| 1. |
- Asimakopoulos, Panagiotis, 1985, et al.
(author)
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Current Sharing inside a High Power IGBT Module at the Negative Temperature Coefficient Operating Region
- 2016
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In: 18th European Conference on Power Electronics and Applications, EPE 2016 ECCE Europe, Karlsruhe, Germany, 5-9 September 2016. - 2325-0313. - 9789075815245
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Conference paper (peer-reviewed)abstract
- This work investigates the current sharing effect of a high power Soft Punch Through IGBT module in the Negative Temperature Coefficient region. The unbalanced current sharing between two of the substrates is demonstrated for different current and temperature levels and its impact on the thermal stressing of the device is evaluated. The results indicate that the current asymmetry does not lead to a significant thermal stressing unbalance between the substrates.
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| 2. |
- Asimakopoulos, Panagiotis, 1985, et al.
(author)
-
Design of a Modular Multilevel Converter as an Active Front-End for a magnet supply application
- 2014
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In: 2014 16th European Conference on Power Electronics and Applications (EPE'14-ECCE Europe), Lappeenranta, Finland, 26-28 August 2014. - 2325-0313. - 9781479930159
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Conference paper (peer-reviewed)abstract
- The aim of this work is to describe the general design procedure of a Modular Multilevel Converter (MMC) applied as an Active Front-End (AFE) for a magnet supply for beam accelerators. The dimensioning criteria for the converter and the dc-link capacitance are presented and the grid transformer requirements are set. Considering the converter design, the arm inductance calculation is based on the specifications for the arm-current ripple and the DC-link fault tolerance, but, also, on the limitation of the second harmonic and the second-order LC resonance of the arm current. The module capacitance value is evaluated by focusing on the required switching dynamics and the capacitor-voltage ripple according to a newly proposed graphical method. The loading of each semiconductor in the half bridge is calculated via simulation, indicating the unsymmetrical current distribution. It is concluded that the current distribution for each semiconductor depends on the mode of operation of the converter. The different criteria for the choice of the number of modules per arm are discussed. Finally, the complete system, including a model for the load and the converter control strategy applied to the converter is simulated and obtained results are presented.
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| 3. |
- Asimakopoulos, Panagiotis, 1985, et al.
(author)
-
Heat sink design considerations in medium power electronic applications with long power cycles
- 2015
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In: 17th European Conference on Power Electronics and Applications, EPE-ECCE Europe 2015, Geneva, Switzerland, 8-10 September. - 9789075815221
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Conference paper (peer-reviewed)abstract
- The aim of this work is to investigate the impact of the heat sink thickness and material, as well as, of the convection coefficient of the water cooling system on the power-electronics module thermal stressing. The heat extraction capability of different thicknesses is tested. It is concluded that the thickest heat sink results in marginally lower temperature variation at the junction level compared to the second thickest one. In the thickest heat sink case, the linear dependence of the thermal resistance on the thickness counteracts the benefit of the increased thermal capacitance. The increase in the cooling medium flow rate, which corresponds to an increase in the convection coefficient between the heat sink bottom surface and the water, can be avoided by increasing the thickness of the heat sink. In this way, the energy consumption of the cooling system is reduced. The increase in the flow rate drastically reduces the thermal stressing in the thinnest heat sink case. The increase of the heat sink thickness can be beneficial for long power cycles. Copper and aluminum are the two materials that are compared, with the copper heat sink exhibiting a slightly increased performance. The study is conducted for a medium power DC-DC converter of a magnet supply with focus on long power cycles.
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| 4. |
- Asimakopoulos, Panagiotis, 1985, et al.
(author)
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IGBT Power Stack Integrity Assessment Method for High-Power Magnet Supplies
- 2019
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In: IEEE Transactions on Power Electronics. - 0885-8993 .- 1941-0107. ; 34:11, s. 11228-11240
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Journal article (peer-reviewed)abstract
- This paper proposes a method for assessing the integrity of a series of insulated-gate bipolar transistor (IGBT) power stacks during factory-acceptance tests and service stops. The key challenge that is addressed in this paper is detecting common assembly issues that affect the power stack thermal path as well as distinguishing the acute aging effects of bond-wire lift-off and solder delamination. The method combines offline Vce measurements with current in the extended Zero Temperature Coefficient (ZTC) operating region as well as with sensing current without modifications to the power stack. It also employs on-the-stack Vce calibration for both the measurements. Additionally, only a fixed duty cycle pattern is needed to control the switches. The paper also presents a sensitivity analysis of the method to various parameters such as the current level in the extended ZTC operating region, the precision of the Vce measurement, as well as the ambient, the cooling-water, and the junction temperatures. The experimental results are obtained from a high-current IGBT power stack used in a magnet power supply for particle accelerators and are compared favorably to results from finite element method and lumped parameter network simulations confirming the applicability of the method.
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| 5. |
- Asimakopoulos, Panagiotis, 1985
(author)
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On integrity assessment of IGBT-based power stacks used in magnet power supplies for particle accelerators
- 2019
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Doctoral thesis (other academic/artistic)abstract
- This thesis analyses an electrical testing method for assessing the integrity of an IGBT-based power stack assembly during factory acceptance tests and service stops. The method combines vce measurements with high current in the Zero Temperature Coefficient (ZTC) operating region and with low sensing current within a specific current cycle using a proposed sampling and filtering technique. Two circuits are presented for the vce measurement. The value of this method is the ability to validate the power stack assembly and to detect IGBT aging without the need for power stack modifications for the vce measurement with sensing and load current. Additionally, no dedicated current control of the IGBTs is required. The aging mechanisms that are targeted with this method are the bond-wire lift-off and the solder delamination. As a part of the method, an on-the-stack vce calibration technique at the sensing current level is proposed for the IGBTs avoiding the need to un-mount and characterize them in a thermal chamber. The reference application is a power electronic converter that is used as a magnet power supply in particle accelerators at CERN, the European Organization for Nuclear Research. Based on the specialized application, the levels of ambient air, junction and cooling water temperature change that could have an impact on the method’s precision are defined. Experimental results, which are obtained with the power stack of a power magnet supply, are presented and are compared favorably with results obtained using Finite Element Method (FEM) and Lumped Parameter Network (LPN) simulations to demonstrate the method’s applicability. For the high-current IGBT module of the application, it is shown that the measurement in the ZTC operating region could detect bond-wire lift-offs when more than half of the bond-wires of the chip have been lifted. A measurement in the Positive Temperature Coefficient (PTC) operating region can be used to detect the early stage aging of a bond-wire lift-off, but the measurement precision is, highly, influenced by temperature. Moreover, the detection of manufacturing issues, such as errors in thermal paste application, is proven to be possible with the help of vce measurements with sensing current. As a potential improvement of the future power stack designs for lifetime prolongation, this work investigates the possibility for IGBT module’s thermal stressing mitigation using the specialized application as a reference. This investigation is based on LPN simulations. Prior to the LPN modeling, the extensive operation of the magnet power supply in the Negative Temperature Coefficient (NTC) operation region is, experimentally, examined. It is demonstrated that the current and thermal stressing unbalances among the chips inside the Soft Punch Through (SPT) IGBT module operating in the NTC operating region can be neglected and do not have to be considered for the thermal modeling. Moreover, the impact of the material, of the thickness and of the heat convection of the cooling plate on the junction temperature variation and maximum junction temperature is evaluated. It can be stated that, for long current cycles of the specialized application, a relatively thick aluminum cooling plate (3cm) with a moderate heat convection coefficient (10kW/(°Cm2)) may exhibit almost the same performance as a copper cooling plate of equal or even greater thickness (5cm) with a high heat convection coefficient (10kW/(°Cm2)). Two strategies are proposed with the switching frequency and the gate resistance as parameters for online thermal stressing mitigation. The first strategy reduces the switching frequency in parts of the cycle where a high precision requirement for the output current is not imposed, in order to limit the power losses and the thermal stressing of the IGBT. The second strategy combines the switching frequency reduction in one part of the cycle with the increase of switching frequency and gate resistance in another. By increasing the power losses the junction temperature fluctuation can be limited. Using four typical current profiles from the specialized application, it is shown that both strategies could prolong the IGBTs’ lifetime. It is shown that the contribution of the mitigation strategy to the lifetime prolongation depends on the current profile.
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| 6. |
- Asimakopoulos, Panagiotis, 1985, et al.
(author)
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On V-ce Method: In Situ Temperature Estimation and Aging Detection of High-Current IGBT Modules Used in Magnet Power Supplies for Particle Accelerators
- 2019
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In: IEEE Transactions on Industrial Electronics. - 0278-0046 .- 1557-9948. ; 66:1, s. 551-560
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Journal article (peer-reviewed)abstract
- Magnet power supplies used in particle accelerators are a specialized application of power electronics that require long lifetime operation with no unscheduled interruptions and high output current precision. In this paper, the V-ce method with sensing current is considered for the estimation of the junction temperature and the aging detection of high-current insulated gate bipolar transistor (IGBT) modules used in this specialized application. First, sensitivity analysis of the sensing current and the gate-emitter voltage are documented to quantify their impact on the precision of the V-ce method for high-current modules independently of the application of interest. Two measuring circuits offering ease of calibration and reduced number of components are proposed but their applicability is not limited to this application. Their performance is tested on a 1.6 kA IGBT module that exhibits the highest current ratings documented for the V-ce method with sensing current. The test is carried out at a switching frequency of 6.5 kHz using an experimental set-up that emulates a phase leg of the considered power supply. The V-ce method with sensing current is evaluated for the aging detection of high-current IGBT modules in general and its effectiveness for the specialized application is verified experimentally.
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| 7. |
- Asimakopoulos, Panagiotis, 1985, et al.
(author)
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Thermal stressing mitigation possibility intended for a DC-current magnet supply based on high power IGBT modules
- 2017
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In: 2017 19th European Conference on Power Electronics and Applications. - 2325-0313. - 9789075815276 ; 2017-January
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Conference paper (peer-reviewed)abstract
- This work investigates the possibility to reduce the thermal stressing of high power IGBT modules in a DC-current application. Using four load current profiles as examples, two mitigation strategies are presented and their benefit to the power stack in terms of lifetime prolongation is evaluated. In the final part of the work, the investigation focuses on the relation between the shape of the load current and the potential for thermal stressing limitation that the proposed mitigation strategies can provide.
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