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This study presents a simulation-based analysis of the impact of device degradation on the thermal and electrical characteristics of a voltage-source inverter (VSI). The goal is to develop a condition monitoring technique for power electronic systems. The study focuses on solder fatigue, gate degradation, and bond-wire lift failures, and discusses potential CM methods based on thermal resistance observation, harmonics identification, on-state resistances identification, and EMI characteristics.
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Aims of study • A simulation study based on semiconductor devices physical models is carried out for a voltage-source-inverter (VSI) to examine the effects of device degradation on the converter thermal and electrical characteristics. • It’s hoped that this work can lead to the development of a condition monitoring (CM) technique for power electronic systems. ESR Network
Cases studied Failure Mode, Mechanism and Effect Analysis (FMMEA) of IGBT ESR Network
Saber physic-based IGBT and diode models Advantages: • Detailed physic model • Electrothermal simulation available • Experimentally verified Disadvantages: • Difficult to parameterize • Encryption of MAST template Hefner IGBT model [1] H. A. Mantooth Diode model [2] [1] A. R. Hefner and D. M. Diebolt, “An Experimentally Verified IGBT Model Implemented in the Saber Circuit Simulator,” Proc. of IEEE Power Electronics Specialists Conference, Cambridge, MA, 1991. [2] H. A. Mantooth, R. G. Perry, J. L. Duliere, “A unified diode model for circuit simulation,” IEEE Trans. On Power Electronics, vol. 12, No. 5 pp. 816-823, September, 1997. . ESR Network
Diode parameters [3] SKM100GB063D Diode parameters (H. A. Mantooth model) [3] John Vincent Reichl, “Inverter Dynamic Electro-Thermal Simulation with Experimental Verification”, M.sc Thesis, Virginia Polytechnic Institute and State University, 2005 ESR Network
IGBT parameters [3] SKM100GB063D IGBT parameters (Hefner model) ESR Network
Thermal model and parameters [4] 4-order Forster RC thermal model for SKM100GB063D [4] [4] Datasheet of SKM100GB063D, SEMIKRON, 2006 ESR Network
Electrothermal calculation for comparison Thermal calculation results are in close agreement with our simulation results, as shown next. ESR Network
Solder fatigue simulation (case 1) (a) Junction temperatures • Tj_t ↑15C , Tj_d ↑1C • Tc↑ Change of case temperature detectable! (b) Current harmonics • Ia_5th ↓5.66 mA • Ua_5th ↓9.4 mV (↓0.8%) Small! ESR Network
Solder fatigue simulation (case 1) (c) On-state resistances Ron_t ↑0.91 mΩ (↑2.42%) Ron_d ↑0.01 mΩ (↑0.09%) Small! (d) dv/dt td_off ↑ 13 ns td_on little change Small! ESR Network
Gate degradation simulation (case 2) (a) Junction temperatures Tj_t and Tj_d: little changes (b) Current harmonics • Ia_5th ↓38.1mA • Ua_5th ↓63.3 mV (↓5.3%) Perhaps Detectable ESR Network
Gate degradation simulation (case 2) (c) On-state resistances Ron_t ↓1.17 mΩ (↓3.12%) Ron_d ↑0.006 mΩ (↑0.05%) (d) dv/dt td_off ↑ 80 ns td_on ↓ 13 ns Notable! ESR Network
Bond-wire lift simulation (case 3) (a) Junction temperatures Tj_t ↑5C , Tj_d: little change (b) Current harmonics • Ia_5th ↑29.0mA • Ua_5th ↑48.2 mV (↑4.1%) Perhaps Detectable ESR Network
Bond-wire lift simulation (case 3) (c) On-state resistances Ron_t ↑3.526 mΩ (↑ 9.12%) Ron_d ↑0.007 mΩ (↑0.05%) Detectable (d) dv/dt td_off ↓54.0 ns td_on: little change Perhaps detectable ESR Network
Results and discussions • Simulation results show that there are changes of converter electrical and thermal characteristics due to the device degradation. With respect to CM, some points can be made as below: • Solder fatigue mainly influences the thermal behaviour of converter, while it has very small effects on the converter terminal electrical characteristics. It’s suggested that thermal characteristics based CM method might be suitable for detection of solder fatigue. • Gate degradation mainly influences the electrical characteristics, especially the harmonics and dv/dt. • Bond-wire lifting mainly influences the electrical characteristics, especially the harmonics and On-state resistances. • Electrical characteristics based CM method might be more suitable for bond-wire lifting and gate degradation failures. However, high sensitive signal detection method is essential for the techniques. ESR Network
Targeted CM methods • Thermal resistance observation based CM • The accuracy of Rth observation under various operating conditions is important. • Characteristics harmonics identification based CM • About 0.1% precision could be achieved according to our preliminary research. • On-state resistances identification based CM • The change of converter terminal resistance can be identified according to the machine’s electromagnetic transient characteristics, when it is comparable to the machine winding resistance. • EMI characteristics based CM • The dv/dt of output PWM voltage will influence the converter EMI characteristics. It is expected that the change of high-frequency characteristics could be used for failure detection. A structured combination of different techniques might be appropriate in practice! ESR Network