IEEE Energy Conversion Congress and Expo 2018


Gary M. Dolny, US Correspondent, Bodo's Power

Gary M. Dolny

Energy Conversion Congress and Expo (ECCE)—the foremost IEEE conference in the field of electrical and electromechanical energy conversion—provided an international audience the opportunity for exchange of technical knowledge, networking, and exposure to the latest technology trends.

The 2018 IEEE Energy Conversion Congress and Exposition (ECCE) was held from September 23 through September 27 at the Portland Convention Center, Portland OR., USA.

ECCE is considered the foremost IEEE conference in the field of electrical and electromechanical energy conversion and provides opportunities for practicing industry engineers, research scientists, students, and professionals from a broad range of disciplines in the energy conversion industry to network, exchange technical knowledge, and develop their skills.

The conference emphasizes both power electronics and electric machines and tends to focus on higher power applications in areas such as smart grid and utility systems, renewable and sustainable energy, data centers and telecom applications, transportation electrification, power converter topologies and optimization, and industrial motor drives. ECCE was co-sponsored by IEEE Power Electronics Society (PELS) and the IEEE Industrial Applications Society (IAS) and supported by industry partners Wolong Electronics and General Motors, as well as media partners Bodo’s Power Systems and others.

 

A well-attended plenary opens the 2018 ECCE.

A well-attended plenary opens the 2018 ECCE.

 

ECCE's Offerings 

This year’s conference marked the tenth anniversary of ECCE, and over that time the conference has experienced phenomenal growth in the number of attendees, from 700 at the initial event to over 1600 at this year’s conference. During that time the technical program has also expanded. This year the conference received a record number of 1788 of paper submissions from around the world, from which 1102 were chosen for inclusion in the technical program. The technical papers were presented in 144 oral sessions and 54 poster sessions. All the technical papers presented at ECCE will be uploaded to the IEEE Explore digital library and will, therefore, be available to the larger research community worldwide.

In addition to the peer-reviewed technical papers, the conference featured, Special Panel Sessions consisting of invited presentations, Student Demonstrations, and Product and Service Sessions. The Special Sessions consisted of oral presentations only, without a formal manuscript appearing in the ECCE Proceedings. This allowed for presentation of information on the latest industrial trends that would not otherwise be publicly discussed at a professional conference.

Special session topics addressed the impact of SiC on smart transformers, trends in GaN, SiC and diamond power devices, simulation of power electronics systems, power electronics for sustainable energy, advances in power supply on a chip, power electronics workforce development and industry/academia collaboration. The Product and Service Sessions were half-hour long industry-driven presentations that provided in-depth discussions of innovative products and services.

There was also a full day of tutorials offering an in-depth discussion of state-of-the-art topics presented by world-class experts in the field on the Sunday prior to the conference opening. The ten parallel sessions in both morning and afternoon covered a wide range of topics including basic magnetic materials, SiC power devices, transformers, motors and motor drives, power converters, lighting, grid-connected systems, and renewable energy.

To complement the extensive technical program, ECCE offered numerous opportunities for professional networking and in-depth discussions. These included a Sunday night opening reception, a Newcomer’s Orientation designed to give first-time attendees tips to navigate the conference, and a Wednesday Industry Night Out Reception featuring food, drinks, and games.

 

Exhibit Hall

A key feature of ECCE is always the large and well-attended exhibit. The exhibit allowed conference attendees to examine and evaluate the latest product offerings from the leading suppliers in the industry. This year’s conference featured more than 40 exhibitors displaying a wide range of products including power supplies, power semiconductor devices, passives, design tools, and test equipment.

 

Discussion Focus: Wide Bandgap Semiconductor Devices

The focus of ECCE makes it a natural venue for discussion of advances in wide bandgap (WBG) semiconductor devices. This year’s conference featured several technical sessions exclusively addressing wide band gap devices including GaN Devices and Applications, SiC Devices and Applications, SiC Device Monitoring and Protection, and SiC Ruggedness. In addition, there were numerous papers treating applications evaluation of WBG devices throughout the technical program.

ECCE opened with a plenary talk from Dr. Victor Veliadis of Power America, entitled “SiC Power Devices—High Impact Applications and the Path to Wide Adoption”. His presentation highlighted the favorable material properties of Silicon Carbide (SiC), which allow for highly efficient power devices with the reduced form factor and relaxed cooling requirements. He also addressed the key cost reduction strategies necessary to enable SiC to be more competitive with Si in high-impact application areas.

These include variable frequency drives for efficient high power electric motors, automotive power electronics with reduced losses and relaxed cooling requirements, novel data center topologies with reduced cooling loads, “more electric aerospace” with weight, volume, and cooling system reductions, and more efficient, flexible, and reliable grid applications with reduced system footprint. He highlighted Power America’s role in accelerating the commercialization of SiC by facilitating the development of SiC manufacturing capability in a commercial foundry. The following plenary talk by Dr. Stephanie Watts-Butler of Texas Instruments entitled “Power Semiconductors Enabling a Powerful Decade of Changes” examined the changes in power management semiconductors over the past decade including device integration, the system in package, voltage levels, and process technologies. She noted that wide bandgap materials, particularly GaN, will play an increasingly important role over the coming decade.

 

SiC Device Monitoring and Protection

The plenary was followed by an entire session devoted to SiC device monitoring and protection.

C. Timms et. al. [1] from the University of Tennessee Knoxville and GE Global Research investigated oscillatory false triggering of parallel Si and SiC MOSFETs during short-circuit turn-off. Their work discussed a potentially destructive oscillation that they observed in paralleled power MOSFETs during short-circuit events. Through the use of a small signal equivalent circuit, they show the existence of a parasitic RLC loop consisting of the gate resistance, parasitic gate and drain inductances, and the gate-to-drain capacitance inherent in the device structure. They concluded that the device gates must be sufficiently decoupled in order to prevent this oscillation. This can be accomplished with increased gate resistance, which negatively impacts switching performance, use of ferrite beads in the gate loop, or using individual buffers to separately drive the gates.

S. Mocevic et. al. [2] from Virginia Polytechnic Institute and General Motors discussed a phase current sensor with short-circuit detection based on Rogowski Coils integrated on the gate driver for a 1.2 kV SiC MOSFET Half-Bridge Module. The key purpose of this work was to examine how increased gate-driver intelligence could benefit SiC-based power modules. They proposed the use of two Rogowski coils embedded in the PCB of the gate driver. Their paper showed this approach to have significant advantages, particularly in the area of short-circuit detection. They demonstrated that the total time required to achieve short circuit detection and protection was only 1.2 microseconds. This prevented the device from reaching destructive energy and also prevented thermal runaway. They noted that the described protection scheme does not interfere with normal switching and conduction, is responsive to all short circuit types, and has high noise immunity.

E. Aeloiza et. al. [3] of ABB Corporate Research Center discussed a novel Active Miller Clamp (AMC) method to improve the reliability of a SiC MOSFET based converter. The clamp consists of a low voltage capacitor that is connected across the gate-source of the SiC MOSFET through a single low-voltage silicon MOSFET. A dedicated -5V supply is directly connected to an auxiliary capacitor in order to minimize the charging/discharging time after every Miller event. Two clamping mechanisms are incorporated which completely bypass the gate resistance and gate loop inductance of the driver. The proposed solution thus bypasses the Miller current in both forward and reverse direction and holds the gate off-state voltage to a sufficiently low level. The solution avoids false triggering of the SiC MOSFET during high dv/dt turn-off and also saves the MOSFETs from excessive negative gate voltages. The operation of the proposed method was optimized using LTSPICE and verified by experiment.

 

SiC Ruggedness and Reliability

Issues of SiC ruggedness and reliability were addressed by several presentations.

J.Gonzalez and O. Alatise of University of Warwick [4] evaluated the impact of gate oxide reliability of SiC MOSFETs on junction temperature estimation using temperature sensitive electrical parameters (TSEPs). They note that measuring the junction temperature through the use of temperature sensitive electrical parameters is a promising technique for increasing the reliability of power devices. Some key temperature sensitive parameters they considered included the drain current, Rdson, gate current, and drain voltage transients during turn-on. However, SiC MOSFETs are known to exhibit a bias temperature instability due to the occurrence of interface state traps and fixed oxide charges, which can cause shifts in the threshold voltage. Since many of the TSEPS used for junction temperature estimation are threshold voltage-dependent, inaccuracies can result depending on the degree of gate stress.

Jiang et. al. [5] of Hunan University presented a study comparing the surge current capability of the SiC MOSFET body diode with that of the SiC Schottky diode. Their work was motivated by recent reports of the improved performance of SiC MOSFETs in synchronous buck converters without the use of anti-parallel Schottky diodes. The paper experimentally compared the non-repetitive surge current capability of the SiC MOSFET’s intrinsic body diode to that of a discrete SiC Schottky diode and analyzed the physical mechanisms of the degradation after surge current stress that was applied according to the JEDEC 282B.01 methodology. Their experimental study showed that the non-repetitive peak surge current of the SiC MOSFET’s body diode is slightly larger than that of the SiC Schottky diodes. The degradation of the SiC Schottky diode after surge current stress is accompanied by an increase of drain leakage current. The degradation of the SiC MOSFET after the body diode’s surge current stress is accompanied by the variation of the threshold voltage and input capacitance of the SiC MOSFET. The analysis shows that the degradation of the SiC MOSFET after the surge current stress may be correlated with the interface traps at the SiC/SiO2 interface.

Similarly, Gendron-Hansen et. al. [6] of Microsemi Corp., investigated the repetitive unclamped inductive switching capability of SiC Schottky diodes and MOSFETs. Their measurements showed only a slight reduction in pulse failure energy for the repetitive UIS compared to single pulse failure indicating that cumulative damage has only a small effect on overall device ruggedness. They also reported that the long-term reliability of the gate oxide was not affected by the repetitive UIS stress and no reduction in time-dependent dielectric breakdown time to failure for the stressed parts was observed.

 

GaN Devices and Circuit Applications

There was also considerable interest in GaN devices and circuit applications.

Kuring et. al. [7] from Technische Universitat Berlin and Ferdinand-Braun-Instuit presented a novel, monolithically integrated GaN HEMT with bidirectional blocking capability. Their device was based on a conventional GaN HEMT structure, but with an additional gate electrode referenced to drain potential. The resultant device structure is effectively equivalent to the integration of two unidirectional HEMT structures with a common drain node. Measurements showed that if both gates are biased in an optimum voltage range the on-state resistance of the bidirectional device is equivalent to a single unidirectional device of the same voltage blocking capability. Dynamic data under hard switched inductive load conditions was also presented.

Sun et. al. [8] of Virginia Polytechnic Institute presented an assessment of switching frequency on a compact, 3-phase GaN inverter design. The paper presented a modular half bridge design using 650V GaN HEMTs, operating at 100 kHz - 500 kHz switching frequency. The intended application was a 1 kW 400 Vdc two-level, three-phase inverter. A double-side power loop was used to achieve a compact size, with an adaptive double side thermal solution.

Williford et. al. [9] of University of Tennessee Knoxville presented a method of characterizing and experimentally modeling dead-time related losses in a 5 kW, single phase, full-bridge inverter, utilizing 600 V GaN HEMTs. Although the experiment specifically utilized Gate-InjectionTransistors, the methodology is valid for other types of GaN HEMT structures as well. The results show that dead-time can contribute up to 30% additional switching loss with 100 ns dead-time, which can be decreased to 5% additional loss with the minimal safe deadtime. However, implementing the minimal dead-time is not necessarily optimal over the entire operating range, as switching loss at light load becomes dominating and contributes greater than 10% of the total loss.

 

ECCE Special Sessions

The growing interest of wide bandgap devices was evident in both the conference special sessions and on the exhibit floor as well as in the technical program. The conference featured two special sessions devoted to wide bandgap devices, titled Smart Transformers: Which Impact of SiC Technology? and Trends in SiC, GaN, and Diamond Power Semiconductor Devices. The exhibit included traditional vendors such as GaN Systems, Infineon, and Wolfspeed, as well as new entries such GaN power International which introduced a line of 650 and 1200 V GaN devices aimed at power converter and EV applications.

 

ECCE 2019 

The 2019 ECCE will be held from September 29-October 3, 2019 in Baltimore, MD, USA. The digest submission date is January 15, 2019. Additional information can be found on the conference website

 

References

  1. C. Timms et. al., “Oscillatory False Triggering of Parallel Si and SiC MOSFETs during Short-Circuit Turn-off”, Proceedings of ECCE 2018, pp 383-386.
  2. S. Mocevic et. al., “Phase Current Sensor and Short-Circuit Detection based on Rogowski Coils Integrated on Gate Driver for 1.2 kV SiC MOSFET Half-Bridge Module”, Proceedings of ECCE 2018, pp 393-400.
  3. E. Aeloiza et. al., “Novel Bipolar Active Miller Clamp for Parallel SiC MOSFET Power Modules”, Proceedings of ECCE 2018, pp 401-407.
  4. J. Gonzalez and A. Alatise., “Impact of the Gate Oxide Reliability of SiC MOSFETs on the Junction Temperature Estimation Using Temperature Sensitive Electrical Parameters”, Proceedings of ECCE 2018, pp 837-844.
  5. X. Jiang et. al., “Comparison Study of Surge Current Capability of Body Diode of SiC MOSFET and SiC Schottky Diode”, Proceedings of ECCE 2018, pp 845-849.
  6. A. Gendron-Hansen et. al., “4H-SiC Junction Barrier Schottky Diodes and Power MOSFETs with High Repetitive UIS Ruggedness”, Proceedings of ECCE 2018, pp 850-856.
  7. C. Kuring et. al., “Novel monolithically integrated bidirectional GaN HEMT”, Proceedings of ECCE 2018, pp 876-883.
  8. B. Sun et. al., “Assessment of Switching Frequency Effect on a Compact Three-Phase GaN-Based Inverter Design”, Proceedings of ECCE 2087, pp 868-875.
  9. P. Williford et. al., “Optimal Dead-time Setting and Loss Analysis for GaN-based Voltage Source Converter”, Proceedings of ECCE 2018, pp 898-905.

 

Source: Bodo's Power Systems, December 2018