Palliyage Srilak Nirmana Perera

Nirmana Perera received the B.Sc. degree in electrical and electronic engineering from the University of Peradeniya, Peradeniya, Sri Lanka, in 2011, and the M.Sc. degree in electrical engineering in the field of power electronics/energy systems from the University of Alberta, Edmonton, AB, Canada, in 2015.

He was an instructor at the University of Peradeniya until 2012. From 2013 to 2015, he was a Graduate Research Assistant under the supervision of Prof. John Salmon at the University of Alberta. He was a lecturer at the Department of Electrical and Electronic Engineering, University of Peradeniya from 2015 to 2017.

Currently he is pursuing his PHD degree at the Power and Wide-band-gap Electronics Research lab under the supervision of Prof. Elison Matioli. His current research interests include power electronic topologies, pulse-width modulation schemes and drive systems.

Hard and Soft Switching Losses in Power Converters: Role of Transistor Output Capacitance

To best utilize power converters, a sound understanding of the relationship between the circuit topology and the power-semiconductor-device characteristics is required. This is especially important in high-frequency switching, where device parasitics start to largely interfere with the circuit. In this regard, the parasitic-output-capacitance of power devices plays a vital role in the losses of the system, which affect both the efficiency of the circuit and the system volume. This thesis studies the characterization of output capacitance as well as its interaction with power electronic topologies at a fundamental level and presents important insights, underlining limitations in the conventional knowledge on the subject.The thesis shows that the analysis of output-capacitance-related losses should be treated based on the type of switching employed, as the circuit-level effect of the output capacitance is different in soft- and hard-switching topologies. For both cases, it is highlighted that the charge-versus-voltage curve of device output capacitance provides the most complete information of its behaviour. First, the correct measurement methods to identify output capacitance losses for soft-switching operations are analysed and validated. Then, it is shown how a fundamentally different charge-discharge mechanism in device output capacitance takes place in hard-switching operation (in contrast to soft-switching), and a new measurement approach is devised to quantify the related loss. These measurement methods are then used to evaluate output-capacitance losses of commercially available Si, SiC, and GaN power transistors. The developed concepts are taken a step further and utilized to separately evaluate gate- and driver-related losses in driving a transistor undergoing zero-voltage-switching. The technique is then used to identify the performance limitations of HF and VHF gate-driver ICs. Finally, consolidating the ideas developed throughout the thesis, an experimental case study is provided for a soft-switching converter.We conclude that output capacitance is a critical device feature that should be considered in high-frequency converter design and be given the same level of attention as device on-resistance in the design stage of a device. We believe this is instrumental to the progress of modern power convertersâespecially, ones based on emerging wide-bandgap devicesâtowards their fullest potential.

EPFL2022

Active-Device Losses in Resonant Power Converters: A Case Study with Class-E Inverters

Jessy Anthony Ançay, Armin Jafari, Elison de Nazareth Matioli, Palliyage Srilak Nirmana Perera, Remco Franciscus Peter van Erp

Recent research has reported an undesirable OFF-state loss in high-frequency soft-switching power converters, such as resonant converters. This loss is attributed to a hysteresis loss related to the charging-discharging process of the output capacitance of the power transistor. However, precise estimation of transistor power loss and its breakdown into ON-state and OFF-state losses is challenging in the MHz-range operation due to the small circuit size, parasitic effects, and limited accuracy in existing methods to measure low-loss systems. We present a measurement concept to perform a complete loss breakdown of MHz-range resonant converters, as well, directly determine the OFF-state losses in transistors, which is demonstrated for a GaN-based class-E inverter operating at 10 MHz. A novel and compact calorimeter was designed to measure the converter active-device losses down to 20 mW within a 5% error. This measured loss is then separated into four components using a combination of average and instantaneous electrical measurements: transistor ON-state loss, transistor OFF-state loss, gate-driver internal loss and gate loss. A simple no-load technique was devised to evaluate the gate-driver internal loss. The proposed approach directly determines output-capacitance hysteresis losses during the actual converter operation, which is not possible with existing measurement methods. The presented knowledge of individual loss components permits better optimization of MHz-range power converters.

IEEE2021

Embedded Microchannel Cooling for Monolithically-integrated GaN Half-bridge ICs

Elison de Nazareth Matioli, Luca Nela, Palliyage Srilak Nirmana Perera, Remco Franciscus Peter van Erp

Efficient and compact power conversion is a key requirement to achieve sustainable electrification of our society. GaN-based power devices offer major benefits compared to their silicon counterparts in terms of efficiency and integration but suffer from severe thermal challenges. Self-heating negatively impacts device performance and reliability, and the lateral integration of power devices and logic on a single integrated circuit cannot be fully exploited without novel cooling methods. In this work, we show a method to integrate microchannel cooling inside the silicon substrate of an off-the-shelf GaN-on-Si power IC and achieve a 25x-reduction on thermal resistance compared to forced air cooling. We investigate measurement techniques to measure the device temperature when no direct physical or optical connection can be made to the chip. A side-by-side comparison in electrical and thermal performance between conventional (forced) air-cooling shows that the integration of liquid cooling reduces the negative effects of self-heating on electrical performance while significantly improving its maximum current capability. The results show a first step toward making high-performance power converters with state-of-the-art thermal performance.

IEEE2021

Hard and Soft Switching Losses in Power Converters: Role of Transistor Output Capacitance

Palliyage Srilak Nirmana Perera

EPFL2022