduced to maintain power for the ship service load.Table 2 shows the improved electrical characteristics of the transient and steady state voltages and the frequency by inserting the energy storage system into the main DC bus.The results (pass/fail) of transient and steady state were determined based on the STA-NAG 1008, even if energy storage system is connected, the full power load rejection case does not satisfy the frequency standard.In order to solve this problem an energy storage system with a sufficiently large capacity must be added.As shown in Figures 8-10, the transient and the steady state voltages satisfy the IEEE Std 1709-2010 limits.However, note that the energy storage system is required to reduce the fluctuation of the generator frequency and the transient times.
Figure 11 shows the simulation results that focused on the stability of the generator frequency after inserting the energy storage system to reduce the transient time.When the energy storage system is connected, the frequency excursion is reduced in all operating conditions.For two operating conditions (acceleration and deceleration, loss of prime mover trip), the transient of the frequency appears to be slightly higher than the limits of STANAG 1008.Despite the insertion of the energy storage system, the transient of the frequency excess and the transient time of full propulsion load rejection and does not satisfy the STANAG limits.In this case, from the operation of the power management system, the output power of the generator is reduced to maintain power for the ship service load.Table 2 shows the improved electrical characteristics of the transient and steady state voltages and the frequency by inserting the energy storage system into the main DC bus.The results (pass/fail) of transient and steady state were determined based on the STANAG 1008, even if energy storage system is connected, the full power load rejection case does not satisfy the frequency standard.In order to solve this problem an energy storage system with a sufficiently large capacity must be added.

Conclusions
Interest has been increasing in AES with a medium voltage DC power system.However, modeling and integration of the whole system is a complex and difficult task.To analyze the electrical characteristic of the medium voltage DC ship power system, this paper proposed the full simulation modeling of the AES with the mechanical and the electrical components by deriving the mathematical equations and using MATLAB/Simulink.The simulation was performed under three different ship operating conditions.The electrical characteristics of the AES that were related to DC bus voltage and generator frequency were analyzed according to the presence or absence of the energy storage system to meet IEEE Std 1709-2010 and STANAG 1008 standards.The effect of the energy storage system to improve the dynamic performance is shown at all operating conditions.

Conclusions
Interest has been increasing in AES with a medium voltage DC power system.However, modeling and integration of the whole system is a complex and difficult task.To analyze the electrical characteristic of the medium voltage DC ship power system, this paper proposed the full simulation modeling of the AES with the mechanical and the electrical components by deriving the mathematical equations and using MATLAB/Simulink.The simulation was performed under three different ship operating conditions.The electrical characteristics of the AES that were related to DC bus voltage and generator frequency were analyzed according to the presence or absence of the energy storage system to meet IEEE Std 1709-2010 and STANAG 1008 standards.The effect of the energy storage system to improve the dynamic performance is shown at all operating conditions.

Figure 1 .
Figure 1.Full simulation model of the AES implemented in MATLAB/Simulink.

Figure 1 .
Figure 1.Full simulation model of the AES implemented in MATLAB/Simulink.

Figure 2 .
Figure 2. Simulation results of the power generation system: (a) Output power of the propulsion motor; (b) Output power of the steam turbine; (c) DC bus voltage; and (d) Frequency of the generator.

Figure 2 .
Figure 2. Simulation results of the power generation system: (a) Output power of the propulsion motor; (b) Output power of the steam turbine; (c) DC bus voltage; and (d) Frequency of the generator.

Figure 3 .
Figure 3. Simulation results of the propulsion system: (a) Torque of the propulsion m of the propulsion motor; (c) Phase currents of the propulsion motor; (d) Output po pulsion motor.

Figure 3 .
Figure 3. Simulation results of the propulsion system: (a) Torque of the propulsion motor; (b) Speed of the propulsion motor; (c) Phase currents of the propulsion motor; (d) Output power of the propulsion motor.

Figure 4 .
Figure 4. Simulation results of the power electronics system: (a) Load power; (b) O the DC/DC converter; (c) Output voltages of the DC/AC inverter.

Figure 4 .
Figure 4. Simulation results of the power electronics system: (a) Load power; (b) Output voltage of the DC/DC converter; (c) Output voltages of the DC/AC inverter.

Figure 5 .
Figure 5. Simulation results of the energy storage system: (a) Battery discharge cur SOC in case of discharge; (c) Battery charge current; (d) Battery SOC in case of char

Figure 5 .
Figure 5. Simulation results of the energy storage system: (a) Battery discharge current; (b) Battery SOC in case of discharge; (c) Battery charge current; (d) Battery SOC in case of charge.

Figure 6 .
Figure 6.Configuration of the power management system.

Figure 6 .
Figure 6.Configuration of the power management system.

Figure 7 .
Figure 7.The operating conditions: (a) Acceleration and deceleration; (b) Loss of prime mover trip; (c) Full propulsion load rejection.

Figure 7 .
Figure 7.The operating conditions: (a) Acceleration and deceleration; (b) Loss of prime mover trip; (c) Full propulsion load rejection.

Figure 8 .
Figure 8. Simulation results of the acceleration and deceleration (without the energy storage system): (a) Output power of the propulsion motor; (b) Main DC bus voltage; (c) Output power of the steam turbine; (d) Frequency of the generator.

Figure 9 .
Figure 9. Simulation results of the loss of prime mover trip (without the energy storage system): (a) Output power of the propulsion motor; (b) Main DC bus voltage; (c) Output power of the steam turbine; (d) Frequency of the generator.

Figure 8 .
Figure 8. Simulation results of the acceleration and deceleration (without the energy storage system): (a) Output power of the propulsion motor; (b) Main DC bus voltage; (c) Output power of the steam turbine; (d) Frequency of the generator.

Figure 8 .
Figure 8. Simulation results of the acceleration and deceleration (without the energy storage system): (a) Output power of the propulsion motor; (b) Main DC bus voltage; (c) Output power of the steam turbine; (d) Frequency of the generator.

Figure 9 .
Figure 9. Simulation results of the loss of prime mover trip (without the energy storage system): (a) Output power of the propulsion motor; (b) Main DC bus voltage; (c) Output power of the steam turbine; (d) Frequency of the generator.

Figure 9 .
Figure 9. Simulation results of the loss of prime mover trip (without the energy storage system): (a) Output power of the propulsion motor; (b) Main DC bus voltage; (c) Output power of the steam turbine; (d) Frequency of the generator.

Figure 10 .
Figure 10.Simulation results of the full propulsion load rejection (without the energy storage system): (a) Output power of the propulsion motor; (b) Main DC bus voltage; (c) Output power of the steam turbine; (d) Frequency of the generator.

Figure 10 .
Figure 10.Simulation results of the full propulsion load rejection (without the energy storage system): (a) Output power of the propulsion motor; (b) Main DC bus voltage; (c) Output power of the steam turbine; (d) Frequency of the generator.

Figure 11 .
Figure 11.Simulation results with the energy storage system: (a) Acceleration and deceleration; (b) Loss of prime mover; (c) Full propulsion load rejection.

Figure 11 .
Figure 11.Simulation results with the energy storage system: (a) Acceleration and deceleration; (b) Loss of prime mover; (c) Full propulsion load rejection.

Figure A5 .
Figure A5.Relationship with parameters for PMS.

Figure A5 .
Figure A5.Relationship with parameters for PMS.

Figure A5 .
Figure A5.Relationship with parameters for PMS.

Figure A6 .
Figure A6.Example of PMS operation in prime mover trip scenario.

Table 1 .
Parameters of the simulation elements.

Table 2 .
Electrical characteristics according to the operation conditions.

Table 2 .
Electrical characteristics according to the operation conditions.