MOSFET SELECTION FOR A THREE PHASE INVERTER
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Transcript of MOSFET SELECTION FOR A THREE PHASE INVERTER
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MOSFET SELECTION FOR A THREE PHASE INVERTER
Team 9JR Alvarez, Matt Myers
Chris Sommer, Scott O’Connor
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Table of Contents• MOSFETs Overview• Three Phase Inverter• Gate Capacitance• Switching Losses• Breakdown Voltage• On Resistance• Heat Dissipation• Insulation• Heat Sink• Package Type• Mounting
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MOSFET Overview
• Switching Device that acts as a voltage controlled current source.
• A change in the gate to source voltage causes a change in the drain to source current.
• To increase the current MOSFETs can be put in parallel.
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• This configuration of MOSFETS allows the conversion of DC voltage to a 3-phase AC voltage
Three Phase Inverter
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Gate Capacitance
VGS - Gate to Source Capacitance VDS - Gate to Drain Capacitance
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Caused by the parasitic capacitance
Switching Losses
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Drain to Source Breakdown Voltage
This specification is gives the maximum drain to source voltage a MOSFET can handle
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Effects efficiency Temperature Dependent
On Resistance
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Heat Dissipation and Efficiency• Matlab analysis of power losses • Gives efficiency at different power
outputs.• The Power Consumed by the motor
controller varies with the square of the current and drain to source resistance.
0 1000 2000 3000 4000 5000 6000 7000 80000.95
0.955
0.96
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1
Power of Motor Controller (W)
Effi
cien
cy o
f MO
SFE
TS (W
)
Efficiency of the MOSFETS vs Motor Controller Power
0 1000 2000 3000 4000 5000 6000 7000 80000
50
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Power of Motor Controller (W)
Pow
er D
isap
ated
in M
OS
FETS
Power Disapated in MOSFETS vs Motor Controller Power
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Insulation Insulation needed to avoid undesired short
circuits. Thermally conducting Electrical insulating Pad vs. Grease
20 40 60 80 100 120 140 1606
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15Power Loss vs Tempature
Pow
er L
oss
(W)
Tempature (C)
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• Rtheta_jc = .28, Rtheta_ja = 50, Rtheta_cs = 1• Temperature Difference / Power Dissipated
= desired Rtheta
• Max Current^2*Rdon = Desired power• For our heat sink this gives• 125 C / 64 Watts = 1.93 C/W• 1.93 – 1.28 = .65 C/W• Our heat sink < .65 C/W
Thermal Properties and Heat Sink
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Package Type
• Three common package types for MOSFETs• PCB• Power Electronics• Lower Powered Surface Mount
TO-247 SOT-227 D2PAK
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Mounting Clipping Screw Holes Personal Heat Sink
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MOSFET comparisonParameters IXFN 120N20 STW88N65M5
Single 2 in parallel
Single 4 in parallel
Break-down VDS 200 V 200 V 710 V 710 V
On resistance 17 mΩ 8.5 mΩ 29 mΩ 7.25 mΩ
Drain current ID 120 A 240 A 84 A 336 A
Thermal resistance 0.22 °C/W 0.22 °C/W 0.28 °C/W 0.28 °C/W
Gate-Source Capacitance 5 nF 2.5nF 5.1 nF 1.275 nF
Gate-Drain Capacitance 16 nF 8 nF 8.4 nF 2.1 nF
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Thank You
Questions?