Multi-objective Optimization of a Surface Mounted PM Motor for Marine Propulsion Applications Georgios Potiriadis, Minos Beniakar and Antonios Kladas National Technical University of Athens, School of Electrical and Computer Engineering, Laboratory of Electrical Machines and Power Electronics, Zografou, Athens, Greece
Contents Application Specifications Design Considerations Materials Consideration Preliminary Design Design Optimization Optimization Results Final Design Selection Simulation Results Summary
Slides 3-4 Slides 5-7 Slide 8 Slide 9 Slides 10-13 Slides 14-15 Slides 16-17 Slide 18-22 Slide 23
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Application specifications (1/2)
Application to a sailboat Hydrodynamic estimations made using Free!Ship software A typical sailboat hull was selected – (LWL≈10m) Power and Resistance coefficients were determined. 3
Application specifications (2/2) BASIC MOTOR SPECIFICATIONS
Rated Power
P=9000 Watt
Rated Speed
n=530 RPM
Rated Torque
T=163 Nm
Rated phase Voltage Amplitude
Vph-emf=30,6 V
Completely electrical autonomous system. Efficiency is of fundamental importance. Minimum phase current, in order to minimize copper losses. Voltage level selection is crucial. Therefore a high battery voltage level was selected, in particular 84 V.
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Design considerations (1/3) Determination of the motor technology and configuration Basic Dimensioning using analytical formulas Consideration of hydrodynamic estimations
Winding configuration – Slot/pole combinations Initial FEM Analysis – Performance and Efficiency indexes Design Optimization using SPEA2 Fine-tuning of key design variables
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Design considerations (2/3) Determination of motor configuration Surface Mounted Permanent Magnet (SMPM) synchronous motors are the most common topology for torque motors. Their main advantages are: high power and torque density high efficiency easier construction improved noise and vibration harshness (NVH) elimination of rotor winding in PM motors compared to classical wound motors.
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Design considerations (3/3) Winding configuration – Slot/pole combinations Fractional Slot Concentrated Windings (FSCW) with non-overlapping coils, further enhance the PMSM`s capabilities. They offer: short-end windings – lower copper losses low cogging torque and torque ripple good fault-tolerant capabilities high constant power speed range (CPSR). easier manufacturing
P=10 Q=12 7
Materials consideration N35SH NdFeB Permanent magnets Br,nom= 1.195 T, HcB= 903000 A/m
Low losses Iron Laminations Thyssen M 235-35A thickness0.35 mm 8
Preliminary design ď ą An estimation of the motor structure is achieved by utilizing classical machine design techniques that provides a good initial point and a sub-optimum set of design variables. ď ą In a further step, parametric 2-D FEMs are introduced to verify the validity of the preliminary solution sets and proceed to any necessary corrections. ď ą The initial reference motor topology is acquired, along with the design parameters that will remain constant during the optimization process.
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Design Optimization (1/4)
Sequential procedures over one optimization iteration 10
Design Optimization (2/4) SPEA-2 Pareto fitness assignment S(strength) = # dominated solutions R(raw fitness) = ÎŁ (strengths of dominants) Density estimation Dk = Distance to the k-th nearest individual
Fitness= R + 1/(2+Dk) 11
Design Optimization (3/4) Obtain initial population Xi=[X1 X2...X6]
START
Flowchart of the implemented optimization routine
Check constraints, Evaluate objective functions F=[F1 F2 F3] Select non-dominated and best solutions and create initial Pareto front
STOP
YES
Optimization profile: 1. Performance 2. Efficiency 3. Power Quality
Iter>Itermax NO
Create matting pool
Perform mutation and crossover Iter=Iter+1 Create next generation Check constraints, Evaluate objective functions F=[F1 F2 F3]
Select non-dominated and best solutions and update Pareto front
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Design Optimization (4/4) Design variables Magnet width expressed as pole pitch percentage Tooth tip width expressed as slot pitch percentage
Abbreviation
DCM DCT
Tooth height
tl
Tooth width
tw
Tooth tip height
htp
Tooth tip radial offset
b
The 6 selected optimization variables – key design parameters: 1. Magnet dimensions 2. Teeth dimensions
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Optimization results (1/2)
Resulting Pareto front after 50 generations 14
Optimization results (2/2)
Matrix-plot of the Pareto front and projections to the respective objective function surfaces
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Final design (1/2) Magnetic flux density distribution at rated load operation (Bmax = 1.8 T)
Generated mesh (36.000 first order elements) 16
Final design (2/2) Basic dimensions and operational characteristics of the final – optimum design Number of Phases
3
Number of Poles
10
Number of Slots
12
Motor Active Length
80 mm
Mean Air Gap Diameter
177 mm
Shaft Radius
15 mm
Rotor Inner Radius
80 mm
Air Gap Width
1 mm
Magnet Thickness
8 mm
Number of Turns per Slot
9 17
Simulation results (1/5)
Electromagnetic torque waveforms for the initial and final design 18
Simulation results (2/5)
Back-EMF waveforms for the initial and final design 19
Simulation results (3/5)
Back- EMF harmonic analysis for the initial and final design 20
Simulation results (4/5) Mean Torque Torque Ripple THD
Initial 157.6 Nm 6.16% 8%
Final 160,4Nm 2.47% 2.74%
Copper Losses
420.45 Watt
384.71 Watt
Iron Losses
23.96 Watt
24.22 Watt
Back-EMF Fundamental Amplitude
28,73 V
29.24 V
Magnet Losses
11.84 Watt
10.98 Watt
Efficiency
94.8%
95%
Performance and efficiency indexes for the initial and the final geometry 21
Simulation results (5/5)
Thermal model and simulated temperature distribution for the final geometry 22
Summary A particular methodology for the optimization of FSCW PMSM motors for marine propulsion applications has been introduced. A multi-objective optimization algorithm based on SPEA2 has been implemented to optimize the most favorable candidate PMSM configurations for marine propulsion applications. A set of Pareto Optimal solutions, in respect with the objective functions set, was acquired. The aforementioned procedure enabled the attainment of improved solutions, in terms of performance, efficiency and power quality compared to the analytical approached solution. The selected, final motor topology achieves suitable performance and efficiency characteristics for this class of applications and clearly outperforms the analytically approached motor design. 23
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
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