“Issues related to the thruster soft starting for AES operation” Georgakopoulos I., Pallis I., Tatakis E., Dallas S.
6th MARINELIVE International Workshop on Power Management Systems” June 3-5, 2013, Athens, Greece
All-Electric-Ship (AES) • AESAES power system power system
▫ All generators and electric loads are
• ▫ Economical ▫ Economical
All-Electric-Ship (AES)
▫ lightning systems ▫ electronic devices ▫ elevators thrusters ▫ lightning systems ▫ electronic devices ▫ thrusters
Thrusters • maneuvering the ship inside the ports • avoid collision accidents • Electric motor ▫ 0.5 to 2.5MW ▫ induction machine. ▫ Torque ~ V2 High inrush currents during startup
Induction machine as thruster ▫ • high inrush current
Startup current value all electric loads. ▫ affecting Voltage rms
▫ (Mechanical load + rotor) inertia • ▫ Voltage rms ▫ (Mechanical load + rotor) inertia à reduce voltage rms or disconnect motor load
Thruster startup
To counterbalance the high load torque at zero blade pitch at 0 degrees. ▫ à the startup load is lowered
Thruster startup effects • High inrush currents à voltage drop
accurate response
Conventional ship
▍  Thruster motors are driven by separate generators,
To control the motor
(all loads are interconnected with the generators)
Thruster operation in AES • Thruster operation impacts
• àgreater thruster start up currents.
Overview of electric power system a
• A real power grid network from a ferry simulated using • TwoMATLAB/SIMULINK 2.1 MVA gensets and two 2.4 MVA shaft generators (AC buson at 440V/60Hz). • From board measurements it was known which where operating during the manoeuvring and loads to the included simulations. • Thruster’s 1 MW induction machine equivalent was estimated from the manufacture’s circuit precise model has been datasheet and a
Overview of electric power system
Figure 1. Ship electric power system model.
Thruster Direct on line (DOL) operation • In this topology, thruster motor is directly connected to the main voltage bus. ▫ motor start current is six times greater than the nominal one. ▫ major voltage drop is noted
Thruster Direct on line (DOL) operation • As a voltage drop appears, the generators’ AVR start to increase magnetization in order to compensate for the increased load currents of the generators. • As the motor reaches the pitching moment, the stator currents quickly reduce and since the generators are now temporarily overmagnetized, a voltage overshoot occurs. • As a consequence, high inrush currents during this transient period may cause a significant voltage disturbance in the power system.
Thruster Direct on line (DOL) operation
Figure 2. Motor start current in DOL operation.
Figure 3. Voltage rms waveform during motor start up in DOL operation.
Thruster SoftStarting • Several softstarting methods, found in several types of ships, using : • autotransformers • capacitors • power electronic devices • generator AVR control. • AVR control of a dedicated to thruster start up generator has been pointed out as a low cost and space saving solution. à not implementable in AES
Thruster Soft Starting • In AES the thruster motor has to be interconnected to the ship power network. ▫ An electronic power converter may be used in order to start smoothly the large induction motor. The electronic softstarter may be bypassed after the start up due to energy saving. R S T
Figure 4. Solid-state softstarter circuit diagram
Soft starters • Motor controlled parameters: ▫ Voltage à Timed Voltage Ramp Method ▫ Current à Current limiting ▫ (Also : Torque, Acceleration)
Timed Voltage Ramp Method • Effects Vo - - -
▫ reduces the start current ▫ reduces start torque ▫ s l o w s m o t o r ’ s acceleration rate
• Control parameters Vrms =0, if t<0 Vrms= Vo+Kv.t, if t>0, [1] where t: motor starting-up time Vo: voltage boost Kv: voltage increment gradient
▫ Ramp slope ▫ Voltage boost
Timed Voltage Ramp Method
Figure 5. Thruster Drive â&#x20AC;&#x201C; Softstarter block parameters.
Zero voltage boost
â&#x2013;Ťâ&#x20AC;Ż Greater voltage drop Figure 6. Voltage rms waveform during motor start up in TVR operation.
Soft starter can offer initially enough voltage to the motor in order to produce
Timed Voltage Ramp Method â&#x20AC;˘â&#x20AC;Ż Several voltage boost values
Figure 7. Voltage rms waveform during motor start up in TVR operation.
Timed Voltage Ramp Method – Voltage boost
Figure 9. Thruster speed during start up for several voltage boost values. Figure 8. Voltage rms waveform during motor start up in boosted TVR operation (slope rate “20”).
Figure 10. Motor start current in boosted TVR operation.
Current Limiting Method Vrms waveform during start up
Vo - - -
Current rms value during start up
• Control parameters ▫ Ramp slope ▫ Voltage boost ▫ Current threshold
(TVR) vs. (CLM)
(TVR) vs. (CLM) Timed Voltage Ramp
Current Limiting
• Open-loop control
• Limited thruster startup current
• No current measurement
• Calculated motor thermal stress
• Shorter startup time
• Minimized voltage drop • Improved power quality
ACKNOWLEDGMENTS
This work has been done within the frame of "DEFKALION" project, which is funded by both European and Hellenic National resources ( "ESPA-Thalis" projects).
ACKNOWLEDGMENT THE
WORK PRESENTED IN THIS PAPER HAS BEEN DEVELOPED WITHIN THE
THALES-DEFKALION PROJECT. THIS RESEARCH HAS BEEN COFINANCED BY THE EUROPEAN UNION (EUROPEAN SOCIAL FUND – ESF) AND GREEK NATIONAL FUNDS THROUGH THE OPERATIONAL PROGRAM "EDUCATION AND LIFELONG LEARNING" OF THE NATIONAL STRATEGIC REFERENCE FRAMEWORK (NSRF) - RESEARCH FUNDING PROGRAM: THALES: REINFORCEMENT OF THE INTERDISCIPLINARY AND/OR INTER-INSTITUTIONAL RESEARCH AND INNOVATION.
FRAMEWORK OF THE
Thank you !