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Simulation of a Shipboard Electrical Network (AES) Comprising Pulsed Loads

Simulation of a Shipboard Electrical Network (AES) Comprising Pulsed Loads F. Kanellos , PhD, postdoc, NTUA, Hellenic Naval Academy I.K. Hatzilau, Prof. Dr.-Ing., Hellenic Naval Academy J. Prousalidis, Ass. Prof., National Technical University of Athens

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Simulation of a Shipboard Electrical Network (AES) Comprising Pulsed Loads

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  1. Simulation of a Shipboard Electrical Network (AES) Comprising Pulsed Loads F. Kanellos, PhD, postdoc, NTUA, Hellenic Naval Academy I.K. Hatzilau, Prof. Dr.-Ing., Hellenic Naval Academy J. Prousalidis, Ass. Prof., National Technical University of Athens E. Styvaktakis, PhD, Hellenic Transmission System Operator

  2. What is the Scope of the Paper ? In this paper the electrical network of a warship in the context ofAES, with aPulsed Load installed,is modeled aiming to propose an operation analysis via Time-domain Simulations. ΑRailgunis assumed for this study.

  3. Paper Scope • Also, this paper aims : • - To make a short but coherent introduction to pulsed loads and voltage/frequency modulation. • To develop a detailed model of a shipboard electrical network comprising pulsed loads. • To study operation of the system for different system parameters. • - To indicate the value of the application of time-domain simulations to complex, multivariate systems such as an IPS comprising pulsed loads.

  4. CONTENTS The arrangement of the paper is the following :1. SYNOPSIS 2. INTRODUCTION AND BACKGROUND 3. MODULATION / PULSED LOADS 4. CASE STUDY 4.1 Railgun model 4.2 Propulsion motor model 5. SIMULATION RESULTS 6. CONCLUSIONS 7. ACKNOWLEDGEMENTS 8. REFERENCES

  5. INTRODUCTION and BACKGROUND New naval weapon systems, referred as“Pulsed loads”, arepower loads that require high power (in order of several GWs), for very short time intervals (in order of milliseconds up to a few seconds). • The operating characteristics of the “Pulsed loads”,will pose many new challenges for shipboard power systems as they : • Lead toVoltageandFrequency Modulation • May affect the operation of several subsystems of the ship such as • radarscopes, communication equipment, missile guidance systems, • weapons, gear systems etc

  6. INTRODUCTION and BACKGROUND Simplified power profile of a Pulsed Load

  7. INTRODUCTION and BACKGROUND • Examples of Pulsed Loads include : • Electromagnetic Guns(Rail Guns, Coil Guns, Lasers, High • Energy Microwaves) • Electromagnetic Aircraft Launch Systems (EMALS) • Radars, Sonars, Communication Systems, High Power • Sensors etc.

  8. INTRODUCTION and BACKGROUND Examples of Electromagnetic Guns Coilgun concept of operation Railgun concept of operation Lasers High Energy Microwaves systems

  9. MODULATION/ PULSED LOADS Voltage and Frequencyperiodic or quasi-periodic variationssuch as might be causedby regularly or randomly repeated loadingwith frequency less than nominalare referred in shipboard Standards (STANAG 1008, IEEE 45) asModulation. Pulsed Loads are the main cause of Voltage/Frequency Modulation.

  10. Modulation / Pulsed Loads Voltage and Frequency Modulation schematic representation

  11. Modulation / Pulsed Loads Voltage and FrequencyModulation are quantified by using the difference between the Maximum and Minimum values of voltage, frequency as a percentage of the double of their respective Nominal Values, as it is shown in Equations (1) and (2) : (1) (2) According to STANAG 1008, 2% and 0.5% limits are proposed for the voltage and the frequency of the system, respectively

  12. Modulation / Pulsed Loads According to STANAG 1008 pulsed loads should not exceed the limits specified by the following equations : Qpulse < 0.065*Ssupplyand Ppulse < 0.25*Ssupply Ppulse, Qpulse=active, reactive power of the pulsed load Ssupply =full rated apparent power of the supply at the occurrence of the pulse.

  13. Modulation / Pulsed Loads Power sources of Electromagnetic Guns require technologies that are very different from the other applications (consumption of ~ 50GW in 6-10 ms). Integration ofPulsed Loads requires a well-designed Energy Storage System and their discharge characteristics will determine the type of the storage system.

  14. Modulation / Pulsed Loads Energy storage options include : Electrochemical:Batteries and Capacitors  Mechanical:Flywheels, Homopolar Generators, Compensated Pulsed Alternators  Electromagnetic:Super-conducting Electromagnetic Storage • Compensated Pulsed Alternators, Homopolar Generators, • Capacitor Banks, Flux Pumpsare more suitable for • millisecond-long pulses. • Flywheels,stand much closer to the commercial applications, • and they are currently extensively researched.

  15. CASE STUDY • An electrical shipboard network in the context of AES is • modelled • Two engines are powering medium voltage generators • generating at 4.16 kV, with nominal powers of 30 and 10 • MW, respectively. • The main MV load is a 30 MW Propulsion Induction Motor • that is controlled by a Pulse Width Modulated four- • quadrant power converter, comprising IGBTs for the output • and input bridges. • A Railgunis connected at 4.16kV supply

  16. Case Study Electrical system configuration

  17. Information about Railguns • Railguns are being pursued as weapons with projectiles that are • given extremely high velocities ,in order of 3500 m/s, and do not • contain explosives • Lorentz electromagnetic force is utilized to propel an • electrically conductive projectile that is initially part of the • current path • The power supply of a railgun must be able to deliver large • currents in very short time-intervals. Capacitors and • Compulsators are being common solutions.

  18. Information about Railguns Railgun operation concept (Lorentz Electromagnetic Force is utilized to accelerate the projectile)

  19. Railgun Model Railgun Model set of equations : Rail inductance dependent on the projectile position (1) : Total rail inductance (2) : Kirchoff’s voltage law applied to railgun circuit (3) : Magnetic flux (4) : Force applied to the projectile (5) : (6) : Projectile acceleration (7) : Projectile acceleration (8) : Projectile velocity

  20. Railgun Energy Storage System • In tis study the Energy Storage System used for railgun supply is a • Capacitor. • The capacitor is connected to the AC supply via a Diode-rectifier • and a Resistance bank. • The Resistance bankis used to vary the resistance between the • diode rectifier and the capacitor in order to limitappropriately, • the peak absorbed current and consequently the capacitor rate of • charging.

  21. Railgun Energy Storage System Schematic representation of the energy storage system for railgun supply

  22. Propulsion Induction Motor System Propulsion system schematic representation

  23. Propulsion Induction Motor System • The propulsion motor is connected to the network via aVoltage • Source Converter cascade. • Both the motor and the grid -side converters employ PWM • techniques. • The proposed drive-system gives full four-quadrant power control • and operates with a fully sinusoidal current and voltage. • It can be connected to the network via a front-end filter without • the need of a transformer. • Furthermore, it is able to provide reactive power to the network in • order to control the voltage and to regenerate into the AC supply • system.

  24. Propulsion Induction Motor System • The desired rotating speed is achieved by the application of an • Indirect Field Oriented Voltagecontroller. • The absorbed active, reactive powersare regulated via output current control, using Hysteresistechnique. • A narrow enough hysteresis band is used in order to eliminate the • produced harmonics. Furthermore, the maintenance of low • switching losses is taken into account.

  25. SIMULATION RESULTS • The aforementioned models were developed in Matlab/Simulink • environment. • All models were combined together to form the model of the case • study system.

  26. RAILGUN SIMULATION • First, the Railgun system is simulated for different projectile vmass and capacitance values and 5600 V is used as capacitor binitial voltage. • Next, the extent that the projectile mass and the capacitanceBaffect the maintaining voltage on the capacitor (after projectile is Blaunched) is examined. • The worst case scenario – corresponding to the lowest remaining vcapacitor voltage - is defined.

  27. current Force Projectile Velocity Capacitor Voltage

  28. Projectile Velocity Capacitor Voltage Capacitor Voltage Capacitor Voltage

  29. Scenario No 1 (C=1.2 mF) Scenario No 2 (m=4 kg) Projectile mass (kg) Voltage(V) remaining on the Capacitor Capacitance (mF) Voltage (V) remaining on the Capacitor 1 3753 1.2 1983 2 2985 1.8 3131 3 2427 2.4 3745 4 1983 3 4148 * Highlighted cells correspond to the worst case scenario where the lower remaining voltage occurs Summarized results for the scenarios examined

  30. SIMULATION OF THE SHIPBOARD ELECTRICAL NETWORK

  31. SIMULATION OF THE SHIPBOARD ELECTRICAL NETWORK • The adopted electrical shipboard network is simulated, • during capacitor charging process and voltage/frequency • variations are obtained. • Different values of theequivalent resistance between rectifier • and the capacitor, are used. • Also, it is assumed that during the simulation the propulsion • motor operates at 67% of its nominal power • corresponding to almost 20 MW, with unit power factor and • no increase or decrease in the reference poweroccurs • during the simulation.

  32. Voltage at ralgun bus Voltage at propulsion motor bus

  33. System frequency Capacitor voltage during charging process

  34. Active Power produced by the Generator set Propulsion Motor Active and Reactive Powers

  35. Railgun input current (during charging) Zoom of Railgun input current (during charging)

  36. R (Ohms) (Resistance bank) Voltage Modulation (%) Frequency Modulation (%) 0.1 1.3 0.98 0.15 1.2 0.94 0.4 0.82 0.63 * Projectile mass=4 kg, Capacitance=1.2 mF Voltage, Frequency Modulation

  37. CONCLUSSIONS • The simulation results of a warship in the context of AES comprising a railgun, indicated the following: • Development of detailed models of all subsystems of an IPS is • very useful in order to assess voltage and frequency • modulation. • The railgun model is used to determine the internal (initial) • conditions before its energy storage system is connected to the • network in order to charge the capacitor.

  38. CONCLUSSIONS • Standards propose deterministic methods to estimate the limits of Pulsed Loads capacity. • Probably, the most effective way toassessthePower Quality Problemsrelated toPulsed LoadsisTime-domain Simulations using available powerful simulation tools such asMatlab, PSCAD, EMTDC.

  39. ACKNOWLEDGEMENTS The work of this paper is part of the research project "Pythagoras-II" within the "Operational Programme for Education and Initial Vocational Training - EPEAEK-II"-frame. The Project is co-funded by the European Social Fund (75%) and Greek National Resources (25%).

  40. Thank you for your attention!

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