ship
Content
Qiuli Yu and Dr. Noel N. Schulz, Mississippi State University
Design, Modeling, and Simulation of Power Generation and Electric Propulsion System for IPS for All-Electric Ships
ABSTRACT
To meet the Navy’s increasing demand for more propulsion power and service power, the whole power system onboard is moving toward the integrated power system (IPS) for future allelectric warships. This paper presents the design, modeling, and simulation of power generation and electric propulsion system for IPS. The architecture of this power generation and electric propulsion system (PGAEPS) is designed as a part of IPS and has an interface to connect other parts of the IPS. Modeling of the whole power generation and electric propulsion system is based on SIMULINK. Simulation results show performance and effectiveness of the power generation and propulsion system, and help better understand the impact of the design of a power generation and propulsion system on the performance of the IPS. around it rather than create a tailored mechanical propulsion system for the ship (Marine Reporter 2002). Sizes and locations of machines in mechanical propulsion systems reduce the space available for cargo and passengers and limit efficient loading and unloading. The considerable length of the shaft in mechanical propulsion systems makes efficient space use challenging. All of these factors limit ship design flexibility (Marine Reporter 2002). In electric propulsion systems, there is no direct link, such as shaft and gearbox, between the prime mover and the propeller. Figure 1 shows a structural comparison between electric and mechanical propulsion (McCoy 2002). The feature of no direct link between the prime mover and the propeller in an electric propulsion system provides ship designers with two advantages. One is that the turbine speed becomes fully decoupled from the propeller speed, making it possible for ship designers to optimize the turbine speed with regard to fuel efficiency. Another is that ship designers have more design flexibility (Sudhoff and et al 1998). On the other hand, high power-to-weight ratio of electric machines in an electric propulsion system reduces the needed ship internal space for machines installation, and can accommodate more cargo and passengers for commercial ships and more weapons and personnel for warships. Compared with mechanical propulsion systems, the electric propulsion systems improve fuel efficiency, provide flexible design ability, and require less internal volume for electric machines installation. Electric propulsion systems are widely used in large commercial ships and especially warships that demand a high level of maneuverability or a lot of slow speed (Marine Reporter 2002).
INTRODUCTION
With the invention and development of external combustion engines and internal combustion engines, traditional commercial and military ships employed a mechanical propulsion system that uses gas turbines as the prime mover. A typical ship mechanical propulsion system includes a gas turbine, a shaft with a gear box, a propeller, ship dynamics, a shaft speed controller, a propellor pitch controller, and a main controller (Izadi-Zamanabadi and Blane 1999). The main controller will coordinate behaviors of the governor and the propellor pitch controller, as well as control ship speed and optimize efficiency. A mechanical propulsion system is so large and heavy that ship designers have to design and construct the rest of the ship
Figure 1. Electrical vs. Mechanical Propulsion (modified from McCoy 2002)
Current large warships demand more and more propulsion power in a way that modern techniques for power generation and ship configuration almost reach a bottleneck. At the same time, growth continues in the need for electric power for hotel loads, pulsed weapons, and high power sensors. In current warships the electric propulsion system separates from ship electric power systems for hotel loads and weapon loads. Large amounts of power locked in the mechanical propulsion system are not available for other uses even when ships do not need to move with full speed. Future all-electric warships with an integrated power system (IPS) are capable of redirecting the large amounts of power dedicated to propulsion and releasing this power for hotel and weapon loads. The IPS for all-electric ships combines the power generation system, the electric propulsion system, the power distribution system with distributed generators (DG), the energy storage system for pulsed weapons, and the power control and management system all together. The move to IPS design will significantly improve efficiency, effectiveness, and survivability. Many papers on electric propulsion systems for ships have been published. Xu, Mindykowski, and Zheng (2004) describe an architecture of an electric propulsion system without detailed modeling and simulation. Yin and Zou (2004) discuss studies on a new electric propulsion system with nuclear power generation. But neither of these papers focus on the combination
of electric generation and electric propulsion, nor aim to future integrated power systems. Several papers, published in the Proceedings of the IEEE Electric Ship Technologies Symposium 2007, dealt with an overview of integrated electric power and propulsion system, and modeling and simulation of electric propulsion system. However, these models are not suitable for IPS. This paper focuses on the design of power generation and electric propulsion system (PGAEPS) for IPS for future all-electric warships. For shipboard power systems, the power and the load have almost the same magnitude. With a real power generation system replacing an ideal power source, the whole power system can show dynamic behavior and provide an accurate platform for later voltage stability analysis. The architecture of the PGAEPS designed here should be easily integrated as a part of IPS and has an interface (common bus) to connect other parts (such as the distribution system, DG, and energy storage system) of the IPS. Modeling and simulation of the PGAEPS are implemented with SIMULINK, based on the consideration of availability, familiarity, and experience with MATLAB/SIMULINK software. Simulation results not only show performance and effectiveness of the PGAEPS, but also illustrate the impact of the PGAEPS design on the performance of the IPS.
DESIGN OF PGAEPS FOR IPS
Figure 2. Power Generation Subsystem for IPS
The IPS for all-electric ships includes the power generation system, the electric propulsion system, and the power distribution system all together. Design of the PGAEPS allows movement closer to the implementation of the IPS, which can provide a platform for further shipboard power system stability analysis, power flow calculation, and fault analysis and protection/reconfiguration design. The power generation subsystem designed consists of a turbine (prime mover), synchronous machine (generator), speed governor, voltage exciter and stabilizer, transformer, and rectifier, as illustrated in Figure 2. Here Pref and Vref are the power reference and voltage reference, respectively. Pe and Vt are the electric power the
generator produces and output voltage of the generator, respectively. The power generation subsystem includes two basic controls: voltage regulation and turbine speed regulation. The rated power and rated voltage are 36 MW and 13.8 kV respectively. These magnitudes are selected to mirror the power system of the proposed DD(X) national ships. The electric propulsion subsystem includes a rectifier, inverter, motor and motor controller, propeller, ship-speed dynamics, and external forces. Combining the power generation subsystem and electric propulsion system together, we create the whole PGAEPS, as illustrated in Figure 3.
Figure 3. Diagram of PGAEPS
Here Vdc is the DC output voltage of the rectifier. T is the torque the propeller produces. Vabc is the vector of three-phase line-to-neutral voltages. In the PGAEPS, a transformer with 13.8 kV/4.16 kV is used to connect the generator and the rectifier. The transformer has twofold roles in the PGAEPS. First, the DC voltage, as the output of the rectifier, will be decreased to around 5 kV. Second, with the delta-delta connection, the undesirable third harmonic magnetizing current, caused by the nonlinear core B-H characteristic, remains trapped inside the delta winding. Third harmonic currents are zero-sequence currents, which cannot enter or leave a delta connection, but can flow within the delta. Thus the power factor of the whole PGAEPS is improved. It should be noted that the PGAEPS also includes a rectifier and an inverter. For a simple PGAEPS, the rectifier and inverter can be removed and the generator can directly drive the motor. However, changes in load magnitude and load frequency will cause changes in power generation and generator frequency. The power generation couples with the load and cannot maintain a common bus with fixed voltage and frequency for future integration to IPS. The rectifier and inverter are used to decouple the power generation system from the motor drive, thus the generator can operate in fuel efficiency mode, as well as maintain a common bus for future IPS. Design of the rectifier is also important for the PGAEPS. There are three kinds of rectifiers for our choice: three-phase full-wave diode rectifier, thyristor-based rectifier, and three-phase threelevel PWM rectifier. The diode rectifier is simple and easy to use, and the output DC voltage can be expressed as
U dc =
3 6
π
VLN cos α
(2)
here α is the fire angle. The thyristor-based rectifier is semi-controllable. The three-phase three-level PWM rectifier controls the output voltage by adjusting the switching frequency and switch duty ratio. Compared with the diode rectifier, the thyristor-based rectifier and threephase three-level PWM rectifier can accurately and dynamically control the DC voltage with more complicated structure and more total harmonic distortion. Based on the fact that the ripple of the DC voltage has no impact on the common bus voltage, and to reduce cost, the diode rectifier was selected.
MODELING OF PGAEPS FOR IPS
A model of the PGAEPS has been developed with the SimPowerSystem virtual environment of MATLAB/SIMULINK, based on availability, familiarity, and experience with MATLAB/SIMULINK software. The generator is modeled as synchronous machine with 45 MV of nominal power, assuming 13.8 kV rated lineto-line RMS voltage and 60 Hz. The exciter and stabilizer are implemented with an excitation system block and a generic power system stabilizer block, respectively. The turbine and governor are modeled by the steam turbine and governor block with 3600 rpm of nominal speed. It should be pointed out that it is unnecessary to add a voltage regulator due to the fact that the generator is set up as a swing bus. Also it should be noticed that a steam turbine is used to model the gas turbine due to SimPowerSystem library limitations. The transformer is implemented with three-phase delta-delta transformer with 13.8:4.16 kV voltage ratio. The rectifier is modeled by the universal bridge block with diodes as power electronics devices. The DC-toAC PWM inverter is also implemented by the universal bridge block with the IGBT and diode as power electronics devices. The gates of the PWM inverter are controlled by the voltage regulator to control load voltage. Due to the fact that information on the notional ship is very
U dc =
3 6
π
VLN
(1)
here Udc is the DC voltage of the rectifier output, and VLN is the input AC voltage in line-to-neutral RMS value. So the output voltage is uncontrollable. The thyristor-based rectifier is a converter with gate turn-on but without gate turnoff. The DC voltage can be expressed as
limited, it is difficult to determine the ship architecture and model the propeller, ship-speed dynamics, and external forces. Thus a simple three-phase parallel RLC load is used to model
<Rotor angle dev iation d_theta (rad)> <Rotor speed wm (pu)> <Rotor speed dev iation dw (pu)> <Stator voltage v d (pu)> <Stator voltage v q (pu)> In In 3 T2 (Gen-LP) T3(LP-HP) [pu] In dw1(Gen) dw2(LP) dw3(HP) [pu]
the propeller, ship-speed dynamics, and external forces. The whole model of the PGAEPS is illustrated in Figure 4.
3
Power Generation and Propulsion System Simulation: Generator: 45MVA 13.8kV 3600rpm Transformer: delta-delta AC-DC Converter: uncontrolled rectifier DC-AC Converter: PWM inverter
1 -CPref
wref dw_5-2 Pref wm Tr5-2 gate
Turbine Pm m A B C
A a B b C c A B C a b c A a B b C c A B C +
d_theta Pm
L
Steam Turbine and Governor Mass 1= Generator Mass 2= LP turbine Mass 3= HP turbine 1 Vff
v ref vd vq In Vstab Vf
Vf_
45 MVA 13.8kV 3600 rpm
B13.8
45 MVA-60 Hz 13.8 kV-4.16 kV
B4.16
Rectifier
C
+ v -
Vdc
Vload
Scope
v stab
Generic Power System Stabilizer
Excitation System
PWM IGBT Inverter
g + A B
+ v -
Vab_inv
+ v -
Vab_load Scope1
A B C A B C A B C Vabc a b c
Vabc_B4160] ? [Vabc_B138] Double click for more info
Vabc_B4160 (V) Vabc_B138 (V) -
A B C
C
Grid
LC Filter
Measure
Continuous
1 z
Pulses Uref
50 kW 380Vrms 50 Hz Voltage Regulator
Vabc (pu) Vd_ref (pu)
Vabc_inv m
Discrete PWM Generator
1 Vref (pu)
modulation index
Figure 4. Model of the PGAEPS
SIMULATION OF PGAEPS FOR IPS
In the real world, some physical systems are not available. Also experiments of physical systems are expensive and even dangerous. This is the reason why modeling and simulation techniques are used to simulate real physical systems, demonstrate behavior and performance of the real physical systems, and evaluate functions and effectiveness of the real physical systems. Other advantages of modeling and simulation include suppressing disturbances in noisy environments, and monitoring variables that are not accessible in the real world. For ship design and construction, it is not practical to build the ship prototypes first and then make further modification due to time and cost consideration. Thus modeling and simulation are an effective approach for ship proactive design.
The whole model of the PGAEPS is simulated with MATLAB/SIMULINK platform. The time step for simulation is 1 microsecond and the sampling time of the voltage regulator for PWM inverter control is 100 microseconds. The outputs of the electric propulsion subsystem are illustrated in Figure 5. Part A in Figure 5 shows rotor speed deviations dw1, dw2, and dw3 in per unit for the generator, low-pressure turbine, and high-pressure turbine, respectively. Part B in Figure 5 demonstrates the torque (T2) between the generator and the low-pressure turbine, and the torque (T3) between the low-pressure turbine and the high-pressure turbine, both in per unit. These curves are periodic and stable, which indicates that the power generation subsystem decouples from the propulsion subsystem and works well with proper parameters selection.
Figure 5. Outputs of the Power Generation Subsystem
Figure 6 shows the output voltage of the PWM inverter. This voltage will drive motor and propeller. The AC voltage is sinusoidal with a little distortion. There is also an overshot in the initial time. However, the voltage quality can satisfy the demand for the motor drive and propeller. With further good design of the filter and inverter controller, the voltage quality can be improved for stricter load demand in the future. The voltages on both high and low sides of the transformer are illustrated in Figure 7. Part A in Figure 7 shows the low side voltage of the transformer. From Part A we can see that the
peak value is about 5890 V, which is equivalent to 4160V RMS value. Part B shows that the high side voltage of the transformer is about 19.55 kV, which is equivalent to 13.8 kV RMS value. With the delta-delta transformer and proper diode rectifier design, the voltage curves are sinusoidal without distortion. This indicates a good power factor characteristic. The high side (13.8 kV) of the transformer will be the common bus for future IPS design. It is essential to maintain 13.8 kV voltage and 60 Hz frequency for the common bus.
Figure 6. Output Voltage of the PWM Inverter
Figure 7. Voltage Curves of the Delta-Delta Transformer
APPLICATION OF MODEL
A shipboard power system differs from a terrestrial power system in that it has limited inertia and very short transmission lines. Traditional power system stability analysis approaches and associated software packages are all based on single-machine infinite bus system or multi-machine infinite bus system, which are not applicable for shipboard power systems. This paper presents a model of power generation and electric propulsion system for all-electric ships. By adding an AC-DC zonal distribution system, this model can be further extended to an IPS, which can provide a platform for shipboard power system stability analysis, power flow calculation, and fault analysis and protection/reconfiguration system design.
with MATLAB/SIMULINK, and performs simulation of the model. Simulation results show the performance and effectiveness of the PGAEPS designed, and impacts of the PGAEPS design on future IPS. For future IPS design, maintaining stable voltage and frequency of the common bus in the PGAEPS is essential, and a harmonic filter is necessary.
ACKNOWLEDGMENTS
This research work has been supported by the Office of Naval Research grant N00014-02-10623. Thanks are also given to the Electric-Ship Group of the Dept. of Electrical and Computer Engineering at Mississippi State University.
REFERENCES
Izadi-Zamanabadi, R. and M. Blanke, “A Ship Propulsion System As A Benchmark for FaultTolerant Control,” Control Engineering Practice 7 pp. 227—239, 1999.
SUMMARY
This paper discusses the design of a PGAEPS, develops an integrated model of the PGAEPS
McCoy, T.J.,“Trends in Ship Electric Propulsion,” Proceeding of IEEE Power Engineering Society Summer Meeting, Vol. 1 pp. 343-346, 2002. Optimal electric ship propulsion system, Marine Reporter, 2002. Prousalidis, J. and D. Muthumuni, “Power Quality On Electric Ships,” www.cedrat.com/software/gallery/embedded/Po wer_quality_on_electric_ships.pdf Sudhoff, S.D., K.A. Corzine, S.F. Glover, H.J. Hegner, and H.N. Robey, Jr., “DC Link Stabilized Field Oriented Control of Electric Propulsion Systems,” IEEE Transactions on Energy Conversion, Vol. 13, No. 1, March 1998. Xu, X., J. Mindykowsky, and H. Zheng, “New Concept of Power Quality Improvement Method in Marine Electric Propulsion System,” 11th International Conference on Harmonics and Quality of Power, Sept. 2004. Yin, B. and Y. Zou, “Studies on New Electric Propulsion System for Nuclear Submarine for Cruising,” The 4th International Power Electronics and Motion Control Conference, Aug. 2004. Quili Yu is currently pursuing his PhD degree from the Electrical and Computer Engineering Department at Mississippi State University. He has a PhD in Aerospace Engineering from MSU in 2001 and a MS in Electrical Engineering in 2003. He also holds an MS in Aerospace Engineering and BS in Mechatronics Engineering from Beijing Institute of Technology (BIT) in Beijing, China. His current area of research is design, modeling and simulation of power systems, and intelligent agent applications to power system reconfiguration. Dr. Noel N. Schulz received her B.S.E.E. and M.S.E.E. degrees from Virginia Polytechnic Institute and State University in 1988 and 1990, respectively. She received her Ph.D. in EE from the University of Minnesota in 1995. She is the recipient of the TVA Endowed Professorship in Power Systems Engineering. She has been an Associate Professor in the ECE department at Mississippi State University since July 2001. Her
research interest is in computer applications in power system operations including artificial intelligence techniques. She is a NSF CAREER award recipient. She has been active in the IEEE Power Engineering Society and is serving as Secretary for 2004-2007. She was the 2002 recipient of the IEEE/PES Walter Fee Outstanding Young Power Engineer Award. Dr. Schulz is a member of Eta Kappa Nu and Tau Beta Pi.
Design, Modeling, and Simulation of Power Generation and Electric Propulsion System for IPS for All-Electric Ships
ABSTRACT
To meet the Navy’s increasing demand for more propulsion power and service power, the whole power system onboard is moving toward the integrated power system (IPS) for future allelectric warships. This paper presents the design, modeling, and simulation of power generation and electric propulsion system for IPS. The architecture of this power generation and electric propulsion system (PGAEPS) is designed as a part of IPS and has an interface to connect other parts of the IPS. Modeling of the whole power generation and electric propulsion system is based on SIMULINK. Simulation results show performance and effectiveness of the power generation and propulsion system, and help better understand the impact of the design of a power generation and propulsion system on the performance of the IPS. around it rather than create a tailored mechanical propulsion system for the ship (Marine Reporter 2002). Sizes and locations of machines in mechanical propulsion systems reduce the space available for cargo and passengers and limit efficient loading and unloading. The considerable length of the shaft in mechanical propulsion systems makes efficient space use challenging. All of these factors limit ship design flexibility (Marine Reporter 2002). In electric propulsion systems, there is no direct link, such as shaft and gearbox, between the prime mover and the propeller. Figure 1 shows a structural comparison between electric and mechanical propulsion (McCoy 2002). The feature of no direct link between the prime mover and the propeller in an electric propulsion system provides ship designers with two advantages. One is that the turbine speed becomes fully decoupled from the propeller speed, making it possible for ship designers to optimize the turbine speed with regard to fuel efficiency. Another is that ship designers have more design flexibility (Sudhoff and et al 1998). On the other hand, high power-to-weight ratio of electric machines in an electric propulsion system reduces the needed ship internal space for machines installation, and can accommodate more cargo and passengers for commercial ships and more weapons and personnel for warships. Compared with mechanical propulsion systems, the electric propulsion systems improve fuel efficiency, provide flexible design ability, and require less internal volume for electric machines installation. Electric propulsion systems are widely used in large commercial ships and especially warships that demand a high level of maneuverability or a lot of slow speed (Marine Reporter 2002).
INTRODUCTION
With the invention and development of external combustion engines and internal combustion engines, traditional commercial and military ships employed a mechanical propulsion system that uses gas turbines as the prime mover. A typical ship mechanical propulsion system includes a gas turbine, a shaft with a gear box, a propeller, ship dynamics, a shaft speed controller, a propellor pitch controller, and a main controller (Izadi-Zamanabadi and Blane 1999). The main controller will coordinate behaviors of the governor and the propellor pitch controller, as well as control ship speed and optimize efficiency. A mechanical propulsion system is so large and heavy that ship designers have to design and construct the rest of the ship
Figure 1. Electrical vs. Mechanical Propulsion (modified from McCoy 2002)
Current large warships demand more and more propulsion power in a way that modern techniques for power generation and ship configuration almost reach a bottleneck. At the same time, growth continues in the need for electric power for hotel loads, pulsed weapons, and high power sensors. In current warships the electric propulsion system separates from ship electric power systems for hotel loads and weapon loads. Large amounts of power locked in the mechanical propulsion system are not available for other uses even when ships do not need to move with full speed. Future all-electric warships with an integrated power system (IPS) are capable of redirecting the large amounts of power dedicated to propulsion and releasing this power for hotel and weapon loads. The IPS for all-electric ships combines the power generation system, the electric propulsion system, the power distribution system with distributed generators (DG), the energy storage system for pulsed weapons, and the power control and management system all together. The move to IPS design will significantly improve efficiency, effectiveness, and survivability. Many papers on electric propulsion systems for ships have been published. Xu, Mindykowski, and Zheng (2004) describe an architecture of an electric propulsion system without detailed modeling and simulation. Yin and Zou (2004) discuss studies on a new electric propulsion system with nuclear power generation. But neither of these papers focus on the combination
of electric generation and electric propulsion, nor aim to future integrated power systems. Several papers, published in the Proceedings of the IEEE Electric Ship Technologies Symposium 2007, dealt with an overview of integrated electric power and propulsion system, and modeling and simulation of electric propulsion system. However, these models are not suitable for IPS. This paper focuses on the design of power generation and electric propulsion system (PGAEPS) for IPS for future all-electric warships. For shipboard power systems, the power and the load have almost the same magnitude. With a real power generation system replacing an ideal power source, the whole power system can show dynamic behavior and provide an accurate platform for later voltage stability analysis. The architecture of the PGAEPS designed here should be easily integrated as a part of IPS and has an interface (common bus) to connect other parts (such as the distribution system, DG, and energy storage system) of the IPS. Modeling and simulation of the PGAEPS are implemented with SIMULINK, based on the consideration of availability, familiarity, and experience with MATLAB/SIMULINK software. Simulation results not only show performance and effectiveness of the PGAEPS, but also illustrate the impact of the PGAEPS design on the performance of the IPS.
DESIGN OF PGAEPS FOR IPS
Figure 2. Power Generation Subsystem for IPS
The IPS for all-electric ships includes the power generation system, the electric propulsion system, and the power distribution system all together. Design of the PGAEPS allows movement closer to the implementation of the IPS, which can provide a platform for further shipboard power system stability analysis, power flow calculation, and fault analysis and protection/reconfiguration design. The power generation subsystem designed consists of a turbine (prime mover), synchronous machine (generator), speed governor, voltage exciter and stabilizer, transformer, and rectifier, as illustrated in Figure 2. Here Pref and Vref are the power reference and voltage reference, respectively. Pe and Vt are the electric power the
generator produces and output voltage of the generator, respectively. The power generation subsystem includes two basic controls: voltage regulation and turbine speed regulation. The rated power and rated voltage are 36 MW and 13.8 kV respectively. These magnitudes are selected to mirror the power system of the proposed DD(X) national ships. The electric propulsion subsystem includes a rectifier, inverter, motor and motor controller, propeller, ship-speed dynamics, and external forces. Combining the power generation subsystem and electric propulsion system together, we create the whole PGAEPS, as illustrated in Figure 3.
Figure 3. Diagram of PGAEPS
Here Vdc is the DC output voltage of the rectifier. T is the torque the propeller produces. Vabc is the vector of three-phase line-to-neutral voltages. In the PGAEPS, a transformer with 13.8 kV/4.16 kV is used to connect the generator and the rectifier. The transformer has twofold roles in the PGAEPS. First, the DC voltage, as the output of the rectifier, will be decreased to around 5 kV. Second, with the delta-delta connection, the undesirable third harmonic magnetizing current, caused by the nonlinear core B-H characteristic, remains trapped inside the delta winding. Third harmonic currents are zero-sequence currents, which cannot enter or leave a delta connection, but can flow within the delta. Thus the power factor of the whole PGAEPS is improved. It should be noted that the PGAEPS also includes a rectifier and an inverter. For a simple PGAEPS, the rectifier and inverter can be removed and the generator can directly drive the motor. However, changes in load magnitude and load frequency will cause changes in power generation and generator frequency. The power generation couples with the load and cannot maintain a common bus with fixed voltage and frequency for future integration to IPS. The rectifier and inverter are used to decouple the power generation system from the motor drive, thus the generator can operate in fuel efficiency mode, as well as maintain a common bus for future IPS. Design of the rectifier is also important for the PGAEPS. There are three kinds of rectifiers for our choice: three-phase full-wave diode rectifier, thyristor-based rectifier, and three-phase threelevel PWM rectifier. The diode rectifier is simple and easy to use, and the output DC voltage can be expressed as
U dc =
3 6
π
VLN cos α
(2)
here α is the fire angle. The thyristor-based rectifier is semi-controllable. The three-phase three-level PWM rectifier controls the output voltage by adjusting the switching frequency and switch duty ratio. Compared with the diode rectifier, the thyristor-based rectifier and threephase three-level PWM rectifier can accurately and dynamically control the DC voltage with more complicated structure and more total harmonic distortion. Based on the fact that the ripple of the DC voltage has no impact on the common bus voltage, and to reduce cost, the diode rectifier was selected.
MODELING OF PGAEPS FOR IPS
A model of the PGAEPS has been developed with the SimPowerSystem virtual environment of MATLAB/SIMULINK, based on availability, familiarity, and experience with MATLAB/SIMULINK software. The generator is modeled as synchronous machine with 45 MV of nominal power, assuming 13.8 kV rated lineto-line RMS voltage and 60 Hz. The exciter and stabilizer are implemented with an excitation system block and a generic power system stabilizer block, respectively. The turbine and governor are modeled by the steam turbine and governor block with 3600 rpm of nominal speed. It should be pointed out that it is unnecessary to add a voltage regulator due to the fact that the generator is set up as a swing bus. Also it should be noticed that a steam turbine is used to model the gas turbine due to SimPowerSystem library limitations. The transformer is implemented with three-phase delta-delta transformer with 13.8:4.16 kV voltage ratio. The rectifier is modeled by the universal bridge block with diodes as power electronics devices. The DC-toAC PWM inverter is also implemented by the universal bridge block with the IGBT and diode as power electronics devices. The gates of the PWM inverter are controlled by the voltage regulator to control load voltage. Due to the fact that information on the notional ship is very
U dc =
3 6
π
VLN
(1)
here Udc is the DC voltage of the rectifier output, and VLN is the input AC voltage in line-to-neutral RMS value. So the output voltage is uncontrollable. The thyristor-based rectifier is a converter with gate turn-on but without gate turnoff. The DC voltage can be expressed as
limited, it is difficult to determine the ship architecture and model the propeller, ship-speed dynamics, and external forces. Thus a simple three-phase parallel RLC load is used to model
<Rotor angle dev iation d_theta (rad)> <Rotor speed wm (pu)> <Rotor speed dev iation dw (pu)> <Stator voltage v d (pu)> <Stator voltage v q (pu)> In In 3 T2 (Gen-LP) T3(LP-HP) [pu] In dw1(Gen) dw2(LP) dw3(HP) [pu]
the propeller, ship-speed dynamics, and external forces. The whole model of the PGAEPS is illustrated in Figure 4.
3
Power Generation and Propulsion System Simulation: Generator: 45MVA 13.8kV 3600rpm Transformer: delta-delta AC-DC Converter: uncontrolled rectifier DC-AC Converter: PWM inverter
1 -CPref
wref dw_5-2 Pref wm Tr5-2 gate
Turbine Pm m A B C
A a B b C c A B C a b c A a B b C c A B C +
d_theta Pm
L
Steam Turbine and Governor Mass 1= Generator Mass 2= LP turbine Mass 3= HP turbine 1 Vff
v ref vd vq In Vstab Vf
Vf_
45 MVA 13.8kV 3600 rpm
B13.8
45 MVA-60 Hz 13.8 kV-4.16 kV
B4.16
Rectifier
C
+ v -
Vdc
Vload
Scope
v stab
Generic Power System Stabilizer
Excitation System
PWM IGBT Inverter
g + A B
+ v -
Vab_inv
+ v -
Vab_load Scope1
A B C A B C A B C Vabc a b c
Vabc_B4160] ? [Vabc_B138] Double click for more info
Vabc_B4160 (V) Vabc_B138 (V) -
A B C
C
Grid
LC Filter
Measure
Continuous
1 z
Pulses Uref
50 kW 380Vrms 50 Hz Voltage Regulator
Vabc (pu) Vd_ref (pu)
Vabc_inv m
Discrete PWM Generator
1 Vref (pu)
modulation index
Figure 4. Model of the PGAEPS
SIMULATION OF PGAEPS FOR IPS
In the real world, some physical systems are not available. Also experiments of physical systems are expensive and even dangerous. This is the reason why modeling and simulation techniques are used to simulate real physical systems, demonstrate behavior and performance of the real physical systems, and evaluate functions and effectiveness of the real physical systems. Other advantages of modeling and simulation include suppressing disturbances in noisy environments, and monitoring variables that are not accessible in the real world. For ship design and construction, it is not practical to build the ship prototypes first and then make further modification due to time and cost consideration. Thus modeling and simulation are an effective approach for ship proactive design.
The whole model of the PGAEPS is simulated with MATLAB/SIMULINK platform. The time step for simulation is 1 microsecond and the sampling time of the voltage regulator for PWM inverter control is 100 microseconds. The outputs of the electric propulsion subsystem are illustrated in Figure 5. Part A in Figure 5 shows rotor speed deviations dw1, dw2, and dw3 in per unit for the generator, low-pressure turbine, and high-pressure turbine, respectively. Part B in Figure 5 demonstrates the torque (T2) between the generator and the low-pressure turbine, and the torque (T3) between the low-pressure turbine and the high-pressure turbine, both in per unit. These curves are periodic and stable, which indicates that the power generation subsystem decouples from the propulsion subsystem and works well with proper parameters selection.
Figure 5. Outputs of the Power Generation Subsystem
Figure 6 shows the output voltage of the PWM inverter. This voltage will drive motor and propeller. The AC voltage is sinusoidal with a little distortion. There is also an overshot in the initial time. However, the voltage quality can satisfy the demand for the motor drive and propeller. With further good design of the filter and inverter controller, the voltage quality can be improved for stricter load demand in the future. The voltages on both high and low sides of the transformer are illustrated in Figure 7. Part A in Figure 7 shows the low side voltage of the transformer. From Part A we can see that the
peak value is about 5890 V, which is equivalent to 4160V RMS value. Part B shows that the high side voltage of the transformer is about 19.55 kV, which is equivalent to 13.8 kV RMS value. With the delta-delta transformer and proper diode rectifier design, the voltage curves are sinusoidal without distortion. This indicates a good power factor characteristic. The high side (13.8 kV) of the transformer will be the common bus for future IPS design. It is essential to maintain 13.8 kV voltage and 60 Hz frequency for the common bus.
Figure 6. Output Voltage of the PWM Inverter
Figure 7. Voltage Curves of the Delta-Delta Transformer
APPLICATION OF MODEL
A shipboard power system differs from a terrestrial power system in that it has limited inertia and very short transmission lines. Traditional power system stability analysis approaches and associated software packages are all based on single-machine infinite bus system or multi-machine infinite bus system, which are not applicable for shipboard power systems. This paper presents a model of power generation and electric propulsion system for all-electric ships. By adding an AC-DC zonal distribution system, this model can be further extended to an IPS, which can provide a platform for shipboard power system stability analysis, power flow calculation, and fault analysis and protection/reconfiguration system design.
with MATLAB/SIMULINK, and performs simulation of the model. Simulation results show the performance and effectiveness of the PGAEPS designed, and impacts of the PGAEPS design on future IPS. For future IPS design, maintaining stable voltage and frequency of the common bus in the PGAEPS is essential, and a harmonic filter is necessary.
ACKNOWLEDGMENTS
This research work has been supported by the Office of Naval Research grant N00014-02-10623. Thanks are also given to the Electric-Ship Group of the Dept. of Electrical and Computer Engineering at Mississippi State University.
REFERENCES
Izadi-Zamanabadi, R. and M. Blanke, “A Ship Propulsion System As A Benchmark for FaultTolerant Control,” Control Engineering Practice 7 pp. 227—239, 1999.
SUMMARY
This paper discusses the design of a PGAEPS, develops an integrated model of the PGAEPS
McCoy, T.J.,“Trends in Ship Electric Propulsion,” Proceeding of IEEE Power Engineering Society Summer Meeting, Vol. 1 pp. 343-346, 2002. Optimal electric ship propulsion system, Marine Reporter, 2002. Prousalidis, J. and D. Muthumuni, “Power Quality On Electric Ships,” www.cedrat.com/software/gallery/embedded/Po wer_quality_on_electric_ships.pdf Sudhoff, S.D., K.A. Corzine, S.F. Glover, H.J. Hegner, and H.N. Robey, Jr., “DC Link Stabilized Field Oriented Control of Electric Propulsion Systems,” IEEE Transactions on Energy Conversion, Vol. 13, No. 1, March 1998. Xu, X., J. Mindykowsky, and H. Zheng, “New Concept of Power Quality Improvement Method in Marine Electric Propulsion System,” 11th International Conference on Harmonics and Quality of Power, Sept. 2004. Yin, B. and Y. Zou, “Studies on New Electric Propulsion System for Nuclear Submarine for Cruising,” The 4th International Power Electronics and Motion Control Conference, Aug. 2004. Quili Yu is currently pursuing his PhD degree from the Electrical and Computer Engineering Department at Mississippi State University. He has a PhD in Aerospace Engineering from MSU in 2001 and a MS in Electrical Engineering in 2003. He also holds an MS in Aerospace Engineering and BS in Mechatronics Engineering from Beijing Institute of Technology (BIT) in Beijing, China. His current area of research is design, modeling and simulation of power systems, and intelligent agent applications to power system reconfiguration. Dr. Noel N. Schulz received her B.S.E.E. and M.S.E.E. degrees from Virginia Polytechnic Institute and State University in 1988 and 1990, respectively. She received her Ph.D. in EE from the University of Minnesota in 1995. She is the recipient of the TVA Endowed Professorship in Power Systems Engineering. She has been an Associate Professor in the ECE department at Mississippi State University since July 2001. Her
research interest is in computer applications in power system operations including artificial intelligence techniques. She is a NSF CAREER award recipient. She has been active in the IEEE Power Engineering Society and is serving as Secretary for 2004-2007. She was the 2002 recipient of the IEEE/PES Walter Fee Outstanding Young Power Engineer Award. Dr. Schulz is a member of Eta Kappa Nu and Tau Beta Pi.
